Patent Application
20130081283
The present disclosure relates generally to knife blades, and in particular to knife blades composed of two or more dissimilar materials.
Knives are used as tools in countless industries and applications, and are available in a vast array of shapes, sizes, and configurations. Most knives, however, share some characteristics in common. Typically, knives include a blade, usually metal, with a sharpened edge, and a handle to which the blade is attached and by which a user can grasp the knife. Higher quality knife blades are generally characterized their ability to take and hold an edge for extended periods of use. A knife that loses its edge quickly and must be sharpened frequently is of limited use except to the most casual user. Accordingly, there is continual and ongoing effort to develop new and better materials and treatments to improve the quality of knife blades, and to produce knives that can be sharpened to a finer edge and hold the edge.
Edge retention is generally a matter of edge geometry and material hardness. While there are some non-steel, and even non-metallic knife blades available, most blades are made from steel, and, increasingly, from stainless steel. In order to achieve a high degree of hardness, knife manufacturers typically harden the steel from which their blades are made, usually by heat treatment. However, there is a more or less direct relationship between hardening of a given alloy and brittleness, meaning that a knife blade having an extremely high degree of hardness will generally also be more easily breakable than other knives. In recent years, advances in metallurgy have produced steel alloys that are inherently harder than more commonly used alloys, and that can be further hardened to a much higher degree than other more commonly used blade steels, but these new and specialized alloys can be significantly more expensive, and knives made from such steels, that are fully hardened to take advantage of their unique properties, are often susceptible to accidental breakage. Thus, the knife manufacturer must find a compromise between hardness and toughness. Depending upon the intended application of the knife, or the intended market, a knife having a harder, longer lasting edge may be more important than the less expensive, more durable one.
This is particularly the case with certain higher quality folding knives, and knives made for professional chefs and others who prepare food, which are often in constant use.
In the case of very high quality hand-made knives, the blacksmith may, after hardening the blade, subject the blade to additional heat treatment designed to draw the hardness out of the back, or spine, of the blade, while allowing the edge to remain hard. This provides the blade with a relatively more flexible back and a hard cutting edge. The tougher back portion of the blade supports and protects the more fragile cutting edge, and reduces the likelihood that the blade will break accidentally or catastrophically. Unfortunately, such differential heat treating processes are labor-intensive and would be prohibitively expensive to employ in manufacturing knives for the mass market.
Knife blades are manufactured by a number of different processes, depending upon a variety of factors, including the materials used in the manufacturing process, and the desired quality of the finished product. Fine blanking is a widely used process that provides a number of benefits to the manufacturer. Fine blanking employs a press to form knife blades from flat sheets of material. In a three step punching process, the material is first clamped in place, then pressed between upper and lower parts of a fine blanking die that forms and separates the knife blade blank from the parent sheet, then the finished blank is ejected from the blanking die. The fine blanking process produces a knife blank that requires very little additional machining or other finish steps. Pivot holes and other features can be formed in a blade to very close tolerances during the same process, and, frequently, edge grinding is the only step remaining to finish the blade, although in some cases there may also be a slight burr on one side of the blade that is removed very easily. Unfortunately, fine blanking is not suitable for extremely hard materials, and many of the alloys that are especially suitable for a knife blade cannot be fine blanked, inasmuch as the harder steel quickly degrades or destroys the blanking die used to form the blades. In the case of steels that are too hard for fine blanking, computer driven laser cutting is one common method for forming blades from harder steels, in which a laser traces the outline shape of the blade, cutting the blank from the parent sheet. After the knife blank is cut out, further machining is performed to finish the edges, pivot holes, and other features of the blade. This process is significantly more time-consuming and expensive than the fine blanking process, which limits the practicality of using very hard alloys for any but the most expensive knives.
U.S. Pat. No. 4,896,424, to Walker, is directed to folding knife with a blade having two sections, in which one section of the blade is made from titanium, while the second section of the blade, which includes the blade edge, is made from a high-carbon stainless steel. The sections are joined by a running dovetail joint. The sections are cut by wire EDM (electrical discharge machining), with the dovetails cut for a friction fit, so that the sections can be joined only by being pressed together, as with an arbor press. Once the sections are pressed together, they are peened, i.e., the joint is hammered to deform the metal of the sections, to make a permanent joint.
However, there are some drawbacks that arise with Walker's method. First, wire EDM is an expensive process for mass production, especially for parts that include holes, such as the tang of a folding knife. Second, the dovetail edges of the blade sections must be cut to very close tolerances to be sufficiently close for a good press-fit, without being so tight that they bind, which is expensive. Third, the press-fitting and peening operations are labor intensive and expensive for a mass production product.
U.S. Pat. No. 6,70,627, to Korb et al., is directed to a composite utility knife blade having a cutting edge from a wire of tool steel welded to an alloy steel backing strip. A continuous ribbon of the backing steel is rolled from a spool and welded, by EBW (electron beam welding), to a wire of tool steel as the ribbon and wire pass under the electron beam, and is then recoiled. The resulting composite ribbon is required to be subjected to a number of additional steps, including anneal, punch and score, straighten, heat treat and temper, grind, and hone before it is finally separated into separate blades. Unfortunately, these processes are not suitable for manufacturing knife blades of the kind discussed above.
According to one embodiment, a composite knife blade is provided, including a cutting-edge piece of a first alloy, a spine piece of a second alloy different from the first alloy, and a brazed joint between the cutting-edge piece and the spine piece. The cutting-edge and spine pieces are interlocked at the joint providing additional mechanical strength to the joint. The brazed joint includes a brazing material such as, for example, copper, bronze, gold, silver, or nickel. The cutting-edge piece has a high Rockwell hardness value, as compared to a hardness of the back piece.
According to another embodiment, a method of manufacture of a knife blade is provided, including fine blanking a first piece of a knife blade from a sheet of a first material, laser cutting a second piece of the knife blade from a sheet of a second material, harder than the first material, and brazing the first piece to the second piece to form a composite blade.
Referring now to
As shown in
According to an embodiment of the invention, the blade blank 130 is allowed to cool to the austenitic temperature of the alloy from which the cutting-edge blank 116 is formed, where it is held for a short time to stabilize, and then quenched to harden the steel of the cutting-edge blank 116. Following quenching, the blade blank 130 may be reheated to an appropriate tempering temperature and held, then slowly cooled, to temper the blade blank 110. According to one embodiment, the back blank is cut from 440A stainless steel, while the cutting-edge blank is cut from D-2 stainless steel, and they are brazed at about 2,030° using copper brazing material. The resulting blade blank is cooled to the austenizing temperature of D-2 steel, about 1850°, and held at that temperature for about 30 minutes, then quenched. At this point, the D-2 steel has a hardness of about 63 Rockwell, but is very brittle. The blank is then reheated to the primary tempering temperature of the D-2 steel, about 350°, and held at that temperature for about two hours, then slow cooled. The reheating step is repeated several times to fully temper the blade. After the tempering is complete, the D-2 steel will have a hardness in the range of 58-62 Rockwell, while the 440A steel will have a hardness of about 50 Rockwell.
The austenitic temperature and the methods of quenching and tempering will vary in accordance with the materials chosen for the cutting-edge of the blade and the desired hardness and toughness of the finished blade. Some alloys cannot be hardened by heat treatment, others do not require a rapid quench to harden, but will “air harden” as the steel cools more slowly. The alloys used for the back blank 120 and cutting-edge blank 116 can be selected such that the back blank 120 will not harden during the process that hardens the cutting-edge blank 116, or they may be selected such that the tempering process will significantly reduce the degree of hardness imparted to the back blank 120 during the hardening process, as in the example described above. The result is a differentially hardened blade having excellent toughness imparted by the back piece 112, as well as extremely high edge retention provided by the harder cutting-edge piece 114.
In some cases it may be advantageous to perform an annealing process before the hardening step, in which case, the blade is subjected to a slow cooling process from the austenitic temperature, rather than the quench or uncontrolled cooling. The blade may then be reheated for hardening after the annealing step, if necessary.
In the embodiment illustrated in
Another benefit of the method described is that by forming the joining edges 118, 122 of the back and cutting-edge blanks 116, 120 for slip-fit assembly, mass production of the blade 110 is simplified. The brazing process easily fills the narrow gap that results.
As illustrated diagrammatically in
The result is that, at least with respect to high-speed operations used for economical production cutting of knife blades, a laser cut blade is considered a rough product and generally cannot be assembled as a component in a knife until further machining or smoothing has been performed.
In one embodiment of this invention, both the back piece and the cutting edge piece are laser cut. Then, without any further machining, milling or grinding, the two parts are bonded together to make a knife blade, which is then finished as though it had been cut as a single piece. In another embodiment, the cutting edge is laser cut and the back piece is fine blanked or stamped. The two parts are then joined together according to the principles of this invention without further machining, milling or grinding of the joining edges of either part. This is unexpected because the two parts were made by very different processes and have different tolerances and different finishes on their mating edges. This also provides a substantial cost and time savings because with this invention, a laser cut part does not need to go through the previously required machining or milling steps before being joined as a component of the knife. The savings is even greater because this permits the mating edges of the laser part to be made any desired shape or length without regard to the need to consider post laser machining or milling steps. Thus, the joining edge of the laser cut part can be made serpentine, with each under cut, reverse cuts, convolutions or any shape that a computer controlled laser can trace over the surface without regard as to whether a machining tool is able to later follow this same trace. Some shapes which could not be machined or shapes which would be expensive and time consuming to machine can now be used in the final product, which was not previously practical, and in some cases not possible.
The design and shape of the mating joint can therefore be selected based on designed strength, aesthetics, and other features without concern for the ability to machine the part initially or even machine it after a laser cutting.
Thus, in one embodiment, both the back and cutting-edge pieces were cut using an industrial CNC driven laser as described above. In other embodiments, one part is formed by fine blanking or stamping and the other part by a different technique such as laser, EDM, ion milling, plasma cutting and the like.
In tests conducted by the inventor, composite blades formed substantially as described above exhibited superior characteristics of strength and toughness, and the joints were found to be stronger than the steel of the blades, such that efforts to cause the pieces to separate invariably resulted in bending or breaking one or both of the pieces, instead of separating them at the joint. It is surmised that this is due, at least in part, to the large contact surface area of the joint, and to the fact, because of the serpentine shape, that there is no single line along which more than a small fraction of the joint can be subjected to concentrated stress.
The brazing paste may be copper based, as described above, or it may be formulated with any of a wide range of available materials, including, for example, bronze, nickel, silver, gold, etc. After the blade has been polished, the joint 132 shows, if at all, as a thin hairline on the blade. The brazing metal may be chosen to minimize the visibility of the joint 132 or to enhance it. For example, a copper braze shows as a thin reddish line, while a nickel based braze will have a color that closely matches most stainless steels. According to an embodiment, the blade is subjected to sandblasting, beadblasting, and/or etching. Such treatments will affect the different alloys of the back and cutting-edge pieces 112, 114 differently, changing their respective appearances. For example, sandblasting or beadblasting can be applied at a force sufficient to add a texture to the surface of the relatively more ductile back piece, without affecting the harder surface of the cutting-edge piece 114, or it may be applied with greater force to texture both pieces. The blade may also be chemically etched to change the surface texture or color of one or both of the pieces, or of the brazing metal, depending on the specific alloys of the blade and the chemicals used.
The brazing compound may also be selected to accommodate specific requirements of the materials selected for the blade. For example, some steel alloys have an austenitic temperature in the range of 2,100°. If such an alloy were brazed using the copper braze described above, then later heat hardened, the copper braze would flow out of the joint at the higher austenizing temperature. To avoid such problems, the cutting-edge blank could be hardened prior to the brazing step, but a more economical process would be to use a nickel brazing paste, for which the liquidus temperature is about 2,200°, permitting the brazing and hardening to be performed in the same heating step.
Principles of the invention have been described above with respect to a blade having two dissimilar alloys. According to other embodiments, three or more pieces with separate characteristics may be joined to form a composite blade.
According to another embodiment, apertures through the blade are formed that are wholly within the back piece, such that, while the finished blade has apertures, the joint of the blade is continuous.
Various embodiment have been described in which separate parts are joined using a brazing process. While this is a preferred method, other joining methods may also be employed, including EBW and HIP (hot isostatic press) cladding. The brazing process provides a number of advantages over these and other joining methods: the blanks can be heat treated or annealed in the same heating process that is used to braze the pieces; a large number of blade blanks can be brazed in an oven simultaneously, while EBW would require a CNC driven system to individually weld each blade, which would be much more time consuming and expensive, while the HIP cladding process requires a specialized pressure chamber that is very large relative to the size of the working space in the interior, and requires special treatment and handling of the blanks to prepare them for the process.
There are a number of terms used in describing characteristics of knife blades and the steel from which they are made. These include hardness, the relative ability of a material to resist plastic deformation; tensile strength, the degree to which a material resists a pulling stress without breaking; toughness, the degree to which a material resists stress in general (tensile, compressive, or shear) without fracturing; ductility, the ability of a material to undergo plastic deformation without fracturing; yield strength, the degree to which a material resists a pulling stress without undergoing plastic deformation; and brittleness, the degree to which a material fractures in response to stress, without first deforming.
The abstract of the present disclosure is provided as a brief outline of some of the principles of the invention, according to one embodiment, as an aid to searching. The abstract is not intended as a complete or definitive description of any embodiment thereof, nor should it be relied upon to define terms used in the specification or claims. The abstract does not limit the scope of the claims.
The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments.
These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.
This application is a continuation application of U.S. application Ser. No. 11/760,624, filed Jun. 8, 2007, which claims the benefit of U.S. Provisional Patent Application No. 60/911,453, filed Apr. 12, 2007, the entire disclosures of which are herein incorporated by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 60911453 | Apr 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11760624 | Jun 2007 | US |
| Child | 13686661 | US |
