Engineering Materials

Engineers have to know the best and most economical materials to use. Engineers must also understand the properties of these materials and how they can be worked. There are two kinds of materials used in engineering (1) – metals and non-metals. Metals are distinguished from non-metals by their high conductivity for heat and electricity, by metalic lustre (2) and by their resistance to electric current. Their properties, such as strength (3) and hardness (4), can be greatly improved by

alloying (5) them with other metals.

We can divide metals into ferrous and non-ferrous (6). The former contain iron and the latter (7) do not contain iron. Cast iron (8) and steel, which are both alloys, or mixtures of iron and carbon, are the two most important ferrous metals. There are some other important groups of metals and alloys. The common metals such as iron, copper, zinc, etc. are produced in great quantities. Aluminium, copper, and the alloys (bronze and brass) are common non-ferrous metals. The so-called precious metals include silver, gold, platinum and palladium. The light metals are aluminium, berillium and titanium. They are important in aircraft and rocket construction.

Many elements are classified as semimetals (bismuth, for example) because they have much poorer conductivity than common metals. Non-metals (carbon, silicon, sulphur) in the solid state are usually brittle materials without metallic lustre and are usually poor conductors of electricity. Non-metals show greater variety of chemical properties than common metals do. Plastics and ceramics are non-metals; however plastics may be machined(9) like metals. Plastics are classified into types – thermoplastics (10) and thermosets (11). Thermoplastics can be shaped and reshaped by heat and pressure but thermosets cannot be reshaped because they undergo chemical changes as they harden (12). Engineers often employ ceramics when materials which can withstand high temperatures are needed.

Materials Science and Technology is the study of materials and how they can be fabricated to meet the needs (13) of modern technology. Scientists are finding new ways of using metals, plastics and other materials. For this purpose they use the laboratory techniques and knowledge of physics, chemistry and metallurgy.

Non-Metals

Non-metals are plastics and ceramics. Non-metals in the solid state are usually brittle (1) materials without metallic lustre (2) and are usually poor conductors (3) of electricity. Non-metals show greater variety of chemical properties than common metals do. Plastics are a large group of materials. They consist of combinations of carbon and oxygen, hydrogen, nitrogen, and other organic and inorganic elements. Plastics is the result of synthesis of such natural materials as water, air, salt, coal, petroleum, and natural gas. The technology is simple and cheap. They are solid in finished state, but are liquid at some stage of manufacture. That is why it is easy to form plastics into various shapes.

There are over 40 different families of plastics in commercial use today, and each may have dozens of variations. Plastics are light, strong and corrosion-resistant (4). They have won many significant applications in industry and transportation. Engineers use plastics in electric and electronic equipment, agriculture, consumer products (5). There is no industry now where plastics are not used.

Fibre (6) technology, in its modern form, is of more recent origin than plastics. The fibre industry can be divided between natural fibres (from plant, animal, or mineral sources) and synthetic fibres. Many synthetic fibres replaced natural fibres, because they often behave more predictably (7) and are usually more uniform in size. For engineering purposes glass, metallic, and organically derived synthetic fibres are most significant.

Nowadays ceramics are gaining an increasing popularity in industry. Advanced (8) ceramic materials have such interesting properties that mechanical engineers are becoming more interested in their use as structural parts (9). Ceramic cutting tools (10) have been in use for some time. However, it is only during the last twenty years that there have been rapid development in this field because of the development of new composite (11) ceramics.

Recently engineers have developed various kinds of composite ceramics which must combine an increased toughness (12) with the same hardness (13) and strength (14) of usual ceramics. Thus, at room and high temperatures the composite ceramics for cutting tools should possess the following properties: high strength, toughness, hardness, high thermal shock resistance (15) and high chemical inertness.

Engineers must know the best and most economical materials to use, understand the properties of these materials and how they can be worked.

Machine Tools

Metal undergoes a number of processes before it is formed into the required shape: casting (1), rolling (2), welding (3), piercing (4), trimming (5), spinning (6), bending (7), drawing (8), etc. The machines which perform all these kinds of work are called machine-tools. Machine-tools are stationary power-driven machines used to shape or form solid materials, especially metals. Machine tools form the basis of modern industry.

Machine tools may be classified under three main categories: conventional chip-making machine-tools, presses, and unconventional machine-tools. Conventional chip-making tools shape the workpiece by cutting away the unwanted portion in the form of chips. Presses employ a number of different shaping processes, including shearing (9), pressing, or drawing (elongating).

Unconventional machine-tools employ light, electrical, chemical, and sonic energy; superheated gases; and high-energy particle beams to shape the exotic materials and alloys that have been developed to meet the needs of modern technology.

Cutting is one of the oldest arts practised in the stone age, but the cutting of metals was not found possible until the 18th century, and its detailed study started about a hundred years ago. Modern machine-tools date from about 1775, when the English inventor John Wilkinson constructed a horizontal boring machine for producing internal cylindrical surfaces. About 1794 Henry Maudslay developed the first engine lathe. Later, Joseph Whitworth developed measuring instruments accurate to a millionth of an inch. His work was of great value because precise methods of measurement were necessary for the subsequent mass production of articles having interchangeable (10) parts.

During the 19^th century, such standard machine-tools as lathes, shapers (11), planers (12), grinders, and saws, as well as milling, drilling, and boring machines reached a high degree of precision, and their use became widespread in the industrializing nations.

Nowadays all machining operations are done more accurately and faster owing to the automation of all the production processes. Numerically controlled machine tools (13) (NC) and flexible manufacturing systems (14) (FMS) have made it possible to do the work automatically. The operator only watches them and corrects them whenever they go wrong.

Most machining operations generate large amounts of heat and use cooling fluids (usually a mixture of water and oils) for cooling and lubrication. Cooling increases tool life and helps to stabilize the size of the finished part. Lubrication reduces friction.

Most materials and their alloys can be machined – some with ease, others with difficulty. Machinability (15) involves three factors: 1. Ease of chip removal. 2. Ease of obtaining a good surface finish. 3. Ease of obtaining good tool life.