Editors of CPi - Welding complete: techniques, project plans & instructions

Notice To Readers

Welding is a dangerous activity. Failure to follow safety procedures may result in serious injury or death. This book provides useful instruction, but we cannot anticipate all of your working conditions or the characteristics of your materials and tools. For safety, you should use caution, care, and good judgment when following the procedures described in this book. Consider your own skill level and the instructions and safety precautions associated with the various tools and materials shown. The publisher cannot assume responsibility for any damage to property or injury to persons as a result of misuse of the information provided.

Welding is all about heat, about using heat to melt separate pieces of metal so they will flow together and fuse to form a single seamless piece. Regardless of the welding or cutting process, your ability to control the heat generated by the flame or arc determines the quality of your welds and cuts.

Certain terms are used to describe the heat and action of all the welding processes. The parts being welded together are referred to as the base metal. Additional metal, called filler, is often added to the weld. The molten puddle is the area of melted base metal and filler metal that you maintain as you create your weld. To have fusion of metals, the base metal and filler metals must have the same composition. Methods for joining metal without fusion are called soldering, brazing, and braze welding. These methods can be used to join similar or dissimilar metals.

Oxyacetylene welding and cutting use flames to generate the heat to melt the metal. Shielded metal arc, gas metal arc, gas tungsten arc welding, and plasma cutting use an electric arc for heat generation. With oxyacetylene welding, you have time to watch the puddle develop as the metal turns red, then glossy and wet looking, then finally melts. With the arc processes, the puddle forms quickly and may be difficult to see because of the intensity of the arc. It is important to have ample lighting and clear vision so you can watch the puddle and move it steadily.

Penetration of the weld is also a critical heat-dependent factor. A strong weld penetrates all the way through the base metal. Matching filler material size and heat input to the thickness of the base metal is important. It is easy to get a good-looking weld that has not penetrated the base metal at all and merely sits on the surface. At the opposite end of the spectrum from a cold, nonpenetrating weld is burn throughwhere the base metal has gotten too hot and is entirely burned away, leaving a hole in the base metal and the weld.

Heat distortion is a byproduct of all welding and cutting processes. It is obvious that applying a flame to metal in the oxyacetylene process makes the metal hotand the electrical arcs are actually four to five thousand degrees hotter than the oxyacetylene flame. When metal is heated, it expands; when it cools, it contracts. If not taken into consideration, this expansion and contraction may cause parts to move out of alignment. This is why tack welding and clamping project pieces is critical to successful welding. It is also important to match the welding process to the base metal thickness. For example, shielded metal arc welding is generally not used on materials less than / thick. The process is too hot and too difficult to control on thin material. On the other hand, gas metal arc welding works well on very thin sheet metal, if you are able to adjust the machine to a low enough voltage.

Oxyacetylene welding