Machine tool

Printer Friendly Format

Bookmark this page

Back to "Tool"

For the shaping of the workpiece the machine tool produces a relative motion between tool and workpiece. Here one differentiates between the main movement (with cutting machines "„the Schnittbewegung "“, e.g. the turn of the spindle) and the feed and/or Zustellbewegung, which are overlaid the rotating motion and a continuous treatment (e.g. splinter acceptance) permitted.

Generally transforming and separating become (i.e. essentially: dividing, cutting and clearing away) as well as adding machine tools among other things in mechanical engineering and used in the tool construction.

Transforming machines serve usually the treatment of metals, like e.g. steel or aluminum and of plastics, dividing and cutting machine tools serve beyond that also the treatment of other materials, like e.g. wood. Among the clearing away machine tools erosion machines and laser processing machines e.g. rank.

The working accuracy (precision) of cutting machine tools lies, depending upon kind of machine, within the range of 1 mm up to 1/1000 mm. reach accuracies of less than 1/1.000.000 mm (e.g. for the treatment of laser optics).

For the transforming and cutting treatment high speed working on tools are needed predominantly. So that these meet the high requirements, they today mostly consist of coated or uncoated tungsten carbide, Cermet, ceramic(s), diamond or boron nitride (CBN).

Building groups of machine tools

Rack/foundation

The machine rack takes up the working on forces and carries the other elements. Remarks from grey cast iron (rare cast steel), concrete (polymere or wet mix aggregate) or welded structural steelworks are typical. With one finds also rack construction units from granite. With smaller machines the racks than table and console design are implemented. For heavier machines bed remarks are used in open (stand) or more closed (portal) building method. With large machines special foundations are necessary, in order to derive the high or, e.g. with transforming machines, jerky loads into the underground.

Guidance

Guidance serve for the accurate delimitation of the movements on a degree of freedom. There are hydrostatic, hydrodynamic, aero-static guidance and Originally predominantly hydrodynamic sliders were used, because of its dynamic characteristics (no stick slip effect, high rates of motion etc.) become generally accepted lately ever more the Since for the production of however special technical know-how is necessary, these are referred predominantly today as part to be bought of suppliers.

Drives

Among the drive units rank the main drive and the feed drives as well as the auxiliary drives. The main drive consisted in former times usually of an engine (usually electric motor), a transmission, a safety clutch (in the simplest case a drive belt in the case of overload slips through) as well as the Hauptspindel as carriers of the tool and/or workpiece. Today's machine tools have usually a Direktantrieb with that the rotor of the electric motor directly on the Hauptspindel sit (engine spindle). Due to the large achievement of the drives, particularly with the use of engine spindles, it is to be exhausted importantly the dissipated heat purposefully, in order to avoid inaccuracies of the machine due to the thermal expansion of the rack. With transforming machines also hydraulic drives come to the employment beside mechanical transmissions (knuckle-joint presses).

As camps of the moving parts are used to 90% antifriction bearing, in addition, hydrodynamic, hydrostatic sliding bearings, air bearings and magnetic bearings.

In former times the feed motion was derived over a transmission from the main drive. Today generally all mobile axles have own feed drives. These consist generally of an electric motor, a Kugelgewindetrieb and a measuring system for the positioning of the mobile rack elements (slideway, - table or - stand). For the translation of the rotatorischen engine movement into a translatorische carriage or stand movement "“rack pinion systems so mentioned"” are used more rarely. Since with linear Direktantrieben high positioning accuracies and high dynamics can be obtained at the same time, these drives are to be found ever more frequent. The drive units (main and feed drives) CNC steered today generally.

With the measuring instruments one differentiates direct and indirect Wegmesssysteme. With both measuring systems over sensors the put back scale sections are counted and calculated by this number then the put back way. With indirect Wegmesssystemen however the scale is in a circle arranged, so that the system measures the angle change of the screw pillar and over the upward gradient of the thread then the change of way computed. With the more exact direct Wegmesssystemen the scale is parallel to the direction of motion attached, so that the length of the sections (multiplies by the number of counted sections) corresponds directly to the put back way.

The drives of supplying aggregates, like the cooling lubricant mechanism, are e.g. called auxiliary drives

Control

see Computerized Numerical control-see switchgear cabinet

Tool change-over switch

Modern CNC steered machine tools are generally equipped with tool storages, from which depending upon need, tools can be exchanged directly or over a load mechanism into the working-spindle. As tool storages (also: There are tool shops) for boring and milling machines to disk, chaining or pallet memory. Centre lathes possess usually for up to twelve tools one or more so-called guns as tool storages, which can be disk, crown or star shaped.

In order to ensure a fast tool change with at the same time high accuracy, the Werkzeugaufnahmen (interface tool holding fixture) are standardized. In former times rotary tools predominantly so-called steep cones were used, are used today due to their technological advantages increased HSK photographs. With HSK photographs (''' H ''' ohl ''' s ''' chaft ''' k ''' egel) stretching on the internal contour whereby the system for higher numbers of revolutions effected among other things is suitable. Still larger accuracies in cyclic testing, self centring and improved stability characteristics offer the Coromant Capto of systems of Sandvik. They differ in the clutch form, a conical Polygon. These systems find ever more resemblance and the HSK photographs will not displace, however soon more frequent application will not find.

Workpiece change-over switch

Modern milling machines and drill presses have often two or more pallets for stretching the workpieces, which can be brought alternating into the work space. This permits it to make clamping operations outside of the work space while at the previous pallet the treatment can take place. Modern centre lathes for smaller workpieces often possess a (diameter usually up to approx. 60 mm). Larger workpieces can be in and replaced with robots.

Measuring instruments

Modern machine tools possess often automated measuring instruments, which can reconduct parameters of the tools or the workpieces into the control, in order correcting, programmed movements of the machine implement to let if necessary (check cuts, lengthening/depth correction cycles).

En and disposal mechanisms

Machine tools of the cutting manufacturing are nowadays predominantly equipped with cooling lubrication mechanisms. These promote usually a water oil emulsion to the work area of the tool, are it over spraying nozzles at the machine, at the ball screw jack head or by nozzles in the respective tool. The cooling lubricant is filtered in the circulation. In the course environment and job-friendly manufacturing however nowadays increasingly on the so-called minimum quantity lubrication (MMS or MMKS) one changes over. A very small quantity with air is atomised and sprayed on the effect place.

Among the en and disposal mechanisms ranks also the splinter promoter, who promotes the separated splinters from the work space to a container.

Machine A LIVINg and safety devices

Machine tools have today usually a machine A LIVINg. This serves the protection of the operator forwards around flying splinters, before and before the developing noise pollution as well as protection from injuries at the moved parts and as Berstschutz (e.g. if a tool breaks). Larger machines and plants are protected by light barriers and lattices.