Patent Application
20150082764
This invention generally relates to a laser hardened knife guard for a sickle bar assembly.
Knife guards are used in sickle style cutting systems. They act as the stationary surface for moving sickle blades to cut against or at least to protect or cover the sickle blades. Examples are shown in U.S. Pat. Nos. 6,962,040, 4,660,361, 7,478,522, and 8,464,506 the disclosures of which are incorporated by reference as the present invention may be applied and/or incorporated into these examples in various embodiments.
Knife guards are primarily constructed of steel and manufactured in a variety of ways including forging, casting, welded fabrication of stamped components, and machining. In some instances, a hardened plate is assembled into the guard to create a surface known as a ledger plate that the sickle runs on and the edge. Past efforts to improve the hardness of the ledger plate and the edge have included hardening via quench and temper or austemper, carborizing or carbonitriding, induction hardening, flame hardening, or boronizing. In some cases, more than one of these treatments is performed on the part in order to impart varying properties within the knife guard.
With the exception of induction hardening, the remaining treatments are high heat processes of over 1500° F. and require the entire part to be raised into these temperature ranges. The knife guard in its original state contains internal stresses. Accordingly, distortion of the part is a factor with these processes. Distortion is not desirable where the knife guard provides a bearing surface supporting sliding movement and reciprocation of a sickle bar. The result is often additional machining or straightening processes to bring the part back within specification. These additional steps increase cost.
In the case of induction hardening, typically very elaborate induction coils and quenching processes are required to perform the process in a repeatable and predictable manner. Induction heat is a resistance type of heating. The result of this process along with flame hardening a heat affected zone which is driven deep into the part. In order to achieve the desired microstructure in knife guard material, a quench process must be used to reduce the internal temperature of the knife guard quickly enough to create the proper metallurgical transformation. In addition, the induction process focuses the energy in the thinner section of the knife guard edge resulting in the risk of melting the material at the edge. The depth of the heat affected zone also creates a similar situation to the previously mentioned treatments in that it causes stresses in the part to be relieved often resulting in distortion of the part.
The present invention is generally directed towards laser hardening the knife guard in one or more select regions. Laser hardening may be done to the ledger plate and edges to produce hardened areas on the ledger bar of the knife guard and may be done along edges of the knife guard so as to maintain the sharpness of the edges of the knife guard. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
In one aspect, the invention provides for a knife guard that comprises a guard body that further comprises a base material. The base material includes a mounting bar that defines at least one bolt hole and at least one tine projecting forward from the mounting bar. The base material has a first hardness. A laser treated material is formed into or in the base material. The laser treated material comprises a second hardness greater than the first hardness.
The knife guard include a ledger surface that is adapted to bear against or at least face a sickle bar assembly. The ledger surface includes a region of laser hardened layer formed integrally with an outer surface of the base material to provide for the laser treated material.
The base material may be steel and the laser hardened layer may be at least 0.5 millimeter in depth thickness along the base material and less than 3 millimeters.
The tines can comprise a central protrusion and a pair of flank surfaces on either side of the protrusion that extend from the bottom surface toward the bearing surface. The flank surfaces intersect the bearing surface at a shearing edge. The region of the laser hardened layer may include at least one portion formed above the flanks along ledger surface that forms part of the shearing edge.
The knife guard may further comprise a free region of base material that is not a laser hardened layer. The free region may be disposed above the central protrusion along the ledger surface and between first and second portions of laser hardened layer. The first and second portions are formed above the flanks along ledger surface and form part of the shearing edge.
An advantage of laser hardening select regions and limited regions leaving free regions is that distortion can be prevented or minimized reducing or eliminating post machining or straightening steps along bearing surfaces.
The knife guard may further include a trash bar. The trash bar extends perpendicularly to an extension direction of the at least one tine. The trash bar connects adjacent tines of the at least one tine. The free region extends along the ledger surface that extends along a trash bar portion of the ledger surface defined by the trash bar. The trash bar is free of the laser hardened layer.
The mounting bar can include a ledger bar that extends perpendicularly to an extension direction of the at least one tine. The ledger bar defines a ledger bar portion of the ledger surface. The ledger bar portion forms part of the region of laser hardened layer along the length thereof.
In one embodiment more than 40% of the ledger surface is free of the region of laser hardened layer. The laser hardened layer may be between 0.5 millimeter and 3 millimeter in depth thickness along the base material at the shearing edge. During erosion of the flank surfaces, the laser hardened layer sharpens into the laser hardened layer.
The at least one portion formed above the flanks along ledger surface that forms part of the shearing edge may be formed in a non-linear oscillation profile to provide a serrated pattern for serrated cutting performance.
In one embodiment over 85% of an outer surface of the knife guard may form an untreated region of base material. The laser treated material may be limited to less than 15% of the outer surface. The base material may have a hardness of less than 50 HRC, and the laser treated material can have a hardness between 50 and 70 HRC and preferably between 50 to 65 HRC. The laser treated material has a hardness at least 5 HRC points higher than the base material and typically 10 HRC points or more higher than the base material.
In another aspect, the invention provides that the knife guard may include at least one tine that comprises a plurality of tines with valleys between the tines. The at least one bolt hole may comprise a plurality of bolt holes. The bolt holes may have respective bolt mounting centers aligned along an mounting axis that extends perpendicularly relative to a forward extending axis direction of the tines. The bolt holes may be formed in mounting bosses formed along the mounting bar. A connecting trashbar may extend perpendicularly relative to the forward extending axis direction and connect adjacent tines. The mounting bar can include a ledger bar. The ledger bar and the tines define a ledger surface that extends in a plane. A sickle clearance channel is formed between the ledger bar and the trash bar. Ribs at a bottom of the sickle clearance channel connect the ledger bar and the trash bar.
The ledger bar may project from a mounting plate portion of the mounting bar. Mounting bosses may be formed into the mounting plate.
In yet another aspect, the invention provides for a cutter bar assembly that can include a linear array of a plurality of the knife guards. The cutter bar assembly can include a cutter bar support having a mounting flange that extends in parallel relation to the linear array. The sickle bar assembly may extend in a longitudinal direction in parallel relation with the cutter bar support in order to reciprocate back and forth in the longitudinal direction for cutting. The sickle bar assembly can include a sickle bar frequently referred to as a knife back and a plurality of sickle knives mounted to the sickle bar. The knife guards may be arranged in side by side relation. The sickle knives may be arranged in side by side relation. The knife guards and sickle knives may be arranged in a vertically overlapping relation wherein the knife guards may be over the sickle knives or wherein the sickle knives may be over the knife guards.
The sickle bar slides along the knife guards along a region of laser hardened layer formed integrally with an outer surface of the base material to provide for the laser treated material.
Another aspect of the present invention is directed toward a method of forming a knife guard. The knife guard can comprise a guard body. The guard body may comprise a base material that includes a mounting bar that defines at least one bolt hole and at least one tine projecting forward from the mounting bar. The method comprises hardening with a laser a region of the base material to provide a second hardness greater than the first hardness.
The hardening with the laser can include using at least one of the following lasers CO2, YAG, Diode and Fiber. The hardening may comprise targeting and confining the application of the laser to the region of an outer surface of the guard body. The region may be less than 20% of an area of the outer surface.
The laser hardening can be conducted without a liquid quenchant. The base material of the guard body operates as a heat sink to allow the part to quench to a hardened microstructure in said region. No further tempering operation is conducted after the hardening with the laser.
The laser hardened region may be formed along a ledger surface that forms a sliding interface with a sickle bar assembly that reciprocates relative to the knife guard in use.
Part of the ledger surface may be free and untreated with the laser with an at least 30% untreated region. Distortion may be eliminated or reduced such that subsequent machining or straightening operations are not conducted on the ledger surface after said hardening. The laser hardened region can be formed along a shearing edge formed along opposing sides of the at least one tine.
Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings:
While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims.
As shown in
The knife guard 10 includes a ledger surface 28 that is adapted to bear against or at least face a sickle bar assembly 30. Typically the ledger surface 28 will come into contact with the sickle bar assembly 30 to guide or maintain linear reciprocating movement of the sickle bar assembly 30.
The base material 14 may be steel and the laser hardened layer 26 is at least 0.5 millimeters and less than 3 millimeters in depth thickness 48 along the base of the material.
The knife guard 10 may further comprise a free region 42 of base material 14 that is not a laser hardened layer. As illustrated in
The mounting bar 16 includes a ledger bar 80 that extends perpendicularly to an extension direction 56 of the at least one tine 20. The ledger bar 80 defines a ledger bar portion 80a of the ledger surface 28 wherein the ledger bar portion 80a forms part of the region of laser hardened layer 26 along the length thereof. More than 30% of the overall ledger surface 28 may be free of the region of laser hardened layer 26. As illustrated in
The laser hardened layer 26 may be between 0.5 millimeter and 3 millimeter in depth thickness 48 along the base material 14 at the shearing edge 38. During erosion of the flank surfaces 34 of the untreated base material 14, the cutting support surface 86 that is part of the laser hardened layer 26 may be sharpened along its lower edge 88 relative to bearing surface 36. This self-sharpening effect may result from the erosion of the softer base material 14 above the hardened zone 24, 26 (as shown for example in
The laser hardening process, due to its fast interaction with the material, can produce compressive stresses at the surface of the heat treated zone, which increases the fatigue properties of the part in certain cases.
The laser hardened portions 40a and 40b formed above the flanks 34 along the ledger surface 28 that forms part of the shearing edge 38 may be formed in a non-linear oscillation profile 50 (which indicates the laser tool application path) that provides for a serrated pattern for serrating cutting performance as shown in
Over 85% of the outer surface of the knife guard 10 may form an untreated region of base material 14. The laser treated material 24 may be limited to less than 15% of the outer surface of the knife guard 10 and as shown, formed preferably only along the ledger surface 28. The base material 14 may have a hardness of less than 50 HRC and the laser treated material 24 may have a hardness between 50 and 70 HRC, less than 50 HRC, and the laser treated material can have a hardness between 50 and 70 HRC and preferably between 50 to 65 HRC. The laser treated material has a hardness at least 5 HRC points higher than the base material and typically 10 HRC points or more higher than the base material.
The at least one tine 20 may comprise plurality of tines 20 with, as shown for example in
An embodiment of the present invention showing two portions of tines 20 is shown in
The laser used to harden the base material 14 may include using at least one of the following lasers; CO2, YAG, Diode and fiber. The laser beam consists of a column of light energy of similar wave length. These different types of lasers produce different wave lengths of light. These lasers each have their own unique characteristics, but all work well in heat treating applications.
The laser hardening of the knife guard 10 results in a hardened area along the edge of the guard 10 necessary to maintain the sharpness of the edge 38 defined by the hardened portion of the ledger surface portions 40a and 40b and the cutting supports surfaces 86. The method of using the laser to laser harden the knife guard 10 has the advantage over other processes currently in use of involving a smaller heat effected zone that is created with the laser. The smaller heat affected zone results in less distortion of the part and minimal disruption to the microstructure of the base part, which allows better material properties in the base part after laser hardening. In some cases, it is desirable to heat treat the base part to a lower hardness to allow for a mixture of strength and toughness. This lower heat effected zone maintains the prior heat treatment and a greater percentage of the base part will compare to induction or flame hardening.
The lower distortion eliminates subsequent machining and/or straightening operations, thus reducing processing time and costs. The process of heat treating the base material 14 for strength and toughness, then machining the surface (if necessary) for the section to ride on, then laser hardening can be performed easily. This process of hardening the edge after heat treat is difficult to perform without distortion or the risk of melting the edge material.
However, with the laser hardening process, the body of the part acts as a heat sink to allow the part to quench to the proper microstructure. With other heat treatment processes, the part must be submerged in a quench (oil, air, water, polymer solution, molten salt, etc.) The rapid quenching by submersion results in a rapid transformation of the part, which can impart internal stresses causing distortion. Oftentimes with other heat treatment processes, a secondary tempering process is necessary to relieve these internal stresses, thus adding another opportunity for the part to deform along with adding additional process steps and costs.
Still with reference to
A laser tool 94 makes an angular approach to laser harden along the length of the bearing surfaces 90A, 92A of the retainer portion 96A and base portion 98A from the cutting edges inwardly towards the center of the bearing surfaces 90A, 92A. Thus, in this two tine 20 embodiment there are eight cutting edges and thus eight portions of laser hardened areas on the bearing surfaces 90A, 92A extending from the cutting edges thereof. It can be readily appreciated as with the previous embodiments only a portion of the bearing surfaces are laser hardened along the cutting edges in order to obtain the same advantages heretofore discussed in the other embodiments, for example, self-sharpening of the cutting edges and decreased wear of the bearing surfaces 90A, 92A of the knife guard 10.
All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
