Tool with feed device and force measuring device for a machining center and method for machining a bore

Abstract

Tool (1) with an integrated feed device (13) and with an interface (7) for connecting the tool (1) to a machine spindle of a machine tool, wherein the tool (1) has a base body (3), wherein the feed device (13) is arranged in the base body (3), characterized in that the tool (1) comprises an exchangeable machining part (5), and that the feed device (13) effects the feed of the cutting body or bodies (39; 62) with a geometrically indeterminate cutting edge present in the machining part (5) with the aid of a transmission element (41).

Description

The invention relates to a tool according to the preamble of claim 1 and to a method for machining a bore according to the preamble of claim 15.With so-called machining centers, a wide variety of workpieces can be machined using a wide variety of machining methods, such as, for example, turning, fine drilling, milling, thread cutting and honing.In order to make the best possible use of the flexibility of the machining centers, it is sought to finish machining a workpiece as far as possible in a clamping and to use different tools if necessary. This results in a better load on the machining center, but also in the number of re-clamping operations of the workpiece being reduced, which has a positive effect on the economic efficiency.Various honing tools are known from DE 35 37 172 C2, DE 10 2006 024 677 A1 and DE 196 06 145 A1.DE 10 2006 028 728 A1 discloses a honing tool which can be used in machining centers and is suitable for finishing bores. This honing tool has an integrated feed device which enables the radial feed of the honing strips. However, only comparatively simple honing operations can be carried out with this tool and the range of results within a series of identically constructed workpieces is comparatively large.The object of the invention is to provide a tool and a method for honing bores, wherein the honing tool according to the invention is intended to be usable in a machining center and is also intended to be able to perform complex honing machining methods reliably and with the highest quality. Furthermore, the claimed invention is based on the object of expanding the field of application of the honing tool according to the invention in order to thus achieve an even higher productivity of the machining center, but also an increased economics of the honing tool according to the invention.According to the invention, this object is achieved in a tool having an integrated feed device and having an interface for connecting the tool to a machine spindle of a machine tool in that the tool comprises a base body and an exchangeable machining part, wherein the feed device is arranged in the base body and brings about the feed of the cutting body or bodies present in the machining part with a geometrically defined or geometrically undefined cutting edge with the aid of a transmission element. Furthermore, the object is also achieved by a method for machining a bore having the features according to claim 15.The tool according to the invention is embodied in two parts with a base body, which comprises the comparatively cost-intensive feed device, and with a machining part, which comprises the cutting bodies, be it honing stones, a cutting plate made of hard metal or means for roughening a bore. This makes it possible to combine the inventive feed device with different machining parts and thereby, for example, fine bore drilling, chamfering, honing and / or roughening a bore. All these machining steps can be carried out using the same tool, wherein only the machining parts have to be exchanged and the base body with its feed device can remain in the spindle of the machining center.In order to be able to carry out complex and high-quality machining processes as well, a force measuring device is provided in the base body in a further embodiment according to the invention. This makes it possible to perform a force-controlled feeding of the honing stones, which is essential especially in the case of technologically demanding honing operations.Of course, the force measuring device according to the invention can also be used in conjunction with a machining part which serves for fine drilling, for monitoring the cutting tip for a cutting break or wear.In order to be able to bring about the feeding of the cutting bodies of the machining part in the simplest way, it is advantageous to prestress the feeding device by a spring, so that a single-acting feeding device which works against the prestressing force of the spring is sufficient to be able to carry out both a feeding movement and an oppositely directed movement of the cutting bodies of the machining part.The same applies to the force measuring device. In particular, when a piezoelectric element is used as the force measuring device, it is important that the piezoelectric element is always subjected to compressive stress and is not subjected to tensile stress. This can be ensured in a simple and reliable manner by the prestress according to the invention by means of a spring.In order to be able to optimally combine the base part with different machining parts, a transmission member is provided between the feed device and the machining part, wherein the transmission member can be a feed rod that can be displaced in the axial direction.Alternatively, it is also possible to configure the transmission member such that it is rotatable relative to the base body and / or the machining part, so that the feed movement can be transmitted by a rotational movement of the transmission member relative to the base body or the machining part.For example, it is possible that a claw clutch or a Hirth toothing is formed on the end face end of the transmission member facing the machining part, which cooperates with a corresponding counter piece in the machining part. In this way, feed movements in both rotational directions can be transmitted reliably and without play.In a further advantageous embodiment of the invention, the machining part can be designed as a honing pile, with at least one, but preferably two or more honing strips.Because not only an adjusting device with a device for detecting the adjusting movement, but also a force measuring device are integrated in the tool according to the invention, complex honing operations can be carried out which are not only controlled away, but also additionally or exclusively force-controlled. As a result, the surface properties of the bore to be machined can be kept constant very reliably. This allows efficient and process-safe series production.Furthermore, the machining part can be designed as a roughening tool, in particular for preparing the bore for a thermal coating, or as a fine drilling tool with at least one, preferably two cutting inserts. This enumeration is of course not exhaustive.It is also possible for one or two cutting inserts to be arranged in the machining part, which cutting inserts are provided for chamfering a bore. It is thus possible, for example, to make the cutting edge arranged at the distal end of the machining part radially adjustable, so that this cutting tip can enter the bore in the "retracted" state. When the blade has reached the rear end of the bore, the blade is advanced radially outwards and a chamfer is provided.When the tool according to the invention is to be moved out of the bore again, the feed adjustment device is actuated in the reverse direction, so that the cutting tip moves radially inward and can be moved out of the bore without touching the bore.In order to enable rapid and process-safe replacement of the machining parts when the base body is clamped in, it is provided that the interface between the base body and the machining part is designed as a detachable interface. This can be realized, for example, by a hollow shaft cone, a threaded connection, a bayonet connection, a collet connection or a hydrostretch chuck.It has proven particularly suitable for the connection of the tool according to the invention to a machine spindle to form the interface between the base body and the machine spindle as a hollow shaft cone interface.In addition, it is advantageous if the interface between the base body and the machine spindle allows the transmission of electrical, hydraulic and / or pneumatic energy. The transmission of signals is also advantageous and is also provided in the case of a force measuring device. If the force-measuring device detects signals about the contact pressure, for example of the honing stones on the bore to be machined, and transmits this information to the higher-order machine control, the machining of the bore can be effected under force control. Optimum results are thereby achieved.The coupling of electrical energy into the tool according to the invention is preferably inductive, since this energy transmission is wear-free and reliable. The same applies to the bi-directional signal transmission between the machine control and the tool according to the invention.Thus, for example, the control of the feed device requires a corresponding signal transmission from the machine control system into the tool according to the invention, while the transmission of the contact pressure force between honing stone and the bore to be machined by the force measuring device according to the invention requires a signal transmission from the tool to the higher-order machine control system.The adjusting device can comprise an electric motor, a reduction gear and / or a screw drive. Alternatively, it is also possible for the delivery to have a linear motor which is driven electrically, hydraulically or pneumatically. In this embodiment, it is often helpful if a hydraulic booster is also provided in order to increase the feed forces, if necessary.Further advantages and advantageous embodiments of the invention can be derived from the following drawing, its description and the patent claims.The following are shown: FIG. 1 shows an exemplary embodiment of a honing tool according to the invention; FIG. 2 shows exemplary embodiments of various machining parts of the honing tool according to the invention; FIG. 3 is a diagram showing the feed force and the feed path over the time axis in a complex honing operation; FIG. 4 shows a flow diagram of a series production with the aid of the honing tool according to the invention, and FIG. 5 shows the interaction of force- and displacement-controlled feeding in the honing tool according to the invention in interaction with the superordinate honing controller.DESCRIPTION OF THE EMBODIMENTSFIG. 1 shows an exemplary embodiment of a tool 1 according to the invention schematically and in longitudinal section. The honing tool 1 according to the invention consists of two assemblies, namely the base body 3 and the machining part 5.The interface 7 comprises a mechanical interface with which the tool 1 according to the invention is inserted, for example, into the spindle of a machining center and positioned and fastened there. This mechanical part of the multifunctional interface 7 can be designed as a conventional hollow shaft cone interface.In addition, electrical energy, for example, can be coupled into the tool 3 via the interface 7. This is preferably carried out inductively with a first primary part (not shown) in the spindle of the machining center and a first secondary part 9 in the tool 1 according to the invention.In a similar manner, it is possible to realize inductive signal transmission between the control of the machining center and the tool 1 according to the invention. For this purpose, a second secondary part 11 is formed in the region of the interface 7. Of course, the number of secondary parts 9, 11 is not limited to two. If necessary, further secondary parts can be provided.It is also possible to transfer electrical, pneumatic and / or hydraulic energy in other ways known from the prior art between the spindle of the machining center and the tool 1.An adjusting device 13 and a piezoelectrically operating force measuring device 15 are integrated in the interior of the base body 3. In the exemplary embodiment shown in FIG. 1, the feed unit 13 comprises an electric motor designed as a servomotor 17, having a stator 19 and a rotor 21, and a control device (not shown) for controlling the servomotor 17 is assigned to the servomotor 17. The rotor 21 is coupled to a mechanical reduction gear 23, which can be designed as a planetary gear or harmonic drive. The output shaft 25 of the reduction gear 23 is formed as an external thread which cooperates with a nut 27. The threaded nut 27 has a nose 29 which is guided in an axial groove 31 of the base body 3. This ensures that the threaded nut 27 cannot rotate relative to the base body 3. As a result, a rotational movement of the rotor 21 is converted into a linear movement in the axial direction of the tool 3 according to the invention via the reduction gear 23 and the threaded nut 27.At the right end of the threaded nut 27 in FIG. 1, the piezoelectric element is arranged, which represents the force measuring device 15 according to the invention. The force measuring device 15 is arranged between the threaded nut 27 and a counter piece 33. The counter piece 33 is prestressed via a disk spring 35 which is supported on the base body 3. The prestress ensures that the force-measuring device 15 is always subjected to compressive loads and that harmful tensile stresses are avoided. Furthermore, it is ensured that no play is present in the feed unit, in particular in the reduction gearing 23 and the threaded nut 27, which might impair the accuracy of the feed.At the right-hand end of the base body 3 in FIG. 1, a second mechanical interface 37 is arranged, in which the machining part 5 is detachably accommodated. The details of this second interface 37 are explained in greater detail below in connection with FIG. 2.The machining part 5 shown in FIG. 1 is a honing tool with a plurality of honing stones 39 and serve as a cutting body. The honing stones 39 of the machining part 5 are advanced radially outwards via a transmission member designed as an infeed rod 41 and two cones 43 connected to the infeed rod 41 as soon as the infeed rod 41 is moved to the right in FIG. 1. Accordingly, the honing stones 39 are pulled back radially inward when the feed rod 41 is pulled back to the left in FIG. 1, i.e. in the direction of the first interface 7, by a corresponding actuation of the feed device 13.As a result, it is possible to feed the honing stones 39 both radially outwards and radially inwards by a movement reversal of the feed unit 13 or the rotor 21.Since the feed force acting between the feed unit 13 and the feed rod 41 is detected by the force measuring device 15 during machining, it is possible to carry out a force-controlled feed of the honing stones 39 in addition to or as an alternative to a path control.Of course, other machining processes can also be carried out under force control or these machining processes can be monitored with the aid of the force measuring device 15 if, for example, other machining parts are inserted into the base body 3. For example, the cutting force during fine drilling can be monitored and a cut break can be detected.In FIG. 2, the second interface 37 is shown and explained in more detail, insofar as it relates to the machining part 5. The illustration in FIG. 2 a corresponds here to the machining part 5 illustrated and described in FIG. 1.FIG. 2 bshows a further possible machining part 5, which can be received in the base body 3 in a detachable manner via the second interface 37. With the machining part 5 shown in FIG. 2 b, a workpiece can be machined by honing and fine drilling or chamfering. The machining part 5 thus represents a combination tool. For cutting, the machining part 5 has a cutting plate 62, for example for chamfering a workpiece, which cooperates via a nose 64 directed radially inward with a feed cone 66 of a push rod 68 of the machining part 5. The push rod 68 has an inner bore 70 for radially guiding the feed rod 41.In addition, the machining part 5 has honing stones 39 which are arranged opposite the cutting plate 62 in FIG. 2 b. The honing stones 39 are moved by the actuation of the feed rod 41 (according to the description of FIG. 1 ). In this machining part 5, both the cutting plate 62 and the honing stone 39 can be adjusted radially separately from one another during machining.The feed rod 41 and the push rod 68 are actuated via the second interface 37. Since they are radially symmetrical with their feed cones 43 and 66, in principle any number of honing stones 39 and cutting inserts 62 can be fed in the machining part 3. The push rod 68 transmits the feed movement to the cutting tip 62 via a pressure force.The force-controlled electromechanical adjusting device 13 offers the possibility of holding a cutting pad in the self-sharpening with a defined adjusting force F. In the case of thin-walled workpieces, the contact pressure acting on the honing stones 39 can be kept at a constantly low value in order to avoid component deformations and thus to achieve high cylinder shape precisions. The force-controlled electromechanical feed device 13 thus makes a substantial contribution to the process optimization.FIG. 3 shows a diagram in which the feed force F and the feed path S are shown over the time axis t in a complex honing operation. The first curve 45 shows the course of the feed force F, the second curve 47 shows the course of the corresponding feed path S. The course 45 of the feed force F, after a desired feed force F 1 has been reached, shows a substantially alternating course within a setpoint value range F S of the feed force F, wherein, in each case after a brief rise in the feed force F (cf. reference sign X), the feed force F again decreases slowly as a result of the progressive machining (cf. reference sign Y). After reaching a starting position S 1 the feed path 47 shows a course 47 which increases in steps, wherein the feed path S is increased in each case as the feed force F increases (cf. reference sign Z). During the decrease of the feed force F, the feed path is constant in each case (cf. reference symbol K).FIG. 4 shows a possible flow diagram of a series production with the aid of the honing tool 1 according to the invention. After a start initiation by a general machine control of the machining center, for example after a tool change, the tool 1 with the honing bars 39 completely retracted enters a bore 48 of a first workpiece 49 without rotational movement and stops in this position. Now the adjusting device 13 receives a start signal (point S 1) and the servomotor 17 expands the honing stones 39 at a predetermined expansion speed. A specific adjustable application torque is predetermined for the servomotor 17 by a honing controller 50 (cf. FIG. 5 ).As soon as the honing stones 39 abut the workpiece 49 and the preset abutting torque is reached (point A), the servomotor 17 stops. This standstill is again recognized by the honing controller 50, the direction of rotation of the servomotor 17 is changed briefly in this case, and the delivery returns a short distance again (point E). The size of the setback is selected in accordance with the tool characteristics such that the honing stones 39 still essentially rest against the bore wall of the workpiece 49, but the adjusting device 13 is mechanically relaxed.The general machine control then receives a signal and switches on the lifting and rotating movement. At the same time, the feed of material by machining begins. The servomotor 17 is assigned a different, generally higher feed force F 1 (machining torque) to be achieved. A constant feed speed (μm / s) is specified. After passing through a predetermined feed path S or when a signal "measure reached" is reached in conjunction with a direct measuring device, e.g. the piezoelectric force measuring device 15, the expansion is stopped.Optionally, the honing controller 50 can switch at measure B to a second delivery speed (degressive delivery).This position is stored. Subsequently, the honing stones 39 are reset by a predetermined amount (point R). Thus, the honing operation for the first workpiece is finished and begins from this position for a second workpiece (point S 2). Only after a full return of the honing stones 39, for example after a tool change, is the feeding started again at the point S 1.FIG. 5 shows the interaction of force- and travel-controlled feeding in the honing tool 1 according to the invention in interaction with the superordinate honing controller 50. Essentially, the feeding device 13 is controlled via a defined and controlled current limit I g for the servomotor 17. This ensures continuous control over feed parameters set in the honing controller 50. A step specification for operating the servomotor 17 is a prerequisite. The delivery parameters are identified in their entirety by the reference numeral 56.In addition to this, the two diagrams at the bottom in FIG. 5 show, on the left side, the principal profile 47 of the feed path S and the profile 58 of the honing diameter D produced thereby in the bore 48 of the workpiece 49. As the feed force profile 45 increases, larger honing diameter distributions 60 result.

Claims

Tool (1) having an integrated feed device (13) and having an interface (7) for connecting the tool (1) to a machine spindle of a machine tool, wherein the tool (1) has a base body (3), wherein the feed device (13) is arranged in the base body (3), characterized in that the tool (1) comprises an exchangeable machining part (5), and in that the feed device (13) brings about the feed of the cutting body or bodies (39; 62), which are present in the machining part (5), having a geometrically undefined cutting edge with the aid of a transmission member (41).Tool (1) according to Claim 1, characterized in that a force-measuring device (15), in particular a piezoelectric force-measuring device (15), is provided in the base body (3).Tool (1) according to claim 1 or 2, characterised in that the feed device (13) and / or the force measuring device (15) is prestressed by a spring (35).Tool (1) according to one of the preceding claims, characterized in that the transmission member (41) comprises a feed rod which is displaceable in the axial direction.Tool (1) according to one of the preceding claims, characterized in that the transmission member (41) is designed to be rotatable relative to the base body (3) and / or the machining part (5).Tool (1) according to one of the preceding claims, characterized in that the machining part (5) is designed as a honing pile with at least one preferably two or more honing strips (39).Tool (1) according to one of the preceding claims, characterized in that the machining part (5) is designed as a roughening tool, in particular for preparing a bore for a thermal coating.Tool (1) according to one of the preceding claims, characterized in that the machining part (5) is designed as a fine drilling tool or as a tool for chamfering with at least one preferably two cutting inserts (62).Tool (1) according to one of the preceding claims, characterized in that the interface (37) between the base body (3) and the machining part (5) is designed as a hollow shank cone, threaded connection, bayonet connection, collet connection or hydrostretch clamping chuck.Tool (1) according to one of the preceding claims, characterized in that the interface (7) between the base body (3) and the machine spindle is designed as a hollow-shank cone interface.Tool (1) according to one of the preceding claims, characterized in that the interface (7) between the base body (3) and the machine spindle allows the transmission of electrical, hydraulic or pneumatic energy.Tool (1) according to one of the preceding claims, characterized in that the interface (7) between the base body (3) and the machine spindle allows the transmission of signals.Tool (1) according to one of the preceding claims, characterized in that the adjusting device (13) comprises an electric motor (17), a reduction gearing (23) and / or a screw drive.Tool (1) according to one of the preceding claims, characterized in that the delivery device (13) comprises a linear motor and / or a hydraulic translator.Method for machining a bore (48) with a tool (1) according to one of the preceding claims, characterized in that the machining of the bore (48) takes place in a displacement-controlled and / or force-controlled manner.

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