Forming press systems for making pressware containers from paperboard are known in the art. Typically, a forming press system includes one or more forming die assemblies oriented on an inclined plane such that scored paperboard blanks are fed between upper and lower die components thereof by way of gravity. Generally, forming die assemblies include an upper male die member or “punch,” and a lower female die member or “die,” which are compressed together to shape and crimp the blank into the desired final product. The male and/or female die members can be provided with knock-out sections, and/or an air ejector system can be included for assisting in removal of the formed product from the forming press. U.S. Pat. No. 6,908,296 to Johns et al., U.S. Pat. No. 4,588,539 to Rossi et al., U.S. Pat. No. 6,592,357 to Johns et al., U.S. Pat. No. 4,242,293 to Dowd, U.S. Pat. Nos. 5,249,946 and 6,284,101 to Marx, and U.S. Pat. No. 3,824,058 to Axer et al. are incorporated herein for background teaching showing the state of the art.
As shown in FIGS. 1-3, forming die assemblies 10 having segmented punch and die mechanisms are known. These commonly include an outer pressure ring 20 mounted to surround an inner punch 22, and an outer draw ring 24 mounted to surround an inner die 26 (both the punch and die components of segmented forming die assemblies are sometimes referred to herein as inner die members, and both the pressure ring and draw ring components are sometimes referred to as outer die rings). The pressure ring 20 and draw ring 24 reciprocate independently of their respective inner die members over at least a portion of the forming stroke. As the forming die assembly is closed, the pressure ring 20 contacts the blank, clamping it against the draw ring 24 and die 26 to provide pleating control during formation. As the forming die assembly closes further, the punch 22 is pressed into the die 26 to form the desired product geometry between the mating punch and die profiles. Internal springs 28 normally bias the pressure ring 20 and the draw ring 24 toward their extended positions relative to the inner die members, as shown in FIG. 1. These springs are compressed as the forming press is closed, allowing the pressure ring and draw ring to remain in contact with the edge of the blank under controlled pressure as the inner die members independently advance into engagement with one another. At the completion of the forming die assembly's compression stroke, the pressure ring 20 and the draw ring 24 are positioned in their retracted positions relative to the inner die members, as shown in FIG. 2.
After completion of the compression stroke, the forming die assembly is opened to remove the shaped product, and the cycle is repeated. Opening of the forming die assembly causes the pressure ring 20 and the draw ring 24 to return under the influence of the internal springs, back into their extended positions relative to the inner die members, as shown in FIG. 1. Angle iron stops 30, 32 are typically attached to the pressure ring 20 and the draw ring 24 at circumferentially spaced apart locations, for abutment against flat shoulders of pockets machined into the side faces of the punch 22 and the die 26, respectively, to limit the extent of travel of the pressure ring and the draw ring relative to the inner die members on the return stroke of the forming die assembly.
Repeated impact of the stops 30, 32 against the punch 22 and the die 26 during high-speed cyclical operation, typically as part of a continuously operating process, often results in considerable wear damage to the stops. And because the stops 30, 32 are typically formed of a hardened steel extrusion having a higher hardness than the material of which the pressure ring 20, the draw ring 24, the punch 22, and the die 26 are formed, wear damage to the die components is also common. Misalignment of the die components resulting from such wear can result in damage to the pressure ring 20 and the draw ring 24. It has now been discovered that cyclical wear-related damage takes place at a relatively high rate in the areas of the stops 30, 32 because of the relatively small surface area of contact between the stops and the abutment shoulders of the inner die members (shown as the cross-hatched areas 60 in FIG. 3).
The relative positioning of the pressure ring 20 and the draw ring 24 with respect to the inner die members affects the pressure applied to the edge of the blank, which in turn effects the pleating control and edge formation of the final product. Thus, wear at the contact areas between the stops 30, 32 and the pressure ring 20 and draw ring 24 can adversely affect product quality. This is of particular concern in the manufacture of products having specialized rim and edge configurations for improved structural performance, such as for example the product geometries identified in U.S. patent application Ser. No. 10/963,686, filed Oct. 13, 2004, and incorporated herein by reference. As a result, replacement of worn or broken stops 30, 32 and/or pressure ring and draw ring components frequently becomes necessary in order to maintain a high degree of quality control. Replacement of these components results in substantial down-time of production equipment, as well as increased parts costs and man-hours of labor.
It has also now been discovered that the moving components of a forming die assembly often tend to move progressively out of alignment during use because of the assembly's inclined orientation. Without being bound by theory, it is believed that gravity tends to pull the pressure ring 20 and the draw ring 24 downwardly due to the assembly's inclined orientation, shifting the pressure ring and draw ring out of alignment with the inner die members. In addition, the weight of the pressure ring 20 also causes friction between the punch 22 and the stops 30 to be higher along the “uphill” side of the forming die assembly than along the “downhill” side. Similarly, friction between the die 26 and the stops 32 is higher along the “uphill” side due to the weight of the draw ring 24. Over a period of cyclical operation, the higher friction at the “uphill” side causes increased wear between the moving components, leading to progressively increasing misalignment. Even a small degree of off-center draw of the die components against the paperboard blanks resulting from such misalignment can have a very negative effect on proper formation of the rim edges of the final product. Because the edge geometry has a substantial effect on product rigidity, it is desirable to minimize misalignment of the forming die assembly's components during operation.
In view of these characteristics of known forming die assemblies, it can be seen that equipment and process improvements that reduce the incidence of wear-related damage and/or better maintain alignment of forming die assembly components during operation would be highly desirable in terms of improved product quality, greater productivity and increased profitability.