Process Control for Additive Manufacturing of Concrete Components

Abstract

Additive manufacturing (AM) processes offer new possibilities in the design of concrete components. The process chain for AM processes generally consists of component design, print path generation, and manufacturing. Within the step of print path generation, the component is commonly divided into layers and filled with waypoints based on the assumption of a constant cross-section of the applied material strands. In contrast to metal or plastic, however, the material properties of fresh concrete are more sensitive to environmental influences such as temperature and humidity. This leads to cross-section variations during the process. Therefore, exclusively relying on an apriori print path planning for large-scale components leads to significant deviations between as-planed and as-printed geometries. The presented research aims to increase the manufacturing accuracy of concrete components by compensating layer inconsistencies through a controlled material application. For this purpose, varying the printing speed and nozzle distance allows for correction of the deviations of subjacent layers. Deviation detection is performed by a 2D laser sensor mounted on the printing nozzle to generate information about the underlying cross-section. Comparing the measured values to precalculated setpoints generates the error values. The control algorithm maps the error data into an adaption of the printing speed and nozzle distance to fulfill the pre-planned geometry. Applying the controller to a medium-sized component and comparing the result to the uncontrolled process shows a considerable accuracy improvement.