Back door handle assembly of today's mainstream cars is composed of handle base and handle. Handle base is connected to rear trunk lid by screws and buckles. It is main structural part and force-receiving part of body. Some of handle bases are also designed with reversing camera inlet. Back door handle refers to part touched by operator's hand when trunk of car is switched, and is generally assembled on handle base by snap, which requires certain strength, wear resistance and good flexibility. In order to ensure that handle can accurately and reliably hold handle when trunk door of car is switched, back door handle is designed as thin-walled deep barrel structure, and outer surface is designed with skin pattern.

Back door handle material of car is PP+EPDM-T20, and shrinkage rate is 1.012%. Shrinkage rate of injection material should be considered when designing size of injection mold cavity and core. Corners of plastic parts are rounded and rectangular, and wall thickness is 1.5mm. Parting surface PL is shown in cross-sectional view of A-A in Fig. 1.

 

(a) Two-dimensional structure of car back door handle

 

(b) Three-dimensional structure of car back door handle

Figure 1 Car back door handle

Groove element is present along circumference of inclined end face of plastic part, which does not affect parting and demoulding of plastic part. However, in cross-sectional view of A-A in Fig. 1, there are two 2.7-1.5=1.2mm boss "obstacle" elements at I, and there are two 4.12-1.5=2.62 mm boss "obstacle" elements at II. Presence of these four bosses "obstacle" on wide side of plastic part will hinder demoulding of car back door handle, so it is necessary to use inner core pulling mechanism to solve demoulding problem of plastic parts. There are two reinforcing ribs at each of two narrow sides of plastic part. Since reinforcing ribs extend to circumferential groove below inclined end surface of plastic part, demoulding is not hindered, and groove of reinforcing rib can be designed only at corresponding position of movable mold cavity.

As shown in Fig. 2(a), plastic melt enters rear door handle of car through flow path and gate into cavity between core insert 3 and cavity plate insert 7. Moving mold and fixed mold are opened, and moving mold is divided by parting surface PL, as shown in Fig. 2(b). If plastic part 5 is ejected by 10mm under action of push rod 8, according to relationship between demolding and core pulling distance of plastic part 5, moving distance of long and short inclined push rod core is calculated as: bc=ab×tgα, where ab=10mm , α = 9.5 °, distance of bc is distance of long and short oblique push rod translation core, and data is substituted into formula: bc = 1.67mm.

 

Figure 2 Injection typing and demoulding status of Car Injection Mold for Back Door Handle

1. Fixed mold base plate 2. Fixed template 3. Core insert 4. Short oblique push rod 5. Plastic part 6. Long inclined push rod 7. Cavity plate insert 8. Push rod 9. Slider 10. Push Rod fixing plate 11. Pushing plate 12. Moving plate seat plate
Calculation of above formula shows that two short inclined push rods 4 and two long inclined push rods 6 on both sides of plastic part are in chute of cavity plate insert 7, and under action of push rod 8, four long and short inclined push rods are moved parallel to center of plastic member 5 by slider 9 to be 1.67 mm, thereby achieving demolding with plastic member 5. As push rod 8 continues to be pushed out, long and short inclined push rods can respectively achieve forced release of 1.2 mm and 2.52 mm boss "barriers" of plastic parts.

Injection mold structure of back door handle of molded car is shown in Figure 3. Specific structure is designed as follows.

 

Figure 3 injection mold structure

1. Fixed mold base plate 2. Screw 3. Gate washer 4. Sprue bush 5. Fixed plate 6. Core insert 7. Guide sleeve 8. Guide post 9. Plastic part 10. Cavity plate insert 11. Moving template 12. Pulling rod 13. Limiting rod 14. Block 15. Push rod fixing plate 16. Pushing plate 17. Moving mold seat plate 18. Reset rod 19. Spring 20. Long inclined rod 21. Outer slider 22. Short oblique push rod 23. Inner slide block 24. Push plate guide post 25. Push plate guide sleeve 26. Push rod 27. Cooling water pipe joint
(1) Formwork and parting surface. Mold base is composed of fixed mold plate 1, fixed plate 5, core insert 6, guide sleeve 7, guide post 8, movable mold insert 10, movable die plate 11, block 14, push rod fixing plate 15, push plate 16, movable mold base plate 17 and screws, including fixed part and movable part. Mold base is platform of injection mold, injection mold mechanisms, components and systems are mounted on mold base to complete different functions of mold.
Fixed mold is composed of fixed mold base plate 1, gate washer 3, sprue bush 4, fixed die plate 5, core insert 6, guide bush 7, and screw.
Movable part is divided by guide post 8, cavity plate insert 10, movable die plate 11, pull rod 12, limit post 13, block 14, push rod fixing plate 15, push plate 16, movable mold seat plate 17, and reset rod 18, spring 19, long inclined push rod 20, outer slide 21, short oblique push rod 22, inner slide 23, push rod 26, push plate guide post 24, push plate guide sleeve 25 and screws.
Parting surface divides injection mold into movable mold part and fixed mold part, parting surface PL is opened, and plastic part 9 is demolded under action of core pulling mechanism.
(2) Gating system consists of runner and gate in gate gasket 3, sprue sleeve 4 and core insert 6 and cavity plate insert 10. Gate gasket 3 is used for positioning with nozzle of injection molding machine, and gate sleeve 4 is used for docking with nozzle of injection molding machine. Molten plastic in the barrel of injection molding machine enters mold cavity through nozzle, runners and gates.
(3) Mold cavity is composed of four core inserts 6 and four cavity plate inserts 10, core and cavity plate constitute cavity of plastic part to be molded, and plastic part 9 is molded by injecting molten plastic.
(4) Inner core pulling mechanism is composed of long inclined push rod 20, short oblique push rod 22, outer sliding block 21 and inner sliding block 23, mold adopts inner core pulling mechanism to avoid boss "obstacle body" on plastic member 9 from blocking demolding movement of plastic member.
(5) Demolding mechanism is composed of push rod fixing plate 15, push plate 16, and push rod 26 to release plastic member 9.
(6) Floc releasing mechanism of casting system is composed of push rod fixing plate 15, push plate 16 and pulling rod 12, and is used for demolding of aggregate in casting system, continuous molding of plastic part 9 can be realized each time mold is opened to remove cementing material of casting system.
(7) Return mechanism is composed of push rod fixing plate 15, push plate 16, reset rod 18 and spring 19. Return mechanism ensures that core pulling and demolding mechanism return to initial state, so as to facilitate next injection molding.
(8) Mold frame guiding system is composed of guide sleeve 7 and guide post 8 to ensure accurate position of opening and closing of moving mold to ensure molding quality of plastic part. Push plate guide is composed of push plate guide post 24 and push plate guide sleeve 25, position of demolding mechanism, flocculation demolding mechanism for movement and resetting is ensured.
(9) Cooling system is composed of cooling water pipe joint 27, core insert 6 and water flow passage in cavity plate insert 10, which prevents injection mold from being continuously heated during continuous molding process, thereby causing carbonization of molded plastic parts due to overheating.