Manually operated chuck

A manually operated chuck for machining of rotationally symmetrical workpieces, the chuck comprising: a base body, attached to clamping jaws radially movable on the base body for securing the workpiece and in which an opening extends at right angles to a longitudinal axis of the base body; a threaded spindle movably mounted in the opening and accessed from outside to change the position, thereof; a wedge bar in the base body proximate the spindle, the wedge bar being connected to the spindle and a clamping jaw in a shape-locking arrangement; a driving ring rotationally mounted in the base body and connected to the threaded spindle and to one of the wedge bars with play between the threaded spindle and driving ring, and/or the threaded spindle and a wedge bar, and/or between the driving ring and wedge bars of the clamping jaws, the workpiece disposed concentrically to a longitudinal axis of the chuck.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a manually operated chuck for machine tools for machining of rotationally symmetrical workpieces involving cutting.

2. Description of the Prior Art

A chuck of the instant kind for lathes is disclosed in DE 2004 889, which relates to a base body in which three clamping jaws are disposed in a radially movable arrangement. The base body is releasably connected to a machine tool. The clamping jaws are moved to and fro in the base body by means of a driving ring, and are used for clamping rotationally symmetrical workpieces. The clamping jaws are arranged on the base body with a pitch angle of 120°.

Two of the three clamping jaws are directly driveably connected to the driving ring by means of a wedge bar, and are moved linearly in the base body between the particular wedge bar and the clamping jaw due to the helical gearing.

The driving ring is in a shape-locking or drivable connection with a threaded spindle inserted in the base body, wherein the threaded spindle is mounted in the base body at right angles to its longitudinal axis and can be moved in this arrangement. The threaded spindle can be operated manually from the outside, for example, by using a spanner as a tool, which accounts for the fact that a chuck of this kind is also referred to as a manually operated chuck, because the clamping force to be applied is generated manually using the tool.

One of the three clamping jaws is in a direct, drivable connection with the threaded spindle by means of a helically geared wedge bar, and is consequently moved by the movement of the threaded spindle, and synchronously with the two other clamping jaws.

It has proven to be, a disadvantage and a particular technical challenge in such manually operated chucks over the past decades that it is not possible optimally to centre the workpiece in relation to the longitudinal axis the base body. This is because there is a fault tolerance resulting from the manufacturing process between the individual components required for operating the clamping jaws, namely the threaded spindle, the driving ring, the corresponding wedge bars and their clamping jaws, as a result of which tolerance the clamping jaws cannot adequately achieve a central fixing of the workpiece. The presence of play leads to the permanent effect that the workpiece slips out of the set position during its rotation and machining, within a limit area of about 5 μm. It is only possible to achieve a lower fault tolerance than 5 μm at the cost of huge expenditure in production, as a result of which it is more cost-effective to manufacture chucks with a lower fault tolerance than chucks with a higher fault tolerance. However, the higher the fault tolerance, the greater the inaccuracies in metal-cutting machining on a workpiece.

The manually operated chucks of prior art do make it possible to compensate for the existing play between the individual components that drive the clamping jaws, e.g. the driving ring, the wedge bars and the threaded spindle, providing the workpieces involved are small. However, the larger the circumference of the driving ring, the larger the magnitude of the play between the driving ring and the individual components required for operating the clamping jaws. The bearing play can also be compensated in the case of lightweight workpieces, because workpieces of this kind do not exert any significant forces on the clamping jaws, with the effect that they may remain in their set position. Consequently, with heavy and large workpieces, it is not possible to compensate for the existing play between the components required for clamping the workpiece, with the effect that there is a permanent fault tolerance.

These bearing plays are inaccuracies which cannot be compensated for when clamping the workpiece, rather these inaccuracies are transferred to the clamping situation of the workpiece in such a way that a considerable inaccuracy arises between the position of the workpiece and the centre of the chuck, which leads to inaccuracies on the workpiece in the course of its machining. As a result, precise production and machining of the workpiece is not possible without further measures being taken.

It has proved to be a further disadvantage in the disclosed, manually operated chucks that clamping errors arise during the machining process which is often time consuming and highly complicated, because the machined workpiece becomes lighter during the machining process as a result of having material removed from it. Such working procedures involving material removal then result in the original position of the workpiece being changed in relation to the chuck and therefore in relation to the machine tool. A readjustment of the workpiece is often time-consuming and complicated to achieve.

The clamped workpieces are rotated by the machine tool in order to be machined. Therefore, in the case of a chuck with three clamping jaws offset at an angle of 120° in relation to one another, and in particular with exceedingly heavy and large workpieces of 20 tonnes inherent weight, for example, it has been observed that one clamping jaw which is located in a certain angular position of the chuck has to carry the weight of the workpiece exclusively, with the effect that it is not guaranteed that this clamping jaw can hold the workpiece reliably. Rather, the weight of the workpiece exceeds the clamping force of the individual clamping jaw, with the effect that it the jaw is forced outwards, the clamping force acting on the workpiece is eliminated. The workpiece is thus not reliably held in the chuck, and consequently its intended clamping position cannot be retained.

SUMMARY OF THE INVENTION

The purpose of the present invention is therefore to develop a manually operated chuck of the aforementioned kind, which has proven itself over many years, in such a way that firstly, the workpiece to be clamped is precisely centred in relation to the longitudinal axis of the chuck and, secondly, there is a centring adjustment possibility available permanently throughout the machining process. Furthermore, the chuck in accordance with the present invention permits a reliable and sustained support, even of extremely heavy workpieces with an inside or outside diameter of at least 0.5 meters.

At least one centring device is provided on a side which applies a centring force radially onto the workpiece, and therefore the workpiece can be centred exactly, once it has been clamped in the three clamping jaws, because the corresponding centring device ensures that the longitudinal axis of the workpiece is positioned flush in relation to the longitudinal axis of the chuck, without the centring force acting on the clamping jaws. This is because the clamping jaws are connected in a shape-locking arrangement with a driving ring and a threaded spindle, via a wedge bar. However, the driving ring, the wedge bar, and the threaded spindle are mounted in the base body of the chuck with a play that is a feature of the manufacturing process, and so this play can be compensated for by means of the corresponding centring device. As a result, the centring force of the corresponding centring device does not act on the clamping jaws and therefore on the components which drive the clamping jaws, but rather compensates for the existing bearing play and/or error tolerances, which are in the region of about 5 μm, in particular, with extremely large outside diameters. These are significant error tolerances for precision components and can therefore be compensated for by the centring devices in such a way that the workpieces in the chuck can be installed precisely centrally in the chuck.

The existing error tolerances of the chuck are therefore no longer transferred to the workpiece during the machining process, but are instead compensated.

During the machining process, half of the existing material and therefore half of the inherent weight are sometimes removed from the workpiece by cutting processes; therefore the inherent weight of the workpiece is reduced during the machining process, with the effect that the geometrical clamping conditions are also influenced. The centring devices can be moved independently from the clamping jaws, therefore such changes in the clamping conditions can be compensated for by the centring devices during the machining process, with the effect that the clamped workpiece can be positioned precisely centrally in relation to the chuck at all times without any variation in the clamping force exerted by the clamping jaws.

Furthermore, the centring device acts on the surface of the clamped workpiece, with the effect that the workpiece is supported not only by the clamping jaws, but also by the centring devices on the base body of the chuck.

It is particularly advantageous if three clamping jaws are arranged offset at an angle of 120° in relation to one another, and if one or two of the centring devices is/are arranged in between two adjacent clamping jaws. This construction results in the situation that six or nine clamping jaws and centring devices converging on one another at an angle of 60° or 40° act on the workpiece, with the effect that the workpiece is reliably supported on the chuck not only by the clamping jaws but also by the centring devices.

The centring devices can exhibit different design configurations. For example, but not exclusively, the centring devices can be configured as wedges, or as hydraulically operated clamping pins, or as threaded spindles. These centring devices have in common that a radially vectored centring force is applied to the surface of the workpiece and, by means of this centring force, it is possible to shift the workpiece and, with that, the longitudinal axis of the workpiece in relation to the longitudinal axis of the chuck.

Furthermore, the centring devices can be actuated synchronously or independently from one another, with the effect that precise alignment of the workpiece is achieved by the one or more of the centring devices, depending on the clamping situation achieved by the clamping jaws.

These setting possibilities mean that the position of the workpiece can be realigned with regard to the material reduction and, therefore, that the centring devices permit the realignment in position due to the change in position of the workpiece in relation to the midpoint of the chuck caused by the reduction in weight. As a result, the workpiece is positioned exactly centrally in relation to the chuck throughout the machining process; there is no need to remove and reclamp the workpiece because the workpiece is permanently held by the clamping jaws of the chuck throughout the machining processes. It is only the centring devices that need to be actuated in order to reposition the workpiece exactly centrally.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1,2and3show a chuck1, by means of which a rotationally symmetrical, preferably round, workpiece2is held from the outside on a machine tool (not shown) for the purpose of machining the workpiece2by metal cutting. The chuck1consists of a base body4, having a longitudinal axis5. Three clamping jaws6,7and8are mounted in a radially movable arrangement in guide grooves18aligned with the longitudinal axis5. The clamping jaws6,7and8are each driven by a wedge bar9arranged movably in the base body4in a usual manner. Helical gearing10is provided between each of the wedge bars9and the clamping jaws6,7or8, with the effect that a shape-locking active connection is provided between each of the clamping jaws6,7or8and the corresponding wedge bar9.

Two of the three wedge bars9, as can be seen in particular inFIG. 3, can be driven by a driving ring21. The driving ring21is normally mounted in the base body4so as to allow the driving ring21to rotate to a limited extent, and is connected in a drivable connection with a threaded spindle24held in a movable arrangement in an opening25in the base body4. As soon as the driving ring21has a force exerted on it acting in a rotating direction around the longitudinal axis5of the base body4, which involves the threaded spindle24moving to and fro in the opening25, this results in the two wedge bars9shifting their position, because they are driveably connected to the driving ring21by a pin22mounted on the wedge bars9and by a sliding block26.

The wedge bar9in a direct drivable active connection with the threaded spindle24moves the clamping jaws6,7,8when the wedge bar9is actuated. By means of the helical gearing10, the clamping jaws6,7and8are nevertheless advanced radially in guide grooves18towards the workpiece2, or moved away from the workpiece2. These movements take place synchronously.

The driving ring21is in a drivable connection with the wedge bars9of the two clamping jaws7and8by means of the pins22in a shape-locking arrangement. The pins22, in turn, are driveably connected to the corresponding wedge bar9by means of the sliding blocks26, i.e. in a shape-locking arrangement, with the effect that the rotation of the driving ring21triggered by the axial movement of the threaded spindle24causes the wedge bars9to be moved into the base body4. As a result of the helical gearing10between the wedge bar9and the clamping jaws7and8, the jaws7and8are advanced synchronously with the clamping jaw6toward the workpiece2, with this advance movement continuing until active contact takes place between the three clamping jaws6,7and8and the workpiece2, by means of which adequate clamping force is exerted on the workpiece2in order to hold the workpiece2.

The clamping jaws6,7and8thus hold the workpiece2in a rotationally fixed arrangement on the chuck1.

The rotationally symmetrical workpiece2has a longitudinal axis that should be arranged as concentrically as possible in relation to the longitudinal axis5throughout the entire machining process of the workpiece2. Due to play23,23′,23″, shown schematically inFIG. 3, between the base body4, the threaded spindle24, and the driving ring21, the wedge bars9, and the clamping jaws6,7and8, however, it is often not possible to achieve this desired concentric, or coaxial, clamping of the workpiece2on the chuck1. In particular, in the case of extremely large and heavy workpieces2which have an outside diameter of more than 0.5 meters and an inherent weight of more than five tons, it is not possible to compensate for the error tolerances that are due to the manufacturing conditions, with the effect that the fault tolerances23,23′,23″ between the wedge bars9and the driving ring21have to be compensated for. When the clamping jaws6,7and8are advanced, this existing play23,23′,23″ results in the situation that the longitudinal axis of the workpiece2cannot be arranged flush or coaxially with the longitudinal axis5of the base body4.

If, however, the workpiece2is machined, this error in the clamping of the workpiece2results in machining errors on the workpiece2. In particular, in the case of precision parts, for example, rotors or shafts in electric motors or other high-quality machines, systems, or the like, error tolerances of this kind cannot be tolerated. The known error tolerances lead to a deviation of, for example, at least 5 μm. This deviation of 5 μm is correspondingly transferred to the clamping situation of the workpiece2on the chuck1, with the effect that these error tolerances occur in equal measure during the machining of the workpiece2, due to a prevailing installation situation.

Furthermore, material is removed from the workpiece2during the machining process involving metal cutting, with the effect that the inherent weight of the workpiece2is continuously reduced during the machining process. This machining, which reduces material, therefore results in the geometrical clamping situations being altered.

In order to set both the exact position of the workpiece2, namely centrally, flush or coaxially in relation to the longitudinal axis5of the chuck1, three centring devices11are provided by means of which a radially acting centring force Fzacts on the workpiece2, in order to compensate for the existing play23,23′,23″. The centring force Fzshould therefore not act on the clamping jaws6,7or8, but should exclusively compensate for the existing longitudinal deviations and align the workpiece2in such a way in relation to the longitudinal axis5that the longitudinal axis of the workpiece2runs flush or coaxially in relation to the longitudinal axis5of the chuck1. It is possible to establish, for example, by electrical sensors or other contact sensors, that the centring devices11are securing the workpiece2in the required clamping situation and that the corresponding centring device11is secured.

The centring device11comprises a housing12which can be attached in a releasable manner on the base body4of the chuck1. For this purpose, a plurality of holes13are provided in the base body4and through-holes are provided in the housing12with screws14passing through them, in order to screw the housing12onto the base body4. Furthermore, a centring pin15is inserted in the housing12, in which case the centring pin15projects from the housing12and has a centring surface16.

The housings12of the three centring devices11must be arranged on the base body4in such a way that the centring surfaces16of the corresponding centring pins15extend along a shared arc17which is somewhat larger than the outside radius of the workpiece2to be machined. The clamping jaws6,7and8are initially provided in order to accommodate the workpiece2and to secure it on the chuck1. As soon as the clamping of the workpiece2by the clamping jaws6,7and8has been accomplished in the familiar way, then the centring pins15of the corresponding centring device11must be set radially in relation to the workpiece2.

FIGS. 4a,4band4cshow three differently designed embodiments of the corresponding centring device11.

FIG. 4ashows a wedge31disposed in the housing12of the centring device11, the wedge31having a tapering clamping surface32. The centring pin15lies on the clamping surface32of the clamping pin31, with the effect that when the pin31is pushed in, the radially acting centring force Fz, already referred to, is created and causes the centring pin15to advance in the direction of the workpiece2, so that the workpiece2has the centring force applied to it. The pin31is pressed against the force of a spring20by means of the pin31being screwed into the housing12. The pin31is held in a clamping thread19in the housing12, with the effect that when the pin31is unscrewed, a return force is applied to the wedge31by the spring20, by means of which the pin31is pushed out of the housing12. A spring is also provided between the housing12and the centring pin15, by means of which the centring pin15is moved back to its starting position when the wedge31is released.

FIG. 4bshows that the centring device11is formed from a hydraulic piston33on which the centring pin15is formed. The two spaces that are separated by the hydraulic piston33are filled with hydraulic fluid by means of two hydraulic connections34, or else the spaces are alternately drained, with the effect that the hydraulic piston33has the radially acting centring force Fzapplied to it via the hydraulic connections34, by means of which the centring pin15is advanced towards the workpiece2or moved away from it.

FIG. 4cshows that the design embodiment of the centring device11is undertaken in such a manner that a threaded spindle36is screwed into a female thread35in the housing12, and the centring pin15is formed on the threaded spindle36. Accordingly, when the threaded spindle36is screwed in, the centring pin15is advanced towards the workpiece2.

The three design embodiments of the centring device11as shown inFIGS. 4a,4b,4cshare the common feature that the centring surface16provided on the centring pin15is advanced out of its starting position corresponding to the arc17(FIG. 1) towards the workpiece2, and the centring surface16exerts a centring force Fzon the workpiece2that acts radially from the outside and the inside. During the advance movement of the corresponding centring pin15, the workpiece2is held by the three clamping jaws6,7, and8on the chuck1, and consequently on the machine tool that is not shown. The play23between the base body4and the actuating element21(driving ring) can therefore be compensated for by the movements of the corresponding centring pin15. The centring pins15of the corresponding centring device11can be adjusted and driven independently of one another or synchronously with one another.

In the sample embodiment shown, the three clamping jaws6,7and8are arranged in an angular position of 120° in relation to one another on the base body4. One each of the centring devices11is provided between two adjacent clamping jaws6,7or8in a centred position, with the effect that these also adopt a 120° angular position in relation to one other and the three clamping jaws6,7and8are arranged at an angle of 60° in relation to the three centring devices11.

The metal-cutting machining on the workpiece2means that its inherent weight is reduced, with the effect that the geometrical clamping situations change. The three clamping jaws6,7and8in this case support the workpiece2on the chuck1. The advance movement of the three centring devices11means that permanent repositioning of the workpiece2is possible in relation to the longitudinal axis5of the chuck1. Therefore, the weight changes of the workpiece2can be compensated for by the centring devices11without the position of the three clamping jaws6,7and8having to be changed.

FIG. 5shows a chuck1′ by means of which a rotationally symmetrical workpiece2′ is clamped. The workpiece2′ in this case is configured as a rotationally symmetrical hollow body. The three clamping jaws6,7and8are arranged inside the workpiece2′ during the clamping position, and exert a clamping force on the workpiece2′ that is directed radially outwards.

The three centring devices11are attached to the chuck1′ in the inside of the workpiece2′, with the effect that they exert a centring force Fzonto the workpiece2′ that is directed radially outwards.

The centring surfaces16of the three centring pins15are on the shared arc17, the radius of which is smaller than the inside radius of the workpiece2′.

The corresponding centring device11can be actuated from the outside, for example by means of a tool that can be passed through the workpiece2′, in order to set the position of the corresponding centring device11manually. It is also conceivable for the corresponding centring device11to be provided with the design embodiments explained inFIGS. 4a,4band4c. The corresponding centring device11can, for example, be actuated using the hydraulic drive unit shown inFIG. 4bwithout the need to reach through the workpiece2′.