Patent Application
20060096424
Embodiments of the present invention relate to cutting blades used with cutting devices, and more particularly to a method and apparatus for applying a cutting edge to a cutting blade.
Cutting blades, such as rotary cutting blades used on lawn mowers, typically have one or more cutting edges that are disposed on a leading edge of the blade to facilitate cutting of material, such as vegetation. The cutting edge may be applied to the blade in a variety of ways, including, but not limited to, milling, grinding, coining, and shearing.
The most common way a cutting edge is applied on a new blade is through the use of a milling machine with one or more milling heads. Milling machines, however, have a number of disadvantages. For example, milling machines require that the blade blank be removed from a press, where most blade processing operations take place, and be placed into a separate milling machine to create the cutting edge. Once the edge is machined, the blade is then placed back into a press for further processing, such as blade forming. This activity not only interrupts the manufacturing process, but can also be time-consuming and expensive. In particular, the mill head inserts used to machine the cutting edge can be expensive and have generally high wear rates, such that replacement can be frequent depending on the hardness of the material being milled.
Coining generally includes the use of a closed set of dies to confine and squeeze the blade material to produce a cutting edge. Coining requires that the material be repeatedly worked and generally does not sufficiently result in a satisfactory cutting edge, especially for lawn mower and other vegetation cutting blades.
A shearing process has also been used to apply a cutting edge to the cutting blade. The shearing processes used, however, have generally failed, particularly with respect to rotary cutting blades, because they do not generate an acceptable cutting edge. The cutting edge quality in prior shearing processes has been deficient for a variety of reasons. One reason, for example, is that despite some sheared surface being generated, a significant amount of breakout would occur between the cutting edge side and the material being removed. Breakout, or blowout, is generally similar to a tearing or ripping of the material, which results in a rough surface. The rough surface on the face of a cutting edge is not conducive to a satisfactory cutting edge. A second and related reason is that the clearance between the die and punch used for shearing typically ranges between 6% and 14% of the cutting blade material thickness, which has been thought to be necessary to ensure tool longevity and performance. Accordingly a substantial amount of breakout may be generated towards the front edge of the cutting edge due to the tool tolerances.
Embodiments of the present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements. Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings.
In the following detailed description, reference is made to the accompanying drawings which form a part hereof wherein like numerals designate like parts throughout, and in which is shown by way of illustration embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of embodiments in accordance with the present invention is defined by the appended claims and their equivalents.
The following description may include terms such as inner, outer, under, between, upward, downward, outward, inward, and the like. Such terms are used for descriptive purposes only and are not to be construed as limiting. That is, these terms are terms that are relative only to a point of reference and are not meant to be interpreted as limitations but are, instead, included in the following description to facilitate understanding of the various aspects of the invention.
Embodiments of the present invention may be directed to a method of applying a cutting edge to a rotary cutting blade using an improved shearing process, also sometimes referred to herein as skiving, where the amount of breakout is kept to a minimum, and the majority of the face of a cutting edge is sheared such that it is generally smooth. Skiving the blade in accordance with embodiments of the present invention may be done within a press similar to other blade processes, which may help maintain the continuity of processing, reduce the amount of times a blade must be handled, and reduce manufacturing and production costs, without sacrificing the quality of the cutting edge.
Punch 14 may be positioned and configured to move relative to the blade blank 10 and die 12. Punch 14 may have a cutting end or working end that has a relief angle, which may be configured to urge material being skived away (i.e. the overhang portion 16) from the cutting edge being applied to blade blank 10. Punch 14 may also include a shear angle 26, such that a first edge 28 may contact a portion of blade blank 10 before a second edge 30 contacts blade blank 10.
The shear angle 26 may be selected based on a variety of factors, including, but not limited to, blade material, blade hardness, desired width of the cutting edge, and the like. In one embodiment, the shear angle 26 may be in the range of 8 to 30 degrees. In one embodiment, it was found that a shear angle of approximately 12 degrees may help in producing a quality skived cutting edge with a low amount of breakout. Likewise, the relief angle may be selected based on similar factors and be job specific. In one embodiment, it was found that a punch having a relief angle of approximately 16 degrees assisted in producing a satisfactory cutting edge with having a cutting edge composed primarily of a sheared surface.
In one embodiment, the clearance 36 is kept at or below 2% of the thickness of the material being skived. In embodiments where the blade blanks have a thickness in a range of 0.12 inches and 0.312 inches, a clearance of approximately 0.5% or less of the blade blank thickness has been found to result in a cutting edge that is primarily a sheared surface, with a relatively small percentage of breakout, and hence produced quality cutting edge. In one embodiment, where the blade blank is approximately 0.2 inches, a clearance of approximately 0.001 inches has been found to help minimize breakout. In one embodiment, the low clearance in combination with the shear angle enables formation of a cutting edge that is dominated by a sheared surface, and helps resist breakout from being evident on the blade's surface.
In one embodiment of the invention, the punch may be positioned relative to the die at an angle in the range of 25 to 40 degrees, such that the resulting cutting edge has a cutting edge angle, with respect to the bottom portion of the cutting blade, which is at substantially the same angle as the relative angle between the punch and the blade blank supporting surface of the die 12 (shown as 38 in
Although in the illustrated embodiment the punch is shown to travel in the vertical direction, in other embodiments, the punch may travel along a path other than vertical, while the die is configured to have an increased or decreased angle with respect to horizontal in order to maintain the desired angular relationship between the punch and die to maintain the resulting cutting edge angle.
In another embodiment of the invention, the first end of the punch may be oriented toward the outer edge of the blade blank, such that the shearing action occurs from the outer portion of the blade blank towards the inner portion of the blade blank. And, in other embodiments, the punch may have a width less than the desired width of the cutting edge being created. In such embodiments, the punch and/or the die may be adapted to move, for example, horizontally, as well as vertically with respect to each other in order to achieve the elongated cutting edge. Yet, in other embodiments of the invention, the first end and the second end of the punch may be co-planar. In such a case, the shear angle may be created by orienting the die at an angle with respect to the cutting edge of the punch, in order to help induce the shearing action of the material.
Embodiments of the present invention may be particularly useful in applying a cutting edge to a rotary cutting blade blank that is made of boron steel in the range of 10B30 to 10B40. In some embodiments, the die, or the cutting portion of the die may be made of a material that is harder than the material of the blade blank itself. In other embodiments, the punch or the cutting portion of the punch may be made of a material that is treated to have a higher hardness than that of the material being sheared.
Although certain embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent embodiments or implementations calculated to achieve the same purposes may be substituted for the embodiments shown and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that embodiments in accordance with the present invention may be implemented in a very wide variety of ways. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that embodiments in accordance with the present invention be limited only by the claims and the equivalents thereof.
