In the Investment Casting (Lost Wax Casting) industry, even with standardized processes like ISO 9001:2015 at CDL LOST WAX CASTING JOINT STOCK COMPANY, scrap rates can reach 10–15% if not strictly controlled. The following 7 common defects account for 90% of scrap causes.

Applying the right solutions can reduce scrap rates to below 3%, increase productivity by 20–30%, and save 15–25% in production costs.

1. Shell Cracking

Description: Horizontal or vertical cracks in the ceramic mold during burnout or pouring, leading to metal run-out.

• Root Causes: Prime coat too thin (<0.8 mm); insufficient drying between layers; or excessive heating rate (>50°C/min).
• Solutions: Strictly control the first 3 layers (0.9–1.1 mm thickness); dry each layer for 2–4 hours at 50–55% humidity; increase kiln temperature at a ramp of 5–8°C/min.
• CDL Result: Shell cracking reduced from 8% to 0.8%.

2. Gas Porosity

Description: Small spherical voids (0.2–2 mm) inside or on the surface of the casting.

• Root Causes: Residual wax decomposition; insufficient deoxidation of molten metal; or pouring temperatures exceeding 1620°C.
• Solutions: Dewax at 170°C and 7 bar for exactly 18 minutes; add 0.1–0.3% Al deoxidizer before pouring; maintain pouring temperatures at 1580–1600°C.
• CDL Tip: Use a spectrometer to verify gas content before every heat.

3. Shrinkage Porosity

Description: Irregularly shaped cavities typically found in thick sections or near gates.

• Root Causes: Poor gating/tree design; uncompensated material shrinkage (SS304 shrinks 1.8–2.2%); or shells that are too thick (>14 mm) slowing down cooling.
• Solutions: Design gates 1.5x larger than the thickest section; add risers at the final thermal centers; use Moldflow simulation to optimize the tree design.

4. Inclusions (Wax, Sand, Oxides)

Description: Dark spots, sand grains, or oxides trapped within the metal.

• Root Causes: Improper dewaxing (burnt wax residue); prime coat spalling; or excessive metal exposure to air (oxidation).
• Solutions: Filter molten metal through 10 PPI ceramic foam filters; inspect the prime coat under UV light; use Argon shielding for high-alloy steels.

5. Surface Roughness

Description: Rough surface finish ($Ra > 6.3$ µm) or “orange peel” textures.

• Root Causes: Coarse primary stucco (100 mesh instead of 200 mesh); improper shot blasting; or burnout temperatures below 980°C.
• Solutions: Use 200–325 mesh Zircon sand for the prime coat; implement 2-stage shot blasting (0.6 mm vertical + 0.4 mm horizontal); ensure burnout at 1050–1150°C.

6. Dimensional Deviation

Description: Dimensions deviating by $\pm$0.3–0.5 mm from the drawing.

• Root Causes: High injection temperatures (>72°C) causing uncontrolled wax shrinkage; shell distortion; or incorrect shrinkage allowance.
• Solutions: Inject wax at 62–68°C; apply precise shrinkage factors in mold design; conduct 100% 3D inspection of wax patterns.
• CDL Result: Stable tolerances of $\pm$0.08 mm for 98% of batches.

7. Hot Tearing / Cracking

Description: Cracks formed during cooling, usually at sharp corners or section thickness transitions.

• Root Causes: Insufficient draft angles (<1°); uneven cooling rates; or high Sulfur/Phosphorus content in the alloy.
• Solutions: Design draft angles $\geq$ 2° and fillets $R \geq$ 1 mm; maintain $S+P \leq 0.04\%$; slow cool in insulation sand after shakeout.

Summary Table: 7 Defects & Solutions

Conclusion

Defects in Investment Casting are preventable through rigorous control of the 10-step process. By implementing the verified solutions used at Lostwaxcasting CDL, you can achieve products that are Precise – Durable – Cost-Effective.

If you are experiencing any of these 7 defects, contact our technical team for a free analysis and a specific solution within 24 hours.