Effect of Crystallographic Orientation on Micro-deformation Processing

Abstract

Deformation processing is widely used in the micro-fabrication of small and precision parts in electronic, optical and computer products. Examples of successful applications include ultra-precision machining of optical components, and precision blanking and forming of high density integrated circuit lead frames, high resolution diffraction gratings, and millimeter wave guide. Micro-deformation processing presents problems not encountered in the conventional bulk deformation processes. The deformation zone geometry is such that only a few grains are involved across the workpiece thickness and the crystallographic orientations of the grains will exert a large influence on the plastic responses of the workpiece materials. Common problems encountered in the micro-deformation processes are accuracy of the formed components, surface undulation in an otherwise smooth surface, and the erratic load imposed on the tool. All these problems have their origin in the plastic strain inhomogeneity caused by the grain anisotropy of the materials. During deformation, the grains will tend to deform independently and take up strain path different from their neighboring grains [1]. For example, under biaxial stress state grains of 110 <001> orientation have a strong tendency to deform in plane strain state while {112} <111> oriented grains will tend to deform towards biaxial strain state. This would result in different thickness strain and undulations in the formed component. Another example of the effect of crystallographic orientation can be found in ultra-precision machining. The variation in micro-cutting force has its origin in the varying crystallographic orientations of the workpiece material the tool has traversed during a revolution of cut [2].