Cutters – for shaping – Rotary cutting tool – Including holder having seat for inserted tool
Reexamination Certificate
1999-11-23
2001-11-27
Tsai, Henry (Department: 3722)
Cutters, for shaping
Rotary cutting tool
Including holder having seat for inserted tool
C407S043000, C407S047000, C407S053000
Reexamination Certificate
active
06322296
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a machining tool, in particular a milling tool for precision machining operations, which is equipped with releasably secured cutting tips.
BACKGROUND OF THE INVENTION
Precision machining operations where high precision is demanded for the workpiece make high demands for precision of the tool as well. For instance, if complicated geometries are to be formed in one milling machining step, then as a rule high speed steel (HSS) milling cutters are used, which can have a relatively complicated contour. In the production of turbine rotors, for instance, undercut slots in a rotor shaft must be made, into which correspondingly shaped roots of turbine blades are thrust. The slots have a Christmas tree profile as a rule and are undercut multiple times. The desired shape of the slot must be formed with a high degree of precision during milling.
To this end, it is known from German Patent DE 196 11 276 C1 to first open the desired slot without an undercut, and then to make the undercuts, using a milling tool equipped with indexable cutting tips, in a roughing-down machining operation. The desired precision is then attained in one or more work steps using an HSS end milling cutter. Such an HSS end milling cutter has only relatively little material to remove. Nevertheless, the feeding speed cannot be increased without limit. HSS milling cutters are inferior in terms of their cutting speed to hard-metal-equipped milling cutters.
HSS milling cutters have to be reground from time to time. In the process, especially if the outer contour of the milling cutter defines the contour of the slot to be made, the milling contour must not be changed in the regrinding. To achieve this, the tool faces are as a rule made curved adjoining the cutting edge, or in other words are provided with a radial relief. The regrinding of the HSS milling cutter is then done by regrinding the chip face, without machining the tool face. This brings about an only slight reduction in the diameter.
In most cases, the slight clearance angle necessitates machining the workpiece in synchronism. This means that the feeding direction of the workpiece essentially matches the direction of motion of the cutting edge in engagement with the workpiece. In an individual case, however, synchronized machining can cause microscopic cracks or roughness in the machined surface, which can be problematic, especially for components subjected to heavy loads.
SUMMARY OF THE INVENTION
An object of the invention is to create a machining tool with which precision machining can be accomplished economically, is at a high machining speed.
This and other objects are attained in accordance with one aspect of the invention directed to a machining tool having a plurality of tip seats, which are arranged to receive correspondingly formed cutting tips. At least one cutting tip, which belongs to at least one set of cutting tips, is assigned to each tip seat. Preferably, however, each tool body is assigned a plurality of sets of cutting tips, and each set of cutting tips contains precisely one cutting tip for each tip seat. The fixed association of the tip seat and cutting tip, once defined, is then kept permanently. As a result, it can be attained that dimensional variations or tolerances in the tip seat and the cutting tip will have no influence on the precision in terms of the shape and position of the cutting edge of a cutting tip relative to the pivot axis of the machining tool. The cutting tip can be released from the tip seat and secured to it repeatedly, without causing any dimensional variation. The tool body acts both as the tool base body in the strict sense and as a cutting tip holder in the fine-machining of the cutting tips. The accuracy of the cutting edges can be substantially greater as a result than the accuracy of the tip seats.
To assure the desired association between the cutting tip and the tip seat and the permanent adherence to this association, the cutting tips are preferably provided with an individual marking, which designates the tip seat to which they are assigned. The marking may be an engraving, a colored mark, or a special shape, or some other permanent labeling that survives the subsequent machining work. This survival can be attained if the tip seats each have independent shapes. However, this can involve additional expense for production. For production reasons and for the sake of a uniform support of the cutting tips on the tool body in as optimal a way as possible, it is preferred that identical tip seats be used. To prevent mistaken placement of the cutting tips, the cutting tips are provided with markings that designate the assigned tip seat. A marking that designates the tool body can be provided as well. This prevents the cutting tip from being incorrectly secured to a tool body that has different tolerances.
Because of the individual association of the tips with the tip seats and tool bodies, a tool accuracy of approximately ±0.01 mm can be attained with the milling tool equipped with the cutting tips. The tool equipped with cutting tips thus makes it possible to perform machining with accuracies that were previously reserved to HSS tools. At the same time, however, a very high machining speed is attained.
The economical use of such tools is still further improved because regrinding is no longer necessary. If the cutting edges are worn, the set of cutting tips is removed from the tool body, and the tool body is then equipped with a new cutting tip set intended for it and individually ground. As a result, the precise shape of the machining tool is established immediately and without complicated adjustment provisions, and it can continue to be employed.
The cutting edges of the cutting tips supplement one another to form at least one complete cutting blade. Particularly in the tooth tip regions, overlapping regions can be provided in which the number of blades is more than one. In this way, the wear of cutting edges disposed obliquely and parallel to the pivot axis can be assimilated to one another.
Not only the cutting edges but also the tip seats can be provided with markings, which enable a simple association with the cutting tip markings. The markings can be provided in the form of symbols or numerals or a letter code.
The cutting tips are preferably provided with a positive clearance angle. The clearance angle is obtained by means of a chamfered ground section adjoining the cutting edge. The tool face rests on a straight line extending away from the cutting edge. As a result, the clearance angle immediately adjacent to the cutting edge is also other than zero. This permits milling machining with a positive effective cutting angle in reverse rotation; that is, as a consequence of the rotation of the milling tool, the cutting edge moves counter to the feeding direction of the tool on the workpiece. This yields a good surface quality even at high cutting speeds. The cutting tips are preferably installed on the tool body with an axial effective cutting angle of 0°, and the result of this is constant cutting conditions along each cutting edge. Relative to one another, the cutting tips are preferably offset in spiral fashion (along a helical line) in order to even out the cutting forces. This is advantageous in terms of chip removal. Furthermore, a relatively uniform force acting radially on the machining tool, whose peak value is less, results. Elastic deformation and thus inaccuracies in machining are minimized.
Once the cutting tips have been produced, for instance in a sintering process, the cutting tips are provided both before and immediately after the initial installation in a tool body with the appropriate marking, which identifies the respective tip seat and tool body. In the installed state, the cutting tips are then ground in a precision-grinding process, so that the outer contour or the geometry of the cutting edges of the milling tool is defined precisely. Once this process is ended, the cutting tips are removed and subjected to further machining. This c
Huber Rolf
Wetli Markus
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Tsai Henry
Walter AG
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