This paper presents a systematic approach to manufacturing high-precision machine tool table castings using 3D printed sand mold technology. Through optimized process design and parameter control, we achieved stable production of castings with dimensional accuracy reaching CT8 grade and surface roughness Ra ≤ 12.5μm.
1. Process Design and Implementation
The gating system design follows the proportional relationship:
$$ΣS_{sprue} : ΣS_{runner} : ΣS_{ingate} = 1 : 1.6 : 0.8$$
Key parameters for 3D printed silica sand are summarized in Table 1:
| Parameter | Value |
|---|---|
| Mesh Size | 70-140 |
| Moisture Content | ≤0.1% |
| Resin Content | 2.1% |
| 24h Tensile Strength | 2.5-3.0 MPa |
| Binder Type | Furan Resin |
2. Metallurgical Control
The chemical composition control equation for HT300 material:
$$CE = C + \frac{Si}{3} + \frac{P}{3} ≤ 4.0$$
Actual chemical composition ranges are shown in Table 2:
| Element | Range |
|---|---|
| C | 3.0-3.1 |
| Si | 2.3-2.4 |
| Mn | 0.7-0.8 |
| S | ≤0.08 |
| P | ≤0.06 |
3. Casting Defect Prevention
Three critical casting defects were addressed through process optimization:
3.1 T-Slot Shrinkage Porosity
The solidification time (t) for T-slot sections is calculated by:
$$t = k \cdot \left(\frac{V}{A}\right)^2$$
Where:
k = Solidification coefficient (2.5 for gray iron)
V = Volume of T-slot section
A = Surface area of T-slot section
3.2 Surface Blowholes
Nitrogen content control equation:
$$[N]_{final} = 0.5[N]_{charge} + 0.3[N]_{additives} ≤ 120ppm$$
3.3 Sliding Surface Porosity
The hydrogen diffusion model in molten iron:
$$D_H = D_0 \cdot e^{-Q/(RT)}$$
Where:
D0 = Pre-exponential factor (2.4×10-7 m²/s)
Q = Activation energy (38.5 kJ/mol)
R = Gas constant
T = Temperature (K)
4. Process Validation
Production statistics for 56 castings:
| Parameter | Value |
|---|---|
| Dimensional Accuracy | CT8 |
| Surface Roughness | Ra ≤12.5μm |
| Shrinkage Defect Rate | ≤0.5% |
| Gas Porosity Rate | ≤0.3% |
| Overall Yield | 98.2% |
The optimized process reduces casting defects through three main mechanisms:
- Thermal management using composite chills
- Strict nitrogen control in metallurgical process
- Precise sand mold moisture control (≤0.3%)
5. Economic Analysis
The cost comparison between conventional and 3D printing processes:
$$C_{saving} = (T_{pattern} \cdot R_{labor}) + (M_{wood} – M_{sand})$$
Where:
Tpattern = Pattern making time reduction (120 hours)
Rlabor = Hourly labor rate ($15/hr)
Mwood = Wood pattern material cost ($2,500)
Msand = 3D printing material cost ($800)
This 3D sand printing technology demonstrates significant advantages in casting defect reduction, production efficiency improvement (40% cycle time reduction), and complex geometry realization. The successful implementation provides valuable experience for large-scale casting digital transformation.