Taking the Mystery out of Micro TIG Welding

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

Micro TIG welding is not new technology; it's been available for more than 10 years (TIG is an acronym for tungsten inert gas). Most people in injection molding have heard of it, and I would wager most have used it. But the fact remains that many people are still somewhat in the dark regarding its uses, advantages, and disadvantages.

Micro TIG welding is identical to conventional TIG welding with a couple of important differences. Both use tungsten to create the arc for the weld, but the amp range and size of the filler rod and tungsten differ. Conventional TIG welding uses a much greater heat range than micro TIG welding, making the two ideal for very different applications.

The amp range in conventional TIG welding is about 50 to 250 amps, as compared to the range for micro TIG welding, which is between 5 and 50 amps. Micro TIG welding also uses a filler rod that measures only between .005 and .015 inch in diameter-not much thicker than a strand of hair. Compare this with traditional TIG welding, which uses rods that typically measure .0625 to .125 inch in diameter. Additionally, micro TIG includes the use of high-tech optics and lighting; these are critical to maintaining the 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 welding can do just as good a job repairing a mold or mold component as micro TIG welding. The truth is, conventional TIG welding, in all its accepted, tried, and true forms cannot provide the same quality, fine weld bead as micro TIG. Nor can conventional TIG welding provide the same control offered with micro TIG welding.

It makes sense that a welding shop would use conventional TIG welding for larger repairs, and micro TIG for the finer, smaller repair jobs. Both provide value. However, it is the microscope and fiber optics used with micro TIG welding that enhance the ability of the operator to enter areas previously inaccessible using 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 requiring secondary machining. One of the benefits of micro TIG welding is that most of the time the finishing process is minimal. When this happens, it's thanks mainly to the skilled micro TIG welder's ability 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 postweld preparations. Such techniques include in-depth inspection of surface contaminants and oxidation, removal of cracked or damaged material around the area to be welded, careful control of critical pre- and postheat temperature, and the ability to produce a weld with minimal or no sink at the heat-affected zone-all of which can save 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 in the mold or component being repaired. Conventional TIG welding can cause added stress to the area around the weld, increasing the possibility of premature failure at the welded area.

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

The Down Side

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

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

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