In micro forming, the increased surface to volume ratio makes ejection of an extruded component to an often complicated process. The aim of this work has been to demonstrate the possibility to reduce the force required to eject the component, by controlled pre-stressing of the die, before, during and after the forming process. The level of required prestress has been evaluated by FE analysis of the interaction between the forming process and the elastic deflection of the tool-system. A test rig has been designed containing four piezo actuators mounted symmetrically around the circumference of the die cavity. Mechanical amplification has been used to increase the pressure created by the piezo actuator to reach the level required for prestressing of a bulk forming tool.The force required to eject the component from the die depends on the tribological conditions combined with the radial pressure between die and component due to elastic deflections remaining after the punch
The central part of the metal forming processes are the forming tools. In the macroscale, these tools are manufactured by means of machining-and drilling operations and subsequently hardened. Due to the required precision, this approach is not possible in the microscale. An investigation of alternative tool manufacturing techniques has been carried out, including jU-EDM, electroforming and machining operations. A series of universal forming tools for simple microcompoents has been manufactured using different techniques, allowing side-by-side comparison. A series of ejectors and punches have also been manufactured using a combination of grinding and jU-EDM processing. Critical tooling parameters including geometry, yield strength, surface roughness and production time has been recorded. A silicon replica method has been utilized to measure the internal geometry of the micro forming tools
Manufacturing techniques for production of small precise metallic parts has gained interest during recent years, an interest led by an industrial demand for components for integrated products like mobile phones, personal digital assistants (PDAs), mp3-players and in the future for spare parts for the human body. Micro components have also found several applications within the medical, audiological and dental industry, applications that impose increased demands for biocompatible and corrosion-resistant materials and cleanness. So far these micro components have mainly been manufactured by traditional machining techniques or chemical etching. However, these traditional machining and etching techniques are generally not well suited for mass production of advanced micro components, due to handling problems, waste of expensive material and long machining times. This calls for development of a novel production system that can meet the demands for high productivity, high reliability, low cost, while being environmental acceptable. Bulk metal forming meets these demands to a great extent, but the technology cannot directly be transferred to the micro scale. A flexible machine system for bulk micro forming has been developed and used to form a number of industrial micro parts in aluminium and silver, with ongoing work on forming of titanium. Manufacture of billets by cropping has been examined using a simple test rig and an automatic cropping device has been designed, manufactured and tested.
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