Two-point coiling is the second popular type of deflection coiling. It is commonly used in Europe. The tooling for two-point coiling consists of a final guide, two coiling points, a pitch tool, a cutter arbor, and a cutter. The final guide and two coiling points create the three-point bending support that permanently forms the spring into shape. Unlike single-point coiling, there is no forming arbor to serve as a bending anvil during the coil forming process. Instead, a cutting arbor positioned inside the coil creates a shear plane for the cutter tool to trim the wire into discrete lengths.
Since the tooling does not contact the inside diameter of the coil, it is possible to achieve much smaller coil diameter-to-wire size ratios (Index) and lends itself to spring applications which require an untouched surface finish on the inside diameter. However, two-point coiling machine setups are more challenging due to the number of tooling alignments and adjustments required to make a spring of the desired shape and size.
A cutter tool trims the wire across the top plane of the cutting 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 cutting arbor tool surface with little to no burr. In two-point coiling the limiting factor for small index coils is typically the size of the coiling point tools and how close they can be positioned to one another. Since the cutting arbor is not used for forming, it can be bigger in cross section and can better withstand 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.
Single point coiling is the more popular type of deflection coiling in the United States.
A variety of metals and alloys are used by the industrial and medical device industries to produce coils.