lap 2+3 Report

MIME 1650 Laboratory 2

Resistance Spot Welding (RSW) Test

Please keep your welded sample for future laboratories.

Objective The student learns the basic knowledge about resistance spot welding and welds a

specimen for future laboratories.

Agenda -Introduction to RSW Machine

-Laboratory 2 procedure

Equipment and tools -Resistance Spot Welding Machine

-Micrometer -Steel Ruler

-Vernier Caliper -Marker (Scriber)

-Protective screen

Sample Low Carbon Steel Sheet

Lab Executants Individual

Lab Period 1 week

Report Individual

Location NE-1100 (Groups first meet TA’s in NE 1061)

Introduction Resistance spot welding (RSW) is one of the most important joining techniques. It is a

very rapid and economical process, extremely well suited to automotive industry.

In RSW, both heat and pressure are used to affect coalescence. The heat is the

consequence of the electrical resistance if the work piece and the interface between them.

The pressure is varied throughout the weld cycle. A certain amount of pressure is applied

initially to hold the workpiece in contact and thereby control the electrical resistance at

the interface. When the proper temperature is attained, the pressure is increased to

facilitate coalescence. Usually the required temperature can be attained and coalescence

achieved in a few seconds or less.

The heat for RSW is obtained by passing a large electrical current through the

workspaces for a short period of time. The amount of heat can be determined by the basic

relationship:

RtIH 2

=

Where H is the total heat input, I is the current, R is the electrical resistance of the circuit,

and t is the length of time in which current is flowing. It is important to note that the

workpieces form part of the electrical circuit, and the total resistance between the

electrodes consists of three components:

1. The resistance of the workpieces 2. The contact resistance between the electrodes and the workpiece 3. The resistance between the surface to be joined, known as faying surface

Figure 1 Spot-Welding Machine

The objective of RSW is to simultaneously bring both of the faying surfaces to the proper

temperature while keeping the remaining material and the electrodes relatively cool. The

electrodes are usually water-cooled to keep their temperature low and to aid in keeping

them in proper condition.

As shown in Figure 2, the overlapping workpiece is positioned between water-cooled

electrodes, which have reduced areas at the tips to produce welds that are usually from

1/16 to ½ in. (1.5 to 13 mm) in diameter. After the electrodes are closed on the

workpiece, the controlled cycle of pressure and current is applied, producing a weld at the

metal interface. The electrodes then open and the workpiece is removed.

A satisfactory spot weld, such as the one shown in figure 3, consists of a nugget of

coalesced metal formed between the faying surfaces. Figure 4 shows the RSW’s squeeze,

weld, hold and off time.

There should be little indentation of the metal under the electrodes. The strength of the

welds should be such that, in a tensile or tear test, the weld will remain intact and failure

will occur in heated affected zone (HAZ) surrounding the nugget. If proper current

density and timing, electrode shape, electrode pressure, and surface conditions are

maintained, sound spot welds can be obtained with excellent consistency.

Figure 2 The Scheme of RSW

Figure 3 A Spot Weld

Experimental Procedure

1. Measure the coupon size (length, width and thickness) Data Sheet 1 2. Mark out the spot-weld location at 1′′ from each edge of the sheet coupon along

the line.

3. At the welding machine, check if the electrodes are fitted and aligned properly. 4. Switch on the red water supply valve located below the weld controller. 5. Connect Air hose to the machine. 6. Switch on the power knob on the Weld Control Unit (WCU). 7. On the door of WCU ensure that

• Schedule #7 is selected • The red Control Stop knob is in released position. • The ‘DAS’ knob is in “Bypass” mode • The knob for welding must be on No Weld.

8. Wait till the Hand Held Terminal (HHT) initializes. It should show the display record the previously made weld.

9. On the HHT, press ‘Program Mode’/‘F1’ (Review Schedule)/‘F2’ (to change Schedule#)/‘07’ (to select Schedule #)/‘Enter’

10. Check the weld schedule parameters. The parameters are: Current 10KA, Cycle 10, Electrode Force (lbs) 800

Electrode tip Diameter 5mm

11. To change the weld parameters:

• Take the cursor key on the HHT to select the function you want to modify. • Enter the new values. • Press ‘F3’ to download changes. • Press ‘Enter’ twice to save changes to WCU#00, and Schedule #7.

12. Place the coupon at the point you want to weld and operate the machine in No Weld.

13. Adjust the position of the coupon so as to get the weld at the correct location. 14. Turn the Weld/No Weld knob to Weld. 15. Set protective screen for safety. 16. Make welds (two welds on one coupon) at the marked locations. See if expulsion

occurs.

17. Go HHT, press “Display Mode/F1/Weld Data” and view and record the welding data.

Figure 4 Schematic diagrams of RSW Stages

Data Sheet

1. Specimen Size Date:

1 st Measure 2

nd Measure 3

rd Measure Average

Sheet 1 Length

Sheet 2

Sheet 1 Width

Sheet 2

Sheet 1 Thickness

Sheet 2

2. Welding Records

Squeeze. ………cycle; Hold….…..cycle

Current

Actual

Setting Max Min Average

Weld

Cycle

Electrode

Force

Expulsion

(Yes/No)

Comment

Weld#1

Weld #2