This invention concerns guide pins and bushings used in the construction of forming dies.
Forming dies are comprised of two die parts, respectively mounted to an upper and a lower press platen. A guide pin or post is mounted to one die part, and a guide bushing is mounted to the other die part in alignment with the pin. The pin and bushing mate with each other when the press is actuated to guide the die parts into accurate registry. Such pins and posts may be press fit into holes in the respective die parts, but this makes disassembly for repairs difficult. To address this difficulty, so-called “demountable” pins and bushings have been developed, in which the pin and bushing are slidably fit in the die bases and are held with clamps engaging a flange on the pin or bushing, pressing the same against the adjacent die-part surface. The die-part surface is ground so that the pin and bushing are thereby precisely aligned with each other.
The flange has conventionally been formed by machining down large-diameter stock to form the pin or bushing, thereby producing much wasted material and increasing the time necessary to produce the pin or bushing. It thus has been necessary to manufacture and stock pins and bushings so as to achieve reasonably rapid delivery times. Stocking pins and bushings substantially increases costs because many configurations and sizes of pins and bushings must be stocked in order to be available for delivery on short notice.
It is an object of the present invention to provide guide pins and bushings and a method of manufacturing guide pins and bushings to a customer order. The method allows pins and bushings to be made rapidly to order while eliminating the need to waste time and material in machining the pins to form an integral flange. The method also reduces or eliminates the need to stock a large number of different pins and bushings.
The above object, and other objects that will become apparent upon a reading of the following specification and claims, are achieved by stocking lengths of standard-diameter shafts and tubes that have been heat-treated and precision-ground to a finished inside or outside diameter. When an order is received, a shaft or tube of the desired diameter is cut to length and machined to form a circumferential groove therein. Retainer pieces are engaged into the groove and provide axial mounting holes that may be used to secure the pin or bushing to a die plate. In this manner the same pin can be installed in a slip fit to the die plate, and thus is easily demountable; or the pin can be pressed into a die plate for maximum rigidity. Each retainer piece is assembled onto the pin or bushing at a specified location in such a way as to perform the retention function traditionally performed by an integral flange.
In one embodiment of the invention, a groove at the desired location of the flange is machined into the outside diameter of the pin or bushing. A plurality of retainer pieces is provided, each piece with an inner diameter section having a substantially uniform inner diameter, and having at least one axially oriented hole passing therethrough. Each retainer piece is engagable in the groove to secure the retainer piece in the groove. The inner diameter of the inner diameter section of retainer piece is matable to the groove diameter, and once engaged, the retainer piece protrudes from the circumferential groove sufficiently to permit at least one mounting hole to be used for securing the pin or bushing element to a die plate.
The invention also includes a method of manufacturing a pin or bushing, the method comprising the following steps: providing stock for a pin or bushing element as described above; forming or cutting the stock to a desired length; machining a circumferential groove into the stock; providing one or more retainer pieces as described above; and assembling the retainer pieces into the groove of the pin or bushing element.
Embodiments of the invention can reduce the cost of a demountable pin and yet provide maximum holding power of the pin to the die plate. This is achieved by having the same pin for demountable or pressed fit condition, thus reducing the cost of producing the pins and reducing inventory of finished goods. This is complemented by having retainers that are easily producible to be precise and strong. This new invention is easier to produce compared to the assembled flanges in U.S. patent application Ser. No. 11/223,134, which are superior to a conventional pin with the conventional integral flange. In the cited patent application, a flange is created in a pin or bushing by press fitting inner split taper ring pieces into the groove in the pin and using an outer taper ring. The groove in the pin, the split taper ring pieces, and the outer taper ring all need a high level of dimensional precision in order to have a good, controlled, tight fit when assembled. This high level of precision is not necessary for the successful use of the invention described in this new disclosure.
In the “Volvo” pin cited as a reference in the cited patent application, the contact of the round ring to the inner edge of the hole in the die plate produces very high stress concentration which could deform the hole in the plate, resulting in too much tightness to the pin and making it more difficult to demount the pin. The retaining bracket needs to be much thicker in order to have sufficient material and strength in the region wrapping over the ring, otherwise it will compromise the holding force capacity.
The invention is best understood from the following detailed description when read with the accompanying drawings.
In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting. The invention is capable of taking many forms and variations within the scope of the appended claims.
Referring to
Preferably the demountable pins and bushings and the retainer pieces are heat treated to a high hardness and strength.
The invention includes a manufacturing method that allows pin and bushing elements to be conveniently manufactured to order. One embodiment of the method includes the following steps: (a) stocking lengths of a series of machined cylindrical stock; (b) cutting the stock to form a rough element of having an ordered length and a main diameter section having a main diameter; (c) machining the rough element to create a circumferential groove in the main section, the circumferential groove having a diameter less than the main diameter; (d) providing a plurality of annular retainer pieces with an inner diameter section having a substantially uniform inner diameter, each annular retainer piece such that the retainer protrudes from the circumferential groove; and (e) assembling the retainer pieces around and within the groove. Any necessary machining operations can be added to this manufacturing method at an appropriate point before or after assembly of the flange. For example, any necessary counterbore may be machined before or after undertaking the steps of the exemplary manufacturing method of the invention.
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 may be made without departing from the spirit and scope of the invention. For example, retainers having a different number of axial mounting holes may be provided. 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 a continuation in part of U.S. application Ser. No. 12/109,607, filed Apr. 25, 2008. In addition, this application claims the priority of U.S. provisional patent application No. 60/949,407, filed Jul. 12, 2007. The following disclosures are incorporated by reference into this application: U.S. application Ser. No. 12/109,607; U.S. application Ser. No. 11/223,134, filed Sep. 9, 2005; and U.S. provisional patent application No. 60/949,407.
Number | Date | Country | |
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60949407 | Jul 2007 | US |
Number | Date | Country | |
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Parent | 12109607 | Apr 2008 | US |
Child | 12171097 | US |