This invention relates to double action presses used to draw hollow articles from a blank, and more particularly but not exclusively to long stroke double action mechanically driven presses used to redraw and wall iron a cup shaped blank, to make a can body.
U.S. Pat. No. 3,696,657 (MAYTAG) describes a press having a first action to drive a ram and second action rod for driving a blank holder to co-operate with dies to redraw and wall iron a cup to a taller can body. The blank holder is mounted on a redraw carriage which is connected to the second action rod by pivotable joints which may wear to spoil the accuracy of blank holder motion. EP-A-0536812 describes a modified "MAYTAG" press in which the weight of the second action rod is supported to reduce wear on the pivotable joints and the redraw carriage is guided by pillars mounted in the die housing. The axis of each pivotable joint is arranged perpendicular to the driving rod to act in the manner of a universal joint permitting tilt but not lateral deviation of the rod direction from the redraw carriage direction by the pillars.
Other longstroke mechanical presses for the purpose of drawing and wall ironing can bodies are described in U.S. Pat. Nos. 3,270,544 (Maeder), 3,663,072 (Cvacho) 3,735,629 (Paramonof) and 4,173,138 (Main). These mechanical presses have served the can making industry well and improvements have permitted increase of stroking speed from about 100 stokes per minute in 1970 to over 300 strokes per minute in 1990. However, there persists a need to increase press speed and reduce lost time arising from tool changes.
In these prior art presses a long ram is urged to move towards and away from a tool support, fixed to the press frame, by a connecting coupling pivotally connected to one end of a lever which swings on a pivot fixed to the press frame. The lever is driven to swing by a connecting rod attached to a crank shaft to constitute a first action linkage. When provided a second action, such as described in U.S. Pat. No. 3,735,629, comprises a pair of second levers pivoted on the frame and driven to swing by cams on the crank shaft to urge a cross head to move a pair of long connecting rods to move a second cross head towards and away from the tool support.
A tubular blank holder is mounted on this second cross head to cooperate with a punch on the ram to permit redrawing of a shallow drawn cup against a redrawing die in the tool support. After redrawing to reduced overall diameter and increased height of side wall, the redrawn cup is pushed through at least one ironing ring to make a can body having a side wall thinner than its bottom wall. Typically the press stroke is about 20 inches long so that the first action ram is over 40" long. Typically, the connecting rods of the second action are also about 40" long. As press speeds increase the inertia forces arising from the combined weight of second action cross heads and connecting rods also increase so an improved support of the blank holder is required. Furthermore, adjustment of the position of the blank holder in respect to the redrawing die and ironing rings required laborious adjustment of the blank holder using adjusting the second crosshead, whenever the blank holder is changed, to ensure application of a correct blank holding force in alignment with the die and rings. Incorrect alignment of the blank holder with a redrawing die gives rise to an uneven holding pressure around the blank so that the height of the redrawn cup varies around the side wall of the redrawn cup.