Machining Process of Casting Shell Parts

According to the structural characteristics and processing difficulties of the cast shell parts, the process is analyzed, the rough datum and the fine datum are correctly selected, the machining allowance is reasonably distributed, the processing problems of the plane and the inner hole are solved, and the parts are finally qualified.

Casting shell parts have complex shapes, many associated dimensions, and high precision. The selection of machining standards is very important. The operating mechanism of a certain type of product is installed in a separable shell. The separable shell is shown in Figure 1. It is composed of No. 1, No. 2 and No. 3 shells. The No. 2 shell is in the middle position, which plays the role of connecting the upper and the lower. There is the No. 1 shell on the top and the No. 3 shell on the bottom, which is equipped with a number of important parts such as shafts. It can be seen that the No. 2 housing is the reference part during assembly, and its machining accuracy will directly affect the assembly accuracy of the operating mechanism.

2 Technical requirements for parts

The blanks of No. 1, No. 2 and No. 3 shells are sand castings, the material is ZL116 aluminum alloy (T5), and the casting accuracy grade is CT9 (HB 6103—2004).

Shell No. 2 is shown in Figure 2. In order to ensure a close fit with No. 1 and No. 3 shells, both sides A and B are required to have good dimensional accuracy (±0.1mm), geometric tolerance (flatness of 0.05mm) and surface quality (surface roughness value Ra= 1.6μm). At the same time, in order to ensure the positional relationship after assembly, there are also quite high requirements for the positioning holes on both sides of A and B. The dimensional accuracy of the hole pitch is ±0.05mm, the dimensional accuracy of the hole diameter is H8, and the surface roughness value Ra=1.6μm. For non-positioning holes, such as general mounting holes and threaded holes, the dimensional accuracy has also reached ±0.1mm.

In addition, in order to ensure that the position of the shaft is installed correctly, the processing of the C hole is also very important. The machining accuracy of the hole will directly affect the installation position of the shaft in it and whether the shaft can rotate flexibly.

Through the above analysis, starting from the assembly requirements and use, the mechanical processing of this part mainly includes two aspects: one is processing A and B surfaces and the positioning holes and mounting holes on them; the other is processing C holes.