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New generation of machinery for manufacture of miniature (1mm) engineering components (machmini)


The PIM is an incremental metal forming tool system; it may be regarded as a semi-static system operating in the range of 5~50Hz; this is several orders lower than the UIM tool system. The vibration of the tool is effected by the Amplified Stacked Ceramic Multi-layer Actuator (ASCMA), which is energised using a specially designed generator. This actuator, which is attached to the head of the forming machine, drives the forming tool. The piezo-stack may be operated without excitation This can vibrate with the frequency (5~50Hz) or the stack can be operated to provide forming tool displacement. The maximum (free) stroke of the ASMCA is 0.5 mm, while the maximum (blocking) force is approximately 400N. However, it should be noted that when the forming tool is loaded with a specific process force, the working stroke would be smaller than the free stroke. For special applications, a Stacked Ceramic Multi-layer Actuator may be used to provide greater working forces at lower working strokes. Preliminary experiments using this tool system have demonstrated that the PIM would be effective for manufacturing of indentations of prescribed distributions on the surfaces of bulk components.
The MACHMINI machine was constructed to enable the tool-system to render functional surfaces of components, which were displaced in a controlled manner relative to the tool-system. This was defined as the operating mode, regardless of the type of type of tool used in the rendering process. The frame is L-shaped and is extended on either side of the machine to support a variety of tools and dividing heads; tools and devices can be mounted either on either the X- or Y-planes to enable the manipulation of components. The machine is essentially a 3-axis CNC machine, except that a Z1-signal was incorporated to drive a tool or spindle to support either the forming of miniature components or form rendering functional surfaces. This additional signal was incorporated to enable the supply of conditioned signals to the tool-system. The machine may be programmed using standard NC codes.
Quantification of the physical characteristics of miniature materials may be performed using conventional tensile tests; however such tests are relevant to straining under simple straining conditions and low strain-rates. As such, the extracted data is not exactly relevant to the FE simulation of manufacturing operations. An innovative mini-press was designed and constructed to resolve the difficulty of extracting meaningful data. This innovations incorporates the following features: - Miniature materials may be tested (thickness=0.1mm, diameter=3mm) - Overall dimensions of the mini-press are 50x100x100mm, which allows incorporation into the vacuum chamber of the SEM for in-situ testing. - Test specimen displacement is effected using 4 stacks of 13 bespoke piezoelectric ring benders; the use of this mini-press has enabled the following operational characteristics: --Range of force and stroke: max force=100N and max stroke=1mm --Strain rate: from quasi-static to 1s-1 This mini-press provides the opportunity to perform tests on materials of miniature scale in an SEM, a feature that has not been available, to-date. The markets for this mini-press are materials testing laboratories, equipped with SEM¿s or Goniometers. This mini-press is being developed further to enable a variable strain-rate, an improvement that would require the addition of force and displacement sensors; when features have been built into the Mini-press, the entire system may be automated using commercially available software, such as Labview, to effect force- and displacement-rate control.
The description of the elasto-viscoplastic behaviour of miniature materials and components the minimum size of which is that of a grain, has to rely on the phenomenological or macroscopic approach. Microscopic constitutive laws, based on the dislocation theory, are used to predict the behaviour of elementary volumes of the material of the scale of 5×5×5mm require the use of powerful computers. The approach developed in the MACHMINI project, for use at meso-scale, is appropriate for the quantification of miniature materials and components. The developed UMAT subroutine is based on a single crystal elasto-viscoplastic constitutive law. Preliminary requirements are to experimentally identify the five significant material parameters with sufficient accuracy to ensure reliability of the FE simulation results. The mini-press was developed in order to conduct this parameter identification task. All components/products that require the simulation of component behaviour, either during the forming operation or in subsequent use, would require test data of the accuracy possible with the use of the mini-press. Commonly, the electronics, sensor, instrumentation, biomedical and control industries require such quantification. UMAT subroutine version V17 was successfully implemented into ABAQUS software. Its capability to reproduce mini component forming processes has been demonstrated. Numerous microstructural data are available from simulation obtained using this program, such as: - Crystallographic texture evolution, - Set of active slip systems, - Density dislocation on all slip systems for every grain, - Intragranular stress state. Usual global information are also accessible with increased accuracy: - Force-displacement characteristic, - Elastic spring-back, - Anisotropy induced by plastic strain, etc.
The UIM Tool System may be classified in the category of the incremental sheet metal forming tools, in a similar manner as the IRM and PIM Tool Systems would be. There are, however, some similarities and important differences between these three systems. Similarities are that this Tool System operates on the MACHMINI Machine using a common die: it may be used to produce prototypes or small-batch quantities or for the conversion of semi-finished miniature components prepared using chemical etching or electrical-discharge slotting. The differences are in the method of operation - the IRM and PIM are static/semi-static tool systems, whereas the UIM system operates at ultrasonic frequency. The forming tool contained in the UIM Tool System is fixed to the punch holder, which is excited by the ultrasonic transducer driven using the signals delivered from the ultrasonic generator. The ultrasonic transducer, booster and punch holder (together with the punch) are fixed to the z-drive of the MACHMINI Machine, to facilitate vertical displacement. The tools vibrate at approximately 20kHz and the amplitude of vibration may be adjusted in the range of 4 -10m. The desired operating condition is that the forming tool retains the pre-operational settings. The Tool System may be operated in different modes. It can be lowered to form a dimple on the miniature material in a sequence to form a series of dimples in a prescribed pattern and to differing depths. The forming tool may also be lowered to a prescribed position to form an impression after which it may be translated to produce a groove. Further, the forming tool may be used to produce drawn sections by progressively indexing the tool into the work-material held over a die-cavity, while the die-cavity is rotated; by these movements, the work-material is incrementally deformed to from the drawn section. The UIM method can be used not only for sheet metal forming but also for bulk metal forming. It is possible to produce swallow indentations on surfaces of thick components and to flatten thin wires in a prescribed sequence and pattern.
The stent is normally coated with a 20nm of a drug to reduce the incidence of rejection and to control excessive tissue growth. This coating is depleted in a short - perhaps 2-3 months. A longer depletion rate would increase the life of the stent and increase the time between replacements. The rendering of the surface of the stent would increase the surface area on which the drugs were contained; further, the receptacles would contain the drugs on the stent for a longer period. Stents were rendered with smg¿s of a nominal prescription before polishing and being tested subjected to a standard laboratory test. As yet, the optimisation of the rendering parameters has not been achieved.
The auto-compensating tool-system, which has now been patented, enables the rendering of functional surfaces with different prescriptions of surface micro-geometries (smg¿s). Typically, the tool-system can be programmed to create smg-depths of between 0.5-30 microns, smg-densities of between 5-50%, in required patterns and orientations, the last two parameters refer to particular applications in which the pattern and orientation of the smg has an influence on performance. The early indications are that each application of smg¿s would require a different prescription; this implies either that exact simulation techniques or experimental validation trails would have to be conducted to establish the optimal prescription. The auto-compensating tool-system may be re-configured to match particular application requirements ¿ for instance, the accuracy of the rendering may require the incorporation of precise components and the rendering of extrusion billets would have to be incorporated in a lathe to operate in parallel with the finishing tool. The patent holders will consider either licensing or outright purchase of the system.
A generator was designed and constructed to supply the Amplified Stacked Ceramic Multi-layer Actuator (ASCMA). The generator consists of the following sub-assemblies: voltage amplifier (20V/V) equipped with a voltmeter, supplier, modulator and the low power voltage source (0-10VDC). The output voltage of the amplifier is 0-200V and the operating frequency is between 5~50Hz. The maximum output voltage 200VDC, with a stable range of ±0.5%, would produce a free stroke of the ASCMA of 0.5mm; stroke is proportional to the supplied voltage; the stroke/voltage characteristic is approximately linear. The frequency in the range 5~50Hz can be used for quasi-static applications; however, it is also possible to use the ASCMA for static applications; in this latter case, the supply of a sinusoidal voltage to the actuator is terminated to allow the device to be operated as a translating device. The main parameters of the generator (the output voltage and frequency) may be adjusted. The frequency is set manually using the built-in potentiometer. The output voltage (the ASCMA stroke) may be adjusted either manually or automatically. For the former case, a voltage-supply unit, equipped with a potentiometer, would have to be connected to the generator. In circumstances when the operation has to be automated, a specially-designed intermediate unit, of the type used for the ultrasonic generator, would have to be connected to the forming machine and the generator. This unit enables the adjustment of the output voltage (the ASCMA stroke) using the control system designed for the MACHMINI machine.