Aluminum connection base is about 0.86kg.The size is 396x290x90mm.The structure is complex and wall thickness is not uniform.The material is AlSi9Cu3(Fe).There is oil tunnel inside so the airtightness must be very good.By X-ray checking,there are shrinkage porosity around tapping hole and air pore on surface of oil tunnel.To minimize the defect,the structure and pouring system need to be improved.
There are several reasons for air pore and shrinkage porosity.
- Molten alloy is not refined properly.Air trapped in the molten alloy.
- Evaporation of release agent during injection.
- Die casting setting is not good,such as injection speed is so fast that air trapped inside cavity.
- Pouring and ventilation system is not good so torrent happen during injection.
- Wall thickness is not uniform.Thick area will have air pore and shrinkage porosity.
From section,the air pore is not distributed evenly.The shrinkage porosity is in different shape and concentrate in one area.
By leakage testing to connection base,there is bubble come out in the area closed to oil tunnel.The oil tunnel is in thick area.The release agent can not spray onto it due to sliders.To reduce weight,the distance between tapping and pocket is just 1.5mm.So there will be some shrinkage porosity during solidification.To optimize the design,
- Increase wall thickness between tapping hole and pocket.
- Add cooling point in pocket in order to increase cooling speed.
By moldflow analyzing,there will following issues that cause air porosity.
- The dimension of oil tunnel is too small.So the molten alloy can not fill up properly.
- Inner sprue is too thin so molten alloy cooling down too fast.
- Ventilation system is not good.Air can not go out properly.
Therefore,some modification need to done as following
- Increase dimension of oil tunnel.
- Add one overflow next to threading area.
Overall,design optimization,increase wall thickness between tapping hole and pocket.Meanwhile,add cooling point and increase cooling speed.It can remove casting defect.Via simulation of pouring,extra overflow added on to tapping hole.It can solve the problem of shrinkage porosity.