In industrial applications, lifting arms are critical automation components that mimic human arm movements for tasks such as grasping and transporting objects. Due to their complex geometry, these components often face defects like shrinkage porosity and cavities during the lost wax investment casting process. This study focuses on optimizing the casting process for a lifting arm made of ZG0Cr18Ni9Ti stainless steel through numerical simulation and experimental design. The initial casting scheme was analyzed using ProCAST software, revealing significant shrinkage defects. Subsequently, the gating system was redesigned, and key process parameters—pouring temperature, pouring speed, and mold shell preheating temperature—were optimized via orthogonal experiments. The results demonstrate that the optimized parameters substantially reduce shrinkage defects and enhance production efficiency.
The lifting arm features a uniform wall thickness of approximately 6 mm, with overall dimensions of 70 mm × 45 mm × 57 mm. Its structure includes a stepped shaft section, a connecting hole segment, and a U-shaped claw working area. The material composition of ZG0Cr18Ni9Ti is detailed in Table 1. Precise control during the lost wax investment casting process is essential to avoid defects such as gas pores and shrinkage, which can compromise the component’s integrity.
| Element | C | P | Cr | Mn | Ni | Si | S | Ti |
|---|---|---|---|---|---|---|---|---|
| Content | ≤0.8 | ≤0.045 | 17.0–20.0 | 0.8–2.0 | 8.0–11.0 | ≤1.5 | ≤0.030 | 0.3–0.7 |
The lost wax investment casting process begins with the design of the gating system, which employs a horizontal sprue, vertical sprue, and ingates to ensure stable filling and directional solidification. A cluster of six castings per mold was utilized to improve productivity. The three-dimensional model of the lifting arm and gating system was meshed with a element size of 4 mm, resulting in 34,928 nodes and 249,485 elements. Key simulation parameters included a mold shell thickness of 6 mm, heat transfer coefficient of 500 W/(m²·K), and interfacial heat exchange coefficient of 1,000 W/(m²·K). The initial pouring speed was determined using the Kalkin formula:
$$ v = \frac{h \cdot \delta}{T} $$
where \( v \) is the pouring speed (cm/s), \( h \) is the casting height (cm), \( \delta \) is the wall thickness (cm), and \( T \) is the pouring temperature (°C). Based on this, an initial pouring speed of 350 mm/s was adopted for simulation. Other parameters included a pouring temperature of 1,530 °C, mold shell preheating temperature of 1,000 °C, and gravity direction set along the negative Y-axis.
Simulation of the initial scheme revealed a filling time of approximately 3.9 s, with the mold cavity filling steadily. However, the solidification analysis indicated that shrinkage porosity primarily occurred at the junctions of the shaft and connecting regions, as well as in the vertical sprue. The solidification fraction reached near unity at 374 s, with complete cooling to 1,235 °C taking 778 s. The shrinkage defect volume fraction exceeded 1.0 in critical areas, highlighting the need for gating system modifications.
To address these issues, two optimized gating systems (Scheme A and Scheme B) were proposed. Scheme A incorporated additional vents at shrinkage-prone areas and interconnected adjacent castings at the U-claw sections to minimize thermal hotspots. Scheme B further enhanced Scheme A by adding extra ingates and enlarging sprue diameters to improve feeding and gas expulsion. Comparative simulations showed that Scheme B significantly reduced the shrinkage ratio to 2.92%, compared to over 10% in Scheme A and the initial design. This underscores the importance of gating design in the lost wax investment casting process.
Further optimization involved orthogonal experiments to evaluate the effects of pouring temperature (A), pouring speed (B), and mold shell preheating temperature (C). The factors and levels are listed in Table 2. A total of nine experiments were conducted, with results analyzed based on shrinkage porosity volume and filling time, as summarized in Table 3.
| Level | A: Pouring Temperature (°C) | B: Pouring Speed (mm/s) | C: Shell Preheating Temperature (°C) |
|---|---|---|---|
| 1 | 1,500 | 350 | 1,000 |
| 2 | 1,530 | 450 | 1,050 |
| 3 | 1,550 | 550 | 1,100 |
| Experiment | A | B | C | Filling Time (s) | Shrinkage Ratio (%) |
|---|---|---|---|---|---|
| L1 | 1 | 1 | 1 | 3.8078 | 1.2453 |
| L2 | 1 | 2 | 2 | 3.8431 | 1.1471 |
| L3 | 1 | 3 | 3 | 4.0174 | 1.3162 |
| L4 | 2 | 1 | 2 | 3.9403 | 1.2634 |
| L5 | 2 | 2 | 3 | 3.7968 | 1.2852 |
| L6 | 2 | 3 | 1 | 4.0297 | 1.2307 |
| L7 | 3 | 1 | 3 | 3.8659 | 1.3176 |
| L8 | 3 | 2 | 2 | 3.9273 | 1.2759 |
| L9 | 3 | 3 | 1 | 3.9167 | 1.2831 |
Analysis of the orthogonal experiments indicated that lower pouring temperatures (Level 1: 1,500 °C) reduced shrinkage, as higher temperatures increase liquid contraction. Moderate pouring speeds (Level 2: 450 mm/s) optimized filling without causing turbulence or cold shuts. Lower shell preheating temperatures (Level 2: 1,050 °C) minimized shrinkage by controlling solidification rates. The optimal parameter combination was identified as A1B2C2, with a pouring temperature of 1,500 °C, pouring speed of 450 mm/s, and shell preheating temperature of 1,050 °C. This combination resulted in a shrinkage ratio of 1.1471% and a filling time of 3.8431 s, as shown in Table 4.
| Parameter | Value |
|---|---|
| Pouring Temperature (°C) | 1,500 |
| Pouring Speed (mm/s) | 450 |
| Shell Preheating Temperature (°C) | 1,050 |
| Filling Time (s) | 3.8431 |
| Shrinkage Ratio (%) | 1.1471 |
Validation simulations under the optimal conditions confirmed that shrinkage defects were predominantly confined to the main sprue, with minimal impact on the casting quality. The lost wax investment casting process, when optimized through systematic gating design and parameter adjustment, significantly enhances the integrity and efficiency of producing complex components like the lifting arm. This approach provides a reliable framework for similar applications in precision investment casting.
In conclusion, the integration of numerical simulation and orthogonal experimentation in the lost wax investment casting process enables effective optimization of gating systems and process parameters. The proposed methodology reduces defects and improves production outcomes, demonstrating the value of advanced modeling techniques in modern foundry practices. Future work could explore additional factors such as cooling rate control and alloy modifications to further refine the lost wax investment casting process for high-performance components.