For two similar casing die-casting parts, two mold structures and two reasonable push-out mechanisms were designed. For thin-walled high-tightening casing castings, use of a two-level ejection mechanism successfully solved problem that castings are easily broken by push rod when cavity is in movable mold; use of auxiliary gates overcome problem of insufficient filling of side gates. Secondary push-out mechanism used has a simple and practical structure and reliable operation.

Figures 1 and 2 are parts diagrams of forward and reverse (YL102) aluminum alloy casing of single flange axial flow fan respectively. It can be seen that it is a composite structure composed of an inner edge end cover and an outer edge flanged cylindrical part. Inner and outer edges are connected by three φ5mm circular cross-section ribs. Difference between two casings is that outer flange and inner end cover of forward casing are at both ends of casing, while outer flange and inner end cover of reverse casing are on same side. It is characterized by low overall strength, thin and long outer edge cylinder wall, strong wrapping force on core. When designing die-casting molds, if traditional full push rod push-out mechanism is used, opposite result will occur.

 

Figure 1 Front casing parts diagram

 

Figure 2 Reverse casing parts diagram
According to traditional structure, cavity is set in fixed mold and core is set in movable mold. Aluminum liquid poured into cold pressing chamber is pressed into sprue of sprue sleeve at high speed by injection punch, is injected vertically upward through lateral runner and inner gate of fixed mold insert 15 into mold cavity under guidance of diverter cone, pressurized and cooled before opening mold; ejection cylinder of die-casting machine pushes push plate 3, then pushes all push rods to eject casing casting. Figure 4 is movable mold insert. Since ejection positions of eight φ4mm outer edge push rods 11 are cleverly placed on φ108mm diameter close to φ102mm inner hole, half of φ4mm push rod end faces coincide with outer edge cylinder wall of casing casting, so that casing casting will not undergo any deformation or breakage when subjected to strong ejection force, thus forward casing can be formed and ejected smoothly.

 

Figure 3 General assembly diagram of forward casing die-casting mold

1. Bottom plate 2. Fastening screw of movable mold 3. Push plate 4. Push rod fixed plate 5. Push plate guide sleeve 6. Push plate guide post 7. Reset rod 8, 21. Rib push rod 9. Moving mold plate 10. Outside Rim cylinder core 11. Outer edge push rod 12. Fixed mold plate 13. Fixed mold guide bush 14. Moving mold guide post 15. Fixed mold insert 16. Installation hole core 17. Fixed mold core 18. Inner edge push rod 19.Bearing chamber hole core 20. Inner core 22. Sprue sleeve 23. Sprue push rod 24. Moving mold insert 25. Diverter cone 26. Moving mold cover 27. Pad 28. Cylindrical head hexagon socket screws

 

Figure 4 Moving mold insert
Wall thickness of reverse casing is only 1mm, while thickness of mounting flange is 4mm. Strength of intersection at the back is very different, and there is severe stress concentration. When push rod is ejected, it is easily broken (see Figure 5). This is because structure of reverse casing determines that outer edge cylindrical cavity can only be placed in movable mold, and outer ejection point can only be placed at base of flange lug on the edge (φ4.5mm mounting hole side), result of which is that lugs of cylinder wall will break during ejection. Swing-bar type two-level push-out mechanism is used to push casing casting in cavity out of cavity after getting rid of large tight force between cylinder wall and core.

 

Figure 5 Fracture location diagram

 

Figure 6 General assembly diagram of reverse casing die-casting mold (re-rolled structure)
1. Sprue sleeve 2. Outer edge cylinder core 3. Inner core 4. Bearing chamber hole core 5. Inner edge push rod 6. Rib push rod 7. Installation hole core 8. Fixed mold core 9. Moving mold Insert 10. Fixed mold guide bush 11. Fixed template 12. Moving mold guide post 13. Moving mold guide bush 14. Reset rod 15. Push plate 16. Push plate push rod 17. Moving template 18. Fastening screw 19 .Moving mold cover 20. Flange outer edge push rod 21. Push plate guide column 22. Front push rod fixed plate 23. Front push plate 24. Rear push rod fixed plate 25. Front push plate guide bush 26. Rear push plate Guide bush 27. Back push plate 28. Base plate 29, 34, 35. Cylindrical head hexagon socket screws 30. Roller 31. Swing bar 32. Rotating shaft 33. Connecting rod 36. Rib push rod 37. Sprue push rod

When considering ejection options, stiffness and strength of die casting should be more comprehensively evaluated. Some die-casting parts seem simple, but they cannot be pushed out at one time; two-stage push-out mechanism is relatively complex, so two-stage push-out mechanism is generally not used. When designing mold, full-pusher push-out mechanism should still be the first choice.