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Posted on Dec 22, 2020
For welding sheet metal, there are quite several ways you can go about it, but in this article, we’ll specifically address three common types: MIG (metal inert gas), TIG (tungsten inert gas), and laser welding. Many variables will depend on the system used. On any of the three processes, below point to remember.
MIG Welding, also known as Gas Metal Arc Welding (GMAW), is a method of arc welding that uses an electrode of continuous solid wire. It is fed by a welding gun where the contact tip is electrically charged, causing ample heat to melt the wire and creating a welding pool that joins the two parts. The pool is protected by shielding gas from chemical pollutants that could cause defects. Due to the spatter produced through welding, MIG is suitable for projects where the presence of cosmetics and welds is of limited significance. Depending on weld size and weld size, manual welding rates are in the 30' per minute range. Robotic welding can be used to increase throughput. To discuss further in terms of material considerations:
On account of speed, MIG welding is favored over TIG welding for carbon steel. It is often used for connecting bits that do not match closely together. An exterior corner weld that needs to be dressed is a typical example of a weld.
Stainless steel sheet metal is similar to carbon steel, but normally uses spatter reduction by Pulse MIG welding. No interaction between the electrode and the pool happens with Pulse MIG welding. The current flashes, or alternates, between high and low temperatures, and a drop of molten metal from the electrode is applied to the pool for each pulse.
TIG welding, also known as gas tungsten arc welding (GTAW), differs from MIG welding in that it uses a tungsten electrode that is not consumable. It produces heat from an arc generated from electricity in the tungsten electrode for welding. For build-up and stabilization of the weld, the filler material is also used. Like MIG welding, the puddle is covered from pollutants by a gas mask. In terms of velocity, TIG speeds are in the 7" to 15" per minute range based on fillet size, application of filler wire, etc. And with specific regard to steel material, TIG welding is normally not used; MIG is typically the preferred option. However, where the MIG gun's scale prevents entry to the weld, TIG can be used.
To elaborate further, due to the clean appearance in a cosmetic environment that is often needed, TIG is mainly used on stainless steel. When stainless TIG welding, heat input, and speed must be regulated Since stainless is prone to uneven heating warpage. This warpage region is called the zone influenced by heat. Unless the application calls for the weld to be brushed to fit the adjoining content, there is usually no post-weld cleanup.
Laser welding is a method of fusion welding that utilizes a laser beam to provide a source of intense heat that melts the materials together. It needs a very similar fit-up of the element where the distance between components can not exceed .005. The precision processing machinery of today is now capable of Maintenance of the required tolerances for consistent laser welding. Gas shielding may not be needed, depending on the appearance desired.
Laser welding advantages include small tiny weld seams and low thermal distortion, in addition to speed. The laser is autogenous (no filler wire is added) as compared to TIG welding, because there is very little weld material aggregation. This also facilitates the welding of even smaller components compared to other methods.
There are two types of laser welding: cosmetic (or conduction) and keyhole. To make for a very smooth, wide weld, the cosmetic weld defocuses the laser. The keyhole weld burns through into the second layer from the first layer of steel. It produces a sturdy weld joint as the molten material cools. A keyhole weld is used where the appearance of a cosmetic weld is not important, but a hermetic seal's integrity is necessary.
Because of the respective wavelengths, current laser welders are known as short or long wavelength machines The wavelength of action within the light spectrum. YAG, disk, or fiber lasers are such short-wavelength laser sources. Long-wavelength sources are usually lasers of the CO2 kind. Laser beams of short wavelengths are more readily absorbed into the substrate and therefore more effective in transmitting light energy. The further the layer shifts to the liquid state, the more light energy that is consumed. In terms of velocity, the speeds range from 50" to 80" per minute. And in terms of steel consideration:
On carbon steel, both decorative and keyhole welding can be used and both short and long wavelength machines can weld carbon steel. Since material build-up is negligible in laser welding, with minimal or no post-weld cleanup, steel pieces will go straight to the paint line.
Stainless steel is also a candidate for all forms of welding and can operate on all types of machines. A post-weld procedure for the removal of heat tint can be needed depending on the application of the component. If stainless steel with a brushed finish is the material being welded, due to the narrow welding seams, regaining and blending will not be needed. An added advantage of stainless laser welding is that, due to the speed of the laser weld, the heat-affected region is greatly decreased or even removed. This is critical for cosmetic criteria since there is no longer disfiguring warpage of the finished product.
Coated galvanized, galvanized steels face a laser welding challenge. In cases, such as Cosmetic laser welding is feasible if the corners that are to be welded are uncoated. In keyhole welding, however, an imperfect weld will result from the various melting points of the coating and substrate material. As the coating transforms to gas and disrupts the solder puddle, a lot of spatter is created. Both types of machines will weld coated steel.
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