07 Tig Einsatz Neuer Technologien Beim Wig Schweissen Gb

8/9/2019 07 Tig Einsatz Neuer Technologien Beim Wig Schweissen Gb

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Fronius Power Plus

INTRODUCTION

The Fronius Power Plus range of microprocessor-controlled power sources for MMAW, TIG-DC and TIGDC/AC welding represents yet another step forward in the field of inverters for use in the construction-site

and workshop sector.In the development of its modular Magic Wave 2600 and TransTig 2600 machine systems, Fronius onceagain gave top priority to the needs of the welder, meeting these with a highly user-friendly design of unitthat does not intimidate the user with an excess of technology for technologys sake.As the Fronius philosophy sees it, a welding machine will ultimately be judged not by the type and quantityof the technology that it incorporates, but by the welding results which it obtains, and by how user-friendlyit is.

THE PLUS FOR TIG WELDING OF ALUMINIUM

Aluminium and its alloys are normally TIG-welded using AC (= alternating current).Before the base metal can be melted (fusion temperature approx. 650 C), it is first necessary to destroythe refractory oxide layer above it (AL 2O 3, S fusion temperature approx. 2000C). The oxide purging action

only occurs when the tungsten electrode has positive polarity, however. In the plus phase of thealternating current, anions (positively charged atoms) escape from the plus pole and impact upon theoxide layer at high velocity.The kinetic energy released by the impacting anions destroys the oxide layer (purging action), and in thesubsequent minus phase the exposed base metal can be melted.

CLEANING FUSION

Fig.1: The TIG-AC welding process, showing the periodic purging/melting actions

When the alternating current periodically crosses the natural zero, a momentary arc extinction takesplace. The arc is re-ignited either by superimposing high-frequency ignition impulses, or by ensuring asteep-sided, square wave alternating current. Each of these methods has its specific advantages anddisadvantages. The change to the arc column resulting from the current change causes an acousticemission, in a similar way to a loudspeaker. Trials have shown that different welding-current wave-formscause different types of sounds on account of their harmonic waves.Sinusoidal currents are very quiet, but have the disadvantage that a high-frequency impulse is needed inorder to re-ignite the arc after the zero crossing. Square-wave power sources have no need of any suchsuperimposition; however, the price that has to be paid here for a stable arc is a very high noise level.Many attempts have been made, over many years, to realise the solution to this problem - that is, a stablearc combined with a low noise level. With the aid of fuzzy logic (a type of logic modelled on the way thathuman beings think) and some elaborate hardware, the first-ever practicable solution has now beenfound.A fuzzy adjustment of the welding-current wave-form is used to set the physically quietest arc for anyparticular amperage. The importance of this lies in the fact that the welders ability to listen to the arc noiseplays a crucial role in enabling him to achieve a correct weld.Over the entire amperage range of the Magic Wave 2600 (5 to 300 A), the arc is beneath the sound-levelthreshold above which the relevant industrial health and safety regulations stipulate that hearingprotectors must be worn.A further result of this hardware/software combination is the stable AC arc, which does not lose any of itsproperties even when large areas of pure aluminium are melted or when existing weld beads are weldedover.


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Fig. 2: Continuous AC waveform generation using fuzzy logic

The high arc pressure that results from the form of the arc column ensures very exact fusion of fillet-weldroots - yet the Power Plus inverters still place only a low load on the electrode. This results in better weldgeometry and thus an optimum arrangement of the lines of force.

Fig. 3: Comparison of root fusion on fillet welds with different cap diameters

The cap-formation process functions automatically, and is activated from the torch trigger. Compared tothe conventional method of forming the cap on a copper plate, this saves a great deal of time and makeswork much easier.

THE PLUS FOR ARC IGNITION

The ignition characteristics of the machine are one of the principal criteria by which a power source shouldbe assessed. A rapid rate of current rise and correct dosage of the ignition energy for a pre-selecteddiameter of electrode together lead to a rapidly stabilising ignition phase.

The RPI (Reversed Polarity Ignition) process (only available on the MW 2600) improves ignition of theTIG-DC arc.In RPI, the plus pole is transferred for fractions of a second to the (usually negatively poled) tungstenelectrode, greatly facilitating the formation of the arc column.RPI is mainly used in mechanised and automated applications, as it is particularly important to ensureabsolutely troublefree ignition in these cases.

THE TECHNOLOGICAL PLUS

Thanks to the realisation of the inverter principle with an elementary frequency of 80 kHz, it was possibleto reduce the weight of the AC/DC power source to only 30 kg (gas-cooled machine). Not only this, but theoutput power was increased by just as much as the weight was reduced - to an impressive 300 A! With a

generous 60 percent at 40C ambient temperature, the duty cycle leaves plenty of reserves, even in thishigh current range. At the rated output, continuous operation with a 100 percent duty cycle is possible.


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The safety of the welder is naturally right at the top of the priority list. The machines thus come asstandard with the CE mark and the S mark (for operation under conditions of increased electrical hazard).The safety Standard EN 60974/1 for welding power sources stipulates IP 23 as the degree of protectionnecessary for safe outdoor operation.The meaning of the figure 23 is as follows:2...Protection against penetration by foreign bodies of over 12 mm diameter 3...Protection against spray-water from the vertical and up to an angle of 60 degrees

After the prescribed spray-water test (duration 10 min) the clearances and creepage distances aresubjected to high-voltage testing to ensure complete galvanic separation of the welding potential and themains potential. Thanks to its engineering design, the Power Plus passes this test with flying colours.Since 1.1.1996, compliance with the EMC directive EN 50 199 (Electromagnetic Compatibility for ArcWelding Machinery) has been mandatory.The Standard lays down both maximum permissible limits for emitted interference and minimumrequirements for interference immunity. A further condition that has to be met in order for a machine tobear the CE mark is compliance with the low-voltage directive 73/23/EEC.

Fig. 4: Power source

5. THE PLUS WITH THE TRANS TIG 2600

In order to meet the varied requirements in the pipeline construction field in terms of different pipediameters and wall-thicknesses, both the TIG welding process and safe vertical-down welding of celluloseelectrodes are used.In terms of their output characteristics, however, both these weld processes make different requirementsof the power source used. The Trans Tig 2600 delivers superlative welding results with both processes.

THE PLUS IN TERMS OF DESIGN

Another big plus is the new design of the machines. Not only because this makes them good to look at,but even more importantly, because it makes them so exceptionally user-friendly. The starting point for thevery many detailed solutions which the machines incorporate was a comprehensive analysis of user

needs. Ease of handling and service are the principal results of the collaboration which took place herewith an experienced industrial designer.The controls of the power source have been designed to cope with the rough-and-tumble of theworkplace. The number of separate controls (all of them in recessed, protected locations) has beenreduced to a minimum with the aid of an expert system, so as to make the arrangement of the controlpanel as straightforward as possible.Behind the spatter-resistant surface of the control panel there is both a clearly laid-out display for thedigital amperage and voltage indications, and several program levels in which many different machineparameters can be individually varied.Together with the integral hosepack and cable-holder, the detachable carrying strap makes the machinesmuch easier to move around.


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Fig. 5: Integral cable holder

Fig. 6: Integral welding-torch holder in travel carriage

THE PLUS WHEN IT COMES TO EXTRAS

When it comes to ensuring an optimum welding result and the greatest possible flexibility, it is essential toconsider the system as a whole. For this reason, the functions outlined here are complemented by a well-rounded assortment of useful additional functions which are a very valuable help to the user.Examples include:Magic Cleaner Set, for electrochemical removal of tarnish discoloration on high-alloy steels.Continuous welding-current regulation directly from torchExtensive range of remote-control unitsAnti-theft lock (electronic code)

Authors:Bernhard Freiseisen(Power Plus Project Manager)

Heinz Hackl (Head of Research & Development Department),both: Fronius International GmbH Austria, A-4060 Wels/Thalheim, Austria.

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07 Tig Einsatz Neuer Technologien Beim Wig Schweissen Gb