Solution of shrinkage defect in die casting front cover by local extrusion

1. Analysis of extrusion position

Because the leakage position is between the two oil passages on the moving die side, the wall thickness at this position is thick and uneven, and the oil passage aperture is relatively small( Φ It is easy to produce shrinkage cavity inside. There is a hole on the side of the static die opposite the oil passage hole Φ 16mm inclined core pulling hole, and the wall thickness between the inclined core pulling hole and the oil passage hole is larger. Through the transformation of the inclined core pulling hole core, the core pulling is replaced by core pulling and extrusion, which can be fed to the shrinkage part of the oil passage hole in a large area and increase the density between the oil passage holes.

2. Extrusion design

In general, the local extrusion function is distributed in the direction of dynamic and static die, which is consistent with the die-casting machine opening direction. The extrusion pin is pulled and inserted at any time after the die opening. In this project, the local extrusion is in the direction of the side inclined slider. Before the machine tool is opened, the extrusion pin must completely return from the casting. Otherwise, the extrusion pin will break the casting after the mold is opened, and if there is exit jam in the production process, the incomplete exit will also cause the casting cracking. In order to prevent the extrusion pin from sticking between the pin sleeve and the moving process and increase the function of core inserting spraying, the extrusion pin needs to be ejected from the bottom position again to receive spraying lubrication to increase the lubricity of the extrusion pin. Then, the extrusion pin returns to the end again, waiting for the die to be pressed. In view of the above production risks and the functional requirements of core inserting spraying, the core pulling and extrusion structure is adopted for local extrusion. After the casting is taken out, the extrusion pin cylinder is pushed out in place signal is controlled by the spraying robot, and the cylinder is driven out during spraying to realize the core inserting spraying function. After injection extrusion, the extrusion pin cylinder is controlled by the die casting machine to exit. If the extrusion pin can not exit to the end, the core pulling signal of the machine will give an alarm to prevent the product from being forced to open the die.

3. Structure of local extrusion

Due to the special position of the extrusion pin, the end face of the extrusion pin is flush with the end face of the product when the extrusion pin is in place, and the bottom hole of the casting is extruded directly when the extrusion pin is injected. It can be seen that this way of pressurization is that the extrusion pin directly extrudes the casting hole to avoid the contact between the liquid aluminum and the extrusion pin, and the liquid aluminum will not enter the extrusion pin sleeve to block or wear it. Moreover, the extrusion pin extends out during spraying, and the lubrication of fixed-point spraying is obtained, which greatly reduces the friction between the extrusion pin and the pin sleeve. In addition, the oil groove on the pin is coated with grease to ensure the continuous production under local pressure.

4. Clearance control of extrusion pin and pin sleeve

The tolerance fit clearance between the extrusion pin and the pin sleeve directly affects the production continuity and the service life of the extrusion pin. In general, the larger the fit tolerance between the extrusion pin and the pin sleeve is, the larger the clearance is, and the extrusion pin sleeve is easy to get into the liquid aluminum and get stuck. The nominal size of die extrusion pin is Φ 15 mm, and the clearance between the pin and the extrusion pin is 0.05-0.11 mm.

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