Joining Processes: Welding, Brazing, Soldering

1. Brazing and Soldering: Melting of filler rod only

• Brazing: higher temperature, ~brass filler, strong

• Soldering: lower temp, ~tin-lead filler, weak

2. Welding: Melting of filler rod and base metals

3. Both: Join inexpensive parts to form complex product

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Types of Joints

Brazing• Steel base metal + Brass filler rod is common

• Lower temp than welding: retains heat treatment (if present), minimizes grain growth.

• Strong but slow (careful preparation, cleanup)

• Furnace brazing is easily automated

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en.wikipedia.org

www.kirkframeworks.com

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Shielded Metal Arc Welding (SMAW): “Stick welding”

• Older, simple technology

• The electrode is also the filler rod

• Only for steel

• Strong welds if done properly (but often not)

• Very high heat input: good for thick parts, bad for grain growth and distortion

Gas Metal Arc Welding (GMAW): “MIG” (Metal-Inert-Gas)• ~Complex mechanism but simple to perform and easy to automate

• The electrode is also the filler rod, fed continuously from a spool. It melts in the arc.

• For steel or aluminum

• Low skill level can achieve good weld

• Medium heat input: distortion and grain growth are significant

Kalpakjian

www.difflock.com

www.scenta.co.uk

www.mig-welding.co.uk

Gas Metal Arc Welding (GMAW): “MIG” (Metal-Inert-Gas)

A fair/typical quality MIG weld (still hot!)

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Gas Tungsten Arc Welding (GTAW): “TIG” (Tungsten-Inert-Gas)

• The electrode is tungsten (not consumed)

• The filler rod is separate and fed manually

• High skill level required to achieve good weld

• Difficult to automate

• Low heat input and small weld bead: distortion and grain growth are minimized

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Gas Tungsten Arc Welding (GTAW): “TIG” (Tungsten-Inert-Gas)

• Typical good quality TIG welds

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Resistance Spot Welding (RSW): “Spot Welding”

• No filler rod: electrical current is passed through metal under pressure

• Low skill level required

• Easy to automate

• Low heat input and no weld bead: distortion and grain growth are minimized

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Distortion from Welding Processes

• Non-uniform shrinkage of weld bead

• Difficult to maintain alignments

• Solution: Rigid fixtures, pre-compensate for warping, loose tolerances

Weld bead profile: Convex or Concave?

• Solidification of molten bead leads to shrinkage

• Shrinkage of a concave bead leads to tension on surface tends to crack

• Shrinkage of a convex bead leads to compression on surface does not crack

• Generally, slightly convex beads are preferred.

Lincoln Electric

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Welding Flaws

www.ndt-ed.org/EducationResources

www.mig-welding.co.uk

Welding Flaws:

Incomplete Penetration

(not enough heat input)

References

Kalpakjian: http://www.nd.edu/~manufact/index3.htm