We are welding .125 5052-H32 to the Military spec mil-w-6858. We have to have a min pull of 1,315 lbs per spot. We're having a dificult time keeping this avg. It's not the spot welding machine, it's more than capable. I've been told that radius tips help increase the quality of the spot without leaving too much of an indentation. Does this sound correct?

-- Scott Hussey (scott@ecweld.com), July 14, 2004

Answers

All a radius electrode does for you is focus the heat. Essentially, you are reducing the surface area, creating more resistance,therefore focusing (and increasing) the heat. This is generally done to reduce sticking. The radius must be retained and very consistent, otherwise, you will have less consistancy than with a flat surfaced electrode. Your problem most likely is in either the maintenance of your electrodes, the tooling for the parts, or the parts themselves. Kurt Tolliver - Unitek Miyachi kurt(at)unitekmiyachi.com

-- Kurt Tolliver (kurt@unitekmiyachi.com), July 17, 2004.

That thickness of aluminum is tough. In addition to the tip radius issue, here is some added info.

Recommend 6 to 10 in. face radius. Also recommend 1" dia. electrodes. In addition, are you using class 1 copper tips? If not contact an electrode supplier for the right electrode material.

Is electrode cooling constant? If not, they will weld differently.

Are you using a 3 phase or DC machine? If not, electrode pickup can be more on a single phase machine than a 3 phase or DC machine. The electrodes weld differently with or without aluminum pickup (independent of tip radius). Hand cleaning of weld tips after as few as 10 welds was common in some mil spec aluminum welding in the recent past to keep the copper face bare, without aluminum pickup.

Is the aluminum surface pretreated? If it is stripped bare, then the time after cleaning and/or the use of hot water rinse can cause a major variation in the aluminum surface; causing a variation in resistance; causing a variation in weld size and strength.

Dr. McMaster (deceased), formerly @ Ohio State U. told a story about one of the fighter plane manufacturers in WWII having the same problem as you. Another manufacturer of the same plane was not. He visited the good manufacturer at midnight on a Saturday and saw the maintenance crew cleaning their clothes in the mil spec rinse tanks used to clean aluminum before welding; puttting a uniform contaminate in the rinse water which transfered onto the aluminum surface; making it very weldable. The other company did not. They used fresh stripping tanks and water rinse. The aluminum was so clean that there was little surface resistance, and variability from rapid oxide reformation.

My last aerospace employer would put raw aluminum in the cleaning tanks after the chemicals were changed to sweeten them. Subsequent aluminum from slightly dirty tanks welded better,

Another issue that occured in aerospace was the discovery that women's menstrual cycles affected aluminum welding on 28 day cycles if the aluminum was handled by a woman before welding. In one company with a lot of woman handlers, the menstrual cycles were tracked. During certain times of the month, women avoided handling aluminum before welding. I think it was around the period time.

One final note, if the aluminum is stripped clean, we found out in aerospace that the longest time after cleaning and before welding was about 14 hours in some applications. An aluminum oxide would form and go away and come back. Times between cleaning and welding had to be controlled to shorter time intervals or recleaning was necessary. In one case, the aluminum welded OK up until about 15 hours; then OK again after about 25 to 28 hours. Weird!

An alternative is to treat the aluminum with a stable oxide surface. Alodyne 1200 from the DC10 days and an FPL treatment were good ones. The aluminum manufacturers have some new ones now that involve a surface lube protective coating.

Some recent materials that I tested from both Alcan and Alcoa would last 6 months on the shelf and weld the same. Without the protective lube or with any change in the cleaning method, the material welded differently. A record of all process variables (cleaning, storage, welding) awareness of the allowables for variation, and strict maintenance to those process control levels is probably all necessary in mil spec aluminum welding.

There is a bunch more stuff about mil spec welding of aluminum, but that should get you by for a while.

From: wwwszabopublishing.com publishers of "Resistance Welding Safety for Operators" and 'Resistance Weld Schedule Development: process windows and weld lobes"

-- bob szabo (bob@szabopublishing.com), August 15, 2004.

Dear Mr. Scott Hussey

I've just come back after commissioning a 400 kVA 3 phase machine for a fighter aircraft manufacturer in India and achieving these figures was not a problem. The machine that we manufactured included closed loop voltage & frequency compensations. However, the excellent qualities achieved could also be because we had excellent guidelines from the aircraft manufacturer.

My suggestion is :

1. use freshly cleaned material - this is v.v.important for consistency

2. choose a Class 1 (CuCd) electrode with dia 1" & tip radius of 4"

3. weld with about 140 to 160 milliseconds with a forge program

4. if you are having a problem with the nugget dia try increasing the tip radius to 6"

Are you using a Frequency Converter machine or a 3ph DC or MFDC machine ?

Contact me offline at prithvish.chakravarti@sondertech.com if you need further help.

Best regards

Prithvish Chakravarti

-- Prithvish Chakravarti (prithvish.chakravarti@sondertech.com), September 09, 2004.