What are the quality inspection standards for precision stamping parts processing?
The quality inspection standards of precision stamping parts revolve around three cores: dimensional accuracy, appearance quality and performance index. Different industries (such as automobiles, electronics and medical care) will superimpose specific requirements on this basis. The following are the general and key inspection standards.
A, size and form and position tolerance standard (core test items)
Size and shape and position accuracy directly determine whether the parts can be assembled normally, which is the core of testing, and is mainly implemented according to international or national general standards.
Dimensional tolerance standard
General standard: ISO 8015 (basic provisions of geometric tolerance and dimensional tolerance) and GB/T 1804 (tolerance of linear and angular dimensions without tolerance) shall be followed.
Accuracy grade: Precision stamping parts usually require IT5-IT8 grade, which shall be marked according to the drawings. For example, a copper sheet with a thickness of 0.5mm may have a tolerance of ±0.01mm；; Aperture tolerance may require 0.005 mm.
Form and position tolerance standard
General standard: according to ISO 1101 (geometric tolerance, shape, direction, position and runout tolerance) and GB/T 1182 (geometric tolerance, shape, direction, position and runout tolerance marking in GPS).
Common inspection items: flatness (such as flatness of mobile phone connector terminal ≤0.02mm/100mm), verticality (such as verticality between stamping bracket and base ≤0.03mm), coaxiality (such as coaxiality of hollow cylindrical parts ≤0.01mm) and roundness (such as roundness of shaft parts ≤0.008mm).
Second, the appearance quality standards (visual inspection items)
Appearance defects may affect the electrical conductivity, sealability or aesthetics of parts, which need to be detected by visual inspection or tools.
General appearance requirements
No obvious defects: the surface shall not have cracks, lack of materials (gaps), deformation, crushing, scratches, etc., among which "cracks" are fatal defects, and once they appear, they shall be directly judged as unqualified.
Burr standard: According to GB/T 6403.4 (rounding and chamfering of parts), the burr height of precision parts is usually required to be ≤0.01-0.03mm (for example, the burr of electronic terminals should be ≤0.01mm to avoid scratching wires), which can be measured by microscope or burr gauge.
Surface roughness standard
General standard: ISO 4287 (surface roughness parameters and their values by surface structure profile method) and GB/T 1031 (surface roughness parameters and their values) are followed.
Common requirements: according to different uses, the surface roughness Ra value is usually between 0.4 and 3.2 μ m.. For example, the surface Ra of stamping parts to be welded is ≤ 1.6 μ m to avoid affecting the welding strength; The appearance piece Ra is less than or equal to 0.8 μ m, ensuring the surface smoothness.
Third, the performance and material standards (functional test items)
Performance testing ensures that the parts meet the mechanical and chemical requirements of the application scenarios, and should be carried out in combination with the material characteristics and application scenarios.
Mechanical performance standard
Test items: including hardness, tensile strength, yield strength and ductility (elongation), which shall meet the mechanical requirements of raw materials or finished products.
Reference standard: According to ISO 6506 (Brinell Hardness Test of Metallic Materials) and GB/T 228.1 (Tensile Test of Metallic Materials Part 1: Room Temperature Test Method). For example, the tensile strength of cold-rolled steel commonly used in automobile stamping parts should be ≥340MPa and the elongation should be ≥30%.
Material and surface treatment standard
Material verification: detect the composition of the material by spectrum analyzer to ensure that it meets the requirements of the drawings (for example, stainless steel should meet the material standard of 304/316, and copper should meet the brass standard of H62). Refer to GB/T 30574 (Determination method of chemical composition of stainless steel).
Surface treatment: implement corresponding standards according to the coating type. For example, galvanized parts should meet GB/T 13912 (technical requirements and test methods for hot-dip galvanized coatings of steel products with metal coating), and the salt spray test should be free of red rust for 48 hours; Nickel-plated parts shall conform to GB/T 12332 (Nickel Plating for Metal Covering Engineering), and the coating thickness shall be ≥ 5 μ m..
Fourth, industry-specific supplementary standards
There will be additional special inspection standards for precision stamping parts in different fields, which are common as follows:
Electronics industry: It is necessary to comply with IEC 60603 (connectors for electronic equipment) and add "conductivity" and "insulation" tests, such as terminal contact resistance ≤10mΩ and insulation resistance ≥100MΩ.
Automobile industry: Follow IATF 16949 (Quality Management System for Automobile Industry), and increase the detection of "temperature resistance" and "vibration resistance". For example, the stamping parts around the engine need to withstand the temperature cycle of-40℃~120℃ without deformation.
Medical industry: It conforms to ISO 13485 (Medical Device Quality Management System), and must pass the "biocompatibility" test (such as cytotoxicity test), and there must be no microbial residue on the surface.
