Reducing Torque Load of Spot Welding Machines

Torque???

Drawing heavy currents while making a spot to join 2steel sheets to getether.

But that's not torque.

Then what is that

Thanks for description let me say SURGE CURRENT when striking spot, we are making almost 40 spots per minute.

Simply welding current but torque load is impossible (LOL)

I don't know all details of spot welding machines. There may be some types that use capacitors or something to build up a charge during the off cycle, and then discharge the needed current without "spiking" from the grid. You seem to have 1.5 seconds between welds, but maybe each weld takes only 0.25 seconds, giving 1.25 seconds to recharge it. (Just a guess.)

Tornado,

You are thinking of what are usually referred to as "Capacitive Discharge" welding machines. They are typically used to fuse metal tabs to batteries and the like, I don't know if the come in sizes big enough for our OP.

Martin

You seem to be talking about the peak torque on a generator when the spot welder is fired. Further information is needed: how long the 250 amps is applied compared to how long it's off, or the duty cycle in percentage of time. Then you can work out the average torque. If you add a heavy flywheel to the generator, or a large capacitor to the DC side of the welder, then the 250 amp surge and its peak torque on the generator, or peak load (spike) on the transformer or power feed will be smoothed out. Give us a bunch of specifications, as listed above. Where's the power for the spot welder coming from? If you're using 250 amps for .25 second, for instance, your average current over time if you fire every 1.5 seconds is one sixth of 250, or about 45 amps. You should be able to reduce peak current or torque by a factor of six. Six times less than peak.

Most people do not understand problem posted bu you. I have done lot of study on this and could solve problems related final product, weld quality, etc. I do not know your application; one way out is to use "Capacitor Discharge" type spot welders. If your through put in more then go for inverter type (but very costly). I can guide but need to know application, secondary current or KJ, number of weld cycles, transformer rating, etc. Forget: VFD, Stebilizers, etc never work for this application.

Everything is possible. If he use the VFD to adjust the current (so as to adjust the torque - his suggestion) to a transformer. Secondary side of this transformer will connect to the welding clamp.

No Sir, not possible. This type welding is used for battery stab inter-connect squeeze (Resistance) welding also. Very high current flows for 6 to 16 half cycles. You can get lot information/ litrature from www.miyachiunitek.com & www.matuschek.de web site.

We cannot apply it same as TIG welder?

dear,

just ask the welding machine suppliers for new technologies. CO2 Copper welding machines need very small currents. surge currents are nullified. Rectifier type DC welds also have lesser surge currents. But, the weld power can not be reduced that will affect the quality of the weld.

There are several ways to do what you are asking. A simple approach is to use a welding transformer with a higher primary voltage rating. If you double the primary voltage, your primary current drain will be significantly reduced. A second method is to switch to capacitor discharge welding. The welders we use deliver up to 250,000 amps of weld current and have a primary current demand of 15 amperes. A third method is to use a more efficient welder. In commercial welding equipment, up to 1/2 of the power is used to generate unwanted magnetic fields. As these fields are reduced, the process becomes more efficient. Finally, if your factory mains cannot support the current of several machines welding at the same time, you can interlock the machines so only one machine can operate at a time.

My understanding of spot welders is that they use current at low voltage to heat the two metals, fusing them together.

Inverter-based spot welders have more control over the waveform and hence power being used to create the weld, but the power reduction between a cheap spot welder and an inverter welder should be similar (unless you are spot welding with too high a current or too long a duration because you cannot adequately set the correct values to optimise the power usage). Finer adjustment could allow you to reduce the power and or time which would give you an energy saving over time.

Capacitive discharge spot welders are different (high current steep discharge slope short duration) and just plain won't work for some applications such as thick materials (you did not mention what you are spot welding or the material thickness).

In the end you would need to compare a similar inverter based spot welder to your existing spot welder and see if it is worth spending the money. Could be if you could reduce the weld time while maintaining the weld quality and hence get more welds done per minute.

Can you supply more information on the application and thickness of metals you are spot welding?

For the benefit all I am providing below resistance welder transformer primary currents (peaks) & voltage (dips), during few weld cycles. Each thin line represents 14 mSecs. Duty cycle 50%, power 60% of 30KVA, Secondary current is 8.2 to 8.6 KA;

Further to my comments in post #18 I would also suggest you look at the Inverter-based spot welder literature and talk with the suppliers to see what power savings you could expect to see.

Small correction to my above post. It is 140mSec instead of 14; The controller measures each cycle current and corrects firing angle of the next cycle. Inverter type on the contrary uses this 140mSec at 1000 cycles/ per sec and control; so better current control. The other benefit is the transformer size will be very small and low I^^2R losses.

"Capacitive discharge spot welders are different (high current steep discharge slope short duration) and just plain won't work for some applications such as thick materials (you did not mention what you are spot welding or the material thickness)."

A variation of spot welding (projection welding) can be used to weld relatively thick metals using the high speed pulses of capacitor discharge welding. It is particularly advantageous in welding applications where temperature sensitive components (such as explosives) are adjacent to the weld joint, and where marking and distortion of the metal surfaces must be minimized. Stud welding is often a form of projection welding. The bottom line is that there are applications where high speed pulses are required.

many thoughts already expressed . . . placing mine now . . .

i have been involved in building resistance welding machines - to deliver 100 spots per minute - for a production shop where 5 such machines are in use together - - - the product there requires spot welding of MS sheets of thickness varying between 0.6mm to 0.7mm - weld time for the spot is set between 5 to 6 cycles.

we have not used VFDs for control because they do not reduce the current demand on our LV bus. we have connected the primaries of our welding transformers between LINES (415V). actually the demand on the bus in our case is for too short a duration and behaves like a surge.

to the subject question -

your welding machine manufacturer will need to look at the questions below and then he will be able to resolve your problem easily.

what thickness of sheets are you welding?

what is the tool tip shape / diameter you are using?

what is the shortest weld time actually required for the job to be carried out?

placing the weld process in front (of your mind) - the total energy per weld has to be determined first - depending on sheet thickness, metal, weld geometry - once the total energy is determined and the current required is known then the next step will be the transformer design.

no matter what design you do for the transformer your current demand on the bus will ultimately depend on the primary voltage available to you. just in case you are presently using a primary connected between a LINE and NEUTRAL conductor then you will do well to switch to a machine with a primary connected between TWO LINES. this will help you reduce the current in the primary - your total energy (and KVA) demand will not reduce - to reduce that you have to address your weld process.