Weld Acceptance Criteria and Repair Procedures Resistance Spot Welds Steel

Transcription

1 WORLDWIDE ENGINEERING STANDARDS Material Specification Metals Weld Acceptance Criteria and Repair Procedures Resistance Spot Welds Steel 1 Scope This standard applies to steels approved by GM for Resistance Spot Welding (RSW). 1.1 Purpose. This standard provides the acceptance criteria and repair procedures for resistance spot welds in automotive products for which GM is responsible for establishing or approving product design. 1.2 Application. The criteria established in this standard become mandatory when referenced on a weld design document. Deviations from any weld criteria provided in this standard must be identified on a weld design document or other product design document and be approved using the Global Deviation Approval Process (GWS-8). 1.3 Usage. 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 standard. Therefore, while the weld quality criteria of this standard 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. Discrepant welds by retaining a portion of their engineering properties may still contribute to the integrity of the assembly. 1.4 Process Control. The welding source is responsible for establishing practices and test methods to assure that the criteria of this standard are met, and are consistent with applicable Welding Process Control Procedures. 1.5 Clarification. For clarification of this standard or editorial comments, the GMNA Weld Council at weld.council@gm.com. Proposed changes to this standard must be presented to the GMNA Weld Council. To suggest a change to this standard, reference the Procedure for Weld Standard Changes on the GMNA Weld Council s webpage. 2 References Note: Only the latest approved standards are applicable unless otherwise specified. 2.1 External Standards/Specifications. None 2.2 GM Standards/Specifications. GMW3059 GMW3001 GMW Additional References. GWS-8 3 Requirements 3.1 Categories of Spot Welds. There are two categories of spot welds: structural and process Structural Spot Welds. Structural spot welds are installed for performance of the welded product. All spot welds are structural unless specifically noted as process welds on the weld design document. Structural spot welds shall be evaluated to the full requirements of sections 3.2, 3.3 and 3.4 of this standard Process Spot Welds. Process spot welds are installed to facilitate in-process assembly, but are not required for structural performance of the product. Process spot welds must be approved by Product and Manufacturing Engineering and shown on the weld design document. Process spot welds shall be evaluated to the requirements of sections , and of this standard. January 2006 Originating Department: North American Engineering Standards Page 1 of 10

2 GM WORLDWIDE ENGINEERING STANDARDS 3.2 Individual Spot Weld Criteria. There are 15 attributes used to evaluate spot weld quality. These attributes are divided into two categories: attributes that make the weld discrepant; and attributes that do not make the weld discrepant, but the attribute is undesirable for appearance or processing Attributes Discrepant Welds. Welds that exhibit any of the following attributes are discrepant welds. The welding process shall be adjusted to its original qualified setup to eliminate the discrepant condition Cracks. Spot welds with any surface crack(s), that are visible without the aid of magnification, are discrepant welds. See Figure Holes. Spot welds that contain holes extending through the weld are discrepant welds. See Figure Edge Welds. Welds in which the spot weld imprint, as defined by the impression left by the electrodes, is not contained within all edges of the sheet metal being welded are discrepant. See Figure 5, welds E & F Missing Welds. When fewer welds exist than are specified on the weld design document, the omitted welds are discrepant Cold Welds. Weld locations that do not produce a weld button after a chisel, pry or destruct test or do not indicate a nugget when the weld location is cross-sectioned are classified as cold welds. Cold welds are discrepant welds Weld Location. Spot welds must be properly located relative to design location as indicated on the weld template and to each other as follows. In a pattern consisting of a single in-line row of welds in which a distinct product feature provides visual reference to the end weld, an end weld installed greater than 10mm in radial distance from the design location is a discrepant weld. A distinct product feature must be a visible trim edge or other recognizable part feature that is perpendicular or nearly perpendicular to the row of welds and within 30mm of the end weld. For all other welds, a spot weld installed greater than 20mm in a radial distance from the design location is a discrepant weld. If the spacing between two adjacent welds in a pattern consisting of a single in-line row of welds exceeds the design spacing by greater than 20mm, the weld furthest from the design location is a discrepant weld. Page 2 of 10 January 2006

3 GM WORLDWIDE ENGINEERING STANDARDS Minimum Weld Size. The weld size may be measured by either using the weld button (Figure 10) or the weld nugget (Figure 13). The minimum weld sizes shown in Table 1 are based on the formula four times the square root of the Determining Thickness (DT), with the DT expressed in millimeters. A spot weld is discrepant when the weld size is less than the minimum acceptable weld size specified in Table 1. Table 1: Minimum Acceptable Weld Size Determining Thickness (DT) Minimum Acceptable Weld Size mm 4.0mm mm 5.0mm mm 6.0mm mm 7.0mm With certain steels or types of loading, a weld button may not always result from destructive testing. In these cases metallurgical examination of the fusion zone must be used to determine weld size Selecting Determining Thickness (DT). The DT of a two or three loose sheet welded stackup is determined as follows: The thickness of the thinner sheet for a two sheet stackup (Figure 1, stackup 2) The thickness of the second thinnest sheet for a three unequal sheet stackup (Figure 1, stackups 4, 5 & 6) The thickness of one of the equal sheets for two or three sheet stackup with two or more equal sheets (Figure 1, stackups 1, 3, 7, 8, 9 & 10) Figure 1: Determining Thickness (2 & 3 Loose Welded Sheets) Laminated Vibration Damping Steel. The minimum weld size specified in Table 1 is required only at the faying surface for laminated steel. There are no minimum weld size requirements for the interface between the layers of the laminated steel. For purposes of determining the minimum weld size, the laminated steel shall be treated as one sheet whose thickness is equal to the sum of the two outer sheets and the inner visco-elastic layer as shown in Figure 2. Visco-Elastic Layer Laminated Sheet Thickness Measure Weld Size at Faying Surface Figure 2: Laminated Steel January 2006 Page 3 of 10

4 GM WORLDWIDE ENGINEERING STANDARDS Attributes Appearance and Processing Considerations. Welds that exhibit the following attributes are undesirable either from an appearance or processing viewpoint. However, these attributes do not make the weld discrepant Extra Welds. The number of spot welds installed shall not exceed the number specified on the weld design document, except as required by the repair procedures described in section 3.5 of this standard. The welding process shall be adjusted to eliminate extra welds Whiskers. Welds exhibiting whiskers should have the welding process adjusted to eliminate the condition. See Figure 14. Note: Welds shall be free of whiskers when using ultrasonic inspection equipment to avoid damage to the transducer Distortion. Spot welds in which the sheet surfaces are distorted more than 25 from the normal plane shall have the welding process adjusted to the original qualified setup in order to reduce the distortion to less than 25. See Figure Thinning. Spot welds exhibiting thinning greater than 30% of the total metal stackup should have the welding process adjusted to the original qualified setup in order to reduce the thinning below 30%. See Figure Trim Edge Deformation. Welds in which the original edge of the weld flange is deformed by the electrodes but whose spot weld imprint is contained within all edges of the sheet metal being welded are not discrepant. The process shall be adjusted to the original qualified setup to eliminate the condition. See Figure 5, welds C and D Indentation. Indentation is a depression on the sheet surface. See Figure 8. The appearance criteria for indentation are listed in Appendix A Surface Eruption. Surface eruption is an upsurge of the sheet surface adjacent to the electrode cap imprint. See Figure 9. The appearance criteria for surface eruption are listed in Appendix A Spatter. Spatter is weld metal expulsion that remains attached to surface(s) adjacent to the weld. See Figure 14. The appearance criteria for spatter are listed in Appendix A. 3.3 Weld Surface Appearance Criteria Classification. The following classifications are used to communicate the desired surface appearance of spot welds and are in addition to requirements specified in section 3.2. Product and Manufacturing Engineering must identify and approve the application of weld appearance classifications IIB and IIC for those welds where appearance is deemed necessary to satisfy perceptual quality requirements. Class III welds shall be considered the default weld appearance classification when no other classification is specified on the welding design document. Welds that do not meet the additional appearance criteria contained in Appendix A for the designated appearance classification are not discrepant but shall have the welding process adjusted (to the original qualified setup) to achieve the desired weld surface appearance criteria Class IIB Welds. Class IIB welds are intended for sheet metal surfaces that are visible on secondary surfaces of completed vehicles. Class IIB welds provide the least visible marking on the sheet metal surface in comparison to Class IIC or III welds Class IIC Welds. 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 marking on the sheet metal surface than attainable with a Class IIB weld, but less visible marking than a Class III weld Class III Welds. Class III welds are intended for general use on sheet metal surfaces where there is no special requirement for surface appearance. Class III welds have no additional appearance criteria Other Procedures. Product or Manufacturing Engineering may require Metal Finishing or other procedures for those spot welds not meeting the criteria for weld surface appearance Confirmation. Confirmation of appearance requirements specified in Appendix A shall be verified using either visual comparison to boundary samples or by direct measurement. Page 4 of 10 January 2006

5 GM WORLDWIDE ENGINEERING STANDARDS 3.4 Spot Weld Pattern Conformance Criteria. A pattern is a collection of spot welds to which a tolerance is applied to meet structural requirements and for determining manufacturing acceptance of the product. Spot weld patterns must include all structural welds and be shown on the weld design document. Process welds shall not be included in any weld patterns. The spot weld pattern is conforming when the number of acceptable spot welds (not discrepant per the requirements of section 3.2 of this standard) within a pattern meets or exceeds the pattern tolerance as stated on the weld design document. Manufacturing acceptance of product is based on all patterns conforming. Known and suspect product with nonconforming patterns must be repaired Missing Welds, Cold Welds, and Welds with Holes. All known missing welds, cold welds or welds with holes detected during in-process inspection must be repaired Repair Exceptions. An exception to specified product repair requirements may be permitted provided there is documented review and approval by the responsible Product Engineer allowing the suspect product to deviate from specification and pattern conformance criteria Surface Appearance. Spot weld surface appearance criteria are not used in determining weld pattern conformance Process Spot Welds. Process spot welds are not to be used in determining weld pattern conformance. Process welds containing holes require product repair. Process welds that do not meet the remaining requirements of section (missing and extra welds) should have the welding process adjusted to its original qualified setup and do not require repair. 3.5 Spot Weld Repair Procedures Repair Procedures. When required, spot welds shall be repaired according to the procedures specifically authorized by the appropriate Product Engineer. In the absence of this repair procedure, the following repair methods shall be used in the following order of preference Resistance Spot Weld Repair. Spot weld with a weld gun that is qualified for the metal types and thicknesses to be welded. One repair spot weld shall be added for each spot weld being repaired. Repair spot welds must meet the requirements of this standard. Locate repair spot welds as close as possible to the original designated weld location without overlapping the existing spot weld Arc Weld Repair. Arc weld repair of laminated steels is not permitted Arc Spot or Plug Weld Repair. For each spot being repaired, weld using GMAW plug or GMAW spot with steel filler wire. The GMAW spot or GMAW plug weld shall conform to the applicable arc spot and plug weld acceptance criteria standard. All repair personnel using this method of repair must be periodically qualified and approved following local procedures Arc Fillet Weld Repair. A GMAW fillet weld may be used for two metal thickness joints. The GMAW repair weld must be located as close as possible to the original designated weld location and must be a minimum of 20mm in length. The repair welds must conform to GMW All repair personnel using this method of repair must be periodically qualified and approved following local procedures. 4 Notes 4.1 Glossary. Terms are grouped by attributes where applicable and not necessarily in alphabetical order. Boundary Sample. A reference used to evaluate the appearance characteristics of a weld based on visual comparison. Appearance characteristics are surface attributes inherent in the manufacturing process (i.e. indentation, surface eruptions, distortion, etc.). Cold Weld. A weld that does not produce a weld button after a chisel, pry or destruct test. At the faying surface of a cold weld there is no indication of fusion. Cold welds do not indicate a nugget when the weld is cross-sectioned. January 2006 Page 5 of 10

6 GM WORLDWIDE ENGINEERING STANDARDS Crack. A fracture type discontinuity characterized by a sharp tip and high ratio of length to width of opening displacement on the exterior surface. See Figure 3. Trim Edge Deformation. A condition in which the original edge of the weld flange is deformed by the electrodes but whose spot weld imprint is contained within all edges of the sheet metal being welded. See Figure 5, welds C and D. F E D C B A Spot Weld Edge Weld Trim Edge Deformation Figure 3: Surface Cracks Distortion. Angle of displacement that the sheet surfaces are distorted from the normal plane. See Figure 4. Angle of Distortion Figure 4: Distortion Weld Imprint Figure 5: Edge Weld Extra Welds. The number of spot welds that exceed the number specified on the weld design document. Faying Surface. The mating surface of two members to be welded. See Figure 6. B A % Thinning = E x 100 B+D E C D Inden Edge Weld. A condition in which the spot weld imprint, as defined by the impression left by the electrodes, is not contained within all edges of the sheet metal being welded. See Figure 5, welds E and F. Faying Surface Figure 6: Faying Surface GMAW. An acronym for Gas Metal Arc Welding. Page 6 of 10 January 2006

7 GM WORLDWIDE ENGINEERING STANDARDS Hole. A perforation in the spot weld that allows light to travel through the material from one exterior surface to the opposing exterior surface of the weld. See Figure 7. Surface Eruption. Upsurge of the metal surface adjacent to the weld imprint. See Figure 9. Figure 9: Surface Eruption Figure 7: Hole Indentation. The depression on the sheet surfaces caused by the welding electrodes. See Figure 8. Figure 8: Indentation & Thinning Weld Button. That part of the weld that tears out in a peel or chisel test. See Figure 10. Missing Welds. The number of spot welds not installed as specified on the weld design document. Original Qualified Setup. The weld parameters established and documented during Weld Verification. Also referred to as Initial Qualified Setup. Pearls. See Weld Spatter. Thinning. The amount of the original total metal stackup thickness reduced by the welding process. See Figure 8. Figure 10: Weld Button Weld Button Size. The weld button size of a symmetrical (round) button is the diameter of the button. The weld button size of an asymmetrical (oval or oblong) button is calculated by adding the measurement of the major axis to the measurement of the minor axis and dividing by 2. See Figure 11. The measurements are to be taken at the faying surface. See Figure 12. Weld Button Size = (d 1 + d 2 )/ 2 d1 d2 Figure 11: Weld Button Size January 2006 Page 7 of 10

8 GM WORLDWIDE ENGINEERING STANDARDS 0.2 mm Weld Button Weld Size. Resistance Spot Weld Size refers to either the weld button size or the weld nugget size. With certain steels or types of loading, a weld button may not always result from a peel or tensile test. In these cases metallurgical examination of the weld must be used to determine weld nugget size. Weld Expulsion. Molten metal that is extruded from between the sheets being welded or from the interface between the outer sheet metal surface and the electrode(s). See Figure 14. Weld Imprint. The impression left in the metal surface by the electrodes after welding. See Figure 5. Weld Spatter. Weld expulsion metal that remains attached to an adjacent metal surface away from the electrodes. The visible weld spatter is sometimes referred to as pearls. See Figure 14. Whiskers. Sharp weld expulsion metal that remains attached to the metal surface adjacent to the weld imprint. See Figure 14. Figure 12: Weld Button Size Measurement Weld Spatter Weld Nugget. The weld nugget is that part of the weld where fusion is evident at the faying surface and extending into the parent metal resulting in a metallurgical structure change. See Figure 13. Weld Nugget Size. The weld nugget size is the dimension of the fusion zone measured from a macro section examination or weld cross section. See Figure 13. Electrode Whiskers Fusion Zone Weld Nugget Size Heat Affected Zone Weld Expulsion Figure 14: Weld Expulsion Weld Design Document. A product document that describes welding requirements such as number of welds, location of welds, applicable weld standards, weld patterns, surface appearance classification, weld notes etc. This document is released and approved by the appropriate Design Release Engineer. Figure 13: Weld Nugget Size Page 8 of 10 January 2006

9 GM WORLDWIDE ENGINEERING STANDARDS Weld Template. An inspection device used to evaluate weld location. Templates are typically created by plotting the weld spot location as defined by the weld design document on a transparent overlay for comparison to the actual weld locations. See Figure Rules and Regulations 5.1 All materials supplied to this specification must comply with the requirements of GMW3001, Rules and Regulations for Material Specifications. 5.2 All materials supplied to this specification must comply with the requirements of GMW3059, Restricted and Reportable Substances for Parts. 6 Coding System This welding standard shall be referenced in other documents, drawings, Vehicle Technical Specifications (VTS), Component Technical Specifications (CTS), GME Specification Design Mechanics (SKR, SKM) etc. as follows:. Figure 15: Weld Template 7 Release and Revisions 7.1 Release. This standard was originated by the Global Weld Standards Team in August 2004 and approved in December 2005 by the CCRW Global Council. This standard was first published in January January 2006 Page 9 of 10

10 GM WORLDWIDE ENGINEERING STANDARDS Appendix A Table A1: Additional Spot Weld Surface Appearance Criteria by Weld Surface Classification Attributes Reference Class IIB Class IIC Edge Welds Section & Figure 5 Not Permitted Not Permitted Trim Edge Deformation Section & Figure 5 Not Permitted Not Permitted Weld Location Section Within 3mm of design location Within 3mm of design location Circular & Symmetrical Spot Weld Imprint with Uniform Perimeter None Required Required Distortion Section & Figure 4 4 O Maximum 4 O Maximum Indentation Figure mm Maximum No Requirement Surface Eruptions Figure mm Maximum No Requirement Spatter (Pearls) Adjacent to the Weld Figure 14 Not Permitted Not Permitted Whiskers Figure 14 Not Permitted Not Permitted Note: Welds that do not meet the appearance requirements listed above must have the welding process adjusted to the original qualified setup to achieve the appearance requirements. With the exception of edge welds, welds that do not meet the appearance requirements listed above are not considered discrepant welds. Page 10 of 10 January 2006