Multi-Model based Additive Manufacturing: A framework for automated large-scale 3D concrete printing with industrial robots*

With the advent of concrete additive manufacturing in construction (AMC), three new challenges have arisen in planning, automatizing, and controlling 3D printing processes and systems. Firstly, most manufactured construction components are single-walled elements such as walls, hollow columns, or pillars. In contrast to common design rules for AM processes, these require explicit print path planning with a wall thickness equal to a single layer width. Secondly, the printing materials - fresh concrete, mortar, or earth - provide a protracted time-dependent compressive strength development. This behavior must be explicitly considered during print path design to prevent component collapse caused by excessive compression loads. Thirdly, there is a significant challenge emerging from the required component size. Printing on a building scale level requires large or even mobile on-site printing systems. Such systems generally do not provide an enclosed workspace to protect the printing process from environmental influences. Environmental influences however affect the material behavior while printing, leading to deviations between as-planned and as-built layer geometries.This publication presents a framework tackling the three challenges by incorporating path planning for components with single-layer wall thickness, considering time-dependent material behavior, and compensating for external influences. The framework extends state-of-the-art path planning and printing control approaches to enable automatized robotic additive manufacturing processes in construction. As part of the framework we specifically contribute a path planning algorithm for the 2.5D and 3D production of single-walled components, algorithmic coupling of path planning and FEM simulation to predict and ensure component stability, and an online control approach to compensation for environmental disturbances. The framework was tested by printing a column with a footprint of approximately 1.5 m² and a height of 2 m using Shotcrete 3D Printing (SC3DP).