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The Deep Drawing process represents an advanced concept for the manufacture of components to be cold formed in a succession of drawing operations from a flat, precut metal blank when the depth of the draw equals or exceeds the minimum part diameter. The various forms produced may be cylindrical or shaped, with straight or tapered sidewalls.
An automatic transfer press transforms metallic material in a coiled, strip form and transforms it into a completed deep drawn stamped component. This transformation is performed incrementally, or progressively, by a series of stations that cut and form the material into the desired shape. The process is similar to a progressive die stamping in that the parts are developed incrementally in a series of stations but different in that the material upon entering the die is cut free from the material strip and progresses through the transfer machine by means of “transfer slide”.
The transfer press drawing process requires a strip of material or coil stock to be fed into the machine at the initial blank station. The blank for the component to be drawn is automatically cut from the strip and pushed down into the transfer slide. Blanks can be cut from the strip in multiple rows by utilizing an oscillating feed. A vertical blank transfer mechanism positively holds and carries the blank to the transfer level. The transfer slide, moving perpendicular to the strip feed direction, carries the blank to the first draw operation, or cupping station. At this point, the blank is drawn into a cup shape with the reduction percentage in accordance with the guidelines of the material type being drawn. As the transfer press returns to the top of the stroke, the transfer slide returns to its original position to accept the next blank. In some cases, the blank and cup operation are combined into one operation to simplify the transfer of the cup.
When the transfer slide is in position to receive the new blank or cup, transfer fingers, attached to the transfer slide, position themselves to carry the newly drawn cup from the first blank. The movement of the slide not only carries the blank to the cupping station, but the first drawn cup is transferred to the next station to be redrawn. This process continues until the transfer slide is “filled” or the part geometry is complete. Once the transfer slide is filled, with every revolution of the machine, a part is produced. Components produced in this manner often do not required annealing between redraw stations. Drawing lubricants are used to create a molecular buffer between the tooling and material to reduce heat and enhance the drawing process.
When completely drawn to size, the components are “harder” than the original raw material due to the effect of cold working the material. However, this increase in hardness varies from the top to the bottom of the part and with the type of material being drawn. Punch and die clearance controls the amount of cold working and wall thickness of the part. |
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