Introduction to MIM Design Guidelines
Metal Injection Molding (MIM) offers exceptional design freedom for metal components. However, realizing this potential requires understanding MIM-specific design principles. Proper design optimization ensures manufacturability, cost-effectiveness, and consistent quality.
This guide provides essential MIM design guidelines for engineers and product designers.
1. Wall Thickness
Uniform Thickness
Guideline: Maintain uniform wall thickness throughout the part.Why It Matters
Prevents differential shrinkage during sintering
Reduces distortion and warpage
Ensures consistent density
Recommended Thickness
Minimum: 0.4mm
Optimal: 0.8-3.0mm
Maximum: 10mm (depends on material)
Thickness Transitions
Guideline: Use gradual transitions between different wall thicknesses.Best Practices
Transition ratio: 3:1 minimum
Use fillets at corners
Avoid abrupt changes
Example
❌ Wrong: 1mm → 3mm abrupt transition ✅ Right: 1mm → 2mm → 3mm gradual transition
2. Tolerances
Standard Tolerances
Guideline: Design to standard MIM tolerances where possible.Typical Tolerances
±0.3% of nominal dimension
±0.05mm minimum
±0.1mm typical
Tighter Tolerances
Possible with additional cost
May require secondary operations
Discuss with manufacturer early
Tolerance Stack-Up
Guideline: Minimize tolerance stack-up in assembly designs.Best Practices
Use datums consistently
Reference features from common datums
Allow for process variation
3. Draft Angles
Ejection Draft
Guideline: Include draft angles for part ejection.Recommended Draft
Minimum: 0.5° per side
Recommended: 1-2° per side
More draft for deeper features
Applications
Side walls parallel to mold opening direction
Internal features (cores)
Textured surfaces (more draft required)
No Draft Required
Exceptions
Features perpendicular to mold opening
Surface textures (may require more draft)
Undercuts (require special mold design)
4. Corners and Fillets
Corner Radii
Guideline: Use generous corner radii.Benefits
Reduce stress concentrations
Improve powder flow during molding
Enhance part strength
Recommended Radii
Internal corners: R0.3mm minimum
External corners: R0.5mm minimum
Larger radii for high-stress areas
Fillet Design
Guideline: Use fillets at all internal corners.Best Practices
Fillet radius: 0.5-1.0x wall thickness
Consistent fillet sizes
Avoid sharp internal corners
5. Holes and Slots
Hole Design
Guideline: Design holes for MIM manufacturability.Hole Size Guidelines
Minimum diameter: 0.5mm
Depth-to-diameter ratio: 3:1 maximum
Spacing: 2x diameter minimum
Hole Types
Through holes: easiest to produce
Blind holes: possible with depth limitations
Cross holes: require special mold design
Slot Design
Guideline: Design slots with MIM in mind.Slot Guidelines
Minimum width: 0.5mm
Depth-to-width ratio: 3:1 maximum
Corner radii: R0.3mm minimum
6. Threads and Knurls
Threads
Guideline: MIM can produce threads directly.Thread Guidelines
Minimum thread size: M2
Thread pitch: standard pitches preferred
External threads: easier than internal
Consider insert for high-stress threads
Knurls
Guideline: MIM can produce knurled surfaces.Knurl Guidelines
Standard patterns preferred
Depth: 0.1-0.3mm
Spacing: 0.5-1.0mm
Consider post-molding knurling for fine patterns
7. Part Consolidation
Combine Parts
Guideline: Consolidate multiple parts into single MIM component.Benefits
Reduce assembly operations
Improve part strength
Reduce inventory
Lower total cost
Example
Traditional: 5 parts + assembly MIM: 1 part, net shape
Design for Assembly
Guideline: Design features for easy assembly.Features to Include
Alignment pins
Snap fits
Locating features
Self-jigging design
8. Material Selection
Material Properties
Guideline: Select material based on application requirements.Selection Criteria
Mechanical properties (strength, hardness)
Corrosion resistance
Magnetic properties
Biocompatibility
Cost considerations
Common Materials
Stainless Steels
316L: general corrosion resistance
17-4PH: high strength
304L: cost-effective
Other Materials
Ti-6Al-4V: lightweight, biocompatible
Fe-2Ni: low-cost, good strength
M2 tool steel: wear resistance
9. Surface Finish
As-Sintered Finish
Guideline: Design to as-sintered surface finish where possible.Typical Finish
Ra 0.8-1.6μm
Consistent across production
Suitable for many applications
Secondary Finishing
Guideline: Plan for secondary finishing if required.Options
Polishing: mirror finish
Bead blasting: matte finish
Plating: decorative/protective
PVD coating: hard, wear-resistant
10. Design Review
Early Collaboration
Guideline: Involve MIM manufacturer early in design process.Benefits
Optimize for manufacturability
Identify potential issues early
Reduce development time
Lower total cost
Design for MIM Checklist
[ ] Uniform wall thickness
[ ] Adequate draft angles
[ ] Generous corner radii
[ ] Appropriate tolerances
[ ] Optimized hole/slot design
[ ] Material selection verified
[ ] Surface finish requirements defined
[ ] Assembly features considered
Conclusion
Following MIM design guidelines ensures manufacturability, cost-effectiveness, and consistent quality. Early collaboration with experienced MIM manufacturers helps optimize designs and avoid costly revisions. Contact BRM engineering team for design review and optimization support.