Flat Springs and Leaf Springs: Design, Materials, and When to Use Them
Flat springs — clips, contact fingers, leaf springs, retainers — are formed from flat strip rather than round wire. They blur the line between "spring" and "stamped part," which is exactly why they are so useful.
When a flat spring beats a wire spring
- The space is a thin slot where a coil cannot fit
- The part must conduct electricity (battery contacts, connector fingers)
- The spring also acts as a latch, guide, or mounting bracket
- You need force in a very short travel with high consistency
- Assembly must be snap-in with no separate fasteners
Common materials
| Material | Strength | Conductivity | Typical use |
|---|---|---|---|
| Stainless 301/304 (tempered) | High | Low | General clips, medical |
| Carbon steel SK5 / 1074 | Very high | Low | Heavy-duty clips (plated) |
| Phosphor bronze | Medium | Good | Electrical contacts |
| Beryllium copper | High | Excellent | High-cycle connectors |
| Stainless 17-7PH | Very high | Low | Aerospace, high temperature |
Design guidelines
- Keep bend radius ≥ 1× material thickness (2× for high-carbon steel) to avoid cracking.
- Orient bends across the rolling direction of the strip where possible.
- Stress concentrates at bend roots: add relief radii at internal corners.
- Grain direction, temper, and burr side all affect fatigue — state the functional direction of flex on the drawing.
How flat springs are made
Low volume: laser or wire-EDM blanks, then press-brake or hand forming. High volume: progressive die stamping with forming stations, which merges blanking and bending into one operation — see our metal stamping services. Tooling pays off quickly above roughly 10,000 pieces per year.
Frequently Asked Questions
Should I specify pre-tempered strip or heat treatment after forming?
Pre-tempered strip (e.g., tempered 301) is cheaper and standard for simple bends. Complex shapes in high-carbon steel are often formed soft and then hardened — the manufacturer will choose based on geometry.
What tolerance can stamped flat springs hold?
Blank dimensions ±0.05 mm is routine; formed angles ±1–2°. Force tolerance around ±10% is typical — tell us the force window that matters.
Can one part combine spring and non-spring features?
Yes — that is the main advantage. A single stamped part can be bracket, contact, and spring at once, eliminating assembly cost.