An engineer working at a shipyard’s sheet metal fabrication shop has to calculate the maximum bend length for a metal sheet that needs to be bent 90° without bottoming.
What We Know:
The shop has a 30-ton press brake. Two V-dies are available with 2” and 1” openings, respectively. The sheet metal is 1/8″-thick AISI 4130 low-alloy steel. The engineer wants to calculate the bending capacity of the break for both dies in order to figure out the optimal cutting pattern for the sheet metal during fabrication.
After not finding a suitable calculation procedure in the manuals he has at-hand, the engineer turns to Knovel.
He begins by entering the search term ‘bending capacity’
The engineer finds an equation for calculating the press capacity along with a calculation example in the title ASM Handbook, Volume 14B – Metalworking: Sheet Forming in section 30.4.1 Sample Calculation.
And finds the desired value in an Interactive Table – Design Mechanical Properties of Military Handbook – MIL-HDBK-5H: Metallic Materials and Elements for Aerospace Vehicle Structures (Knovel Interactive Edition):
He now knows that the tensile strength of the material is 75 ksi and converts 75 ksi into tsias required by the equation he found earlier. Using Knovel’s Unit Converter, he uses the result of the conversion: 5400 tonf/ft2and divides it by 144. The final result is 37.5 tsi and he can now use the equation:
The engineer rewrites equation 1 to calculate the maximum length of the bend:
The die opening of 2″ is equal to 16t, where t is metal thickness. For a 16t opening, the die-opening factor k is 1.2. Thus, the bend length, l, is
If the die opening is 1″ or 8t, the factor k is 1.33. Then, the bend length is
Using the ASM Handbook and other Knovel resources, the engineer was able to calculate the maximum bend length for a steel sheet for 1” and 2” die openings. He then used this information to determine the optimal dimensions of the sheet to be bent and specify the appropriate die for fabrication.