The packaging force will applied to the core during solidification stage of die casting due to alloy shrinkage.The castings still shrink at room temperature after getting off mould.The shrinkage rate is 0.4%-0.7% for die casting.This shrinkage range make designer feel hard to choose during tooling design. The packaging force is subject to draft,roughness,ejector pins layout,release agent quality,mould temperature and casting temperature.Cangzhou Weiheng Metal Products Co.,Ltd Professional Die Casting Supplier.
Thermal expansivity of tooling steel and casting alloy are main factors in die casting manufacturing.
- Thermal expansivity of tooling steel
The most common steel are DIEVAR,H13 and SKD61 etc.The tooling temperature is 75-425℃ in common production.Different tooling will have different working temperature.The manufacture need to check different thermal expansivity.
- Thermal expansivity of aluminum alloy
The thermal expansivity is related to silicon composition of aluminum alloy.At same temperature,the lower thermal expansivity,the higher silicon composition.
- The temperature of die casting parts and mould
The shrinkage refer to the size change of casting from solidification to cooling down.As for ADC12,the highest temperature of tooling is 289.5℃.The outside temperature of casting is 350℃ and inside temperature is about 400℃.
When temperature of casting fall down from 550℃ to 500,450,400,20℃,the thermal expansivity are 25.4,24.8,24.3,23.8×10-6℃-1 respectively.Compare with temperature of casting,the temperature of tooling are 450,400,350,300℃ and thermal expansivity are 12.89,12.69,12.51,12.33×10-6℃-1.
When casting is ejected off mould,inside temperature of casting is 350-400℃ and tooling temperature is 280-300℃.The size of casting is nearly same to the size of mould.When castings get off mould,the temperature of castings is 370℃ and tooling temperature is 290℃.The thermal expansivity is 23.6 and 24.1xx10-6℃-1 respectively.Therefore,castings made from ADC12 is 0.5%.
If there is difficulty that casting hardly get off mould,the most common solution is to put some grease between casting and mould then heating up.
The size of castings and mould will increase when temperature increase.But the speed of increasing is different from castings to mould.When shrinkage of casting make its size smaller than size of mould and packaging force is bigger.Therefore,Heating up castings and make packaging force become lower,however,the castings will be broken by ejector pins if heating up too much.