Assignment 3 Solutions

Topics: Buckling, Elasticity, Metal forming Pages: 5 (372 words) Published: December 2, 2014
1)
Wrinkling in the flange. Wrinkling in a drawn part consists of a series of ridges that form radially in the undrawn flange of the work part due to compressive buckling. Wrinkling in the wall. If and when the flange is drawn into the cup, these ridges appear in the vertical wall.

Tearing. Tearing is an open crack in the vertical wall, usually near the base of the drawn cup, due to high tensile stresses that cause thinning and failure of the metal at this location. This type of failure can also ocur as the metal is pulled over a sharp die corner. Earing. This is the formation of irregularities (called ears) in the upper edge of a deep drawn cup, caused by anisotropy in the sheet metal. If the material is perfectly isotropic, ears do not form.

Surface Scratches. Surface scratches can ocur on the drawn parti f the punch and die are not smooth or if lubrication is insufficient.

2)
In V-bending, the sheet metal is bent between a V-shaped punch and die. Included angles ranging from very obtuse to very acute can be made with V-dies. V-bending is generally used for low-production operations. It is often performed on a pres brake and associated V-dies are relatively simple and inexpensive.

Edge bending involves cantilever loading of the sheet metal. A pressure pad is used to apply a force Fh to hold the base of the part againist the die, while the punch forces the part to yield and bend over the edge of the die. Edge bending is limited to bends of 90° or less. Due to pressure pad, wiping dies are more complicated and costly than v-dies anda re generally used for high production works.

3)

In the plastic region, the volume is constant so;
0∗ 0∗ 0=
∗ ∗
∗ ∗
=1
0∗ 0∗ 0

Then do;

− 0
= 0,15
0

= 1,15
0
Similarly, bu in the opposite direction due to reduction;
− 0
= −0,05
0
0

= 0,915

So;

= 0,95

Then;

=

0
0

=

ln 1,0925
= 1,725
ln 1,0526

Then from the graph, the LDR is almost 2,8 for that material. 4)





The compensation techniques;
Overbending the part in the die
Coining the bend region by subjecting it to high localized compressive stresses between tip of punch and die surface
Elevated temperature bending due to decrease in yield strength of material Strecth bending, in which the part is subjected to tension while being bent.

5)

6)

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