Analysis of defects of valve plate of automobile gearbox in die casting production

After adjusting the production conditions to the appropriate level, the batch trial production was carried out, and it was found that the rejection rate of components exceeded 60%. According to the statistical analysis, there is a certain distribution law of the defect parts

(1) The inner surface of the component block has pores. In the cavity of the component block, it can be found that there are one or more large strip pores on the inner surface, with the width of 1 ~ 2mm and the length of 3 ~ 5mm. The overall distribution is far away from the gate, which directly leads to the functional defects of the whole valve plate, and the density and quality are not up to standard, accounting for 30% of the batch components.

(2) It is found that each screw hole has a serious shrinkage problem, and the diameter after shrinkage becomes about 5mm, accounting for 35% of the batch of components. Shrinkage often occurs in thick parts, such as screw holes.

1.1 Cause analysis of surface porosity in component block

After counting the size, number and location of the gas holes, it is found that they are mainly distributed in the far gate side, especially in the 3 mm thick interlayer structure. Although the original design of 3mm interlayer structure enhances the filling ability, the problem of blowhole discharge has not been improved. In order to reduce the gas mixing and ensure that the local accumulated gas can be fully discharged before the solidification of liquid aluminum, it is necessary to add the filter bag, improve the filling stability of liquid aluminum, and extend the solidification time appropriately.

1.2 Shrinkage analysis of M6 screw hole

The size, quantity and position of screw holes of trial production components are analyzed statistically. According to the analysis of components and 3D data, it can be seen that the local wall thickness of screw holes of the components exceeds 10 mm, far away from the normal value of 4.5mm, and the change of wall thickness will cause local heat joints. When the molten metal flows through the gate, it will absorb a lot of heat. If the loss part cannot be replenished timely and effectively, or the loss rate is far higher than the replenishment rate, the molten aluminum in the gate will solidify first, and the casting can not be compensated by the solution during solidification, resulting in shrinkage cavity defects.

Scroll to Top