Variable wall thickness is one of the most common causes of MIM part distortion. When thick and thin sections shrink at different rates during sintering, internal stresses develop that warp the part. Here is how to manage it.
The golden rule: Keep the ratio of thickest to thinnest wall below 2:1. Design strategies for managing variable walls:| Situation | Problem | Design Solution |
|---|---|---|
| Thick boss on thin wall | Boss shrinks more slowly, pulling the wall out of flat | Core out the boss (hollow), or add a gradual taper over 3x the thickness difference |
| Rib on one side only | Asymmetric shrinkage bends the part | Mirror the rib on both sides, or add a balancing rib |
| Thin wall transitioning to thick flange | Distortion at the transition point | Taper the transition over at least 3x the dimension difference |
| Variable thickness across a flat surface | Center shrinks differently from edge | Add stiffening ribs to resist distortion |
| Thickness Ratio | Distortion Risk | Recommended Transition Length |
|---|---|---|
| 1.5:1 or less | Low | None needed — standard process |
| 1.5:1 to 2.0:1 | Moderate | Taper over 3x the thickness difference |
| 2.0:1 to 3.0:1 | High | Redesign for more uniform wall, or taper over 5x |
| > 3.0:1 | Very high | Must redesign — current design is not suitable for MIM |
Instead of designing a 6 mm thick solid section, core it out to create two 1.5 mm walls with a gap between them. This maintains stiffness while keeping wall thickness uniform. The cored area also reduces material cost and shortens debinding time.
Quick Q: How do I design MIM parts with variable wall thickness?Keep the ratio of thickest to thinnest wall below 2:1. If thicker sections are unavoidable, taper the transition gradually (3-5x the thickness difference) and consider coring out thick sections to create uniform thin walls. Adding ribs on the opposite side can balance asymmetric shrinkage forces. Non-uniform wall thickness is the single most common cause of MIM distortion — addressing it in the design phase is far cheaper than trying to correct it in process development.