RSW Net Electrode Force? (per AWS C1.1)

[CoffeeMan]

The AWS C1.1 spec "Recommended Practices for Resistance Welding" states in Table 20 "Spot Welding Parameters for Stainless Steels" the appropriate parameters for spot welding sheets ranging in thickness from .006 to .125 inches.

I am confused about the Net Electrode Force (lb), and Electrode Diameter and Shape categories.

First the Net Electrode Force: Is this the force output by the ram (in my case a pneumatic cylinder) to which the electrode is attached?

Secondly, the Electrode Diameter and Shape: There are 2 columns for this category giving a lower limit and upper limit for "D".

For the Radius Nose shape, I gather that D is the nose diameter. Going on this assumption, I surmise that for any given thickness there is a range of appropriate diameters from D(lower) to D(higher) for the radius shaped electrode?

Next, for the Truncated Nose shape there is an outside diameter "D" and a tip face diameter "d". In this case would the D(lower) column correspond to the tip face diameter "d" and the D(higher) column correspond to the outer diameter "D"?

Any help you could give me would be really...er, helpful!

Thanks in advance.
CoffeeMan

 

[CWIC]

Coffeeman:
1.) The net electrode force is that applied to the electrodes at the workpiece in making the RSW.
2.) Your assumption on the electrode diameter-shape min/max values are correct. The 3rd critical dimension for the geometry of the elctrode tip is the bevel angle of the tip and at the OD of the electrode, in this case it is 20 degrees.
3.) Two types of electrode configurations are shown in Table 20, one has the truncated geometry as you noted, the other a dome type - where d = effective electrode weld diameter, D = the overall diameter of the electrode.

Hope this helps.

 

[CoffeeMan]

CWIC:

Thanks for your reply, it is quite helpful!

I don't want to beat a dead horse, but just to clarify the Net Electrode Force point...

From Table 20 and .012 Sheet Thickness:

Electrode Tip Face Diameter = 0.13 in (regardless of nose geometry)
>>> Electrode Tip Face Area = pi*(0.13/2)^2 = .0133 sq. in.
Net Electrode Force = 270 lb

My pneumatic cylinder can output 270 lb at 100 psi air pressure. This translates to (270 lb/.0133 sq.in.) = 20,341 psi pressure seen at the electrode/workpiece interface. This seems like a lot. Am I correct in assuming this is the requirement?

 

[CWIC]

Coffeeman:
The pressure at the work should be 270 ft-lb. There are gauges available to verify this pressure at the electrodes for RSW equipment. I would not rely on the line pressure at the cylinder that operates the electrode horns or arms.
The length of the horns vs. the line pressure vs. the cylinder area vs. moment arm should equate to 270 ft-lbs at the tips of the electrodes.

270 ft-lb is exactly what is specified for your thickness of 0.012 per Table 20 of C1.1:2000. Too little pressure may result in voids within the weld nugget. In the past I have recommended ENF pressures that exceed those specified due to the presence of voids, the additional pressure was enough to remove these voids from our macroetch specimens.

Good luck.

 

[CoffeeMan]

CWIC -

Thanks for your time and good advice, they are deeply appreciated. Good luck to you as well.