Materials processing, the series of operations that transforms industrial materials from a raw-material state into finished parts or products. Industrial materials are defined as those utilized in the manufacture of “hard” goods, like more or less durable machines and equipment produced for industry and consumers, as contrasted with disposable “soft” goods, like chemicals, foodstuffs, pharmaceuticals, and apparel.
Materials processing by hand is as old as civilization; mechanization began with the economic Revolution of the 18th century, and within the early 19th century the essential machines for forming, shaping, and cutting were developed. Since then, materials-processing methods, techniques, and machinery have grown in variety and number.
The cycle of producing processes that convert materials into parts and products starts immediately after the raw materials are either extracted from minerals or produced from basic chemicals or natural substances. Metallic raw materials are usually produced in two steps. First, the crude ore is processed to extend the concentration of the specified metal; this is often called beneficiation. Typical beneficiation processes include crushing, roasting, magnetic separation, flotation, and leaching. Second, additional processes like smelting and alloying are used to produce the metal that’s to be fabricated into parts that are eventually assembled into a product.
The processes used to convert raw materials into finished products perform one or both of two major functions: first, they form the material into the specified shape; second, they alter or improve the properties of the material.
Forming and shaping processes could also be classified into two broad types—those performed on the material during a liquid state and those performed on the material during a solid or plastic condition. The processing of materials in liquid form is usually called casting when it involves metals, glass, and ceramics; it’s called molding when applied to plastics and some other non-metallic materials. Most casting and molding processes involve four major steps:
- Making an accurate pattern of the part.
- Making a mold from the pattern,
- Introducing the liquid into the mold, and
- Removing the hardened part from the mold. A finishing operation is usually needed.
There are a variety of metal-cutting processes. In most of them, machining involves the forcing of a cutting implement against the material to be shaped. The tool, which is harder than the material to be cut, removes the unwanted material in the type of chips. Thus, the elements of machining are a cutting device, a method for holding and positioning the workpiece, and typically a lubricant (or cutting oil). There are four basic noncutting removal processes:
- In chemical milling the metal is removed by the etching reaction of chemical solutions on the metal, although usually applied to metals, it can even be used on plastics and glass.
- Electrochemical machining uses the principle of plating in reverse, because the workpiece, rather than being built up by the plating process.
- Electro-discharge machining and grinding erodes or cuts the metal by high-energy sparks or electrical discharges.
- Laser machining cuts metallic or refractory materials with an intense beam of light from a laser.
Another further alteration is also “joining,” the method of permanently, sometimes only temporarily, bonding or attaching materials to each other. The term as used here includes welding, brazing, soldering, and adhesive and chemical bonding. In most joining processes, a bond between two pieces of material is produced by the application of one or a mixture of three types of energy: thermal, chemical, or mechanical. A bonding or filler material, similar to or different from the materials being joined, may or might not be used.
The properties of materials are often further altered by hot or cold treatments, by mechanical operations, and by exposure to some sorts of radiation. Property modification is typically caused by a change in the microscopic structure of the material. Both heat-treating, involving temperatures above room temperature, and cold-treating, involving temperatures below room temperature, are included in this category. Thermal treatment is a process during which the temperature of the material is raised or lowered to change the properties of the initial material. Most thermal-treating processes are based on time-temperature cycles that include three steps: heating, holding at temperature, and cooling. Although some thermal treatments are applicable to most families of materials, they’re most generally used on metals.
Finally, “finishing” processes could also be used to change the surfaces of materials so as to protect the material against deterioration by corrosion, oxidation, mechanical wear, or deformation; to produce special surface characteristics like reflectivity, electrical conductivity or insulation, or bearing properties; or to provide the material special decorative effects. There are two broad groups of finishing processes, those during which a coating, usually of a special material, is applied to the surface and those during which the surface of the material is modified by a chemical process, heat, or mechanical force. the primary group includes metallic coating, like electroplating; organic finishing, like painting; and porcelain enameling.