We speak for at least three types of technologies that may be developed or have just realized with our participation:

  1. Usual technologies, which belong to regular welding-assembling processes coherent the use of coated electrodes and ordinary MIG, MAG and TIG processes, performing in shielding gases, under fluxes, with flux cored wires use as well as with the usage of contact-resistance welding
  2. Technologies of precision joining - especially those based on microplasma and TIG - argon welding
  3. Educational technologies

Here we only give attention to the second type of technologies since at present they are more problematic for a lot of customers which are interested in precision costructions' development and spreading.

Information about the materials, which were used, analyzed or investigated in our technological projects, one may read on www.pogrebis-temp.com/materials.html. Most mentioned above materials are welded with plasma method using direct current (electrode negative). Welding current also can be pulsed - in order to control penetration, heat input, metal structure of weld or its formation. For certain purposes we proposed a special shape of pulsed (modulated) current which gives some additional advantages - especially for edge and flanged welds (please, read our rubric author - Unique innovations). Variable polarity plasma arc welding power sources enhance the joining of materials such as aluminum and magnesium. The Paton Welding Institute developed the method of microplasma welding with the use of the reverse polarity current. During the impulse of staight polarity - between electrode (-) and workpiece (+) - the process of welding is realized, but before, when welding current is absent or interrupted, the impulse of reverse polarity - between plasma forming nozzle (+) and workpiece (-) - is made. Indeed, this latter impulse provides cleaning functions with respect to the surface of a workpiece, extracting from it tenacious aluminium oxides. Immediately after such cleaning welding strictly is produced - by current of staight polarity, which amplitude nearly 2 times exceeds the amplitude of reverse polarity current. Such complex square waveform of currents gives excellent results for welding of aluminium based sheets with thicknesses of 0,15 -1,5 mm. At the same time the tungsten electrode, working under only negative potential, shows prolonged working resource. But in this case helium or helium-argon mixtures are usually used as a shielding atmosphere. We have an idea for creating new technology and equipment that may allow making such welding within an essentially cheaper argon atmosphere.

Our rubric projects gives a list of the most noteworthy technologies, but it would be useful for anybody to see the previous site rubric www.pogrebis-temp.com/technologies.html, where the typical welds (made by plasma) are shown. Also we recommend to visit www.pogrebis-temp.com/last-projects.html.

Since we usually operate with currents of main plasma arc up to 100 A, the majority of technolgies are mostly devoted to :

  1. Microplasma processes, including welding with maximum currents up to 20-30 A.
  2. Medium-current plasma welding which current typically ranges from 20-30 A to 100 A.

Due to big currents of non-transferred arc (which one of our set permits) we may talk about such sets' widened technological possibilities, including, first of all - brazing, brazing-welding, local heat treatment and their combinations (please, see this site's rubric united - Cheap, safe and simple sets).

As compared with electron-beam and laser methods, plasma welding offers an advantage in tolerance to joint gaps and misalignment. Although the arc is constricted, the plasma column has a significantly larger diameter than the beams. Also adding filler metal is accomplished much easier without the risk of its contact with a tungsten electrode which hides inside of plasma forming nozzle. Such problem is usually exists during argon (TIG) welding that, none the less, is usually more tolerant to assembling conditions when compared with plasma welding. We, however, developed original technology and equipment especially designed for overcoming such conditions. One can find out more in the rubric united - Modular-inverter AMC-1 welder. During plasma welding an electrode can usually last for an entire production shift without the need to be regrounded. Developed with our participation plasma torch OB-2322 ( please, see our rubric equipment - Torches and heads) permits adjusting the electrode position with respect to a plasma forming nozzle with an impressive accuracy, without welding process stopping. At the same time the process may be easy transformed to the so-called " welding by stabilized arc" (please see article by D.I.Vainboim, G.V.Ratmanova 'Argon Arc Energy Characteristics Under the Conditions of Burning with Different Pressing Degrees', Svarochnoe Proizvodstvo, 1974, No.5).The stabilized arc (when an electrode goes inside the channel of plasma forming nozzle and may even come out of this nozzle) posesses the middle position between argon and plasma arc and it can open additional technological possibilities for joining processes during manufacturing and repairing of various thin-walled structures - especially when we need to use welding and brazing with a filler material supply or when connection conditions are not stable. As far as we concerned, this method has to be studied more carefully and urgently.

As compared with TIG, the arc of plasma welding tends to be more flexible and less affected by changes in arc length. This allows for longer arc lengths to be used, and that combined with the protected electrode can make it easier to add filler metal when welding manually. At the same time an electrode contact or contamination by the filler metal and the welding puddle completely eliminates.That is why the working resource of tungsten electrodes during plasma processing is much longer than during argon welding. The conical shape of a gas tungsten arc requires that arc length control or arc voltage control equipment be used for automated welding to ensure stable energy density and consistent weld puddle and weld sizes. Also during powderfeed plasma welding the weld puddle can be smaller and the powder rates better controlled to offer excellent weld characteristics. It may be practically used in any required composition of powder that can be made from different alloys which may be produced on a variety of materials. The welding skill level required for powderfeed welding is significantly less than with manual wirefeed. There is a positive experience in microplasma cladding (Kalina P.P, Yarovitsyn A.V. and Yushchenko K.A. "Peculiarities of the microplasma cladding process", Paton Welding Journal, N.4, 2005, p.7-13).

Going back to the beam welding processes, we can note that they are usually limited in sizes and a space position of treated by their help goods, require many rather expensive accessories and preparations, as well as the usage of very skilled operators, complex and, naturally, costly equipment, which sometimes brings ecological and gygienic problems (for health of working and surrounding personnel). In many cases, as compared with argon welding, plasma processes permit the usage of various shielding gases and their mixtures that may be less expensive than a pure argon (for example, nitrogen,carbon dioxide, etc.). Almost every time burning pilot arc helps to see the place which has to be treated and to begin plasma process - exactly at the needed point, so unqualified welders and even beginners may be often invited for manual plasma welding fulfillment as well as generally for welding fabrication.

Main comparative characteristics, or properties, of different joining methods that are valid for thin-walled structures manufacturing had been gathered by us in the followingTable (Wich has been also used in several places of this site):

Comparative

Properties
Joining methods
Gas Tig Plasma Laser Electron beam Resistance spot High frequency
Level of universality high high high limited limited medium limited
Productivity low medium medium / high high high high very high
Energy expences low low low/medium high high high very high
Ecologycal problems yes not not yes not not yes
Materials properties limitation yes almost not almost not without high reflective capability without easy evaporating components except silver and copper yes
Assembling quality demand low low low/medium high high medium high
Hygeinic demand medium low medium high very high medium medium
Post-joining deformations large quite large medium very small very small small small
Operator's qualification high high low very high very high low high
Working room (place) dimensions medium small small medium medium / large medium / large medium / large
Working piece sizes and location every every every limited limited limited limited
Equipment cost very low low medium high high medium medium / high

Thus, it is clear that plasma welding technologies are rather perspective for manufacturing of various thin and especially precision structures. Some of the examples are shown on www.pogrebis-temp/goods.html.

Modern welding tehnologies are often based on different methods combinations: e.g.TIG+PLASMA; PLASMA+LASER, etc. Such, so-called gybrid, methods permit to increase welding speed, quality, to obtain precision structures with improved characteristics. As an example of this one may refer to the research project for tube welding that was performed at the Edison Welding Institute using three torches to make a single-pass weld. Much earlier some working together plasma torches were used in Paton Welding Institute for thin-walled tubes producing (from strip rolls) with the speed of more than 400 m/h. We hope that the new sets and technologies that we propose provide additional possibilities in this direction as well as in the development of brazing-welding processes and - as an option - in microplasma spraying usage.

The readers of this site (which have especially interested in welding) are welcome to visit its rubric applications where one can find many interesting technologies which are mainly realized for the concrete industries, purposes and goods. It will help them to introduce welding and welding-brazing technologies for their aims.

Print this page