In the automotive industry, clutch pressure plates play a critical role in ensuring driving safety by transmitting engine power to the transmission system. These components, primarily made from ductile iron castings, face challenges such as uneven temperature fields during casting, leading to non-uniform distribution of yield strength and elastic modulus. This results in residual stresses that affect dimensional accuracy, service life, and forming quality. To address these issues, I employed finite element software ProCAST to simulate the filling and solidification processes of a ductile iron clutch pressure plate casting. This study focuses on analyzing temperature and stress variations during solidification, residual stress distribution, and deformation displacements, providing insights for optimizing casting processes and enhancing product quality in ductile iron castings.
The clutch pressure plate, a disk-like structure with six lugs on the outer circumference, was modeled with overall dimensions of 254.7 mm in length, an outer diameter of 215.9 mm, and an inner hole diameter of 116 mm. The average wall thickness is 10 mm, with maximum and minimum thicknesses of 11.9 mm at the lugs and 5.5 mm at the plate surface, respectively. The material used is GGV30 ductile iron, with a chemical composition provided in Table 1. The total mass of the casting is 2.06 kg. The three-dimensional model was created and assembled with the gating system in UG software before importing into ProCAST for analysis. This approach ensures accurate representation of the ductile iron castings’ geometry for simulation.
| Element | C | Si | Mn | Cr | Cu | Mg |
|---|---|---|---|---|---|---|
| Content | 3.65 | 2.65 | 0.27 | 0.019 | 0.097 | 0.018 |
For mesh generation, I used tetrahedral elements in ProCAST’s Visual-Mesh module. After checking and repairing surface connectivity issues, overlaps, and intersections, surface meshes were generated and optimized to eliminate small angles and damaged triangles. Volume meshes were then created with a element size of 3 mm, resulting in 157,390 surface elements, 3,225,544 volume elements, and 569,502 nodes. This mesh density balances computational accuracy and efficiency for simulating ductile iron castings. The mesh quality was verified to avoid invalid or negative Jacobian elements, ensuring reliable simulation results.
Parameter settings for the simulation are summarized in Table 2. The casting conditions included a pouring temperature of 1419°C, pouring speed of 0.55 m/s, and pouring time of 7.5 s, with ambient temperature at 25°C and natural air cooling as the surface heat flow condition. The mold material was resin sand, and gravity-driven filling was simulated with an acceleration of 9.8 m/s² in the negative y-direction. The simulation ran for 50,000 steps, stopping when the temperature fell below 500°C. These parameters are typical for ductile iron castings to ensure realistic modeling of thermal and stress behaviors.
| Parameter | Value |
|---|---|
| Material (Casting) | GGV30 Ductile Iron |
| Material (Mold) | Resin Sand |
| Boundary Condition (Interface Heat Transfer Coefficient) | 500 W/m²K |
| Pouring Temperature | 1419°C |
| Pouring Time | 7.5 s |
| Pouring Method | Gravity Pouring |
| Cooling Method | Natural Air Cooling |
| Mold Temperature | 25°C |
| Gravity Direction | Negative Y |
| Gravity Acceleration | 9.8 m/s² |
| Simulation Steps | 50,000 |
| Stopping Condition (Temperature) | <500°C |
The temperature field during filling was analyzed to understand the behavior of ductile iron castings. Metal flow initiated from the pouring cup, filled the sprue, and progressed through the runner, ingates, and risers before entering the mold cavity via the lugs. The entire filling process took 7.35 s, with no defects like cold shuts or misruns observed. At 5.09 s, the lower part of the pressure plate near the inner circle and small lugs cooled to approximately 1300°C, while the upper region remained hotter. Upon complete filling, the temperature distribution showed a maximum gradient of about 124°C, with all areas in the liquid state. This non-uniform cooling in ductile iron castings can lead to residual stresses and potential defects, highlighting the importance of controlled solidification.
Solidification analysis revealed the phase change dynamics in ductile iron castings. The solid fraction distribution indicated that solidification started from the inner and outer regions of the pressure plate, progressing towards the center, with the lugs connected to risers solidifying last. This pattern forms a convergent solidification sequence from the edges to the middle. To quantify this, I selected specific nodes on the casting, as shown in Figure 5, and plotted their solid fraction over time in Figure 6. Nodes near the inner circle (e.g., point 1) solidified first, followed by the plate surface (point 2), and finally the large lugs (point 3), with point 1 solidifying approximately 90 s earlier than point 3. Similarly, points 4 and 6 (inner circle and small lugs) solidified nearly simultaneously, while point 5 (central plate) solidified last, confirming the edge-to-center solidification in ductile iron castings. The solid fraction $f_s$ can be described by the Scheil equation for non-equilibrium solidification: $$ f_s = 1 – \left( \frac{T_m – T}{T_m – T_l} \right)^{1/(k-1)} $$ where $T_m$ is the melting temperature, $T_l$ is the liquidus temperature, and $k$ is the partition coefficient. This equation helps in predicting the solidification behavior and related stresses in ductile iron castings.
Residual stress analysis in ductile iron castings showed that the equivalent stress distribution on the pressure plate surface was non-uniform, with higher stresses near the inner circle and large lugs, reaching up to 360 MPa, indicating a risk of cracking. The stress generally decreased from the inner to outer regions. I examined stress evolution at selected nodes (Figure 8) over time, as shown in Figure 9. The stress curve exhibited three phases: a rapid increase during initial cooling due to constrained contraction, a decrease during secondary phase transformations that reduce hindrance, and a gradual increase post-solidification due to differential cooling rates. The von Mises stress $\sigma_v$ is given by: $$ \sigma_v = \sqrt{ \frac{1}{2} \left[ (\sigma_x – \sigma_y)^2 + (\sigma_y – \sigma_z)^2 + (\sigma_z – \sigma_x)^2 + 6(\tau_{xy}^2 + \tau_{yz}^2 + \tau_{zx}^2) \right] } $$ where $\sigma_x$, $\sigma_y$, $\sigma_z$ are normal stresses and $\tau_{xy}$, $\tau_{yz}$, $\tau_{zx}$ are shear stresses. This formula is crucial for assessing the multiaxial stress state in ductile iron castings and predicting failure zones.
Deformation analysis focused on the Z-direction (normal to the working surface) displacements in ductile iron castings. The deformation map (Figure 10) revealed an outward bulge (negative displacement) near the outer edge and an inward concavity (positive displacement) near the inner edge, reducing flatness accuracy. I measured displacements at 14 nodes along a horizontal line (Figure 11 and Table 3), with the curve in Figure 12 showing symmetric variation: negative displacements at the outer nodes and positive at the inner nodes. The displacement $u_z$ can be related to strain $\epsilon_z$ through: $$ \epsilon_z = \frac{\partial u_z}{\partial z} $$ and the resulting deformation affects the machining tolerance of ductile iron castings. This non-uniform deformation is attributed to the thermal gradients and constraint conditions during cooling, emphasizing the need for optimized cooling rates in ductile iron castings.
| Node | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Displacement (10⁻³ cm) | -1.4 | -1.0 | -0.4 | 0.3 | 1.08 | 1.78 | 2.5 | 2.18 | 1.58 | 0.74 | 0.07 | -0.41 | -0.78 | -0.83 |
Discussion of the results highlights that the temperature gradient during filling and solidification in ductile iron castings contributes significantly to residual stresses. The maximum temperature difference of 124°C at the end of filling, combined with varied wall thicknesses and riser design, led to uneven cooling rates. This induced thermal stresses that persisted as residual stresses, affecting the dimensional stability of ductile iron castings. The stress concentration in inner regions and large lugs is due to higher constraint and slower cooling, aligning with findings in other studies on ductile iron castings. The deformation pattern, characterized by outer convexity and inner concavity, underscores the impact of asymmetric solidification on flatness, which is critical for machining operations in automotive applications involving ductile iron castings.
In conclusion, the simulation of ductile iron castings for clutch pressure plates using ProCAST provided detailed insights into temperature fields, solidification sequences, residual stresses, and deformations. The residual stress distribution showed higher values in inner circles and lug connections, posing crack risks, while deformation reduced flatness accuracy. These findings emphasize the importance of optimizing pouring parameters, riser design, and cooling conditions to minimize defects in ductile iron castings. Future work could explore alternative gating systems or heat treatments to alleviate residual stresses in ductile iron castings, further enhancing the quality and reliability of automotive components made from ductile iron castings.