Patent Publication Number: US-2022234162-A1

Title: Honing apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a National Stage Application filed under 35 U.S.C. 371 based on International Patent Application No. PCT/EP2020/057568, filed on Mar. 19, 2020, which claims priority to German Patent Application 10 2019 113 032.8 filed May 17, 2019. The entire disclosures of each of the foregoing are hereby incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     The present invention relates to an apparatus for honing a bore in a workpiece. 
     Apparatuses of this kind are known from the prior art and are used in particular for honing crank bores and camshaft bores in crankcases. 
     Honing often requires multiple honing operations using different honing tools. For example, a first honing operation can be used to correct the diameter and dimensional accuracy of a bore and the second honing operation can be used to smooth or otherwise topographically process the surface, e.g. so as to have an intended (for example high or differently defined) roughness. For this purpose, apparatuses of the type mentioned at the outset generally have a tool changing device for changing the honing tools in an in particular automated manner. The tool changing device typically comprises a tool magazine for receiving a plurality of honing tools, it being possible to displace the tool magazine relative to a honing unit such that the tool magazine can approach the honing unit in order to replace a honing tool. It is possible for a gripping unit comprising a gripping arm to be provided, which feeds the honing tool from the honing unit to the tool magazine or vice versa. The known solutions have a complex structure, which generally leads to high manufacturing costs and increased effort required to put the apparatus into operation. 
     DE 10 2016 201 456 A1 and DE 20 2016 002857 U1 each disclose an apparatus having the features of the preamble of claim  1 . 
     SUMMARY OF THE INVENTION 
     The problem addressed by the present invention is that of simplifying a tool change in an apparatus of the type mentioned at the outset. In particular, it is desirable for the apparatus to have a structurally simple and inexpensive design. 
     This problem is solved according to the invention by an apparatus. 
     The apparatus according to the invention is used for honing a bore in a workpiece. In particular, the apparatus according to the invention is an apparatus for honing a crank bore in a crankcase. In the context of the invention, a crank bore is understood to mean in particular the bore in a crankcase that is used to support a crankshaft in the crankcase. 
     The apparatus comprises an apparatus base which, as seen in a viewing direction orthogonal to the apparatus base, is preferably rectangular. In particular, a longitudinal extension and a transverse extension of the apparatus base are dimensioned such that the apparatus can be transported on conventional means of transport, in particular on a truck, which makes it easier to transport the apparatus to a destination. 
     The apparatus also comprises a turntable arranged on the apparatus base. In particular, the turntable is designed as a lifting turntable. The turntable can be rotated about a vertical turntable axis and has a plurality of workpiece receptacles. The workpiece receptacles are arranged such that a workpiece received in a workpiece receptacle can be transported to different work stations of the apparatus by a rotary movement of the turntable about the turntable axis. 
     The workpiece receptacles are preferably arranged so as to be offset from one another along a circumference around the turntable axis. In particular, four workpiece receptacles are provided which are arranged so as to be offset from one another at an angle of 90°. It is also advantageous for the workpiece receptacles to be arranged at in particular the same radial distance from the turntable axis. 
     The apparatus also comprises at least one loading station for loading and unloading the workpiece receptacles, the at least one loading station forming a work station of the apparatus. Loading and unloading the workpiece receptacles is understood to mean in particular the workpiece receptacles being loaded with workpieces and the workpieces being removed from the workpiece receptacles. 
     The apparatus also comprises a honing station having a horizontal honing unit and having a displacement device for displacing the horizontal honing unit relative to the turntable. The at least one honing station forms a further work station of the apparatus. A honing spindle which has a honing tool comprising honing stones is coupled or couplable to the horizontal honing unit such that the honing spindle can be rotated about a horizontal spindle axis and can be moved back and forth in a direction parallel to the spindle axis. In this respect, translational and rotational relative movements between the workpiece and the honing tool can be superimposed, which superimposition is characteristic of a honing process. The apparatus preferably comprises a spindle drive for driving a rotational movement of the honing spindle about the spindle axis. The back and forth movement of the honing spindle is preferably provided by the horizontal honing unit being displaced by means of the displacement device. 
     The apparatus also comprises a tool magazine for receiving a plurality of honing spindles. Honing spindles comprising differently designed honing tools can therefore be kept available for different honing operations. For an automated tool change, i.e. automated replacement of a honing spindle coupled to the horizontal honing unit, it is also preferred when the honing spindles each have an interface for automatic change, for example an HSK interface. This can reduce the time required for a tool change, which has a positive effect on productivity. 
     The at least one tool magazine is fixed in an immovable manner relative to the device base, at least with respect to translational movements. In this respect, the at least one tool magazine is fixed such that at least translational movements of the at least one tool magazine are not possible. In other words, the tool magazine does not have any translational degrees of freedom, but in this regard is attached such that it is rigid with respect to the apparatus base. The honing tools received in the tool magazine are in this case held in a fixed and predetermined position in the fixed tool magazine. 
     The at least one tool magazine is positioned or positionable with respect to the at least one honing station such that the at least one tool magazine takes up a tool-changing position in which relative movements between the at least one tool magazine and the horizontal honing unit of the at least one honing station, which movements are required for a tool change—in order to place a honing tool in the at least one tool magazine and/or in order to receive a honing tool from the tool magazine—can be provided by displacement movements of the horizontal honing unit by means of the displacement device. In this respect, a tool change can take place with the tool magazine fixed. It is therefore not necessary to provide the at least one tool magazine with an additional displacement device (for example NC axes) in order to make an automated tool change possible. 
     An apparatus according to the invention is structurally simple and inexpensive (with no additional displacement device for displacing the at least one tool magazine). Furthermore, an apparatus according to the invention is characterized by comparatively fast operational readiness, since a process in which such a displacement device for displacing the at least one tool magazine is set up (for example calibrating the NC axes) can be omitted. In an apparatus according to the invention, the effort required for maintenance is also reduced, since fewer moving components are present by comparison with the apparatuses known from the prior art. 
     The at least one tool magazine is expediently positioned in the tool-changing position such that a longitudinal axis of a honing tool received in the tool magazine is aligned substantially parallel to the spindle axis of the horizontal honing unit. This allows a particularly simple and quick tool change, since the honing tools in the tool magazine already have the same orientation as in a state coupled to the horizontal honing unit. It is accordingly no longer necessary to pivot the magazine which is in any case translationally fixed. In this respect, in particular no tilting or pivoting movement of the horizontal honing unit is required in order to pick up or put down a honing tool. The honing tools are preferably arranged in the tool magazine so as to be one above the other in the vertical direction, which promotes a particularly space-saving arrangement in a horizontal plane. 
     In principle, it is possible for the at least one tool magazine to be fixed in an immovable manner with respect to the apparatus base, i.e. for both translational movements and rotational movements of the at least one tool magazine to not be possible. In other words, the tool magazine is arranged such that it is completely rigid with respect to the apparatus base. The at least one tool magazine can, however, be connected to the apparatus base via a pivot joint, a pivot axis of the pivot joint being oriented such that the at least one tool magazine can be pivoted between the tool-changing position and a maintenance position, the at least one tool magazine being positioned, when in the maintenance position, at least partially outside the apparatus base as seen in a viewing direction orthogonal to the apparatus base (in plan view). The maintenance position thus allows free access to the honing tools received in the at least one tool magazine, so that the honing tools can be replaced in a convenient manner. The pivot axis can be oriented horizontally. However, it is preferred when the pivot axis is oriented vertically. 
     It is also preferred when the horizontal honing unit can be displaced in three spatial directions by means of the displacement direction. The displacement device preferably comprises three NC axes, which are in particular oriented orthogonally to one another. A first spatial direction is aligned parallel to the spindle axis, and the other two spatial directions extend orthogonally to one another and span a plane which is oriented orthogonally to the spindle axis or first spatial direction. As a result, a position of the horizontal honing unit, in particular a position of a honing tool coupled to the horizontal honing unit, can be easily adapted to an exact position of a bore in a workpiece that is to be machined. In this respect, the apparatus can be set up particularly quickly. In particular, any center deviations between the honing tool and the bore can be easily corrected, which promotes precise machining. In addition, an embodiment of this kind makes it possible to machine different types of workpiece (which have different bore positions) using the same apparatus, in particular without the need for manual set up. For this purpose, it is conceivable, for example, for the spatial coordinates of a bore to be machined to be part of a data record that is stored in a control device of the apparatus for the machining of a particular workpiece. By being able to displace the horizontal honing unit by means of the displacement direction, the horizontal honing unit can also easily approach the tool magazine. 
     The workpiece receptacles can be arranged in relation to the turntable such that a bore axis of a bore in a workpiece received in a workpiece receptacle, which bore is provided for being honed by the horizontal honing unit, is oriented substantially tangentially to the turntable. In the context of the invention, “oriented substantially tangentially to the turntable” means “oriented substantially tangentially to the circular path on which the workpiece receptacles of the turntable are moved during the rotary movement about the turntable axis.” In this respect, the workpiece receptacles are positioned in such a way that a vertical plane containing the bore axis does not contain the turntable axis of the turntable. The workpiece receptacles are preferably arranged on the turntable via one or more arms, in particular such that the workpiece receptacles are arranged so as to be radially spaced from the turntable, in particular at the same radial distances. This promotes free access to the bore for honing. 
     It is also possible for the horizontal honing unit to be positioned or positionable with respect to the turntable such that the spindle axis is oriented substantially tangentially to the turntable, i.e. substantially tangential to the circular path on which the workpiece receptacles of the turntable are moved during the rotary movement. This allows the apparatus to be constructed in a particularly compact manner, since the horizontal honing unit can be arranged almost “next to” the turntable. 
     In the context of an alternative possible embodiment, the workpiece receptacles are arranged in relation to the turntable such that a bore axis of a bore in a workpiece received in a workpiece receptacle, which bore is provided for being honed by the horizontal honing unit, is oriented substantially radially to the turntable axis. In this respect, the workpiece receptacles are positioned in such a way that a vertical plane containing the bore axis contains the turntable axis of the turntable. The horizontal honing unit is in this case preferably positioned such that the spindle axis is oriented substantially radially to the turntable axis. A radial arrangement of the workpiece receptacles makes it possible to additionally provide at least one vertical honing unit for honing cylinder bores in a crankcase, it being possible for the at least one vertical honing unit to be fastened to one or more carriages above the turntable and in this case operate two workpiece receptacles. 
     In particular, the apparatus has at least one first measuring station comprising at least one first measuring unit for measuring cylinder bores in a crankcase, the at least one first measuring station forming at least one work station of the apparatus. The at least one first measuring unit is used in particular to remeasure cylinder bores which, for example, have previously been honed on a separate honing machine. The at least one first measuring unit preferably comprises at least one measuring spindle which can be inserted into a bore to be measured and has a measuring head for measuring the bore (for example with regard to diameter, dimensional accuracy, surface roughness, etc.). The at least one first measuring unit is in particular arranged such that the at least one measuring spindle extends substantially vertically. The cylinder bores can then be measured without the need for the position of the workpiece to be changed between the at least one honing station and the at least one first measuring station. 
     It is also possible for the apparatus to have at least one second measuring station comprising at least one second measuring unit, the at least one second measuring unit being designed to measure the bore that is provided for being honed by the horizontal honing unit (e.g. with regard to diameter, dimensional accuracy, surface roughness, etc.). The at least one second measuring station forms a further work station of the apparatus. In particular, the at least one second measuring unit is a measuring unit for measuring a crank bore in a crankcase. 
     The at least one second measuring unit can comprise at least one measuring spindle which can be inserted into the bore to be measured and has a measuring head for measuring the bore. It is also possible for the at least one second measuring station to have a displacement device for displacing the at least one second measuring unit relative to the turntable, in particular in three spatial directions. It is also advantageous for the at least one second measuring unit to be positioned or positionable such that a longitudinal extension of the at least one second measuring unit, in particular a longitudinal extension of the at least one measuring spindle, is oriented substantially tangentially to the turntable. The crank bore can then be measured without the need for the position of the workpiece to be changed between the honing station and the second measuring station. 
     At least one measuring spindle magazine for receiving a plurality of measuring spindles for the at least one second measuring unit is preferably arranged on the at least one second measuring station. This makes it possible to have measuring spindles comprising differently designed measuring heads available for different measuring operations. The at least one measuring spindle magazine is preferably positioned or positionable such that a longitudinal axis of a measuring spindle received in the measuring spindle magazine is oriented substantially tangentially to the turntable. 
     It is also preferred when the at least one loading station has at least one loading unit for loading and unloading the workpiece receptacles. This can make loading and unloading the workpiece receptacles easier. The loading unit can be operated manually. However, it is preferred when the loading unit can be operated by machine. The workpiece receptacles can then be loaded and unloaded in an automated manner. The at least one loading unit can be, for example, a portal robot (gantry robot), a roller conveyor, a robot or the like. In particular, the workpiece receptacles are directly loaded from above. 
     In principle, each functional unit (horizontal honing unit, loading unit, optionally first measuring unit, optionally second measuring unit) can have its own base (machine bed). These individual parts can then be connected to form an apparatus base. However, it is preferred when the at least one horizontal honing unit and/or the at least one first measuring unit and/or the at least one second measuring unit and/or the at least one loading unit is/are arranged on the apparatus base, the apparatus base being formed as one piece. In particular, all of the functional units are arranged on the one-piece apparatus base. The apparatus base thus forms a common base for all of the functional units. An arrangement of this kind is particularly stable, and therefore relative positions between the functional units can be established and maintained particularly precisely. In addition, it allows the apparatus to have a particularly compact design. In particular, an arrangement of this kind makes it possible for the apparatus to be transported to a destination as a pre-assembled structural unit on conventional means of transport (for example trucks). In addition, the time required for on-site start up can be reduced, since there is no need to assemble and align the functional units on-site. 
     The apparatus preferably has at least one switch cabinet (for example for accommodating electronic devices such as control devices, safety devices, power supply devices, etc.), and this at least one switch cabinet is arranged on the apparatus base. It is particularly preferred when the at least one switch cabinet is rigidly connected to the apparatus base. A structure of this kind is particularly compact. In addition, the time required to assemble and put the apparatus into operation can be reduced, since there is no need for the time-consuming laying of cables between the apparatus and a switch cabinet that is provided separately, in particular spatially separated, from the apparatus. The at least one switch cabinet preferably at least partially forms a housing wall of an apparatus housing which defines the work stations. 
     It is also preferred when at least one workpiece monitoring device is provided for monitoring the size and/or position and/or alignment of a bore of a workpiece to be honed. A workpiece monitoring device of this kind comprises at least one workpiece monitoring element which is arranged on a particular residential tool and is designed, when the honing tool is inserted into the bore, to check whether the bore in the workpiece has a sufficient bore width and/or to check for a positioning or alignment error of the bore in the workpiece. Ways of designing the workpiece monitoring device can be similar or identical to the solutions described in WO 2019/020779 A1—the disclosure of which is incorporated into the present description by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features, possible applications and advantages of the invention can be found in the following description of embodiments of the invention, which are explained with reference to the drawings; the features may be essential for the invention both alone and in different combinations, without being explicitly referred to again. In the drawings: 
         FIG. 1  is a sketched illustration of an embodiment of an apparatus according to the invention in a first perspective view; 
         FIG. 2  is a sketched illustration of the apparatus from  FIG. 1  in a second perspective view; and 
         FIG. 3  is a simplified sketched illustration of the apparatus from  FIG. 1  in a plan view. 
     
    
    
     DETAILED DESCRIPTION 
     In the following figures, corresponding components and elements have the same reference signs. For the sake of clarity, not all of the reference signs are shown in all of the figures. 
     In the figures, an apparatus is shown which is designated as a whole by the reference sign  10 . The apparatus  10  is used for honing a bore  12  in a workpiece  14 ; in the present example, the workpiece  14  is formed by a crankcase  14  and the bore  12  is formed by a crank bore  12  in the crankcase  14  (cf.  FIG. 3 ). The crankcase  14  is designed as an engine block, for example, and, in addition to the crank bore  12 , has four cylinder bores  16  oriented orthogonally to the crank bore  12  (cf.  FIG. 3 ). 
     In the figures, a coordinate system is also shown, which has axes (X, Y, Z) orthogonal to one another. 
     The apparatus  10  comprises an apparatus base  18  which, as seen in a viewing direction orthogonally to the apparatus base  18 , is by way of example and preferably substantially rectangular (cf.  FIG. 3 ). An extension of the apparatus base  18  along a longitudinal axis (in the figures along the X-axis) is greater than an extension of the apparatus base XX along a transverse axis (in the figures along the Y-axis). 
     The apparatus  10  also comprises a turntable  20  which is arranged, as seen in a longitudinal direction  22  (in the figures in the X-direction), approximately in the front third and, as seen in a transverse direction  24  (in the figures in the Y-direction), approximately centrally on the apparatus base  18 . The turntable  20  can be rotated, by means of a rotary drive  26  arranged below the turntable  20 , about a vertical turntable axis  28  parallel to the Z-axis of the coordinate system shown. By way of example and preferably, the turntable  20  is designed as a lifting turntable which can be displaced along the turntable axis  28  by means of a lifting drive  30 . 
     Four workpiece receptacles  32 A,  32 B,  32 C,  32 D are arranged on the turntable  20 , each for receiving a workpiece  14 . The workpiece receptacles  32 A,  32 B,  32 C,  32 D are arranged so as to be offset from one another at an angle of 90° along a circumference around the turntable axis  28  (cf.  FIG. 3 ). In the present example, the workpiece receptacles  32 A,  32 B,  32 C,  32 D are each fastened to the top of the turntable  20  via an arm  34  and are arranged so as to be radially spaced apart from the turntable  20  at the same distances (cf.  FIG. 1 ). 
     In the embodiment of the apparatus  10  shown in the figures, the workpiece receptacles  32 A,  32 B,  32 C,  32 D are arranged in relation to the turntable  20  such that a bore axis  36  of the crank bore  12  of a crankcase  14  received in a workpiece receptacle  32 A,  32 B,  32 C,  32 D is aligned substantially tangentially to the circular path on which the workpiece receptacles  32 A,  32 B,  32 C,  32 D of the turntable  20  are moved during a rotary movement of the turntable  20  about the turntable axis  28  (cf.  FIG. 3 ). 
     In embodiments which are not shown, it is also possible for the workpiece receptacles  32 A,  32 B,  32 C,  32 D to be arranged in relation to the turntable  20  such that a bore axis  36  of the crank bore  12  of a crankcase  14  received in a workpiece receptacle  32 A,  32 B,  32 C,  32 D is aligned substantially radially to the circular path on which the workpiece receptacles of the turntable are moved during a rotary movement of the turntable  20  about the turntable axis  28 . 
     The turntable  20  is used as a transfer unit within the apparatus  10  and makes it possible for a workpiece  14  received in a workpiece receptacle  32 A,  32 B,  32 C,  32 D to be transported to different work stations of the apparatus  10  by a rotary movement of the turntable  20  about the turntable axis  28 . In the present example, with four workpiece receptacles  32 A,  32 B,  32 C,  32 D offset from one another at an angle of 90°, a total of four work stations can be approached by workpieces  14  at the same time. 
     A first work station is formed by a loading station  38  for loading and unloading the workpiece receptacles  32 A,  32 B,  32 C,  32 D. The loading station  38  is arranged in the region of the transverse side  40  of the apparatus base  18 , which transverse side is at the front in the longitudinal direction  22 . The loading station  38  preferably has a motor-driven loading unit (not shown), for example in the form of a portal robot. As can be seen from  FIGS. 1 and 2 , a workpiece receptacle  32 A,  32 B,  32 C,  32 D is accessible from above in the loading station  38 , so that the workpiece receptacles  32 A,  32 B,  32 C,  32 D can be loaded or unloaded from above (in the figures in the Z-direction). 
     By rotating the turntable  20  by 90° clockwise, a workpiece  14  received in a tool receptacle  32 A,  32 B,  32 C,  32 D can be transported from the loading station  38  to a honing station  42 . The honing station  42  is arranged in the region of a first longitudinal side  44  of the apparatus base  18  and forms a second work station of the apparatus  10 . 
     The honing station  42  has a horizontal honing unit  46  for honing the crank bore  12  of the crankcase  14 . The horizontal honing unit  46  comprises a spindle box  48  to which a honing tool  50  comprising honing stones is detachably coupled in a manner known per se (cf.  FIG. 2 ). The honing tool  50  is mounted on the spindle box  48  so as to be rotatable about a horizontal spindle axis  52 . A spindle drive  54  is provided to drive a rotary movement of the honing tool  50  about the spindle axis  52 . 
     As can be seen from  FIG. 3 , the horizontal honing unit  46  is positioned with respect to the turntable  20  such that the spindle axis  52 , or a longitudinal axis  56  of a honing tool  50  coupled to the horizontal honing unit  46 , is oriented substantially tangentially to the turntable  20 . In this respect, the spindle axis  52  or the longitudinal axis  56  is aligned parallel to the bore axis  36  of the crank bore  12  of a crankcase  14  received in a workpiece receptacle  32 A,  32 B,  32 C,  32 D when the crankcase  14  is in the honing station  42  (in  FIG. 3  in the workpiece receptacle  32 C). 
     In order to displace the horizontal honing unit  46  relative to the turntable  20  or relative to a workpiece  14  received in a workpiece receptacle  32 A,  32 B,  32 C,  32 D, the apparatus  10  also has a displacement device  58 . 
     As can be seen from  FIG. 1 , the spindle box  48  is mounted on a support  60  so as to be displaceable along a vertical axis (in the figures along the Z-axis). A motor  62  is provided for driving a displacement movement of the spindle box  48  along the vertical axis. 
     The support  60  is mounted on a carriage  64  so as to be displaceable along the longitudinal axis of the apparatus  10  (in the figures along the X-axis). For this purpose, two mutually parallel guide rails  66  are mounted on the carriage  64 , on which guide rails the support  60  runs (cf.  FIG. 3 ). A motor  68  is provided for driving a displacement movement of the support  60  along the longitudinal axis. A displacement movement of the support  60  along the longitudinal axis causes, in particular, a movement of the honing tool  50  into the bore  12  to be honed and the back and forth movement of the honing tool  50  that is characteristic of the honing process. 
     The carriage  64  is in turn mounted on the apparatus base  18  so as to be displaceable along the transverse axis (in the figures along the Y-axis). For this purpose, guide rails  70  are mounted on the apparatus base  18 , on which guide rails the carriage  64  runs (cf.  FIG. 1 ). A motor  72  is also provided for driving a displacement movement of the carriage  64  along the transverse axis. 
     The apparatus  10  also has a tool magazine  74  for receiving a plurality of honing tools  50 . The tool magazine  74  has a plurality of honing tool receptacles  76  for receiving one honing tool  50  each (cf.  FIG. 2 ). The honing tool receptacles  76  are preferably arranged in the tool magazine  74  so as to be one above the other in the vertical direction. 
     In the present example, the tool magazine  74  is arranged adjacent to the horizontal honing unit  46  in the region of the longitudinal side  44  of the apparatus base  18 . The tool magazine  74  is connected to the apparatus base  18  via a pivot joint  78 , a pivot axis  80  of the pivot joint  78  preferably being oriented vertically. The tool magazine  74  can be pivoted between a tool-changing position (shown in the figures) and a maintenance position (not shown) in which the tool magazine  74  is pivoted, starting from the tool-changing position shown for example in  FIG. 3 , clockwise, preferably by approximately 90°, about the pivot axis  80 . Translational movements of the tool magazine  74  are blocked, however. 
     In the tool-changing position (cf.  FIG. 3 ), the tool magazine  74  is positioned such that the relative movements between the tool magazine  74  and the horizontal honing unit  46 , which movements are required for a tool change, can be provided by displacement movements of the horizontal honing unit  46  by means of the displacement device  58 . In order to replace a honing tool  50 , the horizontal honing unit  46  can, for example, approach a honing tool receptacle  76  and place a honing tool  50  in the honing tool receptacle  76  and/or pick up a honing tool  50  from the honing tool receptacle  76 . In the tool-changing position, the tool magazine  74  is positioned such that a longitudinal axis  82  of a honing tool  50  received in a honing tool receptacle  76  is oriented substantially parallel to the spindle axis  52  (cf.  FIG. 3 ). 
     In the maintenance position, the tool magazine  74  is positioned such that the tool magazine  74  is positioned at least partially outside the apparatus base  18  as seen in a viewing direction orthogonal to the apparatus base  18 . This allows free access to the honing tool receptacles  76 , so that honing tools  50  received in the honing tool receptacles  76  can be replaced easily. 
     Starting from the honing station  42 , a workpiece  14  received in a workpiece receptacle  32 A,  32 B,  32 C,  32 D can be transported to a first measuring station  84 , which forms a third work station of the apparatus  10 , by a further rotation of the turntable  20  by 90° clockwise. 
     The first measuring station  84  has a first measuring unit  86  for measuring the cylinder bores  16  in the crankcase  14 . The first measuring unit  86  is held on a carriage  88  which is mounted on an arm  90  of a transverse support  92  so as to be displaceable along the transverse axis (in the figures along the Y-axis). The transverse support  92  is held on two support columns  94  at a vertical distance above the turntable  20  and overlaps the turntable  20  in the transverse direction  24 . In this respect, the first measuring unit  86  is held at a vertical distance above the turntable  20 . 
     The first measuring unit  86  has two measuring spindles  96 , each comprising a measuring head, for measuring the cylinder bores  16 . The measuring spindles  96  of the first measuring unit  86  extend substantially vertically. In order to insert a measuring spindle  96  into a cylinder bore  16 , each measuring spindle  96  can be displaced along a vertical axis (in the figures along the Z-axis) by means of a motor  98 . By displacing the first measuring unit  86  along the transverse axis, cylinder bores  16  arranged next to one another can be approached one after the other. 
     Starting from the first measuring station  84 , a workpiece  14  received in a tool receptacle  32 A,  32 B,  32 C,  32 D can be transported to a second measuring station  100 , which forms a fourth work station of the apparatus  10 , by a further rotation of the turntable  20  by 90° clockwise. 
     In the present example, the second measuring station  100  is arranged in the region of the longitudinal side  102  of the apparatus base  18  opposite the honing station  42  and has a second measuring unit  104  for measuring the bore  12  (crank bore  12 ) provided for being honed by the horizontal honing unit  46 . 
     The second measuring unit  104  has one or more measuring spindles  106  which each comprise a measuring head  108 , the second measuring unit  104  being positioned such that a longitudinal axis  110  of a particular measuring spindle  106  is oriented substantially tangentially to the turntable  20  (cf.  FIG. 3 ). In this respect, the longitudinal axis  110  of a particular measuring spindle  106  is aligned parallel to the bore axis  36  of the crank bore  12  of the crankcase  14  when the crankcase  14  is in the second measuring station  100  (in  FIG. 3  in the workpiece receptacle  32 A). 
     The second measuring unit  104  can be displaced in three spatial directions by means of a displacement device  112 . The displacement device  112  preferably comprises three NC axes oriented orthogonally to one another, a first axis being aligned parallel to the longitudinal axis  110  of the measuring spindle  106  and being used to insert the measuring spindle  106  into a bore  12  to be measured. The two other axes span a plane which is oriented orthogonally to the longitudinal axis  110  of the measuring spindle  106  and are used to align the measuring spindle  106  relative to a position of the bore  12 . 
     A measuring spindle magazine  114  for receiving a plurality of measuring spindles  106  is also provided at the second measuring station  100 . The measuring spindle magazine  114  is arranged and positioned on the apparatus base  18  such that relative movements between the second measuring unit  104  and the measuring spindle magazine  114 , which movements are required for a measuring spindle change, can be provided by displacement movements of the second measuring unit  104  by means of the displacement device  112  (cf.  FIG. 3 ). The measuring spindle magazine  114  is positioned such that a longitudinal axis of a measuring spindle  106  received in the measuring spindle magazine  114  is aligned substantially tangentially to the turntable  20  (cf.  FIG. 3 ). 
     The apparatus  10  also comprises a plurality of switch cabinets  116  for accommodating electronic devices (for example control devices, safety devices, power supply devices, etc.). In the present example, the switch cabinets  116  are arranged on the transverse side  118  of the apparatus base  18  opposite the loading station  38  and are rigidly connected to the apparatus base  18 . The switch cabinets  116  preferably partially form the wall of an apparatus housing (not shown) which defines the work stations. 
     The apparatus  10  also comprises an operating unit  120  in the form of an operating terminal for operating the apparatus  10 .