Details that need to be paid attention to during the cooling process of Dongguan precision castings

Dongguan precision castings use a large number of production processes during the production process, in which the cooling process is an integral part of all casting processes. In this link, the relevant metal solid-state phase changes change the internal structure of the metal, or get what we need organizational structure.

When the thin-walled part of the casting undergoes solid phase transformation, the thick-walled part is still in a plastic state. If the new phase is greater than the old phase, the thin-walled part expands and the thick-walled part is plastically stretched, and there is only a small tensile stress inside the casting. , and gradually disappear as time goes by. At this time, if the casting continues to cool, the thick-walled part will undergo phase change and increase in volume, because it is already in an elastic state, and the thin-walled part will be elastically stretched internally, forming a tensile stress. The thick-walled part forms pressure stress through external elastic contraction. In this case, the remaining phase change stress and the remaining thermal stress have opposite signs and can cancel each other out.

When the solid phase transformation occurs in the thin-walled part of the casting, the thick-walled part is already in an elastic state. If the new phase volume is greater than the old phase, the thick-walled part is elastically stretched, forming a tensile stress, while the thin-walled part is elastically contracted, forming a Temporary compressive stress. At this time, the sign of the phase change stress is the same as the sign of the thermal stress, that is, stress superposition. When the casting continues to cool until the phase change occurs in the thick-walled part, the specific capacity increases and the attack expands, thereby disappearing the phase change composed of the previous section. stress.

It can be seen from the above that when the alloy with solid phase transformation is significantly different from the old one and the sign of the tangential phase transformation stress is consistent with the thermal stress, the superposition of the two stresses will have the effect of cracking and deformation. Therefore, during the cooling process , we should strictly follow the process procedures. A little carelessness may lead to defective products.