Engineering the AiCell

2 April 2019
Author: Leonidas Leonidou
“Note: This article was originally published in 2019 while Aibuild was involved in the development of hardware products that are later discontinued with the emergence of a strong collaboration with our trusted hardware partners.”

How designing a robot enclosure with a controlled environment helped eliminating material shrinkage and warping.

3D Printing is usually associated with a number of problems that make it difficult for new users to achieve good quality prints and it is more common than not that people who get into 3D printing have to deal with a large number of failed prints due to issues such as warping, material shrinkage and bad layer adhesion, just to name a few.

When scaling up from a desktop 3D printer to one that operates on the furniture or construction elements scale, one must consider the significant increase in the magnitude of the material forces involved, thus rendering all of the above-mentioned problems even more difficult to deal with and eventually eliminate. Through rigorous experimentation at Ai Build, we realized that one of the most important factors in determining a print’s quality and consistency is the environmental conditions in which the printer is operating.

During a cold winter day it would be almost impossible to achieve good adhesion between the print and printing bed, but it would be much easier to print perfect quality lattice structures. Conversely, during summer, bed adhesion would be almost effortless, while achieving a clean, high-quality lattice became extremely difficult as the print would take longer to solidify with the increased ambient air temperature. Another realization was that printing a perfectly straight element in the vertical direction would be very challenging, as the layers that were printed first would cool and shrink at a different rate to those printed later, such that the final result would look in elevation more like a curve instead of a straight line.

Initial sketches from the design of the AiCell.

After coming to these realizations, a number of brainstorming sessions followed in order to come up with an idea on how we can ensure printing quality consistency despite temperature and humidity fluctuations, and this is how the concept of the AiCell was born. The main idea was simple: create an enclosure around the robot and printing bed so that the environmental conditions during printing always remain stable. Incorporate a structure to support filament spools and feed the filaments to the extruder, place the whole structure on wheels in order to make it portable, and there you have it: an all-in-one solution for large scale 3D printing. After that, a number of sketches and ideas were put on the table, and the first version of the AiCell began taking shape.

It should be mentioned at this point that although enclosures are not a new concept in desktop 3D printing, scaling up to a robotic arm enclosure while maintaining portability presented a major engineering challenge. The structure had to be strong enough not only to carry the weight of the robot, heated bed, filament spools, print and any required equipment, but also to withstand torque forces from the motion of the robot, while at the same time the total weight of the cell had to be kept low enough in order to be able to be carried on wheels. On top of that, other parameters such as ease of assembly, component standardization and performance added extra layers of complexity in the engineering process.

Ai Build team at work — building the AiCell v1.0.

The first design for the AiCell came together in a very short time and the whole element sourcing and construction process was done in an experimenting way, but the prototype offered very promising results in terms of printing quality.

The AiCell v1.0 comprised of an aluminium frame of hollow sections welded together, with insulation boards fixed between the aluminium sections in order to create a closed thermal envelope for minimising heat transfer between the enclosure and its surrounding environment. The use of double glazing offered a significant boost in isolating the printing environment in terms of heat and noise, while the installation of fan heaters allowed control of the temperature inside the cell. The controlled environment was also equipped with a cast aluminium heated bed with a maximum temperature of 90°C, which helped eliminate any remaining bed adhesion issues. MDF boards were used as cladding around the cell in order to give it a more distinct look while also reducing printing noise.

Installing the first prototype of the AiCell at the V&A museum in London as part of the Digital Design Weekend exhibition in September 2018.

After the first cell was built, we started running print tests extensively in it and we realized that the initial assumptions were confirmed indeed. The controlled environment together with the heated bed helped to eliminate defects due to non-uniform material shrinkage and warping and to produce prints whose dimensions were really close to that of the digital model.

The explanation behind the success of the cell stemmed from its ability to allow the printed object to maintain an almost homogeneous temperature distribution throughout its surface while being printed, as the bed was heated at 60°C and the space had a stable temperature of around 40°C. In this way, material shrinkage was prevented as there were not any areas of the print that would get significantly colder, and once the print was complete, the space and heated bed would cool down. This in turn allowed the print to cool uniformly, hence preventing differential shrinking between parts of the print that would cool more than others and lead to dimensional inaccuracies.

The latest version of AiCell boasting a modular structure and aluminium finishes, while also including a number of major upgrades over v1.0.

Following the positive findings of having a controlled printing environment, a number of major improvements were introduced in the AiCell versions that followed, with the cell becoming part of Aibuild’s technology that is currently offered on a subscription basis for powering large scale 3D printing facilities. The latest version of the AiCell comprises of a modular structure that allows easy modifications and additions, boasting a much lighter unit that is easy to be transported and moved around, while the overall aesthetics of the cell have also been upgraded significantly since v1.0, combining functional design with precise engineering.