A study on gas penetration behaviour in gas-assisted powder injection moulding

The effects of process parameters on gas penetration depth of gas-assisted injection moulding (GAIM) were investigated for polypropylene (PP) and 316 stainless steel (SUS316L) powder feedstock by the Taguchi method. The process parameters were melt temperature, shot size, gas pressure, and gas delay time. The most significant parameters affecting gas penetration depth were shot size for PP and gas delay time for SUS316L, respectively. The different significance of gas delay time between SUS316L and PP was mainly due to the higher thermal diffusivity and cooling effect of SUS316L as compared to PP. Simulation was also conducted to compare the thermal and rheological properties of materials and to analyse gas penetration behaviour. The higher thermal diffusivity and cooling effect of the SUS316L also caused the increase of the viscosity and shear heating for SUS316L at the time of gas injection. Gas fingering behaviour by the shear heating effect was confirmed.