Final Report Summary - DYNAMILL (Dynamic manufacturing of thin-walled work pieces by milling process)
Executive Summary:
DynaMill – Dynamic manufacturing of thin-walled work pieces by milling process
Light weighted components are becoming increasingly important in key European industries like aerospace, automotive, energy sector and bio-medical engineering. In order to minimize weight, complex thin-walled structures are frequently designed and manufactured utilizing high-strength materials. However, the lack of rigidity of many of these thin-walled parts presents a considerable challenge in terms of machining: It is vital to reduce the dynamic excitation caused by tool engagement, to minimize the static deflections arising from milling forces and to mitigate deformation resulting from clamping forces. The aim of the EU-funded Research Project »DynaMill« is, therefore, to master milling operations carried out on thin-walled parts and to optimize these operations using a holistic approach in order to eliminate any danger of unwanted dynamic effects which could give rise to surface defects and poor quality. Process planning (module 1), adaptive clamping systems (module 2) and cutting conditions (module 3) must be designed to interlock with one another in the »DynaMill Technology« in order to achieve the required quality in conjunction with considerable reduction in manufacturing time and resource input.
Module 1 – Process Planning
The aim is to develop a CAx (Computer Aided Technologies, e.g. CAD/ CAA/ CAM) software tool, capable of taking account at the CAM planning stage of the oscillation and resonance behavior of work in process part during machining. It is envisaged that dynamic simulations and numerical calculation will achieve stable milling operations in the machine tool and simultaneously improve surface quality and form accuracy of the work pieces.
Module 2 – Adaptive Clamping Systems
Investigation into dynamic effects of part clamping is a further milestone of this project. Initially, a design methodology is developed for clamping systems with good dynamic characteristic and subsequently effects of various damping mechanisms in clamping systems are investigated. To achieve a robust machining operation for thin-walled parts, clamping systems will be developed on the basis of highly efficient damping materials or with passively and actively controlled anti-vibration devices.
Module 3 – Cutting Conditions
The aim of this module is to ensure higher levels of process stability during milling operations conducted on thin-walled parts by introducing improved cutting tools technology: Systematic analysis of micro and macro geometry of cutting tools in association with the use of highly efficient damping materials will increase the damping effect in the machining process. Crossing over with the module 1, additional work will focus on optimized machining strategies which will be conducive to more homogeneous cutting conditions and less excitation of system eigenfrequencies.
»DynaMill Technology«
The developed three modules were integrated and combined in a machine tool as a robust platform so that a fully integrated manufacturing solution is possible. The comparison of the former and newly developed manufacturing processes as well as evaluation was also foreseen in the project. For example, based on the demonstration 1b (blade of about 700 mm length) a reduction of machining time of about 10% was possible. Despite realizing a faster process, the sound pressure (noise signal) and the Power in Band (PIB) value which are within the project definied measures for process stability could be decreased by about 65% and 50%. Furthermore, regarding the tool wear an improvement of about 50% was achieved. Summarized, the »DynaMill Technology« achieved very good results and reached the predefinied objectives.
Project Context and Objectives:
DynaMill – Dynamic manufacturing of thin-walled work pieces by milling process
Light weighted components are becoming increasingly important in key European industries like aerospace, automotive, energy sector and bio-medical engineering. In order to minimize weight, complex thin-walled structures are frequently designed and manufactured utilizing high-strength materials. However, the lack of rigidity of many of these thin-walled parts presents a considerable challenge in terms of machining: It is vital to reduce the dynamic excitation caused by tool engagement, to minimize the static deflections arising from milling forces and to mitigate deformation resulting from clamping forces.
The aim of the EU-funded Research Project »DynaMill« is, therefore, to master milling operations carried out on thin-walled parts and to optimize these operations using a holistic approach in order to eliminate any danger of unwanted dynamic effects which could give rise to surface defects and poor quality. Process planning, adaptive clamping systems and cutting conditions must be designed to interlock with one another in the »DynaMill Technology« in order to achieve the required quality in conjunction with considerable reduction in manufacturing time and resource input.
Module 1 – Process Planning
The aim is to develop a CAx (Computer Aided Technologies, e.g. CAD/ CAA/ CAM) software tool, capable of taking account at the CAM planning stage of the oscillation and resonance behavior of work in process part during machining. It is envisaged that dynamic simulations and numerical calculation will achieve stable milling operations in the machine tool and simultaneously improve surface quality and form accuracy of the work pieces.
Module 2 – Adaptive Clamping Systems
Investigation into dynamic effects of part clamping is a further milestone of this project. Initially, a design methodology is developed for clamping systems with good dynamic characteristic and subsequently effects of various damping mechanisms in clamping systems are investigated. To achieve a robust machining operation for thin-walled parts, clamping systems will be developed on the basis of highly efficient damping materials or with passively and actively controlled anti-vibration devices.
Module 3 – Cutting Conditions
The aim of this module is to ensure higher levels of process stability during milling operations conducted on thin-walled parts by introducing improved cutting tools technology: Systematic analysis of micro and macro geometry of cutting tools in association with the use of highly efficient damping materials will increase the damping effect in the machining process. Crossing over with the module 1, additional work will focus on optimized machining strategies which will be conducive to more homogeneous cutting conditions and less excitation of system eigenfrequencies.
The overall objective of the DynaMill project is to strengthen the European thin-walled manufacturing community in manufacturing of thin-walled work piece by realising a better control of the milling process for thin-walled work pieces. This will be achieved through the development and demonstration of an integrated solution, named »DynaMill Technology«, which is a robust platform for machining of thin-walled work pieces. The DynaMill project will impact the competitiveness of the European manufacturers of thin-walled work pieces by:
• Enhancing process knowledge and capability in milling of thin-walled work pieces
• Enhancing process knowledge and capability in application of clamping devices
• Increasing product and process quality, precision as well as output
• Improving life time and capability of milling tools
• Impacting on production efficiency and the strategically crucial time-to-market factor for manufacturing companies
The overall Scientific and Technological (S/T) objective of the DynaMill project are development, demonstration and evaluation of the »DynaMill Technology« for the manufacturing of thin-walled work pieces. DynaMill is built-on three distinct technology modules, the several S/T objectives that have to be accomplished in three modules are the following:
Module 1 – Process Planning
• Prediction of the natural response of the thin-walled work piece system
• Prediction of the dynamic beahaviour of thin-walled work piece systems during machining based upon the simulation of material removal process
• Improved process control for CAM of thin-walled work pieces by parameterizing of the influencing factors
• Development of a CAM process planning based on modal calculations
Module 2 – Adaptive Clamping Systems
• Gathering knowledge on vibrations and continuum mechanics in clamping devices
• Development of clamping devices with approaches of locator/ positioning
• Development of clamping devices with enhanced damping
• Development of clamping systems with adjustable degrees of freedom in locators
• Development of the choice and arrangement of sensors and the proper analysis of the signals
• Developing of an active damped clamping device on demonstrator level
Module 3 – Cutting Conditions
• Developing milling tool designs which increase process stability
• Crossing over with the module 1: Developing a optimized machining strategies for achieving homogenized cutting conditions and less excitation of system eigenfrequencies.
Project Results:
Major task of the first project months was to define the diferent project demonstrators.
• Large and midsize turbine blades of the energy sector, material: alloy steel
• Small turbine blade of the aviation sector, material: titanium
• Prismatic satellite part of the space flight sector, material: aluminium
• Knee bone part of the medical sector, material: titanium
• Prismatic parts of the print media sector, material: steel
Based on these demonstrators the developments of the »DynaMill Technology« (modules 1, 2 and 3) were derived.
Module 1 – Process Planning
The aim of module 1 is to provide a process planning tool for calculating adapted NC code for thin-walled workpieces. This is achieved in a so called DynaMill loop. Figure 1 (in attached pdf) depicts this loop and the respective partners for the relevant developments. This was performed in work package 2. Additionally, the overall system is demonstrated in work package 7 on demonstrator workpieces from the end users of the consortium. The topics of module 1 are covered within the workpackages 2 and 7. During task 2.1 (T2.1) a method to build the simulation model for the prediction of dynamic behaviour of thin-walled work pieces has been developed and verified by testing on simplified prismatic shaped parts. The method involves an approach to develop a process model based upon an FEM simulation method and a simplification of the FEM simulation node-net model which also improves the computation efficiency. During T2.2 the material removal simulation models have been developed and tested on CAM models of representative cases of part and raw material. An orthogonal 3 phase needle model has been utilized to predict the machined part models and improved polygon meshing techniques have been applied to enhance the accuracy and completeness of model data structure. The coupling and integration has been implemented during task T2.3. Testing and error fixing of the integration and related components including above two simulation models was done subsequently. T2.4 involves parameterizing the models developed in T2.1 and T2.2 against the variation in part geometries. The relevant types of cutting tools geometries have been specified and the prediction models are being evaluated. Evaluation between the numerical and analytical models and the interfaces for coupling either of them with the results of task T2.3 have been specified. In T2.5 the first step is to identify the types of machining process, this has been completed and based upon the spectrum of demonstrator parts. The implemented CAM strategy is executed into a computer software and produce numerical control (NC) data to control the machine tool. T2.6 has been completed. The integrated CAM module has been developed as a prototypic implementation within Siemens NX. The toolpath planning of blade profiles is possible in three different strategies. The first aspect of this task is the development of algorithms to produce NC data with the variable spindle revolutions and corresponding, variable feedrates. The variable spindle revolutions and feedrate values are applicable to different areas of a thin-walled workpieces. Two partition strategies were implemented in the CAM tool. The first one foresees a change of the process settings with varying position of the tool along the blade vector – the direction from the tip to the foot of the blade. The second strategy divides the blade surface into checkerboard like rectangles and for each rectangle an individual setting of spindle speed and feedrate can be made, based on the FRF calculations. The second strategy was implemented based on the experience from experiments. For example, to suppress torsion-like vibrations in the blade, different settings in the center region compared to the edge region is required. The strategies can be transfered to other types of workpiece geometries as well. In workpackage 7, the developments made in work package 2 are demonstrated and evaluated. Using the process planning software, the dynamic behaviour of the demonstrator parts were determined, based on calibration frequency response measurements. The performance of the agile spindle was evaluated during the demonstrations. In the demonstration activities T7.1 has been completed and was focused upon the demonstration results of dynamic simulation model developed during task T2.1. In T7.2 the partner consultation has been performed to define the conditions of pre-finished parts and build them into the integrated process planning model of taks T2.5. The start of T7.4 is linked with T2.6. T7.4 was initiated during the final phase of the CAM module developments and the connection of the CAM module with the simulation routines. During month 30, experiments at project partner Starrag were made to show the spindle speed variation at demonstrator 2. There, the strategy of a varying spindle speed as a function of the position along the blade vector was used (see Figure 2 in attached pdf). The demonstration of the »DynaMill Technology« on two different demonstrators were performed at project partner Alstrom and IPT. There, the checkerboard strategy was applied. The results included also the results from modules 2 and 3, damping-optimized fixture system and improved milling tools.
Module 2 – Adaptive Clamping Systems
Based on the information described in the DynaMill DoW, in work package 3 all tasks are accomplished. In T3.1 existing know-how regarding the design of clamping systems was gathered. Existing clamping solutions have been analyzed with regard to stiffness and occurring workpiece vibrations. These analyses have been supported by RCMT and IPT with FEM simulations. HPS and STH with the support of IPT have constructed and installed improved conventional clamping devices. Based on the perceived know-how, a procedure for constructing improved clamping systems with enhanced stiffness has been deduced. In T3.2 novel approaches to use highly efficient damping materials in clamping device designs have been realized. Appropriate milling trials showed promising results for passive damping systems in clamping devices. A novel damping system for magnetic clamping systems has been developed. A tuned mass damper (TMD) was developed and tested by HPT and IPT. FRE and IPT developed a hydraulic absorber device for vices (see Figure 3 in attached pdf). The experiments showed that the damping factor was increased over a factor of about 8. Furthermore, a root clamping device was developed (see Figure 4 in attached pdf) which was used for the demonstrator 1a. The root clamping device works with a floating clamping mechanism, which is important to compensate the cast oversize and the surface roughness. Demonstrations confirmed the high damping properties of the clamping device. In T3.3 a steady-rest system for balde manufacturing developed by Starrag has been improved. A novel automated clamping device for large turbine blades has been developed. In T3.4 a market research regarding available sensors has been conducted and simulations for the design of the active damping device have been realized. In T3.5 the active damping device was developed and tested in milling tests. The tests showed the high potential of this approach. Based on the described reseach avtivities, in WP6 and WP8 it was shown, that chatter marks on the demonstrator surface can be avoided, that the tool wear can be reduced over about 60% and that the noise can be reduced significant with developed DynaMill clamping devices. For example, when machining demonstrator 1b, the developed DynaMill clamping device (see Figure 5 in attached pdf) raised the process stability significantly, so that the efficiency of the milling process could be increased as well.
Module 3 – Cutting Conditions
In a first step predominant measures to increase tool damping in milling process of thin walled work pieces were determined (T4.2). Based on this, the development and allocation of innovative damping tool concepts were deduced, manufactured and characterised (T4.3 T4.5 T4.7). Important approaches are the integration of high damping metals, adapted clearance chamfers for milling cutters with indexable inserts as well as solid carbide milling tools with variable helix angles (see Figure 6 in attached pdf). Several approaches to modify the milling tool system design regarding damping and stiffness properties were realized and analyzed. The effect of materials with improved damping properties in the milling tool system was investigated. Analysis of the frequency response functions as well as milling trials showed that damping properties of the milling tools and therefore dynamic process stability can be increased. The adapted chamfers are applicable for milling cutters which are common used for machining turbine blades and other freeform geometries. Focused was the investigation of the influence of different chamfer angles and chamfer widths. Regarding the milling tools with helix angles the influence of different and variable helix angles as well as uneven pitch angles is investigated. The use and integration of high damping metals into a milling cutter body also showed a positive effect on the process stability in milling thin-walled work pieces. Summarized, regarding the milling tools with adapted chamfers and variable helix angles as well as uneven pitch angles a deeper technological understanding for the machining of thin-walled workpieces was compiled by fundamental and systematic analysis. Therefore, a contribution to an optimized finishing process showing increased process stability was made. By using an existing test bench concrete conclusions regarding the occurring process forces could be made and thus increase the know-how for the use of chamfer based milling tools (T4.3). Furthermore, in preliminary trials in real milling process with simplified geometries several prototypes of different damping milling tools were tested and evaluated (T4.4). The micro simulation of the contact conditions helped to get a deeper understanding regarding certain milling processes and influences of process parameters (T4.6). Parallel to the development of damping milling tools optimized machining strategies for achieving homogenized cutting conditions and less excitation of system Eigenfrequencies were developed and investigated (T4.1). All the know-how and developments were implemented in the DynaMill CAM Module (T4.8 crossing over with the module 1) and applied in the predefined demonstration activities (T9.1 T9.2). With the help of the predefined demonstrator workpieces for module 3 the manufactured damping milling tools were demonstrated and evaluated in a pilot application within a real industrial setting. The trials were carried out together with end users at their own manufacturing facilities. The support regarding the trials (e.g. supply of milling tools and planning of trials) was carried out by Walter AG and IPT. Demonstrations regarding insert based tools with partner Alstom on a blade geometry showed the best results for the tools with integrated high damping metals (e.g. decrease of roughness Rmax of about 10%). Similar results were gathered in tests with a basic test setup at the Fraunhofer IPT which shows a good transferability from research to demonstration. Trials regarding solid carbide tools with partner Technoplast on a satellite part showed best results for a milling tool with uneven pitch angle. The decrease of roughness Rz was about 200% compared to the worst result. Furthermore, demonstrations regarding insert based end mill tools on a knee bone part of partner Technoplast showed best values of roughness Ra for a tool with integrated discs made out of high damping metals. Regarding the optimized machining strategies for achieving less excitation of system Eigenfrequencies the demonstrations showed that there is a reduction of machining time of about 15% possible.
»DynaMill Technology«
The developed three modules were integrated in the machine tool as a robust platform so that a fully integrated manufacturing solution is possible (T5.1). Hence, the machine operator can access to all resources and assure a improved control of the milling process of thin-walled work pieces. This means that the machine tool, that is used for the demonstration must be able to:
• Data from the process planning module
• Support the mounting of the adaptive clamping devices
• Use the different dampening tools in their optimum process parameters
The technological development realised in WP2 to WP5 were combined, tested, further optimized (T5.1 T5.2 T5.3) and demonstrated (T6.2 T6.3) in realistic set-ups with predefined demonstrator parts (T6.1) under industrial conditions to build the so-called »DynaMill Technology«. Regarding the DynaMill CAM module (module 1), in respect to a widespread applicability in industry it was essential to not use custom file formats but standards already available (T5.4). The demonstrations were performed on three blades, demonstration parts 1a, 1b and 2. These blades have been machined with the complete DynaMill Technology, meaning from the DynaMill CAM module up to the clamping systems and milling tools everything was used. In a chronological order the industrialization started on demonstrator 2 (T6.2). The results and findings that were made during the tests on Demonstrator 2 helped to improve the technology for the demonstrator parts 1a and 1b where the complete potential of the »DynaMill Technology« was included (T6.3). The CAM module (module 1) helps to avoid chatter by adaption of the spindle speed based on the dynamic bahavior of the workpiece so that critical Eigenfrequencies of the blade are not excited. Algorithms were created that help the user in selecting the proper spindle speed. Setting up the simulation model for the process however requires information and a calibration to know the characteristics and dampening of the machine tool and the clamping system. Within module 2 it was shown how important a stiff and dampening clamping system is. By using a proper clamping system vibrations on the part could be drastically reduced. The milling tools that were developed in module 3 also showed that they can have a significant improvement on the process stability and therefore tool wear and surface quality. The comparison of the former and newly developed manufacturing process as well as evaluation was also foreseen in the project (WP10). For example, based on the demonstration 1b (blade of about 700 mm length) a reduction of machining time of about 10% was possible. Despite realizing a faster process, the sound pressure (noise signal) and the Power in Band (PIB) value which are within the project definied measures for process stability could be decreased by about 65% and 50%. Furthermore, regarding the tool wear an improvement of about 50% was achieved.
Summarized, the »DynaMill Technology« achieved very good results and reached the predefinied objectives. Following main S & T results/ foregrounds can be highlighted:
• Module 1: Process Planning
o Process planning CAM tool
o Calculation of workpiece behaviour by RCMT model
o Different spatial NC code partition approaches
• Module 2: Adaptive clamping devices
o Systematic know-how/ deeper technological understanding clamping devices for the machining of thin-walled workpieces
o Passive damping concepts in clamping
o Knowledge how to design passive dampening clamping devices
o First promising active clamping concepts
• Module 3: Cutting conditions
o Systematic know-how/ deeper technological understanding regarding milling tools for the machining of thin-walled workpieces
o Several innovative concepts/ prototypes of damping milling tools
o Integration of High Damping Metals (HiDaMets) into the milling tool/ Know-how regarding HiDaMets
• DynaMill Technology and Process Chain to layout or improve processes (see Figure 9 in attached pdf)
o In step 1 a first machining of the workpiece with standard or experience-based process parameters by usage of a DynaMill adaptive clamping device is conducted. Afterwards (step 2), the measuring of calibration FRFs of the workpiece which is fixed in the machine tool is realized. In step 3, the measured calibration FRFs are used as input parameter for the CAM planning module to be able to predict the dynamic behavior of the workpiece and to compile the needed NC code(s) for machining. Finally (step 4), by additional usage of the milling tools which increase process stability, the optimized machining of the workpiece based on the »DynaMill-Technology« can be carried out. Based on this approach the required thin-walled workpiece quality in conjunction with considerable reduction in manufacturing time and resource input can be achieved.
Potential Impact:
Increase in competitiveness and production flexibility
The development and demonstration of an integrated technology to achieve complete control of advanced multi-axis milling processes of thin-walled work pieces in DynaMill will lead to a significant increase of competitiveness and production flexibility in the manufacturing industries focussing on thin-walled and labile work pieces such as energy, aviation, automotive and medical technology. DynaMill will provide improved clamping devices and damping tools that reduce vibrations, displacements and deformation of the work piece during milling.
Increased tool and equipment life
Through the consequent avoidance of critical process states and work piece excitation, the strain on tools will be reduced significantly, especially during process set-up. Currently tool failure during set-up trials is a common phenomenon. With the »DynaMill Technology«, unforeseen events during set-up and production will be reduced considerably.
Reduction of the number of rejected components/waste and amount of raw-material used
In the milling of thin-walled work pieces, the majority of rejected components and scrap accrue during process set-up. Due to the high quality and safety requirements of the industries that commonly use thin-walled work pieces, instable processes that lead to larger numbers of rejected components are not acceptable. The potential for saving rejected components and waste therefore lies in the set-up phase.
Reduction of finishing operations
In the current situation, suboptimal production planning and excitation during finishing often lead to surface defects on the work piece. In some cases, this is not relevant (e.g. structural parts of helicopters), in many other cases (e.g. turbines) however, an additional manual polishing step has to be added to achieve a surface of sufficient quality. With the »DynaMill Technology«, it will be possible to achieve an evenly milled surface, which may not requiring any subsequent manual polishing operations.
Overview of the main dissemination activities
Dissemination activities of different types were undertaken during the project duration. Following, a detailed list is given:
• A DynaMill website ( http://www.dynamill.eu ) is carried out by IPT. The project website is online since short before the KickOff Meeting in 2012. Among others things, the website presents the project, achieved results and information on publications and events. So far more than 3000 visitors did visit the website.
• A project flyer and poster describing the project and its objectives has been designed and printed.
• Rollup at the "ICTM – 2nd International Conference on Turbomachinery Manufacturing"
• Publication at the 4th Machining Innovations Conference "New Production Technologies in Aerospace Industry", Hannover, September 2013 (Proceedings including paper "Impact of Clamping Technology on Horizontal and Vertical Process Chain Performance" with public DynaMill know-how)
• Test bench at Aachen Machine Tool Colloquium (AWK), May 22-23, 2014 in Aachen, Germany
• Publication at the 11th High Speed Conference, HSM 2014, 11th International Conference on High Speed Machining, Prague, September 11-12, 2014, (Paper “Simulation model for quick predictions of workpiece dynamic response in machining”)
• Presentation of DynaMill at ICTM 2015 – International Conference on Turbomachinery Manufacturing in Aachen
• DynaMill presentation poster at Turbine Technology Days 2015 of partner Starrag
• Several participations and presentations at the Impact Workshops in Brussels (2013, 2014, 2015)
Following dissemination activities are planned for the future after the official project end:
• Publication of successful machining based on the new possibilities of CAM module (module 1)
• Commercialization of CAM module via Fraunhofer IPT spin-off Aixpath (module 1)
• Publication about developed clamping system and relevant milling tests (module 2)
• Publication about basic test setup and relevant milling tool prototypes (module 3)
• ICTM 2017 Conference, Aachen (presentation and/ or test bench about the »DynaMill-Technology«)
• AWK 2017 Conference, Aachen (presentation and/ or test bench about the »DynaMill-Technology«)
Exploitation of results
• Possible patent proposal to ensure the protection of the DynaMill technology, in line with certain IPR principles.
• Internal and external workshops
• Definition of guidelines for the application of the DynaMill technology, which will stipulate the optimal approach for using single modules or the integrated technology as a whole. These guidelines are an important requirement for the exploitation and smooth application of the project results by a wide variety of industry stakeholders.
List of Websites:
http://www.dynamill.eu
Fraunhofer Institute for Production Technology IPT
Dr.-Ing. Thomas Bergs
Managing Director
Steinbachstraße 17
52074 Aachen, Germany
DynaMill – Dynamic manufacturing of thin-walled work pieces by milling process
Light weighted components are becoming increasingly important in key European industries like aerospace, automotive, energy sector and bio-medical engineering. In order to minimize weight, complex thin-walled structures are frequently designed and manufactured utilizing high-strength materials. However, the lack of rigidity of many of these thin-walled parts presents a considerable challenge in terms of machining: It is vital to reduce the dynamic excitation caused by tool engagement, to minimize the static deflections arising from milling forces and to mitigate deformation resulting from clamping forces. The aim of the EU-funded Research Project »DynaMill« is, therefore, to master milling operations carried out on thin-walled parts and to optimize these operations using a holistic approach in order to eliminate any danger of unwanted dynamic effects which could give rise to surface defects and poor quality. Process planning (module 1), adaptive clamping systems (module 2) and cutting conditions (module 3) must be designed to interlock with one another in the »DynaMill Technology« in order to achieve the required quality in conjunction with considerable reduction in manufacturing time and resource input.
Module 1 – Process Planning
The aim is to develop a CAx (Computer Aided Technologies, e.g. CAD/ CAA/ CAM) software tool, capable of taking account at the CAM planning stage of the oscillation and resonance behavior of work in process part during machining. It is envisaged that dynamic simulations and numerical calculation will achieve stable milling operations in the machine tool and simultaneously improve surface quality and form accuracy of the work pieces.
Module 2 – Adaptive Clamping Systems
Investigation into dynamic effects of part clamping is a further milestone of this project. Initially, a design methodology is developed for clamping systems with good dynamic characteristic and subsequently effects of various damping mechanisms in clamping systems are investigated. To achieve a robust machining operation for thin-walled parts, clamping systems will be developed on the basis of highly efficient damping materials or with passively and actively controlled anti-vibration devices.
Module 3 – Cutting Conditions
The aim of this module is to ensure higher levels of process stability during milling operations conducted on thin-walled parts by introducing improved cutting tools technology: Systematic analysis of micro and macro geometry of cutting tools in association with the use of highly efficient damping materials will increase the damping effect in the machining process. Crossing over with the module 1, additional work will focus on optimized machining strategies which will be conducive to more homogeneous cutting conditions and less excitation of system eigenfrequencies.
»DynaMill Technology«
The developed three modules were integrated and combined in a machine tool as a robust platform so that a fully integrated manufacturing solution is possible. The comparison of the former and newly developed manufacturing processes as well as evaluation was also foreseen in the project. For example, based on the demonstration 1b (blade of about 700 mm length) a reduction of machining time of about 10% was possible. Despite realizing a faster process, the sound pressure (noise signal) and the Power in Band (PIB) value which are within the project definied measures for process stability could be decreased by about 65% and 50%. Furthermore, regarding the tool wear an improvement of about 50% was achieved. Summarized, the »DynaMill Technology« achieved very good results and reached the predefinied objectives.
Project Context and Objectives:
DynaMill – Dynamic manufacturing of thin-walled work pieces by milling process
Light weighted components are becoming increasingly important in key European industries like aerospace, automotive, energy sector and bio-medical engineering. In order to minimize weight, complex thin-walled structures are frequently designed and manufactured utilizing high-strength materials. However, the lack of rigidity of many of these thin-walled parts presents a considerable challenge in terms of machining: It is vital to reduce the dynamic excitation caused by tool engagement, to minimize the static deflections arising from milling forces and to mitigate deformation resulting from clamping forces.
The aim of the EU-funded Research Project »DynaMill« is, therefore, to master milling operations carried out on thin-walled parts and to optimize these operations using a holistic approach in order to eliminate any danger of unwanted dynamic effects which could give rise to surface defects and poor quality. Process planning, adaptive clamping systems and cutting conditions must be designed to interlock with one another in the »DynaMill Technology« in order to achieve the required quality in conjunction with considerable reduction in manufacturing time and resource input.
Module 1 – Process Planning
The aim is to develop a CAx (Computer Aided Technologies, e.g. CAD/ CAA/ CAM) software tool, capable of taking account at the CAM planning stage of the oscillation and resonance behavior of work in process part during machining. It is envisaged that dynamic simulations and numerical calculation will achieve stable milling operations in the machine tool and simultaneously improve surface quality and form accuracy of the work pieces.
Module 2 – Adaptive Clamping Systems
Investigation into dynamic effects of part clamping is a further milestone of this project. Initially, a design methodology is developed for clamping systems with good dynamic characteristic and subsequently effects of various damping mechanisms in clamping systems are investigated. To achieve a robust machining operation for thin-walled parts, clamping systems will be developed on the basis of highly efficient damping materials or with passively and actively controlled anti-vibration devices.
Module 3 – Cutting Conditions
The aim of this module is to ensure higher levels of process stability during milling operations conducted on thin-walled parts by introducing improved cutting tools technology: Systematic analysis of micro and macro geometry of cutting tools in association with the use of highly efficient damping materials will increase the damping effect in the machining process. Crossing over with the module 1, additional work will focus on optimized machining strategies which will be conducive to more homogeneous cutting conditions and less excitation of system eigenfrequencies.
The overall objective of the DynaMill project is to strengthen the European thin-walled manufacturing community in manufacturing of thin-walled work piece by realising a better control of the milling process for thin-walled work pieces. This will be achieved through the development and demonstration of an integrated solution, named »DynaMill Technology«, which is a robust platform for machining of thin-walled work pieces. The DynaMill project will impact the competitiveness of the European manufacturers of thin-walled work pieces by:
• Enhancing process knowledge and capability in milling of thin-walled work pieces
• Enhancing process knowledge and capability in application of clamping devices
• Increasing product and process quality, precision as well as output
• Improving life time and capability of milling tools
• Impacting on production efficiency and the strategically crucial time-to-market factor for manufacturing companies
The overall Scientific and Technological (S/T) objective of the DynaMill project are development, demonstration and evaluation of the »DynaMill Technology« for the manufacturing of thin-walled work pieces. DynaMill is built-on three distinct technology modules, the several S/T objectives that have to be accomplished in three modules are the following:
Module 1 – Process Planning
• Prediction of the natural response of the thin-walled work piece system
• Prediction of the dynamic beahaviour of thin-walled work piece systems during machining based upon the simulation of material removal process
• Improved process control for CAM of thin-walled work pieces by parameterizing of the influencing factors
• Development of a CAM process planning based on modal calculations
Module 2 – Adaptive Clamping Systems
• Gathering knowledge on vibrations and continuum mechanics in clamping devices
• Development of clamping devices with approaches of locator/ positioning
• Development of clamping devices with enhanced damping
• Development of clamping systems with adjustable degrees of freedom in locators
• Development of the choice and arrangement of sensors and the proper analysis of the signals
• Developing of an active damped clamping device on demonstrator level
Module 3 – Cutting Conditions
• Developing milling tool designs which increase process stability
• Crossing over with the module 1: Developing a optimized machining strategies for achieving homogenized cutting conditions and less excitation of system eigenfrequencies.
Project Results:
Major task of the first project months was to define the diferent project demonstrators.
• Large and midsize turbine blades of the energy sector, material: alloy steel
• Small turbine blade of the aviation sector, material: titanium
• Prismatic satellite part of the space flight sector, material: aluminium
• Knee bone part of the medical sector, material: titanium
• Prismatic parts of the print media sector, material: steel
Based on these demonstrators the developments of the »DynaMill Technology« (modules 1, 2 and 3) were derived.
Module 1 – Process Planning
The aim of module 1 is to provide a process planning tool for calculating adapted NC code for thin-walled workpieces. This is achieved in a so called DynaMill loop. Figure 1 (in attached pdf) depicts this loop and the respective partners for the relevant developments. This was performed in work package 2. Additionally, the overall system is demonstrated in work package 7 on demonstrator workpieces from the end users of the consortium. The topics of module 1 are covered within the workpackages 2 and 7. During task 2.1 (T2.1) a method to build the simulation model for the prediction of dynamic behaviour of thin-walled work pieces has been developed and verified by testing on simplified prismatic shaped parts. The method involves an approach to develop a process model based upon an FEM simulation method and a simplification of the FEM simulation node-net model which also improves the computation efficiency. During T2.2 the material removal simulation models have been developed and tested on CAM models of representative cases of part and raw material. An orthogonal 3 phase needle model has been utilized to predict the machined part models and improved polygon meshing techniques have been applied to enhance the accuracy and completeness of model data structure. The coupling and integration has been implemented during task T2.3. Testing and error fixing of the integration and related components including above two simulation models was done subsequently. T2.4 involves parameterizing the models developed in T2.1 and T2.2 against the variation in part geometries. The relevant types of cutting tools geometries have been specified and the prediction models are being evaluated. Evaluation between the numerical and analytical models and the interfaces for coupling either of them with the results of task T2.3 have been specified. In T2.5 the first step is to identify the types of machining process, this has been completed and based upon the spectrum of demonstrator parts. The implemented CAM strategy is executed into a computer software and produce numerical control (NC) data to control the machine tool. T2.6 has been completed. The integrated CAM module has been developed as a prototypic implementation within Siemens NX. The toolpath planning of blade profiles is possible in three different strategies. The first aspect of this task is the development of algorithms to produce NC data with the variable spindle revolutions and corresponding, variable feedrates. The variable spindle revolutions and feedrate values are applicable to different areas of a thin-walled workpieces. Two partition strategies were implemented in the CAM tool. The first one foresees a change of the process settings with varying position of the tool along the blade vector – the direction from the tip to the foot of the blade. The second strategy divides the blade surface into checkerboard like rectangles and for each rectangle an individual setting of spindle speed and feedrate can be made, based on the FRF calculations. The second strategy was implemented based on the experience from experiments. For example, to suppress torsion-like vibrations in the blade, different settings in the center region compared to the edge region is required. The strategies can be transfered to other types of workpiece geometries as well. In workpackage 7, the developments made in work package 2 are demonstrated and evaluated. Using the process planning software, the dynamic behaviour of the demonstrator parts were determined, based on calibration frequency response measurements. The performance of the agile spindle was evaluated during the demonstrations. In the demonstration activities T7.1 has been completed and was focused upon the demonstration results of dynamic simulation model developed during task T2.1. In T7.2 the partner consultation has been performed to define the conditions of pre-finished parts and build them into the integrated process planning model of taks T2.5. The start of T7.4 is linked with T2.6. T7.4 was initiated during the final phase of the CAM module developments and the connection of the CAM module with the simulation routines. During month 30, experiments at project partner Starrag were made to show the spindle speed variation at demonstrator 2. There, the strategy of a varying spindle speed as a function of the position along the blade vector was used (see Figure 2 in attached pdf). The demonstration of the »DynaMill Technology« on two different demonstrators were performed at project partner Alstrom and IPT. There, the checkerboard strategy was applied. The results included also the results from modules 2 and 3, damping-optimized fixture system and improved milling tools.
Module 2 – Adaptive Clamping Systems
Based on the information described in the DynaMill DoW, in work package 3 all tasks are accomplished. In T3.1 existing know-how regarding the design of clamping systems was gathered. Existing clamping solutions have been analyzed with regard to stiffness and occurring workpiece vibrations. These analyses have been supported by RCMT and IPT with FEM simulations. HPS and STH with the support of IPT have constructed and installed improved conventional clamping devices. Based on the perceived know-how, a procedure for constructing improved clamping systems with enhanced stiffness has been deduced. In T3.2 novel approaches to use highly efficient damping materials in clamping device designs have been realized. Appropriate milling trials showed promising results for passive damping systems in clamping devices. A novel damping system for magnetic clamping systems has been developed. A tuned mass damper (TMD) was developed and tested by HPT and IPT. FRE and IPT developed a hydraulic absorber device for vices (see Figure 3 in attached pdf). The experiments showed that the damping factor was increased over a factor of about 8. Furthermore, a root clamping device was developed (see Figure 4 in attached pdf) which was used for the demonstrator 1a. The root clamping device works with a floating clamping mechanism, which is important to compensate the cast oversize and the surface roughness. Demonstrations confirmed the high damping properties of the clamping device. In T3.3 a steady-rest system for balde manufacturing developed by Starrag has been improved. A novel automated clamping device for large turbine blades has been developed. In T3.4 a market research regarding available sensors has been conducted and simulations for the design of the active damping device have been realized. In T3.5 the active damping device was developed and tested in milling tests. The tests showed the high potential of this approach. Based on the described reseach avtivities, in WP6 and WP8 it was shown, that chatter marks on the demonstrator surface can be avoided, that the tool wear can be reduced over about 60% and that the noise can be reduced significant with developed DynaMill clamping devices. For example, when machining demonstrator 1b, the developed DynaMill clamping device (see Figure 5 in attached pdf) raised the process stability significantly, so that the efficiency of the milling process could be increased as well.
Module 3 – Cutting Conditions
In a first step predominant measures to increase tool damping in milling process of thin walled work pieces were determined (T4.2). Based on this, the development and allocation of innovative damping tool concepts were deduced, manufactured and characterised (T4.3 T4.5 T4.7). Important approaches are the integration of high damping metals, adapted clearance chamfers for milling cutters with indexable inserts as well as solid carbide milling tools with variable helix angles (see Figure 6 in attached pdf). Several approaches to modify the milling tool system design regarding damping and stiffness properties were realized and analyzed. The effect of materials with improved damping properties in the milling tool system was investigated. Analysis of the frequency response functions as well as milling trials showed that damping properties of the milling tools and therefore dynamic process stability can be increased. The adapted chamfers are applicable for milling cutters which are common used for machining turbine blades and other freeform geometries. Focused was the investigation of the influence of different chamfer angles and chamfer widths. Regarding the milling tools with helix angles the influence of different and variable helix angles as well as uneven pitch angles is investigated. The use and integration of high damping metals into a milling cutter body also showed a positive effect on the process stability in milling thin-walled work pieces. Summarized, regarding the milling tools with adapted chamfers and variable helix angles as well as uneven pitch angles a deeper technological understanding for the machining of thin-walled workpieces was compiled by fundamental and systematic analysis. Therefore, a contribution to an optimized finishing process showing increased process stability was made. By using an existing test bench concrete conclusions regarding the occurring process forces could be made and thus increase the know-how for the use of chamfer based milling tools (T4.3). Furthermore, in preliminary trials in real milling process with simplified geometries several prototypes of different damping milling tools were tested and evaluated (T4.4). The micro simulation of the contact conditions helped to get a deeper understanding regarding certain milling processes and influences of process parameters (T4.6). Parallel to the development of damping milling tools optimized machining strategies for achieving homogenized cutting conditions and less excitation of system Eigenfrequencies were developed and investigated (T4.1). All the know-how and developments were implemented in the DynaMill CAM Module (T4.8 crossing over with the module 1) and applied in the predefined demonstration activities (T9.1 T9.2). With the help of the predefined demonstrator workpieces for module 3 the manufactured damping milling tools were demonstrated and evaluated in a pilot application within a real industrial setting. The trials were carried out together with end users at their own manufacturing facilities. The support regarding the trials (e.g. supply of milling tools and planning of trials) was carried out by Walter AG and IPT. Demonstrations regarding insert based tools with partner Alstom on a blade geometry showed the best results for the tools with integrated high damping metals (e.g. decrease of roughness Rmax of about 10%). Similar results were gathered in tests with a basic test setup at the Fraunhofer IPT which shows a good transferability from research to demonstration. Trials regarding solid carbide tools with partner Technoplast on a satellite part showed best results for a milling tool with uneven pitch angle. The decrease of roughness Rz was about 200% compared to the worst result. Furthermore, demonstrations regarding insert based end mill tools on a knee bone part of partner Technoplast showed best values of roughness Ra for a tool with integrated discs made out of high damping metals. Regarding the optimized machining strategies for achieving less excitation of system Eigenfrequencies the demonstrations showed that there is a reduction of machining time of about 15% possible.
»DynaMill Technology«
The developed three modules were integrated in the machine tool as a robust platform so that a fully integrated manufacturing solution is possible (T5.1). Hence, the machine operator can access to all resources and assure a improved control of the milling process of thin-walled work pieces. This means that the machine tool, that is used for the demonstration must be able to:
• Data from the process planning module
• Support the mounting of the adaptive clamping devices
• Use the different dampening tools in their optimum process parameters
The technological development realised in WP2 to WP5 were combined, tested, further optimized (T5.1 T5.2 T5.3) and demonstrated (T6.2 T6.3) in realistic set-ups with predefined demonstrator parts (T6.1) under industrial conditions to build the so-called »DynaMill Technology«. Regarding the DynaMill CAM module (module 1), in respect to a widespread applicability in industry it was essential to not use custom file formats but standards already available (T5.4). The demonstrations were performed on three blades, demonstration parts 1a, 1b and 2. These blades have been machined with the complete DynaMill Technology, meaning from the DynaMill CAM module up to the clamping systems and milling tools everything was used. In a chronological order the industrialization started on demonstrator 2 (T6.2). The results and findings that were made during the tests on Demonstrator 2 helped to improve the technology for the demonstrator parts 1a and 1b where the complete potential of the »DynaMill Technology« was included (T6.3). The CAM module (module 1) helps to avoid chatter by adaption of the spindle speed based on the dynamic bahavior of the workpiece so that critical Eigenfrequencies of the blade are not excited. Algorithms were created that help the user in selecting the proper spindle speed. Setting up the simulation model for the process however requires information and a calibration to know the characteristics and dampening of the machine tool and the clamping system. Within module 2 it was shown how important a stiff and dampening clamping system is. By using a proper clamping system vibrations on the part could be drastically reduced. The milling tools that were developed in module 3 also showed that they can have a significant improvement on the process stability and therefore tool wear and surface quality. The comparison of the former and newly developed manufacturing process as well as evaluation was also foreseen in the project (WP10). For example, based on the demonstration 1b (blade of about 700 mm length) a reduction of machining time of about 10% was possible. Despite realizing a faster process, the sound pressure (noise signal) and the Power in Band (PIB) value which are within the project definied measures for process stability could be decreased by about 65% and 50%. Furthermore, regarding the tool wear an improvement of about 50% was achieved.
Summarized, the »DynaMill Technology« achieved very good results and reached the predefinied objectives. Following main S & T results/ foregrounds can be highlighted:
• Module 1: Process Planning
o Process planning CAM tool
o Calculation of workpiece behaviour by RCMT model
o Different spatial NC code partition approaches
• Module 2: Adaptive clamping devices
o Systematic know-how/ deeper technological understanding clamping devices for the machining of thin-walled workpieces
o Passive damping concepts in clamping
o Knowledge how to design passive dampening clamping devices
o First promising active clamping concepts
• Module 3: Cutting conditions
o Systematic know-how/ deeper technological understanding regarding milling tools for the machining of thin-walled workpieces
o Several innovative concepts/ prototypes of damping milling tools
o Integration of High Damping Metals (HiDaMets) into the milling tool/ Know-how regarding HiDaMets
• DynaMill Technology and Process Chain to layout or improve processes (see Figure 9 in attached pdf)
o In step 1 a first machining of the workpiece with standard or experience-based process parameters by usage of a DynaMill adaptive clamping device is conducted. Afterwards (step 2), the measuring of calibration FRFs of the workpiece which is fixed in the machine tool is realized. In step 3, the measured calibration FRFs are used as input parameter for the CAM planning module to be able to predict the dynamic behavior of the workpiece and to compile the needed NC code(s) for machining. Finally (step 4), by additional usage of the milling tools which increase process stability, the optimized machining of the workpiece based on the »DynaMill-Technology« can be carried out. Based on this approach the required thin-walled workpiece quality in conjunction with considerable reduction in manufacturing time and resource input can be achieved.
Potential Impact:
Increase in competitiveness and production flexibility
The development and demonstration of an integrated technology to achieve complete control of advanced multi-axis milling processes of thin-walled work pieces in DynaMill will lead to a significant increase of competitiveness and production flexibility in the manufacturing industries focussing on thin-walled and labile work pieces such as energy, aviation, automotive and medical technology. DynaMill will provide improved clamping devices and damping tools that reduce vibrations, displacements and deformation of the work piece during milling.
Increased tool and equipment life
Through the consequent avoidance of critical process states and work piece excitation, the strain on tools will be reduced significantly, especially during process set-up. Currently tool failure during set-up trials is a common phenomenon. With the »DynaMill Technology«, unforeseen events during set-up and production will be reduced considerably.
Reduction of the number of rejected components/waste and amount of raw-material used
In the milling of thin-walled work pieces, the majority of rejected components and scrap accrue during process set-up. Due to the high quality and safety requirements of the industries that commonly use thin-walled work pieces, instable processes that lead to larger numbers of rejected components are not acceptable. The potential for saving rejected components and waste therefore lies in the set-up phase.
Reduction of finishing operations
In the current situation, suboptimal production planning and excitation during finishing often lead to surface defects on the work piece. In some cases, this is not relevant (e.g. structural parts of helicopters), in many other cases (e.g. turbines) however, an additional manual polishing step has to be added to achieve a surface of sufficient quality. With the »DynaMill Technology«, it will be possible to achieve an evenly milled surface, which may not requiring any subsequent manual polishing operations.
Overview of the main dissemination activities
Dissemination activities of different types were undertaken during the project duration. Following, a detailed list is given:
• A DynaMill website ( http://www.dynamill.eu ) is carried out by IPT. The project website is online since short before the KickOff Meeting in 2012. Among others things, the website presents the project, achieved results and information on publications and events. So far more than 3000 visitors did visit the website.
• A project flyer and poster describing the project and its objectives has been designed and printed.
• Rollup at the "ICTM – 2nd International Conference on Turbomachinery Manufacturing"
• Publication at the 4th Machining Innovations Conference "New Production Technologies in Aerospace Industry", Hannover, September 2013 (Proceedings including paper "Impact of Clamping Technology on Horizontal and Vertical Process Chain Performance" with public DynaMill know-how)
• Test bench at Aachen Machine Tool Colloquium (AWK), May 22-23, 2014 in Aachen, Germany
• Publication at the 11th High Speed Conference, HSM 2014, 11th International Conference on High Speed Machining, Prague, September 11-12, 2014, (Paper “Simulation model for quick predictions of workpiece dynamic response in machining”)
• Presentation of DynaMill at ICTM 2015 – International Conference on Turbomachinery Manufacturing in Aachen
• DynaMill presentation poster at Turbine Technology Days 2015 of partner Starrag
• Several participations and presentations at the Impact Workshops in Brussels (2013, 2014, 2015)
Following dissemination activities are planned for the future after the official project end:
• Publication of successful machining based on the new possibilities of CAM module (module 1)
• Commercialization of CAM module via Fraunhofer IPT spin-off Aixpath (module 1)
• Publication about developed clamping system and relevant milling tests (module 2)
• Publication about basic test setup and relevant milling tool prototypes (module 3)
• ICTM 2017 Conference, Aachen (presentation and/ or test bench about the »DynaMill-Technology«)
• AWK 2017 Conference, Aachen (presentation and/ or test bench about the »DynaMill-Technology«)
Exploitation of results
• Possible patent proposal to ensure the protection of the DynaMill technology, in line with certain IPR principles.
• Internal and external workshops
• Definition of guidelines for the application of the DynaMill technology, which will stipulate the optimal approach for using single modules or the integrated technology as a whole. These guidelines are an important requirement for the exploitation and smooth application of the project results by a wide variety of industry stakeholders.
List of Websites:
http://www.dynamill.eu
Fraunhofer Institute for Production Technology IPT
Dr.-Ing. Thomas Bergs
Managing Director
Steinbachstraße 17
52074 Aachen, Germany
