How to Choose the Right Manufacturing Process: MIM vs CNC vs Die Casting

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.