What is it for:
3D printing technology has become a significant fabrication technology for the fabrication of prototypes as well as small series production during the recent years. Compared to other technologies such as milling processes the needed material is only deposited where it is needed. Under ideal conditions items can be produced without the side effect of producing lots of waste materials. The 3D printing is referred to be a “tool less” fabrication technology. What does that mean? Can the printer be regarded as a tool? In a way – yes! However there are no conventional tools such as e.g. cutting devices, drills, …, involved to shape the desired object. If it comes to the processing of polymers, one well known technology is the injection molding, where melted polymer is pressed into a mold tailor made for one specific item. That means, that if even a small deviation in the design of that given object should be made, a completely new mold has to be produced. Now consider the costs of such a mold – they can easily exceed several thousands of Euro, Pounds or Dollars (depending where you are from). That renders the injection molding process only suitable for large scale productions. Now consider the open fuel cell as it may be used in your school, university or especially in your own hobby laboratory: is it a large scale production? Not at all!
Also, it should be considered that lots of complex geometries that can be produced by using 3D-printing technologies are not accessible by using conventional e.g. milling processes or injection molding. Considering these advantages different variations of 3D-printing h
Therefore: if it comes to the fabrication of all the components made of polymer used for the open fuel cell the 3D-printing was the technology of choice. To be more specific: The components produced by means of 3D-printing are the anode and cathode end-plates and all the sealing elements.
What are the requirements:
Like with the open fuel cell itself, the 3D-printers and the involved fabrication technology should be easy to handle and affordable. This requirements hold for both: for the printer itself and the processed material. The 3D-printing technologies that come with low price tag and therefore are accessible for hobby and educational applications are the “fused deposition modelling” (FDM) and the resin based “stereolithography” (SLA) printers. Both 3D-technologies are used for the open fuel cell project. The pros and cons of the FDM and SLA printing technologies are:
FDM: Filaments made of thermoplastics are processed with these types of printers. What does thermoplastics mean? This type of polymer become soft and can be formed once they are heated to high enough temperatures. With a great variety of different pure and composite materials available all these filaments have one thing in common. They can easily be stored. The drawback of this technology is, that the special resolution is limited compared to that of an SLA printer. Also, the printed parts are, unless specially adapted settings for the printer are applied, in most cases not really gas and water tight. Due to the fact that the processed polymers are all thermoplasts, all the 3D printed components have quite a low maximum operating temperature. For the most commonly used polymers within the “entry level” 3D FDM printing, namely the PLA and the PETG, these maximum temperatures are about 50°C for the PLA and about 75°C for the PETG.
SLA: These printers are processing a liquid resin that is cured into a solid polymer by exposure to UV-light. The advantages of the SLA printing is, that the objects can be printing with a very high special resolution. For example it is possible to print a thread for an M6 screw, something that is impossible using an FDM printer. Furthermore the SLA printed components are water and gastight and optical transparent. However, since the resin is cured by UV light special care should be taken while storing the resin. It is also no a good idea to expose the SLA printer to direct sunlight with the UV-protective cover left open.
What equipment did we choose:
As a FDM printer we are using the PRUSA I3 MK3S (https://www.prusa3d.com/de/kategorie/original-prusa-i3-mk3s/) (please observe the information previously given: we do not have any relation with the companies mentioned in this chapter. All information and (if considered as such) advice is based on our own experience). While this printer is not necessarily at the lower end of the price scale, it has some benefits such as a very rugged design and the option to add multi material unit (https://www.prusa3d.com/de/kategorie/mmu2-mmu2s/ ) that allows to process different materials within one print. Furthermore this printer is available as an assembly kit. As already mentioned in relation with the CNC-milling, assembling your own printer is the best way to get to know that machine.
In order to process the composite materials such as carbon fiber reinforced PETG a specially hardened extruder nozzle has to be used due to the abrasive nature of the carbon fibers. In our case we used the RUBY nozzle (https://www.prusa3d.com/de/produkt/der-olsson-ruby/ ) with a diameter of 0,4 mm.
What to learn from it:
Foremost you will get a deep insight into an upcoming industrial manufacturing technology. This refers to the design a setup of the printers itself as well as the processing of the different types of polymers such as the rigid materials like PETG used to print the end plates or the very soft and flexible material used to print the sealing elements. Even if it sounds quite easy: load the CAD-model of the desired object into the printer, press the start-button and soon the idea will materialize, the reality is far apart. Sometimes lots of experiments involving the fine tuning of the settings and parameters for the printer and testing of the functionality of the produced components are required. In addition to the handling of the printer itself you will get a deep insight into all the small details including a quality assurance that are required to assure a high quality production process – components of high quality are definetly required in order to get the open fuel cell running.