[Chinalco.cn] In the technical exchange last week, we briefly introduced products such as precision punching equipment, precision molds, and die-casting molds. As a professional stamping equipment manufacturer, we also hope that we can make you faster in a short period of time. To understand the stamping related knowledge, we will focus on the surface defects and preventive measures of aluminum die castings that we are concerned about.
First, the die characteristics and test methods: In the mold opening surface showed a strip of tensile traces, there is a certain depth, severe facial scars. The other is the adhesion of the molten metal to the mold, resulting in an overwhelming or missing material on the surface of the casting.
Causes: 1. Damage to the surface of the cavity (crush or knock). 2, the stripping direction is too small or oblique. 3, when the top out of balance, top skew. 4, the casting temperature is too high, the mold temperature is too high resulting in adhesion of the alloy liquid. 5, mold release agent is not good. 6, aluminum and gold content of iron content is less than 0.6%. 7, rough cavity is not smooth, mold hardness is low.
Preventive measures: 1, repair the damage surface of the mold surface, correct the draft angle, improve the mold hardness (HRC45 ° ~ 48 °), improve the mold finish. 2, adjust the top rod, so that the top out of balance. 3, replace the demoulding effect of a good mold release agent. 4, adjust the alloy iron content. 5, reduce the pouring temperature, control the mold temperature is stable and balanced. 6, adjust the direction of the gate, to avoid the molten metal straight core, wall.
Second, the bubble characteristics and test methods: the surface of the casting has different sizes of uplift, or a subcutaneous cavity.
The reasons are as follows: 1. The metal fluid is too low in the injection chamber (controlled at 45% to 70%), easy to generate gas, and the initial injection rate is too high. 2, mold casting system is not reasonable, poor exhaust. 3, smelting temperature is too high, gas content is high, the melt is not degassed. 4, the mold temperature is too high, mold retention time is not enough, the metal solidification time is insufficient, the strength is not enough to open the mold prematurely, the pressurized gas expands. 5. Excessive amount of release agent and injection head oil. 6. The air blowing time after spraying is too short, and the water on the mold surface is not dried.
Preventive measures: 1, adjust the die casting process parameters, injection speed and high pressure shooting speed switching point. 2, modify the mold runner, additional overflow tank, exhaust slot. 3, reduce the mold temperature in the defect area, thereby reducing the pressure of the gas. 4, adjust the smelting process, 5, extend the mold time, adjust the spraying time after spraying. 6, adjust the release agent, shot oil consumption.
Third, the characteristics of cracks and test methods: the surface of the casting has a linear or irregular narrow lines, under the influence of external forces have a development trend. Cold cracking - The metal is not oxidized at the cracking point. Hot cracking - Metals in the cracks are oxidized.
Causes: 1. The amount of iron in the alloy 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 containing too much magnesium. 4, the mold temperature is too low. 5. The thickness of the casting has drastic changes, and shrinkage is hindered. 6, leaving a long mold time, stress. 7, when the top out of force.
Preventive measures: 1, the correct control of the alloy composition, in some cases can be added to the alloy ingot pure aluminum to reduce the amount of magnesium in the alloy; or in the alloy aluminum silicon intermediate alloy to increase the silicon content. 2, change the casting structure, increase the fillet, increase the draft angle, reduce the wall thickness difference, 3, change or increase the top position, so that the top out of the force. 4, to shorten the mold or core pull time. 5, increase the mold temperature (mold working temperature 180 ° -280 °).
Fourth, the deformation characteristics and test methods: die casting geometry does not match the drawings. Overall deformation or local deformation.
Causes: 1. The structural design of the casting is poor, causing uneven shrinkage. 2, premature opening, casting rigidity is not enough. 3, die deformation. 4. The setting of the top rod is unreasonable, and the force is uneven when ejected. 5, improper method of removing the gate.
Preventive measures: 1, to improve the casting structure. 2, adjust the mold opening time. 3. Reasonably set the position and number of jacks. 4, choose a reasonable method to remove the gate. 5, eliminate the pull factor.
V. Remaining traces and pattern features and inspection methods: The appearance inspection shows that the surface of the casting has stripes that are in line with the flow direction of the molten metal, and there are clearly visible lines that are not the same as the color of the metal substrate, and there is no development trend.
The reasons are as follows: 1. The metal liquid that enters the cavity first forms a very thin and incomplete metal layer, and is left behind by the metal liquid. 2, the mold temperature is too low. 3. Spilling occurs when the cross-sectional area of ​​the gate is too small and the position is improper. 4. The pressure on the molten metal is insufficient. 5, pattern: excessive use of paint and injection oil.
Preventive measures: 1, increase the mold temperature. 2. Adjust the cross-sectional area or position of the ingate. 3. Adjust the velocity and pressure of the metal in the runner. 4, choose the appropriate coating, injection of oil and adjust the amount of paint injection.
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