Also, high pressure can cause thinning of the metal and cause a weakness. The depth of depression on the sheet surfaces caused by welding electrodes should never exceed 25 percent of the sheet metal thickness. Typically a body shop welds steel between 16 gauge and 24 gauge. If a spot welder has adjustable length tongs, a pressure gauge should be used to properly set the pressure.
The pressure is important and should not be guessed at. A standard weld timer controls the amount of time the current flows into the welding transformer.
The inherent problem is that if welding is not taking place the timer is still ticking. Therefore, if welding current is only flowing for part of the cycle, a weld may not be formed before the timer runs out. What generally happens is, the technician increases the length of time the timer will run. This can cause overheating of the welding tools and transformer! Double cycling on the weld zone is also a technique which is used, but it also causes overheating.
Manual control : Sometimes the timer is bypassed by the operator and he times the welds manually. A digital timer control verifies welding is taking place. This type of timer checks all cycles of a 60 cycle second and will not increment the timer unless welding current is flowing!
The Digital timer has a precise interface for selecting and adjusting the power and timer settings. The digital control that verifies welding puts the least amount of thermal stress on the welding tools and transformer.
Weld current and weld time are inversely proportional. Welding current and time are used to bring the metal to welding temperature Degree F. Welding current in a body shop environment has a range of to amperes. Welding current i and weld time t are to be controlled by the technician. Resistance R is determined by the gauge of the parts being welded. Since welding current is squared, changes in weld current are much more dramatic than changes in weld time.
If weld current is at the low end of the range, weld time must be increased. Conversely, if weld current is high then weld time is decreased.
NOTE 2: Using high weld current increases the problem of expulsion. Expulsion is molten metal squirting from between the layers of steel. So we can see, welders that do not control weld current will be more difficult to use. There are two types of weld current controls, Analog : uses a knob and it is set like a radio knob. Digital : uses a LED display that tells the technician the exact power setting.
The usual interface is a push button. The Ideal Welding Controller is digital with a preheat timer and weld current verification. The digital interface is so precise that the operator can set the machine easily. Very small changes in power or time can be made quickly to make perfect welds while eliminating expulsion. A verified preheat timer is the best way to minimize expulsion. Preheating allows the primers that we want to leave between the layers of steel, to be burned out of the way, slowly.
Galvanized coatings can be vaporized Degree F. The temperature is determined by the length of time we preheat the weld zone. Preheating also allows the steel to bend a little and fit perfectly before the welding power is turned on. All these things can happen only if we have preheat current verification!
Verification is the magic that makes the job go faster. The ideal welding controller validates the welding current, eliminating the problem of overwelding. The technician is able to produce good welds every time without overwelding and reduce the heat stress on the welding tools and transformer. Welding tip diameter is very important.
Welding tips have a flat face when new. This face crowns quickly with use, and this crowning effect should be encouraged. The crowning radius should be about 1. There are three forms of weld inspection. First there is a visual inspection; the welds should look uniform, have a small dent from the welding tip, and should have very little expulsion when the weld is formed. It is obvious that the destructive testing should be done on scrap steel before the process of welding on the vehicle is begun.
The peel test consists of peeling apart a spot weld. The button should be measured and the average diameter should be calculated. The chisel test consists of forcing a tapered chisel into the gap on each side of the weld being tested until the weld or base metal fails.
The edges of the chisel must not touch the weld being tested. Wati Ka. KeerthiPratheek Reddy. GRD Journals. Guillermo Hector De Francesco. Chetan Ganesh Raut.
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