As installation carrier of camshaft, camshaft cover is tightly connected with cylinder head and used to seal cylinder head, valve chamber and camshaft. It is a key component of engine assembly. Compared with other automotive parts, camshaft covers are prone to deformation, require high surface quality and dimensional accuracy. Die castings are widely used in many industrial fields, especially in automobile manufacturing. If design of die-casting mold pouring system is unreasonable, air is easily trapped during high-speed die-casting process, defects such as pores, shrinkage cavities, and shrinkage porosity will be formed after solidification, which will adversely affect mechanical properties of die-casting parts, especially large and medium-sized precision and complex parts.
Computer simulation has been widely used in the field of die casting. Through simulation of mold filling, solidification and other processes, casting defects can be effectively predicted and mold design optimized. In order to optimize process design, improve die casting quality and shorten production cycle. Based on ProCAST software, die-casting mold pouring system of an automobile aluminum alloy camshaft cover part is optimized and designed to provide a reference for its application.

Aluminum alloy camshaft cover part has a rectangular frame structure, and its three-dimensional model is shown in Figure 1. Outline size is 361mm*160mm*44mm, volume is about 4.34* 105mm3, maximum wall thickness is 8mm (see circled position in Figure 1a), and minimum wall thickness is 4mm. Based on structural characteristics of casting and design theory of gating system, three gating system schemes were designed, as shown in Figure 2. Plan 1 has 6 ingates, distributed at 5 beam positions and ends with U-shaped grooves on long side of casting. In order to prevent air entrainment and shrinkage holes on short side of casting near semicircular platform near the gate, an overflow groove is added in Plan 2, as shown in Figure 2b. Considering that the two horizontal sprues at the end of casting are prone to air entrapment at intersection of liquid flows, Plan 3 merges two inner gates on the left into one, and retains overflow tank added in Plan 2, as shown in Figure 2c .

 

(a) Outside of casting (b) Inside of casting
Figure 1 Three-dimensional view of camshaft cover casting

Table 1 Main design parameters of die-casting mold

 

(a) Option 1 (b) Option 2 (c) Option 3
Figure 2 Design scheme of camshaft cover casting gating system

Table 2 Calculation conditions
Simulation results of filling process of three gating system design schemes are shown in Figure 3. Figure 3a shows filling process of Scheme 1. It can be seen that molten metal enters mold cavity along sprue, and overall sequential filling is satisfied. However, due to frame structure of camshaft cover, molten metal flows and merges multiple times, increasing tendency of air entrainment. When mold filling rate is 50%, molten metal merges at circle marked position, and compressed gas cannot be discharged through cavity formed by casting beam, easily causing gas entrainment and welding marks here. Filling process of Scheme 2 is shown in Figure 3b. Compared with Scheme 1, flow pattern of molten metal is similar. When filling rate is 50%, molten metal also forms a flow convergence at circle marked position, but merged flow is in the cavity channel, so possibility of producing pores and weld marks is low. At the same time, since Plan 2 has an overflow groove on one side of casting truncated cone, air entrainment and shrinkage cavity defects can be reduced. Compared with the first two schemes, Scheme 3 has a confluence position of liquid flow in circle-marked area close to side of overflow tank and also at position of cavity channel, see Figure 3c. Option 3 avoids intersection and mutual impact of two molten metals inside casting, thereby reducing possibility of eddy currents, air entrapment, and oxidized slag inclusions, pouring and filling process is more reasonable. Judging from filling status when mold filling rate is 70% and 95%, filling conditions of three gating system designs are similar. After mold cavity is filled, cold and dirty metal liquid, excess metal liquid and air in cavity can smoothly enter overflow tank, be discharged.

 

(a) Scheme 1 filling process

 

(b) Scheme 2 filling process

 

(c) Scheme 3 filling process
Figure 3 Filling process of castings under three pouring schemes

 

(a) Option 1

 

(b) Option 2

 

(c) Option 3
Figure 4 Solidification process of three pouring system solutions

 

(a) Option 1 (b) Option 2 (c) Option 3
Figure 5 Prediction of shrinkage cavities in castings under different pouring schemes

 

(a) Filling process

 

(b) Solidification process
Figure 6 Filling process and solidification process of the improved plan
Through analysis and comparison of filling and solidification process, shrinkage cavities and shrinkage porosity, it is believed that option 3 has the best effect. However, according to filling simulation results the mold is 50% filled in Figure 3c, molten metal convergence is on cavity channel, filling and exhaust conditions are good. At the same time, simulation results of shrinkage cavities and shrinkage porosity show that pores at casting B have not changed significantly among the three solutions. Therefore, it is considered to remove overflow groove near B in Figure 4f, which can reduce temperature in this area, accelerate solidification, and improve die-casting efficiency. Simulation results of shrinkage cavities, porosity and trial castings of improved scheme are shown in Figure 7. Compared with results in Scheme 3 (see Figure 5c), Figure 7a shows that one of the three shrinkage cavities in thick area of casting was directly eliminated, and volume of the other two shrinkage cavities was reduced. Volume of shrinkage cavities in casting was 1.43×10-3cm3. Simulation results show that optimized scheme meets quality requirements of castings, so optimized scheme is used for mold opening and mold trial. Trial mold casting is processed and shown in Figure 7b.

 

(a) Improvement plan Shrinkage and porosity (b) Trial die casting

Figure 7 Shrinkage simulation results and trial castings of improved scheme

 

(a) Casting D (b) Casting E (c) Casting F

 

(d) Casting cutting section
Figure 8 Casting defect detection X-ray flaw detection

(1) Reducing number of lateral sprues in frame-type camshaft cover castings can improve flow pattern of molten metal and reduce internal pores caused by gas entrainment.
(2) Optimization plan of gating system reduces temperature in this area by removing overflow groove near semicircular platform of casting, and can eliminate pores formed by solidification shrinkage of many thick parts. The overall solidification time of casting is shortened to 46.7 seconds, which improves production efficiency.
(3) Casting cutting and X-ray inspection only found two holes in non-critical locations, and quality of casting meets usage requirements.