Plating Options for Metal Stamped Parts

Plating options for metal stamped parts should be selected according to the substrate, operating environment, electrical or mechanical function, and final dimensional requirements. Zinc can provide economical corrosion protection for steel brackets, while tin, silver, or gold may be required for stamped terminals that need solderability or reliable electrical contact.

For OEM production, coating thickness, underplates, selective plating, hydrogen embrittlement risk, and the sequence between stamping and plating can also affect cost and finished-part performance. These requirements should be considered before tooling and production specifications are finalized.

Common Plating Options for Metal Stamped Parts

No single plating provides the best combination of corrosion resistance, conductivity, solderability, wear performance, and cost. The values below are reference ranges rather than universal drawing requirements.

Actual coating thickness should follow the substrate, service condition, functional surface, customer drawing, and applicable specification.

Zinc Plating for General Corrosion Protection

Zinc plating provides economical sacrificial corrosion protection for steel stamped parts. It is commonly used on stamped brackets, housings, fasteners, and general industrial hardware exposed to moderate atmospheric conditions.

Performance depends on the complete coating system, including zinc thickness, conversion coating or passivation, and any sealer. Standard zinc is therefore a practical starting point for many cost-sensitive steel stampings, but more demanding environments may require a different system.

Zinc-Nickel Plating for Higher Corrosion Requirements

Zinc-nickel is commonly considered when conventional zinc cannot reliably meet the required corrosion performance. Automotive, outdoor, and other exposed stamped components are typical applications.

Its performance depends on alloy composition, coating thickness, passivation, sealer, and process control. Reference data can show substantially greater salt-spray resistance than conventional zinc, but this is not a fixed performance multiplier.

Salt-spray hours are qualification data, not a direct prediction of field service life. Real corrosion performance also depends on the actual environment, temperature, contaminants, coating damage, and service conditions.

Nickel Plating for Wear, Corrosion, and Underplating

Nickel plating can provide corrosion resistance, surface hardness, wear performance, and an underlayer for other functional coatings. On steel, it primarily provides barrier protection rather than the sacrificial protection associated with zinc.

Electroless nickel may also be considered when complex geometry requires more uniform coating thickness than conventional electroplating can readily provide.

Tin Plating for Stamped Electrical Terminals

Tin plating is widely used on stamped terminals, solder tabs, and electrical components because it provides solderability and useful electrical performance at moderate cost.

The substrate matters. When tin is applied over brass, a copper or nickel underplate may be specified to reduce zinc diffusion from the substrate into the tin layer.

Tin whiskers can also be a reliability concern in electronic applications. Whisker-control requirements should follow the applicable plating specification or customer standard rather than being assumed from coating thickness alone. ASTM B545 provides requirements for electrodeposited tin coatings.

Silver Plating for High-Current Contacts

Silver plating is useful for stamped contacts where current-carrying performance is a primary requirement. Its high conductivity and low contact resistance make it suitable for power terminals, battery and cable terminal lugs, conductive inserts, and other high-current components.

Required thickness depends on electrical load, contact pressure, wear, and mating cycles. Tarnishing and sulfur-containing environments should also be considered.

Silver is typically selected for current-carrying performance, while gold is selected when long-term contact-interface stability is the higher priority.

Gold Plating for Reliable Connector Contacts

Gold is commonly used on precision connector contacts and signal terminals where stable contact resistance and oxidation resistance justify its higher cost.

It is often deposited over a nickel underplate rather than directly onto the copper-alloy substrate. Because only part of a stamped terminal may require these properties, gold is particularly suitable for selective plating.

Copper Plating as a Conductive Underlayer

Copper provides high electrical and thermal conductivity and is frequently used as an intermediate layer in multilayer coating systems.

For stamped electrical components, it may support subsequent functional coatings rather than serving as the primary corrosion-protection finish for exposed steel parts.

How to Choose Plating for a Metal Stamped Part

Instead of selecting a coating by name first, define four engineering requirements:

1. What must the surface resist? Consider humidity, outdoor exposure, chemicals, temperature, and other corrosion conditions.

2. What must the surface do electrically? Determine whether the part requires solderability, high-current conductivity, low contact resistance, or stable signal contact.

3. What is the substrate? Carbon steel, high-strength steel, stainless steel, copper, and brass can require different pretreatment or underplating strategies.

4. Will coating buildup affect a functional feature? Mating surfaces, slots, press-fit features, and connector interfaces may require dimensional allowance for plating.

Wear should also be considered for spring contacts and repeatedly mated components. Contact force, sliding motion, mating cycles, coating hardness, and underplate can affect whether the functional surface survives for the intended service life.

Selective Plating Can Reduce Connector Terminal Cost

Different sections of a stamped terminal often perform different functions.

A typical connector terminal may contain:

• A mating zone requiring stable electrical contact

• A transition area requiring only an underplate

• A crimp area with different mechanical requirements

• Carrier sections used during progressive stamping

Applying precious metal uniformly across all of these areas can add cost without providing equivalent functional value.

Selective plating concentrates gold, silver, or another functional coating on the required contact zone. This is especially valuable in high-volume terminal production, where small reductions in precious-metal coverage can produce meaningful material savings across large production runs.

Why Nickel Is Often Used Under Gold

A common connector coating structure consists of a copper-alloy substrate, a nickel underplate, and gold on the functional contact surface.

Nickel provides a barrier and foundation for the gold layer. The final gold coverage and thickness can then be matched to the electrical contact and wear requirements instead of applying the same precious-metal coating across the entire terminal.

Should Parts Be Plated Before or After Stamping?

The manufacturing sequence depends on geometry, coating function, production volume, and whether cut-edge coverage or selective surface control is required.

Pre-plated strip enters stamping with an existing functional surface. This can reduce downstream finishing, but blanking creates exposed cut edges and forming may affect the existing coating.

Post-plating applies the coating after the part geometry has been formed. This can cover completed surfaces, although recessed or shielded features may make uniform electroplating more difficult.

For high-volume electrical terminals, parts may also remain connected to a carrier strip for downstream strip or selective plating. This allows functional coating zones to be coordinated with terminal position while maintaining controlled strip handling.

The appropriate sequence should therefore be established before tooling is finalized rather than treated as an isolated finishing decision.

Plating Thickness Can Change Final Part Dimensions

Plating adds material to a stamped surface. Tight-tolerance features should therefore be evaluated in their final coated condition when the coating buildup is significant relative to the allowable dimensional variation.

For simplified tolerance planning, assuming approximately equal coating thickness on opposing surfaces:

Final slot width ≈ stamped slot width − 2t

Final external width ≈ stamped width + 2t

where t is the coating thickness on each relevant surface.

Actual electroplating thickness can vary with part geometry and current distribution, so these relationships are planning approximations rather than substitutes for the coating tolerance defined on the drawing.

Where Plating Buildup Matters Most

Coating buildup deserves particular attention around:

• Small holes and narrow slots

• Mating surfaces

• Connector contact interfaces

• Press-fit features

• Crimp features

• Tight-clearance assemblies

A feature that meets its stamping tolerance can therefore fall outside the final requirement after plating.

For functional mating features, the final coated dimension is often the controlling requirement. Tooling allowance, coating buildup, and inspection strategy should be coordinated before mass production.

Plating Quality Starts With the Stamped Surface

Plating cannot fully compensate for problems created during stamping. Burr condition, lubricant residue, contamination, and geometry can affect coating adhesion or distribution.

Blanking and piercing create rollover, burnished, fracture, and burr regions along the cut edge. Excessive burrs and sharp edges can affect coating distribution and downstream assembly, making punch-to-die clearance and tool condition relevant even when the component will subsequently be plated.

Stamping oils and drawing compounds must also be sufficiently removed before surface activation. Cleaning should be compatible with the actual lubricant and substrate used in production.

Part geometry can influence the plating method. Barrel plating can suit small, durable stampings that tolerate tumbling, while rack plating provides greater control over orientation and may be more appropriate for complex geometry or critical surfaces.

Hydrogen Embrittlement in High-Strength Steel Stampings

Electroplating high-strength steel requires additional attention because hydrogen introduced during pretreatment or plating can enter susceptible material and contribute to delayed brittle failure under stress. Cold forming can add residual stress, making spring clips, retaining parts, high-strength brackets, and heat-treated stampings important applications to evaluate.

Hydrogen embrittlement susceptibility generally increases with steel strength and hardness, but a single threshold should not be treated as universal. The material, forming condition, coating process, and governing specification all matter.

Applicable standards such as ASTM B633 should be reviewed when zinc electroplating high-strength steel. Susceptible components may require controlled post-plating hydrogen-relief treatment according to the applicable specification.

The coating callout should therefore account for substrate strength and post-treatment requirements rather than specifying the plating metal alone.

What Should an OEM Plating Specification Include?

A drawing that only states “zinc plated” or “tin plated” can leave important manufacturing requirements undefined.

Depending on the component, the specification may need to identify:

• Base material

• Plating material

• Coating thickness or service class

• Underplate

• Conversion coating or passivation

• Selectively plated areas

• Functional contact surfaces

• Masked or non-plated areas

• Hydrogen embrittlement requirements

• Applicable ASTM, SAE, or customer standard

• Whether critical dimensions apply before or after plating

A weak specification might simply state:

Zinc plated

A more complete specification defines the engineering structure:

Base material + coating system + thickness or class + conversion coating + functional areas + applicable standard + final dimensional requirements

The exact callout should follow the OEM drawing, operating environment, and applicable customer or industry requirements.

Common Plating Standards

A standard reference provides more manufacturing information than the coating name alone. The applicable standard and revision should be confirmed for the specific project.

Quick Plating Selection Guide for OEM Stamped Parts

These are engineering starting points rather than universal prescriptions. Final selection should reflect the complete part function, substrate, geometry, production sequence, and applicable specification.

Frequently Asked Questions

What Is the Most Common Plating for Stamped Steel Parts?

Zinc is commonly used for general steel stampings because it provides sacrificial corrosion protection at relatively low cost. More demanding environments may require zinc-nickel or another protective coating system.

What Plating Is Commonly Used for Stamped Electrical Terminals?

Tin is widely used when solderability is important. Silver can suit high-current contacts, while gold over nickel is commonly used where stable contact resistance and oxidation resistance are critical.

Does Plating Cover the Cut Edges of Stamped Parts?

It depends on the manufacturing sequence. Stamping pre-plated strip exposes bare material along newly cut edges, while plating after blanking can provide coating on accessible cut surfaces. Actual coverage still depends on geometry and the plating process.

Can Plating Be Limited to the Contact Area of a Stamped Terminal?

Yes. Selective plating can concentrate gold, silver, or another functional coating on the required contact zone rather than coating the entire terminal with the same material. This can reduce precious-metal consumption in high-volume production.

Does Plating Thickness Affect Stamping Tolerances?

Yes. Coating buildup can increase external dimensions and reduce openings such as slots. Tight-tolerance mating, press-fit, and connector features should therefore be evaluated in their final plated condition.

Can High-Strength Steel Stamped Parts Be Electroplated?

Potentially, but hydrogen embrittlement risk must be evaluated according to material strength, forming condition, plating process, and the governing specification. Susceptible parts may require additional process and post-plating controls.

Conclusion

Plating options for metal stamped parts should be selected according to finished-part function, substrate, operating environment, and manufacturing sequence. Coating requirements should not be isolated from the stamping process.

For high-volume metal stamping programs, coordinating plating with part geometry, tolerance control, selective functional areas, carrier-strip strategy, and final inspection before tooling is finalized can improve dimensional consistency and production stability.