Presses – Methods
Reexamination Certificate
2002-05-22
2004-04-06
Ostrager, Allen (Department: 3725)
Presses
Methods
C100S257000, C100S299000, C072S448000, C083S530000
Reexamination Certificate
active
06715409
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a shutheight adjustment mechanism for use in press machines, and, more particularly, to a method and apparatus for modifying the spatial relationship between the parts of the shutheight adjustment mechanism such as the threaded nut and screw members by inducing a deformation activity therein which is sufficient to displace the threaded portions into an interlocking engagement that eliminates the free clearances therebetween.
2. Description of the Related Art
Mechanical presses of the type performing stamping and drawing operations employ a conventional construction including a frame having a crown and bed portion and a slide supported within the frame for reciprocating movement toward and away from the bed. The slide is driven by a crankshaft having a connecting arm coupled to the slide. These mechanical presses are widely used for a variety of workpiece operations employing a diverse array of die sets, with the press machine varying substantially in size and available tonnage depending upon its intended use. The availability of a diverse selection of die sets for installation into the press machines requires an adjustment capability that tailors the shutheight dimension to the particular configuration of press machine and die assembly.
One conventional press arrangement employs a slide configured for connection to the crankshaft by a connecting rod that is adjustable in length or which is connected to another device such as a connection screw that is adjustable in its spatial separation from the slide, thereby permitting adjustments to be made to the shutheight dimension in order to accommodate various die sets. Adjustment mechanisms of the type employing an adjustable connecting rod or connection screw have typically been arranged such that the individual working parts are disposed within the slide, requiring that any shutheight adjustments be made only through changes in the position of the slide relative to the bed. Alternatively, the bed portion or bolster assembly of the press may have its position adjusted relative to the slide so as to adjust the shutheight therebetween. Regardless of the mode of shutheight adjustment, the slide is generally guided on the uprights of the press frame extending between the crown and bed so that the parts of the die set remain in accurate registration as the slide reciprocates.
One conventional adjustment mechanism employs a plurality of connection screw assemblies configured within the slide and actuated simultaneously by means of a worm-gear arrangement, which is driven either manually or by means of an operator controlled motor. This arrangement effectuates a change in the shutheight by changing the position of the slide relative to each of the connection screws. As known, the manufacture and assembly of any form of shutheight adjustment mechanism requires the development of various spatial clearances between the discrete parts of the mechanism. Additionally, it is necessary to implement various working tolerances between the connected portions of the press, specifically the connections that couple the shutheight adjustment mechanism to the slide or bolster. Proper formation of these clearances and tolerances allows the worm gear, adjustment nuts, and connection screws, for example, to be rotated and otherwise moved so that the adjustment mechanism may be suitably operated.
However, the existence of such clearances and tolerances present various difficulties in accurately controlling press shutheight and in reproducing a constant bottom-dead-center operating range since the clearances permit small but adverse displacements of the adjustment mechanism parts and the attached slide or bolster beyond their normal operating range under certain load conditions. Current problems with shutheight adjustment mechanisms include the transfer of punching and snap through loads through the adjustment mechanism during press operation. A press load is the load created by the mechanical press when the slide is urging its associated die member into contact with the workpiece. When the workpiece fractures in the die, the slide attempts to rapidly accelerate downward, which corresponds to the snap through action. This snap through load is comprised mainly of the downward acceleration and the downward slide crank inertial acceleration of the die and slide combination. The failure to implement measures aimed at counteracting such snap through loads or retarding such snap through action may cause an unwanted change in the shutheight and lead to excessive die penetration beyond its normal operating range.
The clearances also prevent the uniform transmission of pressure loads throughout the press machine since certain force components may be communicated more or less extensively within the machine relative to other force components depending upon the degree that the force-transmitting parts shift within the clearances. This uneven distribution of forces may cause particular parts to experience concentrated impact forces leading to breakdown or failure. Again, the clearances between the parts permit the shutheight to variably change during operation of the press, resulting in workpieces that may not meet design specifications.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method and apparatus for substantially eliminating the free clearances present within shutheight adjustment mechanisms that are configured for use in press machines. One illustrative arrangement of the shutheight adjustment mechanism includes a male threaded member provided in the form of a screw that threadedly engages a female threaded member provided in the form of an adjustment nut disposed about the screw. Relative rotation between the screw and adjustment nut effectuates a change in the shutheight. A clearance space is defined between respective threaded portions of the screw and adjustment nut to enable actuation of the shutheight adjustment mechanism, e.g., rotation of the adjustment nut relative to the screw.
An apparatus is provided according to the present invention to induce a deformation activity in at least one of the screw and adjustment nut that is sufficient to enable these parts to be brought into substantial interlocking engagement with one another at their respective threaded portions. This locking condition is particularly characterized by the substantial elimination of the original free clearances existing between the threaded portions of the screw and adjustment nut, thereby preventing relative rotation between the parts and effectively opposing any occurrence of snap through or other causes of excessive die penetration. This interlocking engagement is produced in one embodiment by a hydraulic assembly that directs a pressurized fluid against an outer periphery of the adjustment nut to effectively exert a compressive action upon the adjustment nut that radially displaces the threaded portion thereof into locked engagement with the threaded portion of the screw. The deformation activity in the adjustment nut may be sufficiently ordered to induce further an accompanying elongation thereof along its axial dimension to close out any clearance spaces formed adjacent the axial end surfaces of the adjustment nut. In another embodiment, a hydraulic assembly is arranged to hydraulically pressurize an interior space of the screw to effectively exert an expansive action upon the screw that radially displaces the threaded portion thereof into locked engagement with the threaded portion of the adjustment nut. The induced deformation activity present in both the screw and adjustment nut is preferably reversible and remains intact by maintaining the holding pressure upon the affected part until it is desired to restore the shutheight adjustment mechanism to an actuatable condition.
The invention, in one form thereof, comprises a press machine having a frame structure with a crown and a bed; a slide guided by the frame structure for operative reciprocating movement i
Bornhorst Donald
Brewer W. Craig
Burns Bradley
Pax Bryan
Schockman Robert
Knuth Randall J.
Nguyen Jimmy
Ostrager Allen
The Minster Machine Company
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