MILLING TOOL

Abstract: The present invention relates to a tool for rotary chip removal machining. The tool comprises a cutting head (10), a retention means (11) and a shank (12). The cutting head (10) is provided with at least one cutting edge (27) which is integral with the cutting head. The cutting head and the retention means comprise overlapping asymmetrical means (15, 19) for mounting of the cutting head to the shank. The cutting head comprises two cutting edges (27), each major cutting edge (27) comprising a substantially straight edge (27A) and a convexly curved preferably part-circular edge (27B). The convex edge (27B) is provided radially outside the substantially straight edge (27A). The invention further relates to a cutting head for the tool.

Description: Milling tool Background of the invention The present invention relates to a milling tool for rotary chip removal machining and to a cutting head for the tool according to the preambles of the independent claims. Prior art It is previously known through applicants US-A-4,850,759 to provide a solution to the problem of providing milling tools in small dimensions with interchangeable cutting edges. However in some cases it has become apparent that during milling of profiles in tool steel the cutting velocity during upwards ramping is not especially high. This depends on that the maximum cutting depth during upwards ramping is relatively small in the known tool. It is furthermore known to provide end milling cutters with screwn, circular cutting inserts to be used inter alia during upwards ramping. Since the dimensions most often are small the hollow inserts become relatively weak, which has resulted in tool breakage. Objects of the invention One object of the present invention is to provide a tool, which solves the above- captioned problems. Another object of the present invention is to provide a tool, which combine the advantages of circular cutting inserts with favorable strength. Still another object of the present invention is to provide a tool, which easily cuts in the work piece. Still another object of the present invention is to provide a cutting head, which enables upwards ramping with a high cutting velocity. These and other objects of the present invention are realized by a tool and a cutting head of the above-mentioned type, which havev obtained the characteristics indicated in the appended claims. Short description of the figures Below an embodiment of the present invention is described with reference to the enclosed drawings, wherein Fig. 1 shows a tool according to the present invention in an assembled condition, partly in cross-section, in engagement with a work piece; Figs. 2A and 2B show side views of a cutting head according to the present invention, more in detail; Fig. 3 shows a cross section according to the line Ill-Ill in Fig. 2, and Fig. 4 shows a top view of the cutting head. Detailed description of the invention The embodiment of a tool according to the present invention shown in Fig. 1 , comprises a cutting head 10, a retention means in form of a locking screw 1 1 and a shank 12. The tool comprises hook-shaped means 1 5, 1 9 provided on the cutting head and on the locking screw. The cutting head 10 is provided with cutting edges at the end 1 3 facing away from the shank 12. A preferred shape of the cutting head 10 is shown in detail in Figs. 2A - 4. The cutting head 10 is performed in hard material, preferably cemented carbide and comprises two major cutting edges 27. The number of major cutting edges may alternatively be one to six. Each major cutting edge 27 comprises a straight edge 27A and a convex curved, preferably part-circular edge 27B and is formed along the intersection line of a clearance surface 28 and a chip surface 29. The major cutting edges 27A are straight and lie in a common, imaginary cylinder, which is concentric with the axis CL of rotation of the cutting head and of the tool. Alternatively, the cutting edges 27A may be arranged in an imaginary truncated cone, the apex of which faces the shank 12. The diametrical distance between the major cutting edges is depicted by C, which normally is in the magnitude of 6 - 16 mm. Each major cutting edge 27B connects to an associated straight edge 27A via a corner having a radius R1 , of maximum 1 mm. The major cutting edges 27B have a circular extension from the radius R1 to a plane P perpendicular to the center axis CL. Each major cutting edge 27B is defined by a radius R2, the center of which lies on a bisector B. The bisector is defined by an imaginary corner formed by the plane P and a line touching the radially outermost point of the major cutting edge 27B, said line being parallel to the rotational axis CL. A major portion of the major cutting edge 27B is provided above the bisector while a minor part thereof is provided below the bisector. The diametrical distance between the major cutting edges 27B is depicted by D and is some millimeters larger than the distance C. The convexly curved cutting edge 27B transforms into a minor cutting edge 30 in said plane P, with which said edge substantially coincides and extends radially inwards in. The radius R2 is less than one half of the diameter D, normally in the range of 1 - 6 mm. The minor cutting edge 30 forms an angle σ with the rotational axis CL which is 90° or some degree less to improve the cutting properties during milling. Each chip surface 29 is substantially concavely formed and extends from the major cutting edge 27 radially inwards and from the minor cutting edge 30 in direction axial ly inwardly away from the free end 13 of the cutting head. The chip surface 29 forms an acute angle α, of 60° to 80° with the clearance surface 28A, 28B. The minor cutting edge 30 is formed at the intersection of the chip flute 29 and a clearance bevel 31 and its radial extension commences radially inside the imaginary cylinder. The minor cutting edge 30 connects to a cross-cutting edge 40 which intersects the rotational axis CL of the cutting head such that the tool shall be able to drill into the work piece during milling. The length of the cross-cutting edge 40 is 0.5 - 1 .5 mm. Cut-out surfaces 41 are provided in line with the cross- cutting edge 40 in order to diminish the feed force during drilling. The clearance bevel 31 has a clearance angle β, of 10° to 20°, and is chosen preferably more acute than the clearance angle α of the major cutting edge to allow high feed during inwards ramping or drilling. The radial extension of the minor cutting edge 30 and the convex edge 27B can be described by an angle ε, Fig. 2B, which is 120° - 140°. It should be noted that by the term "ramping" is here meant milling with feed directions in all angles relative to the rotational axis CL which is not the conventional drilling direction. At the end facing towards the shank 12 the cutting head is provided with a first conical portion 14, which is provided with a first means for engagement 1 5, which in the shown embodiment comprises a first lip 16 as well as a first recess 1 7. The intermediate portion of the cutting head 10 is provided with a key grip 32, the application of which is explained below. The locking screw 1 1 , which preferably is performed in steel, has a second conical portion 18 at the end facing towards the cutting head, which is provided with a second means for engagement 19, which is intended to cooperate with the first the means for engagement 15. Such as shown in Fig. 1 the provision of the second means for engagement 19 implies that a substantial part of the second conical portion 18 has been removed. The second means for engagement 19 comprises a second lip 20 as well as a second recess 21 . In active position the first lip 16 cooperates with the second recess 21 and the second lip 20 with the first recess 1 7. Axially inside the second means for engagement 19, in the axial direction, the locking screw 1 1 has an externally threaded, preferably cylindrical portion 22. An Allen key grip can be provided at the axially innermost end of the locking screw 1 1 , whereby loosening or tightening of the locking screw 1 1 is made possible through the internal channel 24 of the shank 12. Normally however tightening or loosening of the locking screw is accomplished through the external key grip 32.

Claims: Alternatively the thread 26 may be arranged at an end of a releaseable sleeve, the other end of which then is provided with an external thread as well as a key grip. The shank 12 is provided with a conical seat 25 at the end facing towards the cutting head 10, which receives the first and second conical portions 14 and 18 of the cutting head 10 and the locking screw 1 1 , respectively. Inside the conical seat 25 the shank 12 has a substantially cylindrical, internally threaded portion 26, which cooperates with the external threaded portion 22 of the locking screw 1 1 . Mounting and dismounting of the tool is more closely described in US-A- 4,850,759, which hereby is incorporated into the present description. Cooperation between the external thread 22 and the internal thread 26 entails that the locking screw 1 1 and thereby also the cutting head 10 are displaced axially into in the shank 12 until the cone-shaped portion 14 comes into abutment against the conical seat 25, i.e. the position according to Fig. 1 has been achieved. The cutting head 10 is now anchored in the shank 12 in a satisfactorily manner. The threads 22 and 26 are performed as right-hand threads at tools for right-hand cutting and as left-hand threads at tools for left-hand cutting. For the above described embodiment the cone angle for the cutting head and seat should be less than 25°. In addition shall be pointed out that the described embodiment relates to milling cutters, i.e. tools which rotate about their longitudinal center axes. Milling cutters with small cutting portions are expected to be the domineering area of application for the present invention. From Fig. 1 is evident that if the milling tool shall ramp a shoulder in the work piece 42 the tool is brought against the shoulder in the direction of the arrow I during rotation such that the tool will cut itself into the position shown in Fig. 1 . Then the tool is fed while rotating, perpendicularly outwards from the work piece in the direction of the arrow O and therefore the new border surface of the shoulder will become the one depicted by the dotted line in the figure. By means of the circular major cutting edge a relatively sharp corner, having the radius R2, can be obtained while the tool can cut material also in direction towards the spindle, not shown. The milling tool according to the present invention thus can perform milling as conventional end mills of cemented carbide and yet cut material during a returning stroke towards the spindle. During the latter operation tension arises in the cutting head and therefore the chosen principal for retention is superior to other known solutions. The invention is in no way limited to the above described embodiments but may be freely varied within the limits of the subsequent claims. Claims 1. Milling tool for rotary chip removal machining, said tool comprising a cutting head (10), a retention means (11) and a shank (12), wherein the cutting head (10) is provided with at least one cutting edge (27,30), which is integral with the cutting head, said cutting head and the retention means comprising overlapping asymmetrical means (15,19) for mounting of the cutting head to the shank, said tool having an axis (CL) of rotation, characterized i n that the cutting head comprises one to six major cutting edges (27), each major cutting edge (27) comprising a substantially straight edge (27A) and a convexly curved preferably part-circular edge (27B), said convex edge (27B) being provided radially outside the substantially straight edge (27A). 2. Milling tool according to claim 1, characterized in that the straight edges (27A) lie in a common, imaginary cylinder having a first diameter (D), said cylinder being concentric with the axis (CL) of rotation of the tool or being arranged in an imaginary truncated cone, the apex of which faces towards the shank (12) and in that the convex edges (27B) at least partly are provided radially outside of said cylinder or said cone. 3. Milling tool according to anyone of claim 1 or 2, characterized i n that the overlapping asymmetrical means consist of hook-shaped means (15,19) and that the cutting head is performed in cemented carbide and that the retention means is performed in steel and in that the retention means (11) has an externally threaded portion (22) and is intended to be in engagement with a internally threaded recess (26) in the shank (12) or an internally threaded sleeve in an active position of the tool, said cutting head (10) being provided with a conical portion (14) and the shank (12) being provided with a conical seat (25), which receives the conical portion (14) in active position of the tool, said cutting head (10) being releaseably connected with the retention means (11) via the hook-shaped means (15,19). 4. Milling tool according to any of the preceding claims, characterized i n that the cutting head has two major cutting edges (27) and in that the diametrical distance between the convex edges (27B) are some millimeters larger than the diameter (C) of the cylinder and in that the convexly curved edge (27B) transforms into a minor cutting edge (30) in a plane (P) which is perpendicular to the rotational axis. 5. Cutting head with at least one cutting edge (27,30), said cutting head intended to enter into a tool for rotary chip removal machining, said tool comprising a cutting head (10), a retention means (11) and a shank (12), wherein the cutting head (10) is provided with at least one cutting edge (27,30) which is integral with the cutting head, said cutting head and said retention means comprising overlapping asymmetrical means (15,19) for mounting of the cutting head to the shank, characterized in that the cutting head comprises one to six major cutting edges (27), each major cutting edge (27) comprising a substantially straight edge (27A) and a convexly curved preferably part-circular edge (27B), said convex edge (27B) being provided radially outside the substantially straight edge (27A). 6. Cutting head according to claim 5, characterized in that the straight edges (27A) lie in a common, imaginary cylinder having a first diameter (D), said cylinder being concentric with the axis (CL) of rotation of the tool or being arranged in an imaginary truncated cone, the apex of which faces towards the shank (12) and in that the convex edges (27B) at least partly are provided radially outside of said cylinder or said cone. 7. Cutting head according to claim 5 or 6, characterized in that the cutting head is performed in cemented carbide and in that each said major cutting edge (27A,27B) is formed along the line of intersection between a clearance surface (28A,28B) and a chip surface (29). 8. Cutting head according to claim 7, characterized i n that the overlapping asymmetrical means consists of a hook-shaped means (15). 9. Cutting head according to claim 8, characterized in that each major cutting edge (27) connects to a minor cutting edge (30) and that the cutting head has two major cutting edges (27) and in that the diametrical distance between the convex edges (27B) are some millimeters larger than the diameter (C) of the cylinder and in that the convexly curved edge (27B) transforms into a minor cutting edge (30) in a plane (P) which is perpendicular to the rotational axis.

Inventors: STRAND BENGT, STRAND, BENGT
Applicants: SECO TOOLS AB
Application year: 1997
Main classification: B23C5
IPC codes: B23B31, B23C5