A Machine for the Production of Sophisticated Extended Loop Springs

By Matthias Grauer, Wafios AG

The great worldwide demand for automobiles persists. Due to the enormous pricing pressure to which suppliers of auto manufacturers are exposed, they must identify ways to optimize production permanently. Furthermore, a multitude of automobile types and shorter car model cycles require highly flexible processes.

Figure 1: FSO 3 production examples.

This especially affects spring manufacturers, as their situation is intensified by high steel and wire prices.

Therefore, Wafios went about the task of designing a high-performance machine for the production of windshield-wiper springs. These springs feature:

• Wire diameters between 2 mm and 3 mm (0.08" - 0.12").

• A very tight coiling ratio.

• High initial tension.

• Partly recut loops.

• A possible bend at the spring leg

In the ’70s, the company Karl Hack very successfully sold special machines, types ASF/BSF, for the production of these kinds of springs. The machines were equipped with several hydraulically driven bending units, which carried out the following functions:

• Setting spring legs upright.

• Bending loops.

• Re-cutting loops.

These machines reached a maximum output of up to 20 extended loop springs per minute, which then was an outstanding achievement. Until 1985, about 150 of these successful machines had been in use. Their disadvantage, however, was that they had long retooling times. When the machine needed to be retooled for a different spring, it took several days to complete the task. When the settings of one processing station were changed, settings at the succeeding stations had to be changed as well.

Figure 2: Station-by-station diagram of the spring-production process.

What was needed was a new machine type that could produce these sophisticated extended loop springs in very large batches with high production outputs and short retooling times. These were the challenges that Wafios met in the development of the CNC tension spring coiler FSO 3.

With an intelligent machine design, the new FSO 3 produces the spring body with spring legs that stick out tangentially (Figure 2, page 67). Springs with high initial tension or with pitch can be coiled. Then the spring body is transported to the first CNC turnstile table. Here, six gripper arms transport the spring body to the different processing stations, as enumerated in Figure 2: The first spring leg is set upright (2). The first loop is bent (4) and re-cut (5). The scrap wire of the re-cutting station can be extracted. If necessary, an additional bend is made at the upright spring leg (3). The spring body is form-fittingly held in all processing stations.

Then the spring is transported to the second turnstile table (6). During the transfer, the spring body is positioned in such a way that possible deviations of the spring leg have no effect in the bending and looping station. In the second turnstile table, the second extended loop is produced analogous to the first extended loop (7-10).

Figure 4: Spring application range includes windshield wipers, drum brakes & sports equipment

Up to 32 CNC axes control all movements of the machine. Electronic shafts are freely programmable in order to guarantee an optimum timing diagram. Programming is very simple in four subsystems. Hydraulic units – with their well-known disadvantages like high energy and maintenance costs, limited precision and inflexibility – are not needed.

The sequential production process – coiling of spring body, setting spring legs upright, bending of spring legs and re-cutting, then ejection – enables a high production out-put of 2,400 springs per hour. Each succeeding spring is coiled after the previous one has left the coiling station and has been transported to the first turnstile table.

Simple tools enable very short setup times. A new spring can be set up in about six hours, and a previously set up spring can be set up again in about three hours – a fraction of previous setup times. Tools are easily adjusted by means of stops. Tool positions are visualized by means of displays.

An optical measuring system monitors spring dimensions. Faulty springs are sorted out.

In addition to windshield-wiper springs, extended loop springs can be produced for brake systems or sports equipment. The FSO 3 offers economic and cost-efficient production.

Matthias Grauer, Dipl.-Kaufmann, is with Wafios AG in Reutlingen, Germany. He has a master’s degree in business. Readers may contact him by phone at +49 7121/146-0, e-mail at sales@wafios.de or Web site at www.wafios.de.