Process capability study of flow formed shell diameter

Abstract

Flow forming is an advanced cold forming process to produce net shape, precision thin walled shells. The process is capable of realising cylindrical components with uniform wall thickness throughout the length maintaining stringent dimensional as well as form tolerances. Process capability study has been adopted to determine the ability of the existing flow forming process to satisfy user requirement as far as the internal and external diameter of flow formed shell is concerned. Flow forming of Maraging Steel (Grade-250) shells has been carried out and the diameters of the shells have been measured at different stations. Process capability indices have been computed based on the measured diameter readings of flow formed shell without considering measurement inaccuracies. Such process capability study is beneficial to improve quality of flow formed tube by identifying root cause of variation and eliminating causes behind such variations during subsequent production process of flow formed shell. The present study reports the spread of the measured diameter values in the form of histogram and ability of the existing flow forming process to meet user requirement in the form of process capability indices such as Cp&Cpk. The study further shows that the process is adequately capable to satisfy consistently the user requirement for both internal as well as external diameter. However, from the measured data it is clearly evident that further suitable measures may be taken up to minimise the spread of the output variable i.e diameter readings, thus improving the process capability further.