MIM Additive Manufacturing

mim additive manufacturing refers to an industrial process to produce small, complex metal parts at high volumes. A composite metal powder feedstock is molded into a green-state shape using injection molding equipment, debound, and then sintered to achieve full density.

MIM leverages the geometric flexibility of polymer injection molding and green-forming with the performance capability of metal alloys. With additive manufacturing processes expanding options, this guide covers MIM compositions, properties, applications, specifications, process flows, suppliers, tradeoffs, and FAQs.

Composition of MIM Alloys

Many compositions are available as MIM feedstocks:

Material	Common Alloys	Overview
Stainless steel	316L, 17-4PH, 420	Corrosion resistant, high hardness, for medical uses
Tool steel	H13, P20	High strength, heat resistance, for molded tooling
Aluminum alloy	2024, 6061, 7075	Lightweight, high strength-to-weight ratio
Titanium alloy	Ti-6Al-4V	Lightweight with corrosion resistance and high strength for aerospace uses
Nickel alloy	Inconel 625 and 718	Heat/corrosion resistance suited for turbo machinery
Tungsten	WHA, WC	Extremely high density perfect for balancing applications

Both standard and custom formulations are available depending on needs.

Properties of mim additive manufacturing

In addition to composition tailored to performance requirements, key resulting properties include:

Property	Description
Density	Ranges from near pure metal density to greater than 95% theoretical density
Tensile strength	250 MPa to over 1300 MPa depending on reinforcement strategies
Hardness	Up to 70 HRC achieved based on alloy choice
Corrosion resistance	Varying resistance levels possible based on compositions selected
Surface roughness	As molded <6 μm Ra up to <0.2 μm Ra after plating/polishing
Complex geometry	Molding allows intricate shapes unachievable with other processes
Feature resolution	Small slots, holes, threads down to ~100 μm » achievable
Wall thickness	As low as ~0.25 mm walls molded based on geometry
Tolerances	Tighter tolerances than metal AM, typical ±0.3% of dimensions

These capabilities make MIM suitable for end-use precision components.

Applications of MIM Additive Manufacturing

MIM’s geometric flexibility and tailored composition suit various industries:

Industry	Component Examples
Automotive	Gears, rocker arms, turbocharger components
Aerospace	Turbine blades, impellers, nozzle guide vanes
Firearms	Triggers, safeties, slides, ejectors, muzzles
Medical/Dental	Scalpel handles, forceps, skull plates, crowns
Oil and Gas	Valve parts including bodies, stems, actuators
Micro Electronics	Shields, connectors, pins, spacers, actuators

MIM also helps create tooling inserts capable of mass production molding/forming operations.

MIM Feedstock Specifications

Feedstock properties require careful control for tolerance and feature capability:

Parameter	Typical Specification	Test Method
Powder particle size	3 – 20 μm	Laser diffraction
Powder loading	>55 vol%	Thermogravimetric analysis
Powder apparent density	2.5 – 4 g/cm3	Hall flowmeter
Tap density	>4 g/cm3	Tapping volumeter
Viscosity curve	Shear rate dependent	Capillary rheometry
Pellet size distribution	2 – 4 g sensitive to shape	Sieving

These specifications promote mold flow while ensuring green-body and sintered strength.

Overview of the MIM Manufacturing Process

1. Develop composite feedstock with desired powder + binder system
2. Pelletize feedstock for precision volumetric shot control
3. Injection mold parts with tight tolerances and surface finish
4. Chemically debind and remove polymer content
5. Sinter pellets at >92% theoretical density
6. Machine features as needed if geometry allows
7. Apply supplementary plating, heat treating, coating, etc. if necessary
8. Quality assurance testing and validation for production

This continues to be optimized for reliability at high volumes.

MIM Equipment and Feedstock Suppliers

Company	Materials	Capabilities
BASF	Wide range of MIM alloys	Complete quality feedstocks
Sandvik Osprey	316L, 17-4PH, more	Atomization expertise transferred to MIM
MPP	Tool steels, stainless steels, custom	Leading MIM equipment too
CN Innovations	Custom alloys	Specialists in novel compositions
Parmatech Corp	Ti alloys, tool steels, Fe alloys, exotics	Equipment and feedstocks

Suppliers offer complementary equipment like molding machines and furnaces to enable turnkey production.

Tradeoffs When Considering MIM AM

Pros:

• Highly complex geometries and assemblies consolidated
• Excellent mechanical properties from uniform fine grains
• Great surface finish resolution as molded
• Proven mass production scalability once qualified
• Low wasted raw material relative to metal printing
• Leverages existing injection molding know-how

Cons:

• High up front costs for feedstock formulation and tooling
• Intensive qualification for new parts and applications
• Limited size range to under several pounds
• Restricted to alloys available as powders
• Generally lower ultimate strength than forgings
• Per-part cost higher than other processes until >10k volume

MIM hits the sweet spot for small complex metal components with its established track record.

Frequently Asked Questions

How small of features can MIM practically mold?

Typical lower range limits fall around 100-150 microns for hole diameter and mold wall thicknesses around 0.3 mm (~12 thou), thinner in certain geometries.

What determines the size range limits for MIM parts?

General difficulty handling thin-walled shapes over approximately 5” flow length without sagging or distortion. Maximum thickness typically under 0.5” and weights up to 5 pound range.

Does MIM allow functionally graded (FGM) composites?

Yes, advanced molding processes now support tailored porosities or spatially graded multi-powder feedstocks within a single molded component during manufacturing.

How many alloys are commercially available as MIM feedstocks?

Over 60+ base formulations exist – 300 series stainless steels comprise over 50% of the total market, followed by tool steels, titanium alloys, and nickel superalloys seeing growth.

What finishing processes typically follow MIM?

Common secondary operations include barrel finishing/vibratory deburring, surface grinding, shot peening, laser marking, passivation, plating, heat treating, joining, and inspection.

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