Automotive air conditioning system mainly consists of a blower, evaporator, compressor, radiator, dryer, and expansion valve. Blower, commonly known as air box, is located inside vehicle cabin, while other components are located in engine compartment. Blower is core component and main air source of automotive air conditioning system.
This article introduces injection mold structure and design experience of left and right covers of air conditioning blower of a certain brand of automobile.

Figures 1(a) and (b) are plastic parts of left cover of air conditioning blower of a certain new energy vehicle, Figures 1(d), (e), and (f) are plastic parts of right cover of air conditioning blower of same brand of automobile. Plastic part material is a blend of polyamide 6 (PA6) and polyamide 66 (PA66) modified, then reinforced with 30% glass fiber (GF) (PA6+PA66+GF30), with a shrinkage rate of 0.35%. Plastic parts require high precision, reaching MT3 level (GB/T 14486—2008). Shapes are complex, with 11 undercuts across two parts, side parting and core-pulling mechanisms are quite intricate. Three-dimensional views and parting lines of left and right covers of automotive air conditioning blower are shown in Figures 1(c) and (g).

 

Figure 1: Left and right cover plastic parts of automotive blower

Molded plastic parts are medium-sized components, produced in large batches, with high requirements for molding quality and dimensional accuracy. Mold adopts a hot runner gating system, with single-point injection for both cavities. Gate is located above plastic part, allowing melt to directly enter mold cavity via hot runner gating system. Compared to a three-plate mold with a point gate, this eliminates need for a fixed-distance parting mechanism and four long guide pillars, significantly simplifying mold structure. Because melt directly enters cavity without solidification in gating system, injection cycle is greatly shortened, significantly improving molding quality. Hot runner gating system of mold consists of a primary hot nozzle, a secondary hot nozzle, a hot runner plate, other positioning and insulation parts, as detailed in Figure 2.

 

Figure 2 Hot runner gating system of mold

Left cover plastic part of automotive air conditioning blower has 6 undercuts (S1~S6), and right cover plastic part has 5 undercuts (S7~S11). Mold needs to design 11 side core pulling mechanisms. Among them, core pulling directions of S4 and S6 interfere with each other, and core pulling of S9 is affected by outer ring of plastic part. These three side core pulling mechanisms are design challenges.

Undercut S5 is on the inner side of plastic part, mold can only use a slanted push rod side core pulling mechanism [Figure 3(a)]. Undercut depth on inner side of plastic part is 5 mm. Adding a safety distance, core pulling distance for S5 is 7.7 mm. Based on height of plastic part, ejection distance is taken as 110 mm. Therefore, tilt angle of inclined push rod α = arc tg7.7/110 = 4°.

 

1-S1 Side Core Pulling; 2-Bent Pin; 3-S1 Locking Block; 4-S1 Slider; 5-Moving Core; 6-Moving Core Drive Block; 7-DME Positioning Lock; 8-S6 Side Core Pulling; 9-Angled Push Rod; 10-Angled Push Rod Guide Block; 11-Left Cover Moving Mold Insert; 12-Positioning Pin; 13-Moving Mold Core; 14-S2 Side Core Pulling; 15-S2 Slider; 16-S2 Locking Block; 17-Angled Guide Pillar Fixing Plate; 18-Angled Guide Pillar; 19-Left Cover Fixed Mold Insert; 20-S3 Locking Block; 21-S3 Angled Slider; 22-S4 Angled Slider; 23-S4 Locking Block
Figure 3: Side core-pulling mechanism of injection mold for left cover of an automotive air conditioning blower
Side core-pulling mechanism of inclined push rod includes inclined push rod, guide block, and inclined push rod base.
Undercut S2 is on the left outer side of plastic part. Mold adopts a "slanted guide post + slider" side core-pulling mechanism. Core-pulling distance of S2 is not large, only 4.5 mm, but core-pulling area is large. To facilitate removal of molded plastic part, core-pulling distance is taken as 20 mm, and tilt angle of inclined guide post is taken as 20°, as shown in Figure 3(a).
The most complex side core-pulling mechanism for left cover is S4 and S6. These two side core-pulling directions interfere with each other. To solve this problem and ensure that both cores can be successfully demolded, mold adopts a composite core-pulling mechanism of delayed core pulling and slider moving on top of slider. Locking blocks S3 and S4, fixed to fixed mold plate A, are both locking components and driving components for core-pulling of sliders. During mold opening, due to large gap between bent pin 2 and slider 4, slider 4 remains stationary for first 58 mm. Locking blocks (also driving blocks) of S3 and S4 drive sliders 21 of S3 and 22 of S4 to pull core outwards. After S3 and S4 complete core-pulling, bent pin then drives slider 4 of S1, mold begins lateral core-pulling of S1 and S6. Since undercut depth of S1 is 115 mm, core-pulling distance of slider 4 is 120 mm.

Similar to left cover, inner undercut S10 uses a slanted push rod lateral core-pulling mechanism. Undercut depths of left and right covers are same, therefore tilt angle is 4°. Both consist of a slanted push rod, a guide plate, and a base, as detailed in Figure 4(e).

 

24 - Movable Core; 25 - S8 Side Core Pull; 26 - Angled Guide Post Fixing Block; 27 - Angled Guide Post; 28 - S7 Side Core Pull; 29 - S7 Locking Block; 30 - S7 Slider; 31 - S7 Positioning Part; 32 - S9 Side Core Pull; 33 - Guide Block; 34 - Angled Push Rod; 35 - T-Snap Locking Block; 38 - S8 Positioning Part; 39 - S8 Slider; 40 - S8 Locking Block; 41 - S8 Angled Guide Post; 42 - S11 Side Core Pull; 43 - Angled Guide Post Fixing Block; 44 - S11 Locking Block; 45 - S11 Angled Guide Post; 46 - S11 Slider; 47 - DME Positioning Clamp
Figure 4. Side core-pulling mechanism of injection mold for right cover of an automotive air conditioning blower
Right cover has four outer undercuts: S7, S8, S9, and S11. S9 is the most difficult to pull because a protruding structure in pulling direction obstructs side core pulling. To solve this problem, a composite side core-pulling mechanism is used. During mold opening, inclined guide post 41 drives slider 39, side core pullers 25 and T-shaped clips 35 fixed on slider. T-shaped clips 35, in turn, drive longitudinal movable core 24 to slide downwards and detach from plastic part. During this process, spring 31 holds S9 side core pull in place. After movable core 20 completes longitudinal core-pulling distance, small pull rod 33 pulls S9 side core puller to the left, detaching it from the undercut. Depth of undercut S8 is approximately 125 mm. Including a safety distance, S8 slider core-pulling distance is 130 mm, positioned by a stop pin and ball bearings. Due to large core-pulling distance, inclination angle of inclined guide post 37 is 25°.
S7 side core-pulling mechanism is relatively simple, mainly composed of inclined guide pillars 24, sliders 26, locking blocks 25, and positioning parts 27.
In summary, side core-pulling mechanism is the most complex core structure in injection mold of right cover of an automotive air conditioning blower. From perspective of direction of side core pulling, there are core pulling perpendicular to mold opening direction and also inclined core pulling not perpendicular to mold opening direction; from perspective of power source driving side core pulling, there are moving mold inclined guide pillar core pulling, bent pin core pulling, inclined slider and inclined push rod core pulling; from perspective of core pulling position, there are moving mold core pulling and fixed mold core pulling; from perspective of nature of side core pulling, there are forced core pulling and delayed core pulling; from perspective of side core pulling structure, there are single slider side core pulling and composite core pulling with a large slider and a small slider in the middle; slider positioning includes both "stop pin + ball + spring" positioning structure and DME positioning clamp positioning. It can be said to be one of classic structures of side core-pulling mechanisms for injection molds. Core-pulling sequence of 11 side-mounted core-pulling mechanisms is: S2, S3, S4, S7, S8, S9, S11 → S1, S6 → S5, S10.

Injection molds for left and right covers of automotive air conditioning blower employ a combined temperature control system of "straight-through cooling water pipes + partition-type cooling water wells," totaling 13 cooling water channels. Four channels are for fixed mold, and nine for moving mold, as detailed in Figures 5 and 6. Cooling water channels are designed for all molding parts and sliders of each side-mounted core-pulling mechanism. Cooling water channels for molding parts all enter and exit through mold plate, facilitating disassembly and assembly, preventing damage to pipe joints. As shown in figures, cooling system is crisscrossed and evenly distributed, enabling rapid and balanced cooling of mold, significantly improving mold's cooling efficiency and dimensional accuracy of molded parts. Injection molding cycle is 33 seconds, dimensional accuracy reaches MT3 level (GB/T 14486—2008). Compared with similar vehicle models, production efficiency is increased by 10%, and accuracy is improved by one level.

 

Figure 5: Mold Temperature Control System

 

Figure 6: 3D Schematic Diagram of Mold Temperature Control System

Mold adopts a non-standard mold base, a hot runner gating system, and a total of 11 side core-pulling mechanisms. Maximum external dimensions of mold are 850 mm * 700 mm * 852 mm, and the total weight is 3397 kg (1687 kg for fixed mold and 1710 kg for moving mold), classifying it as a large injection mold. To improve precision and lifespan of mold, both moving mold guide bushing and ejector pin fixing plate guide bushing are closed-type standard ball bearing guide bushings with two sealing rings. Moving mold guide bushing is R06020 80 10 (80 mm in diameter), and ejector pin fixing plate guide bushing is R06020 30 10 (30 mm in diameter). Ball bearing guide bushings are characterized by high precision, easy installation, and space saving, and are only used in large, precision injection molds. The overall mold assembly structure is shown in Figure 7. Mold working process is as follows:

 

1-S1 Side core pull 2-S1 Bent pin 3-S1 Locking block 4-S1 Slider 5- Movable core 6- Movable core drive block 7- DME positioning lock 8-S6 Side core pull 9- Angled push rod 10- Angled push rod guide block 11- Left cover moving mold insert 12- Positioning pin 13- Moving mold core 14-S2 Side core pull 15-S2 Slider 16-S2 Locking block 17- Angled guide post fixing plate 18- Angled guide post 19- Left cover fixing insert 24- Movable core 25-S8 Side core pull 26- Angled guide post fixing block 27- Angled guide post 28-S7 Side core pull 29-S7 Locking block 30-S7 Slider 31-S7 Positioning part 32-S9 Side core pull 33- Guide block 34- Angled push rod 35- T-shaped locking block 38-S8 Positioning Part; 39-S8 Slider; 40-S8 Locking Block; 41-88 Angled Guide Post; 42-S11 Side Core Pull; 43-Angled Guide Post Fixing Block; 44-S11 Locking Block; 45-S11 Angled Guide Post; 46-S11 Slider; 47-DME Positioning Clamp; 48-Moving Mold B Plate; 49-Push Rod Fixing Plate; 50-Push Rod Base Plate; 51-Moving Mold Fixing Plate; 52-Right Cover Moving Mold Key; 53-S10 Angled Push Rod Base; 54-Right Cover Core; 55, 58-Push Rod; 56-Injection Molding Machine Ejector Roller Connecting Post; 57-S5 Angled Push Rod Base; 59-Push Rod Plate Ball Bearing Guide Sleeve; 60-Push Rod Plate Guide Post; 61-Reset Rod; 62-Fixed Mold A Plate; 63-Frame Plate; 64-Fixed Mold Fixing Plate; 65-Hot Runner Plate; 66, 70-Secondary Hot Injector Nozzle; 67-Positioning Ring 68 - Grade hot injection nozzle; 69 - Right cover fixed mold insert; 71 - Fixed mold positioning sleeve; 72 - Guide pillar; 73 - Ball bearing guide sleeve; 74 - Moving mold positioning sleeve; 75 - Square iron block.
Figure 7 Injection mold structure for left cover of an automotive air conditioning blower
(1) Melt enters hot runner plate 65 through primary hot nozzle 68, then enters mold cavity through secondary hot nozzles 66 and 70.
(2) After filling cavity, mold is held under pressure and cooled. When it has solidified to a sufficient rigidity, injection molding machine pulls moving mold. Mold opens from parting surface between fixed mold plate A 62 and moving mold plate B 48. Mold opening process is as follows: ① First, molded plastic part is separated from fixed mold cavity. ② Next, inclined guide post 18 moves slider 15, which drives side core puller 14 to complete S2 side core pull; inclined guide post 27 moves slider 30, which drives side core puller 28 to complete S7 side core pull; inclined guide post 41 moves slider 39, which drives side core puller 25 to complete S8 side core pull; T-shaped buckle 35 moves fixed mold inclined slider 24 to complete S9 side core pull; T-shaped buckles 20 and 23 move fixed mold inclined sliders 21 and 22 respectively to complete S3 and S4 side core pulls; inclined guide post 45 moves slider 46, which drives side core puller 42 to complete S11 side core pull. ③ After mold opens to 58 mm, bent pin 2 moves slider 4, driving inclined core pull 1 to complete S1 side core pull; simultaneously, T-shaped buckle 6 drives movable core 5 downward to detach from molded plastic part. ④ Finally, slider 4 drives side core pull 8 to complete S6 side core pull.
(3) After mold opening stroke is completed, injection molding machine ejector roller, threaded to mold connecting column 56, pushes mold ejector plate 49 and ejector base plate 50, thereby pushing ejector rods 55 and 58 to push plastic part away from moving mold inserts 11 and 52, cores 13 and 54; simultaneously, inclined ejector rods 9 and 34 push molded plastic part out of mold while moving laterally to complete side core pull of inner undercut S5 and S10. (4) After molded plastic part safely detaches from mold, injection molding machine pushes moving mold to close. During mold closing process, inclined guide post 18 pushes slider 15 to reset, bent pin 2 pushes slider 4 to reset, inclined guide post 41 pushes slider 39 to reset, T-shaped buckle 35 pushes slider 24 to reset, inclined guide post 27 pushes slider 30 to reset, inclined guide post 45 pushes slider 46 to reset, and push rod fixing plate is pushed to reset by reset rod 61. During reset process, push rod fixing plate pulls push rods 55 and 58, as well as inclined push rods 9 and 34 to reset.
(5) After limit switch 31 is activated, mold is locked, and mold begins next injection molding.

(1) Hot runner gating system of mold greatly improves quality of molded plastic parts and simplifies mold structure. In addition, rapid and balanced cooling system significantly improves cooling efficiency of mold and dimensional accuracy of molded plastic parts. Compared with molds for similar vehicle models, production efficiency is increased by 10%, and accuracy of molded plastic parts is improved by one level, reaching MT3 level.
(2) Mold's side core-pulling mechanism adopts a composite core-pulling mechanism and a delayed side core-pulling mechanism, effectively solving problems of complex molded plastic parts structure and mutual interference in side core pulling.
(3) Mold's guiding and positioning system uses standard ball bearing guides, greatly improving mold's accuracy and lifespan. Mold structure is complex, but design of each mechanism is scientific, advanced, novel, and practical. Side core-pulling action is safe and reliable. Since its commissioning, mold has operated smoothly, and quality of molded plastic parts has met design requirements.