Causes of blow holes in aluminum die castings

First, human factorsDoes the release agent spray too much? Due to the large amount of gas released from the mold, when the amount is too much, it is not burned before pouring, so that the volatile gas is wrapped on the surface of the casting. So under the same conditions, one of the reasons that some workers produce more air holes when operating. Select a small amount of mold release gas, the amount of thin and uniform, mold after burning.Do you often clean the overflow and exhaust ports?Is it premature to open a mold? Has the mold been warmed up? Whether or not the parts are slowly and uniformly heated, so that the surface temperature of the cavity and the core is 150°C to 200°C.Is the product produced at the beginning of low mold temperature isolated?If there is no preheating device, do you use aluminum alloy material to slowly push into the cavity to preheat or heat by other methods?Do you take clean 5083 aluminum coil strip and inject the oxide layer into the pressure chamber?When pouring material, whether the spoon is close to the injection port of the pressure chamber to avoid splashing, oxidizing or air cooling.Once the molten metal is poured into the pressure chamber, is it injecting, and is there any decrease in temperature?Cooling and mold opening, whether to choose mold opening time according to different products?Are there any fears of using normal die casting pressure due to the fear of flying out of the liquid (flying water)? Even more afraid to try to increase the specific pressure.Does the operator strictly follow the die casting process?Is there a quantitative casting? How to determine the amount of pouring?

Second, the machine (equipment, mold, tooling) factors: mainly refers to the mold quality, equipment performanceIs die casting mold design reasonable and will it lead to porosity? Reasons for die casting molds:1) Whether the position of the gate and the shape of the guide flow are improper, resulting in a frontal collision of the molten metal into the cavity and a vortex. (Reduce the injection speed to avoid turbulence)2) Whether the sprue shape is bad or not?3) Is the gate speed too high, creating turbulence?4) Is the exhaust poor?5) Is the mold cavity position too deep?6) Is the machining allowance too large? Through the surface of the dense layer, exposing the subcutaneous pores? The die-cutting mechanical machining allowance should be smaller, generally about 0.5mm, which can reduce the weight of the casting, reduce the amount of cutting processing to reduce the cost, and avoid the exposure of subcutaneous air holes. The margin is preferably not more than 0.5mm, so that the surface that is processed can hardly see the pores because of the protection of the hard layer.Is the exhaust hole blocked and the air exhaust does not come out?Is the punch lubricant too much or scorched? This is also one of the sources of gas production.Gate location and diversion shape, with or without metal fluids on the parting surface of the overflow system?Is the location of the gate inside unreasonable, and the metal passing through the inner gate immediately hits the wall and generates turbulence. The gas is entrained in the metal stream?Exhaust position is wrong, resulting in poor exhaust conditions?Is the overflow airway area large enough, is it blocked, and is it located in the final filling area? Does the mold exhaust area often clean up? Avoid the loss of the exhaust effect due to clogging of the release agent.Is the mold temperature too low?Is the runner turning round? Increase the ingate properly?Is there an air vent in the deep chamber or is added in an insert?Is there an unreasonable design due to die casting and the formation of difficult-to-exhaust parts?Is the sum of the overflow outlet cross-sectional area less than 60% of the sum of the in-gate cross-sectional area and the slag discharge effect is poor?Is it possible to increase the thickness of the inner gate to reduce the filling speed under conditions that satisfy good molding conditions?Is there an excessively high velocity in the in-gate, turbulent movements, serious metal flow into the gas?Is there an excessively small cross-sectional area of??the in-gate area and the injection is serious?Is there an orderly fill to facilitate the discharge of the gas in the cavity and the length of the sprue and runner is sufficient?

Third, the material factor

Is there a good control over the ingredients of the supplier's raw materials? How much iron content? (required below 0.7)Is there any guarantee of the purity of 5052 aluminum coil strip?Is the secondary material (outflow material) used too much and is not ready for slag removal?Is there any excess waste slag in the liquid during the production process and poured together with oxide scale during pouring?Does the company have a secondary use of controlled waste materials? How to perform? Who checked?Is it possible to add scrap to the molten aluminum of important customer products?Try to change the ratio of new material to recycled material?Is the charge clean?

Fourth, the method of factors: mainly refers to the die-casting parameters, operating process

Is there a choice of process parameters based on different products? (Casting aluminum liquid temperature 630-670oC) Reasonable choice of die casting process parameters, especially shot speed. Adjust the starting point for high-speed switching.Is there any way to reduce the amount of moisture in the mold release? Is there a small amount of mold release agent?Is the alloy smelting temperature too high?How to determine the temperature of aluminum liquid? Is the thermometer accurate?Is there a conversion point for adjusting the injection speed and the slow injection rate and the rapid injection rate in time according to the product?Is there a large die-casting small part in the machine and the pressure in the chamber is too small?

Fifth, environmental factors

Is the die casting environment high in air humidity? Under normal circumstances, the amount of hydrogen in the surrounding air is not much, but if the relative humidity in the air is large, the solubility of the gas in the aluminum liquid will increase, forming seasonal air holes, such as in the rainy season, due to high humidity, when the aluminum alloy is smelted The phenomenon of pinholes is more serious. Of course, when the air humidity is high, aluminum alloy ingots, smelting equipment, tools, etc. will also increase the amount of surface water adsorption due to air humidity, so it should pay more attention to take strong preheating and drying protective measures to reduce the generation of air holes.

Collect some aluminum information and share with you