Precision springs

Custom precision springs and wire forms

Sierxi makes custom compression, extension and torsion springs and wire forms from 0.2 to 2.0 mm wire on six CNC spring machines in Suzhou. Capacity is over two million pieces a month and orders start at 1,000 pieces. Springs can ship together with matching stamped contacts and clips from the same factory.

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Capabilities at a glance

Machines	6 CNC spring machines
Wire diameter	0.2–2.0 mm
Types	Compression, extension, torsion, wire forms
Capacity	2,000,000+ pcs per month
Minimum order	1,000 pcs

Precision springs

Custom compression springs

Straight, conical and variable-pitch compression springs, 0.2–2.0 mm wire.

CNC spring machine used for extension springs

Precision springs

Custom extension springs

Tension springs with loops and hooks, initial tension to specification.

Torsion springs and wire forms made by Sierxi

Precision springs

Custom torsion springs

Single and double torsion springs with custom legs, torque to specification.

Spring types

Compression springs — straight, conical, closed and ground ends
Extension springs — hook and loop ends
Torsion springs — single and double
Wire forms — clips, pins and custom bent shapes

Compression and torsion springs made by Sierxi

Which spring wire material?

Qualitative comparison. Material availability for each wire size is confirmed in the quote.
Material (JIS)	Strength	Corrosion resistance	Typical use
Piano wire SWP-A / SWP-B	Very high	Low — needs coating or oil	General mechanisms, indoor products
Stainless SUS304-WPB	High	Good	Electronics, food and medical devices, humid environments
Stainless SUS631J1 (17-7PH)	Higher than 304	Good	Higher-stress stainless springs
Phosphor bronze	Moderate	Good	Springs that also carry current

Spring design rules: index, rate and buckling

The spring index C is the mean coil diameter divided by wire diameter (D/d). As a rule of thumb, an index between about 4 and 12 coils consistently. Below about 4 the wire is overstressed during coiling; above about 15 springs tangle and dimensions drift.

The rate of a helical compression or extension spring is k = G·d⁴ / (8·D³·n), where G is the shear modulus of the wire, d the wire diameter, D the mean coil diameter and n the number of active coils. Because rate depends on d⁴ and D³, small changes in wire size or diameter move the load a lot — which is why we ask for load at a given length rather than dimensions alone.

Compression springs whose free length is more than about four times the mean diameter can buckle under load unless they run in a bore or over a rod.

Compression spring end types

End type	Seats squarely	Cost	Notes
Closed and ground	Best	Highest	Common for heavier wire; less practical on very fine wire
Closed, not ground	Good	Lower	Common on fine wire and small springs
Open	Poor	Lowest	Rarely used where the spring must sit square

Extension and torsion spring details

Extension springs: specify initial tension, hook type and the relative orientation of the two hooks
Extension springs: most failures start at the hook bend, so avoid sharp hook radii
Torsion springs: give leg lengths, leg angles in the free position and the torque at a stated angle
Torsion springs: state wind direction and load the spring in the direction that closes the coils
Torsion springs: allow clearance over the mandrel, because the coil diameter shrinks as the spring is wound up

What to put on the drawing

Wire diameter and material, outer or inner diameter, free length, number of active coils, end type, and the load at a given length (or the rate). For torsion springs, give leg lengths and the torque at a given angle.

Also state which dimensions are critical and the tolerance grade — for example JIS B 2704 or EN 15800 — plus any requirement for set removal, finish or passivation. Finishing is done by qualified partners.

How springs are inspected

We run an ISO 9001:2015 quality system. Free length, diameters and leg geometry are measured on a vision measuring system at first article. Load at a given length is checked with push-pull gauges. Production lots are inspected by AQL sampling, and a dimensional report can ship with each lot.

Vision measuring system used for spring dimensions

Coil spring or stamped flat spring?

Coil springs give long travel and a predictable, near-linear rate in a small diameter. Stamped flat springs and clips fit low-profile spaces, can combine a spring with a contact, mounting tab or locating feature in one part, and are made on a die rather than a spring machine. Many products use both — for example a battery contact plate with a conical coil spring. Because we make both in one factory, we can advise which suits your space and force requirement.

Packing small springs

Fine springs, especially extension springs with open hooks, tangle in bulk. Packing — layered trays, separators or small bags — is chosen per part and confirmed in the quote. Freight is quoted per destination.

Frequently asked questions

What wire sizes can you coil?

From 0.2 mm to 2.0 mm wire diameter.

What is the minimum order for springs?

1,000 pieces.

Do I need to pay for tooling for a custom spring?

CNC spring machines mainly use standard tooling, so custom springs usually need little or no dedicated tooling. Any tooling cost is confirmed per project in the quote.

What spring index is best?

As a rule of thumb, a spring index (D/d) between about 4 and 12. Outside that range springs are harder to make consistently.

How do you check spring load?

With push-pull gauges at the specified length, on first articles and production lots.

Can you supply springs with matching stamped parts?

Yes. We stamp contacts and clips in the same factory, so both can be sampled, inspected and shipped together.

Precision springs