Rotary cutting tool having a cutting edge made of multiple materials

Abstract

The present invention relates to a multi-material rotary cutting tool (1) and a method for manufacturing such a tool that includes at least one continuous or substantially continuous cutting edge (8, 9) made of at least two different successive materials. The extremity or top (10) of the tool is a point off-centered in relation to the axis of rotation (5) of the tool.

Claims

1. A multi-material cutting tool having a body and a head with a height h and at least one continuous or substantially continuous cutting edge comprising at least two successive different materials, the tool comprising an elongate core about an axis and at least one lip or thread crowned with a continuous or substantially continuous cutting edge, the middle or inner radial portion of the core and the distal portion of the lip or thread being made of a first material enabling a low cutting speed (V.sub.c<50 m/min) and the periphery or outer radial portion of the core of the tool and the proximal portion of the lip or of the thread crowned with the corresponding cutting edge being made of a second material enabling a high cutting speed (V.sub.c<500 m/min), the continuous or substantially continuous cutting edge being overall radial to the axis of rotation of the tool and comprising the first material in the zone closest to the axis of rotation and the second material in the zone further away from the axis, characterized in that the body is made of the first material and in that the core is off-centered in relation to the axis of rotation of the tool.

2. The tool as claimed in claim 1, characterized in that one of the materials is a metal or carbide-based material with metal binder and the other material is a ceramic material or a ceramic-matrix composite material.

3. The tool as claimed in claim 2, characterized in that the material with metal binder is tungsten carbide with cobalt binder.

4. The tool as claimed in claim 1, characterized in that it has a chipbreaker notch on the cutting edge at the interface between materials.

5. The tool as claimed in claim 1, characterized in that it has a chipbreaker notch on the cutting edge that is offset from the interface between materials.

6. The tool as claimed in claim 1, characterized in that it has a cutting edge made of at least three different successive materials.

7. The tool as claimed in claim 1, characterized in that the cutting edge is substantially continuous and has a cutout between the different materials of width e of less than 2 mm.

8. The tool as claimed in claim 1, characterized in that the cutting edge is continuous.

Description

(1) The invention is further explained in the description below of different embodiments given by way of non-limiting examples. The description relates to the attached drawings, in which:

(2) FIG. 1A is a top view of a drill extremity according to a first embodiment of the invention.

(3) FIG. 1B is a partial top view of a drill extremity according to a second embodiment of the invention.

(4) FIG. 1C is a cross section along IC-IC in FIG. 1B, level with the cutout.

(5) FIG. 1D is a partial view of a cutting edge with chipbreaker notch H according to an embodiment of the invention.

(6) FIG. 2 is a perspective view of the drill extremity in FIG. 1.

(7) FIG. 3 is a top view of another embodiment of a drill according to the invention.

(8) FIGS. 4 and 5 are respectively a side view and a perspective view of a drill extremity of another embodiment according to the invention.

(9) FIGS. 6A to 6C show schematically the steps of an embodiment of a method for manufacturing a tool for drilling according to the invention.

(10) FIG. 7 is a cross section and top view of the extremity of the drill obtained with reference to FIGS. 6A to 6C.

(11) FIGS. 8A to 8C show schematically the steps of another method for manufacturing a tool for milling.

(12) FIGS. 9 and 10 are perspective views of two different embodiments of a milling tool with a hemispherical head (FIG. 9) and a cylindrical or tapered head (FIG. 10) respectively.

(13) FIGS. 1A and 2 are top and perspective views of a drill 1 having a head 2 forming the cutting extremity of the tool, and a body 3, that is for example cylindrical, enabling the tool to be held and rotated.

(14) In the embodiment explained in greater detail herein, the tool has a cylindrical core 4 made of tungsten carbide with cobalt binder, provided with a cylindrical extremity 4 and two flanges or lips 6 and 7 each crowned with a cutting edge 8 and 9 that are joined at the extremities or tops 10 of the drill off-centered in relation to the center 5 of the extremity 4 of the core.

(15) In the embodiment described in greater detail here, on account of the off-centering (in relation to the center 5) of the extremity 10, through which the axis of rotation of the tool passes, the edge portions of a material are not of equal length, the edge being conversely of substantially identical shape (in rotation in relation to the tip 10) and have for example a squashed S shape.

(16) The lips 6 and 7 form, in a known manner, the helical tapered inclined surface of the peripheral extremities of the drill.

(17) According to the embodiment of the invention described in greater detail here, the lips have a continuous edge 8, 9 from the tip 10 to the peripheral radial extremity 11 and 12, said edge being multi-material.

(18) In this case, the cutting edges 8 and 9 are therefore continuous and are as a whole radial in relation to the axis of rotation passing through the top 10 of the drill.

(19) Each edge is a cutting edge and enables material to be removed when using the tool.

(20) More specifically, each edge (see FIG. 2) is made of the metal material 13 or material with metal binder forming the core 4 and the extremity 4 of same, and the portion of the lips closest to the center 5 (distal or inner part), the two forming the middle or inner radial part of the tool, and a second ceramic material 14 that is more brittle but has greater thermal resistance, forming the outer radial portion of the tool with the portion of the lips furthest away from the axis (outer or proximal portion).

(21) Each edge has an edge portion made of one material and another portion made of another material.

(22) The edge portions made of the same material in each edge are also of different length.

(23) The materials 13 and 14 separated by the join line 15 are rigidly connected together, for example by high-temperature vacuum brazing, as described below with reference to the method described in greater detail.

(24) Henceforth in FIGS. 1B to 1D, the same reference signs are used to identify the same or similar elements.

(25) FIG. 1B is a partial top view of a drill that has two substantially continuous cutting edges 8 and 9 with a discontinuity or cutout E of width e, for example 1 mm.

(26) This cutout is found identically along the entire join 15 between the materials of the extremity 4 of the core 4 and of the remainder of the flanges or lips 6 and 7.

(27) FIG. 1C is a cross section of the cutout E along I.sub.c-I.sub.c in FIG. 1B.

(28) The material, for example ceramic, of the flange 6 is attached to the core 4 at 6, for example by brazing.

(29) FIG. 1D shows another embodiment of the cutting edge 8 in FIG. 1B with a chipbreaker notch H on the edge, but removed from the cutout E.

(30) In another embodiment, H may also be superposed on E.

(31) By way of example, and for a predefined use, the depth of H is greater than the turning advance value, i.e. the penetration length of the tool into the part along the axis of rotation of the tool for one revolution, in order to ensure chip breaking. This results in cutting of the part being machined, with no discontinuity.

(32) FIG. 3 shows a drill 16 according to another embodiment of the invention in which the flanges 17, 18 or peripheral parts are not inscribed within a cylinder, but within a parallelepiped (dot-dash line 19).

(33) In this case, the cutting edges 8, 9 are substantially continuous, i.e. they have a cutout E of width e, for example of 2 mm. The join line 15 then forms a slot of any section, for example rectangular, and of a depth corresponding to the thickness of the peripheral material.

(34) FIGS. 4 and 5 show another embodiment of a drill 20 according to the invention. It includes a cutting head 21 and a metal cylindrical body 22.

(35) The body of the tool and the head include a recess 23 forming a chip pocket having, in a known manner, a curved surface from the extremity of the head or tip of the drill 24 to a zone 25 upstream of the head.

(36) In this embodiment, the second material 26, which is different from the first material 27, is separated from this latter by a join line (surface) 28 and has a single cutting edge 29, the axis of rotation of the tool 30 being offset from the tip 24 of the drill, which acts as an auger.

(37) A method for manufacturing the drill shown in FIGS. 1A and 2 is described below with reference to FIGS. 6A to 6C and 7.

(38) It involves at least two elements made of different materials.

(39) The first element 33 is ultimately intended to form the body and the core 34 (see 6C) of the head of the tool. It is initially, for example, in the form of a metal cylindrical bar 35, for example made of tungsten carbide alloy with cobalt binder.

(40) A first operation involves reducing the diameter of a portion of the extremity 36 of the cylindrical bar such as to form a cylindrical tenon 37 with a section of reduced diameter, which projects from the extremity with an annular flat surface.

(41) The tenon is for example off-centered in relation to the rotational axis of symmetry 38 of the bar.

(42) The gap between the axis of the tenon 39 and the axis of symmetry 38 is between 0% and 50% of the diameter, for example 15%.

(43) The second element 40 is intended to form the outer radial part of the lips or peripheral portions.

(44) It is formed for example by a cylindrical disk 41, for example made of ceramic, having the same diameter as the bar.

(45) The disk 41 has a through hole or recess 42 centered complementarily on the tenon, i.e. having a diameter enabling insertion of the tenon 37.

(46) Once the tenon has been inserted into the hole (FIG. 6B), the assembly, in the example described in greater detail here, forms a cylinder with an off-center head, and the tenon may even be flush with or project from the upper surface 42 of the disk.

(47) The two materials are then assembled to ensure continuity of the material, i.e. they are for example assembled using any mechanical or metallurgical method ensuring a strong link, such as brazing, hooping, diffusion welding or using powder metallurgy.

(48) This link is symbolized in the figures using a double line 43, which does not necessarily indicate that said link has a visible thickness.

(49) Advantageously, high-temperature vacuum brazing is used in this case (notably 800 C.)

(50) Also advantageously, the assembly may be carried out using spark plasma sintering (SPS) or pulsed electric current sintering (PECS) methods. SPS and PECS are based on square-wave high-intensity pulses of a charge or of an electrical current.

(51) These techniques enable rapid, localized diffusion welding and/or sintering with a high temperature-increase speed that is nonetheless short lived with little or no crystal growth.

(52) This temperature distribution enables the formation of very compact articles at lower overall temperatures.

(53) Assembly also includes a pressurization step of the tool by pressing (not shown).

(54) Such high-pressure, compression and application of electrical current force the diffusion welding. Compression of one part into the other results in overlapping of said parts on to one another, including after cooling. It may also result in upsetting of hot material from the tenon pressed in this way. Upsetting then fills the internal discontinuities of the join, i.e. it brings material to the interface of the two materials.

(55) The interface thus forms a continuous assembly of material.

(56) The length of the slot can therefore be further reduced, including to zero, thereby ensuring the continuity of the edge.

(57) The mechanical strength of the link against impacts is therefore also greater at the interface on account of the continuity of the interface join. This increased strength enables the notch or slot to be positioned, in the embodiments where it is present, away from the radial periphery of the interface but anywhere on the edge.

(58) In such an embodiment, the tenon may be centered.

(59) The bar/disk assembly is then machined (FIGS. 6C and 7) to form the dual-material continuous-edge drill, the tenon 37 in this case forming the extremity of the core 34 of the head.

(60) Another method for manufacturing a rotary cutting tool is described with reference to FIGS. 8A to 8C, in this case for manufacturing a milling cutter.

(61) In this case, the tool is also obtained from a cylindrical bar 44, for example made of a WC alloy with cobalt binder and a corresponding full ceramic disc 45.

(62) The cylindrical bar 44 and the disk 45 of thickness 1 have flat surfaces 46, 47 that cooperate with one another at the extremities of same.

(63) These two elements are assembled (FIG. 8B) using means such as those mentioned above, i.e. for example by high-temperature vacuum brazing (double line 48).

(64) The tool is then formed (see schematic representation in FIG. 8C) in the cylindrical assembly 49 of the bar and the disk, creating longitudinal recesses 50 forming at least one edge 51 at a height h of a length greater than the thickness of the disk 1.

(65) FIGS. 9 and 10 show respectively two milling cutters 51 and 52 obtained using the method described with reference to FIGS. 8A to 8C.

(66) FIG. 9 shows a cylindrical milling cutter 51 having a hemispherical head 53 and dual-material helical cutting edges 54 made of ceramic 55 and metal 56.

(67) The length of the continuous cutting edge 54 is greater than the thickness of the material used to form the extremity of the head.

(68) The milling cutter 52 has a tapered head 57 provided with composite helical cutting edges 58.

(69) The cutting edge then runs from the extremity of the head to the other extremity of the different materials 59 and 60 successively.

(70) The use of a tool according to the invention is described below, for example with reference to the drill in FIG. 1.

(71) The rotary cutting tool is then assembled on a turning motor (not shown).

(72) Assembly can be carried out by attaching the cylindrical body 3 of the tool using any known mechanical means (Morse taper, etc.).

(73) Once put into rotation, the tool is brought into contact with the mechanical part to be machined.

(74) The first portion of the tool to come into contact with the part is the extremity or tip of the head 2 made of metal or a material with metal binder.

(75) This has a low rotation speed, which gets lower as it approaches the axis 10 of rotation, where it reaches zero.

(76) The material chosen for the core is selected to be efficient at low speed and not very brittle, and enables an initial penetration of the tool in the part. In the embodiments described in greater detail, this material is metal, metal alloy, or tungsten carbide with metal binder.

(77) The peripheral portions or flanges (lips) 6 and 7 come into gradual contact with the part as the tool enters the part.

(78) As the points of these peripheral portions are increasingly radially distant from the axis of rotation 10, they have a rotational speed much higher than the rotational speed of the points on the core 4. The use of a more efficient but more brittle material, such as ceramic, from a certain distance from the axis 10 enables the exceptional performance levels observed to be obtained.

(79) The distance to be observed for the change of material from the axis is determined by the person skilled in the art as a function of the desired performance levels in consideration of the operating speeds used.

(80) However, for example and advantageously, the ratios (on the radius of the drill or of the reamer) between the first central material and the second outer material is ; or ; or ; .

(81) Thus, according to the invention and as the mechanical part is penetrated, each part of the tool is working in the rotational speed conditions most suited to the composition of same.

(82) Naturally, and in consideration of the foregoing, the present invention is not limited to the embodiments described in greater detail. On the contrary, it encompasses all of the variants and in particular those relating to the dimensions of the tools, which could be anything, and those in which three, four or five materials are used, in particular by stacking discs of different materials, those in which the shape of the drills and/or of the reaming tools is different and/or for example the cores, bars and tenons are not cylindrical, and those in which the materials are different, for example two metal materials having different characteristics.