7451 Oakmeadows Drive Worthington, Ohio 43085 | (614) 847-9410

MicroMIG Applications

1) Weld Repairing Casting Defects in "Unweldable Alloys"

Some of today's nickel- and cobalt-based superalloys are weldable. Some are unweldable. The defining characteristic that makes an alloy weldable or not is it's tendency to exhibit micro cracks in the heat affected zone from welding. These micro cracks are caused from the difference in chemistry between the grains and the grain boundaries.

When the part is cast, the grain boundaries become enriched with certain alloying elements, principally Aluminum and Titanium, upon solidification. These enriched grain boundaries have a melting point slightly lower than the melting point of the grains themselves. Immediately after the weld bead solidifies, the weld bead and the adjacent grains begin to shrink as they cool. If the grain boundary's melting temperature is different enough from the that of the grains themselves, the shrinking grains can pull apart from each other at the grain boundaries since they are still liquid or have just solidified and have very little strength. This leaves small tears between the grains. These small tears are, collectively, known as "micro cracking". Since this happens adjacent to, but not in the weld bead itself, and since it is caused from the differences in melting points between the grains and the grain boundaries, engineers label this type of cracking as "heat affected zone grain boundary liquation cracking". The more common name is "micro cracking".

Some of today's superalloys exhibit this type of welding difficulty. Some do not. It depends upon their chemistry or chemical make-up. The alloying elements that make certain alloys in this family extra strong at very high temperatures are also the same alloying elements that cause these certain alloys to be labeled "unweldable". MicroMIG welds do not exhibit this kind of micro cracking, principally because we use lots of very small weld beads rather than one or a few large weld beads. The advantage of MicroMIG is that we can weld on these alloys without micro cracking. However, the downside is that it takes time to do this. Consequently, a MicroMIG repair is more expensive than a conventional weld repair. However, for those applications where micro cracking is unacceptable (because under fatigue loading these tiny micro cracks grow into bigger cracks), MicroMIG provides a quality repair. In fact, MicroMIG welded jet engine parts have been flying in both military and commercial gas turbine jet engines since the early 1990's.

2) Finished Machined Components

If you have a part that is finished, or it should be finished, but there are small surfaces that are undersized from the machining operations, we can probably help. Typically, engineers think of welding first when repairing metal component parts. However, welding usually has a down side - distortion. Whether it's called distortion, warping, "moving out of tolerance", heat bending, thermal movement, etc. it's all the same thing. Welding causes local stresses that can distort and warp parts. If the part has enough mass to resist this movement or if the part can be fixtured adequately, then much of the time, we can come up with a weld repair that doesn't warp the part bad enough to cause it to be "rejected - due to being out of tolerance".

However, for parts that are finished machined to tight tolerances, especially parts that are not very thick or strong, welding often warps these parts out of acceptable tolerance. That's where MicroMIG can really shine. We routinely weld on parts that are finish machined without distorting them. Complex turbine engine parts that are both very expensive and very sensitive to welding distortion are regularly returned to "full service status" or "Class A condition" by being MicroMIG repaired.

The same unique qualities that allow us to repair these tight tolerance parts also make the repair typically more expensive than traditional weld repairs. Therefore, parts that are fairly inexpensive are not good applications. If the value of the part is measured in hundreds or thousands of dollars, the part is just slightly out of tolerance, and the part is a nickel, cobalt, or stainless steel alloy, we can probably help you fix it. Great applications include ...

* press fit hole diameters that are just a few thousands too large to press fit

* small locating surfaces or datum surfaces that are shy by thousandths, not by sixteenths

* seals that are undersized and will thus leak

* interfacing areas between parts that are a little shy for good fit up

* Z-notch surfaces in turbine blades

* split face or slash face surfaces in turbine vane segments

* small bearing areas that allow a shaft to spin in the bearing

3) Dissimilar Metals

If you need to apply a small amount of dissimilar metal on a component for any one of a number of reasons, we may be able to help. Rather than secondary joining or bonding mechanisms, our MicroMIG welds are fully fusion welded to the surface. However, because our welds are very small, the weld layers thin, and the weld thermal cycles are pretty quick, we can often avoid the metallurgical issues of trying to combine two different metals in their liquid state that do not want to mix.

For example, we can weld nickel alloys on stainless alloys on cobalt alloys on steels on etc. etc. etc. If your designers or engineers desire a different surface in a certain area than the base material of the part, we may be able to help you achieve just that. Whether your reasons for desiring a different surface are for chemical resistance, electrical property difference, wear resistance, etc. we may be able to help you with our unique MicroMIG welding process.

One particularly unique area we help our customers in is wear resistance. In our weld filler material, we can add certain wear resistant materials such as a variety of carbides or hard face alloys. This means that we can weld on a layer of material that is very different from the base metal. This layer's thickness is usually measured in thousandths, however, it's hardness can be from Rc50's to Rc70's depending upon the hardfacing material chosen. There are some special tricks, tools, procedures, and welding components to our MicroMIG system that are used to weld hard layers versus superalloy weld metal. We've even given this unique welding system, which is an offshoot of our MicroMIG welding system, it's own name. We call it T-REX. We thought it sounded strong!

* With this process, very hard layers are welded on components without distorting or warping them. Good applications include ...

* greatly increasing the life of special machining cutters

* eliminating the routine "scraping in" of the ways on machine tools

* dramatically increasing the working life of certain ultrasonic welding horns, especially those welding materials that are more abrasive to the horns

* anywhere where galling between lubed surfaces is a problem

* increasing the lube holding ability of a surface for minimizing wear

* eliminating the sticking tendency in areas on sheet metal working dies

* avoiding the wearing issues on certain components of plastic injection molding dies and equipment

We are a company that thinks "out of the box" when it comes to helping you overcome your welding material issues, your mismachined parts issues, or your wear issues. Give us a call. We'd love to help!