Effects of single and multiple tool pass strategies of cryogenic assisted micro-milling for microchannel fabrication on soft polymers

Soft polymers are difficult to cut material and are characterized by significant tearing and waviness during machining at room temperature due to their low stiffness values. While cryogenic assisted machining has been recently attempted to improve the machinability of such difficult to cut materials but there is no comprehensive understanding of the temperature effect on material removal mechanism of soft polymers yet. Due to the complexity in prediction of the point of phase transition along the thickness during cryogenic cooling, determining the choice of appropriate cutting technique of soft polymer is still challenging. In this work, a paradigm is presented to show how machining of the soft polymer at higher channel depth could be materialize from multiple passes over single pass of larger cutting depth. But, there is an open question on how the temperature-dependent stiffness of the viscoelastic polymer would affect the cutting mechanism when considering the multi pass cutting strategy under cryogenic assisted cooling to improve the machinability up to a larger axial depth. To elucidate these aspects, here, by means of cutting different soft polymer samples, mainly two peculiarities of the cutting mechanism of these structures are reported. The first one is that the chip formation includes, up to now unobserved, extrusion of glassy phase of polymer at multi pass condition. Secondly, the formation of burrs and the deburring process, adjusted by increasing the number of tool passes, will impact the smooth initiation of the polymer surface beneath the machine. Thus, this work is unique in its approach of multiple tool pass strategy to maintain required stiffness at cryogenic conditions for cutting of micro channels with improved features.