What problems are often encountered in molds in die-casting production

1. Example of pouring system and overflow system
(1) Requirements for the mold sprue on the cold chamber horizontal die casting machine:
①The size of the inner diameter of the pressure chamber should be selected according to the required specific pressure and the degree of 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 wires compared with the deviation of the inner diameter of the pressure chamber, so as to avoid the difference between the sprue sleeve and the pressure chamber. Indoor diameters are not coaxial, causing the punch to be stuck or worn out, 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 delivery lead of the injection punch, so that the paint can come out of the pressure chamber.


②The inner hole of the pressure chamber and the sprue sleeve should be finely ground after heat treatment, and then ground along the axis direction, and the surface roughness should be ≤Ra0.2μm.


③ The shunt and the cavity forming the paint, the depth of the concave is equal to the depth of the runner, its diameter matches the inner diameter of the sprue sleeve, and has a 5° slope along the demolding direction. When the coating introduction type sprue is used, the fullness of the pressure chamber can be improved because the volume of the effective length of the pressure chamber is shortened.

(2) Requirements for the mold runner
①The entrance of the runner of the cold horizontal mold should generally be located at more than 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.


②The cross-sectional area of ​​the runner should gradually decrease from the sprue to the inner gate. If the cross-section is enlarged, negative pressure will appear when the molten metal flows through, and it is easy to inhale the gas on the parting surface and increase the flow of the molten metal. The vortex in the air is wrapped in air. Generally, the section at the outlet is 10-30% smaller than that at the inlet.


③The 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 not only affect the productivity but also increase the amount of return 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 entering the mold. The cross-sectional area of ​​the main runner should be larger than that of each branch runner. ⑤ Both sides of the bottom of the runner should be rounded to avoid early cracks, and the two sides can be made with a slope of about 5°. The surface roughness of the runner part is less than or equal to Ra0.4μm.

(3) Inner gate
①The parting surface should not be closed immediately after the molten metal enters the mold, and the overflow groove and the exhaust groove should not impact the core directly. After the molten metal is poured into the mold, the flow direction is as far as possible along the cast ribs and heat sinks, filling from the thick wall to the thin wall.


②When selecting the position of the inner gate, make the molten metal flow as short as possible. When using multi-strand inner gates, it is necessary to prevent several strands of molten metal from converging and impacting each other after molding, resulting in defects such as eddy current slug and oxidation inclusions.


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

(4) Overflow tank
①The overflow groove should be easily removed from the casting, and try not to damage the casting body.
②When setting up an exhaust slot on the overflow slot, pay attention to the position of the overflow port to avoid blocking the exhaust slot prematurely and making the exhaust slot ineffective.

③Several overflow ports or a very wide and thick overflow port should not be opened on the same overflow tank 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.

2. Casting rounded corners (including corners) are often marked with requirements such as unmarked rounded corners R2 on the casting drawing. We must not ignore the role of these unmarked rounded corners when opening the mold, and never make clear or too small corners. rounded corners. The casting fillet can make the molten metal fill smoothly, make the gas in the cavity discharge sequentially, reduce stress concentration and prolong the service life of the mold. (The casting is also less prone to cracks or various defects due to poor filling). For example, the standard oil pan mold has more upper cleaning corners. Relatively speaking, the brother oil pan mold is the best at present, and there are more heavy oil pans.

3. The demoulding slope is strictly prohibited from artificial undercuts in the demolding direction (often the castings are stuck in the mold during the mold test, and when handled in an incorrect way, such as drilling, hard chisel, etc. to make local concave).

4. Surface roughness The molding parts and the pouring system should be carefully polished according to the requirements, and should be polished along the demoulding direction. Since the metal liquid enters the casting system from the pressure chamber and fills the cavity, the entire process takes only 0.01-0.2 seconds. In order to reduce the resistance of the molten metal flow and minimize the pressure loss, it is necessary to have a high surface finish. At the same time, the heating and erosion conditions of the gating system are poor, and the worse the finish, the more easily damaged the mold is.

5. The hardness of the mold forming part of aluminum alloy: about ° copper: about ° When processing, the mold should try to leave a repair allowance, make the upper limit of the size, and avoid welding.