In the manufacturing of bearing bush components, steel casting plays a critical role due to its ability to achieve complex geometries and high mechanical performance. This article presents a systematic approach to overcoming challenges in producing thin-wall steel castings with 3D-printed sand molds, focusing on material optimization, process design, and computational validation.
Material Composition and Performance Requirements
The bearing bush, made of ZG15Cr12 alloy, requires precise control of chemical composition and mechanical properties. Table 1 summarizes the material specifications.
| Element | C | Si | Mn | Cr | Ni | S | P |
|---|---|---|---|---|---|---|---|
| Content (wt%) | ≤0.15 | ≤0.8 | ≤1.0 | 11.5–13.5 | ≤0.6 | ≤0.025 | ≤0.035 |
| Property | Rm (MPa) | ReL (MPa) | Elongation (%) | Reduction (%) |
|---|---|---|---|---|
| Value | ≥590 | ≥390 | ≥25 | ≥55 |
Casting Process Design
The critical challenge in steel casting of thin-wall bearing bushes lies in achieving complete filling of 4mm cooling ribs. The governing equation for minimum wall thickness in sand casting is expressed as:
$$ t_{min} = k \cdot \sqrt[3]{V} $$
Where \( t_{min} \) is the minimum achievable thickness (mm), \( V \) is the casting volume (cm³), and \( k \) is the material constant (0.8–1.2 for low-alloy steels). For the given component with \( V \) = 165 cm³, conventional sand casting theoretically requires \( t_{min} \) = 9mm, necessitating advanced solutions for 4mm features.
3D-Printed Sand Mold Technology
The vertical gating system with top riser design (Figure 2) demonstrates significant advantages for steel casting:
| Component | Sprue | Runner | Ingate |
|---|---|---|---|
| Area ratio | 1 | 2 | 5 |
| Diameter (mm) | 40 | 30×25 | 15×4 |
The modulus-based riser design follows Chvorinov’s rule:
$$ M_r \geq 1.2M_c $$
Where \( M_r \) is riser modulus and \( M_c \) is casting modulus. For the bearing bush with \( M_c \) = 0.48 cm, the selected cylindrical riser (\( \varnothing\)80mm × 120mm) provides \( M_r \) = 1.63 cm, ensuring adequate feeding capacity.
Computational Simulation and Validation
CAE analysis using ProCAST software incorporated the following thermal parameters:
$$ \frac{\partial T}{\partial t} = \alpha \left( \frac{\partial^2 T}{\partial x^2} + \frac{\partial^2 T}{\partial y^2} + \frac{\partial^2 T}{\partial z^2} \right) $$
Where \( \alpha \) is thermal diffusivity (6.8×10⁻⁶ m²/s for ZG15Cr12). Solidification simulation confirmed riser effectiveness with shrinkage porosity limited to feeder regions (Figure 5).
Production Implementation
Key process parameters for successful steel casting:
| Parameter | Value |
|---|---|
| Pouring temperature | 1595±5°C |
| Mold preheat temperature | >120°C |
| Cooling rate | 30–50°C/min |
The final steel casting exhibited complete formation of thin-wall features with surface roughness Ra ≤12.5μm, meeting hydrostatic test requirements of 1.5MPa for 15 minutes.
Conclusion
This steel casting methodology combines 3D sand printing with computational optimization to overcome traditional limitations in thin-wall component production. The integration of modulus-based design and controlled solidification enables reliable manufacturing of bearing bushes with complex geometries, establishing a framework for high-performance steel casting applications.