Spring load and various shape-forming processes
During the stamping process to form the disc spring, small grooves may form on the machined surface running in the stamping direction. Under load a series of tangential tensile stresses will occur particularly on the external edge of the spring.
The inner and outer diameters of SCHNORR® disc springs are finished by lathe turning to counteract these critical conditions. That way, this critical condition is avoided. The turning pattern that inevitably occurs during the turning process runs in an uncritical tangential direction and thus into the direction of the acting tensile strength so that the danger of breakage is reduced to a minimum with SCHNORR® disc springs.
During the turning procedure the stamping grooves are completely eliminated. The radial machining grooves occuring during the turning process run in the direction of the main tension of the spring and are thus not critical.
During fine-blanking the stamping grooves occur across the tangential tension which leads to an increased notch sensitivity (see figure 1) if these are not completely removed.
The stamping grooves are smoothed during the tumbling or vibratory grinding process.
Stamped only variant:
During simple stamping accentuated stamping grooves occur across the main direction of tension resulting in a much higher notch sensitivity. We do not recommend this variant for dynamic requirements. Due to the punching cracks, a higher service life cannot be guaranteed.
Benefits of turned disc springs
- By turning the key surfaces of the spring, stamping cracks across the main direction of tension have been completely removed. This eliminates the risk of the notch effect.
- As the bearing surfaces are fully turned then friction between components is significantly reduced. This benefit can only be achieved by individually turning the disc springs (see figure 1b).
- Zones of work hardening which may occur on the cutting edges during fine-blanking are removed as far as possible during turning. The hardening process is clearly more uniform than with punched or fine-blanked surfaces which are then tumbling or vibratory ground only (see figure 1a and 1b).
- To achieve particularly high precision, the disc springs can be fine-turned to final dimension once again after the hardening process.
- With normal stamping and subsequent turning, material grades with a higher tensile strength than 600 N/mm2 which do not have sufficient shaping capability for fine-blanking and are thus subject to the danger of crack formation can also be processed.