3 Common Defects in Investment Casting (And How to Prevent Them)

Investment casting (also known as lost-wax casting) is a high-precision metal casting process used in industries like aerospace, automotive, medical, and defense for producing complex, near-net-shape parts. While known for excellent dimensional accuracy and smooth surface finishes, the process can still encounter defects during production.

In this article, we explore the 3 most common defects in investment casting—their causes, impact, and best practices to prevent them—to help manufacturers improve casting quality, reduce scrap rates, and optimize production efficiency.

1. Porosity: Gas & Shrinkage Defects

What Causes Porosity?

Porosity appears as small voids, bubbles, or pinholes in the cast part, caused by:
✅ Gas Porosity – Trapped air or gas from wax burnout or molten metal reactions.
✅ Shrinkage Porosity – Insufficient feeding during metal solidification.

How to Prevent Porosity?

✔ Optimize venting in ceramic molds to allow gas escape.
✔ Control melting & pouring temperatures to reduce gas absorption.
✔ Use high-quality degassed alloys (especially for aerospace & medical parts).
✔ Design proper gating & risers to ensure complete feeding.

Industries Affected: Turbine blades (aerospace), medical implants (Ti-6Al-4V), pump housings (316 stainless steel).

2. Mold Cracking & Metal Penetration

What Causes Mold Cracking?

Investment casting relies on ceramic shell molds, which can crack due to:
✅ Thermal shock (rapid heating/cooling).
✅ Improper shell drying or burnout.
✅ Excessive metal pressure during pouring.

Metal penetration occurs when molten metal seeps into cracks, causing rough surfaces & dimensional inaccuracies.

How to Prevent Mold Cracking?

✔ Gradual preheating of ceramic molds to reduce thermal stress.
✔ Optimal shell coating (enough layers for strength).
✔ Controlled pouring speed & temperature.
✔ Use of high-refractoriness ceramic materials.

Industries Affected: Automotive turbochargers, industrial valve bodies, defense components.

3. Misruns & Incomplete Castings

What Causes Misruns?

A misrun happens when molten metal solidifies prematurely, leading to incomplete part filling. Causes include:
✅ Low pouring temperature.
✅ Poor gating system design (restricted flow).
✅ Slow pouring speed.

How to Prevent Misruns?

✔ Optimize metal pouring temperature (depends on alloy—e.g., stainless steel vs. aluminum).
✔ Improve gating design (larger runners, proper taper).
✔ Use vacuum or pressure-assisted casting for thin-walled parts.

Industries Affected: Complex aerospace components, thin-wall hydraulic fittings, surgical instruments.

Conclusion: Quality Control in Investment Casting

While defects in lost-wax casting can occur, they are preventable with proper process control, material selection, and mold design. Implementing X-ray inspection, dye penetrant testing, and metallurgical analysis can further enhance defect detection.

Looking for defect-free investment castings? Our precision casting process minimizes errors with strict quality checks—contact us for high-performance aerospace, medical, and automotive-grade castings!