Monday, May 9, 2011

TIG welding vs. Fillet/Lug Brazing

In earlier post, I talked a little bit about the benefits of different joining methods. I've talked to various frame builders as well as metal fabricators in the area, and have come to some interesting conclusions regarding strength and endurance of different joints. Traditional thought would suggest that TIG welding is the strongest joining method; whereas with brazing there is simply a different metal compound that more or less 'glues' the two pieces of metal together, welding actually joins the two pieces into one.

True Temper, a well know fabricator of high quality golf clubs (and lesser known, bicycle tubing) engaged in a test of the 3 different joining methods: TIG, fillet, and lug. Each tests examined the strength of all the different joints without changing the quality of the joint (i.e. having a fixed frame builder for all 3 methods equally experiences in all techniques) or the forces of the test. Fillet and lug brazing both out lasted TIG in True Temper's test. A few conclusions were reached:

1. The greater temperature that TIG inflicts on the steel compromised the strength of the welds to a noticeable degree.

2. Though strong against blunt trauma, TIG as a long standing process did not hold out as long against constant applied pressure.

3. Silver brazing rod was far superior to brass brazing rod in both fillet and lugged joints. Being better at penetrating the grooves between miters and lugs, the surface area covered by silver was a significant improvement over brass of the same quality.

Though TIG was weaker as a lasting joining method, it was not by a considerable margin. All 3 joints proved to withstand the pressures that the average cyclist inflicts on them, leading to some other frame failure before joint failure.

Beyond strength, there are other benefits. With TIG and fillet, there is more freedom with different sizing and customization of the frame geometry due to the precision of the miters. With lugging, each tube is easier to replace if damaged. Aside from this, joining methods often boils down to aesthetic choice.

Finishing details on the frame drawing (or at least the first one.) Will post pictures when completed.

5 comments:

  1. I once attended a meeting of the EAA (Experimental Aircraft Association) and asked if fillet brazing was ever used in construction of light aircraft. They laughed at me! I explained that bicycles have proven that fillet brazing is a reliable method of joining 4130 tubing, but I got no positive responses. In aircraft, use only oxyacetylene or TIG, they insisted. Yet I wonder. Is anyone aware of any quantitative studies of the strength of fillet brazing?

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    1. I don't know what their reasoning was but there are a couple things I can think of..
      1) (from my understanding) fillet brazing is a lot more time consuming than TIG
      2) strength benefits are only marginal
      3) oxyacetylene and TIG are more traditional methods

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  2. Another benefit of using Tig is the amount of different metals you can join with it. Stainless steel and Carbon Steel is the most used ones, but it's also possible to join non ferrous metals like aluminum, copper and magnesium. When welding Carbon or stainless steel DC (direct currency) is used to fuse the metals, though it is possible to use AC, it's not preferable. To weld for example Aluminum with the highest quality AC is most of the times used.

    brazing equipment singapore

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  3. Hi,
    Thanks for the great details about welding, i really appreciate your research & knowledge in this domain.

    We are leading stainless steel welding company engaged in MIG Welding, TIG Welding, Stainless Steel Welding.

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  4. I can't find a record of True Temper's test anywhere. Do you have a link to the test?

    ReplyDelete