Air conditioning vent molded components of new energy vehicles are an important part of automotive interior. They not only affect air quality inside vehicle but also comfort of passengers. Generally speaking, vent molded components include a shell, decorative panel, support frame, single-control switch, lock cover, deflector, lower support plate, mounting holes, connecting rods. Functions completed after assembly of molded components mainly include airflow adjustment and fragrance diffusion. Design of molded component structure should ensure that molded components are easy to install and disassemble during assembly. Due to complex structures of some plastic parts in components, injection molding is typically used for mass production. This process efficiently produces plastic parts with complex shapes and high precision requirements. During injection molding of these complex structural parts, strict control of material heating temperature, injection pressure, cooling time is necessary to ensure quality and performance of plastic parts. Material selection is a crucial step in manufacturing of vent plastic components. Commonly used materials include polyamide (PA), acrylonitrile-styrene-acrylate copolymer (ASA), glass fiber reinforced plastic (GF). These materials possess good mechanical properties, chemical stability, meeting usage requirements of vent plastic components in various environments. For example, ASA and GF modified plastics such as PA+ASA+GF8 / GF10 / GF15 / GF20 / GF30 exhibit weather resistance, high rigidity. While some plastic parts in components have relatively simple structures, corresponding injection mold design and manufacturing are also relatively simple. However, parts such as decorative panels, shells, lower support plates are relatively complex, making mold structure design, manufacturing more challenging. This paper addresses problems encountered in injection molding of lower support plate plastic parts, such as injection imbalance, demolding difficulties, numerous potential defects. Using CAE, a hot runner injection mold was designed to optimize molding process. Innovative range-extended lifter mechanism within mold solves challenges of automated injection molding of this plastic part, providing a design reference for design of automated injection molds for similar plastic parts.

Shape of lower support plate plastic part of an automotive air vent assembly is shown in Figure 1. Complex structural features are mainly located on inner wall (shown in the bottom view) and four periphery (shown in the top view). These features affect layout of mold cavity and design of demolding mechanism, representing a significant challenge in mold design.

 

A1~A4 side edge W - outer surface; B1~B4 - inner recessed platform; k1~k6 - hook; T1~T3 - hook platform; c1, c2 - rocket foot; G1 - groove; H1, H2 - large square hole; x1, x2 - sloped surface; h side hole; j1, j2, j3 - reinforcing rib; Fb1, Fb2 - reverse edge; X+, X-, Y+, Y-, Z+, Z- - mold coordinate axis direction.
Figure 1. Car door inner panel part drawing
As shown in the top view, four sides of plastic part are A1, A2, A3, and A4. Of these four sides, only holes and reinforcing ribs on side A2 can be directly demolded along Z-direction of mold cavity. The other three sides, A1, A3, and A4, require lateral core-pulling demolding to achieve automatic demolding of all these sides.
For side A1, both its inner and outer walls require lateral core-pulling demolding. As shown in Y+ direction view, its outer wall has recessed platforms B1, B2, B3, B4, as well as multiple side holes h of different shapes. This means that demolding of outer wall can only be performed via core-pulling in Y- direction. Similarly, demolding of inner wall also requires lateral core-pulling because: firstly, undercuts formed by four recessed platforms B1~B4 hinder separation of these four inner wall features from plastic part; secondly, reverse edge Fb2 formed by inner wall of this side also forms an undercut, hindering separation of molded part from plastic part; thirdly, multiple reinforcing ribs j3 are provided on inner wall of side A1, arranged at a certain lateral angle.
For side A3, its outer wall forms a reverse edge Fb1 in Z- direction, and multiple side holes h also exist, causing demolding of outer wall of this side to be limited to core-pulling demolding in Y+ direction.
For side A4, groove G1 and its two side holes h, and two ramps x1 and x2 with their four side holes h, necessitate side core-pulling demolding along X+ direction for demolding outer wall of this side.
As shown in the top view, inner wall of plastic part's outer surface W features six hook features k1~k6 for snap-fit installation in automobiles. To reduce length of hooks, hook platforms T1, T2, and T3 are respectively provided below hooks k1, k2, and k3 as bases for these three hooks. T1 and T2 also have positioning rocket feet c1 and c2 respectively. Hook platforms T1, T2, and T3 are thin-walled, single-sided open box-shaped features. Hooks k4 are directly set in grooves on outer wall of outer surface W, while hook k6 is directly set on inner wall of outer surface W.
Two holes, H1 and H2, are set in the center of W-shaped surface. Sidewalls of H1 and H2 can only be demolded in Z-direction.
Molding material for plastic part is PA+ASA+GF10, a high-performance engineering plastic that combines advantages of PA, ASA, and GF. This material is typically used in applications requiring high strength, chemical resistance, and a good appearance. Its characteristics include high impact strength, chemical resistance, high melt flow rate, good noise reduction, good matte finish, no need for painting, and weather resistance. Its density is 1.22 g/cm³, shrinkage rate is 0.20%~0.60%, Vicat softening temperature is 104℃, UL flame retardant rating is UL94 HB, and the total production of plastic part is 300,000 pieces.
Based on plastic part dimensions shown in Figure 2, design difficulties of molding die are as follows:

 

A1~A4, B1~B4, k1~k6, T1~T3, cl, c2, G1, H1 H2, x1,x2, h, j1、j2、j3, Fb1, Fb2, X+、X-、Y+、Y-、Z+、Z- same as Figure 1
Figure 2 Plastic part structural dimensions
(1) Gate location of gating system is difficult to select. Plastic part has a complex structure and varying heights. From a horizontal perspective, shapes of parts are both different and similar. During mold filling, a single gate makes it difficult to achieve even filling at each end, inevitably causing initially filled end to be prematurely pressurized. Excessive pre-pressurization pressure will cause overflow and flash defects.
(2) Plastic part is large, requiring a certain melt flow length from plastic material. Otherwise, melt may solidify prematurely along flow path, clogging flow channels and making it difficult to fully fill mold cavity, resulting in insufficient material in molded part.
(3) Complex shape of plastic part, especially features on inner wall, causes uneven volume distribution on each side, making it difficult to achieve sufficient and even cooling in mold cavity. In severe cases, uneven cooling can lead to large deformations, making it difficult to obtain dimensionally stable and qualified products (molding dimensional accuracy of MT4~MT6 grade).
(4) Additional features on sides (A1-A4) and inner walls of plastic part (B1-B4, k1-k6, T1-T3, c1, c2, G1, H1, H2, x1, x2, h, j1, j2, j3, Fb1, Fb2, etc.) are difficult to automate demolding. Different demolding mechanisms need to be flexibly designed according to specific features of each part to ensure smooth demolding.

Mold design scheme for plastic part follows this logical approach. First, optimize gate location and quantity. Based on reliable cavity filling, determine gating system (including venting system). Then, optimize cooling system based on production efficiency requirements. Next, based on cooling and automatic demolding requirements of plastic part, optimize and coordinate demolding system design. Finally, design the overall mold structure requirements, optimizing the overall mold structure design based on manufacturing difficulty of components and the overall mold manufacturing cost.
As shown in Figure 3, optimization process of gating system of mold cavity is as follows. First, a single-point gating optimization analysis is performed on mold cavity. Optimal single-point gating position is set as shown in Figure 3(a). Optimal gating area is Q1 area. Under this condition, gating g1 is set as shown in Figure 3(b). There are three problems with filling mold cavity with g1: First, it is impossible to achieve balanced filling, especially right end of side A4 where filling pressure is close to 0, indicating that filling pressure at this end will be insufficient. Under standard filling condition of 30 MPa, potential molding defect at this point is that material shortage will occur. Second, inner wall of plastic part where g1 gate is located is inconvenient to open because inner wall of side A1 needs to open a side core-pulling demolding mechanism, and processing of g1 gate is also relatively inconvenient. Third, since plastic part is a large-sized plastic part, in order to shorten length of cold runner in gating system and ensure that flow path of melt is as short as possible, main runner in runner composition should use a hot runner. Obviously, if a platform surface is needed at the end of hot main runner to realize installation of corresponding hot nozzle, a local platform area needs to be set in parting surface of hole in the center of hole H2 [platform PT in Figure 3(c)]. If gate is opened at position of g1, platform opening area is not enough. Therefore, by moving gate to side where H2 hole is located on the side of A2, this problem can be effectively solved. Further optimization of gate location is shown in Figure 3(c), where gate is set to gate g2. With gate g2 filling, maximum filling pressure required for mold cavity is 28.06 MPa, lower than standard requirement of 30 MPa. At the end of filling, left end of A4 side is final filling end, with a filling pressure of 2.064 MPa. Full filling of mold cavity is not a problem. Further analysis shows that filling pressure difference between two ends of A2 side and lower right end of A4 side is not large, around 5 MPa, pressure difference with lower end of A1 and left end of A4 is around 14 MPa, lower than 15 MPa. Therefore, possibility of over-pressure problems during filling is relatively small. In summary, gating system of mold cavity is optimized into a hot-and-cold composite gating system consisting of a hot runner RH segment, a cold runner platform PT, a cold runner RL, and a cold gate g2. Gate g2 is a rectangular side gate with an initial cross-sectional size of 8 mm * 2 mm.

 

A1~A4, 112 are shown in Figure 1; 01 - Optimal gate area for single gate; R11 - Hot runner; RI - Cold runner; g1, 82 - Gate; CAE-mesh - CAE mesh; W1~W11 - Cooling water channels.
Figure 3 CAE Optimization Analysis
As shown in Figure 3(d), based on gating system shown in Figure 3(c), considering demolding requirements of demolding mechanisms on inner and outer walls of side A1, side A3, and outer side of side A4, as well as multiple side core-pulling mechanisms on inner wall of outer surface W, a contour-following water channel design is implemented for mold cavity. Ultimately, 11 water channels W1~W11 are designed for mold cavity cooling. Under temperature control of this cooling system, ejection time of plastic part can be controlled at approximately 23.97 s, and single molding cycle can be controlled at 30 s, as shown in Figure 3(e). Correspondingly, maximum deformation of plastic part is 2.275 mm, as shown in Figure 3(f), occurring at lower end of A1 side. According to research, this deformation value is close to MT4 grade b-type dimensional tolerance (2.0~2.2 mm, basic size 305 mm), and deformation does not exceed dimensional accuracy requirements of plastic part.
Demolding of local features of plastic part requires different demolding mechanism designs based on specific structural composition, as follows:
(1) For demolding of hooks k1~k6 on inner wall of exterior surface W, different demolding methods are required based on base features at their roots. As shown in Figures 4(a) and (b), L1 lifter is used to form internal undercut groove of T1 and half of features of k1 and c1, and core is pulled to side in F1 direction for demolding. L2 lifter forms the other half of k1 and c1, core is pulled to side in F2 direction for demolding. As shown in Figures 4(c) and (d), ejection directions of L1 and L2 lifters are D1 and D2 respectively, forming a split-type lifter, as shown in Figure 4(e).

k1~k6 - Hooks; T1~13 - Hook stands; c1, c2 - Rocket feet; j1, j2 - Reinforcing ribs; D1~D4 - lifter direction; L1~L4 - lifter number; b1~b6 - Partial profiles; I1, I2 - Partial inserts; F1~F4, F_Y+ - Core pulling direction.

Figure 4 Demolding Design of Local Features of Inner Wall

As shown in Figure 4(f), L3 lifter is used to form the entire k2, half of c2, and internal undercut groove of T2, to perform side core pulling in F3 direction. L3 lifter ejects in D3 direction. As shown in Figures 4(h) and (i), L4 lifter is used to form the entire k3 and internal undercut groove of T3, and to perform side core pulling in F4 direction. Ejection direction of L4 lifter is D4. As shown in Figure 4(j), demolding of k4/k5 is achieved by separating core insert 1 from cavity insert. As shown in Figure 4(m), S1 slider is used for forming and side core pulling demolding in FY+ direction. As shown in Figures 4(l) and (o), ribs j1 and j2 require local inserts I1 and I2 to reduce processing difficulty of molding features at these locations.
(2) For demolding of three side walls of plastic parts A1, A3, and A4, following mechanisms need to be designed for core-pulling demolding. As shown in Figure 5(a), two lifters, L5 and L6, are set for inner wall of side A1 to perform molding and side core-pulling demolding. L5 lifter ejects in D5 direction, and L6 lifter ejects in D6 direction. Corresponding side core-pulling directions are F5 (non-horizontal) and F6 (non-horizontal). As shown in Figure 5(b), one S2 slider is set for outer wall of side A1 to perform molding and side core-pulling in FY-direction. As shown in Figure 5(c), one S3 slider is set for side of A3 to perform molding and side core-pulling in F7 (oblique) direction. As shown in Figure 5(d), an S4 inclined slider is set for A4 side to implement molding and side core pulling is carried out in F8 direction (oblique direction).

 

A1~A4 side edges, B1~B4 concave platform, G1 groove, x1, x2 slope, h side hole; j3 reinforcing rib, Fb12, Fb2 reverse edge, L5, L6 lifter, D5, D6 ejection direction, F5, F6, FY, F7, F8 core pulling direction, S2, S3, S4 slider number.
Figure 5 Demolding design of A1, A3, A4 side
(3) Design of demolding mechanism. For above demolding molding part design, corresponding mechanism arrangement is shown in Figure 6. As shown in Figure 6(a), in slider mechanism, S1, S2, S3, S4 mechanisms are inclined guide post driven slider mechanisms. As shown in Figure 6(b), design of lifter mechanism of L1~L6 is divided into 4 types: one is a double round lifter rod cross lifter mechanism driven by a single inclined guide post (L5), one is a single round lifter rod cross lifter mechanism driven by double inclined guide posts (L6), one is a body-type square ejector rod lifter mechanism (L1, L2, L3), one is a round ejector rod driven lifter block type lifter mechanism (L4). L1~L4 are commonly used lifter mechanisms. Because volume of lifter block at its head is small, required ejection force is also small. Therefore, a round or square ejector rod with a smaller cross-sectional size can be used to eject formed lifter block. Lower end of round or square ejector rod is mounted on corresponding lifter seat. When push plate 4 pushes out, lower end of round or square ejector rod experiences little resistance to movement, has sufficient strength, and does not affect flexibility of lifter movement.

 

1. Core feeder; 2. Hot nozzle; PT. Hot nozzle docking platform; 3. Cover plate; 4. Push plate; 5. Moving mold base plate; 6. Moving template; 7. L5 Lifter head; 8. Wear-resistant guide sleeve; 9. Angled dome bushing; 10. Guide slider; 11. Cross slider; 12. Sliding seat; 13. Angled guide post and guide sleeve; 14. Angled guide post; 15. Movable pin; 16. Pressure block; 17. Water nozzle; PL. Main parting surface; S1~S4. Slider; L1~16. Lifter; j3. Reinforcing rib; D5. Ejection direction (L5 Lifter); H. Push plate 4 ejection and separation; a, a', p, q. Motion reference points; d₁. Horizontal axis core movement distance of Lifter head 7; d₁'. Actual side core pulling distance generated in F10 direction after the angled dome rod 9 completes the ejection distance H of push plate 4; d₂. Moving distance of sliding seat 13; d₃. Retraction distance of angled dome bushing 9 along D5 direction. d₄ - Distance oblique dome 9 ejects along D5 when cross slider 11 moves horizontally; d₄' - Actual ejection distance of oblique dome 9 along D5 when cross slider 11 moves along inner groove of sliding seat 12; F_D - Axial direction of oblique guide 14; F_Z+ - Ejection direction of push plate 4; Core pulling direction on one side of F9 and F10; T_r1~T_r4 - Vector triangle numbering; 0₁ - Mold opening direction axis; 0₂ - Axis of oblique guide post 14; 0₃ - Axis of oblique dome rod 9; 0₄ - Moving direction line of sliding seat 12; 0₅ - Moving direction line of cross slider 11 within groove of sliding seat 12; 0₆ - Horizontal reference line; α - Angle between O₁ and O₂; β - Angle between O₁ and O₃; θ - Angle between O₄ and O₅; λ - Angle between demolding direction and O₆.
Figure 6. Demolding Mechanism Design and Working Principle of Double-Fork Lifter Mechanism
However, this is not always case for large forming lifter blocks such as L5 and L6 lifters. Lower end of its round ejector rod has a large movement resistance on lifter seat, and round ejector rod is prone to breakage or damage. It is necessary to reduce its movement resistance. Therefore, a new type of cross lifter mechanism was innovatively designed. Taking L5 lifter as an example, as shown in Figure 6(c), components of mechanism include parts 7 to 17. Mechanism's operating principle is as follows: When push plate 4 pushes sliding seat 13 upward at FZ+, sliding seat 13 will force cross slider 11 in sliding groove to move in opposite direction at D5 within sliding seat 13. However, cross slider 11 as a whole still moves upward at D5. Cross slider 11 pushes angled round ejector rod 9 out at D5 until lifter head 7 completes side core pulling at a distance d1 in F10 direction. Core pulling distance d1 in F10 direction is used to ensure that lifter head 7 can completely achieve side core pulling demolding at F5 direction. Function of mechanism is to reduce torsional force of round lifter rod 9, reduce motion resistance at lower end of round lifter rod 9, make ejection movement of mechanism flexible, and ensure its service life. Kinematic relationship of mechanism is shown in Figure 6(d), specifically as follows:
(I) When push plate 4 moves upward at F2, inclined guide post 14 will drive sliding block 13 to move in horizontal direction F9. Its motion vector triangle is Tr2. Therefore, distance d2 that sliding block 12 moves in F9 direction is: d2=Hxtan(a)
(II) When push plate 4 pushes out a distance of H, vector triangle that sliding block 13 forces cross slider 11 to move is Tr3. Cross slider 11 moves in opposite direction of D5, that is, from point p to point a'. Its movement distance d3 is: d3= d2 x sin(θ)
(III) When push plate 4 is pushed out, if cross slider 1 does not move according to groove in sliding seat 12, but moves according to horizontal sliding groove of conventional inclined push mechanism in direction of F9 (in horizontal plane), then inclined round rod 9 (moving synchronously with cross slider 11 and two are tightly combined) is pushed out in direction of D5 by a distance d₄ according to vector triangle T_r1, which is: d4=H+cos(B)
However, due to inclined groove in sliding seat 12, pushing distance d4 of inclined round rod 9 in direction of D5 is reduced by a distance of d₃. Therefore, actual pushing distance d₄ of inclined round rod 9 in direction of D5 is: d₄’=d₄-d₃. Therefore, combining with vector triangle T_r1, actual side core-pulling distance d₁' generated in F10 direction after inclined dome rod 9 pushes out a distance H from push plate 4 is: d₁'=d₄'xsin(B)=(d₄-d₃)xsin(B)
Substituting equations (1), (2), and (3) into equation (5), we have: d₁'= (H / cos(B) - Hx tan(a)x sin(θ))xsin(B); d₁'= H x (tan(B) - sin(B)xtan(a)xsin(θ))
(IV) Since angle between j3 rib on inner wall of A1 and horizontal plane is θ, actual core-pulling distance of inclined dome 7 in F5 direction is calculated according to vector triangle T_r4, so core-pulling distance d₅ is: d₅ = d₁' / cos(1) = H x (tan(B) - sin(B)xtan(a)xsin(θ)) + cos(1)
Measurements show that maximum core-pulling distance ds is 14.3 mm, A = 7.4°. Calculations show that a = 12°, β = 9°, θ = 15°, and H = 225 mm are sufficient to meet mechanism's motion requirements.
(V) Main parting surface of mold cavity uses parting surface PL shown in Figure 6a. Hot runner is constructed using an extended hot nozzle 2. Hot nozzle platform P_t is located at the center of core insert 1 and mates with bottom of hot nozzle 2.
The overall mold structure design is shown in Figure 7. Mold is a two-plate hot runner mold with a one-cavity layout, single mold opening, and mold opening surface is PL surface. Cavity insert obtained by parting mold cavity at PL parting surface is directly machined from fixed platen 20, while moving mold is equipped with a core insert 1, then four sliders and six lifters are assembled to form core assembly of mold cavity, which is installed on moving platen 22.

 

18 - Positioning ring; 19 - Heat insulation plate; 20 - Fixed template; 21 - Water drain; 22 - Guide rail; 23 - Mold foot; 24 - Hydraulic cylinder; 25 - Lifting module; 26, 27 - Integrated socket; 28 - Protective pillar; 29 - Mold locking plate; 30 - Support pillar; 31 - Push plate guide pillar; 32 - Limit block; 33 - L6 angled ejector mechanism; 34 - L5 angled ejector mechanism; 35 - Ejector pin; 36 - L3 angled ejector mechanism; 37 - L4 angled ejector mechanism; 38 - Guide sleeve; 39 - Angled guide pillar; 40 - Angled guide rail; 41 - Reset rod wear-resistant plate; 42 - Counter; 43 - Side lock; 44 - S3 slider; 45 - 11 - Insert; 46 - S1 slider; 47 - S4 slider; 48 - 12 - Insert; 49, 53 - Balance block; 50 - Guide pillar; 51 - Wear-resistant plate; 52 - S2 slider; 54 - Pull rod; 55 - L2 angled ejector mechanism; 56 - L1 angled ejector mechanism; PL - Parting surface.
Figure 7 Mold Structure
In mold ejection mechanism, push plate 4 uses two hydraulic cylinders 24 for ejection. Push plate 4 is equipped with six lifter mechanisms (L1~L6), multiple ejector pins 35, and pull rods 54. Of four sliders in moving mold, sliders S2 (52), S1 (46), S3 (44), and S4 (47) are all driven by inclined guide post 39 installed on one side of fixed mold. Locking is achieved through inclined locking surface within fixed mold platen 20.
Working principle of mold is shown in Figure 8, and is completed through following steps:

 

1~56, PL, F_{z -} same as Figure 7
Figure 8: Working Principle of Mold
(1) Mold Installation, Debugging, and Closing. After mold is installed on injection molding machine and debugged, it is driven to close by injection molding machine, awaiting injection.
(2) Injection. Injection molding machine barrel completes injection filling, pressure holding, and cooling processes of closed mold cavity through hot nozzle 2, preparing for mold opening.
(3) Mold Opening. Moving mold portion below PL surface moves downwards under drive of moving mold platen of injection molding machine by pressing FZ+. Mold opens at PL surface. During opening process, inclined guide posts of four slider mechanisms drive their respective sliders 46, 44, 47, and 52 to complete side core-pulling action. Plastic part remains on moving mold side of mold.
(4) Ejection. After PL surface is fully opened, two hydraulic cylinders 24 on both sides of mold operate synchronously, driving push plate 24 to eject plastic part from core insert 1 via ejector pins 35, pull rods 54, and six lifter mechanisms 33, 34, and 56. Then, injection molding machine robot ejects plastic part from these ejection components, achieving complete demolding.
(5) Closing. Before mold closes, hydraulic cylinder 24 drives push plate 4 to reset. Then, mold is closed at PL surface by moving mold platen of injection molding machine, initiating next injection cycle.
Actual mold and trial molded plastic part are shown in Figure 9. After three trial molding corrections, molding quality of plastic part is stable and meets requirements of mass injection molding production.

 

Figure 9. Actual plastic part and mold

(1) Molding difficulties of lower support plate plastic part were analyzed. There are two main difficulties: establishment of gating system, realization of automated demolding of plastic part.
(2) Mold cavity gating system was optimized and obtained using CAE analysis. Gating system adopts a hot and cold composite runner + side gate form. Initial size of side gate is a rectangular cross-section of 8 mm * 2 mm. Under this condition, cavity filling pressure is less than 28 MPa. Cavity cooling uses 11 contoured pipes with an inlet temperature of 25 ℃. Under this control condition, plastic part deformation is less than 2.275, which meets molding accuracy requirements. Injection cycle is controllable to 30 s.
(3) Mold structure is a two-plate hot runner mold with a one-cavity layout. To address demolding difficulties of plastic part, four slider mechanisms and six lifter mechanisms are set up for automatic demolding of plastic part. In lifter mechanism, a novel cross lifter mechanism was innovatively designed. Lifter seat of lifter was improved to a sliding lifter seat driven by an inclined guide column, which effectively reduced motion resistance of lifter rod and ensured service life of mechanism. Key design parameters in mechanism are α=12°, β=9°, and θ=15°.