aluminum die electronic appliance housing
It is a set of electronic housing and cover. Once the customer purchased it from an east european gravity casting foundry. The gravity cast electronic housing and cover has a much coarse surface quality and very heavy. While the market demand of the electronic equipment increased, the awkward yield of gravity casting process can not keep in pace. Thus the customer decided to adapt it to the high pressure die casting process. When they shift to high pressure die casting process, the surface quality can be improved impressively, reduce lots of post machining for the high pressure die casting process can achieve much tighter tolerance than former gravity casting process, reduce the weight of each part and mainly increase the yield dramatically. That is to say the customer can achieve much desired product with much cheaper price. However the investment for the high pressure die casting molds must be higher than that for a gravity casting mold.
Generally speaking, it is a simple housing and cover, without any complicated feature. The housing has two types one of which has bottom holes while the other has a solid bottom. So we made two solid cores to achieve such design. When the bottom holes are needed, we add the particular solid core to achieve them. If not, we use the other solid core. That is also a common and easy way to cast two types of similar products which only have some different sections. The molds of die cast housing and cover were delivered in 40 days as scheduled. Then we tested them in out sister company. As customer instructed, the high pressure die cast housing and cover should have corrosion resistance from water. And they asked us to cast it with the particular material of AlSi10Mg which has low copper content and a good corrosion resistance. The ALSi10Mg is exactly china aluminum cast alloy of YL104, which is also a common material in china material.
We cast out 100 sets of each type during sample testing. Proudly speaking, the quality of the first batch of samples is absolutely complete. In the following 5 days, we trimmed and machined the 200 sets of raw castings. Inside the housing, there is a mounting plate which should be milled to achieve a flatness of 0.1mm with 5 lug bosses. It seems that everything was simple and easy. But our sample submission failed, because the products can't be protective from corrosion resistance.
The customer dipped the die cast electronic housing into water for two days, then air dried it in atmosphere while lots of white rust flowers happened on the surface of the die cast housing. The customer insisted that the former gravity cast housing can be rust proof from water without any surface treatment.
When we came to Holland and visited the customer, we found the gravity cast housing once was tumbled. Commonly while tumbling, some particular corrosion resistance solution will be added into tumbling container. But we were not sure if they used such protective solution.
As customer's advice, we used another type cast aluminum alloy of AlSi12(Fe) which only have a copper content lower than 0.003%. European institute ensured that the high pressure die casting part made by such material without any surface treatment can be free from rust after being dipped into water for two days and air dry in atmosphere.
We booked such die cast aluminum alloy from the aluminum foundry directly. And cast another batch of 100 pieces. But the water test still failed, though the white rust flowers were much slighter than the first batch. We checked the material by our spectrometer, and the spectral analysis showed the chemical composition of the aluminum ingot was right, but the sample collected in the furnace showed a little higher copper content. But the working furnace is a new one which should be free from extra copper content. As for such trouble, we discussed with customer if we can do post surface treatment for the die cast electronic housing without any increase of price. For it is hard to clean a furnace to be free from any copper content.
We processed some die cast electronic housing with surface treatment and tested them with the un-treated one. The result showed that the treated one can be protective from rust but the un-treated one still has white rust flowers.
For this project, the interesting thing is its corrosion resistance requirement. Commonly the high pressure die casting parts can be tumbled with particular protective solution just as treated with similar solution to achieve desired corrosion resistance.
