Tolerance Grades a Toolroom Signs under DIN 16742
DIN 16742 defines nine tolerance grades based on resin shrinkage variance, requiring toolmakers to split tool-bound and parting-line tolerances during sign-off.
DP1 Tool Bound
Meaning
Mold design tolerance classifications define the achievable accuracy of feature dimensions formed entirely within a single rigid mold component without crossing moving tool interfaces. Specifications designated as dp1 tool bound establish the tightest dimensional limits available for features cut into a single steel block or core pin. Machine opening variations and parting line flash do not affect these dimensions because no tool movement disrupts the cavity geometry during solidification.
Datasheet shrinkage values must match the specific resin grade to hold these narrow limits across production runs. Molders use these values to verify cavity steel dimensions prior to tool sign-off.
Steel Geometry
Machining tolerances in mold steel directly govern the baseline dimensions of the finished plastic part. Achieving dp1 tool bound status requires wire electrical discharge machining or precision CNC milling of core and cavity inserts. Thermal expansion of tool steel during long production cycles remains the primary source of drift for these rigid features.
Toolmakers compensate for calculated polymer shrinkage when cutting the steel cavity.
Shrinkage Control
Polymer crystalline structure and cooling rate dictate whether a part retains its machined boundaries. Applying dp1 tool bound standards requires tight control over mold surface temperature and melt temperature to prevent differential contraction. Unfilled resins exhibit higher volumetric shrinkage than reinforced grades, which impacts final part dimensions.
Regrind addition alters melt elasticity and can cause parts to drift out of specification.
Boundary Condition
Tool wear over extended production shifts gradually changes cavity dimensions. Measuring dp1 tool bound features requires calibrated optical comparators or coordinate measuring machines to detect micron-level steel erosion. Repairing worn cavity walls demands laser weld steel deposition followed by re-machining to restore initial tolerances.
Process monitoring relies on keeping mold temperatures within narrow bands.