Taking the Mystery out of Micro TIG WeldingTaking the Mystery out of Micro TIG Welding

Editor's note: Welding to repair, maintain, and change toolsis still very much an art in the injection molding industry. Still,the last few years have seen the introduction of a number of productsdesigned to help make the process easier and more precise. SteveBales, president of Bales Mold Service Inc., has developed someguidelines in the application of micro TIG welding and offerssome insight on how it's best used.

MicroTIG welding is not new technology; it's been available for morethan 10 years (TIG is an acronym for tungsten inert gas). Mostpeople in injection molding have heard of it, and I would wagermost have used it. But the fact remains that many people are stillsomewhat in the dark regarding its uses, advantages, and disadvantages.

Micro TIG welding is identical to conventional TIG weldingwith a couple of important differences. Both use tungsten to createthe arc for the weld, but the amp range and size of the fillerrod and tungsten differ. Conventional TIG welding uses a muchgreater heat range than micro TIG welding, making the two idealfor very different applications.

The amp range in conventional TIG welding is about 50 to 250amps, as compared to the range for micro TIG welding, which isbetween 5 and 50 amps. Micro TIG welding also uses a filler rodthat measures only between .005 and .015 inch in diameter-notmuch thicker than a strand of hair. Compare this with traditionalTIG welding, which uses rods that typically measure .0625 to .125inch in diameter. Additionally, micro TIG includes the use ofhigh-tech optics and lighting; these are critical to maintainingthe extremely small arc gaps necessary for low-amperage welding.

A Myth Dispelled

Of the many misunderstandings that surround micro TIG welding,one in particular stands out. It is that conventional TIG weldingcan do just as good a job repairing a mold or mold component asmicro TIG welding. The truth is, conventional TIG welding, inall its accepted, tried, and true forms cannot provide the samequality, fine weld bead as micro TIG. Nor can conventional TIGwelding provide the same control offered with micro TIG welding.

It makes sense that a welding shop would use conventional TIGwelding for larger repairs, and micro TIG for the finer, smallerrepair jobs. Both provide value. However, it is the microscopeand fiber optics used with micro TIG welding that enhance theability of the operator to enter areas previously inaccessibleusing conventional TIG welding techniques.

Finish Work

While most repairs done with micro TIG welding are quite small,there will always be the need for some kind of finishing. Typically,these repairs can be reworked by a skilled polisher without requiringsecondary machining. One of the benefits of micro TIG weldingis that most of the time the finishing process is minimal. Whenthis happens, it's thanks mainly to the skilled micro TIG welder'sability to deposit only enough weld material to complete the repair.

Properly used with strict adherence to good welding techniques,micro TIG welding provides a platform for efficient pre- and postweldpreparations. Such techniques include in-depth inspection of surfacecontaminants and oxidation, removal of cracked or damaged materialaround the area to be welded, careful control of critical pre-and postheat temperature, and the ability to produce a weld withminimal or no sink at the heat-affected zone-all of which cansave time and money.

Long-term Savings

Because you have more control over the pre- and postheat temperature,micro TIG welding generally causes far less residual stress inthe mold or component being repaired. Conventional TIG weldingcan cause added stress to the area around the weld, increasingthe possibility of premature failure at the welded area.

Micro TIG is a low-current, localized weld that can't createthat kind of costly damage. Heat is the enemy of dimensional stability.Because micro TIG welding produces minimal heat and buildup, aswell as easily machinable welds, the process helps maintain thestructural integrity of the mold or mold component. As mentionedearlier, micro TIG welding leaves few or no sink marks.

The Down Side

For all its potential to do good, there is one primary disadvantageto consider when using micro TIG welding. Too often, many weldingcustomers request micro TIG welding for repair jobs that requirea heavy accumulation of weld.

They see the advantages, such as less stress to the mold orcomponent, but they don't realize that, for example, a 1-by-1-inchweld is not suited to micro TIG welding because it simply takesfar more time to fill. This makes it a costly process where conventionalTIG welding could have rectified the situation in far less time.

So do yourself and your welder a favor. Request the properkind of welding for your repair job. Better yet, use a welderwho knows his craft. An honest craftsman will not only refuseto fill large welds using micro TIG welding, he or she will explainwhy and show you the difference. It can't be emphasized more:Knowing the distinctions between micro TIG and conventional TIGwelding can save both time and money.