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.
Parting Line Deflection
Meaning
Elastic separation between mold cavity and core plates along the primary parting plane occurs when peak hydraulic cavity pressure exceeds machine clamping force during injection. Parting line deflection creates unwanted clearance gaps that allow molten plastic to escape, generating flash on molded components. The condition governs clamping force requirements and mold platen rigidity, stopping when cavity pressure drops below the mechanical sealing threshold.
Structural Displacement
High injection pressure spreads mold half surfaces apart during peak packing phases. Experiencing parting line deflection alters part wall dimensions near the parting surface and causes severe aesthetic flash. Machine platen bending or improper support pillar placement amplifies local tool gap formation under load.
Thin-viscosity resins like polyoxymethylene readily flow into microscopic parting line gaps, creating thin plastic fins that require manual trimming.
Clamping Adjustments
Molders prevent tool separation by increasing tonnage settings or optimizing injection velocity profiles. Controlling parting line deflection requires calculating projected cavity area and selecting press sizes with adequate reserve clamping capacity. Balancing runner systems ensures uniform pressure distribution across multi-cavity tools, preventing localized steel separation.
Regular tool maintenance prevents foreign material buildup on land areas from causing uneven parting line sealing.
Quality Limits
Excessive mold deflection leads to permanent steel deformation and parting line land damage over extended production runs. Eliminating parting line deflection protects tool longevity and prevents costly secondary flash removal operations. Quality audits measure flash thickness and part weight variations to detect tool movement before tool steel suffers permanent deformation.