TRW EF&C is the world's largest automotive parts supplier. Currently, TRW EF&C division has 16 factories worldwide, located in 10 countries, providing support to customers worldwide. EF&C has engineering and technical centers in Germany, South Korea, and China. Currently, it has two factories in Ningbo and Langfang, its China headquarters and technical center in Shanghai.
EF&C division's products include fastener lines and functional parts lines. The fastener line includes fasteners, interior fasteners, pipe fasteners, plugs, pressure reducing valves, engine components, and other fastener products. Functional parts line includes instrument panel components (air vents, center panels, ashtrays, cup holders, storage boxes), ceiling components (handles), and other functional parts.

Moldflow software was used to analyze injection molding process of automobile pressure reducing valve, and its warpage analysis results were obtained. Analysis showed that main factor affecting warpage is volume shrinkage.
Moldflow was used to simulate pre-deformed model in detail and accurately, and warpage pre-deformation of product was optimized. Mold opening results showed that warpage pre-deformation after moldflow optimization was accurate and reasonable, warpage deformation of molded product was significantly reduced, greatly improving product quality.

Moldflow: automobile pressure reducing valve, mold flow analysis, warpage, pre-deformation, optimization.
Automobile injection molding is a complex multi-factor processing process. Especially for parts with complex structures, it is necessary to perform numerical simulation of their molding process, analyze their molding results and predict quality defects, use this to improve mold structure and set reasonable process parameters in order to achieve the best injection molding results. This paper uses Moldflow software as a research object for a specific automotive pressure-reducing valve. We conduct detailed and accurate mold flow simulation analysis, evaluate results, and optimize them. Further optimization calculations are performed on pre-deformed model to determine optimal value for warpage pre-deformation. Furthermore, mold opening test results demonstrate that warpage pre-deformation achieved through Moldflow optimization analysis is accurate and reasonable, significantly reducing warpage in molded product and significantly improving product quality.

Pressure-reducing valve is a typical narrow, thin-walled injection molded part, as shown in Figure 1. The overall dimensions are 360mm * 90mm * 30mm, with an average wall thickness of 1.4 mm. Part is made of PP-PE P230HS, and material processing parameters are shown in Figure 2.

 

Large size of part requires multiple gates to achieve flow balance. Furthermore, significant warpage is likely to occur along length. Therefore, a well-designed gating and cooling system is crucial for filling and cooling injection molded melt. Plastic part was poured using two points, with cooling pipes located at upper and lower ends. Completed gating system and runner system are shown in Figure 3.

 

Process parameters were set as follows: mold surface temperature of 60℃, melt temperature of 240℃, filling control of 1 second, and mold opening time of 5 seconds, as shown in Figure 4.

Warpage deformation occurs when shape of plastic part deviates from shape of mold cavity and is one of main defects in injection molding. For automotive pressure relief valves, since their primary function is one-way pressure relief and exhaust, the other direction must be completely sealed. Therefore, requirements for warpage deformation in mold opening direction are particularly strict; otherwise, one-way pressure relief function cannot be achieved. Figure 5 shows deformation in each direction and the overall deformation, and Figure 6 shows cause of deformation.
Figure 5 shows that plastic part warps in mold opening direction by approximately 1.3mm, forming an arched bridge shape. This defect is most detrimental to product and can significantly impact product performance, leading to serious problems. To improve product quality, further optimization of various parameters is required to reduce warpage.

 

Warpage can be attributed to following four factors:
1) Uneven cooling, caused by uneven cavity surface temperature distribution, temperature variations along thickness direction, and thermal properties of mold;
2) Uneven shrinkage, caused by large variations in part thickness, improper cooling system design, and inappropriate molding process parameters;
3) Inconsistent molecular orientation, caused by uneven shrinkage in parallel or perpendicular directions of material molecules;
4) Corner effects.
Figure 6 shows that uneven shrinkage is primary factor causing warpage in this injection molded part.

 

5.3.1 Initial Pre-deformation
Once product material is determined, gating and cooling systems are optimized, adjusting process parameters is the simplest and most direct way to improve warpage in injection molded parts. Analysis revealed that varying process parameters did not significantly improve warpage, so an attempt was made to reduce shrinkage-induced warpage through product pre-deformation.

 

Initial plan was to pre-deform pressure reducing valve frame in opposite direction by 2.0mm, as shown in figure above.
5.3.2 Simulation Analysis Results of Pre-Deformation Model
According to simulation analysis results, frame still had approximately 0.7mm of deformation in mold opening direction, which was consistent with pre-deformation direction, as shown in Figure 8.

 

According to pre-deformation analysis results, deformation caused by a pre-deformation of 2.0mm was somewhat excessive. Final pre-deformation was determined to be 1.3mm.

 

Based on pre-deformation data optimized after Moldflow simulation, mold development was carried out and injection molding experiments were conducted. Figure 9 shows results after mold opening. Measurements showed that actual product warpage was very ideal, approximately 0.2mm, and consistent with pre-deformation direction. This indicates that pre-deformation was still too conservative. On the other hand, it also shows that simulation analysis results had an accuracy rate of over 95%. This project, thanks to simulation analysis, was successfully debugged on the first try, eliminating mold rework and rework, reducing costs, saving significant time and money, earning customer trust, and significantly improving company's technical capabilities.

Before aforementioned project (H60A), our company had previously developed a similar product, T6, as shown in Figure 10 above. Upper image shows H60A, product currently being molded, while the lower image shows T6, a similar product. As can be seen from comparison, T6 is smaller and wider than H60A. Structurally, its shape is more regular, and its deformation should theoretically be easier to control. However, because T6 was developed before H60A, simulation analysis was not considered at the time. Instead, engineers from engineering, mold, and injection molding departments relied on their experience. Without simulation analysis prior to mold creation, images above show significant deformation of T6 frame, similar to simulation analysis results for initial H60A design.
This significant deformation caused soft rubber seal above frame to become loose, leaking air and failing to meet one-way pressure relief requirements. This resulted in numerous customer complaints and significant pressure on our factory.
Furthermore, because such a serious problem was discovered late in product development, after molds for both pressure relief valve frame and soft rubber cover had already been developed, adjustments and improvements were extremely challenging. After trying various methods (processing, materials, and molds), none were successful. Finally, soft rubber mold was redeveloped, using it to compensate for warping of frame, which only barely resolved issue.
Lack of simulation analysis during early development phase led to a significant loss of time and money due to mold redevelopment. Furthermore, product quality issues also impacted company's reputation.

This study analyzed key process parameters affecting warpage of automotive pressure relief valves. Detailed mold flow simulation analysis was conducted using Moldflow to address this warpage issue. Furthermore, pre-deformation data model was further optimized and simulated to determine optimal pre-deformation data for product model. Open mold test results demonstrated that warpage pre-deformation data optimized using Moldflow was accurate and reasonable, significantly reducing warpage in open molded product and significantly improving product quality. Simulation validation validated results.