Seam Welding Seam Welding Lesson Objectives When you

Seam Welding

Seam Welding Lesson Objectives When you finish this lesson you will understand: • The various forms of seam welding • Nugget formation mechanisms • Quality testing of Seam Welds Learning Activities 1. View Slides; 2. Read Notes, 3. Listen to lecture 4. Do on-line workbook 5. Homework Keywords Roll Spot Weld, Overlapping Seam Weld, Continuous Seam Weld, Lap Seam Weld, Mash Seam Weld, Metal Finish Seam Weld, Butt Seam Weld, Foil Butt Seam Weld, Projection Seam Weld, Weld Current-Pulse Time, Welding Speed, Overlap Distance, Nugget Formation, Seam Weldability, Pillow Test

Introduction to Resistance Seam Welding Roll Spot Weld Upper Electrode Wheel Knurl or Friction Drive Wheel Overlapping Seam Weld Continuous Seam Weld Workpiece Lower Electrode Wheel Throat [Reference: Welding Handbook, Volume 2, p. 553, AWS]

Lap Seam Weld Overlapping Weld Nuggets Electrodes Travel Front view Side View [Reference: Welding Handbook, Volume 2, p. 554, AWS]

Effect of Weld Current and Pulse Timing 3 on, 2 off (60%) 4 on, 3 off (57%) 6 on, 5 off (54%) Resistance Welder Manufacturers Association Bulletin # 23

Effect of Cool Time (Heat %) on Nugget Properties @ 6 Cycle Heat 75% 6 on, 5 off (54%) 66% 60% 54% 50% 46% Heat Resistance Welder Manufacturers Association Bulletin # 23

Effect of Electrode Force Increased Electrode Force increases nugget penetration Increased Electrode Force causes increase in nugget width while reducing penetration, more electrode cooling Resistance Welder Manufacturers Association Bulletin # 23

Welding Speed Resistance Welder Manufacturers Association Bulletin # 23

Seam Welding Multiple Thickness Sheets Resistance Welder Manufacturers Association Bulletin # 23

Improper selection of Parameters Leads to Porosity in Weld Resistance Welder Manufacturers Association Bulletin # 23

Mash Seam Weld Slightly Lapped Sheets Wide, Flat Electrodes Weld Nuggets Before welding After Welding [Reference: Welding Handbook, Volume 2, p. 554, AWS]

Effect of Sheet Overlap on Mash Lap Joint properties Resistance Welder Manufacturers Association Bulletin # 21

Effect of Electrode Force on Mash Seam Weld Resistance Welder Manufacturers Association Bulletin # 21

Metal Finish Seam Weld Finish Side Chamfered Electrode Broad, Flat Electrode Before Welding Flash After Welding [Reference: Welding Handbook, Volume 2, p. 554, AWS]

Effect of Weld Current and Electrode Force on Finish Seam Welds Resistance Welder Manufacturers Association Bulletin # 24

Effect of Current on Metal Finish Seam Weld Resistance Welder Manufacturers Association Bulletin # 21

Recommended Sheet Positioning Resistance Welder Manufacturers Association Bulletin # 24

ASM Handbook Vol 6, 1993

Porter, Galvanizing and welding structural steel, Metal Construction, Nov 1983

ASM Handbook Vol 6, 1993

Nugget Formation in Continuous Seam Weld

Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

1 2 3 4 Stage 1 Takes 1 - 4 cycles, Increased resistance due to increased temp outweighs reduction in resistance due to better surface contact through asperity softening and surface oxide breakdown Peak occurs earlier with thinner materials Resistance Curve for Establishment of Leading Edge of a Continuous Nugget Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

1 2 3 4 Stage 2 Drop in resistance because of current shunting into the mushy and solid state bonded region Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

1 2 3 4 Stage 3 Instability in current path, nugget approaching a steady state growth mode Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

Stage 1 Nugget Initiates Stage 2 Nugget Moves Toward Exit Stage 3 Approaching Steady State

1 2 3 4 Stage 4 Steady State Growth of Nugget until either expulsion or current off time and new nugget formation Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

Particular Interest in Steady State Region Actual Data (effect of Speed) 2 m/min 4 m/mim Attorre, Heat Development in Resistance Seam Weldi Ironmaking and Steelmaking, 1996

At Lower Speeds At Higher Speed • Increased Current Ahead of nugget • Less Heat Extracted through Electrode • Larger thru Sheet Nugget Growth Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

Through Sheet Nugget Growth 2 m/min 6 m/min 16 m/min Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

Factors Promoting Thru Thickness Growth • High Welding Speeds • Increased Sheet Metal Thickness (less electrode cooling) • Increased Sheet Metal Resistivity • Increased Force (increased Electrode Arc Contact-Current Length) • Increased Current

Steady State Heat Flow Patterns (Examine HAZ in Front of Nugget Formation) Enter Exit Increased Speed Nugget Type A HAZ Length of Heat Zone Increased Speed HAZ Nugget Type B Unstable Transition Pattern Nugget Type C HAZ

Sheet Thickness 0. 7 mm 1. 2 mm 2. 0 mm For Type A Pattern

2 m/min 10 m/min At High Speeds, Current Flow and Heat Generation Extended to Sheet Surface Higher Speeds move from “A” to “C” Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

Exit End Enter End Transverse Longitudinal Higher Speeds Result in Nugget Moving toward Exit End and Expulsion on Exit

Waddell, Mechanism of weld formation…, Welding and Metal Fabrication, Aug 1995

Increased Electrode Force Contact Area Nugget Moves Back Heat Zone Increases Increased Indentation

Nugget Formation in Pulsed Welds

ASM Handbook Vol 6, 1993

Schematic of seam weld. Length of electrode footprint holds 3 welds ASM Handbook Vol 6, 1993

Irregular nuggets irregular pulses that does not give time for heat flow ASM Handbook Vol 6, 1993 RSW Certification Training Class, Boeing

Dynamic Resistance Series of Overlapping Nuggets Continuous Seam Weld Time Attorre, The influence of welding parameters on formation of solute bands…, Welding In the World, Vol 37, 1996

Parameter (Lobe) Curves for Seam Weld Pulsed Current No Cooling Between Continuous Pulses in Continuous Therefore Lower Current Porter, Galvanizing and welding structural steel, Metal Construction, Nov 1983

Expulsion or Overheating Speed Limited for Pulse or Continuous Current Options Minimum Condition for Continuous Weld Gould, Resistance Seam Weldabilit, Report MR 9112, EWI, 1991

What About Coated Sheets?

Resistance Seam Weldability of Low-Carbon Steel Lower Speed Surface Eruption, Cu Contamination Cracking Higher Current Non-Continuous Seam Uncoated Steel Hot-Dipped Galvanized AWS Welding Handbook , Vol 4, 1998

Exit Entry Expulsion Weld Coating Melts and Extrudes Out High Speed Peterson, “High Speed Seam Welding. . ” AWS Sheet Metal Welding Conf. VI, 1994

Coated Steels have lower contact resistance delaying heating until coating is removed thus slower speeds are required to get coating out Peterson, “High Speed Seam Welding. . ” AWS Sheet Metal Welding Conf. VI, 1994

Factors Limiting Travel Speed Bulk Resistivity The higher the bulk resistivity of the material, the higher the heating (H=I 2 Rt) and thus the higher the travel speed possible Current Density As travel speed increases, more material is presented to the rolls per half cycle of current thus reaching a limit to the current density in the part Conductive Coating Materials When conductive coatings are present at the faying surface, they offer an increased shut path for current and thus also reduce current density. Welding takes place when these coatings are melted and extruded out of the weld zone. Expulsion With increased travel speed, complete nugget formation is delayed until the weld forms outside the pressure influence of the rolls (see next slide) and expulsion is easier.

Projection Seam Welds Experimental Procedure to Maximize Current Density

Peterson, “High Speed Seam Welding. . ” AWS Sheet Metal Welding Conf. VI, 1994

Seam Weld Quality Tests Tensile Tests Resistance Welder Manufacturers Association Bulletin # 21 Pillow Tests

Typical data from Pillow Testing 6 x 6 inch Pillow 6 x 10 inch Pillow

Douglas Process Standard DPS 10. 800, Mc. Donnell Douglas Corp, 1996

Seam Welding