Meaning
Dimensional states where the cavity volume is too large to meet part specifications require the addition of material to the tool. Entering a metal-unsafe condition means the toolmaker must use welding or inserts to decrease the cavity size. This situation typically arises from machining errors or unexpected changes in resin shrinkage.
It is the opposite of a conservative design approach.
Repair Strategy
Welding introduces heat which can warp the surrounding tool steel. When a metal-unsafe condition is identified, the toolmaker must choose between laser welding and machining a pocket for a new insert. Laser welding offers a localized heat source but may not match the hardness of the base material.
Inserts provide a more stable repair but introduce parting lines on the part surface.
Cost Burden
Rectifying an oversized cavity adds substantial time and expense to the project timeline. A metal-unsafe condition often leads to delays in the approval of the first article inspection. It may require multiple rounds of rework to achieve the correct surface finish.
The cost of these repairs is usually absorbed by the tool shop if the error occurred during the build.
Structural Risk
Thermal cycles in the injection press can cause welded areas to crack or delaminate. Avoiding a metal-unsafe condition is preferred because uniform material properties ensure even cooling. Any mismatch in thermal expansion between the base steel and the repair material can cause stress concentrations.
