A review of a weld report on welding 60 mm tubular stainless 0.050
parts. The parts are typically used in catalytic convertors, flexible
fittings and exhaust components used on cars and trucks.

 

Aug. 2004.

The primary issue I found with these automated MIG welded parts was the 0.053 thickness. On MIG welded gage parts that are less than 0.075 “sensitivity to weld burn” through is the major concern on parts that are to be welded
with the spray transfer or pulsed transfer modes. The weld burn through issue is further compounded when the weld has to be larger to compensate for a gap or weld joint dimensional deviations.

This client used argon 2 oxygen, with 035, 1 mm, 308L, MIG wire. For the majority of the clients tubular applications which were greater gage thickness than 0.070 I had used spray transfer as it was more consistent and provided superior production than the pulsed modes available from the Miller pulsed weld equipment available on the Bancroft weld machines.

The traditional spray mode requires a minimum of approx. 180 amps with a 1 mm stainless wire and argon oxygen gas. The 180 amps and 24 volts was too hot for the 0.050 lap joints. Using the same wire and gas the traditional short circuit mode did not put out sufficient weld energy for this specific weld joint which had unique leak test requirements

Its not a decision I make often, however I decided that pulsed MIG was the logical choice. An evaluation of the suitability of the XMT 304 Miller pulsed power source attached to the Bancroft machines and an available Lincoln Pulsed Power MIG 300 power source took place.

On an application like this a wide, soft arc plasma is important for the 3/16 wide lap welds on the 0.050 parts. The Lincoln power source is simple to use and requires no pulsed expertise. I set the wire feed at 300 ipm. The Lincoln power source provided with the 035 wire a wide, soft plasma suitable for the applications.

Using the 035, 308L, wire and argon oxy gas mix set at 35 cu ft /hr optimum welds were produced with the tubular weld joint mounted vertical. This position greatly reduced the weld burn through potential.

Lincoln MIG 300 Power Source Procedure:
Set at the pulsed stainless program #32.
[] Wire feed 300 ipm.
[] Pulsed Average Amps delivered 113 amps.
[] Volts 20
[] Part Rotation speed 35 - 40 ipm.
[] Weld Cycle time 10 – 11 secs.

I tried to duplicate the low amp pulsed weld characteristics with the Miller XMT 304 equipment attached to the Bancroft machines. With the Miller equipment and a wire feed rate of 300 ipm, the built in pulsed weld schedule provided higher weld current with a narrower digging plasma. I also used the Miller pulsed program that allows
pulsed parameter adjustments. The Miller pulsed weld results were a disappointment. Achieving
a consistent pulsed MIG weld under 120 amps, a weld with a suitable plasma configuration was not going to happen with the Miller equipment.


Conclusion.

[a] If your company is designing stainless tubular parts less than 1.6 mm make sure the designers who typically dont have a clue about welding are aware of the potential MIG weld quality / productivity issues that will occur from their thin gage designs. God help them if they ever read a book on this dam subject.

[b] Be aware that the pulsed mode is recommended for this applications however as each pulsed power source provides different pulsed out put weld characteristics, the pulsed power source in your plant may not provide the optimum pulsed arc characteristics necessary for your gage stainless application.

[c] If this application had been steel, the pulsed mode would not have been necessary as there would have been sufficient weld energy from the traditional short circuit transfer mode.

[d] On applications sensitive to weld burn through, the weld position presented can dramatically reduce the weld burn through potential and provide consistent weld quality.

[e] This company was using 309 for the 304 applications. Use 308 for 304 applications instead of 309. The 308 is less sluggish provides better weld wetting and fusion.

A discussion was had on the necessary equipment required for this low to moderate volume application. Bancroft machines are great however they are also expesive. For this application the part can be successfully automatically welded on a rotary positioner (cost $1000, with the Lincoln power source, costs approx $4000 a fixed torch, costs $600 mounted on a bracket, a gun on-off switch and an arc on, arc off timer. The bottom line. For less than $6000 this application can be automatically welded with the same quality and productivity successas achieved from automated equipment that cost five to ten times more.

It's not often I thank Lincoln, but this time I thank them for producing a reasonable priced pulsed weld power source that actually provided a real world weld benefit. Please keep in mind that after 20 years of evaluating pulsed MIG applications, I could use the fingers on one hand to count the applications in which pulsed has provided weld benefits for steel applications.

 

A lttle weld reality from Ed Craig.