Modular drill with defined side support

A rotary cutting tool has a shank and an interchangeable cutting tip which can be coupled to the shank. The shank has a locking geometry having an undercut into which a locking projection of the cutting tip projects. Numerous lateral supporting surfaces and supporting counter-surfaces are provided for laterally fixing the cutting tip in the shank.

BACKGROUND

1. Field of the Invention

The invention relates to a rotary cutting tool, in particular a drill, comprising a shank and an interchangeable cutting tip which can be coupled to the shank in a form-fitting manner.

2. Background Information

An example of a known cutting tool having an interchangeable cutting tip is described in WO 2006/046227 A1. The cutting tips, as soon as they have become severely worn, are removed from the shank in a nondestructive manner using a tool and are replaced by a new cutting tip. The cutting tip is fastened by means of form-fitting locking, similar to a bayonet catch, in which an undercut against the direction of rotation is provided in the shank, into which undercut a locking projection of the cutting tip projects during the rotary locking. The rotary movement is likewise transmitted to the cutting tip via a form fit. To absorb lateral cutting forces, a supporting surface is provided in the region of the rear-side end of the cutting tip, to be more precise in the region of the locking geometry. The cutting tip has a cylindrical section axially between the locking surface and the drill point, the cylindrical said section being at a slight distance from the shank via a gap.

EP 0 984 841 B1 shows an alternative embodiment of a known cutting tool having an interchangeable cutting tip, wherein a small, stub-like pre-centering extension projects from the rear-side end face of the cutting tip. The pre-centering extension performs the task of roughly centering the cutting tip relative to the shank.

Although generally suitable for their intended uses, there is still room for improvements in such cutting tools, particularly in improving the locking of the cutting tip in the cutting tool.

SUMMARY OF THE INVENTION

Deficiencies in the prior art are addressed by embodiments of the present invention. As one embodiment of the invention, a rotary cutting tool, which in particular is designed as a drill, having a shank and an interchangeable cutting tip which can be coupled to the shank in a form-fitting manner is provided. The shank has a locking geometry having an undercut against the direction of rotation, into which undercut a locking projection of the cutting tip projects, in order to secure the cutting tip axially to the shank. Furthermore, the shank has a lateral first supporting surface lying axially offset from the locking geometry and a lateral second supporting surface lying axially in the region of the locking geometry, wherein a first counter-surface and a second counter-surface, respectively, of the cutting tip bear with an interference fit against the supporting surfaces.

In the example cutting tool according to an embodiment of the invention, the lateral cutting forces are absorbed not only by supporting surfaces in the region of the locking projection but also additionally, axially offset therefrom, by a first supporting surface, such that the first and the second supporting surfaces interact. The interference fit at the two supporting surfaces ensures that both supporting surfaces also have a supporting effect when the cutting tip is exchanged and in the face of the production tolerances which inevitably occur. The support is effected in the assembled state even if lateral forces are still not exerted on the cutting tool.

According to a preferred embodiment of the present invention, the first and the second supporting surfaces lie substantially within the same diameter range. In particular, they are at most at a distance from one another which is less than 15% of the diameter of the larger of the two supporting surfaces.

At least one supporting surface, and preferably both supporting surfaces, is/are formed by a plurality of supporting sections circumferentially separate from one another. Between the supporting sections of each or of one of the supporting surfaces, there is no contact between the cutting tip and shank. This can be achieved either by an axial groove in the shank or by an axial slot.

The supporting surfaces are preferably arranged diametrically opposite one another. In addition, in the preferred embodiment, only two supporting sections are provided.

The interference fit is achieved relatively simply in particular by the shank having axially projecting fingers, on the radial inner side of which at least the second supporting surface, preferably both supporting surfaces are provided. As a result of these axial fingers, which are circumferentially separate from one another, certain radial flexibility is achieved, such that the fingers are easily bent elastically radially outward when the cutting tip is fastened.

The elasticity is achieved to a special degree owing to the fact that, according to one embodiment, the fingers have an axial length which is greater than/equal to, preferably at least twice as large as, the radial finger thickness.

In addition, the locking geometry should also be formed on the fingers.

At least the first supporting surface and the first counter-surface, alternatively or additionally also the second surfaces, can have geometries which deviate from one another as viewed in the axial direction. These geometries are designed in such a way that the counter-surface exerts an increasing radial pressure on the first supporting surface during the rotary locking, that is to say when the cutting tip is being fastened to the shank. In this connection, however, a deviating geometry does not mean to provide merely different dimensions in the same shape. On the contrary, a deviating geometry means that the counter-surface on the cutting-tip side is moved increasingly closer to the supporting surface during the rotary locking in order to finally strike it and press it increasingly outward in order to ensure the interference fit.

An example of such a pair of different geometries consists in the fact that at least the first supporting surface has the geometry of a circular cylinder segment and the corresponding counter-surface has a geometry bulging radially outward relative to a circular cylinder segment as viewed in the axial direction. Such a geometry bulging outward can be realized, for example, by an ellipse segment in which the counter-sections opposite the supporting sections in the unlocked position are at a smaller distance from the axis of rotation than the circular cylinder segment, and the bulging-out section is at a maximum distance from the axis of rotation which is greater than that of the circular cylinder segment. Of course, both surfaces, that is to say the supporting surface and its counter-surface, could also have geometries differing from a circular cylinder, or the counter-surface could have a circular cylinder segment, whereas the supporting surface is of elliptical design.

Where numerous exchanges of drill points are carried out on the same shank, it is important that the wear of the components is slight and that, both with a shank in new condition and with a highly worn shank, firstly the exchange takes place easily and reliable locking is also constantly ensured. In order to be able to meet these different requirements, the first supporting surface has an insertion slope in the rotary locking direction. This insertion slope avoids crushing or catching when locking a drill point on a new shank.

The locking projection, as viewed in the radial direction, preferably runs in a wedge shape in the circumferential direction; that is to say, the wedge extends in the direction toward the locking geometry. Additionally or alternatively, the locking projection bears against an axial stop surface, running in the circumferential direction, on the shank. In this connection, the locking geometry should as far as possible ensure an axial restraint between the shank and the cutting tip, to be precise possibly only at an axial stop surface, so that double fits do not occur.

The axial stop surface can merge into an engagement slope which lies in front of the stop surface in the rotary locking direction so that easy locking of drill points on new shanks is also ensured in this region.

The preferred embodiment provides for the axial stop surface to be a section of a step on the finger, said step projecting freely in the circumferential direction.

The second supporting surface should lie closer to the drill point than the first supporting surface, which is made possible by the provision of a supporting pin, projecting on the rear side, on the cutting tip, on which supporting pin the first supporting surface is provided.

A centering pin provided with a smaller diameter, that is to say smaller than that of the supporting pin, can also project from the supporting pin on the rear side, said centering pin engaging in a matching opening in the shank and thus pre-centering the cutting tip upon insertion. However, this centering pin has a clearance fit relative to the corresponding opening in the shank in order to eliminate double fits.

The axial length and/or the area of the first supporting surface is greater than that of the second supporting surface.

In addition, the first and second supporting surfaces should as far as possible directly adjoin one another in the axial direction and are at most separated from one another by a small step. This step could be formed by a bevel.

Parts corresponding to one another are provided with the same designations in all the figures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a rotary cutting tool10in the form of a drill, having a shank12and a cutting tip14, which are both produced as separate parts. The cutting tip can be fastened to the shank12in a detachable and interchangeable manner. Similarly, the rotary cutting tool can also be designed as a countersinking, milling or reaming tool.

The cutting tool10has a flute16which extends over the shank12and the cutting tip14, which also has the drill point17.

The tip-side end of the shank12can be seen inFIG. 2, the shank12being split by an axial slot18into two axially projecting fingers20. The axial slot18is in this case arranged in such a way that it merges into the flute16.

The fingers20have “locking geometries”22in the circumferential direction. These locking geometries22have undercuts24against the direction of rotation of the cutting tool10. As will be explained later, corresponding locking projections of the cutting tip14come into engagement with these undercuts24in order to lock the cutting tip14on the shank12.

The undercuts24are preferably formed by planar surfaces26,28which run toward one another in the circumferential direction, such that, as viewed in the radial direction, each undercut24runs in a wedge shape.

In addition, the fingers20have, broadly speaking approximately at the center of the axial extent thereof, axial stop surfaces30which face the subsequent drill point17. These stop surfaces30are oriented in particular at a right angle to the center axis A (seeFIG. 1) of the cutting tool10.

The stop surfaces30preferably lie outside the undercut24and are separated from the latter via an axially and radially running groove32.

On its end opposite the undercut24, each stop surface30merges into an “engagement slope”34, which forms, as it were, the transition of the stop surface30to a side wall36of the finger20. The engagement slope34can be designed, for example, as a beveled or preferably rounded-off edge. As will be explained later, it is intended to prevent or reduce damage to the cutting tip14during insertion and locking on the shank12.

The side wall36runs, with respect toFIG. 2, obliquely downward in the axial direction to the shank end and also in the direction of the undercut24. The side wall36together with the stop surface30, as viewed in the radial direction toward the axial center (seeFIG. 5), therefore forms a step38which projects freely in the circumferential direction.

The stop surface30divides each finger20into a bottom, first section and a top (tip-side), second section.

In the region between the diametrically opposite fingers20, the shank12has a cylindrical locating opening40for the cutting tip14. The bottom, first part of this opening is formed by a first supporting surface42which is formed on the fingers20radially on the inside and which, on account of the slot18, is subdivided into two circumferentially separate first supporting sections. One supporting section is provided, as it were, on one finger20and the other diametrically opposite supporting section is provided on the other finger20. Both first supporting sections together form the first supporting surface42. In the locking direction, an insertion slope44running obliquely and radially outward is provided at the start of each “first supporting section”, said insertion slope44forming, as it were, the transition between the first supporting section and the side wall36.

In the axial direction at the level of the stop surface30, the first supporting surface42merges with a slight, sloping step46into the “second supporting surface”48, which is likewise formed on the fingers20radially on the inside but lies axially at the level of the locking geometry22. Here, too, on account of the slot18, the second supporting surface48is subdivided into two sectional surfaces, which are called second supporting sections below. These second supporting sections also lie diametrically opposite one another. The slot18ends in the axial direction at a preferably plane base surface50, which has a centering opening52.

With respect toFIG. 2, it should also be mentioned that the supporting surfaces42,48lie substantially within the same diameter range, that is to say that they deviate radially from one another at most only slightly. In the example shown, the second supporting surface48lies radially somewhat further on the outside than the first supporting surface42. Apart from that, the second supporting surface48is smaller and axially shorter than the first supporting surface42.

FIG. 3shows the cutting tip14, which is produced from a harder material than the shank. Suitable materials for the cutting tip14are in particular carbide, cermet, ceramic and HSS, in each case coated or uncoated, although tipping with PCD or CBN is also possible. The cutting tip14can be produced by metal injection molding (MIM process) or can be finish-machined in a conventional manner by grinding.

The cutting tip14has an axially obliquely running recess, which forms the flute16, and two radially projecting lobes54, which have the cutting edges. In the rotary locking direction V (the rotary locking direction is opposed to the subsequent direction of rotation of the tool), the lobes54have locking projections55, which, as viewed in the radial direction, run in a wedge shape in the circumferential direction. Each projection55is oriented toward the locking geometry22and its surfaces56,58are preferably adapted in their inclination to the surfaces28and26, respectively. In the rotary locking direction V in front of the lobes54, the cutting tip14has a preferably cylindrical supporting counter-surface60, which is formed by two first supporting counter-sections, namely in each case a section in front of the respective lobe54. In the locked state, this supporting counter-surface60bears against the second supporting surface48of the shank12and is therefore designated as second supporting counter-surface60.

A “supporting pin”62is integrally formed on that side of the lobe54which faces axially away from the drill point17. In the locked state, this supporting pin62lies in the region of the first supporting surface42and therefore has a first supporting counter-surface64, which is subdivided by the flute16into two second supporting counter-sections.

The supporting pin62has an elliptical cross section as viewed in the axial direction, said cross section being interrupted only by the two flutes16, whereas the supporting surfaces42form a circular cylinder, to be more precise, on account of the slot18, circular cylinder segments. With respect to the elliptical geometry, it should also be mentioned that the major axis of the ellipse coincides approximately with the center of the first supporting counter-sections. The minor axis of the ellipse thus falls within the region of the flute16(seeFIG. 6).

That side of the supporting pin62which faces away from the drill point17has a centering pin66, which has a markedly smaller diameter than the supporting pin42. The centering opening52, into which the centering pin66penetrates, is provided for pre-centering with an oversize relative to the centering pin66.

FIG. 4shows the shank12with inserted cutting tip14, where it can be seen that, on the one hand, the centering pin66lies with clearance in the corresponding centering opening52and that, on the other hand, the cutting tip14is held free of clearance in the shank12both laterally via the first supporting surface42and via the second supporting surface48by these surfaces bearing with an interference fit against the first and the second supporting counter-surfaces64and60, respectively. The bearing contact runs in this case even preferably right up to the free end of the fingers20.

It can also be seen that the radially outermost sections of the lobes54project laterally relative to the fingers20. The axial mounting cannot be seen inFIG. 4, said axial mounting being achieved by the surface68bearing on the stop surface30, said surface68lying inFIG. 3on the underside of the lobes54. However, the base surface50is at a small distance from the bottom end face of the supporting pin62(seeFIG. 4).

FIG. 5shows the cutting tip14in the shank12in the still unlocked, but already inserted position. It can be seen that the engagement slope34makes it easier for cutting tips14to be rotated in locking direction V, even in the case of unused shanks12. Apart from that, the locking is also improved by the insertion slope44in the region of the first supporting surface42.

When the cutting tip14is rotated in rotary locking direction V, the locking projection55engages in the assigned undercut24, such that the two parts are locked together in the axial direction. As a result, the cutting tip14is secured to the shank12, and the torque from the shank12, which is required for drilling or milling, can be transmitted to the cutting tip14. The two surfaces58and26are positioned axially relative to one another in such a way that, during the locking, an axial clamping force is exerted on the cutting tip14, which presses the cutting tip14against the stop surface30.

Furthermore, during the locking, the second supporting counter-surface60lying in front of the locking projection55moves behind the associated finger20and presses against the second supporting surface48.

The supporting surface42also bears, in the locked state, with an interference fit against the first supporting counter-surface64, as shown with the aid ofFIGS. 6 and 7. As stated, the supporting pin62has an elliptical geometry and is inserted with the major axis of the ellipse oriented toward the slot18. This unlocked state is shown inFIG. 6. In this case, there is at most slight contact, but not yet any interference fit, between the supporting pin62and the fingers20.

However, during the rotation in the locking direction (seeFIG. 7), the major axis of the ellipse moves between the fingers20. Since the length of the major axis of the ellipse is greater than the diameter of the first supporting surface42, the supporting pin62presses the fingers20radially slightly outward, such that, here, too, an interference fit is formed between the first supporting surface42and the first supporting counter-surface64. During the locking, the radial force exerted on the fingers20therefore increases (cf.FIGS. 6 and 7).

As a result of the fingers20, which are circumferentially separate from one another, certain radial flexibility is achieved, for which reason the fingers20, as already mentioned, are easily bent elastically radially outward in the case of a fixed cutting tip14.

To achieve sufficient elasticity, the fingers20have an axial length which is greater than or equal to, preferably at least twice as large as, the radial finger thickness. The fingers20therefore have an elongated shape in the axial direction.

The centering pin66serves merely for pre-centering during the insertion of a new cutting tip14. No force is transmitted via the centering pin66during the cutting operation.