Uncoated Plain Carbon Steel Process Variables Continued

Uncoated Steel – Process Variables Continued Lesson Objectives When you finish this lesson you will understand: the effect that various welding parameter variables have on the weld quality of uncoated steels (continuation from last module) Learning Activities 1.Look up Keywords 2.View Slides; 3.Read Notes, 4.Listen to lecture 5.View Demo 6.Do on-line workbook 7.Do homework Keywords Electrode Material, Electrode Design, Electrode Coating, Shunting, Post Weld Temper

Process Variables Process Parameters: (Manufacturer’s Control) Weld Current Type Weld Time Hold Time Pulsing Electrode Force Electrode Material Electrode Designs Electrode Cooling Postweld Temper Material Parameters: (Steel Company Control) Chemistry Cleanliness Surface Condition Material Processing Thickness

Electrode Materials RWMA Class # Electrical Conductivity Composition (%) Ultimate Strength (ksi) Annealing Temperature (°C) Thermal Conductivity (Cal/cm-sec-°C) Cu 99-Cu, 1-Cd 99.2-Cu, 0.8-Cr 97-Cu, 2.5- Co, 0.5-Be Cu & Be Cu & Al (C) 82 (F) 48 (C) 52 (F) 20 (C) 23 (F) (F) 30 (C) 62 (F) 95 (C) 105 (F) 110 (C) 170 (F) (C) 0.75 (F) 0.43 (C) 0.45 (F) 0.18 (C) 0.19 (F) 930 (C) 900 (F) 1020 (C) 900 (F) * C = Cast, F = Forging

R 500 C < % IACS* * Percent Internatinal Annealed Copper Standard ~90 Uncoated Steel

Turn to the person sitting next to you and discuss (1 min.): Besides alloy content, what other factors might effect the electrical conductivity of copper electrodes? How might this change your decision in the manufacturing technique used to manufacture these electrodes? Would the fact that you are welding steel (as opposed to say aluminum) have any bearing on the manufacturing technique?

Process Variables Process Parameters: (Manufacturer’s Control) Weld Current Type Weld Time Hold Time Pulsing Electrode Force Electrode Material Electrode Designs Electrode Cooling Postweld Temper Material Parameters: (Steel Company Control) Chemistry Cleanliness Surface Condition Material Processing Thickness

Electrode Geometry “A” 6° 20° 45° ° Pointed Dome Truncated Cone Truncated Cone [Reference: Welding in the Automotive Industry, p.135, D. W. Dickinson]

Electrode Face Dia. Vs Welding Current Range inch (0.71 mm) 0.05C-0.09P 0.25 inch (6.4 mm) Electrode inch (7.9 mm) Electrode 1300A 3300A Weld Time 15 cycles Electrode Pressure 13ksi Hold Time 30 cycles Current, kA Button Diameter, inch mm [Reference: Welding in the Automotive Industry, p.137, D. W. Dickinson]

Effect of Electrode Diameter on Current Range Electrode Diameter, in. Current Range, Amp Current Range: 0.15 in. Button to Expulsion [Reference: “Spot Weldability of High-Strength Sheet Steels”, Welding Journal 59 (January 1980), Baker & Sawhill]

Codes and Equations Used for Electrode Face Selection Ayers & Fisher D = 1.5t (Leng) D = 2t (AWS) Ford BA 13-4

Turn to the person sitting next to you and discuss (1 min.): It is surprising that with the many different people who have developed codes governing the electrode face diameter as a function of sheet thickness, they all come to about the same size vs. sheet thickness. Why do you suppose this is the case?

Process Variables Process Parameters: (Manufacturer’s Control) Weld Current Type Weld Time Hold Time Pulsing Electrode Force Electrode Material Electrode Designs Electrode Cooling Shunting Material Parameters: (Steel Company Control) Chemistry Cleanliness Surface Condition Material Processing Thickness Upslope/Downslope/ Postweld Temper

Hirsch R., Influence of Water Temp& Flow on Electrode Life SMWC VII, AWS, 1996 Poor Cooling Increased Electrode Wear

Hirsch R., Influence of Water Temp& Flow on Electrode Life SMWC VII, AWS, 1996 Warm Water Slower Flow

Room Temp Refrigerated Dickinson, Welding In Auto AISI, 1981

Baysore, J, DCT Inc, Private Communications, July 2000 No Water Cooling

Turn to the person sitting next to you and discuss (1 min.): What design criteria did the NOWAT people have to consider when they developed their robots that do not need electrode cooling water?

Process Variables Process Parameters: (Manufacturer’s Control) Weld Current Type Weld Time Hold Time Pulsing Electrode Force Electrode Material Electrode Designs Electrode Cooling Shunting Material Parameters: (Steel Company Control) Chemistry Cleanliness Surface Condition Material Processing Thickness Upslope/Downslope/ Postweld Temper

Shunting Effect AB IBIB IAIA I total = I A + I B I A R A = I B R B I B /I total = 1 - R B /(R A + R B ) [Reference: Resistance Welding Manual, p.1-7, RWMA]

Effect of Shunting Distance (Spot Spacing) AC welding 1/4 in. x 3 in. mild steel Class “8” weld Average shear strength of 24 welds, 17,570 lbs Stock temp 25°C All welds made with one shunt circuit Curve estimated below 2-1/2 in. shunt distance Shunt Distance, in. Shunt Distance, cm Shear Strength of Single Weld, % [Reference: Welding Handbook, Volume 2, p. 551, AWS]

Process Variables Process Parameters: (Manufacturer’s Control) Weld Current Type Weld Time Hold Time Pulsing Electrode Force Electrode Material Electrode Designs Electrode Cooling Shunting Material Parameters: (Steel Company Control) Chemistry Cleanliness Surface Condition Material Processing Thickness Upslope/Downslope/ Postweld Temper

Upslope/Downslope, Hold Time, & Temper Weld Current Temper Current Electrode Pressure Current Squeeze Time Weld Time Off Time Hold Time Upslope Downslope Temper