Patent Application
20090142997
The invention relates to a device for the finish machining of circumferential surfaces of substantially rotationally symmetrical workpiece portions on workpieces, which have a workpiece axis and several workpiece portions arranged in offset manner along the workpiece axis, particularly for the precision machining of bearing points on camshafts and crankshafts, according to the preamble of claim 1.
Finishing is a precision machining method, in which the circumferential surfaces of substantially rotationally symmetrical workpiece portions on workpieces such as crankshafts, camshafts, gear shafts and other components for machines and motors are worked for producing a desired precision surface structure. Finishing involves a machining tool having a granular cutting compound being pressed by a pressing device onto the circumferential surface to be worked. To produce the cutting speed necessary for material removal, in many method variants the workpiece is rotated about its workpiece axis and simultaneously an oscillating relative movement parallel to the workpiece axis is produced between the workpiece and the machining tool engaging on the circumferential surface. As a result of the combination of the rotary movement of the workpiece and the superimposed oscillatory movement a so-called crosshatch pattern can be produced, so that the worked workpiece circumferential surfaces are particularly suitable e.g. as contact surfaces for roller or plain bearings, etc.
The workpieces can e.g. be camshafts or crankshafts. Such crankshaft-like workpieces are provided in axially spaced manner with mutually rotationally symmetrical workpiece portions serving as bearing points. The so-called main bearings or centre bearings are positioned coaxially to the workpiece axis and serve to mount the shaft for its rotary movement. Immediately alongside a main bearing are provided one or two so-called stroke or lift bearings, whose axes are parallel and displaced eccentrically to the workpiece axis. Other parts of a machine, e.g. the connecting rods of pistons of an internal combustion engine or a pump or a compressor engage on the lift bearings.
During the finish machining of such workpieces, use is generally made of devices making it possible to simultaneously work or machine several of the workpiece portions to be worked or machined. Such finishing devices have a number of finishing units, each of said finishing units having at least one finishing arm with a pressing device for pressing cutting compounds onto the workpiece surface and with each of the workpiece portions to be machined in a machining phase is associated a finishing unit. Examples of devices with which it is possible to carry out a parallel machining of juxtaposed bearing surfaces on crankshafts and the like are described in EP 318 966 B1, U.S. Pat. No. 5,951,377 or EP 997 229 B1.
EP 997 229 B1 discloses a belt finishing machine, which for the simultaneous machining of main bearings and rod bearings has several axially juxtaposed finishing units placed on a common support. Each of the finishing units has two which are pincer-like and pivotable towards and away from one another and on each of which is fixed a pressing device in the form of a workpiece-dependently dimensioning finishing shell, with the aid of which finishing belt is pressed onto the workpiece surface to be machined. In each case the finishing units are very narrow, so as to be able to simultaneously machine juxtaposed bearing points. The width of the finishing units (measured parallel to the workpiece axis) cannot exceed the axially measured width of the workpiece portion to be machined, plus the proportionate, half axial dimensions of adjacent crank webs.
The axial spacing of the centres of immediately adjacent bearings is here also referred to as the bearing spacing and in the case of crankshafts for internal combustion engines corresponds to half the cylinder spacing, i.e. the bore spacing, also referred to as the inside micrometer, of directly adjacent cylinder bores. Typical cylinder spacings for in-line four cylinder motors with an approximately two litre capacity can e.g. be approximately 90 mm, so that a value of approximately 45 mm, as a function of the precise distribution of the shaft, is obtained for the maximum width of the juxtaposed finishing units. On the basis of smaller motors with capacities of e.g. 1.2 to 1.4 litres, the admissible widths of adjacent finishing units become smaller and can e.g. be approximately 40 mm. Therefore the possible arm spacings, i.e. the possible spacings of corresponding elements (e.g. the centre axes) of adjacent finishing units in conventional crankshaft finishing machines is of the same order of magnitude.
The finishing units of belt finishing machines generally comprise not only the fixing arms provided for supporting the pressing devices, together with optionally swivel bearings and linear guides, but also devices for finishing belt conveying and sensors for monitoring the machine functions and supply equipment. Also in the case of finishing devices operating with finishing stones, the finishing units are complex assemblies, which can only undergo a size reduction with considerable effort and cost. If the bearing spacings present on the workpiece drop below the minimum possible arm spacings of the finishing units, the finishing units necessary for machining have hitherto been distributed over a number of stations, which leads to corresponding increased costs and space requirements, as well as longer machining times for the overall machining process.
The problem of the invention is to provide a device for the finish machining of circumferential surfaces of substantially rotationally symmetrical workpiece portions on shaft-like workpieces enabling the economic machining of workpieces with different dimensions. The device must in particular make it possible to economically machine workpieces with bearing spacings of less than 40 mm. These aims are to be achieved whilst maintaining accessibility to the workpieces to be machined for workpiece conveying and preferably whilst bringing about a reduction in manufacturing costs, whilst at the same time the machining quality of conventional finishing devices must be equalled and preferably improved.
For solving this problem the invention proposes a finish machining device having the features of claim 1. Advantageous further developments are given in the dependent claims. By express reference the wording of all the claims is made into part of the content of the description.
In the case of the finish machining device according to the invention, the finishing units are subdivided into a first group of finishing units and a second group of finishing units and axially directly adjacent finishing units are alternately associated with the first and second groups and the first group of finishing units is angularly displaced from the second group of finishing units with respect to the workpiece axis.
In all two or more finishing units can be provided. As a rule there are far more than two finishing units, e.g. 4 or more, 6 or more, 8 or more or 10 or more. A group of finishing units can consist of a single finishing unit, but normally such a group has two or more finishing units.
As a result of the inventive arrangement, directly adjacent finishing units, which are intended to machine immediately adjacent workpiece portions, are displaced relative to the workpiece axis in the workpiece circumferential direction, so that the corresponding pressing devices of immediately adjacent finishing units engage from directions oriented in angularly displaced manner to the workpiece axis on the workpiece. Thus, a finish machining device with separate finishing packages for the lift bearings and the main bearings can be provided. As a result of the angularly displaced arrangement of groups of finishing units, the conventional restriction with respect to the minimum arm spacing can be obviated, so that a maximum width of a finishing unit, measured parallel to the workpiece axis, can be greater than the minimum settable distance between corresponding structural elements of directly adjacent pressing devices. Whereas hitherto the maximum width of a finishing unit could be no greater than the bearing spacing of immediately adjacent bearings of a shaft to be machined, this restriction is eliminated as a result of the angularly displaced arrangement. If e.g. immediately adjacent finishing units of a group are in each case arranged in parallel juxtaposed manner, i.e. in a row, now the maximum width of adjacent finishing units of a group is only limited by the cylinder spacing which is twice the bearing spacing. This constructionally simplifies the making available of all the functional elements necessary for the functioning of the finishing units, such as bearings, guides, optionally belt conveyors, sensor systems, etc., which cuts down costs and may be able to improve the functionality of the finishing units.
Thus, in the case of many constructional embodiments, it is possible for the fixing units in the vicinity of the pressing devices to have a width of less than 40 mm and said width can also be 35 mm or less or 30 mm or less or 25 mm or less.
Although the finishing units of a group can also be angularly displaced against one another, generally the finishing units of a group are arranged in a row. This simplifies the mounting of the finishing machine bed and it is possible to easily adjust the reciprocal spacings of the finishing units.
In an embodiment the first finishing arms of the first finishing units of the first group are linearly displaceably mounted for machining first workpiece portions, arranged coaxially to the workpiece axis, in the radial direction of said axis. The pressing device of a finishing arm can consequently be moved by a translatory movement towards or away from the workpiece, which simplifies the construction of the first finishing units.
A first finishing unit preferably only has a single finishing arm. As a result of the one-sided pressing, the pincer-like shape of conventional finishing units can be obviated and as a result a constructionally relatively easily implementable, operationally reliable and stable one-sided construction of the first finishing units is obtained.
The first finishing units can e.g. be placed below a horizontal plane defined by the workpiece axis and in particular in such a way that the finishing arms of the first finishing units perform a substantially vertical displacement movement between a retracted rest position (e.g. for tool change) and a machining position with engagement on the workpiece.
Preferably second finishing units of second workpiece portions (lift bearings) arranged eccentrically to the workpiece axis are equipped with at least one swivel arm swivellable about a swivel axis for supporting at least one pressing device. The second finishing units can be constructed in pincer-like, conventional manner. Preferably the second finishing units have only one finishing arm in the form of a swivel arm with a pressing device, so that there is a one-sided construction for the second finishing units.
A one-sided or one-armed construction of the second finishing units is inter alia advantageous because the lift bearings to be machined therewith are fitted eccentrically to the workpiece and on rotating the workpiece about its axis perform a circular motion about said axis which must be followed by the finishing unit. For this purpose an individual drive is not normally used and instead the finishing arms are carried along by the workpiece. As a result of the one-armed construction, the carried along masses of the second finishing units provided for the lift bearings can be significantly reduced compared with pincer-like constructions, so that inertia-caused fluctuations of the pressing force and the consequent quality losses when machining the lift bearings can be reduced.
A support device for the second finishing units can be placed alongside the workpiece, e.g. in such a way that the swivel axis of the swivel arm is in a horizontal plane with the workpiece axis. The swivel arm of the second finishing unit can be so positioned that in its machining position it is substantially horizontally oriented and engages from above on the workpiece and can be swivelled away upwards from the machining position with workpiece engagement into a rest position.
The overall arrangement of the finishing units in certain embodiments is chosen in such a way that first finishing units and second finishing units are so positioned that the associated pressing devices engage on the workpiece essentially from opposite sides. Thus, e.g. linearly displaceable finishing arms of first finishing units for the main bearings can engage from below, whereas swivellable finishing arms of second finishing units for the lift bearings in the machining position engage on the workpiece essentially from the opposite top side. Thus, the finishing units which are in machining engagement provide closely juxtaposed bearing points on alternately opposing sides, so that the pressing forces of the first and second finishing arms compensate one another and consequently a sagging of the workpiece during machining possible in the case of only one-sided pressing forces is avoided.
Inventive finish machining devices can be set up for different finishing machining processes.
In some embodiments the workpiece is rotated about its axis for producing the cutting speed necessary for material removal. At the same time an oscillatory relative movement between the workpiece and the machining tool engaging on the circumferential surface parallel to the workpiece axis is produced. For this purpose the workpiece can be given an axial oscillatory movement. It is alternatively or additionally possible to produce the oscillatory movement through the machining tool.
In some embodiments the device is set up as a belt finishing device. In the case of so-called belt finishing, a finishing belt is pressed onto the workpiece surface with the aid of a pressing device. A finishing belt has a belt-like, flexible support where, with the aid of a binder, cutting granules are applied to the front side facing the workpiece. Use is frequently made of a tear resistant, low-elongation polyester film as the support material for the grain binder structure. Sometimes fabric belts are used. At the end of or during a machining cycle the finishing belt used for machining can be moved further away, so that fresh cutting compound is available for material removal purposes, so that readily reproducible results are obtained.
The finishing tool can also be constituted by finishing stones. These are essentially rigid cutting bodies, where the granular cutting compound is bonded by synthetic resin, ceramically or in a metal matrix produced e.g. by electrodeposition or soldering, or in some other way. The side of the grinding wheel facing the workpiece is frequently profiled in accordance with the geometry of the workpiece surface to be machined in order to ensure a large-area machining engagement.
Particularly if the workpiece surface is only to be smoothed, belt finishing methods are known where the finishing belt is pressed without any workpiece-dependent finishing shell. Use is frequently then made of e.g. pressing rolls, which produce a linear contact, which in the case of rubberized rolls can also be in areal form. Here again there is a stepwise or continuous belt advance.
These and further features can be gathered from the claims, description and drawings and the individual features, both singly or in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions. Embodiments of the invention are described hereinafter relative to the drawings, wherein show:
The main bearings 114 and lift bearings 116 are arranged in axially alternating manner with in each case interposed crank webs 115 linking the main and lift bearings. For the definition of the dimensions of the crankshaft use is normally made of the cylinder spacing Z and bearing spacing L, the cylinder spacing Z corresponding to the axial spacing of the bore axes of adjacent cylinder bores of the corresponding motor and the bearing spacing L=Z/2 corresponds to the centre distance or spacing of directly adjacent bearings. In the case of an e.g. modern in-line four cylinder motor with an approximately 1.2 litre capacity and approximately 67 mm cylinder bore diameter, the cylinder spacing is typically approximately 70 mm corresponding to a bearing spacing L of approximately 35 mm.
The finishing machine 100 has a conventionally constructed and consequently not further shown workpiece retaining device for retaining the workpiece with a horizontal workpiece axis. The workpiece is rotated about its axis by means of a not shown rotating device for machining purposes and is simultaneously brought by an oscillatory device in an axially, short-stroke oscillating movement with strokes of a few millimetres. The rotating device can e.g. have an electric geared motor and the oscillating device can comprise a cam drive operated as a function of workpiece rotation. The rotating device and oscillating device can e.g. engage at the driven end of crankshaft 110. The oscillating device can also contain a drive which is independent of workpiece rotation, e.g. a pneumatic or electromotive oscillator.
The belt finishing device 100 has eleven finishing units, which by means of two mutually spatially separated supporting devices are placed on a common machine bed 120. In workpiece-dependent manner, the machine is in each case set up in such a way that the number of finishing units corresponds to the number of workpiece portions to be machined on the workpiece. The finishing units are subdivided into two groups corresponding to the two different bearing types to be machined, namely a first group with seven first finishing units 200 and which are in each case provided for machining the main bearings arranged coaxially to the workpiece axis, and a second group of four second finishing units 300 which are in each case set up for machining the second workpiece portions (lift bearings) revolving eccentrically to the workpiece axis 112. As can be seen in
The finishing units of the individual groups are in each case arranged within the group in juxtaposed manner in a row running parallel to the workpiece axis, so that in the axial view of
In special machines the finishing units can also be subdivided into more than two groups, e.g. into three groups. This can e.g. be appropriate if thrust bearings are to be machined in addition to main and lift bearings.
The first finishing units 200 are jointly fixed to a first support device connected to the machine bed and are individually displaceable relative thereto axially parallel to the workpiece axis and can be fixed in different axial positions of the first support device in order to adapt the mutual spacing and axial position of the first finishing units to the dimensions of the given workpiece.
Each first finishing unit has a single, linearly movably guided, first finishing arm 250. The linearly displaceable finishing arms 250 of the first finishing units 200 are in each case positioned below the workpiece on the movable part of a vertical slide or carriage 220, whose machine-fixable part is fixed to a support arm 215 of the first finishing unit 200. With the aid of a hydraulic lift cylinder 210 placed between the support arm and the finishing arm, each of the first finishing arms can be linearly displaced in the vertical direction between a lower release position and an upper machining position with machining engagement on the workpiece. On the end of the first finishing arms facing the workpiece, are replaceably fitted workpiece-dependently dimensioned, first pressing devices 255 with upwardly opened, substantially semicircular recesses.
The replaceable, first pressing devices 255 are in each case designed for pressing a first finishing belt 260 covered with a cutting compound onto the workpiece portion circumferential surface to be machined over a predeterminable contact angle with a pressing force provided for the machining process. The finishing belt rests during machining, so that the cutting speed necessary for material removal is produced exclusively by the rotary movement of the workpiece combined with the superimposed, axial oscillatory movement of said workpiece, in order to produce on the workpiece surface a crosshatch pattern which is advantageous for suitability as a plain bearing surface. For the conveying on of the first finishing belt shown in broken line form during machining intervals, a first belt conveyor is provided and to it belong the conveying wheels 265 fitted to the first finishing unit 200.
The second finishing units 300 are jointly fixed to a second support device 310 connected to machine bed 120 and are individually axially displaceable relative to the machine-fixed part thereof parallel to the workpiece axis and can be fixed in the in each case desired axial position. Each of the two finishing units has a horizontal slide or carriage 320 freely displaceable on a horizontal linear guide and which is positioned roughly level with the workpiece axis 112 of a clamped workpiece. On the horizontal carriage side facing the workpiece is swivellably coupled a second finishing arm 350, constructed as a swivel arm, by means of a swivel bearing 306 with a horizontal swivel axis 307, which is in a horizontal plane with the workpiece axis 112. In the vicinity of the free end of the second finishing arm 350, on the workpiece-facing side is fitted a workpiece-dependent, replaceable, second pressing device 355. For conveying on the second finishing belt 360, shown in broken line form, during machining intervals a second belt conveyor is provided and to it belong the conveying wheels 365 fitted to the second finishing unit 300.
The pressing force producible with the aid of a second finishing arm 350 is produced essentially by a hydraulic cylinder 330 which can be bilaterally supplied with hydraulic pressure and which on the one hand is fixed to a fixed part of the horizontal carriage 320 and on the other in the vicinity of swivel axis 307 in a knee region of the L-shaped, second finishing arm. Hydraulic cylinder 330 also serves as a closing cylinder for swivelling the second finishing arm 350 between the raised release position of
In this machine concept, the first finishing units 200 for machining the main bearings and the second finishing units 300 for machining the lift bearings are completely spatially separated from one another. They are also angularly displaced from one another relative to workpiece axis 112, because the first finishing units for the main bearings engage from vertically below and are linearly displaced into the machining position, whereas the second finishing units are arranged on a horizontal carriage, i.e. are angularly displaced by 90ø to the first finishing units and otherwise can be swivelled about a horizontal swivel axis, so that they engage on the workpiece from the opposite side thereof. Thus, in the machining and discharge position shown in
The finishing machine can operate as follows. For loading the machine with a workpiece the first finishing arms 250 are retracted linearly downwards and the second finishing arms are swivelled upwards into the retracted position of
Then the rotary drive gives the workpiece a rotary movement about the workpiece axis and simultaneously by means of the oscillating drive is given an oscillatory, short-stroke movement parallel to the workpiece axis, so that material removal takes place due to the finishing belt pressed onto the workpiece portions. During workpiece rotation the first finishing arms 250 placed beneath the workpiece remain substantially stationary. The second pressing devices of the second finishing units in each case press against an eccentrically revolving workpiece portion. The vertical component of the eccentric movement is substantially compensated by the swivelling movement of the second finishing arms 350, whilst the horizontal component of the eccentric movement is made possible as a result of the horizontal reciprocating movement of the passively following horizontal carriage 320. As the hydraulic cylinder 330 is fitted to the movable part of the horizontal carriage, only the vertical component of the swivelling movement of the lever acts as a pumping movement on the hydraulic cylinder 330, so that the resulting pressing force fluctuations of the finishing belt remain relatively small.
At the end of machining the first finishing arms 250 are once again drawn downwards and the second finishing arms 350 are swivelled upwards, so that the workpiece becomes accessible for workpiece change purposes. Simultaneously, as a result of the automatic belt conveyor, the finishing belt of each finishing unit is advanced by a predetermined amount, so that fresh, unused finishing belt for the next machining step becomes available in the vicinity of the pressing device. The workpiece can be removed and replaced by an as yet unmachined workpiece.
The novel machine concept offers a number of advantages. It is possible to significantly reduce the arm spacings between the finishing units compared with conventional finishing machines. In the case of conventional finishing machines the finishing units were packaged in juxtaposed manner, so that limits were placed on the arm spacing reduction. In the case of the novel machine concept the finishing units for lift bearings and the finishing units for main bearings are completely spatially separated.
In the exemplified case where the finishing machine is set up for a handling-loading from above, the finishing units for the main bearings are placed below the crankshaft and the finishing units for the lift bearings laterally of said crankshaft on the side remote from the operator or a handling robot. The spatial separation inter alia makes it possible to machine shafts with a much smaller bearing spacing than hitherto, because the permitted maximum width B of the individual finishing units can now be greater than the bearing spacing L, which has hitherto limited the maximum width of the finishing units.
In addition, a reduction of manufacturing costs and carried along masses for the lift bearing arms is possible. There is in each case only a unilateral pressing action on the finishing belt both for the lift bearings and the main bearings. As a result of the unilateral construction of the finishing arms the conventional pincer-like construction can be completely obviated, which permits a mass-reduced construction.
The first finishing units for machining the main bearings are completely differently constructed to the second finishing units for machining the revolving lift bearings. The first finishing units are only linearly pressed, because there is no need for guide devices and bearing devices for permitting a following compensating movement to the machined bearing. The lift bearing arms are movable, because they are intended to follow the rotary movement of the revolving lift bearings. Carrying along takes place due to the pressing contact of the pressing devices (finishing shells) with the given lift bearing. In order to force the pressing device with the machined lift bearing onto a circular path, significant forces are required and they change both in direction and amount during a revolution. The one-armed construction of the lift bearing finishing units offers a considerable mass reduction compared with pincer-like constructions and consequently the resulting inertia forces are reduced, so that machining is less influenced by the eccentric rotary movement of the lift bearing. In the case of unilateral finishing arms the pressing force of the pressing device is in each case made available by hydraulic cylinder 330, which is on the one hand fixed to the horizontal carriage and on the other to the moving swivel arm and therefore performs a pumping movement during shaft rotation. The hydraulic design ensures that the resulting fluctuations in the pressing force remain relatively limited. To this end relatively large pipe and valve cross-sections are combined with relatively small cylinder cross-sections and optionally a hydraulic accumulator can also be provided.
The main bearing arms have a very simple construction. As the main bearings are positioned centrally, they do not perform a circular movement. The main bearing arm is vertically infed by a simple linear movement and then remains in the intended machining position in the case of an adjustable pressing pressure. The specific construction with protection plates also protects the mechanical components against abrasive coolants.
Conventional pressing devices can be used in the novel finishing machines. The pressing devices of the first finishing units for the main bearings and the second finishing units for the lift bearings can have an identical construction. However, different pressing devices can be used for the main bearings and lift bearings. For example, the pressing devices can be used in the same way as described in the applicant's EP 997 229 B1. The pressing devices can comprise at least one support member constructed for direct support on the workpiece surface and one or more pressing elements supported on the support member for pressing finishing media onto the workpiece surface. There can e.g. be at least two circumferentially displaced pressing elements supported on the support member and which can be operated independently of one another for pressing the finishing medium onto the workpiece surface. As a result of the direct support on the workpiece surface the pressing force acting on the finishing medium (e.g. finishing belt or stone) is not influenced by dynamic additional forces, such as can e.g. occur with eccentrically revolving crankshaft pins.
In the described embodiment the spatially separated arrangement of the lift and main bearing arms (i.e. second and first fixing units) are combined with the one-armed construction with unilateral pressing action, so that the advantages of both measures are obtained. The first and second group of finishing units are completely separate from one another and there is no mutual influencing. Thus, the arm spacings can be significantly reduced. In addition, the pressing devices of the first or second group of finishing units engage on opposite sides of the crankshaft and on directly adjacent points and therefore ensure that even in the case of high pressing forces any bending or sagging of the workpieces is prevented.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 059 926.0 | Dec 2007 | DE | national |
