Automotive engine timing chain covers are manufactured using aluminum alloy high-pressure casting. Installed on the side of engine, they serve as a protective cover for engine timing gear and chain. Lightweighting has always been a key goal in automotive component development, and aluminum alloy high-pressure castings tend to be thin-walled and complex in shape. Due to unique structure and shape of timing chain cover, coupled with stringent requirements for size, performance, and surface quality, casting process presents significant challenges. Therefore, in the early stages of development, numerical simulation analysis of gating systems with different structures using AnyCasting software was used to quickly determine optimal process solution, reducing mold development costs and time.
Figure 1 shows a 3D image of a newly developed timing chain cover. Part appears to be horn-shaped, with a large hollowed-out area in the center, reinforcing ribs in thin-walled areas, and irregular, narrow sealing surfaces around perimeter. Casting's overall dimensions are 590 mm * 356 mm * 46 mm, with a weight of 2.135 kg. Central wall thickness is typically 2 mm. Casting is made of ADC12 alloy, and required sealing performance is a maximum allowable leakage of 10 mL/min at a pressure of 100 kPa. Because timing chain cover is mounted on the side of engine and serves as a visual component, surface defects such as flow marks and cold shuts are not permitted.
Wall thickness and draft angle of timing chain cover were analyzed (see Figure 2). Central wall thickness is 2 mm, with a maximum edge thickness of 21.9 mm. Draft angle is ≥1.5°, meeting process requirements. Parting line is determined based on casting's draft angle. Main parting surface is located at maximum contour of casting and is a flat parting surface. Partial parting surfaces are designed based on the shape of parting line for any irregular shapes. Since casting lacks side cores or recesses, a side core pull parting surface is not required.
Location of ingate is crucial for gating system design. Ingates are generally located in thick wall area of casting at parting surface to facilitate injection pressure transmission. For this timing chain cover, ingate can be located at thick wall of outer edge. To prevent ingate from impacting core, casting is suitably filled with multiple branch runners in separate areas.

 

Figure 1: 3D view of timing chain cover

 

Figure 2: Determination of casting parting surface
Projected area of casting is 980 cm², and projected area of gating system is 30% of projected area, for a total projected area of approximately 1,274 cm². Because casting is a thin-walled seal, injection pressure is 100 MPa, with a safety factor of 1.2. After calculation, a 16,000 kN die-casting machine was selected.
Based on wall thickness and structural characteristics of casting, ingate filling speed is 50 m/s, and filling time is 0.03 s. Calculated cross-sectional area of ingate is 658 mm². Chamber diameter was selected as φ105 mm, and calculated ejection speed of punch was 3.8 m/s.
Figure 3 shows commonly used gating systems for horizontal cold chamber die casting machines. Horizontal gating system provides a smooth and controllable pouring process, is suitable for most parts. Vertical gating system is suitable for parts with complex or special structures, particularly those shown in Figures 3c and 3d. However, due to structural design of runners, inconsistent gate heights can complicate initial casting process adjustments. Therefore, numerical simulation is required to determine feasibility of process before finalizing design.
Due to unique and complex structure of timing chain cover, gating system schemes shown in Figures 3a and 3c were initially selected during design phase (see Figure 4). Horizontal runner enters from one side of timing chain cover, with slag collection ladles and exhaust channels on the other three sides. Vertical runner arrangement positions irregular "ram's horn" shape of part upward, with runners filling from both sides of casting. Slag collection ladles are provided at the top and bottom of filling end. AnyCasting software was used to analyze filling, venting, solidification, and temperature processes to determine optimal process plan.

 

Figure 3 Common gating system structure for horizontal die castings
1. Casting 2. Runner

 

Figure 4 Timing chain cover structure with gating system
1. Runner 2. Casting 3. Slag bag
Before using AnyCasting software for mold flow analysis, modeled entities in original 3D file must be exported as STL format and imported into simulation software. Variable meshing was then performed. When meshing, ensure that each cross-section of part in X, Y, and Z directions has at least three layers of mesh, including gate and overflow channel. Sufficient meshing ensures accurate simulation calculations. Timing chain cover's automatic meshing minimum size was set to 1, and maximum size ratio was set to 2. Automatic transition smoothing factor was set to 1.1, and maximum size ratio was set to 3. A total of 5.67 million meshes were generated for horizontal runner, and 4.82 million for vertical runner.
Timing chain cover is made of ADC12 alloy, with a liquidus temperature of 595℃ and a solidus temperature of 540℃. Pouring temperature is set at 645℃, and solidification shrinkage volume change is 7.14%. Die casting mold in contact with aluminum alloy is made of imported hot-work die steel W350, as per design requirements. The total mass of casting including gating system is 4.77 kg, cylinder diameter is φ105 mm, and length is 780 mm. First-stage injection speed of punch is 0.15 m/s, and second-stage fast injection speed is 3.8 m/s.
A simulation analysis of timing chain cover using horizontal single-sided gating system shown in Figure 4a is performed, and results are shown in Figure 5. It can be seen that: ① Filling process is relatively smooth, with high-speed switching starting at 0.4542 s and completing mold filling at 0.4972 s, resulting in a casting filling time of 0.0430 s. Because middle region B has thin walls and numerous voids that hinder aluminum filling, boost pressure struggles to transfer from region B to thicker region C, leading to casting defects such as cold shut and poor filling in region C, further from runner. ② Analysis of air entrapment during filling process revealed no significant turbulence or air entrapment within casting cavity. Overflow and venting slots were strategically placed at the end of filling process to facilitate gas discharge. ③ Gate velocity was unstable during filling process. As shown in Figure 5c, gate velocity at a certain time instant in the middle region exceeded 80 m/s, resulting in jet flow, poor filling in region C, and severe mold erosion, impacting casting quality and mold life. ④ During solidification, due to uneven wall thickness of casting (2 mm in the middle), region B solidified first, while region C, with its thicker walls (partially up to 21.9 mm) and further from runner, solidified last, forming isolated liquid phases that resulted in shrinkage cavities in region C.

 

Figure 5 Numerical Simulation of Horizontal Single-Sided Filling
Based on numerical simulation analysis of horizontal gating system for timing chain cover, this gating system presents a high risk of casting defects during filling and solidification processes, and reduces mold life, making it unsuitable for die-casting of timing chain covers.
A simulation analysis of vertical double-sided filling gating system for timing chain cover was performed according to Figure 4, with results shown in Figure 6. It can be seen that: ① Filling process achieves sequential filling of casting, with high-speed switching starting at 0.4479 s and completing filling at 0.4776 s, for a total filling time of 0.0297 s. This enables rapid filling of thin-walled castings. Furthermore, bidirectional filling is employed, with ingates entering mold cavity from thick wall on both sides, facilitating transmission of injection pressure. ② Analysis of air entrainment during filling process: Lower branch runner corresponds to internal cavity of casting. After entering cavity, molten metal impacts cavity wall, causing localized turbulence and air entrainment (see Figure 6d). Overflow and venting slots are strategically placed in upper air entrainment area at the end of filling process to facilitate gas discharge. However, no venting duct is available in lower air entrainment area. ③ Velocity of ingate during filling is relatively stable, with an instantaneous velocity of less than 60 m/s, making it suitable for filling thin-walled aluminum alloy parts. ④ During solidification, central thin-walled area solidifies first, followed by thicker wall areas on either side. During solidification, ingate increases pressure and shrinkage in thicker wall areas on either side, eliminating isolated liquid phase regions and risk of shrinkage cavities.

 

Figure 6: Numerical simulation of longitudinal double-sided filling
Based on numerical simulation of longitudinal gating system for timing chain cover, this gating system is suitable for this casting. However, there are issues with air entrainment process analysis: vortex air entrainment occurs in the center of cavity during filling, and no venting duct is available in lower air entrainment area. This results in internal porosity defects, which can severely affect sealing of casting. Longitudinal double-sided gating system was further optimized, as shown in Figure 7. Slag collection bag at lower metal confluence point was replaced with a branch runner, accelerating filling speed in this area, ensuring a smoother and more even filling process. Two slag collection bags were added to central through-hole, based on metal flow direction and location of air entrapment, to improve air entrapment. Optimized gating system exhibits a "U"-shaped filling pattern. Numerical simulations, shown in Figure 7, demonstrate smooth, sequential filling and unimpeded venting. Two added overflow troughs assist in venting during filling process. Solidification analysis revealed no isolated liquid phase regions, eliminating risk of shrinkage cavities. Temperature field analysis confirmed a balanced casting temperature, significantly reducing risk of shrinkage cavities and deformation during cooling. Based on these simulation results, longitudinal U-shaped gating system is suitable for die-casting this timing chain cover.

 

Figure 7 Numerical simulation of longitudinal U-shaped filling

 

Figure 8 Timing chain cover part
Based on results of numerical simulation analysis of longitudinal gating system for timing chain cover, a new product mold was developed and trial-produced using this longitudinal U-shaped gating system. Using a 16,000 kN die-casting machine, die-casting parameters optimized by numerical simulation were: casting pressure of 100 MPa, slow shot speed of 0.15 m/s, and fast shot speed of 3.8 m/s. Casting exhibited no obvious defects such as flow marks or cold shuts. Cleaned timing chain cover part, shown in Figure 8, was subjected to X-ray inspection and seal testing, demonstrating excellent product quality, with OTS sample passing the first pass. It has now entered mass production, with a product qualification rate exceeding 96%, surpassing similar products in quality.