In current booming automotive industry, heat exchange systems, as core components of automotive engine cooling, directly affect engine's efficiency and stability. Straight pipe water chambers, as key plastic parts in heat exchange systems, play a crucial role in distribution, transmission, sealing of coolant, requiring extremely high quality, precision. With advancement of automotive lightweighting and high-performance trends, PA66/30%GF material has become a commonly used material for straight pipe water chamber plastic parts due to its excellent mechanical properties, such as high strength, oil resistance, good thermal stability. However, this material has strong water absorption and a large deformation coefficient, posing many challenges to molding of plastic parts. At the same time, complex structure of straight pipe water chamber plastic parts, closely integrated with multiple metal components, significantly increases difficulty of mold design and manufacturing, especially in demolding process, where traditional mold design struggles to meet demands of efficient production. Therefore, developing an innovative mold design to solve molding problem of straight-pipe outlet water chamber plastic part is of great significance for improving performance and production efficiency of automotive heat exchange systems.

Straight-pipe outlet water chamber Q1 and inlet water chamber Q2 of automotive heat exchange system are elongated shell-shaped parts (Figures 1 and 2). This shape design aims to meet flow path of coolant and spatial layout requirements of heat exchange system. Taking Q1 as an example, its dimensions are 452 mm * 115 mm * 70 mm, and Q2's dimensions are 452 mm * 140 mm * 75 mm. Unit weights are 360 g (Q1) and 314 g (Q2), respectively.

 

Figure 1: 3D view of straight-pipe outlet water chamber Q1

 

Figure 2: 3D view of straight-pipe inlet water chamber Q2
Product has 11 fasteners distributed around it that mate with metal parts. Dimensional and positional accuracy requirements for these fasteners are extremely high. In actual assembly, deviations in snap-fit accuracy can lead to loose fits with metal components, increasing risk of leakage. Statistics show that for every 0.1 mm increase in snap-fit dimensional deviation, probability of leakage increases by approximately 15%. Bottom plane of product mates with rubber ring to seal coolant; flatness requirements for bottom are extremely stringent. Flatness errors must be controlled within a very small range; otherwise, sealing effect will be severely affected, reducing efficiency of heat exchange system.
Average wall thickness of plastic part is 2.5 mm, with some areas reaching 2.9 mm. This wall thickness design, while ensuring strength of plastic part, needs to consider flow and cooling uniformity of melt during injection molding. Uneven wall thickness leads to inconsistent melt flow rates, causing varying degrees of shrinkage during cooling, resulting in defects such as shrinkage marks and deformation, affecting product's appearance quality, mechanical properties.
Water chamber products are used in critical cooling components of automotive engine heat exchange systems, requiring extremely high standards for side straightness and bottom flatness. Deviations in side straightness alter coolant flow pattern, reducing heat exchange efficiency; substandard bottom flatness leads to seal failure and coolant leakage. Studies show that for every 0.1° increase in side straightness deviation, heat exchange efficiency decreases by approximately 3%; for every 0.01 mm increase in bottom flatness error, probability of coolant leakage increases by approximately 10%. Therefore, we will utilize pre-deformation technology for the entire mold, along with continuous mold repair and compensation, to achieve mass production using methods similar to conventional products.
As shown in Figure 3, old project's snap-fit design, to allow snap-fit on both sides to be ejected through front mold direction, prevented anti-collision blocks from being made larger. However, in actual use, because left and right snap-fits were exposed, they were not protected by anti-collision blocks. During transportation, impacts caused snap-fits to break, leading to an increased product defect rate. To reduce risk of snap-fit breakage due to product impacts, engineers widened and lengthened anti-collision blocks, protecting most of left and right snap-fit shapes within them. This improved product design increased difficulty of mold design. This design, which involves demolding process being completed inside slider, significantly increased sliding space, made mold manufacturing process more complex, and significantly increased maintenance costs. Meanwhile, due to complex internal structure, it is difficult to design an effective water cooling system, leading to heat accumulation during injection molding, which affects molding quality of plastic parts and mold life.

 

Image 3: Customer's snap-fit design type
To ensure functional requirements of this snap-fit, a slider-double-lifter composite structure was designed. As shown in Figure 4, S13 snap-fit position structure of product's straight pipe outlet water chamber Q1 is special. Due to restriction of bottom and top anti-collision blocks, left and right snap-fits cannot be demolded through front and rear mold opening method. This results in snap-fit needing to achieve demolding in three directions on same slider structure: first direction is left snap-fit, second direction is right snap-fit, and third direction is slider movement direction, with a horizontal demolding undercut of 2.8 mm on both sides. Difficulty of this product lies in fact that slider movement requires lifter structure to complete snap-fit movement of left and right snap-fits simultaneously. After left and right snap-fits are snapped, lifter structure still needs to move 20 mm along slider movement direction to complete snap-fit movement. To solve this problem, structural principle of slider's secondary movement and lifter movement is utilized. By controlling mold opening sequence of slider-type lifter structure, a double-lifter design on slider is implemented, combined with a secondary slider mechanism to achieve demolding in three directions within mold.

 

Figure 4. Straight pipe outlet water chamber Q1 (S13 snap-fit cross-section)

Straight pipe inlet water chambers Q1 and Q2, as functional parts, need sufficient strength and good sealing to ensure stable coolant transfer in heat exchange system. Average wall thickness of main body is designed to be 2.5 mm, with maximum deviation controlled within 0.5 mm. Thickness of side ribs is designed to be 3 mm, ensuring strength while fully considering shrinkage; wall thickness design is reasonable.
Given shape characteristics and functional requirements of plastic part, using a cold runner would make it difficult to guarantee product strength and uniform injection. Therefore, this mold adopts a two-point integral needle valve type hot runner design (Figure 5). To achieve uniform filling of product, hot runner nozzle was positioned in the center of product without affecting product assembly. Filling analysis was performed using Moldflow software, and nozzle position was continuously adjusted to determine optimal solution. Optimizing nozzle position allows plastic part to be molded under relatively low injection pressure, ensuring rapid and uniform melt filling while maintaining part's strength requirements during holding pressure stage.

 

Image 5 Gating System (Hot Runner)
During operation of hot runner system, opening and closing of needle valve generates friction with mold core. To avoid damage to mold core, diameter of glue column was increased without affecting product assembly. This design provides more suitable space for hot runner nozzle, effectively reducing risk of contact between needle valve and mold core, extending mold life, and ensuring product quality.
To address challenge of achieving three-directional demolding at S13 snap-fit position on same slider structure, a double-lifter composite structure was designed for mold slider. Components of lifter are clearly visible in 3D exploded view of mold (Figure 6). In mold-closed state (Figure 7), all components fit tightly together, preparing for injection molding. When mold opens after injection molding, inclined guide pillars on fixed mold side play a crucial role, driving slider seat and slider insert outwards. Wear-resistant block at the bottom of slider has a limiting groove feature; under action of limiting pin, lifter seat remains stationary. When slider insert moves outwards by 45 mm, under action of its internal angle, it drives left and right lifters to move 4.7 mm along set direction of lifter seat, completing first release movement (Figure 8), achieving initial demolding of two side latches.

 

Image 6 Slider double lifter composite structure

 

Image 7 Slider double lifter mold-closed state

 

Image 8 Slider double lifter first movement state
When slider insert moves to set 45 mm position, limiting pin moves to limit position designed on the bottom surface of slide seat. At this time, under continued pulling of inclined guide pillar and action of guide slope of wear-resistant block, limiting pin moves upwards along guide slope, releasing its positioning from wear-resistant block. Slider seat drives slider insert and lifter assembly to move outwards by 20 mm, completing second movement (Figure 9), thus achieving final demolding. This design, through ingenious motion planning, successfully solves demolding problem of complex snap-fit joints, simplifies internal structure of mold, and optimizes slider's water cooling, improving mold's reliability and service life. Compared with traditional demolding designs, this composite structure reduces number of internal mold parts by 10%~15% and number of maintenance operations by 30%~40%.

 

Figure 9. Slider double lifter demolding state
Both core and cavity adopt an embedded integral design. Moving and fixed mold cores are made of 1.2344 plastic mold steel, which has good wear resistance, corrosion resistance, and thermal stability, meeting long-term high-intensity use requirements of mold and effectively improving its lifespan. To control overall mold costs, mold frames for both moving and fixed molds are made of low-cost pre-hardened plastic mold steel P20. Remaining components, such as hot runner plate, ejector plate, ejector faceplate, faceplate, base plate, and square iron, are made of high-strength medium carbon steel S50C. This ensures both structural strength and reasonable cost control. The overall dimensions of mold blank are 800 mm * 1150 mm * 871 mm. These dimensions were determined after comprehensively considering factors such as size of plastic part, mold structure, and specifications of injection molding machine, ensuring stable installation and operation of mold on injection molding machine.
Bottom surface of product is used to install a sealing ring for water sealing. To ensure sealing performance, an embedded integral design is adopted, avoiding problems such as water leakage or shortened product lifespan that may be caused by insert lines in conventional insert designs. Furthermore, to reduce machining workload of rear mold core, save materials, three rear mold inserts are added per cavity after avoiding waterproof area. Considering need for aging tests, to ensure successful testing, venting grooves (7.5 mm * 5 mm * 0.03 mm) are installed every 10 mm on parting surface of rear mold (Figure 10). This ensures smooth venting during rapid melt flow within cavity, preventing defects such as porosity, scorching caused by gas accumulation.

 

Figure 10 Parting Surface and Venting
Since main snap-fit parts are located within cavity, a large core insert design is used to facilitate mold processing and subsequent maintenance. Inserts are further added for key dimensions such as snap-fit parts and deep ribs. Large core inserts simplify the overall mold structure and reduce processing difficulty; adding inserts at critical locations helps improve processing and assembly accuracy of these parts. All inserts are designed to be removable from surface for easy maintenance during subsequent production. Wear or damage to inserts allows for timely replacement, reducing mold repair time and costs.
Product is small but slender, with outer wall and snap-fit parts located on fixed mold side, and inner wall on moving mold side. To ensure sufficient cooling, uniform cooling inside and outside shell (Figure 11), two sets of three-dimensional circulating water channels are designed on fixed mold cavity side, and four sets of three-dimensional circulating water channels are designed on moving mold side. Due to large contact area between slider and plastic part, one set of three-dimensional circulating water channels is designed in each slider. Finally, water channels are connected in series outside mold, forming two large groups, with eight sliders in one group for easy production and maintenance. Hot runner is located in the hottest area of mold. In addition to main cooling design of hot runner, water channels are also designed near hot nozzle of front mold core to effectively remove heat, ensure the overall temperature uniformity and stability of mold.

 

Figure 11: Cooling System (Red for front mold water channels, green for rear mold water channels, purple for slider water channels)
Considering high hygroscopicity and easy deformation of product material, pre-deformation technology is introduced. First, in-depth simulation analysis is performed using Moldflow software to evaluate deformation trend of product during injection molding (Figure 12). Using pre-deformation design scheme shown in Figure 13, preliminary deformation mode is predicted (Figure 14). Based on Moldflow's analysis results and company's internal knowledge database, combined with actual production data, actual deformation of product was calculated. Based on these calculations, new product drawings were designed, comprehensively considering product's structural characteristics and functional requirements. Mold structure was redesigned according to new product drawings, subjected to high-precision machining to ensure mold's manufacturing accuracy and quality.

 

Image 12 Straight pipe outlet chamber Q1, straight pipe inlet chamber Q2; Moldflow x, y, z direction deformation data

 

Image 13 Pre-deformation design scheme

 

Image 14 Initial pre-deformation design data
After mold trial molding was completed, a special fixture was used to fix product, a specially developed 3D measurement program was used to precisely measure product to ensure that it met predetermined quality and accuracy. Comprehensive analysis of 3D measurement data and knowledge database further optimized product model, improved the overall product quality. Based on optimized new product drawings, mold structure was adjusted as necessary, re-precision machined to ensure that mold perfectly matched final requirements of product.
Specifically, as can be clearly seen from Figures 12(a), (b), and (c), deformation range is between -0.92 and 1.01 mm in x-axis direction; -1.34 and 1.57 mm in y-axis direction; -1.27 and 0.84 mm in z-axis direction.
Since engineers have been deeply involved in design and manufacturing of water chamber molds for 18 years, they have built a comprehensive company knowledge database based on long-term product data accumulation. Product length in this design is 452 mm. It was matched to knowledge database, searching for products with the highest similarity in length and snap-fit as a reference. Upon searching, similar products were found to have a deformation of 1.9/2 mm in x-axis direction, 0.1 mm in y-axis direction, and 1.5/1.7 mm in z-axis direction. 2D straightness requirement for this product is: under natural conditions, error should not exceed 0.2 mm within a 35 mm range. Based on this requirement, above mold flow analysis data was exported at 20 mm intervals. Subsequently, mold flow data was combined with a knowledge database for analysis, and initial actual deformation data was calculated as shown in Figure 14.
Deformation range of straight pipe outlet chamber Q1 in x-axis direction is 0~1.7 mm, y-axis deformation range is 0~0.1 mm, and z-axis deformation range is 0~1.4 mm; deformation range of straight pipe inlet chamber Q2 in x-axis direction is 0~1.8 mm, y-axis deformation range is 0~0.1 mm, and z-axis deformation range is 0~1.6 mm (above calculated data are based on maximum deformation of similar products as a reference, mold flow data was fitted to obtain initial pre-deformation results). Finally, final deformation data were calculated based on actual three-dimensional measurement data and knowledge database analysis (Figure 15). X-axis deformation of straight pipe outlet chamber Q1 is 0~2.1 mm, y-axis deformation is 0~0.15 mm, and z-axis deformation is 0~2 mm. X-axis deformation of straight pipe inlet chamber Q2 is 0~2.2 mm, y-axis deformation is 0~0.15 mm, and z-axis deformation is 0~2.3 mm.

 

Figure 15 Final pre-deformed product image

 

Table 4 pCOP and pCO2P data of EP and EP composites
Finally, we further analyzed mass loss rate (MLR) and char residue of pure EP and its composites to explore their combustion characteristics and flame retardant mechanism. As shown in Figure 6 and Table 5, experimental results show that introduction of high-fraction PN filler can significantly reduce mass loss rate of EP composites and significantly increase char residue after combustion. Addition of PN effectively inhibits pyrolysis and volatilization of matrix material during combustion, thereby reducing MLR. Meanwhile, increase in residual carbon content indicates that PN filler promoted formation of carbonized layer during combustion. As a physical barrier, carbonized layer not only effectively isolates further transfer of heat and oxygen, but also plays a good protective role for internal matrix material. This protective effect directly reduces generation of heat, smoke and harmful gases during combustion, thereby significantly improving the overall flame retardant performance of composite material.

 

Figure 6 MLR and mass curves of EP and EP composite materials
Mold working process: Melt is injected into hot runner nozzle through injection molding machine nozzle, enters hot runner nozzle through hot runner manifold, and completes injection into mold cavity from hot runner nozzle. After mold cavity is filled, cooled, and pressure-held, and solidified to a sufficient rigidity, injection molding machine pulls moving mold, mold opens from parting surface between fixed mold side plate and moving mold side plate. Mold opening process: (1) Because all inclined guide pillars are fixed on fixed mold side plate (20), as moving mold side plate (23) moves in mold opening direction, it also drives inclined guide pillars to pull core laterally. During first movement of slider, lifter is simultaneously driven to complete left and right side snap-out (located in horizontal direction of product). Second movement occurs when lifter on both sides has disengaged, and under action of inclined guide post, slider and the entire lifter structure move outward by 20 mm to complete disengagement movement (Figure 16). (2) When moving mold side moves to position set by injection molding machine, KO insert of mold is ejected by injection molding machine pull rod, thereby driving ejector plate and ejector base plate to complete ejection of product by ejector, lifter, and limit switch contact block. When limit switch contact block touches limit switch of ejection type, ejection stops, and robot arm will remove product according to designed circuit (Figure 17). When robot arm retracts to range set by robot arm, injection molding machine pull rod retracts KO insert of mold. When limit switch contact block retracts to limit switch of retraction type, retraction stops. Mold is closed, and mold begins next injection molding.

 

Figure 16: 2D structural diagram of S13 slider double-lifter composite structure

 

Figure 17: Product image
Traditional secondary slider designs typically involve a smaller slider inside a larger slider, with a control and limiting structure ensuring smaller slider exits first, followed by larger slider. This new slider double-lifter composite structure utilizes principles of secondary slider and lifter motion, employing a secondary slider limiting structure to limit lifter seat. During slider movement, lifter first completes locking and unlocking process, and finally, lifter moves together with large slider to complete locking and unlocking. This innovative design achieves three-directional reverse locking and unlocking within a single slider, simplifying internal mold structure, reducing number of mold parts, lowering mold manufacturing and maintenance costs. Simultaneously, it optimizes water cooling system of mold slider, improving heat dissipation efficiency, ensuring quality of molded plastic parts, effectively solving problems caused by large slide space and difficult cooling in traditional designs.
Traditional mold manufacturing solutions use customer-provided product data for mold parting, resulting in need for jigs for product correction and requiring a large number of operators for production, leading to low production efficiency, high costs, and a high defect rate. This design utilizes software analysis and an experience database to achieve overall pre-deformation design of product before production. Through a series of steps including Moldflow software simulation analysis, actual data calculation, product drawing design, mold design and processing, quality control measurement, product model optimization, mold structure adjustment and reprocessing, continuous verification and repair are carried out to finally obtain data that meets product requirements. This allows product to be packaged directly after production without need for fixture correction. Inspection fixtures are only used for quick verification of product quality during machine setup and occasional spot checks during mass production. This design significantly improves overall production efficiency, reduces fixture and labor costs, and effectively reduces product defect rates.

(1) This mold design achieves innovative breakthroughs in many aspects. Gate adopts a two-point integral needle valve hot runner, hot nozzle position is optimized by combining mold flow analysis, which not only effectively ensures product strength and uniform injection but also significantly extends mold's service life. Demolding structure adopts a slider double-lifter composite design, cleverly integrating secondary slider and lifter movement principles, successfully solving demolding problem of complex snap-fits, while simplifying mold structure and optimizing cooling effect. In terms of parting, an embedded integrated solution is adopted, taking into account both product sealing performance and convenience of mold processing and maintenance. Cooling system, through a rationally laid-out water channel, ensures uniform temperature distribution in mold, effectively reducing plastic part deformation.
(2) Mold operates stably and reliably, with a high degree of automation and close coordination among all components, effectively guaranteeing product quality and production efficiency. Compared to traditional molds, this design represents a significant advancement in both structure and pre-deformation technology. Slider double-lifter composite structure breaks traditional limitations, achieving three-way inverted demolding on a single slider, optimizing internal structure and cooling system of mold. Whole-product pre-deformation design overturns traditional manufacturing methods, enabling products to meet assembly requirements without need for jig correction, significantly improving production efficiency and product quality.
(3) Mass production verification shows that mold operates smoothly, quality of plastic parts meets expected standards, satisfies 45-second production cycle requirement, fully demonstrating rationality and effectiveness of its design. Product defect rate has been significantly reduced from approximately 15% to less than 3%, significantly improving production efficiency. This mold has good applicability. It is not only suitable for plastic parts with straight pipe inlet chambers in automotive heat exchange systems, but also has important reference value for design of plastic parts with similar materials and structures, providing new ideas and methods for design of automotive parts molds.