The biggest mistake: treating MIM like machining
Engineering teams often upload a machined brass drawing and ask for a material swap. MIM is a near-net-shape process — the mold, binder removal, and sintering cycle all impose constraints that machining does not.
The good news: a proper redesign usually improves the part — fewer joints, lighter weight, and more consistent internal geometry.
Step 1 — Wall thickness audit
| Zone | Target | Risk if violated |
|---|---|---|
| General walls | 1.5–4.0 mm | Too thin → green part handling damage |
| Heavy bosses | ≤ 2× adjacent wall | Mass differential → warp in sintering |
| Sharp internal corners | R ≥ 0.3 mm | Stress concentrators, incomplete fill |
Use your CAD thickness analysis tool before sending drawings. We flag problem zones in our DFM report.
Step 2 — Draft and parting line
Injection molding rules apply to MIM green parts:
- 1–2° draft on internal cores
- Parting line placed away from pressure-bearing sealing surfaces
- Avoid deep blind pockets without venting strategy
Step 3 — Gate and ejector placement
Gate vestige lands on a non-functional surface when possible. For valve bodies, we typically gate on a flange face that gets finish-machined post-sinter.
Ejector pin marks are planned on low-stress zones — never on threads or seat surfaces.
Step 4 — Sintering shrinkage compensation
304 MIM shrinks approximately 12–15% linearly from molded green part to sintered final. Mold cavities are scaled accordingly. Critical bores and threads are undersized and machined to final tolerance after sinter.
This single post-sinter op is still cheaper than 3–5 full machining ops on brass bar stock.
Step 5 — Assembly consolidation example
A typical fire sprinkler valve conversion:
- Before: Brass body + brass bonnet + 2 brazed ports = 4 leak paths
- After: Single MIM 304 body with integral ports = 1 gasket interface
Field warranty data from comparable programs shows 30–45% reduction in leak-related returns.
Pilot tooling timeline
| Week | Milestone |
|---|---|
| 1–2 | DFM review + gate proposal |
| 3–6 | Mold design and fabrication |
| 7–8 | T1 samples + density/metallurgy report |
| 9–10 | FAI + customer validation testing |
| 11+ | Production ramp |
Start your conversion project — attach STEP files and annual volume estimate.
Download the Copper Price Intelligence Brief to build your ROI model.
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