Cutting by use of rotating axially moving tool – With means to apply transient – fluent medium to work or product – Including tool with duct
Reexamination Certificate
2001-01-31
2003-02-04
Howell, Daniel W. (Department: 3722)
Cutting by use of rotating axially moving tool
With means to apply transient, fluent medium to work or product
Including tool with duct
C408S227000, C408S231000, C408S713000
Reexamination Certificate
active
06514019
ABSTRACT:
BACKGROUND ART
The invention relates to a boring tool according to the preamble of claim
1
, especially a pointed boring tool, with an exchangeable cutting insert which is secured against loosening.
From European Patent B 0625395 there is known a boring tool of the class in question which is provided with a holder with an axial clamping slit, in which there is inserted a plate-shaped boring cutter as the exchangeable cutting insert in such a way that it bears against the clamping-slit base face. The nonpositive fastening of the boring cutter to the holder is achieved via at least one threaded stud, which is provided with a head and which engages in a bore in at least one of the clamping-slit branches as well as in a bore in the boring cutter. The central axis of the bore in the clamping-slit branch is offset in longitudinal and transverse direction of the boring tool relative to the central axis of the bore in the boring cutter. Furthermore, at least one of two circumferential rims of the threaded stud and boring-cutter bore facing one another is chamfered. In order to permit exact centering of the boring cutter relative to the axis of rotation of the holder, there is inserted, in a bore extending from the clamping-slit base face into the holder, a portion of a centering pin, whose other portion engages in a centering slit in the side of the boring cutter bearing against the clamping-slit base face, in order to center the boring cutter relative to the axis of rotation of the holder. The nominal width of the centering slit is made larger than that of the portion of the centering pin engaging in the centering slit. The direction and size of the offset of the central axes of the bore in the boring cutter and the bore in the clamping-slit branch are also chosen so as to ensure that, in the clamped condition of the threaded stud, only one centering-slit side face bears against one side of the centering pin when the boring cutter is in centered position.
By means of the configuration of the boring tool described in the foregoing it is indeed possible to make the tolerance range of the position of the centering-slit side face bearing against the centering pin as small as desired, but it suffers from the disadvantage of the highly complex manufacturing operations which must be performed to produce the centering slit in the boring cutter in view of the arrangement relative to the bore for receiving the centering pin in the holder. Another apparent disadvantage of the boring tool described hereinabove is that extremely high precision is necessary in machining the clamping slit and making the bore in the clamping-slit base face or the centering slit in the boring cutter in view of the minimal possible play between the boring cutter and the clamping slit. Even with very small tolerances, it is conceivable that, although the boring cutter, by means of the threaded stud, will indeed fit into correct position in the clamping slit immediately after assembly, the boring cutter will not always be able to bear stably against the clamping-slit base face in the desired manner during operation of the boring tool. For example, unwanted gaps may develop between the clamping-slit base face and the side of the boring cutter bearing against the said clamping-slit base face, and these gaps may be further enlarged by the vibrations occurring during operation of the boring tool.
Furthermore, when the boring cutter is in a centered position as described in the foregoing discussion, a centering pin of a cylindrical shape or a square shape in cross section bears against one centering-slit side face of the boring cutter. Aside from the high mechanical stress and strain on the centering pin during clamping of the boring cutter in the clamping slit of the holder by operation of the threaded stud, the centering pin must withstand large dynamic loads during operation of the boring tool. The boring tool is usually exposed to strong vibrations and stresses during its operation, for example due to discontinuous cutting. Under the influence of compressive forces resulting from the stresses and vibrations, deformation in the form of rectangular flattening develops on the centering pin, especially if it has cylindrical geometry, as well as on the side face in question in the clamping slit of the boring cutter. Furthermore, strong bending deformations due to the large compressive forces can be produced in the cylindrical centering pin and also in the centering pin having square cross section, since only a relatively small cross-sectional area can be achieved in the transverse direction of the boring tool, or in other words in the direction of the groove, even in the case of a centering pin with square cross section. Such deformations permit offset, albeit only slight, of the boring cutter in the clamping slit of the holder. This is detrimental to the intended exact and play-free centering of the boring cutter relative to the axis of rotation of the holder. The consequences can include development of inaccurate concentric running of the boring cutter, especially of its point, and thus shortening of the service life of the boring cutter and of the boring tool as a whole.
Aside from the highly complex manufacturing operations, another disadvantage is considered to be equipment complexity, from the viewpoint of compactness of the boring tool and of exact and true positioning of the boring cutter by means of the centering pin in the clamping slit of the holder.
DISCLOSURE OF INVENTION
The object of the invention is therefore to improve the boring tool of the class in question described in the introduction by means of an exchangeable cutting insert which is secured against loosening, such that the cutting insert can be centered and fixed relative to the holder in a manner that is simple from the equipment viewpoint but is nevertheless stable, exact and true.
This object is achieved by the inventive boring tool according to the features of the present invention. Advantageous embodiments of this boring tool are also the subject matter of the present invention.
A boring tool of the class in question with an exchangeable cutting insert as described in the preamble of claim
1
is generally operated at high cutting speeds. To ensure that the vibrations resulting from the high cutting speeds as well as the dynamic stresses and strains caused thereby can be withstood, such a boring tool is usually provided with a relatively large web diameter. The inventive improvement of the boring tool of the class in question now comprises in particular the fact that the cutting insert, which incidentally is preferably made of carbide metal, is provided with an extension which runs in the direction of the longitudinal axis of the boring tool and which reaches into a recess extending from the groove base face in the direction of the longitudinal axis to the shank portion and is pressed against a second stop face, provided in the recess, for fixation of the cutting insert in the direction of the transverse axis. The fact that the web diameter of boring tools of the class in question is generally relatively large is therefore utilized advantageously in the inventive improvement in order to form the recess for receiving the axial extension of the cutting insert. Since adequate space is available by virtue of the relatively large cross section of the boring-tool web, the recess can be formed without substantially reducing the strength and thus the stability of the boring tool.
Centering and fixation of the cutting insert on the holder are therefore accomplished via two stop faces, wherein the first stop face is intended to position the cutting insert primarily in the direction of the longitudinal axis and the second stop face is intended to position the cutting insert primarily in the direction of the transverse axis. By appropriate orientation of the first and second stop faces, for example by forming them as flat faces, each of which lies in a plane that is not normal relative to the longitudinal axis, it is naturally also possible for the first an
Dr. Joerg Guehring
Howell Daniel W.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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