Effectiveness of Fixture Design on Cooling of Viscoelastic Soft Polymer during Cryogenic Assisted Micro-milling Process

Abstract

This study investigates the impact of fixture design on cooling soft viscoelastic polymers below their glass transition temperature (T_g) during cryogenic assisted micro-milling. The proposed fixture design targets effective cooling of subsurface layers, enhancing the structural stiffness of the polymer workpiece at larger depths of cut. The effectiveness of the cooling technique is quantified and compared with the performance of a standard fixture, focusing on shear stress, surface roughness, and microchannel cleanliness. However, due to size effect in micro-milling, influence cutting parameter become crucial to optimize. Therefore, proper selection of cutting parameter is initially obtained in terms of output parameters like shear stress, surface micrograph and surface roughness. The results demonstrate that the novel fixture design achieved an 83% reduction in shear stress at a feed rate of 1.66 μm/tooth, compared to 70% with the normal fixture. Additionally, the novel fixture maintained a maximum temperature variation of only 2 °C, compared to 4–5 °C with the standard fixture. At feed rates above the minimum uncut chip thickness value of 1.66 μm/tooth, the surface roughness remained consistently below 3 μm, ensuring high-quality finishes. Furthermore, the novel fixture produced small, powdery chips at a feed rate of 1.66 μm/tooth, indicating superior cooling that facilitated effective chip breaking and brittle fracture. These findings highlight the significant role of fixture design in optimizing cooling efficiency and machining performance of soft polymers.