In the automotive industry, the stability of components is increasingly critical due to complex operating conditions. The fixed disk, which supports the air conditioning compressor, is subject to unpredictable environmental stresses, making the optimization of its manufacturing process essential. This article focuses on the design and refinement of the lost wax investment casting process for a fixed disk component using ProCAST simulation software. Through numerical modeling and orthogonal experiments, key parameters such as shell thickness, preheating temperature, pouring temperature, and pouring speed are analyzed to minimize defects like shrinkage porosity and cavities. The lost wax investment casting method is particularly suitable for this complex, thin-walled part, as it allows for high precision and surface finish. By leveraging simulation, I aim to predict and mitigate issues during filling, solidification, and cooling, thereby enhancing product quality and production efficiency. The insights gained from this study can serve as a reference for similar components in automotive applications, emphasizing the importance of process parameter optimization in lost wax investment casting.
The fixed disk is a critical component made from JDMB2K4140 alloy steel, equivalent to AISI 4140 or ISO 42CrMo4 steel, known for its high strength and toughness. Its chemical composition is detailed in Table 1, which includes elements like carbon, silicon, manganese, chromium, and molybdenum, contributing to its mechanical properties. The part features a complex geometry with uniform wall thickness averaging 7 mm, and dimensions of 126 mm × 75 mm × 72 mm. It comprises a base, curved surfaces, and a through-hole with a diameter of 15 mm. Defects such as slag inclusions and cracks are unacceptable, as they compromise the integrity of the casting. Using UGNX10.0 software, I developed a three-dimensional model to accurately represent the part’s structure, facilitating subsequent simulation and analysis in the lost wax investment casting process.
| Element | C | Si | Mn | Cr | Mo | P | S | Ni | Cu |
|---|---|---|---|---|---|---|---|---|---|
| Content | 0.38-0.45 | 0.17-0.37 | 0.50-0.80 | 0.90-1.20 | 0.15-0.25 | ≤0.035 | ≤0.035 | ≤0.30 | ≤0.30 |
The lost wax investment casting process begins with the design of the gating system, which is crucial for ensuring smooth metal flow and directional solidification. For the fixed disk, I employed a sprue-runner-gate configuration to promote sequential solidification and reduce shrinkage defects. The three-dimensional model of the gating system was created based on the part geometry, and automatic meshing was performed with a grid size of 5 mm, resulting in 56,352 elements and 435,310 nodes. This finite element model, as shown in the illustration below, serves as the foundation for simulation in ProCAST. Key parameters were set to mirror real-world conditions: an environmental temperature of 800°C, constant shell temperature, shell thickness of 6 mm, and material properties for 42CrMo4 steel. The heat transfer coefficient was defined as 500 W/(m²·K), and the convection coefficient between the casting and air was 1000 W/(m²·K). Gravity was accounted for with an acceleration of 9.8 m/s², and the pouring temperature was initially set to 1580°C, above the liquidus temperature of 1494°C, to ensure proper fluidity.
To determine the optimal pouring speed, I applied the Carlin formula, which relates casting height, wall thickness, and pouring temperature. The equation is given by:
$$v = \frac{0.22 \sqrt{h}}{\delta \cdot \ln \frac{T}{380}}$$
where \(v\) is the pouring speed in cm/s, \(h\) is the casting height in cm, \(\delta\) is the wall thickness in cm, and \(T\) is the pouring temperature in °C. For the fixed disk, with \(h = 7.2\) cm, \(\delta = 0.7\) cm, and \(T = 1580°C\), the calculated speed is approximately 266.105 mm/s. Considering practical factors, I used 300 mm/s for initial simulations. The solidus temperature was set to 1425°C, and the shell, composed of six layers of quartz sand and silica sol, was preheated to 1000°C. The top-pouring method was employed in air, with natural cooling post-filling. The negative x-direction was assigned as the gravity direction to simulate realistic conditions.
In the initial process simulation, the filling behavior was analyzed over time. The metal flow remained stable without excessive turbulence or shell erosion. For instance, at 0.577 s, the sprue filled completely, and by 1.423 s, the metal entered the first cavity group. By 3.826 s, near-complete filling was achieved, indicating a smooth process. Solidification analysis revealed that the casting began to solidify at the outer surfaces by 4 s, with the entire part solidifying by 48 s and the full system by 468 s. This sequential solidification from the workpiece inward to the sprue is desirable for minimizing defects. However, shrinkage porosity and cavities were predicted in curved areas and the sprue, with a maximum porosity volume fraction exceeding 1.0%, as illustrated in the simulation results. These defects align with actual production issues, validating the simulation’s accuracy and highlighting the need for parameter optimization in lost wax investment casting.
To optimize the process, I focused on three key parameters: pouring temperature, shell preheating temperature, and pouring speed. These factors significantly influence the quality of lost wax investment casting by affecting fluidity, thermal gradients, and defect formation. Based on industry standards, the pouring temperature for such alloys typically exceeds the liquidus by 50–100°C; for thin-walled complex parts like the fixed disk, a range of 1550–1580°C was selected. Shell preheating temperatures between 800–1015°C are common, but to enhance formability, I considered 900°C, 1000°C, and 1100°C. Pouring speeds of 200 mm/s, 300 mm/s, and 400 mm/s were chosen, balancing filling time and potential turbulence. An orthogonal experiment design, specifically an L9(3^3) array, was employed to efficiently evaluate these parameters, as shown in Table 2.
| Level | Factor A: Pouring Temperature (°C) | Factor B: Pouring Speed (mm/s) | Factor C: Shell Preheating Temperature (°C) |
|---|---|---|---|
| 1 | 1550 | 200 | 900 |
| 2 | 1560 | 300 | 1000 |
| 3 | 1580 | 400 | 1100 |
Nine experimental schemes were simulated, and the results, including filling time and shrinkage porosity rate, are summarized in Table 3. The shrinkage porosity rate, calculated as the sum of porosity values from the simulation, served as the primary quality indicator. For example, Scheme L5 (A2B2C3) exhibited the lowest shrinkage rate of 1.7984%, while L2 (A1B2C2) had the highest at 1.9368%. This variation underscores the impact of parameter combinations on casting quality in lost wax investment casting.
| Experiment No. | Factor A | Factor B | Factor C | Filling Time (s) | Shrinkage Porosity Rate (%) |
|---|---|---|---|---|---|
| L1 | 1 | 1 | 1 | 3.9216 | 1.8529 |
| L2 | 1 | 2 | 2 | 3.7005 | 1.9368 |
| L3 | 1 | 3 | 3 | 3.3782 | 1.8499 |
| L4 | 2 | 1 | 2 | 3.1731 | 1.8775 |
| L5 | 2 | 2 | 3 | 3.7413 | 1.7984 |
| L6 | 2 | 3 | 1 | 3.6028 | 1.8182 |
| L7 | 3 | 1 | 3 | 3.5219 | 1.8972 |
| L8 | 3 | 2 | 2 | 3.3782 | 1.9170 |
| L9 | 3 | 3 | 1 | 3.0732 | 1.8877 |
Using range analysis on the orthogonal results, the optimal parameter combination was identified as A2B2C3, corresponding to a pouring temperature of 1560°C, pouring speed of 300 mm/s, and shell preheating temperature of 1100°C. The shell thickness remained at 6 mm. This optimized setup resulted in a filling time of 3.74 s, solidification time of 368.67 s, and a shrinkage porosity rate of 1.80%, demonstrating a significant improvement over the initial process. Simulation of the optimal scheme showed uniform filling, with complete filling achieved by 2.925 s, and solidification progressing smoothly from the exterior to the interior, reducing defects in critical areas. The shrinkage distribution was minimized, confirming the efficacy of the lost wax investment casting optimization.
In conclusion, the integration of ProCAST simulation and orthogonal experimentation effectively optimized the lost wax investment casting process for the fixed disk. The optimal parameters—shell thickness of 6 mm, shell preheating temperature of 1100°C, pouring temperature of 1560°C, and pouring speed of 300 mm/s—collectively enhance casting quality by minimizing shrinkage defects. This study highlights the importance of parameter prioritization in lost wax investment casting, where factors like pouring temperature and speed must be balanced to achieve desirable outcomes. The methodologies applied here can be extended to other complex castings, promoting efficiency and reliability in automotive component manufacturing. Future work could explore additional variables, such as cooling rates or alloy modifications, to further refine the lost wax investment casting process.