Castings produced by die-casting process have high dimensional accuracy, fine structure, small processing allowance, and high production efficiency. They are widely used in automobiles, home appliances, mechanical equipment and other fields. Valve body studied in this project is an important carrier for installation of automobile oil cylinder parts. Its shape is relatively complex, and it has high requirements for air tightness, precision, and mechanical properties. It also needs to be mass-produced, so it is produced by die-casting process. By analyzing structure and technical requirements of valve body, two die-casting processes were designed, ProCAST software was used for numerical simulation, simulation results were analyzed, and process was optimized. Finally, shrinkage defects of castings were eliminated, and die-casting process that meets the technical requirements of valve body was obtained, which provides a reference for production of such parts.
Graphical results
Casting is a valve body of an automobile oil cylinder component produced by a company. Its three-dimensional structural diagram is shown in Figure 1, where dark gray area is processing surface, processing allowance is 0.3mm, outline size is 115.5mm*74.5mm*71.9mm, maximum wall thickness is 24.6mm, minimum wall thickness is 2mm, main wall thickness is 7mm, weight is 0.36kg, material is ADC12, and its mechanical properties are shown in Table 1. Casting requires deburring, draft angle is 1.5°~3°, shrinkage rate is 0.5%, there are no casting defects such as shrinkage cavities, shrinkage, cracks and cold shuts, and surface is shot peened.

 

Figure 1 Schematic diagram of three-dimensional structure of casting

Table 1 Mechanical properties of ADC12 alloy

 

Figure 2 Schematic diagram of parting surface scheme

 

Figure 3 Schematic diagram of three-dimensional structure of gating system

 

Figure 4 Schematic diagram of three-dimensional structure of overflow trough

 

Figure 5 Schematic diagram of filling process of gating system 1

 

Figure 6 Schematic diagram of filling process of gating system 2

 

Figure 7 Temperature field of casting after solidification
Prediction results of shrinkage defect of gating system 1 are shown in Figure 8. As shown in Figure 8, shrinkage defects are generated in thick wall area of casting. Shrinkage volume of casting is 0.46 cm3 (excluding overflow groove), and shrinkage rate at section is 80% to 90%. It can be seen that casting system 2 also produces shrinkage defects in thick wall area of casting. Shrinkage volume is 0.16 cm3, and shrinkage rate at section is 80% to 85%, which is less than that of casting system 1. Main reason is that molten metal starts to fill thick wall area earlier under conditions of casting system 1. During solidification, temperature of thick wall area is high, solidification rate is slow, it is easier to produce isolated liquid phases and shrinkage defects. Therefore, casting system 2 is better.

 

Figure 8 Schematic diagram of shrinkage defect distribution of gating system 1

 

Figure 9 Simulation results of shrinkage distribution of castings produced by gating system 2

 

Figure 10 Schematic diagram of shrinkage defect of casting after process optimization

 

Figure 11 Actual picture of casting
Through analysis of valve body structure, two die casting processes were designed and numerical simulation was performed. Results show that shrinkage defects occur in thick wall area of casting. Process of filling thick wall area with molten metal first produces more shrinkage defects. Reason for shrinkage defects is that solidification rate of thick wall area of casting is slow, and some areas are isolated because they cannot be compensated by molten metal. Process is optimized by adding a cooling system in thick wall. Results show that optimized casting has no shrinkage defects and has been verified in production, meeting technical requirements.