Die-casting process plays an important role in current lightweight production of automotive parts. For some automotive die-cast aluminum alloy parts with closed peripheral designs, no matter where on periphery is chosen as inlet when designing mold, it will cause erosion to sealing groove position, an important forming part of mold, resulting in partial failure of mold (generally around 20,000 molds). Currently commonly used countermeasure is to design a mosaic structure and replace vulnerable parts.
Combined with actual production, a new design scheme was proposed, which adopted a three-plate mold-double center pouring structure, optimized mold locking, limiting and other structures, matched some functions of die-casting machine, greatly extended mold life, and achieved remarkable on-site production results.

A V8 engine chain cover shell, as shown in Figure 1, is made of A380 aluminum alloy, with a density of 2.45g/cm3, an outline size of 305.059mm×243.811mm×88.683mm, a weight of 0.83kg, a volume of 309cm3, and a surface area of 856.03 cm2, basic wall thickness ≥2.1mm, casting shrinkage rate 0.55%, because it is a sealing groove structure, there are flatness requirements. During production, it was found that due to special structure of die casting, ingate directly punched into inside of sealing strip installation groove of die casting, causing premature cracking of mold at this location and formation of raised cracks on die casting. Since this is where sealing strip is installed, if there are cracks on die casting, it will have a serious impact on sealing of die casting, so there are strict requirements on the surface quality of casting here. After analysis and testing, a three-plate formwork structure with central pouring was adopted. Based on basic conditions of die-casting parts, a preliminary design was carried out. Select remote pouring to reduce direct erosion force on two central cores and comply with general design specifications. Figure 2 shows initial design plan.

 

Figure 1 3D diagram of parts

 

Figure 2 Conventional pouring method

 

Figure 3 Failure location diagram of die casting parts

 

Figure 4 Mold inlay method
After analyzing die-casting parts, it was found that sealing groove should be avoided when pouring. The only positions that can be selected on die-casting parts are the two holes in the middle of die-casting part. Moreover, basic shape of die-casting part is a circular pie-shaped structure, with two holes in the middle, and ribs are in the shape of a radiating umbrella. Therefore, use of center pouring has a very good effect on exhaust of die castings. It was decided to adopt design of double center pouring and three mold plates, as shown in Figure 5.

 

Figure 5 Design scheme of double-center pouring three-plate mold

Table 1 Main design parameters after optimization

 

Figure 6 Flow-3D temperature field mold flow

 

Figure 7 Flow-3D velocity field mold flow

 

Figure 8 Mold diagram

Table 2 Comparison of production effects between two mold plates and three mold plates
Cutter material is H13, hardness is HRC44~46, and knife edge is at an angle of 45° to avoid aluminum sticking. Locking force of elastic mold clamping device is 40kN, which prevents movable platen and fixed mold moving plate from being separated in advance. Guide pillars and mold plates of mold must be made with high precision. Fixed mold fixed plate, fixed mold movable plate, and movable mold plate need to be molded at the same time, mold clamping oil must be evenly distributed. Mold is installed on die-casting machine, and fixed mold moving plate is pushed by hand without obvious jamming.

 

Figure 9 Actual product picture
Two-plate mold has mature structural design, stable mechanism, high yield rate, and is widely used in actual production. Advantage of advance separation structure of main runner of three-plate mold is that it is suitable for various round cake-shaped products. However, structure or style may be different and needs to be designed according to actual situation. This application breaks idea of pouring in conventional die-casting solutions and greatly improves applicable scope of die-casting process.