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Causes of Cold Insulation Defects in Die Casting and Rectification Plan for Mold End
Cold shut is a high-frequency appearance and structural defect in die-casting parts, where two streams of aluminum liquid converge and fuse poorly. The mold structure, sprue, and mold temperature can all affect the occurrence of defects. Xinfeng Machinery has sorted out the rectification path on the mold side.
1、 Characteristics and risks of cold insulation defects on castings
Cold insulation is a linear fusion joint, which is prone to fracture at the stress location. If a pressure bearing component experiences cold insulation, it is directly judged as scrap. Statistics show that approximately 32% of cold shut problems are caused by unreasonable gate position and runner section design, as well as a large temperature difference between the two streams of aluminum liquid. Thin walled heat dissipation shells and slender brackets are most prone to such defects.
2、 The influence of sprue and pouring gate design on material flow
The gate section is too small, the aluminum liquid flow rate is too fast, and it cools down prematurely; Unreasonable gate layout and early diversion of material flow can easily lead to cold insulation when the temperature difference between two streams of aluminum liquid exceeds 60 ℃. The simulation in the die casting mold design stage can predict the position of the material flow convergence, adjust the gate direction in advance, and let the material flow fill the cavity sequentially.
3、 Amplified cold shut probability due to insufficient mold temperature
The initial temperature of the mold is below 160 ℃, and when the aluminum liquid reaches the distal cavity, the temperature rapidly drops and the fluidity decays. In continuous production, the mold temperature remains stable within the range of 180-240 ℃, and the cold insulation failure rate can be reduced by about 21%. Many factories deliberately lower the mold temperature to reduce sticking, resulting in repeated cold insulation defects.
4、 Differentiation between Low Pressure Casting Cold Insulation and Die Casting Cold Insulation
The filling speed of low pressure casting is gentle, and cold insulation mostly occurs at the end of the filling process, usually caused by insufficient hydraulic pressure and blockage of the lifting pipe. Alloy wheel mold shows cold separation of the spokes, priority should be given to checking the hydraulic pressure curve and the temperature of the aluminum liquid coming out of the furnace. The rectification logic is different from high-speed die-casting.
5、 Key points for distinguishing easily confused defects
Cold insulation is different from flow lines and scratches: cold insulation has fusion boundaries and weak strength; Flow patterns are only surface patterns, and the body is continuous. When repairing die and mold, it is not enough to simply rely on increasing the injection speed, as speeding up can easily introduce air pockets. Metal injection mold weld marks belong to the same logic, but the feeding and temperature window parameters are completely different and cannot be applied to die-casting schemes. Google's "die casting cold shut solution" is a high-frequency search term for overseas process engineers.
FAQ
Can adding a gate to the cold insulation position solve the problem? Most of them are effective, but adding new gates will increase the workload of subsequent machining and removal.
Can increasing the temperature of aluminum melt eliminate cold insulation? Short term effectiveness, high temperatures can exacerbate aluminum adhesion and burn mold cavities.
Is infiltration repair effective for cold insulation castings? Structural strength defects cannot be repaired by infiltration, and the stressed parts must be directly scrapped.
Will blocking the exhaust duct cause cold insulation? Poor exhaust results in back pressure, hindering the flow of material and indirectly inducing cold insulation.
How to adjust the cold insulation of low-pressure wheel hub spokes? Increase the charging and boosting rate, and check if the liquid lifting tube is partially blocked.
Are cold insulation and weld marks the same type of defect? The mechanism is similar. In the die-casting industry, defects in die-casting parts are generally referred to as cold shuts, while MIM is often called weld marks.
Can spraying more molds improve cold insulation? The effect is weak, and excessive spraying brings cooling, which can actually worsen the defects.
Can simulation predict the cold insulation position in advance? The simulation of filling solidification can predict the convergence position of the material flow and optimize the plan in advance.
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