Fabrication of smooth and deep microchannels on soft polymer by stretching enhanced cryogenic assisted micro milling

Soft viscoelastic polymer is typically difficult –to-machine up to larger depth by cryogenic assisted micro milling (CAMM) process. Stretching enhanced cryogenic assisted micro milling (SECAMM), a single stage and unfilled processing method for soft polymer, is proposed in this study. Tensile stress is initially generated in bulk polymer by uniaxial stretching; then CAMM is performed to fabricate microchannel. To investigate the impact of structural change by directional stretching on deformation response, SECAMM is performed at different stretching ratio (1, 1.1, 1.25, 1.5, and 2) and cutting directions (0°, 45°, and 90°). Further to evaluate the changes in mechanical properties of bulk polymer under cryogenic environment, a scratch based method is used to determine coefficient of dynamic friction (CODF) and fracture toughness under different cutting condition. The study highlights that increase in stretch ratio reduces CODF and fracture toughness with minimum value along 90° direction. Results showed that SECAMM process helps to reduce surface roughness value of machined surface to 2.30 μm for 100 μm depth microchannel. Compared to CAMM, SECAMM along 90° direction reduces the material recovery percentage by 45–55 %, improves the microchannel dimensional accuracy, and enhance surface flatness.