Quick Q: Can MIM produce cosmetic-grade textured surfaces?
Yes — MIM can produce cosmetic surfaces with textures from fine matte (VDI 15) to deep grain (VDI 36). The texture is machined or EDM'd into the mold cavity surface and transfers directly to the molded part. Key requirements: (1) draft angle must increase by 1.0-1.5° per 0.025 mm of texture depth, (2) the gate must be placed on a non-cosmetic surface, (3) the parting line must be hidden on an edge or non-visible surface, (4) the mold cavity for the textured surface must be polished before texturing.
VDI texture standards for MIM:
| VDI Number |
Surface Description |
Texture Depth (µm) |
Minimum Draft |
Typical Application |
| VDI 12-15 |
Fine matte, satin |
2-5 |
1.0° |
Premium electronics, watch cases |
| VDI 18-21 |
Medium matte |
5-10 |
1.5° |
Automotive interiors, consumer goods |
| VDI 24-27 |
Coarse matte |
10-18 |
2.0° |
Industrial tools, grips |
| VDI 30-33 |
Rough grain |
18-30 |
2.5° |
Tool handles, textured grips |
| VDI 36-39 |
Deep grain (leather) |
30-50 |
3.0° |
Decorative, heavy texture |
Design rules for cosmetic MIM parts:
| Design Element |
Requirement |
Why |
| Gate location |
Non-cosmetic surface (back, inside, or hidden edge) |
Gate vestige always visible — cannot be hidden on textured surfaces |
| Parting line |
Edge or corner — never through a flat cosmetic face |
Parting line flash on a flat cosmetic surface requires manual blending |
| Ejector pin marks |
Non-cosmetic surface |
Ejector pins leave slight witness marks |
| Draft angle |
See VDI table above — textured surfaces need more draft |
Texture creates micro-undercuts that resist ejection |
| Texture depth |
Uniform across the cavity — no sharp transitions in texture |
Inconsistent texture depth looks like a defect |
Post-processing for cosmetic MIM parts:
| Finish |
MIM As-Sintered |
After Surface Prep |
After Coating |
| Brushed metal |
Ra 2.0 µm |
Ra 0.6 µm (brushed) |
Ra 0.6 µm + PVD |
| Mirror polished |
Ra 2.0 µm |
Ra 0.1 µm (polished) |
Ra 0.1 µm + clear coat |
| Matte texture (VDI 21) |
Ra 2.0 µm → VDI 21 |
VDI 21 direct from mold |
VDI 21 + PVD |
| PVD coated |
Ra 2.0 µm |
Ra 0.4-1.6 µm (polished) |
Ra 0.4-1.6 µm + TiN/CrN/DLC |
| Black oxide / passivation |
Ra 2.0 µm |
No additional prep needed |
Ra 2.0 µm (black/grey) |