GB/T 37778-2019Recommended process for laser beam welding on stainless steels (English PDF)

3.1 Appearance quality

The appearance effects of the face of weld and root surface, such as the quality requirements for spatter, penetrated fusion, smoothness, point imperfections and scratches and other minor defects.

3.2 Smoothness

An indicator for evaluating the degree of unevenness on the back of welds of incomplete penetration lap joints.

3.3 Point imperfection

Non-penetrated point-like protrusions or depressions formed by local excessive heat of welding area.

3.4 Scratch

Marks on a smooth material surface due to mechanical effects.

5.1 General

For laser beam welding on stainless steel, in addition to meeting the requirements of this standard, the welding operation shall also comply with the requirements of relevant product standards (such as GB/T 25343.1). Laser beam safety shall comply with the requirements of GB 7247.1 and GB/T 18490.1 and related technical documents.

5.2 Personnel qualifications

5.2.1 Product assembler

Product assemblers shall understand the laser beam welding technology and pass pre-work process training before starting operations.

5.3 Process equipment

5.3.1 Laser beam welding equipment

Laser beam welding equipment shall be regularly inspected to be in normal working condition.

5.3.2 Tooling and fixture

The tooling and fixture shall use the materials, which have good heat dissipation conditions and can form a good protection for stainless steel, such as aluminum alloy or copper alloy.

5.4 Workpiece

5.4.1 Materials

Stainless steel raw materials shall meet the design requirements; their performance indicators shall meet the requirements of GB/T 33239; it can meet the high-precision forming requirements of laser beam welded parts.

5.4.2 Processing requirements

The parts can be processed by punching, laser cutting, stamping or other suitable methods. The processed parts shall be removed of residual burrs at the cutting part.

5.5 Environmental requirements

The welding site shall be kept clean and have necessary isolation measures.

6.1 General principles

For the design documents and drawings of the product, it shall be based on the product usage to determine the design requirements, such as mechanical properties, structural form, appearance quality, etc.

6.4 Quality level requirements for imperfections

According to the different mechanical properties and appearance quality requirements of the weld, the imperfections are divided into six levels. level B, level BF, level C, level CF, level D, level DF, based on severe, medium, ordinary. See Table 1 for details.

6.5 Weld inspection level requirements

The inspection level of each joint is determined according to the weld quality level of the joint, as detailed in Table 2.

6.6 Mechanical performance requirements of welded joints

6.6.1 Tensile strength of butt joints

The tensile strength of the butt joint shall not exceed the lower limit of the tensile strength required by the standard of base metals of lower strength grade; if the strength of the base metal is obtained through the cold rolling process, the tensile strength of the joint shall not be lower than the lower limit of the tensile strength of the base metal before cold rolling.

6.6.2 Tensile shear strength of lap joint

The tensile shear force when the weld length of the lap joint is 30 mm may, if there is no special requirement, be carried out according to the requirements of Table 3.

7.1 Limit value of imperfection size

7.1.1 Butt joint

7.1.1.1 Undercut

7.1.1.4 Misalignment

The misalignment of the welded joint (Figure 4) shall meet the requirements of Table 7.

7.1.3 T-joint

For different levels of T-joint weld offset, the specified joint axis limits (see Figure 9) are controlled in accordance with Table 12.

7.2 Acceptance criteria for weld imperfection

7.2.1 Cracks

In all types of welded joints, all cracks except for microcracks (the length and width of the crack are less than 1 mm) are not allowed to exist.

Crater cracks are not allowed, for levels B/BF, C/CF welded joints; local crater cracks are allowed, for level D/DF welded joints (the crack length and width are both less than 1 mm).

7.2.7 Other imperfections

7.2.7.1 Spatter

Whether the spatter (Figure 15) is allowed or not, for the levels B, C, and D, it shall be implemented according to product technical conditions or through negotiation between the two parties. For levels BF, CF, DF welds, the spatter is not allowed on the face of weld, however, it is allowed on the root surface.

7.2.7.2 Melt through

The laser beam penetrates the opposite side of the welding surface to form a perforation. Whether the welds of levels B, C, D are allowed or not depends on the specific application conditions; it is not allowed for the welds of levels BF, CF, DF.

7.2.7.3 Point imperfections Whether

point imperfections are allowed for welds of levels B, C, D depends on the specific application conditions; welds of levels BF, CF, DF do not allow protrusion, however, it allows dents;

7.2.7.4 Smoothness

The smoothness is the height difference H between the base metal of the back of the weld and the center of the back of the weld at a distance of 15 mm from the center of the weld (Figure 16).

8.1 Welding procedure qualification

8.1.1 General requirements

When performing process qualification, the general butt weld test piece and T- joint test piece shall be assessed according to the requirements of GB/T 29710; the lap weld test piece shall be prepared according to the requirements of 8.1.2.

8.1.2 Test piece for lap weld

8.1.2.2 Shape and size of test piece for lap penetration weld

The lap penetration weld (double layer) is as shown in Figure 18. Lap penetration welds include the following types.

8.1.3 Test and inspection

Various test pieces shall be tested and inspected according to Table 16. See Chapter 9 for specific methods.

8.1.4 Conformity assessment

All test and inspection items shall be judged according to Chapter 9; they shall be qualified if they meet the restrictive requirements. In case of unqualified items, it is allowed to double the quantity of test pieces for retest. If the additional test piece still does not meet the relevant requirements, the welding procedure qualification is unqualified.

8.3 Welding

8.3.1 Assembly before welding

The grinding wheel blades, chisels, pressing devices, hammers and other craft tools are all dedicated for stainless steel, to avoid direct contact between carbon steel and stainless steel.

8.3.2 Welding control requirements

8.3.3.2 During welding

During the welding procedure, the welding sequence and welding procedure parameters shall be continuously monitored or regularly checked.

8.3.3.3 After welding

After the welding is completed, it shall carry out the appearance quality inspection of the welded joints and the conformity inspection of the product drawings; meanwhile, retain the inspection records.

9.1 Inspection method

9.1.1 Visual test (VT)

Visual test of appearance shall be carried out in accordance with GB/T 32259.

Check the weld surface for defects such as cracks, surface grooves, incomplete penetration; check the misalignment of the joint and the amount of surface depression, etc.; judge and record in accordance with the provisions of Chapter 7.

9.1.3 Non-destructive testing

9.1.3.1 Penetration testing (PT)

Penetration testing is carried out in accordance with GB/T 18851.1; the acceptance level shall meet the requirements of GB/T 26953 or relevant documents.

9.1.3.2 Radiographic testing (RT)

Radiographic testing is carried out in accordance with GB/T 3323.

9.2 Test method

9.2.1 Transverse tensile test

9.2.1.1 Method

The transverse tensile test shall be carried out at room temperature (or other specified temperature). The specimens and test methods for transverse tension of butt joints shall comply with the requirements of GB/T 2651.

9.2.1.2 Qualified level

Unless otherwise specified before the test, the tensile strength of the specimen shall generally not be lower than the minimum value specified in the base metal standard.

9.2.2 Bend test

9.2.2.1 Method

The bending specimen and test of the butt joint shall meet the requirements of GB/T 2653. […]