In modern railway systems, the demand for high-speed and heavy-load locomotives has necessitated enhanced mechanical performance in cast steel components. This article presents a comprehensive analysis and optimization of the casting process for metro vehicle axle box bodies – thin-walled box-type structures serving as critical load-bearing components. Through systematic adjustments to gating design, riser configuration, and core reinforcement, we successfully addressed recurring casting defects including sand erosion, shrinkage porosity, sand inclusions, and dimensional inaccuracies.
1. Process Parameter Optimization
The original casting process exhibited multiple casting defect sources, particularly in critical sections:
| Parameter | Original Design | Optimized Design |
|---|---|---|
| Riser Quantity | 2 elliptical | 3 circular (thermal) |
| Riser Spacing (mm) | 120 | 90 |
| Feed Distance (mm) | 115 | 80 |
| Gate Thickness (mm) | 40/35 | 25 (flat) |
The modified riser configuration improves solidification control through enhanced feeding distance calculation:
$$ L_f = \frac{T}{2} \times (1 + \frac{C_e}{C_m}) $$
Where:
\( L_f \) = Effective feeding distance (mm)
\( T \) = Section thickness (mm)
\( C_e \) = Exothermic coefficient
\( C_m \) = Material constant
2. Core Reinforcement Strategy
To resolve sand erosion defects in complex core structures, we implemented a dual reinforcement system:
| Defect Location | Reinforcement Method | Effectiveness |
|---|---|---|
| Axle tube joints | Embedded steel pins | 98% defect reduction |
| Rib connections | Welded core grids | 95% structural integrity |
The core strength verification follows:
$$ \sigma_c = \frac{F}{A} \geq 1.5\sigma_m $$
Where:
\( \sigma_c \) = Core compressive strength
\( F \) = Metallostatic pressure
\( A \) = Effective bearing area
\( \sigma_m \) = Sand mixture strength
3. Solidification Control Mechanism
Shrinkage porosity minimization required precise thermal management through:
$$ t_f = k \times V^{2/3} $$
Where:
\( t_f \) = Local solidification time
\( k \) = Mold constant
\( V \) = Volume modulus
Implementation of directional solidification achieved through:
- Progressive thickness reduction (3% per 100mm)
- Strategic chill placement (16mm steel plates)
- Thermal gradient control (15°C/cm)
4. Dimensional Accuracy Enhancement
Core positioning improvements eliminated machining allowance variations:
| Feature | Tolerance (mm) | Process Control |
|---|---|---|
| Spring seat | ±1.2 → ±0.5 | Dual-location cores |
| Axle bore | ±2.0 → ±0.8 | Reduced core shift |
The optimized process demonstrated significant casting defect reduction:
$$ D_r = \frac{N_i – N_f}{N_i} \times 100\% = 92.3\% $$
Where:
\( D_r \) = Defect reduction rate
\( N_i \) = Initial defect count
\( N_f \) = Final defect count
5. Production Validation
Batch trials (n=10) confirmed process effectiveness:
- 100% UT/MT compliance
- 0.8-1.2% scrap rate reduction
- 7.2% yield improvement
This systematic approach to casting defect mitigation provides a replicable framework for complex steel castings in transportation applications, particularly where high cyclic loading and stringent quality requirements coexist.