Workpiece blanking apparatus

Details Workpiece blanking apparatus Workpiece blanking apparatus

2000-03-30

2001-10-23

Crane, Daniel C. (Department: 3725)

Metal deforming

With cutting

By composite tool

C072S326000, C072S345000, C083S127000

Reexamination Certificate

active

06305209

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a workpiece blanking apparatus for blanking a workpiece of predetermined shape out of a metal plate.
2. Description of the Related Art
Known workpiece blanking apparatus comprise a vertically movable upper die assembly, a blanking punch vertically movable with respect to the upper die assembly and having a shape corresponding to the shape of a workpiece to be blanked, and a lower die assembly with a die fixedly mounted thereon. When the blanking punch is lowered toward a metal plate placed on the die, a desired workpiece is blanked out of the metal plate.
Specifically, a pad biased to move downwardly by a biasing means is disposed around the blanking punch. The pad has a lower end which is at the same height as the lower end of the blanking punch or projects slightly downwardly from the lower end of the blanking punch when the upper die assembly is in an elevated position. When the upper die assembly is lowered, the pad descends with the blanking punch and engages the metal plate on the die simultaneously with or slightly earlier than the blanking punch, thus resiliently holding the metal plate on the die. The blanking punch is continuously lowered into the metal plate to blank the workpiece out of the metal plate and depress the blanked workpiece.
The die on the lower die assembly has a vertically movable counterpunch disposed in confronting relationship to the blanking punch and normally biased to move upwardly. The counterpunch has an upper end which lies at the same height as the die when the upper die assembly is in the elevated position, i.e., before the workpiece is blanked out of the metal plate. As the workpiece is depressed by the blanking punch, the counterpunch is lowered while being pressed against the lower surface of the workpiece. After the workpiece is blanked, the blanking punch is lifted to a predetermined position, e.g., a position above the die, the pad is released from the downward push and displaced upwardly away from the metal plate.
Since the counterpunch is biased upwardly, when the blanking punch is lifted, the workpiece is raised to the position of the upper surface of the die by the counterpunch. Therefore, before the pad is spaced from the metal plate, the workpiece is pushed back to the metal plate, and tends to be deformed because its outer edge contacts the severed edge of the metal plate. As a result, the blanked workpiece is liable to have an inaccurate shape.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a workpiece blanking apparatus which is capable of blanking a workpiece highly accurately out of a metal plate.
According to the present invention, a workpiece blanking apparatus includes a die, a pad for holding a plate of metal on said die, a blanking punch for depressing the plate on said die downwardly of the die to blank a workpiece out of the plate, a counterpunch vertically movably disposed in said die in confronting relationship to said blanking punch and movable downwardly with the workpiece blanked by said blanking punch, and counterpunch urging means for normally urging said counterpunch upwardly. The workpiece blanking apparatus also has holding means for holding said counterpunch in a lowered position after the workpiece is blanked by said blanking punch until said blanking punch is spaced from the workpiece, said pad is spaced from the plate, and said blanking punch and said pad are lifted to a predetermined position, and for releasing said counterpunch in said lowered position and allowing said counterpunch to displace said workpiece out of said die when said blanking punch and said pad are lifted to said predetermined position.
The workpiece blanking apparatus operates as follows: The pad is lowered to press the plate against the die. Then, the blanking punch is lowered to blank a workpiece of desired shape out of the plate. When the blanking punch is lowered, the counterpunch is lowered with the workpiece sandwiched between the counterpunch and the blanking punch. After the blanking punch reaches a lowered position, blanking the workpiece, the blanking punch is lifted and the pad is lifted. At this time, the holding means holds the counterpunch at rest in the lowered position.
Since the counterpunch is not lifted even when the blanking punch is lifted, the blanked workpiece is not pushed back to the plate pressed against the die by the pad. The blanked workpiece is thus prevented from contacting and being damaged by the plate and can have a highly accurate shape.
When the blanking punch is spaced from the workpiece, the pad is spaced from the plate, and the blanking punch and the pad are lifted to the predetermined position, the holding means releases the counterpunch in the lowered position. The counterpunch now starts to ascend under the bias of the counterpunch urging means. As a result, the blanked workpiece is lifted by the counterpunch, and hence can smoothly be displaced out of the die while maintaining the highly accurate shape.
According to a first aspect of the present invention, the holding means has a pusher vertically movably disposed below said die for transmitting a biasing force from said counterpunch urging means to said counterpunch. A concave follower is integrally mounted on an upper surface of said pusher, and a slider is disposed for movement along the upper surface of said pusher in a horizontal direction transverse to said counterpunch. A cam integrally projects from a lower surface of said slider and movable into and out of engagement with said follower, for preventing said pusher from ascending upon movement into engagement with said follower and allowing said pusher to ascend upon movement out of engagement with said follower. The holding means also has slider driving means for moving said slider horizontally in a direction to bring said cam out of engagement with said follower when said pusher is lowered in response to downward movement of said counterpunch depressed by said blanking punch, and for moving said slider horizontally in a direction to bring said cam into engagement with said follower when said blanking punch and said pad are lifted to said predetermined position.
With this arrangement, after the workpiece is blanked and until the blanking punch and the pad are lifted to the predetermined position, the cam and the follower are held out of engagement with each other, preventing the pusher and the counterpunch from being elevated. After the blanking punch and the pad are lifted to the predetermined position, the cam and the follower are brought into engagement with each other, and the counterpunch is lifted to push the workpiece above the die. Therefore, the workpiece is not pushed back toward the plate, and hence the outer edge of the workpiece is prevented from contacting and being damaged by the plate. As a result, the workpiece is blanked to a highly accurate shape.
In the first aspect of the present invention, said concave follower has a horizontal upper surface for engaging said cam when said cam is out of engagement with said follower and a first slanted surface inclined continuously obliquely downwardly from said horizontal upper surface, for guiding said cam to slide from said horizontal upper surface. The concave follower also has a horizontal lower surface contiguous to said first slanted surface for allowing said cam to slide horizontally thereon, and a second slanted surface inclined continuously obliquely upwardly from said horizontal lower surface in confronting relationship to said first slanted surface at a progressively increasing angle, for limiting sliding movement of said cam from said horizontal lower surface.
When the cam and the follower are brought into engagement with each other by movement of the slider, the cam slides smoothly from the horizontal upper surface of the follower continuously along the first slanted surface to the lower surface. In this manner, wear on contacting surfaces of the cam and the follower is reduced. Then, the

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