Cemented carbide cutting insert having integral structure for securing the insert in a holder

A cutting insert intended for chip removing machining includes a body forming at least one cutting edge, a securing structure such as a helical thread disposed at one side of the body, and a key grip such as a profiled recess disposed at an opposite side. The insert is formed of injection molded cemented carbide such that the body, the securing structure, and the key grip are all integral with one another. The insert is secured in a holder by rotating the insert using a key which engages the key grip, whereupon the securing structure engages a complementary securing structure on the holder to pull the insert body against the holder.

BACKGROUND OF THE INVENTION
 The present invention relates to a tool for cutting machining, a cutting
 insert and a method for mounting such a cutting insert.
 PRIOR ART
 Traditionally circular indexable inserts are used having a diameter down to
 about 5 mm. The smallest circular indexable inserts are to be regarded as
 rings of cemented carbide in order to obtain space enough to accommodate a
 retaining screw, which holds the cutting insert in the cutting insert
 pocket. Through WO 98/13161 is previously known a ball nose milling cutter
 comprising a milling head attached via a pull rod to a shank. The milling
 head comprises injection molded cemented carbide and has a cutting edge
 which extends towards the rotational axis of the tool. The milling head
 has a thread, which is integral with, and thereby made of the same
 material as, the cutting edge. The milling head comprises a key grip
 consisting of diametrical opposite planar surfaces. Through WO 95/33590 is
 previously known an injection molded cutting insert with an integral
 thread. Through U.S. Pat. No. 5,496,137 is previously known an end mill
 with a head having an integral thread and manufactured in accordance with
 an older technique. The problem of prior art tools of the above-noted
 types is that if these tools are of small dimensions, then less strength
 is obtained and the tools are difficult to manipulate.
 OBJECTS AND SUMMARY OF THE INVENTION
 One object of the present invention is to provide a tool for cutting
 machining having advantages of the prior art tools.
 Another object of the present invention is to provide a tool for cutting
 machining and a cutting insert with improved strength and which is easy to
 manipulate.
 Still another object of the present invention is to provide a tool for
 cutting machining and a cutting insert, the designs of which enable the
 cutting insert to be secured more tightly during operation.
 Still another object of the present invention is to provide a method to
 easily mount such a cutting insert.
 These and other objects have been achieved by a tool for cutting machining,
 a cutting insert and a method for assembling such a tool. The cutting
 insert comprises a body having at least one cutting edge, securing means
 disposed on a first side of the body, and a key grip disposed on a second
 side of the body. The securing means is adapted to secure the body against
 a holder in response to rotation of the insert about an axis of the
 securing means. The key grip is configured to be rotated about the axis by
 a key. The insert comprises injection molded cemented carbide, whereby the
 body, the securing means, and the key grip are integrally formed with one
 another.
 The method comprises the steps of:
 A) providing the above described cutting insert;
 B) positioning the cutting insert on a holder such that the securing means
 engages second securing means disposed on the holder;
 C) engaging a key with the key grip; and
 D) rotating the cutting insert, using the key, in a direction so that the
 second securing means pulls the first securing means toward the holder to
 cause the body to abut the holder.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
 In FIGS. 1A and 1B is shown a cutting insert 10A according to the present
 invention, which insert preferably is intended for longitudinal turning.
 The cutting insert 10A has a round geometry of so called R type. The
 cutting insert has an upper side 11 and a substantially planar, opposite
 lower side 12, the sides 11, 12 being interconnected by a cylindrical edge
 surface 13. The cutting insert has a circular cutting edge 14 formed along
 a line of intersection between the upper side 11 and the edge surface 13.
 The cutting insert 10A has a center line CL. The cutting insert comprises
 securing means 15 to be used for securing the cutting insert against a
 holder. The diameter of the cutting insert is considerably larger than the
 diameter of the securing means 15. The securing means 15 is integrated
 with the cutting insert and thereby formed of the same material as the
 cutting edge 14. This has been obtained through injection molding with
 suitable equipment and subsequent sintering. The cutting insert is made by
 mixing powder of sintered hard alloy with an organic binder, such as
 plastic, and shaping the mixture into pellets or granules. Said pellets or
 granules are cast by means of an injection molding process, whereafter the
 obtained product is sintered at a temperature of 1300 to 1500.degree. C.
 The injection molding technique has been more closely described in EP
 96913765.2, the contents of which are hereby is incorporated in the
 present description. The securing means 15 projects perpendicularly from
 the center part of the lower side 12. The securing means 15 comprises an
 externally threaded spigot 16 the center axis of which substantially
 coincides with the centerline CL of the cutting insert. In the shown
 embodiment the thread has one entrance and one exit. Alternatively the
 thread may be a multiple thread type having at least two entrances and at
 least two exits of the type provided on the insert 10A' shown in FIG. 3B.
 In other words, the securing means 15 comprises one or more external,
 helically shaped grooves.
 The upper side 11 of the cutting insert 10A, i.e., the side of the insert
 11 opposite said securing means 15, comprises at least one key grip 17.
 The key grip 17 has the shape of a profiled recess 18 intended to
 cooperate with a key during clamping of the cutting insert against the
 holder. The key grip 17 has a center axis, which substantially coincides
 with the centerline CL of the cutting insert. The profile of the key grip
 is of the type Torx.RTM. or an Allen key, or similar, that is a profile
 which comprises more than two surfaces for driving, preferably six such
 surfaces. Consequently, the centerline of the securing means 15
 substantially coincides with the centerline of the key grip 17. The grip
 17 is arranged within an imaginary cylinder 24, the diameter of which
 substantially corresponds to the average diameter of the thread 16.
 Likewise, it can be noted that the cutting edge 14 preferably occupies one
 plane. The cutting edge 14 surrounds the key grip 17 by being provided
 radially outside of, and at a distance from, the key grip relative to the
 centerline CL.
 FIGS. 2A-2D show a turning tool 19A according to the present invention
 comprising a holder 20A and the cutting insert 10A. The holder 20A
 comprises a shank having one end provided with a cutting insert pocket
 while the other end provided to be fastened in a machine for turning. The
 holder is made of steel. The cutting insert pocket comprises a bottom
 surface 21 and a side support surface 22, FIG. 2D. The holder 20A
 comprises means for clamping the cutting insert in the cutting insert
 pocket, the means being in the form of a threaded hole 23, which extends
 substantially perpendicularly to the plane of the bottom surface 21. The
 thread in the hole 23 has one entrance and one exit in the shown
 embodiment. Alternatively the thread may have at least two entrances and
 at least two exits. In other words, the means 23 comprises one or more
 internal, helically shaped grooves.
 The hole 23 is provided centrally in the substantially round bottom
 surface. The side support surface 22 is part-cylindrically concave in
 order to fit the convex edge surface 13 of the cutting insert.
 Mounting of the cutting insert 10A in the holder 20A is done as follows.
 The cutting insert is brought in a direction towards the bottom surface 21
 of the cutting insert pocket such that the centerline of the securing
 means or spigot 15 is aligned with the centerline of the hole 23. The
 cutting insert is pushed towards the cutting insert pocket such that the
 threads abut against each other. Subsequently, the cutting insert 10A and
 the associated threaded spigot 15 are rotated as a one-piece unit by hand
 or with the aid of a suitable key, not shown, in engagement with the key
 grip 17, until the lower side 12 of the cutting insert abuts the bottom
 surface 21 of the cutting insert pocket. Then the key should be used to
 firmly tighten the cutting insert against the bottom surface in order to
 create a pre-tension in the more elastic steel threads of the hole 23. In
 the preferred embodiment the cutting insert 10A has a diameter about 4 mm,
 a metric thread M2.2 and a key grip T07. More generally, the diameter of
 the cutting insert lies in the range of 3-5 mm. The thread may be of any
 type and optionally may be right-hand or left-hand. A type of thread which
 is well adapted to being made of sintered cemented carbide is a rope
 thread, see FIG. 2E. The thread in FIG. 2E is a left-hand rope thread,
 which in connection with the round cutting edge 14 tends to tighten the
 threaded connection during machining with the insert.
 Alternatively, as shown in FIG. 2F, the thread of the spigot 15 can be
 replaced by one or more right-angel shaped grooves having an axial portion
 100A and a circumferential portion 100B. The circumferential dimension of
 which is smaller than 360.degree.. The groove or grooves shall then fit
 with a corresponding radial protrusion(s) in the hole of the holder in
 order to create a bayonet type of coupling. It will then be possible to
 index the cutting insert into as many positions as there are grooves, in
 order to position a fresh cutting edge for cutting. The circumferential
 portion could be somewhat helical to cause the insert to be pulled against
 the holder as the insert is rotated.
 Indexing of the cutting insert of FIG. 1A may alternatively be achieved by
 providing a shim between the bottom surface of the holder and the lower
 side of the cutting insert to restrict the extent to which the insert can
 be rotated. The thickness of the shim could, for example, be chosen to
 equal one-half of the pitch of the thread in order to achieve indexing by
 180.degree..
 In FIG. 3A is shown an alternative embodiment of a tool 19B according to
 the present invention. The difference between this embodiment and the
 above-described tool is partly that the cutting insert 10B has a positive
 basic geometry and partly that the side support surface of the holder is
 omitted.
 Thereby all cutting forces are received by the bottom surface and the
 thread in the holder 20B.
 In FIG. 4A is shown an alternative embodiment of a cutting insert 10C and a
 tool 19C according to the present invention. The difference between this
 embodiment and the above-described tool according to FIG. 3A is that both
 the spigot and the hole of the holder comprise cylindrical guiding
 surfaces 25 and 26, respectively, provided radially beyond the imaginary
 cylinder 24. The diameters of the guiding surfaces 25, 26 are adapted for
 a mutual sliding fit. In this case all cutting forces are received by the
 bottom surface, the guiding surfaces 25, 26 and the thread in the holder.
 In FIG. 4B is shown an alternative embodiment of a cutting insert 10C and a
 tool 191 according to the present invention. The difference between this
 embodiment and the above-described tool according to FIG. 4A is that the
 thread in the holder now has been replaced by a thread in a loose nut 211
 having a Torx.RTM. grip 221. The nut and the cutting insert 10C are
 rotated relative to each other in order to mount or dismount the cutting
 insert. FIG. 4C shows the nut and the cutting insert 10C of FIG. 4A
 separate from the holder. FIG. 4D shows an alternative nut 231 with
 external Allen grip 241 and the cutting insert 10C from FIG. 4A.
 In FIGS. 5A and 5B is shown an alternative embodiment of a cutting insert
 10D according to the present invention. The difference between this
 embodiment and the above-described tool according to FIG. 3A is that the
 edge surface or the clearance surface of the cutting insert is generally
 concave and comprises a frusto conical portion 11D and a cylindrical
 portion 12D which intersect one another. If the insert should break, the
 line of fracture will be guided toward that line of intersection.
 In FIG. 6 is shown an alternative embodiment of a cutting insert 10E
 according to the present invention in a top view. The difference between
 this embodiment and the above-described tools is that the key grip 18E
 comprises a hexagonal recess, i.e., a so-called Allen grip.
 In FIGS. 7A and 7B is shown an alternative embodiment of a cutting insert
 10F according to the present invention. The difference between this
 embodiment and the above-described tool according to FIG. 3A is that the
 key grip includes a profiled projection 18F on the cutting insert. The
 projection comprises a male portion for a so-called Torx.RTM. connection.
 The projection shall cooperate with a female portion of similar but
 inverted geometry. The projection also serves as a chip former or chip
 breaker. Alternatively, the projection may consist of a male portion of an
 Allen key connection, that is a projection with a hexagonal cross-section.
 The use of such a projection may however be considered as an inferior
 technical solution as compared to the earlier described use of a recess
 (e.g. recess 18) for tools of small diameters and small chip spaces.
 In FIGS. 8A and 8B is shown an alternative embodiment of a cutting insert
 10G according to the present invention. The difference between this
 embodiment and the above-described tool according to FIG. 3A is that the
 helically formed grooves now are on a female portion, i.e. they are formed
 in a center recess 27 in the cutting insert. The recess 27 transforms into
 the key grip recess 18G at the mid portion of the cutting insert. The
 thread of the recess 27 shall cooperate with a screw (not shown) in the
 holder, whereby the thread constitutes a securing means for the insert.
 The screw could be either firmly anchored in the holder or rotatable in
 the holder. The recess may include one or more internal, helically shaped
 grooves.
 In FIG. 9 is shown an alternative embodiment of a cutting insert 10H
 according to the present invention. The difference between this embodiment
 and the above-described tool according to FIGS. 8A and 8B is that the key
 grip 18H is a projection.
 In FIGS. 10A and 10B is shown an alternative embodiment of a tool 19D
 according to the present invention with a cutting insert 10D previously
 described in connection with FIGS. 5A and 5B. The difference between this
 embodiment and the above-described tool according to FIG. 2D is mainly
 that the threaded hole of the holder is made larger than the thread of the
 spigot 16D and is displaced by a distance towards the side support surface
 22 such that the center line CL of the hole is offset in said direction
 with respect to the center line CL' of the cutting insert. The hole's
 smallest diameter is larger than the largest diameter of the spigot, so
 the spigot can be inserted deeply without rotation into in the hole of the
 holder, whereafter rotation of the cutting insert can start. Then, only
 the parts of the threads which face away from the side support surface
 will be in engagement with the hole thread during tightening,
 simultaneously as the edge surface of the cutting insert bears against the
 side support surface 22. In this manner a quick attachment function is
 obtained. Said feature can also be obtained by means of mutually
 substantially identical conical threads whose center lines coincide.
 In FIGS. 11A-11C is shown an alternative embodiment of a tool 19E and a
 grooving-type cutting insert 101 according to the present invention. The
 tool 19E is intended for inside grooving and comprises a cylindrical
 holder 20E and the grooving insert 101 which has a projecting cutting
 portion 14E. The cutting insert is mounted in a selected one of the
 above-described manners and optionally the geometries of the threads may
 be arranged such that the final position for the cutting edge of the
 cutting portion is predetermined.
 In FIGS. 12A-12C is shown an alternative embodiment of a tool 19F and a
 cutting insert 10J according to the present invention. The tool 19F is
 intended for example for end milling and comprises a cylindrical cutting
 insert 10J, which does divide each chip. The cutting insert is mounted in
 a selected one of the above-described manners, and since the cutting
 insert comprises a number of symmetrically placed cutting portions and is
 to be rotated, there is no need for indexing. Alternatively, the cutting
 insert is developed as a chip-dividing, cylindrical end-milling insert, or
 a thread milling insert, or a broaching insert, or a truncated conical
 head for end-milling of dove tail slots (wherein the latter has a cone
 apex directed towards the holder), or a similar insert. Common for all of
 these tools is that they replace conventional end mills in high-speed
 steel where smaller dimensions (5 to 15 mm in diameter) often are
 desirable.
 In FIGS. 13A-13C is shown an alternative embodiment of a tool 19G and
 cutting insert 10B, shown in FIG. 3A, according to the present invention.
 The tool 19G is intended for example for grooving and it comprises two of
 the earlier described cutting inserts 10B, whereof one of the cutting
 inserts overlaps the rotational axis of the tool such that the milling
 cutter also can drill.
 In FIGS. 14A-14C is shown an alternative embodiment of a tool 19H and
 cutting insert 10B, previously described in connection with FIG. 3A,
 according to the present invention. The tool 19H is intended for example
 for face milling and it comprises eight cutting inserts 10B.
 In FIGS. 15A and 15B is shown an alternative embodiment of a cutting insert
 10K according to the present invention. The difference between this
 embodiment and the above-described tool according to FIG. 3A is that the
 upper side 11 of the cutting insert comprises a chip breaker. A
 reinforcing chamfer 30 is connected to the cuffing edge 14. The chamfer
 further connects to a concave chip surface 32 which in turn connects to a
 rear surface 34. FIG. 15 C shows a cross-section of a modified insert 10K'
 similar to FIG. 15B but without a reinforcing chamfer. In FIG. 15C a
 projection 38 is depicted. A number of separate projections 38 is provided
 with even spacing along the chip surface periphery. FIG. 15D shows a
 cross-section of a modified insert 10K" similar to FIG. 15B but without a
 concave chip surface. A planar chip surface connects to the reinforcing
 chamfer. In FIG. 15D a recess 40 is depicted by a dotted line. A number of
 separate recesses is provided with even spacing along the chip surface
 periphery.
 In FIG. 16 is shown an alternative embodiment of a cutting insert 100L
 according to the present invention. The difference between this embodiment
 and the above-described tool according to FIG. 3A is that the upper side
 11 of the cutting insert comprises a ring of material which is more wear
 resistant than cemented carbide, such as cubic boron nitride or diamond.
 The ring surrounds the key grip.
 The present invention consequently relates to a tool for cutting machining,
 a cutting insert with improved strength and ease of handling and a method
 to easily mount such a cutting insert. More specifically, by the cutting
 insert in itself been designed as a screw or nut, the hard to handle
 screws used today in connection with tools according to known technique
 with little diameters are avoided. A solution according to the mentioned
 WO 98/13161 is not suitable for turning tools where there is a side
 support surface on the holder, since the side support surface would
 obstruct the movement of one arm of the key during attempted rotation
 thereof. Consequently the shown embodiments may be combined into tools and
 cutting inserts not specifically illustrated in the present patent
 application.
 Although the present invention has been described in connection with
 preferred embodiments thereof, it will be appreciated by those skilled in
 the art that additions, modifications, substitutions and deletions not
 specifically described may be made without departing from the spirit and
 scope of the invention as defined by the appended claims.