What are the defense methods often encountered by molds in die casting production

Update:04-12-2020
Summary:

What are the defense methods often encountered by molds […]

What are the defense methods often encountered by molds in die casting production

  
In the production of die casting, the mold often encounters the defense methods of the pouring system, the overflow system, the runner, the inner gate, and the overflow groove.

  
1. Pouring system, overflow system

① The 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 sleeve should be appropriately enlarged by a few more than the deviation of the pressure chamber diameter, so as to avoid The internal diameter is different from the axis, causing the punch to jam or wear serious problems, and the wall thickness of the crate mould sleeve should not be too thin. The length of the sprue sleeve should generally be less than the ejection lead of the injection punch, so that the paint can escape from the pressure chamber.

② The inner hole of the pressure chamber and the sprue sleeve should be finely ground after heat treatment, and then ground along the axis. The surface roughness is less than or equal to Ra0.2μm.

③ The diverter and the cavity forming the paint have a recessed depth equal to the depth of the runner, and its diameter matches the inner diameter of the sprue sleeve, with a 5° slope along the demolding direction. When a coating-introduction sprue is used, the fullness of the pressure chamber can be increased because the effective length of the pressure chamber is shortened.

  
2. Requirements for the mold runner

① The entrance of the runner for cold horizontal molds should generally be located at a position above 2/3 of the inner diameter of the upper part of the pressure chamber to prevent the molten metal in the pressure chamber from entering the runner prematurely under the action of gravity and starting to solidify in advance.

② The cross-sectional area of ​​the runner should be gradually reduced from the sprue to the inner gate. In order to expand the cross-section, negative pressure will appear when the molten metal flows through, which can easily inhale gas on the parting surface and increase the flow of molten metal. The vortex in the air. Generally, the cross section at the exit is 10-30% smaller than that at the entrance.

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 will cool down quickly, and if the depth is too deep, the condensation will be too slow, which will affect the productivity and increase the amount of recycled material.

④ The cross-sectional area of ​​the runner should be greater than the cross-sectional area of ​​the inner gate to ensure the speed of the molten metal. The cross-sectional area of ​​the main runner should be larger than the cross-sectional area of ​​each branch runner.

⑤ The two sides of the bottom of the runner should be rounded to avoid early cracks. The two sides can be inclined at about 5°. The surface roughness of the runner part is less than or equal to Ra0.4μm.

  
3. Inner gate

① The parting surface should not be closed immediately after molten metal is injected into the mold, and the overflow groove and exhaust groove should not impact the core directly. After the molten metal enters the mold, the flow direction is as far as possible along the cast ribs and fins, and fills from the thick wall to the thin wall.

② When selecting the position of the inner gate, make the molten metal flow as short as possible. When using multiple internal gates, it is necessary to prevent several molten metal from converging and impacting each other after entering the mold, resulting in defects such as vortex entrapment and oxidation inclusion.

③ The thickness of the inner gate of the thin-walled parts should be appropriately smaller to ensure the necessary filling speed, and the setting of the inner gate should be easy to cut, and the casting body should not be damaged (eat meat).

  
4. Overflow tank

① The overflow groove should be easy to remove from the casting, and try not to damage the casting body.

② When opening an exhaust groove on the overflow groove, pay attention to the position of the overflow port to avoid premature blockage of the exhaust groove and make the exhaust groove inoperative.

③ There should not be several overflow openings or a very wide and thick overflow opening on the same overflow groove, so as to prevent the cold liquid, slag, gas, paint, etc. in the molten metal from returning to the cavity from the overflow groove , Resulting in casting defects.