Two questions decide whether a custom shaped spring is the right answer: what the part actually has to do inside the assembly, and how many of them the project needs per year. The geometry, which is what most enquiries open with, is the easiest of the three to settle.
What the term covers
Shaped springs are a broader family than the name suggests. It takes in helical springs with a geometry other than cylindrical – conical, barrel, hourglass, variable diameter or variable pitch – and it takes in wire forms, where the elastic function is carried by a bent length of wire rather than by a coiled body.
The second group covers mounting clips, pressure clamps, cable retainers, sprung frames and contact elements. From a production standpoint they share one property: they cannot be described by four dimensions from a table, and the tooling has to be prepared for that specific geometry.
Conical springs: a characteristic that is not a straight line
In a cylindrical spring every coil works at the same time and the characteristic is linear. In a conical spring the coil diameter grows towards the base, so the largest coils deflect most and close first. Once they are closed, fewer active coils remain and the rate rises.
The result is a progressive characteristic: soft at the start of the stroke, increasingly stiff towards the end. In practice that gives a component which holds its rest position gently and still transmits a high force at large deflection, without increasing the wire diameter.
The second advantage is purely geometric. With a suitable pitch the coils telescope into one another and the solid height approaches a single wire diameter instead of the sum of all coils. Wherever the installation space is flat – in seats, latch mechanisms and equipment housings – that is often the only way to fit the part at all.
A conical spring is also far less prone to buckling than a slender cylindrical one, because the wide base stabilises it without a guide.
Variable pitch, when resonance is the problem
A cyclically loaded spring has a natural frequency of its coils. Once the excitation frequency approaches it, coil resonance appears: a wave travels along the body, the coils hammer against each other and the part loses life much faster than the stress level alone would suggest.
Winding with a variable pitch detunes the system. Individual sections of the body have different natural frequencies, so the wave does not build up. As a side effect the characteristic becomes progressive, because the closely pitched coils close earlier.
Barrel and hourglass shapes: stability instead of a guide
A barrel spring has its largest diameter in the middle, an hourglass spring the opposite, with the waist in the centre and wider ends. Both solve the same problem: stable operation without an arbor and without a guide sleeve.
The hourglass form also centres itself in a pocket of a given diameter, which simplifies automated assembly. The barrel form suits designs where the seats are small in diameter but the spring still needs a long stroke.
Wire forms with a spring function
A separate group covers parts where the spring is a bent length of wire. A clip holding a luminaire in a suspended ceiling, a clamp pressing an LED module against a heat sink, a cable retainer, a sprung frame positioning a sub-assembly inside a housing – all of them work on the same principle: controlled elastic deflection of a bent section.
They are designed differently from helical springs. There is no rate equation; there is bending geometry, radii, arm lengths and support points. The force is normally arrived at iteratively, on prototypes, because the result also depends on how far the material springs back after forming.
That springback is the main reason why the first part never matches the 3D model exactly. The bending tool is set with an angular overshoot, and the size of that overshoot depends on the grade, the wire diameter and the bend radius.
When one custom part replaces three catalogue items
The most common reason engineers move to a dedicated part has nothing to do with force. It has to do with the number of components in the assembly.
A typical mounting point can consist of a catalogue spring, a spacer, a screw and a washer. The same duty can often be met by a single bent element that presses, positions and snaps into its seat at once. Several part numbers disappear from the bill of materials, several assembly operations disappear from the line, and so does the risk of fitting them in the wrong order.
The arithmetic is then straightforward: a more expensive part, a cheaper assembly. Above a few tens of thousands of pieces a year the saving in assembly time usually outweighs the difference in piece price, and integrating the functions also reduces the spread of the clamping force, because the tolerance chain of several components is removed.
This direction is worth considering while the design is still open. Changing the geometry of a seat in a finished injection mould costs many times more than a wire bending tool.
Documentation: what replaces the parameter table
For a cylindrical spring a table is enough: wire, diameters, length, forces, coil count. For a shaped part that format stops working.
What is needed is a 3D model, preferably STEP, together with a clear statement of which dimensions are functional and which are resultant. A description of the duty helps just as much: what force, on what arm, at what deflection, in what mounting position. A bent part can be made in several different ways, and only that description allows the right one to be chosen.
Tolerances where there is no standard
EN 15800 covers cold coiled compression springs of round wire, DIN 2097 covers extension springs and DIN 2194 torsion springs. For conical springs with complex geometry and for wire forms there is no equivalent – tolerances are agreed between supplier and customer.
In practice that comes down to three decisions. First, identifying the critical dimensions, of which there are usually a few rather than a dozen. Second, agreeing the inspection method: gauge, template, optical measurement or a force measurement on a fixture. Third, agreeing a reference standard, meaning an approved master part from the first run.
That last point is the one most often skipped, and it is the most useful. With three dimensional geometry a physical master settles disputes faster than any dimensional note.
Material and treatment after forming
| Material | Standard | Temperature range | Typical use in shaped parts |
|---|---|---|---|
| Patented wire SH / DH | EN 10270-1 | -200 to +80 °C | clips and clamps inside dry equipment |
| 1.4310 | EN 10270-3 | -200 to +160 °C | luminaire components, humidity, outdoor mounting |
| 1.4568 | EN 10270-3 | -200 to +200 °C | large elastic deflections with corrosion resistance |
| 1.4401 | EN 10270-3 | -200 to +300 °C | chemical environments and elevated temperature |
After forming, the part needs stress relieving by heat treatment. Skipping that step produces a component that measures correctly at inspection and then changes geometry after a few weeks in storage or after the first working cycle.
Tooling and the break-even volume
A shaped spring requires tooling, and that is a one-off cost spread over the volume. At a few hundred pieces the tooling share dominates the unit price. At a few tens of thousands it becomes irrelevant.
The first question at quotation stage is therefore not about geometry but about annual volume and project horizon. At low volumes it is sometimes cheaper to build the function from two catalogue items than to make one dedicated part. At high volumes the opposite holds, because an integrated part shortens assembly.
An in-house CNC toolroom shortens the path here: tooling is made on site, so a correction after the sample run takes days rather than weeks.
From STEP model to series production
The usual route looks like this: a STEP model or 2D drawing plus a description of the duty, a quotation split into tooling and piece price, a sample run with force and geometry measurement, a tool correction, master part approval, then production release.
We manufacture shaped parts on multi axis machines within our CNC wire and tube bending and technical spring production. A large share of them goes to the lighting industry, where sprung clips and clamps hold fixtures in place and press modules against heat sinks, and therefore take part in thermal management.
Have a geometry that appears in no catalogue? Send us your enquiry with the 3D model – we will quote the tooling and the piece price for your volume.
