Casting Structure & Design Requirements in Different Casting Processes

1) Investment casting

– It should be convenient for the manufacture of wax models

– The holes and grooves on the castings should not be too small or too deep. The holes and grooves are too small or too deep, which is not conducive to the smooth filling of the corresponding holes in the investment mold with paint and sand particles during the shell making to form a suitable cavity. At the same time, too deep holes and grooves also bring difficulties to the sand removal of castings. Generally, the hole diameter should be greater than 2mm (thin parts ＞ 0.5mm). In case of through hole, the hole depth/hole diameter is less than 4-6, and in case of no through hole, the hole depth/hole diameter is less than 2. The slot width should be greater than 2mm, and the slot depth should not exceed 2-6 times of the slot width.

– Reduce hot spot and strive for uniform wall thickness. Generally speaking, the riser is not set separately in investment casting, but the thickened sprue is used as the riser to directly feed the casting. To adapt to this process, thin wall structure should be adopted as far as possible, and the wall thickness distribution should conform to the principle of directional solidification.

– Avoid large flat plate structure. Because the high temperature strength of the melt mold shell is low, it is easy to deform. Therefore, when designing the casting structure, try to avoid large flat surface.

2) Metal casting:

– The shape and inner cavity of the casting should be as simple as possible, the structural slope of the casting should be increased as much as possible, and holes with too small or too deep diameter should be avoided, so as to facilitate the extraction of the core and ensure the smooth removal of the casting.

– The wall thickness of castings should be uniform to prevent shrinkage porosity and crack defects. At the same time, it should be noted that the wall thickness should not be too thin, and large horizontal walls should be avoided as far as possible to prevent defects such as pouring failure and cold shut. For example, the minimum wall thickness of aluminum silicon alloy castings is 2mm-4mm, and the minimum wall thickness of aluminum magnesium alloys is 3mm-5mm.

3) Die casting:

– The side recesses and deep cavities of die castings should be eliminated as far as possible.

– Thin wall structure with uniform wall thickness should be adopted as far as possible. The appropriate wall thickness of die castings is generally: zinc alloy 1mm-3mm, aluminum alloy 1.5mm-5mm, copper alloy 2mm-5mm.

– Inserts can be used for die casting, and the advantages of inserts should be given full play to make complex parts, improve the local performance of die castings and simplify the assembly process. In order to ensure the reliable connection of the insert in the casting, the insert should be inserted into the casting to make grooves, bosses or knurls.