Posts by Align Manufacturing

What it is, how it works, when to use it, and how it compares to alternative manufacturing methods

Why MIM Matters in Modern Manufacturing

As consumer products become more compact, functional, and refined, the components inside them must meet higher standards—mechanically and visually. That’s where Metal Injection Molding (MIM) stands out.

MIM is a modern manufacturing method that blends the precision of machining with the scalability of injection molding. It’s designed for small, complex metal parts that need to be produced in high volumes, with the performance characteristics of solid metal.

For brands working on everything from wearables to medical devices or even firearm components, MIM offers a reliable path from prototype to scale. Let’s explore how this innovative process works and why it might be the manufacturing solution your next product needs.

What Is Metal Injection Molding?

Metal Injection Molding (MIM) is best described as plastic injection molding for metal.

Instead of molten metal, the process uses metal powder mixed with a plastic binder to form a moldable pellet (feedstock). These pellets are injected into a mold—just like plastic parts—and then go through a heat-driven process to burn off the plastic and fuse the metal, creating a fully dense component.

Think of it as a three-phase process:

1. Mold the shape using a plastic-metal hybrid
2. Remove the plastic binder
3. Sinter the part into solid metal

This gives you the freedom to design intricate geometries, internal features, and tight tolerances that would be expensive (or impossible) to CNC.

Understanding these fundamentals helps explain why MIM offers unique advantages for certain applications. Now, let’s look at exactly how the process unfolds…

How the MIM Process Works: Step-by-Step

1. Feedstock Preparation

Fine metal powders (typically 1-20 μm particle size) are precisely blended with thermoplastic binders (usually a combination of polymers, waxes, and surfactants) in a ratio of approximately 60% metal by volume (90% by weight). This mixture is compounded into homogeneous pellets that can be fed into standard injection molding equipment.

2. Injection Molding

These feedstock pellets are heated to 150-180°C and injected into precision molds at pressures ranging from 50-200 MPa. The result is a “green part”—the shape is formed, but it’s not yet solid metal. At this stage, the part is approximately 15-20% larger than the final desired dimensions to account for later shrinkage.

3. Debinding

The green part undergoes a carefully controlled debinding process to remove the binder material:

• Primary Debinding: Often uses solvent extraction (water, ethanol, or specialized solvents) to remove 30-40% of the binder
• Secondary Debinding: Thermal debinding at 200-600°C removes the remaining binder, leaving behind a fragile “brown part” that is approximately 60% porous

4. Sintering

This brown part is placed in a precisely controlled atmosphere furnace and heated to near the melting point of the metal (typically 1,200–1,400°C). During this process:

• The metal particles fuse together through solid-state diffusion
• The part shrinks uniformly by 15-20% in all dimensions
• Density increases to 96-99% of theoretical full metal density
• The microstructure develops to provide the desired mechanical properties

5. Secondary Operations (Optional)

Depending on application requirements, MIM parts may undergo additional processing:

• Heat Treatment: Annealing, hardening, or tempering to optimize mechanical properties
• Precision Machining: For critical features requiring tighter tolerances than as-sintered
• Surface Treatments: Including plating, coating, polishing, or PVD for enhanced performance
• Quality Inspection: Dimensional verification, material testing, and non-destructive evaluation

Process Quality Control

Throughout the MIM process, manufacturers implement rigorous quality control measures:

• Feedstock testing for consistent rheological properties
• In-process monitoring of molding parameters
• Statistical process control for dimensional stability
• Microstructural analysis and mechanical testing of finished parts

This careful, multi-step process results in parts with specific characteristics that make MIM particularly valuable in certain industries and applications.

Where MIM Shines: Ideal Applications

MIM is particularly suited for:

• High-volume production of small metal parts
• Intricate designs that would be costly to machine
• Applications where mechanical strength, complexity, and cost need to balance

Common industries using MIM include:

• Firearms: Triggers, safeties, linkages
• Automotive: Small actuators, gears, sensor housings
• Medical: Surgical instruments, dental brackets, implants
• Consumer Electronics: Hinges, structural frames, wearable components

To determine if your component is suitable for MIM, it helps to understand the specific parameters and design considerations that optimize the process.

Part Characteristics and Design Guidelines

• ✅ Size Range: Most MIM parts range from 2 grams to 100 grams, with optimal performance for small, complex components
• ✅ Tolerances: MIM can hold tolerances of ±0.3% (minimum of ±0.075mm/0.003″), which is excellent for precise applications
• ✅ Geometries: Undercuts, thin walls (down to 0.5mm), logos, internal features, and complex shapes that would be difficult or impossible to machine
• ✅ Material Density: MIM produces parts with 96-99% density, significantly higher than many other metal forming processes
• ✅ Surface Finish: As-sintered parts typically achieve 1-2 μm Ra without additional finishing

Compatible Materials for MIM

MIM works with a wide range of metal powders, categorized into four main groups:

1. Stainless Steels
   
   • 316L (excellent corrosion resistance, medical applications)
   • 17-4PH (high strength, good corrosion resistance)
   • 420 (high hardness, moderate corrosion resistance)
   • 440C (excellent wear resistance)
2. Low Alloy and Carbon Steels
   
   • 4140 (high fatigue strength)
   • 8620 (excellent carburizing properties)
   • 1070 (high carbon for wear applications)
   • 4605 (high strength, good toughness)
3. Specialty Alloys
   
   • Titanium (Ti-6Al-4V, medical and aerospace)
   • Inconel (high temperature applications)
   • Kovar (controlled expansion for electronics)
   • Tungsten alloys (high density applications)
4. Soft Magnetic Alloys
   
   • Fe-Ni alloys (high magnetic permeability)
   • Fe-Si (low core loss)
   • Soft ferrites (high frequency applications)

Design Tips for MIM Success:

• Maintain consistent wall thickness (ideally between 0.5-6mm)
• Design with uniform cross-sections where possible
• Account for 15-20% shrinkage during sintering
• Include draft angles of 0.5° or greater
• Avoid sharp corners (use radii of at least 0.25mm)
• Consider gating locations in the design phase

With these characteristics in mind, how does MIM compare to other common manufacturing methods? This comparison highlights where MIM truly offers an advantage.

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MIM vs. CNC vs. Die Casting

Feature	MIM	CNC Machining	Die Casting
Volume Suitability	High (10k+ parts)	Low to medium	Medium to high
Design Complexity	Very high	High	Moderate
Material Density	~98% solid metal	100%	Typically lower
Surface Finish	Smooth, uniform	Variable	Good
Setup Cost	Moderate (tooling required)	Low	High
Per-Part Cost	Low (at scale)	High	Moderate

Use MIM when your part is:

• Small and complex
• Needed in volume
• Doesn’t justify expensive machining
• Requires good mechanical properties

While the advantages are compelling, being aware of MIM’s limitations helps ensure you’re making the right manufacturing choice.

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Advantages and Limitations of MIM

Key Advantages

• Complex Geometries: MIM can produce intricate shapes that would be difficult or impossible with other methods
• Material Efficiency: Up to 98% of material can be converted to usable parts, reducing waste compared to machining
• Single-Process Manufacturing: Complex parts can be produced in one go, eliminating the need for assembly of multiple components
• Cost-Effective at Scale: For high volumes, MIM can be more economical than investment casting, machining, and sometimes even stamping
• Superior Mechanical Properties: Parts feature excellent strength, hardness, and density comparable to wrought metals
• Excellent Surface Finish: As-sintered parts typically have smooth surfaces requiring minimal post-processing

Limitations to Consider

• Tooling Time: Expect 6–10 weeks for tool creation
• Material Shrinkage: Parts shrink ~15–20% during sintering—Design for Manufacturability (DFM) is essential
• Minimum Volume: MIM makes most sense at 10,000+ units annually
• Size Restrictions: Generally limited to small parts under 100 grams
• Initial Investment: Tooling costs can be significant, though they’re amortized over large production runs
• Limited Material Selection: While diverse, not all metal alloys are compatible with the MIM process

MIM vs. Alternative Metal Manufacturing Processes

When considering Metal Injection Molding, it’s helpful to understand how it compares to other metal manufacturing processes:

Process	Advantages over MIM	Disadvantages compared to MIM
Die Casting	Faster cycle times, larger parts possible	Lower material properties, more porosity, fewer material options
Investment Casting	Larger parts, wider material range	Higher cost per part, lower detail resolution
Metal 3D Printing (DMLS)	No tooling costs, design freedom	Much higher per-part cost, slower production, surface finish limitations
Metal Binder Jetting	Larger build volumes	Lower density, requires infiltration for full density
CNC Machining	No tooling needed, 100% density	Expensive for complex geometries, material waste, limited internal features
Metal Stamping	Very high production rates	Limited to thin, flat parts with simple geometries

Brands often work with manufacturing partners like Align to get early design input, manage tooling, and prevent production issues. This partnership approach helps mitigate risks while maximizing the benefits MIM can offer.

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Industry Applications and Case Studies

Automotive Industry

MIM components are widely used in automotive applications, including:

• Powertrain Components: Turbocharger vanes, fuel injector parts, valve components
• Safety Systems: Airbag initiators, seatbelt components, sensor housings
• Interior Hardware: Gear selectors, switch components, decorative trim parts

Case Study: A major automotive manufacturer replaced a machined stainless steel transmission component with a MIM alternative, reducing part cost by 43% while improving wear resistance through better material uniformity.

Medical and Dental Sector

The biocompatibility and excellent surface finish of MIM make it ideal for:

• Surgical Instruments: Forceps, hemostats, endoscopic tools
• Implantable Devices: Orthopedic implant components, dental brackets
• Diagnostic Equipment: Precision components for medical devices

Case Study: A medical device company utilized MIM to produce titanium components for surgical tools, achieving complex geometries with thin walls that would have been prohibitively expensive to machine.

Firearms Industry

MIM has revolutionized firearms manufacturing for components like:

• Triggers and Fire Control Groups: Complex geometries with precise tolerances
• Hammers and Sears: High-wear components requiring excellent mechanical properties
• Safety Mechanisms: Intricate components with precise operational requirements

Case Study: A leading firearms manufacturer converted 14 different machined components to MIM, reducing production costs by over 60% while maintaining all performance specifications.

Consumer Electronics

As devices become smaller and more feature-rich, MIM is increasingly used for:

• Hinge Mechanisms: In smartphones, laptops, and wearables
• Structural Frames: For strength in compact devices
• Heat Sink Components: Thermal management in small form factors

Case Study: A smartwatch manufacturer implemented MIM for their watch case components, achieving complex aesthetics with integrated structural functionality that couldn’t be produced using alternative methods.

Final Thoughts: Is MIM Right for Your Product?

If your product includes small, high-detail metal components and you’re planning to scale, MIM could dramatically cut costs while improving part quality and consistency.

It’s particularly compelling for:

• Consumer brands scaling hardware production
• Product teams converting from CNC to something more scalable
• Engineers needing structural performance in a small form factor
• Designers seeking to consolidate multiple parts into single components

Decision Framework for MIM Implementation

When deciding whether MIM is right for your product, consider these key factors:

1. Production Volume
   
   • Under 50,000 units/year: Consider machining or metal 3D printing
   • 50,000-1
   • 0,000 units/year: MIM begins to be competitive, especially for complex parts
   • Over 100,000 units/year: MIM typically offers significant cost advantages
2. Part Complexity
   
   • Simple geometries: May be better suited for traditional manufacturing
   • Moderate complexity: Compare MIM with machining based on volume
   • High complexity: MIM likely offers substantial advantages, especially with internal features
3. Material Requirements
   
   • Standard alloys: Readily available in MIM
   • Specialized properties: Verify compatibility with your MIM supplier
   • Certification requirements: Discuss material certification capabilities early
4. Timeline Considerations
   
   • Prototype phase: 2-4 weeks for initial samples
   • Tooling development: 6-10 weeks for production tooling
   • Production ramp-up: 2-4 weeks after tooling approval
5. Cost Structure Analysis
   
   • Initial investment: $15,000-$50,000 for tooling (depending on complexity)
   • Per-part cost: Typically 30-60% lower than machining at volume
   • Total cost of ownership: Consider assembly elimination and secondary operation reduction

The best approach is to consult with manufacturing experts early in your design process. They can help evaluate your specific requirements and determine if MIM offers the optimal balance of cost, quality, and manufacturability for your application.

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🔗 Explore Align’s MIM Capabilities
Looking for help with MIM design, sourcing, or production? Align can manage your entire Metal Injection Molding process—from design validation to delivery.