Failure Mode And Analysis Of Die-casting Dies For Aluminum Alloy

The vigorous development of the automobile industry and the need for lightweight, so that Aluminum alloy Die-casting is to the large-scale and complex direction of rapid development. Die-casting dies as the main equipment of Die-casting production is to achieve the basic guarantee of high quality and efficient production of Die-casting, its life directly affects the quality of Die-castings, production, as well as the production cost of enterprises and market competitiveness.

At present, in most countries, the low service life of the Aluminum alloy Die-casting dies problem becomes the main factor that restricts the further development of die-casting industry, the failure mode of Aluminum alloy die-casting dies is more problematic.

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1. Working environment of Aluminum alloy Die-casting dies

Aluminum alloy Die-casting dies as a carrier of high temperature, high pressure, high speed Aluminum liquid, its working environment is extremely harsh. When working, the cavity surface is repeatedly flushed by the Aluminum liquid, the specific pressure is more than 40MPa, the inner sprue speed is 30~65m/s, the mold cavity surface temperature can reach 1112°F or more instantly, and after opening the mold, the mold cavity surface temperature drops sharply due to spraying and other reasons.

This kind of hot and cold alternating effect in the die-casting cycle repeatedly, making the mold cavity surface temperature changes dramatically.

2. Failure mode and analysis of Die-casting dies

According to the field statistics, the common failure forms of Die-casting dies are cracked, cracking, erosion, adhesion, and deformation, etc. Among them, cracked, cracking, erosion, and adhesion mainly occur in the mold cavity surface.

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(1) Cracked: In each Die-casting cycle, due to the existence of intense heat exchange, the mold temperature changes dramatically, the resulting thermal stress leads to thermal fatigue on the surface of the mold cavity, forming micro cracks. With the increase of Die-casting cycle, the micro-cracks further expand and form crack. This is the main mode of Die-casting dies failure field.

(2) Cracking: In the Die-casting production, in addition to thermal stress, due to the high-pressure impact of Aluminum, in the mold internal also produced other stresses. When these stresses exceed the fatigue limit of the mold material will produce cracking, especially easy to produce stress concentration of the sharp corner parts, the possibility of cracking is greater. In addition, if the stress generated during the processing of the mold is not completely eliminated, the mold is more likely to crack.

(3) Erosion: Aluminum high speed filling cavity friction heat, so that the surface temperature of the area on the surface of the mold cavity towards the inner sprue, coupled with the violent impact of Aluminum, so the surface protection layer of this part is easy to be destroyed. The Aluminum solution further reacts with the exposed metal substrate to produce harder compounds. In the process of removing these compounds, it is easy to take away the substrate material and expose the fresh surface, and so on, intensifying the damage of the cavity surface, forming a serious erosion.

(4) Adhesion: Pressure injection, the instantaneous temperature of the cavity surface at 1112°F. above, at this time, the affinity between the mold material and Aluminum liquid, strong adhesion, easy to form cavity adhesion.

(5) Deformation: In the Die-casting process, Die-casting dies to withstand the clamping force, injection backpressure, and other stresses, if the template stiffness is not enough, the mold in these stresses under the long-term role of bending deformation.

(6) Movement Obstacle: In Die-casting production, the temperature difference between inside and outside the mold, resulting in different thermal deformation of each part of the mold. Different heat deformation amount leads to different changes in the size of each part of the mold, thus changing the fit relationship between the mold parts. This change of fit relationship may cause significant movement obstruction of the mold parts with relative movement.