Abstract: A cold runner two-platen family injection mold was designed for injection molding of reflector base shell plastic parts inside left/right headlights of a new type of new energy vehicle. Mold cavity layout is a mirror-image family layout with two cavities per cavity, and each cavity uses two side gates for casting. To achieve automated demolding of plastic part, each cavity of mold is equipped with one fixed mold side three-turn hydraulic cylinder core-pulling mechanism for first core-pulling demolding of one side hole undercut on one side of cavity, one moving mold inclined guide pillar slider mechanism for demolding of side wall features of plastic part, six moving mold plate opening driven inclined core-pulling mechanisms for inclined core-pulling demolding of six inclined local features on inner wall of plastic part, two lifter rod push block mechanisms for inclined core-pulling demolding of local groove features on inner wall of plastic part, and several ejector pins for fully ejecting plastic part for automated demolding. Demolding mechanism is driven in following sequence: First, hydraulic cylinder core-pulling mechanism completes core-pulling action of fixed mold before mold opens. Then, mold opens for first time, driving six inclined core-pulling mechanisms to simultaneously complete core-pulling action. Next, mold opens a third time, completing demolding of plastic part from cavity and side core-pulling action of one inclined guide pillar slider mechanism on side wall. Finally, push plate pushes several ejector pins and two lifter rod push block mechanisms for complete ejection and demolding of plastic part.
In the structure of headlight module assembly, design and molding of light distribution lens and reflector are key and challenging aspects of headlight module design. For light distribution lens, focus is on ensuring optical performance under injection molding conditions; materials and injection molding processes are crucial, while mold structure is relatively simple. For reflector, challenges lie not only in optical performance and materials/injection molding processes, but also in design of injection mold structure for reflector's base shell. Based on injection molding requirements of front headlight reflector base shell plastic part for a new type of new energy electric vehicle, this paper designs a family-layout type two-cavity two-stage mold with two plates. Mold parting design, demolding mechanism design, and overall mold structure design solve some practical problems encountered in design of reflector base shell molds, providing a design reference for mold design of similar new energy vehicle plastic parts.

As shown in Figure 1, automotive front headlight module assembly is an important component of automotive headlight. Headlight module controls lighting in vehicle, and driver's control switch signal is processed by module. A key reason why new energy electric vehicles effectively attract consumers is their industrial appearance design, in which personalized design of front headlights is an indispensable part.

 

Figure 1. Automotive front lamp module assembly
Front headlight reflector base shell plastic part consists of two structurally similar plastic parts: reflector base shell plastic parts inside left and right headlights. Structure of reflector base shell plastic part inside left headlight is shown in Figure 2. External dimensions of plastic part are 310 mm * 299 mm * 165 mm. Eighteen local structural features (T1~T13, J1, h1, G1, G2, G3) on plastic part significantly impact design difficulty of molding die. These features are distributed as follows: Front end of plastic part has five reflective grooves (C1~C5). Reflective groove C1 contains a light bulb mounting hole (T1), reflective groove C2 contains a light bulb mounting hole (T2), reflective groove C3 contains a light bulb mounting hole (T4), reflective groove C4 contains a side snap-fit hole (T5), and reflective groove C5 contains a light bulb mounting hole (T6). T3 is a concave sealing edge. Back of plastic part has studs (T7, T8, T13) for fastening, rocket-shaped pins (T9, T10, T11, T12) for positioning insertion holes, and a reinforcing rib (J1) for fastening other plastic parts, along with its side hole (h1). Three additional features are localized oblique grooves (G1, G2, G3) formed due to need for reinforcing ribs.

 

Fig. 2 Front lamp reflector bottom shell plastic part
T1~T13, J1, h1—Feature number; C1~C5—Reflection groove; G1, G2, G3—Groove at bottom of rib
Plastic part is made of a blend of polycarbonate (PC) and acrylonitrile-butadiene-styrene (ABS) plastic (ABS+PC), with an average shrinkage rate of 0.6%. Molding size grades are MT4~MT5, and the total production of left and right front lamp reflector bottom shell plastic parts is 400,000 sets (800,000 pieces).

Based on structural characteristics of plastic part in Fig. 1, main challenges in designing a single plastic part mold are as follows:
(1) Numerous demolding directions make it difficult to arrange mold cavity of plastic part in mold, and main parting surface is difficult to select, resulting in a challenging parting design for molded part.
(2) Demolding of local features is difficult, requiring design of special demolding mechanisms, such as features T5, T7, T8, T13, h1, etc.
(3) Gate location is inconvenient to design, requiring arrangement of gate location and number of gates only after demolding scheme is determined.
Based on above difficulties, mold design scheme for reflector bottom shell plastic part inside left headlight is as follows:
(1) Using demolding direction classification and centralized design method, demolding directions are divided into following cases. Demolding directions of grooves C1~C5, T1, T2, T4, T6, T10~T12, J1 are same as demolding directions of main walls and surfaces of plastic part, and direction is mold opening direction FZ+ shown in Figure 3a. T3, T5, T7~T9, T13, G1~G3, h1 are all different and also different from FZ+. Therefore, main demolding direction is considered to be FZ+ direction. For demolding of other features T3, T5, T7~T9, T13, G1~G3, and h1, separate demolding mechanisms are set up to implement core-pulling demolding in individual directions. Corresponding directions are FT3, FT5, FT7~FT9, FT13, FG1~FG3, and Fh1, respectively. FT3 and FT5 are set to same direction as mold coordinate axis FY-, while the other directions are not aligned with mold coordinate axis.

 

Fig. 3 Parting and molded part design
T1~T13, J1, h1, C1~C5, G1, G2, G3—Came as Fig.2; PL—Parting surface; ST3—Slider; FX+, FX-, FY+, FY-, FZ+, FZ——Mould coordinate axis; MP—Moving mold plate; MB—Moving mold backing plate; K1—First mold opening surface; Y1—Hydraulic cylinder; Y2—Cross beam slider; gate; Rz—Main runner; R1, R2—Diversion runner; Df—T-groove drive seat; WC1, WC2, WC3, WC5—Water way
(2) Under condition that main demolding direction FZ+ is determined, mold cavity is opened using FZ+ direction. Mold cavity parting surface PL is obtained by extending maximum outer edge contour line corresponding to plastic part around perimeter. PL surface is a combination surface of multiple types of curved surfaces, as shown in Figure 3b. Among mold cavity molding parts obtained by dividing mold cavity by PL surface, there are cavity molding parts above PL surface and core molding parts below PL surface. In configuration of cavity molding parts above PL surface, main part is a fixed mold plate. Main molding features of mold cavity part are directly processed from fixed mold plate of mold. At the same time, in order to facilitate processing, molding parts of reflective groove features C1~C5 are designed as inserts IC1~IC5. Further, as shown in Figure 3c, molded parts of features T1, T2, T4, and T6 are also designed as independent inserts, namely IT1, IT2, IT4, and IT6, respectively, are correspondingly set within inserts IC1, IC2, IC3, and IC5. Feature T5 is molded using insert IT5. Inserts IC1~IC5, IT1, IT2, IT4, and IT6 move in FZ direction and separate from plastic part during mold opening, but this is on the condition that molding insert IT5 of T5 must first complete core pulling in FT5 direction (FY direction) before inserts IC1~IC5, IT1, IT2, IT4, and IT6 can separate from plastic part. Insert IT5 is set within IC4, meaning that insert IT5 must first be core pulled on fixed mold side of mold.
(3) As shown in Figure 3c, in core molding part below PL surface, main body of molding part is mainly moving mold plate MP, which is inlaid with a CO central core and nine inserts: Ih1, IG3, IT13, IT7, IG1, IG2, IT8, and IT9. CO central core separates from plastic part in FZ direction, the other corresponding directions are Fh1, FG3, FT13, FT7, FG1, FG2, FT8, and FT9. Core-pulling direction of these eight inserts is different from FZ direction. For molding and demolding of feature T3, as shown in Figure 3d, slider ST3 is used to perform side core-pulling demolding in FY direction. Inserts Ih1, IT7, IT8, IT9, IT13 are driven by separation motion of moving mold plate MP and moving mold base MB. Specifically, when mold opening surface K1 opens, T-slot drive seats (Df, etc.) mounted on moving mold base MB drive inserts Ih1, IT7, IT8, IT9, IT13 to separate from plastic part according to their respective core-pulling directions. IG1, IG2, and IG3 are made in the form of lifter blocks, which are ejected from plastic part by mold ejector pins via their respective ejector pins.
(4) As shown in Figure 3d, insert IT5 on fixed mold side is first driven by Y1 cylinder. Y1 cylinder first drives Y2 crossbeam slider to pull core in FX- direction. Then, Y2 crossbeam slider drives Y3 transmission rod to pull core in FZ+ direction through inclined T-slot at its front end. Inclined T-slot at lower end of Y3 transmission rod then drives insert IT5 to pull core in FT5 direction (same as FY- direction), thus completing fixed mold core-pulling action of feature T5.
(5) As shown in Figure 3b, mold cavity is filled using cold runner side gates g1 and g2. RZ main runner supplies material to corresponding gates g1 and g2 through runners R1 and R2. As shown in Figures 3b and 3d, cooling design of molded part is limited by fact that molded part is divided into multiple local inserts, thus restricting design space of cooling water channels. Therefore, in order to ensure sufficient and balanced cooling of mold cavity, in addition to water channels in main molded part fixed mold plate, insert CO, and moving mold plate, inserts IC1, IC2, IC3, and IC5 are respectively provided with water channels WC1, WC2, WC3, and WC5. Insert CO is provided with one water channel WCO. All cooling water channels in mold use Ø10 mm pipes.

The overall mold structure is shown in Figure 4. Since plastic parts are two plastic parts, left headlight and right headlight reflector bottom shell, mold structure layout uses a family mold cavity layout. There are two mold cavities in mold: left headlight reflector bottom shell mold cavity VL and right headlight reflector bottom shell mold cavity VR. Molded parts and mechanisms of two cavities are designed in a mirror-symmetric relationship. Mold is a two-plate mold, and gating system is a cold runner side-gate gating system. Each cavity has two rectangular cross-section gates, g1 and g2. Mold opens in two stages: first, K1 surface opens, then K2 surface opens. Arrangement of molded parts in each cavity is shown in Figure 3. Demolding mechanism in each cavity is also arranged as shown in Figure 3, with a total of 10 mechanisms: Mechanism M1/M1' for pulling core from fixed mold side of drive insert IT5; mechanism M2/M2' for pulling core from slider ST3; moving plate opening driven oblique core pulling mechanism for pulling oblique cores of aforementioned inserts Ih1, IT13, IT7, IT8, IT9, and IG2; two oblique ejector mechanisms for inserts IG1 and IG3, which are ejected by push plate 7.

 

Fig. 4 Mold structure
1—Upper clamping plate; 2—Fixed mold plate; 3—MP moving mold plate; 4—MB moving mold backing plate; 5—Mould foot; 6—Ejector retainer plate; 7—Ejector plate; 8—Lower clamping plate; 9—Lifter Df T-groove drive seat; 10—Angle ejector rod; 11, 12, 13, 14, 15—IT9, IT8, IG2, IT7, IG1 insert; 16, 17—Straight guide bush; 18—Guide pin; 19—Sprue bushing; 20—Locating ring; 21, 22, 23—IC4, IC3, IC2 insert; 24—Angle pin; 25, 32—Spring; 26—ST3 slider; 27—Guide rails; 28—Ejector; 29, 36—Angle core Df T-groove drive seat; 30—Runer pull rod; 31—Ih1 insert; 33—Balance cushion block; 34—Angle wear resistant and locking plate; 35—ICO central core insert; FX+, FY+, FZ—Mould coordinate axis; g1, g2—Side gate; M1, M1'—Fixed mold core pulling mechanism; M2, M2'—Slider mechanism; VL, VR—Mould cavities number; K1—First mold opening surface; K2—Second mold opening surface

Installation of mechanism components in mold is shown in Figure 5. In slider mechanism M2, ST3 slider 26 is driven by two inclined guide pillars 24. ST3 slider 26 is mounted on MP moving platen 3 via guide strips 27. When K2 surface of mold is opened, inclined guide pillars 24 drive ST3 slider 26 to complete side core pulling with assistance of springs 25. After core pulling, a limiter limits movement to facilitate slider reset.

 

Fig. 5 Installation of mechanical components
1~36—Same as Fig.4; 37—Y1 hydraulic cylinder; 38—Y2 cross beam slider; 39—Movable block; 40—Y3 transmission rod; 41—IT5 insert; 42—Small insert; 43—Ih1 insert; 44—Ejector; 45—IG3 insert; 46,50—Angle ejector rod; 47—Angle slide block; 48—IT13 insert; 29, 36, 49, 52, 53, 54—Angle core Df T-groove drive
As shown in Figure 5a, a core-pulling mechanism M1 is implemented on fixed mold side of insert IT5 to perform core-pulling first. M1' is installed on fixed mold side. Y1 cylinder 37 is installed on the outside of fixed mold platen. Y2 beam slider 38 is installed inside fixed mold platen 2. Y3 transmission rod 40 is installed inside IC4 insert 21. IT5 insert 41 is also installed inside IC4 insert 21 and can slide within its corresponding sliding groove. Y2 beam slider 38 drives Y3 transmission rod 40 to move up and down through its front-end inclined T-slot. Y3 transmission rod 40 also drives IT5 insert 41 to move in FY+/FY- direction through its lower end inclined T-slot, thus realizing core-pulling function of insert. As shown in Figure 5b, insert Ih1 43 is driven by angled core-pulling Df T-slot drive seat 29, insert IT13 48 is driven by angled core-pulling Df T-slot drive seat 49, insert IT9 11 is driven by angled core-pulling Df T-slot drive seat 52, insert IT8 12 is driven by angled core-pulling Df T-slot drive seat 53, insert IG2 13 is driven by angled core-pulling Df T-slot drive seat 54, and insert IT7 14 is driven by angled core-pulling Df T-slot drive seat 36. Angled core-pulling Df T-slot drive seats 29, 36, 49, 52, 53, and 54 are all mounted on MB moving mold base plate 4, each has a corresponding angled T-slot for driving corresponding molded insert to perform angled core-pulling when K1 surface is opened. To facilitate machining and installation of insert Ih1 43, insert ICO 35 is further divided into smaller inserts 42.
As shown in Figure 5b, the IG3 insert 45 is ejected by sliding block 47 installed in lifter seat on ejector plate 7 via lifter rod 46, and IG1 insert 15 is ejected by lifter seat 51 installed on ejector plate 7 via lifter rod 50. Inclined T-slots are provided on both inclined slider 47 and lifter seat 51.

After mold is installed and debugged on injection molding machine, it awaits start of injection molding cycle, as shown in Figure 6. Working principle of mold is as follows:

 

Fig. 6 Mold working principle
1~54, K1, K2—Same as Fig. 4; 55—Injection molding machine ejector; Pa—Plastic part
(1) Injection: After injection molding machine nozzle completes injection, holding pressure, and cooling processes for two mold cavities, it awaits mold opening.
(2) Fixed mold core pulling: Before mold opens, hydraulic cylinders 37 of mechanisms M1 and M1' drive IT5 insert 41 to complete initial core pulling.
(3) K1 surface opening: Mold opens in FZ- direction. During opening, due to supporting effect of spring 32 in Figure 4, mold first opens at K1 surface. During opening process of K1 surface, 11 drive seats (11 in total for a two-cavity mold, 6 for a single cavity, of which part 29 is shared by both cavities) synchronously drive 12 inclined core pulling inserts, including IG2 insert 13, to complete inclined core pulling action first. Opening distance of K1 surface is 50 mm.
(4) K2 surface opening: Moving mold continues to retract in FZ- direction, and mold opens at K2 surface. During opening process, inclined guide pillars 24 of mechanisms M2 and M2' drive ST3 slider 26 to complete side core pulling action. Opening distance of K2 surface is 212 mm.
(5) Ejection: As moving mold continues to retract, ejector plate 7 is held in place by injection molding machine ejector pin 55 and cannot continue to retract. Therefore, as moving mold continues to retract, plastic part Pa is ejected from ICO central core insert 35 and moving platen 3 by ejector pin 44, IG1 insert 15, etc., and remains on these ejector elements. Finally, injection molding machine robot removes part, achieving complete demolding.
(6) Resetting: When mold resets and closes, hydraulic cylinders 37 of M1 and M1' mechanisms act first, driving IT5 insert to reset, then ejector plate 7 resets, K2 surface closes, and finally K1 surface closes, driving all 12 inserts, including inclined core-pulling insert IG1 insert 15, to reset. After mold is completely closed, next injection cycle begins.

A two-plate family cavity injection mold was designed to meet injection molding requirements of left and right headlight inner reflector bottom shell plastic parts for molding. Integrated classification method using demolding direction simplifies design of demolding mechanisms in plastic molds, effectively reducing mold manufacturing costs by more than 15%. Special runner design, structural layout, and gate arrangement are employed to achieve surface quality requirements without need for primer coating. Design of hydraulic cylinder-driven fixed mold core-pulling mechanism, platen opening and closing driven inclined core-pulling mechanism, and push plate-driven lifter mechanism in mold gives it significant advantages in manufacturing cost, structural flexibility, raw material selection, technological innovation, finished product quality, environmental adaptability. These advantages not only improve performance and quality of automotive lighting products but also bring greater economic and social benefits to manufacturers.