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.
Specific Shrinkage Variance SWS
Meaning
Mathematical expressions describing local dimensional deviation relative to nominal mold cavity dimensions define volumetric contraction fluctuations across a molded part. Specific shrinkage variance SWS quantifies non-uniform dimensional changes induced by differential cooling and holding pressure gradients. The parameter governs precision tooling offsets, stopping where part geometries exhibit pure isotropic behavior without thermal gradients.
Metric Definition
Measuring dimensional changes across multiple points on a part isolates anisotropic behavior caused by material flow and cooling differentials. Evaluating specific shrinkage variance SWS allows toolmakers to identify areas requiring cavity steel modification before final tool hardening. Higher values indicate severe local dimensional distortions that lead to part warpage and assembly fit issues.
Polymer fiber orientation and wall thickness changes drive localized variation in shrinkage values.
Molding Factors
Injection speeds, melt temperatures, and cooling channel layout directly influence local volumetric contraction. Controlling specific shrinkage variance SWS requires balancing gate placement and packing pressure profiles across the cavity space. Uneven mold wall temperatures create thermal gradients that increase shrinkage variance across opposite part faces.
Processors optimize cooling circuit flow rates to minimize temperature differences between cavity and core surfaces.
Specification Threshold
Component drawings mandate narrow variance thresholds for precision components used in medical devices and optical assemblies. Uncontrolled specific shrinkage variance SWS causes assembly interference, optical distortion, and mechanical housing failure. Molders utilize simulation software to predict variance distributions and optimize tool geometries before machining steel.