Final Report Summary - MIDEMMA (Minimizing Defects in Micro-Manufacturing Applications)
Executive Summary:
Zero defects manufacturing is an objective long aspired in modern industries. Producing parts that do not meet the requirements leads to negative economic impacts, from wasted manufacturing resources to the need of more expensive equipment for manufacturing and quality control. Moreover, more and more sectors cannot allow defect parts in critical applications due to safety issues.
This project aims at contributing to this on-going effort in optimizing manufacturing processes combining the minimisation of defects within reasonable economic conditions, but not aiming at general manufacturing, but focusing on micro-manufacturing, considered here as the production of small parts with functional features in the range of the micrometer and medium size parts with form requirements below the micrometre and surface roughness requirements even below the nanometre (typically optical elements). Silicon based microsystems are not considered in the project, focusing the activity to engineering micro-components and high precision optics and lenses.
Micro-manufacturing requires 'Zero-Defect' oriented approaches, both in large scale and in short-run production. Current quality control approaches, coming from macro-manufacturing, are mainly based on post-process geometric control, which produces a large time lag between the defect generation and its detection, usually leading to large amount of defect parts (large scale) or wasted high value processing (short run). Moreover, this approach does not immediately point the error source to help with error correction, and other criteria such as material integrity, physical properties, surface topography and piece or component functionality are not taken into account typically.
There is clear need for extending the final product validation to a process monitoring approach in micro-manufacturing, where all the manufacturing process is monitored, from the raw material to the fabrication processes and the manipulation of the final parts, and where all this information is processed in real time with suitable models for error prediction, automatic detection and process optimization by system correction.
The project will give a global solution for the 'zero defect' approach in micro-manufacturing, with a focus on the aspects that are specific to micro-manufacturing. The developed technologies concepts are expected to have in impact in the competitiveness of the micro-manufacturers in the following ways:
• reducing process variability detecting defects as soon as they are generated or in the case that it is possible, are going to be generated by predicting models.
• allowing the use of less expensive machines, that can reduce their variability through monitoring.
• requiring less skilled working force, thanks to acquired process setting knowledge and the development of smart decision-making tools.
Project Context and Objectives:
Objective 1: Work piece manipulation and metrology
General Concept On-machine devices for work piece manipulation and metrology, which reduce impact of raw material variability and provide information for online process control and for feeding process models.
Objective 1.1 Work piece manipulation and clamping.
Concept Development of a work piece chucking system with high damping capacity.
Technology Work piece clamping device based on UV-curable adhesives, that can provide high repeatability, sufficient stiffness and damping, and not leaving clamping damages on the workpiece
Benefit Work piece positioning with sub-micron repeatability and with no damage on the work piece, adapted to micro-components and optical surfaces.
Achievements MONTH 36
• Requirement definition for clamping devices to be developed within the project.
• Definition of the technologies and methodologies to be employed for the design of clamping devices.
• Prototypes for the workpiece manipulation devices.
• Evaluation of prototype performance and industrial validation.
Objective 1.2 Work piece metrology.
Concept Devices for measurement of work piece geometric characteristics and raw material properties. Work piece geometry, surface roughness, tool-work piece relative position, raw material metallography, grain size etc. will be measured, before, during or after the machining process.
Technology Development of contact probes for 3D point measurement with uncertainty below 100 nm, optical microscopy devices for 3D topography, surface roughness and metallography. Integration of these devices on the machine. Develop models and algorithms for extracting relevant information for the process.
Benefit Avoid errors due to raw material variability. On-machine monitoring actual workpiece condition, for adapting the process and for final validation.
Achievements MONTH 36
• Identification of the requirements to be applied to measurement devices the characterization of features related to micromanufacturing applications.
• Determination of the metrology strategies to be developed on the design of work piece and tool characterization devices.
• Prototypes for the workpiece metrology devices.
• Performance evaluation for the prototypes and industrial validation.
Objective 2: Process monitoring
Concept Develop measuring devices and monitoring strategies that can provide meaningful information for online process control and for feeding process models.
Technology - Tool monitoring: Optical devices for on-machine tool inspection, adapted to precision machining processes as micro-milling, turning and microEDM.
- Laser ablation monitoring: Laser pulse energy analysis, autofocus system and thermal camera for online monitoring of laser micro-machining process.
- Replication monitoring: Analyse optimal sensor type, number and location for monitoring mould injection cycle for a variety of parts specifications
Benefit Provide information to the control on the actual process conditions so that the variability of the process result coming from effects such as tool wear, tool breakage, loss of laser focus or thermal damage. The information is also used to build statistical models.
Achievements MONTH 36
• Determination of the present requirements related to process monitoring (tool status, process parameters) with application to micromanufacturing applications.
• Definition of the process monitoring approaches to be applied on the test-cases defined within the project.
• Evaluation of the developed monitoring techniques regarding their behaviour on industrial conditions.
Objective 3: Process control
General Concept Develop and implement on machine active and adaptive strategies to optimise the processes addressed in the project: Precision machining, Laser micro-manufacturing, micro-EDM and Replication.
Objective 3.1 Precision machining
Technology Strategies to actively adapt process conditions and detect need for tool replacement due to wear or breakage in function of tool wear and alignment on-machine monitoring information.
Benefit Higher machining accuracy through reducing variability due to tool wear and alignment errors. Reduced tool cost through optimal tool replacement strategy. Early tool breakage detection.
Achievements MONTH 36
• Identification of the existing necessities related to tool wearing and breakage control on chip removal processes for micromanufacturing applications.
• Proposal for the strategies to be followed for the correction of the measured deviations on the tools in order to avoid the flaw generation on the workpieces.
• Analysis of the effect of the tool wearing on the workpiece quality.
• Industrial validation of the control strategies for machining processes in comparison to the defined objectives.
Objective 3.2 Laser micro-manufacturing
Technology Strategies for adaptive process control, integrating laser pulse energy monitoring system, laser auto-focus system and thermal camera to ensure optimal laser ablation.
Benefit Laser focus control leads to higher process repeatability (less defects) and accuracy (more demanding tasks feasible). Thermal control avoids thermal damage (less defects) and permits higher productivity with safe operation.
Achievements MONTH 36
• Determination of the requirements associated to error identification and elimination from the laser ablation process.
• Definition of the adaptive control methodologies to be applied for the elimination of defects from the laser ablation process.
• Assessment of the capabilities of the laser process monitoring techniques developed for the fulfilment of the defined project objectives.
Objective 3.3 Micro-EDM
Technology Active control techniques to adapt the machining strategies (including CAM) for the compensation and re-generation of the EDM micro-machining data (both tool path and process strategies) based on tool and workpiece monitoring information.
Benefit Higher process accuracy and repeatability, and thus possibility of achieving more demanding tolerances and minimising defects due to process variability
Achievements MONTH 36
• Identification of the needs related to tool status and spark analysis for process control.
• Determination of the control strategies to be applied for the application of zero-defect manufacturing concepts to the µEDM process.
• Validation of the analysis developed for the µEDM regarding the characterization of the process state on industrial conditions.
Objective 3.4 Replication
Technology Predictive virtual tools and models to process monitoring information and define the best moulding configuration and to assess the quality of the mould after each production run. Sensoring of moulds for monitoring.
Benefit Higher process repeatability and early mould failure detection. Time reduction in mould tuning and process set-up
Achievements MONTH 36
• Identification of the existing needs for the control of the microinjection process on a zero-defect frame.
• Definition of the approaches to be applied for the error detection on the microinjection process.
• Development and industrial validation of the process control scheme based on the parameters identified as key regarding the process quality.
Objective 4: Process modelling and data management
Objective 4.1 Process prognosis models
Concept Develop statistical models for micro-manufacturing processes based on extensive monitoring information
Technology Statistical models that relate process variability and defect generation with the inputs from the monitoring information to help determining achievable tolerances, frequency of maintenance (tool replacement), etc.
Benefit Virtual prediction of process tolerances and defect ratios at process definition stage and during processing.
Achievements MONTH 36
• Determination of the data to be employed for the development of process prognosis models.
• Identification of the process indicators and the vital parameters for each process
• Industrial implementation of software tools for process data analysis and evaluation, focusing on error identification and avoidance.
Objective 4.2 Proactive data management
Concept Integrate error prediction methodology into a decision making tool in order to allow a early recognition of planning deviations, ensuring quality standards.
Technology Smart data management tool integrating data reduction (extensive monitoring leads to data rich environment), key variable selection, online quality prediction and decision making strategies.
Benefit Automatic management of process and monitoring information for fast prognosis and proactive quality control.
Achievements MONTH 36
• Identification of the hardware and software requirements for the development of proactive data management tools for the end-users within the project.
• Definition of the quality assurance structure for the PDMT
• Development of the structure for the PDMT, applicable to the different manufacturing processes addressed on the project.
Project Results:
1 Improvements on micro-manufacturing processes
The micro-manufacturing processes, due to their lower-scale nature, show several problems and difficulties in comparison to common manufacturing processes. The small geometrical features to be manufactured and the very tight tolerances for dimensional and surface characteristics induce not just a quantitative difference regarding the quality management, but a qualitative jump in comparison to average manufacturing processes. The verification of the employed tools and manufactured workpieces require the use of on-machine devices for the preparation and inspection of the processes. Besides, concerning the possibility to define process control scenarios, the low process signal (forces, power, current,…) amplitudes and their poor signal-to-noise ratio make the usual monitoring devices on the market not suitable for micro-manufacturing applications. This way, several solutions have been proposed to overcome the difficulties on the implementation of zero-defect manufacturing schemes related to different micro-manufacturing processes. Next, these solutions are grouped concerning each manufacturing process addressed during the MIDEMMA project.
1.1 Micro milling
Concerning the micromilling processes, and related to the expected improvements defined by the end-user Createch-Medical, the work has been focused on the avoidance of geometrical defects and process quality instabilities generated by the appearance of wool wear during the machining process.
In the case of the geometrical defects induced by the appearance of the tool wear, IK4-Ideko has developed a methodology for the accurate on-machine tool shape measurement using a non-contact laser device from BLUM-Novotest (Figure 2 left), linked to the analysis of the actual surface machined by the tool. These measurements have been validated by their comparison to high resolution confocal measurements (Figure 2 right), obtaining uncertainty values as high as 0,5 µm.
Figure 1 Tool measurement results (let) and confocal measurement used for validation (right)
Besides, once identified the actual tool geometry and the surface shape to be machined with it, a tool wear compensation method has been developed IK4-Ideko too, based on simple geometrical models developed for the machined part (Figure 3 left). The application of this method has been evaluated by analysing the strains induced on a fitting part machined with a worn tool when it is clamped (Figure 3 right). Results show that the developed method can significantly reduce the deviations induced by the worn tools and help avoiding the defect generation on parts designed for accurate fitting.
Figure 2 Surface geometrical model (left) and strains generated on fitting part (right)
Regarding the variation of the process state due to the appearance of tool wear, the monitoring and statistical treatment of process signals has been tackled by Brunel and Leuphana universities, in order to define a frame where an in-line evaluation of the process state could be done. After the analysis of several measurable process signals and different data treatment techniques, a good correlation was found between the appearance of tool wear and the increase of a wavelet coefficient from the cutting force (Figure 4).
Figure 3 Tool wear-cutting force pairs and evolution of wavelet coefficients with tool wear
Once identified the signal features with high correlation with the tool wear, a monitoring scheme has been defined in order to enable the in-line evaluation of the cutting forces. By the use of a piezoelectric dynamometer, a charge amplifier and an acquisition board, it is possible to evaluate in real time the cutting force signals (Figure 5 left). Finally, a software tool has been developed by Leuphana University for the evaluation of the obtained signals (Figure 5 right). This tool can compare the present signals with previously recorded ones in order to identify excessive tool wearing or process instabilities, helping the user on the decision making related to the process control so excessive waste of time and materials can be avoided.
Figure 4 Cutting force acquisition scheme (left) and GUI for the data treatment software (right)
1.2 Precision grinding
In the case of the precision grinding processes (Figure 6), the issues to be solved during the project were related to the optical component manufacturing processes from Kaleido technology. As in the case of the micromilling process, the most important deviations on part quality are related to the appearance of tool wear and its effect on the generated part geometry and surface quality, together with the generation of process instabilities.
Figure 5 Image of the precision grinding set-up
The first development linked to the precision grinding process has been oriented to the accurate on-machine measurement of the actual geometry for the grinding tools. Using a non-contact on-machine laser device from BLUM-Novotest (Figure 7), the University of Bremen has developed an automatic method for the accurate characterisation of the grinding tools. Validated against off-machine optical measurements for the same tools, this method allows for the identification of the shape deviations of the actual tool regarding the theoretical geometry defined for it with an accuracy of 0,1 µm.
Figure 6 Grinding tool measurement and profile deviations for different worn tool profiles
Next, the evolution of the grinding process state as the tool wears off has been analysed. The University of Bremen has worked on the realisation of cutting tests while monitoring several process signals. When comparing the obtained signal values and their evolution with the processing time (Figure 8), together with the appearance of the tool wear, correlations have been found that could later be used for the in-line analysis of the process state and estimation of the generated process quality.
Figure 7 Evolution of the cutting forces with the cutting time and the appearance of tool wear
The data generated on tool wearing and process signal evolution has been employed by the University of Leuphana for the development of a statistical analysis tool for the in-line evaluation of the state for the grinding process. Once developed a prognosis engine for the identification of the process state, a software tool with a user friendly human interface (Figure 9) has been developed.
Figure 8 GUI for the grinding process signal analysis tool
This tool can help on identifying process instabilities and quality deviations on the machined part. Also, it can provide the machine operator with recommendations for the modification or stopping the process in order to generate the desired part quality and avoid the scraping of parts.
1.3 Ultra-short pulse laser ablation
The part cutting based on ultra-short pulse laser ablation process (Figure 10) is directly linked to the manufacturing problems addressed by the industrial end-user Micreon, working with femtosecond (fs) laser systems. In this case, different difficulties related to the high process dynamics have been tackled as: instabilities on the laser source output, the identification of the laser focal position of the part and the need for in-line information regarding the workpiece state (cut width, part temperature) so the final workpiece quality could be estimated.
Figure 9 Example of a part cut by ultra-short pulse laser ablation
In this case, the Laser Zentrum Hannover (LZH) has worked on the implementation of different methods for the in-line process monitoring (Figure 11). On the one hand, a simple and cheap device for the measurement of the energy from single laser pulses down to 20 fs has been developed. Also, a system for the in-line identification of the cut width has been developed, obtaining accuracy values bellow 2 µm when working with feed rates up to 400 mm/min. Besides, a commercial auto-focus device has been implemented to work properly within a fs-laser context and, finally, a thermo-camera has been implemented on the machining set-up so part temperatures above 80 ºC can be identified and avoid the burning or the workpieces.
Figure 10 Representative images for each of the developed monitoring devices
Once the different monitoring devices were developed, the LZH has worked on the development and implementation of an adaptive process control scheme. Employing the in-line data obtained by the monitoring devices, rules for the actuation on the laser machine parameters have been developed. Figure 12 depicts the capability of the developed control to modify the laser output and stabilize the desired process variable. Thanks to this control scheme, the process parameters can be modified in real-time in order to generate the desired quality on the machined part.
Figure 11 Effect of the developed control on the laser output
Besides the adaptive process control approaches defined for this process, the development of statistical tools for the analysis of process trends and the prediction of non-controllable process deviations has been undertaken too. The University of Leuphana has worked on the analysis of the data provided by the auto-focus system implemented by LZH. Based on this data, the identification of high focal deviations is carried out. Thanks to this, it is possible to detect a part that would require too many corrections to attain the desired quality and suggest its scrapping to avoid excessive costs.
Figure 12 In-line focus control scheme and high focal deviation identification module
1.4 Micro injection
The micro injection processes have been tackled by the project too, defining the resolution of the manufacturing problems addressed by EuroOrtodoncia as the objective for some RTD tasks. Some of the problems found when manufacturing transparent bracket lids are the premature erosion of the mould, the occurrence of unfilled parts, the appearance of flashing on the parts or the trapping of parts on the mould.
As the first step, a new mould concept has been developed by EuroOrtodoncia and Tekniker. Besides providing the possibility to introduce sensors for the in-line monitoring of the micro injection process, the part location on the new mould would allow for higher throughput while avoiding the appearance of premature wearing on the moulding parts. The new part location involved considerable difficulties on the accurate manufacturing of the mould, but it was undertaken by the project partners KUL and Sarix with great success.
Figure 13 New injection mould concept with monitoring capabilities
After the inclusion of sensors on a test mould for the monitoring of process signals as pressure and temperature, IK4-Tekniker has carried out an experimental analysis concerning the effect of the values taken for different process signals and the quality generated on the micro injected part. This way, it has been possible to define several relationships between the process signals obtained on different mould locations and the obtained part quality.
Figure 14 Differences on process signals obtained from both good and bad parts
Besides, EuroOrtodoncia has worked on the implementation of an in-line inspection system for every manufactured part on their manufacturing chain. This system obtains images from the gripper that takes the parts away from the mould (Figure 16) and identifies the presence of the part together with some injection related problems as flashing. Thanks to this system, it is possible to automatically link the process data with the obtained part quality for the generation of an extensive manufacturing data log for its later treatment.
Figure 15 Images taken of the gripper with (left) and without (centre) injected part and main image of the quality control tables (right)
Both the actual manufacturing data obtained from the monitoring and the empirical modelling for the part quality previously carried out has been implemented by the University of Leuphana on a software module for the analysis of the micro injection process. Analysing the historical process monitoring data, this tool can identify different trends on the manufacturing quality for the generation of statistical models that could represent the actual process behaviour. Then, identifying deviations on the process parameters that could generate defective parts, and taking into account the high part throughput on this process, this tool can aid on the avoidance of high volume part scrapping.
Figure 16 Human interface for the micro injection data analysis tool
1.5 Micro electro discharge machining
In the case of micro electro discharge machining (µEDM) processes, they have been analysed within the project following the difficulties stated by the industrial end-user Sarix. The main problem found when analysing these processes is the appearance of a wrong inter-electrode gap due to the generation wear on the electrode working as the tool or the wrong positioning of the machine axes. Besides, due to the nature of the process itself the part material is modified during the machining, generating a heat affected zone (HAZ) on the machined surfaces that can be detrimental for the mechanical behaviour of the part.
On the one hand, the proper identification of the actual electrode geometry has been undertaken by the University of Leuven and BLUM-Novotest (Figure 18). By both contact (electrical spark analysis) and non-contact methods (laser system), an electrode measurement routine has been developed obtaining measurement uncertainties below 0,5 µm.
Figure 17 Images of the different electrode measurement methods analysed
Once developed an accurate way for the identification of the electrode geometry, the University of Leuven has carried out several experimental tests in order to analyse the wear generation along the µEDM process and implement the obtained results into a model for its application to actual machining processes. This model has been introduced by Sarix into their NC system, allowing the automatic tool wear compensation on µEDM milling operations (Figure 19).
Figure 18 Scheme for the wear compensation and Sarix NC with the implemented feature
Also, thanks to the possibility to accurately identify the contact between the electrode and a machined surface and the better understanding of the electrode wearing along the µEDM process, Sarix has added several features on their own CAM (Figure 20) for the improvement of the depth accuracy on the machined features and the generation of optimized tool paths yielding considerably lower processing times.
Figure 19 GUIs for the new developments implemented on the Sarix CAM system
Besides, Tagueri has worked on a system for the analysis of single sparks up to a frequency rate of 100 Mhz. This analysis has enabled the in-line identification of ‘good’ and ‘bad’ sparks during a µEDM process (Figure 21), making it possible to detect variations or trends along a machining process. The in-line application of this analysis can help aid the machine operator on decision making related to the modification of process parameters or even the stopping of a process based on the historical data and the observations during the machining process.
Figure 20 Representation of the different types of sparks identified
Finally, trying to face the material modification (HAZ) during the µEDM process, the University of Brunel has worked on the development of a machine prototype (Figure 22 left) for micro electro chemical machining (µECM). Due to the chemical nature of this process, it is possible to remove part material without modifying its state. After the development of a machine structure, an innovative pulse generator and a new control system, the performance of the prototype has been proven on the manufacturing of micro stylus for precision probes (Figure 22 right).
Figure 21 Overall image of the µECM prototype (left) and machined micro stylus (right)
2 Improvements on workpiece manipulation and metrology
The reduced work piece dimensions, feature sizes and/or surface roughness requirements in micro-manufacturing processes introduce some new challenges, which are not so critical in macro-manufacturing. Regarding the workpiece manipulation and clamping, they must ensure stiffness, damping, accuracy and possibility of automation (as in macro-manufacturing), but ensuring that the micro-features are not damaged. In the case of the metrology, it must be taken into account that measuring workpiece features with micrometre range geometries and (sub)-nanometre range surface roughness is very close to the limits of existing measurement principles.
The machines used for micro-manufacturing technologies differ drastically from state of the art macro-machining systems. Aerostatic or hydrostatic guide ways and spindles, optical encoders or even interferometers and thermally stabilised direct drives allow for a positioning precision down to the lower sub-micron scale. Opposite to the highly sophisticated machinery, the manipulation, alignment and clamping of workpieces as well as tools are mostly carried out manually with only little technical support. The necessary accuracy in the submicron range cannot be achieved by conventional workpiece handling and metrology systems used in the macro technology
2.1 Workpiece manipulation
In order to face some of the difficulties related to workpiece clamping and re-positioning for the micro-manufacturing of complex 3D geometries, the University of Leuven has developed a novel part fixing concept (Figure 23). On the one hand, it allows for clamping the parts by adhesive means in order not to damage micro sized geometrical features or optical surfaces and, due to the nature of the used adhesive, introduces additional damping capabilities (~30%) in comparison to the usual mechanical clamping devices. Besides, the system allows for the modification of the part fixing position, ensuring the re-positioning of the part with a location uncertainty lower than 1 µm.
Figure 22 Adhesive based part clamping and re-positioning system
Brunel University has worked on the development of a smart clamping system capable of monitoring the forces acting on different sections of the part (Figure 24). This way, it is possible to control the clamping forces in order to avoid possible geometrical distortions on the manufactured part. Also, it can work as an in-line dynamometer, providing the possibility for a detailed process state monitoring without the need to include an additional measuring element on the manufacturing equipment.
Figure 23 Prototype for the smart clamping system and example of measurement
2.2 Workpiece metrology
Facing metrology difficulties related to the high accuracy requirements for part positioning inside the machine-tools, the University of Leuven has developed a robust unidirectional measurement system based on the use of a moving measuring scale and a capacitive sensor. The design of the device has been carried out minimizing the Abbe errors and the ones coming from thermal and environmental sources. The preliminary validation of the prototype has shown a great consistency, attaining measurement uncertainties around 20 nm.
Figure 24 Measurement system and results from stability tests
Trying to provide capabilities for high precision on-machine measurements, IBS Precision Engineering has developed a full 3D ultra-precision contact probe capable of working within machine-tools on workshop environments. This probe has been tested to work on ultra-precision lathes for the measuring of calibrated artefacts and manufactured optical components (Figure 26), yielding measurement uncertainties below 50 nm.
Figure 25 On-machine contact probe, obtained measurement and uncertainty results
In order to improve probe measurements carried out off-machine, the National Physical Laboratory (NPL) has worked on the design and development of a vibrating micro-probe capable to work on non-contact mode. The stylus is placed on a MEMS structure allowing the generation of a controlled vibration of the probe tip (Figure 27). The performance tests carried out on an ISARA 400 ultra-precision coordinate measuring machine (CMM) have shown that the probe is capable of measurement accuracy below 60 nm.
Figure 26 Image of the MEMS structure for the stylus and overall image of the probe on the ISARA 400
Besides probe based measurement systems, optical measuring devices have been developed within the project too. Sensofar has developed a miniaturised microscope head capable for on-machine measurements, both by confocal and interferometry techniques. This on-machine microscope has been tested to work properly within the manufacturing environment at Kaleido (Figure 28), probing very helpful not just for the verification of the manufactured parts, but also for the machine and tooling set-up.
Figure 27 On-machine microscope and images for obtained measurements
Concerning optical metrology, the development of an optical CMM has been carried out by IK4-Ideko, implementing a 5-axis positioning structure on a PLu Neox optical profiler from Sensofar. Thanks to this structure, it is possible to obtain detailed measurements from complex 3D parts and treat them on the same reference system (Figure 29). Besides, in order to make this system competitive in comparison to contact based CMMs, Sensofar has worked on the development of a focus variation measurement technique, enabling very fast measurements with a high spatial resolution.
Figure 28 Image of the 5-axis microscope (left) and 3D representation of different measurements taken on a same workpiece (right).
Linked to the use of optical means for the characterization of complex parts with small and even damaged features, the development software for the treatment of the obtained measurements has been undertaken during the project too. Tagueri has worked on a tool that, applying statistical data mining techniques (Figure 30) is able to identify and disregards ‘bad’ points from the measurements, increasing the reliability of the results obtained from the optical measurements.
Figure 29 Graphical representation of the data treatment on the PDMT for measurements.
Finally, trying to bridge the gap between contact and optical form and roughness measurements, the NPL has analysed the possibility to define traceability routes between both types of measurements. While evaluating the measurement results yielded by different optical measurement methods in order to define their application range, calibration procedures and artefacts (Figure 31) have been defined for optical measurement equipment.
Figure 30 Areal Calibration Set from NPL
Potential Impact:
Concerning the exploitation of the project outcomes, several activities have been carried out along the project duration in order to define the possible exploitable results and ensure the achieving of the defined exploitation objectives. Two Exploitation Strategy Seminars have been undertaken; the first one (19/03/2013 at Hannover, M18) was the first attempt within the project for the definition of the exploitable results and their characterization. During the second one (18/07/2014 at Leuven, M33), the strategies to be followed to ensure their exploitability and market reach were verified and redefined when needed. These actions leaded to the next exploitation outcomes from the project:
• 4 New products / 2 Product improvement
• 2 Software developments close to industrialization
• 4 New services
• 5 Beta-users (industrial implementations)
• 1 PPP partnership
• 1 new company (start-up)
• 1 licence
1 Demonstration/Industrial validation
The technical outcomes generated during the project have been demonstrated and validated by their application to manufacturing problems defined by the industrial end-users. For each of them, different problems were identified related to their value chains and involved manufacturing processes. This way, the identified problems defined the test-cases to be treated during the project, as well as the objectives for the technical tasks of the project.
Next, each industrial end-user is briefly introduced together with the test-cases related to them.
1.1 Createch-Medical
Createch Medical designs and manufactures metallic frames for dental prostheses that are personalized to meet each patient’s case requirements. Starting from a model of the actual implants provided by the doctor, Createch manufactures the frame attached to the implants and the supporting base for the teeth.
The frame and teeth supporting base are mainly manufactured on single piece Ti6Al4V or CrCo by micromilling. During the design and manufacture of the prosthesis, exceptional care must be taken on the frame-implant connections. A slight deviation on the position of one of those connections would generate stresses on the jaw of the patient and, thus, pain; making the prosthesis unacceptable. Moreover, the stresses induced by the clamping of the prosthesis could even generate the rejection of the implants.
1.1.1 Defined test-cases
Concerning the case of Createch Medical, three test-cases have been defined for their analysis within the project. They are related to the present manufacturing chain from Createch-Medical, covering the characterization of the model with the dental implant analogues and the precision milling process of the dental frames. Related to these test-cases, different working groups have been assembled in order to define and develop solutions for the different problems defined by the industrial end-user. Next, the different test-cases and the tasks related to their solution are exposed briefly. Figure 32 shows a poster summarizing visually the technical work carried out during the project related to the test-cases from Createch-Medical.
Test-case 1: Implant model characterization
5-axis microscope to work as optical CMM: IK4-Ideko+Sensofar
Optical measurement treatment for optimum data extraction: Tagueri
Test-case 2: Dental prosthesis micromilling
Smart vice for the measurement of cutting and clamping forces: Brunel
On-machine actual tool shape characterization and compensation: IK4-Ideko+BLUM
Cutting force signal based tool state monitoring and control: Brunel+Leuphana
Figure 1 Poster summarizing the work carried out for the solution of the problems related to Createch-Medical
1.2 Kaleido Technology
Kaleido is developing wafer level optics for production of small lenses mainly for the mobile phone market. The company is doing only R&D and not actual production and thus does not have any large-scale automated production facilities. Kaleido Technology is currently maturing the technology for large-scale production and, therefore, focusing on stabilizing the manufacturing and minimizing manual assistance in the process. The main aim has been to implement in-line checks of the tooling quality and the definition of strategies for the avoidance of defective geometries.
1.2.1 Defined test-cases
Concerning the manufacturing processes from Kaleido Technology, two test-cases have been defined for their analysis within the project. They are related to the manufacturing of lens replication moulds on different materials as tungsten carbide and non-ferrous metals (Figure 33) by precision grinding and diamond milling. This way, the work carried out has been divided into two main groups: one relative to the own manufacturing process and its control, the second one focused on the characterization of the manufactured optical devices.
Figure 2 Precision grinding of an optical mould array on a tungsten carbide wafer
Related to these test-cases, different working groups have been assembled in order to define and develop solutions for the different problems defined by the industrial end-user. Next, the different test-cases and the tasks related to their solution are exposed briefly. Figure 34 shows a poster summarizing visually the technical work carried out during the project related to the test-cases from Kaleido Technology.
Test-case 1: Optical mould manufacturing
On-machine tool shape monitoring and compensation strategies: Bremen+BLUM
Process evolution analysis and smart decision making tool: Leuphana
Test-case 2: Optical mould characterization
Ultra-precision on-machine 3D contact probe: IBS-PE
Vibrating non-contact probe: NPL
On-machine microscope: Sensofar
Traceability routes for contact and non-contact measurements: NPL
Figure 3 Poster summarizing the work carried out for the solution of the problems related to Kaleido Technology
1.3 Micreon
Micreon GmbH, located in Hannover (Germany), is a contract manufacturer for ultrafast laser micro machining. Applied techniques are laser micro cutting, laser micro drilling, and laser micro engraving. Processing is done with ultrashort pulse lasers. These lasers allow for precise, burr-free laser ablation of all solid and gel materials.
From the manufacturing of single proto-types to mass production, Micreon offers the complete range of material processing. The expertise in the field of ultrashort pulse lasers and high-precision positioning systems allows Micreon to provide industrial micro-machining systems using ultrafast laser technology. Micreon operates as a technical interface between laser manufacturers and industrial users of ultrafast lasers. As specialists in ultrafast laser technology, the Micreon team offers training and coaching of the technical staff that operates the laser work stations for industrial applications.
1.3.1 Defined test-cases
The two MIDEMMA test cases of Micreon are wolfram foil cutting for X-ray emitters and biocompatible polymer stent cutting. Both have in common the application of ultrashort pulse laser microcutting. The most important differences are material and shape – plane metal parts in the case of the X-ray emitters and highly heat-sensitive biopolymer tube material in the case of the stents. Cutting widths are 30 to 50 µm. The metal sheet thickness for the emitters is 100 µm. The tube wall thickness for the stents is 300 µm. Figure 35 shows both test case parts and their applications.
Figure 4 X-Ray emitter (left) and biopolymer stent (right)
Related to these test-cases, different working groups have been assembled in order to define and develop solutions for the different problems defined by the industrial end-user. Next, the different test-cases and the tasks related to their solution are exposed briefly. Figure 36 shows a poster summarizing visually the technical work carried out during the project related to the test-cases from Micreon.
Test-case 1: Tungsten foil cutting for X-Ray emitters
In-line process monitoring techniques: LZH
Ultra-short pulse laser ablation process adaptive control: LZH
Process evolution analysis and smart decision making tool: Leuphana
Test-case 2: Biopolymer stent cutting
Thermal load monitoring and control: LZH
Figure 5 Poster summarizing the work carried out for the solution of the problems related to Micreon
1.4 EuroOrtodoncia
EuroOrtodoncia (EO) is a Spanish SME company located in Alcorcón (Madrid), devoted to orthodontic and dental market. EO is the only European company manufacturing transparent self-ligating brackets, which makes EO a leader in aesthetical orthodontic solutions.
EO, besides producing and commercializing its own orthodontic products, also trains orthodontic specialists. This unique structure allows EO to have a direct feedback from sector professionals and their patients and this way, be able to answer accordingly evolving in a continuous improvement.
1.4.1 Defined test-cases
In the case of EuroOrtodoncia (EO) the industrial test case, provided to MIDEMMA project, is the Chameleon self-ligating bracket cap (Figure 37 left). The caps clamp to the bracket bases, which are glued to patients' teeth and tighten the wire. The bracket cap has some critical features in the clip area having sizes around 100µm (Figure 37 right), especially concerning the clamping of the bracket cap.
Figure 6 Image of the self-ligating bracket cap (left) and detail of its critical features (right)
The proper replication of those micro-sized features is critical to ensure a correct orthodontic treatment, since the force transmission from the wire to the teeth is by means of the correct clamping of the cap to the bracket base. Due to the nature of the micro-injection process, several difficulties (unfilled/flashed parts, stuck mould, cavity erosion,…) are faced for the manufacturing of flawless caps, appropriate for their use in orthodontic treatments.
Related to this test-case, different working groups have been assembled in order to define and develop solutions for the different problems defined by the industrial end-user. Next, the different tasks related to the solution of the test-case are exposed briefly. Figure 38 shows a poster summarizing visually the technical work carried out during the project related to the test-cases from EuroOrtodoncia.
Test-case: Self-ligating bracket cap micro-injection
New mould concept: KUL+Sarix
Injection mould sensorization and process behaviour analysis: IK4-Tekniker
Image capture and machine monitoring integration on quality chain: EuroOrtodoncia
Process evolution analysis and smart decision making tool: Leuphana
Figure 7 Poster summarizing the work carried out for the solution of the problems related to EuroOrtodoncia
1.5 Sarix
SARIX SA is a Swiss micro-EDM solution provider founded in 1993. It has a long experience in EDM machine design, with the objective of satisfying the demand for EDM machines for the application of micro-erosion and micro-holes in several markets like automotive and aeronautics industry, for electronic and medical applications as well as for watch and toolmakers. SARIX has supplied his micro-EDM solutions to more than 15 technical universities and research organisations worldwide.
SARIX has developed a range of machines, with different standards of precision, for the manufacturing of miniaturized parts, the production of micro-holes, micro-milling and micro-machining. Since 2009 SARIX manufactures machining centres combining EDM with additional machining technologies like laser. SARIX has reached a leader position in his field in the Swiss and European markets and is currently expanding throughout the rest of the world. Machines have been sold in Asia and the USA. A network of local agents assures the support of the SARIX products worldwide. The company structure maintains a strong accent toward research, machine- and application-development. SARIX maintains its position as leader in the field of micro-erosion and micro-machining through considerable investments in development both in manpower and infrastructures.
1.5.1 Defined test-cases
Two main test-cases have been defined within the context of micro-EDM and related to Sarix. On the one hand, the manufacturing of the micro-injection mould for the EuroOrtodoncia test-case has been selected for the evaluation of the achievable process accuracy. On the other hand, the hybrid laser ablation + micro-EDM process used for the drilling of turbine blades has been analysed too during the project.
Related to these test-cases, different working groups have been assembled in order to define and develop solutions for the different problems defined by the industrial end-user. Next, the different test-cases and the tasks related to their solution are exposed briefly. Figure 39 shows a poster summarizing visually the technical work carried out during the project related to the test-cases from Sarix.
Test-case 1: Micro-injection mould manufacturing
Adhesive based clamping device for complex part handling and flipping: KUL
High accuracy machine positioning measurement system: KUL
On-machine tool wear measurement and adaptive compensation: KUL+Sarix+BLUM
Discharge pulse analysis and evolution tool: Tagueri
Test-case 2: Turbine blade hybrid laser-EDM drilling
In-line measuring system + electrode centering procedure: LZH+Sarix
Micro-ECM machine and technology development: Brunel
Figure 8 Poster summarizing the work carried out for the solution of the problems related to Sarix
List of Websites:
www.midemma.eu
Zero defects manufacturing is an objective long aspired in modern industries. Producing parts that do not meet the requirements leads to negative economic impacts, from wasted manufacturing resources to the need of more expensive equipment for manufacturing and quality control. Moreover, more and more sectors cannot allow defect parts in critical applications due to safety issues.
This project aims at contributing to this on-going effort in optimizing manufacturing processes combining the minimisation of defects within reasonable economic conditions, but not aiming at general manufacturing, but focusing on micro-manufacturing, considered here as the production of small parts with functional features in the range of the micrometer and medium size parts with form requirements below the micrometre and surface roughness requirements even below the nanometre (typically optical elements). Silicon based microsystems are not considered in the project, focusing the activity to engineering micro-components and high precision optics and lenses.
Micro-manufacturing requires 'Zero-Defect' oriented approaches, both in large scale and in short-run production. Current quality control approaches, coming from macro-manufacturing, are mainly based on post-process geometric control, which produces a large time lag between the defect generation and its detection, usually leading to large amount of defect parts (large scale) or wasted high value processing (short run). Moreover, this approach does not immediately point the error source to help with error correction, and other criteria such as material integrity, physical properties, surface topography and piece or component functionality are not taken into account typically.
There is clear need for extending the final product validation to a process monitoring approach in micro-manufacturing, where all the manufacturing process is monitored, from the raw material to the fabrication processes and the manipulation of the final parts, and where all this information is processed in real time with suitable models for error prediction, automatic detection and process optimization by system correction.
The project will give a global solution for the 'zero defect' approach in micro-manufacturing, with a focus on the aspects that are specific to micro-manufacturing. The developed technologies concepts are expected to have in impact in the competitiveness of the micro-manufacturers in the following ways:
• reducing process variability detecting defects as soon as they are generated or in the case that it is possible, are going to be generated by predicting models.
• allowing the use of less expensive machines, that can reduce their variability through monitoring.
• requiring less skilled working force, thanks to acquired process setting knowledge and the development of smart decision-making tools.
Project Context and Objectives:
Objective 1: Work piece manipulation and metrology
General Concept On-machine devices for work piece manipulation and metrology, which reduce impact of raw material variability and provide information for online process control and for feeding process models.
Objective 1.1 Work piece manipulation and clamping.
Concept Development of a work piece chucking system with high damping capacity.
Technology Work piece clamping device based on UV-curable adhesives, that can provide high repeatability, sufficient stiffness and damping, and not leaving clamping damages on the workpiece
Benefit Work piece positioning with sub-micron repeatability and with no damage on the work piece, adapted to micro-components and optical surfaces.
Achievements MONTH 36
• Requirement definition for clamping devices to be developed within the project.
• Definition of the technologies and methodologies to be employed for the design of clamping devices.
• Prototypes for the workpiece manipulation devices.
• Evaluation of prototype performance and industrial validation.
Objective 1.2 Work piece metrology.
Concept Devices for measurement of work piece geometric characteristics and raw material properties. Work piece geometry, surface roughness, tool-work piece relative position, raw material metallography, grain size etc. will be measured, before, during or after the machining process.
Technology Development of contact probes for 3D point measurement with uncertainty below 100 nm, optical microscopy devices for 3D topography, surface roughness and metallography. Integration of these devices on the machine. Develop models and algorithms for extracting relevant information for the process.
Benefit Avoid errors due to raw material variability. On-machine monitoring actual workpiece condition, for adapting the process and for final validation.
Achievements MONTH 36
• Identification of the requirements to be applied to measurement devices the characterization of features related to micromanufacturing applications.
• Determination of the metrology strategies to be developed on the design of work piece and tool characterization devices.
• Prototypes for the workpiece metrology devices.
• Performance evaluation for the prototypes and industrial validation.
Objective 2: Process monitoring
Concept Develop measuring devices and monitoring strategies that can provide meaningful information for online process control and for feeding process models.
Technology - Tool monitoring: Optical devices for on-machine tool inspection, adapted to precision machining processes as micro-milling, turning and microEDM.
- Laser ablation monitoring: Laser pulse energy analysis, autofocus system and thermal camera for online monitoring of laser micro-machining process.
- Replication monitoring: Analyse optimal sensor type, number and location for monitoring mould injection cycle for a variety of parts specifications
Benefit Provide information to the control on the actual process conditions so that the variability of the process result coming from effects such as tool wear, tool breakage, loss of laser focus or thermal damage. The information is also used to build statistical models.
Achievements MONTH 36
• Determination of the present requirements related to process monitoring (tool status, process parameters) with application to micromanufacturing applications.
• Definition of the process monitoring approaches to be applied on the test-cases defined within the project.
• Evaluation of the developed monitoring techniques regarding their behaviour on industrial conditions.
Objective 3: Process control
General Concept Develop and implement on machine active and adaptive strategies to optimise the processes addressed in the project: Precision machining, Laser micro-manufacturing, micro-EDM and Replication.
Objective 3.1 Precision machining
Technology Strategies to actively adapt process conditions and detect need for tool replacement due to wear or breakage in function of tool wear and alignment on-machine monitoring information.
Benefit Higher machining accuracy through reducing variability due to tool wear and alignment errors. Reduced tool cost through optimal tool replacement strategy. Early tool breakage detection.
Achievements MONTH 36
• Identification of the existing necessities related to tool wearing and breakage control on chip removal processes for micromanufacturing applications.
• Proposal for the strategies to be followed for the correction of the measured deviations on the tools in order to avoid the flaw generation on the workpieces.
• Analysis of the effect of the tool wearing on the workpiece quality.
• Industrial validation of the control strategies for machining processes in comparison to the defined objectives.
Objective 3.2 Laser micro-manufacturing
Technology Strategies for adaptive process control, integrating laser pulse energy monitoring system, laser auto-focus system and thermal camera to ensure optimal laser ablation.
Benefit Laser focus control leads to higher process repeatability (less defects) and accuracy (more demanding tasks feasible). Thermal control avoids thermal damage (less defects) and permits higher productivity with safe operation.
Achievements MONTH 36
• Determination of the requirements associated to error identification and elimination from the laser ablation process.
• Definition of the adaptive control methodologies to be applied for the elimination of defects from the laser ablation process.
• Assessment of the capabilities of the laser process monitoring techniques developed for the fulfilment of the defined project objectives.
Objective 3.3 Micro-EDM
Technology Active control techniques to adapt the machining strategies (including CAM) for the compensation and re-generation of the EDM micro-machining data (both tool path and process strategies) based on tool and workpiece monitoring information.
Benefit Higher process accuracy and repeatability, and thus possibility of achieving more demanding tolerances and minimising defects due to process variability
Achievements MONTH 36
• Identification of the needs related to tool status and spark analysis for process control.
• Determination of the control strategies to be applied for the application of zero-defect manufacturing concepts to the µEDM process.
• Validation of the analysis developed for the µEDM regarding the characterization of the process state on industrial conditions.
Objective 3.4 Replication
Technology Predictive virtual tools and models to process monitoring information and define the best moulding configuration and to assess the quality of the mould after each production run. Sensoring of moulds for monitoring.
Benefit Higher process repeatability and early mould failure detection. Time reduction in mould tuning and process set-up
Achievements MONTH 36
• Identification of the existing needs for the control of the microinjection process on a zero-defect frame.
• Definition of the approaches to be applied for the error detection on the microinjection process.
• Development and industrial validation of the process control scheme based on the parameters identified as key regarding the process quality.
Objective 4: Process modelling and data management
Objective 4.1 Process prognosis models
Concept Develop statistical models for micro-manufacturing processes based on extensive monitoring information
Technology Statistical models that relate process variability and defect generation with the inputs from the monitoring information to help determining achievable tolerances, frequency of maintenance (tool replacement), etc.
Benefit Virtual prediction of process tolerances and defect ratios at process definition stage and during processing.
Achievements MONTH 36
• Determination of the data to be employed for the development of process prognosis models.
• Identification of the process indicators and the vital parameters for each process
• Industrial implementation of software tools for process data analysis and evaluation, focusing on error identification and avoidance.
Objective 4.2 Proactive data management
Concept Integrate error prediction methodology into a decision making tool in order to allow a early recognition of planning deviations, ensuring quality standards.
Technology Smart data management tool integrating data reduction (extensive monitoring leads to data rich environment), key variable selection, online quality prediction and decision making strategies.
Benefit Automatic management of process and monitoring information for fast prognosis and proactive quality control.
Achievements MONTH 36
• Identification of the hardware and software requirements for the development of proactive data management tools for the end-users within the project.
• Definition of the quality assurance structure for the PDMT
• Development of the structure for the PDMT, applicable to the different manufacturing processes addressed on the project.
Project Results:
1 Improvements on micro-manufacturing processes
The micro-manufacturing processes, due to their lower-scale nature, show several problems and difficulties in comparison to common manufacturing processes. The small geometrical features to be manufactured and the very tight tolerances for dimensional and surface characteristics induce not just a quantitative difference regarding the quality management, but a qualitative jump in comparison to average manufacturing processes. The verification of the employed tools and manufactured workpieces require the use of on-machine devices for the preparation and inspection of the processes. Besides, concerning the possibility to define process control scenarios, the low process signal (forces, power, current,…) amplitudes and their poor signal-to-noise ratio make the usual monitoring devices on the market not suitable for micro-manufacturing applications. This way, several solutions have been proposed to overcome the difficulties on the implementation of zero-defect manufacturing schemes related to different micro-manufacturing processes. Next, these solutions are grouped concerning each manufacturing process addressed during the MIDEMMA project.
1.1 Micro milling
Concerning the micromilling processes, and related to the expected improvements defined by the end-user Createch-Medical, the work has been focused on the avoidance of geometrical defects and process quality instabilities generated by the appearance of wool wear during the machining process.
In the case of the geometrical defects induced by the appearance of the tool wear, IK4-Ideko has developed a methodology for the accurate on-machine tool shape measurement using a non-contact laser device from BLUM-Novotest (Figure 2 left), linked to the analysis of the actual surface machined by the tool. These measurements have been validated by their comparison to high resolution confocal measurements (Figure 2 right), obtaining uncertainty values as high as 0,5 µm.
Figure 1 Tool measurement results (let) and confocal measurement used for validation (right)
Besides, once identified the actual tool geometry and the surface shape to be machined with it, a tool wear compensation method has been developed IK4-Ideko too, based on simple geometrical models developed for the machined part (Figure 3 left). The application of this method has been evaluated by analysing the strains induced on a fitting part machined with a worn tool when it is clamped (Figure 3 right). Results show that the developed method can significantly reduce the deviations induced by the worn tools and help avoiding the defect generation on parts designed for accurate fitting.
Figure 2 Surface geometrical model (left) and strains generated on fitting part (right)
Regarding the variation of the process state due to the appearance of tool wear, the monitoring and statistical treatment of process signals has been tackled by Brunel and Leuphana universities, in order to define a frame where an in-line evaluation of the process state could be done. After the analysis of several measurable process signals and different data treatment techniques, a good correlation was found between the appearance of tool wear and the increase of a wavelet coefficient from the cutting force (Figure 4).
Figure 3 Tool wear-cutting force pairs and evolution of wavelet coefficients with tool wear
Once identified the signal features with high correlation with the tool wear, a monitoring scheme has been defined in order to enable the in-line evaluation of the cutting forces. By the use of a piezoelectric dynamometer, a charge amplifier and an acquisition board, it is possible to evaluate in real time the cutting force signals (Figure 5 left). Finally, a software tool has been developed by Leuphana University for the evaluation of the obtained signals (Figure 5 right). This tool can compare the present signals with previously recorded ones in order to identify excessive tool wearing or process instabilities, helping the user on the decision making related to the process control so excessive waste of time and materials can be avoided.
Figure 4 Cutting force acquisition scheme (left) and GUI for the data treatment software (right)
1.2 Precision grinding
In the case of the precision grinding processes (Figure 6), the issues to be solved during the project were related to the optical component manufacturing processes from Kaleido technology. As in the case of the micromilling process, the most important deviations on part quality are related to the appearance of tool wear and its effect on the generated part geometry and surface quality, together with the generation of process instabilities.
Figure 5 Image of the precision grinding set-up
The first development linked to the precision grinding process has been oriented to the accurate on-machine measurement of the actual geometry for the grinding tools. Using a non-contact on-machine laser device from BLUM-Novotest (Figure 7), the University of Bremen has developed an automatic method for the accurate characterisation of the grinding tools. Validated against off-machine optical measurements for the same tools, this method allows for the identification of the shape deviations of the actual tool regarding the theoretical geometry defined for it with an accuracy of 0,1 µm.
Figure 6 Grinding tool measurement and profile deviations for different worn tool profiles
Next, the evolution of the grinding process state as the tool wears off has been analysed. The University of Bremen has worked on the realisation of cutting tests while monitoring several process signals. When comparing the obtained signal values and their evolution with the processing time (Figure 8), together with the appearance of the tool wear, correlations have been found that could later be used for the in-line analysis of the process state and estimation of the generated process quality.
Figure 7 Evolution of the cutting forces with the cutting time and the appearance of tool wear
The data generated on tool wearing and process signal evolution has been employed by the University of Leuphana for the development of a statistical analysis tool for the in-line evaluation of the state for the grinding process. Once developed a prognosis engine for the identification of the process state, a software tool with a user friendly human interface (Figure 9) has been developed.
Figure 8 GUI for the grinding process signal analysis tool
This tool can help on identifying process instabilities and quality deviations on the machined part. Also, it can provide the machine operator with recommendations for the modification or stopping the process in order to generate the desired part quality and avoid the scraping of parts.
1.3 Ultra-short pulse laser ablation
The part cutting based on ultra-short pulse laser ablation process (Figure 10) is directly linked to the manufacturing problems addressed by the industrial end-user Micreon, working with femtosecond (fs) laser systems. In this case, different difficulties related to the high process dynamics have been tackled as: instabilities on the laser source output, the identification of the laser focal position of the part and the need for in-line information regarding the workpiece state (cut width, part temperature) so the final workpiece quality could be estimated.
Figure 9 Example of a part cut by ultra-short pulse laser ablation
In this case, the Laser Zentrum Hannover (LZH) has worked on the implementation of different methods for the in-line process monitoring (Figure 11). On the one hand, a simple and cheap device for the measurement of the energy from single laser pulses down to 20 fs has been developed. Also, a system for the in-line identification of the cut width has been developed, obtaining accuracy values bellow 2 µm when working with feed rates up to 400 mm/min. Besides, a commercial auto-focus device has been implemented to work properly within a fs-laser context and, finally, a thermo-camera has been implemented on the machining set-up so part temperatures above 80 ºC can be identified and avoid the burning or the workpieces.
Figure 10 Representative images for each of the developed monitoring devices
Once the different monitoring devices were developed, the LZH has worked on the development and implementation of an adaptive process control scheme. Employing the in-line data obtained by the monitoring devices, rules for the actuation on the laser machine parameters have been developed. Figure 12 depicts the capability of the developed control to modify the laser output and stabilize the desired process variable. Thanks to this control scheme, the process parameters can be modified in real-time in order to generate the desired quality on the machined part.
Figure 11 Effect of the developed control on the laser output
Besides the adaptive process control approaches defined for this process, the development of statistical tools for the analysis of process trends and the prediction of non-controllable process deviations has been undertaken too. The University of Leuphana has worked on the analysis of the data provided by the auto-focus system implemented by LZH. Based on this data, the identification of high focal deviations is carried out. Thanks to this, it is possible to detect a part that would require too many corrections to attain the desired quality and suggest its scrapping to avoid excessive costs.
Figure 12 In-line focus control scheme and high focal deviation identification module
1.4 Micro injection
The micro injection processes have been tackled by the project too, defining the resolution of the manufacturing problems addressed by EuroOrtodoncia as the objective for some RTD tasks. Some of the problems found when manufacturing transparent bracket lids are the premature erosion of the mould, the occurrence of unfilled parts, the appearance of flashing on the parts or the trapping of parts on the mould.
As the first step, a new mould concept has been developed by EuroOrtodoncia and Tekniker. Besides providing the possibility to introduce sensors for the in-line monitoring of the micro injection process, the part location on the new mould would allow for higher throughput while avoiding the appearance of premature wearing on the moulding parts. The new part location involved considerable difficulties on the accurate manufacturing of the mould, but it was undertaken by the project partners KUL and Sarix with great success.
Figure 13 New injection mould concept with monitoring capabilities
After the inclusion of sensors on a test mould for the monitoring of process signals as pressure and temperature, IK4-Tekniker has carried out an experimental analysis concerning the effect of the values taken for different process signals and the quality generated on the micro injected part. This way, it has been possible to define several relationships between the process signals obtained on different mould locations and the obtained part quality.
Figure 14 Differences on process signals obtained from both good and bad parts
Besides, EuroOrtodoncia has worked on the implementation of an in-line inspection system for every manufactured part on their manufacturing chain. This system obtains images from the gripper that takes the parts away from the mould (Figure 16) and identifies the presence of the part together with some injection related problems as flashing. Thanks to this system, it is possible to automatically link the process data with the obtained part quality for the generation of an extensive manufacturing data log for its later treatment.
Figure 15 Images taken of the gripper with (left) and without (centre) injected part and main image of the quality control tables (right)
Both the actual manufacturing data obtained from the monitoring and the empirical modelling for the part quality previously carried out has been implemented by the University of Leuphana on a software module for the analysis of the micro injection process. Analysing the historical process monitoring data, this tool can identify different trends on the manufacturing quality for the generation of statistical models that could represent the actual process behaviour. Then, identifying deviations on the process parameters that could generate defective parts, and taking into account the high part throughput on this process, this tool can aid on the avoidance of high volume part scrapping.
Figure 16 Human interface for the micro injection data analysis tool
1.5 Micro electro discharge machining
In the case of micro electro discharge machining (µEDM) processes, they have been analysed within the project following the difficulties stated by the industrial end-user Sarix. The main problem found when analysing these processes is the appearance of a wrong inter-electrode gap due to the generation wear on the electrode working as the tool or the wrong positioning of the machine axes. Besides, due to the nature of the process itself the part material is modified during the machining, generating a heat affected zone (HAZ) on the machined surfaces that can be detrimental for the mechanical behaviour of the part.
On the one hand, the proper identification of the actual electrode geometry has been undertaken by the University of Leuven and BLUM-Novotest (Figure 18). By both contact (electrical spark analysis) and non-contact methods (laser system), an electrode measurement routine has been developed obtaining measurement uncertainties below 0,5 µm.
Figure 17 Images of the different electrode measurement methods analysed
Once developed an accurate way for the identification of the electrode geometry, the University of Leuven has carried out several experimental tests in order to analyse the wear generation along the µEDM process and implement the obtained results into a model for its application to actual machining processes. This model has been introduced by Sarix into their NC system, allowing the automatic tool wear compensation on µEDM milling operations (Figure 19).
Figure 18 Scheme for the wear compensation and Sarix NC with the implemented feature
Also, thanks to the possibility to accurately identify the contact between the electrode and a machined surface and the better understanding of the electrode wearing along the µEDM process, Sarix has added several features on their own CAM (Figure 20) for the improvement of the depth accuracy on the machined features and the generation of optimized tool paths yielding considerably lower processing times.
Figure 19 GUIs for the new developments implemented on the Sarix CAM system
Besides, Tagueri has worked on a system for the analysis of single sparks up to a frequency rate of 100 Mhz. This analysis has enabled the in-line identification of ‘good’ and ‘bad’ sparks during a µEDM process (Figure 21), making it possible to detect variations or trends along a machining process. The in-line application of this analysis can help aid the machine operator on decision making related to the modification of process parameters or even the stopping of a process based on the historical data and the observations during the machining process.
Figure 20 Representation of the different types of sparks identified
Finally, trying to face the material modification (HAZ) during the µEDM process, the University of Brunel has worked on the development of a machine prototype (Figure 22 left) for micro electro chemical machining (µECM). Due to the chemical nature of this process, it is possible to remove part material without modifying its state. After the development of a machine structure, an innovative pulse generator and a new control system, the performance of the prototype has been proven on the manufacturing of micro stylus for precision probes (Figure 22 right).
Figure 21 Overall image of the µECM prototype (left) and machined micro stylus (right)
2 Improvements on workpiece manipulation and metrology
The reduced work piece dimensions, feature sizes and/or surface roughness requirements in micro-manufacturing processes introduce some new challenges, which are not so critical in macro-manufacturing. Regarding the workpiece manipulation and clamping, they must ensure stiffness, damping, accuracy and possibility of automation (as in macro-manufacturing), but ensuring that the micro-features are not damaged. In the case of the metrology, it must be taken into account that measuring workpiece features with micrometre range geometries and (sub)-nanometre range surface roughness is very close to the limits of existing measurement principles.
The machines used for micro-manufacturing technologies differ drastically from state of the art macro-machining systems. Aerostatic or hydrostatic guide ways and spindles, optical encoders or even interferometers and thermally stabilised direct drives allow for a positioning precision down to the lower sub-micron scale. Opposite to the highly sophisticated machinery, the manipulation, alignment and clamping of workpieces as well as tools are mostly carried out manually with only little technical support. The necessary accuracy in the submicron range cannot be achieved by conventional workpiece handling and metrology systems used in the macro technology
2.1 Workpiece manipulation
In order to face some of the difficulties related to workpiece clamping and re-positioning for the micro-manufacturing of complex 3D geometries, the University of Leuven has developed a novel part fixing concept (Figure 23). On the one hand, it allows for clamping the parts by adhesive means in order not to damage micro sized geometrical features or optical surfaces and, due to the nature of the used adhesive, introduces additional damping capabilities (~30%) in comparison to the usual mechanical clamping devices. Besides, the system allows for the modification of the part fixing position, ensuring the re-positioning of the part with a location uncertainty lower than 1 µm.
Figure 22 Adhesive based part clamping and re-positioning system
Brunel University has worked on the development of a smart clamping system capable of monitoring the forces acting on different sections of the part (Figure 24). This way, it is possible to control the clamping forces in order to avoid possible geometrical distortions on the manufactured part. Also, it can work as an in-line dynamometer, providing the possibility for a detailed process state monitoring without the need to include an additional measuring element on the manufacturing equipment.
Figure 23 Prototype for the smart clamping system and example of measurement
2.2 Workpiece metrology
Facing metrology difficulties related to the high accuracy requirements for part positioning inside the machine-tools, the University of Leuven has developed a robust unidirectional measurement system based on the use of a moving measuring scale and a capacitive sensor. The design of the device has been carried out minimizing the Abbe errors and the ones coming from thermal and environmental sources. The preliminary validation of the prototype has shown a great consistency, attaining measurement uncertainties around 20 nm.
Figure 24 Measurement system and results from stability tests
Trying to provide capabilities for high precision on-machine measurements, IBS Precision Engineering has developed a full 3D ultra-precision contact probe capable of working within machine-tools on workshop environments. This probe has been tested to work on ultra-precision lathes for the measuring of calibrated artefacts and manufactured optical components (Figure 26), yielding measurement uncertainties below 50 nm.
Figure 25 On-machine contact probe, obtained measurement and uncertainty results
In order to improve probe measurements carried out off-machine, the National Physical Laboratory (NPL) has worked on the design and development of a vibrating micro-probe capable to work on non-contact mode. The stylus is placed on a MEMS structure allowing the generation of a controlled vibration of the probe tip (Figure 27). The performance tests carried out on an ISARA 400 ultra-precision coordinate measuring machine (CMM) have shown that the probe is capable of measurement accuracy below 60 nm.
Figure 26 Image of the MEMS structure for the stylus and overall image of the probe on the ISARA 400
Besides probe based measurement systems, optical measuring devices have been developed within the project too. Sensofar has developed a miniaturised microscope head capable for on-machine measurements, both by confocal and interferometry techniques. This on-machine microscope has been tested to work properly within the manufacturing environment at Kaleido (Figure 28), probing very helpful not just for the verification of the manufactured parts, but also for the machine and tooling set-up.
Figure 27 On-machine microscope and images for obtained measurements
Concerning optical metrology, the development of an optical CMM has been carried out by IK4-Ideko, implementing a 5-axis positioning structure on a PLu Neox optical profiler from Sensofar. Thanks to this structure, it is possible to obtain detailed measurements from complex 3D parts and treat them on the same reference system (Figure 29). Besides, in order to make this system competitive in comparison to contact based CMMs, Sensofar has worked on the development of a focus variation measurement technique, enabling very fast measurements with a high spatial resolution.
Figure 28 Image of the 5-axis microscope (left) and 3D representation of different measurements taken on a same workpiece (right).
Linked to the use of optical means for the characterization of complex parts with small and even damaged features, the development software for the treatment of the obtained measurements has been undertaken during the project too. Tagueri has worked on a tool that, applying statistical data mining techniques (Figure 30) is able to identify and disregards ‘bad’ points from the measurements, increasing the reliability of the results obtained from the optical measurements.
Figure 29 Graphical representation of the data treatment on the PDMT for measurements.
Finally, trying to bridge the gap between contact and optical form and roughness measurements, the NPL has analysed the possibility to define traceability routes between both types of measurements. While evaluating the measurement results yielded by different optical measurement methods in order to define their application range, calibration procedures and artefacts (Figure 31) have been defined for optical measurement equipment.
Figure 30 Areal Calibration Set from NPL
Potential Impact:
Concerning the exploitation of the project outcomes, several activities have been carried out along the project duration in order to define the possible exploitable results and ensure the achieving of the defined exploitation objectives. Two Exploitation Strategy Seminars have been undertaken; the first one (19/03/2013 at Hannover, M18) was the first attempt within the project for the definition of the exploitable results and their characterization. During the second one (18/07/2014 at Leuven, M33), the strategies to be followed to ensure their exploitability and market reach were verified and redefined when needed. These actions leaded to the next exploitation outcomes from the project:
• 4 New products / 2 Product improvement
• 2 Software developments close to industrialization
• 4 New services
• 5 Beta-users (industrial implementations)
• 1 PPP partnership
• 1 new company (start-up)
• 1 licence
1 Demonstration/Industrial validation
The technical outcomes generated during the project have been demonstrated and validated by their application to manufacturing problems defined by the industrial end-users. For each of them, different problems were identified related to their value chains and involved manufacturing processes. This way, the identified problems defined the test-cases to be treated during the project, as well as the objectives for the technical tasks of the project.
Next, each industrial end-user is briefly introduced together with the test-cases related to them.
1.1 Createch-Medical
Createch Medical designs and manufactures metallic frames for dental prostheses that are personalized to meet each patient’s case requirements. Starting from a model of the actual implants provided by the doctor, Createch manufactures the frame attached to the implants and the supporting base for the teeth.
The frame and teeth supporting base are mainly manufactured on single piece Ti6Al4V or CrCo by micromilling. During the design and manufacture of the prosthesis, exceptional care must be taken on the frame-implant connections. A slight deviation on the position of one of those connections would generate stresses on the jaw of the patient and, thus, pain; making the prosthesis unacceptable. Moreover, the stresses induced by the clamping of the prosthesis could even generate the rejection of the implants.
1.1.1 Defined test-cases
Concerning the case of Createch Medical, three test-cases have been defined for their analysis within the project. They are related to the present manufacturing chain from Createch-Medical, covering the characterization of the model with the dental implant analogues and the precision milling process of the dental frames. Related to these test-cases, different working groups have been assembled in order to define and develop solutions for the different problems defined by the industrial end-user. Next, the different test-cases and the tasks related to their solution are exposed briefly. Figure 32 shows a poster summarizing visually the technical work carried out during the project related to the test-cases from Createch-Medical.
Test-case 1: Implant model characterization
5-axis microscope to work as optical CMM: IK4-Ideko+Sensofar
Optical measurement treatment for optimum data extraction: Tagueri
Test-case 2: Dental prosthesis micromilling
Smart vice for the measurement of cutting and clamping forces: Brunel
On-machine actual tool shape characterization and compensation: IK4-Ideko+BLUM
Cutting force signal based tool state monitoring and control: Brunel+Leuphana
Figure 1 Poster summarizing the work carried out for the solution of the problems related to Createch-Medical
1.2 Kaleido Technology
Kaleido is developing wafer level optics for production of small lenses mainly for the mobile phone market. The company is doing only R&D and not actual production and thus does not have any large-scale automated production facilities. Kaleido Technology is currently maturing the technology for large-scale production and, therefore, focusing on stabilizing the manufacturing and minimizing manual assistance in the process. The main aim has been to implement in-line checks of the tooling quality and the definition of strategies for the avoidance of defective geometries.
1.2.1 Defined test-cases
Concerning the manufacturing processes from Kaleido Technology, two test-cases have been defined for their analysis within the project. They are related to the manufacturing of lens replication moulds on different materials as tungsten carbide and non-ferrous metals (Figure 33) by precision grinding and diamond milling. This way, the work carried out has been divided into two main groups: one relative to the own manufacturing process and its control, the second one focused on the characterization of the manufactured optical devices.
Figure 2 Precision grinding of an optical mould array on a tungsten carbide wafer
Related to these test-cases, different working groups have been assembled in order to define and develop solutions for the different problems defined by the industrial end-user. Next, the different test-cases and the tasks related to their solution are exposed briefly. Figure 34 shows a poster summarizing visually the technical work carried out during the project related to the test-cases from Kaleido Technology.
Test-case 1: Optical mould manufacturing
On-machine tool shape monitoring and compensation strategies: Bremen+BLUM
Process evolution analysis and smart decision making tool: Leuphana
Test-case 2: Optical mould characterization
Ultra-precision on-machine 3D contact probe: IBS-PE
Vibrating non-contact probe: NPL
On-machine microscope: Sensofar
Traceability routes for contact and non-contact measurements: NPL
Figure 3 Poster summarizing the work carried out for the solution of the problems related to Kaleido Technology
1.3 Micreon
Micreon GmbH, located in Hannover (Germany), is a contract manufacturer for ultrafast laser micro machining. Applied techniques are laser micro cutting, laser micro drilling, and laser micro engraving. Processing is done with ultrashort pulse lasers. These lasers allow for precise, burr-free laser ablation of all solid and gel materials.
From the manufacturing of single proto-types to mass production, Micreon offers the complete range of material processing. The expertise in the field of ultrashort pulse lasers and high-precision positioning systems allows Micreon to provide industrial micro-machining systems using ultrafast laser technology. Micreon operates as a technical interface between laser manufacturers and industrial users of ultrafast lasers. As specialists in ultrafast laser technology, the Micreon team offers training and coaching of the technical staff that operates the laser work stations for industrial applications.
1.3.1 Defined test-cases
The two MIDEMMA test cases of Micreon are wolfram foil cutting for X-ray emitters and biocompatible polymer stent cutting. Both have in common the application of ultrashort pulse laser microcutting. The most important differences are material and shape – plane metal parts in the case of the X-ray emitters and highly heat-sensitive biopolymer tube material in the case of the stents. Cutting widths are 30 to 50 µm. The metal sheet thickness for the emitters is 100 µm. The tube wall thickness for the stents is 300 µm. Figure 35 shows both test case parts and their applications.
Figure 4 X-Ray emitter (left) and biopolymer stent (right)
Related to these test-cases, different working groups have been assembled in order to define and develop solutions for the different problems defined by the industrial end-user. Next, the different test-cases and the tasks related to their solution are exposed briefly. Figure 36 shows a poster summarizing visually the technical work carried out during the project related to the test-cases from Micreon.
Test-case 1: Tungsten foil cutting for X-Ray emitters
In-line process monitoring techniques: LZH
Ultra-short pulse laser ablation process adaptive control: LZH
Process evolution analysis and smart decision making tool: Leuphana
Test-case 2: Biopolymer stent cutting
Thermal load monitoring and control: LZH
Figure 5 Poster summarizing the work carried out for the solution of the problems related to Micreon
1.4 EuroOrtodoncia
EuroOrtodoncia (EO) is a Spanish SME company located in Alcorcón (Madrid), devoted to orthodontic and dental market. EO is the only European company manufacturing transparent self-ligating brackets, which makes EO a leader in aesthetical orthodontic solutions.
EO, besides producing and commercializing its own orthodontic products, also trains orthodontic specialists. This unique structure allows EO to have a direct feedback from sector professionals and their patients and this way, be able to answer accordingly evolving in a continuous improvement.
1.4.1 Defined test-cases
In the case of EuroOrtodoncia (EO) the industrial test case, provided to MIDEMMA project, is the Chameleon self-ligating bracket cap (Figure 37 left). The caps clamp to the bracket bases, which are glued to patients' teeth and tighten the wire. The bracket cap has some critical features in the clip area having sizes around 100µm (Figure 37 right), especially concerning the clamping of the bracket cap.
Figure 6 Image of the self-ligating bracket cap (left) and detail of its critical features (right)
The proper replication of those micro-sized features is critical to ensure a correct orthodontic treatment, since the force transmission from the wire to the teeth is by means of the correct clamping of the cap to the bracket base. Due to the nature of the micro-injection process, several difficulties (unfilled/flashed parts, stuck mould, cavity erosion,…) are faced for the manufacturing of flawless caps, appropriate for their use in orthodontic treatments.
Related to this test-case, different working groups have been assembled in order to define and develop solutions for the different problems defined by the industrial end-user. Next, the different tasks related to the solution of the test-case are exposed briefly. Figure 38 shows a poster summarizing visually the technical work carried out during the project related to the test-cases from EuroOrtodoncia.
Test-case: Self-ligating bracket cap micro-injection
New mould concept: KUL+Sarix
Injection mould sensorization and process behaviour analysis: IK4-Tekniker
Image capture and machine monitoring integration on quality chain: EuroOrtodoncia
Process evolution analysis and smart decision making tool: Leuphana
Figure 7 Poster summarizing the work carried out for the solution of the problems related to EuroOrtodoncia
1.5 Sarix
SARIX SA is a Swiss micro-EDM solution provider founded in 1993. It has a long experience in EDM machine design, with the objective of satisfying the demand for EDM machines for the application of micro-erosion and micro-holes in several markets like automotive and aeronautics industry, for electronic and medical applications as well as for watch and toolmakers. SARIX has supplied his micro-EDM solutions to more than 15 technical universities and research organisations worldwide.
SARIX has developed a range of machines, with different standards of precision, for the manufacturing of miniaturized parts, the production of micro-holes, micro-milling and micro-machining. Since 2009 SARIX manufactures machining centres combining EDM with additional machining technologies like laser. SARIX has reached a leader position in his field in the Swiss and European markets and is currently expanding throughout the rest of the world. Machines have been sold in Asia and the USA. A network of local agents assures the support of the SARIX products worldwide. The company structure maintains a strong accent toward research, machine- and application-development. SARIX maintains its position as leader in the field of micro-erosion and micro-machining through considerable investments in development both in manpower and infrastructures.
1.5.1 Defined test-cases
Two main test-cases have been defined within the context of micro-EDM and related to Sarix. On the one hand, the manufacturing of the micro-injection mould for the EuroOrtodoncia test-case has been selected for the evaluation of the achievable process accuracy. On the other hand, the hybrid laser ablation + micro-EDM process used for the drilling of turbine blades has been analysed too during the project.
Related to these test-cases, different working groups have been assembled in order to define and develop solutions for the different problems defined by the industrial end-user. Next, the different test-cases and the tasks related to their solution are exposed briefly. Figure 39 shows a poster summarizing visually the technical work carried out during the project related to the test-cases from Sarix.
Test-case 1: Micro-injection mould manufacturing
Adhesive based clamping device for complex part handling and flipping: KUL
High accuracy machine positioning measurement system: KUL
On-machine tool wear measurement and adaptive compensation: KUL+Sarix+BLUM
Discharge pulse analysis and evolution tool: Tagueri
Test-case 2: Turbine blade hybrid laser-EDM drilling
In-line measuring system + electrode centering procedure: LZH+Sarix
Micro-ECM machine and technology development: Brunel
Figure 8 Poster summarizing the work carried out for the solution of the problems related to Sarix
List of Websites:
www.midemma.eu
