8/18/2019 make erttyyththddddd

1/1

blankholders pressure is a perfectly feasible process. In production, the blankholder pres-sure is adjusted with respect to the part drawn. The object is additionally observed forappearance of wrinkles, buckling, or tearing, with the pressure corrected accordingly.Aside from drawn-material mechanical properties, blankholders pressure is addition-ally affected by the type and length of draw beads or draw steps, plus the sizeof the draw-ing punch.9-10-4 Draw Beads and Their DesignDraw beadsare structural addition to the flat die surface, which are intended to slow thedrawn materials progress down the die cavity. With dependence on theirheight and ontheir radius, the drawn material can be slowed down only very slightly, or it can be almosttotally stopped.Draw beadscan be machined along with the drawing die surface, or they can be insertedinto a recess, or welded where appropriate. Obviously, their shape must blend with the diesurface without any interruptions or abrupt transitions, for any such defects wi

ll transfer tothe part in the form of scars, tears, or other distortions.Material of draw beads must be highly resistant to abrasion, as theadvancing drawnstock abuses their surface considerably. With greater height or sharper radius of the beads,more forming and reforming takes place, which results in greater slow-down of the mater-ial and also in greater strain hardening and greater heat. (See Fig. 9-87).Step beads, shown in Fig. 9-88, do not produce as much strain hardening as conven-tional half-round draw beads. Here, the material is not so severely formed, unless of course,

it does not become squeezed too tight by the binder. To avert such condition, standoffs areused to control the metal flow consistency.A sample of standoffs is shown in Fig. 9-89. These are small metalblocks placed atapproximately three places around the parts circumference. They are usually mountedbetween the draw die and the binder to keep the offset needed for the material thickness.The height of standoffs is usually 10 percent greater than the thickness of drawn material,and their ease of adjustment can provide for any variations needed. Their surface area

should be as large as possible and they should be made of impact-resistant toolsteel.