What are the common defects of metal precision castings and how can we avoid them？

1. Pinholes

Measures to prevent the formation of pinholes on precision castings: It is strictly prohibited to use contaminated cast aluminum alloy materials, organic compounds, and severely oxidized materials. Control the smelting process and strengthen degassing and refining. Control the thickness of the metal coating, as excessive thickness can easily cause pinholes. The mold temperature should not be too high, and cooling measures such as copper inlay or watering should be taken for thick walled parts of castings. When using sand molds, water should be strictly controlled and dry cores should be used as much as possible.

2. Air hole

Measures to prevent porosity: Improve the pouring and riser system to ensure stable liquid flow and avoid air entrainment. The mold and core should be preheated, then coated, and must be baked before use. The design of molds and cores should consider taking sufficient exhaust measures.

3. Oxide slag inclusions

Measures to prevent oxidation and slag inclusion: Strictly control the smelting process, quickly smelt, reduce oxidation, and thoroughly remove slag. Aluminum magnesium alloy must be melted under a covering agent. The furnace body and tools should be clean, free of oxides, and preheated. The paint should be dried after use. The designed casting system must have stable flow, buffering, and slag skimming capabilities. Adopting a tilted pouring system to ensure stable liquid flow and prevent secondary oxidation. The selected coating has strong adhesion, and slag is formed inside the casting during the pouring process without peeling off.

4. Cracking

Measures to prevent thermal cracking: In actual pouring systems, local overheating should be avoided to reduce internal stress. The mold and core slope must ensure the above 5 degrees, and the inverted riser can be formed by core pulling during solidification. Sand cores can replace metal cores when necessary. Control the thickness of the coating to ensure consistent cooling speed of the casting. Select the appropriate mold temperature based on the thickness of the casting. Refine the alloy structure and improve its thermal cracking ability. Improve the structure of castings, eliminate sharp corners and sudden wall thickness changes, and reduce the tendency for hot cracking.

5. Loose

Measures to prevent loose production: Reasonable riser setting to ensure solidification and shrinkage ability. Reduce the working temperature of the metal mold appropriately. Control the coating thickness to reduce the thickness of thick walls. Adjust the cooling rate of each component of the metal mold to provide greater cooling capacity for the thick walled castings. Reduce the pouring temperature of the metal appropriately.