Description

Helical compression springs are made of oil-hardened and tempered spring steel wire, stainless spring steel wire and patented-drawn spring steel wire as indicated in EN 10270. After drawing, the wire is coiled in a spring coiling machine. The residual stress developed in the spring wire during the cold shaping then has to be relieved by a tempering stage as the next step in manufacture. The degree of residual stress will be dependent on the spring index of the springs. After tempering, there are further possible manufacturing steps, basically grinding and deburring of the ends of the springs. Shot peening is used to extend fatigue life, followed by further heat treatment. The presetting introduces a form of stress into the spring wire that will be favourable for the later loadbearing, ensuring that the threatened shortening (setting) of the spring in use is all but avoided. The final stages of spring manufacture are surface coating and the measuring and testing of the spring properties.
Thus, the production of helical springs for engineering purposes involves a series of processes, among which coiling, peening, presetting and in particular the different tempering processes will significantly change the properties of the spring steel wire and thereby the functional and strength properties of the springs. These changes are not completely known even today, which means that optimisation of spring production can take place only by means of the sample spring process with all its costs in time and money. To enable these alterations in the material to be taken account of at the dimensioning stage for the springs, it is necessary for the characteristic values to be known for the spring steel wire after the various treatment stages of tempering, pre-setting and so on.