Aluminum casting is traditional technology. With the development of technology, people now divide aluminium casting into more detail, for example, sand casting, gravity casting, high pressure die casting, etc. speaking to Die Casting,With the development of society, the demand for die-casting products is getting bigger and bigger, and the requirements are also increasing. How to reduce or avoid the defects in castings production, becomes the top priority. let’s talk about more detail on those pressure die casting defects and solutions. hope it can help your product improvement. here we go.
Die Casting Defects
Flow mark in Die castings;There are stripes on the surface of the casting Parts, consistent with the flow direction of the molten metal. It is obviously different from the metal matrix, and has no direction of the grain.
1. The first layer of the molten metal into the cavity to form a very thin and incomplete cold metal layer, which is compensated by the subsequent molten metal.
2. The mold temperature is too low.
3. The cross-sectional area of the inner runner is too small and the position is improper to cause splashing.
4. The pressure acting on the molten metal is insufficient.
1. Increase the mold temperature.
2. Adjust the cross-sectional area and position of the gate.
3. Adjust the speed and pressure of the gate.
4. Appropriate selection of coatings and adjustment of dosage.
Porosity in castings is very commen Problem;During the solidification of the molten metal, the circular, elliptical, waist-shaped or pear-shaped void formed by the gas trapped in the casting is called gas porosity. The names of gas porosity in production include gas porosity, air holes,shrinkage porosity, sand holes, pinholes, and so on.
The first layer is the skin layer, which is a die-cast crust block, which is generally not very bright, and the layer needs to be polished to see the luster.
The second layer is a dense layer, which is relatively dense in grain, and is generally less prone to pores, and the thickness is affected by the die casting process. The third layer is the inner layer, which is relatively loose in grain and has more pores, which is generally difficult to avoid.
The appearance of gas porosity in different layers is as follows:
1) Surface porosity: multiple or clustered small holes or small depressions distributed on the surface of the casting.
2) Porosity under surface : A small number of porosity present in the dense layer are irregularly distributed.
3) Internal porosity: inside the casting, especially in the wall thickness
Porosity is a common, multiple defect. In general, the amount of scrapped castings due to porosity accounts for 25%-80% of the casting reject rate. Therefore, prevention and elimination of porosity defects is one of the important contents to ensure the quality of castings parts.
The Porosity has the following hazards:
1) The porosity reduce the effective bearing area of the casting parts and cause stress concentration and reduce the mechanical properties of the casting parts, mainly plasticity, toughness and fatigue resistance. Internal porosity that are difficult to find can be a serious hazard for sudden failure of the product during operation.
2) The porosity seriously damage the surface quality of the product and cause the product to be scrapped.
3) The air hole reduces the airtightness of the product that needs to withstand the working pressure of the fluid, and easy to leakage.
4) The sand holes will effect subsequent processes such as plating and spraying.
Analysis of the causes of Air Porosity
1. Air Exist inside the molten metal
2. Air is generated during the filling process
3. Effect of release agent
The performance of the release agent is not good, the composition is improperly reacted with the molten metal to generate air, the volatilization point is too high, and the gas generation amount is large.
The amount of the release agent used is too much, the spraying time is too long and the unevenness causes the surface temperature of the mold to be too low, and the water vapor on the surface of the mold cannot evaporate for a while, and a large amount of air is generated after the mold is closed.
melting of alloy
All raw materials and melting tools must be carefully removed from the surface of the rust, oil and slag, etc., poor quality of the recycle material should not be used in large quantities. Metal raw materials, refining agents, stirring spoons, etc. should be dried before use.
Pouring and draining system
In the gating system, the ingate is a major influence on the generation of porosity. Attention should be paid to the following points in the design: the molten metal is filled from the thick wall of the casting; after the molten metal enters the cavity, the parting surface and the drainage system cannot be closed immediately; the metal liquid is opposite to the inner wall and the core of the inner gate Impact; use a single ingate as much as possible to avoid the metal liquid impact each other, forming eddy currents and splashes; use a moderate thickness of the inner gate to ensure the flow rate and flow rate of the alloy liquid; increase the cross-sectional area of the runner and improve the runner The direction of the flow.
Use a low-volatility release agent without excessive use and ensure uniform spray. Reduce the concentration of the release agent to reduce the amount of Air
1. The two metal streams are butted together, but they are not completely fused and no inclusions are present. The bonding force of the two metals is weak.
2. The pouring temperature or mold temperature is low.
3. The alloy is improperly selected and the fluidity is poor.
4. The runner is not in the right position or the flow path is too long.
5. The filling speed is low.
6, the injection pressure is lower than the pressure.
1. Appropriately increase the pouring temperature.
2. Increase the specific pressure of the injection and shorten the filling time.
3. Increase the injection speed and increase the cross-sectional area of the gate.
4. Improve exhaust conditions.
5. Select the alloy correctly to improve the fluidity of the alloy.
Crack of aluminum alloy die casting parts
1. The content of iron is too high or the content of silicon is too low.
2. The content of harmful impurities in the alloy is too high, which reduces the plasticity of the alloy.
3, aluminum-silicon alloy, aluminum-silicon-copper alloy containing zinc or copper content is too high; aluminum-magnesium alloy contains too much magnesium
4, the mold, especially the core temperature is too low
5, the casting wall thickness changes drastically
6, the mold holding pressure time is too long
7. Uneven force when jacking out
1. Correctly control the alloy composition. In some cases, a pure aluminum ingot may be added to the alloy to reduce the magnesium content in the alloy; or an aluminum-silicon intermediate alloy may be added to the alloy to increase the silicon content.
2, increase the mold temperature
3. Improve the structure of castings
4, high-speed core pulling machine or even force the Ejector rod
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