Patent Application
20080282760
The invention relates generally to rotary bending tools, such as those used in die presses.
Embodiments of the invention concern rotary bending tools, which are typically used to form bends in a sheet metal workpiece by wrapping around an edge of an anvil die. In particular, the invention relates to bending tools of the type that have a rocker rotationally mounted in a cylindrical seat in a saddle. In an illustrative bending tool to which the invention pertains, the rocker has a lengthwise V-shaped recess that wraps the edge of a sheet metal blank around an anvil die edge as the saddle is driven down in a press. As it descends, the rotation of the rocker wraps the sheet material around the lower die edge.
Such devices are used in high volume production of formed steel panels and thus are subject to considerable wear. Rockers for long length rotary bending tools have been constructed of very high strength alloys which are hardened prior to machining, necessitating costly post hardening machining to very close tolerances. The durability and ease of maintainability of a rotary bending apparatus is greatly dependent on the lubricity of the rocker and saddle interface. Therefore, sophisticated lubricating systems are necessary for smooth movement between the rocker and the saddle. Additionally, the surface of the cylindrical seat in the saddle must be extremely smooth. This can be problematic because it is difficult to hone the internal diameter of the seat to a smooth enough surface. Accordingly, there is a need for an apparatus that has low friction between the rocker and saddle, yet can withstand high volume production applications, is cost effective, and is low maintenance.
Advantageously, embodiments of the invention provide a rotary bending tool saddle that increases the flexibility of selecting appropriately matched rocker and liner materials for the best fit to the application requirements.
Embodiments of the invention include a rotary bending tool having a saddle having an elongated member formed with an at least partially cylindrical open recess extending lengthwise along the saddle; and a rocker having an elongated member with at least a partially cylindrical outer surface fit to the at least partially cylindrical portion of the saddle recess, such that the saddle recess allows relative rotation of the rocker therein; wherein the saddle comprises a high strength housing with a liner disposed therein, the liner formed of a low friction material.
The liner may be constructed of various materials such as, bronze, bearing bronze, aluminum bronze, polymers, filament wound composites and graphite composites. The rocker may also be formed of various materials including graphite composites.
The invention is best understood from the following detailed description when read with the accompanying drawings.
Illustrative embodiments of the invention include a unique saddle used in a rotary bending tool. The saddle has a housing, preferably comprising a durable, stiff, low cost material that is easily manufactured, such as steel. The saddle housing has a low friction liner, such as a bearing bronze to reduce friction between the rocker and saddle. The inner diameter of the saddle can also be honed to a very smooth surface prior to being inserted into the saddle housing, reducing or eliminating the need to grind the saddle recess.
A series of pins 20 are each received in one of a series of holes 22 in saddle 14. A compression spring 26 is associated with each pin 20. Rocker 12 is retained in position by pins 20 inserted through respective holes 22 in saddle 14 and received in respective pockets 24 in rocker 12. The tapered end pins 20 are urged towards rocker 12 by compression springs 26 compressed by set screws 28 installed in threaded sections of holes 22. Compressed springs 26 allow pins 20 to be forced back as rocker 12 is rotated by contact of a recess edge 32 with workpiece P. The rotary bending tool 10 can be installed in a die press by means of cap screws (not shown) and mates with a lower die D having an elongated forming contour C around which a sheet metal workpiece P is wrapped, as described in the above referenced patent, which process is well known in the art, and will not be further described here.
Depending on the materials of the liner and rocker, and the formation of those parts, liner 40 can reduce friction to the extent additional lubrication is not necessary. Under certain conditions, however, one or more supplementary lubricating mechanisms may be desirable.
One such lubrication mechanism includes use of lubricating plugs in the saddle. In the illustrative embodiment of the invention shown in
Instead of, or in addition to, lubricating plugs, the liner material may be impregnated with a lubricant, such as oil. In an illustrative embodiment of the invention, the liner may be sintered bronze, which has intrinsic porosity and is easily impregnated with lubricant.
It was noted above that a suitable material for the saddle housing is steel. Other high strength materials are also suitable, but cost will often be a factor. A high strength alloy steel is particularly desirable in many applications. Other illustrative materials include cast iron, extruded aluminum and molded structural polymers.
The saddle liner may be constructed of various low friction materials. Bronze, which is typically 60% copper and 40% tin, has very little metal-on-metal friction, and therefore, is quite suitable for a liner material. Bronze having other elements incorporated therein, such as bearing bronze, aluminum bronze and phosphor bronze, manganese bronze, and silicon bronze are also suitable. Additional illustrative examples of liner materials include graphite, graphite composites, polymers, and filament wound composites.
Filament winding is a well known process for the production of composites. In a typical filament wound composite a continuous filament of reinforcing material, such as glass fiber, is coated with a resin. The key characteristic of a suitable filament wound composite is low friction.
Graphite composites may include for example graphite or Teflon® or various combinations, such as DuPont's Delrin® or DuPont's Vespel®. Delrin® comprises an acetal resin (acetal polyoxymethylene (POM)) with homopolymer and copolymer grades available. Delrin® products may contain various other components such as Kevlar® or Teflon® and silicone oil. Stronger composites, such as HyComp® thermoplastics are also suitable. These may include materials made by HyComp® such as WearComp® and FibreComp®, which are comprised of carbon fiber with a polyimide binder. Generally, “composites” as used herein will have a fiber reinforcement component and a polymer binder or matrix material. The WearComp®, WearComp®200, and FibreComp® materials use a thermoset polyimide binder. These materials are typically compression molded. Thermoplastics, which can be injection molded, can also be used. These may include for example PEEK, manufactured by Victrex® and Torlon® manufactured by Amoco.
Polymer-containing materials can usually be extruded to the saddle shape, or the liner, thereby eliminating machining except for the spring hole. The aforementioned composites can be used with a steel rocker without a liner, or they can be used for the liner with a steel rocker. Also, they may be used to form the rocker, which can be implemented with a steel saddle. It may also be possible to have both the rocker and the saddle or liner made of the same composite.
Advantageously, when machining is eliminated, heat treating, grinding, and honing may also be eliminated. There may be minimal smoothing of the parts, but significantly less than with machined parts. Additionally, tool marking will be reduced on the workpiece, friction will be reduced, and it can be easier for the user to alter the components when needed, for example for fine-tuning the rocker angle.
The liner is a partial cylinder, which will generally be formed by removing a section or quadrant of the cylinder. With most materials, the internal diameter of the liner will shrink when the section is removed. A sizing rod can be used to expand the inner diameter to the desired size.
The liner may comprise a plurality of individual lengths instead of being one continuous cylinder. This can be advantageous to produce long lengths that are consistent in dimensions.
The saddle liner may be attached to the saddle housing by various mechanisms, including for example pins 48, bolts, or adhesive.
The saddle liner wall thickness is preferably 8%-10% of the rocker diameter. If the wall is too thin, there is an insufficient amount of reserve oil in the graphite plugs that can be contained in the saddle wall, requiring more frequent replacement. Additionally, if the liner wall is too thin, it can be difficult to attach pins and bolts to the apparatus.
The rocker may be formed of a graphite composite, such as DuPont's Delrin® or DuPont's Vespel®. Another illustrative rocker material is high strength alloy steel. Softer rocker materials having low contact friction, such as the DuPont polymers mentioned, are desirable when bending parts for which appearance may be critical, such as prepainted or polished stainless steel or aluminum. The softer rocker will minimize unwanted marking of the part. It has been found that having a rocker of the same material as the liner can optimize reduction of wear and friction. In a particular embodiment of the invention, Delrin® or an equivalent is used for both the rocker and liner. It is also noted that particular Derlin® or Vespel compositions work better with certain metals such as aluminum or steel, so rocker material should be matched appropriately with liner material to achieve a desired balance of friction, strength, and effect in the workpiece. Reduction of friction reduces the bending load, which also reduces the tool's marks on the part being bent. If the life of the rotary bending tool components is the primary objective and slight burnishing on the part is acceptable, a steel rocker can be used with a Derlin® liner. Advantageously, having a liner in the saddle increases the flexibility and of selective rocker and liner materials for the best fit to the application requirements.
The housing dimensions are generally dictated by the space required for the rocker, return spring and the mounting holes. The outer dimensions of the rotary bending tool are generally dictated by the available space in the apparatus in which it is incorporated.
The invention also includes a method of fabricating the embodiments of the rotary bending tools described herein. The methods include forming a saddle housing, forming a saddle liner, and inserting the saddle liner in the saddle housing. The saddle housing and liner are formed of the materials described herein or their equivalents. A further illustrative method includes forming the liner of a plurality of lengths. The formation and insertion of other components as provided above comprise further illustrative embodiments and steps of the inventive methods. This includes for example, formation and insertion of various types of friction reducing plugs.
Embodiments of the invention also include a method of bending a workpiece using any of the embodiments of the rotary bending tool described herein.
Embodiments of the invention also include a die press having any of the embodiments of the rotary bending tool described herein incorporated into it.
While the invention has been described by illustrative embodiments, additional advantages and modifications will occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to specific details shown and described herein. Modifications, for example to materials used in the rotary bending tool components and the type of tool incorporating the inventive technology, may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention not be limited to the specific illustrative embodiments, but be interpreted within the full spirit and scope of the appended claims and their equivalents.
This application is based on, and claims priority to, provisional application Ser. No. 60/938,735, having a filing date of May 18, 2007, entitled Rotary Bender with Hybrid Saddle.
| Number | Date | Country | |
|---|---|---|---|
| 60938735 | May 2007 | US |
