Metal Injection Molding Guide: MIM Process, Materials, Tolerances

This metal injection molding guide explains how MIM works, which materials are available, how to design parts that mold and sinter reliably, and what drives cost. It is written for engineers and procurement managers sourcing custom metal parts, with automotive and other high-volume applications in mind.

MIM sits between press-and-sinter powder metallurgy and machining. It uses injection molding to form complex three-dimensional shapes from metal-powder feedstock, then debinds and sinters the part. The result is a near-net-shape component that needs little or no machining on most features.

Read this page for orientation, then use the chapter map below to go deeper on design, process steps and material selection. Every technical figure here comes from published MIM design guides and MPIF material standards, and is labeled typical where supplier capability varies.

This metal injection molding guide is organized into focused chapters so you can jump straight to the topic you need. Each chapter below covers one decision area in the sourcing process.

This metal injection molding guide is a sourcing reference for engineers and buyers. It explains how MIM turns fine metal powder and binder into complex, near-net-shape parts, and which design, process and cost decisions matter before you request quotes.

Typical design starting points covered in the chapters include a minimum wall thickness of about 0.060 in (1.5 mm), a minimum hole diameter of about 0.060 in (1.5 mm) and an as-sintered tolerance of about ±0.3%, for example 1.000 in ±0.003 in (25.4 mm ±0.076 mm). Metal powder is typically finer than 0.0008 in (20 µm). Supplier capability varies, so confirm limits for your geometry and material.

Each chapter gives the condensed version of its topic. Detailed numbers, tables and worked examples live in the individual guides.

MIM processing always follows the same sequence: mix metal powder with a binder, injection-mold the feedstock, remove the binder, and sinter. The main variation is how binder removal is handled and which secondary operations are added.

1. Feedstock preparation Fine metal powder, typically less than 0.0008 in [20 µm] particle size, is mixed with a polymer or wax binder system to create a moldable feedstock.
2. Injection molding The feedstock is injection-molded into a tool cavity to form the green part. The tool is sized to compensate for shrinkage during sintering.
3. Debinding Binder is removed in controlled stages. Routes include conventional solvent or thermal debinding, catalytic debinding, or molding followed by partial debinding and then furnace debinding.
4. Sintering The part is sintered in a controlled atmosphere. Powder particles bond and the part densifies, reaching properties approaching wrought materials.
5. Optional secondary operations Machining, repressing, heat treatment, HIP, coating or finishing can improve selected features or properties.

How MIM differs from similar processes

MIM feedstocks cover stainless steels, tool and alloy steels, titanium and other alloys. Material designations and engineering property data are published in MPIF Standard 35-MIM, whose 2025 edition added titanium and other updates.

MIM design rules govern wall thickness, hole size, draft and dimensional tolerance. The values below are typical starting points from MIM design guides; actual capability depends on geometry, material, tooling and process control.

Applying the rules to a real part

• Keep nominal walls uniform where possible; thick-to-thin transitions promote distortion and long cycle times.
• Design holes at or above the practical minimum diameter and check the aspect ratio against supplier guidance.
• Add draft to blind holes and deep features so the green part releases cleanly from the tool.
• Set tolerances by feature. Use the as-sintered capability for most dimensions and reserve tighter tolerance for critical features, accepting secondary operations where justified.
• Define datum structures early so inspection and shrinkage compensation are consistent between the tool and the drawing.

MIM cost is driven mainly by tooling, annual volume, part complexity and any secondary operations. Tooling cost is fixed, so piece price falls as volume rises and the tool is amortized.

• Annual volume, not order quantity alone, determines how much fixed tooling and qualification cost each part carries.
• Part size and complexity affect tool design, feedstock consumption and cycle time.
• Material choice sets feedstock cost; titanium and specialty alloys cost more than standard stainless steels.
• Tolerance and finish requirements drive secondary operations, which add cost, lead time and handling. Repressing can tighten tolerance to about ±0.1% where suitable, but it raises piece price.
• Debinding and sintering routes affect furnace capacity use and process-control effort.
• Inspection and documentation scope adds cost, particularly where critical features require dedicated gauging.

As a rule of thumb, MIM is economical when complex parts require medium-to-high production volume. For prototypes, low quantities or extremely tight localized tolerances, compare against machining or metal additive manufacturing before committing to tooling.

Use this metal injection molding guide as a checklist when preparing a request for quote. Share CAD, drawing tolerances, annual volume, material grade, surface requirements and critical-feature definitions, so suppliers can price tooling and secondary operations accurately. SR collects quotes from its vetted supplier network, with a typical turnaround of 5-7 working days.

Use this checklist to compare MIM suppliers on capability and evidence rather than price alone. Ask for documented answers, not verbal assurances.

• Confirm the supplier can mold and sinter the material grade you specified, with material property data traceable to a published standard such as MPIF Standard 35-MIM.
• Ask for as-sintered and, where relevant, repressed tolerance capability by feature class and part size.
• Verify debinding and sintering routes match your part's complexity and risk profile.
• Request the inspection plan, including which dimensions are checked, at what frequency, and with what gauges.
• Confirm quality-system requirements your program needs, such as IATF 16949 or a PPAP submission for automotive work.
• Check secondary operation capability: in-house machining, repressing, heat treatment, HIP, coating and finishing, or vetted subcontractors.
• Review capacity, lead-time behavior at volume, and how changes are controlled after tooling is approved.
• Agree on documentation: material certificates, dimensional reports and traceability from feedstock lot to shipped part.

A complete RFQ package gets you an accurate quote faster. Sourcing Repository collects quotes from a vetted supplier network, manages quality and inspection, and delivers parts. Sourcing Repository does not own factories or machines.

What to include in a sourcing request

• 3D CAD files and a controlled 2D drawing with tolerances, datums and critical-feature definitions.
• Annual volume, expected release schedule and any seasonal demand pattern.
• Material grade and condition, including any standard designation you require.
• Surface finish, cosmetic and marking requirements.
• Inspection plan expectations, certifications and documentation scope.
• Any secondary operations already anticipated, so they can be quoted in the same cycle.

Sourcing Repository reviews each request, matches it to suppliers with the relevant MIM capability, and coordinates inspection before parts ship. Send your drawing package to killol@sourcingrepository.com or start a request through the quote form.