In Investment Casting (Lost Wax Casting), dimensional tolerance and surface roughness are the two decisive factors accounting for 60–70% of the final product quality. A deviation of just 0.1 mm or an $Ra$ exceeding 3.2 µm can result in assembly failure, rejection of export certifications, or costly customer returns.
At CDL LOST WAX CASTING JOINT STOCK COMPANY (Dong Nai) – an ISO 9001:2015 certified facility (Certificate No. 9199302839085-QMS) – we strictly adhere to ISO 8062 (CT4–CT7) for dimensional tolerances, ASTM E125 for surface inspection, and MSS SP-55 for cast steel quality. Consequently, we maintain a stable tolerance of $\pm$0.08 mm and surface roughness of $Ra \leq 3.2$ µm (reaching $\leq 1.6$ µm for food-grade applications) across 98% of our stainless and alloy steel products.
1. ISO 8062 – The Global Standard for Casting Tolerances
ISO 8062 defines 16 grades of casting tolerances (CT). For high-precision Investment Casting, CT4 to CT7 are the industry benchmarks.
ISO 8062 Tolerance Table (mm)
| Nominal Dimension (mm) | CT4 | CT5 | CT6 | CT7 |
| $\leq$ 10 | $\pm$ 0.10 | $\pm$ 0.14 | $\pm$ 0.18 | $\pm$ 0.26 |
| 10–30 | $\pm$ 0.12 | $\pm$ 0.17 | $\pm$ 0.22 | $\pm$ 0.32 |
| 30–100 | $\pm$ 0.18 | $\pm$ 0.25 | $\pm$ 0.32 | $\pm$ 0.45 |
| 100–300 | $\pm$ 0.28 | $\pm$ 0.38 | $\pm$ 0.50 | $\pm$ 0.70 |
At CDL:
- Stainless Steel 304/316: Typically achieves CT5–CT6.
- Carbon/Alloy Steel: Typically achieves CT6–CT7.
- We utilize precise shrinkage allowances (1.3–2.5%) in wax tool design to consistently stabilize at CT5.
2. ASTM E125 – Surface Roughness and Visual Inspection
ASTM E125 categorizes surface roughness into 5 distinct grades:
- Grade 1: $Ra \leq 1.6$ µm (Ultra-smooth; used for Food/Pharma).
- Grade 2: $Ra \leq 3.2$ µm (The global export standard).
- Grade 3: $Ra \leq 6.3$ µm (General engineering).
CDL Inspection Protocol:
After shot blasting and acid pickling, every batch is measured using the Mitutoyo SJ-410 roughness tester. 92% of our output consistently hits Grade 2 or better.
3. MSS SP-55 – Quality Standard for Steel Casting Surfaces
MSS SP-55 specifically addresses surface discontinuities in steel castings, identifying 12 types of defects (A through M):
- A (Hot Tears) & C (Shrinkage): Zero tolerance allowed.
- B (Inclusions): Must be $\leq$ 1 mm.
Our Carbon and Alloy steel components consistently achieve Level 1–2 according to MSS SP-55, ensuring structural integrity and aesthetic quality.
4. Tolerance & Roughness Control in the CDL 10-Step Process
- Pattern Injection: Precise shrinkage compensation based on ISO 8062 (CT5).
- Shell Building: Maintaining 9–11 mm shell thickness to ensure uniform cooling and shrinkage.
- Burnout: Controlled at 1050–1150°C with a 5°C/min ramp to prevent thermal distortion.
- Finishing: Utilizing 0.4–0.6 mm steel shot to achieve $Ra \leq 3.2$ µm per ASTM E125.
- Measurement: 100% verification using 3D CMM and digital profilometers for export batches.
5. Comparative Matrix by Material
| Material | ISO 8062 Grade | Average Ra | ASTM E125 Grade | MSS SP-55 Level |
| SS 304/316 | CT5 ($\pm$0.14–0.22 mm) | 2.8–3.2 µm | Grade 2 | – |
| SS 316L | CT4–CT5 ($\pm$0.10–0.18 mm) | 2.5–3.0 µm | Grade 1–2 | – |
| Carbon Steel 1045 | CT6 ($\pm$0.22–0.32 mm) | 3.2–4.0 µm | Grade 2 | Level 2 |
| Alloy Steel 4140 | CT6 ($\pm$0.22–0.32 mm) | 3.0–3.5 µm | Grade 2 | Level 1–2 |
6. Proven Success Stories
- Case 1 – Food Industry (EU Market): Achieved ISO 8062 CT5 and ASTM E125 Grade 1 for gas burner components. Results: $\pm$0.12 mm tolerance and 2.8 µm $Ra$, leading to a 40% increase in export orders.
- Case 2 – Marine Engineering (THACO): Cast in Alloy 4340 achieving CT6 and MSS SP-55 Level 1. This saved the client 18% in secondary machining costs.
Conclusion
ISO 8062, ASTM E125, and MSS SP-55 are the “triple threat” standards that ensure dimensional precision and surface excellence. At Lostwaxcasting CDL, our rigorous adherence to these protocols delivers stainless steel and alloy steel components that are “Precise – Smooth – Export Ready.”
