The Weld Nugget (Winter 2011) - A Newsletter to inform, educate, and entertain

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Does spatter really matter?

During welding, the parts being welded reach very high temperatures which leads to bubbling and boiling in the weld pool. As a consequence, some of the molten material takes on enough energy to break the bonds of surface tension and launch itself in the form of small droplets. These droplets are like shooting stars, flaming out as they zip through air. The most dramatic example of spatter is seen during flash butt welding, and almost looks like a fireworks show.

One of the main problems with spatter is that it lands everywhere: on fixtures, nozzles, parts themselves, the floor, and on the operator. Since spatter is quite hot, often in soft/molten state, it will land and adhere quite strongly to just about anything. Sometimes spatter will get oxidized as it flies through the air and forms hard and brittle particles. Spatter results in jamming or rapid wear of fixtures, blocking of shielding gas nozzles, setting inflammable material such as grease and cloth on fire, and embedding itself in human skin. Spatter often falls back on the part itself, especially on a prepared surface, and produces either a visual defect or at least one that requires rework by having to remove the spatter which is not easy and may not be allowed if the parts are very delicate. In micro-resistance welding applications, welds can throw off spatter that damage nearby electronic circuits and sensors.

If too much spatter flies off, especially from a localized instability in the weld, it can leave a deep pocket in the weld, referred to as blowout. Blowouts are a cause for concern since they present a location of weakness for crack propagation. If deep enough, blowouts can provide a leak path in hermetic welds. Blowouts also have the potential to trap moisture and/or chemicals during post-weld processing leading to corrosion or poor visual appearance and often need costly rework.

Safety issues with spatter are not trivial. Spatter has been known to start fires and electrical shorts in machinery and controls surrounding the weld station. Any spatter embedding into the skin will also produce long-term harm; operators should be adequately protected with proper clothing and safety glasses. Given all the associated issues, one has to be mindful of weld spatter. Of course, if you don't mind, it doesn't matter.

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Tailor Welded Blanks

Tailor welded blanks (TWBs) are a unique solution to the problems faced by the auto industry - making cars that are lighter, cheaper, safer, and more reliable. One of the ways to do that is to use the least amount of the most appropriate steel in car body construction. To do so, car manufacturers have been using a process in which two pieces of steel of different thickness, coating, and/or composition are welded together to form one blank - a piece of sheet steel which is the starting point for other operations. For example, two rectangular pieces could be welded together to form a square. By using different steels for the two rectangles, engineers are able to "tailor" the properties of the final square blank. If this square is used to form a car door frame, then the lower half could be of steel that has good corrosion resistance while the upper half could be regular steel in order to reduce cost. From the manufacturing perspective, TWBs allow for fewer parts, reduced reinforcements, and reduced process steps during body assembly.

Welding process that can make TWBs include mash seam welding (a form of resistance welding), electron beam welding, induction welding, CO2 laser welding, and YAG laser welding. Selection criteria for choosing one of these processes include ability to weld dissimilar steels, industrial integration, ability for weld to be formed after welding, and edge preparation prior to welding. Of all the process, it appears that YAG laser welding, especially with reduced operating costs from new technologies, appears to be increasingly the method of choice.

TWBs are essentially composites, but at a macro scale. Most commonly used composites are mixtures of materials at a micro scale which have properties that are better than the original constituents but are homogenous on a macro scale.   TWBs are essentially designed to match the requirements of a sheet metal part with different characteristics at different locations - tailored to suit.

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You say splatter, I say spatter 

Is there a real difference between the two? I have seen both terms being used interchangeably so thought would be interesting to find out. According to the dictionary (dictionary.com), spatter is defined as "to scatter, sprinkle, or send out small particles or drops". On the other hand, splatter is defined as "to splash and scatter upon impact". So it appears that the process of droplets leaving the weld pool and go flying should be called spatter. If the spatter (now used as noun) is still liquid by the time in lands and then gets splashed on the surface, the effect could be called splatter. Putting it all together, one would be correct in saying the "the spatter got splattered on the fixture".

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