RU2795861C2 - Cutting head containing end part with radially oriented front cutting edges with negative and positive rake angles, and rotating cutting tool - Google Patents

Abstract

FIELD: cutting heads.

SUBSTANCE: invention relates to a cutting head and to a rotary cutting tool with such a cutting head for use in metal cutting in general and drilling in particular. The cutting head (20) is rotatable about the first axis (A1) in the direction of rotation (DR) and includes an intermediate part (22) and an end part (24). The intermediate part contains a number of front edges (28) that define the cutting diameter (DC), and the end part contains an extreme front end point (NT) in the axial direction and a number of front surfaces (30) with external (32) and internal cutting edges (34). The outer front surface (40) adjacent to each outer cutting edge has a positive outer rake angle, and the inner front surface (42) adjacent to each inner cutting edge has a negative inner rake angle. Each outer front surface is located in the groove (44) of the head, crossing one of the leading edges, and each inner front surface is located in the cavity (46), crossing one of the grooves of the head. Each root extends to an end point (NP) of the cavity trajectory located on the first distance axially backward from the end point, while the first distance exceeds thirty percent of the cutting diameter.

EFFECT: efficient chip removal is ensured.

20 cl, 10 dwg

Description

The field of technology to which the invention belongs

The present invention relates to a cutting head comprising an end portion with radially oriented cutting edges, and to a rotary cutting tool with such a cutting head, for use in metal cutting in general and drilling in particular.

State of the art

Cutting tools used for drilling use various cutting heads with cutting edges designed to accommodate increased wear of the radially outer parts due to relatively high cutting speeds and/or reduced tool life of the radially located inner parts due to relatively high cutting forces.

US 8,801,344 discloses a drill having at least one major cutting edge and at least one central cutting edge, wherein the drill has a longitudinal axis, and wherein at least one major and at least one central cutting edges have a rake surface. The drill is characterized in that the front surface of at least one central cutting edge contains at least two faces perpendicular to the longitudinal axis of the drill and forming an obtuse angle with each other, that is, at least one central cutting edge contains at least two parts of the cutting edge .

WO 2018/075921 A1 discloses a drill comprising a plurality of bands extending towards the cutting edge, adjacent bands being separated by grooves whose basic contour is included in a common helical configuration along the central axis of the drill body. The drill also contains a plurality of contour tips, each of which has a linear part extending towards the outer diameter of the drill, and an arcuate part extending from the linear part towards the drill bit. The drill also contains a plurality of cavity contours located within the plurality of grooves. The contours of the valleys extend from the cutter of the drill body and are inclined towards the base contours of the flutes.

Patent document WO 2018/079489 A1 discloses a cutting tool with a rod-shaped body, a cutting blade located at the first end of the body, and a groove extending in a spiral from the cutting blade towards the second end of the body. The cutting blade includes a first blade that intersects with the axis of rotation when viewed from the front, and a second blade extending from the first blade to the outer peripheral surface of the body. The groove comprises a first constriction section positioned so that it is connected to the first blade, and a second constriction section positioned so that it is connected to the second blade. The taper angle of the first taper section is less than the taper angle of the second taper section.

It is an object of the present invention to provide an improved cutting head with radial outer cutting edges of increased wear resistance and radial inner cutting edges of increased durability and strength.

It is a further object of the present invention to provide an improved cutting head having cavities adjacent to the radial inner cutting edges for effective chip evacuation.

It is a further object of the present invention to provide an improved cutting head capable of operating at high feed rates.

It is a further object of the present invention to provide an improved rotary cutting tool in which the cutting head is removably mounted on a shank.

Disclosure of invention

The present invention provides a cutting head rotatable about a first axis in the direction of rotation and comprising:

an intermediate part containing an integer number N, N ≥ 2 peripheral surfaces spaced from each other along the circumference, and each peripheral surface contains a leading edge, and a plurality of leading edges define the cutting diameter; And

an end part containing an extreme front end point on the first axis and N frontal surfaces, each frontal surface containing a radially oriented frontal cutting edge containing an outer cutting edge extending radially inward from one of the front edges, and an inner cutting edge extending radially inward from said outer cutting edge, each inner cutting edge abutting its associated outer cutting edge at the transition point of the cutting edge,

wherein:

in a cross section taken in a first vertical plane parallel to the first axis and intersecting any of the outer cutting edges, the outer front surface adjacent to said outer cutting edge is inclined at a positive outer rake angle; And

in a cross section taken in a second vertical plane parallel to the first axis and intersecting any of the inner cutting edges, the inner front surface adjacent to said inner cutting edge is inclined at a negative inner rake angle,

wherein:

each outer front surface is located in the head groove extending axially rearward from the end portion and intersecting one of the leading edges; And

each inner front surface is located in a cavity extending axially rearward from the end portion and intersecting one of the grooves of the head,

and in which:

each depression has a trajectory defined by a plurality of vertices of the cone of depressions from a series of sections taken in planes perpendicular to the first axis and intersecting the depression along its axial extent;

each trough path extends to an end point of the trough path located a first distance axially backward from the end point; And

the first distance exceeds thirty percent of the cutting diameter.

In addition, the present invention provides a rotary cutting tool comprising the above-described cutting head and a shank having a longitudinal axis and N shank grooves alternating circumferentially with N belts.

Brief description of the drawings

To improve understanding, the invention will be described below by way of example with reference to the accompanying figures, in which the dotted lines show the cut-off boundaries of the individually depicted fragments, and which show:

Figure 1: perspective view of a cutting head according to the present invention.

Figure 2 is a side view of the cutting head shown in FIG. 1.

Figure 3: top view of the cutting head shown in FIG. 1.

Figure 4: Cross section of the cutting head shown in FIG. 3 taken along the line IV-IV.

Figure 5: Cross section of the cutting head shown in FIG. 3 taken along the line V-V.

Figure 6: Cross section of the cutting head shown in FIG. 2 taken along the line VI-VI.

Figure 7: Cross section of the cutting head shown in FIG. 2 taken along line VII-VII.

Figure 8: Cross section of the cutting head shown in FIG. 3 taken along line VIII-VIII.

Figure 9: perspective view of a rotary cutting tool according to the present invention.

Figure 10 is an exploded view of the rotary cutting tool shown in FIG. 9.

Implementation of the invention

Let us first consider Fig. 1-3, which show a cutting head 20 which may be made by pressing and sintering a hard metal such as tungsten carbide and may or may not be coated.

According to the present invention, the cutting head 20 is rotatable about the first axis A1 in the direction of rotation DR and includes an intermediate part 22 and an end part 24.

As shown in FIG. 1-3, the intermediate portion 22 includes a plurality of peripheral surfaces 26 circumferentially spaced apart by a distance N. Each peripheral surface 26 includes a leading edge 28, and the plurality of leading edges 28 define a cutting diameter DC.

In some embodiments of the present invention, each leading edge 28 may be oriented in a direction opposite to the direction of rotation DR as it extends axially rearward from the end portion 24.

In addition, in some embodiments, implementation of the present invention, each leading edge 28 may be oriented in a spiral along the first axis A1.

As shown in FIG. 1-3, end portion 24 comprises an axially frontmost end point NT on a first axis A1 and a plurality of N front surfaces 30, each front surface 30 having a radially oriented front cutting edge 31 comprising an outer cutting edge 32 extending radially inward. from one of the leading edges 28, and an inner cutting edge 34 extending radially inward from said outer cutting edge 32.

Each front surface 30 further comprises a back surface 36 adjacent to its associated outer and inner cutting edges 32, 34, and each inner cutting edge 34 adjacent to its associated outer cutting edge 32 at a cutting edge transition point NR. As described below, the outer cutting edge 32 is associated with a positive rake angle and the inner cutting edge 34 is associated with a negative rake angle. Thus, the cutting edge transition point NR corresponds to a point on the front cutting edge 31 at which the rake angle changes from positive to negative when moving along the front cutting edge 31 in a radially inward direction towards the extreme end point NT.

As shown in FIG. 3, a plurality of cutting edge transition points NR define an imaginary first circle C1 with a first diameter D1.

In some embodiments of the present invention, the first diameter D1 may exceed thirty percent of the cutting diameter DC, ie D1 > 0.30*DC.

As shown in FIG. 1-3, the end portion 24 may also include N cutter edges 38, each of which is formed by two adjacent back surfaces 36 and extends radially from the end point NT to one of the inner cutting edges 34.

Throughout the specification and claims, N is understood to be an integer equal to at least two, i.e. N ≥ 2.

In some embodiments, implementation of the present invention, the cutting head 20 may have N-fold rotational symmetry about the first axis A1.

In addition, in some embodiments of the present invention, N may be 3, the intermediate portion 22 may include three leading edges 28, and the end portion 24 may include three outer cutting edges 32 and three inner cutting edges 34.

The presence of three outer cutting edges 32 and three inner cutting edges 34 allows the cutting head 20 to operate at high feed rates.

As shown in FIG. 4, in cross section taken in a first vertical plane PV1 parallel to the first axis A1 and intersecting any of the outer cutting edges 32, the outer rake surface 40 adjacent to said outer cutting edge 32 is inclined at a positive outer rake angle α1.

By "vertical plane" in this description is meant any plane parallel to the first axis A1, but not necessarily including the first axis A1.

Throughout the specification and claims, "rake angle" refers to the acute angle formed between the front surface and an imaginary reference line parallel to the first axis A1.

It should also be appreciated that the outer cutting edges 32 are subject to more wear than the inner cutting edges 34 due to their relatively higher cutting speeds, and that the positive external rake angle α1 reduces wear on the outer cutting edges 32, thereby extending their life.

As shown in FIG. 3, a plurality of outer front surfaces 40 face the direction of rotation DR.

In some embodiments of the present invention, in a cross section taken in any plane parallel to the first axis A1 and intersecting any of the outer cutting edges 32, the outer rake surface 40 adjacent to said outer cutting edge 32 may be inclined at a positive outer rake angle α1 .

In addition, in some embodiments of the present invention, in a cross section taken in the first vertical plane PV1, the positive external rake angle A1 may have a value of more than 5 degrees, while in other embodiments, the positive external rake angle α1 may have a value of more than 10 degrees.

As shown in FIG. 4, in cross section taken in the first vertical plane PV1, the rear surface 36 is inclined at a positive external relief angle β1.

Throughout the description and claims, "back angle" refers to the acute angle formed between the back surface and an imaginary reference line perpendicular to the first axis A1.

As shown in FIG. 5, in cross section taken in a second vertical plane PV2 parallel to the first axis A1 and intersecting any of the inner cutting edges 34, the inner rake surface 42 adjacent to said inner cutting edge 34 is inclined at a negative inner rake angle α2.

It should be noted that the inner cutting edges 34 are subject to more impact forces than the outer cutting edges 32 due to relatively low cutting speeds, especially at high feed rates, and that a negative internal rake angle α2 increases the tool life and strength of the inner cutting edge 34, prolonging the most of its service life.

As shown in FIG. 3, a plurality of inner front surfaces 42 face in the direction of rotation DR.

In some embodiments of the present invention, in a cross section taken in any plane parallel to the first axis A1 and intersecting any of the inner cutting edges 34, the inner rake surface 42 adjacent to said inner cutting edge 34 may be inclined at a negative internal rake angle α2 .

In addition, in some embodiments of the present invention, in a cross section taken in the second vertical plane PV2, the negative internal rake angle α2 may exceed 5 degrees.

As shown in FIG. 5, in cross section taken in the second vertical plane PV2, the rear surface 36 is inclined at a positive internal relief angle β2.

In some embodiments, implementation of the present invention, the internal relief angle β2 may exceed the external relief angle β1, that is, β2>β1.

In addition, in some embodiments of the present invention, the internal relief angle β2 may continuously increase when measured in a number of parallel cross sections taken in parallel vertical planes gradually approaching the first axis A1.

Gradually increasing the internal relief angle β2 radially inwards reduces the high cutting and impact forces typically associated with very low cutting speeds and acting towards the center of the cutting head.

As shown in FIG. 1-3, each outer front surface 40 is located in a head groove 44 extending axially rearward from the end portion 24 and intersecting one of the leading edges 28, and each inner front surface 42 is located in a recess 46 extending axially rearward from the end portion. part 24 and crossing one of the grooves 44 of the head.

In addition, as shown in FIG. 1-3, each trough 46 has a trough path GP defined by a plurality of trough cone vertices from a series of parallel sections taken in parallel planes, each perpendicular to the first axis A1 and intersecting the trough 46 along its axial extent.

Throughout the description and claims, for each cross-section taken in a plane perpendicular to the first axis A1 and intersecting cavity 46, the associated vertex of the cone of depressions is located at the center of the segment of the associated profile of minimum radius, and the minimum radius is +0.20 / -0.00 mm.

According to the present invention, as shown in FIG. 2, each root path GP extends to a root path end point NP located at a first distance d1 axially backward from the end point PT, the first distance d1 being greater than thirty percent of the cutting diameter DC, that is, d1 > 0.30*DC.

Increasing the axial length of each root path GP, due to the fact that the first distance d1 exceeds thirty percent of the cutting diameter DC, advantageously contributes to an increase in the root volume and efficient chip removal.

In some embodiments of the present invention, the first distance d1 may exceed forty percent of the cutting diameter DC, that is, d1 > 0.40*DC.

Furthermore, in some embodiments of the present invention, each trough path GP may extend in a direction opposite to the direction of rotation DR, i.e. axially backward from the end portion 24.

In addition, in some embodiments of the present invention, each root path end point NP may be located radially farther from the first axis A1 than any of the cutting edge transition points NR.

Positioning each end point NP of the root path at the maximum radial distance from the transition points NR of the cutting edge improves chip evacuation along the root 46.

As shown in FIG. 6, in cross section taken in a first horizontal plane PH1 perpendicular to the first axis A1 and intersecting a plurality of internal cutting edges 34, each trough 46 may have a concave first profile P1.

In some embodiments, implementation of the present invention, each first profile P1 may have a continuous curvature.

The continuous curvature of each first profile P1 improves chip evacuation in the respective cavity area.

As shown in FIG. 6, the first profile P1 has a minimum first radius R1 measured along the first profile segment S1, the first profile segment S1 containing the first vertex NA1 of the trough cone.

In some embodiments of the present invention, the minimum first radius R1 may exceed six percent of the cutting diameter DC, ie R1 > 0.06*DC.

The minimum first radius R1 of each first profile P1 greater than six percent of the cutting diameter DC promotes smooth chip movement in the cavity 46 and reduces the risk of chip jamming.

In addition, the minimum first radius R1 of each first profile P1 exceeding six percent of the cutting diameter DC increases the core strength of the end portion 24.

In some embodiments of the present invention, the minimum first radius R1 may preferably exceed eight percent of the cutting diameter DC, ie R1 > 0.08*DC.

In addition, in some embodiments of the present invention, the minimum first radius R1 may be less than fifteen percent of the cutting diameter DC, ie R1<0.15*DC.

As shown in FIG. 6, each first profile P1 may have a radially inward first point NI1 located on its first segment S1.

In some embodiments, implementation of the present invention, the first segment S1 may form an angle of more than 15 degrees at the first center point E1 of the minimum first radius R1.

The location of the extreme radially inner first point NI1 of each first profile P1 in the first section S1 allows you to more efficiently arrange a plurality of depressions 46 around the circumference, that is, to obtain a cutting head configuration in which N exceeds 2, that is, N > 2.

As shown in FIG. 7, in cross section taken in a second horizontal plane PH2 perpendicular to the first axis A1 and intersecting a plurality of leading edges 28, each trough 46 may have a concave second profile P2.

In some embodiments of the present invention, every second profile P2 may have a continuous curvature.

The continuous curvature of every second P2 profile improves chip evacuation in the corresponding root area.

As shown in FIG. 7, the second profile P2 has a minimum second radius R2 measured along the second profile segment S2, the second profile segment S2 containing the second vertex NA2 of the trough cone.

In some embodiments of the present invention, the minimum second radius R2 may be greater than six percent of the cutting diameter DC, ie R2 > 0.06*DC.

The minimum second radius R2 of each second profile P2, which is greater than six percent of the cutting diameter DC, promotes smooth chip movement in the cavity 46 and reduces the risk of chip jamming.

In some embodiments of the present invention, the minimum second radius R2 may preferably exceed eight percent of the cutting diameter DC, ie R2 > 0.08*DC.

Furthermore, in some embodiments of the present invention, the minimum second radius R2 may be less than fifteen percent of the cutting diameter DC, ie R2<0.15*DC.

The minimum second radius R2 can be from eighty-five to one hundred and fifteen percent of the minimum first radius R1, i.e. 0.85*R1 < R2<1.15*R1.

As shown in FIG. 7, each second profile P2 may have a radially innermost point NI2 located on its second segment S2.

In some embodiments, implementation of the present invention, the second segment S2 may form an angle of more than 15 degrees at the second center point E2 of the minimum second radius R2.

The location of the radially innermost point NI2 of each second profile P2 on the second segment S2 makes it possible to more effectively distribute the plurality of depressions 46 around the circumference, i.e. to obtain configurations of cutting heads in which N is greater than 2, i.e. N > 2.

In embodiments of the present invention in which N is 3, as shown in FIG. 6 and 7, the first profile P1 may form a chase curve with the first start point NS1 located in the circumferential direction ahead of the first end point NE1, and the second profile P2 may form a chase curve with the second start point NS2 located in the circumferential direction ahead of the second end point NE2. .

The term "pursuit curve" in the description and formula refers to the shape of the curve described in https://en.wikipedia.org/wiki/Pursuit_curve as of July 2, 2019, i.e. the curve tracked by the pursuer while pursuing the target, while the target moves in a straight line and always tangent to the pursuer.

As shown in FIG. 1, the head groove 44 and its associated cavity 46 intersect along the cavity-groove boundary line GFB. As shown in FIG. 7, in cross-section taken in a third horizontal plane PH3 perpendicular to the first axis A1 and intersecting a plurality of leading edges 28, each pit 46 intersects its associated head groove 44 at the pit and groove intersection point IG, the pit and groove boundary GFB comprising a plurality of such points IG of the intersection of the depression and the groove in various similar horizontal planes.

In some embodiments of the present invention, each such trough-groove intersection point IG, with the exception of the associated cutting edge transition point NR itself, may be located in the circumferential direction in front of its cutting edge transition point NR.

In addition, in some embodiments of the present invention, the second and third horizontal planes PH2, PH3 may coincide.

As shown in FIG. 8, in cross section taken in the third vertical plane PV3 containing the first axis A1 and intersecting the rear surface 36, the rear surface 36 may have a concave rear profile PC.

In some embodiments of the present invention, each concave relief profile PC may have a relief radius PC in the range of fifty to one hundred and fifty percent of the cutting diameter DC, i.e., 0.50*DC < PC < 1.50*DC.

In addition, in some embodiments of the present invention, each concave rear profile PC may have a continuous curvature and smoothly extend towards the first axis A1.

Next, consider Fig. 9 and 10, which show a rotary cutting tool 48 according to the present invention, containing a cutting head 20 and a shank 50 with a longitudinal axis L.

The shank 50 comprises N shank grooves 52 alternating in the circumferential direction with N collars 54, each shank groove 52 being able to extend helically along the longitudinal axis L.

As shown in FIG. 9 and 10, the cutting head 20 may have a bottom surface 56 facing back in the axial direction, the shank 50 may have a bearing surface 58 perpendicular to the longitudinal axis L, and the cutting head 20 may be removably mounted on the shank 50 so that the bottom surface 56 was in contact with support surface 58.

The embodiment in which the cutting head 20 is removably mounted on the shank 50 allows the cutting head 20 to be made from a fairly hard material, such as tungsten carbide, and the shank 50 from a less hard and less expensive material, such as high speed steel. Shank 50 can be reused after disposal of a worn or damaged cutting head 20.

In some embodiments, implementation of the present invention, each groove 44 of the head can intersect the bottom surface 56 and interact with one of the grooves 52 of the shank.

In addition, in some embodiments of the present invention, the bottom surface 56 may be perpendicular to the first axis A1, the bearing surface 58 may be perpendicular to the longitudinal axis L, and the first axis A1 may be coaxial with the longitudinal axis L.

As shown in FIG. 2, the bottom surface 56 is a second distance d2 axially backward from the end point PT, and the first distance d1 may be greater than seventy percent of the second distance d2, i.e., d1 > 0.70*d2.

In some embodiments, implementation of the present invention, the cutting head 20 may include a mounting ledge 60 extending axially rearward from the bottom surface 56.

In other embodiments of the present invention (not shown in the figures), the cutting head 20 and shank 50 may be of a one-piece design, and each head groove 44 may merge with one of the shank grooves 52.

As shown in FIG. 9-10, the intermediate portion 22 of the cutting head 20 may comprise N torque transmission surfaces 62 facing in the direction of rotation DR, the shank 50 may comprise N drive protrusions 64, with each drive protrusion 64 comprising a drive surface 66 facing in the direction of rotation DR, and each torque transmission surface 62 may be in contact with one of the drive surfaces 66.

In some embodiments of the present invention, the first distance d1 may be less than ninety percent of the second distance d2, i.e. d1<0.90*d2.

In embodiments of the present invention in which N is 3, a first distance d1 less than ninety percent of the second distance d2 provides sufficient space for the plurality of actuating lugs 64 to engage with the cutting head 20 without interfering with the smooth movement of the chips between the troughs 46 and the flutes 52 of the shank.

In some embodiments of the present invention, each torque transmission surface 62 may intersect one of the peripheral surfaces 26.

In embodiments of the present invention in which N is 3, as shown in FIG. 1-3, each trough 46 may intersect one of the torque transmission surfaces 62 at the radially extreme point NO of the trough.

In some embodiments of the present invention, as shown in FIG. 3, the three radially extreme points NO of the valley can define an imaginary second circle C2 with a second diameter D2 greater than seventy percent of the cutting diameter DC, that is, D2 > 0.70*DC.

The option in which the imaginary second circle C2 has a second diameter D2 greater than seventy percent of the cutting diameter DC contributes to an increase in the volume of the cavity and efficient chip removal.

Although the present invention has been described in some detail, various changes and modifications can be made without departing from the spirit or scope of the invention as set forth in the following claims.

Claims (49)

1. Cutting head (20) rotatable about the first axis (A1) in the direction (DR) of rotation and containing: an intermediate part (22) containing an integer number N, N≥2 peripheral surfaces (26) spaced from each other along the circumference, and each peripheral surface (26) contains a leading edge (28), and a plurality of leading edges (28) determine the diameter (DC) cutting; And an end part (24) containing an axially frontmost end point (NT) on the first axis (A1) and N frontal surfaces (30), each frontal surface (30) containing a radially extending frontal cutting edge (31) containing an outer a cutting edge (32) extending radially inward from one of the front edges (28), and an inner cutting edge (34) extending radially inward from said outer cutting edge (32), with each inner cutting edge (34) adjacent to an associated its outer cutting edge (32) at the point (NR) of the transition of the cutting edge, and: in a cross section taken in the first vertical plane (PV1) parallel to the first axis (A1) and intersecting any of the outer cutting edges (32), the outer front surface (40) adjacent to said outer cutting edge (32) is inclined under the positive outer rake angle (α1); And in a cross section taken in the second vertical plane (PV2) parallel to the first axis (A1) and intersecting any of the inner cutting edges (34), the inner front surface (42) adjacent to said inner cutting edge (34) is inclined under the negative internal rake angle (α2), and: each outer front surface (40) is located in a head groove (44) extending axially backward from the end portion (24) and intersecting one of the front edges (28); And each inner front surface (42) is located in a cavity (46) extending axially backwards from the end part (24) and crossing one of the grooves (44) of the head, and moreover: each trough (46) has a trough path (GP) defined by a plurality of trough vertex points from a series of sections taken in planes perpendicular to the first axis (A1) and intersecting the trough (46) along its axial extent; each valley path (GP) extends to an end point (NP) of the valley path located a first distance (d1) axially backward from the end point (PT); And the first distance (d1) exceeds thirty percent of the cutting diameter (DC). 2. The cutting head (20) according to claim. 1, in which in the cross section, taken in the first horizontal plane (PH1), perpendicular to the first axis (A1) and crossing a plurality of internal cutting edges (34), each cavity (46) has a concave the first profile (P1); the first profile (P1) has a minimum first radius (R1) measured along the first segment (S1) of the profile, the first segment (S1) containing the first top point (NA1) of the valley; And the minimum first radius (R1) is greater than six percent of the cutting diameter (DC). 3. The cutting head (20) according to claim 2, wherein each first profile (P1) has an outermost radially inward first point (NI1) located on its first segment (S1). 4. The cutting head (20) according to claim 2, wherein each first profile (P1) has a continuous curvature. 5. The cutting head (20) according to claim. 1, in which in the cross section, taken in the second horizontal plane (PH2), perpendicular to the first axis (A1) and crossing a plurality of leading edges (28), each cavity (46) has concave second profile (P2); the second profile (P2) has a minimum second radius (R2) measured along the second segment (S2) of the profile, the second segment (S2) containing the second top point (NA2) of the valley; And the minimum second radius (R2) is greater than six percent of the cutting diameter (DC). 6. The cutting head (20) according to claim 5, in which each second profile (P2) has a radially innermost second point (NI2) located on its second segment (S2). 7. Cutting head (20) according to claim 5, wherein every second profile (P2) has a continuous curvature. 8. The cutting head (20) according to claim 1, in which, in a cross section taken in any vertical plane parallel to the first axis (A1) and intersecting any of the outer cutting edges (32), the outer front surface (40) adjacent to said outer cutting edge (32) is inclined at a positive external rake angle (α1). 9. The cutting head (20) according to claim 1, in which, in a cross section taken in any vertical plane parallel to the first axis (A1) and intersecting any of the inner cutting edges (34), the inner front surface (42) adjacent to said inner cutting edge (34) is inclined at a negative internal rake angle (α2). 10. The cutting head (20) according to claim 1, in which, in the cross section taken in the second vertical plane (PV2), the negative internal rake angle (α2) exceeds 5 degrees. 11. The cutting head (20) according to claim 1, in which each trajectory (GP) of the cavity runs in the direction opposite to the direction (DR) of rotation, that is, in the axial direction extends back from the end part (24). 12. The cutting head (20) of claim 1, wherein each end point (NP) of the root path is located radially farther from the first axis (A1) than any of the transition points (NR) of the cutting edge. 13. The cutting head (20) according to claim 1, in which each front surface (30) contains a rear surface (36) adjacent to its associated outer and inner cutting edges (32, 34); And in cross section taken in the third vertical plane (PV3) containing the first axis (A1) and intersecting the rear surface (36), the rear surface (36) has a concave rear profile (PC). 14. The cutting head (20) according to claim 13, wherein each concave rear profile (PC) has a continuous curvature and runs smoothly towards the first axis (A1). 15. The cutting head (20) according to claim 13, in which the end part (24) contains N edges (38) of the cutter; And each edge (38) of the cutter is formed by two adjacent back surfaces (36) and extends radially from the end point (NT) to one of the inner cutting edges (34). 16. The cutting head (20) according to claim 13, in which: in the cross section taken in the first vertical plane (PV1), the rear surface (36) is inclined at a positive external clearance angle (β1), in a cross section taken in the second vertical plane (PV2), the rear surface (36) is inclined at a positive internal clearance angle (β2), and the inner clearance angle (β2) is greater than the outer clearance angle (β1). 17. The cutting head (20) according to claim 16, in which: internal clearance angle (β2) continuously increases when measured in a series of parallel cross sections taken in parallel vertical planes gradually approaching the first axis (A1) 18. The cutting head (20) according to claim 1, wherein the plurality of cutting edge transition points (NR) define an imaginary first circle (C1) with a first diameter (D1), and the first diameter (D1) is greater than thirty percent of the cutting diameter (DC). 19. The cutting head (20) according to claim 1, wherein the cutting head (20) has N-fold rotational symmetry about the first axis (A1). 20. The cutting head (20) according to claim 1, in which N=3. 21. Rotating cutting tool (48), containing: cutting head (20) according to claim 1; And a shank (50) with a longitudinal axis (L) and N grooves (52) of the shank alternating in the circumferential direction with N bands (54). 22. Rotary cutting tool (48) according to claim 21, in which: the cutting head (20) contains a bottom surface (56), facing back in the axial direction; the shank (50) contains a bearing surface (58) perpendicular to the longitudinal axis (L), and the cutting head (20) is mounted with the possibility of removal on the shank (50) in such a way that the lower surface (56) is in contact with the bearing surface (58).

Images