Apparatus for machining workpieces

Details Apparatus for machining workpieces Apparatus for machining workpieces

1999-06-18

2001-05-22

Wellington, A. L. (Department: 3722)

Metal working

Plural diverse manufacturing apparatus including means for...

With means to feed work intermittently from one tool station...

C029S03300H, C029S564000, C029S006010, C082S106000, C082S129000, C409S199000, C409S200000

Reexamination Certificate

active

06233810

ABSTRACT:

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 g

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