Metal deforming – By use of closed-die and coacting work-forcer – Cup or shell drawing
Reexamination Certificate
1999-07-19
2001-05-15
Larson, Lowell A. (Department: 3725)
Metal deforming
By use of closed-die and coacting work-forcer
Cup or shell drawing
C072S379400
Reexamination Certificate
active
06230538
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and apparatus for forming sheet metal, and more particularly relates to a method and apparatus for performing deep drawing operations.
BACKGROUND OF THE INVENTION
Sheet metal blanks are deep drawn into various shapes to form cases for use in a number of different applications. According to conventional deep drawing techniques, a blank is clamped in place over a die and a punch pushes the blank through an opening in the die to form the case. The depth of the case that can be formed in a single drawing operation depends on the tensile strength and thickness of the metal. In general, one or more redrawing operations are necessary to obtain a case with the desired depth and size.
In a specific application, blanks are drawn to form cylindrical battery cases. For example, casings for small size batteries (e.g., AA, AAA) have a relatively long side wall and a relatively small diameter. Because of the depth and small diameter, a blank typically undergoes one drawing and at least one redrawing operation to obtain the desired dimensions. Therefore, it is desirable to have a method and apparatus which performs all of the necessary drawing operations to form a blank into the desired shape and size.
Previous methods and apparatus for performing multiple drawing operations involve the use of a deep drawing transfer press. The deep drawing transfer press carries out an in-line process during which workpieces are transferred through a series of work areas. Transfer presses typically have a beam which carries a plurality of punches. The punches are aligned with matching dies so that when the beam is lowered, the punches pass through the corresponding dies. The drawing means are shaped to perform different drawing operations and are arranged so that the last set forms the desired shape.
Unfortunately, the use of a deep drawing transfer press overly limits the rate at which cases are produced. In operation, conventional transfer presses typically load a blank at a first work area corresponding to the first drawing means. The beam is then lowered so that the first punch forces the blank through the first die to perform a first drawing operation. After the first drawing operation is completed, the workpiece is transferred to a second work area for performing a second drawing operation with the second drawing means, and so on. It will be appreciated that each workpiece must dwell at each work area so that the drawing apparatus can perform the associated operation. As a result, techniques using a deep drawing transfer press proceed in a step-by-step fashion which limits the rate at which cases are formed. Accordingly, typical transfer presses have a maximum production rate of approximately 170 parts per minute. Furthermore, it will be appreciated that when the beam is lowered, it performs a number of different drawing operations simultaneously. The discrete repetition of simultaneous drawing operations creates a significant noise problem.
Deep drawing transfer presses have additional problems in transferring each workpiece through the work areas. Transfer presses typically use fingers which clamp onto the workpiece for transfer to the next work area. The workpieces are held until the next punch pushes the pieces out of the fingers while performing a drawing operation. The fingers may interfere with the drawing apparatus associated with the work area and therefore are often broken, requiring downtime for repair or replacement. In addition, the fingers may disrupt the drawing procedure, causing additional delays or slower operation of the press.
SUMMARY OF THE INVENTION
A general aim of the present invention is to provide a method for continuously forming cases from blanks.
In that regard, a more detailed object of the present invention is to provide a method and apparatus for forming cases which maximizes the rate at which the cases are formed.
A related object of the present invention is to provide deep drawing apparatus which automatically centers each blank with drawing apparatus without interfering with the drawing operation being performed.
A more detailed object of the present invention is to provide deep drawing apparatus which reduces the level of noise generated during operation.
In light of the above, it is a feature of the present invention to provide a method for deep drawing blanks into cases using rotary turrets. The blanks are fed into a rotary turret having multiple sets of drawing apparatus. Each set includes a punch, centering mechanism, and ejector. In a first turret and any intermediate turrets, each set of drawing apparatus also includes a redraw sleeve. Each turret has cams shaped to drive each set through a deep drawing operation as the turret rotates. Depending on the desired dimensions, a first and subsequent redraw turrets may be used to form cases having the desired shape and size. In light of the above, therefore, the present invention provides a method and apparatus for forming blanks into cases using rotary turrets which are continuously operated. The cams are shaped so that each set of drawing apparatus on a given turret is positioned at a different stage in the drawing operation and therefore each set completes the operation at a different time. As a result, the level of noise generated during operation of the deep drawing apparatus is minimized.
These and other objects, advantages, and features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.
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Larson Lowell A.
Leydig , Voit & Mayer, Ltd.
RD Systems
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