How to Improve Casting Surface Finish through Process Optimization
20 Years of Expertise from SIMIS Investment Casting
In the investment casting industry, surface finish is a critical quality benchmark. As an export-oriented enterprise with two decades of experience, SIMIS Investment Casting has successfully reduced the surface roughness of key castings to below Ra 1.6 μm through continuous process innovation. This article details our technical approach to achieving this goal.
1. Key Factors Affecting Casting Surface Finish
Our longitudinal quality data identifies primary influencing factors:
Wax Pattern Quality: Scratches exceeding 0.02mm directly replicate on finished products.
Slurry Ratio: Zircon flour-to-silica sol ratio tolerance must stay within ±1%.
Firing Process: Heating curves impact micro-crack formation on mold inner surfaces.
Pouring Parameters: Optimal synergy between molten steel superheat and mold temperature.
Table: Impact of Process Variables on Surface Roughness
| Factor | Weight | Improvement Potential |
|---|---|---|
| Wax Pattern Surface | 35% | Ra 0.8–1.2μm |
| Mold Inner Surface | 30% | Ra 0.5–1.0μm |
| Pouring Temperature | 20% | Ra 0.3–0.6μm |
| Post-Processing | 15% | Ra 0.2–0.4μm |
2. SIMIS’s Optimization Strategies
2.1 Wax Pattern Investment Control
German-grade modeling wax (±0.5°C melting point stability).
Mitsubishi Slow Wire-Cut EDM for dies (cavity roughness Ra 0.4μm).
Climate-controlled injection room (22±1°C, 50±5% RH).
2.2 Shell Mold Enhancement
Nano-grade zircon flour for the first two coating layers.
Proprietary slurry viscosity auto-adjustment system (±0.5s/ cup investment).
Extended interlayer drying (1.5× conventional duration).
2.3 Melting & Pouring Innovations
Spectrometer-equipped medium-frequency furnace for alloy monitoring.
"Gradient Heating" firing process (40% higher mold strength).
±15°C control over metal-mold temperature differential.
3. Case Study: Automotive Connecting Rod (Ra≤1.6μm)
Initial: Ra 2.2–2.8μm (68% pass rate).
Optimized: Ra 1.2–1.5μm (98% pass rate).
Client Savings: €120,000/year in polishing costs.
4. Quality Assurance & Continuous Improvement
CMM: Dimensional and geometric tolerances.
Profilometer: Roughness quantification (20 samples/batch).
Metallography: Surface grain refinement tracking.
Monthly Reviews: Top 3 defect analysis.
Technical Director Wang Zhiqiang notes:
Through 37 process trials over three years, we identified the third-layer slurry penetration as decisive for final finish. Our process window is now 40% tighter than industry standards.
5. Buyer Recommendations
Request ≥3 batches of surface roughness reports.
Scrutinize dimensional transition zones (fillets, steps).
For critical parts, conduct trial runs (5–10 validation pieces).