Fig. 1.4. Stick electrode welding is simple—it only requires a power source and an inexpensive electrode holder. The heart of the process is the stick electrode that has a metal rod in the center, which is coated with a mixture of flux ingredients, small amounts of metal alloy, and a liquid binder. The coated rod is baked to harden the binder.
The heart of the process is the stick electrode itself. For steel welding, the center core is typically a non-alloyed steel rod. The rod is cut into short lengths, such as 14 inches. Flux ingredients are mixed with small amounts of metal alloy and a binder, often liquid sodium silicate. The dough-like mixture is extruded around the core wire. The coated rod is baked to harden the binder. A short section at the end has the coating removed, so the electrical power can be transferred to the core rod. When an arc is struck between the core wire and the workpiece, the flux melts and some gaseous products, such as carbon dioxide, are formed, and this helps protect the weld puddle from oxidation and nitrogen contamination. The flux ingredients melt and form a slag that floats to the top of the weld puddle and protects it from atmospheric contamination as it cools. A variety of electrode types are available. Some can weld high-strength steels and match their strength and toughness.
Fig. 1.5. Oscar Kjellberg, founder of ESAB, invented (and received a patent for) stick electrode welding in 1904. Stick welding became more prevalent through the 1920s, 1930s, and 1940s and became the leading welding method until displaced by MIG welding. ESAB grew to be a worldwide leader in the welding field.
Note the official AWS designation for stick welding is SMAW for shielded metal arc welding. The common term “stick welding” is used throughout this book.
In 1950, Gibson, Muller, and Nelson, working at the Airco development laboratories, patented the MIG (metal inert gas) welding process. Over the ensuing decades it evolved, and today it is used to deposit more than 60 percent of the filler metal in the United States.
Fig. 1.6. The MIG welding process utilizes a constant-voltage power supply. The output is similar to a car battery in which the voltage stays relatively constant as current rises. A small-diameter wire, typically .035 or .045 inch, is fed from a spool through a flexible cable and MIG gun. The wire exits the gun and current flows to an arc, which forms between the wire and workpiece.
The MIG process utilizes a constant-voltage power supply. Similar to a car battery in output characteristics, the voltage stays relatively constant as current rises. A small-diameter solid wire, typically .030 to .045 inch, feeds from a spool through a flexible cable and MIG gun. The MIG gun has a copper nozzle that directs shielding gas to protect the weld from oxidation and nitrogen contamination. The wire exits the front of the gun through a copper contact tip where it picks up electrical power. Current flows from the copper contact tip to the small diameter wire. As current passes through the wire on the way to the workpiece, resistant heating increases the temperature to perhaps to 500 degrees F. Then an arc forms between the end of the wire and the workpiece, and as a result, the arc melts both the wire and the workpiece. Unlike TIG welding that requires careful hand manipulation to maintain the arc length, MIG arc length is maintained automatically. However, the weldor must still control the distance from the MIG nozzle to the work to achieve proper welding performance. This is covered in detail, with examples, in Chapter 6.
MIG welding can be used for steel, stainless steel, aluminum, and some other materials. The official AWS designation for MIG welding is GMAW (gas metal arc welding), but the common term MIG is used throughout this book. For those outside of the United States, the term MIG is only used when 100 percent argon or argon-helium shielding gas mixtures as used when welding aluminum. For any shielding gas that includes oxygen or an oxygen compound, such as carbon dioxide, MAG (metal active gas) is used. My purest friends cringe when I use MIG at AWS Section talks. I tell them it is far better than calling the process wire welding!
The title of this section was purposely changed from “Oxyacetylene Welding” to “Oxyfuel Cutting.” The AWS term for the process is OFC (oxyfuel cutting). OAW is commonly used for welding because acetylene is the only gas that can be effectively used for welding, while a number of other fuel gases can be used for cutting. In fact, natural gas can be used for automatic cutting machines.
Fig. 1.7. Similar to the oxyacetylene welding torch, a cutting torch uses a special tip. Mixed oxygen and fuel gas exit multiple holes around the outer edge of the tip producing high-temperature flames. A large center hole in the cutting tip emits a high flow rate of pure oxygen, and this oxygen does the cutting. The flame preheats the steel and the oxidation of iron generates the heat to maintain the cut.
The process for cutting steel is shown in Figure 1.7. Similar to a welding torch, a cutting torch utilizes a special tip that has multiple small holes around the outside of a larger center hole. These small holes flow mixed oxygen and fuel gas and produce the high-temperature preheat flames. A larger center hole in the cutting tip has a high flow rate of pure oxygen only, and that oxygen does the cutting.
The hot outer flames preheat the steel, and the oxygen converts the hot iron to iron oxide. This chemical oxidation generates the heat to keep the cut going! Therefore, any fuel gas can be used to start the process, but depending on which fuel gas, it may take longer to start the cutting action. However, with a steady hand, the cut can be made.
Acetylene is often the preferred fuel gas. If you don’t have a steady hand, the cutting may stop with other fuel gases. When using the hotter, more intense acetylene flames even with slight hesitation it continues cutting, and that makes it easier to operate.
I found that out by experience when I was troubleshooting a welding job and needed to take a sample of a 1-inch-thick weld on the airplane. All of the weldors and cutters were at lunch so I offered to make the sample cut. I picked up the torch and proceeded. My experience had been cutting with oxyacetylene. This torch was using propane as a fuel gas. After a number of starts and stops, the cut was made, but it wasn’t pretty!
Bob Gage, working for the Linde Development Labs (my former employer), invented plasma cutting in 1957. Welding was discussed in the patent, but the process has gained much more popularity for cutting. Initially, the process used nitrogen cutting gas; today, manual systems mostly use compressed air as the plasma gas. The process creates an arc between a non-consumable electrode in the plasma torch and the workpiece. However, unlike TIG welding, the arc is forced to go through a very small hole that concentrates the heat and raises the temperature of the exiting plasma gas. The exiting gas in the center of the arc column reaches more than 30,000 degrees F, and that melts and blows away any conductive material. The innovative design and the rapidly swirling plasma gas in the nozzle