Types of materials used::
Automatic steels (or for high speed machining) are specially made to be processed on automatic machines with chip removal, such as CNC lathes and turning centres. The distinctive feature of automatic steels is that they contain a certain amount of sulphur or lead which, by ensuring higher machinability, enable faster machining speeds, therefore increasing production capacity while, at the same time, preserving the tools.
These include construction steels, with a carbon content of <0.25%, destined for carburizing surface hardening treatment, which consists of the carbon enrichment of the part’s surface and subsequent hardening that confers a high surface hardness with excellent resistance to wear, while the low carbon content of the core enables increased toughness in the underlying mass. Case-hardening steels are used for the construction of mechanical parts such as all types of gears, axles, cones, pins, bushings, nuts, distribution gears and transmission shafts, etc.
These include construction steels destined for hardening treatment (hardening followed by tempering at 600°C). In general, hardened steels are used in the construction of mechanical parts that are subjected to static and dynamic loads, and they are widely used in mechanical industries, for all types of shafts, drive shafts, rods, connecting rods, linkages, levers, rods for power hammers, columns, presses, etc.
Common steels are low-medium resistance steels, used for the manufacture of parts that must withstand modest static type stresses. They are generally characterized by good weldability. They do not contain additional alloying elements and are not subjected to heat treatments (except annealing and normalizing).
Stainless steels are those alloys of iron, chromium and carbon that may contain other elements such as Ni - Mo - Si - etc., whose main characteristic is its resistance to corrosion. This characteristic is due to its tendency to become passivated in the presence of an oxidizing environment (therefore also in air). Passivation consists of the formation of an invisible layer of oxide, which varies according to the chemical composition of the steel. A minimum of 11% chromium is an essential condition for the formation of the protective layer.
Brasses are alloys of copper (Cu) and zinc (Zn). First we must distinguish between binary brasses, consisting only of copper and zinc, and ternary brasses, which contain a third element characterizing the alloy or other quaternary brasses which contain other chemical elements. Alloys with Zn percentages of more than 45% are of no practical interest. The machine tool workability of copper-zinc binary alloys is good, but its toughness results in the formation of very long chips. In this case, lead (Pb) is added which, being insoluble and extraneous to the crystalline structure, is distributed in microscopic globules throughout the metal: thus breaking up the machining chips, or even turning them powdery, and the tools are subjected to less wear and heating, with a consequent improvement in quality and machining times. Other elements can be added to the alloys to achieve certain properties, e.g. manganese, iron, aluminium, antimony and arsenic, nickel and silicon.
Aluminium is a silver-coloured ductile metal which is extracted mainly from bauxite ore and is remarkable for its softness, lightness and resistance to oxidation, due to the formation of a thin oxide layer that prevents oxygen corroding the underlying metal. Raw aluminium is worked through various industrial production processes, such as casting, forging or moulding. Aluminium is used in many industries for the manufacture of millions of different products and is very important for the world economy.