GM4488M Automotive Resistance Spot Welds - Steel.pdf

ENGINEERING STANDARDS Materials and Processes - Metals GM4488M Automotive Resistance Spot Welds - Steel © Copyright 2004 General Motors Corporation All Rights Reserved June 2004 Originating Department: North American Controls, Conveyors, Robotics 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 to 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 This specification shall be called up in other documents, drawings, Vehicle Technical Specifications (VTS), etc. as follows; GM4488M. 1.6 For clarification of this specification or editorial comments, email the Weld Council at weld.councilgm.com. 2 Referenced Standards Note: Only the latest approved standards are applicable unless otherwise specified. GM4491M GM6122M GM9621P 3 Requirements. 3.1 CATEGORIES OF SPOT WELDING. 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 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 require- ments of 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 4.10 and 7.0. 4.1.2 Processing spot welds shall be evaluated to the require- ments of 4.3, 4.4, 4.7, 4.10 and 7.0. 4.2 SIZE. A spot weld whose measured button or fuse size is equal to or larger than the appropriate value in Table 1 is an acceptable weld. Undersize welds are discrepant. TABLE 1 MINIMUM WELD SIZE FOR RESISTANCE SPOT WELDS Metal Thickness Thinnest Sheet Dia of Button or Fused Area mmmm 0.40 0.593.0 0.60 0.79 3.5 0.80 1.39 4.0 1.40 1.99 4.5 2.00 2.49 5.0 2.50 2.99 5.5 3.00 3.49 6.0 3.50 3.99 6.5 4.00 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 the plane of the faying surface (see Figure 1). GM ENGINEERING STANDARDS GM4488M © Copyright 2004 General Motors Corporation All Rights Reserved June 2004 Page 2 of 6 4.2.2 The button is that part of the weld, including all or part of the nugget, that 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. 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 less than the specified number of welds exist, the number omitted are discrepant welds. 4.6 EDGE WELD. A spot weld in which the are 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). 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 distor- tion to below 25°. 4.9 INDENTATION. A spot weld in which the depth of the depression on the sheet surfaces caused by the welding elect- rodes 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. 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 10. The welding process is to be corrected to eliminate the extra welds. GM ENGINEERING STANDARDS GM4488M © Copyright 2004 General Motors Corporation All Rights Reserved June 2004 Page 3 of 6 5 Spot 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 consid- ered as distinct patterns unless this would result in patterns of a single spot weld. A pattern may have only one structural classifi- cation. A row, string, or group of spot welds interrupted by another pattern or a nonspot welded area should be considered as 2 or more patterns. All welds in a pattern must be installed by the same manufacturing plant. 6 Spot 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 pat- tern tolerance shown in Table 2 or as stated on the weld drawing, except when the conditions described in 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 (2) 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 2 1 3 2 4 3 5 4 6 4 7 5 8 6 9 7 10 8 NOTE 3: 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 4: 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 Enginnering must identify and approve the application of weld appearance classifications IIA, IIB and IIC to those welds where appearance is critical. Class III welds shall be considered the default weld appearance classification when no other classification is specified on the welding documentation. 7.1.2 Welds that do not meet the Appearance criteria contained in Annex A for the designated appearance classification must have the welding process adjusted to achieve the desired weld surface appearnace criteria. Pattern tolerances do not apply for the spot weld appearance criteria. 7.2 Class IIA welds are intended for sheet metal surfaces that are visible on secondary surfaces of completed vehicles. Class IIA welds shall provide the least visible marking on the sheet metal surface in comparison to Class IIB, IIC or III welds. 7.3 Class IIB welds are intended for sheet metal surfaces that are visible on secondary surfaces of completed vehicles. Class IIB welds will have more visible marking on the sheet metal surface than attainable with a Class IIA weld, but less visible marking than a Class IIC or III weld. 7.4 Class IIC welds are intended for sheet metal surfaces not visible on completed vehicles, but where 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. 7.5 Class III welds are intended for general use on sheet metal surfaces where there is no special requirement for surface appearance. 7.6 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 discrepant welds in nonconforming patterns must be repaired. 8.2 All known spot welds that are discrepant due to cracks or holes as described in 4.3 and 4.4 must be repaired. 8.3 Exceptions to 8.1 and 8.2 are permitted based on docu- mented review and approval by the appropriate Product Engineer (e.g., Production Action Authorization or PAA). 9 Spot Weld Repair Procedure. 9.1 Discrepant spot welds with cracks (see 4.3) or holes (see 4.4) shall be ground as necessary and repaired with gas metal arc welding (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. GM ENGINEERING STANDARDS GM4488M © Copyright 2004 General Motors Corporation All Rights Reserved June 2004 Page 4 of 6 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 specifled spot weld location (see 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 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 Welds. 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 9.2.1 is 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 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. 10 Release and Revisions. This standard origin- nated in April 1985. The latest revisions include. Rev Date Description C 3/92 General Editorial D 5/95 Complete Revision E 6/04 Revised Weld Surface Appearance Section and added Annex A. Eliminated Spot Weld Classification and renumbered as required. GM ENGINEERING STANDARDS GM4488M © Copyright 2004 General Motors Corporation All Rights Reserved June 2004 Page 5 of 6 Annex A Spot Weld Appearance Criteria by Weld Surface Classification Weld Surface Classification Appearance Evaluation Criteria GM4488M Reference Class IIA Class IIB Class IIC Class III Edge welds 4.6 & Figure 3 No edge welds or distortion of the original trim edge (as illustrated in Welds C,D, E and F of Fig 3) No edge welds or distortion of the original trim edge (as illustrated in Welds C,D, E and F of Fig 3) No Appearance Criteria No Appearance Criteria Spot location 4.7 Within 3mm of templated location Within 3mm of templated location No Appearance Criteria No Appearance Criteria Angular distortion of the sheet surface from the normal plane 4.8 No visible distortion No visible distortion Less than or equal to 10° as controlled by boundary sample No Appearance Criteria Electrode indentation as a percentage of the visible surface metal thickness 4.9 less than or equal to 10% of sheet metal thickness as controlled by boundary sample less than or equal to 25% of sheet metal thickness as controlled by boundary sample No Appearance Criteria No Appearance Criteria Surface eruptions as a percentage of the visible surface metal thickness Figure 6 10% 20% No Appearance Criteria No Appearance Criteria Weld whiskers No Additional References Not permitted Not permitted Not permitted No Appearance Criteria GM ENGINEERING STANDARDS © Copyright 2004 General Motors Corporation All Rights Reserved January 2004 Page 6 of 6 Visible spatter (pearls) adjacent to the weld No Additional References Not permitted Not permitted Not permitted No 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.