production process of coil springs
Spiral/coil springs production process: coiling/winding → end surface processing(compression springs) /making hooks(extension springs and torsion springs) →hot processing test→ Prestressing/shot blasting.
Coiling/winding is to coil the spring wire which meets the technical requirements around the core bar. For the massive production, Use universal automatic spring winding machine. For single or small amount of production, use normal lathe or manually wind.
For the winding, we have cold winding and hot winding. We choose cold winding when the diameter of spring wire is less than 8/10mm, otherwise, use hot winding. Cold winding is to wind overheat treatment cold-drawn non-alloy steel wire for springs at normal temperature and no need quenching treatment after winded. Eliminate the internal stress by low tempering. Hot winding, first needs heating( normally 800℃---1000℃ according to the diameter of spring wire), after winded, use quenching and tempering.
Use prestressing treatment or shot blasting and other strengthening measurements to increase the carrying capacity of springs after springs are made. Prestressing treatment is to make springs to stay 6 to 48 hours with limit load. Shot blasting is to peen shot or cast iron shot with certain speed to springs. These two kinds of treatments will cause plastic deformation at the surface of springs and reserve useful residual stress. Part of working stress can be eliminated during loading because the direction between residual stress and working stress is opposite. The springs after strengthening treatment can not work at the place with higher temperature (150℃--450℃)and at the place with vibration and corrosion medium for a long time.
And springs should have processing test and precision, impact and fatigue tests according to the requirements of spring technology to test if the springs meet the technical requirements. The lasting strengthening and anti-impacting strengthening of springs are depended on the surface conditions of spring wire. Therefore, the surface of spring wire should be clean and bright, no cracks and marks. Surface decarburization will influence the lasting strength and anti-impact strength seriously. For the springs with important usage, surface protection treatment is needed(for example, galvanizing). For normal springs, use basting or painting.