Working different materials such as metal, iron alloys, wood and some plastics calls for specific machining machines. These are known as machine tools, and their job is to shape solid workpieces. They are typically stationary, large in size and capable of three types of machining.
What are the types of machining?
In the metalworking industry there are three types of machining: with chip removal, without chip removal and by abrasion. The first type involves the removal of surplus material from the surface of a workpiece in small particles known as swarf; this kind of machining is carried out by machines such as lathes and milling machines.
Machines that work without chip removal use other processes to shape the workpiece. One example is the press in its various forms. Presses are used to deform metal plates, known as sheet metal, but they do not remove chips. EDM machines, laser cutting machines, plasma cutters and so on can also be regarded as non-chip-removal machines.
Finally, abrasive machining is a process in which the workpiece is worn away using a grinding wheel. The grinding wheel is made up of abrasive grains held together by a bond, which wear down the surface of the workpiece. The machines that carry out these operations are grinding machines.
What are machining machines?
Machining machines, or machine tools, are characterised by using a power source other than human effort, although many machines also require input from operators when no other power source is available. These machines have a very long history; in fact, the first lathe is believed to have been invented in Antiquity. The lathe as we know it today was created around 1751 and included a mechanically adjustable cutting tool.
However, the great technological leap for these machines came during the Industrial Revolution, with the invention of the steam engine. It was from this revolution onwards that the milling machine became widespread and, together with the lathe, one of the most widely used pieces of equipment in workshops.
These machines can be operated by handwheels, gears and levers, but also by automatic, computer-based control. Computer numerical control was invented in the 60s, when computers were added to machines to speed up processes. This equipment features the most sophisticated technology and makes it possible to boost production while cutting lead times and labour. It also allows parts with far more complex designs to be produced.
Interestingly, machining machines are known as mother machines, because they are capable of building all other machines, including themselves. They can also manufacture parts of very different sizes used across many industries, from a screw to an aircraft fuselage.
Types of machines
Machining machines can be classified into three different types, regardless of the type of machining they perform: roughing machines (which remove chips), presses (which form parts by deformation) and special machines. The latter use different machining techniques such as laser cutting, plasma or EDM.
The main roughing machines, also called conventional machines, are:
- Lathe: machines rotationally symmetrical parts that turn while clamped in a chuck, as the cutting tool approaches the surface and removes chips. Lathes are used to machine cylindrical and conical shapes. They can also drill holes when fitted with a drill bit.
- Milling machine: uses a multi-edge cutting tool called a milling cutter. The machine head remains stationary while the workpiece is moved towards it to remove material.
- Drilling machine: used to drill holes by rotating a tool (the drill bit).
- Grinding machines or polishers: use an abrasive disc or wheel that wears down the surface of the workpiece to improve its finish.
Presses come in different types, such as mechanical and hydraulic, and are used for forming processes. The workpiece is placed on a die beneath a punch which, when actuated, strikes the workpiece and deforms it beyond its elastic limit.
The non-conventional and special machining machines are:
- EDM machine: uses electrical sparks, which melt particles of the material. There are sinker and wire (conductive wire) versions. The workpieces are immersed in a non-conductive fluid.
- Plasma arc: uses a jet of gas at very high temperature and pressure to cut the material.
- Laser: laser machining cuts surfaces by vaporising the material at high temperatures.
- Ultrasonic: uses vibrations at ultrasonic frequencies together with abrasives and water to machine by friction.