Analysis of Crown Shrinkage in Gravity Die Cast Aluminium Alloy LM 13 Piston

Abstract

Background/Objectives:Optimization of process parameters to obtain shrinkage free engine piston based on Al-Si casting alloy LM 13 fabricated by gravity die casting. Method/Statistical Analysis: Experimental analysis of design and process parameters like riser sleeve size, center core temperature, pouring metal temperature and solidification time was carried out on Al-Si casting alloy LM 13 based engine piston fabricated by die casting technique. The die casting experiments with different solidification time 90, 120 and 150 seconds and volume of molten metal consumed by different sleeve size were carried out to obtain optimum conditions to produce shrinkage free engine pistons. The die casted engine piston were sectioned and checked for shrinkage at different design and process parameters. Results/Findings: The results showed that there is an effect of centre core temperature towards the shifting of shrinkage from the crown to riser. The center core temperature should not be maintained below 200°C and should be in the range of 200 - 238°C. But it cannot be concluded that the crown shrinkage is only due to the centre core temperature. The molten metal Al-Si is less dense as a liquid than as a solid so castings shrink upon cooling, which can leave a void at the last point to solidify. Risers prevent this by providing molten Al-Si alloy to the casting as it solidifies, so that the shrinkage forms in the riser and not the in engine piston casting. It was found that the size of sleeve size is indirectly proportional to the occurrence of crown shrinkage and increase in size of sleeve size reduces the chances of shrinkage. Engine piston section results showed the shrinkage shifting from casting to riser side by increasing the sleeve size. However the effect of different solidification time and pouring metal temperature was not so significant on the occurrence of shrinkage. Applications/Improvements: The optimized center core pin temperature and riser sleeve size successfully prevented the shrinkage formation in the Al-Si casting alloy LM 13 engine piston casting. This not only helps in improving the casting quality but also in increasing the production.