Spot Welding

Questions and Answers

JOULES LAW STATES:

Joules Law

In this equation the current, resistance and time are the variables. The controller or timer can alter both the time and the current. The resistance of the parts being welded is fixed but the resistance can be changed by altering the force/pressure used in the welding process. The question is which will have the largest affect upon the process.  The answer is the current (I).

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Per the definition of the Resistance Welding Manufacturers Alliance:

RESISTANCE WELDING IS THE JOINING OF METALS BY APPLYING
PRESSURE
AND PASSING
CURRENT
FOR A LENGTH OF
TIME
THROUGH THE METAL AREA WHICH IS TO BE JOINED

            Reference: RWMA - Resistance Welding Manual 4th Edition

 

Weld schedules are available in the Resistance Welding Manual and AWS Standard C1.1 for many of the most frequently used materials. The information commonly provided is the proper electrode design, size and material. The weld force, weld time and weld current are also published. The minimum distance between welds is usually listed and the expected nugget or button size is shown. Tensile properties frequently are also published.  Other sources are the Tuffaloy and CMW Catalogs.

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A weld schedule is an instruction to set up a resistance welder for a given job. It includes all of the specific settings of the machine, control settings, tools, electrodes, forces, times, rates and all other pertinent data related to a job. It also includes the information about the part, including material, thickness, number of welds, weld locations, quality requirements, and precleaning. This information is stored and can be used to set up the job on it’s next run. It also can be used as a ground zero if parameters have changed and you want to go back to when the job started.

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Resistance welding over a lip, in a corner, or in a box might be a perfect application for a double bend electrode.

Double Bend Sketch

Above is a sketch showing an example of a double bend electrode welding in a tight area. There are many applications like this that a double bend full size electrode or double bend shank and cap will allow you to reach an otherwise difficult location to weld. Double bends can be water cooled to increase life.  Double bends come in many offsets and sizes as shown below.

bent electrodes2

       DOUBLE BEND ELECTRODES

Reference: RWMA - Resistance Welding Manual 4th Edition

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