WO1999007507A2 - Procede et appareil pour l'usinage des metaux durs - Google Patents

Procede et appareil pour l'usinage des metaux durs Download PDF

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Publication number
WO1999007507A2
WO1999007507A2 PCT/US1998/016682 US9816682W WO9907507A2 WO 1999007507 A2 WO1999007507 A2 WO 1999007507A2 US 9816682 W US9816682 W US 9816682W WO 9907507 A2 WO9907507 A2 WO 9907507A2
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WO
WIPO (PCT)
Prior art keywords
tool
cutting edge
workpiece
cutting
engagement
Prior art date
Application number
PCT/US1998/016682
Other languages
English (en)
Other versions
WO1999007507A3 (fr
Inventor
Milton C. Shaw
Amitabh Vyas
Original Assignee
Arizona Board Of Regents, A Body Corporate Acting On Behalf Of Arizona State University
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Arizona Board Of Regents, A Body Corporate Acting On Behalf Of Arizona State University filed Critical Arizona Board Of Regents, A Body Corporate Acting On Behalf Of Arizona State University
Priority to US09/554,319 priority Critical patent/US6733365B1/en
Publication of WO1999007507A2 publication Critical patent/WO1999007507A2/fr
Publication of WO1999007507A3 publication Critical patent/WO1999007507A3/fr

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23B—TURNING; BORING
    • B23B27/00—Tools for turning or boring machines; Tools of a similar kind in general; Accessories therefor
    • B23B27/10—Cutting tools with special provision for cooling
    • B23B27/12—Cutting tools with special provision for cooling with a continuously-rotated circular cutting edge; Holders therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23B—TURNING; BORING
    • B23B2226/00—Materials of tools or workpieces not comprising a metal
    • B23B2226/18—Ceramic

Definitions

  • This invention relates to a method and apparatus for hard machining a hardened workpiece, and more particularly to such methods and apparatus in which the cutting tool is moved to bring a fresh, unworn portion of a cutting edge into cutting engagement with the workpiece.
  • hard turning or “hard machining.” This involves removing material from a workpiece in a machining operation with the workpiece in a hardened state.
  • parts such as ball and roller bearings, gears, cams, etc.
  • parts that must be hardened to decrease wear, by the following sequence of steps: rough machine a part in its soft state, heat treat the part, and rough and finish grind the part to provide desired accuracy and surface finish.
  • hard machining the hardened part is machined to produce a part in a single operation instead of the more costly sequence indicated above.
  • Hard machining has become an option with the appearance of improved tool materials such as cubic boron nitride or polycrystalline cubic boron nitride
  • CBN CBN or PCBN, " respectively
  • PCBN PCBN
  • the CBN or PCBN is very expensive (comparable to diamond in this respect), while the latter, hard-cutting ceramics, have a much shorter tool life, but a much lower cost. It would be possible to use the less expensive ceramic tool material, a superior grade of carbide or other low cost tool material capable of hard machining, provided the nonproductive tool changing time could be reduced and the tool material could be used more efficiently.
  • An improved method and apparatus for combining a comparatively coarse, roughing cut at a high removal rate and a finishing cut at a low removal rate are employed that are useful in hard turning operations.
  • the new method and apparatus make it possible to use a much less expensive tool material such as ceramic in place of PCBN that is now used in hard turning operations. This is accomplished by offsetting the lower tool life of a lower cost tool relative to that of a PCBN tool by providing the tool with an extended cutting edge extending along a path of translation and moving the tool to move the cutting edge along the path of translation so that a fresh cutting edge portion is brought rapidly into cutting position.
  • a fresh cutting edge portion is moved into position to replace the portion of cutting edge being used for the finishing cut, which finishing portion of the cutting edge is less than the entire portion in engagement with the workpiece.
  • the method and apparatus of the invention achieves the above objectives by: using a large diameter cylindrical tool of ceramic having a large number of new cutting edges (or cutting portions of the continuous circular cutting edge) along the periphery of the face of a single cylindrical tool, and reducing the nonproductive downtime to change tools to essentially zero by merely rotating the cylindrical tool through a small arc when a new cutting edge is required.
  • the substitution of a ceramic tool material for CBN or PCBN has an important thermal advantage in the combined roughing/finishing cut employed in hard turning. CBN has a much higher thermal diffusivity than does a ceramic. While this is advantageous relative to tool wear in conventional machining applications, this is not the case for the type of cut employed in hard turning as shown in Fig.
  • d is the depth of cut and f is the feed per revolution (fpr).
  • a chip region of large thickness (t r ) responsible for most of the removal (and hence temperature rise) is contiguous with the finishing region of the chip having low thickness (t f ) (and hence low removal rate and low temperature rise).
  • the finish of the surface produced is influenced primarily by the thickness of the chip t f , while the bulk of the material is removed in the region where the chip thickness is t r .
  • the bulk of the heat generated and hence most of the tool wear will be in the t r region. Relative to surface finish, tool wear in the t f (finishing cut) region is more important than that in the t r (comparatively coarse cut) roughing region.
  • Figure 1 is a fragmentary diagrammatic illustration showing the shape of a chip being formed when cutting is confined to the nose radius of a tool.
  • Figure 2 is a fragmentary diagrammatic illustration showing a conventional hard turning operation with only a small portion of a tool face consisting of PCBN.
  • Figure 3 is a fragmentary diagrammatic illustration showing the scallop left behind on the finished surface where the depth of the scallop (R m ) is the peak-to-valley roughness which depends upon the radius at the tool tip and the feed per revolution (f).
  • Figure 4 is an enlarged diagrammatic illustration of a portion of the scallop of Fig. 3 showing the relation between peak-to-valley roughness (R ra ) and centerline-average-roughness (R a ), where the centerline is located so that the areas above and below the centerline are equal, and R a is the mean distance from the centerline to the ⁇ surface of the scallop over one feed distance f.
  • Figure 5 is a diagrammatic illustration showing the relation between a cylindrical tool of large radius and the work in accordance with the present invention.
  • Figure 5 A is a diagrammatic, fragmentary cross-sectional view along the line A - - A of Fig. 5.
  • Figure 6 is a diagrammatic representation of an apparatus providing one means of rapidly indexing the cutting edge of the cylindrical tool of Fig. 5 each time a new surface is to be provided that eliminates the adverse effects of tool wear on the geometry of the surface left behind on the workpiece.
  • Figure 6 A is a diagrammatic top plan view, partially in section of a stepper motor and driven worm gear for effecting the rapid indexing of the apparatus of Fig. 6.
  • Figure 7 is a fragmentary diagrammatic view, partially block diagram, showing the tool of Figs. 5 and 5 A in the environment of a lathe.
  • FIG. 2 at present hard turning is performed using a tool 11 having an expensive polycrystalline CBN insert 12.
  • PCBN is a composite of small single crystal particles bonded together by sintering.
  • a typical application is shown in Figs. 1 and 2 where:
  • f is the feed rate, inches per rotation (hereinafter “ipr")
  • d is the depth of cut
  • inches hereinafter “in. "
  • N are the rotations per minute (hereinafter “rpm” of a workpiece 15
  • V is the cutting speed defined as 7rDN (in. per minute), perpendicular to the paper, and "r” is the radius (in.) of the tool insert 12.
  • the surface finish depends primarily upon a scallop 16 generated by the nose of the tool having a radius r.
  • Figure 3 shows this scallop 16 with feed (f) greatly magnified relative to r, and where R m is the depth of the scallop. R m is called the peak-to-valley roughness.
  • Figs. 5 and 5A show a cylindrical tool 21 of large radius r.
  • the tool 21 has a tool face 23 and a tool flank 24, both as seen in Fig. 5 A.
  • the tool 21 is mounted with its axis inclined to provide a negative rake angle and a positive clearance angle ⁇ from a workpiece 20.
  • a small portion of the edge formed by the tool face and the tool flank will be in use.
  • a depth of cut (d) equal to lOf or 0.09 in. (0.23 cm.)
  • a total arc of contact equal to cos " '(l - 0.09/0.5) or 35°
  • a minimum tool change per cylindrical tool of 10 based on complete arc of contact ⁇
  • a critical arc ⁇ equal to cos _1 (l - 40xl0 "6 /0.5) or 0.72°
  • the cutting edge in order to take full advantage of the multiple cutting edge aspect of a relatively large cylindrical tool, the cutting edge should be as perfectly circular as possible and the tool rotation should be performed rapidly and without shift of the center of rotation.
  • the tool 21 is a disc-shaped ceramic material (or other comparatively low cost tool material suitable for hard machining).
  • the tool 21 is attached to the top of a metal piston 32 restrained by a retaining member 33 with a lapped bearing surface 34, with very small clearance. After the ceramic tool 21 is attached, the tool face 23 and tool flank 24 surfaces are diamond ground with the piston 32 in place in the lapped
  • the tool face 23 is generally perpendicular to the axis of the cylindrical piston 32.
  • the tool flank 24 is substantially perpendicular to the tool face, but may be varied to present the correct cutting edge with respect to the workpiece.
  • the tool 21 is contacted with the workpiece (not shown is Fig. 6).
  • the tool 21 is rotated as needed to maintain a cutting surface capable of producing the required finish. After the entire edge of the cylindrical tool has been utilized, it may be possible to regrind the tool face and tool flank surfaces with the piston in place in the lapped retaining member 33 to obtain a whole new set of cutting edges.
  • a means for rapid and precise rotary indexing and prevention of rotation of the cylinder during cutting can also be provided. This is achieved by a gear 40 attached to the bottom of the piston 32.
  • An adjustable stepping motor 41 actuates a worm gear 42 engaging the gear 40.
  • a thrust bearing 44 supports the gear
  • the tool 21 and its movable support provisions 35 may be used in the environment of a conventional machine tool, such as a lathe having a rotational drive 51 for rotating the workpiece 20.
  • a longitudinal feed 52 effects relative movement (feed) between the tool 21 and the workpiece 20.
  • a transverse drive 53 forces the tool 21 into cutting engagement with workpiece 20 and thus establishes the arc of engagement between the cutting surface and the workpiece as illustrated in Fig. 5.
  • drives like those drives 51, 52 and 53 diagrammatically indicated in Fig. 7 can be conventional drives as known to those skilled in the art and suitable for turning, lapping, milling or other machining operations.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Turning (AREA)
  • Cutting Tools, Boring Holders, And Turrets (AREA)

Abstract

La présente invention concerne un procédé d'usinage des métaux durs utilisant un outil cylindrique en céramique ou en un autre matériau d'usinage dur ayant relativement le même bas prix, présentant un bord tranchant circulaire devant s'engager en relation de coupe avec une pièce à usiner durcie avant son usinage. Lorsque le bord tranchant de l'outil s'use, l'outil est mis en rotation autour d'un petit angle de manière à mettre en contact la pièce à usiner avec une nouvelle partie du bord tranchant. Cependant, il n'est pas nécessaire de trop mettre en rotation cet outil pour remplacer toute la partie du bord tranchant engagée avec l'outil. Par ailleurs, on soumet l'outil à un mouvement angulaire suffisant pour remplacer la partie la plus importante dans la finition du bord tranchant de la pièce usinée, c.a.d le côté tranchant où le copeau retiré est le plus fin.
PCT/US1998/016682 1997-08-12 1998-08-11 Procede et appareil pour l'usinage des metaux durs WO1999007507A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US09/554,319 US6733365B1 (en) 1997-08-12 1998-08-11 Method and apparatus for hard machining

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US5547997P 1997-08-12 1997-08-12
US60/055,479 1997-08-12

Publications (2)

Publication Number Publication Date
WO1999007507A2 true WO1999007507A2 (fr) 1999-02-18
WO1999007507A3 WO1999007507A3 (fr) 1999-11-18

Family

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Family Applications (1)

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PCT/US1998/016682 WO1999007507A2 (fr) 1997-08-12 1998-08-11 Procede et appareil pour l'usinage des metaux durs

Country Status (1)

Country Link
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005021191A3 (fr) * 2003-09-02 2005-10-13 Kennametal Inc Ensemble a insert rotatif tranchant et procede d'utilisation
US8573901B2 (en) 2003-09-02 2013-11-05 Kennametal Inc. Assembly for rotating a cutting insert during a turning operation and inserts used therein

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5006685A (en) * 1987-08-04 1991-04-09 Yamazaki Mazak Corporation Machine tool with grinding function and truing/dressing method of grinding stone using it
US5343656A (en) * 1989-08-01 1994-09-06 Hurth Maschinen Und Werkzeuge G.M.B.H. Grinding tool and the like made of a ceramic material coated with extremely hard abrasive granules
US5495844A (en) * 1991-11-06 1996-03-05 Toyoda Koki Kabushiki Kaisha Segmental grinding wheel
US5564966A (en) * 1993-11-08 1996-10-15 Sumitomo Electric Industries, Ltd. Grind-machining method of ceramic materials

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5006685A (en) * 1987-08-04 1991-04-09 Yamazaki Mazak Corporation Machine tool with grinding function and truing/dressing method of grinding stone using it
US5343656A (en) * 1989-08-01 1994-09-06 Hurth Maschinen Und Werkzeuge G.M.B.H. Grinding tool and the like made of a ceramic material coated with extremely hard abrasive granules
US5495844A (en) * 1991-11-06 1996-03-05 Toyoda Koki Kabushiki Kaisha Segmental grinding wheel
US5564966A (en) * 1993-11-08 1996-10-15 Sumitomo Electric Industries, Ltd. Grind-machining method of ceramic materials

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005021191A3 (fr) * 2003-09-02 2005-10-13 Kennametal Inc Ensemble a insert rotatif tranchant et procede d'utilisation
US7156006B2 (en) 2003-09-02 2007-01-02 Kennametal Inc. Method and assembly for rotating a cutting insert during a turning operation and inserts used therein
US7611313B2 (en) 2003-09-02 2009-11-03 Kennametal Inc. Method and assembly for rotating a cutting insert during a turning operation and inserts used therein
US8573901B2 (en) 2003-09-02 2013-11-05 Kennametal Inc. Assembly for rotating a cutting insert during a turning operation and inserts used therein

Also Published As

Publication number Publication date
WO1999007507A3 (fr) 1999-11-18

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