Many manufacturers need small, complex metal parts. Traditional machining often incurs high costs and results in material waste. Powder metallurgy has limitations in terms of strength and detail. Metal Injection Molding solves these problems. It combines the details of plastic injection molding with the strength of metal. MIM can produce strong, detailed parts at a lower cost.
MIM sounds like a mix of plastic and metal processes. That’s because it is. Now, let’s look closer at how it works and where it’s used.
What Is Metal Injection Molding?
El moldeo por inyección de metal (MIM) es un método de fabricación que utiliza polvo metálico y un aglutinante plástico. En primer lugar, el polvo metálico se mezcla con el aglutinante para formar una materia prima. Esta mezcla se inyecta en un molde, de forma muy similar a como se fabrican las piezas de plástico.
After molding, the binder is removed in a step called debinding. Then, the part is heated in a furnace during the sintering process. This step bonds the metal particles, making a dense and strong final part. The result is a metal component with high accuracy and a good surface finish.
MIM is excellent for making small and complex parts in large quantities. It also reduces material waste and post-processing work.
Materials Used in Metal Injection Molding
Selecting the right materials is crucial for MIM. The process needs fine metal powders and binders that can form, flow, and then cleanly burn away. Each part of the mix plays a different role.
Types of Metal Powders
MIM uses excellent metal powders. These powders are usually less than 20 microns in size. Smaller particles help the mixture fill the mold more effectively and sinter into a denser part.
Common metals used in MIM include:
- Acero inoxidable: for corrosion resistance and strength
- Low alloy steel: for structural parts
- Titanio: for lightweight and high-strength
- Cobre: for good electrical conductivity
- Tungsten and carbide alloys: for wear resistance and hardness
Binder Materials and Their Role
The binder holds the metal powder together during molding. It provides a feedstock with a plastic-like flow, allowing it to fill the mold just like plastic resin.
Binders are usually made of:
- Waxes
- Polymers
- Additives to improve mixing or molding
After the part is molded, the binder must be removed. This step is called debinding. The binder must burn off cleanly and leave no residue that could affect sintering.
Material Selection Based on Application
The metal and binder you choose depend on what the part needs to do. For example:
- Use stainless steel for medical tools or watch parts.
- Use titanium for aerospace or surgical parts.
- Use low alloy steel for strong mechanical parts.
The Metal Injection Molding Process
MIM has four main steps. Each one plays a crucial role in shaping the metal and transforming the powder into a finished part. The process is repeatable and suitable for complex shapes.
Feedstock Preparation
First, metal powder is mixed with a binder. This mix is called feedstock. The binder helps the metal powder flow during the molding process.
The mix must be uniform. If the powder and binder are not well mixed, it can cause defects later. Once ready, the feedstock is converted into pellets, similar to plastic resin.
Injection Molding Stage
The pellets are heated and injected into a mold under pressure. This step works like plastic injection molding. The mold defines the part’s shape and surface features.
The result is a “green part.” It has the shape of the final piece but is still held together by the binder. The green part is fragile. It must be handled with care before the next steps.
Debinding Process Explained
Next, the binder is removed. This step is called debinding. There are a few ways to do it:
- Solvent debinding: uses a liquid to dissolve part of the binder
- Thermal debinding: heats the part slowly to remove the rest
After this, you get a “brown part.” It still retains its metal shape but lacks a binder. It’s very porous and weak at this stage.
Sintering and Densification
The brown part goes into a furnace. It’s heated close to the metal’s melting point but not melted. This is sintering. During sintering, the metal particles bond together. The part shrinks and becomes dense.
After sintering, the part has its final shape, strength, and size. The shrinkage is typically around 15–20%, so it must be factored into the design.
Design Considerations for MIM
To get the best results with MIM, the part must be designed with the process in mind. Some features are easy to make. Others require extra consideration to avoid defects or incurring added costs.
Tolerances and Wall Thickness
MIM parts can hold tight tolerances. Typical tolerances are ±0.3% of the part size. In many cases, secondary machining is not needed.
Wall thickness should be even. Thin walls under 0.5 mm are possible but may cause warping. Thick walls may slow down the debinding and sintering processes. A good range is 0.5 mm to 4 mm.
Sudden changes in wall thickness should be avoided. Gradual transitions reduce stress and distortion.
Undercuts, Threads, and Complex Geometries
MIM shines in making complex shapes. Undercuts, holes, and fine details are easier here than with mecanizado o fundición.
Features like:
- Inner threads
- Side holes
- Gear teeth
- Logos or textures
These can be molded directly into the part. However, some may require specialized tooling, such as slides or cores.
Designers should avoid sharp corners and deep agujeros ciegos. These can trap the binder or cause stress during the sintering process.
Volume and Part Consolidation
MIM is best for high-volume production. The tooling cost is high, but part cost drops with volume. Good applications start at thousands of pieces per year.
MIM also allows part consolidation. Instead of machining and joining several parts, MIM can mold them into a single piece. This reduces cost, weight, and assembly steps.
Advantages of Metal Injection Molding
MIM offers several significant benefits, particularly when producing small, intricate metal parts in large quantities. It fills the gap between machining and traditional powder metallurgy.
High Precision for Complex Parts
MIM can create parts with very tight tolerances and fine details. It handles complex or expensive-to-machine shapes. Features like small holes, sharp edges, and textured surfaces can be molded directly.
Cost Efficiency for Mass Production
Once the mold is made, MIM is highly cost-effective for large runs. Parts come out of the mold nearly finished. You save time and labor. The per-part cost drops as volume increases.
Minimal Waste and High Material Utilization
MIM uses almost all the metal powder in the final part. There is a tiny scrap. This is a significant advantage over CNC machining, which involves cutting away large amounts of metal.
Enhanced Mechanical Properties
MIM parts are firm and dense. They can reach over 95% of wrought material density. This gives them excellent strength, hardness, and wear resistance.
Limitaciones y desafíos
While MIM has numerous benefits, it also has its limitations. These should be understood early in the project to avoid surprises during production.
Elevados costes iniciales de utillaje
MIM requires custom molds. These molds are costly to design and build. If your production volume is low, the tooling cost may not be worth it.
Material Shrinkage and Distortion
MIM parts shrink during sintering. The shrinkage is around 15–20%. If not managed well, this can cause distortion or uneven part sizes.
Best Suited for Small to Medium-Sized Parts
MIM is ideal for small parts, usually under 100 grams. Larger parts are more challenging to process evenly. Debinding and sintering are more time-consuming and carry a higher risk.
Applications of Metal Injection Molding
MIM is used across many industries. It helps produce small, high-strength parts where precision and volume are crucial. These parts often go unnoticed but play key roles in critical systems.
Medical Devices and Surgical Tools
MIM is often used in surgical tools, dental brackets, and orthopedic devices. These parts need to be small, strong, and corrosion-resistant. MIM offers the needed accuracy and cleanliness required for medical use.
Componentes aeroespaciales y de defensa
Aerospace and defense parts must be lightweight, durable, and precise. It’s used in sujetadores, sensor housings, locking systems, and brackets. These parts benefit from the strength and detail MIM can deliver.
Consumer Electronics and Mobile Devices
MIM is common in mobile phones, wearables, and laptops. Parts such as hinges, camera modules, and connectors are often made using MIM. It allows for slim profiles, smooth surfaces, and detailed designs that fit tight device layouts.
Automotive Engine and Transmission Parts
In vehicles, MIM is used for gears, turbocharger components, levers, and locking mechanisms. These parts must withstand heat, pressure, and wear.
Conclusión
Metal Injection Molding is a method that combines plastic injection molding and metal processing. It uses fine metal powder mixed with a binder to mold complex shapes. MIM is ideal for producing small, complex metal parts in high volumes. It offers precision, strength, and cost savings.
Do you need custom metal parts with tight tolerances and exceptional strength? Get in touch with us to explore how MIM can help your next project. Our team is ready to support your production from prototype to full scale.
Hola, soy Kevin Lee
Durante los últimos 10 años, he estado inmerso en diversas formas de fabricación de chapa metálica, compartiendo aquí ideas interesantes de mis experiencias en diversos talleres.
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Kevin Lee
Tengo más de diez años de experiencia profesional en la fabricación de chapas metálicas, especializada en corte por láser, plegado, soldadura y técnicas de tratamiento de superficies. Como Director Técnico de Shengen, me comprometo a resolver complejos retos de fabricación y a impulsar la innovación y la calidad en cada proyecto.
