Abrading – Machine – Rotary tool
Reexamination Certificate
1998-08-06
2001-05-22
Ostrager, Allen (Department: 3725)
Abrading
Machine
Rotary tool
C451S204000, C451S206000, C451S048000
Reexamination Certificate
active
06234881
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method, and to a machine to carry out the method, to grind cylindrical surface regions of cutting tools, typically drills, boring tools, reamers, or the like, and especially such tools which have comparatively large recesses, forming flutes or grooves, e.g. to remove cutting chips.
BACKGROUND
It is frequently necessary to grind surfaces and surface regions of cutting tools to precisely predetermined dimensions. This is especially so for stepped tools of all kinds, for example drilling tools, drills with stepped diameters, reamers, milling tools in general, end mills, circumferential mills, roll-over milling tools, and the like.
Briefly, the tools for which the present invention is especially applicable are stepped tools with straight, spiral or angular grooves or flutes, step drills with straight spiral or angular flutes and made of high-speed steel, carbide, or with brazed cutting edges; reamers and step reamers with straight, spiral or angular flutes; end mills having cylindrical and/or conical chip removal grooves of various shapes; milling cutters in general, and especially side milling cutters, hobbing tools. All the tools are made of high-speed steel, carbide, ceramic, or other materials used in cutting tools, or may have brazed-on cutting inserts. The surface quality of the surfaces of such tools should be as good as possible and the dimensions of the tools should be highly accurate.
In the specification that follows, the term “cutting tools” will be used generically for any and all of the above tools for which the present invention is especially applicable.
Grinding processes are used for manufacturing cutting tools, as well as to sharpen cutting tools which have been used. For grinding, a grinding element, for example a grinding disk (also known as a grinding wheel), is engaged with the respective cutting tool. A not insignificant engagement pressure is exerted by the grinding element on the cutting tool. Generally, the engagement pressure acts more or less perpendicularly to the outer circumference of the cutting tool. The cutting tool can be rotated about its longitudinal axis, so that the grinding element covers the entire circumference of the cutting tool. In this axial rotation, the cutting tool is engaged only intermittently by the grinding element due to the presence of the chip removal flutes or grooves, or by other recesses which may be formed in the cutting tool. When the grinding element is facing such a flute, groove or recess, it runs freely. When the cutting tools have relatively large flutes or recesses, the grinding tool is in engagement with the cutting tool only for a fraction of the overall time during which the grinding operation takes place. The non-grinding time is used up by the grinding element running free, for example when it is opposite a chip removal flute located between the cutting surfaces or cutting surface portions of the cutting tool which are actually to be ground.
Comparatively long cutting tools, such as drills, boring tools, reamers, and the like, have slight lateral, that is, radial resilience or elasticity which may lead to problems with regard to accuracy of the grinding. If the cutting tool deflects only slightly when the grinding element, typically a grinding disk, is in engagement with the surface region to be cut, the surface which will be ground will no longer be precisely cylindrical but, rather, slightly bulged or eccentric or barrel-shaped, or otherwise deviates from an ideal design shape and size. Precision tools have diameter tolerances in the region of 1 &mgr; meter. Such deflections, thus, may lead to quality problems.
THE INVENTION
It is an object of the present invention to provide a method for grinding cylindrical surfaces of cutting tools which ensures high quality and accuracy of the surface to be ground.
Briefly, a grinding element, such as a grinding disk, carrying out a grinding movement, typically being driven and rotated about its axis, is applied against the surface region of the cutting tool which is to be ground to cylindrical shape and, while so engaged, the cutting tool is rocked or oscillated or pivoted to-and-fro about its longitudinal axis. This longitudinal axis defines a cylindrical cutting surface which is to be produced. Rocking or oscillating the cutting tool about its axis during the grinding operation results in a cylindrical ground surface.
The cutting tool, thus, is not continuously rotated about its longitudinal axis but, rather, is rocked back-and-forth about the axis in a predetermined range, that is, essentially in the range in which the grinding element engages the surface region to be ground. This avoids loss of engagement of the grinding element with the cutting tool when the grinding element is over the regions in which the outer surface of the cutting tool is formed with recesses, for example chip removal grooves or flutes. The grinding process is carried out with engagement of a surface region of the cutting tool so that the grinding element is preferably in continuous engagement with the surface of the cutting tool. This is particularly true for cutting tools having spiral grooves, such as drills.
The method of the invention results in several advantages: The engagement pressure between the grinding element and the cutting tool, effective upon cutting, is continuously present. Alternating deflection of the cutting tool towards and away from the grinding tool is eliminated. This substantially increases the accuracy of the grinding operation. In prior art grinding, the cutting tool is continuously rotated when carrying out a cylindrical grinding process; thus the respective flutes adjacent the cylindrical surfaces are passed again and again by the grinding disk, requiring operating time. In accordance with the method of the present invention, however, a free space resulting in a run or empty run must be covered, ideally only once, and at most only a few times and high-speed indexing can be used. The overall operating time for grinding thus can be reduced, while achieving higher accuracy and precision in the tool on which the operation is carried out.
The rocking or oscillating movement is comparatively slow, and results in continuous engagement between the grinding element and the cutting tool. Since the engagement is continuous, no vibration will result which otherwise occurs if an interrupted cylindrical surface is rotatably carried in engagement with a grinding element, typically a grinding disk. Eliminating vibration results in a substantially improved surface quality on the cutting tool.
Wear, or consumption, of the grinding disk material is reduced via the invention, as compared to the previous traditional method. This is due to the many interrupted engagements which occur at high speed in the traditional method whereas the invention has significantly fewer interrupted engagements, each of which is made at a relatively low speed. Thus, the benefit is lower disk consumption (cost savings) and better tool accuracy.
In general principle, it is possible to use the method of the invention also on cylinders which have a continuous circumferential surface. It is, however, particularly suitable—as above set forth—for surface regions of cutting tools which extend only over a portion of the circumference of the cutting tool itself, being interrupted by flutes or grooves. The oscillating or rocking movement of the cutting tool can be so dimensioned that the grinding element and the cutting tool to be ground come out of engagement only for short periods of time. This may occur especially in tools which have straight grooves or flutes. The short-time separation between grinding element and cutting tool is not critical when the oscillating movement is relatively slow, so that a very short-time interruption of engagement pressure, which otherwise occurs between the cutting tool and the grinding element, does not result in impact or cause vibrations. The loss of operating time as a flute is passed is substantially less than upon con
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Hong William
Ostrager Allen
Walter AG
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