For previous article reading, please refer to "Talking about mold optimization from perspective of injection molding process 1, 2.
Optimization of ejection system is basis of automation and unmanned operation. If ejection of plastic parts is poor, it will cause production problems. Plastic parts are prone to defects such as white ejection, cracking, deformation, sticking, broken plastic column, and even broken needles, burned needles, mold damage, mold pressing, and ejection imbalance.

 

Optimization of ejection system is as follows:
1. Ejection method should be determined according to structure of plastic part and actual needs of product demolding;
2. Number of ejector pins is not evenly distributed, and number of ejector pins must be sufficient;
3. Position of ejector pin must be reasonable (it should be set at rib position, column position, bone position and other parts with strong mold adhesion);
4. Size of ejector pin should be appropriate (ejector pin diameter should be increased as much as possible within allowable range to prevent pin from breaking);
5. Ejector pin and ejector pin hole must be in a sliding fit state;
6. Ejector pin should be made into an exhaust ejector pin as much as possible (not easy to burn pin, no need to apply ejector oil);
7. Flat ejectors should be set at rib or bone position (to prevent rib or bone from breaking in mold and reduce shrinkage);
8. Screw column needs to be ejected with a sleeve (to prevent screw column from being elongated or broken and to reduce shrinkage);
9. Bottom of lifter needs a positioning box, head of lifter needs to be opened with an anti-slip groove;
10. Flat ejector needs to be flush with mold core and length should be consistent (to prevent unbalanced ejection, deformation of rubber part and white ejection);
11. Ejection stroke is generally 5-10mm longer than depth of plastic part, and ensure that compression of ejector plate return spring does not exceed 75% (to prevent spring from being compressed beyond limit and fatigue fracture);
12. A limit pin should be added to ejection stroke to prevent ejection stroke from being too large, causing spring to be over-compressed and easy to break;
13. Ejectors should be set on both sides of hole and distance between ejector and edge of mold core should be more than 1mm to ensure that strength of mold core is not affected;
14. Distribution of ejectors should consider whether ejection force of rubber part is uniform. Otherwise, inner side of shallow side wall should be bitten;
15. Diameter of ejector pins of each set of molds should be as consistent as possible (except for flat ejector pins used at rib/bone position) for easy processing;
16. For deep cavity molds, ejection blocks should be used at deep side walls, and an air inlet device should be added to mold core (to prevent vacuum suction and mold release deformation);
17. Narrow frame plastic parts should be ejected as a whole using ejection blocks to prevent deformation of plastic parts due to unbalanced ejection of ejection pins;
18. Cylindrical plastic parts, thin-walled containers and deep shell plastic parts should be ejected using push plates;
19. For deep cavities, thin-walled plastic parts that are difficult to demold, and when vacuum suction is large, pneumatic ejection can be selected;
20. If ejection device is prone to interference with core pulling mechanism such as slider , it is necessary to install a reset mechanism of ejector plate first (to prevent collision with die);
21. Plastic parts with deeper screws (when demolding cannot be forced), a rotary demolding mechanism is required;
22. Design of lifter structure needs to be optimized, and bottom needs to be installed on lifter seat. Head of lifter is sealing surface, and wall below is as empty as possible. Lifter hole should use wear-resistant steel (and add wear-resistant blocks) to prevent burning;
23. A pull buckle needs to be set at the end of main channel, and pipe position direction of multiple pull buckles should be consistent;
24. Processing accuracy of ejector hole should be sufficient to prevent burning or breaking needle;
25. Sealing position of ejector head should not be too long by 2-3mm, and gap should not be larger than overflow gap of plastic (try to use exhaust ejectors);
26. For mold that is "pressed back" when closing mold by ejector plate guide column, part of front mold that is hit by ejector plate guide column should be equipped with an anti-collision pin (to prevent damage to mold surface);
For later reading, please refer to "Talking about mold optimization from perspective of injection molding process 4, 5, 6, 7, 8".