Causes of porosity defects in die-casting molds, investigation guide for overseas casting factories
The production porosity of die casting mold is a high-frequency defect, with causes spanning across the mold, process, and raw materials. Xinfeng Machinery's layered investigation approach helps factories quickly identify the source of the problem.
1、 Package gas caused by defects in exhaust structure design
Insufficient cross-sectional area of the exhaust groove and premature sealing of the exhaust groove are the highest causes of the proportion of air holes in die-casting, with approximately 44% of the air hole problems coming from unreasonable exhaust design. The standard exhaust groove depth control is 0.03-0.08mm. If the depth is too large, it will cause flash, and if it is too small, the gas cannot be discharged. The exhaust of each branch of the multi cavity mold is unbalanced, and some cavity pores will continue to appear repeatedly.
2、 The moisture content of aluminum liquid and the problem of gas entrapment in the material barrel
Aluminum alloy raw materials are affected by moisture, and the proportion of recycled materials is too high. The dissolved hydrogen content in the aluminum liquid exceeds the standard, and after solidification, it precipitates and forms pores. Industry data shows that when the hydrogen content in liquid aluminum exceeds 0.25ml/100g, the scrap rate of gas holes in airtight components will rapidly increase. Many small and medium-sized factories overseas do not control the use of recycled materials, resulting in long-term mixing of oily and water containing waste materials, and repeated defects that cannot be cured.
3、 Improper setting of die-casting process parameters
The injection speed is too fast, causing eddy currents to wrap around the air at the front end of the aluminum liquid. The timing of starting the high-speed section is the core control point. The speed of the slow injection section is generally 0.15-0.3m/s, and switching to high speed too early can easily result in large-scale gas entrainment. Many operators are accustomed to speeding up and pursuing the pace, sacrificing the internal quality of castings, and long-term increasing the scrap rate.
4、 The Influence of Mold Temperature and Spray Lubrication
The mold temperature is too low, causing rapid crust formation on the surface of the aluminum liquid and preventing internal gas from escaping; Excessive temperature can easily lead to aluminum adhesion and coarse grain size. The initial preheating temperature of the conventional ADC12 die-casting mold is stable in the range of 180-240 ℃. Excessive spraying of release agent causes moisture to vaporize and remain in the mold cavity, resulting in point like porosity defects. The spraying amount needs to be standardized.
5、 Key points for distinguishing between low-pressure casting porosity and die-casting porosity
Most of the air holes in low pressure casting come from hydrogen in the aluminum liquid or gas leakage in the riser, and the proportion of rolled air holes is much lower than that in die casting. The priority inspection for porosity in alloy wheel hub molds is sealing and aluminum refining, which is different from the defect investigation path for high-speed die-casting. The pore source of metal injection mold is insufficient feed debonding, and the defect system is completely independent. B2B platform defect long tail keywords have high accuracy and are suitable for accumulating FAQ content to attract traffic.
FAQ
How to easily distinguish the appearance of pores and shrinkage cavities? The inner wall of the pore is smooth and circular; The shape of the shrinkage cavity is irregular, the inner wall is rough, and it is mostly located in thick and large section positions.
How to clean the blocked die-casting exhaust groove? Shutdown grinding and cleaning, routine inspection of exhaust smoothness is required for production of 500-1000 molds.
Can degassing of aluminum liquid eliminate all pores? It can only remove dissolved hydrogen gas, but cannot solve the problem of air being drawn into the mold cavity by injection vortices.
What is the appropriate ratio of mold release agent to water? The universal dilution ratio is 1:80~1:120, and there are differences in different working conditions and different brands of release agents.
Is it easier for thick walled castings to produce porosity? Thick walled components solidify slowly, have a longer window for hydrogen evolution, and have a significantly higher risk of porosity compared to thin-walled components.
Is it necessary to configure a die-casting mold temperature machine? Recommended configuration for mass-produced airtight components, stable mold temperature can reduce defect fluctuations, and the yield rate can be increased by about 12%.
What is the maximum proportion of recycled materials to be added? The safety control should not exceed 30%, and the recycled materials need to be dried, degreased, and refined.
Will porous castings still fail after infiltration? Infiltration is suitable for isolating small pores, while connected large pores may still leak under pressure after infiltration.
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