Device for the inductive heating of a toolholder

ABSTRACT

The induction coil of a device that heats a toolholder () inductively for the tool change comprises a shielding collar () of magnetizable material which, firstly, concentrates the magnetic flux of the induction coil () in a sleeve section () of the toolholder () which holds the shaft () of a rotary tool with a press fit and, secondly, shields the part of the tool shaft () that projects out of the sleeve extension (), in order to facilitate unclamping the tool from the toolholder (). On its side facing the winding () of the induction coil () axially, the shielding collar () has an outer circumferential surface () which widens conically away from the sleeve extension () and an axial height (h) which is at least 1.5 times the diameter (d) of the tool shaft (). The shielding collar () runs on all sides at a distance from a yoke shell () of magnetizable material which encases the winding () of the induction coil ().

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a toolholder , in one part here but possibly also made of many parts, of an at least electrically conductive but here also magnetizable material, such as steel, which has at its one axial end a standard connecting piece, such as a steep taper , and at its axial other end a sleeve section . Centrally in relation to the axis of rotation of the toolholder, the sleeve section has a holding opening for a rotary tool which can be inserted with its shaft into the holding opening in a manner further explained below, but otherwise not specifically illustrated, for example a drill, a mill or a reaming tool. The external diameter of the shaft is somewhat larger than the free nominal diameter of the holding opening , so that the shaft inserted into the sleeve section is held in a press fit for the transmission of the working torque.

In order to be able to insert the tool shaft into the toolholder or remove it from the latter, the sleeve extension is widened by heating. Heating is carried out by means of an induction coil which is placed on the sleeve extension and encloses the latter concentrically with radial spacing of its internal diameter from the outer circumference of the sleeve section , which is held by means of a holder, indicated at , of an induction shrinkage device such that it can be displaced axially parallel to the axis of rotation and is fed by a current generator with alternating current or pulsed direct current at a frequency of, for example, 10 to 50 kHz. The magnetic flux generated by an approximately cylindrical winding induces in the sleeve section eddy currents, which heat the sleeve section in a relatively short time and therefore widen the holding opening sufficiently for the insertion or withdrawal of the tool shaft .

On the inside, the induction coil has a coil former consisting of temperature-resistant plastic or ceramic, to which the multilayer winding is applied. The outer circumference and the end surface of the winding that faces axially away from the tool is covered by a single-part, but possibly also multi-part, yoke shell consisting of a magnetizable, electrically non-conductive material, which concentrates the magnetic flux in this surrounding region of the winding onto the yoke shell . The yoke shell can be produced from ferromagnetic material or composite magnetic materials based on ceramic or plastic, such as ferrite.

The winding provided with the yoke shell extends substantially over the entire length of the holding opening and the sleeve section intended to hold the tool shaft . With its end adjacent to the tool-side end surface of the sleeve section , the winding extends axially until approximately at the height of the end of the sleeve section .

In order to deflect the magnetic flux from the yoke shell , projecting axially somewhat beyond the winding on this side, in an optimum fashion toward the end of the sleeve section and, at the same time, to shield that part of the tool shaft which projects beyond the sleeve section and protect it against inductive heating, a shielding collar approximately in the shape of a conical shell is placed on the end surface . The shielding collar runs on all sides at a distance from the yoke shell which, in the exemplary embodiment illustrated, does not extend beyond the tool-side end surface of the winding but merely projects somewhat beyond this end surface. The tool-side end surface of the winding in the exemplary embodiment illustrated is covered with a spacer disk which consists of non-magnetic material, for example temperature-resistant plastic. In a variant, this disk , ending with its inner circumference in turn at a distance from the shielding collar , can likewise consist of the magnetic material of the yoke shell , that is to say it can be a constituent part of the yoke shell .

In the region between the outer circumference of the sleeve section and the inner circumference of the winding , on the side pointing axially toward the winding , the shielding collar can have an outer circumferential surface which is shaped like a cone or truncated cone with an angle of inclination α of about 60°, as based on the axis of rotation . The likewise conical inner circumferential surface facing axially away from the winding has a generatrix which is approximately parallel to the outer circumferential surface . The shielding collar has a flat contact surface which faces the sleeve section axially and runs normal to the axis, with which it rests flat on the end surface of the sleeve section . On the outer circumference of the conical region of the shielding collar , the latter is provided with an annular extension which projects axially away from the sleeve section and has an annularly cylindrical outer circumferential surface . The external diameter of the annular extension , and therefore the shielding collar , is smaller than the internal diameter of the winding . The axial total height h of the shielding collar , with which it extends axially above the end surface , is more than twice as great as the shaft diameter d of the tool shaft immediately outside the sleeve section . In the present case, the height h is somewhat more than three times as great as the diameter d.

Even though the annular gap remaining between the yoke shell and the shielding collar increases the magnetic resistance in the magnetic flux circuit of the induction coil , this portion of the magnetic circuit, extending in air, in conjunction with the conical shielding collar , permits, in the region of the tool shaft , a concentration of the magnetic flux onto the sleeve section which is to a large extent free of scattered field. In this way, the sleeve section can be heated inductively and therefore widened without excessive heating of the tool shaft occurring, which facilitates unclamping of the tool shaft from the toolholder . Otherwise, the axially adjacent region of the shielding collar extends in the sleeve section , forming an annular gap at a radial distance from the tool shaft .

The shielding collar is fixed to an annular disk of a temperature-resistant plastic or of ceramic and is replaceably connected to the holder or a housing of the induction coil which is fixed to the holder to form a structural unit. For the replaceable connection, the annular disk and the housing can be locked to each other, for example in the manner of a bayonet catch. In this way, the shielding collar not only ensures the axial positioning of the induction coil relative to the sleeve section , but can also be replaced in order to adapt one and the same induction coil on the toolholder to different diameters of the holding opening or of the sleeve extension .

In the following text, variants of the device described using FIG. 1 will be explained. Components with the same effect are designated by the reference numbers from FIG. 1 and, to distinguish them, are provided with a letter. In order to explain the construction and the mode of action, reference is made to the preceding description and, in particular, the description relating to FIG. . The embodiments described below differ substantially only in the configuration of the shielding collar of the induction coil. The generator is present, although not illustrated.

The shielding collar in FIG. 2 differs from the shielding collar from FIG. 1 substantially in the fact that the angle α is chosen to be smaller, of the order of magnitude of about 45° here, while the axial height h is about five times the diameter d of the tool shaft . The largest external diameter of the shielding collar is in turn chosen to be somewhat smaller than the minimum internal diameter of the winding . Since the generatrix of the inner conical circumference is inclined at a somewhat greater angle with respect to the axis of rotation than the generatrix of the outer conical circumference , the shielding collar tapers outward. The conical surfaces and extend as far as the radially outer end of the shielding collar and, accordingly, this shielding collar has no annular extension similar to the extension from FIG. .

The shielding collar illustrated in FIG. 3 differs from the shielding collar from FIG. 1 substantially only in the fact that the generatrix of the inner circumferential surface is inclined at a smaller angle with respect to the axis of rotation than the generatrix of the outer circumferential surface and, furthermore, extends rectilinearly as far as the front edge facing axially away from the contact surface . Although the shielding collar therefore has a circular-cylindrical circumferential surface , it does not form an annular extension similar to the annular extension in FIG. . The dimensioning of the angle a and the axial height h based on the tool shaft diameter d corresponds to the variant in FIG. .

The embodiment of the shielding collar in FIG. 4 differs from the, shielding collar of FIG. 2 primarily in the fact that the angle of inclination a of the generatrix of the outer conical circumference is smaller than in the variant of FIG. and is of the order of magnitude of about 15°. The generatrix of the inner conical circumference runs approximately parallel to the generatrix of the outer conical circumference . The axial height of the shielding collar is again about five times the diameter d of the tool shaft

The variant of the shielding collar in FIG. 5 differs from the variants explained above in that the axially normal contact surface , with which the shielding collar rests on the end surface of the sleeve section , reaches substantially as far as the cylindrical outer circumference , that is to say there is no outer conical surface, as illustrated at in FIG. . However, the axial height h of the shielding collar is also here a multiple, five times in the exemplary embodiment illustrated, of the diameter d of the tool shaft . The inner circumference of the ring formed in this way is provided with an inner conical surface which, oriented axially away, widens radially outward, which makes it easier to grip the tool shaft . As indicated by a dash-dotted line , the inner conical surface can be provided with an annular throat, which produces an annular extension on the shielding collar

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are to be explained in more detail below using a drawing, in which:

FIG. 1 shows an axial longitudinal section through an induction coil for the inductive heating of a toolholder and

FIGS. 2-5 show axial longitudinal sections through variants of the induction coil.

CLAIMS

1. A device for the inductive heating of a sleeve section (5) of a toolholder (1) which contains a central balding opening (9) for a shaft (11) of a rotary tool, said toolholder holding the shaft (11) of the tool seated in the holding opening (9) with a press fit and releasing it when heated, comprising: a) an induction coil (13), which encloses the sleeve section (5) of the toolholder (1) annularly with a radial spacing for the heating; b) a generator (17) that feeds the induction coil (13) with electric current of periodically changing amplitude; and c) a ring element (27), enclosing the shaft (11) of the tool close to the tool-side end of the sleeve section (5) of the toolholder (1) and made of a magnetizable material that concentrates the magnetic flux, the ring element (27), in the region of its smallest diameter, being closely adjacent to the tool-side end of the sleeve section (5), wherein the surface (31) of the ring element (27) which faces the interior of the induction coil (13) axially, at least in a subregion, extends radially between the outer circumference of the tool-side end of the sleeve section (5) and the inner circumference of the induction coil (13) and axially obliquely radially outward away from the end of the sleeve section (5).

2. The device as claimed in claim 1, wherein the ring element (27) is formed as a shielding collar which projects axially beyond the tool-side end of the sleeve section (5) overan axial height (h) of at least 1.5 times the diameter (d) of the shaft (11) of the tool and whose greatest diameter is smaller than the greatest winding diameter of the induction coil (13).

3. The device as claimed in claim 2, wherein the ring element (27) projects axially beyond the tool-side end of the sleeve section (5) over an axial height (h) of at least twice the shaft diameter (d).

4. The device as claimed in claim 3, wherein in the region radially between the sleeve section (5) and the induction coil (13), on its side facing axially toward the toolholder (1), the ring element (27) has an outer circumferential surface (31) which widens conically axially away from the toolholder (1).

5. The device as claimed in claim 4, wherein on its side facing axially away from the toolholder (1), the ring element (27) has an inner circumferential surface (33) which widens conically axially away from the toolholder (1).

6. The device as claimed in claim 5, wherein the outer (31) and inner (33) circumferential surfaces have approximately the same cone angle.

7. The device as claimed in claim 6, characterized in that, in the region of its outer circumference, the ring element (27) has a substantially cylindrical circumferential surface (39).

8. The device as claimed in claim 7, wherein in the region of its outer circumference, the ring element (27) has an annular extension (37) that projects axially away from the toolholder (1).

9. The device as claimed in claim 8, wherein the surface (31) of the ring element (27) which faces the interior of the induction coil (13) axially and runs obliquely runs inclined at an angle of between 10° and 80°, with respect to the axis (7) of the shaft (11) of the tool.

10. The device as claimed in claim 9, wherein the ring element (27) adjacent to the sleeve section (5) of the toolbolder (1) has a flat end surface (35) running axially normally to the axis of rotation (7) of the tool shaft (11), in order to rest flat on a flat end surface (25) of the sleeve section (5).

11. The device as claimed in claim 10, wherein the greatest diameter of the ring element (27) is smaller than the smallest winding diameter of the induction coil (13).

12. The device as claimed in claim 11, wherein in the region of its outer circumference and at one or both of its ends, the induction coil (13) has a jacket (23) of a magnetizable material that concentrates the magnetic flux.

13. The device as claimed in claim 12, wherein the ring element (27) runs on all sides at a distance from the jacket (23).

14. The device as claimed in claim 13, wherein the ring element (27) is held on a structural unit which encloses the induction coil (13), by means of a disk (41) of non-magnetizable material.

15. The device as claimed in claim 14, wherein the ring element (27) is fitted firmly to the disk (41), and the disk (41) is held replaceably on the structural unit during operation.

16. A device for the inductive heating of a sleeve section of a toolholder which contains a central holding opening for a shaft of a rotary tool, said toolholder holding the shaft of the tool seated in the holding opening with a press fit and releasing it when heated, the device comprising: a) an induction coil, which encloses the sleeve section of the toolbolder annularly with a radial spacing for the heating; b) a generator that feeds the induction coil with electric current of periodically changing amplitude; and c) a ring element, enclosing the shaft of the tool close to the tool-side end of the sleeve section of the toolholder and made of a magnetizable material that concentrates the magnetic flux, the ring element, in the region of its smallest diameter, being closely adjacent to the tool-side end of the sleeve section, wherein the ring element is formed as a shielding collar which projects axially beyond the tool-side end of the sleeve section over an axial height (h) of at least 1.5 times the diameter (d) of the shaft of the tool and whose greatest diameter is smaller than the greatest winding diameter of the induction coil.

17. The device as claimed in claim 1, wherein the ring element (27) in the region of its smallest diameter bears on the sleeve section (5).

18. The device as claimed in claim 9, wherein the surface (31) of the ring element (27) which faces the interior of the induction coil (13) axially and runs obliquely runs inclined at an angle of between 20° and 70°, with respect to the axis (7) of the shaft (11) of the tool.

19. The device as claimed in claim 14, wherein the ring element (27) is held on a structural unit which encloses the induction coil (13), by means of a disk (41) of plastic or ceramic.

20. The device as claimed in claim 11, wherein in the region of its outer circumference or at one or both of its ends, the induction coil (13) has a jacket (23) of a magnetizable material that concentrates the magnetic flux.

21. The device as claimed in claim 16, wherein the ring element in the region of its smallest diameter bears on the sleeve section.

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