MIM can produce walls as thin as 0.3 mm — but not thinner. Three physical constraints set this limit.
1. Powder particle size: MIM powder particles are D50 < 20 µm. For a feedstock to flow reliably, the flow channel must be at least 10-15 times the particle diameter. Below 0.3 mm (300 µm = 15 × 20 µm), the powder particles begin to bridge at the gate and in the cavity, causing short shots. 2. Feedstock viscosity: MIM feedstock is approximately 50-100x more viscous than molten plastic. As the wall thickness decreases, the injection pressure required to fill the cavity increases exponentially. At 0.3 mm, pressures of 150-200 MPa are already required. Below 0.3 mm, the required pressure exceeds what most MIM injection molding machines can deliver. 3. Green part strength: After molding, a 0.2 mm wall thickness green part would be so fragile that it would break during handling or ejection. The green strength (15-25 MPa) is simply insufficient to hold a sub-0.3 mm feature without damage. Design recommendations for thin walls:| Wall Thickness | Feasibility | Design Consideration |
|---|---|---|
| ≥ 0.8 mm | Excellent — standard MIM | No special considerations |
| 0.5-0.8 mm | Good — requires optimized process | Fine-tune gate location, increase injection speed |
| 0.3-0.5 mm | Challenging — possible with care | Requires premium powder, high injection pressure, robust mold design |
| < 0.3 mm | Not recommended | Short shot risk >30%; consider alternative process |
The limit is set by three factors: powder particle bridging (feedstock cannot flow through channels smaller than ~15x the particle diameter), viscosity limitations of MIM feedstock (pressure required becomes impractical below 0.3 mm), and green part fragility (sub-0.3 mm features cannot survive ejection and handling). For walls below 0.3 mm, consider metal stamping, chemical etching, or laser cutting.