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Keyhole GTAW (or TIG) has similarities to keyhole plasma arc welding Keyhole PAW), and so a good first indication is whether or not you think keyhole PAW is a possibility. Of course this is not the whole story, but you will be looking at a welding application with the following constraints:
- You are most likely looking at production lines rather than jobbing shop work
- The welding must be automated
- Welding will be in the down-hand (flat) or perhaps the horizontal position
- You want to improve welding productivity
- You have good joint fit-up and presentation
- Material is typically 3mm thick or greater
- Material is not highly conductive (such as aluminium or copper)
- You desire a single pass process with simple I-joint preparation (i.e. square-butt)
- Full penetration is very important
Perhaps the most obvious application would be in a tube mill. In such a well controlled environment you can expect to get the most from the process with a minimum of disruption. If you consider, say, seam welding 6mm stainless steel at 500 mm/minute (20 inches/minute), without using any filler wire, the process could pay for itself within weeks. Of course the process can handle up to 12mm austenitic stainless steels in a single pass operation. Also, you will most likely have all the equipment you need to implement the process, other than the torch itself and operating manual.
The next ‘easiest’ application would involve joining large plates. Now you will need to take care with joint fit-up and your mechanisation system. But, the more expensive the material, the more you will like the process. The difference between joining plates and operation on a tube mill is that you will be more concerned with opening and closing the keyhole.
Pipe-to-pipe and pipe-to-flange work is next in line. Here the savings can be massive, (depending on the material and wall-thickness) but now keyhole opening and closing must be properly addressed. There are a variety of methods to deal with this, including programmed start and stop routines and the use of “Y” preparations with a keyhole root run followed by a filling pass, (a small sacrifice in productivity in return for ‘no hassles’). Please contact us if you are looking at such an application as we are soon to release products that will be of interest to you.
The pipe or flange must be rotated so that the weld can remain in the flat position, or alternatively, the welding may be attempted in the horizontal position.
Our packages are very reasonably priced, and we believe offer outstanding value for money. However, you will need to contact us for a quotation because we provide a range of packages depending on your requirements and existing facilities. Bear in mind that as a minimum the process requires the following:
- a keyhole welding torch
- a technology transfer package (if you do not already operate the process)
- a 600 to 1000 amp DC constant current welding supply
- water cooler
- arc ignition capability (HF, HV etc)
- appropriate mechanization for the application
Note that Ultratig does not supply welding power sources or mechanization.
One of the satisfying aspects of this process is that it is a variant of the traditional TIG welding. This means that for most welding people coming to terms with this process is a matter of building on their existing knowledge. So many aspects will look familiar – choosing the best electrode, grinding the tip, selecting the right shielding gas, setting the welding parameters. Of course there are some ‘secrets’ as well, but allow yourself a day or so to get the feel of it and you will be ready to go.
Opening and closing the keyhole can be an issue, just as with other keyhole processes. The problems posed are very much dependent on the circumstances – it probably is of no concern on a tube mill, but will be the main issue when joining pipe sections. Generally it is recommended that a well-controlled start-up or close-out procedure is developed and proven before committing to production. The two factors of most concern are the material thickness and the pipe diameter. Controlled ramping of the welding current is likely to be needed if the wall thickness is over 8mm (3/8”) or the pipe diameter is under 200mm. In some instances wire feed may be used for crater-filling.
Ultratig is soon to release an upgrade that largely eliminates concerns in this area. Please watch our “What’s New” pages.
With modern communications technical assistance is only a phone-call or email away. Furthermore, as the process is based on conventional GTAW (TIG) and tends to use conventional equipment, problems can usually be resolved in-house quite quickly. Nevertheless, Ultratig is aware of the need for rapid access to hands-on technical support and spares will always be valued, and is taking the necessary steps to ensure this will be the case.
Keyhole TIG can be a real advantage to you even if the material is too thick for a single pass keyhole weld. In such cases it is suggested that you present the joint with a Y preparation. The keyhole mode can then be used to supply the root pass, and subsequent filling runs using Tig, mig or submerged arc can then be minimized. For example a 13 mm steel plate could be prepared with say, a V with a 7 mm landing. The joint would then be completed in two or three passes – a high speed keyhole root pass followed by one or two mig passes.
Once again you are advised to keep track of the “What’s New” pages as Ultratig is currently developing methods to extend the range of the process.
The process can be operated very successfully with back-purge. However, if not correctly applied a build-up in back pressure will occur and seriously disrupt the process. Back-purge units designed for non-keyhole processes generally will not be suitable. Please talk to us if your application requires back-purging.
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