Metal Injection Molding Process, Benefits, And Tips

Metal injection molding, usually abbreviated as MIM, is commonly used to create small metal parts with complex designs. Although the process is similar to plastic injection molding, a few notable differences make it unique. Get to know what injection molding metal entails and how you can use it for your metal parts project.

What is Metal Injection Molding?

Metal injection molding (MIM) describes the process where small, intricate metallic products are manufactured using a conventional injection molding machine. It is also commonly called powdered metal injection molding since metal powder is the key ingredient.

The history of metal injection molding goes back to the late 1970s when Raymond Wiech is credited to have developed the technology. Since, then, the process has been steadily increasing in popularity and used to create parts in various industries, including aerospace, automotive, and medical.

How Does Metal Injection Molding Work?

Metal injection molding works by combining the workability of plastics with the rigidity and strength of metals. A mix of powdered metal and polymer binders is used to create a feedstock and shaped in an injection molding machine, although additional steps are often required. Let’s start with the machine itself.

Metal Injection Molding Machine

The metal injection molding machine is no different than a standard injection molding machine. It consists of the typical components, such as an injection unit, clamping unit, mold, and control systems.

The injection unit is composed of a hopper to receive the material and a reciprocating screw to melt it. This screw also forces the feedstock into the mold where it is held under pressure while cooling to produce the finished part.

The clamping unit holds the two halves of the metal injection mold together, ensuring that they remain tightly clamped when it’s time for molding. The control system monitors the injection pressure and speed, temperature, and other critical parameters to ensure that the part is produced correctly.

Metal Injection Molding Products

In the injection molding industry, the use of MIM results in a wide number of parts and products. From small components used in consumer electronics to automotive parts, medical implants, aerospace components, and even jewelry – the possibilities are endless.

Typically, MIM is best suited for complex shapes with intricate details that would otherwise be impossible or too expensive to produce using other methods. Examples of metal injection molding applications are:

• Medical implants
• Orthodontic brackets
• Automotive parts
• Aerospace components

It’s good to note that metal injection molding products are currently limited to parts that are less than 5 cm in size and usually weigh between 5-100 grams, although larger parts can be produced.

Metal Injection Molding Process

The metal injection molding process begins with the mixing of metal powder and a binder to form what’s known as a feedstock. This is what will be injected into the injection molding machine. Metal injection binder materials can be anything from polymers to resin and wax.

Once the raw material is formed, usually in the form of granules and 60:40 metal-to-binder ratios, the molding process can begin. Here are the steps involved:

1. The metal injection molding feedstock is heated and poured into the injection molding machine. Here, it’s heated and pushed forward by a screw.

2. The injection molding machine pushes the pressurized material into a heated cavity or pre-form. This preform is what will give the desired shape to the finished product.

3. The mold is made larger than the desired product size. This is to allow for the shrinkage of the material when the binding material will be removed in the next step.

4. The solid part is ejected from the mold and the binder is removed. This can be done through a variety of methods such as heat, catalyst, or solvent extraction.

5. The part is then sintered. In metal injection molding, sintering increases the material’s overall density by melting particles together so they form a solid structure and reach its final strength. It also removes any remaining binding material.

Metal Injection Molding Advantages and Disadvantages

Why would you want to use metal injection molding for your parts and components? A look at the advantages and disadvantages can help give some perspective.

Metal Injection Molding Advantages

Metal injection molding advantages range from part complexity to design flexibility. Here are reasons why you might want to choose metal injection molding:

High volume: The metal injection molding process is well-suited for mass production, resulting in lower parts costs than traditional machining.

Complex designs: Metal injection molding allows for complex parts and components with intricate geometries and detailed features.

Material options: There are many options for metal injection molding materials, stainless steel, titanium alloys, copper alloys, carbon steel, nickel alloys and so on, which means different properties to fit different applications

Low waste: As the feedstock of metal powder and polymer binder is mixed, any excess material can be reused in future batches.

Durable parts: Metal injection molding parts are highly durable and wear-resistant. That makes them ideal for a variety of uses.

Tight tolerances: Metal injection molding tolerances can be quite tight. This suits many high-precision applications.

Metal Injection Molding Disadvantages

Although metal injection molding has many advantages, it does have some drawbacks to consider. Here are potential disadvantages to metal injection molding:

Expensive tooling: The cost of metal injection molding tooling can be quite high compared to other methods. The high metal injection molding cost also includes that of the raw materials.

Long lead time: The tooling process can take several weeks, which is longer than other processes.

Metal Injection Molding Vs. Machining

Metal injection molding and machining are two popular methods for producing parts, but each has its benefits and drawbacks. To help you compare metal injection molding vs. machining, here are some key facts about the two processes.

• Metal injection molding involves mixing a binder with a metal powder and injecting it into a cavity to shape it. Machining, on the other hand, starts with solid blocks of metal and shapes them using computer-controlled cutting tools.
• Also, while metal injection molding requires a mold, machining does not. Instead, machining is done using cutting tools and machines to shape the metal.
• In terms of cost, metal injection molding can be more expensive due to the cost of tooling upfront. Machining generally has a lower upfront cost but can require more material depending on how complex the product is.
• Additionally, the metal injection molding process produces fewer waste materials while machining often creates a large amount of scrap and burrs.

Overall, each process has its pros and cons, so it’s important to assess the requirements of your project and determine which the best option for you is.

Conclusion

Metal injection molding is a versatile process that’s well-suited for mass production and handling complex designs. It requires minimal waste, has tight tolerances, and produces durable parts. Although it requires more steps than plastic injection molding and machining, the benefits often outweigh the time and cost associated with it