Meaning
Thermal processing removes internal tensions that accumulate during heavy machining or welding operations. Stress relief tempering involves heating the tool steel to a temperature below the transformation point and holding it there. This process allows the atoms to rearrange without altering the final hardness of the metal.
It ensures that the tool remains dimensionally stable during subsequent precision grinding.
Dimensional Stability
Internal stresses can cause a mould base to warp or twist over time. Performing stress relief tempering after rough machining prevents these movements from ruining the final alignment. This is especially important for large tools where small percentages of movement lead to excessive errors.
Machining Sequence
Strategic use of heat treatment allows the toolmaker to maintain tight tolerances throughout the build. After the bulk of the material is removed, the stress relief tempering cycle prepares the steel for the final finishing cuts. It reduces the risk of the tool moving when the final skin of metal is removed.
This step is mandatory for high precision components.
Fatigue Life
Tools that operate under high clamp tonnages are susceptible to cracking if they harbour residual stresses. Stress relief tempering improves the long term durability of the mould by creating a more uniform internal state.
