Overview
What this metal finishing services guide covers and who it is for.
Sourcing Repository guide
Metal Finishing Services Guide
This metal finishing services guide explains the processes, materials, tolerances and cost drivers behind cleaning, anodizing, plating, coating and passivation. Use it to specify finishes that survive inspection.
- Processes at a glance
- Material table
- Design rules
- Cost drivers
Guide chapters
Chapter map
Every chapter in the guide with a one-line summary.
Processes
Mechanical, chemical, electrochemical and coating routes at a glance.
Materials
How aluminum, steel, stainless, copper and magnesium behave under finishing.
Design and tolerances
Core rules for thickness, masking, edges, threads and inspection.
Cost
The drivers that move a finishing quote and what to confirm.
Choosing a supplier
A checklist for capability, documentation and quality control.
Next steps
How to build an RFQ and which related chapters to read next.
Quick answer
A metal finishing services guide is a practical reference to the mechanical, chemical, electrochemical and coating processes that modify, protect, clean or texture metal surfaces. It covers cleaning, polishing, blasting, anodizing, plating, conversion coating, passivation, painting, powder coating and mass finishing, plus design, tolerance and RFQ points.
Overview: what this metal finishing services guide covers
Metal finishing services modify, protect, clean or texture metal surfaces through mechanical, chemical, electrochemical or applied-coating processes. This guide is written for engineers, procurement managers and founders who need to specify a finish, compare routes and check a supplier before releasing a purchase order.
The guide moves from process selection to material compatibility, design rules, cost drivers and supplier checks. It closes with an RFQ checklist and related chapters on anodizing, heat treatment, passivation and plating, and coating comparisons.
Mechanical, chemical, electrochemical, coating
Scope
Cleaning, polishing, blasting, anodizing, plating, passivation, painting, powder coating, mass finishing.
Function first, appearance second
Primary decision
Corrosion, wear, conductivity and masking requirements drive the route.
Coatings add, polishing removes
Dimensional risk
Check threads, bores and press fits after finishing.
Drawing-specific capability study
Verification
Critical dimensional allowance is unverified without process, substrate, geometry and drawing requirements.
Treat every finish as a process step with its own tolerance, inspection method and acceptance criteria, not as a cosmetic add-on at the end of the build.
Chapter map: every chapter in this metal finishing services guide
Each chapter below covers one decision area, from process selection to supplier qualification. Read them in order for a full picture, or jump to the chapter that matches your current question.
- Overview: what this metal finishing services guide covers, who it is for and how to use it.
- Chapter map: a one-line summary of every chapter with a link to the full page.
- Processes: mechanical finishing, chemical preparation, anodizing, electroplating, conversion coating, powder coating and passivation at a glance.
- Materials: how aluminum, steel, stainless steel, copper and magnesium behave under common finishes.
- Design and tolerances: core rules for thickness, masking, edges, threads and post-finish inspection.
- Cost: the drivers that move a finishing quote, including process, thickness, quantity and inspection.
- Choosing a supplier: a checklist for capability, documentation and quality control.
- Next steps: how to build an RFQ and which related services to pair with finishing.
Related chapters: anodizing Type II vs Type III and colors, heat treatment basics (T6, hardening), passivation and plating for stainless and steel parts, and powder coating vs painting vs plating.
Processes: key metal finishing services at a glance
The main finishing routes fall into mechanical, chemical, electrochemical and applied-coating families. The table below summarizes what each process does and the trade-offs to weigh before you specify it.
| Process | Typical route | Pros and cons |
|---|---|---|
| Mechanical finishing | Grinding, polishing, brushing, blasting, tumbling or vibratory finishing. | Removes burrs and improves appearance; may alter dimensions, create directional marks or round edges. |
| Chemical preparation | Degreasing, descaling, pickling, etching, rinsing and drying. | Produces a clean, active surface; chemistry can etch the substrate, generate waste or cause hydrogen-related risks. |
| Anodizing | Clean, etch, anodize aluminum, optionally dye, seal, rinse and dry. | Provides corrosion and wear resistance; dimensions and color uniformity can vary with alloy and geometry. |
| Electroplating | Clean and activate the part, electrically deposit metal, rinse, dry and post-treat. | Enables controlled conductivity, appearance and corrosion protection; thickness distribution is weaker in recesses and stronger on edges. |
| Conversion coating | Chemically convert the surface, commonly using phosphate or chromate chemistry, then rinse and dry. | Improves paint adhesion and corrosion resistance; coating is thin, chemistry-specific and may involve regulated substances. |
| Powder coating | Clean, optionally pretreat, apply dry powder, then heat and cure. | Durable and efficient with low solvent emissions; curing temperature may affect substrates and dimensional requirements. |
| Passivation | Clean stainless steel, treat chemically, rinse and dry to remove free iron and restore passive behavior. | Improves corrosion resistance without adding a significant coating; does not remove scale or repair poor surface condition. |
Typical thickness ranges for anodizing and plating
| Parameter | Typical range | Standard or source |
|---|---|---|
| Type I, IB, IC or IIB anodize thickness | 0.00002–0.0007 in [0.5–17.8 µm] | MIL-A-8625F summary. |
| Type II anodize thickness | 0.00007–0.0010 in [1.8–25.4 µm] | MIL-A-8625F summary. |
| Type III hard anodize thickness | 0.0005–0.0045 in [12.7–114.3 µm] | MIL-A-8625F summary. |
| Anodize thickness tolerance | As low as ±0.0001 in [±2.5 µm] | MIL-A-8625F summary; actual capability is process- and geometry-dependent. |
| Zinc plating thickness | 5–25 µm [0.0002–0.0010 in] | Manufacturer technical summary citing ASTM B633 and ISO 2081. |
| Nickel plating thickness | 5–50 µm [0.0002–0.0020 in] | Manufacturer technical summary citing ASTM B689. |
| Salt-spray exposure | Project-specific; commonly 96, 240 or 500 hours | ASTM B117 practice; duration and acceptance criteria must be specified. |
| Critical dimensional allowance | Unverified without process, substrate, geometry and drawing requirements | Supplier capability study and drawing-specific requirements required. |
How to compare similar finishing routes
| Comparison | Key differences |
|---|---|
| Anodizing vs powder coating | Anodizing is an integral aluminum oxide layer; powder coating is an applied cured polymer. Anodizing preserves metallic appearance and controls thickness differently; powder coating offers broader color and texture options. |
| Electroplating vs electroless plating | Electroplating uses external current and generally has geometry-dependent distribution; electroless deposition uses chemical reduction and can provide more uniform coverage. Exact capabilities are unverified. |
| Passivation vs electropolishing | Passivation chemically restores stainless-steel corrosion resistance without materially leveling the surface; electropolishing removes a controlled amount and improves smoothness. Exact removal allowances are unverified. |
| Mechanical polishing vs chemical polishing | Mechanical polishing uses abrasives and may create directional marks; chemical polishing removes material chemically and can reach complex geometry, with process-specific roughness and dimensional risks. |
| Zinc plating vs paint | Zinc provides sacrificial protection on steel; paint forms a barrier and offers broader appearance options. Duplex systems may combine both, subject to compatibility and specification. |
Surface preparation is not optional. ISO 27831-2 covers degreasing, descaling, pickling, etching, polishing and related preparation, and poor preparation is a common root cause of coating adhesion failures.
Materials: how substrates behave under metal finishing services
Substrate choice limits which finishes are practical and how tightly thickness can be controlled. The table below summarizes common metals and their typical finishing behavior.
| Material | Grade | Finishing properties | Typical uses |
|---|---|---|---|
| Aluminum | Unspecified alloy | Commonly anodized; coating thickness depends on anodizing type. | Enclosures, machined parts, aerospace components, architectural parts. |
| Steel | Unspecified grade | Common substrate for zinc, nickel, chromium, paint and powder coatings. | Fasteners, brackets, machinery, automotive components. |
| Stainless steel | Unspecified grade | Can be passivated, electropolished, plated or mechanically polished. | Medical, food-processing, chemical and architectural equipment. |
| Copper | Unspecified grade | High electrical conductivity; often plated or polished. | Electrical contacts, busbars, heat exchangers, fittings. |
| Magnesium | Unspecified alloy | Requires substrate-compatible cleaning and conversion or anodic treatment. | Lightweight housings and aerospace components. |
Alloy and part size affect the finish
Base-metal alloy and part size influence coating uniformity, color and achievable thickness. Aluminum alloys anodize at different rates and can shift color between lots, while large parts and deep recesses are harder to coat evenly than small, simple geometry.
Name the alloy and temper on the drawing. "Aluminum" alone is not enough to predict anodize color or thickness, and "steel" alone does not define the correct plating or pretreatment sequence.
Design and tolerances: core rules for finishing
A metal finishing services guide must treat design rules as part of the process, because finishing adds or removes material. Apply these rules before releasing a drawing for quote.
- State the finish, specification revision and class on the drawing, not in a separate email.
- Define coating thickness as a range with a measurement method, not a single nominal value.
- Allow for coating build-up on threads, bores and press fits, and specify masking where fit is critical.
- Check dimensions after finishing, especially threads, bores and press fits.
- Avoid sharp edges and deep blind recesses where coating distribution is weakest.
- Specify surface roughness and any directional appearance requirement, such as brushed or mirror finish.
- Identify surfaces that must stay conductive, unpainted or free of coating.
- Require a first-article or capability study when the dimensional allowance is critical.
Thickness tolerance is process- and geometry-dependent
In a metal finishing services guide, anodize thickness tolerance is typically as low as ±0.0001 in [±2.5 µm] per the MIL-A-8625F summary, but actual capability depends on the process and part geometry. For any critical dimensional allowance, the value is unverified without the process, substrate, geometry and drawing requirements, so ask for a supplier capability study.
Electroplating thickness distribution is weaker in recesses and stronger on edges. If a bore or internal feature has a tight tolerance, plan for masking, a secondary machining step or a different process.
Cost: what drives metal finishing services pricing
Finishing cost is driven by process complexity, part geometry, quantity and the amount of inspection and documentation required. The same part can price very differently across routes, so compare quotes against the same specification.
- Process type and number of steps, including preparation, coating and sealing.
- Coating thickness and tolerance: tighter thickness control costs more.
- Part size, weight and geometry, especially recesses, blind holes and large surface areas.
- Masking and selective finishing requirements.
- Quantity and batch size, which affect setup and racking efficiency.
- Color, texture and cosmetic acceptance criteria.
- Inspection and test scope, such as thickness measurement, salt spray or dimensional checks.
- Packaging and handling requirements that protect the finished surface.
Cost questions to settle before quoting
Ask whether the price includes preparation, masking, inspection and packaging, and whether rework or re-finishing is covered if the first lot fails inspection. Confirm which specification revision the supplier is pricing against, because a class change can move both cost and lead time.
Choosing a supplier: metal finishing services checklist
A finishing supplier is only as good as its process control and documentation. Use this checklist to qualify a source before the first production lot.
- Confirm the supplier runs the exact process and specification revision your drawing calls out.
- Ask for a capability study or sample parts for critical thickness and dimensional requirements.
- Verify in-house or subcontracted preparation, since preparation quality drives adhesion.
- Confirm inspection equipment and methods for thickness, appearance and any required testing.
- Check how the supplier handles masking, racking marks and contact points.
- Confirm traceability from incoming material to finished lot.
- Ask how nonconforming parts are contained, reworked or scrapped.
- Confirm packaging that protects the finish during transit.
- Request PPAP or equivalent documentation when the part is automotive.
- Confirm the supplier works to IATF 16949 or an equivalent quality system where required.
Sourcing Repository does not own factories or machines. SR collects quotes from a vetted supplier network, manages quality and inspection, and delivers parts, so you can compare finishing routes against one specification.
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FAQ
Common questions
Can finishing change part dimensions?
Yes. Coatings add thickness, while polishing, blasting, etching and chemical treatment can remove material. Any metal finishing services guide should advise setting process allowances for critical dimensions and inspecting them after finishing, especially threads, bores and press fits.
What information should an RFQ include?
Include material and grade, part drawing, quantity, finish, thickness range, masking, color, dimensional limits, test requirements, packaging and required certifications. A complete RFQ lets suppliers quote the finishing route accurately and reduces rework caused by unclear callouts or missing specification revisions.
Does salt spray predict service life?
No. ASTM B117 standardizes how the salt-spray chamber is operated. Exposure hours, commonly 96, 240 or 500, are not a direct prediction of field life, so set application-specific acceptance criteria and state the duration on the drawing.
Are all finishing standards interchangeable?
No. Standards differ by substrate, chemistry, coating, test method, class and acceptance criteria. Confirm the exact revision and applicable callout on the drawing, and ask the supplier to confirm it can meet that specific standard before you release the order.
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