Cutters – for shaping – Including holder having seat for inserted tool – With separate means to fasten tool to holder
Reexamination Certificate
1997-04-08
2001-07-17
Tsai, Henry (Department: 3722)
Cutters, for shaping
Including holder having seat for inserted tool
With separate means to fasten tool to holder
C407S107000, C407S117000
Reexamination Certificate
active
06261032
ABSTRACT:
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° and 90°. 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.
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Duwe Jurgen
Stricker Rudolf
Morgan & Finnegan , LLP
Schwarzkopf Technologies Corporation
Tsai Henry
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