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GM4488M

Automotive Resistance Spot Welds Steel

October 2006

Originating Department: North American Engineering Standards

Page 1 of 6

1 Scope

This specification provides acceptance criteria for resistance spot welds in automotive products for which GM is responsible for establishing or approving product design.

1.1 The application of the requirements of this specification is mandatory, unless a specific note on the weld drawing establishes different weld criteria. Any exception from the requirements of GM4488M must be made in accordance with good engineering practice. 1.2 Welded structures are considered satisfactory when they carry the intended service loads for a required period. Service loads on weldments in a vehicle are varied in both type and magnitude and cannot be addressed by this specification; therefore, while weld quality criteria of this specification are consistent with service loading requirements, they have been established specifically for use in process and product monitoring. Any attempted application of this document to other uses, such as post-crash weld quality assessment, may lead to an erroneous result or conclusion.

1.3 Spot welds are considered discrepant when they do not meet the criteria of this specification. Discrepant spot welds by retaining a portion of their engineering properties may still contribute to the integrity of the assembly.

1.4 The welding source is responsible for establishing practices and test methods to assure that the criteria of this specification are met, and are consistent with GM9621P Welding Process Control Procedure.

1.5 For clarification of this specification or editorial comments, email the Weld Council at weld.council@https://www.sodocs.net/doc/073235339.html,.

2 Referenced Standards

Note: Only the latest approved standards are applicable unless otherwise specified.

2.1 External Standards/Specifications.

None 2.2 GM Standards/Specifications.

GM4491M GM9621P GM6122M GMW3059

3 Requirements

3.1 Categories of Spot Welds. There are two categories of spot welds: structural and processing.

3.1.1 Structural Spot Welds. Structural spot welds are installed for performance of the product. All spot welds are structural, unless specifically noted as processing welds on the weld drawing. All structural spot welds shall be assigned to patterns.

3.1.2 Processing Spot Welds. Processing welds are installed to facilitate in-process assembly, but are not required for structural performance of the product. Processing spot welds must be approved by Product Engineering and shown on the weld drawing.

4 Individual Spot Weld Acceptance Criteria

4.1 Spot welds are to be evaluated to the following criteria:

4.1.1 Structural spot welds shall be evaluated to the requirements of Section 4.2, Section 4.3, Section 4.4, Section 4.5, Section 4.6, Section 4.7, Section 4.8, Section 4.9, Section 4.10 and Section 7.

4.1.2 Processing spot welds shall be evaluated to the requirements of Section 4.3, Section 4.4, Section 4.7, Section 4.10 and Section 7.

4.2 A spot weld whose measured button or fuse size is equal to or larger than the specified value in Table 1 is an acceptable weld. Undersize welds are discrepant.

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GM ENGINEERING STANDARDS

GM4488M

Page 2 of 6

October 2006

Table 1: Minimum Weld Size for Resistance Spot Welding

Metal Thickness Thinnest Sheet

Diameter of Button or Fused Area

mm mm 0.40 to 0.59

3.0 0.60 to 0.79 3.5 0.80 to 1.39

4.0 1.40 to 1.99 4.5 2.00 to 2.49

5.0 2.50 to 2.99 5.5 3.00 to 3.49

6.0 3.50 to 3.99 6.5 4.00 to 4.50

7.0

Note 1: To determine the minimum weld size for a two metal stackup, use the metal thickness which is the thinner of the two sheets when referencing Table 1. When three or more sheets are being welded, the second thinnest metal thickness in the total stack up will determine the minimum weld size for each pair of contacting sheets where fusion is required when referencing Table 1. The minimum, metal thickness specified by Product Engineering on the part drawing or change authorization should be used.

Note 2: Equipment set-up diameters, which are larger than the values in Table 1, are normally established. They are not provided in this specification.

4.2.1 Fused diameter is measured in either the plane of the faying surface or in a cross-section (see Figure 1).

Figure 1: Measurement of Fused Area 4.2.2 The button is that part of the weld, including all or part of the nugget, which tears out in a destructive weld test. The average button diameter is calculated by adding the measurement of the major axis to the measurement of the axis perpendicular to the first axis and dividing by 2 (see Figure 2). The measurements are taken at the faying surface.

Figure 2: Measurement of Weld Button 4.2.3 With certain steels or types of loading, a button may not always result from destructive testing. In these cases metallurgical examination of the fusion zone must be used to determine acceptability.

4.3 Cracks. Spot welds which crack around the circumference are discrepant welds. Spot welds with surface cracks confined within the impression left by the electrodes are not discrepant welds.

4.4 Holes. Spot welds which contain holes which extend through the weld are discrepant. 4.5 Missing Welds. When fewer than the specified number of welds exist, the omitted welds are discrepant.

4.6 Edge Weld. A spot weld in which the area of the spot weld, as defined by the impression left by the electrodes, is not contained within all edges of the sheet metal is a discrepant weld (see Figure 3).

Figure 3: Weld Edge

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GM4488M

GM ENGINEERING STANDARDS

October 2006 Page 3 of 6

4.7 Location Tolerance. A spot weld which is placed on the assembly greater than 10 mm from the indicated location when a locating dimension to an identifiable feature is specified, or 20 mm from the indicated position when no

locating dimension is specified, is a discrepant weld.

4.8 Distortion. Spot welds in which the sheet surfaces are distorted more than 25° from the normal plane (see Figure 4) must have the welding process adjusted to reduce the distortion to below 25°.

Figure 4: Distortion

4.9 Indentation. A spot weld in which the depth of the depression on the sheet surfaces caused by the welding electrodes results in a reduction of the sheet metal thickness of any individual sheet that exceeds 50% (see Figure 5) must have the welding process adjusted to reduce the indentation.

Figure 5: Indentation

4.10 Extra Welds. The number of spot welds installed should not be more than the number specified on the weld drawing, except as required by the repair methods described in Section 9. The welding process is to be corrected to eliminate the extra welds.

5 Weld Patterns

5.1 Spot weld patterns are normally described on the drawing, the following guidelines apply: A spot weld pattern is a row, string, or group of spot welds joining one part to another. Changing combinations of parts (i.e., double and triple thickness conditions in the same row, string, or

group) should be considered as distinct patterns unless this would result in patterns of a single spot weld. A pattern may have only one structural classification. A row, string, or group of spot welds interrupted by another pattern or a nonspot welded area should be considered as two or more patterns. All welds in a pattern must be installed by the same manufacturing plant.

6 Weld Pattern Conformance Criteria

6.1 A spot weld pattern is conforming when the number of acceptable spot welds within a pattern meets or exceeds the pattern tolerance shown in Table 2 or as stated on the weld drawing, except when the conditions described in Section 6.3 are present.

6.2 If no pattern tolerance is stated on the weld drawing, the tolerances in Table 2 shall apply. 6.3 Two or more adjacent welds missing or breaking in the same pattern cause the pattern to be nonconforming.

Table 2: Number of Acceptable Welds

Per Pattern

Pattern Size

Number of Acceptable

Welds

213243546475869710

Note 1: For patterns over 10 – use value for 10 weld pattern for each multiple of 10, then add the value shown for the remaining welds.

Note 2: Weld patterns of 1, mandatory welds and end welds are not to be used.

7 Weld Surface Appearance

7.1 The following classifications are used to communicate the desired surface appearance of spot welds and are in addition to requirements specified in Section 4.

7.1.1 Product Engineering must identify and approve the application of weld appearance classifications IIB and IIC to those welds where appearance is critical. Class III welds shall be considered the default weld appearance

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GM ENGINEERING STANDARDS

GM4488M

Page 4 of 6

October 2006

classification when no other classification is specified on the welding documentation.

7.1.2 Welds that do not meet the appearance criteria contained in Appendix A for the designated appearance classification must have the welding process adjusted to achieve the desired weld surface appearance criteria. Pattern tolerances do not apply for the spot weld appearance criteria.

7.2 Class IIB welds are intended for sheet metal surfaces that are visible to the customer on secondary surfaces of completed vehicles. Class IIB welds will have the least visible marking on the sheet metal surface in comparison to Class IIC or Class III welds. 7.3 Class IIC welds are intended for sheet metal surfaces that are visible to the customer on secondary surfaces of completed vehicles and applicable where the product design enablers for a Class IIB weld cannot be met. Class IIC welds can also be applied to sheet metal surfaces not visible on completed vehicles, and where either downstream processes require welds to be free of jagged surface eruptions or where weld spatter may create an appearance problem in the immediate area adjacent to the weld. Class IIC welds have more visible markings on the sheet metal surface than attainable with a Class IIB weld, but less visible marking than a Class III weld.

7.4 Class III welds are intended for general use on sheet metal surfaces where there is no special requirement for surface appearance. Class III welds shall be considered the default weld surface appearance classification when no other classification is specified on the product design document.

7.5 Product or Manufacturing Engineering may require Metal Finishing or other procedures for those spot welds not meeting the criteria for weld appearance.

8 Spot Weld Repair Requirements

8.1 All known spot welds that are discrepant due to cracks or holes as described in Section 4.3 and Section 4.4 must be repaired.

8.2 All known discrepant welds in nonconforming patterns must be repaired. 8.3 Exceptions to Section 8.1 and Section 8.2 are permitted based on documented review and

approval by the appropriate Product Engineer [e.g., Production Action Authorization (PAA)].

9 Spot Weld Repair Procedure

9.1. Discrepant spot welds with cracks (see Section 4.3) or holes (see Section 4.4) shall be ground as necessary and repaired with GMAW so the discrepant condition is no longer present. The resulting weld must meet the remaining requirements of Section 5 if it is part of a nonconforming weld pattern.

9.2 All discrepant spot welds within a nonconforming pattern will be repaired according to procedures specifically authorized by Product Engineering, or to the following order of preferred process:

9.2.1 Resistance Spot Weld Repair. Spot weld with a gun which is qualified for the metal types and thickness to be welded. The repair spot weld shall be placed within the specified spot weld location (see Section 4.7). One repair spot weld shall be added for each spot being repaired. Repair spot welds must meet the requirements of this specification.

9.2.2 Arc Spot or Plug Weld Repair. If the procedure described in Section 9.2.1 is not used, a GMAW Spot or a GMAW Plug Weld with steel filler may be used as one for one replacement for discrepant resistance spot welding. The arc spot and plug welds must conform to the requirements of GM4491M “Arc Spot, Plug and Slot Welding Specification”. All repair personnel using this method of repair must be periodically qualified and approved through a local procedure.

9.2.3 Fillet Weld Repair. If the procedures described in Section 9.2.1 are not used, a GMAW fillet weld may be used for two-thick joints. The GMAW repair weld must be located within 6mm of the spot weld being repaired and must be at least 20mm long. The repair welds must conform to the requirements of GM6122M, “Automotive Arc Welding Specification.” All repair personnel using this method of repair must be periodically qualified and approved through a local procedure.

9.3 When the procedures described in Section 9.2 are not used, Product Engineering must authorize the appropriate repair to be used. All verbally authorized repairs must be documented according to local procedures. Examples of this type repair are bolts, blind rivets, etc.

Provided by IHS under license with General Motors Company Sold to:Stant USA Corp, 778206

Not for Resale,11/07/2012 07:40:33 MST

No reproduction or networking permitted without license from IHS

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GM4488M

GM ENGINEERING STANDARDS

October 2006 Page 5 of 6

10 Coding System

This specification shall be called up in other documents, drawings, Vehicle Technical Specifications (VTS), etc. as follows: GM4488M

11 Notes

11.1 Glossary. Not Applicable.

11.2 Acronyms, Abbreviations, and Symbols. GMAW Gas Metal Arc Welding PAA

Production Action Authorization

12 Additional Paragraphs

12.1 All parts or systems supplied to this specification must comply with the requirements of GMW3059, Restricted and Reportable Substances for Parts.

13 Release and Revisions

13.1 Release. This standard was originated in July 1984 and approved in July 1985. 13.2 Revisions.

Rev Approval Date

Description (Organization)

E JUN 2004 Revised Weld Surface

Appearance Section and added Annex A. Eliminated Spot Weld Classification and renumbered as required (CCRW). F OCT 2006 Revised Weld Surface

Appearance (Section 7 & Annex A) eliminated Class IIA welds. Miscellaneous editorial revisions (CCRW). Editorial update to Appendix A Indentation and Eruptions.

Provided by IHS under license with General Motors Company Sold to:Stant USA Corp, 778206

Not for Resale,11/07/2012 07:40:33 MST

No reproduction or networking permitted without license from IHS

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GM ENGINEERING STANDARDS

GM4488M

Page 6 of 6

October 2006

Appendix A: Spot Weld Appearance Criteria by Weld Surface Classification

Table A1: Spot Weld Appearance Criteria

Note: Welds that do not achieve the appearance criteria listed above must have the welding process adjusted to achieve the designated criteria for the applicable Weld Surface Classification.

Weld Surface Classification

Appearance Evaluation Criteria

GM4488M

Reference

Class IIB

Class IIC

Class III Edge welds

4.6 and Figure 3

No edge welds or distortion of the original trim edge (see Welds C,D, E and F of Figure 3) No edge welds or distortion of the original trim edge (see Welds C,D, E and F of

Figure 3) No

Appearance Criteria Spot location

4.7

Within 3mm of templated

location

Within 3mm of templated

location

Appearance Criteria Angular distortion of the sheet surface from the normal plane 4.8 4° Maximum 4° Maximum

Appearance Criteria Electrode indentation

4.9 0.2mm Maximum No Appearance Criteria

Appearance Criteria Surface eruptions Figure A1 0.15mm Maximum No Appearance Criteria

Appearance Criteria Weld whiskers

No Additional References Not permitted Not permitted

Appearance Criteria Visible spatter (pearls) adjacent to the weld

No Additional References

Not permitted Not permitted

Appearance Criteria

Circular & Symmetrical Spot Weld Imprint with Uniform Perimeter No Additional

References

Required Required No

Appearance

Criteria Figure A1: Surface Eruption

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GM4488M

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