Iterative Factoring Processes for Double Curved Concrete Formworks

Florian Landsteiner

In various projects of contemporary architecture freeform generation plays a big role. Digital programs allow the controlled generation of almost any form and its production. But there is still the problem, that the fabrication, typically CNC-milling of foam blocks is time consuming, uneconomical and cost intensive. Due to various reasons, but especially the existence of many unlike and various elements, especially within the specific field of parametric-design, where the necessity to manufacture a separate form for each part, which can only be used once, is common. The aim of the presented work faces this problem and is the prototypical manufacturing of double curved formworks for complex facade or shell structure based on a neutral, re-usable material. To reach this goal, an iterative process-cycle is developed which is based on the interaction between a computer, an industrial robot and a commercial 3D Scanner. This cycle is set to reach a final formwork through continuous repetition of three steps. The main focus of the production is set on three related target points: First, on the sensory determination of the actual state and the derived algorithmically initialized steps, second, on the reversible plastic deformation of the source material, and third, on the savings caused by the source material, which can be re-used as often as desired, also after successful deformation process and thus allows a resource-saving and economical production of the formwork To determine the current state of a non-fixed blank and to translate / convert this via sensory information into a digital model, a commercial 3D –Scanner (a Microsoft Kinect® in this case) is used. This digital model is calibrated using a custom written script within Grasshopper®. This programming environment included in the program Rhino®, enables via plugins like HAL® and Firefly® a direct communication between all the components. Throughout the script the calibrated model is compared with the final geometry of the formwork and from this compared difference between the blank and the to-reach formwork, press paths are calculated, transmitted and executed via an industrial robot. To reduce the plastic deformation of the mold material (a wax based plasteline) the area is screened specifically according the dimensions of the deformation tool attached on the robots lowest axis. The plastic deformation by displacement of material, caused by a tool which main focus is set on pressing or hammering, is, as opposed to subtractive production like milling, of lower precision. Therefore, to compensate this lack of precision, a subsequent scan is initialized at the end of one pressing cycle, to determine the altered state of the formwork and the deviation to the final form. This data is used to detect if the formwork matches the digital model, and if necessary to calculate any further potential press cycles. In order to keep both, time efficiency of the process, as well as the plastic deformation caused by the displacement of the raw material on the mind, the number of points which are inscribed within each of the grated segments and which act as targets for the robot, can be reduced. This reduction causes a decrease in precision, as well as in production time during the first few intermediate scans. For finalizing purpose, the count of points is raised again, and, despite the additional time needed to complete the last cycle, therefore grants a high level of control regarding the smoothness/ accuracy of the surface.  
The master thesis Iterative Factoring Processes for Double Curved Concrete Formworks was supervised by Stefan Peters (Institute of Spatial Design).