Aluminum die casting signal box for telecommunication equipment
Step one :Aluminum sand cast prototype for signal box housing
Step two :Aluminum high pressure die cast signal box housing
The aluminum sand cast and post machined prototype of signal box is approved well.Then we start to prepare for the aluminum high pressure die casting mold for the project.
As we know, for the whole high pressure die casting process, a good high pressure die casting mold or die must be the most important factor of a successful die casting project. Thus we chose our long term cooperating high pressure die casting mold manufacturer Ningbo Huihuang Machinery Co., Ltd. to produce the dies for us, which is one of the biggest high pressure die casting mold manufacturer in China.
Compared with sand casting process, the high pressure die casting process can apply much smaller draft angles for the casting. We adapted the larger draft angle to 0.5 degree for the whole die cast signal box. And the bottom fins were also increased to 26 pieces. Most importantly, we can remove lots of machining allowance for the die cast part, for the die casting process can achieve thin-walled part rather than sand casting process.
When the 3-d pattern of the die cast housing and cover got approval of the final customer, the die casting mold manufacturer started to produce the molds. After the feeding analysis by special software, we worked out the proper locations of the running system and ejectors. The undesired point was that we had to locate ejector points on the sealing groove, for there is no place rather than the groove on the right top of the four-sided walls can stand the ejecting force and push out the whole part properly. However such arrangement led to post milling of the whole groove, as the production cost increased.
The customer accepted our mold building proposal, as there was no way to revise the drawings of the die cast signal box after the other components were fixed. And totally it took us 50 days to finish the die casting mold as scheduled.
The housing mold was tested on a 1250 tons cold chamber die casting machine. Actually we would had planned to use a 800-1000 tons die casting machine to cast, but considering the concentrated bottom fins are subject to insufficient feeding, we finally choose the larger tonnage machine to cast it. The sample testing was started in midnight. After 30 minutes of heating cold die, the expected products were cast out. The surface of the raw die castings was quite good. And the deformation of the large opening was within the expected range. So the following step was to measure the full dimensions of the housing. We were patient to wait till the raw casting body got cold.
While the housing testing, the mold of the over was tested on a 500 tons of cold chamber die casting machine. The raw casting part had a good surface quality. However, the large flat plate was deformed as our thought. Fortunately we had prepared modification fixture for the large flat cover. The die cast housing and cover was tested by assembling patterns fist and they matched each other quite well. Then the trimmed die cast housing and cover was moved on a CMM machine for full-dimension inspection. It actually took us 2 days to finish full-dimension inspection by CMM for first 5 sets of samples.
Appreciation to the excellent dies, the CMM report showed the first 5 samples were qualified. The die casting process achieved nearly all features of the signal box and cover, the post machining was quite simple only including milling the sealing groove and tapping the mounting holes on the whole body of the housing and cover. The machining fixture was worked out according to the raw cast part and was ready when the CMM report was available. Therefore we only take half day to finish the post machining. The machined part was inspected again by go or no go gauge for all the drilled and tapped holes. And most importantly the assembled set was tested by water proof by being dipped into a water pool for 5 minutes. The five samples passed the water proof test successfully.
Then the five die cast samples were forwarded to the powder coating factory (Ningbo Dongxing Powder Coating Factory). Processed as common procedure,the machined die cast housing and cover was pre-treated for one day ,then powder coated in the next day. The critical point we need to mentioned here, for the high pressure die casting has impressive porosity, while the work piece was coating, it should be heated to around 300-350 cent degrees, then the air in the pores will be activated to escape from the casting body resulting to damage of the casting. That is another reason why we choose a 1250 tons die casting machine to cast the signal box. The higher the pressure,the lower the porosity.
As for the powder coated signal box, another point need to emphasize is the protective work for the powder coated work piece during moving in the workshop and transportation between different cooperating factories. The powder coated surface is subject to scratch and damage in the rough handling and transportation. In the mass production, we made a special batch of bubble boxes to hold the die cast signal housing.
The powder coated signal box was performed with salt spray test for checking the thickness of the powder layer and its corrosion resistance. As our expectation, the test showed the powder coating factory is quite good.
The 5 pieces of the die cast signal box were shipped to the customer by Fedex, and we got their good news in one week. The sample submission passed their final approval. We started to prepare for mass production of high pressure die cast signal box.
