Meaning
Securing a workpiece under high pressure causes mechanical shifts in part positioning when the internal stresses are released. The effect of fixture clamping relaxation appears when the pressure of the clamps is removed after the machining process is complete. If the part was distorted by the clamping force, it springs back to its original shape, potentially taking the newly machined features out of tolerance.
This movement often happens instantly upon the opening of the fixture.
Elastic Distortion
Every material possesses a degree of elasticity that responds to the load of the fixture. If the clamping force is too high, the workpiece deforms before the tool ever touches it. Upon release, this fixture clamping relaxation reveals that the dimensions measured while the part was held are no longer accurate.
Force Optimization
Balancing the need for a secure hold against the risk of deformation requires careful planning of the grip points. Low profile clamps or hydraulic systems with adjustable pressure help maintain a consistent and minimal force. Placing supports directly beneath the clamp points reduces the tendency of the material to bend.
Machining Sequence
Roughing cuts often relieve internal stresses in the raw material, necessitating a second clamping setup for finishing. If the fixture clamping relaxation is extensive, the operator might loosen and re tighten the clamps before the final pass. This technique allows the part to settle into its natural state for the most critical dimensions.
