Cold formingThe geometry of the coil spring is achieved in its first phase by chipless cold-forming of the spring wire in a coiling or winding process. The production of torsion springs is mostly done by means of a winding process in which the spring wire is wound around a mandrel. Compression and tension springs are brought into the desired form by means of a coiling process. The illustration on the left demonstrates the principle of the cold-forming process. The spring-hard material is pressed by means of feeder rollers into the coiling rods; in this process, adjustment and position of the coiling rods represent the exterior diameter of the manufactured spring. By means of the inclination rod, respectively wedge, the wire is then pushed out of the coiling centre. The variable positioning of the coiling rods and the inclination rod make it possible to produce a great variety of spring geometries. In the last phase, the wire is cut by the blade which can be moved in various ways. A rotational cut produces spring ends almost without burrs. For cold forming we have at our disposal more than 50 of the most modern coiling machines with a wire dimension spectrum from 0.3 mm to 16mm.
Thermal treatmentThe internal stresses caused by the plastic deformation of the spring-hard material are removed by a thermal treatment process, the tempering or annealing. Depending on spring geometry and manufactured quantity, different annealing ovens are at our disposal. By continually recording temperatures high product quality is guaranteed.
Grinding of spring ends
The design of the end coils is very important for compression springs. End coils are laid together and subsequently plane-ground; this allows the best possible axial spring compression during force transmission.
The VDF-Federn company disposes of more than 25 up-to-date CNC-controlled grinding machines for spring ends. Through the effective cooling of the grinding process and the high performance of extractor and filter units, an optimum of product quality is achieved. Furthermore many grinding machines are equipped with fully automated feeding units.
Shot peeningVery important for many demanding customer applications is the fatigue strength of the spring used. Shot peening can considerately increase the fatigue strength of the spring. By means of shot-blast machines, rounded cut-wire shot of defined strength and size is blasted at the springs with high velocity. This causes compressive stress and strain hardening at the outer layers of the spring material, and enhances fatigue strength. The smoothing of the surface also reduces the negative effects of surface defects. We have at our disposal several turn blast and hanger tape machines for different products and applications.
PlasticisingThe plasticising of springs, also called setting or presetting, is used to maximise the utilisation of the materials and to optimise the spring characteristics. The residual stress caused by over-elastic load demand reduces the load stress later on when the spring is in operation. This additional process avoids a loss of length (setting loss) when later on the spring is in use, and raises the load-bearing capacity of the spring.
We have at our disposal various warm and cold setting devices for the different applications of our customers. Here, too, the utilisation of automated feeding devices ensures efficient production.