Modern machine tools are primarily defined by their ability to produce and machine work pieces by employing certain tools. As work machines, they (rather than humans) determine the movements and countermovements of work piece and tool relative to each other. Along with measuring and test equipment, fixtures and conventional tools, they are part of a company’s operating resources, and they can be classified in a number of ways.
As a result of recent technical developments, machine tools are now increasingly categorised not only as mechanised but also often as automated operating resources. The latter reflects the current efforts and technical progress being made within the industry: the automation and interplay of machines with intelligent systems have a great impact on the nature and role of machine tools within the industrial sector.
The diversity of machine tools is enormous, and the same applies to their applications and fields of use, yet their configurations are generally relatively similar, as there are many features that they have in common. They are typically composed of a combination of modular assembly units. This building block principle not only makes them easy to put into operation but also enables them to satisfy the specific requirements of a variety of applications. It also means that system components can be subsequently exchanged should the need arise.
The fundamental module and basis of any machine tool is the frame. It is the component that gives the machine as a whole its physical appearance and that supports and connects its other components. A machine tool’s frame is of particular relevance in large and complex configurations that are designed to withstand large loads. In contrast to small machines, whose frame is frequently in the form of a modified table, large machine frames must display a high level of resistance to elastic deformation. When selecting the construction materials of the frame, it is important to take into consideration such factors as density, damping, and heat conductivity. Some machine tools require a cast metal foundation to ensure the necessary degree of rigidity.
The assembly unit containing the guides and mountings plays a central role in ensuring a machine tool’s continuous functionality. It determines the axes that the machine components move along. Being in direct contact with other system components, the guides and mountings are susceptible to a degree of wear, which can however be minimised, for example, by employing ball bearings.
The motor and gears making up the primary drive unit are responsible for generating the machine tool’s movements. In addition, a number of secondary drives serve various purposes, in particular as advancers for positioning the tool. The various drive elements are not only responsible for putting a machine tool in motion, but also play a defining role in determining its operating precision and, in turn, the quality of the work pieces it produces. Such characteristics are displayed by the Harmonic Drive® FHA, CHA and CanisDrive® series of hollow shaft drives. Featuring reinforced output bearings with maximum precision and tilt rigidity, these drives are able to quickly and unproblematically absorb high load levels, as well as offering a long service life and short swivel times.
The principle purpose of the controller is to determine the machine’s automatic operation. It performs a number of tasks that were previously conducted either manually or with the aid of mechanical assistance. It controls and guides the production steps, stores machine and tool-related data, and backs up production programs. Modern machine tools incorporate electronic components, such as semiconductor elements and relays. The latter offer considerably greater flexibility than many other process controllers.
Other assembly units found in modern machine tools include tool magazines, tool changers, work piece changers, tool holders and supply & disposal facilities. There are also safety facilities and measuring systems (for example for determining the tool position).
There are numerous ways of classifying machine tools. It can be done on the basis of the number of axes, kinematics, precision, or the degree of automation. The most commonly used method of distinguishing between different machine types is according to their work process. Lathes and milling machines as well as drills, sawing machines, grinders and other similar devices are examples of material reducing/chip forming equipment, while bending and rolling machines and presses etc. are classified as shaping tools. Guillotines and die-cutting machines are types of cutting equipment, while ablative processes are performed by laser-ablation and water-jet-cutting machines. Joining machines perform such activities as welding, soldering and bonding.
The mass production of utility and consumer goods in the 21st century is largely a result of the constant development in machine tools. Today, powerful and almost completely automated machines are an integral part of any modern production and manufacturing facility in the industrial sector. However, the history of machine tools did not just begin in the last few decades; in fact, the precursors of today’s modern machine tools were created centuries – or sometimes even millennia – ago. The invention of the first machine tool, in the form of a primitive drilling apparatus, could have been as long as 6,000 years ago. Even though historical devices, such as turning lathes and grinding machines, cannot be compared with today’s equipment, they nevertheless satisfied some of the criteria by which machine tools are still defined today.
The industrial revolution and the social changes that it brought about created a demand for increasingly powerful and advanced machine. The degree of auxiliary manual activity that was required started to fall, while new innovations achieved a greater cost-effectiveness and higher production quantities. The rapid growth in demand not only enhanced the popularity of these machines but also promoted their inexorable technical advancement. It was only through the development of special turning and drilling machines in the 18th and 19th centuries, for example, that metal was able to establish itself as a commonly used material. The 20th century saw the next major leap in development, in the form of computerised numerical control, or CNC systems. These enable machine tools to be controlled in a manner that is individually modified to the respective application, usually with their own separate operating system and user interface.