Finishing Options for Stamped Metal Parts
Short answer: the finishing choice is usually made by the function, not the look. For electrical contact and solderability, tin at 2–5 µm or nickel at 1–3 µm; for low, stable contact resistance, gold flash to 0.5–1.5 µm or hard gold; for corrosion without conductivity, passivation or zinc plating; for appearance and wear, anodizing or electropolishing on aluminium. Indicated cost runs from under $0.01 per part for a barrel tumble to $0.05–$0.30 for selective precious-metal plating. Match the finish to the joint, the environment and the budget.
A stamped part leaves the press with a shape, a material and a surface that is only as good as the coil. Finishing is what makes it survive the application. The mistake buyers make is treating finish as a cosmetic afterthought; in practice, finish decides whether a contact stays low-resistance for years, whether a housing resists corrosion, and whether a solder joint forms reliably on the line.
Start from the Function, Not the Look
Ask what the surface must do. If it carries a signal or power, its contact resistance and solderability matter most. If it sits in a moist or salty environment, corrosion resistance matters most. If it is visible, appearance and wear matter. Once the function is fixed, the shortlist of finishes narrows fast. Plating serves electrical needs; conversion coatings and paints serve environmental needs; mechanical finishes serve appearance and dimensional needs. Trying to serve all three with one finish usually means overpaying for something the part does not need.
Electroplating Options for Stamped Parts
Electroplating deposits a metal layer that changes conductivity, solderability and corrosion resistance. It is the default finish for contacts, terminals and shield cans.
| Finish | Thickness | Cost indication | Electrical role | Best use |
|---|---|---|---|---|
| Tin | 2–5 µm | Low | Solderable, moderate resistance | Terminals, solder tabs |
| Nickel | 1–3 µm | Low–mid | Barrier layer, wear-resistant | Under gold, shield cans |
| Gold flash | 0.1–0.5 µm | Mid | Low, stable resistance | Low-cost contacts |
| Hard gold | 0.8–1.5 µm | High | Wear-resistant, stable | Mating contacts, cycles |
| Silver | 2–5 µm | Mid–high | Lowest resistance | High-current contacts |
| Zinc | 5–10 µm | Low | Sacrificial corrosion | Steel brackets under paint |
Note the layering habit: nickel under gold is standard because gold diffuses into base metal otherwise, and a 1–3 µm nickel barrier keeps the gold layer stable. For pure corrosion protection on steel, zinc works by sacrificing itself, so it protects cut edges too — useful on stamped brackets that will see weather.
Conversion Coatings and Anodizing
Anodizing on aluminium builds a hard oxide layer. Type II decorative anodizing is 5–25 µm, Type III hard anodizing is 25–50 µm and very wear-resistant. Both are non-conductive, so they never belong on a contact face — mask those areas. Passivation on stainless removes free iron and restores the natural oxide, improving corrosion resistance with no dimensional change, which suits stamped stainless parts that must keep tight tolerances.
Chromate conversion coating on aluminium or zinc gives a thin, mildly conductive corrosion barrier and is often the pragmatic choice when the part must still ground through its own surface. For a plain appearance finish on stainless, electropolishing brightens and deburrs at the same time, which kills two birds for a welded or formed part.
Mechanical Finishes and Their Limits
Tumbling, vibratory finishing and bead blasting deburr and smooth stamped edges. Barrel tumbling is the cheapest option, often under $0.01 per part, because parts are processed in bulk. It rounds edges, removes the sharp burr that a stamped part carries, and gives a uniform matte look. It cannot hold a sharp corner or a cosmetic Class A surface, so it suits functional parts, not visible ones. Bead blasting gives a more uniform matte and is often used before anodizing to hide forming marks.
The limit to remember is dimensional. Tumbling removes material, typically a few microns at edges, so it must come before tight-tolerance inspection and never after plating. A tumbled edge on a thin part can also round more than intended, changing fit. When a stamped part needs both a clean burr-free edge and tight tolerance, deburring is done in-die or by a controlled process rather than by bulk tumbling — a subject covered in burr control in stamping.
Choosing Plating Thickness and Spot Plating to Save Cost
Precious-metal plating is often the largest single cost in a stamped contact, so engineers spot-plate it. Instead of gold over the whole part, the die or a mask limits gold to the contact zone, and the rest gets tin or nickel. Selective plating can cut precious-metal use by 60–80% with no electrical penalty, since only the mating face needs gold.
The other lever is thickness. Gold flash at 0.1–0.5 µm is enough for a low-cycle, dry-environment contact; hard gold at 0.8–1.5 µm is needed where the part mates and unmates many times. Specifying hard gold "everywhere" is a common and expensive habit. Thickness should match the number of mating cycles and the environment, nothing more.
| Requirement | Recommended finish | Indicative cost/part |
|---|---|---|
| Solderable joint | Tin 2–5 µm, matte | $0.005–$0.03 |
| 1,000+ mating cycles | Hard gold 0.8–1.5 µm over Ni | $0.05–$0.30 |
| Outdoor steel bracket | Zinc 5–10 µm + clear | $0.01–$0.05 |
| Aluminium corrosion + look | Anodize Type II 10–20 µm | $0.03–$0.12 |
| Deburr only, functional | Barrel tumble | under $0.01 |
Indicative only; cost scales with part area and plating thickness, and selective masking adds tooling.
How Finishing Interacts With Stamping Quality
The finish cannot fix a bad press surface. Scratches, roll marks and orange peel that form during stamping show through most platings; plating a scratched contact makes the scratch conductive and visible. That is why surface quality is controlled at the die, with polished form surfaces and clean lubricant, not at the finisher. Equally, plating thickness varies with current density, so a part with deep recesses may plate thin in the recess and thick on the edge — a design and racking issue worth raising early.
For a stamped part that must both resist corrosion and stay electrically functional, the clean answer is usually a layered or selective finish: tin or zinc where corrosion matters, nickel plus gold where contact matters. Getting that split right on the drawing, before tooling, is far cheaper than changing a finish after 200,000 parts are plated.
Frequently Asked Questions
Q: What is the best finish for stamped electrical contacts?
A: Tin at 2–5 µm for solderable joints, and nickel plus hard gold at 0.8–1.5 µm for contacts that mate many times. Spot-plating gold only on the contact zone cuts precious-metal cost by 60–80% with no electrical penalty.
Q: How thick should plating be on a stamped part?
A: Match thickness to function. Tin 2–5 µm for solderability, nickel 1–3 µm as a barrier, gold flash 0.1–0.5 µm for low-cycle contacts, hard gold 0.8–1.5 µm for high-cycle mating, silver 2–5 µm for high current.
Q: Can anodized aluminium parts still conduct?
A: No — anodizing is non-conductive, so contact or ground areas must be masked or left un-anodized. A chromate conversion coating is the better choice when the surface must still ground through itself.
Q: Does tumbling affect stamped part tolerances?
A: Yes, barrel tumbling removes a few microns at edges, so it must run before tight-tolerance inspection and before plating. For thin parts, in-die deburring is more controllable than bulk tumbling.
Q: How do I reduce the cost of gold plating on stamped contacts?
A: Spot-plate gold only where contact happens and use a tin or nickel finish elsewhere. Also drop to gold flash unless the part sees many mating cycles, since hard gold is only justified where wear is real.
Related Resources
- Finishing stamped parts: plating, coating and deburring choices mapped to function.
- Metal stamping services: stamped parts finished in-house with controlled plating and deburring.
- About BQUQ: an ISO9001-certified source factory in Dongguan running stamping, CNC, springs and heat sinks under one roof.
- Contact us: send your drawing and finish spec for a quote within 12 working hours.
Authored by the BQUQ Engineering Team. BQUQ is an ISO9001-certified source factory in Dongguan, China, running CNC machining, metal stamping, custom springs, heat sink and collet lines under one roof. Send drawings to sc@bquq.com or WhatsApp +86 13713157787 for a quote within 12 working hours. www.bquq.com
