# Optimization Strategy for Precision Casting Process Scheme

Precision casting (such as lost wax casting and investment casting) serves as a core technology for manufacturing complex and high-precision parts, widely applied in aerospace, automobile, medical device and other industries. Its core target is to ensure the dimensional accuracy (IT5-IT7) and surface quality (Ra≤1.6μm) of castings, while reducing internal defects including shrinkage cavity, porosity and cracks. This paper systematically illustrates the optimization scheme of precision casting technology from the aspects of structural design, process simulation, material treatment and quality control.

## 1. Optimization of Casting Structure Design: Reducing Process Difficulty at the Source

Structural design is the starting point of process optimization, and unreasonable structure will directly cause casting defects. The main optimization measures are as follows:

1. Uniform wall thickness. Avoid sudden thickness change; inclined transition and rounded corner shall be designed at the junction of thick and thin walls to eliminate hot spots prone to shrinkage defects. For instance, the wall thickness deviation of aero-engine blades shall be controlled within ±0.1 mm. CAD modeling is adopted to simulate heat distribution and adjust structural parameters to eliminate local overheating.

2. Simplify complex structures. For deep cavities and narrow grooves with poor mold filling performance, block casting combined with welding or reserved process holes can be adopted to improve molten metal filling. As for orthopedic implants in medical equipment, complex curved surfaces are divided into castable modules and then spliced by laser welding.

3. Set process allowance. According to the shrinkage rate of different alloys (about 1.5% for stainless steel and 2% for aluminum alloy), machining allowance is reserved on the mold to compensate dimensional deviation caused by cooling shrinkage. Meanwhile, reasonable draft angle (0.5°-2°) is designed to prevent damage to wax patterns during demolding.

## 2. Simulation Optimization of Process Scheme: Data-driven Process Decision

CAE software including ProCAST and MAGMAsoft is used to simulate the casting process, predict potential defects in advance and optimize technical parameters.

1. Gating system optimization. Simulate the flow path of molten metal to adjust the sprue position (bottom gating for reduced air entrapment), riser size for feeding efficiency and runner section to avoid sand erosion caused by excessive flow velocity. Symmetrical multi-gating design is adopted in turbine blade casting to realize uniform mold filling and reduce porosity.

2. Adjust key process parameters. Explore the influence of pouring temperature (1550-1600℃ for stainless steel, 700-750℃ for aluminum alloy) and pouring speed (0.5-1.5 m/s) on filling status and defects. High pouring speed is recommended for thin-walled parts to prevent cold shut, while properly low pouring temperature for thick-walled castings to reduce shrinkage porosity.

3. Optimize cooling schedule. Simulate temperature field distribution and adopt stepwise cooling, which cools hot spots rapidly and controls overall cooling rate slowly, so as to lower thermal stress and deformation. Water-cooled molds are used for local cooling of hot zones in automotive engine cylinder block casting to realize uniform shrinkage.

## 3. Optimization of Material and Melting Process: Improving Purity of Molten Metal

The quality of molten metal determines the comprehensive performance of castings.

1. Alloy composition control. Strictly limit impurity content (sulfur ≤0.01%, phosphorus ≤0.02%) and add trace elements to improve casting performance, such as titanium grain refiner added in aluminum alloy. For aerospace titanium alloy castings, oxygen content shall be controlled below 0.15% to avoid embrittlement.

2. Degassing and slag removal during melting. Adopt vacuum melting, inert gas blowing (argon) and flux addition such as CaF₂ to remove gas and inclusions. Vacuum induction melting combined with electroslag remelting is applied in stainless steel casting to reduce oxygen content below 0.005%.

3. Precise pouring temperature control. Infrared thermometers are used for real-time temperature monitoring to prevent poor fluidity from supercooling and excessive oxidation as well as shrinkage defects from overheating. The pouring temperature of superalloy castings needs to be controlled within a tolerance of ±5℃.

## 4. Optimization of Pattern Making and Shell Molding Process: Enhancing Surface Accuracy

Wax pattern and ceramic shell quality are critical to lost wax casting.

1. Wax pattern precision control. Select low-shrinkage pattern materials (paraffin-stearic acid mixed wax with shrinkage ≤0.5%) and high-precision injection molding equipment with repeat accuracy of ±0.02 mm. Polishing treatment is required at wax pattern joints to avoid shell defects.

2. Shell molding optimization. Multi-layer coating is applied: fine zircon powder coating for the inner layer to ensure smooth surface, and coarse corundum powder coating for the outer layer to improve shell strength. The shell drying environment is controlled at humidity 30%-50% and temperature 25-35℃ to prevent cracking. Aerospace blades require 5 to 7 coating layers with drying time no less than 8 hours for each layer.

3. Dewaxing improvement. Adopt steam dewaxing (120-150℃) or microwave dewaxing to eliminate wax residue and shell porosity. Segmented dewaxing is used for large-scale castings to reduce shell deformation.

## 5. Post-treatment and Closed-loop Quality Optimization: Continuous Process Improvement

1. Optimize post-treatment process. Adopt vibration shell cleaning, sand blasting (Ra≤1.6μm) and electrochemical polishing to upgrade surface finish. Heat treatment including solution treatment and aging treatment is carried out to eliminate residual stress and enhance mechanical properties. Vacuum annealing at 800-900℃ is applied for titanium alloy castings to relieve stress.

2. Quality inspection and feedback mechanism. Nondestructive testing technologies such as X-ray flaw detection, ultrasonic testing and CT scanning are used for internal defect inspection, while coordinate measuring instruments for dimensional verification. Test data is fed back to process design to realize iterative optimization of gating system, riser layout and wax pattern dimension, forming a closed-loop quality management system.

## Conclusion

The optimization of precision casting technology is a systematic project requiring full-process coordination covering structural design, simulation analysis, material smelting, pattern-shell manufacturing and post-treatment. Through data-based simulation design, strict quality control and continuous process iteration, the dimensional accuracy and qualification rate of precision castings can be significantly improved to meet the market demand for high-precision components. In the future, with the combination of AI defect prediction and 3D printed wax pattern technology, precision casting will develop further towards intelligence and customized production.