Single point coiling is the more popular type of deflection coiling used in the United States. With single-point coiling, the tooling consists of a final guide, a forming arbor, a single coiling point, a pitch tool, and cutter. The arbor acts as an anvil around which the wire is bent (deflected) to achieve the desired coil size and diameter. As shown in the figure below, the single coiling point holds the wire against the arbor allowing adjustment of the coil diameter by increasing or decreasing the amount of bend which is induced. Bending is induced by moving the coiling point toward or away from the arbor centerline. A groove in the coiling point is matched to the wire size to control the wire as it is fed through the tooling. The combined actions of the final guide, arbor, and coiling point create three-point bending support which induces enough plastic strain to permanently form the wire into the desired coil shape.
A pitch tool controls the spacing between the turns of the coil. As the wire exits the coiling point it slides against the face of the pitch tool. The pitch tool is pushed against the wire to create the desired degree of inter-coil spacing. The pushing action induces plastic strain about the wire axis to permanently form the coil pitch spacing. Compression springs require spacing between turns to allow the spring to compress and generate a resisting mechanical force. Conversely, extension springs are produced with no pitch spacing between turns so they can apply a resisting mechanical force when stretched. Torsion springs can be produced with or without pitch spacing to achieve the desired resisting torque and is mostly independent of pitch spacing.
A cutter tool trims the wire across the top plane of the arbor to create coils and springs of discreet lengths. Enough wire is fed through the tooling to create the desired length of spring. The cutter then shears the wire cleanly across the top of the arbor tool surface with little to no burr. In single-point coiling the limiting factor for small coil diameter-to-wire size ratios (Index) is typically the arbor. If the arbor cross section is too small, it will not be able to withstand the cutting forces.
The diagram below defines coil index and provides a comparison of coil index verses ease of coiling.
The deflection coiling process relies on the theory of elasticity and plasticity to produce helical springs of all shapes and forms.
Deflection coiling utilizing two coiling point tools.
Deflection coiling utilizing one coiling point tool.