Metal Injection Molding

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Metal injection molding with 3ERP

Injection molding is the world’s most popular manufacturing process for plastic components. With a few adjustments, however, the process can also be used to create metal parts.

Metal injection molding (MIM) uses metal powder mixed with a binder to create precise, repeatable metal parts in large quantities — ideal for mass production across a range of industries. The process requires just a few extra steps, including granulation, debinding and sintering.

3ERP is an experienced provider of metal injection molding services and is capable of creating molded metal parts for any application.

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Metal injection molding materials

Common metals

Alloy steel
Carbon steel
Stainless steel
Iron
Copper
Nickel
Titanium

Common binder materials

Wax
Polypropylene

3ERP's Metal Injection Molding Services is Trusted by Worldwide Engineers

The parts for the nylon plastic clips have been working very good so far. We have had the product in production for about 3 months now and have not found any issues.
I am introducing you now to our partner, Jay. He is CC’d on this email. He will be ordering the parts from you directly with the next order.
Also, I think we did about 125,000 units with this tooling so far. How many more units do you expect we can run before needing another tooling?

David

CEO

What is metal injection molding?

As its name suggests, metal injection molding is a form of injection molding in which the feedstock consists of finely powdered metal mixed with binder material (instead of the usual plastic resin). Common metals used in MIM include steels, irons and nickels, while binder materials are typically polymers such as polypropylene.
Once the metal powder and binder have been mixed and granulated into usable feedstock (pellets), the metal injection process closely mirrors traditional injection molding.

During the molding process, the feedstock is dispensed from a hopper into a heated chamber, where it becomes liquid and is moved toward the mold with a reciprocating screw. Once injected into the mold, the liquid cools and solidifies, and the solid part is then removed from the mold — just like a plastic part.

But that’s only half the story. The so-called ‘green’ part — the object removed from the mold — is not yet ready for use, because the binder material must be removed from the part using solvents, heat or another process, leaving behind a porous (and fragile) metal part. Once this debinding process is complete, the part is said to be in its ‘brown’ stage.

The final step involves sintering the brown part at a very high temperature, increasing its density and making it stronger. The finished part can then be subjected to any necessary finishes, adjustments or heat treatments.

MIM process summary:

Mix metal powder and binder to make feedstock
Melt feedstock and inject it into mold
Eject solidified molded part
Remove binder with solvent, heat, etc.
Sinter metal part to increase density
Carry out any required assembly or post-processing procedures

Advantages of metal injection molding

Metal injection molding offers many of the advantages provided by traditional injection molding, with additional benefits provided by the metals and their unique mechanical properties. Specific advantages of MIM include:

Large production volumes

Molds can be used many times over, which makes it possible to fabricate huge quantities of identical metal parts, from tens of thousands to hundreds of thousands. If large volumes are required, metal injection molding may present a significant advantage over other metalworking processes like CNC machining.

Good surface finish

Plastic molded parts are favored for their smooth surface finish, and metal injection molding provides similar benefits with metal parts. MIM does not produce unsightly burrs and tooling marks, reducing the need for post-processing.

Complex shapes with detailed features

As long as it’s possible to create the mold itself, metal injection molding is fully capable of creating complex parts with delicate or intricate details. Because the reciprocating screw injects the liquid material with force into the mold, the material reaches every fine crevice.

Strong parts

Metal injection molding is compatible with a range of high-quality engineering materials, and the sintering stage of the process ensures that the molded parts possess good mechanical properties.

Minimal metal waste

Once the feedstock has been injected into the mold, there is generally no need to cut away any excess material. This makes the process very efficient in terms of material usage, with the only material wastage occurring during mold production and debinding.

All-in-one process

Although metal injection molding involves multiple stages, it can actually shorten manufacturing cycles by eliminating extra setups and finishing procedures. Adding internal threads or embossed text, for example, will not drastically increase lead times, since these features can simply be incorporated into the mold (instead of being added to each individual molded part).

Limitations of metal injection molding

Metal injection molding isn’t suitable for all projects. Its limitations include:

Small envelope not suitable for large parts
Thin walls required
Can be slower than alternatives
Can be more costly than alternatives

Standard tolerances & dimensions

	Typical	Possible
Tolerance	± 0.005” (0.13 mm)	± 0.0015” (0.04 mm)
Max wall thickness	0.25” (6.35 mm)	1.2” (30.48 mm)
Surface finish	25–35 μin	16–80 μin

Industries & common products

Metal injection molding is a suitable process for large volumes of small, detailed metal parts. For small quantities or larger parts, other processes like CNC machining lost wax casting or sheet metal fabrication may be more suitable.

The ability of MIM to produce detailed metal parts in large volumes makes it popular in the industrial, aerospace, automotive, medical, dental and commercial sectors.

Common metal injection molded parts include but are not limited to:

Consumer products
Surgical tools
Cellphone parts
Laptop parts
Watch cases
Knives
Firearm parts
Heat sinks
Hinges
Armatures

Design considerations

In general, design rules for injection molding also apply to metal injection molding. These include:

Incorporate radii
Hollow out parts
Include ribs
Keep consistent wall thicknesses
Avoid undercuts

The following rules also apply to MIM:

Include most features

Part features like surface texture, threads, text and logos can all be incorporated into the mold instead of being added after the molding process.

Forget draft

Unlike plastic injection molding, metal injection molding often does not require any draft at all. This is because the polymer binding material is less rigid than a solidified molding polymer, and because the metal part is often not fully solidified when it is removed from the mold.

Thin walls

Thin walls are recommended with all forms of injection molding due to their positive effect on injection and cooling times. With metal injection molding, however, thin walls have the added benefit of reducing the time taken for debinding and sintering.

Start Your Injection Molding Project Today

3ERP provides injection molding services and prototyping at highly competitive prices. We offer a wide variety of available plastic resins, custom colors, and finishing options and we can deliver injection molding prototype parts in as little as 15 days. As part of our injection molding service, we use CAD/CAM part and mold design, design for manufacturability (DFM), and mold flow simulation. We offer overmolding, insert molding, unscrew molding, and mold trial reporting. For more information about our injection molding and prototyping capabilities, please contact 3ERP today.