ARCTEKJim

TIG Welding
Tungsten inert gas (TIG) welding became an overnight success in the 1940s for joining magnesium and aluminium. Using an inert gas shield instead of a slag to protect the weldpool, the process was a highly attractive replacement for gas and manual metal arc welding. TIG has played a major role in the acceptance of aluminium for high quality welding and structural applications.
Process characteristics
In the TIG process the arc is formed between a pointed tungsten electrode and the workpiece in an inert atmosphere of argon or helium. The small intense arc provided by the pointed electrode is ideal for high quality and precision welding. Because the electrode is not consumed during welding, the welder does not have to balance the heat input from the arc as the metal is deposited from the melting electrode. When filler metal is required, it must be added separately to the weldpool.
Power source
TIG must be operated with a drooping, constant current power source - either DC or AC. A constant current power source is essential to avoid excessively high currents being drawn when the electrode is short-circuited on to the workpiece surface. This could happen either deliberately during arc starting or inadvertently during welding. If, as in MIG welding, a flat characteristic power source is used, any contact with the workpiece surface would damage the electrode tip or fuse the electrode to the workpiece surface. In DC, because arc heat is distributed approximately one-third at the cathode (negative) and two-thirds at the anode (positive), the electrode is always negative polarity to prevent overheating and melting. However, the alternative power source connection of DC electrode positive polarity has the advantage in that when the cathode is on the workpiece, the surface is cleaned of oxide contamination. For this reason, AC is used when welding materials with a tenacious surface oxide film, such as aluminium.
Arc starting
The welding arc can be started by scratching the surface, forming a short-circuit. It is only when the short-circuit is broken that the main welding current will flow. However, there is a risk that the electrode may stick to the surface and cause a tungsten inclusion in the weld. This risk can be minimised using the 'lift arc' technique where the short-circuit is formed at a very low current level. The most common way of starting the TIG arc is to use HF (High Frequency). HF consists of high voltage sparks of several thousand volts which last for a few microseconds. The HF sparks will cause the electrode - workpiece gap to break down or ionise. Once an electron/ion cloud is formed, current can flow from the power source.
Note: As HF generates abnormally high electromagnetic emission (EM), welders should be aware that its use can cause interference especially in electronic equipment. As EM emission can be airborne, like radio waves, or transmitted along power cables, care must be taken to avoid interference with control systems and instruments in the vicinity of welding.

HF is also important in stabilising the AC arc; in AC, electrode polarity is reversed at a frequency of about 50 times per second, causing the arc to be extinguished at each polarity change. To ensure that the arc is reignited at each reversal of polarity, HF sparks are generated across the electrode/workpiece gap to coincide with the beginning of each half-cycle.

Electrodes
Electrodes for DC welding are normally pure tungsten with 1 to 4% thoria to improve arc ignition. Alternative additives are lanthanum oxide and cerium oxide which are claimed to give superior performance (arc starting and lower electrode consumption). It is important to select the correct electrode diameter and tip angle for the level of welding current. As a rule, the lower the current the smaller the electrode diameter and tip angle. In AC welding, as the electrode will be operating at a much higher temperature, tungsten with a zirconia addition is used to reduce electrode erosion. It should be noted that because of the large amount of heat generated at the electrode, it is difficult to maintain a pointed tip and the end of the electrode assumes a spherical or 'ball' profile.
Shielding gas
Shielding gas is selected according to the material being welded. The following guidelines may help:
Argon - the most commonly-used shielding gas which can be used for welding a wide range of materials including steels, stainless steel, aluminium and titanium.
Argon + 2 to 5% H2 - the addition of hydrogen to argon will make the gas slightly reducing, assisting the production of cleaner-looking welds without surface oxidation. As the arc is hotter and more constricted, it permits higher welding speeds. Disadvantages include risk of hydrogen cracking in carbon steels and weld metal porosity in aluminium alloys.
Helium and helium/argon mixtures - adding helium to argon will raise the temperature of the arc. This promotes higher welding speeds and deeper weld penetration. Disadvantages of using helium or a helium/argon mixture is the high cost of gas and difficulty in starting the arc.
Applications
TIG is applied in all industrial sectors but is especially suitable for high quality welding. In manual welding, the relatively small arc is ideal for thin sheet material or controlled penetration (in the root run of pipe welds). Because deposition rate can be quite low (using a separate filler rod) MMA or MIG may be preferable for thicker material and for fill passes in thick-wall pipe welds.
TIG is also widely applied in mechanised systems either autogenously or with filler wire. However, several 'off the shelf' systems are available for orbital welding of pipes, used in the manufacture of chemical plant or boilers. The systems require no manipulative skill, but the operator must be well trained. Because the welder has less control over arc and weldpool behaviour, careful attention must be paid to edge preparation (machined rather than hand-prepared), joint fit-up and control of welding parameters.

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custom built t tops/towers/hardtops etc
www.arctekmarine.com CLINTON, CT

FMF

You can't possibly spit all these facts out by memory.....excellent read!

ChuckA

Definately good info up there ,I've been welding steel with arc and mig welders for 30 years ,So I tried tig welding 2 pieces of aluminum I can make some pretty good snots It is an art of a quality craftsman to do the work that comes from Jims shop,I'm going to know how to weld that stuff one of these days .It amazes me to watch straight pieces of aluminum tubing become a custom T-top or arch. AWESOME and the is good too

workskiff

Greetings all,

I am self taught in virtually everything I do and consider myself to be possesed of above average mechanical ability and a stick-to-it mentality that has served me well enough to learn things like MIG welding, cabinetry, fiberglass work, solid surface material fabrication and even bicycle frame building (brazing). And I have this tendency to acquire tools prior to knowing what to do with them. So....

I bought a Miller Syncrowave 200 this past summer and managed to do some welding on mild steel with it but of all the things I've tried to teach myself this seemed to be most challenging and am thinking that I would benefit from some professional instruction. I'm not looking to make a career of it or anything, I just like making stuff. I have an aluminum boat and at some point I'd like to be able to do my own mods but wouldn't dare touch it right now. I live in Fairfield Co. CT an would appreciate any leads on instructors/classes. Thanks for reading.

workskiff

...for some practice material and some urging to think about doing the repairs on my skiff myself. I have burned up about 3 lbs of a 5 lb box of 1/8" 5356 rod. The early going was frustrating but I have made some real progress. In addition to the drops you gave to practice on I went over to a local scrap yard and picked up some 5052 and 5086 sheet in 1/8" and 3/16" thicknesses to practice on. First I tried just drawing a staright bead, then learned how to feed filler (the hardest part), then I drilled and filled about 100 holes in various positions to give me practice for filling the holes in my boat. I also practiced making butt and fillet welds and can do them pretty nicely now but only on the thickness and material I had. The practice has taught me how filler, heat, and preparation all play a part in the outcome of the weld. I'll give it another week of practice trying to put in 20-25 more hours before firing up the torch on my boat. Next up is learning how to use the thumb control I just bought for out of position stuff. Thanks again for the helpful tips during my visit to your shop. Still a ways to go before putting in an applcation at ARC TEK but I'm on my way!

ARCTEKJim

wheres my 20 hp suzuki??? lol.........

__________________
custom built t tops/towers/hardtops etc
www.arctekmarine.com CLINTON, CT

workskiff

I'll come by the shop beginning of next week and drop it off because I 'd like to clear it out of my garage while I have my boat in there for work. We'll work something out because I'll still need you to do the higher amperage stuff and most assuredly the work that requires serious skills like welding a transducer bracket on the transom and some tabs on the floor to mount the center console. Filling holes I'll be glad to try but the real work I'll lleave to a pro. See you next week. Thanks again!!

old mud

HEY jim: GOOD tech. info. Thanks!! .........Don

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