1.The reasons why the dimensional accuracy is difficult to control
Automobile investment casting size is difficult to control, there are mainly these reasons. First of all, thermal expansion and contraction, hot metal water poured into the mould, cooling will shrink. But the casting thick place cool slowly, thin place cool quickly, the degree of contraction is not the same, the final casting is easy to deformation. Mould design is also critical. In order to counteract the metal's cooling contraction, the mould has to be a little larger than the actual size of the casting. But this 'a little bigger' is how much, the casting size is not correct if you miscalculate. If the mould itself is not made accurately, the casting size will naturally be off. Moreover, when the casting is cooled, there will be forces inside like a rubber band pulling. If these forces are not evenly distributed, or the casting structure is too complex, after cooling automobile investment casting will be twisted and bent.
2. The consequences of precision misalignment
Automobile investment casting parts made large or small, and other parts of the car can not be tightly fit together, loaded can not be mounted, or mounted on the loose, that can be a problem. In order to make the castings dimensionally acceptable, it is often necessary to carry out additional machining, such as using machines to cut off the excess parts, or to correct the deformed castings. These are additional processes that can greatly increase production costs. Insufficient dimensional accuracy of the castings may lead to inappropriate fitting gaps between components, affecting friction, sealing or transmission efficiency. In the long run, it will also accelerate wear and shorten the life of the whole component.
3.How to manufacture
In the design of the mould, we should be like a 'divine arithmetic', accurately calculate the amount of metal shrinkage, and then make the mould a little larger than the final automobile investment casting, which is called 'shrinkage compensation'. The actual actuality that the actual actuality is not a good idea. Strictly control the temperature of the liquid metal, as well as the casting cooling speed in the mould.