Torsion Spring Coiler

Overview

A torsion spring coiler turns a continuous coil of metal wire into finished torsion springs. A torsion spring stores energy by twist: the wire is wound into a helical body and the two ends are bent out into straight legs, and when the legs are rotated relative to each other the body winds tighter and pushes back. These springs are everywhere, in clothes pegs, garage doors, hinged lids, mousetraps, ratchets and door closers. The coiler pulls wire off a spool, straightens it, wraps it around an arbor to form the body, then bends each end into a leg at a set angle and cuts the spring free. The sequence repeats by itself, so one machine makes up to 120 springs a minute with no handling between cycles. This unit coils wire from 0.3 to 3.5 mm into bodies from 2 to 40 mm in diameter.

The machine is built on the Machine Frame, a welded base topped by a ground faceplate. The faceplate carries the Coiling Head and presents the flat datum every tool references. Wire enters from the Spool Payoff Stand, runs through the Servo Feed Unit and the Roller Straightener, and reaches the coiling head where the body is wound. The Leg Forming Station then forms the legs and cuts the spring off, and the whole sequence is run by the Control Cabinet.

Feed and straightening

Wire comes off the spool with a permanent curve, called cast, and with the slack that comes from unwinding. The Spool Payoff Stand handles the supply side: a Payoff Reel carries the coil and a sprung Dancer Arm keeps a steady pull while a drag brake stops the reel overrunning when the feed pauses.

The Servo Feed Unit meters the wire forward. A Servo Motor turning through a Helical Gear Pair drives hardened Feed Roller grooved to the wire size, with idler rollers clamping the wire so it cannot slip. An Encoder counts the length fed, which is what sets how many coils go into the body and how much wire is left for each leg. A Feed Grip Cam releases the grip while a leg is bent and closes it again for the next spring. Before the wire reaches the coiling point it passes through the Roller Straightener, two banks of Straightening Roller at right angles. Flexing the wire past these offset rollers works the cast out, and a straight wire is what lets the coil diameter and the leg geometry repeat.

Coiling the body

The Coiling Head forms the helical body, and this is the part that defines a coiler. The straightened wire is fed against a Coiling Point, a hardened grooved tool that deflects the wire into a curve. As the feed keeps pushing, the deflected wire wraps around a Coiling Arbor whose diameter sets the inner diameter of the body. The coiling point sits in a Coiling Point Block that adjusts its offset from the arbor, and that offset is what tunes the coil diameter. Many machines use two points, a starting point and a finishing point, to hold the diameter steady as the body grows.

Left alone, the turns would stack flat against each other and give a body with no pitch. A Pitch Tool solves this: a hardened wedge, carried on the Pitch Slide, enters between the turns as they form and pushes each new coil along the arbor. The programmed travel of the pitch slide sets the spacing between coils and so the free length of the body. A Wire Entry Guide presents the wire to the coiling point at the right angle so the start of the body is clean.

Forming the legs

A torsion spring is defined by its legs as much as its body, since the legs are what the load acts on. Once the body is wound, the Leg Forming Station bends the two wire ends into radial legs. A Leg Bend Arm swings a Leg Bend Tool against the wire end and folds it over a Leg Radius Mandrel, which sets the bend radius where the leg meets the body. The leg length is set by how much wire the feed left beyond the body.

The angle between the two legs is the spring's key dimension, and a Leg Index Table sets it by rotating the spring relative to the bending tools between the first leg and the second. When both legs are formed, a Cut-off Slide carries a moving Cut-off Blade across the wire against a fixed lower blade and crops the finished spring free. The shear is driven by a Pneumatic Cylinder, the spring drops clear, and the next cycle starts from the new wire end.

Control

The Control Cabinet runs the machine. A multi-axis Motion Controller keeps the feed length, the pitch tool, the two leg bends and the index table in phase, because a leg bent before the body is to length spoils the spring. Each axis has its own Servo Drive, and the operator enters the coil count, body length and leg angle at the Touchscreen HMI touchscreen, which stores spring recipes for quick changeover.

Materials and use

The coiling point, the arbor, the bend tools, the cut-off blades and the feed rollers are made from hardened tool steel or carbide because they take the full forming load on every cycle. The wire itself is usually music wire, stainless or oil-tempered spring steel, drawn to a tight diameter tolerance so the coils and legs repeat. Torsion spring coilers are used by spring makers supplying the automotive, appliance, hardware and furniture trades. Against a hand-set bench coiler, a CNC coiler changes from one spring to another by loading a recipe and swapping the arbor and a few tools, which makes short runs and prototypes economic alongside long production. The working area sits behind Guarding & Interlocks with interlocked doors so the fast leg arms and the shear stay enclosed while the machine runs.