Figure 1-2. Arc welding setup
Wire Feed Welding or MIG Welding
In this process, welding wire within the welding gun is both the electrode and the filler material. Welding begins as the section of electrode wire between the tip and the base metal is heated and deposited into the weld. As the wire is consumed, the feed mechanism supplies more electrode wire at the pre-adjusted rate to maintain a steady arc.
The wire feed processes consume over 70 percent of total filler materials used today, and this percentage continues to grow. While this welding equipment may cost more than arc welding equipment of the same capabilities, it offers higher productivity, and it is easy to learn. Not having to stop a bead, change electrodes, and restart again increases metal deposition rates and reduces weld discontinuities. Also, these processes are readily adapted to robotic/computer-controlled operations. Wire feed processes are relatively easy to learn, especially to those already trained in shielded metal arc welding, once the power source differences and voltage- amperage variables are understood. See Figure 1-3.
Figure 1-3 Wire feed welding setup
Non-Consumable Electrode or TIG Welding
A continuous arc forms between a tungsten electrode on the welding torch and the work. The electrode in this process is not consumed. However, some applications require the use of a filler rod.
Although this process requires more skill than most other processes and does not have high metal deposition rates, improvements in shielding gas mixtures, torch design, and power supply electronics have made it an indispensable tool where high quality welds are essential on aluminum, magnesium, or titanium. It can weld most metals, even dissimilar ones. See Figure 1-4.
Figure 1-4 TIG welding setup
How Are Welding Joints Prepared?
Some elements of welding are common to all types, such as joint preparation, welding terminology, and the like. They will be covered here. For specific techniques, see the chapters dealing with each of the main welding processes.
Joint preparation provides access to the joint interior. Without it the entire internal portion of the joint would not be fused or melted together making the joint weak. Remember that a properly made, full-penetration joint can carry as much load as the base metal itself, but full penetration will only occur with the correct joint preparation.
Usually, joints are prepared by flame cutting, plasma arc cutting, machining, or grinding; however, castings, forgings, shearing, stamping, and filing are also common methods used to prepare material for welding. See figure 1-5.
Figure 1-5 Edge shapes for weld preparation
Figures 1-5 and 1-6 Proper joint preparation is essential to ensure strong welds. Here a portable grinder is used to bevel the edges of two thin sheets of metal
Joint Types
Figure 1-6 Joint types.
Common Welding Types
The V-and U-groove joints are common joints used in welding. The parts of the joints include
•Depth of bevel
•Size of root face
•Root opening
•Groove angle
•Bevel angle
Figure 1-7 Parts of V- and U-groove joint preparations
Joint Preparations for Butt Joints
Figure 1-8 Single-groove and double-groove weld joint
Joint Preparations for Corner Joints
Figure 1-9 Weld preparation for corner joints
Joint Preparations for T-joints
Figure 1-10 Weld preparations for T-joints
Joint Preparations for Edge Joints
Figure 1-11 Weld preparations for edge joints
Joint Preparations for Lap Joints
Figure 1-12 Weld preparations for lap joints
Common Weld Preparations
Figure 1-13 A few typical weld preparations
What are some basic types of welds?
The Groove Weld
As the name implies and the illustration below shows, this is a weld made in a groove between work pieces. See “Common Weld Preparations,” on the opposite page, for some typical weld dimensions.
See Figure 1-14.
Figure 1-14 Parts of a groove weld
Fillet Weld
Fillet welds are triangular in shape and used to join materials that are at right angles to one another in a lap, T-, or corner joint. The face of the weld can be convex or concave. See Figure 1-15 A&B.
Figure 1-15A Parts of a convex fillet weld
Figure 1-15B Parts of a concave fillet weld
Plug and Slot Welds