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.
TG1 to TG9
Meaning
Standardized dimensional tolerance classifications established by standard bodies categorize achievable manufacturing accuracy for plastic molded components. TG1 to TG9 defines the spectrum of tolerance groups ranging from precision high-accuracy molding down to wide-tolerance commercial molding. The classification system governs drawing specifications between part designers and molders, stopping where custom micro-molding or optical machining guidelines supersede standard limits.
Classification System
Engineering standards assign tolerance groups based on resin type, part dimensions, and processing capability. Categorizing parts from TG1 to TG9 establishes realistic manufacturing expectations based on material stability and mold accuracy. Class TG1 represents extreme precision achieved only with specialized unreinforced resins and controlled molding environments.
Classes TG8 and TG9 apply to large, low-cost structural parts molded from flexible or highly variable materials like recycled polyolefins.
Production Impact
Reaching tight tolerance groups requires high-precision tooling, stable machine control, and raw resin with narrow viscosity distributions. Specifying TG1 to TG9 guides molders on necessary process control investments and inspection frequencies. Tight groups demand continuous cavity pressure monitoring and temperature regulation in climate-controlled cleanrooms.
Relaxing tolerance requirements to wider groups reduces tooling costs, shortens cycle times, and lowers scrap rates.
Tolerancing Limits
Requesting overly tight tolerance classes for hygroscopic or high-shrinkage polymers inflates production costs unnecessarily. Mismatches in specified TG1 to TG9 tiers relative to resin capabilities lead to frequent part rejections during quality control audits. Procurement contracts reference these tolerance groups to establish legally binding acceptance criteria for incoming part dimensions.