This chapter reviews the basic equipment used with each of the welding and cutting processes that are presented in detail in subsequent chapters. Process basics provide an understanding of why and how they work. Detailed equipment specifics of each process are covered in the separate chapters.
Oxyacetylene welding is more than 100 years old and is one of the oldest of the welding processes. My old friend, Butch Sosnin, was a welding training consultant and the 1979 president of the American Welding Society. To start all his weldor training, Butch used oxyacetylene because it was slow and students could easily learn welding fundamentals. A student could actually see the molten puddle develop.
Fig. 1.1. Oxyacetylene welding uses oxygen and acetylene gas supplied in cylinders. Regulators reduce the cylinder pressure and hoses deliver the gases to a torch where they are mixed and exit through a small hole in a welding tip. At the hottest part of the flame tip, the gas mixture burns at 5,720 degrees F. Acetylene is the only fuel gas that can achieve this high temperature in a small concentrated area. (Figure adapted from ESAB’s Oxyacetylene Handbook with sketch by Walter Hood)
After teaching oxyacetylene welding, he followed with TIG welding, which was similar to oxyacetylene in that the heat and filler additions were independent, and there was time to watch the weld puddle develop.
He proceeded to teach stick and MIG welding after some proficiency in the other two methods was achieved. Both stick and MIG welding are more difficult for a beginner to watch because the puddle process happens so fast!
The sequence of this book follows Butch’s course instruction and presents the welding processes in the order Butch would teach them.
My friend and colleague, Bob Bitzky, former training manager for ESAB Welding and Cutting Products, agrees with Butch’s instructional approach, and starts his new trainees with oxyacetylene followed by TIG welding.
The basic oxyacetylene welding process starts with two cylinders of gas—one oxygen and the other acetylene (Figure 1.1). Regulators reduce the cylinder pressure and hoses bring the gases to a torch where they are mixed and exit through a small hole in a welding torch tip. This mixed gas burns at 5,720 degrees F at the hottest part of the flame tip. Other fuel gases may even generate more total heat, but do not have this concentrated, high temperature at the flame tip.
Fig. 1.2. My old friend Butch Sosnin was a weldor training consultant and the 1979 President of the American Welding Society. Butch insisted on starting his weldor training with the oxyacetylene process because it was relatively slow and students could see the puddle develop. Bob Bitzky, former training manager for ESAB Welding and Cutting Products, supports Butch’s logic, stating, “It still holds true today.”
The oxyacetylene flame is the only one that can truly be used for welding. Other fuel gases can be used for cutting and brazing but are not effective for welding. It is the concentration of heat that allows welding to occur. Don’t be fooled by just temperature comparison with other gases.
Discussing combustion intensity is a way to explain the temperature concentration of various gases. Without going into too many technical details or specifying the units, an oxyacetylene flame produces more than 10,000 while the next best fuel gas produces about 5,000, or half the value. Steel has the highest melting point of materials that are typically welded. It melts at about 2,500 degrees F. The high-heat concentration and 5,720-degree F flame temperature can melt and fuse two pieces of steel.
Although difficult to master, oxyacetylene welding can be used to weld aluminum. However, unlike steel that turns red then white before forming a molten puddle, aluminum does not. Aluminum melts at 1,200 degrees F and gives little indication it is about to melt.
Note the AWS designation for oxyacetylene welding is straightforward—OAW, although few folks use it.
Gas flow rates for oxyfuel welding are relatively high compared to the shielding gas flow rates in TIG and MIG welding. Needle valves in the torch handle adjust the flow of the two gases. Setting the correct mixture is covered in the individual process section. However, carefully read the manufacturer’s instructions because controlling the flow rate of these gases is very important and potentially a significant safety issue. Be sure to follow the manufacturer’s recommendations for adjusting the cylinder regulators. Particularly for the oxygen cylinder, where the pressure adjusting screw must always be backed out before opening the contents valve on the cylinder. Failure to do this properly can cause a surge of high-pressure oxygen to rush into the small chambers of the regulator. Like a Diesel engine, this rapid rise in pressure creates heat and can ignite whatever is in the regulator, including the brass body. In pure oxygen, everything burns, and burns explosively! Follow the manufacturer’s recommendations carefully.
Tungsten inert gas (TIG) welding was first developed in the 1940s to weld aluminum and magnesium. Today it is used to weld many materials, including a variety of steels. TIG creates an arc between a non-consumable tungsten electrode and the workpiece and uses an inert gas, usually argon, to shield the molten puddle. A DC or AC power source supplies the electric power. The tungsten is held in place with a collet inside a TIG torch. The argon shielding gas protects the molten puddle as well as the tungsten, which may be 6,000 degrees F at the tip. The arc itself is much hotter than the oxyacetylene flame. It is 12,000 to 15,000 degrees F on the outer part of the arc to twice that near the tip of the tungsten. A major advantage of the process is the ability to have a stable arc exist from very low currents (3 amps) up to maximum torch capacity, which can be over 500 amps on automatic machine torches.
Fig. 1.3. TIG welding uses an inert gas, usually argon, to shield the molten puddle, which is created by an arc between a non-consumable tungsten electrode and the workpiece. Electric power is supplied by a DC or AC source. A major advantage of the process is the ability to have a stable arc at settings as low as low 3 amps.
For gas tungsten arc welding, the official AWS designation for TIG welding is GTAW. The common term TIG for tungsten inert gas is used throughout the book. Note: If taking welding courses and the instructor insists on the use of GTAW, use it!
Oscar Kjellberg, the founder of ESAB, invented and was issued a patent for stick electrode welding in 1904. Its use grew rapidly through the 1920s, 1930s, and 1940s and became the leading welding method until displaced by MIG welding.
Stick electrode welding is simple to use, requiring only a power source and an inexpensive electrode holder. It is still preferred when welding outdoors because it can make acceptable welds in significantly more wind than gas shielding processes. The AWS Bridge Welding Code, for example, specifies maximum wind speeds of 5 mph for MIG and TIG welding, while stick welding is allowed up to 20 mph. However, when TIG welding, a gas lens should be used for up to a 4-mph wind. In addition, TIG is more sensitive to the need for quality shielding than MIG.
Stick welding utilizes a simple power source, such as an AC welding transformer. DC power is also widely used and for welding outdoors; portable engine-driven DC generators are often employed. All these power sources are called constant current, referring to setting the desired welding current level, which stays relatively fixed regardless of the arc voltage. Thus, welding starts at a high voltage