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Metal stamping
Stamped spring clips and spring contacts
Sierxi stamps flat spring clips, grounding fingers and battery and spring contacts from stainless steel and copper-alloy strip in Suzhou. Because we also run six CNC spring machines, a stamped contact and its matching coil or torsion spring can be developed, inspected and shipped together, from 1,000 pieces.
Capabilities at a glance
| Part types | Spring clips, grounding fingers, battery contacts, retaining clips |
|---|---|
| Materials | SUS304 and copper alloys |
| Tolerance | ±0.02 mm |
| Paired springs | Wire 0.2–2.0 mm on 6 CNC spring machines |
| Minimum order | 1,000 pcs |
Contact force and set
A spring contact is specified by force at working deflection, not just by shape. Give us the target force, deflection and cycle requirement with the drawing; we check force on samples with push-pull gauges before production.
“Set” is the permanent loss of height after the contact is pressed. It happens when the bending stress exceeds the material’s elastic limit. A design that looks right in CAD can still take a set on first assembly, which lowers the contact force for the rest of the product’s life.
How to estimate spring contact force
For a straight cantilever finger of width b, thickness t and free length L, standard beam theory gives a first estimate. Force at deflection δ is F = E·b·t³·δ / (4·L³), and the peak bending stress at the root is σ = 3·E·t·δ / (2·L²), where E is the elastic modulus of the material.
Two things follow. Force rises with the cube of thickness, so a small change in strip thickness changes force a lot. Stress rises with deflection and falls with the square of length, so a longer finger is the easiest way to avoid set. Formed shapes, dimples and preloads need FEA or sample testing, which is why we confirm force on samples.
Design rules for stamped spring contacts
- Keep peak stress below the elastic limit of the chosen temper with a margin — as a rule of thumb, well below the published yield strength
- Use the longest free length the space allows, and add a radius at the root rather than a sharp corner
- Bend across the rolling direction for spring-temper material to avoid cracking at the bend
- Specify force tolerance realistically; for stamped contacts a range of roughly ±10–20% is common, tighter needs tuning
- Add an overstroke stop if the contact can be pushed beyond its working deflection in assembly or a drop
- Put a formed dimple at the contact point for a defined contact area, and state the plating there
Materials for spring clips and contacts
| Material | Strength | Conductivity | Notes |
|---|---|---|---|
| SUS304 (spring tempers) | High | Low | Grounding fingers, retaining clips; in regular production |
| SUS301 spring stainless | Higher | Low | Higher-stress clips; quoted on request |
| C7701 nickel silver | Good | Low | Corrosion-resistant contacts; in regular production |
| C5191 phosphor bronze | Good | Moderate | Battery and signal contacts; quoted on request |
Battery contacts and grounding fingers
Battery contacts usually pair a stamped plate or clip with a conical or cylindrical coil spring. Because we run stamping presses and spring machines in the same factory, both parts can be sampled together and checked as a set for height and force.
Grounding fingers for enclosures and PCBs are usually stainless or nickel silver, sometimes plated at the contact point. Plating is done by qualified partners and should be specified with thickness on the drawing.
How spring contacts are inspected
Dimensions are measured on a vision measuring system at first article and by AQL sampling on each lot, with automated optical inspection on critical features. Force at the working height is checked with push-pull gauges. Cycle testing requirements are agreed per project.
What to put on a spring contact drawing
- Material grade, temper and thickness — temper matters as much as grade for spring parts
- Free height and working height, with the force required at working height and its tolerance
- Maximum deflection the part may see in assembly or misuse
- Plating at the contact point, with thickness
- Burr direction and any edges that touch a PCB, battery or cable
- Required mating or compression cycles, if any
- Annual volume, and whether the clip ships with a matching coil spring
Frequently asked questions
What information do you need to quote a spring contact?
A drawing with material and thickness, the working deflection and target force at that deflection, plating, and annual volume.
How do you check contact force?
With push-pull gauges at the working height, on samples before production and on production lots.
Can you supply the coil spring that goes with the contact?
Yes. We coil 0.2–2.0 mm wire on six CNC spring machines and can ship both parts together.
Why does my spring clip lose force after assembly?
Usually because it was deflected beyond its elastic limit and took a permanent set. A longer finger, lower deflection or stronger temper usually fixes it.
What is the minimum order?
1,000 pieces. Sample cost and lead time are confirmed per project in the quote.
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Materials
SUS304 stainless steel for stamping and sheet metal
Austenitic stainless for corrosion-resistant stamped parts and enclosures.
Materials
C7701 nickel silver for shielding cans and contacts
Solderable, springy copper-nickel-zinc alloy for shields and contacts.