Influence Of Local Coating Process Of Die-Casting Mold On The Quality Of Die-Casting Parts
In the production process of custom die casting, due to the high local temperature of the die, local high temperature thermal joints of the die will appear on the sintered aluminum, which not only affects the appearance of the casting, but also forms a coating on the casting surface due to the destruction of the density of the sintered aluminum. Risk of leakage. Die castings are often swept away from the gate of the mold near the end of the filling process by the aluminum, the mold is often strained, and cracks will appear in serious cases; the appearance of flaking, unable to meet customer needs. In response to the above appearance problems of the castings, the die casting mold was partially closed. It has proved to overcome the above appearance defects of castings and is easy to handle.
Along with the increasing customer requirements for die casting quality, strict requirements are made not only for mechanical properties and internal organization, but also for appearance defects. For example, aluminum alloy die casting in the casting process, after sintering aluminum adhesion, tightening and shot blasting treatment of castings, the phenomenon of flaking, can no longer meet the customer requirements for the appearance of the quality of the casting, not only reduces the casting qualification rate, limiting the production efficiency, while increasing production costs.
For die-casting sintering, aluminum adhesion, strain, cracking and other casting defects, a coating process will be applied to die-casting mold parts to reduce the emergence rate of casting defects and leakage rate.
1 die-casting mold coating process introduction
1.1 Microstructure of die casting die after coating
From the metallographic microstructure of the coating (see Figure 1),
after the coating of the die, an alloy layer is formed on the outer surface of the base material, covering the reinforcement layer with a thickness between 0.02 and 0.03 mm, with an increase in the thickness of the covered part. In order to ensure the tolerance range required by the dimension of the casting drawing and to improve the coating effect, the coating area of the mold can be coated in multiple layers, and the thickness of the coating layer can be controlled from 0.01 to 0.1 mm, which can be freely adjusted according to the actual situation.
The mold design is influenced by the structure of the casting. In the actual production process, the process window is relatively narrow and casting defects occur at the same time due to the limitation of pouring system design. In principle, the internal quality of the casting should be ensured first, but the appearance of the casting often fails to meet the customer’s requirements. For example, the sprue of the casting is pulled and cracked due to the erosion of the sprue; the cooling water cannot be adjusted at the sharp corners of the mold, resulting in temperature If the temperature is too high, it burns and sticks to the aluminum; there are many indentations on the mold and the resistance is relatively high during the filling of the molten aluminum, forming flow marks on the surface of the casting.
Considering these problems, the coating process was introduced in the preliminary design of the mold and product
The mold partial coating process can effectively solve the strain and cracking of the gate in the mold. The local coating process of the mold can effectively solve the aluminum sticking and sintering of the local hot joint of the mold. After the casting is shot blasted, covering the peeling part on the mold can effectively solve the peeling problem of the casting caused by shot blasting. By covering the mold, it solves the appearance quality problem of castings in daily production, reduces the missed work and time, and improves the production efficiency.
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