The choice of manufacturing process determines 60 to 80 percent of the unit cost — and yet it is often made on the basis of historical habit. This article shows at which volume, geometry and material requirement Metal Injection Molding (MIM) is structurally superior — and when it is not.
The three processes in profile
Here we compare MIM with the two most common alternatives for small to medium-sized steel, stainless and titanium components: investment casting (lost-wax process) and machining from bar stock.
| Criterion | MIM | Investment casting | Machining |
|---|---|---|---|
| Typ. weight range | 0,1 – 250 g | 10 – 50.000 g | open |
| Economical volume / year | > 20.000 | > 500 | < 5.000 (series-typical) |
| Geometric complexity | very high | high | medium |
| Standard tolerance class | ±0,3 % nom. dim. | ±0,5 % nom. dim. | IT6–IT9 |
| Surface without rework | Ra 0,8–1,6 µm | Ra 3,2–6,3 µm | Ra 0,4–3,2 µm |
| Material utilisation | > 97 % | ~ 90 % | 30–60 % |
| Tooling costs | high | medium | none / low |
When MIM wins structurally
MIM is not a universal miracle process. It is a very good series process for small, geometrically complex components. Three constellations almost always lead to a MIM recommendation:
- Small component, high volume — typically from 50,000 parts/year at weights below 50 g. The tooling costs are amortised and the unit-price advantages over machining come fully into play.
- Geometry with undercuts, openings, thin walls — features that require long set-up times and special tools in turning and milling. MIM captures them once in the tool and reproduces them in an automated manner.
- Materials that are expensive to machine — austenitic stainless steels (316L), titanium (Ti-6Al-4V), nickel-based alloys (Inconel). The cutting-tool costs in machining explode, whereas MIM feedstock becomes only moderately more expensive.
When MIM is the wrong process
There are clear contraindications. We communicate them actively — because the wrong process is more expensive than a lost order.
- Components heavier than 250 g. Debinding and sintering processes become uneconomical. Investment casting or sintered-metal pressing are superior here.
- Volumes below 10,000 parts per year. The tooling costs are not amortised. Either machining or — in the case of geometric complexity — laser sintering as an interim solution.
- Ultra-high surface requirements (Ra < 0.4 µm without rework). MIM delivers Ra 0.8 µm directly from the sintering process. Mirror surfaces must be polished — in which case machining or investment casting may be more economical.
- Pure rotational geometries without undercuts. Here, turning on modern multi-spindle automatic lathes is often unbeatable — especially at volumes up to 200,000.
Investment casting vs. MIM — the distinction
Investment casting and MIM are often perceived as competing processes. In practice they overlap only to a limited extent: investment casting dominates from weights above 100 g, MIM below that. In the intermediate range, the geometry decides.
Key differences:
- Density. Investment casting reaches > 99.5 % without an additional process. MIM reaches 95–98 % after sintering and requires HIP for aerospace quality.
- Geometric tolerance. MIM delivers tighter series tolerances at consistent process capability (Cpk ≥ 1,33 standard).
- Tooling costs. Investment-casting wax patterns are cheaper than MIM injection tools. In return, the MIM tool set is amortised faster for series > 50k.
- Alloy flexibility. Investment casting has historically known more special materials. MIM has caught up over the past ten years — 17-4 PH, Ti-6Al-4V and Inconel are MIM standard.
The decision matrix in three questions
If you are still unsure whether your component is MIM-suitable, three questions help:
- Does it weigh between 1 g and 200 g? If yes → MIM becomes possible in principle.
- Will you take more than 20,000 parts per year? If yes → MIM pays off in most cases.
- Does the component have undercuts, openings or thin walls? If yes → MIM will almost always be the most cost-effective solution.
If you have answered "yes" twice or more, a concrete feasibility check is worthwhile. With us, that takes a maximum of 24 hours.
Further reading
Related articles on this topic:
- Design for MIM: 12 design rules — how to prevent your component from failing MIM feasibility already in CAD.
- Material Matrix — an interactive comparison of the most important MIM series materials.
- Guide-Price Calculator — a concrete price corridor for your component in 60 seconds.