Introduction to Metal Parts Manufacturing
Selecting the right manufacturing process is one of the most critical decisions in product development. The choice between Metal Injection Molding (MIM), CNC machining, and die casting directly impacts your product's cost, quality, lead time, and scalability.
This guide compares the three most common metal parts manufacturing processes to help engineers and procurement professionals make informed decisions.
Understanding the Three Processes
Metal Injection Molding (MIM)
MIM combines powdered metallurgy with plastic injection molding. Fine metal powder is mixed with a binder, injected into a mold, then debound and sintered to produce dense metal parts.
Key characteristics:
Typical part size: under 100mm
Tolerance: ±0.1-0.3%
Minimum order quantity: 5,000+ pieces
Lead time: 3-6 weeks
CNC Machining
Computer Numerical Control (CNC) machining removes material from a solid metal block using computer-controlled cutting tools. It is a subtractive manufacturing process.
Key characteristics:
Part size: unlimited
Tolerance: ±0.01mm
Minimum order quantity: 1 piece
Lead time: 1-2 weeks
Die Casting
Die casting forces molten metal under high pressure into a reusable steel mold. It is commonly used for zinc, aluminum, and magnesium alloys.
Key characteristics:
Part size: 10-300mm
Tolerance: ±0.1-0.5%
Minimum order quantity: 1,000+ pieces
Lead time: 4-8 weeks
Detailed Comparison
Complexity and Design Freedom
| Feature | MIM | CNC Machining | Die Casting |
|---|---|---|---|
| Geometric complexity | Very high | Medium | High |
| Undercuts | Yes | Limited | Yes |
| Thin walls | 0.3mm+ | 0.5mm+ | 0.8mm+ |
| Internal channels | Yes | Limited | Limited |
| Thread integration | Direct | Secondary | Secondary |
MIM excels at producing parts with complex geometries that would require multiple CNC operations or assembly of several die-cast components.
Precision and Surface Finish
| Metric | MIM | CNC Machining | Die Casting |
|---|---|---|---|
| Dimensional tolerance | ±0.1-0.3% | ±0.01mm | ±0.1-0.5% |
| Surface roughness (Ra) | 0.8-1.6μm | 0.2-0.8μm | 1.6-3.2μm |
| Consistency | Excellent | Excellent | Good |
| Secondary operations | Minimal | Extensive | Moderate |
CNC machining delivers the highest precision, making it ideal for prototypes and tight-tolerance features. MIM provides excellent consistency for high-volume production.
Cost Analysis by Production Volume
| Annual Volume | MIM (per unit) | CNC (per unit) | Die Casting (per unit) |
|---|---|---|---|
| 1-100 | $50-120 | $80-200 | $100-200 |
| 100-1,000 | $30-80 | $50-120 | $40-80 |
| 1,000-10,000 | $10-30 | $30-80 | $20-50 |
| 10,000-100,000 | $5-15 | $20-50 | $10-30 |
| 100,000+ | $2-8 | $15-40 | $5-15 |
The cost crossover point: MIM becomes more economical than CNC at approximately 5,000-10,000 pieces per year, depending on part complexity.
Material Options
| Material Category | MIM | CNC | Die Casting |
|---|---|---|---|
| Stainless steel | 316L, 17-4PH, 304L | All grades | Limited |
| Tool steel | Yes | All grades | No |
| Titanium alloys | Ti-6Al-4V | Ti-6Al-4V | No |
| Low alloy steel | Fe-Ni, Fe-Cu | All grades | No |
| Aluminum | Limited | All alloys | ADC10, A380 |
| Zinc | No | Limited | ZA-8, Zamak |
| Copper alloys | Yes | All alloys | Limited |
| Magnetic materials | NdFeB, SmCo | Limited | No |
MIM supports the widest range of ferrous and specialty alloys, while die casting is primarily limited to non-ferrous metals.
Decision Framework
Choose MIM When:
Parts are under 100mm with complex geometry
Annual volume exceeds 5,000 pieces
Multiple components can be consolidated into one MIM part
Ferrous or specialty alloy materials are required
Consistent quality across high volumes is critical
Choose CNC Machining When:
Prototyping or low-volume production (under 1,000 pieces)
Extremely tight tolerances (±0.01mm) are required
Part size exceeds 200mm
Material selection is non-standard or experimental
Design changes are expected during development
Choose Die Casting When:
Parts are 50-300mm in size
High volumes (10,000+) of non-ferrous parts are needed
Surface finish requirements are moderate
Aluminum, zinc, or magnesium alloys are acceptable
Cost per unit at very high volumes is the primary concern
Real-World Examples
Automotive Sensor Housing
A sensor manufacturer needed a complex housing with integrated threads and mounting features. The part was 40mm × 30mm × 25mm, requiring 316L stainless steel at 50,000 pieces per year.
Initial approach: CNC machining from solid bar stock at $45 per unit.Optimized solution: MIM process at $8 per unit, with 80% cost reduction and improved dimensional consistency.
Medical Instrument Handle
A surgical instrument company required ergonomic handles in titanium Ti-6Al-4V for 2,000 pieces annually during the validation phase, scaling to 20,000 pieces for commercial production.
Phase 1 (validation): CNC machining for rapid design iteration at $120 per unit.Phase 2 (production): Transitioned to MIM at $18 per unit, maintaining material properties and achieving complex ergonomic geometry.
Conclusion
The choice between MIM, CNC machining, and die casting depends on your specific requirements for part complexity, production volume, material, precision, and cost. In many cases, a hybrid approach—using CNC for prototyping and MIM for production—delivers the best balance of development speed and manufacturing economy.
For complex metal parts in medium to high volumes, MIM consistently offers the best combination of design freedom, material versatility, and unit cost. Contact our engineering team for a free process evaluation and cost analysis for your specific application.