In your current immediate environment, there are probably 5 or more items made with metal injection molding. It’s one of the fastest and most cost-effective ways of making metallic parts and products. Metal injection molding was invented in the 70s by Raymond Wiech, a physicist and NASA researcher.
Today, most of the world’s metal injection molding and manufacturing is done in China, where costs are low, and the technology is far advanced. EzraMade is a leader in this space.
What Is the Definition of Metal Injection Molding (MIM)?
Metal injection molding refers to the production of metallic parts using the injection molding process. The materials used include finely blended metal and thermoplastic powders. The injection and molding process is done just like in plastic injection molding, although there are a few differences between the two, as you will discover later.
Metal injection molding is instrumental in the production of automotive parts, consumer electronics, medical devices, and aerospace components. In other words, its applications are extensive, and as you would expect, the demand is huge.
Raymond made his discovery by improving on years of research and advancements in metallurgy in the aerospace industry. MIM creates complex, dimensional parts faster and much more cost-effectively. It’s a mass production technique.
Global governing standards such as ISO and MPIF guide the quality and safe use and manufacturing of MIM parts. With recorded densities of up to 95%, MIM parts are robust and hardy like wrought metal parts.
What is the Difference between Metal Injection Molding and Powder Metallurgy?
Feedstock Differences
Powder metallurgy is the creation of metallic parts by solidifying fine metal powders using controlled heat and pressing (no melting). Metal injection molding involves first mixing metal powders and thermoplastic binder materials. This blended feedstock is then melted and injected into a pre-shaped mold.
Shaping Process
In powder metallurgy, fine metal powder is forced into a die and pressed into the desired shape using hydraulic or mechanical presses. After that, the formed part goes through sintering, where the particles form metallurgical bonds through solid-state diffusion.
With metal injection molding, binders, which are typically waxes and polymers that can burn quickly, are used to hold metal powders together before injection and molding. After injection and molding, the binders are removed with heat.
Geometric Capability Comparison
As stated before, powder metallurgy requires uniaxial pressing to shape the metal powder into the die cavity. But this process limits the design freedom and geometric possibilities of the output part.
Therefore, PM can only work with simple designs that often exclude:
- Undercuts
- Internal cavities and channels
- Thin walls
Integrated threads and fasteners
Because metal injection molding involves pressing molten material blends into the mold cavity, you can design parts with complex geometric profiles. This means that parts spend less time in assembly and post-processing.
Compact Part Manufacturing
The demand for miniature parts is high in the medical devices and consumer electronics industries. Unlike powder metallurgy, which uses large particle sizes for structural strength, MIM powder particles can be as small as 5–10 microns. This makes it possible for MIM to produce tiny, lightweight parts with excellent product performance in these applications.
Density and Mechanical Properties
MIM parts have more tensile strength and yield strength than PM parts. The European Powder Metallurgy Association found that metal injection molding parts can attain high densities of 95% after sintering.
In comparison, powder metallurgy processes only yield densities of up to 94%. MIM’s high-density outputs result in parts that are stronger and more fatigue-resistant. In medical manufacturing, this is a beneficial qualification for implants and device components.
The high-density advantage of MIM parts also makes them less prone to corrosion. Materials Science and Engineering research shows that, indeed, the low chances of porosity in MIM actually improve the corrosion resistance of parts.
In marine applications, this is a highly needed property. Companies such as General Dynamics and BAE Systems prioritize corrosion resistance, tensile strength, and hardness when sourcing parts, in line with ASTM standards.
Tooling and Production Economics
At first, PM appears to be the cheaper path to high-quality metal parts production. Metal injection molding tooling is also more costly at first. However, down the road, when the production volume increases, MIM costs per part drop significantly. This makes it a cost-effective option for high-volume metallic parts production.
PM tooling costs are lower and perfect for low-volume production. Even so, you’ll come face to face with the design limitations we mentioned earlier, and that can be problematic in industries that reward or demand innovation.
Before you make the decision, you also have to think about scalability. Between the two, PM and MIM, the only approach that allows you to scale faster, leveraging precision and repeatability without inflating costs is — you guessed it — metal injection molding.
Application Suitability
Powder metallurgy works wonders for simple structural parts, including:
- Gears
- Bearings
- Engine parts
Metal injection molding is a high-precision metallic part production approach preferred in:
- Highly regulated industries
- Automotive sensors and actuators manufacturing
- ISO13485 Medical devices – surgical instruments, dental implants
- Mobile phone parts, cameras, and watches
- AS9100 defense and aerospace parts manufacturing
How Does the Metal Injection Molding Process Work Step by Step?
Metal Injection Molding (MIM) combines thermoplastics injection molding and powder metallurgy techniques. There are more steps involved in it as compared to standard plastic injection molding.
Feedstock Preparation
This is the material preparation stage and involves mixing fine metal powder together with thermoplastic binder resins. The binder material improves flow and the “injectability” of the metal materials. A precise ratio of about 60 (metal) to 40 (binder) helps achieve superior parts quality later after molding.
But the actual mixing is done with shear mixers and twin screw extruders. The goal is to achieve super fine blending so that parts don’t come out with density gradients. Finally, the materials are heated and converted into free-flowing feedstock.
Injection Molding Stage
The feedstock is injected into a steel mold at high temperature and pressure. High pressure helps ensure that the molten material fills the cavity fully so as to achieve high geometrical accuracy in the finished part.
The molded part, also called a green part, is dimensionally accurate but has weak mechanical strength. The binder is what holds everything together. Unlike standard injection molding, MIM Engineers always have to plan for shrinkage and tolerance loss in the later stages of production.
Debinding Process
Debinding is the removal of the thermoplastic binder from the green part in preparation for sintering. This can be done with:
- Solvents
- Heat
- Gas catalysts
The debinding process must be done carefully to prevent cracking. After the removal of thermoplastics, the result is known as a brown part. This is essentially a porous, binder-free molded metallic part that’s ready for sintering.
Sintering Stage
Sintering involves heating the brown part close to the material’s melting point for the sole purpose of strengthening the fusion and binding of the particles. During the process, the brown parts shrink because pores close during solid-state diffusion.
The sintering process adds unique value to metal injection molding. Through sintering, manufacturers are able to produce robust parts with high load-bearing capacities. This happens because in the heat-driven process, individual particles lose their individuality and form a single grain structure. This merging creates stronger metallurgical bonds, making sintered parts hard and fatigue-resistant.
Secondary Operations
Depending on the applications, sometimes parts have to go through secondary finishing before assembly or shipping. Expect these secondary operations to be minimalistic as compared to other metal manufacturing processes. Well-designed parts typically don’t require post-processing. MIM finishing operations typically involve:
- Heat treating to improve wear resistance
- Surface treatments for enhanced aesthetics
- Machining
What Are the Pros and Cons of Metal Injection Molding?
The profit potential of metal injection molding is limitless, but there are also many drawbacks to consider when choosing this manufacturing method.
Pros
- MIM creates parts with complex shapes and dimensions
- Multiple parts can be molded together into a single part
- MIM parts have near-wrought mechanical properties due to strong bonding during sintering
- Material wastage is quite minimal
- Production costs are lower because tooling expenses are amortized over high-volume runs.
Cons
- There is always a risk of distortion during sintering when working with large or thick parts
- Tooling lead times are significantly longer than machining, making it unsuitable for prototyping
- Low-melting materials don’t sinter well
- Small variations in process parameters lead to large defects
What Are Some Common Examples of Metal Injection Molding Products?
Industries that require high-volume production of high-precision parts are the biggest clients of metal injection molding. Some of them are:
Medical Devices
MIM parts continually receive preferential treatment from medical manufacturers. This is driven by the strength and corrosion resistance properties that MIM makes possible, along with biocompatibility. Examples of MIM parts in the medical field include:
- Surgical scissors
- Forceps head components
- Needle holders & biopsy forceps tips
- Laparoscopic instrument jaw & gripper parts
- Orthopedic brackets and fixation devices
Firearms and Defense Parts
After Raymond perfected the metal injection molding process, firearm manufacturers were the first customers on the line. MIM made it possible to make pistol and gun parts that are stronger, geometrically precise, and consistent. Examples of MIM parts in firearms are safeties, hammers, and triggers.
In defense operations, products must survive rapid accelerations, vibrations, and heat stress. Mechanical parts must have tighter tolerances and be dimensionally accurate, even in compact products. MIM makes it possible to produce parts that meet these requirements in missile and munitions systems, military aircraft, and UAVs:
- Safety-and-arming device components
- Actuator housings
- Guidance system mechanical carriers
- Electrical connector housings
- Sensor mounts
- Cooling system brackets
Consumer Electronics
Metal injection molding is commonly used to make electronic parts like connectors, hinges, and brackets. These parts can be made with thin walls without sacrificing their dimensional accuracy.
Similarly, MIM is fundamental in the production of SIM card trays, hinge pins, and camera module brackets in smartphones. These parts are produced with high-quality surface finishes.
For the smart watch industry, consistent mass production of button shafts, hinge elements, and optical sensor mounts wouldn’t be possible without MIM. This manufacturing process is highly preferred because of its ability to produce parts that are:
- Durable
- Consistent
- Safe skin contact
- Compact and highly functional
Automotive Components
Auto makers rely on trusted MIM partners to consistently supply them with high-performance sensors and actuators. For reliability and the safe operability of motor vehicles, these nitty-gritty parts must meet high expectations in precision and resilience.
To achieve and exceed these expectations, metal injection molders usually choose high-temperature alloys, and thankfully, MIM makes it possible to achieve the complex functional geometries needed for their top performance.
Industrial and Aerospace Parts
Industrial equipment and aerospace manufacturers rely on metal injection molding to make high-precision parts, including:
- Harmonic drive elements
- Locking cams and dents
- Encoder housings
- Seat recline mechanisms
- Flow control housings
- Gearbox gears
- Overhead bin latches
What Is Metal Injection Molding Used For?
Here are the common instances when metal injection molding makes more sense than all the alternative manufacturing approaches.
Miniaturization
Smart systems from wearable devices in consumer electronics to industrial and defense applications now need to be smaller and lighter. Compact designs boost their user friendliness, performance, and power efficiency. MIM delivers robust micro-level parts through a specialized variation of the process called micro metal injection molding.
Precision Engineering
MIM can produce parts with tight tolerances, high density, and high mechanical strength. Performance and fit are fine-tuned with strategic design adjustments. The parts behave predictably in structural applications because of thorough bonding during sintering.
Scalable Manufacturing
Metal injection molding makes it possible to scale the production volume of metallic parts without quality inconsistencies. You get the speed and design flexibility of plastic injection molding and the strength and performance of metallurgical manufacturing processes. Once tooling is done, the rest of the process is repeatable, fast, and cost-effective.
Compliance Manufacturing
In highly regulated industries, parts often need to have strict tolerances and material properties that improve repeatability and process validation.
MIM parts require minimal post-processing, so this lowers the risks of inconsistency during compliance audits. The manufacturing is done in alignment with ISO, FDA, FAA, and IASTM regulatory standards.
How Metal Injection Molding Differs from Other Manufacturing Technologies
See the following comparison table to understand where and how MIM differs from other manufacturing technologies.
| Comparison | Metal Injection Molding (MIM) | Powder Metallurgy (PM) | Casting (Die / Investment) | CNC Machining | Additive Manufacturing (Metal 3D Printing) | Metal Stamping / Forming |
| Scalability | High | Very High | Medium–High | Low–Medium | Low | Very High |
| Part Complexity | Excellent (undercuts, thin walls) | Limited | Moderate | High but costly | Excellent | Low |
| Density (% of wrought) | 95–99% | 85–94% | 90–98% | 100% | 95–99% | 100% |
| Mechanical Properties | Near-wrought, isotropic | Directional, lower fatigue | Variable, grain defects | Wrought | Directional, heat-affected | Wrought |
| Surface Finish | Very good | Fair | Fair–Good | Excellent | Poor–Fair | Excellent |
| Dimensional Tolerance | Tight (±0.3% typical) | Moderate | Loose–Moderate | Very tight | Moderate | Tight |
| Tooling Costs (Upfront) | High | Medium | Medium–High | Low | None | High |
| Material Waste | Very low | Low | Medium | High | Medium | Very low |
| Typical Part Size | Small (<100 g) | Small–Medium | Medium–Large | Any | Small–Medium | Thin sheet parts |
| Lead Time to Production | Medium–Long | Medium | Medium | Short | Short | Medium |
Metal Injection Molding vs Powder Metallurgy
If your project involves simple designs and large parts, choose powder metallurgy. However, because of their porosity, PM parts have very limited applications. If you want to mass-produce complex parts without the anisotropic mechanical limitations typical in PM, then choose metal injection molding.
Metal Injection Molding vs Casting
Casting is reliable when producing large and thick parts with looser tolerances. Expect lower tooling costs and the freedom to work with a diverse range of materials. But when applications require tighter tolerances and fine features, you should choose metal injection molding. You can achieve thin walls and robust grain structures with stable internal features.
Metal Injection Molding vs. Machining
Choose machining if speed matters more to you in low-volume production and prototyping. The design flexibility in machining is relatively extensive, but it only works well for large parts with simpler geometries. Although lead times are longer with MIM, per-part costs are extremely low in high-volume runs.
Metal Injection Molding vs. Additive Manufacturing
The greatest advantage of additive manufacturing over MIM is design freedom, given how parts can be made with internal features from the onset. Choose AM if you want more customization and if you can’t bear high tooling costs. However, metal injection molding delivers higher consistency in high-volume runs.
Metal Injection Molding vs. Metal Stamping
Metal stamping is super low-cost when mass-producing parts of simpler geometrical profiles. You also get to the finished part much faster than with MIM. But for the best results with small, intricate parts, you will need MM. You get high-density and high-strength parts while the rate of defects is near zero.
How Much Does Metal Injection Molding Cost?
Tooling is the biggest cost driver in metal injection molding. But the final amount will be heavily influenced by the type of materials you choose and the production volume.
Tooling Costs
Hardened steel molds are the most frequently used, and these can cost a few thousand dollars to hundreds of thousands of dollars. Complex molds cost more than simpler molds, but overall tooling costs amortize well over thousands and millions of units to near zero.
Material Costs
Expect to pay about $100 per pound for refined metal powders. Stainless steel powders cost more than carbon powders. In addition, you’ll need binder materials, which often cost $10- $12 per pound.
Processing and Labor Costs
Metal injection molding processes can be fully automated, which helps cut down labor costs. The biggest cost drivers on the production floor are energy consumption and equipment monitoring. High runs of over 100K parts typically have lower processing and labor costs of $1- $3 per part. In low-volume runs, these fees can be as high as $5 per part.
Secondary Operations Cost
Secondary operations like heat treatment, coating, and machining add to the overall costs. Expect to pay $.50 to $5 per part in post-processing. These costs can be eliminated by optimizing the designs before starting production.
Also Read
How Much Does Custom Injection Molding Cost?
Design Guidelines and Limitations for Metal Injection Molding
Wall Thickness and Uniformity
Maintain uniform wall thickness for consistent results in production. When the design has varying wall thickness, the end product may shrink or warp. When everything is standardized, cycle times reduce, output quality increases, and the risk of defects is lowered.
Tolerances and Shrinkage Control
Although shrinkage is part of the nature of MIM, you can make up for it with strategic tooling adjustments. On average, the brown part shrinks 10 – 20% upon sintering, and so the mold cavity has to be 10 – 20% larger than the final part. Tolerances must be as high as ±0.3% to minimize the need for post-sintering operations.
Feature Design and Complexity
You can design complex 3D shapes with undercuts, threads, and cross-holes. These design adjustments eliminate the need for assembly and post-processing operations, and their costs can be written off with tooling amortization. Avoid sharp corners, but feel free to use fillets for better strength and cavity filling.
Material Selection Constraints
The most preferred high-performance alloys for metal injection molding include steel, copper, and aluminum. When choosing metal injection materials, consider the desired part performance and mechanical properties. For corrosion resistance and strength, steel is the most recommended material.
Conclusion
Metal injection molding is a highly effective manufacturing technology with cross-industry applications. The success of this production method depends on the design, material selection, and diligent process control. In industries where precision and miniaturization are of great importance, MIM proves to be extremely valuable.
Choose EzraMade for the best results in metal injection molding. Through our expert design optimization, material selection guidance, and process control discipline, we help you overcome common pitfalls and achieve great success with your product. Start your project here.
FAQs
In high-volume production, MIM can eliminate most machining, but it rarely replaces it completely. Critical features such as ultra-tight tolerances, bearing surfaces, or mating interfaces may still require light secondary machining.
MIM usually becomes cost-effective when annual volumes exceed several tens of thousands of parts. Below that threshold, tooling amortization may outweigh the benefits compared to machining or additive manufacturing.
From finalized design to production-ready parts, timelines commonly range from 8 to 16 weeks. This includes tooling fabrication, feedstock tuning, trial runs, and process validation.
Yes, MIM parts can be welded, brazed, or mechanically fastened, but the high density and alloy composition must be considered.
Yes, when properly designed and validated, MIM parts are widely used in safety-critical applications such as medical instruments, automotive systems, and aerospace mechanisms due to their high density and isotropic strength.
Recycled metal powder is rarely used in critical MIM applications because particle size, chemistry, and flow consistency are difficult to control. Virgin powders are preferred for predictable quality and performance.
