Efficient production of sensory machine elements by a two-stage rotary swaging process—Relevant phenomena and numerical modelling

A process sequence enabling an efficient production of hollow sensory machine elements with adapted wall-thickness and a smooth outer contour is presented. The applied conjoint forming approach aims to simultaneously form a tubular part to its final shape whilst integrating a functional element into it. Additionally, the forming process is adjusted in order to set up a pre-tension in the assembly. Thus, a lift-off of the sensor element in case of tensile forces during application is prohibited and a high sensor linearity is ensured. In order to predict the achievable pre-tension and to determine the maximum process force, a three-dimensional numerical model is introduced. The underlying mechanisms of the pre-tensioning process are discussed on the basis of a forming process with and without a mandrel. A direct comparison of the two basic swaging strategies – recess and infeed swaging – reveals advantages of the infeed swaging strategy to achieve a high pre-tension of the assembly. The cold work hardening of the preform, the thermal heating and the machine stiffness are relevant phenomena of the process which influence the forces significantly. A detailed validation proves the necessity to include the mentioned effects in the numerical model. Furthermore, a trial of a sensory rod is presented. The high linearity of the sensory structure underlines the high potential of the proposed process to integrate sensor elements into massive metallic structures.