Figure 1 (b) shows original mold feeding scheme of clutch housing. The overall dimensions of casting are 590mm * 543mm * 178mm, and blank weight is 14.3kg. Clutch housing has uneven wall thickness, with an average wall thickness of 7mm, a maximum wall thickness of 25mm, and a minimum wall thickness of 6mm. There is a large through hole in the center of casting with a diameter of φ115mm, which is produced using a 2500T cold chamber die casting machine. During production of castings, there were large shrinkage holes and cold shutoff defects in central circle. MAGMA software was used to simulate filling effect of castings. During actual production, X-Ray equipment was used to inspect castings to confirm internal quality.

 

Through simulation analysis and production tracking, it was found that casting qualification rate of original central feeding scheme was low, die-casting defects were mainly cold shut and shrinkage cavities. Moreover, when using this feeding scheme, process debugging space was limited, and cold shut could not be effectively solved. Filling aluminum liquid at high speed too early will form a wrap, and filling aluminum liquid at high speed too late will form a cold insulation. As shown in Figure 2, annual comprehensive pass rate of some clutch housings is only about 74%, which cannot reach 95% pass rate target.
In order to solve problem of casting qualification rate not meeting standard, molds for newly formed similar products in the later period have abandoned center gate feeding and changed to bottom feeding (i.e. flange surface feeding). Casting qualification rate has reached more than 95%, but corresponding casting production rate drops from 75% to about 65%, which increases burning loss of molten aluminum and causes waste. Three-plate molds have relatively mature applications in other products, with a pass rate of up to 95%. However, due to complex mold structure and many production failures, actual production of three-plate molds has not been carried out. To sum up, central feed port of an ordinary two-plate mold is semicircular, and aluminum liquid forms a large intersection under gate, as shown in Figure 2(c). Cold materials and gas cannot be effectively discharged, resulting in poor molding of castings, serious shrinkage cavities and cold insulation, and low casting qualification rates. Due to effect of gravity, aluminum liquid will enter bottom of mold cavity prematurely, causing cold shut-off, and ordinary two-plate mold structure cannot open full-circuit gates.

 

In order to solve problem of feeding existing two-plate mold, a die-casting mold with a center-feeding full-circumferential gate is used, as shown in Figure 3. It not only combines center-feeding scheme of three-plate mold to ensure quality of casting, but also avoids complex structure of three-plate mold. It can solve problems existing in clutch housing molds and can also be used in structural design of similar product molds that can open gates in the center.

 

1. Moving mold plate 2. Moving mold core 3. Fixed mold core 4. Fixed template 5. Sprue sleeve 6. Split cone 7. Disc spring 8. Push rod fixed plate 9. Push plate 10. Split cone push rod 11. Moving mold base plate

Figure 3 Mold Structure

Inner gate scheme is shown in Figure 4, and filling simulation effect is shown in Figure 5. A new die-casting mold inner gate design is adopted, combining advantages of two-plate molds and three-plate molds, that is, gate (inlet) in die-casting mold is not fixed as usual. Instead, as internal mechanism of mold moves during injection process, diverter cone moves forward and backward as needed, allowing feed port to automatically close and open as needed. In mold closing state, diverter cone is in a forward state. When punch moves slowly, feed port is closed, as shown in Figure 6(a), to prevent aluminum liquid from entering mold cavity prematurely and forming cold material; During high-speed movement, diverter cone retreats and feed port opens automatically, as shown in Figure 6(b). Through above movement, aluminum liquid can be filled sequentially along periphery of mold cavity during die-casting process, thereby improving molding quality of casting.

 

 

Mold working process is as follows.
Stage 1: Mold closing state is shown in Figure 7(a). As disc spring stretches and pushes out diverter cone, diverter cone moves forward by an inner gate thickness K. At this time, front end of diverter cone is in contact with front end of gate sleeve. Inner gate is in a closed state (see Figure 6(a)). Depth of splitter cone installation groove is thickness K of inner gate plus height of splitter cone, moving distance of diverter cone on limit screw is thickness K of ingate.

 

5. Gate sleeve 6. Diverter cone
Figure 6 Feeding port status
Stage 2: Injection starts and when aluminum liquid moves slowly, inner gate is still closed. When pressure of punch breaks through elastic force of disc spring, disc spring compresses, diverter cone retreats a distance K, and inner gate is opened (see Figure 6(b)), aluminum liquid enters mold cavity along full circumferential gate, as shown in Figure 7(b), achieving sequential filling.
Stage 3: Mold opening stage is shown in Figure 7(c). Moving and fixed molds are separated. At this time, diverter cone is still in a retreated state (see Figure 6(b)).
Stage 4: Ejection stage, diverter cone push rod moves forward driven by push plate, disc spring 7 also moves forward due to its own compression, diverter cone push rod and disc spring jointly push diverter cone to move forward K distance, As shown in Figure 7(d), runner condensate is ejected, casting is taken out, and mold is closed to enter next cycle (see Figure 7(a)).

 

Through simulation analysis with Cast-designer software, above die-casting mold gate scheme can be used to fill aluminum liquid sequentially and collect it on outer large plane. Gas and cold material are discharged from casting through slag bag, which reduces aluminum liquid encirclement, also reduces probability of pores and cold insulation defects, improves the casting quality. Modified mold structure is shown in Figure 8, and castings produced using optimized pouring plan are shown in Figure 9. Through production verification, castings produced after mold optimization have a dense structure and no visible shrinkage defects inside. As shown in Figure 10, casting qualification rate has been significantly improved.