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To determine the distribution of stress within the frame of a 30-ton cast iron punch press with the object of altering the design to reduce weight without sacrificing strength or rigidity, a number of SR-4 electric strain gages were affixed to the press frame and connected to suitable recording instruments as shown in the Fig. 1. The load was applied to the press by means of a mechanical jack. Strains at the several points of gage attachment were determined with the tie rods tight and with the rods loose. Deflection readings and press rotation under load were observed. Very high stress concentrations were found at the platen fillets and at the gibb way fillet. At 30-ton s punch load the stress at the platen fillets was calculated to be 23,600 psi. and 9400 psi. at the gibb fillet; over the rest of the frame the stresses were generally not more than 4500 psi. Enlarging these fillets reduced the stresses substantially, and these stresses were further reduced through tightening the tie rods thus prestressing the fillets in compression. In order to convert strain to stress, it was necessary to know the modulus of elasticity of this particular cast iron. Two cast bars were obtained from the foundry and standard A.S.T.M. round specimens were machined from the bars and tested. The modulus of elasticity of these coupons was found to be roughly 13 × 106 psi.
Brewer, Given A.
Anthony and Sons, Inc., New Bedford, Mass.