Abstract
Radial-Axial Ring Rolling (RARR) is an industrial forging process for making strong, seamless metal rings. Conventionally, rings are made circular with constant cross-section. In this work we demonstrate a sensing and control strategy to create rings with variable radial wall thickness and variable curvature using standard RARR hardware. This has a number of potentially useful applications but also provides an understanding of how to control these properties for conventional RARR. The sensing uses a calibrated video camera to take a series of images of the ring top surface. Image processing is employed to measure and track the ring material in-situ. The complete state of the ring is represented by the ring thickness and curvature as a function of its volume fraction, which is computed by combining the measurements from the unoccluded areas with estimates of the ring shape elsewhere. Additionally, we present a marking technique for tracking of material as it rotates through the rolling machine, even after significant deformation of the ring has occurred. We show that rings with a wide range of variation in local thickness and curvature can be formed using conventional RARR hardware and a photogrammetric state measurement technique, combined with open-loop scheduling and feedback control of thickness and curvature. Rings with both variable thickness and non-circular shapes have been produced virtually using numerical simulations and in reality using modelling clay as a material to simulate metals at forging temperatures. We demonstrate that this technique extends the range of shapes achievable with standard RARR hardware.
Highlights
– the radial roll gap between the mandrel and forming roll is closed over successive rotations to reduce the radial wall thickness;
This work has described in detail a sensing and control strategy for adapting the conventional radial-axial ring rolling process to produce rings with variable wall thickness and variable curvature
Previous work has described the processes in isolation, but this is the first time that their combination has been shown to produce rings with a wide range of shapes. This is shown through numerical simulations and clay trials for two different target rings
Summary
Radial-Axial Ring Rolling (RARR) is an industrial hot forging process that produces seamless metal rings with. When the ring passes under the axial rolls or through the radial roll gap, its upper surface edges are occluded from view by the camera In these zones the thickness of the ring material perpendicular to the midline and the length of the midline is assumed not to change until it crosses the XZplane of the mill (Fig. 1). The open-loop tool path is determined under the assumption of rigid plastic material behaviour, meaning that the resulting ring thickness is equal to the roll gap. The used open-loop tool path does not account for the effect of transverse strain and reduced thinning, i.e. it is assumed that the radial thickness after both passes is equal to the roll gap (tkr+1 = urk). The normal angle is used as the target for the internal PID controller of the speed of the axial rolls relative to the speed of the radial rolls
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