Processes.
Molding, which is a basic operation in the metal industries, is a comparatively simple process especially when standardized parts are being cast, and it is not necessarily heavy work since castings in various metals, may be of any size and weight. Molten metal, pure or alloyed, is poured into a mold formed by a pattern in sand or loam. In many instances castings must be finished by machinery.
When a part is to be subjected to hard usage or to severe strains and stresses, forging or hammering rather than casting may be the process employed in shaping it. Drop forgings are made by means of automatic power hammers and dies. With few exceptions forgings, also, must be finished by machining.
Sheet-metal workers lay out work on sheet metal, cut it, shape or bend it, and solder, rivet or weld it into various forms, such as are required in building up ornamental cornices for buildings, or in constructing hot-air heating apparatus, or in manufacturing filing cases, various sorts of containers, and many other articles. Some of the work is outside work, but an increasing number of processes are being performed in the shop with the use of machinery. Metal stamping and electric welding machines are used to form and weld together parts of, for example, automobile bodies, doors, and fenders.
Of all the metal-working trades, that of the machinist is the most varied in its hand and machinery processes, although many workmen never learn more in the trade than how to operate some one automatic machine, or how to do some one simple task. In general the machinist should know how to operate all of the machinery of his trade, and in addition he must acquire skill of hand in metal working, and especially in the processes of building, repairing, assembling, and erecting every sort of engine and machine.