Executive Summary
Custom metal springs and electrical contacts are small components with disproportionate influence on product reliability. A spring may provide force, motion, retention, or a controlled return. A contact must carry current and survive mating, temperature, corrosion, and disturbance. The right specification begins with function and environment, not a familiar part number.
This guide translates product requirements into a manufacturable design, covering materials, forming, finishes, specifications, validation, failure modes, and RFQ essentials. It supports early engineering and sourcing decisions.
Start With Function, Not Geometry
The same general shape can perform very different jobs. A compression spring stores energy along its axis, while a cantilever spring produces contact force through deflection. A torsion spring supplies rotational torque, and a wave spring provides axial preload where installation space is limited. A stamped retaining spring may be intended primarily to hold a cover, battery, shield, or connector component in position. “Spring contact” can likewise mean a current-carrying beam, a grounding finger, a battery terminal, or a compliant probe interface.
The specification should state the required output at defined positions. For a mechanical spring, that normally includes free height or length, working deflection, force at one or more deflections, solid height or minimum clearance, and the allowable cycle count. For an electrical contact, it should add initial and minimum normal force, contact resistance, current, voltage, mating cycles, and the permitted temperature rise. These values should be tied to the assembled product, because a spring’s performance depends on guides, stops, neighboring parts, and installation orientation.
A useful early question is whether the component must be elastic throughout its operating range. If a beam is over-deflected during assembly, it may take a permanent set even when the nominal operating deflection is safe. A positive mechanical stop, controlled insertion path, or assembly fixture can protect the part more effectively than simply increasing material thickness. Design reviews should distinguish the intended working envelope from accidental overload conditions.
Material Selection: Strength, Conductivity, and Environment
Spring materials are selected by balancing elastic strength, fatigue resistance, forming behavior, conductivity, magnetic response, and corrosion performance. Common families include carbon spring steels, stainless spring steels, copper alloys, nickel alloys, and specialty materials used for demanding thermal or electrical conditions. No material is best on every axis. Higher conductivity can come with lower strength, while a stronger alloy may require more forming force or a more deliberate heat-treatment route.
Stainless spring steels are often considered where corrosion resistance and mechanical durability matter. Copper alloys are common for contacts because they combine useful conductivity with adequate spring behavior, particularly when the design uses a suitable temper and a plated contact zone. Nickel-based alloys can be justified by elevated-temperature stability, resistance to relaxation, or aggressive environments, although their cost and forming requirements may be higher. The final choice should be based on the actual temperature, atmosphere, stress, current, and service life rather than on a generic label such as “rustproof” or “high conductivity.”
Temper and thickness are as important as nominal alloy family because they affect yield behavior, formability, force, tooling load, and sensitivity to handling. Ask the supplier to confirm the material standard, temper, thickness range, grain-direction considerations, and lot traceability expected for the program.
For electrical contacts, the base alloy and surface system must be evaluated together. Tin is widely used for practical, economical interfaces, while nickel can serve as a diffusion or barrier layer. Gold finishes are selected when low and stable interface resistance, fretting resistance, or environmental performance justifies their added cost. Silver and other systems may suit particular current or switching conditions. Plating thickness, porosity, underplate, contact wipe, mating material, and storage conditions all influence results. A finish is not a substitute for sufficient contact force and a stable mechanical design.
Choosing a Manufacturing Process
Most custom metal springs and contacts are produced from strip or wire by a sequence of cutting, bending, coiling, forming, heat treatment, finishing, and inspection operations. The best route depends on volume, geometry, material, dimensional risk, and the need for integrated features such as lances, hooks, holes, embossments, or solder tails.
Wire Forming and Coiling
CNC wire forming suits three-dimensional springs, prototypes, low-to-medium volumes, and designs still changing during development. Define coil diameter, pitch, end configuration, wire straightness, stress relief, and the method for measuring force. Wire-forming marks, residual stress, and end variation can affect seating and performance.
Stamping and Progressive Dies
Stamping is typically attractive for flat springs, contact beams, terminals, clips, and high-volume parts. A progressive die can combine blanking, piercing, forming, coining, and cutoff in a controlled sequence. It can also reduce handling and make orientation features repeatable. Tool design determines feed direction, carrier strategy, bend sequence, grain orientation, and access for inspection.
Blanking creates a sheared edge with distinct zones. Burr direction and height matter near insulation, seals, mating contacts, or moving surfaces. Critical edges may need deburring, coining, controlled tooling clearance, or a design change. Identify functional edges and their limits instead of applying an unnecessarily restrictive finish requirement everywhere.
Secondary Operations and Tooling Decisions
Secondary operations may include heat treatment, cleaning, selective plating, riveting, welding, or carrier removal. Forming after plating can damage a finish at the bend, while forming before plating can complicate dimensional control. Selective plating reduces material use but requires clear masks, plating windows, and inspection criteria.
Consider tooling cost alongside tool life, maintenance access, spare inserts, and engineering-change policy. Ask which features drive tool complexity before comparing suppliers on piece price alone.
Specification Details That Prevent Ambiguity
A production drawing should define datums based on assembly function. Dimensions should be taken from stable reference features, not from an arbitrary edge that may vary with the carrier or cutoff. For formed parts, identify the measurement condition: free state, restrained state, or installed state. A spring that is dimensionally acceptable in a fixture may not meet the product requirement if it is inspected without the same support.
Force specifications need a test method. State the loading direction, rate where relevant, fixture geometry, conditioning, measurement points, and acceptable hysteresis or relaxation. For contacts, specify whether force is measured at initial touch, at the nominal wipe position, or at final insertion. Contact resistance should define the test current, measurement method, stabilization time, and whether the result is initial, after cycling, or after environmental exposure.
Geometric tolerances should be linked to risk. Flatness, angular position, hole location, beam height, coil diameter, and free length may all matter, but not every dimension deserves the same control. A capability study on representative production can help separate critical-to-function characteristics from informational dimensions. If a tolerance is tighter than the process can reliably hold, the likely result is sorting, rework, or unstable supply rather than better product performance.
Packaging is part of the specification: define presentation, orientation, corrosion protection, cleanliness, and allowable handling marks. For automated assembly, provide feeder requirements early.
Common Failure Modes and Trade-Offs
**Permanent set** occurs when stress exceeds the elastic range or when elevated temperature causes relaxation. Increasing thickness can raise force and margin, but it may also increase insertion load and reduce available travel. A longer beam can lower stress for a given deflection, yet it consumes space and may introduce unwanted modes of vibration. The solution is usually a coordinated change to geometry, material temper, stop design, and operating deflection.
**Fatigue cracking** commonly starts at a sharp bend, notch, burr, tooling mark, or plating defect. Generous bend radii, favorable grain orientation, clean edges, and controlled forming reduce risk. A smooth appearance alone does not prove fatigue suitability; cycling should represent the actual displacement, rate, preload, and environment.
**Contact resistance increase** can result from inadequate normal force, contamination, oxide or fretting debris, insufficient wipe, plating porosity, or loss of force with temperature. More plating may not correct a poor interface geometry. Review force retention, wipe length, contact overlap, cleaning controls, and the galvanic relationship between mating materials.
**Cracking or flaking finish** can follow excessive post-plating forming, poor surface preparation, excessive bend strain, or an incompatible underlayer. The design should state where coating is functional and where it is cosmetic or protective. Cross-section analysis, coating-thickness checks, adhesion evaluation, and visual inspection should be selected according to the application risk.
**Assembly damage and field variation** often arise from an uncontrolled insertion angle, an unprotected beam, or a tolerance stack that forces the spring beyond its intended travel. Use assembly simulation, physical gauges, and worst-case stack-up review. A supplier cannot compensate for an assembly condition that the drawing does not reveal.
RFQ and Pre-Production Checklist
Give prospective suppliers a complete functional package rather than a two-dimensional outline alone. The following checklist is a practical starting point:
- State the application, annual volume, launch timing, forecast pattern, and expected program life.
- Identify the spring or contact function, operating temperature, humidity, chemicals, vibration, and storage environment.
- Define material family, temper preference, conductivity or magnetic constraints, and acceptable alternatives.
- Provide force, travel, torque, current, resistance, cycle, retention, and overload requirements with test conditions.
- Mark critical datums, functional edges, burr limits, coating zones, cleanliness needs, and packaging orientation.
- Share mating-part drawings, assembly constraints, insertion loads, stops, and any automated handling requirements.
- Request the proposed process flow, tooling concept, heat-treatment and plating route, inspection plan, and change-control assumptions.
- Agree on sample quantities, first-article evidence, capability data for critical features, validation testing, and lot documentation before production release.
During design-for-manufacture review, ask what feature the supplier would change first and why. The answer can reveal whether the constraint is a bend radius, material availability, die access, plating coverage, measurement method, or assembly risk. It is also useful to request a controlled prototype route that resembles production enough to expose springback, edge quality, and finish problems before hard tooling is finalized.
Qualification and Ongoing Control
Approval should combine dimensional inspection with functional and environmental evidence. Measure free-state geometry, force or torque, contact resistance where applicable, coating characteristics, burrs, and visual condition. Test the installed part under representative cycling and relevant temperature, humidity, vibration, chemical, or current conditions. Preconditioning and post-test measurements make force loss or resistance drift visible.
Production control is stronger when critical characteristics are measured at the process step that creates them. Tooling checks can monitor wear, forming checks can monitor geometry, plating controls can monitor thickness and coverage, and final tests can confirm function. Any material, temper, plating chemistry, tool, or process change should follow an agreed approval path because small changes can affect force, fatigue, solderability, or resistance.
Conclusion
Custom metal springs and contacts should be purchased as engineered functions, not as generic pieces of bent metal. A robust program connects force, travel, current, life, environment, and assembly conditions to suitable material, process, finish, measurement, and packaging. A clear RFQ and disciplined qualification support better quality, continuity, and total-cost decisions.