How Strong Are Welds?

 In Manufacturing Processes

A common concern of engineers when designing parts intended to be welded together (weldments) is how strong the welded joints will be. Performing computer simulation (FEA) on beams or other structural entities is relatively straightforward, however, it can be more difficult to get reliable simulation results on welded joints due to the many variables (weld thickness, skill of welder, type of weld and process used, etc). The short answer is, assuming your joint is designed properly and you have an experienced welder performing the work, your welded joint will be as strong as the base materials it is joining. To learn more about welding and other engineering techniques listen to our engineering podcast (Being An Engineer).

There are two main types of welding: MIG (Metal Inert Gas) and TIG (Tungsten Inert Gas) MIG

MIG welding creates an arc between a continuously fed wire filler metal and the workpiece. Shielding gas protects both the molten metal and the arc from the atmosphere. This process is suitable for most metals and alloys, such as the following:

  • carbon steels
  • low-alloy steels
  • stainless steel
  • 3000, 5000, and 6000-series aluminum alloys
  • magnesium alloys

Other alloys that can be MIG-welded via special methods include the following:

  • 2000 and 7000-series aluminum alloys
  • high-zinc-content copper alloys
  • high-strength steels

TIG welding produces an arc between a nonconsumable tungsten electrode and the workpieces. Inert gas is used to shield the arc and the work; filler metal is optional. Like MIG, TIG can be used to join most metals and alloys, but produces higher quality welds because of the absence of weld spatter. Unlike MIG, TIG can be used to produce fuse-welded joints without filler metal, resulting in minimal eruption above the base metal. Welds can be made in all positions, but the process is considerably slower than other welding processes. Compared to MIG, TIG typically takes a minimum of twice as long to complete the same type of weld.

Keep in mind that the strength of a weld will be determined in part by how clean the base materials are before the weld is created. Make sure your workpieces are free of foreign contaminants, oil, grease, etc. Typically, cold-rolled steel parts require little cleaning, while hot-rolled steels may require special cleaning. Aluminum alloys require wire brushing or etching before welding to remove oxidation and produce the highest quality welds (which increases total costs).

Want to learn more about the discipline of engineering? Check out our Being An Engineer podcast.

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