Construction 3D printing, also known as concrete 3D printing, is the process of printing structures with concrete materials. Even though these printers use the additive manufacturing principle, they face different challenges, and the 3D printing process is thus slightly different in terms of the equipment used, the parameters to be controlled, and the systems to print a structure.
We take a quick look at the stages of 3D printing, the factors influencing print quality, and the process involved in construction 3D printing.
Concrete 3D Printing Stages
A typical concrete 3D printing process follows three stages of Data preparation, Concrete material preparation and 3D printing.
The data preparation stage involves path generation for the robotic arms. The nozzle is attached to the robotic arm, and it moves around with the help of massive guide rails. These also form the boundaries of the print area. The robotic arm with its nozzle moves within the confines of the area in the same way that an extruder in an FDM 3D printer does.
The advanced software creates individual slices of the model to be 3D printed. The path is then charted out and movement of the arm is optimised for 3D printing the concrete structure.
Concrete Material Preparation
The concrete material preparation stage prepares the material for use in the 3D printer. The concrete material is more difficult to work with than other traditional 3D printing materials. Preparing, mixing, and loading the concrete 3D printing material into a container are all part of the material preparation stage. This freshly prepared material is then pumped into the nozzle as and when needed during printing. Primarily, four factors influence print quality during this stage.
- Pumpability: The ease with which material is moved through the pump delivery system.
- Printability: The ease and dependability with which material can be deposited using a deposition device.
- Buildability: A deposited wet material’s resistance to deformation under load.
- Open time: The time period during which the other three properties are consistent within acceptable tolerances.
The behaviour of fresh concrete, particularly its pumpability and buildability, deteriorates over time in concrete 3D printing processes, and it is critical to balance it for satisfactory results. Flowability also decreases over time, which can result in intermittent gaps in material deposition. These properties, however, are difficult to control and vary greatly depending on the manufacturer’s concrete mix, the delivery systems used, and the deposition device used. A slight variation in any of these elements can have a significant impact on print quality.
Concrete 3D Printing Process
There are multiple construction 3D printing technologies but the printing process is generally carried out through gantry systems or robotic arm systems.
In the gantry system, the manipulator, a device to manipulate the concrete material eliminating the need for physical contact by an operator, is mounted onto the overhead to locate the print nozzle in XYZ coordinates. But this also restricts the amount of freedom of the 3D printer.
In the robotic arm systems, as it eliminates the use of manipulator, the system offers additional degrees of freedom to the nozzle, allowing more accurate printing workflows such as printing with tangential continuity method.
But, regardless of the system used for construction 3D printing, the coordination between the nozzle travel speed and the material flow rate is crucial to the outcome of the printed filament. If needed, multiple robotic arms can be programmed to run simultaneously to reduce the overall printing time.
After the 3D printing, post-processing procedures can be applied to remove any excess parts created as support structures or any surface finishing is required. This can also be automated in some cases.
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