【Abstract】Introduces practical structure of injection mold for B-pillar exterior trim panel of automobile front door, and discusses working process of mold. This mold adopts needle valve type hot runner to cold runner, large gate fan gate and latent gate two-point injection, two cavities (left and right parts), horizontal injection molding. Using NX11 to complete parting surface design of plastic parts, innovatively designed structural characteristics of secondary ejection mold composed of ejector rod, straight ejector, inclined ejector and slider. With help of MoldFlow2016, a pipeline circulation cooling system was created, filling time, cooling effect and warpage deformation of plastic parts were simulated and analyzed, and reasonable injection molding parameters were obtained to guide actual production of mold.

Plastic part shown in Figure 1 is exterior trim panel of B-pillar of front door of automobile. It is an important part of exterior trim of automobile and a key assembly part, which is produced in large quantities. The overall dimensions of B-pillar trim panel of front door of car are 495.3*91.6*60.4mm, average wall thickness of plastic parts is about 3.6mm, maximum thickness is about 3.9mm, and volume is 1.6*106mm2. Plastic parts are larger in size and more complex in structure. Required accuracy grade of plastic parts is MT3, which is a high-precision tolerance grade, and surface profile tolerance requirement is ±0.5mm.
Requirements after molding of plastic parts: smooth surface, no shrinkage, no burrs, no ejection marks, no damage to buckle, clamping force reaches predetermined target value, and no obvious defects in other parts. Plastic part is composed of inner and outer parting parts; exterior of plastic part is A-grade surface, and surface is treated with dermatoglyphics; there are 4 structural features of undercuts inside plastic parts: 1 BOSS column-type glue barb, which can be realized by left and right core pulling with a sloping ejector and a slider; 1 inner barb with a length of about 401mm and a width of about 10mm can be realized by a core-pulling mechanism of a slender lifter; a length of about 10mm 468mm, inner and outer hooks with a width of about 17mm can be considered to be realized by a combined core-pulling ejection mechanism of a slider and a straight ejector.

 

Figure 1 B-pillar exterior trim panel of automobile front door

Selected material is PC/ABS (Kumho Sunli HAC8270), density of this material is 1.15g/cm3, shrinkage rate is 0.5%~0.7%, mold forming temperature range is 40℃~60℃, and melt temperature range is 230℃～270℃. It has formability of ABS material, mechanical and comprehensive properties of PC, high impact resistance, chemical stability, good electrical properties, creep resistance, small shrinkage, good dimensional stability, temperature resistance, ultraviolet (UV) resistance, etc. It can be widely used in automobile interior parts, business machines, communication equipment, household appliances and lighting equipment. Rheological viscosity curve and PVT performance performance curve of material are shown in Figure 2.

 

Fig.2 Rheological viscosity and PVT curve of PC/ABS
a——Rheological viscosity curve b——PVT curve

NX11 software is used to model exterior trim panel of B-pillar of car front door, MoldFlow Doctor module is used to trim small rounded corners and chamfers that do not affect analysis results in 3D data of front door B-pillar exterior trim panel, and trimmed model is imported into MFI 2016. Model of B-pillar exterior trim panel of front door of car is divided into double-layer meshes, and mesh model is shown in Figure 3. Triangular mesh body is 59,480, surface area is 1,094.61cm2, mesh maximum aspect ratio is 9.99, average aspect ratio is 1.87, minimum aspect ratio is 1.16, shared edge is 132681, mesh matching rate is 93.0%, and mutual percentage is 92.1%. Meshing quality is very high, which can ensure accuracy of subsequent analyses.

 

Figure 3 Mesh model of B-pillar exterior trim panel of front door

As shown in Figure 4, the overall wall thickness distribution of plastic parts of B-pillar exterior trim panel of automobile front door is relatively uniform, with a thickness of 3.6mm, which almost achieves uniform thickness on any section of plastic part, avoiding transition of wall thickness. Resulting dimensional instability also ensures that there will be no obvious defects on the surface of plastic parts. In Figure 4, thickness of 4.625mm is connection between upper rib of plastic part and main wall thickness, size is sum of distance between thickness of outer surface and inner rib; and 0.484mm is minimum thickness of reinforcing rib on inner side of plastic part.

 

Figure 4 Wall thickness analysis of plastic parts

Using MFI gate position analysis module, theoretical "optimal gate position" of B-pillar exterior trim panel of automobile front door is obtained, as shown in Figure 5a, which is at the middle of large end of plastic part. Taking into account high quality requirements of main surface of plastic parts, gate marks are not allowed on outer surface, it is convenient for core-pulling structure, mass production, specific structure and layout of mold, a gating system with a 3-point needle valve type hot runner to cold gate is designed as shown in Figure 5b. Main runner adopts a hot runner system with a diameter of ϕ16mm; cold branch runner adopts a common U-shaped cross-section runner with a size of 10*8mm; cold main gate G0 adopts a fan-shaped gate side feeding, its cross-section is rectangular, and its size is 40* 2.5mm; pressure-holding gate G1 adopts a lurking gate with a circular cross-section and a diameter of ϕ1.5mm.

 

Figure 5 Analysis of optimal gate location
a——Gate position analysis b——Proposed gate position 

According to aforementioned gating system scheme, molding simulation analysis was carried out on filling time, flow front temperature, pressure during speed/pressure switching, freezing layer factor, weld line, air pocket, clamping force, sink mark, volume shrinkage rate, Reynolds number of cooling circuit, deformation, etc., which affect surface quality and size of B-pillar exterior trim panel of automobile front door. Results are shown in Figure 6.
(1) Figure 6a shows injection filling time. It can be seen from Figure 6a that there is no translucent area in plastic parts of B-pillar outer trim panel of automobile front door, indicating that filling process is smooth, flow is balanced, there is no short shot and insufficient filling. .
(2) Figure 6b shows flow front temperature. It can be seen from Figure 6b that the overall temperature of plastic part is within molding range, temperature difference on appearance surface is 3.9℃ (target value ≤ 5℃), temperature difference on non-appearance surface is 15.3℃ (target value ≤ 20℃) , temperature distribution of plastic parts is relatively uniform, and there will be no color difference on the surface.
(3) Figure 6c shows pressure when speed/pressure is switched. Results show that at V/P switching position, maximum required pressure for filling is 88.59MPa, and there is no transparent area in figure, indicating that injection pressure is reasonable.
(4) From distribution diagram of frozen layer factor of the two plastic parts at the end of filling in Figure 6d, distribution of frozen layer of the two plastic parts is relatively uniform, and there is no excessively fast freezing area. Although freezing time of nozzle will be a little faster than that of plastic part, when injection time is well controlled, short shots will generally not occur, and filling will not be affected.

 

Figure 6. Simulation analysis of mold flow of B-pillar exterior trim panel of automobile front door
a——filling time b——flow front temperature c——speed/pressure switching pressure d——frozen layer factor e——welding line f——cavitation g——clamping force h——sink mark i—— - volume shrinkage j - cooling circuit Reynolds number k - total deformation l - shrinkage deformation
(5) From Figure 6e, there is no welding mark on the surface of plastic part, which means that this glue feeding method is more suitable for molding, and surface quality of plastic part is more guaranteed.
(6) Observe air pockets in Figure 6f, and only scattered distributed air pockets can be seen at the edge of plastic part and ribs. It shows that gas in mold can basically be discharged, ribs of plastic part can be used as inserts and edge of mold can be used to exhaust gas.
(7) From Figure 6g, when maximum clamping force occurs at 4.061s, clamping force is 548.3t, which meets set clamping force of injection molding machine (1,300t for machine).
(8) From sink mark shown in Figure 6h, maximum sink mark size is 0.037mm, and sink mark is located at edge R of plastic part, so sink mark has little effect on quality of product.
(9) From Figure 6i, average volume shrinkage of part near outer surface of plastic part is relatively uniform, the largest shrinkage is at junction of gate and runner, so it does not affect plastic part.
(10) Reynolds number of cooling circuit shown in Figure 6j has a minimum value of 10,000 and a maximum value of 12,266, indicating that cooling effect is very good and waterway design is reasonable.
(11) It can be seen from Figure 6k that the total deformation of plastic part is 0.259 to 1.627 mm, and maximum deformation is at the small end of plastic part.
(12) It can be seen from Figure 6l that main reason for deformation of plastic parts is uneven shrinkage. Due to requirements of assembly and surface profile tolerance requirement of ± 0.5mm, current deformation cannot meet requirements of plastic parts. Because injection process conditions in this scheme are relatively reasonable, no optimization will be made, and plastic parts will not be changed. Under premise of structure, pre-deformation scheme will be used to adjust mold, and finally plastic parts will meet customer's needs.
To sum up, proposed mold casting system scheme for B-pillar exterior trim panel of front door of automobile is feasible.

Based on above-mentioned warpage deformation analysis results and past successful injection experience of such plastic parts, a pre-deformation scheme as shown in Figure 7 was formulated. Use the overall deformation “” command in NX11 to complete data adjustment of pre-deformation in opposite direction of demoulding of plastic part. The overall small end is 1.3mm, and big end is 0.9mm. Data comparison of plastic parts after pre-deformation is shown in Figure 8.

For shape and structure of exterior trim panel of B-pillar of front door of car, A surface of the entire appearance of plastic part as shown in Figure 9 is used as parting surface, which is divided into two parts, and parting line is at PL. Mold cavity adopts a two-cavity structure with plastic part arrangement as shown in Figure 6, and is designed using NX11 software.

 

Figure 7 Pre-deformation scheme

 

Figure 8 Data comparison of plastic parts after pre-deformation
Setting parting surface as shown in Figure 9 is beneficial to use small gaps at joint surface of mold (including joint surface of fixed and movable molds, joint surfaces of each slider, lifter, insert, main core and cavity) for exhausting. It is also more conducive to placement of plastic parts in mold, setting of fixed and movable molds, also provides convenience for design of core-pulling mechanism, thereby reducing difficulty of demolding plastic parts and difficulty of designing mold, facilitating processing of burrs on clamping surface of plastic part after mold is used for a long time.

 

Figure 9 Design of parting surface

Mold is a three-plate hot runner horizontal mold structure, and the overall appearance structure of designed mold diagram is shown in Figure 10.

 

Figure 10 3D drawing of mold structure
Divide plastic parts of B-pillar exterior trim panel of front door of car according to outer contour of A surface of the whole appearance, cavity part of upper part is used as a fixed mold and a cavity; while cavity part of lower part is used as a moving mold and a core, buckle part is used as a core-pulling structure such as a slider and a lifter, mold cavity mold structure of B-pillar exterior trim panel of front door of car is shown in Figure 11 in 3D.
(1) Cavity structure. Mold cavity part consists of a fixed plate 3 and a hot nozzle 15, as shown in Figure 11a. Fixed mold plate 3 forms glue position on outer surface of upper half of plastic part; hot runner system is fixed on hot runner plate 2, hot nozzle 15 passes through fixed mold plate 3, and hot runner junction box 23 is placed on sky side near center of mold to prevent it from interfering with mold slot. Hot runner control valve 20 is placed on operating side for easy manipulation by injection molding personnel, and hot runner water collecting block 4 is placed on non-operating side for easy connection with injection molding machine, as shown in Figure 12b. Inclined guide posts 10, 17 and inclined wedge 18 on movable die slider are all fixed on fixed plate 3, as shown in Figure 11a.
In selection of fixed mold plate 3, due to requirements of skin texture on the surface of plastic parts, mold steel Gelitz XPM with relatively high sun texture requirements is used. It has excellent polishing performance, machining performance, heat conduction performance, welding performance, uniform hardness, high toughness, especially suitable for mass-produced plastic molds, its factory state is pre-hardened and tempered, with a hardness of 38~42HRC.
(2）Core structure. Mold core part is composed of movable mold plate 24, straight ejector 26, slider 31, lifter 47, movable mold insert 48, slider 50 and lifter 51, as shown in Figure 11c. Among them, movable mold plate 24 and movable mold insert 48 form glue position on outer surface of lower half of plastic part, straight ejector 26, slider 31, lifter 47, slider 50 and lifter 51 form buckle and internal structure of plastic part. Runners pass on movable die plate 24 and movable die inserts 48 . Movable die insert 48 is fixed on movable die plate 24 . Due to large batch size and complex structure of B-pillar exterior trim panels of automobile front door, mold has a long service time, and at the same time, in order to prevent wear of molding clamping surface and collapse of cavity, straight ejector 26, slider 31, lifter 47, slider 50 and lifter 51 are all movable parts. Hot work die steel Gelitz 2343ESR with excellent polishing performance, easy cutting, high toughness, wear resistance and high ductility is selected, conducts heat treatment to ensure that heat treatment hardness is 48~50HRC.

 

Figure 11 3D drawing of cavity mold structure of B-pillar exterior trim panel of automobile front door

1. Fixed die seat plate 2. Hot runner plate 3. Fixed mold plate 4. Hot runner water collecting block 5. Water nozzle 6, 21, 41. Waterway nameplate 7. Cavity water collecting block 8. Fast water nozzle 9. Side support Column 10. Inclined guide column 11. Lock module 12. Guide column 13, 42. Side lock 14. Reset rod spacer 15. Hot nozzle 16. Plastic parts 17. Inclined guide column 18. Wedge 19. Hot runner nameplate 20. Hot runner control valve 22. Thermometer 23. Hot runner junction box 24. Moving template 25. Reset rod 26. Straight ejector 27. Counter 28. Guide sleeve 29. Side support column 30. Moving mold fixing plate 31, 50. Slider 32 .Limiting blocks 33, 49. Balance blocks 34, 46, 53, 54. Wear-resistant blocks 35. Lengthened water nozzles 36. Water pipes 37. Wear-resistant blocks 38. Guide blocks 39. Die feet 40. Slider blocks 43. Mandrel plate III 44. Mandrel plate II 45. Mandrel plate I 47, 51. Inclined roof 48. Moving die insert 52. Mandrel 55. Limit screw 56. Slider block

 

Figure 12 3D diagram of hot runner system structure of B-pillar exterior trim panel of front door of automobile
a——3D diagram of hot runner system structure b——3D diagram of fixed structure of hot runner system
57. Main filling nozzle 58. Hot runner manifold 59. Heating ring 60. Wire rack 61. Air cylinder 62. Support block 63. Screw 64. Positioning pin
Movable die plate 24 and movable die inserts 48 are all made of Baosteel P20, a pre-hardened die steel with good cutting performance, good welding repair performance and polishing performance, and high cost performance. Factory hardness is 28~34HRC.

Since exterior trim panel of B-pillar of automobile front door is an irregular-shaped plastic part, surface requirements are high, and mold structure is complex. Guide and positioning combined system composed of guide post guide sleeve, side lock, 1° wear-resistant block and original 10° tiger mouth, as shown in Figure 13. It can not only achieve fast and precise guidance of mold during operation, but also prevent dislocation caused by mold wear after long-term production.

 

Figure 13 Schematic diagram of guiding and positioning structure of B-pillar exterior trim panel of front door of automobile

Because front door B-pillar outer trim panel is a plastic part with a total of 4 internal barb structural features (see Figure 1). There are 3 barbs that can be realized by conventional slider and core-pulling mechanism of lifter. Core-pulling structure of slider shown in Figure 14a is mainly composed of inclined guide post 17, inclined wedge 18, wear-resistant block 34, slider 50, wear-resistant block 54, limit screw 55, slider pressing block 56, screws 65, 66 and spring 67; inclined guide column 17 and inclined wedge 18 are fixed on fixed mold plate 3, wear block 54 and slider pressure block 56 are fixed on movable plate 24, slider 50 is restricted to move between wear-resistant block 54 and slider pressure block 56. Principle is to use pulling force of inclined guide column 17 and pre-pressure of spring 67 to force slider 50 to move on wear-resistant block 54 and slider pressure block 56 to complete core-pulling action when mold is opened. Lifter core-pulling structure shown in Figure 14b only describes action of one lifter, which is mainly composed of lifter 51, guide sleeve 68, hollow iron sleeve 69, retaining spring 70, ejector rod 71, lifter base 72, universal head 73 and guide sliding piece 74; lifter 51 is fixed on ejector rod 71, ejector rod 71 is connected with universal head 73 through guide sleeve 68 and hollow iron sleeve 69, forms a certain inclination angle with ejection direction of mold.Guide sleeve 68 and hollow iron sleeve 69 are fixed in movable mold plate 24 by circlip 70, inclined ejector base 72 is fixed on ejector plate 44, guide sliding piece 74 is sleeved on universal head 73 and installed in slot of lifter base 72. Principle is that ejector rod plate 44 drives lifter seat 72 to push guide slide 74, universal head 73, ejector rod 71, lifter 51, etc. to move along lifter guide sleeve 68 when ejecting, converts single linear motion of ejector plate along mold axis direction into lateral movement of lifter along mold axis direction and perpendicular to direction, and lateral movement of lifter completes lateral core pulling.

 

Figure 14 3D drawing of slider and lifter core-pulling structure of B-pillar exterior trim panel of automobile front door
a——3D drawing of slider core-pulling structure b——3D drawing of inclined ejector core-pulling structure Inclined ejector base 73. Universal head 74. Guide slider 75. Guide block 77. Guide block
The other one is about 468mm long and 17mm wide combined inner and outer barbs. If a conventional slider or inclined ejector core pulling is used, plastic parts will be damaged and defective due to direct forced demoulding. In this design, we will innovatively design an injection mold structure with a combination of a slider and a straight ejector to eject core-pulling mechanism, and a secondary ejection mechanism, as shown in Figure 15, Figure 16 and Figure 17. Principle is to let plastic part first separate from core part except straight ejector, and then eject it together with straight ejector, then take part after there is a deformation space to turn outward, so that plastic parts will not be damaged due to forced demoulding, and design imagination space of plastic parts is improved.
Slider in combined ejector core-pulling is mainly composed of inclined guide column 10, slider 31, limit block 32, balance block 33, wear-resistant block 34, guide block 38, slider pressure block 40, spring 78 and wear block 80. Guide block 38, slider pressure block 40 and wear-resistant block 80 are fixed on movable mold plate 24, slider 31 is restricted to move between guide block 38, slider pressure block 40 and wear-resistant block 80; straight ejector mechanism is mainly composed of a straight ejector 26 and a ejector rod 84. Straight ejector 26 is fixed on ejector rod 84, ejector rod 84 is fixed on ejector rod plate 45 through guide sleeve 81 and avoidance iron sleeve 82, guide sleeve 81 and hollow iron sleeve 82 are fixed in movable mold plate 24 by circlip 83. Secondary ejection mechanism is mainly composed of a limit guide post 96, a spring sheet 98, a guide sleeve 99 and a guide sleeve base 101, as shown in Figure 11, Figure 16, and Figure 17. They are under action of mold opening force of injection molding machine. As shown in Figure 11, Figure 14, Figure 15 and Figure 16, fixed and movable molds 3 and 24 are separated. Slider 31 moves backward under force of inclined guide post 10 and spring 78, core pulling is completed under restriction of limit block 32 ( Note: At this time, plastic part 16 will not be forcibly demolded due to blocking of straight ejector 26, and the other slider 50 also completes same core-pulling action). Then ejector rod of injection molding machine pushes ejector rod plate 45 against ejector rod pad 85 to move, ejector rod 84 on ejector rod plate 45 pushes straight ejector 26 to start moving upward, and nitrogen gas spring 95 on ejector rod plate 45 compresses upward under action of ejection force; at the same time, under action of secondary ejection mechanism, ejector rod plate 44 and ejector rod plate 43 also push ejector rod 52 and lifter base 72 to move upward, and thrust forces lifter 51 to move along lifter guide sleeve 68, converting single linear motion of ejector plate along mold axis direction into lifter's lateral movement along mold axis direction and perpendicular to this direction (Note: another lifter 47 also performs same core-pulling action). When limit guide post 96 in secondary ejection mechanism contacts with guide sleeve base 101, the first ejection distance H1 is completed. At this time, ejector rod 52 has completed ejection action, inclined ejectors 47 and 51 have also been completed lateral core pulling (Note: plastic part 16 is still attached to straight ejector 26 at this time). Continue to eject, spring sheet 98 in secondary ejection mechanism is retracted under action of limiting guide post 96, guide sleeve 99 and guide sleeve base 101 begin to separate, ejector plate 45 is also disengaged from ejector plate 44 until the entire ejection distance H is completed under limitation of limit block 103, robot will take out plastic part 16 attached to straight ejector.

 

Figure 15 2D diagram of combined ejection core-pulling and secondary ejection structure of B-pillar exterior trim panel of automobile front door

78. Spring 79. Guide rod 80. Wear-resistant block 81. Guide sleeve 82. Escape iron sleeve 83. Circlip 84. ejector rod 85. ejector rod pad 86. Spacer plate 87. Balance block 88. Guide post 89 .Support column 90. Guide sleeve 91. Universal head 92. Inclined ejector base 93. Screw 94. Spacer 95. Gas spring 96. Limit guide column 97. Pressure plate 98. Spring sheet 99. Guide sleeve 100. Gas spring base 101. Guide sleeve base 102. Fixed seat 103. Limit block 104. Return needle cover 105. Garbage nail 106. Socket 107. Sejector block 108. Stroke switch (Note: H1—first ejection distance H—total ejector out distance)

 

Figure 16 Schematic diagram of core pulling and ejecting key components

 

Figure 17 3D diagram of structure of assembly of slider, straight ejector and secondary ejector mechanism

(1) Reset mechanism.
In order to ensure accuracy of mold opening and closing sequence, flexible and smooth movements of lateral parting mechanism and ejector mechanism, mold is designed with 6 reset rods with a diameter of ϕ30mm evenly arranged near guide column guide sleeve and center of mold for mold clamping and reset. Reset rod 25 is fixed on ejector rod plate 45, six nitrogen gas springs 95 with a diameter of φ38mm are evenly arranged on ejector rod plate 45 near reset rod 25 and ejector rod backing column 85 . As shown in Figure 15 and Figure 18.

 

Figure 18 3D drawing of ejection and reset assembly structure
(2) Cooling system.
In order to ensure that temperature of mold is always within temperature range specified by production process, mold adopts a circulating cooling water circuit arrangement on hot runner system, fixed mold plate 3, movable mold plate 24, straight ejector 26, and slider 31. This mold cooling system can ensure uniform cooling in all parts of cavity, short forming cycle and high quality of plastic parts.

When mold is in use, first remove lock module 11, connect mold cooling system to external cooling source, connect interfaces of hot runner system to outside, and connect travel switch plug to outside.
When mold is opened: under action of mold opening force of injection molding machine, fixed and movable molds 3 and 24 are separated, slider 31 moves backward under force of inclined guide post 10 and spring 78, and completes core pulling under limit of limit block 32. (Note: At this time, plastic part 16 will not be forcibly demolded due to blocking of straight ejector 26, and the other slider 50 also completes same core pulling action). Then ejector rod of injection molding machine pushes ejector rod plate 45 against ejector rod pad 85 to move, ejector rod 84 on ejector rod plate 45 pushes straight ejector 26 to start moving upward, nitrogen gas spring 95 on ejector rod plate 45 compresses upward under action of ejection force; at the same time, under action of secondary ejection mechanism, ejector bar 44 and ejector bar 43 also push ejector bar 52 to move upward, lifter base 72 fixed on lifter plate 44 pushes guide sliding piece 74, universal head 73, lifter 71, lifter 51, etc. to move along lifter guide sleeve 68, converts single linear motion of ejector plate along mold axis direction into lifter’s lateral movement along mold axis direction and perpendicular to this direction (Note: the other inclined roof 47 also performs same core pulling action). When limit guide post 96 in secondary ejection mechanism contacts with guide sleeve base 101, the first ejection distance H1 is completed. At this time, ejector rod 52 has completed ejection action, lifters 47 and 51 have also completed lateral core pulling (Note: plastic part 16 is still attached to straight ejector 26 at this time). Continue to eject, spring sheet 98 in secondary ejection mechanism is retracted under action of limiting guide post 96, guide sleeve 99 and guide sleeve base 101 begin to separate, and ejector plate 45 is also disengaged from ejector plate 44. Until the entire ejection distance H is completed under restriction of limit block 103, robot will take out plastic part 16 attached to straight ejector.
When mold is closed: in mold opening state, ejector bar on injection molding machine is recovered, nitrogen gas spring 95 in compressed state is released and rebounded, ejector bar plates 43, 44, 45 follow return, drive reset rods 25, straight tops 26, lifters 47, 51, and ejector rods 52 and other components fixed on them to return to their original positions; under action of clamping force of injection molding machine, movable mold part moves back, sliders 31, 50 begin to compress springs 67, 78 under pulling force of inclined guide posts 10, 17 to advance and return; continue to close mold until compressed nitrogen gas spring 95 returns, balance blocks 33, 49 and 87 on movable platen 24, straight ejector 26 and slider 31 begin to contact and close end face of fixed platen 3 until parting surface is closed.

In process of injection molding process analysis and mold design of B-pillar exterior trim panel of automobile front door, through analysis of plastic part structure, molding material properties and plastic part wall thickness of B-pillar exterior trim panel of automobile front door, mold flow analysis of B-pillar exterior trim panel of automobile front door was carried out with help of MoldFlow2016 software. Under specific circumstances of "optimal gate location", mass production and special mold structure, etc., a gating system scheme with two-point glue feeding using needle valve type hot runner to cold runner large gate fan gate and latent gate was formulated. In analysis of injection molding process, factors affecting surface quality and size of B-pillar exterior trim panel of automobile front door are analyzed and discussed. When using NX11 for mold design, design including: mold parting surface selection, cavity, core structure, guide and positioning mechanism, lateral parting and ejection mechanism, reset mechanism, cooling system, etc., has been completed. Points, key points and difficulties of injection molding of front door B-pillar exterior trim panel are explained in detail. In this process, a combined guide and positioning system composed of guide post guide sleeve, side lock, 1° wear-resistant block and original 10° tiger mouth was adopted, a core-pulling combination mechanism consisting of a straight ejector and a slider, and an injection mold structure with a secondary ejection mechanism are used to improve molding quality of plastic parts.
This case has strong practicability, solves limitation of multiple undercuts inside plastic part, and improves design imagination space of plastic part. It can not only reduce defect rate in mass production process, save cost of molds, but also solve limitations of structural design of plastic parts, which has important reference value for guiding actual production.