| JP03121707 | HOLD CONFIRMING DEVICE FOR POWER CHUCK |
| WO/2003/002295 | CHUCK FOR HOLDING A HUB ASSEMBLY |
| WO/2003/059623 | MERHOD OF MAKING STRUCTURAL CELLULAR CORES SUITABLE TO USE OF WOOD |
NANNINI, Egisto (Via Migliari, 2 Pieve a Presciano, Pergine Valdarno, I-52020, IT)
CLAIMS
1. A tool holder-tool coupling for machine tools, in which the tool is provided with a cylindrical coupling shank (1) which protrudes from a flat contrast surface (6) which is oriented along a plane which is normal to the axis of the tool to which it belongs, a corresponding seat (2) in a tool holder assembly being delimited at the front by a flat contrast surface (7) which is oriented along a plane which is normal to the axis of said cavity or seat (2), said cavity having a cylindrical shape and a diameter which is adapted to receive internally the shank ( 1 ) of the tool, characterized in that the shank (1) is constituted by two cylindrical segments (4, 3) whose diameter increases starting from the outermost one (3) and in that said two cylindrical segments (4, 3) are joined by a blending surface (5), the seat (2) intended to receive said shank (1) being characterized by a coupling cavity constituted by two coaxial cylindrical cavities (8, 9) in succession, in that the outermost cavity (8) is the one having the largest diameter, equal to the diameter of the wider cylindrical portion (4) of the shank (1) increased by a few thousandths of a millimeter and having a length which is greater than the length of the wider cylindrical portion (4) of said shank (1) of the tool.
2. The coupling according to claim 1, characterized in that the blending surface (5), which connects the two cylindrical segments (3, 4) of the shank (1 ), is frustum-shaped, with an inclination on the axis comprised between 60° and 15°.
3. The coupling according to claim 1, characterized in that the length of the cylindrical segment (3) of the shank (1) is comprised between 0.3 and 1.5 times its diameter.
4. The coupling according to claim 1 , characterized in that the seat (2) in the tool holder assembly has the outermost cylindrical cavity (8) which has a diameter equal to the diameter of the wider cylindrical segment (4) of the shank ( 1 ) with an increase comprised between 1 and 10 thousandths of a millimeter.
5. The coupling according to claims 1 and 4, characterized in that the increase in the diameter of the larger cylindrical segment (4) of the shank (1) is comprised between 2 and 5 thousandths of a millimeter. |
TOOL HOLDER-TOOL COUPLING FOR MACHINE TOOLS
Technical field
The present invention relates to a tool holder-tool coupling for machine tools, particularly machine tools which perform very high precision machining.
Background Art
Machines are known which use tools with a coupling shank and tool holder means, which in some machines are constituted by a spindle provided with a receptacle in which the tool is fixed in order to be turned axially.
The coupling between the shank of the tool and the receptacle in the tool holder assembly designed to receive it provides, in the tool, a conical shank and, in the corresponding tool holder assembly, a frustum-shaped cavity, as well as axial screw-type traction means, by way of which the shank of the tool is pulled toward the tool holder assembly.
The tool further has, at the widest end of its shank, an annular abutment surface which contrasts against a corresponding surface on the tool holder assembly, so as to stabilize the position of the tool in the coupled state. The perfect positioning of the tool and therefore its perfect coaxial position with respect to the tool holder should be ensured by the coaxial guiding surfaces, by the flat contrast surfaces, and by the traction of the means, normally of the screw type, with which the tool is pulled axially into the seat of the tool holder. Such configurations, combinations of parts and axial stresses, however, do not ensure the perfect positioning of the tool, particularly when it has been inserted and removed several times from the seat that accommodates its shank.
The conical surfaces should in fact adhere to each other simultaneously with respect to the contrast and abutment surfaces which
have an annular shape; this, however, does not occur, since either the conical surfaces adhere or the contrast surfaces adhere, particularly after the corresponding surfaces have undergone deformations and wear, albeit micrometric, due to repeated mounting and removal of the tool. Likewise, the axial traction of the screw means, after repeated activation-deactivation, is imperfect due to the deformations that the threads of the two coupled parts undergo.
These imperfections, which lead to imperfect positioning of the tool in the tool holder assembly intended to support it and turn it rapidly axially, have been disclosed in EPl 193011, in which the shank of the tool is frustum-shaped, is relatively massive and in any case is treated so as to not undergo deformations. The tool holder assembly, at the seat intended to accommodate, and thus interact with, the shank of the tool, is instead shaped and sized so as to undergo such elastic deformations that the frustum-shaped body of the shank, under the traction of the screw-type axial traction means, presses against the frustum-shaped surface of the seat that accommodates it in the tool holder assembly and causes its elastic deformation, until the annular adhesion surface at the top of the shank adheres against the corresponding contrast and abutment surface in the tool holder. Perfect coaxiality is therefore reached both with the mutual adhesion of the contrast and abutment surfaces, which determine at least the parallel arrangement of the axes of the tool and of the tool holder, and with the adhesion of the frustum-shaped surfaces of the shank and of the seat that accommodates it, which should make the two axes overlap. However, this is true only in theory, since the non-uniformity of the thicknesses of the metal that delimits the seat of the shank of the tool in the tool holder and the nonuniform elasticity of the metal of which the tool holder assembly is made, due to non-uniform heatings and coolings during use, make the assumption of uniform elastic deformation unreliable. All this, therefore, can lead to less than perfect coaxiality of the tool
and of the tool holder assembly and therefore to machinings performed in imperfect manner, particularly when the tool has been mounted into and removed from the seat of the tool holder several times. Disclosure of the Invention The aim of the present invention is to provide a coupling between the shank of the tool and the shank receptacle in the tool holder which is easy to provide and therefore entails a low cost.
Within this aim, an object of the present invention is to provide a tool shank-shank receptacle coupling in the tool holder which is structured so as to allow quick and safe replacement of one tool with another one or reinsertion of the same tool in the seat that accommodates its shank.
Another object of the invention is to provide a coupling of the shank of the tool with the seat intended to accommodate it in the tool holder assembly which is safe and precise, even after many mountings and removals of the tool in or from the tool holder.
This aim and these and other objects which will become better apparent hereinafter are achieved by the coupling according to the invention, which is provided by means of:
- a tool with a shank constituted by two cylindrical segments of increasing diameter, starting from the outermost one, joined by a blending surface, the wider segment ending on the flat annular contrast surface that lies on the plane which is normal to the axis of said tool;
- a tool holder in which the seat of the shank is delimited at the front by the flat contrast surface and is constituted by two cylindrical cavities in succession, the wider one having a diameter which is equal to the diameter of the wider cylindrical portion of the shank increased by a few thousandths of a millimeter and longer than said wider cylindrical portion of said shank. A coupling provided with means thus shaped is advantageous because
the machinings required on the shank and on the seat intended to receive it, being cylindrical, are easy to provide even when the required tolerances are on the order of microns.
It is advantageous because the first cylindrical portion of the shank, the smaller one, does not require particular precisions, since it is designed to facilitate the match-up of said shank in the seat intended to accommodate it.
It is advantageous because the blending between the two cylindrical portions of the shank can be frustum-shaped or can even have a curved profile, since it has the function of facilitating the completion of the coupling of the shank with the seat adapted to receive it and therefore to guide the wider cylindrical segment of the shank into a coaxial position with respect to the seat intended to receive it, after the smaller portion has been inserted in said seat.
It is advantageous because the substantially identical diameters of the wider cylindrical segment of the shank and of the wider cylindrical cavity in the seat intended to receive it make the coupling substantially perfect. Moreover, the length of the wider cylindrical portion of the seat in the tool holder which is slightly greater than the length of the wider cylindrical segment of the shank ensures adhesion between the contrast surfaces: the surface of the shank and the surface of the tool holder thus ensuring their axial parallelism.
It is advantageous because the direct interaction between the tool holder and the tool limited only to the contrast surfaces allows the technological treatments intended to make the interacting parts, i.e., the tool shank and the seat intended to receive it in the tool holder, very hard, and this allows to achieve very high precisions of the coupling which are not altered by the number of times that the tool has been coupled or detached from the tool holder assembly. Brief description of the drawings Further characteristics and advantages of the invention will be
understood easily, particularly by the persons skilled in the art, with the detailed description that follows, which illustrates the embodiment to which the invention relates, and wherein:
Figure 1 is a front view of the shank of the tool; Figure 2 is an exemplifying axial sectional view of the shank of
Figure 1;
Figure 3 is a front view, in a different scale, of the shank of the tool and of the seat intended to receive it in the tool holder, separated from each other, both shown in cross-section along an axial plane and reproduced only in the part that relates to their coupling.
It is understood that the drawings, of the exemplifying type, are provided with the sole purpose of facilitating the understanding of the invention, without constituting any limitation thereof. Ways of carrying out the Invention Substantially, the invention relates to the particular shape and structure of the parts which, by moving, determine the coupling between the seat provided in the tool holder assembly and the rear part or shank of the tool. The tool is provided with a cylindrical coupling shank 1 which protrudes from a flat contrast surface 6 which is oriented along a plane which is normal to the axis of the tool to which it belongs.
A corresponding seat 2 in the tool holder assembly is delimited at the front by a flat contrast surface 7, which is oriented along a plane which is normal to the axis of the cavity or seat 2, said cavity or seat having a cylindrical shape and a diameter which is adapted to receive internally the shank 1 of the tool.
The shank 1 is constituted by two cylindrical segments 4 and 3 in mutual succession, with a diameter which increases starting from the outermost one 3, the two cylindrical segments 4 and 3 being joined by a blending surface 5. Such blending surface is frustum-shaped, with an inclination on the axis of the shank comprised between 60° and 15°, while
starting from the outer end of said shank it has a length comprised between 0.3 and 1.5 times its diameter, as specified hereinafter from the functional aspect.
The cavity or seat 2 in the tool holder assembly, intended to receive the shank 1 , is constituted by two cylindrical cavities 8 and 9 in succession which are mutually coaxial and separated by an annular blending surface, the outermost cavity 8 having a larger diameter equal to the diameter of the wider cylindrical segment 4 of the shank 1 , increased by a few thousandths of a millimeter, and being longer than the wider cylindrical segment 4 of the shank 1, so that the play between them is minimal and barely sufficient to allow them to perform mutual axial sliding movements.
In the practical embodiments, the cylindrical cavity 8 has a diameter which is equal to the diameter of the wider cylindrical segment 4 of the shank 1 with an increase comprised between 1 and 10 thousandths of a millimeter and normally comprised between 2 and 5 thousandths of a millimeter.
The shank 1 and the cavity or seat 2, thanks to the cylindrical segment 3 of the shank 1 which is narrower than the hollow portion 8 of the seat 2, are mutually coupled with relative ease, thus allowing the tool to be arranged in a substantially coaxial position with respect to the cavity that must accommodate it in its rear part or shank.
The annular portion 5 that joins the cylindrical segments 3 and 4 of the shank 1 has such a taper as to facilitate the insertion and sliding of the cylindrical segment 4 within the cylindrical portion 8 of substantially the same width in the cavity 2, therefore such as to prevent jamming of the cylindrical segment 4 and at the same time the excessive elongation of the shank 1 for an equal length of the cylindrical segment 4 which is the part of the shank that keeps it positioned within the cavity 2.
The shank 1 , in the embodiment exemplified in the drawings, has the initial portion which is cylindrical with at least one facet 10, which by
interacting with a corresponding flat surface 1 1 in the tool holder assembly turns said tool, while the axial traction means through a cavity 13 in the tool holder assembly reach a threaded cavity 12 within the shank 1 , applying thereto traction until the contrast surfaces 7 and 6 adhere to each other. During production, the tool holder and the tool may be shaped in any manner, without altering the parts intended to mate, the shape of which constitutes the foundation of the invention, as defined by the appended claims.
The disclosures in Italian Utility Model Application No. AR2007U000002 from which this application claims priority are incorporated herein by reference.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.