As market competition increasing,customers have higher requirement on die casting parts.They not only request enough strength but also better surface finishing.The defect of surface finishing affect air tightness of die casting parts.
The surface defect mostly due to the fact that castings stick to cavity of tooling.The main reason for that is as per followings
- Interface reaction
Aluminum alloy is more likely to react with steel.Some kind of chemical compound come out while melted aluminum alloy meet inner surface of tooling.The higher melted alloy and tooling temperature,the worse melted alloy etch tooling.The workers usually clean the sticky stuff by grinding or polishing,which will destroy the protection layer of inner surface of tooling.
- Tooling design
Sometimes,castings stick to inner surface of tooling due to bad tooling design or secondary processing of tooling manufacturing.The protection layer of inner tooling will not last long time if heat treatment are not be done properly.There are other issues that cause problem as well.For example,minor draft,spure not set properly,melted alloy directly flush into cavity or core.
Structure of tooling fail
Not enough cooling line distributed into tooling.The high temperature of tooling might cause problem.High temperature melted alloy etch sprue badly.If not control it properly,the area closed to spure and runner will be etched badly.
- Releasing Spray Agent
Releasing spray agent directly contact inner surface of tooling and provide extra layer between melted alloy and inner surface of tooling,which make sure that castings get off mould smoothly.Therefore,quality of releasing spray agent is very important during die casting process.Good quality releasing spray agent will not increase gas or vapor air inside tooling.
- Proper setting of die casting machine
High pressure die casting can improve filling to tooling but the negative fact is that casting might have flashes around parting line.It is difficult to clean up flashes which also increasing sticking strength between castings and inner surface of tooling.
Method to resolve the problem
- Lower the temperature of tooling
The higher the temperature of tooling,the worse casting stick to tooling.Therefore,cooling line have to be set up properly for die casting tooling.
- Releasing spray agent selection
Good quality releasing spray agent can provide extra protection for tooling and help to avoid casting sticking to tooling.
- Lower pressure of injection
Higher injection pressure is not only way to remove shrinkage pore or porosity.Higher pressure will cause that casting stick to tooling.
- Regular maintenance of tooling
Regular maintenance of tooling is necessary.Polish is not good choice if inner surface of tooling have extra protection layer.Polish might make sticking problem worse.