Solutions to Chapter 17 rev

# 20 bending is plastic deformation about a linear axis

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20. "Bending is plastic deformation about a linear axis with little or no change in surface area. When multiple bends are made in a single operation, that operation is often called "forming". If the axes of deformation are not linear, or are not independent, the process is called drawing". 26. Whenever possible, the bend axis should be perpendicular to the direction of previous rolling. If two perpendicular bend axes are involved, the metal should be oriented with the rolling direction at 45 0 to both axes. Problems: 1. a. With no rake angle, the stroke required to blank the piece would be equal to the thickness of the sheet. With a rake angle of 1t, the total blanking stroke increases to 2t. Figure 18-12 compares the force-stroke profiles for blanking without a rake angle and blanking with rake angle. Since the area under the two curves is the same (the work required to shear the metal), doubling the stroke will result in halving the average blanking force. The change in the maximum force will depend upon the specific conditions of the length of cut and thickness. b. If the rake height were increased to 3t, the blanking stroke is now 4t and the average blanking force is now ¼ of the average blanking force with no rake angle. Again, the specifics of maximum cannot be determined, but are likely to be quite a bit lower.

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Problem ( for reference): The figure below shows the forming limit diagram for aluminum alloy and low-carbon steel, where points 1 and 2 are from aluminum alloy, and 3, and 4 from low-carbon steel. Please indicate whether the metals at each point can be shaped without risk of fracture or not by circling “yes” or “no” for each point . (4 points) Point 4 Point 3 (1) At point 1: Yes No (2) At point 2: Yes No (3) At point 3: Yes No (4) At point 4: Yes No
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