Title of Invention

CUTTING UNIT AND TOOL WITH CUTTING UNIT

Abstract

Disclosed herein is a Cutting Unit comprising a generally flat cutting-insert body of polygonal shape and opposite sides, said body being formed along at least one of said sides with a cutting comer defined between two angularly adjoining cutting edges at junctions between a rake face formed on said one of said sides and respective clearance faces extending between said sides, a spherically segmental indentation being formed in said rake face at said comer and intersecting said cutting edges with respective arcs where said cutting edges adjoin at said comer, said cutting edges being linear over stretches thereof extending away from said arcs.

Full Text

The invention concerns with a cutting unit for chip-forming machining of workpieces, especially for the roughing and finish machining while face milling of grey cast iron with multiple cutting edges adjoining the rake faces, of which two cutting edges limiting against each other form a cutting comer, and with at least one trough-shaped indentation breaking open the cutting edge. The invention further concerns with a tool, consisting of a tool holder with at least one recess for receiving one such cutting unit. Milling operations are frequently carried out in two machining cycles, one pre-machining (rough milling) and one finish machining. Thus, in a combined roughing-cum-finishing tool, calculations can be done, so that one portion of the cutting units clamped in the recesses provided (insert seats) in the tool holder is used as pure roughing tool, and the other balance portion as finishing tool. Examples of finish-cutting units are described in the Indian Application No. 1763/MAS/97. The cutting unit therein, which preferably has a regular hexagonal rake face, possesses many main cutting edges and side cutting edges adjoining these main cutting edges. As described in this publication, the cutting unit therein is used in combination with a pure cutting unit for rough machining. The cutting unit described in the said Indian Patent Application, produces at the junction at the side cutting edge, a concave chip-forming groove, whose radius lies between 0.5 mm and 0.8 mm. Through this chip-forming grove, the side rake angle may be adjusted between 10 deg. and 20 deg. Also, along the main cutting edge, a chip-forming groove extends, which produces a radius of curvature of 0.5 mm measured in the cross-section. This publication does not deal with purely rough milling throw-away inserts. A cutting unit is known as per the patent publication DE 28 40 610 C2, which, in the rake face along the cutting edge, has indentations, whose width or biggest extension parallel to the cutting edge is greater than the distance between two neighbouring indentations. Each of these indentations breaks the cutting edge, which, due to this, changes in its shape in the region of the interruptions, i.e., it does not form any more straight lines, but produces shapes in the region of the interruptions, these shapes lying behind the straight cutting edge portions and being provided in the direction of chip flow. Through these measures, compressions are generated in the flowing chip, which lead to a breakage of the chips into short pieces. The region of a cutting comer could, however, be free from indentations, and instead of this, could possess a flat chip face piece or a negative strengthening face, in order to avoid hardened chip-forming compressions in the comer region. As per the document DE 28 40 610 C2, the said indentations can be arranged also in a chip-forming trough running along the cutting edge. Especially, in the said publication, a triangular-shaped cutting unit for drilling is discussed, which is not suitable for rough milling operations. The US Patent Document US-A 4 710 069 describes a cutting unit, which has a chamfer along its cutting edge, and a groove-shaped recess at the junction of the chamfer with the region away from the cutting edge. The limiting line between the said chamfer and the groove-shaped recess is broken by many cavities arranged equidistantly, whose depth could be smaller than 0.1 mm. The cavities are essentially partly ball-shaped recesses Avith a radius of curvature of 0.5 mm. This type of cutting unit is, however, suitable only for turning operations. The present shape design of roughing cutting units shows a chip-forming trough at the jimction of the cutting edge and extending over its entire length. This chip-forming trough, in the region of a cutting edge comer, is interrupted by stiffening surfaces lying at a relatively higher level. The roughing-finishing machining is however carried out using depths of cut lying in the range of 0.5 to 1 mm. Hereby, essentially, machining is done with rounded cutting comer, so that any change in the chip-forming groove by way of too high chip-forming angles does not represent any real improvement. In addition, for an elongation of a chip-forming groove in the cutting comer regions with reduction of the width of the stiffening surfaces, limits are already thus set, so that the remaining sharp edged projections, especially in the cutting comer regions, are subjected easily to cracks, which reduces the tool life on the cutting unit considerably. Thus, the purpose of the present invention is to present a cutting unit for roughing and finishing, wherein the axial forces encountered in the milling unit is markedly reduced. This purpose is solved by the cutting unit according to the invention, characterized in that, the indentation is arranged in the cutting comer region, and interrupts both the cutting edges adjoining there. As against the method, proclaimed especially in the pubUcation DE 28 40 610 C2, of leaving the cutting comer region free from trough-shaped cavities or indentations, the cutting units designed according to the invention shown considerably reduced cutting forces, and also because of this, a conventional cutting unit causes improved life. By application of ball tunnel-shaped recess in the cutting comer region, considerably higher rake angle can be achieved, and, with the cutting unit clamped in a tool holder, higher effective radial as well as axial rake angles can be realized. The linear cutting edge, with the exception of the cutting comer region, is bent by the indentation, restricted in the direction at the cutting comer, in a concave manner in the rear portion, whereby the cutting comer is situated somewhere at the height of the cutting edge level running linearly, or negligibly lower than that level. This is repeated in a corresponding manner with the cutting edge adjoining at the junction at the cutting comer. The cutting unit, in the case of milling, is set in such a manner that, preferably, solely the concave cutting edge portion falling from the cutting comer cuts effectively at both the sides of the cutting comer. According to the desired depth of cut, the maximum width of indentation at the cutting comer region is decided. In the region of the effectively-cutting cutting comer, in each case, there adjoins a falling flank portion limited by the trough, the flanks producing an optional, desired positive rake angle. Preferably, the indentation is arranged symmetrically to the cutting comers, bisecting the angle. As per another version of the invention, the indentations are shaped to be of part ball segment type, whereby the radius of curvature of the concave indentations lies between 4 mm and 10 mm. The maximum depth of the indentation shall not preferably be more than 0.4 mm to 0.6 mm. Since the cutting comer is used only with an effective depth of cut of 0.5 mm to 1 mm, the maximum diameter of the indentation amounts to 4 mm. In order to achieve an adequate stability of the cutting comer, the rake angle γ in the cutting comer region must lie between +5 deg. and +20 deg., preferably between +8 deg. and +5 deg. In order that the cutting unit could be used not only on one side, but also on the top face as well as on the bottom face, for the production of a two-sided support face, a middle rake face plateau is provided, which overhangs the cutting edge plane. The middle rake face plateau possesses, according to another version of the invention, nose-shaped protrusions, which overhang in the rear region of the indentations. Preferably, the cutting unit as per the invention possesses a regular hexagonal shape, with which the respective cutting edges lying beside each other are arranged under an obtuse angle of 120 deg. The cutting edges are rounded, whereby, as per a version of the invention, the cutting comer rounding has a radius of between 0.4 mm and 3 mm. As explained already, the cutting unit is designed to be usable on both the sides, so that there result twelve cutting comers that are useful for machining. The cutting unit, according to the invention, is preferably set and clamped in a tool holder designed as milling body in a recess (insert seat) provided for this purpose. Clamping keys serve for clamping, by fixing the cutting unit with reference to the cutting tool axis. Likewise, it is also possible to arrange cutting units in cassettes, which are then clamped in the desired devices in the tool carrier. According to the invention, a device of the cutting unit for rough machining is selected, with which there results an effective axial rake angle γp of+5 deg. to +10 deg. and/or an effective radial rake angle γf of 0 deg, to +8 deg. in the recess of the cutting unit. An example of a version of the invention is represented in the figures. In the accompanying drawings: Fig, 1 shows the front view of a throw-away insert according to the invention, Fig. 2 shows a part view of this throw-away insert; Fig. 3 shows the throw-away insert with reference to its fitting position; Fig. 4 and Fig. 5 shows the respective part views of the throw-away insert as per the invention for representing the rake angle in the comer region; Fig. 6 shows the same part region as in Fig. 5, in the case of milling unit; Fig. 7 and Fig. 8 shows the respective part views of a cutting comer region for the representation of the ball tunnel-shaped design and position; Fig. 9 shows a partial view of cutting comer for the representation of the rake angle of the cutting edge in the rake face; and [ Fig. 10 shows a partial part view of the cutting comer for the representation of the radial rake angle γr. The cutting unit 11 represented in the drawings has a rake face shaped in the form of regular hexagon, which is limited by the six cutting edges 12 of which the cutting edges 12 lying one beside the other form a cutting comer 13. The cutting comers 13 are rounded, whereby the cutting edges 12 are adjoined by respective flat relief faces 14 and relief face sections 15 rounding at the cutting comers. In the rake face, the cutting unit has a middle rake face plateau which is built star-shaped, and shows nose-shaped projections 17, respectively overhanging in the direction of the cutting comer. Between two cutting comers are arranged more projections 18, which are directed somewhere in the middle of the respective cutting edge 12. The cutting unit 11, according to the invention, has ball tunnel-shaped indentations 19 in the region of each cutting comer 13 in the rake face. A chip-forming groove 20 extending along the cutting edge 12 runs parallel to the cutting edge, outside the region of the ball tunnel-shaped indentations 19. As can be seen, especially, from Fig. 1, the nose-shaped projections 17 and 18 contain a lower concave portion and an upper convex portion. The projections can however possess also flat falling flanks, or convexly-or concavely-shaped flanks. The throw-away insert has a thickness d of, e.g., S.56 mm and an inscribed circle diameter of 16.2 mm. The throw-away insert with double-sided design is assembled preferably for milling in a tool holder, which rotates about the rotary axis 21. The cutting units 11 run at a milling cutter radius Rf, whereby the cutting unit (besides further roughing cutting units) is moved in the direction of the arrow 22. The machining operation hereby carried out can be seen in detail in Fig.6. The work-piece 23 is machined with a face milling cutter with a depth of cut of ap, whereby many roughing cutting units 11 come to operation. In these milling operations, a positive axial rake angle γp is provided over the tunnel design described (see Fig.4) Fig. 5 shows, referred to a depth of cut ap of, e.g., 0.5 mm, a rake angle γ0 at distance b of about 0.5 mm from the cutting edge of a measuring length, which corresponds to the feed per tooth fz selected here as 0.5 mm. It is clear from Fig. 7 that the indentation 19 is part of a ball tunnel segment. The present ball or partial ball 14 is to be taken from Fig. 7. The present ball radius RK lies between 4 mm and 10 mm, and the maximum tunnel depth t within values of 0.4 mm to 0.6 mm. Fig. 9 shows the rake angle γ, under which the rake face region adjoining fee straight line portion of the cutting edge is inclined. The radial rake angle γf, which results from the fitting position of the cutting unit in the tool holder, is represented in Fig. 10. The milling cutters attached with cutting units 11 were used for the cutting of an work piece 23. In contrast to the usually-applied six-comered throw-away inserts known as per the state-of-the-art, reduction in passive force Fp of about 40% was observed. WE CLAIM: 1. Cutting unit (11) for chip-forming machining of workpieces (23), expecially for roughing-finishing machining in face milling of grey cast iron, comprising a generally flat cutting-insert body of polygonal shape and opposite sides, said body being formed along at least one of said sides with a cutting comer defined between two angularly adjoining cutting edges at junctions between a rake face formed on said one of said sides and respective clearance faces extending between said sides, a spherically segmental indentation being formed in said rake face at said comer and intersecting said cutting edges with respective arcs where said cutting edges adjoin at said comer, said cutting edges being linear over stretches thereof extending away from said arcs. 2. Cutting unit as claimed in claim 1, wherein, the indentation (19) is arranged symmetrically with the bisector of the angle of the cutting comer. 3. Cutting unit as claimed in claim 1 or 2, wherein, the indentation (19) is a partial ball segment, and/or has a radius of curvature (RK) of between 4 mm and 10 mm. 4. Cutting unit as claimed in any one of the claims 1 to 3, wherein, the maximum depth (t) of the indentation (19) lies between 0.4 mm and 0.6 mm. 5. Cutting unit as claimed in any one of the claims 1 to 4, wherein, the maximum diameter (d) of the indentation (19) amoxmts to 4 mm. 6. Cutting unit as claimed in any one of the claims 1 to 5, wherein, the rake angle (γO) in the cutting comer region lies between +5 deg. and +20 deg., preferably between +8 deg. and +15 deg. 7. Cutting unit as claimed in any one of the claims 1 to 6, wherein, in the rake face is arranged a middle rake face plateau (16) with a nose-shaped projection (17) protruding in the rear side regin of the indentation (19). 8. Cutting unit as claimed in any one of the claims 1 to 7, wherein, a regular hexagonal shaped cutting comers (13), preferably with rounded cutting comers; are provided. 9. Cutting unit as claimed in claim 8, wherein, the cutting comer rounding has a radius of between 0,4 mm and 3 mm. 10. Tool, made of a tool holder with at least one recess for receiving of a cutting unit (11) as claimed in any one of the claims 1 to 9, wherein, the cutting unit (11) is designed to have an effective axial rake angle (γp) of +5 deg. to +10 deg. and/or an effective radial rake angle (γf) of 0 deg. to +8 deg. in the cutting unit recess.

Documents:

434-mas-1999-abstract.pdf

434-mas-1999-claims filed.pdf

434-mas-1999-claims granted.pdf

434-mas-1999-correspondnece-others.pdf

434-mas-1999-correspondnece-po.pdf

434-mas-1999-description(complete)filed.pdf

434-mas-1999-description(complete)granted.pdf

434-mas-1999-drawings.pdf

434-mas-1999-form 1.pdf

434-mas-1999-form 26.pdf

434-mas-1999-form 3.pdf

434-mas-1999-form 4.pdf

434-mas-1999-pct.pdf