MIM Design Guidelines | Wall Thickness, Draft and Tolerances

MIM Design Guidelines: A Practical Checklist from Wall Thickness to Draft Angles

Metal injection molding combines powder metallurgy with plastic injection. Following MIM design guidelines determines whether a part can be produced reliably and at a sensible cost. This article covers wall thickness, draft, holes, tolerances and material selection as a checklist engineers can apply directly. Yujiaxin Tech has shipped many MIM programs, and the rules below come from repeated production validation.

Why the design stage decides MIM success

MIM tooling cost sits at the front of the project, so changes become expensive once the design is locked. Many parts reveal problems only at first molding, and rework costs far more than an early review. Applying MIM design guidelines during drawing review is the most effective way to control lead time and yield. We recommend a manufacturability review before quoting; the overview of metal forming processes helps decide if MIM fits.

Wall thickness uniformity is rule one

MIM parts suffer most from local thick sections. Keep wall thickness between 1.5 and 6 mm and keep variations small across the part. Large differences cause shrinkage voids and warpage during sintering. Use gradual transitions instead of abrupt steps where thicker sections are required. MIM design guidelines put wall thickness first, and that requirement should be locked in the first revision.

Draft angles and ejection

The molded green part must release from the tool. Provide at least 0.5 degree draft on vertical faces, and 1 to 2 degrees on deep cavities. Undercuts and side holes raise tool complexity; prefer positive geometry over slides when possible. MIM design guidelines are clear on draft: secure ejection first, then discuss feature complexity.

Holes, slots and threads

Through holes should be at least 0.8 mm in diameter, and blind holes no deeper than five times the diameter. Long thin slots are more stable when finished by CNC after sintering. Internal threads are usually not molded in MIM; leave stock and tap after sintering. MIM design guidelines set firm limits on holes and slots, and features beyond those limits belong in a later operation. Our precision metal parts product line covers these combined processes.

Tolerances and finishing limits

Standard MIM tolerance is around IT8 to IT9; tighter accuracy comes from sizing or CNC after sintering. Flatness and position depend on sintering support, so reserve machining datums in the design. Surfaces that seal or mate should carry a separate finishing note. MIM design guidelines treat tolerances and finishing as separate concerns, one for design and one for process. For deeper background see the full MIM process walkthrough.

Material selection

Stainless 316L and 17-4PH are the most common MIM materials; titanium suits medical and aerospace parts. Tungsten serves counterweight and shielding, tool steel serves wear parts. Consider sintering shrinkage and post processing together when selecting. MIM design guidelines require matching shrinkage to the tool enlargement calculation. Powder metallurgy standards are documented by MPIF standards resources and ASM International materials handbook. Yujiaxin Tech MIM capabilities span most of these systems.

Conclusion

The core of MIM design guidelines is writing production constraints into the first revision of the drawing. This approach has been proven on programs such as medical grade precision parts. Yujiaxin Tech supports projects from review and tooling to volume production. If you are evaluating whether a part suits MIM, request a manufacturability assessment and our engineering team will return a tailored conclusion.