Most MIM design guides emphasize the minimum wall thickness (0.3 mm). But there is also a maximum — typically around 10 mm. Walls thicker than this create problems that cannot be solved by simply running the process longer.
The primary constraint: debindingThe debinding process removes binder by diffusion from the inside of the part to the surface. For catalytic debinding (the most common method), the nitric acid vapor diffuses through the porous brown part, catalyzing binder decomposition. The maximum effective diffusion distance is approximately 5-6 mm from any surface. This means the maximum wall thickness from any surface to the center is about 5-6 mm, for a total wall of 10-12 mm if both surfaces are exposed.
What happens with walls thicker than 10 mm:| Wall Thickness | Debinding Feasibility | Consequence |
|---|---|---|
| < 6 mm | Excellent — fully debound within standard cycle | No issues |
| 6-10 mm | Possible — requires extended cycle time (up to 2x) | Longer cycle, higher cost, acceptable quality |
| 10-15 mm | Very difficult — center may not fully debind | Residual binder in center → carbon contamination, black lines |
| > 15 mm | Not feasible | Center binder cannot be removed — severe internal defects |
Even if debinding is somehow achieved for a thick wall, sintering presents another challenge: the center of a thick wall lags behind the surface during heating, creating a thermal gradient that leads to non-uniform shrinkage, internal stress, and potentially cracking.
Design alternatives for thick sections:If a part requires a thick section, do not design it as a solid block. Instead:
- Core out the center to create a shell with uniform wall thickness
- Use a honeycomb or ribbed structure for stiffness without mass
- Specify the part as cored or hollow
The primary limit is debinding — the binder removal process can only penetrate approximately 5-6 mm from any surface. For walls thicker than 10-12 mm, the center binder cannot be removed within practical cycle times, leading to carbon contamination and internal defects during sintering. Design MIM parts with uniform walls under 6 mm where possible. For thicker sections, use cored or ribbed designs.