Meaning
Tooling design strategies where critical dimensions are initially machined to leave excess steel on the mould allow for subsequent adjustment after sample parts are measured. Adopting a steel safe design approach ensures that if the moulded part shrinks more or less than predicted, the tool can be adjusted by removing metal rather than adding it. This method is standard in high-precision tooling where tolerances are tight and shrinkage is difficult to predict.
The technique avoids the high cost and weakness of welding or inserting.
Sizing Strategy
Mold cavities are machined with slightly smaller dimensions for external features and larger dimensions for internal features. In a steel safe design, this arrangement means the resulting moulded part will have excess material on its features. If the part is too large, the toolmaker can remove a small amount of steel from the cavity to make the part larger, or add steel to the core to make a hole smaller.
Removing metal from the tool is much easier and cheaper than adding it. This strategy is applied to all critical tolerances.
Adjustment Method
Once the first sample parts are moulded and measured, the toolmaker calculates the required steel removal based on the actual shrinkage. This adjustment is done by precision milling or grinding the specific areas of the inserts. This method is highly precise and preserves the structural integrity of the tool.
If the tool is not designed to be steel safe, correcting a dimension might require laser welding or making new inserts, which increases the tool cost. This step is part of the tool tuning process.
Risk Mitigation
Reducing the financial risk of tool development by avoiding the need to rebuild mold components makes this approach highly valuable. Tooling projects can proceed with more confidence, knowing that final dimensions can be adjusted. This strategy is essential for parts with complex shapes where shrinkage is non-uniform.
It ensures that the final part meets the required specifications.
