Wafios spring coiler around 1900.

Photos: Wafios

Compression spring coiler series by Wafios.

Development of compression spring coilers

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An essential characteristic of mechanical spring coilers is the limited wire infeed length and the “one-motor principle” on which all tool motions (control shaft) as well as their synchronization (gear) were based by means of sophisticated mechanical solutions. The precision and regularity of the processes was considerably deteriorated by material stress and mechanical clearances. These machines could only be operated by highly experienced spring makers; cam discs (pitch / spring shape) had to be adjusted individually in accordance with the material and the spring produced.
There were high maintenance costs, long set-up times and thus only low flexibility. Therefore, the production of small batches was very expensive. These machines would not meet the requirements of modern spring manufacturers.

The spreading of electric motors after 1945 enabled the construction of electrically driven machines. A clutch connected the axes for the feed rollers and the tool motions with the motor that ran continuously. One revolution of the control shaft corresponded to the production of one spring. Cams on the central shaft controlled the clutch and let the feed rollers rotate for a certain revolution of the control shaft. As soon as a certain infeed length had been reached, the control shaft was disengaged from the drive motor. While the feed unit was stopped, the cutting shaft could be rotated by means of a clutch. The cutting shaft connected the cutter tool for the rest of the control shaft’s revolution with the drive motor. During this time, all other tool motions were blocked. Larger machines had a claw clutch installed. Here the cams of the control shaft triggered a sudden engagement of the mechanical system. Very great physical forces were created and the claws were extremely stressed. In addition, there was a lot of noise during the engagement process. All smaller spring coilers were equipped with friction clutches. With these clutches, the motor could be engaged slowly with the gear. Sudden shocks were avoided and the machines ran quietly. The essential problem of these machines was, however, that the infeed length did not remain the same.
The wire infeed length varied depending on the time the clutch needed to engage completely. Depending on the condition of the clutch, the springs were longer or shorter.
Another common characteristic of all clutch machines was a continuous feed speed. The adjustment of the forming speed to e.g a spring with a big spring index, was not possible.

The continuously running motor was connected with the feed segment by means of an oscillating link block. The segment drove the feed rollers in one direction by means of the forwards movement. During the return stroke, a freewheel disengaged the feed rollers from the segment and interrupted the wire feed. At the same time, a mechanical brake stopped the infeed while the cut was made. The amplitude of the oscillating segment corresponded to the wire infeed length, the amplitude of the segment (the swinging motion of the pendulum) could be adjusted through the eccentricity of the link block.

One version of the segment control was the toothed-rack-controlled spring coiler which aimed at a high output. A spring coiler driven by toothed racks produced two springs during one 360°-revolution of the control shaft. This was possible because the second spring was produced on the return stroke of the toothed rack.

The development of low-cost machine controls and powerful computers enabled the construction of electronic multi-axes machines. As the spring production was rather expensive due to the cam discs employed, smaller batch sizes could not be produced anymore with acceptable set-up times.
In electronic spring coilers, a multiprocessor system synchronized the five axes. The high output requested had increased the demands on machine controls. Besides the control of axes movements, the computing power enabled the processing of input data, the triggering of forming operations or e.g. the activation of additional monitoring and measuring devices.
For the production of high-quality springs, sufficient motor power was needed for the infeed and shaping of the wire. Moreover, high rigidity of the machine body was necessary in order to avoid vibrations and to compensate temperature fluctuations.
The quality of the spring was even more enhanced by the introduction of the rotary cut which reduced the creation of burrs. Although burrs could not be completely avoided, they were reduced to a minimum.
Mechanical improvements for increasing the machine’s availability were achieved by constructive solutions like, e.g. the separated coiling plate or the mounting fixtures for holding pre-set tools.

Besides sophisticated solutions for the flexible production of small batches, there are even today machines needed for economical mass production. This is where two-axes electro-mechanic spring coilers are the solution. One axis is used for feeding in any length of wire and the second motor controls the tool motions of the cut, pitch and shape. This compromise between conventional mechanic machine and fully electronic machine is even today a powerful and economical alternative.

Modern CNC spring coilers are more and more subject to economic aspects. The integration in networked production systems, which enable open communication on production level, workshop management and e.g. job control, plays an important role. It serves for the reduction of downtimes and the ideal use of the available machinery also when producing very small batches.
When acquiring new machines, not only the costs per unit based on output and material costs are considered, but the machine’s lifetime has become a crucial factor. Criteria like energy efficiency, machine availability and zero-error production gain more importance in the catalog of requirements. The decision for or a against the acquisition of a new machine is not merely based on its price but rather on the total cost of ownership (TCO) which include the required floor space, the fees for demolition and recycling and the machine’s running time. Therefore, questions about increasing the energy efficiency by means of the materials used, by means of energy recovery (intermediate circuit/energetic recovery system), by an optimized design of energy consumers like airconditioning units and axes etc. play an important role in the development of new machines.
In the future, the main challenge will be to increase the machine capability and not to reduce downtimes or to maximize the output. The efficiency of the employed machine can be improved, e.g. by testing systems in combination with monitoring and measuring technology for achieving a zero-error production or by monitoring the production process for determining the ideal machine speed to minimize the production of defective parts. Increasing the machine capability may also mean to process different materials and thus increase the flexibility of the machine.