Influences of size effect and workpiece temperature during cryogenic micro milling of soft viscoelastic polymer: An experimental assessment

Abstract

It is necessary to create different micro-features on stretchable polymers for making sensing components in wearable sensors, and to make them work like human tissue. Such micro-features are currently fabricated through soft lithography process that requires long processing time. However, tool based micromachining which is faster and able to create any customized and complex structures has not yet been applied as soft polymer shows high adhesion and low elastic modulus at room temperature. This study aims to evaluate the machinability of typical viscoelastic soft polymer and understand the effect of material and process parameters on machining performances. In this study, a mechanical micro milling process using cryogenic assisted cooling is proposed and the importance of temperature control towards glass transition zone was particularly addressed. To identify insight of machinability in micro domain, this article also determines minimum uncut chip thickness (MUCT) and size effects by considering the variations of cutting force and surface integrity with the ratio of h/re (uncut chip thickness (h) to cutting edge radius (re)). The experimental results reveal that consideration of size effect during micro milling of soft viscoelastic polymer helps in reduction of machined surface roughness (Sa) value. Based on the cutting force pattern, it is evaluated that higher machining stability can be achieved during cryogenic machining by reduction of specific cutting force value. By control tuning of temperature, machining performances exact at glass transition temperature zone show more promising experimental results compared to other cooling zones.