In my work on casting process design, I focused on the upper half of a front bearing seat, a critical casting part used in automotive and aerospace applications. This casting part serves as a key component in suspension systems, supporting and fixing bearings for wheels, and must exhibit high strength, rigidity, and stability under complex loads. The material chosen was HT-250 gray cast iron, known for its good castability, mechanical properties, and cost-effectiveness, making it suitable for such medium-load applications. The casting part has a complex shell-like structure with asymmetric wall thicknesses, posing challenges like shrinkage porosity, gas holes, and sand inclusions. My goal was to design and optimize the gating system, risers, and chills to eliminate defects through numerical simulation using ProCAST, ensuring a high-quality casting part.
The casting part, as shown in the figure below, has overall dimensions of 1085 mm × 810 mm × 380 mm, with a net weight of 566 kg. Its maximum wall thickness is 150 mm, and the minimum is 20 mm, leading to significant thermal gradients during solidification. The structure includes thin-walled sections and thick bosses, which are prone to hot spots and defects. Technical requirements mandate no shrinkage cavities, porosity, or other flaws that could affect performance. For production, I selected manual molding with furan urea-formaldehyde resin sand for high dimensional accuracy and surface quality. Process parameters included a dimensional tolerance grade of CT13, machining allowance G, shrinkage rate of 0.9%, and a cooling time of 1 hour.
In analyzing the castability of this casting part, I considered two pouring position and parting plane schemes. Scheme A involved pouring from the top, which ensured precision for bearing slots but risked defects in thick sections due to unfavorable solidification patterns. Scheme B involved pouring from the bottom, with the bearing seat face down, improving surface quality and reducing defects like slag inclusions. Based on preliminary assessments, Scheme B was chosen because it promoted better feeding and minimized hot spots, essential for this casting part. The parting plane was set at the bottom surface of the bearing seat to facilitate molding and core assembly.
For the gating system design, I adopted a bottom-pouring semi-closed system to ensure smooth filling, reduce turbulence, and aid slag trapping. The area ratios for the gating channels were set as ΣAsprue : ΣArunner : ΣAgate = 1 : 1.25 : 0.83, based on handbook guidelines for medium-sized gray iron castings. To calculate the choke area, I used the following formulas. First, the pouring time t was estimated using:
$$ t = S_1 \sqrt[3]{\delta G_L} $$
where S1 is a coefficient (taken as 2 for normal conditions), δ is the average wall thickness (approximated as 20 mm from critical sections), and GL is the molten metal weight (700 kg including gating). This yielded t ≈ 43 s. The minimum sprue height HM was calculated using the pressure angle method:
$$ H_M = L \tan \alpha $$
with L = 500 mm (horizontal distance to farthest point) and α = 20°, giving HM ≈ 170 mm. The actual static pressure head Hp was set to 360 mm. The choke area Ag was then derived from the Bernoulli-based Ozan formula:
$$ A_g = \frac{G}{\rho t \mu \sqrt{2g H_p}} $$
where ρ = 7.2 g/cm³ (density), μ = 0.5 (flow coefficient), and g = 981 cm/s². Substituting values, Ag ≈ 17 cm². From this, the individual channel areas were computed: sprue area = 20.4 cm² (50 mm minor diameter, 62 mm major diameter), runner area = 25.5 cm² (split into two trapezoidal sections), and gate area = 17 cm² (divided into four trapezoidal gates). A basin-type pouring cup was designed with a capacity of 125 kg to ensure steady flow. Table 1 summarizes the gating system dimensions for this casting part.
| Component | Total Area (cm²) | Number | Area Each (cm²) | Dimensions |
|---|---|---|---|---|
| Sprue | 20.4 | 1 | 20.4 | Ø50–62 mm, length 600 mm |
| Runner | 25.5 | 2 | 12.75 | Trapezoidal section |
| Gate | 17 | 4 | 4.25 | Trapezoidal section |
I performed numerical simulations using ProCAST to analyze the filling and solidification of this casting part. The model was meshed with 120,164 surface elements and 2,272,604 volume elements. Pouring temperature was set to 1350°C, and pouring time to 43 s. The filling velocity field showed that metal entered the casting part at 1.9 s, spread evenly across the bottom by 10 s, and fully filled the cavity by 43 s. Minimal turbulence was observed, except for mild convergence at central rings, which did not adversely affect the casting part. Temperature distributions indicated cooler thin-walled tops and hotter zones between square holes and the base, highlighting potential defect regions. Defect analysis revealed shrinkage porosity primarily at four locations: top bosses, side holes, and the gating system, with a total shrinkage volume of 0.48% of the casting part volume. Top sections exhibited sinking and hot spots due to inadequate feeding, as illustrated in the solidification results.
To optimize this casting part, I first designed risers and chills based on modulus calculations. The riser neck modulus MC was computed using:
$$ M_C = \frac{V_C}{A_C} $$
where VC is the volume at the riser neck and AC is the cooling area. For the top bosses, MC ≈ 30 mm, leading to a riser neck diameter dR of:
$$ d_R = (1.48 \text{ to } 2.5) M_C $$
取 dR = 60 mm. Riser dimensions followed DR = (1.55–2.0)dR and HR = (2–4)DR, resulting in DR ≈ 60 mm and HR ≈ 180 mm. Initially, four risers were placed on top bosses. For chills, thickness δ was determined by:
$$ \delta = (0.25 \text{ to } 0.5) T $$
where T is the hot spot diameter (75 mm), giving δ = 30 mm. Two chills, each 100 mm long, were positioned between side holes and the base to accelerate cooling and reduce defects in this casting part.
After the first optimization, simulation showed reduced defects, but issues persisted: side regions still had shrinkage, riser distribution was uneven, and some risers were undersized. This prompted a second optimization for the casting part. I increased chill count to four and added two small risers on minor bosses, while consolidating larger risers into two with increased dimensions (DR ≈ 90 mm, HR ≈ 270 mm). The updated riser and chill layout is summarized in Table 2, highlighting the evolution for this casting part.
| Stage | Risers (Number) | Riser Dimensions (mm) | Chills (Number) | Chill Dimensions (mm) | Key Changes |
|---|---|---|---|---|---|
| Initial | 0 | N/A | 0 | N/A | Base design with gating only |
| First Optimization | 4 | Ø60 × 180 | 2 | 30 × 100 | Added risers and chills |
| Second Optimization | 5 (2 large, 3 small) | Large: Ø90 × 270; Small: Ø41 × 124 | 4 | 30 × 100 | Adjusted riser size/count; added chills |
Simulating the optimized casting part revealed significant improvements. Filling remained smooth, with complete fill at 42 s and gases vented through risers. Temperature fields showed uniform cooling, with chills effectively eliminating hot spots in side regions. Defect analysis indicated nearly zero shrinkage in the casting part itself, with any residual defects confined to the gating system. Solidification sequences demonstrated directional solidification from bottom to top, aided by risers providing adequate feeding. The final gating system, with optimized risers and chills, ensured a sound casting part, as shown in the porosity and hot spot distributions.
The final process for this casting part employed bottom-pouring with the bearing seat face down, two-box manual molding using alkaline phenolic resin sand, and a semi-closed gating system with area ratios of 1:1.25:0.83. It included five top risers (two large, three small) and four side chills. The yield was calculated as:
$$ \eta = \frac{\text{Casting weight}}{\text{Total metal weight}} \times 100\% = \frac{566}{625} \times 100\% \approx 90.5\% $$
This optimized process effectively addressed defects, producing a high-quality casting part suitable for demanding applications.
In conclusion, through systematic design and simulation, I successfully optimized the casting process for the upper half front bearing seat, a complex casting part. Key steps included selecting a bottom-pouring scheme, designing a semi-closed gating system, and iteratively optimizing risers and chills based on ProCAST simulations. The final casting part exhibited minimal defects, with shrinkage porosity reduced to negligible levels and hot spots eliminated. This approach underscores the importance of numerical simulation in enhancing casting quality, particularly for intricate casting parts like this one. Future work could explore other alloys or scaling for similar casting parts, but the current results validate the efficacy of the optimized process for producing reliable casting parts in industrial settings.
Throughout this study, the term “casting part” has been emphasized to highlight the focus on the component itself, reflecting its significance in manufacturing. The integration of formulas and tables, as shown, provides a clear framework for replicating such optimizations for other casting parts. By adhering to principles of feeding and cooling control, similar methodologies can be applied to diverse casting parts to achieve defect-free outcomes, advancing the field of castings.