Investigation of Effect of Material Properties on Forces during Flow Forming Process

Abstract

Missile casing, rocket motor case, cartridge case, etc. for aviation, aerospace and defense sectors are manufactured by flow forming process. It is a non linear process with complex characteristics of plastic deformation. In this process, a deformable workpiece is placed over rigid mandrel and rotating rollers are deforming it under contact zone. There are two strategies normally adopted during process i.e. forward and reverse. In forward strategy, the directions of deformation and roller feed are same & in reverse strategy, the directions of deformation and roller feed are opposite. It is necessary to understand the effect of material properties on forming forces in order to design the tooling (rollers and mandrel) for various geometrical and material conditions. Basically, three forces are encountered during the process i.e. axial, radial and circumferential. It is discerned that some limitations are associated with commercial production during this process. Specifically, costly raw materials required for experimental trials and commercial machines do not have facility of online force measurement. Hence a simulation model is developed to investigate effect of material property parameters on forces during the process. Strain hardening exponent (n), strength co-efficient (K) and density (ρ) are the material properties taken for five different materials viz. aluminum, titanium, magnesium, copper and stainless steel. Apart from these, friction factor (μ) and temperature (T) are also considered during the study. Five levels of each parameter are used by incorporating Taguchi L25 orthogonal array. Taguchi had developed this design of experiment technique for costly and time consuming experiments. It has been observed that axial force is found highest. Radial force is found to be second predominant and circumferential force is least. Further it has been also observed that forces reduce with the increase in the temperature. Moreover, some other critical observations are also reported.