Meaning
Standardized dimensional limits established by the German Institute for Standardisation define the allowable variation for plastic molded parts produced from thermoplastic and thermosetting compounds. Engineers applying DIN 16742 injection moulding tolerance assign tolerance groups based on material shrinkage behavior, mold design complexity and production stability. The standard applies strictly to molded plastic geometries and excludes post-molding machining operations or secondary assembly steps.
Moulding Precision
Resin shrinkage characteristics govern the assigned tolerance group, dividing materials into low, medium and high shrinkage categories. When working with unreinforced amorphous polymers, DIN 16742 injection moulding tolerance permits tighter dimensional bands than with highly crystalline polymers like polyoxymethylene. Linear mold shrinkage variations between virgin polymer lots directly shift part dimensions outside the designated tolerance class.
Moulders must verify tool cavity dimensions against resin datasheet shrinkage rather than relying on generic mid-point estimates.
Shrinkage Fluctuation
Processing parameters directly affect whether a part stays within specified limits across a production run. Fluctuation in melt temperature, injection speed, or holding pressure causes localized density changes that alter shrinkage. Applying DIN 16742 injection moulding tolerance requires separating tool-making tolerances from process-induced part variations.
Tooling wear, multi-cavity imbalances and thermal gradients in mold cooling channels expand part size distribution beyond nominal engineering limits.
Material Constraint
Reinforced polymers containing glass fibers introduce anisotropic shrinkage that complicates tolerance compliance along different mold axes. Fiber alignment along flow lines leads to lower shrinkage along the flow direction and higher transverse shrinkage, which can cause warpage. While DIN 16742 injection moulding tolerance provides guidance for mold design, regrind usage above ten percent alters viscosity and shrinkage rates, often pushing part dimensions beyond the specified class limits.
Moulders must adjust cavity dimensions or holding pressures when processing regrind blends to maintain compliance.
