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GM Global Manufacturing Engineering
Global Welding Standard Test Procedures Resist si sta ance nc e Spot Weld Weldin ing g of Steel teel GWS-5A
Apr Ap r i l 2011
DOCUMENT MANAGEMENT INFORMATION Auth Au th or s:
Ap pr ov al:
John Bohr Mark Gugel
-
ME Body ME Body
GM Global Weld Council
Sponsoring Group:
GM Manufacturing Center – Global Weld Council Forward Questions Questions and Comments Comments to :
Global Weld Council at
[email protected] Proposed changes to this standard must be presented to the GM Global Weld Council. To suggest a change to this standard, reference the “Procedure for Weld Standard Changes” on the Global Weld Council’s webpage. Addi Ad di tion ti on al Cop ies
Any printed printed copy copy of this document document is considered considered an “uncontrolled “uncontrolled”” copy. Access Access to the the controlled controlled document can be made through the GM internal website, Socrates, at http://crw.gm.com by selecting Standards and Specifications and then the specific welding document. Access from outside the GM internal network can be made at the GM SupplyPower website at http://www.gmsupplypower.com. The pdf file may be read using Acrobat Software on most Microsoft Windows-compatible computers. Document Expiration Expiration Date: Date:
This document will expire May 2016. 2016. It may be revised, reaffirmed reaffirmed or withdrawn prior to this date. Contact the organization listed above for the latest version. Document Revision Revision s: Date Date August August 2007 April 2, 2008 2008 April 15, 2008
April 27, 2011
Revisio Revisio n
Editorial Editorial Editorial Editorial
Revision Revision History Initial Release Release Figure in Table 2-1 2-1 revised revised for clarity. clarity. Figure in Table 2-1 2-1 revised revised for accuracy. accuracy. Corrected Corrected measurement measurement from 0.015mm to 0.15mm Revised Revised to allow allow weld weld size evaluation evaluation of interfacial interfacial fractures. fractures.
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors
Global Manufacturing Engineering TABL E OF CONTENTS
Section
Descripti on
Page
1.
General ........................................................................................................................................ 1 1.1 Scope ................................................................................................................................. 1 1.2 Purpose .............................................................................................................................. 1 1.3 Weld Deviation Process .......................... ........................... ................................ ................. 1 1.4 References ......................................................................................................................... 2 1.4.1 Normative ............................................................................................................. 2 1.4.2 Informative ....................... ........................... .......................... ........................... ..... 2 1.5 Definitions, Acronyms and Abbreviations......................... .......................... .......................... 2 1.5.1 Definitions ....................... ........................... .......................... ........................... ...... 2 1.5.2 Acronyms and Abbreviations ........................ ........................... .......................... .... 4
2.
Weld Lobe Test ........................................................................................................................... 5 2.1 Equipment Requirements ........................ ........................... .......................... ....................... 5 2.1.1 Welding Equipment ........................ ........................... ........................... ................. 5 2.1.2 Water Flow Rate ................................................................................................... 5 2.1.3 Inspection, Measurement and Test Equipment ......................... .......................... ... 5 2.1.4 Tools..................................................................................................................... 6 2.2 Material Requirements ........................ .......................... ........................... ........................... 6 2.3 Selection of Test Parameters ................................ .......................... ........................... ......... 6 2.4 Predressing of Electrode Caps ......................... ........................... ........................... ............. 6 2.5 Electrode Alignment ......................... .......................... ........................... .......................... .... 6 2.6 Test Procedure ................................................................................................................... 7 2.6.1 Conditioning Welds ........................ ........................... .......................... .................. 7 2.6.2 Weld Lobe Generation ........................ .......................... ........................... ............. 7 2.6.2.1 Minimum Weld Size Range........................ .......................... ..................... 7 2.6.2.2 Expulsion Range ......................... ........................... .......................... ........ 8 2.7 Reasons to Reject Steel and/or Metal Stackup for Production Applications ........................ 10
3.
Elect ro de Cap Perfo rman ce Test ............................................................................................. 12 3.1 Equipment Requirements ......................... ........................... .......................... .................... 12 3.1.1 Welding Equipment ......................... ........................... ........................... .............. 12 3.1.2 Water Flow Rate ................................................................................................. 12 3.1.3 Inspection, Measurement and Test Equipment ......................... ........................... 12 3.1.4 Tools................................................................................................................... 12 3.2 Material Requirements ........................ ........................... ........................... ........................ 12 3.3 Predressing of Electrode Caps .......................... ........................... .......................... ........... 13 3.4 Electrode Alignment ......................... ........................... .......................... ........................... . 13 3.5 Test Procedure ................................................................................................................. 13 3.5.1 Electrode Cap Performance .......................... .......................... ........................... . 13 3.6 Reasons to Reject Steel and/or Metal Stackup for Production Applications ........................ 14
Annex A: Fig ur es ......................... ........................... .......................... ........................... .......................... 1
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors
1.
General
1.1
Scope
Global Manufacturing Engineering
This document establishes the procedures to evaluate the resistance spot weldability of sheet steel based on the following global initiatives: electrode cap dressing global weld schedules global acceptance criteria (i.e. GMW14057) global welding equipment (i.e. GWS-2D, GWS-2E & GWS-2T) This document also establishes the procedures to determine electrode cap performance when welding different grades and types of steels, steel coatings and/or various metal stackups.
The procedures established in this document are used to determine the practical limits of production weldability of sheet steel joined by the resistance spot welding process, utilizing weld lobes in conjunction with data from destructive weld tests and metallurgical examinations. This document is intended for Steel Manufacturers, Electrode Cap Manufacturers, Material Engineers, Product Design Release Engineers, Design Follow-up Engineers, Weld Engineers and other individuals that are responsible for selecting steels, electrode caps, and material stackups that are processed for production resistance spot welding in vehicle designs for which GM is responsible. 1.2
Purpose
The purpose of this procedure is to describe the standard weld tests used to determine resistance spot welding characteristics of sheet steels, stackups, and coatings. The test methods and data from the completed tests are used to evaluate any or all of the following: 1. New steel grades, or new steel coatings (e.g. pre-primed steels) 2. Effect of steel manufacturing process changes to approved steels 3. Proposed production stackups that do not meet GWS-1A requirements 4. Proposed welding conditions (e.g. use of non-standard electrodes) 5. Establishing and validating production weld schedules 6. To evaluate new and existing suppliers of sheet steel and/or electrodes 1.3
Weld Deviation Process
Any deviations to this test procedure require the advanced written approval of the GM Manufacturing Engineer - Welding responsible for the project. Any approved deviation shall only apply to that specific instance, and it shall not be considered a change to this test procedure.
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors 1.4
Global Manufacturing Engineering
References
1.4.1
Normative
The following normative references contain provisions that, through reference in this document, constitute provisions of this standard. The editions indicated were valid at the time of publication. All normative documents are subject to revision and the most recent editions of the normative standards indicated below shall apply. GWS-1A, Weld Design Standards, Section A: Resistance Spot Welding. GWS-1A Associated Files: Weld Schedules. GWS-2D, Resistance Welding Equipment, Section D: DC Welder Controls. GWS-2E, Resistance Welding Equipment, Section E: Electrode Cap Dresser. GWS-2T, Resistance Welding Equipment, Section T: Transformer-Rectifiers. GMW14057, Acceptance Criteria and Repair Procedures: Resistance Spot Welds-Steel. 1.4.2
Informative
None 1.5
Definitio ns, Acronyms and Abbreviations
1.5.1
Definitions Carbon Imprint: The carbon paper impression left on paper by the electrode face when the electrodes are closed with no welding current. This is used to verify the alignment of the electrodes before a test is begun and to measure electrode face diameter. See Figure A - 3 and Figure A - 9. Coupon: A steel sheet of predetermined size used to install welds for testing. It is also referred to as “Weld Coupon.” Cycle: Unit of time. For this procedure 60 cycles is equal to 1 second. Delamination in Base Steel: Refers to discontinuity in sheet steel where the sheet separates by layers. Discontinuity: An interruption of the typical structure of a material, such as a lack of homogeneity in its mechanical, metallurgical or physical characteristics. Electrode Cap: Consumable part of the electrode that is used to apply the weld force and weld current. Electrode Cap Sticking : A term used to describe a condition where the electrode cap appears to be welded to the surface of the steel sheet. With minimal force the cap can be separated from the steel without distorting the steel or having the cap release from the shank.
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors
Global Manufacturing Engineering
Expulsion: Molten metal that is extruded from between sheets being welded or from the interface between the outer sheet metal surface and the electrode(s). See glossary in GMW14057. Electrode Imprin t: The impression left in the metal surface by the electrode face after welding. Faying Surface: The surface where welding is initiated. Fracture: Full Interfacial Fracture: A type of weld fracture mode that shows evidence of fusion but shows neither evidence of a through-sheet button pull nor a partial thickness fracture. See Figure A - 4. Partial Interfacial Fracture: A type of weld fracture mode that shows evidence of fusion for part of the area, and other fracture modes for the remainder of the fused area. See Figure A - 4. Partial Thickness Fracture: A type of weld fracture mode that shows removal of parent metal by the weld from the mating sheet, for all or part of the fused area, but not a full button pull (characterized by a hole in the parent metal sheet). See Figure A - 4. Weld Fracture Mode: The type of weld characteristic achieved during destructive testing. Global Weld Exp ert Team: A group of individuals designated by the Global Weld Council. Usually this includes the authors of a given standard or specification and Subject Matter Experts (SME) from the other GM regions. Grain: The direction the steel sheet is rolled during the steel processing sequence. Parent Material: Refers to the area around the weld that has not been affected by the weld current and is not part of the weld button. Shunt Weld: See Figure A - 5. The first weld(s) on the coupon that will create a parallel path for part of the weld current used in the subsequent welds. Stackup: A descriptive method used to identify the position and number of sheets to be welded. Test Weld: See Figure A - 5. Usually the second weld on the coupon that will be used for peel testing and evaluation. Weld Butt on: That part of a weld, including all or part of the nugget, which tears out in the destructive testing of a weld. 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. Refer to GMW14057. The measurements are to be taken at the faying surface. Weld Schedule: The parameters specified or set to make a weld. 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 examination of the fusion zone must be used to determine weld size.
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors
Global Manufacturing Engineering
Weldability: The robustness of a steel to be welded to itself, other steels and in various stackups (under imposed limits) determined by its: welding lobe welded mechanical properties (that perform satisfactorily for the intended service) electrode cap performance. The imposed limits are representative of production conditions (i.e. high volume, low cost, global processing and global weld schedules).
1.5.2
Acronyms and Abbreviations DT: Determining Thickness FSC: Faying Surface Condition HSLA: High Strength Low Alloy steel IMAX: The value of welding current determined during testing that will produce weld expulsion IMAX-200: Welding current value determined by subtracting 200A from IMAX l/ MIN: liters per minute kA: 1000 Amperes kN: 1000 Newtons MPa: 1,000,000 Pascals ms: milliseconds NDE: Non Destructive Evaluation NOK : not okay (not acceptable) OK: okay (acceptable) TRIP: Transformation Induced Plasticity TWIP: Twinning Induced Plasticity
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors 2.
Global Manufacturing Engineering
Weld Lob e Test
A weld lobe is a means of graphically expressing the numerous weld current and weld time combinations that produce acceptable welds under a specified set of conditions. Weld current values are plotted on the horizontal axis as shown in Figure A - 6. The left boundary of the lobe displays weld current and weld time combinations that produce welds of the minimum acceptable weld size. Points to the left of this boundary produce undersize welds. The right boundary of the lobe displays weld current and weld time combinations that produce the first occurrence of expulsion. Points to the right of this boundary produce welds with excessive heat energy evidenced by excessive expulsion, electrode indentation and electrode sticking or any combination of these occurrences. The weld current and weld time combinations in the area between the two boundaries (i.e. Weld Lobe) produce welds with acceptable weld size per the requirements of GMW14057. The distance between these two boundaries at a given weld time is referred to as the “Weld Current Range.” A wide Weld Current Range indicates that the metal stackup would be tolerant to variables in the manufacturing process [e.g., tip wear, voltage fluctuations, metal contamination (rust or foreign material)], and other normal changes in the weld equipment. This section defines the test procedure used to determine the weld lobe. 2.1
Equip ment Requirements
2.1.1
Welding Equipm ent
The following equipment is required to generate the data used to determine a weld lobe. 1. Resistance Spot Welder (e.g. fixture type, robotic or manual) with an air-operated cylinder (or other specified method used to generate weld force) that is capable of consistently producing the required weld forces listed in the Associated Files (Global Weld Schedules) of GWS-1A and capable of being operated at 30 welds/min. 2. Welding Transformer-Rectifier: manufactured to GWS-2T by one of GM’s approved suppliers. 3. Welder Control: manufactured to GWS-2D by one of GM’s approved suppliers. 4. Electrode Cap Dresser: manufactured to GWS-2E by one of GM’s approved suppliers. 5. Electrode Cap: Unless otherwise specified, the standard electrode cap is a GMWZ-16x20, mounted on an open shank and pre-dressed to a specified diameter as specified in the Associated File (Global Weld Schedules) of GWS-1A. 2.1.2
Water Flow Rate
The water flow per electrode cap shall be 2 l/min - 4 l/min. 2.1.3
Inspecti on, Measur ement and Test Equipm ent
The following calibrated equipment shall be used: 1. current analyzer (e.g. Miyachi Model # MM-326B or equivalent) 2. digital read-out force gage capable of reading up to 8.9 kN 3. dial caliper (e.g. Mitutoyo Model # CD-6C or equivalent) to measure weld size 4. flow meter to measure water flow 5. tensile test machine 6. ultrasonic testing equipment (optional) April 2011
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors
2.1.4
Tools
1. 2. 3. 4. 5. 2.2
Global Manufacturing Engineering
end nippers (e.g. Channel Lock #148-14 or equivalent) wire cutters for removing excess parent material from the buttons bench vise hammer chisel
Material Requi rements
A minimum of three square meters of flat production-intent steel sheet material is required for the weldability procedure. Steel sheets shall be sheared into coupons with the grain of the steel in line with the coupon length. Steel coupons shall be sheared to the dimensions shown in Figure A - 5 and Figure A - 7. 2.3
Selection of Test Parameters
Use the associated file ( Weld Schedules) of GWS-1A to select the weld schedule based on the DT and FSC of the steel stackup. Set the “squeeze time” to ensure welding occurs at 100% of weld force. Note: 1. Welding one weld gun force higher than specified is allowed in manual operations. However, this increased weld force may result in higher weld current requirements. 2. When the total metal stackup exceeds 2.5 times the DT, it may be necessary to increase the weld time as much as two DT intervals. However, this increase in weld time may result in higher weld current requirements and could increase the weld current as much as 1000A. 2.4
Predressin g of Electrod e Caps
The electrode caps shall be predressed to the specified diameter in the associated file ( Global Weld Schedules) of GWS-1A using a GWS-2E electrode cap dresser. 2.5
Electrode Alignment
The upper and lower electrodes shall be aligned as shown in Figure A - 1. Prior to start of testing, the alignment of the electrode caps must be verified by making carbon imprints using the following procedure: 1. Set and verify the test weld force. 2. Program the test weld schedule. 3. Switch the welder control to the ‘No Weld’ mode. 4. Insert paper with cardboard and carbon paper between electrode caps as shown in Figure A - 2. 5. Initiate the welder control. 6. Inspect carbon imprint made by electrode caps on the paper. Electrode alignment is considered acceptable when the carbon imprint (See Figure A - 3) from both the upper and lower caps is: circular in shape uniform in color diameter meets the specified predressed value
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors
2.6
Global Manufacturing Engineering
Test Procedur e
2.6.1
Condi tion ing Welds
After the electrode caps are predressed and aligned, make 50 conditioning spot welds using a weld current that yields minimum sized welds at the nominal weld time. These conditioning welds reduce the scatter of test data. 2.6.2
Weld Lobe Generation
2.6.2.1 Minimu m Weld Size Rang e
1. Set the welder control to the Constant Current mode and the weld and cool times to the next higher DT interval values shown in the appropriate table for that FSC from Associated Files (Global Weld Schedules) of GWS-1A or as indicated on the Test Request. Based on the DT, select a weld current (below the value shown in the Global Weld Schedules) that should produce an undersized weld as defined by GMW14057. 2. Spot weld one coupon and peel the coupon to measure the weld size. Increase the weld current (in 100A increments) and spot weld coupons until the measured weld size is equal to or greater than the minimum required size. DETERMINING POINT ‘A’ OF THE WELD LOBE
3. Spot weld one coupon as shown in Figure A - 5 using the weld schedule determined in step 2. Peel the coupon as shown in Figure A - 5 to verify the weld size of Test Weld #2 is greater than or equal to the minimum required size. Achieving three consecutive coupon samples with an acceptable weld diameter from Test Weld #2 establishes Point A on the Weld Lobe shown in Figure A - 6. If an acceptable weld is not met for three consecutive coupons, continue to increase the weld current using 100A increments until an acceptable weld size on Test Weld #2 is met on three consecutive coupons. Note: If an interfacial fracture occurs (during testing to determine weld size) and the fusion zone has an acceptable weld size, note the interfacial fracture condition on the test report and communicate the fracture condition to the Program Lead Weld Engineer.
4. Weld the following additional number of coupons to be used for: Tensile/Shear – 3 coupons (See Figure A - 7). Cross-Tension – 3 coupons (See Figure A - 7). Hardness traverse and metallurgical examination of Test Weld #2 – 1 coupon See Figure A - 8.
DETERMINING POINT ‘B’ OF THE WELD LOBE
5. Using the weld current from Point A, set the welder control to the Constant Current mode and the weld and cool times to the DT interval values shown in the appropriate table for that FSC from Associated Files (Global Weld Schedules) of GWS-1A or as indicated on the Test Request. Spot weld one coupon and peel test as shown in Figure A - 5. Achieving three consecutive samples with an acceptable weld size establishes Point B on the Weld Lobe shown in Figure A - 6. If an acceptable weld size is not met for three consecutive coupons, continue to increase the current using 100A increments until a weld of an acceptable size on Test Weld #2 is met for three consecutive coupons. April 2011
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors
Global Manufacturing Engineering
6. Repeat Step 4 above for Point B.
DETERMINING POINT ‘C’ OF THE WELD LOBE
7. Using the weld current from Point B, set the welder control to the Constant Current mode and the weld and cool times to the next lower DT interval values shown in the appropriate table for FSC from Associated Files (Global Weld Schedules) of GWS-1A or as indicated on the Test Request. Spot weld one coupon as shown in Figure A - 5. Achieving three consecutive samples with an acceptable weld size on Test Weld #2 establishes Point C on the Weld Lobe shown in Figure A - 6. If an acceptable weld is not achieved for three consecutive coupons, continue to increase the current using 100A increments until acceptable welds on Test Weld #2 is met on three consecutive coupons. 8. Repeat Step 4 above for Point C.
2.6.2.2 Expulsion Range DETERMINING POINT ‘D’ OF THE WELD LOBE
1. Using the weld current from Point C plus 200A, set the welder control to the Constant Current mode and the weld and cool times to the next higher DT interval values shown in the appropriate table for that FSC from Associated Files (Global Weld Schedules) of GWS-1A or as indicated on the Test Request . If expulsion does not occur on Test Weld #2, increase the weld current (in 200A increments) until expulsion occurs on Test Weld #2. 2. The first occurrence of expulsion on Test Weld #2 establishes Point D on the Weld Lobe shown in Figure A - 6. 3. Weld the following additional number of coupons to be used for: Tensile/Shear – 3 coupons See Figure A - 7. Cross-Tension – 3 coupons See Figure A - 7. Hardness traverse and metallurgical examination of Test Weld #2 – make one coupon (See Figure A - 8)
DETERMINING POINT ‘E’ OF THE WELD LOBE
4. Using the weld current from Point D plus 200A, set the welder control to the Constant Current mode and the weld and cool times to the nominal DT interval values shown in the appropriate table for FSC from Associated Files (Global Weld Schedules) of GWS-1A or as indicated on the Test Request. If expulsion does not occur on Test Weld #2, increase the weld current (in 200A increments) until expulsion occurs on Test Weld #2. 5. The first occurrence of expulsion on Test Weld #2 establishes Point E on the Weld Lobe shown in Figure A - 6. 6. Repeat step 3 above for Point E. DETERMINING POINT ‘G’ OF THE WELD LOBE
7. Weld one additional coupon at Point G (minus 200A from Point E) to be used for metallurgical examination of Test Weld #2. This establishes Point G on the Weld Lobe as shown in Figure A - 6. DETERMINING POINT ‘F’ OF THE WELD LOBE
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Global Manufacturing Engineering
8. Using the weld current from Point E plus 200A, set the welder control to the Constant Current mode and the weld and cool times to the next lower DT interval values shown in the appropriate table for FSC from Associated Files (Global Weld Schedules) of GWS-1A or as indicated on the Test Request. If expulsion does not occur on Test Weld #2, increase the weld current (in 200A increments) until expulsion occurs on Test Weld #2. 9. The first occurrence of expulsion on Test Weld #2 establishes Point F on the Weld Lobe shown in Figure A - 6. 10. Repeat step 3 above for Point F.
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors 2.7
Global Manufacturing Engineering
Reason s to Reject Steel and/or Metal Stackup for Produ ctio n Appli cations
The Weld Lobe is not solely used to judge the production weldability of a steel and/or metal stackup. If delamination of the steel is observed during the peel test, the steel is rejected. Any of the following conditions may result in rejection by the Global Weld Expert Team of a proposed steel and/or metal stackup: 1. Narrow Weld Current Range: A 1.0 kA minimum weld lobe current range cannot be met. 2. Inconsistent Weld Size Samples: Consistent weld size cannot be produced. 3. Weld Lobe Position on Graph: The weld lobe does not overlap sufficiently with those previously developed for approved steel sources. 4. Hardness Traverse: The hardness traverse indicates a brittle weld structure. 5. Metallurgical Cross-Section Examination: The metallurgical examination reveals any of the following discontinuities. a. Thinning greater than 30% as described in GMW14057. b. Penetration less than 10% into each sheet. c. Any void not wholly contained within the weld nugget. See figure in Table 2-1. d. Cracks are observed see Table 2-1.
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors
Global Manufacturing Engineering Table 2-1: Acceptability of Surface Cracks (By Location) Inside Electrode Imprint Outer Outer Inner 80% 10% 10% OK NOK NOK depth < 0.15mm OK NOK NOK depth < 0.15mm OK NOK NOK depth < 0.15mm OK NOK NOK depth < 0.15mm
Steels
GMW3399M TRIP GMW3399M TWIP GMW3399M DP (950MPa and higher) GMW14400M Boron GMW3399M MS (950MPa and higher) All others listed in GWS-1A Associated File: Global Approved Steels for Welding
Surface Crack Outside the Electrode Imprint (NOK)
NOK
OK depth < 0.15mm
OK
OK
Outside Electrode Imprint
NOK NOK NOK NOK
NOK
NOK
OK
NOK
Electrode Imprint
Surface Crack (< 0.15mm) Inside the Electrode Imprint (OK)
Void
10%
80%
10%
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors 3.
Global Manufacturing Engineering
Electrod e Cap Perfo rmance Test
The following items are required to generate the data used to determine electrode cap performance within the interval of cap dressing. Use the Electrode Cap Test Data Form shown in Figure A - 11. 3.1
Equip ment Requirements
3.1.1
Welding Equipm ent
The following equipment is required to generate the data used to determine electrode cap performance. 1. Resistance Spot Welder (e.g. fixture type, robotic or manual) with an air-operated cylinder (or other specified method used to generate weld force) that is capable of consistently producing the required weld forces listed in Associated Files (Global Weld Schedules) of GWS-1A or as indicated on the Test Request and capable of being operated at 30 welds/min. 2. Welding Transformer-Rectifier: manufactured to GWS-2T by one of GM’s approved suppliers. 3. Welder Control: manufactured to GWS-2D by one of GM’s approved suppliers. 4. Electrode Cap Dresser: manufactured to GWS-2E by one of GM’s approved suppliers. 5. Electrode Cap: Unless otherwise specified, the standard electrode cap is a GMWZ-16x20, mounted on an open shank and pre-dressed to a specified diameter as specified in Associated Files (Global Weld Schedules) of GWS-1A or as indicated on the Test Request. 3.1.2
Water Flow Rate
The water flow per electrode cap shall be 2 l/min - 4 l/min. 3.1.3
Inspecti on, Measur ement and Test Equipm ent
The following calibrated equipment shall be used: 1. current analyzer (e.g., Miyachi Model # MM-326B or equivalent) 2. digital read-out force gage capable of reading up to 8.9 kN 3. dial caliper (e.g., Mitutoyo Model # CD-6C or equivalent) to measure weld button size 4. flow meter to measure water flow 3.1.4
Tools
1. end nippers (e.g., Channel Lock #148-14 or equivalent) 2. wire cutters for removing excess parent material from the buttons 3. bench vise 3.2
Material Requirements
The electrode cap performance procedure is used for several types of evaluations, which have unique material requirements. See Table 3-1.
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors
Global Manufacturing Engineering Table 3-1: Material Requirements Evaluation s
performance of an electrode cap material specific stackup or welding condition new steel 3.3
Minimu m Material Requirements
1 square meter of 0.8mm GMW2M-ST-S HD70G70GU 0.5 square meter of each steel 1 square meter
Predressin g of Electrod e Caps
The electrode caps shall be dressed to the specified diameter in listed in the Associated Files (Global Weld Schedules) of GWS-1A or as indicated on the Test Request using a GWS-2E electrode cap dresser. 3.4
Electrode Alignment
The upper and lower electrodes shall be aligned as shown in Figure A - 1. Prior to start of testing, the alignment of the electrode caps must be verified by making carbon imprints using the following procedure: 1. Set and verify the test weld force. 2. Program the test weld schedule. 3. Switch the welder control to the ‘No Weld’ mode. 4. Insert paper with cardboard and carbon paper between electrode caps as shown in Figure A - 2. 5. Initiate the welder control. 6. Inspect carbon imprint made by electrode caps on the paper. Electrode alignment is considered acceptable when the carbon imprint (see Figure A - 3) from both the upper and lower caps are: circular in shape uniform in color
3.5
Test Procedur e
3.5.1
Electrod e Cap Perfo rmance
1. If Section 2 was performed, use I Max-200 and skip to Step 5 of this section. 2. If Section 2 was not performed, set the weld force and weld time to the values listed in the Associated Files (Global Weld Schedules) of GWS-1A or as indicated on the Test Request. Determine the weld current required to obtain a minimum acceptable weld size as specified in GMW14057. 3. Determine the weld current (using Constant Current mode) required for obtaining the first occurrence of expulsion on Test Weld #2 on the coupon as shown in Figure A - 5. 4. Decrease the current by 200A and begin the test. 5. Make imprints of the electrode caps at the start, and every 50-weld interval thereafter. See Figure A - 9. Note: A record of electrode imprints must be kept.
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6. Weld at a rate of 30 welds/min on 125mm x 400mm coupons (or other predetermined coupon size). Note: Do not make a weld on the “footprint” of a previous weld as this will accelerate electrode cap deterioration.
7. After every 48-weld interval, make two welds on a coupon as shown in Figure A - 5. This is referred to as the 50-weld interval check. 8. Perform a peel test as shown in Figure A - 5 on Test Weld #2 on the coupon and record the following information on a test data sheet. A typical test data sheet is shown in Figure A - 11. a. weld number b. programmed current in kA c. measured current in kA d. measure weld size per GMW14057 e. profile (drawing) of each button (e.g. round, oval or crescent) f. comments (e.g. weld quality, button pulled or no button, excessive expulsion, sticking, etc.) 9. When the weld size does not meet the minimum requirements at the 50-weld interval check, record the data and end the test. 10. Continue the test until one of the following conditions occur: 500 acceptable welds are produced The metal sticks to the electrode cap, requiring a substantial force to free it (i.e., excessive electrode sticking). Other conditions exist (as stated in the Special Instructions on the test request).
11. Record the total number of welds at the termination of the test. Note: The ME Body Weld Engineer should be notified of any modifications or errors that occur during electrode cap performance testing. 3.6
Reason s to Reject Steel and/or Metal Stackup for Produ ctio n Appli cations
The Electrode Cap Performance is not solely used to judge the production weldability of a steel and/or metal stackup. The following conditions may result in rejection by the Global Weld Expert Team of a proposed steel and/or metal stackup. Does not achieve 500 acceptable welds Excessive electrode cap sticking. Does not meet requirements of Special Instructions.
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An nex A: Fi gu res Figure A - 1: Electrode Ali gnment
CL
CL
CL Unacceptable
CL Acceptable
Figure A - 2: Testing of Electrode Align ment
CL
Folded Paper
Cardboard ~0.30mm Thick
Folded Carbon Paper
A-1
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Figure A - 3: Carbon Imprints Used For Verification of Electrode Cap Alignment
Lower Cap
Upper Cap
Lower Cap
Upper Cap
e n i L d l o F r e p a P
e n i L d l o F r e p a P
Acc ept abl e Elect ro de Al ig nm ent o Imprints are circular o Imprints are uniform with uniform deep coloring
Unacceptable Electrode Alignment Imprints are oval o o Imprints are circular but not uniform in coloring
Figur e A - 4: Interfacial Fractures
Partial Button
Full Interfacial Fracture Partial Interfacial Fracture
Partial Thickness Fracture
A-2
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Figur e A - 5: Peel Test Weld Coup ons for Generating Weld Lobes and/or Electrode Cap Performance
V X W #2
#1
L Descripti on Test Weld #1 (first weld/shunt weld) Test Weld #2 Offset Weld Spacing per GWS-1A Coupon Length Coupon Width
Symbol #1 #2 V X L W
Dimension /Tolerance N/A N/A 6 + 3mm ± 6 mm 150 ± 3mm 50 ± 3mm
Typic al Peel Test
End Nippers
Test Weld # 2
Test Weld # 1 Bench Vise
A-3
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Global Welding Test Procedures (GWS-5A) Sectio n A: Resist ance Spot Welding of Steel General Motors
Global Manufacturing Engineering Figure A - 6: Weld Lobe
A
Maximum
) s m ( e m i T d l e W
D
Region of Excessive Expulsion Weld Lobe
Nominal
B
G
E
Region of Undersized Weld
C
Minimum
F
0 Weld Current (kA)
Minimum Acceptable Weld Size on Test Weld # 2 First Occurrence of Expulsion on Test Weld # 2 Weld Lobe Range
A-4
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Global Manufacturing Engineering Figure A - 7 : Tensile/Shear & Cross -Tensi on Weld Coupo n Test L W
W
Tensile/Shear Coupon
(Coupon Width & Overlap) L (Coupon Length) Weld L ocation
Dimensions (mm) 50 ± 3 150 ± 3 W/2 ± 3 from center of overlap area W
L
Cross-Tension Coupo n
A-5
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Figur e A - 8: Hardness Traverse
Hardness testing shall be performed as shown in Figure A - 9 (diagonal traverse across the weld from base metal of top coupon to base metal of bottom coupon) using a suitable instrument for microindentation hardness testing (i.e. Vickers or Knoop). All hardness testing shall be performed at a temperature of 23° ±5°C. A constant force that is between 0.2kg (1.961 N) and 1kg (9.807 N) shall be used for all indentations. All indentations shall be made at 0.4mm spacing or no less than three times the mean diagonal of any two adjacent indentations. Note: If the distance between the centers of two adjacent indentations is less than three times the mean diagonal of either indentation, the spacing has to be increased. The approach velocity of the indenter shall not exceed 200mm/second. The time from initial application of force until the test force is reached shall not exceed 10 seconds. The duration of the test force shall be 10 to 15 seconds. The results shall be reported in tabular or graphical form and include the following headings: Sample Test Forc e Tabul ar Report
Position
Base Metal
TEST FORCE REPORT Hardness Values Heat-Affected Zone Weld Nugget
Heat-Affected Zone
Base Metal
A-6
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Global Manufacturing Engineering Figure A - 9: Electrod e Impri nt Histo ry (50 weld in tervals)
0 50 100 150 200 250 300 350 400
Figure A - 10: Surface Cracks
A-7
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Global Manufacturing Engineering Figur e A - 11: Typic al Electrod e Cap Performanc e Test Data Sheet
Requestor:
Date:
Test # :
Material:
Performed by:
Page # :
Stackup:
Weld Machine:
Upper Cap #:
Dressed Cap Face Dia (mm):
Welder Control: Water Flow (l/min):
Lower Cap #:
Dressed Cap Face Dia (mm): Weld Schedule
Water Flow (l/min):
Squeeze Time (ms):
Weld Time (ms):
Cool Time (ms):
# of Pulses:
Hold Time (ms):
Weld Force (kN):
Weld #
Programmed Measured Current Current kA
kA
Measured Button A Diameter mm
Button A Shape drawing
Measured Button B Button B Shape Diameter mm drawing
Total Pages:
COMMENTS (e.g., expulsion, cap sticking, cap imprint)
Weld Size A is between the first and second sheet and Weld Size B is between the second and third sheet. See example below for metal stackup (G1.5G-B1.7B-G2.0G) NOTE: A weld button is the result of a peel test.
Weld Size A
Metal Stackup Illustration
Weld Size B G1.5G B1.7B G2.0G
A-8
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