Tool drive having a spindle shaft and operating method

Abstract

A tool drive with spindle shaft for a chip-forming machining includes at least one electromagnetic axial actuator and a control and/or regulation apparatus for the operation of the axial actuator for changing the position of the spindle shaft along the longitudinal axis. The control and/or regulation apparatus is designed to drive the axial actuator for the generation of microvibration movement of the spindle shaft, independently of and superimposable on a feed movement, in order to affect the chip size and chip shape of the removed material. At least one axial magnetic bearing and/or one linear motor is provided as at least part of the axial actuator, hi an operating method for an above-mentioned tool drive with a spindle shaft and an axial magnetic bearing is proposed, wherein an adjustable axial microvibration movement of the spindle shaft is superimposed through at least one electromagnetic axial actuator, independently of a feed, in order to influence the chip size and chip shape of the material removed from holes.

Claims

1. Operating method for a tool drive with a spindle shaft, the tool drive with the spindle shaft comprising at least one electromagnetic axial actuator, a control and/or regulation apparatus for the operation of the axial actuator for changing the position of the spindle shaft along the longitudinal axis, wherein the control and/or regulation apparatus is configured to drive the axial actuator for the generation of microvibration movement of the spindle shaft, the method comprising superimposing, through the at least axial actuator and the control and/or regulation apparatus an adjustable axial microvibration movement of the spindle shaft, independently of and superimposed on a feed movement, in order to influence the chip size and chip shape of the material removed from holes during a drilling process, using at least one axial magnetic bearing and/or one linear motor as the axial actuator for generating axial microvibration movements, choosing a setpoint oscillation curve of the axial microvibration movement depending on directly or indirectly determinable drilling parameters, adjusting the axial microvibration movement during a drilling process, and specifying, via a setpoint value curve of the microvibration movement, a lower feed rate at or before contact of the tool on the workpiece.

2. Operating method according to claim 1, wherein at least one radial magnetic bearing is used for the generation of a radial movement.

3. Operating method according to claim 2, comprising guiding the spindle shaft radially by the radial magnetic bearing, in order to generate a controlled spindle movement for deburring a hole opening and/or a radial expansion of a drill channel.

4. Operating method according to claim 1, comprising limiting the control current for operation of the axial actuator by control and regulation loops within the control and/or regulation apparatus to specifiable maximum values.

5. Operating method according to claim 1, comprising evaluating changes in the directly or indirectly determinable drilling parameters and/or parameters of the actual value curve of the microvibration movement generation with respect to a wear of the tool.

6. Operating method according to claim 1, comprising deflecting the spindle shaft eccentrically with respect to the spindle shaft axis to compensate for imbalances.

7. Operating method according to claim 1, wherein the control and regulation apparatus limits the process forces that arise to specifiable maximum values.

8. Operating method according to claim 1, comprising detecting unwanted collisions of the tool by means of a position sensing system of the magnetic bearings comprised within the regulation and/or control apparatus, and initiating measures to rectify a collision state.

9. Operating method according to claim 1, comprising performing a controlled radial spindle movement through at least one radial magnetic bearing and performing a deburring of an opening of a drilled hole and/or a radial extension of a drill channel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages emerge from the description of the drawings below. The drawing shows exemplary embodiments of the invention. The drawing, description and the claims contain numerous features in combination. The expert will expediently also consider the features individually and combine them into useful further combinations.

(2) Here:

(3) FIG. 1 shows a first exemplary embodiment of a tool drive with a spindle shaft on magnetic bearings according to the invention;

(4) FIG. 2 shows a second exemplary embodiment of a tool drive with a spindle shaft on magnetic bearings according to the invention;

(5) FIG. 3 shows a diagram of a macroscopic feed of a spindle shaft;

(6) FIG. 4 shows a diagram of an axial microvibration superposition of a spindle shaft according to the invention;

(7) FIG. 5 shows a superposition diagram of the macroscopic and microscopic movements of FIG. 3 and FIG. 4;

(8) FIG. 6 shows a schematic illustration of individual drilling process steps when drilling through a composite workpiece with a form of embodiment of the invention;

(9) FIG. 7 shows a schematic illustration of a burr formation of a through-hole;

(10) FIG. 8 shows a block circuit diagram of a form of embodiment of the control and/or regulation apparatus of the invention;

(11) FIG. 9 shows a further exemplary embodiment of a tool drive with a spindle shaft on magnetic bearings according to the invention.

DETAILED DESCRIPTION

(12) The same reference codes have been used to identify components that are identical or similar type in the figures.

(13) FIGS. 1 and 2 each show an apparatus for hole machining in workpieces, in particular in metal, plastic or composite workpieces according to forms of embodiment of the invention.

(14) As shown in FIG. 1, the fundamental structure of such an apparatus comprises a tool drive 1 with a spindle shaft 3 that can be driven to rotate by a spindle drive 2, to which a tool 5 that works on the workpiece 4 is fastened. The tool 5 is fastened by a tool holder 6 to the spindle shaft 3, and rotates around the spindle axis S or tool axis. The tool 4 is fastened to a workpiece receptacle 7 or workpiece holder, and can, if appropriate, also rotate around the workpiece axis W. A mechanical feed apparatus 8 for the tool drive 1 is furthermore provided in the exemplary embodiment according to FIG. 1. The feed apparatus 8 (or advance unit) comprises a feed slide 9 or advance slide which is movable by means of a feed drive 10 or advance drive at a machine frame 11. The tool drive 1 is arranged fixedly on the feed slide 9 by means of a spindle holder 12.

(15) The spindle shaft 3 is mounted in the tool drive 1 in least two radial bearings 13a, 13b and in at least one axial bearing 14 in five axial directions. The axial bearing 14 comprises two annular coil magnets which are arranged in opposition to a slide anchor which is arranged non-rotatably about the spindle shaft, by means of which a shift of the shaft in an axial direction is possible. An upper and a lower, or a rear and front, radial bearing 13a, 13b are furthermore provided, the spindle drive 2 being arranged between these two radial bearings 13a, 13b. The spindle drive 2 in the exemplary embodiment is a multi-pole asynchronous motor.

(16) Both the radial bearings 13a, b and the axial bearing 14 are designed as magnetic bearings. The bearing parts of these magnetic bearings are held without contact, with an air gap, by magnetic forces, the magnetic forces being generated and adjusted by electromagnets. This allows the spindle axis S to be moved within certain limits and adjusted in the radial direction in the radial bearings 13a, 13b and in the axial direction in the axial bearing 14.

(17) FIG. 1 additionally shows that the exemplary embodiment comprises a control or regulation apparatus 16 which is connected with the two radial bearings 13a, b and with the axial bearing 14 and the spindle drive 2. With the aid of the control and/or regulation unit 16, which comprises a plurality of regulation modules 17, the radial displacement V and the adjustment angle can initially be dynamically and changeably adjusted. At least one measuring transducer 18, 19 is assigned to each of the radial bearings 13a, 13b and the axial bearing 14, where the measuring transducer 18 is preferably integrated into the magnetic bearings 13a, b, 14.

(18) The control and/or regulation apparatus 16 affects the axial bearing 14 as well as the two radial bearings 13a, b in such a way that vibration movements in the direction of the longitudinal axis as well as in the radial direction can actively be applied in a controlled manner with adjustable frequency and amplitude, in order to achieve desired chip sizes and chip shapes, to minimize the heat development, to increase the service life and to shorten drilling times.

(19) Since not only the radial bearings 13a, 13b but also the axial bearing 14 are designed as magnetic bearings, it is possible in the context of the invention for the position of the spindle shaft 3 in an axial direction also to be adjustable within the tool drive 1 by means of the axial bearing 14. This is achieved through exact, adjustment of the magnetic gap within the axial bearing 14 and the modulation of an adjustable vibration movement, so that the advance movement or feed movement can be made within certain limits through the drive to the axial bearing 14. In this way an axial advance of the tool 5 is initially achieved in very small steps, independently of the feed apparatus 8, which is driven by an electric motor and which may additionally be present, which can provide a coarse adjustment of the axial position and moves the entire tool drive 1. The feed distance, feed velocity and, in particular, the feed force or pressing force of the tool 5 against the workpiece 4, can be influenced through the magnetic axial bearing 14.

(20) Taking the integrated measuring transducers 19 into account, a force-controlled or a force-and-displacement-controlled chip-forming machining with modulation of microvibration movements is achieved. The measured values determined via the bearings permit conclusions to be drawn about the condition of the tool 5 and regarding any possible tool fracture, so that here again a simple and reliable monitoring can take place without separate measuring transducers having to be employed.

(21) The control/regulation apparatus 16 can be designed as an Industry PC, or as part of an. Industry PC which is connected to the measurement transducers 18, 19. This PC converts the current values measured in the bearings by the transducers 18 and/or 19 into force values which are passed on to a displacement controller so that a combined force-displacement-control/regulation can take place in the machining, and the vibration movement can be adjusted to currently present drilling conditions.

(22) A modified form of embodiment of the invention is explained with reference to FIG. 2. This shows the drilling at a free-form surface with a tool 5 with coated cutting material for high precision surface machining, for example a diamond stylus. Since the tool 5 is freely and fully automatically positionable within certain limits axially and radially by means of the spindle 3 with the help of the magnetic radial bearings 13a, b and the axial magnetic bearing 14, it is possible, through electronic drive of the bearings 13a, 13b, 14 through the control or regulation apparatus to ensure a precise positioning of the tool taking into account the free-form surface that is to be created or to be machined. A free-form surface that has already been formed can here be adaptively machined using chip-forming machining by means of a force control system. It is, however, also possible for the free-form surface to be machined or generated with material removal, taking into account values that have previously been precisely calculated and entered into the control or regulation apparatus.

(23) A desired continuous tool feed of a drilling tool is illustrated in FIG. 3, wherein the angle of rotation of the tool is displayed in degrees n on the abscissa, and the ordinate shows a penetration depth in [mm]. The aim is to achieve a desired feed of 0.06 mm per rotation of the drilling tool.

(24) Corresponding to this, FIG. 4 shows a setpoint value curve of an axial vibration movement in the drilling direction which the drilling tool performs in one embodiment of the invention, where a stroke amplitude of the drilling tool of 0.13 mm at a stroke frequency of 1.5 Hz should be achieved. In the lower region of the stroke in the section P of the setpoint value curve, the cutter of the drilling tool touches the drilling ground and thus the surface of the workpiece. In the region of the section P of the setpoint value curve, the axial speed can be influenced in such a way that a tool head contacts a workpiece surface gently, whereby an impact pulse is reduced and the service life of the tool can be increased. The setpoint value curve in the region of the section P can be adjusted taking predetermined material parameters and process parameters into account. The setpoint value curve of the vibration oscillation can be adapted dynamically to the drilling process.

(25) In sequence, FIG. 5 shows an overlaid setpoint value curve of the continuous feed according to FIG. 3, and an optimized vibration oscillation movement according to FIG. 4, whereby a continuous feed and an axial oscillation of the position of the cutting edge along the longitudinal axis is achieved, so that, in particular when deep drilling, easily removable drilling chips can be achieved, heat development reduced, service life increased and machining time shortened. The section P that is drawn in shows the contact of the drilling tool with the drilling ground at which tool engagement with the workpiece begins and the formation of chips with a reduced, adjustable feed starts. FIG. 6 shows a through-hole 30 in a composite workpiece 38 with an upper, metal applied layer 38a and a lower carbon fibre composite layer 38b, as is used, for example, on a wing of an aircraft. In step S1 the drilling tool 32, which is rotating around the axis 34, makes contact with the cutting tip 36 on the surface of the metal layer 38a in order to form an inlet opening 40. In the further steps S2 and S3 the drilling tool 32 drills, overlaid with vibration movements on the longitudinal axis, as far as the boundary surface 44 between the metal layer 38a and 38b. Since the cutting process and the chip formation is changed in the lower composite layer 38b, the frequency and amplitude of the vibration oscillation can be changed, for example the amplitude increased and the frequency reduced, and thereby an increased feed rate can be achieved with a chip size and chip shape that remain the same. Reaching or passing through the layer boundary 44 can be detected indirectly through a change in the energy consumption or a change in the dynamic behaviour, e.g. the torque or feed rate, of the drilling tool 32, or, if the geometry is known in advance, detected by reaching a predetermined penetration depth into the hole 30, so that the overlaid vibration movement can be adjusted. The second layer of material 38b is drilled through in steps S4 to S5, until a lower outlet opening 42 is created, through which the drilling tip 36 emerges through the drill channel 46.

(26) FIG. 7 illustrates a drill channel 46 of a through-hole 50 through a workpiece 52. As a rule, both the inlet opening 40 and the outlet opening 42 have drilling burrs 54 which result from the displacement of material. Burrs 54 are unwanted, since in the bonding process they lead to unwanted spacings, present a risk of injury, and, for example, impair aerodynamic functions. The burrs that are formed are usually removed subsequently by deburring tools. Through a drilling process according to the invention, with appropriate adaptation of the vibration movements when creating the inlet and outlet openings 40, 42 of the through-hole 46, the burr formation can be significantly reduced, so that a rework becomes unnecessary, or only has to be carried out to a small extent.

(27) FIG. 8 shows a block circuit diagram of a form of embodiment of a regulation and control apparatus 60 which can be employed in a tool drive 1 according to the invention for drive of an electromagnetic axial actuator of a spindle shaft 3 for driving a rotating tool 5, 32 such as a drilling or milling machine. The apparatus 60 can be integrated into an axial actuator regulator. The control and/or regulation apparatus 60 comprises a microvibration regulation unit 62 which can be designed as a programmable actuator processor system. A memory unit 62 which stores a large number of setpoint value curves of a microvibration oscillation as well as managed macroscopic profiles for different drilling processes, for example for different materials, composite materials, deep drilling processes, milling processes etc. is attached to the regulation unit 66. A memory unit 64 for operating parameters and actual value curves, which records changes in operating parameters and stores actual value curves of the vibration oscillation, is also connected to the regulation unit 66, so that a wear condition of the tool 5, 32 can be determined from changes to the parameters and/or the actual value curves. In this way, direct and indirect drilling parameters such as, for example, motor current I.sub.mot, tool rotation speed N.sub.rot, setpoint feed rate SV.sub.set, tool torque M.sub.mot, actual axial spindle position ASP.sub.act and actual radial spindle position RSP.sub.act can be stored directly through sensors or indirectly through derived values. The regulation unit 66 supplies one or more control currents IS.sub.mag for drive of the axial actuator or actuators, and, if relevant, of the radial actuator or actuators, and in addition can pass on status information to a higher-order machine-tool controller. In addition, one or a plurality of function inputs and outputs for input of external programming and adjustment of the behaviour of the microvibration regulator, and to be able to read parameters out, can be present at the control and/or regulation unit.

(28) A further exemplary embodiment of a tool drive 1 according to the invention is illustrated in FIG. 9, with a spindle shaft 3, a tool holder 6 and a chip-forming tool 5. The spindle shaft 3 is fundamentally constructed according to the embodiment in FIG. 2. Deviating from that, at the axial end of the spindle shaft 3, the tool holder 6 with the tool 5 is not connected non-rotatably in the direction of the longitudinal axis to the spindle shaft 3, but rather the rotational axis of the tool holder 6 is pivoted by means of an angular deflector 23, for example an angular gear, through 90 with respect to the rotational axis of the spindle shaft 3. A kinematic interchange of the axial and radial movements of the spindle shaft 3 with respect to the radial and axial movement of the tool 5 results from this. An axial movement of the tool 5 can be generated by the radial magnetic bearings 13 of the spindle shaft, and a radial deflection of the tool 5 can be achieved through the axial magnetic bearing 14 and also through the radial magnetic bearings 13. The use of the angular deflection element 23 reduces the structural size of the tool drive 1, so that it can, for example, be retrofitted in the machine base of a machine tool. It is also possible in this exemplary embodiment, if a radial movability of the tool 5, at least in one direction, is not required, for the axial magnetic bearing 14 to be omitted.

LIST OF REFERENCE SIGNS

(29) 1 Tool drive 2 Spindle drive 3 Spindle shaft 4 Workplace 5 Chip-forming tool 6 Tool holder/tool chuck 7 Workplace holder 8 Mechanical feed apparatus 9 Feed slide 10 Feed drive 11 Machine frame 12 Spindle holder 13 Radial magnetic bearing 14 Axial magnetic bearing 15 16 Control and/or regulation apparatus 17 Control module 18 Measuring transducer 19 Measuring transducer 30 Through-hole 32 Drilling tool 34 Tool axis 36 Cutting tip 38 Material layer 40 Inlet opening 42 Outlet opening 44 Material layer boundary surface 46 Drill channel 50 Through-hole 52 Workplace 54 Burr 60 Regulation and/or control apparatus 62 Setpoint value curve memory unit 64 Operating parameters and actual value curve memory unit 66 Microvibration control unit