EP0212338A2 - Method for machining the surface of a cam - Google Patents

Abstract

One method is used for machining a surface of profiles with a contour deviating from a circular shape, in particular for grinding cams of a camshaft. It is, starting from a raw contour (30/31/32), the profile by removing the surface with a target contour (30a / 31a / 32a) by moving a processing tool and the profile relative to each other so that on the one hand in each Intervention on the surface of the section of the machining tool is guided along the contour in web operation and, on the other hand, is fed in infeed operation by the surface distance between the raw contour (30/31/32) and the target contour (30a / 31a / 32a). In order to reduce the machining time and to increase the machining quality, the section is first moved from a first point (40) on the surface of the raw contour (30/31/32) in the delivery mode to a second point (42) of the target contour (30a / 31a / 32a) and then guided along the target contour (30a / 31a / 32a) in rail operation.

Description

The invention relates to a method and a device for machining a surface of profiles with a contour deviating from a circular shape, in which, starting from a raw contour, the profile is passed through Removal of the surface is provided with a target contour by moving a processing tool and the profile relative to one another such that, on the one hand, a section of the processing tool that is in engagement on the surface is guided along the contour in web operation, and on the other hand in the feed operation by the surface distance between the raw contour and Target contour is delivered.

Such methods are known, they are used, for example, to grind cams from camshafts.

In the known method, the camshaft is rotatably arranged about a fixed axis, and a grinding wheel is rotatably mounted about an axis parallel to the camshaft axis. In order to grind a predetermined target contour of the cams, the distance between the grinding wheel axis and the camshaft axis is changed with the camshaft rotating slowly in such a way that the surface section of the grinding wheel which is in engagement in each case removes the surface of the cam in such a way that the desired target contour is finally created.

• Zum einen ist die Abstandsvariation erforderlich, um die jeweilige Kontur des zu bearbeitenden Nockens zu kompensieren. Diesen Teil der Abstandsvariation bezeichnet man als "Bahnbetrieb".

The variation of the distance between the grinding wheel axis and the camshaft axis obeys two boundary conditions:

• On the one hand, the distance variation is necessary in order to compensate for the respective contour of the cam to be machined. This part of the distance variation is referred to as "railway operation".

On the other hand, however, the distance between the axes must be varied in such a way that a certain infeed of the grinding wheel takes place, i.e. an approximation to the cam to be machined by the amount of the distance from the raw dimension to the target dimension. This part of the distance variation is referred to as "delivery operation".

The known methods, which usually use numerically controlled processing machines, provide for simultaneous execution of rail operations and delivery operations.

In one of these known methods, the next point to be approached is continuously interpolated depending on the rotation of the camshaft, the path movement and the infeed movement being numerically superposed as part of the interpolation.

In another known method, the grinding wheel is mounted on a two-part carriage, one part of which runs on the other part, one part of the carriage being controlled as a function of the rail operation and the other as a function of the infeed operation. In this known method, the required superposition is achieved by mechanical superimposition.

A common feature of the two known methods explained above is that the point of a surface section of the grinding wheel that is respectively in engagement is located moved from the raw contour to the target contour on a spiral winding path, which movement always has a radial component due to constant infeed and - as already mentioned - must be set by continuous superposition of rail operation and infeed operation.

• Zum einen erfordert die ständige Superposition von Bahnbetrieb und Zustellbetrieb einen erheblichen Aufwand. Bei einer Superposition im Rahmen der Interpolation des nächsten anzufahrenden Bearbeitungspunktes ist nämlich entweder eine sehr schnelle und damit teure Recheneinheit erforderlich, oder aber es wird eine einfachere Recheneinheit verwendet, wodurch sich dann jedoch die Bearbeitungszeit drastisch erhöht, weil die erforderliche Rechenzeit zum Bestimmen des nächsten anzufahrenden Punktes unzuträglich hoch wird.

The two known methods therefore have the following major disadvantages:

• On the one hand, the constant superposition of rail operations and delivery operations requires considerable effort. In the case of a superposition within the framework of the interpolation of the next processing point to be approached, either a very fast and therefore expensive computing unit is required, or a simpler computing unit is used, but this then increases the processing time drastically because the computing time required to determine the next one to be approached Point becomes unacceptably high.

The mechanical superposition in accordance with the second of the known methods described gives rise to considerable mechanical problems, in particular because circular areas occur in sections during machining of cam contours, during which the web operation has a constant control variable. The part of the feed intended for railway operation must therefore stand still during the machining of this circular section, which, however, hardly within the scope of the precision of the machining required in the present context is possible. In practice, trembling movements occur, which are still justifiable for the positioning of the railroad operating feed, which result from small control cycles around a constant position.

Finally, the known methods have the common disadvantage that, as a result of the continuous infeed, there is always a radial component of the machining direction, which can either lead to problems with the surface quality or else make a separate aftertreatment necessary.

The invention is based on the object of developing a method of the type mentioned in such a way that the desired target contours can be achieved without loss of accuracy with significantly reduced effort and high processing speed.

This object is achieved according to the invention in that the section is first guided from a first point on the surface of the raw contour only in the infeed mode to a second point in the nominal contour and then is guided along the nominal contour only in rail operation.

The object underlying the invention is thus completely achieved.

The strict time separation of delivery operations and rail operations into successive procedural steps ensures that the position control is only under one point of view, so that the above-described disadvantages resulting from the simultaneous operation can be avoided.

When using a numerical control, only one of the movements can be interpolated during each of the two successive phases, which shortens the computing time and / or reduces the demands on the required computing unit. When using a mechanical superposition, on the other hand, while the one feed part is taking effect, the other feed part can be mechanically locked in a controlled manner, so that no errors can occur.

The method according to the invention is therefore in principle independent of how the profile and the processing tool are arranged relative to one another and are moved relative to one another, it is also independent of the type of profile processed in each case, as well as of the type of processing tool provided.

In a preferred embodiment of the invention, the machining tool can be rotated about a first axis.

Although it is possible in principle to use spatially fixed tools, for example spark erosion devices, lasers or the like, tools which can be rotated about a first axis are preferred because this allows the use of tried and tested types of tools, as are customary in particular for metalworking.

In a further preferred embodiment of the invention, the profile can be rotated about a second axis, although in principle spatially fixed profiles can also be processed. However, the rotatability of the profile about a second axis has the advantage that defined relationships can be set in a simple manner, because the machining points to be approached in each case can easily be determined as a function of the angle of rotation of the second axis, as is known per se.

In a further preferred embodiment of the invention, the first axis runs parallel to the second axis, and the distance between the axes is adjustable in the direction of a third axis running perpendicular thereto, in particular the second axis is spatially fixed.

This measure has the advantage known per se that only the first axis has to be adjusted in the direction of the third axis for the rail operation and the delivery operation, depending on the angle of rotation of the profile.

Another particularly preferred embodiment of the invention consists in that the first point and the second point define an angle of rotation of the second axis which is less than 180 ° and is preferably in the range between 20 ° and 180 °.

This measure has the advantage that the target contour is approached in a purely infeed mode on a relatively small circumferential area when using a grinding wheel by so-called deep grinding, so that the major part of the contour is then finished to the specified size exclusively in the railway mode.

A particularly good effect is also achieved if the processing tool is guided in the infeed mode with a uniform infeed.

With this procedure, the locus of the respective processing point has the form of an Archimedean spiral, which can be handled particularly easily for control tasks in numerical control.

Furthermore, an embodiment is preferred in which, after the section has been guided on the target contour, it is first guided from a third point on the target contour only in the delivery mode to a fourth point of a second target contour and then is only guided along the second target contour in rail operation.

With this measure, in which the steps according to the invention are thus carried out several times in succession, the effect according to the invention can also be achieved with large volumes of material to be removed. This is particularly advantageous if the raw contour is very irregular, so that the required target contour cannot be achieved with a single machining process for machining reasons. In contrast to the prior art, even with this procedure, the point of the machining tool that is in engagement is not along a spiral that is wound several times, but the infeed area is always limited to a spatially narrow surface area, while the rest of the route is in turn only operated by rail. Apart from the small infeed area, the location curve of the processing point thus has the shape of several location curves concentrically running at a parallel distance.

As already mentioned, a particularly preferred field of application, on the other hand not restricting the invention, is the machining of cams. Cams with at least one circular section are particularly preferably used, and the infeed mode is set in the region of the circular section.

This measure has the particular advantage that, in the region of the circular section, it is particularly easy to dispense with railway operation because the surface there has a constant radius to the axis of rotation of the profile.

In a preferred development of this embodiment, the circular section is a base circle of the cam, this has the advantage that the circumference of the base circle is particularly long, so that the delivery operation can be carried out in wide areas around the circumference, depending on the requirements.

Further advantages result from the description and the attached drawing.

It goes without saying that the features described above and those yet to be explained below can be used not only in the respectively specified combination, but also in other combinations or in each case without departing from the scope of the present invention.

• Fig. 1 und 2 eine Vorrichtung zum Durchführen des erfindungsgemäßen Verfahrens in zwei senkrecht zueinander liegenden Ansichten;
• Fig. 3 und 4 einen stark vergrößerten Ausschnitt aus der Vorrichtung gemäß den Fig. 1 und 2 zur Erläuterung des erfindungsgemäßen Verfahrens in zwei Bearbeitungsphasen;
• Fig. 5 eine schematische Darstellung einer Ortskurve eines Bearbeitungspunktes bei in mehreren Schichten erfolgender Bearbeitung des Profils.

Embodiments of the invention are shown in the drawing and are explained in more detail in the following description. Show it:

• Figures 1 and 2 an apparatus for performing the method according to the invention in two perpendicular views;
• 3 and 4 show a greatly enlarged detail from the device according to FIGS. 1 and 2 to explain the method according to the invention in two processing phases;
• Fig. 5 is a schematic representation of a locus of a machining point when machining the profile in several layers.

1 and 2, 10 denotes a grinding machine as a whole, as can be used to carry out the method according to the invention.

A camshaft 12 is rotatably arranged about a fixed axis 11, which is also referred to in technical terms as the C axis. For this purpose, the camshaft 12 is clamped between two tips 13 and 14 of a headstock 15 or a tailstock 16, and a rotationally fixed connection 17 between the camshaft 12 and a spindle of the headstock 15 ensures that the camshaft 12 is driven.

In the operating position shown in FIGS. 1 and 2, a cam 18 of the camshaft 12 is being machined by means of a grinding wheel 19. The grinding wheel 19 is actuated by a drive 20 which can be moved by means of a feed 21 relative to a fixed base 22 along an axis 23, which is also referred to in technical terminology as the x-axis. The grinding wheel 19 itself is rotatable about an axis 24, so that the feed 21 is able to adjust the distance between the axes 11 and 24 in the direction of the axis 23 perpendicular thereto.

For the sake of clarity, FIGS. 1 and 2 do not show the control and regulating units which derive control signals for the feed 21 from the respective rotational position of the camshaft 12 in a manner known per se.

3 and 4 show, in a greatly enlarged representation and rotated 90 ° clockwise in relation to the representation of FIG. 1, the conditions when machining the cam 18 by means of the grinding wheel 19.

3 shows the starting position of the cam 18. The cam 18 is provided with an outer contour in which a base circle 30 and a secondary circle 31 occur, which are connected to one another by straight or curved flanks 32. The sections 30, 31, 32 drawn thick in FIGS. 3 and 4 denote a raw contour, i.e. a not yet finished cam, while the reference numerals 30a, 31a, 32a denote the corresponding elements of a target contour that is to be produced by the method according to the invention. For this purpose, an infeed 33 is required, which corresponds to the distance of the contour 30/31/32 from the contour 30a / 31a / 32a.

An arrow 34 indicates the direction of rotation of the cam 18, and an arrow 35 indicates the direction of rotation of the grinding wheel 19.

Fig. 3 shows the cam 18 in the starting position. The grinding wheel 19 has been moved up to the point where the cam 18 comes into contact with it, namely that the cam 18 in this basic position is aligned in its rotational position such that the cam 18 and grinding wheel 19 are at a first point 40 in the transition from the flank 32 to the base circle Touch 30.

In a first process step, the cam 18 is now rotated in the direction of the arrow 34, and at the same time the grinding wheel 19 is moved linearly along the axis 23 to the left. With suitable coordination of the The angular velocity of the cam 18 and the advancing speed of the grinding wheel 19 thus result in a locus 41 drawn in FIG. 4 from the first point 40 on the raw contour to a second point 42 on the target contour, which is reached within an angle of rotation y of, for example, 120 °. Due to the linear feed of the grinding wheel 19, the locus 41 has the shape of an Archimedean spiral.

In the illustration of FIG. 4, the grinding wheel 19 has thus been moved in a linearly controlled manner from the position 19 ′ shown in broken lines to the position 19 shown in solid lines.

After reaching the second point 42, a transition is now made to a second process step.

In this second step of the method, the deflection of the grinding wheel 19 in the direction of the x-axis 23 is set such that the point in engagement on the surface of the grinding wheel 19 exactly follows the desired contour 30a / 31a / 32a.

This has the effect, among other things, that the material is always removed tangentially with respect to the target contour 30a / 31a / 32a in this process section. This is illustrated in FIG. 4 by means of a position 45 of the grinding wheel 19 relative to the cam 18, and it can be clearly seen that the grinding wheel 19 in this position 45 has the desired contour, in in that case touches the flank 32a at a single point 46.

Finally, FIG. 5 shows a variant in which the sequence of the two process sections described above is repeated cyclically.

The thick curve in Fig. 5 of the respective processing point again starts at the first point 40 and runs in the manner described in the pure delivery mode along the locus 51 to the second point 42, where the method changes to the rail mode, so that the path curve now runs along the desired contour 30a / 31a / 32a, as already described. This rail operation now continues to a third point 40 a, which is located radially next to the first point 40. When the third point 40a is reached, the method returns to the pure infeed mode, and the path curve of the respective processing point in turn runs along a locus 41a which runs within the locus 41 already described. The pure infeed operation now continues up to a fourth point 42a, which is located radially next to the second point 42, at which point the method again switches to pure rail operation, so that a further target contour 30b / 31b / 32b is created. This further target contour is continued via a fifth point 40b located radially next to the first point 40 and the third point 40a, so that the further target contour 30b / 31b / 32b is traversed to the fourth point 42a, so that the desired further target contour 30b / 31b / 32b is now completely processed.

In a practical embodiment of the method according to the invention, a four-cylinder camshaft was machined at a peripheral speed of the grinding wheel 19 of 45 m / s, the cams of which had a base circle of 38 mm in diameter and a cam stroke of approximately 10 mm. The radial grinding allowance was between 2 and 2.5 mm.

The cam was rotated a total of four times for pre-grinding, a feed operation and a rail operation being set successively in the manner described. It was followed by a turn in pure rail operations. In the subsequent finish grinding, three revolutions with infeed operation and subsequent rail operation were set, and five revolutions without infeed operation followed.

The ratio of infeed speed and angular speed of the cam was chosen so that an angle Winkel of 30 ° was set during pre-grinding and an angle ψ of 60 ⁰ during finish grinding.

In this way, it was possible to reduce the total grinding time per cam to less than half compared to the conventional method.

Claims (14)

1. Method for machining a surface of profiles with a contour deviating from a circular shape, in which, starting from a raw contour (30/31/32), the profile by removing the surface with a target contour (30a / 31a / 32a; 30b / 31b / 32b) is provided by moving a machining tool and the profile relative to one another in such a way that on the one hand a section of the machining tool that is in engagement on the surface is guided along the contour in web operation and on the other hand in feed operation by the surface distance between the raw contour (30 / 31/32) and target contour (30a / 31a / 32a; 30b / 31b / 32b), characterized in that the section first of all from a first point (40; 40a) on the surface of the raw contour (30/31/32) only in delivery mode to a second point (42; 42a) of the target contour (30a / 31a / 32a; 30b / 31b / 32b) and then only in rail mode along the target contour (30a / 31a / 32a; 30b / 31b / 32b) becomes. 2. The method according to claim 1, characterized in that the machining tool is rotatable about a first axis (24). 3. The method according to claim 1 or 2, characterized in that the profile is rotatable about a second axis (11). 4. The method according to claim 2 and 3, characterized in that the first axis (24) runs parallel to the second axis (11) and that the distance between the axes (11, 24) in the direction of a third axis (23) running perpendicular thereto is adjustable. 5. The method according to claim 3 or 4, characterized in that the second axis (11) is spatially fixed. 6. The method according to any one of claims 3 to 5, characterized in that the first point (40; 40a) and the second points (42; 42a) define an angle of rotation ψ of the second axis (11) which is less than 180 ° and is preferably in the range between 20 ° and 180 °. 7. The method according to any one of claims 1 to 6, characterized in that the machining tool is performed in the delivery mode with uniform delivery. 8. The method according to any one of claims 1 to 7, characterized in that after guiding the section on the target contour (30a / 31a / 32a) this from a third point (40a) on the target contour (30a / 31a / 32a) initially in Infeed operation is guided to a fourth point (42a) of a second target contour (30b (31b / 32b) and then is guided along the second target contour (30b / 31b / 32b) in rail operation. 9. The method according to any one of claims 1 to 8, characterized in that the profile is a cam (18). 10. The method according to claim 9, characterized in that the cam (18) has at least one circular section (30, 31; 30a, 31a; 30b, 31b) and that the infeed operation in the region of the circular section (30, 31; 30a, 31a, 30b, 31b) is set. 11. The method according to claim 10, characterized in that the circular section (30, 31; 30a, 31a; 30b, 31b) is a base circle (30; 30a; 30b) of the cam (18). 12. The method according to any one of claims 1 to 11, characterized in that the processing tool is a grinding wheel (19). 13. The method according to any one of claims 1 to 12, characterized in that the section is guided by means of a numerical control, which has first control means for the delivery operation and second control means for the rail operation and that the control means are switched on one after the other. 14. Device for performing the method according to one of claims 1 to 13.

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