THREAD MILLING CUTTER

Abstract

A thread milling cutter having a main body which includes a shank and a cutting portion, which is cylindrical in its basic shape, an axis of rotation and a plurality of cutting teeth, which are spaced in the peripheral direction and which are arranged on the cutting portion in at least two different radial planes extending perpendicularly to the axis of rotation is provided. The thread milling cutter combines the advantages of high working efficiency of one-piece thread milling cutters having a plurality of cutting teeth and cutting lobes with the advantages of thread milling cutters having indexable cutting inserts without being restricted to large diameters. The cutting portion, respectively, has at least two seats for receiving a respective standard cutting insert in each of at least two different radial planes and the cutting teeth are formed by cutting corners of standard cutting inserts.

Claims

1. A thread milling cutter comprising a main body having a shank, a cutting portion having a cylindrical shape, an axis of rotation, and a plurality of cutting teeth spaced in a peripheral direction and arranged on the cutting portion in at least two different radial planes and extending perpendicularly to the axis of rotation, wherein the cutting portion has at least two seats for receiving a respective standard cutting insert in each of at least two different radial planes, the cutting teeth being formed by cutting corners of the standard cutting inserts.

2. The thread milling cutter according to claim 1, wherein at least three cutting inserts are respectively arranged on a same rotational circle in a radial plane.

3. The thread milling cutter according to claim 1, wherein the cutting inserts are arranged in overall at least three different radial planes.

4. The thread milling cutter according to claim 1, wherein the cutting inserts in the radial planes are arranged in a mutually displaced relationship in the peripheral direction.

5. The thread milling cutter according to claim 1, wherein the cutting inserts include rake surfaces and provided in front of the rake faces of the cutting inserts are chip spaces formed by cavities, which are set back radially with respect to a cylindrical envelope of the cutting portion, a displacement of mutually closest cutting inserts of adjacent radial planes in the radial direction corresponding to a twist angle which is so selected that the chip spaces of the mutually closest cutting inserts arranged in adjacent radial planes overlap in the peripheral direction.

6. The thread milling cutter according to claim 1, wherein the spacing of the radial planes is an integral multiple of one or more standard thread pitches.

7. The thread milling cutter according to claim 1, wherein in a plan view of the rake face the cutting inserts have a shape of an equilateral triangle and are mounted radially in a respective seat.

8. The thread milling cutter according to claim 1, wherein tips of the cutting corners are rounded or trimmed back.

9. The thread milling cutter according to claim 7, wherein axially most forwardly disposed cutting edges of the cutting inserts having a triangular basic shape axially project in a region radially within a profile-forming cutting corner with respect to the main body of the cutting portion.

10. The thread milling cutter according to claim 1, wherein side faces of the cutting inserts are drawn in between adjacent cutting corners in the direction of a center of the cutting insert and/or expanded out from the center.

11. The thread milling cutter according to claim 1, wherein the cutting inserts are double-sided indexable cutting inserts.

12. The thread milling cutter according to claim 1, wherein in a plan view of the rake face the cutting corners overall are a complete profile shape of at least one thread flight and a thread base.

13. The thread milling cutter according to claim 5, wherein the insert seat has a seat face for a contact face of the cutting insert that is opposite to the rake face, wherein the seat face has a seat face portion extending radially outwardly beyond the cylindrical envelope of the cutting portion.

14. The thread milling cutter according to claim 13, wherein the seat face portion is formed by an end face of a web, which peripherally extends in the radial plane and which is interrupted only in a region of the seats and the chip spaces.

15. The thread milling cutter according to claim 1, wherein the cutting teeth of a front radial plane which is further remote from the shank and at least the front radial plane which is most remote from the shank have a small radial projection of 1 to 100 m in relation to cutting teeth of next following radial planes with respect to the cutting teeth of all radial planes occurring in succession in a direction of the shank to compensate for radial deflection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 shows a side view of a thread milling cutter according to the invention.

[0045] FIG. 2 shows a view on an enlarged scale of the cutting portion of the milling cutter of FIG. 1 without cutting inserts.

[0046] FIG. 3 shows an end view from below of the cutting portion of FIG. 2.

[0047] FIG. 4 shows a sectional view containing the axis of the milling cutter.

[0048] Fig. shows a sectional view perpendicular to the axis along a radial plane containing the cutting tip.

[0049] FIG. 6 shows various variants of cutting corners.

DETAILED DESCRIPTION

[0050] Referring to FIG. 1, the main body of a milling cutter includes a substantially cylindrical shank 1 and a substantially cylindrical cutting portion 2, which are assembled together in one piece and have a common axis of rotation 3, which is also the axis of symmetry of the shank 1 and the cylindrical envelope of the cutting portion 2, wherein the cylindrical envelope of the cutting portion 2 is defined only by the cylindrical portion outside cutting insert seats and chip spaces and without the peripherally extending webs 7, which serve to support the cutting tip of individual cutting inserts 5.

[0051] The cutting inserts 5 are standard cutting inserts in the basic shape of an equilateral triangle with a correspondingly triangular top side and an underside substantially parallel thereto, which are connected together by peripherally extending edge faces. At the transition between the edge faces and the top side (in the case of double-sided indexable inserts also the underside) there are formed respective cutting edges. In the plan view of the top side and the underside respectively, the cutting edges come together at cutting corners 15, wherein the cutting corners 15 are formed by the end portions of the cutting edges, which come together at the corners of a triangle of the cutting insert and a rounded transition therebetween. The flanks of the cutting corners include with each other an angle of 60 that is usual for thread flanks.

[0052] It should be appreciated that deviations from that 60 angle are possible insofar as the top side and the underside are of a shape differing from the shape of an equilateral triangle, for example by constricting or expanding the edge faces in the direction towards or away from the center of the cutting insert respectively. A respective central fixing bore is disposed in the center of each of the cutting inserts.

[0053] Insofar as this makes it easier to describe various cutting inserts 5 and radial planes 4, reference numerals 5 and 4 respectively are provided with additional indices.

[0054] FIG. 2 shows the cutting portion 2 without cutting inserts so that the seats 6 of the cutting inserts can be better seen, which are respectively defined by a base face 6a and by lateral contact faces 6b and 6c, wherein in the case of the insert seats, which are arranged furthest forwardly on the cutting portion 2, the lateral contact faces 6c are omitted so that cutting inserts 5 which are arranged in the front row of insert seats 6 are exposed with their entire front cutting edge 11 between two cutting corners so that those cutting edges can be used inter alia for chamfering edges, in particular at the edge of the opening of a thread bore. The chamfering operation can be effected optionally prior to or after milling of the thread, the former being preferred.

[0055] The space in front of the respective insert seat 6 is in the form of a chip space 8 and forms a respective recess in the cylindrical main body of the cutting portion 2. Provided in the region between insert seats and chip spaces on the outside of the cutting portion are peripherally extending webs 7 whose profile approximately corresponds to the profile of the cutting corners and which are arranged in the same radial plane as the cutting corners 15. In the region of the insert seats 6 the respective end faces of the webs 7 form a contact face 7a which is disposed in the same plane as the base face 6a of the insert seat 6 and thus forms a part of the seat face 6a.

[0056] Bores 9 optionally open on the rear side of the respective webs 7, that is towards the respective chip space 8, the bores 9 being provided for the discharge of a flushing and/or cooling agent which is injected in the direction of the cutting tips 15 into the chip spaces 8, which are in front of the cutting tips 15.

[0057] The webs 7 provide for effective support for the cutting tips 15, wherein the profile of the webs 7 should be slightly set back with respect to the profile of the cutting tips.

[0058] The end view in FIG. 3 shows three cutting inserts in the furthest forwardly disposed radial plane 4.sub.1, the reference numerals of which are provided with the index 1 to distinguish the cutting inserts in subsequent planes. The cutting inserts in the subsequent planes 4.sub.2 . . . 4.sub.5 are correspondingly denoted by 5.sub.2 . . . 5.sub.5.

[0059] As can be seen from FIG. 3 and also FIG. 2, the cutting insert seats 6, like the cutting inserts 5 of a plane directly following the respectively preceding plane, are set back in opposite relationship to the direction of rotation through an angle which in the present case is 24. In that respect, the direction of rotation arises out of the arrangement of the cutting inserts and the chip spaces 8 arranged in front of same in the direction of rotation.

[0060] It should be appreciated that the angular displacement between cutting inserts of adjacent planes can also assume any other values, in which respect it is desirable for the cutting inserts overall to be so arranged that, at any moment during rotation of the milling cutter in a bore hole, the at least approximately equal number of cutting inserts should as far as possible always be in engagement at the same time with the wall of the hole and mills out a corresponding portion of a thread flight. As in the present case, the cutting inserts are distributed over 5 different radial planes 4 the displacement between adjacent radial planes 4 is a fifth of the peripheral spacing (120) between cutting inserts in the same radial plane 4 so that the cutting inserts 5 are overall distributed uniformly along the periphery. That ensures relatively vibration-free and smooth running of the milling cutter in operation. FIG. 4 is a cross-sectional view, containing the axis of rotation 3, of the milling cutter already shown in FIGS. 1 through 3, with three respective cutting inserts in five different radial planes and with a displacement of the cutting inserts along a notional twist angle in the manner already just described. This view shows the chip spaces 8, which are respectively provided in front of the cutting inserts, and which extend in the peripheral direction of the cutting portion 2 over about 90.

[0061] Similarly to the cutting inserts 5, the chip spaces 8 are also arranged in mutually displaced relationship along the same twist angle and they thus have respective regions overlapping each other in the peripheral direction so that the sequence of chip spaces 8 overall forms a kind of continuous chip flute, but with a correspondingly non-flat base and stepped transitions. That can be advantageous in particular in relatively narrow bore holes in which the diameter of the hole and the thread to be produced are only slightly larger than the diameter of the rotational circle of the cutting tips, because in that way the chips produced in the milling operation can also be transported further in the axial direction between the individual spaces and out of the bore hole. In that respect, it would further be possible for the transitions between adjacent chip spaces to be still further flattened off and smoothed so that the impression and also the effect of a chip flute is still further improved.

[0062] The radial sectional view in FIG. 5 again shows three cutting inserts 5 arranged in a radial plane 4 with chip spaces 8 in front of same. In addition, it is possible to see threaded bores 13 in the seat face 6a of the insert seat, which are not completely aligned with the through bores 12, so that when a corresponding clamping screw which engages into the threaded bore 13 is tightened the cutting inserts 5 are brought into fixed contact not only with the base face 6a of the insert seat but also with the lateral contact faces 6b and 6c.

[0063] The cutting inserts used in the present embodiment are one-sided indexable cutting inserts with a positive cutting geometry, specifically a wedge angle of less than 90 at the cutting edge 11 between the relief face and the rake face, wherein the rake face can also be structured by chip forming grooves, chip breakers and the like.

[0064] The cutting inserts 5 and their seats 6 can then be so arranged in particular that the cutting edges 11 are disposed substantially in a plane containing the axis of rotation 3.

[0065] The number of cutting inserts, which are arranged in a respective radial plane should be at least 2 so that female threads can be correspondingly quickly and efficiently produced with such a milling cutter. The number of cutting inserts per radial plane can also be greater than 3, in particular for milling cutters of larger diameter which also produce threads of correspondingly large diameter, in other respects however the number of cutting inserts is limited by the necessary maintenance of stability of the milling cutter or the cutting portion respectively and the size of the available standard cutting inserts.

[0066] As the provision of insert seats and chip spaces necessarily reduces the cross-section of the cutting portion and limits the stability or flexural strength of the cutting portion an embodiment of the disclosure can provide that the cutting tip of axially further forwardly disposed cutting inserts, in relation to the cutting tips of axially further rearwardly cutting inserts, that is to say, which are closer to the shank, is in each case larger by some micrometers than in the radial plane next following towards the shank. That takes account of the fact that, in a thread milling operation, the furthest forwardly disposed portions of the milling cutter or the cutting tips thereof are displaced slightly radially inwardly.

[0067] The spacing d between adjacent radial planes 4.sub.1, 4.sub.2 . . . 4.sub.5 in the present embodiment is 12 mm and is thus a common integral multiple of 1; 1.5; 2; 3; 4 and 6. That makes it possible, using such a thread milling cutter as is shown in FIG. 1, to produce different threads with the thread pitches 1; 1.5; 2; 3; 4 and 6, in which case the three cutting inserts of each radial plane respectively produce a thread portion of a 12 mm axial length and with a suitable forward feed movement the thread flights produced by the cutting inserts 5.sub.1, 5.sub.2 . . . 5.sub.5 run into each other in accurately fitting relationship. The overall thread length is then 60 mm. Threads using inch sizes are to be produced in an entirely similar fashion, wherein in the case of single-flight threads the spacings of the radial planes for producing threads using inch sizes respectively correspond to an integral multiple of the thread pitch expressed in inches. In this case too, once again spacings in respect of the radial planes which are a common integral multiple of a plurality of standard thread pitches (with inch sizes) are preferred.

[0068] It should be appreciated that the number of radial planes occurring in succession in the axial direction, with cutting inserts, can also be varied, but like the number of cutting inserts in a radial plane should be at least two. The efficiency of a corresponding thread milling cutter, that is to say the number of threads of a predetermined length, which are produced therewith per unit of time, rises with the number of cutting inserts per radial plane and the number of radial planes in which cutting inserts are provided.

[0069] In operation, for example, the milling cutter shown in FIG. 1 is firstly engaged into a suitably prepared bore to such an extent that the cutting tips of the cutting inserts of the furthest axially set-back radial plane 4.sub.5 are disposed approximately in the region of the bore opening while the portion of the cutting portion is engaged into the bore, with the other cutting inserts in the radial planes 4.sub.1 to 4.sub.4. Then (or also already before or during engagement into the bore) the milling cutter is set in rotation and is then displaced radially outwardly until the cutting teeth come into engagement with the wall of the bore and begin to produce a respective portion of a thread flight, whereupon the entire milling cutter is moved in a spiral around the axis of the bore and in that case at the same time axially in accordance with a desired thread pitch in the forward direction until the cutting teeth of an axially following radial plane reach in precisely fitting relationship the thread flights produced by the teeth of the axially previous radial plane, whereupon the milling cutter is again centered with respect to the axis of the thread bore and axially withdrawn. In that way, a thread is produced of a depth, which, in the case of single-flight threads, corresponds to n-times the spacing between the radial planes, wherein n is the number of various radial planes with cutting inserts.

[0070] The thread milling cutter shown in the present figures have a considerably increased level of effectiveness in comparison with the thread milling cutters discussed in the Background, and at the same time can be used in highly versatile fashion, and can also be produced with relatively small rotational circle diameters in respect of the thread tips of for example 30 mm, and is in that respect relatively inexpensive in operation by virtue of the use of standard cutting inserts. For producing female threads of markedly smaller diameters than 30 mm firstly the number of cutting inserts per radial plane is to be reduced while the number of cutting inserts arranged in various radial planes in the axial direction is ultimately limited only by the thread lengths to be produced.

[0071] FIG. 6 shows various shapes of conceivable cutting corners which here are shown on a single cutting insert 5, in which respect it should be appreciated that generally cutting inserts are uniformly provided with the same respective cutting corners as the cutting seats must be matched to the shape of the cutting corners in order to produce a given desired thread.

[0072] The cutting corner 15.sub.1 is of a substantially trapezoidal profile, in which respect self-evidently the transitions between the cutting edge portions which are angled relative to each other can in turn be of a smaller radius. In the case of the cutting corner 15.sub.2, the end portions of the cutting edges 11 are angled in such a way that they include a larger angle than 60 so that with such a cutting corner it is possible to produce threads whose flank angle is greater than 60.

[0073] In the case of the cutting corner 15.sub.3, the cutting edge 11 is displaced somewhat inwardly behind the end portion so that a smaller angle than 60 is included between the end portions of the cutting edges 11 so that threads with flank angles of less than 60 can be produced with such a cutting corner. Optionally the end portions of the cutting edges 11 could also extend approximately parallel in order for example to produce threads for a spindle drive.

[0074] For the purposes of the original disclosure it is noted that all features as can be seen by a man skilled in the art from the present description, the drawing and the appended claims, even if they are described in specific terms only in connection with certain other features, can be combined both individually and also in any combinations with others of the features or groups of features disclosed here insofar as that has not be expressly excluded or technical aspects make such combinations impossible or meaningless. A comprehensive explicit representation of all conceivable combinations of features and emphasis of the independence of the individual features from each other is dispensed with here only for the sake of brevity and readability of the description.