Metal-Working Processes | Research & Encyclopedia Articles

Metal-Working Processes

Historians can only speculate on how metals were first discovered and worked. Since most metals must be softened by heat in order to be extracted from their ores, campfires and hearths may have been where metals were initially observed and subjected to experimentation. Some observant individual might have noticed that rocks near the heat softened and rehardened. Eventually, someone learned to manipulate the metal ore and searched for ways to obtain more of the new material. The same act of discovery of any single metal may have been repeated in different parts of the world.

Simultaneous discoveries in metallurgy occurred in more recent times with such inventors as William Kelly and Sir Henry Bessemer, the Siemens brothers and Pierre-Emile Martin; and Charles Martin Hall and Paul-Louis-Toussaint Héroult. It seems reasonable to suppose similar multiple discoveries occurred even more often in prehistory or early historical periods, when communication of technology was much more limited than it has been in the last two or three centuries.

Early metalworkers had to extract, or reduce, metal from rock by repeated heating and hammering with stone or wooden mallets. Although it was laborious, people realized that metal was more useful than stone or wood for many purposes, and metallurgy became an important part of human culture. However, it took thousands of years for metals to become the everyday substances they are today. Not until the nineteenth century were metal implements mass-produced cheaply. Before that, metal was costly and used only for important tools or for items associated with wealth and prestige. The metal nails, kettles, and other implements that commoners owned were expensive items to be guarded closely and used carefully. Repeated hammering not only shaped the metal but allowed impurities to be worked out and burned off. This process, called forging, takes metal from its natural state and turns it into a useable commodity.

Around 2000 b.c., other methods of working metal, such as molding, inlaying, soldering, and enameling appeared. People increasingly used alloys of metals as well. Bronze, a mixture of copper and tin, was the first metal alloy; it made implements stronger and more workable. The period of about 3000 to 2000 b.c. is known as the Bronze Age, so named for the widespread use of bronze during that time. The making of coins probably started in Greece during the seventh century b.c. and spread throughout the Mediterranean. One of the first improvements in metalworking were the bronze dies used to strike, or mint, identical images on coins. By doing this, a ruler could spread his image throughout his domain. The Lydian king Croesus (died 546 b.c.) is supposed to have been the first to mint such standardized coins.

Throughout the first millennium a.d., knowledge of metals gradually increased. Zinc, antimony, and nickel were discovered, and monks established foundries to make bells for monasteries and iron tools for the surrounding region. In Sheffield, England, metalworking was taken to artistic heights with the manufacture of fine cutlery. During the 700s a.d. the productive output of forges increased with the development of the Catalan forge which achieved a hotter sustained heat by blowing air into the furnace. The blast furnace, as it is called, was gradually improved over the centuries, but working the metal still required hammering. Another advance in metalworking during the Middle Ages was wire drawing, the means whereby metal is elongated into wire by pulling. First developed about 1000 a.d., it was later improved by Rudolf of Nuremberg in 1350.

Although the Industrial Revolution is associated with the steam engine and the beginnings of automation, the advances in metalworking which occurred during the seventeenth and eighteenth centuries prepared the way for new machinery, which often required large amounts of strong, well-worked metal to withstand pressure and stress. Mechanical, or drop forging using large trip hammers was regularly practiced by the 1700s. The drop hammer had a moving die that dropped onto a stationary die, delivering a powerful blow to the molten metal while counterblow forging used converging dies. Abraham Darby, founder of the ironworking industry, introduced coke to the blast furnace, which mass-produced large quantities of cast iron in the early 1700s.

One of the first practical metal lathes was the screw-cutting machine Henry Maudslay (1771-1831) invented in 1800. It automatically cut the threads into the shaft of the screw. Other advancements were also made prior to and during the Industrial Revolution, such as the development of milling machines. These devices are similar to lathes except that the workpiece, the item being milled, is held stationary while the cutter does the moving. In the lathe, the workpiece is turned. After several prototype milling machines were introduced, the universal milling machine developed by American engineer Joseph R. Brown (1810-1876) in 1867 was adaptable to circular cutting, square cutting, boring, grooving, and grinding.

At the turn of the twentieth century, another American engineer, B. Atha, developed the first continuous casting process for steel, in which the metal was poured into a vertical mold, however, he experienced problems with the metal clinging to the mold during cooling. In 1935 Dr. Siegfied Junghans solved Atha's problem by creating a reciprocating mold that reduced the risk of clinging. The continuous sheet mill first appeared in Teplice, Bohemia, in 1892. It was abandoned, then resumed in America, first by Charles W. Bray in 1902, then by John B. Tyrus in 1923. This final attempt led to the founding of the American Rolling Mill Company (Armco). Shell molding was invented in 1941 at a foundry in Hamburg owned by Johannes Croning (1872-1962). The mold was made of sand held together by phenolic resin. Since this was a wartime invention, it was not used outside Germany until the late 1940s, when Ford Motor Company used it to form automobile exhaust valves.

A more recent development is explosive metal-working, in which metal is shaped by impulse waves transmitted by a chemical explosion. Initial work was done by the National Aeronautics and Space Administration (NASA) in the 1960s for space-technology metals. After funding ran out, the program was picked up on an experimental basis by several international companies. The process is problematic because it has so far proven too dangerous for use in conventional factories and not adaptable to mass production.

Metal-working methods for fusing metals together include welding and soldering. Oxyacetylene welding, invented in 1903, can also be used to cut metal. Electroplating uses electrolysis to coat base metals with attractive, less corrosive metals, such as chromium, nickel, or silver. Galvanizing protects iron or steel with a protective layer of zinc. Alloys and composites combine two or more metals in order to utilize the unique characteristics of each. Alloys thoroughly combine metals, while composites introduce units of one metal into a matrix of another.