Study On The Roughness And Residual Stress Of Micro-Milled Surface

With the increasing demand for miniaturization products in fields such as civil market and national defense, much attention has been given to the issues involving in the design, development and manufacturing of micro-parts. Micro milling technology plays an important role in complicated three dimensional micro parts manufacturing. However, at present, most three dimensional micro parts made of metal materials are manufactured in conventional ultra-precision machines, which have high cost, low efficiency, high energy consummation, comparatively low spindle speed. In contrast, micro machine not only could improve space utilization ratio and reduce cost, but also could easily attain high manufacturing speed and high precision motion control due to less inertia. Thus, study on the roughness and residual stress of micro-milled surface that based on micro machine is significant for production and scientific test.Firstly, based on the manufactured experimental prototyping micro machine, the parameters of machine tool control system on PMAC card are set. The micro machine has adopted piezoelectric ceramic motor to drive workbench directly, and the locating accuracy of feeding system has great impact on the machining precision. Thus, the research makes the locating accuracy meet certain requirements to serve as the platform for the subsequent micro milling experiments. Secondly, dual-factor design is adopted in the micro-groove milling experiments.The influence of cutting parameters, such as overhang length of tool, diameter of tool, depth of cut and feed per tooth is studied, and their interactions on surface roughness are analyzed. And then, central composite design of response surface method and regression analysis method are employed to establish a surface roughness model in micro milling. With this model, not only the effect of the individual cutting parameter on surface roughness can be comparatively analyzed, but also the parameters can be optimally selected according to the requirements before the actual milling process, which could predict and control the surface roughness and improve metal removal rate in micro milling.Finally, the residual stress in the micro-milled surface is estimated via dynamic simulation of the micro-milling process by finite element software of Deform-3D. Then with micro milling technology, 3J21 elastic alloy film micro-bridges, whose thicknesses are about 10μm, are manufactured successfully. And a nanoindenter XP system is used to get the load-deflection curves of them. Theoretical model of nanoindentation and theory of elasticity are proposed to evaluate the elastic modulus and residual stress of these thin films simultaneously, in order to verify the results of finite element simulation. And the result shows that micro-bridge testing method is feasible to evaluate residual stress of micro-milled surface.