Abstract:
This paper focuses on the optimization of the investment casting process for a 304 stainless steel ball valve. Through simulation and defect analysis using ProCAST software, the causes of shrinkage porosity and shrinkage holes in the traditional process were identified. By redesigning the gating system and adjusting process parameters, an optimal set of parameters was found to eliminate defects in the valve body and flange corners.
1. Introduction
With the improvement of global technology, the demand for energy is increasing, and material conservation has become a goal for all countries. The traditional casting industry is labor-intensive and costly, while investment casting can achieve near-net-shape processing. The combination of computer simulation and actual casting processes has been increasingly applied in the casting industry, producing products with scientific basis and meeting production standards. The 304 stainless steel ball valve is widely used in fluid transport control routes and must withstand high pressure, making production quality requirements strict. Defects such as cracks, cold shuts, and shrinkage porosity are not allowed.
2. Defect Analysis of the Traditional Process
2.1 Casting Structure and Pre-processing
The dimensions of the stainless steel ball valve are 186mm×186mm×120mm, with an average flange thickness of 12.5mm. The material is 304 stainless steel. A 3D model of the ball valve was created in SolidWorks and imported into the ProCAST Mesh module for mesh quality inspection. The chemical composition of 304 stainless steel is shown in Table 1.
Table 1: Chemical Composition of 304 Stainless Steel
| Element | C | Cr | Mn | Mo | Ni | S | Si |
|---|---|---|---|---|---|---|---|
| wt% | 0.08 | 18 | 1.5 | 0.5 | 8 | 0.03 | 1 |
2.2 Process Parameter Settings
Simulation parameters were set in the CAST module, with the material edited based on Table 1. The mold shell material was zircon sand. Traditional process parameters included a pouring temperature of 1550°C, mold shell preheating temperature of 1150°C, gravity filling, and pouring speed of 1.5 kg/s. The interface heat transfer coefficient was set to COINC type.
3. Process Improvement
3.1 Gating System Design
The design of the gating system directly affects casting quality. The gating system consists of a pouring basin, sprue, runner, and ingate. Considering the special structure of the ball valve, modifying the structure and size of the gating system can effectively reduce overall shrinkage defects. Two ingates were placed on each end face of the casting to avoid large shrinkage porosity defects at the corners. The design ensured that important machining surfaces of the casting were facing down or sideways.
Table 2: Gating System Design Parameters
| Parameter | Value |
|---|---|
| Sprue length | 100 mm |
| Sprue diameter | 24 mm |
| Runner cross-sectional shape | Circular |
| Ingate cross-sectional shape | Fan-shaped |
| Ingate length | 12 mm |
| Number of ingates | 2 |
3.2 Simulation Analysis Results
After designing the gating system, a 3D model of the casting and gating system was created and imported into ProCAST for defect prediction. The mesh density was set to 4, resulting in 147,072 face grids and 785,303 volume grids. Simulation results showed improved shrinkage porosity at the corners, with a maximum shrinkage porosity rate of 3.75%.
4. Adjustment of Process Parameters
4.1 Orthogonal Experiment Design
Although the redesigned gating system significantly reduced shrinkage porosity, further optimization was needed. An orthogonal experiment was designed to investigate the effects of pouring temperature, pouring speed, and mold shell preheating temperature on maximum shrinkage porosity rate.
Table 3: Orthogonal Experiment Design and Results
| Test No. | Pouring Temp. (°C) | Pouring Speed (kg/s) | Mold Shell Preheating Temp. (°C) | Max. Shrinkage Porosity Rate (%) |
|---|---|---|---|---|
| 1 | 1550 | 1.5 | 1150 | … |
| 2 | 1550 | 1.0 | 1100 | … |
| … | … | … | … | … |
4.2 Range and Variance Analysis
The range (R) and variance analysis were conducted to determine the significance of each factor. The results showed that pouring speed had the greatest impact on shrinkage porosity rate, followed by mold shell preheating temperature, and pouring temperature had the smallest impact.
Table 4: Variance Analysis of Maximum Shrinkage Hole and Shrinkage Porosity
| Factor | Sum of Squares | Degrees of Freedom | Mean Square | F-Value |
|---|---|---|---|---|
| Pouring Temp. | 0.0104 | 2 | 0.0052 | 13.96 |
| Pouring Speed | 1.0637 | 2 | 0.5319 | 119.30 |
| Mold Shell Preheat | 0.3422 | 2 | 0.1711 | 38.41 |
| Error | 0.0356 | 2 | 0.0178 | – |
5. Conclusion
5.1 Simulation Results
Using ProCAST software for casting numerical simulation, the shrinkage porosity of the 304 stainless steel ball valve was analyzed. Results showed severe shrinkage porosity under traditional process conditions, particularly at the valve body and flange corners.
5.2 Optimization Results
By analyzing the causes of shrinkage porosity in the traditional process, the gating system was redesigned and optimized. An orthogonal experiment was conducted to adjust process parameters, resulting in an optimal set of parameters: pouring temperature of 1550°C, pouring speed of 1.0 kg/s, and mold shell preheating temperature of 1150°C. Under these parameters, the maximum shrinkage porosity rate was reduced to 2.29%. Actual production verification confirmed the elimination of defects at the valve body and flange corners.
In conclusion, the investment casting process optimization of the 304 stainless steel ball valve significantly improved product quality by eliminating defects and providing a scientific basis for production.