Roughly four out of five MIM enquiries we receive are initially turned down — not because the component is conceptually unsuitable, but because it was not designed for MIM in CAD. This guide explains the twelve most common sources of error that can already be identified in the 3D model before the enquiry is submitted.
Why DfMIM matters
Metal Injection Molding is a process involving a threefold dimensional change: the part is moulded (+ excess from the binder), debound (loss of weight) and sintered (shrinkage 15–22 %). Each of these phases imposes geometric requirements that differ from classic machined or cast parts.
Those who know the rules can design a MIM-suitable component in 30 minutes. Those who don't produce scrap during sampling — or nothing at all, because the tool cannot be demoulded.
The twelve rules
01 · Keep wall thicknesses uniform
Wall thicknesses should be between 0.8 mm and 8 mm, ideally in the range of 2 to 5 mm. Large jumps in wall thickness lead to uneven shrinkage and warpage. Rule: the ratio of thickest to thinnest wall should not exceed 3:1.
02 · Observe the nominal-thickness principle
Relieve local thickenings (bosses, rib intersections) with cavities. The idea: the nominal wall thickness determines the cycle time, not the maximum wall thickness. Values above 8 mm require core pulls or thinning by means of ribs.
03 · Plan for draft angles
MIM tools require at least 0.5° of draft on outer surfaces; 1° is standard. Internal geometries may be made somewhat steeper. Without draft, the feedstock remains in the tool — ejector marks or damage to the surface are the result.
04 · Use undercuts deliberately
Undercuts are possible in MIM, but expensive. They require slides, lifters or even side cores in the tool. Before every undercut decision it is worth asking: can the function also be achieved without one (e.g. by shifting it across the parting plane)?
05 · Avoid sharp internal corners
Internal corners should be rounded with a radius of at least 0.3 mm. Sharp edges lead to stress cracks during the sintering process and can hardly be corrected later during calibration.
06 · Resolve concentration points
Points where three or more walls meet (rib intersections) are prone to voids and porosity nests. Resolve them by offsetting or by using fillets of at least R = 0.5 × wall thickness.
07 · Lay out holes geometrically correctly
Holes are MIM-suitable up to a length-to-diameter ratio of 5:1. Blind holes should have a slightly conical profile. Cross-intersecting holes require slides — which drives up the tool price.
08 · Do not sinter threads directly
MIM-sintered threads are possible, but rarely recommended for load-bearing functions. Better: sinter in threaded inserts (insert) or cut/form the thread after sintering. For M3–M8, thread cutting after sintering is the most economical method.
09 · Keep narrow sections and openings at least 0.5 mm
The smallest openings and gaps that MIM can reproduce are 0.5 mm wide. Anything smaller requires laser machining after sintering — or is not feasible at all.
10 · Set tolerances realistically
Standard series tolerances for MIM are ±0.3 % of the nominal dimension, with a minimum of 0.05 mm. Tighter tolerances require calibration — expensive, but feasible. Important: concentrate tolerances on critical functional surfaces rather than applying them across the entire component.
11 · Account for material flow
The feedstock flows like a plastic. Very thin walls far from the gate may fill incompletely. Rule: keep the flow-length-to-wall-thickness ratio < 100:1.
12 · Account for shrinkage in the drawing
MIM shrinkage is directionally dependent — often somewhat greater parallel to the pressing direction than transverse to it. For tight fits, this anisotropy must be compensated for already in the drawing and later in the tool.
How we help you
As soon as you upload a drawing (STEP or 2D PDF), an automated DfMIM check runs at our end. Our engineering team returns it to you within 24 hours — with specific notes on which rules are violated and how they can be resolved by design. At no cost, without obligation.
Further reading
- MIM vs. investment casting vs. machining — when each process pays off.
- Material Matrix — which materials permit which geometric freedom.
- Guide-Price Calculator — a price estimate based on your design data.