Three points to pay attention to in die casting production
Jul 23, 2021
Die casting mold is one of the three major elements of die casting production, so the quality of the mold directly affects the success or failure of the die casting. Here are some points that need to be paid attention to in the die casting production process:
Pouring system, overflow system
1. Requirements for the straight runner of the mold on the cold chamber horizontal die-casting machine:
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 bushing should be appropriately enlarged by a few more than the deviation of the pressure chamber diameter, so as to avoid the pressure caused by the sprue bushing and pressure. The internal diameter is different from the axis, which causes the punch to jam or wear serious problems, and the wall thickness of the sprue 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 axial direction. 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 bushing, with a 5° inclination along the demolding direction. When using a coating-in sprue, the fullness of the pressure chamber can be increased due to the shortened volume of the effective length of the pressure chamber.
2. Requirements for mold runners
① The entrance of the runner of cold horizontal mold should generally be located at the position above 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 prematurely under the action of gravity and starting to solidify in advance.
② The cross-sectional area of the runner should gradually decrease from the sprue to the inner gate. In order to increase the cross-section, negative pressure will appear when the molten metal flows through, which can easily inhale the gas on the parting surface and increase the flow of the 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 larger 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 greater 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 enters the mold, and the overflow groove and exhaust groove should not impact the core from the front. After the molten metal is poured into the mold, the flow direction should follow the cast ribs and fins as much as possible, and fill 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 multiple internal gates are used, it is necessary to prevent several molten metals from converging and impacting each other after entering the mold, resulting in defects such as vortex entrapment and oxidation inclusions.
③ The thickness of the inner gate of the thin-walled parts should be appropriately smaller to ensure the necessary filling speed. The setting of the inner gate should be easy to cut, and the casting body should not be damaged (eating meat).