For important springs, strong pressure treatment is also required. The strong pressure treatment is to make the spring under the ultimate load load for 6 to 48h, so as to produce plastic deformation and residual stress in the dangerous area of the spring wire section. Since the sign of the residual stress is opposite to the working stress, the maximum working stress of the spring after high pressure treatment is relatively small, and one high pressure treatment can increase the static load carrying capacity of the spring by 25%. If it is shot peening, it can increase by 20%. However, springs used in long-term vibration, high temperature and corrosive media, and springs for general purposes should not adopt this strengthening process.
In the manufacture of spiral tension and torsion springs, at present, except for a few manufacturers who have introduced foreign CNC numerical control spring forming machines to automatically form and process various styles of tension and torsion springs at one time. The vast majority of manufacturing plants still use traditional processing methods to manufacture, and here is a brief introduction.
1. Spiral tension spring. The process is basically the same as that of the helical compression spring. The only difference is the hook loop processing at the end. The forming method of the tension spring is as follows:
1) Use the same method as the spiral compression spring, after winding and forming, perform stress relief annealing, and then perform hook loop processing, except for special-shaped hook loops or spiral tension springs that require high initial tension. In addition to coiling, most springs are coiled by automatic spring coiling machines.
2) Use straight-tail spring coiling machine to roll. It is a vertical centered spring coiling machine with vertical mandrel. After rolling, stress relief annealing is performed, and then hook and loop processing is performed. There are many types of end structures of helical tension springs and many processing methods. Commonly used are: small springs are manually processed with pliers-type special tools or special process devices; ordinary spiral tension springs are processed by manual or automatic operation methods with hooks or molds; long arm hook and loop stretching For springs, the length of the material required for the hook is generally reserved during winding, or the number of turns required for processing is reserved after rolling. The ends are straightened with a straightening tool, and then the hook and loop is bent with a special tool.
The process specification of stress relief annealing is as described above. After the spring is coiled, stress relief annealing is performed first, and then cut and the shackle processing is performed. After the shackle processing is completed, the stress relief annealing is generally performed 1 to 2 times. In order to prevent the relative angle of the two shackles from changing, the temperature after the shackle processing should be 20-30°C lower than the temperature after the rolling during the stress relief annealing. Spiral tension springs are generally not subject to shot blasting and strong drawing.
2. Spiral torsion spring. The process is basically the same as that of the spiral compression and extension springs, and the difference is also embedded. In the case of small batch production and complicated torsion arms, most of them are formed by manual or semi-automatic mandrel coil springs, and then used The tooling and fixture will process the torsion arm according to the drawing requirements. In mass production, it can be rolled on a straight tail spring coiling machine and a special torsion spring machine. If the torsion arm cannot be completed according to the drawing, it can be processed by tooling and fixtures in the process. According to the characteristics of spiral torsion springs, the following two points should be paid attention to when designing and manufacturing:
1) The torsion arm at the end of the spiral torsion spring should be bent once during manufacture to avoid processing defects and corrective shaping. After the torsion arm is processed, the second stress relief annealing should be carried out;
2) The current spiral torsion springs are mostly dense coils, so that a compression force similar to the initial tension of the tension spring is generated between the coils. When loading and unloading, there will be friction and hysteresis. When the load is the same as the rotation direction or the number of turns increases, this tendency increases; in addition, it also brings difficulties to the surface treatment process. Therefore, when designing and forming, there should be a slight gap between the spring coils. In mass production, the manufacturer can use hydraulic and pneumatic methods to process the spiral stretching, torsion spring unfolding, bending, hooking and other processes if conditions permit.