Die-casting mold is one of the three major factors of die-casting production, so the quality of the mold directly affects the success or failure of the die-casting part. Here are some important points that the mold needs to pay attention to during the die casting production process:
First, the pouring system, the drainage system
1. Requirements for the mold sprue on the cold chamber horizontal die casting machine:
1 The size of the inner diameter of the pressure chamber should be selected according to the required specific pressure and the fullness of the pressure chamber. At the same time, the deviation of the inner diameter of the sprue bushing should be appropriately enlarged by a few wires than the deviation of the inner diameter of the pressure chamber, so that the sprue bushing and pressure can be avoided. The indoor diameter is different from the shaft, which causes the punch to be stuck or worn seriously, and the wall thickness of the sprue sleeve cannot be too thin. The length of the sprue bushing should generally be less than the feed lead of the shot punch so that the paint can escape from the press chamber.
2 The inner hole of the pressure chamber and the sprue bushing should be refined after heat treatment, and then ground in the axial direction, the surface roughness ≤ Ra0.2μm.
3 The diverter and the cavity forming the coating have a concave depth equal to the depth of the runner, and the diameter is matched with the inner diameter of the sprue sleeve and has a slope of 5° along the demolding direction. When the coated sprue is used, the fullness of the press chamber can be increased by shortening the volume of the effective length of the press chamber.
2. Requirements for mold runners
1 The entrance of the cold horizontal mold runner should generally be located 2/3 of the inner diameter of the upper part of the pressure chamber, so as to prevent the molten metal in the pressure chamber from entering the runner too early under the action of gravity, and start to solidify in advance.
2 The cross-sectional area of the runner should be gradually reduced from the sprue to the ingate. In order to enlarge the cross section, negative pressure will occur when the molten metal flows through, and the gas on the parting surface is easily inhaled, which increases the flow of molten metal. The eddy in the air. Generally, the section at the exit is 10-30% smaller than the inlet.
3 The runner should have a certain length and depth. The purpose of maintaining a certain length is to stabilize the flow and guide. If the depth is not enough, the molten metal is cooled quickly and the depth is too deep, because the condensation is too slow, which affects the productivity and increases the amount of the recycled material.
4 The cross-sectional area of the runner should be larger than the cross-sectional area of the gate to ensure the speed of the metal liquid. The cross-sectional area of the main runner should be greater than the cross-sectional area of each branch runner.
5 The bottom sides of the runner should be rounded to avoid early cracking, and the sides can be inclined by about 5°. The surface roughness of the runner portion ≤ Ra 0.4 μm.
3, the inner gate
1 The parting surface should not be closed immediately after the metal liquid is inserted into the mold. The overflow tank and the exhaust groove should not be impacted on the front. The flow direction after the metal liquid is introduced into the ribs and the fins as far as possible is filled as much as possible at the thin wall.
2 When selecting the position of the gate, make the molten metal flow as short as possible. When using multiple in-line gates, it is necessary to prevent the metal liquids from joining and impacting each other after entering the mold, thereby causing defects such as eddy aeration and oxidation inclusions.
3 The thickness of the inner gate of the thin-walled part should be suitably small to ensure the necessary filling speed. The setting of the inner gate should be easy to cut off, and the casting body should not be damaged (eat meat).
4, overflow trough
1 The overflow tank should be easily removed from the casting and try not to damage the casting body.
2 When opening the exhaust groove on the overflow tank, pay attention to the position of the overflow port to avoid prematurely blocking the exhaust groove, so that the exhaust groove does not work.
3 Do not open several overflow openings on the same overflow tank or open a wide and thick overflow to prevent the cold liquid, slag, gas, paint, etc. in the molten metal from returning to the cavity from the overflow tank. , causing casting defects.
Second, casting rounded corners (including corners)
Casting drawings often indicate the requirements of unfilled corners R2, etc. We should not neglect these unmarked fillets when opening the mold, and must not make clear corners or too small rounded corners. The casting fillet can make the molten metal fill smoothly, and the gas in the cavity can be sequentially discharged, and the stress concentration can be reduced, and the service life of the mold can be prolonged. (The castings are also not prone to cracks there or various defects due to improper filling). In the case of the standard oil pan mold, there are more clear corners. Relatively speaking, the brother oil pan mold is well opened, and the heavy oil pan is also more.
Third, the draft angle
In the direction of demolding, it is strictly forbidden to cause the undercut (usually the casting is stuck in the mold when the mold is tested, and when it is treated by an incorrect method, the drill is drilled, the hard chisel, etc. is partially recessed).
Fourth, the surface roughness
The molding part and the pouring system should be carefully polished as required, and the light should be polished in the direction of the mold release. Since the molten metal enters the casting system from the press chamber and fills the cavity, the entire process is only 0.01-0.2 seconds. In order to reduce the resistance of the molten metal flow, as much as possible, the pressure loss is small, and the smoothness of flowing through the surface is required to be high. At the same time, the heating and erosion conditions of the casting system are harsh, and the worse the finish, the more susceptible the mold is.
Fifth, the hardness of the mold forming part
Aluminum alloy: HRC46° or so Copper: HRC38° When processing, the mold should be left with the remaining amount of repair, and the upper limit of the size should be made to avoid welding.