Cutting tool with clamping device

The invention describes a cutting tool, preferably a cutoff parting tool, having one or more replaceable cutting inserts. The cutting inserts comprises on the supporting and/or clamping surfaces embossed elements. Upon clamping the cutting inserts these elements cause a plastic deformation of the contact surfaces on the toolholder. In this fashion, the cutting inserts are additionally stabilized against lateral compressive forces and tensile forces forcing them out of the seat.

BACKGROUND OF THE INVENTION
 1. Field of The Invention
 The invention relates to a cutting tool and, more particularly, to a
 cutting tool having one or more replaceable cutting inserts which can be
 clamped to the toolholder and which feature, on the supporting and/or
 clamping surfaces, elements for achieving a formfitting, correctly located
 positioning.
 2. Description of the Related Art
 In cutting tools having replaceable cutting inserts, the cutting inserts
 are fixed to the toolholder using a wide variety of clamping elements. One
 widely used clamping method consists of providing the cutting inserts with
 a central hole, which are fixed to the toolholder by means of screws with
 appropriate head shapes or with clamping elements that engage directly on
 the wall of the central hole, such as eccentrics or tilting pins. Other
 known clamping elements are, for instance, clamping claws that engage the
 cover surface of the indexable, replaceable insert, causing the cutting
 insert to be attached to the toolholder.
 In the case of cutting inserts for cutoff or parting, which as a rule are
 extended in length, it is customary to improve clamping by providing the
 cutting inserts with a concave or convex V-shaped supporting and/or
 clamping surface and to subject the clamping surface to the necessary
 clamping force via a threadable clamping claw or by means of elastic
 segments of the toolholder and/or the seating blade through the elastic
 deformation of these segments.
 Inasmuch as on modern machine tools the cutoff inserts are often used not
 only for parting or recessing, but also for producing surface contouring
 by turning or facing, it is unavoidable that such cutting inserts are also
 stressed by lateral compressive or tensile forces. For such cutting
 operations, the clamping force exerted upon the cutting insert is often
 insufficient so that, despite these V-shaped supporting and/or clamping
 surfaces, there may result a shifting or even a pullout of the cutting
 insert from the toolholder. This results in dimensional deviation of the
 work piece in process, reduced working life because of premature wear,
 breakage or loss of the cutting insert, as well as damage to the tool bit
 seat or the clamping parts on the toolholder.
 Such deficiencies involving an occasionally inadequate attachment of the
 cutting insert to the toolholder led to the introduction-over and above
 the customary clamping elements--of mutually coordinated elevations and
 recesses in the contact surfaces between the cutting insert and the
 toolholder. This was done to provide an additional positive form fit
 between the cutting insert and the toolholder and thus leads to improved
 positioning possibilities and to an improved clamping of the cutting
 inserts in the toolholder. Examples of such designs of cutting inserts and
 toolholders are described in DE-OS 36 17 119, DE-OS 26 53 222 and DE-GM 92
 01 113.
 A disadvantage of such known tool bit attachments is the fact that the
 production of such additional formfitting registering elements is
 expensive; they must be provided both on the tool bits and on the
 toolholders and must be precisely adjusted to one another, in order to
 ensure that the tolerances required for the cutting tool with respect to
 the position of the cutting edge are maintained.
 SUMMARY OF THE INVENTION
 Consequently, one of the objects of the present invention is to provide a
 cutting tool having one or more replaceable cutting inserts that can be
 clamped to the toolholder, the cutting inserts including elements for
 providing formfitting, correctly located positioning on the supporting
 and/or clamping surfaces of the toolholder, which will avoid the
 above-mentioned deficiencies.
 This and other objects are achieved by the present invention in that the
 elements are designed to be embossed in such a manner that one achieves a
 plastic deformation by means of the surface pressure exerted by the
 respective clamping installation upon the corresponding contact surfaces
 on the toolholder when fastening the cutting inserts.
 In this fashion, a novel advantage of the present invention is that the
 material from which the cutting inserts are made features a greater
 hardness than the material of the toolholder.
 By the design of the elements in accordance with the present invention
 (which, compared to the previously known elements are substantially
 smaller in dimensions), it is now only necessary to provide the cutting
 insert with embossed elements, which can be achieved in a simple manner by
 appropriately shaped pressing tools. The previously required expensive,
 precise coordination of the respective recesses in the toolholder may be
 eliminated completely since the latter are achieved in a simple manner,
 automatically and correctly located, by means of plastic deformation when
 the cutting insert is clamped fast to the toolholder. It was not expected
 that upon using even small-size embossed elements alone, an excellent
 formfitting attachment of the cutting insert to the toolholder would be
 attained to such an extent. In addition, such an attachment brings with it
 a clear-cut improvement of the positioning and fastening of the cutting
 insert with respect to lateral compressive and tensile forces. The precise
 form and dimensioning of the elevations should be adjusted in accordance
 with the differences in the hardness of the materials used for the cutting
 insert and for the toolholder, the size of the cutting insert and the
 magnitude of the clamping force. To those who are of ordinary skill in the
 art, these adjustments are merely routine steps of the art.
 The invention can be used not only on cutting tools with cutting inserts
 made of cemented carbide or other superhard material and to steel as the
 material for the toolholder, but also to cutting inserts which, like the
 toolholder, are made of steel. The only important factor is that the
 difference in hardness between the cutting insert and the toolholder be
 sufficiently great to permit a plastic deformation of the toolholder. The
 practice has shown that hardness differences of at least about 20 HRC are
 required. It is furthermore practical to make the elements as sharp-edged
 as possible. With respect to their dimensions, practice has shown that,
 when cemented carbide is used for the cutting insert, it is advantageous
 to provide a projection in the range between 0.08 mm and 0.1 mm for the
 supporting and/or clamping surface.
 A particularly advantageous form of the elements proved to be sharp-edged
 roof-shaped elevations with an acute angle between 80.degree. and
 90.degree.. It is particularly advantageous to apply the invention to
 cutting inserts for cutoff parting, with a V-shaped supporting and/or
 clamping surface. Cutting inserts designed in this fashion then lend
 themselves in an excellent manner for contour- and form-turning, without
 leading to a shifting or pull-out of the cutting insert from the
 toolholder.
 In this connection, it proved particularly advantageous to design the
 supporting and/or clamping surface of the cutting inserts with a
 multiplicity of roof-shaped elevations, arranged parallel to one another
 and perpendicular to the longitudinal axis of the cutting insert.
 The foregoing specific objects and advantages of the invention are
 illustrative of those that can be achieved by the present invention and
 are not intended to be exhaustive or limiting of the possible advantages
 which can be realized. Thus, these and other objects and advantages of
 this invention will be apparent from the description herein or can be
 learned from practicing this invention, both as embodied herein or as
 modified in view of any variations which may be apparent to those skilled
 in the art. Accordingly, the present invention resides in the novel parts,
 constructions, arrangements, combinations and improvements herein shown
 and described.

DETAILED DESCRIPTION
 FIG. 1 illustrates a cutoff tool according to the present invention. The
 cutoff tool comprises a toolholder 1 having an indexable, replaceable
 cutting insert 2 made of cemented carbide. The blade-shaped front section
 of the toolholder 1 includes a recess to accommodate the cutting insert 2,
 which recess changes at the end into a slit 9. In this fashion, a rigid
 supporting segment 6 and an elastic clamping claw 7 are formed, each of
 which include convex, V-shaped contact surfaces 5 to accommodate the
 cutting insert. The surface of these contact surfaces 5 is smooth and made
 without recesses. As can also be seen in FIGS. 2-4, the cutting insert 2
 comprises appropriately formed concave, V-shaped supporting and clamping
 surfaces 3a and 3, respectively.
 Both the supporting surface 3a and the clamping surface 3 are designed to
 feature elements--e.g., elevations 4 preferably made with a generally
 roof-shaped cross-section, perpendicular to the longitudinal axis of the
 cutting insert 2. The elevations 4 are preferably formed with an acute
 angle between 60.degree. and 90.degree.. The elevations 4 are preferably
 made sharp-edged with an acute angle of 90.degree. and feature a height of
 about 0.08 mm starting from the supporting and clamping surfaces 3a and 3,
 respectively.
 In order to clamp the cutting insert 2 in the toolholder 1, the cutting
 insert 2 is inserted within the recess until it abuts the stop. By
 threading the set screw 8 within the toolholder 1, the clamping claw 7
 presses upon the clamping surface 3 of the cutting insert 2, and therefore
 forces the supporting surface 3a against the contact surface 5 of the
 supporting segment 6. As is shown in detail in FIG. 5, for the contact
 surface 5 of the clamping claw 7 and the clamping surface 3 of the cutting
 insert 2, the clamping force presses the elevations 4 of the cutting
 insert 2 into the contact surfaces 5 of the clamping claw 7 and the
 supporting segment 6, respectively, and deforms these contact surfaces 5
 in a plastic manner. In this fashion, visibly formed V-shaped grooves are
 produced in the contact surfaces 5, which are sufficiently deep to
 stabilize the cutting insert 2 against lateral forces as well as tensile
 forces from the recess, but are shallow enough to permit the cutting
 insert 2 to be readily removed from the recess after the clamping screw 8
 has been released. Attention should be paid to ensure that, when the
 cutting insert 2 is clamped fast for the first time, it is pushed in or
 inserted until it abuts the stop and therefore is correctly positioned to
 press in and form the notches in the contact surfaces 5 at the right
 locations. When the cutting insert 2 is replaced, a new cutting insert 2
 may be automatically positioned in the correct location by the notches
 previously formed in the contact surfaces 5.
 In an experiment to determine the amount of force necessary to pull the
 indexable, replaceable tool bit or cutting insert out of the toolholder,
 two identical cutoff tools--one provided with cutting inserts in
 accordance with the present invention having roof-shaped elevations as
 illustrated in FIGS. 2-3, and the other provided with cutting inserts
 having smooth clamping and supporting surfaces--were compared on a tensile
 testing installation.
 The individual indexable, replaceable tool bits or cutting inserts were
 clamped fast within each tool holder by tightening the clamping screw with
 a tightening torque of 8 Nm. The toolholders were clamped fast and the
 respective cutting inserts were pulled out of the toolholder with a
 pull-out velocity of 1 mm/min. In the case of the cutting tool according
 to the invention, the forces to pull out the cutting inserts from the
 toolholder averaged about 1350 N. In contrast, with respect to the cutting
 inserts without roof-shaped elevations, the measured pull-out forces
 averaged about 700 N. In other words, the pull-out forces were increased
 to a value almost twice as large by use of the roof-shaped elevations
 according to the present invention.
 Although an illustrative preferred embodiment has been described herein in
 detail, it should be noted and will be appreciated by those skilled in the
 art that numerous variations may be made within the scope of this
 invention without departing from the principle of this invention and
 without sacrificing its chief advantages. The terms and expressions have
 been used herein as terms of description and not terms of limitation.
 There is no intention to use the terms or expressions to exclude any
 equivalents of features shown and described or portions thereof and this
 invention should be defined in accordance with the claims which follow.