Effect of Die Clearance on Peak Punching Force During Cryogenic Micropunching of Polycaprolactone

Abstract

Microscale holes were punched at cryogenic conditions in Polycaprolactone (PCL) membranes to create synthetic 3D tissue scaffolds through multilayer stacking of 2D porous membranes. Punching forces were experimentally measured, and finite element modeling of the punching process was validated by comparing punching force results. Holes of nominal diameter of 200 µm were punched in PCL films of two different thicknesses: 40 µm and 70 µm. Die clearances used for holes in 40 µm thick films were 15.0 %, and 30.0 %, and 45.0 %. Die clearances used for holes in 70 µm films were 8.6 %, 17.1 %, and 25.7 %. All holes were punched while the PCL film was in thermal equilibrium with a bath of boiling liquid nitrogen. Punching forces were analyzed to study the effect of die clearance and film thickness. A 3D finite element simulation of the punching process was done using DEFORM 3D software. Cryogenic material properties of PCL used in the simulation were determined experimentally. It was concluded that finite element simulation for the cryogenic micropunching process can be used to predict peak punching forces with reasonable accuracy which is a key factor to be considered while designing the punching dies. The finite element simulations did not predict an optimal die clearance to minimize peak punching force. However, the measured peak punching forces for 70 µm thick film seem to favor the smallest die clearance to minimize peak punching force.