DE102016116161A1 - Machine tool and method for finishing machining of workpieces - Google Patents

Abstract

The invention relates to a machine tool (10) for finish machining of workpieces, comprising a machine frame (12), with at least one finishing tool holder (14) for holding at least one finishing tool for finish machining of a workpiece section, with a headstock (20) and a tailstock for receiving the workpiece and for rotation of the workpiece about an axis of rotation (24), with an oscillating drive (25) for generating an oscillating relative movement between the finishing tool and workpiece parallel to the axis of rotation, wherein the headstock and the tailstock relative to the machine frame along a transverse to the Between a machining position (B), in which a recorded between the headstock and tailstock workpiece machinable, and a transfer position in which a workpiece to be finished between the headstock and tailstock can be accommodated and a finishend machined workpiece is deliverable. The invention further relates to a method for finishing machining of workpieces.

Description

The invention relates to a machine tool for finish machining workpieces, with a machine frame, with at least one finishing tool holder for holding at least one finishing tool for finishing machining a workpiece section, with a headstock and a tailstock for receiving the workpiece and for rotation of the workpiece about an axis of rotation with an oscillation drive for generating a parallel to the axis of rotation, oscillating relative movement between the finishing tool and the workpiece.

Machine tools of the aforementioned type are used in particular for machining bearing surfaces of workpieces in the form of crankshafts or camshafts. In this case, the bearing surfaces of the workpieces are machined by means of a finishing tool (for example a finishing stone or a finishing tape) by pressing the finishing tool against a workpiece section. During this machining, the workpiece rotates about a rotation axis. This movement is superimposed on an oscillating movement directed parallel to the axis of rotation, which takes place between the workpiece and the finishing tool.

With the method described above, particularly high surface qualities can be produced. Such surface qualities are not representable with only a grinding workpiece machining or only with an extremely high cost. However, the equipment required for finishing a workpiece, equipment expense is relatively high. This is also because, in the course of a finish machining of a workpiece, work piece peripheral surface sections concentrically arranged to a workpiece axis are often finish-machined, for example, the bearing surfaces for a connecting rod bearing of a crankshaft. These bearing surfaces follow an orbit as the crankshaft rotates, so the finishing tool that processes that bearing surface must also follow an orbit and must have appropriate degrees of freedom of movement. In addition, when machining a crankshaft, the number of cylinders of an engine corresponding to many bearing surfaces are provided for connecting rod bearings. At the same time, an even higher number of main bearing surfaces of the crankshaft are usually machined so that along the crankshaft for the crankshaft of, for example, a four-cylinder in-line engine, nine finishing tools for four connecting rod bearings and five main bearings are engaged with the crankshaft. In order that all bearing surfaces can be machined at the same time, it is necessary for the individual finishing tools to be built very narrow in order to be able to arrange them next to one another and parallel to the axis of rotation of the crankshaft on the machine tool.

The above factors contribute to the fact that the finish machining of workpieces requires a high expenditure on equipment. However, since it is necessary to maintain the surface qualities that can only be produced by finish machining, there is a need to reduce the equipment expense required for finish machining a workpiece.

On this basis, the present invention has for its object to provide a machine tool and a method for finishing machining of workpieces, which allow a more cost-effective finish machining.

This object is achieved according to the invention in a machine tool of the type mentioned above, that the headstock and the tailstock are movable relative to the machine frame along a transverse to the axis of rotation traverse axis, between a machining position in which a recorded between the headstock and tailstock work finishend is, and a transfer position in which a workpiece to be finished between the headstock and tailstock recordable and a finishend machined workpiece can be issued.

According to the invention, it is provided that the headstock and the tailstock can be moved relative to the machine frame along a transverse axis, in particular perpendicular, to the axis of rotation. Although this is initially accompanied by an increase in equipment expense compared to a conventional machine tool, since appropriate longitudinal guides and a travel drive must be provided for the headstock and the tailstock. However, it is possible by the mobility of the headstock and the tailstock to dispense with a mobility of the finishing tools and the corresponding finishing tool holder in the direction transverse to the axis of rotation.

According to the following disadvantages of the prior art have been recognized: In the finishing of a crankshaft, each of the bearing surfaces of the crankshaft is machined with its own finishing belt, which is respectively brought with pincer-like arms into engagement with a respective bearing surface of the crankshaft. In order to be able to introduce a crankshaft into the engagement region of the forceps-like arms, ie into the working area of the finishing tool, the arms are opened, the crankshaft is positioned and the forceps arms are closed again. After finish machining, it is sufficient for a conventional, fixed headstock and tailstock not to just open the pincer-like arms; Rather, the pincer-like arms of the individual finishing tools must be moved in the direction transverse to the axis of rotation of the crankshaft, so that access to a arranged between the headstock and tailstock workpiece is possible. Such access is made in conventional machines, in particular with a gantry loader, which brings an unprocessed workpiece from above into the area between the fixed headstock and tailstock and removes a machined workpiece in the upward direction from the area between the headstock and tailstock.

The mobility of the finishing tools in a direction transverse to the axis of rotation, which is necessary in conventional machine tools, is disadvantageous, since the finishing tool holders must each be individually supplied with energy so that the pincer-shaped pressure arms can be acted upon by a hydraulic pressure force, whereby the respective finishing tapes can be machined against a finish end Workpiece section can be pressed. These power supply lines must be laid in a machine tool with a fixed headstock and tailstock so that they ensure a reliable and secure power supply regardless of the position of the finishing tools. Due to the mobility of the finishing tool holder and finishing tools of conventional machine tools, the laying of the connections of the power supply lines in the conventional machine tools is relatively complex.

The machine tool according to the invention now makes it possible to arrange the finishing tool holders and finishing tools stationary on the machine frame of the machine tool, so that the connection and the installation of corresponding power supply devices is considerably simplified. This advantage is more valuable than the additional effort required for the movability of the headstock and tailstock, especially for a large number of finishing tools.

In the context of the invention, it is possible to equip the machine tool in a conventional manner by means of a gantry loader. For this purpose, it is sufficient to move the headstock and the tailstock in the transfer position to remove a machined finish workpiece and can pass an unprocessed workpiece.

Preferably, the travel axis is in the horizontal direction, so that the headstock and the tailstock can be moved in a horizontal plane. In this way, the effort required to drive the headstock and tailstock along the travel axis is minimized.

In particular, it is preferred if the headstock and the tailstock are arranged on a carriage which is movable along the travel axis. Suffice a single drive motor to drive the carriage, which then moves along with the headstock and the tailstock along the travel axis.

The traverse axis can be an NC axis. In any case, it is preferable that the machining position and the transfer position of the headstock and the tailstock are defined by mechanical stops. Preferably, such stops are firmly connected to the machine frame. Further, it is preferred if the stops are adjustable at least during the commissioning of the machine tool.

As already mentioned above, it is possible to supply the machine tool in a conventional manner by means of a gantry loader from above with unprocessed workpieces and to remove machined workpieces upwards again.

However, it is particularly preferred if the machine tool has a workpiece changing device with two workpiece holders, wherein the workpiece holders are each displaceable between a change position, which corresponds to the transfer position of the headstock and the tailstock, and an additional position. In this way, a buffer can be provided by means of which, during the finish machining of a first workpiece, a second, unprocessed workpiece can be kept in the vicinity of the working range of the machine tool. A transfer of a workpiece between the headstock and tailstock on the one hand and the workpiece change device on the other hand takes place in the transfer position of the headstock and the tailstock and in the change position of the workpiece changing device.

The additional position is provided spatially removed from the change position and forms an interface of the machine tool for feeding an unprocessed workpiece and for the removal of a machined workpiece.

In the event that a workpiece changing device is provided, it is preferred if the finishing tool holders and tools are arranged immovably or only to a slightly adjustable extent on the machine frame, since in this way the required space for the power supply lines of the finishing tools space can be minimized. The space saved in this way is then in return and with unchanged large machine frame for the workpiece changing device available.

In particular, it is preferred if a workpiece transport device is provided, which supplies the workpiece exchange device finishend to be machined workpieces and which of the tool changing device finishend machined workpieces decreases. This may be a known portal loader, which then does not serve directly for the placement of the headstock and the tailstock, but for equipping the workpiece changing device. Such assembly (and a decrease of a machined workpiece) is preferably carried out in the additional position of one of the workpiece holders of the workpiece changing device.

Further, it is preferred if the workpiece holders are displaceable by means of a common drive. This makes it possible to simultaneously move a machined workpiece from the change position to the additional position and an unprocessed workpiece from the additional position to the change position. In addition, the effort required for the displacement of the two workpieces can be limited, since only one drive must be controlled.

In a preferred embodiment, the common drive is a rotary drive, wherein the workpiece holders are each displaceable along a circular trajectory about a central axis. In this way, the workpieces are handled in a plane of movement which is transverse to the axis of rotation, wherein the rotary drive allows a "swap" of two workpieces in a small space. In the event that the change position and the additional position with respect to the direction of gravity are arranged at the same height, moves in the course of "swapping" of two workpieces of one of the workpieces along a first semicircular trajectory in an area above the central axis of rotation; the other workpiece moves in the same direction of rotation about the axis of rotation, but along a second semicircular second path of movement in an area below the central axis of rotation.

For a simple and reliable recording of the workpieces on the workpiece changing device, it is preferred if the workpiece holders have prismatic workpiece supports, wherein a compensation device is provided, by means of which the orientation of the workpiece holders remains unchanged along the circular paths of movement of the workpiece holders. The prismatic workpiece supports make it possible to hold workpieces on the workpiece holders solely by gravity. The compensation device now causes the counter to the direction of gravity upwardly open workpiece supports are not rotated, which would solve the workpieces of the workpiece holders. The compensation device can be a mechanical or control technology-coupled with the drive of the workpiece changing device auxiliary drive. It is particularly preferred to couple the drive movement of the drive of the workpiece changing device with a mechanical positive control, which always keeps the workpiece holders in the same orientation.

• – Anordnen eines finishend zu bearbeitenden, ersten Werkstücks an einer Werkstückaufnahme der Werkstückwechseleinrichtung
• – Anordnen der Werkstückaufnahme in der Wechselposition und Anordnen des Spindelstocks und des Reitstocks in der Transferposition
• – Übergeben des ersten Werkstücks von der Werkstückaufnahme an Spindelstock und Reitstock
• – Verfahren des Spindelstocks und des Reitstocks mit dem ersten Werkstück in die Bearbeitungsposition
• – Anlegen des Finishwerkzeugs an einen Werkstückabschnitt des ersten Werkstücks und Materialabtrag bei Rotation des Werkstücks und gleichzeitiger Oszillation des Werkstücks und/oder des Finishwerkzeugs in zu der Rotationsachse paralleler Richtung
• – Entfernen des ersten Finishwerkzeugs von dem Werkstückabschnitt
• – Verfahren des Spindelstocks und des Reitstocks mit dem ersten Werkstück in die Transferposition
• – Übergeben des ersten Werkstücks an eine erste Werkstückaufnahme der Werkstückwechseleinrichtung, die sich in der Wechselposition befindet,
• – Verlagern der ersten Werkstückaufnahme und des ersten Werkstücks in die Zusatzposition.

The invention further relates to a method for finishing workpieces using a machine tool described above, the method comprising the following steps, preferably in the order given:

• - Arranging a finishend to be machined, first workpiece on a workpiece holder of the workpiece changing device
• - Arranging the workpiece holder in the change position and arranging the headstock and the tailstock in the transfer position
• - Passing the first workpiece from the workpiece holder to the headstock and tailstock
• - Moving the headstock and the tailstock with the first workpiece in the machining position
• - Applying the finishing tool to a workpiece portion of the first workpiece and material removal during rotation of the workpiece and simultaneous oscillation of the workpiece and / or the finishing tool in the direction parallel to the axis of rotation
• Removing the first finishing tool from the workpiece portion
• - Moving the headstock and the tailstock with the first workpiece in the transfer position
• Passing the first workpiece to a first workpiece holder of the workpiece changing device, which is in the change position,
• - Relocating the first workpiece holder and the first workpiece in the additional position.

In a particularly preferred method, it is additionally provided that a) a second workpiece to be finish-machined is arranged on the second workpiece holder of the workpiece changing device and b) the second workpiece holder and the second workpiece are displaced into the interchangeable position.

The step a) is preferably performed while the spindle and tailstock are in the machining position and the first workpiece is finish-machined. In this way, the provision of a second, still unedited Workpiece be performed in a period in which the machine tool is currently working on another workpiece, that is active in the context of a main time.

The step b) is preferably performed simultaneously with the displacement of the first workpiece holder and the first workpiece from the transfer position to the additional position, so that the non-productive times for transferring the first workpiece from the change position to the additional position and for transferring the second workpiece from the additional position in the Changeover position occur at the same time and do not add up.

Further features and advantages of the invention are the subject of the following description and the diagrammatic representation of a preferred embodiment.

In the drawing shows

1 a front view of an embodiment of a machine tool;

2 a view of the machine tool according to 1 along a in 1 sectional plane designated II-II;

3 a side view of the machine tool according to 1 according to one in 1 designated III, with a headstock and a tailstock occupy a processing position; and

4 one of the 3 corresponding view, wherein the headstock and the tailstock occupy a transfer position.

An embodiment of a machine tool is in the 1 to 4 total with the reference numeral 10 designated. The machine tool 10 has an erectable on a footprint machine frame 12 on, the arrangement of finishing tool holders 14 serves. In particular, the finish tool holders 14 Pliers-shaped pressure arms 16 on, which is a per se known and therefore not shown finishing belt against workpiece sections of a workpiece 18 press down. At the workpiece 18 it is in particular a crankshaft or a camshaft.

In the course of further description, a workpiece is generally denoted by the reference numeral 18 designated. In connection with the handling of different workpieces 18 becomes a first workpiece with the reference numeral 18a and a second workpiece with the reference numeral 18b designated.

For holding and rotating a workpiece 18 points the machine tool 10 a headstock 20 and a tailstock 22 on. The headstock 20 and the tailstock 22 define a rotation axis 24 around which a workpiece 18 in the course of a finishing machining turns. This rotational movement is superimposed on an oscillatory movement. This involves a relative movement between the finishing tool and the workpiece 18 instead of. This can be achieved by having a whole of headstock 20 , Workpiece 18 and tailstock 22 by means of an oscillation drive 25 in a direction parallel to the axis of rotation 24 is driven back and forth (oscillating). It is also possible by means of an oscillation drive, the finishing tool holder 14 and the finishing tools or a common base 26 for a plurality of finish tool holders 14 and finishing tools in a direction parallel to the axis of rotation 24 to drive oscillatingly.

The headstock 20 and the tailstock 22 are each on carriers 28 . 30 stored and relative to the carriers 28 . 30 in to the axis of rotation 24 movable parallel directions, so that the distance between headstock 20 and the tailstock 22 for a fitting with a workpiece 18 is enlargeable and for a clamping of a workpiece 18 is reducible. This movability of the headstock 20 and the tailstock 22 is in 1 indicated with double arrows, with 20a and 22a are designated.

The carriers 28 and 30 in turn are at a common sled 32 arranged, by means of a carriage drive 34 (see 2 ) along a horizontal axis 36 is movable. In the carriage drive 34 it may, for example, be a hydraulic cylinder. The travel axis 36 is defined by at least one, preferably a plurality of linear guides 38 (see. 1 ), which between the machine frame 12 and the sled 32 are effective.

In the 2 are the headstock 20 and the tailstock 22 arranged in the machining position, so that one between headstock 20 and tailstock 22 held workpiece 18 can be machined with a finishing tool. In the 2 and 3 is the sled 32 positioned so that the headstock 20 and the tailstock 22 assume their machining position. This position is in 4 denoted by the letter B. In 4 is the sled 32 represented in an additional position removed from the processing position B. From the comparison of 2 to 4 it can be seen that the transfer of the carriage 32 from the processing position B in the transfer position a horizontal transport of a workpiece 18 allows without using the pliers-like arms 16 the finishing tool holder 14 to collide.

It would be possible the headstock 20 and the tailstock 22 in the transfer position with a workpiece transport device 40 in the form of a gantry loader with workpieces 18 to equip.

However, it is particularly preferred if the machine tool 10 a workpiece changing device 42 in particular with respect to the machine frame 12 is stationary and more preferably with the machine frame 12 connected is.

The workpiece changing device 42 includes a carrier 44 for connection to the machine frame 12 , On the carrier 44 is a drive motor 46 arranged over a gearbox 47 a central axis of rotation 48 drives, which in turn a holding arm 50 around the central axis of rotation 48 twisted. At the opposite ends of the support arm 50 are two workpiece holders 52 and 54 provided on each of which a workpiece 18 is receivable.

The workpiece changing device 42 includes additional gearbox 56 with the central axis of rotation 48 mechanically positively coupled and on axes of rotation of the workpiece holders 52 . 54 Act. The additional gear 56 cause the workpiece holders 52 and 54 with upwardly open, prismatic workpiece supports 58 . 60 be kept in a constant position with respect to their orientation, regardless of where a workpiece holder 52 . 54 along a circular trajectory about the central axis of rotation 48 located. The additional gear 56 thus form a balancing device.

In 2 is a first workpiece holder 52 presented in a change position, which is the transfer and acceptance of a workpiece to and from headstock 20 and tailstock 22 allows them to be in their transfer position.

A second workpiece holder 54 is in 2 shown in the additional position. It is preferred that the workpiece transport device 40 , For example, a gantry loader, unprocessed workpieces of the workpiece changing device 42 feed and that in an additional position of a workpiece holder 52 . 54 ,

The following is the operation of the machine tool 10 and a preferred method for finish machining of workpieces 18 described.

In an initial state of the machine tool 10 are the pincer-like arms 16 the finishing tool holder 14 open. The headstock 20 and the tailstock 22 are in the transfer position and have an increased distance to each other. The workpiece holder 52 and 54 are blank. The first workpiece holder 52 is in the additional position; the second workpiece holder 54 in the exchange position.

Starting from this initial state becomes a first workpiece 18a by means of the workpiece transport device 40 fed and in the first workpiece holder 52 stored. Subsequently, the first workpiece holder 52 by means of the drive 44 from the additional item to the change position.

Then the distance between headstock 20 and tailstock 22 shortened, so that tips of headstock 20 and tailstock 22 with end faces of the first workpiece 18a engage and clamp the workpiece between them.

Then the headstock 20 and the tailstock 22 moved from the transfer position to the machining position, using the carriage drive 34 ,

Now the in 2 achieved state shown.

This is followed by a finish machining of the workpiece 18a by the pliers-like arms 16 closed and the (not shown) finishing tapes against the individual workpiece sections of the first workpiece 18a be pressed. This is the workpiece 18a by means of the headstock 20 rotating around the axis of rotation 24 driven; This rotational movement is superimposed on an oscillatory movement in the manner described above, so that each finished machined workpiece section is provided with a characteristic for the finishing process cross-cut structure.

During the above-described finishing machining of the first workpiece 18a becomes the second workpiece holder 54 by means of the workpiece transport device 40 a second, unprocessed workpiece 18b fed. Here is the second workpiece holder 54 in the additional position.

After completing finishing machining of the first workpiece 18a open the pliers-like arms 16 for a release of the first workpiece 18a , In the between headstock 20 and tailstock 22 still clamped state becomes the first workpiece 18a by means of the carriage 32 from the processing position to the transfer position according to 4 spent.

Then the distance between the headstock 20 and the tailstock 22 enlarged so that the first workpiece 18a is released and on the first workpiece holder 52 is stored, which is in the change position.

In the condition now described, the finish-machined first workpiece thus lies 18a in the change position of the first workpiece holder 52 on the prism-shaped workpiece support 58 on. The second, still unprocessed workpiece 18b lies on the prism-shaped workpiece support 60 and the second workpiece holder 54 on, which is in the additional position.

Starting from this state becomes the drive 44 the workpiece changing device 42 controlled so that the holding arm 50 180 ° around the central axis of rotation 48 rotates. Here then move the workpiece holders 52 and 54 each along semicircular trajectories about the central axis of rotation 48 around until the workpiece holders 52 and 54 and the workpieces held there 18a . 18b have reversed the positions, so so the first workpiece 18a was moved from the change position to the additional position and at the same time the second workpiece 18b has been moved from the additional item to the exchange item.

Subsequently, the first workpiece 18a by means of the workpiece transport device 40 from the workpiece changing device 42 be removed by the workpiece transport 40 the first workpiece 18a from the prism-shaped workpiece support 58 the first workpiece holder 52 extracts.

Simultaneously with the removal of the first workpiece 18a may be the second tool 18b in the change position of the second workpiece holder 54 between the headstock 20 and the tailstock 22 be clamped and then fed to the processing area of the finishing tools by the carriage 32 from the transfer position is moved back to the processing position.

The time in which the second workpiece 18b finishing can be used again to a third (not shown) workpiece 18c to supply, which is the first workpiece holder 52 is supplied, which is located in the additional position of the workpiece holder and which by removing the first workpiece 18a has become free.

The machine tool described above 10 allows one in the rear area of the finish tool holder 14 considerably simplified and space-saving design. During the machining of a workpiece 18a It is possible to equip it with a following workpiece 18b prepare so that the actual exchange between a finishend machined workpiece 18a and a raw workpiece 18b can be done in a short time.

Claims (10)

Machine tool ( 10 ) for finishing machining of workpieces ( 18 ), with a machine frame ( 12 ), with at least one finishing tool holder ( 14 ) for holding at least one finishing tool for finish machining a workpiece section, with a headstock ( 20 ) and a tailstock ( 22 ) for receiving the workpiece ( 18 ) and the rotation of the workpiece ( 18 ) about a rotation axis ( 24 ), with an oscillation drive ( 25 ) for generating a to the axis of rotation ( 24 ) parallel, oscillating relative movement between finishing tool and workpiece ( 18 ), characterized in that the headstock ( 20 ) and the tailstock ( 22 ) relative to the machine frame ( 12 ) along a transverse axis to the axis of rotation ( 24 ) running axis ( 36 ) are movable between a machining position in which a between headstock ( 20 ) and tailstock ( 22 ) received workpiece ( 18 ) finishendierbar, and a transfer position in which a workpiece to be finished ( 18 ) between headstock ( 20 ) and tailstock ( 22 ) and a finish machined workpiece ( 18 ) is deliverable. Machine tool ( 10 ) according to claim 1, characterized in that the travel axis ( 36 ) is horizontal. Machine tool ( 10 ) according to one of the preceding claims, characterized in that the headstock ( 20 ) and the tailstock ( 22 ) on a carriage ( 32 ) are arranged along the travel axis ( 36 ) is movable. Machine tool ( 10 ) according to one of the preceding claims, characterized in that the machine tool ( 10 ) a workpiece changing device ( 42 ) with two workpiece holders ( 52 . 54 ), wherein the workpiece holders ( 52 . 54 ) each between a change position, with the transfer position of the headstock ( 20 ) and the tailstock ( 22 ) Corresponds, and an additional position are displaced. Machine tool ( 10 ) according to claim 4, characterized in that a workpiece transport device ( 40 ) is provided which of the workpiece changing device ( 42 ) finishing to be machined workpieces ( 18 ) and which of the Workpiece changing device ( 42 ) finish-machined workpieces ( 18 ) decreases, preferably in the additional position of one of the workpiece holders ( 52 . 54 ) of the workpiece changing device ( 42 ). Machine tool ( 10 ) according to claim 5, characterized in that the workpiece holders ( 52 . 54 ) by means of a common drive ( 46 ) are relocatable. Machine tool ( 10 ) according to claim 6, characterized in that the common drive ( 46 ) is designed as a rotary drive and that the workpiece holders ( 52 . 54 ) each along a circular trajectory about a central axis of rotation ( 48 ) are relocatable. Machine tool ( 10 ) according to claim 7, characterized in that the workpiece holders ( 52 . 54 ) prism-shaped workpiece supports ( 58 . 60 ) and that a compensation device ( 56 ) is provided, by means of which the orientation of the workpiece holders ( 52 . 54 ) along the circular paths of movement of the workpiece holders ( 52 . 54 ) remains unchanged. Method for finish machining of workpieces using a machine tool ( 10 ) according to one of the preceding claims, comprising - arranging a first workpiece to be finish-machined ( 18a ) on a workpiece holder ( 52 ) of the workpiece changing device ( 42 ) - Arranging the workpiece holder ( 52 ) in the change position and arranging the headstock ( 20 ) and the tailstock ( 22 ) in the transfer position - transfer of the first workpiece ( 18a ) from the workpiece holder ( 52 ) on headstock and tailstock - procedure of the headstock ( 20 ) and the tailstock ( 22 ) with the first workpiece ( 18a ) in the machining position (B) - applying the finishing tool to a workpiece portion of the first workpiece ( 18a ) and material removal during rotation of the workpiece ( 18a ) and simultaneous oscillation of the workpiece ( 18a ) and / or the finishing tool in to the axis of rotation ( 24 ) parallel direction - removal of the first finishing tool from the workpiece portion - method of the headstock ( 20 ) and the tailstock ( 22 ) with the first workpiece ( 18a ) in the transfer position - transfer of the first workpiece ( 18a ) to a first workpiece holder ( 52 ) of the workpiece changing device ( 42 ), which is in the change position, - moving the first workpiece holder ( 52 ) and the first workpiece ( 18a ) in the additional position. A method according to claim 9, characterized in that a) a second, finishend to be machined workpiece ( 18b ) on the second workpiece holder ( 54 ) of the workpiece changing device ( 42 ) and b) the second workpiece holder ( 54 ) and the second workpiece ( 18b ) are shifted to the change position.

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