With rapid development and fierce competition in automotive industry, automobiles have become an indispensable part of people's lives. While rapid increase in number of automobiles brings convenience to our lives, it also generates environmental problems, such as vehicle exhaust pollution. Carbon monoxide, carbon dioxide, other greenhouse gases contained in vehicle exhaust are a major contributor to global warming. Energy conservation, emission reduction, lower exhaust emissions are crucial directions for automotive technology development in low-carbon era.
Since 1990s, automotive thermal system chambers have gradually shifted from aluminum to polyamide/glass fiber plastics. However, due to easily deformable nature of polyamide/glass fiber, thermal system chambers experience significant warping after injection molding. After removal from injection molding machine, before complete cooling, chambers need to be clamped in a jig, then placed in cold water for approximately 10 minutes for straightening before assembly, posing significant challenges to production efficiency and quality control. Through research on molds for angled nozzle chambers in automotive plastic functional parts, optimal product data for angled nozzle chamber molds were developed, and a manufacturing scheme for nozzle chamber molds that meets assembly requirements was designed, with good results.
Angled nozzle chambers have their own structural design methods and requirements. First, since product is a functional component, material needs to be PA66/(30%~50%)GF. Due to poor fluidity of this material, when designing inclined nozzle air chamber mold, in order to reduce weld line of mold, plastic part must be injection molded using a single-point hot runner. Second, cooling of plastic part should be as uniform as possible to avoid product instability due to uneven cooling during production and cracking caused by assembly stress during later assembly and use. To avoid this situation, it is necessary to design a demolding mechanism for inclined nozzle feature, in which a three-stage slider mechanism exists at a key position of inclined nozzle. This paper focuses on three-stage slider mechanism and pre-deformation technology of inclined nozzle air chamber, and proposes a relatively novel structural design idea, which can be used as a reference for relevant enterprises.

(1) Poor applicability. Because internal space of product is small, only a hydraulic cylinder-type slide can be designed, and demolding is first performed in slider, resulting in a large mold size, high mold manufacturing and maintenance costs.
(2) Long production cycle. Traditional air chamber mold production methods require product to be clamped in a jig and placed in cold water for approximately 10 minutes for straightening after being removed from injection molding machine before it can be fully cooled, before assembly.
(3) Increased defective products. Varying cooling times due to manual placement lead to inconsistent product jig straightening, increasing dimensional instability.
(4) Considering above, product design is constrained by manufacturing costs and production processes, avoiding the use of PA66/30%GF material and opting for traditional aluminum parts. This hinders lightweight design process of replacing metal parts with plastic parts.

Figures 1 and 2 show two different air chamber products with a 1+1 cavity design, namely angled nozzle air chamber Q1 and circulating air chamber Q2. This paper mainly studies inclined tube chamber. Inclined tube opening of chamber is 37.5° (Figure 3). Slide needs to be ejected along inclined direction of tube opening. Undercut at tube opening is 1.2 mm, resulting in only 27 mm of usable space inside product, which increases difficulty of mold structure design.

 

Figure 1 3D view of circulating air chamber Q2

 

Figure 2 3D view of inclined tube chamber Q1

 

Figure 3 Cross-sectional view of inclined tube chamber Q1
This product is divided into two research directions: (1) In terms of mold, in order to solve problem of small internal space and undercut ejection, a new mold structure was designed, which realizes internal movement and release design scheme of mold through a 3-stage slider mechanism. (2) In terms of product, combined with research on PA66/30%GF material, product pre-deformation analysis design was adopted. Final product achieved expected effect, and at the same time solved problem of dimensional instability during production process of product.

Plastic part is made of PA66/30%GF, with a density of 1.2~1.4 g/cm3. PA66 is lightweight, with a service temperature range of -30~140℃ and a melting point of 290℃. It softens at around 280℃. Its unique characteristics include good mechanical properties, toughness, oil resistance, self-lubrication, a low coefficient of friction. Its biggest drawback is its high hygroscopicity, which affects dimensional stability. It is widely used in manufacture of parts for machinery, automobiles, chemical, electrical equipment, such as gears, rollers, pulleys, shafts, pump impellers, fan blades, high-pressure seals, valve seats, gaskets, bushings, various handles, support frames, inner layers of wires. This material has potential to replace traditional metals in applications.

Based on characteristics of mold cavity and core, both core and cavity adopt an embedded integral design. To improve mold life, materials for both moving and fixed mold cores are selected as 1.2344 hot work die steel. Due to its excellent wear resistance, high strength, high temperature stability, and good machinability, it is widely used in molds, die-casting molds, extrusion molds, plastic molds, and other fields.
To reduce the overall cost of mold, materials for both moving and fixed mold frames are low-cost high-strength medium carbon steel S50C. Simultaneously, to improve mold's venting effect and prevent scorching at parting surface, venting grooves with dimensions of 3 mm x 5 mm and a depth of 0.03 mm are provided approximately every 10 mm on cavity side and parting surface of slider, ensuring smooth venting when melt flows rapidly within cavity. Because PA66/30%GF produces glass fiber powder during production, which can easily clog venting grooves and lead to product scorching. Therefore, secondary venting distance is designed to be 2 mm from injection point, mold's PL surface needs to be cleaned and maintained every production shift.
Since automobiles require installation of air chamber products, and each product is sold to different countries, this product needs to withstand extremely cold and hot operating environments, undergo "aging tests." Therefore, quality and precision requirements of this product are very high. To ensure quality and molding accuracy of plastic part, to facilitate smooth demolding, parting surface is selected at maximum profile of plastic part's cross-section (Figure 4), inserts are all designed as face inserts, allowing for better maintenance during production.

 

Figure 4: Parting Surface and Venting

Space at undercut position of this product is narrow, and demolding stroke is long, so a simple structure cannot be used to complete demolding. Considering precision and production efficiency requirements of injection molded parts, the overall injection mold structure is designed as a 1-mold, 2-cavity, 3-slider design (Figure 5).

 

1. Wear-resistant block; 2. Large slider insert; 3. Shrink insert; 4. Pipe insert; 5. Small slider seat; 6. Shrink insert shovel; 7. Limiting fixing seat; 8. Limiting pin; 9. Large slider seat; 10. Stroke screw; 11. Pressure strip; 12. Inclined guide post pressure block; 13. Inclined guide post; 14. Positioning ring; 15. Front mold heat insulation plate; 16. Fixed mold side panel; 17. Hot runner plate; 18. Front mold core; 9. Fixed mold plate; 20. Rear mold core; 21. Extrusion block; 22. Moving mold plate; 23. Square iron; 24. Ejector plate; 25. Ejector base plate; 26. Support head; 27. Moving mold side panel; 28. Rear mold heat insulation plate.
Figure 5: 2D Overall Structure of Mold
Through design of 3-slider mechanism, internal mold experiences 3 movements for uncoupling, while simultaneously allowing undercut position at nozzle to be demolded (Figure 6). After injection molding is completed (Figure 7), at the moment front and rear molds open, under action of inclined guide pillars, small slider seat 5 first drives tube core insert 4 to move 26 mm, completing first movement (Figure 8). At this time, under continued action of inclined guide pillars, large slider seat 9 drives shrinking shovel 6 and small slider to continue moving 15.5 mm. Because large slider insert 2 remains stationary under action of wear-resistant block 1 and limit pin 8 is fixed, shrinking insert 3 moves down 9 mm under action of shrinking shovel to complete release of undercut position (by calculating design angle of 30° and movement distance of 15.5 mm through trigonometric functions, movement of 9 mm can be completed), completing second movement (Figure 9). At this time, limit pin 8 has moved to limit position designed on the bottom surface of slide seat. At this time, under action of inclined guide pillars and guide slope, limit pin 8 will move upward and release positioning with wear-resistant block. Simultaneously, under action of inclined guide pillar, large slider seat continues to drive small slider. Furthermore, under action of stroke screw 10 in large slider seat 9, large slider insert 2 moves another 10.5 mm to complete third movement (Figure 10). After moving mold moves to position set by injection molding machine, ejector plate 24 of mold is ejected 50 mm by injection molding machine pull rod. Robot arm will then remove product according to designed path (Figure 11).

 

Figure 6: 3-stage slider mechanism

 

Figure 7: Original mold closing state

 

Figure 8: First movement state

 

Figure 9: Second movement state

 

Figure 10: Third movement state

 

Figure 11: Actual image of air chamber
In actual production, this mold is highly efficient, space-efficient, operates safely and stably, resulting in fewer defects in molded plastic parts. It effectively solves problem of difficult demolding of such products. This is an innovative point in design of this mold structure.

This functional component uses PA66/30%GF, with a shrinkage of 1.005 and a plastic density of 1.2~1.4 g/cm3. Product's single weight is (73.53+88.61) g. To avoid defects at product's snap-fit position, this design adopts a two-point integral needle valve type hot runner design (Figure 12).

 

Figure 12 Gating System (Hot Runner)
In actual production, cooling time accounts for a large proportion of production cycle; therefore, controlling mold temperature has a significant impact on production efficiency and product quality. Due to product's large surface area and thick, thin walls, three sets of water channels were designed on moving mold side to achieve better cooling, as shown in Figure 13. Rear mold's water channel has a diameter of 8 mm, slider's water channel has a diameter of 8 mm, forming a three-dimensional circulating water system. Because slider has a large contact area with plastic part, it also needs cooling; therefore, each slider has its own 8 mm diameter three-dimensional circulating water channel. To simplify water channel connection, flexible hoses are used to connect slider water channels as one set. Two 10 mm diameter three-dimensional circulating water channels were designed on fixed mold cavity side. Plastic part has pipe inserts; to enhance cooling in critical areas, two 12 mm diameter water wells with baffles were designed to remove more heat (red for front mold water channel, green for rear mold water channel, and purple for slider water channel).

 

Figure 13 Cooling System

Since this product is a functional component, material is PA66/30 %GF, which has high hygroscopicity and is easily deformed. Traditional manufacturing processes cannot guarantee production of qualified products. To solve this problem, team adopted product pre-deformation technology: (1) First, product analysis team used Moldflow to conduct simulation analysis, then set parameters based on years of injection molding experience to analyze initial deformation trend and data of product during injection molding. (2) Product design team calculated actual deformation data (Figure 15) based on data from Moldflow (Figure 14) and knowledge database. After calculating actual deformation data based on customer's original product, product was mathematically modeled. (3) Mold was designed using newly designed product drawings. (4) After mold trial was completed, quality control team used a specially developed fixture to fix product and measured product using a specially compiled 3D measurement program. (5) By combining 3D measurement data and knowledge database, product design team re-optimized product model (Figure 16). (6) Mold design team revised mold structure and reprocessed mold based on new product drawings. (7) Products injection molded using new mold directly meet assembly requirements and do not require fixture correction.

 

Figure 14: Deformation data of inclined nozzle air chamber Q1 and circulating air chamber Q2 in X, Y, and Z directions using Moldflow

 

Figure 15: First pre-deformation design data

 

Figure 16: Final pre-deformed product image
Data from Moldflow (Figure 14) shows that X-axis deformation of inclined nozzle air chamber Q1 and circulating air chamber Q2 is -0.58~0.3 mm, Y-axis deformation is -0.63~0.66 mm, and Z-axis deformation is -0.45~0.51 mm. As shown in Figure 15, actual deformation data was calculated by combining mold flow data with a knowledge database, first pre-deformation design was performed: X-axis deformation of inclined nozzle air chamber Q1 was 0~0.5 mm, Y-axis deformation was 0~0.1 mm, Z-axis deformation was 0.1~0.6 mm. X-axis deformation of circulating air chamber Q2 was 0~0.4 mm, Y-axis deformation was 0~0.1 mm, and Z-axis deformation was 0.1~0.5 mm.
As shown in Figure 16, product design team calculated final data based on 3D measurement data combined with knowledge database: X-axis deformation of inclined nozzle air chamber Q1 was 0~0.28 mm, Y-axis deformation was 0~0.15 mm, and Z-axis deformation was 0.1~0.9 mm. X-axis deformation of circulating air chamber Q2 was 0~0.4 mm, Y-axis deformation was 0~0.15 mm, and Z-axis deformation was 0.3~0.8 mm.

Based on above experimental content and verification data, optimal product data for nozzle air chamber was designed. From optimal data, it can be seen that middle part of inclined nozzle air chamber Q1 has rib support and did not deform, while middle part of circulating air chamber Q2 lacks rib support and has a relatively large deformation (maximum 0.4 mm). Therefore, product effectively solved problem of product deformation through pre-deformation optimization design. This is a major highlight of pre-deformation design of this product.

(1) Traditional designs involve adding a hydraulic cylinder core puller to ordinary slider. Before ordinary slider moves, core is demolded vertically from tube opening, then ejected along with ordinary slider, leading to increased mold and product costs. This mold design uses a three-stage slider mechanism at critical position of inclined tube opening, achieving three-stage internal movement and release within mold. This effectively reduces probability of operational failures, significantly lowers mold manufacturing costs, and improves production efficiency.
(2) A novel structural design approach is proposed using pre-deformation technology. After repeated verification, optimal mathematical model for air chamber was designed, effectively addressing issue of easy deformation of polyamide/glass fiber used in air chamber.
(3) Production verification shows excellent mold performance. Mold structure is rationally designed, with smooth mold movements, a more compact spatial structure, stable operation, and fewer defects in molded plastic parts. Through pre-deformation analysis and design, product dimensions are stable, and production can be completed without fixture correction, effectively saving fixture and personnel costs and significantly improving production efficiency.