ROTATABLE TOOL FOR FORMING BY METAL CUTTING A CIRCULAR GROOVE

Abstract

A rotatable tool for producing a circular groove through metal cutting in a metal work piece and a method of forming the circular groove with the rotatable tool is disclosed. The rotatable tool includes a front end and a second end. The front end includes a first radially outer cutting edge and a second radially inner cutting edge, where the first radially outer cutting edge is located at a larger radial distance from the tool center axis than any other cutting edge of the rotatable tool, and where the second radially inner cutting edge is located at a smaller radial distance from the tool center axis than any other cutting edge of the rotatable tool.

Claims

1. A rotatable tool for forming by metal cutting a circular groove in a metal work piece, the tool comprising: a front end and a rear end; and a tool center axis, the rotatable tool being rotatable in a given direction of rotation around the tool center axis, which is a longitudinal axis of the rotatable tool, the front end including two cutting edges located on opposite sides and at a distance from the tool center axis, the two cutting edges forming a first radially outer cutting edge, a first radially inner cutting edge and a second radially inner cutting edge, wherein the first radially outer cutting edge is located at a larger radial distance from the tool center axis than any other cutting edge of the rotatable tool, and the second radially inner cutting edge is located at a smaller radial distance from the tool center axis than any other cutting edge of the rotatable tool.

2. The rotatable tool according to claim 1, further comprising a first corner cutting edge, a second radially outer cutting edge and a second corner cutting edge, wherein the first radially outer cutting edge and the first radially inner cutting edge converge towards and are connected by the first corner cutting edge, wherein the second radially outer cutting edge and the second radially inner cutting edge converge towards and are connected by the second corner cutting edge, wherein the a first radially inner cutting edge and the second radially outer cutting edge are located on opposite sides and at a distance from the tool center axis, wherein the first corner cutting edge and the second corner cutting edge are located on opposite sides and at a distance from the tool center axis, wherein the first corner cutting edge is located at a first distance from the tool center axis, and wherein the second corner cutting edge is located at a second distance from the tool center axis.

3. The rotatable tool according to claim 2, wherein the first distance is equal or larger than the second distance.

4. The rotatable tool according to claim 2, wherein the first radially outer cutting edge forms a first outer edge angle with the tool center axis, wherein the first radially inner cutting edge forms a first inner edge angle with the tool center axis, wherein the second radially outer cutting edge forms a second outer edge angle with the tool center axis, wherein the second radially inner cutting edge forms a second inner edge angle with the tool center axis, wherein the first and second radially outer cutting edges converge away from the rear end, and wherein the first and second radially inner cutting edges converge towards the rear end.

5. The rotatable tool according to claim 4, wherein the first outer edge angle is larger than the second outer edge angle, wherein second inner edge angle is larger than the first inner edge angle, wherein the first outer edge angle is larger than the first inner edge angle, and wherein the second outer edge angle is smaller than the second inner edge angle.

6. The rotatable tool according to claim 2, further comprising a first cutting insert and a second cutting insert, wherein the first cutting insert includes the first radially outer cutting edge, the first radially inner cutting edge and the first corner cutting edge, and wherein the second cutting insert includes the second radially outer cutting edge, the second radially inner cutting edge and the second corner cutting edge.

7. The rotatable tool according to claim 6, wherein the first cutting insert has a parallelogram shape where the first radially outer cutting edge and the first radially inner cutting edge form two adjacent sides of the parallelogram and the first corner cutting edge forms a corner of the parallelogram, wherein the second cutting insert has a parallelogram shape where the second radially outer cutting edge and the second radially inner cutting edge form two other adjacent sides of the parallelogram and the second corner cutting edge forms another corner of the parallelogram, wherein the first and second cutting inserts are identical, and wherein the first corner cutting edge and second the corner cutting edge are located at longitudinal equidistant positions.

8. The rotatable tool according to claim 1, further comprising a radial positioning arrangement, such that at least one of the first radially outer cutting edge and second radially inner cutting edge can be positioned on at least two different radial distances from the tool center axis.

9. A method for forming by metal cutting a circular groove in a metal work piece, the method comprising the steps of: providing a rotatable tool, the rotatable tool including a front end; a rear end and a tool center axis, the tool being rotatable in a given direction of rotation around the tool center axis, which is a longitudinal axis of the rotatable tool, the front end having two cutting edges located on opposite sides and at a distance from the tool center axis, the two cutting edges forming a first radially outer cutting edge, a first radially inner cutting edge and a second radially inner cutting edge, wherein the first radially outer cutting edge is located at a larger radial distance from the tool center axis than any other cutting edge of the rotatable tool, and the second radially inner cutting edge is located at a smaller radial distance from the tool center axis than any other cutting edge of the rotatable tool; providing a metal work piece having a surface which is perpendicular to a groove center axis of the circular groove; setting the tool center axis parallel and at a distance from the groove center axis; rotating the rotatable tool around the tool center axis; rotating the tool center axis around the groove center axis; moving the rotatable tool in a forward longitudinal direction towards the work piece such that the first radially outer cutting edge and the second radially inner cutting edge of the rotatable tool enter the metal work piece; gradually decreasing the distance between the tool center and grove center axes; and simultaneously moving the rotatable tool in a forward longitudinal direction, thereby forming a circular groove in the metal work piece the circular groove including a bottom surface, an inner wall surface formed by the second radially inner cutting edge, and an outer wall surface formed by the first radially outer cutting edge, and an opening in the surface of the work piece, which is perpendicular to the groove center axis of the circular groove.

10. The method according to claim 9, wherein the tool includes a first corner cutting edge, a second radially outer cutting edge and a second corner cutting edge, the method further comprising the steps of entering the work piece with the corner cutting edges, and when the corner cutting edges enter the work piece setting X=(F+P−P′)/2, where X is the distance between the tool center and grove center axes, P is a distance that the first corner cutting edge is located from the tool center axis, P′ is a distance that the second corner cutting edge is located from the tool center axis and F is the width of the opening of the circular groove when the width F is in a plane perpendicular to the groove center axis.

11. The method according to claim 10, wherein the method further comprises the steps of when the corner cutting edges are at the bottom surface of the circular groove, setting X=(C+P−P′)/2, where C is the width of the bottom surface of the circular groove, when the width C is in a plane perpendicular to the groove center axis.

12. The method according to claim 10, wherein the method further comprises the step of setting P+P′=2E, where E is the distance from the groove center axis to a center point of the circular groove.

13. The method according to claim 11, wherein the method further comprises the step of setting P≦P′+C/2, where C is the width of the bottom surface of the circular groove, when the width C is in a plane perpendicular to the groove center axis.

14. The method according to claim 10, wherein the first radially outer cutting edge forms a first outer edge angle with the tool center axis, the second radially outer cutting edge forms a second outer edge angle with the tool center axis wherein the first radially inner cutting edge forms a first inner edge angle with the tool center axis, and wherein the second radially inner cutting edge forms a second inner edge angle with the tool center axis, the method further comprising the steps of setting the first outer edge angle to be equal to an outer wall angle, the outer wall angle being an angle the outer wall surface forms with the groove center axis; setting the second inner edge angle (β′) to be equal to an inner wall angle, the inner wall angle being the angle the inner wall surface forms with the groove center axis; setting the sum of the first outer edge angle and the first inner edge angle to be smaller than the sum of the outer wall angle and the inner wall angle; setting the sum of the second outer edge angle and the second inner edge angle to be smaller than the sum of the outer wall angle and the inner wall angle; and forming the bottom surface such that the bottom surface is located in a plane perpendicular to the groove center axis.

15. The method according to claim 14, wherein the method is for forming a seal ring groove.

16. A computer program having instructions, which when executed by a computer numerical control machine cause the computer numerical control machine to perform the method according to claim 9.

Description

BRIEF DESCRIPTION OF THE APPENDED DRAWINGS

[0023] FIG. 1 is a perspective view of a rotatable tool according to the invention.

[0024] FIG. 2 is a side view of the rotatable tool as in FIG. 1.

[0025] FIG. 3 is a front view of the rotatable tool as in FIG. 1.

[0026] FIG. 4 is perspective exploded view of the rotatable tool as in FIGS. 1-3, showing the slide and cutting head in detail.

[0027] FIG. 5 is a side view of the rotatable tool as in FIGS. 1-4, as well as a work piece in which a circular groove has been formed by metal cutting using the rotatable tool.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0028] In FIGS. 1-5, a rotatable tool 1 is shown. It is has a longitudinally rear end in the form of a coupling part 3 suitable to be coupled in a machine tool spindle in a machine, such as a CNC-machine, e.g. a machining center. Alternatively, it is connected to an extension part or extension tool, which is coupled in a machine tool spindle. The coupling part 3 is substantially symmetrical around the tool center axis, which is a longitudinal axis; also the axis around the tool rotates during machining. The coupling part 3 is conical in shape, with a narrow portion at a longitudinal end, and a wider portion closer to a longitudinal front part of the tool. The tool body part 2 is located between the rear coupling part and the longitudinal front part. In the front part, there are formed insert seats, or pockets, in which first and second cutting inserts 5, 5′ can be mounted by screws through a center hole in each of the inserts. Alternatively, the inserts can be arranged in the seats by top clamps, which press against a top surface of each of the inserts. The top surface is a rake face, i.e. a surface against which chips during metal cutting are pressed against. Opposite the top surface is a bottom surface, which is in contact with the insert seat. A hole for a screw has openings in the top surface and the bottom surface. The top surface and the bottom surface of each cutting insert 5, 5′ are connected by side surfaces, at least one of which during metal cutting is a clearance surfaces. Each cutting insert 5, 5′ has cutting edges 6, 6′, 7, 7′, 8, 8′ connecting the top surface and the side surfaces. Each insert has a parallelogram shape in a top view, i.e. with the rake face against the viewer. Opposite acute corners of the parallelogram are 35 degrees, which is within a preferred range of 20-45 degrees. Opposite obtuse corners are 145 degrees. At the acute corners of the parallelogram shaped cutting inserts 5, 5′ there are formed corner cutting edges 8, 8′. The corner cutting edges 8, 8′ are the part of the tool which first cuts chips from the work piece. The corner cutting edges 8, 8′ are longitudinal front end points or longitudinal front end portions of the tool, where the tool center axis A2 is a longitudinal axis, and the rear coupling part 3 comprise a longitudinal rear end.

[0029] The top surfaces of the first and the second inserts 5, 5′ are located in different planes, i.e. not in a common plane. The first and the second cutting inserts 5, 5′ are located, i.e. mounted, upside down relative to each other, when the rotatable tool 1 is viewed with the front against the viewer, as can be seen in FIG. 3. The first and the second cutting inserts 5, 5′ are located on opposite sides of the tool center axis A2. When the tool 1 is rotated 180 degrees around the tool center axis A2, the first cutting insert 5 is at the starting position of the second cutting insert 5′, and vice versa.

[0030] The rotatable tool 1 is suitable to be rotatable around a tool center axis A2 thereof in one way, or in one rotational direction only. That direction is such that the top surface of each cutting insert 5, 5′ is moving in front of the bottom surface of that cutting insert.

[0031] The rotatable tool comprise radial positioning means 30-42 such that at least one of the first radially outer cutting edge 6 and second radially inner cutting edge 7′ can be positioned on at least two different radial distances from the tool center axis A2. These radial positioning means are shown in FIG. 4, the rotatable tool 1 comprises slides 30 which are attachable to the tool body part 2 by fixation means in the form of screws 40, which can be attached in threaded holes 37 in the tool body part 2, whereby the screws penetrate through holes 39 in the slides. The through holes 39 are elongated in such a way that a screw 40 which penetrate a screw hole 39 can be attached in two separate threaded holes 37. In such way two different radial positions, i.e. radial distances from the tool center axis A2, of the slide 30, are possible. By this, the tool 1 can be used for machining circular grooves of a wider diameter range. Each slide 30 comprise a rear elongated ridge 38, arranged to be located in a corresponding elongated groove 33 in the tool body part 2, and an opposite front attachment surface 41. Each attachment surface 41 is formed to hold a cutting head 31. The cutting head 31 has an insert seat where a cutting insert 5, 5′ is or can be clamped, e.g. by means of a screw or a clamp. Adjoining the seat is a curved support 44, which is curved in a way such that there is enough clearance when cutting, while at the same time support the insert 5, 5′. The cutting head 31 further comprise an attachment surface arranged to be mounted, i.e. firmly connected, to the attachment surface 41 of the tool body part 2, by attachment means in the form of screws 42, which penetrate through holes 43 in the cutting head 31. The two cutting heads 31 which are part of the rotatable tool 1 are different in shape. More specifically, the insert seats which are suitable for the cutting inserts 5, 5′ are different in such a way that the cutting inserts 5, 5′ when mounted have their respective radially outer cutting edges 6, 6′ at different angles. The cutting head 31 can be mounted on two different radial positions against the attachment surface 41. By this, the tool 1 can be used for machining circular grooves of a wider diameter range. The slide can be radially adjusted, i.e. set, in a step less manner, i.e. fine adjustment. This functionality is possible by an arrangement, where by turning an adjustment screw 34 which passes through a threaded through hole in a pull-pin 36, the slide 30 moves radially by a force applied from the pull-pin 36. During fine-adjustment, screws 40 shall be in an open position, i.e. in a position such that the slide 30 can move relative to the tool body part 2. After fine-adjustment, the screws 30 are tightened such that the slide 30 is firmly locked or attached to the tool body part 2.

[0032] In FIG. 5, it is shown that each of the inserts 5, 5′, which have a parallelogram shape, are located such that a radially outer cutting edge 6, 6′ and radially inner cutting edge 7, 7′ extends in a longitudinally forward direction, i.e. towards the metal work piece 20 or away from the rear coupling portion 3, and are connected by a corner cutting edge 8, 8′. Each radially inner cutting edge 7, 7′ is located between a radially outer cutting edge 6, 6′ of the same insert 5, 5′ and the tool center axis A1. The first radially outer cutting edge 6, part of the first cutting insert 5, forms an first outer edge angle α with the tool center axis A2. The first radially inner cutting edge 7, part of the first cutting insert 5, forms a first inner edge angle β with the tool center axis A2. The angles α and β are measured or determined as in FIG. 5: the rotating tool 1 is arranged perpendicular to a viewing direction such that the first and second cutting inserts 5, 5′ are at a largest distance from each other, when the viewer observes the rotating tool 1. Then, the rotating tool 1 is projected on a plane which comprises the tool center axis A2. Then, the angles α and β are measured or determined. In a corresponding way, the radially outer cutting edge 6′ of the second cutting insert 5′ forms an second outer edge angle α′ with the tool center axis A2, and the inner cutting edge 6′ of the second cutting insert 5′ forms a second inner edge angle β′ with the tool center axis A2. The radially outer cutting edges 6, 6′ of the first and second cutting inserts 5, 5′ converge away from the rear coupling part 3 at an area or point located at a distance from the tool center axis A2, the area or point being closer to the corner cutting edge 8′ of the second cutting insert 5′ than the corner cutting edge 8 of the first cutting insert 5. The first outer edge angle α is larger than the second outer edge angle α′, and the second inner edge angle β′ is larger than the first inner edge angle R. In this way, only one cutting edge, i.e. the radially outer cutting edge 6 of the first cutting insert 5, will generate or cut the final shape of the outer wall surface 23 of the circular groove 21. In a corresponding way, only one cutting edge, i.e. the second radially inner cutting edge 7′, part of the second cutting insert 5′, will generate or cut the final shape of the inner wall surface 22 of the circular groove 21. By this, any dimensional tolerances or imperfections in the rotating tool 1 including the cutting inserts 5, 5′ will be reduced. A further benefit is that the same sets of inserts, e.g. two inserts with 35 degree nose angle, can be used for machining or cutting finishing circular grooves of different outer and inner wall angles δ, γ. The nose angle of the inserts 5, 5′ in FIGS. 1-5, i.e. the angle between radially outer 6, 6′ and radially inner 7, 7′ cutting edges is 35 degrees, a common ISO turning insert designation being VBMT.

[0033] In FIG. 5, the metal work piece 20 is shown. It show how the circular groove 21 is formed in the work piece after a machining operation, i.e. metal cutting. The circular groove 21 has a groove center axis A1. The circular groove is formed in, and has an opening in, a surface 25 of the work piece 20 which is perpendicular, at least in an area adjacent the circular groove 25, to a groove center axis A1. The circular groove is tapered in such a way that it is widest at the opening and has a most narrow portion thereof at a bottom surface 24. The bottom surface 24 is located perpendicular to the groove center axis A1. The circular groove 21 has a depth H, which is the distance from the bottom surface 24 to the opening, i.e. the surface 25, measured parallel to the groove center axis A1. The circular groove 21 has a width of the opening F, and a width of the bottom surface C, both distances measured perpendicular to the groove center axis. The width of the opening F is larger than the width of the bottom surface C. Preferably, F is within the range 5-18 mm. Preferably, H is within the range 3-9 mm. Preferably, C is within the range 1.5-11 mm. Preferably, 1.6<F/C<2.8. Preferably, 1.4<F/H<2.2. Preferably, 0.7<H/C<2.0. The circular groove 21 has an inner wall surface 22, which forms an inner wall angle δ with the groove center axis A1. The circular groove 21 has an outer wall surface 23, which forms an outer wall angle γ with the groove center axis A1. The inner wall surface 22 is located between the outer wall surface 23 and the groove center axis A1.

[0034] When producing or making a finished circular groove by machining or cutting, the rear coupling part 3 of the rotatable tool 1 is clamped in a machine tool spindle. It rotates around the tool center axis A2 thereof, i.e. a first rotation. Preferably, the number of revolutions per minute is above 60. Preferably, the number of revolutions per minute is less than 1000. The tool center axis is set parallel and at a distance X from the groove center axis A1, i.e. a center axis A1 of a circular groove 21 which is to be produced. The tool center axis A2, and hence the rotatable tool 1, is rotated around the groove center axis A1. This second rotation is preferably in an opposite direction to the rotational direction of which the rotating tool 1 rotates around the tool center axis A2 thereof. The benefit of this is a longer tool-life. Preferably this second rotation is of a lower number of revolutions per minute than the number of revolutions per minute of the first rotation. Even more preferably, this second rotation has a number of rotations per minute which is between 1/20 to 1/200 of the value of the first rotation. In other words, when the rotatable tool 1 has rotated between 20 and 200 revolutions around the tool center axis A2 thereof, the tool center axis A2 has rotated 1 revolution around the groove center axis A1. Both rotations are preferably of a constant value at least during the part of the operation in which the cutting inserts 5, 5′ are in cut. The rotatable tool 1 has a movement towards the work piece 20 in a longitudinal direction, i.e. a longitudinal feed. This longitudinal feed is preferably at a constant rate. As the corner cutting edges 8, 8′ reaches the surface 25 of the work piece 20, the formation of the circular groove 21 starts, i.e. the cutting inserts 5, 5′ go into cut, and chips from the work piece 20 are removed. The movement in the longitudinal direction, i.e. the longitudinal feed, stops when at least one of the corner cutting edges 8, 8′ reaches the bottom surface 24 of the circular groove 21. From the point where at least one of the corner cutting edges 8, 8′ go into cut, i.e. enters the work piece, until at least one of the corner cutting edges 8, 8′ reaches the bottom surface 24 of the circular groove 21, the distance X is gradually reduced. With this method, chip thickness is reduced. This gives the possibility of increased cutting data, e.g. cutting speed, which reduces the cutting time. All motions are relative motions between the rotatable tool 1 and the metal work piece 20. Preferably, the metal work piece 20 is still, i.e. does not move, during the machining operation or cutting. Described in a different way, a distance L is a longitudinal distance, i.e. parallel to the groove center axis A1 and the tool center axis A2, from the bottom surface 24 of the circular groove 21 to the corner cutting edges 8, 8′, or to the one of the cutting edges 8, 8′ which is closest to the bottom surface 24. When L is equal to H, the cutting starts. When L is equal to zero, the cutting stops. Then the rotatable tool 1 is retracted, i.e. moved in a direction away from the bottom surface 24 of the circular groove 21, preferably in a longitudinally rearward direction parallel to the groove center axis A1.

[0035] Each cutting insert 5, 5′ have a nose angle, i.e. α+β or α′+β′, which is smaller than groove angle, i.e. δ+γ. In this way, the same set of inserts can be used for grooves having a wide range of groove angles. Also, the bottom surface 24 of the circular groove 21 has a different shape than the corner cutting edges 8, 8′. Hence, the rotatable tool 1 do not have cutting inserts 5, 5′ that have an corresponding shape to the circular groove 21 to be machined or cut.

[0036] Preferably the corner cutting edges 8, 8′ are longitudinally spaced apart by less than 2 mm, even more preferably by less than 0, 5 mm. They do not have to be longitudinally spaced apart. Preferably the distance P, which is the distance from the tool center axis A2 to the corner cutting edge 8 of the first cutting insert 5, and P′, which is the distance from the tool center axis A2 to the corner cutting edge 8′ of the second cutting insert 5′, are so related that P is greater than or equal to P′. P may be equal to P′. P is preferably less than 1 mm longer than P′.

[0037] The radially outer and radially inner cutting edges 6, 6′, 7, 7′ have a length of preferably 2-30 mm, even more preferably 4-12 mm. The rotatable tool 1 has clearance between the cutting inserts 5, 5′, in other words, there is no material of the rotatable tool 1 between the radially inner cutting edges 7, 7′.