HOW TO DETERMINE PARAMETERS OF THE WELD

2. HOW TO DETERMINE PARAMETERS OF THE WELD

by Sam Belkin, MSEE

Lets see how an operator can determine parameters of the weld. For this objective it is necessary to implement a new parameter D = total thickness of sheets being welded. Then, the welding parameters can be easily found as a function of D . The most common case in industrial and automobile repair applications is the welding of low-carbon steel up to 1/8" of thickness. For this instance the following plain equations may be used:

1. Electrical current in amperes:

I = 1.250 x 10⁵ x D where D in inches and

I = 4.935 x 10³ x D where D in millimeters.

2. Welding time in cycles:

T = 120 x D where D in inches

T = 4.73 x D where D in millimeters.

3. Electrode force in pounds:

F = 8.5 x 10³ x D where D in inches.

4. Electrode force in Newton:

F = 1.5 x 10³ x D where D in millimeters.

5. Electrode contact tip diameter in inches:

D = 0.18 + D where D in inches.

6. Electrode contact tip diameter in millimeters:

D = 4.54 + D where D in millimeters.

The weld size diameter D_w can be easily found as approximately 2/3 of the electrode contact tip diameter.

These formulae are easy to use and allow to quickly obtain all of the numbers. For example, in the case when the two sheets of low-carbon steel 0.04" (1.0mm) thick must be welded, the approximate values for the welding variables would be as follows:

Welding current:

I = 1.250 x 10⁵ x 0.04 x 2 = 10000 A = 10 kA or

I = 4.935 x 10³ x 1.0 x 2 = 9870 A = 10 kA.

Welding time:

T = 120 x 0.04 x 2 = 9.6 = 10 cycles or

T = 4.73 x 1.0 x 2 = 9.46 = 10 cycles.

Electrode force:

F = 8.5 x 10³ x 0.04 x 2 = 680 lb or

F = 1.5 x 10³ x 1.0 x 2 = 3000 N.

Contact tip diameter:

D = 0.18 + 0.04 x 2 = 0.26" or

D = 4.54 + 1.0 x 2 = 6.54 mm.

Weld diameter:

D_w = 2/3 x 0.26" = 0.17" or

D_w= 2/3 x 6.54 = 4.36 mm.

Due to inherent properties of controlling equipment, real timing can be adjusted only with one cycle step (sometimes with half-cycle step). This is why the welding time T needs to be rounded to the closest bigger integer.

Despite that the numbers from these formulae are approximate, they are very good first approximation. Quality of the weld will depend on the material being welded, welding schedule, how well the welding parameters were determined, electrode surface condition, welding current constancy and etc.

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