Automobile lamps are mainly used for lighting, which can be said to be eyes of car. Car lamps are a general term for all automobile lighting systems. Appearance requirements of automobile lamps are high. Several important parts are transparent parts, electroplated parts, etc. It can be said that parts with the highest requirements for automobile appearance are car lamps, so requirements for mold design and manufacturing are extremely high. Main lighting parts of general cars are front and rear headlights. Different car series have different configurations of car lamps, and same car series has different configurations according to high and low configurations.
Main parts of front and rear lights of cars are: left and right lenses, left and right decorative frames, left and right lamp shells, left and right reflectors, etc. Appearance requirements of automobile lamps are extremely strict. This article selects a famous brand car headlight mold for introduction. This article introduces design experience and key points of automobile lamp injection molds in detail, and takes headlights of a certain brand car as a case for analysis.

A car lampshade structure

Figure 1 shows a part diagram of a headlight housing of a certain brand of automobile. Material is PP+TD20, where PP is base of housing cover and TD20 is 20% talcum powder added to material, mainly to improve rigidity of housing cover. Non-appearance parts, internal functional parts.
Characteristics of plastic parts are as follows: (1) Non-appearance parts, appearance of plastic parts is not allowed to have spots, shrinkage depressions, weld marks, flash and other defects (appearance shrinkage mark requirements are not very high). (2) Plastic parts are internal functional parts, and assembly requirements for lamp holder holes, rear cover holes, etc. are high. (3) Shape of plastic part is complex, and there are 6 undercuts on outer side of plastic part. Except for lamp holder hole, which is not a left-right mirror image, other features of lamp housing are left-right mirror images. (4) There are 6 undercuts on outer side of plastic part, and a lateral core pulling structure is required. (5) According to characteristics of plastic part, lamp housing plastic part has risk of sticking to mold, and plastic part design needs to prevent sticking to mold.

 

External dimensions of automobile lampshade are relatively large. Due to presence of multiple thin-walled connectors and positioning jacks on outer part of main body, multiple side core pulling mechanisms are required around periphery. Final cavity layout adopts a 1-cavity structure. Pouring method adopts hot runner + ordinary runner, latent gate feeding, plastic part and gate condensate do not need to be separated manually. According to calculation and design experience, main dimensions of pouring system are determined as follows: main channel is 369mm long, main channel taper is 2°, and small end diameter is 5mm; branch channel is designed to be circular with a radius of 5mm and a gate diameter of Φ2mm. Final pouring system design is shown in Figure 2(a).
Plastic part is imported into MoldFlow software, and filling simulation of automobile lampshade is performed. Result analysis is shown in Figure 2(b). Time for plastic melt to fill cavity is 2.4s, the filling effect is good, and there is no underfilling.
A reasonable temperature control system can achieve rapid demolding of plastic parts, further improve shaping quality and production efficiency of automobile lampshade shell. During design of injection mold cooling system, three main structures are cooling water pipes, cooling water and heat transfer rods. Cooling water pipe is a circular hole drilled in mold, cooling water and other media are passed into circular hole to take away heat.
Layout of mold cooling water pipe is shown in Figure 2(c). There are 8 water channels on movable mold side and 6 water channels on fixed side. Diameter of mold cooling water hole is Φ11.5mm and Φ18mm. Mold core, cavity plate and each mold plate contact surface are sealed with sealing rings to prevent water leakage. Layout design of cooling system ensures uniform cooling of plastic parts, improves molding quality and production efficiency of molded plastic parts.

 

1.φ8mm round push rod 2.φ12mm push tube 3.φ12mm round push rod 4.φ10mm round push rod

"Slider + inclined guide column" side parting and core pulling mechanism is usually used in core pulling mechanism on outer side of movable mold and core pulling mechanism on inner side of movable mold. Among them, core pulling mechanism on outer side of movable mold is the most commonly used, with characteristics of reliable action, compact structure, and convenient manufacturing. It is suitable for occasions with small core pulling distance and small pulling force.

 

Side core pulling mechanism layout
N1. Side core pulling mechanism I N2. Side core pulling mechanism II N3. Side core pulling mechanism III N4. Side core pulling mechanism IV N5. Side core pulling mechanism V
This mold selects surface with the largest cross-sectional profile of plastic part as parting surface. Based on above parting design principles, after setting main parting surface of plastic part, it is further considered that side slider core pulling mechanism is set on fixed mold side, which will make mold structure more complicated and a lampshade needs to be installed outside lampshade. Surface with high roughness requirements is set on movable mold side to meet quality requirements. Finally, side slider is set on movable mold side, and inclined guide column is set on fixed mold side. In view of features existing on periphery of its main body, a total of 5 inclined guide column side slider side core pulling mechanisms are set, as shown in Figure 4. When cavity is opened, inclined guide column fixed on fixed mold side drives slide to move along 7-shaped strip direction to complete demolding of local features. Among them, N1 forms M4 positioning slots, N2 forms M3 positioning jacks, N3 forms M7 positioning slots, N4 forms M1 plug-in thin-wall and M6 positioning slots, and N5 forms M2 plug-in thin-wall and M5 positioning slots.

 

(a) Moving mold (b) Fixed mold (c) Overall structure of mold
Figure 5 Three-dimensional structure of mold

 

Figure 6 Two-dimensional structure of mold
1. Moving mold plate 2. Spring 3. Inclined guide pin 4. Fixed mold plate 5. Screw plug 6. Fixed mold base plate 7. Inclined guide pin 8. Spring 9. Pad 10. Push rod fixing plate 11. Push plate 12. Moving mold base plate 13. Push tube 14. Spring 15. Inclined guide pin 16. Insert pin 17. Inclined guide pin 18. Spring 19. Push rod 20. Reset spring 21. Reset rod 22 Hot nozzle 23. Hot runner junction box 24. Inclined guide pin 25. Spring 26. Insert pin 27. Slide 28. Slide 29. Limit stopper 30. 7-shaped pressure strip 31. Slide 32. Pressure strip positioning pin 33. Slide 34. Slide 35. Guide sleeve 36. Guide pillar 37. Runner insert
Mold frame uses a two-plate mold frame with a mold frame size of 1060mmx800mmx960mm. Two-dimensional structure of mold is shown in Figure 6. Basic working process of mold: During injection, high-temperature melt enters ordinary runner system through hot runner system, and then enters cavity through three latent gates at the same time. Molded automobile lampshade shell is opened after pressure-maintaining cooling. Relying on mold opening force of injection molding machine, inclined guide pillars set on fixed mold side respectively drive slides 27, 28, 31, 33, and 34 to move along direction of matching 7-shaped strips to complete demolding of local features. Limit devices of each slide are jointly guaranteed by limit block and spring.
Because movable mold side is equipped with multiple core pulling mechanisms and fixed mold cavity wall is polished, it is ensured that plastic parts can stay on movable mold side due to clamping force. Subsequently, movable mold side continues to open mold, ejector pushes push rod fixing plate to drive push rod and push tube to move simultaneously, pushing plastic part and gate condensate out of movable mold cavity together, with a push distance of 100mm. After that, mold is closed, ejection mechanism is reset by reset rod and reset spring, and side core pulling mechanism is reset by inclined guide column. After mold is closed, prepare for next injection molding.
Surface of automobile headlight shell is mostly curved, and the more assembly features on periphery of main body are not conducive to demolding. Finally, mold adopts a 1-cavity layout setting, and pouring system uses a hot runner to ordinary runner + latent gate feeding method to mold plastic parts. In order to ensure smooth demolding of plastic parts, mold is equipped with a total of 5 inclined guide column side slider core pulling mechanisms according to local characteristics of automobile headlight shell. One push tube and 27 round push rods are used to ensure force balance when plastic parts are pushed out. After actual mold trial verification, mold operation process is stable, and quality of molded plastic parts meets customer requirements, which can provide a reference for design of injection molds for structural plastic parts on automobiles.