Abstract:
The present invention relates to an apparatus for machining workpieces (W 1  to W 4 ) by stock removal, in particular the main (a 1  to a 5 ) and/or connecting rod bearing journals (b 1  to b 4 ) of crankshafts. For this purpose the apparatus is equipped with at least two guideways ( 7, 8 ) which are distanced from one another and are arranged parallel with respect to one another and on which at least one workpiece fixture ( 9, 10 ) holding a workpiece (W 1 to W 4 ) each can be moved from a transfer position (P 1,  P 2 ) to a working position (A 1  to A 6 ), and with two discoid cutters ( 17, 18, 21 ) of which each can be moved on a cutter guideway ( 13, 14, 19 ), which is arranged between the guideways ( 7, 8 ), from a first working position (A 1 , A 2 , A 5 ) in which it works on the workpiece (W 1 , W 3 ) held by the first workpiece fixture ( 9 ) to a second working position (A 3 , A 4 ) in which it works on the workpiece (W 2 , W 4 ) held by the second workpiece fixture ( 10 ). The apparatus in accordance with the invention allows performing the machining with high precision of the workpieces.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an apparatus for machining workpieces by stock removal, in particular the main and/or connecting rod bearing journals of crankshafts. Such apparatuses are known, for example, from the publication of the PCT application WO 96/17705 or the German patent specification DE 196 26 627 C1. 
     In the apparatus as known from DE 196 26 627 C1 the workpiece is held during the machining in a workpiece fixture which is equipped with at least one turntable drive. The turntable drive is used to rotate the workpiece, which is otherwise stationary, about its longitudinal axis. At least two milling cutters are provided in the known apparatus to machine the workpiece, which cutters machine the workpiece simultaneously. All advance motions which are required for example as a result of the eccentricity of the surface areas to be machined during the machining of the connecting rod bearing journals of crankshafts are performed by separate actuating drives of the milling cutters. 
     The advantage of the apparatus known from DE 196 26 627 C1 is that short machining cycles are achieved with highly specialized tool units in the apparatus per se. In this process, the machining operations are performed simultaneously by several milling cutters. The disadvantage is, however, that when two main and connecting rod bearing journals are machined simultaneously by means of two discoid milling cutters the cutters must be arranged with a left-hand and right-hand design. The simultaneous machining of two main or connecting rod bearing journals of a crankshaft additionally has an unfavourable effect on the precision of the machining. 
     An apparatus is known from WO 96/17705 in which the machining of the workpiece is also performed simultaneously by two discoid cutters. In contrast to the aforementioned known apparatus, the apparatus as described in WO 96/17705 comprises two workpiece fixtures and a conveying device for conveying the workpiece. The workpiece fixtures are flush with respect to one another and with respect to the conveying devices arranged in front of and behind the apparatus, so that the conveying device can convey the workpiece in a linear movement from the first conveying apparatus to the first workpiece fixture and from there to the second workpiece fixture and further to the second conveying apparatus. The discoid cutters are linearly movable between the two workpiece fixtures, so that they can first perform machinings on the workpiece gripped in the first workpiece fixture in a first working position and thereafter machinings on the workpiece gripped in the second workpiece fixture in a second working position. 
     For machining purposes the workpiece which in the known apparatus reaches the apparatus by way of the first conveying apparatus is loaded by the conveying device at first into the first workpiece fixture. Thereafter the workpiece is machined, with the discoid cutters assuming their first working position. After the end of the first machining operations the workpiece is removed by the conveying device from the first workpiece fixture and brought to the second workpiece fixture. Then further machining is performed by the discoid cutters on the workpiece gripped in the second workpiece fixture. During the machining steps the workpiece is turned by the turntable drive of the workpiece fixture. The advance and longitudinal motions are performed by the discoid cutters during the machining. Once the workpiece is gripped in the second workpiece fixture the conveying device can bring a new workpiece to the first workpiece fixture, so that the discoid cutters can commence with the machining of the new workpiece immediately after ending the machining of the workpiece gripped in the second workpiece fixture. 
     In the apparatus as known from WO 96/17705 the flow of material is improved in such a way that such an apparatus can be included in an automated production sequence. For this purpose, however, it is necessary to rechuck the workpiece at least once during the machining. This not only leads to the problem of the additional machining time required for the rechucking and conveying process, but also to a considerable increase in the complexity of the apparatuses required for controlling and monitoring the machining as well as for automated transport of the workpieces within the apparatus per se. 
     The disadvantage in this case too is that when two main or connecting rod bearing journals of a crankshaft are simultaneously machined by means of two discoid cutters it is necessary to provide them with a left-hand and right-hand design. 
     The simultaneous machining of two main and connecting rod bearing journals of a crankshaft and the rechucking of the crankshaft also have an unfavourable influence on the precision of the machining. 
     It is the object of the present invention, based on the aforementioned state of the art, to provide an apparatus of the kind mentioned above which allows a high machining precision. 
     SUMMARY OF THE INVENTION 
     This object is achieved by an apparatus for the machining of workpieces by stock removal which is equipped with at least two guideways which are arranged at a distance from one another and parallel to each other and on which at least one workpiece fixture each holding a workpiece can be moved from a transfer position to a working position, and with two discoid cutters, of which each cutter is movable on a cutter guideway, which is arranged between the guideways, from a first working position at which it works on the workpiece held by the first workpiece fixture to a second working position at which it works on the workpiece held by the second workpiece fixture. 
     In contrast to the known state of the art, two workpiece fixtures which are each movable on a separate guideway are provided in the apparatus in accordance with the invention. The workpiece fixtures per se can travel in this way from the actual machining position to a transfer position in which they receive the workpiece. Simultaneously, each discoid cutter can be moved back and forth between the workpiece fixtures, so that it can work successively alternatingly on the workpieces gripped between the two workpiece fixtures. The actuating movements in the longitudinal direction that may be required during the machining of the workpiece are performed by the respective workpiece fixture, so that a respective mobility of the cutter can be omitted. If the workpiece is turned about its longitudinal axis during the machining, any feed motion of the tool in the radial direction that may be required as a result of the eccentricity of the workpiece can be performed by the cutter per se. The complexity of the apparatuses required for performing and controlling the workpiece machining is thus reduced to a minimum. 
     The parallel arrangement of the guideways additionally allows that during the machining of the one workpiece the respective other workpiece fixture can receive a new workpiece and move it to the machining position. After the end of the machining of the first workpiece the workpiece to be newly machined is ready, so that the discoid cutter merely has to be moved to the working position of said new workpiece. The unloading of the previously finished workpiece, the loading of the respective workpiece fixture with a new workpiece and the conveyance of the workpiece fixture with the new workpiece to its working position take place in the meantime. 
     As a result of the parallel processed sequence of a plurality of conveying, transferring and machining steps as are enabled by the apparatus in accordance with the invention, the dwell times of a workpiece between its transfer in the introduced state and its return in the finished state are short, although, as a rule, only one discoid cutter is in engagement with the respective workpiece at a time. 
     In the embodiment of the invention there are several discoid cutters which work successively on the same workpiece. As a result of the parallel arrangement of the cutter guideways and the simultaneous movability of the workpiece fixtures on the guideways that are assigned to the same it is ensured at all times that each discoid cutter comprises a working position on the one guideway as well as on the other guideway. The machining steps can be processed in a time-staggered manner in such a way that in the case of a respective linkage of the beginning of the workpiece transfer and the machining times it is possible to achieve an even higher workpiece throughput. 
     If more than two discoid cutters are provided, their working positions can be accessed successively by the workpiece fixtures. The substantial adaptability of the apparatus in accordance with the invention to a wide variety of machining tasks and geometrical conditions of the workpieces to be machined is thus ensured at all times in this way. 
     The apparatus in accordance with the invention is particularly suited for milling occurring parallel to the axis, milling occurring orthogonally and/or cylindrical surface grinding of crankshafts or camshafts for motor construction. 
     Further preferable embodiments of the invention are given in the dependent claims and will be explained below in closer detail by reference to embodiments shown in the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically depicts a workpiece to be machined; 
     FIG. 2 is a schematic plan view of a first embodiment of an apparatus for milling crankshafts; 
     FIG. 3 is a schematic front view of the apparatus in accordance with FIG. 2 on an enlarged scale; 
     FIG. 4 is a schematic plan view of a second embodiment of an apparatus for milling crankshafts. 
    
    
     Coincident components are designated with the same reference numerals in the figures. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A workpiece W 1  which is to be machined and, in its capacity as a crankshaft, is provided with five main bearing journals a 1 , a 2 , a 3 , a 4 , a 5  and four connecting rod bearing journals b 1 , b 2 , b 3 , b 4  and has already been finished at the ends c 1 , c 2  and at the first main bearing journal al. The finish-machining of the main and connecting rod bearing journals a 2 , a 3 , a 4 , a 5 , b 1 , b 2 , b 3 , b 4  takes place in an apparatus in accordance with FIGS. 2 and 3. 
     The apparatuses as illustrated in FIGS. 2 through 4 are each provided with an engine bed  1 . On each of the longitudinal sides  2 ,  3  of said bed there are arranged a plane inclined surface area  4 ,  5 . The inclined surface areas  4 ,  5  are inclined towards one another and converge into a horizontally aligned central surface area  6  in the central portion of the engine bed  1  which extends, like the inclined surface areas  4 ,  5 , over the entire length L of the engine bed  1 . A linearly extending guideway  7 ,  8  formed by two rails is arranged on each of the inclined surface areas  4 ,  5  parallel to the longitudinal sides  2 ,  3 , with the length of the guideway substantially being equivalent to the length L of the engine bed  1 . The guideways  7 ,  9  are used for guiding one workpiece fixture  9 ,  10 . 
     Each of the workpiece fixtures  9 ,  10  is movable by actuating devices (not shown herein in closer detail) on the assigned guideway  7  or  8  from a transfer position P 1 , P 2  to at least two working positions A 1 , A 2 , A 3 , A 4 , A 5 , A 6 . In addition, each workpiece fixture  9 ,  10  is equipped with a clamping chuck in which a workpiece W 1 , W 2 , W 3 , W 4  is gripped. The workpieces W 1  to W 4  can be turned about their longitudinal axis by a turntable drive  11 ,  12  of the workpiece fixtures  9 ,  10 . 
     The workpieces W 1  to W 4  concern the same crankshafts in the examples as explained herein. Similarly, camshafts or other oblong components can also be machined in the described apparatuses. 
     The apparatuses shown in FIGS. 2 and 4 are equipped with a control device CD which coordinates the motion of rotation of the workpieces W 1  to W 4  with an advance motion of the cutters  17 ,  18 ,  21  during machining. 
     Every one of the apparatuses as shown in FIGS. 2 to  4  is provided with two rectilinearly arranged cutter guideways  13 ,  14  on which one cutter unit  15 ,  16  each is movable by means of actuating drives (not shown). The cutter guideways  13 ,  14  are aligned orthogonally to the guideways  7 ,  8 , and are mounted on the central surface area  6  of the engine bed  1  and extend substantially over the entire width of said surface area  6 . In this way the cutter units  15 ,  16  and, in combination with them, the discoid cutters  17 ,  18  which are carried by the same can be advanced on each of the guideways  7 ,  8 . Each cutter  17 ,  18  is rotatingly driven by way of a drive (not illustrated in detail) of each cutter unit  15 ,  16 , 
     The apparatus as illustrated in FIGS. 2 and 3 comprises two cutter guideways  13 ,  14  which are arranged in parallel at a distance from one another. The embodiment in accordance with FIG. 4 additionally comprises a third cutter guideway  19  which is arranged on the side of the guideway  13  in a parallel manner and at a distance to the same, which side of guideway  13  is opposite of cutter guideway  14 . A third cutter unit  20  with a discoid cutter  21  is held on the cutter guideway  19 , which cutter unit is also displaceable by means of an actuating drive (not shown). The mobility of the cutter units  16  and  20  corresponds to the mobility of the cutter unit  15 , so that each of the cutter units  15 ,  16 ,  20  can reach both a working position A 3 , A 4  and A 6  at the guideway  8  as well as a working position A 1 , A 2  and A 5  at the guideway  7 . 
     The axes of rotation of the respective cutters  17 ,  18  and  21  as well as the axes of rotation of the workpieces W 1  to W 4  which are machined on the respective apparatuses are disposed in a plane E, so that the cutters  17 ,  18  and  21  can be guided in a positionally correct and simple manner to the sections of the workpiece W 1  to W 4  which are to be machined and the movements of the respective cutter  17 ,  18 ,  21  and the workpiece W 1  to W 4  can be coordinated in a similarly simple manner during the machining. 
     In the apparatus in accordance with FIGS. 2 and 3 the workpiece fixture  9  is moved to the transfer position P 1  for the purpose of machining the workpiece W 1 . There, a transfer device (not shown) will transfer the workpiece W 1  to be machined which is chucked into the chucking apparatus of workpiece fixture  9 . 
     In the meantime, cutter  17  machines the connecting rod bearing journals of workpiece W 2  which is gripped in the workpiece fixture  10 . The workpiece W 2  is turned about its longitudinal axis by the turntable drive of the workpiece fixture  10 . Simultaneously, cutter  17  is moved in an axis of motion X directed normally to the axis of motion Z of the workpiece fixture  10 . In this way the movement of the cutter  17  is adjusted in the direction of the axis of motion X to the movement which is performed by the connecting rod bearing journals about the longitudinal axis of the workpiece W 2 . After finishing the machining of the first connecting rod bearing journal, the workpiece W 2  is moved by the workpiece fixture  10  in the direction of the axis of motion Z until the next connecting rod bearing journal of the workpiece W 2  to be machined is located in the working zone of the cutter  17 . Cutter  17  then commences the machining of the respective connecting rod bearing journal in the manner as described above. In this way all of the connecting rod bearing journals of the workpiece W 2  which are to be machined are successively subjected to machining by the cutter  17 . 
     If orthogonal milling is performed during the machining, the actuating drive of the cutter unit  15  will perform the required advance of cutter  17  in the direction of the axis of motion X. For milling parallel to the axis, on the other hand, workpiece W 2  is moved by the workpiece fixture  10  in the Z direction during the machining. 
     Two workpieces W 1 , W 2  are machined simultaneously in the apparatus in accordance with FIGS. 2 and 3. The following machining steps are performed for the workpiece W 1 : 
     Loading of the workpiece fixture  9  with the workpiece W 1  in the transfer position P 1 ; 
     alignment and chucking of workpiece W 1  on workpiece fixture  9 ; 
     displacement of workpiece fixture  9  to the working position A 1 ; 
     machining of the four main bearing journals a 2 , a 3 , a 4 , a 5  of the workpiece W 1  by cutter  18 , and in this process displacement of the workpiece W 1  by the workpiece fixture  9  in the Z direction in order to bring the respective main bearing journals into the working zone of cutter  18 ; 
     displacement of workpiece fixture  9  to the working position A 2 ; 
     machining of the four connecting rod bearing journals b 1 , b 2 , b 3 , b 4  of the workpiece WI by cutter  17 , and in this process displacement of the workpiece W 1  by the workpiece fixture  9  in the Z direction in order bring the respective connecting rod bearing journals into the working zone of the cutter  17 ; 
     displacement of the workpiece fixture  9  to the transfer position P 1 ; 
     Unloading of the finished workpiece W 1 . 
     The machining steps are performed as follows for the workpiece W 2 : 
     loading of the workpiece fixture  10  with the workpiece W 2  in the transfer position P 2 ; 
     alignment and chucking of workpiece W 2  on workpiece fixture  10 ; 
     displacement of workpiece fixture  10  to the working position A 3 ; 
     machining of the four connecting rod bearing journals of the workpiece W 2  by cutter  17 , and in this process displacement of the workpiece W 2  by the workpiece fixture  10  in the Z direction in order to bring the respective connecting rod bearing journals into the working zone of cutter  17 ; 
     displacement of workpiece fixture  10  to the working position A 4 ; 
     machining of the four main bearing journals of the workpiece W 2  by cutter  18 , and in this process displacement of the workpiece W 2  by the workpiece fixture  10  in the Z direction in order bring the respective main bearing journals into the working zone of the cutter  18 ; 
     displacement of the workpiece fixture  10  to the transfer position P 2 ; 
     unloading of the finished workpiece W 2 . 
     As a result of the staggered performance of the individual partial operations of the machining, maximum production times of the cutters  17 ,  18  are achieved. The parallelization of loading and unloading operations, the machining of the main bearing journals by cutter  18  and the machining of the connecting rod bearing journals by cutter  17  lead to the effect that within the cycle time for a workpiece W 1  a second workpiece W 2  can be completely machined in an offset manner. As a result, machining times with an apparatus as arranged in accordance with the invention are reduced considerably in comparison with the known state of the art. 
     As in the apparatuses in accordance with FIGS. 2 and 3, two workpieces W 3 , W 4  are machined in the embodiment in accordance with FIG.  4 . Additional machining operations are performed by the cutter  21 . The respectively machined workpiece W 3  and W 4  is positioned by the respective workpiece fixture  9 ,  10  in the respective working zone A 5 , A 6  of cutter  21 . Cutter  21  performs the machining of the first main bearing journal a 1  if the same has not yet been finished in the introduced workpieces W 3 , W 4 .