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Reliability in micro-manufacturing - case studies and optimization strategies

Hartl C., Chlynin A.

Zeszyty Naukowe Instytutu Pojazdów / Politechnika Warszawska

2017

z. 3/112

83--92

Micro-manufacturing methods are increasingly applied for the production of miniaturized components as well as of micro-sized geometrical features on conventionally sized products in economically and socially high relevant sectors. The individual techniques can be categorized into Micro-Electrochemical Systems (MEMS)-based process-es, and non-MEMS-based techniques. Traditional MEMS-based manufacturing is performed in volume production since many years. Non-MEMS manufacturing technologies, however, were predominantly developed during recent years by scaling down manufacturing processes for conventionally sized components. In particular, for the application of non-MEMS technologies in volume production, the miniaturization is associated with size-effects, which in many cases increase the scattering of process parameters and influence with this crucially production reliability. The paper provides a survey of cur-rently applied strategies to optimize reliability and process stability in production with an emphasis on non-MEMS technologies for micro-manufacturing.

Die Produktion von Bauteilen und Strukturen für die Mikrotechnik gewinnt zunehmend an Bedeutung. Neben den seit Langem in der Serienfertigung eingesetzten und etablierten MEMS-basierten Technologien (MEMS: Micro-Electrochemical Systems), werden seit einigen Jahren in zunehmendem Maße Verfahren entwickelt, die auf einer Übertragung konventioneller Fertigungsverfahren vom Makro- auf den Mikro-Maßstab aufbauen. Schwierigkeiten treten hierbei durch sogenannte Skalierungseffekte auf, die sich durch vergleichsweise hohen Streuungen von Prozessparametern bemerkbar machen, die sich mit der technischen Zuverlässigkeit des Produktionssystems überlagern. Der vorliegende Beitrag gibt einen Überblick über den derzeitigen Stand der Technik im Umgang mit der Zuverlässigkeit und Prozessstabilität in der Fertigung für die Mikrotechnik mit skalierten Fertigungsverfahren.

Prediction Accuracy of Failure Criteria in FE-analyses of Hydroforming Processes

Hartl C., Radetzky M.

Machine Dynamics Research

2014

Vol. 38, No. 4

69-77

Simulations of tube hydroforming processes require a reliable prediction of the occurrence of plastic instabilities, which are limiting the maximum feasible expansion of the formed tube. To determine the onset of necking, as one of the important instabilities in hydroforming, the use of forming limit diagrams is a well-established practice. This method was initially developed for sheet metal forming processes and is commonly applied also for hydroforming, in spite of the fact that the prediction accuracy depends on the strain path at the analysed position of the formed component. To establish according forming limit diagrams, experimental as well as theoretical techniques exist. Ductile fracture criteria, based on the calculation of forming-history-dependent damage values and considering the development of continuum variables such as stress and strain, are alternative methods of failure prognostication and appealing because of their simplicity. Against the background to obtain an information about the quality in failure prediction of theoretically determined forming limit diagrams and damage-value-based methods for hydroforming component design, an evaluation of , selected examples, of these methods was conducted using simulations with the finite element method. To enable a reliable comparison with experiments, published results of aluminium tube hydroforming were taken where load paths for the forming operation were applied which resulted in a predominantly constant strain ratio at the point of maximum expansion. It was found that the investigated criteria resulted in different prognostication for the onset of plastic instability.