Reduction of the residual stresses in cold expanded thick-walled cylinders by plastic compression

We suppose that in order to maintain high accuracy of holes and to lower residual stresses after cold expansion of thick-walled cylinders, which undergo cross-section plastic deformation, it is necessary to perform axial plastic compression and subsequent cold expansion with small interferences. To test this hypothesis, we studied hoop, radial and axial residual stresses in cylinders made of carbon steel AISI 1050 with hole diameter of 5 mm, outer diameter of 15 mm and length of 30 mm by Sachs method as well as accuracy of expanded holes. It is found that double cold expansion with total interference equal to 5.1% generates hoop residual stresses with largest absolute value equal to 284 MPa and ensures high holes accuracy (IT7). After plastic compression with strain equal to 0.5 and 1% the mentioned stresses reduced to 120 and 75 MPa respectively, and accuracy of the holes reduced as well. Subsequent cold expansion with small interference equal to 0.9% helps to restore holes accuracy (IT7) gained by double cold expansion and ensure that absolute value of hoop residual stresses (177 MPa) is lower compared to double cold expansion.