Surface texturing of interface parts has been shown to improve the frictional behavior and wear and fatigue life of the components. Creating surface texture via micro-forming would provide an inexpensive and precise method of imbuing products including metals, polymers, and certain ceramics with desired three-dimensional surface geometry. The research objective is to systematically develop a design strategy for innovative surface texture fabrication through fundamental understanding of deformation at the micro scale. Currently, surface texturing with a feature size under 100 μm can be achieved via machining, laser ablation, embossing, or chemical means. Micro-forming will provide a valuable alternative; it is a well balanced method, combining tolerances comparable to machining with the speed o f lasers under a relatively inexpensive and environmentally friendly framework.
For this project, an array of precise micro-punches will be used to generate micro surface texture features. Using numerical and analytical means, the surface texture pattern of
this novel technique will be optimized to improve the tribological and optical properties of the product. Previous studies demonstrated that surface texturing has a profound impact on tribological properties [1]. Using a laser system it was found that a textured surface prolonged tooling life by 45% with 10% of the tool area textured and 69% with 20% textured [2]. These increases are attributed to improved lubrication conditions and removal of wear particles. Well-designed surface textures can improve surface and subsurface stress fields and distribute lubricant micro-reservoirs that effectively retain an interfacial medium for lubrication enhancement in moving interfaces.The initial phase of the project entails a detailed comparison of experimentally
texturing surfaces with laser, mechanical machining, and micro-forming techniques. Each
fabrication method will generate differing residual stresses in the product, resulting in varying effects on tool life and dimensional accuracy. The novel three-dimensional laser texturing system, funded by the NSF, being designed and constructed by several faculty members at Northwestern University will be useful for investigating the laser surface texturing process.The second phase will be a thorough investigation of the grain size effect encountered during the fabrication of micro features, focusing on micro-forming operations [3]. As component dimensions approach the grain size, material behavior becomes inconsistent due to the orientation and anisotropy of the individual grains. Friction anisotropy as large as 30% has been found for two orthogonal directions in some surface topographies [4]. The anisotropic behavior of surface texture patterns will be investigated through the development of analytical and numerical methods.
The goal of the project is to experimentally and numerically investigate micro-pressing as a function of feature size and final performance. This work will enhance our understanding of basic science in interface engineering, systematically model the effect of surface texturing on miniaturized products and processes, and enable the improvement of micro-manufacturing precision while reducing fabrication costs. Micro-punching can be applied in the field of tribology for contact surfaces such as journal bearings and additional interfaces such as turbine blades in jet engines. The process could also be used to create textured surfaces for display screens and monitors, including those currently used in HDTVs or in the creation of textured substrates for ultra-thin, flexible solar arrays.
References
1. Wang, Q., Nanbu, T, Yasuda, Y., and Zhu, D., (2006) “Investigating the Effect of Micro Texture on Lubrication,” STLE Annual Meeting, Calgary, Canada.
2. Geiger, M., Popp, U., and Engel, U., (2002) “Excimer Laser Micro Texturing of Cold Forging Tool Surfaces – Influence on Tool Life”, CIRP Annals, Manufacturing Technology, 51, 1, pp. 231-4.
3. Krishnan, N., Cao, J. and Dohda K. (2007) “Study of the Size Effect on Friction Conditions in Microextrusion: Part 1 – Micro-Extrusion Experiments and Analysis”, accepted ASME J. Manufacturing Science and Engineering.
4. He, B., Chen, W., and Wang, Q., (2006), “Friction, Friction Anisotropy, and Wettability of A Micro-Textured Elastomer: Poly(dimethylsiloxane) (PDMS),” in revision for Tribology Letters.
5. Wicht Technologie Consulting, (2005), “NEXUS Market Analysis for MEMS and Microsystems III”
