GB/T 40742.3-2021
Geometrical product specifications (GPS)—Geometrical precision verification—Part 3：Functional gauges and fixtures—Verification when applying maximum material requirements and minimum material requirements (English Version)
- Standard No.
- GB/T 40742.3-2021
- Language
- Chinese, Available in English version
- Release Date
- 2021
- Published By
- General Administration of Quality Supervision, Inspection and Quarantine of the People‘s Republic of China
- Latest
- GB/T 40742.3-2021
- Scope
- This document specifies general requirements for the testing and verification process applying maximum and minimum physical requirements and general requirements for the design of fixtures for testing. This document is applicable to the inspection and verification of the elements under test and/or datum elements when the maximum physical requirements and minimum physical requirements are applied using functional gauges and fixtures.
- Introduction
Interpretation of the core content of the standard
As the third part of the GB/T40742 series of standards, this document focuses on standardizing the detection and verification methods of functional gauges and fixtures when applying the maximum material requirements (MMR) and the minimum material requirements (LMR). For the first time, the standard clearly distinguishes the application scenarios of physical functional gauges and virtual functional gauges, and establishes a theoretical framework for digital detection.
Key terminology system
Terminology Definition points Detection significance In vitro effective dimension Fitting dimension with external constraint of entity Key parameter for determining MMR compliance In vivo effective dimension Fitting dimension with internal constraint of entity Core indicator for determining LMR compliance Functional gauge Full-shape gauge (including physical/virtual types) Direct tool for boundary verification
Test process specifications
Maximum material requirement (MMR) test process
- Initial inspection of local dimensions: verify whether the dimensions are within the MMS-LMS range
- Boundary verification:
- Physical gauge: simulate the maximum material effective boundary (MMVB)
- Virtual gauge: calculate the in vitro effective dimension and compare it with MMVS
Special treatment of minimum material requirement (LMR)
Because physical gauges cannot achieve LMR verification, the standard requires the use of virtual functional gauges to complete the verification by calculating the in vivo effective dimension and comparing it with LMVS.
Key points of fixture design
Chapter 5 of the standard clarifies the three benchmark principles of fixture design:
- The positioning device needs to be fully in contact with the part's benchmark elements
- Shape error of the guiding part ≤0.02mm (H-level accuracy)
- Surface roughness Ra≤0.2μm (mirror-level treatment)
Association with GPS matrix
As shown in Appendix B, this standard belongs to the GPS general standard and forms a technical closed loop with the following standards:
Associated standards Technical connection points GB/T16671 Mathematical definition of entity requirements GB/T8069 Manufacturing tolerance of physical gauges GB/T24637.2 Uncertainty assessment model
Implementation suggestions
Three-step method for enterprise implementation
- Gauge selection: Physical gauges are preferred for batch testing, and virtual gauges are used for complex surfaces
- Environmental control: Maintain a testing environment of 20℃±1℃ and humidity ≤45%
- Periodic calibration: Physical gauges must be reviewed by MMVB after every 500 uses
Note: In case of dispute arbitration, a reference gauge with a wear amount of less than 5% should be used for retesting.
GB/T 40742.3-2021 Referenced Document
- GB/T 1182 Geometrical product specifications(GPS)—Geometrical tolerancing—Tolerances of form, orientation, location and run-out
- GB/T 16671 Geometrical product specifications (GPS)—Geometrical tolerancing—Maximum material requirement (MMR), least material requirement (LMR) and reciprocity requirement (RPR)
- GB/T 17851 Geometrical product specifications (GPS)—Geometrical tolerancing—Datums and datum systems*， 2022-12-30 Update
- GB/T 24637.1 Geometrical product specifications (GPS)—General concepts—Part 1: Model for geometrical specification and verification
- GB/T 24637.2 Geometrical product specifications (GPS)—General concepts—Part 2: Basic tenets, specifications, operators, uncertainties and ambiguities
- GB/T 38762.1 Geometrical product specifications (GPS)—Dimensional tolerancing—Part 1: Linear sizes
GB/T 40742.3-2021 history
- 2021 GB/T 40742.3-2021 Geometrical product specifications (GPS)—Geometrical precision verification—Part 3：Functional gauges and fixtures—Verification when applying maximum material requirements and minimum material requirements