GMAW Pulse WPS

By Lawrence (*****)

Date 12-06-2010 22:03

I admit I'm not where the rubber meets the road on this issue but for what it's worth I think the following.

Each model of GMAWP power supply (even different models within a brand and ***Even the same model with different software updates) are going to produce different average current and voltage readings and It prolly takes a high end oscillascope and MIT masters degree to accuratly determine the numbers.

But if the visual and mechanicals are being met. Why not record the specific settings for each control... Down to crater times/speeds, hot start speeds/percentages and times, trim, wfs and propriatary program numbers and software/pulse program update numbers.

This will give you more consistancy in production and probably satisfy code/contract requirements.

Since most of these settings can be recoreded in percentages or tenths of a point digitally a production WPS can be generated later that have parameter ranges that fit the scope of the code.

To distill all that blather... Record what works in the language of the power supply.

By TimGary (****)

Date 12-07-2010 13:20

Thanks for your reply Lawrence, I see your point.

Currently, our machines have the Wire Feed Speed locked in to the WPS range to ensure penetration requirements. By locked in, I mean the programmable feeder is not able to be adjusted outside the pre-set WFS range, by the welder.
The arc adjust and arc control settings are not locked and allow the welder to fine tune the machine in order to match the profile and bead size as required multiple joint configurations and bead sizes called out on the drawings. This is very useful in maintaining our weld quality requirements, which are much more stringent than those allowed by the codes.
My purpose is to include our existing WPS's into a new C-Spec database, making corrections where needed, and to add some new WPS's to the list. I'm working to D1.1, D1.3, D14.3 and B2.1.
I would much rather not further restrict our machines settings capability, unless absolutely required by the code.
As long as Pulse welding has been around, I'm disapointed that AWS barely even recognizes it as a viable transfer method and leaves so much open for interpretation.
OK, I'm done whining now...
Has anyone seen something in the codes, that I'm missing, that might clarify?

Thanks,
Tim

By js55

Date 12-09-2010 14:39

If your dealing with the AWS codes I do not believe they are even close to even considering a resolution to this technological problem. If your talking ASME then Marty be the man.

By 803056

Date 12-09-2010 20:19

The welding codes are behind the eight ball regarding the pulse transfer mode of GMAW. Part of the problem is that it is still in the development stage and no two companies have settled on the best way to achieve the best operating characteristics.

The codes list the minimum requirements that must be met. AWS is no different than ASME in that respect. The level of detail required differs from one code to another, but the similarities between the different codes are striking. The devil is in the detailed differences.

There is one issue that must be recognized when working with AWS D1.1, which is the power supply used for prequalified WPS when using either the GMAW or FCAW welding processes. D1.1 states that the power supply must be constant voltage (same as constant potential). That means the slope characteristics of the amp versus voltage must have a "flat" slope as compared to the drooping characteristics of a constant current power supply. Therein lies the problem, some manufacturers utilize a puling system where the relationship between amps and voltage varies with time and welding conditions. That simply means that the WPS must be qualified by testing per clause 4.

Qualifying a WPS for pulse transfer is complicated by the fact that no two models produced by the same manufacturer uses the same logic or the same programs when building the machine or programming the pulsing parameters. What that means in simple terms is that the PQR qualified is good for the one machine model used to weld the test coupon. That's a white lie, because if you have the wherewith all to monitor the welding parameters of the "host" machine with a multichannel oscilloscope and you faithfully record the parameters, you can program other machine models and the machines manufactured by other companies to operate like the "host" machine. However, few people and few companies have the luxury of having the necessary equipment and training to properly monitor the sophisticated parameters of pulsing systems.

ASME now requires the use of a power meter to record the "power" when welding with a pulsing system. Nice try, but I do not believe it is going to allow you to simply move from one machine to another and get acceptable results. It s a step in the right direction, but it falls short of what is needed to allow the user to qualify a pulsing procedure on one machine model and move to a different manufacturer or model power supply.

Just my thoughts on the issue.

Best regards - Al