Page 51 - MetalForming November 2017

Tooling by Design
Elliptical Cup
Wrinkling most severe at small radius
Circular flange
Fig. 3
disruption of the uniform compressive loads in axis-symmetric cup drawing.
Compressive forces in elliptical cup drawing peak in the area of the smaller radius. Failures such as tearing and fracturing are more likely to occur in this area. Reduce some of these com- pressive loads by notching the blank in the small radius area, providing that
the final product trim is not adversely affected. It also may be necessary to reduce the percent reduction or cup- wall height in order to successfully draw elliptical shapes.
Another example of a nonsymmet- rical cup: a flat side on an otherwise round cup. The blank material at the flat portion of the cup may flow too rapidly and leave loose material in that portion of the cup wall. The material flow in the area of the flat may need to be controlled or restricted by the use of a draw bead.
Draw beads control blank move- ment, particularly when deep drawing irregular shapes. Draw beads force material to bend and unbend before entering a die cavity, creating a restrain- ing force on the sheetmetal that causes the material to enter the die cavity under tension and at a reduced rate of speed. The height, shape and size of the draw beads determine the amount of retraining forces generated. Altering
the height of the bead increases, or decreases, the amount of restraining force.
A special type of draw bead known as an active draw bead can be used to lock out material near the bottom of the draw stroke to help promote stretching of the drawn part, reducing wrinkles and controling springback. These draw beads sit in a pocket during the drawing process and are raised (usually by pins under the beads) a fraction of an inch from the bottom of the press stroke to increase the restrain- ing forces on the blank flange. The dis- tance that active draw beads travel can be adjusted to finely tune the restrain- ing forces required to produce an acceptable part.
To learn more about deep-drawing processes, attend PMA’s Deep Drawing Technology Seminar in Cleveland, OH, December 5-6, 2017. Contact Marianne Sichi, msichi@pma.org, for more infor- mation and to register. M F
REGISTER NOW January 30-31, 2018 | Nashville Airport Marriott
Attend PMA’s Metal Stamping Technology and Tool & Die Conference to network and learn about new, emerging, evolving and maturing technologies that are impactful
to metal stamping, die design and die construction companies.
The 2018 conference will include:
• Educationalbreakoutsessions
• Tool&Die
• Stamping
• Emergingtechnology • Industrytrends
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