Metalworking is the process of shaping and reshaping metals in order to create useful objects, parts, assemblies, and large scale structures. As a term, it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale: from huge ships, buildings, and bridges, down to precise engine parts and delicate jewellery.
The historical roots of metalworking predate recorded history; its use spans cultures, civilizations and millennia. It has evolved from shaping soft, native metals like gold with simple hand tools, through the smelting of ores and hot forging of harder metals like iron, up to and including highly technical modern processes such as machining and welding. It has been used as an industry, a driver of trade, individual hobbies, and in the creation of art; it can be regarded as both a science and a craft.
Modern metalworking processes, though diverse and specialized, can be categorized into one of three broad areas known as forming, cutting, or joining processes. Modern metalworking workshops, typically known as machine shops, hold a wide variety of specialized or general-use machine tools capable of creating highly precise, useful products. Many simpler metalworking techniques, such as blacksmithing, are no longer economically competitive on a large scale in developed countries; some of them are still in use in less developed countries, for artisanal or hobby work, or for historical reenactment.
Prehistory The oldest archaeological evidence of copper mining and working was the discovery of a copper pendant in northern Iraq from 8,700 BCE.Hesse, Rayner, W. (2007). Jewelrymaking through History: an Encyclopedia. Greenwood Publishing Group. p. 56. . The earliest substantiated and dated evidence of metalworking in the Americas was the processing of copper in Wisconsin, near Lake Michigan. Copper was hammered until it became brittle, then heated so it could be worked further. In America, this technology is dated to about 4000–5000 BCE. The oldest gold artifacts in the world come from the Bulgarian Varna Necropolis and date from 4450 BCE.
Not all metal required fire to obtain it or work it. Isaac Asimov speculated that gold was the "first metal".Asimov, Isaac: "The Solar System and Back", pp. 151 ff. Doubleday and Company, Inc. 1969. His reasoning being, that, by its chemistry, it is found in nature as nuggets of pure gold. In other words, gold, as rare as it is, is sometimes found in nature as a native metal. Some metals can also be found in meteors. Almost all other metals are found in ores, a mineral-bearing rock, that require heat or some other process to liberate the metal. Another feature of gold is that it is workable as it is found, meaning that no technology beyond a stone hammer and anvil is needed to work the metal. This is a result of gold's properties of malleability and ductility. The earliest tools were stone, bone, wood, and sinew, all of which sufficed to work gold.
At some unknown time, the process of liberating metals from rock by heat became known, and rocks rich in copper, tin, and lead came into demand. These ores were mined wherever they were recognized. Remnants of such ancient mines have been found all over Southwestern Asia.Percy Knauth et al. "The Emergence of Man, The Metalsmiths", pp. 10–11 ff. Time-Life Books, 1974. Metalworking was being carried out by the South Asian inhabitants of Mehrgarh between 7000 and 3300 BCE.Possehl, Gregory L. (1996). Mehrgarh in Oxford Companion to Archaeology, Brian Fagan (Ed.). Oxford University Press. The end of the beginning of metalworking occurs sometime around 6000 BCE when copper smelting became common in Southwestern Asia.
Ancient civilisations knew of seven metals. Here they are arranged in order of their oxidation potential (in volts):
Iron +0.44 V, Tin +0.14 V Lead +0.13 V Copper −0.34 V Mercury −0.79 V Silver −0.80 V Gold −1.50 V.
The oxidation potential is important because it is one indicator of how tightly bound to the ore the metal is likely to be. As can be seen, iron is significantly higher than the other six metals while gold is dramatically lower than the six above it. Gold's low oxidation is one of the main reasons that gold is found in nuggets. These nuggets are relatively pure gold and are workable as they are found.
Copper ore, being relatively abundant, and tin ore became the next important substances in the story of metalworking. Using heat to smelt copper from ore, a great deal of copper was produced. It was used for both jewelry and simple tools. However, copper by itself was too soft for tools requiring edges and stiffness. At some point tin was added into the molten copper and bronze was developed thereby. Bronze is an alloy of copper and tin. Bronze was an important advance because it had the edge-durability and stiffness that pure copper lacked. Until the advent of iron, bronze was the most advanced metal for tools and weapons in common use (see Bronze Age for more detail).
Outside Southwestern Asia, these same advances and materials were being discovered and used around the world. People in China and Great Britain began using bronze with little time being devoted to copper. Japanese began the use of bronze and iron almost simultaneously. In the Americas it was different. Although the peoples of the Americas knew of metals, it was not until the European colonisation that metalworking for tools and weapons became common. Jewelry and art were the principal uses of metals in the Americas prior to European influence.
About 2700 BCE, production of bronze was common in locales where the necessary materials could be assembled for smelting, heating, and working the metal. Iron was beginning to be smelted and began its emergence as an important metal for tools and weapons. The period that followed became known as the Iron Age.
History
By the historical periods of the Pharaohs in Egypt, the Vedic kings in India, the Tribes of Israel, and the Maya civilization in North America, among other ancient populations, humans had begun to attach value to precious metals over and above any available functional metal tools and weapons. Gold or silver trinkets became luxury goods in antiquity. In some cases rules for ownership, distribution, and trade were created, enforced, and agreed upon by various peoples. By the above periods metalworkers were very skilled at creating objects of adornment, religious artifacts, and trade instruments of precious metals (non-ferrous), as well as weaponry (usually of ferrous metals and/or alloys). Sophisticated techniques were practiced by artisans, blacksmiths, atharvavedic practitioners, alchemists, and other categories of metalworkers around the globe. For example, the granulation technique occurs in numerous ancient cultures before the historic record shows people traveled to far regions to share this process. Metalsmiths today still use this and many other ancient techniques.
Over time, metal objects became more common and ever more complex. The need to further acquire and work metals grew in importance. Skills related to extracting metal ores from the earth began to evolve, and metalsmiths became more knowledgeable. Metalsmiths became important members of society. Fates and economies of entire civilizations were greatly affected by the availability of metals and metalsmiths. The metalworker depends on the extraction of precious metals to make jewelry, build more efficient electronics, and for industrial and technological applications from construction to shipping containers to rail, and air transport. Without metals, goods and services would cease to move around the globe on the scale we know today.
General processes
Metalworking generally is divided into three categories: forming, cutting, and joining. Most metal cutting is done by high speed steel tools or carbide tools., mechanicalsite.com, retrieved 2019-14-05. Each of these categories contains various processes.
Prior to most operations, the metal must be marked out and/or measured, depending on the desired finished product.
Marking out (also known as layout) is the process of transferring a design or pattern to a workpiece and is the first step in the handcraft of metalworking. It is performed in many industries or hobbies, although in industry, the repetition eliminates the need to mark out every individual piece. In the metal trades area, marking out consists of transferring the engineer's plan to the workpiece in preparation for the next step, machining or manufacture.
Calipers are hand tools designed to precisely measure the distance between two points. Most calipers have two sets of flat, parallel edges used for inner or outer diameter measurements. These calipers can be accurate to within one-thousandth of an inch (25.4 μm). Different types of calipers have different mechanisms for displaying the distance measured. Where larger objects need to be measured with less precision, a tape measure is often used.
+ Compatibility chart of materials versus processes Material Process Iron Steel Aluminium Copper Magnesium Nickel Refractory metals Titanium Zinc Brass Bronze Sand casting X X X X X X 0 0 X Permanent mold casting X 0 X 0 X 0 0 0 X Die casting X 0 X X Investment casting X X X 0 0 0 X Ablation casting X X X 0 0 Open-die forging 0 X X X 0 0 0 Closed-die forging X 0 0 0 0 0 0 Extrusion 0 X X X 0 0 0 Cold heading X X X 0 Stamping & deep drawing X X X 0 X 0 0 Screw machine 0 X X X 0 X 0 0 0 X X Powder metallurgy X X 0 X 0 X 0 Key: X = Routinely performed, 0 = Performed with difficulty, caution, or some sacrifice, blank = Not recommended
Casting
Casting achieves a specific form by pouring molten metal into a mold and allowing it to cool, with no mechanical force. Forms of casting include: Investment casting (called lost wax casting in art) Centrifugal casting Die casting Sand casting Shell casting Spin casting
Forming processes These forming processes modify metal or workpiece by deforming the object, that is, without removing any material . Forming is done with a system of mechanical forces and, especially for bulk metal forming, with heat.
Bulk forming processes
Plastic deformation involves using heat or pressure to make a workpiece more conductive to mechanical force. Historically, this and casting were done by blacksmiths, though today the process has been industrialized. In bulk metal forming, the workpiece is generally heated up. Cold sizing Extrusion Drawing Forging Powder metallurgy Friction drilling Rolling Burnishing
Sheet (and tube) forming processes
These types of forming process involve the application of mechanical force at room temperature. However, some recent developments involve the heating of dies and/or parts. Advancements in automated metalworking technology have made progressive die stamping possible which is a method that can encompass punching, coining, bending and several other ways below that modify metal at less cost while resulting in less scrap. Bending Coining Decambering Deep drawing (DD) Foldforming Hydroforming (HF) Hot metal gas forming Hot press hardening Incremental forming (IF) Spinning, Shear forming or Flowforming Planishing Raising Roll forming Roll bending Repoussé and chasing Rubber pad forming Shearing Stamping Superplastic forming (SPF) Wheeling using an English wheel (wheeling machine)
Cutting processes
Cutting is a collection of processes wherein material is brought to a specified geometry by removing excess material using various kinds of tooling to leave a finished part that meets specifications. The net result of cutting is two products, the waste or excess material, and the finished part. In woodworking, the waste would be sawdust and excess wood. In cutting metals the waste is chips or swarf and excess metal.
Cutting processes fall into one of three major categories: Chip producing processes most commonly known as machining