Micromachining and Burr Formation for Precision Mechanical Components (2007)

Micromachining and Burr Formation for Precision Mechanical Components J. Hartnett1, S. Min1, D. Dornfe|d1 Laboratory for Manufacturing and Automation, Department of Mechanical Engineering University of California Berkeley, California 94720-1 740 Abstract An understanding of burr formation and edge defects is critical to efficient production of machined features in precision components. Analytical models of burr formation and edge effects including the tool/workpiece interaction and material inﬂuences are necessary for building databases describing cutting conditions for optimal edge quality, and design rules for burr and edge defect prevention. This paper reviews recent research work done on the fundamentals of burr formation in micro-milling of microfluidic devices using the Mori Seiki NV150O DCG Vertical Milling Machine as part of the MTTRF machine loan program at the University of California at Berkeley. Specific applications of micromachining and burr formation test results for of micro-scale components are presented and discussed. Keywords: Micromachining, burrs, experimental data bases 1 INTRODUCTION Micro-machining as a manufacturing technique represents a continued trend towards miniaturization across all areas of manufacturing. However, there still remain many technical hurdles prior to widespread use of micro-machining, and speciﬁcally micro-milling, industry- wide. This is mainly due to the fact that as feature sizes continue to decrease, effects considered to have little or no influence at larger scales become dominant factors with strong inﬂuences on part accuracy, surface generation, and integrity of components [1]. These factors need to be addressed when developing process parameters to ensure machined parts meet desired form and tolerance speciﬁcations. It has been the goal of the Laboratory for Manufacturing and Sustainability over the years to conduct research on the fundamental aspects of burr characterization, minimization, prevention, and removal. it is a goal to continue to expand this research to machining at the micro-scale. As these issues are addressed the applications where micro-milling can be utilized as a manufacturing technique will increase. it is increasingly common to see milling used for meso-scale electronics, plastic injection molds, and devices such as micro-turbines and pumps. An interesting application for micro-milling is the area of micro-fluidic devices. These are miniaturized devices that are used to manipulate micro- and nano-liter volumes in an effort to understand cellular mechanisms. The devices are used for live cell experimentation to better understand inter- and intra-cellular interactions [2]. Typical applications of these devices are: - Drug screening and testing - Biological and chemical sensing - Genetic analysis Figure 1 displays a sample micro-fluidic device known as a micro-mixer. Efﬁcient mixing of reagents is desirable for applications where fast diagnosis results are needed [3]. The size of the features makes micro-milling a viable option for manufacture of the device. Micro-ﬂuidic devices typically make use of more traditional microfabrication techniques used to pattern integrated circuits on silicon wafers [2]. The device illustrated in Figure 1 used a typical method of device fabrication where SU-8 and OmniCoat photoresist were spin coated on a nickel disk. The disks were then electroplated with nickel before removing the photoresist. Finally the nickel disks were used in a plastic injection molding process to make a polymer mold. There are many advantages to traditional microfabrication techniques such as lithography, including being able to attain microscopic feature sizes, and high ﬁdelity replication of desired features. However these traditional methods are limited in the complexity as they can only create features in 2.5-dimensions. Additionally they typically require longer lead times for manufacture. For example the electroplating process described above took in excess of 6 hours. ()iit.Eet tlou Figure 1: Micro-mixer micro-fluidic device [3]. Micro-milling may be a viable alternative to these processes due to the ability to manufacture true 3-