I certainly don't intend to speak for Lawrence but I sense his meaning was, not that he isn't aware of an effect that stirring would have, but what practical advantage does it serve.
From my point of view, if the main benefit from stirring is mixing the junk being pushed at the leading edge of the solidification front then I suppose the question changes somewhat to: 1) does it actually do this or does preferrable homogeneously tending soldification still force S, Ph, etc. out ahead of itself (is there still tramp segregation)?
And assuming it does, as I do 2) Is this an advantage over simply reducing heat input in non pulsed GTAW which has proven successful in eliminating hot cracking, along with reduced tramp content?
I think you're on to something with magnetic stirring which eliminates the necessity for pulsing, and can maintain productivity, though with tubes in your application the difference is probably negligable.
But again, I would ask, does it solve a practical problem? And does the solution to this issue justify the added cost and complication?
Has hot cracking become an issue in particular alloys where reduced heat input is ineffective? Having argued this, it does seem to me I read something about an alloy where this does indeed help. I can't remember off hand though.
But the argument would then be, is it justified beyond these special alloys?

Hey Henry!

Thank you so much for your kind answer and  - of course - your willingness to talk and collaborate with me. Please know that it is truly a great pleasure and honor for me to have the opportunity to learn from yours and the other fellows always brilliantly replies and advices!

CMT...

Well, fortunately I can say that I am working with FRONIUS since ~ 10 years, and I am truly proud of being a member of this fantastic company! Although my Forum activities are, and should honestly not be influenced by the job I am performing at FRONIUS. Here in the AWS-Forum I am only active as the Individual AWS-Member "Stephan" (due is paid by myself) and nothing else more, i.e. no kind of "advertising" will be found, coming from my side. Nonetheless I guess that I would be able for giving you any information about the FRONIUS Cold Metal Transfer process you would be interested in to get to know - of course. Why not, it's really a great and impressive process and one of my main activities in FRONIUS is to managing complete large industrial projects on a global customer level where CMT is being used for joining thin sheet metals.

I can confirm what you say when you are talking about using this process for substituting processes like GTAW or PAW or - at least - using CMT as an economical precious and considerable alternative to these processes. Many welding-experts do currently consider about using CMT as a more economical but with regard to quality absolutely comparable process to the non consumable processes like TIG or Plasma-Welding. Therefore, when you need specific, i.e. in depth technical information, please feel free to define any question and it would be a great pleasure for me to try to answer these questions as good as I am able to and to give you any material which is available in regard to CMT and the applications where the process is already being used! Meanwhile there are a lot of these...

Thank you also for your reply with regard to Laser-GMA-Hybrid-Welding. Your "hint" regarding the use of the "correct" acronym is precious for me. Please know that there was already a lively discussion about the correct terminology for Laser-Gas Metal Arc-Welding on the IIW-Assembly 2005 in Prague (Czech Republic). Should it be named Laser-GMA-Hybrid Welding, or better GMA-Laser-Hybrid Welding..? A very worthwhile input came from a Japanese fellow (I am sorry for not being sure who it was). He stated that it should be reasonable to distinguish precisely between the both process variants mentioned above. Because they are definitely not the same. Therefore one has to define firstly when talking about Laser-GMA-Hybrid Welding which of the combined energy-sources is the dominantly of both, Laser or Arc. This again can be done by finding out what the specific process details (mainly the spatial distance between Laser and Arc) are. This means, is the Laser being used to perform the inner seam properties (depth of fusion etc.) and "only supported" by the arc - thus the GMAW process being used for performing mainly outer seam properties (appearance, throat etc.) - the Hybrid-process should be defined as »Laser-GMA-Hybrid-Welding«. However, is the Arc again the dominant energy source, being used e.g. for increasing the deposition rate and the Laser "supports" the arc mainly firstly for increasing the deposition speed and only secondly for increasing the depth of fusion, the process should be named »GMA-Laser-Hybrid-Welding«. Although, from my personal point of view a real "Hybrid"-Process should be defined by a close spatial distance between the Laser- and the Arc-Energy Source resulting in a common weld-bead and using both processes advantages in an optimal way. I have read about some "Laser-Arc-Hybrid"-Applications where the Laser and the Arc have been positioned with 15 mm spatial distance to each other, thus - from my point of view - you will receive two welding processes: Laser-Welding + Gas Metal Arc-Welding but not a »Hybrid-Process« at all. And this is - also from my point of view - the true art and crucial point of real Laser-GMA-Hybrid Welding. Ensuring that both processes can be used in an optimal, stable combination by having the optimal equipment for achieving reproducible optimal qualitative and economical results. And here some very interesting and most sophisticated applications also in relatively thin sheet metal welding by using Laser-GMA-Hybrid Welding can be stated intermediately.

Therefore once again thanks for the hint with the process' acronym. I guess it is very important to work on the fundamentals of process designations and definitions before expecting that the process will find its way into the industrial production. If you allow I would like to cite you on the IIW-Meeting over the next three days in Spain. I am sure that your predication about the acronym shows one of the to be answered key-questions in regard to Hybrid-Welding, i.e.: "What is Laser-GMA-Hybrid Welding in general?" "Are there specific differences?" "How can it be used for improving quality and efficiency?" etc. etc. Most of the engineers I am talking to about Laser-GMA-Hybrid Welding do see only the (not low) invest for the Laser and therefore saying "No" to this great process. But when considering all the facts with regard that the process can increase both quantitative and qualitative output in a never known way, many of these people say: "Hey, this is interesting and it is worthy to think a bit more about it!"

I am personally one of the greatest admirers of the process. Not only due to the technical (and physical) aspects by combining both Laser + Arc but also due to the real benefits the process can bring by being used e.g. within High-Volume production.

If you allow, I will keep you informed about what has been discussed in Vigo Spain...

My very best regards,
Stephan

Hey Henry!

I must apologize for "almost" having forgotten to provide the promised information with regard to the discussions about the definitions for Laser-Arc-Hybrid Welding on the Joint Meeting of the IIW Commissions IV and XII in Vigo Spain.

Firstly, it was - once again - a very impressive opportunity for me, to attend an IIW conference. A lot of national and international experts have travelled to Vigo to discuss the current status of the industrial utilization of:

·  "Arc augmented" Laser Processes (Prof. Muneharu Kutsuna - Nagoya University Japan)
·  "Hybrid Laser MAG Welding Processes" (Mr. Chris Allen - The Welding Institute England),
·  "Hybrid-Welding" (Mr. Ambroise Vandewyckele - AIMEN Institute Spain)
·  "Laser-MAG-Hybrid Welding" (Prof. Muneharu Kutsuna - Nagoya University Japan)
·  "Laser Submerged Arc Hybrid Welding" (Prof. Dilthey - ISF University of Aachen Germany)
·  "Hybrid-Laser-Welding" and Laser-Hybrid-Welding" (Prof. Danut Iordachescu - Centro Laser University of Madrid Spain)

As you certainly can imagine, there have been held some pretty fine presentations from all over the world and - what was once again impressive for me - almost all experts have used different acronyms for the process, which all were discussing about(!).

As promised, and I hope you have allowed ;-) , I have tried to start the technical discussion about the "correct" technical term(s) to be used, when talking about "LASER-ARC-Hybrid Processes". I have mentioned to having an interesting interchange with US-American Welding Experts about the question of what Laser-Hybrid-Processes really are and how to define the combination of both used processes. And, Henry, what should I say else than the truth, also the venerable experts are seriously intended to clarify this basically question to pointing the direction for a better understanding of the process. I have asked - since the presentations been held treated of course different fields of Laser-Arc-Hybrid applications - several times of what the main reasons were, to name the process within the presentation such as can be seen in the list above. As you surely can imagine all the aspects therefore sounded reasonable, but nonetheless all the fellows admitted that there is yet a lack of standardization in regard to the general technical terms for the process.

When I have asked the question: "At which distance between the Laser and the Arc we can speak of "LASER-ARC-Hybrid" or different to that only "Arc assisted Laser-Welding"?" the most reasonable answers were given by Prof. Kutsuna and Prof. Dilthey who both are admitted as two pioneers in the field of Laser-Arc-Hybrid Welding. They replied, by using the term of "common interaction" of both process-plasmas which has to be observable when speaking of "Laser-Arc-Hybrid Welding". This means, there can not be stated or defined, respectively, a specific distance between the Laser and the Arc for defining a concrete use of the term "Laser-Arc-Hybrid Welding". Mainly because - as always - the coherences, specific to the application to be carried out by using the process, are so intricate that it's hard to find even this specific value! Or in other words... the boundary conditions are "fluently" (i.e. dynamical). However, when such an interaction of both energy source process plasmas (Laser + Arc) can be observed, one can talk of having a "Laser-Arc-Hybrid Welding Process".

Finally I would like to cite some sentences coming from the greatly appreciated fellow Prof. Dan Iordachescu, written down in the conference proceedings. As you perhaps can remember, I have mentioned Dan a time ago in another post, as one of the "driving forces" on an international level for solidifying the standardization of the "Metal Droplet Transfer Classification" in GMA-Welding. In Vigo, once again Danut Iordachescu was one of the fellows who have expressed seriously the necessity for finding common valid terms or acronyms, respectively, when speaking of Hybrid-Welding Processes. Therefore please let me cite what he has written in the proceedings:

"Important development of Laser Hybrid Welding (LHW) was noticed in the last decade, following the path from research to industrial application in shipbuilding [..], automotive [..], aircraft [..] and other industries. This generic name and concept is widely understood as combination of two classic processes: GMA Welding and Laser Welding (LW), respectively. Because the Hybrid concept may involve any two or more different welding/brazing/joining processes, it is welcome to state clearly what processes are involved. Thus a more correct name could be Laser-GMA Hybrid Welding. For the sake of simplicity, everybody admits that LHW without any other specification addresses Laser-GMA Hybrid Welding. On the other hand, the name Hybrid Laser Welding can be found in many issues..." "...We find this denomination as inappropriate, because not laser, but the welding process is hybrid..." "...When approaching LHW, specialists have a look firstly at the advantages of arc welding: low cost energy source, gap bridgeability, microstructure that can be influenced etc. On the other hand, the advantages of using Laser Welding are also clear: increased penetration, high welding speed, low thermal influence, high mechanical performances at the joint. As a holistic approach, LHW is meant to bring low heat input, low deformation, better metallurgical quality, higher welding speed, low distortion, higher bridgeability and lower spattering, as too..." (quote Prof. Dr.-Ing. Danut Iordachesu - Conference Proceedings of the IIW Intermediate Meeting Commissions IV and XII, Vigo, Spain, 11-13th April 2007).

As you can see Henry, I guess here is a lot of future work to do before we all can use the correct acronym for Laser-Arc Hybrid Welding, I hope you may agree with me.

But nonetheless I am sure that all the people who are involved in either using the process as a great alternative to "conventional" welding processes or who are involved in Research and Development are on the right way for finding these terms in the future. From my very personal point of view, the first steps have been done already only by having seen that there is the necessity to create a common valid predefinition of terms, for at least helping the potential process-user to basically understand what he is talking about.

My best regards,
Stephan