Watertight Vat for Ultrasound Printing
Summary
With the fast development of 3D printing technology, more printing techniques besides Fused Deposition Modeling have emerged, where a lot of them use resin and other liquid to fabricate the models. This project provides a novel solution to the current design of the ink vat of FUS-printing which would increase the efficiency of ink vat preparation and prevent leakage of ink during the printing process.
Background
The resin vat is widely used in light-aided 3D printing such as Stereolithography (SLA) and Digital Light Processing (DLP) as well as Focus Ultrasound (FUS) printing which all require a sealed vat bottom and transparent window for the transmission of light or soundwave. Since the photoinitiator in the viscous ink is extremely sensitive to the light so the bottom of these vat should be as thin as possible to not reflect or deflect any wave. The current resin vat uses Polytetrafluoroethylene or Fluorinated Ethylene Propylene as the bottom which are usually transparent and allows the light to pass through and focus on the surface of material. These materials are usually tough and have high light transmittance which ensures high precision of SLA and DLP printing. In the FUS-printing, the ultrasound has different transmittance in the same medium and the film should be even thinner.
However, since FUS printing hasn’t been discovered until recently, there is not a mature design of the ink vat. The current design contains a hollow frame where both sides are covered by plastic wrap sealing with UV glue. For the research usage which requires repetitive experiment and vat preparation, this design is time consuming and highly varied from batch to batch. Moreover, the plastic has a weak mechanical property and can be easily wrinkled or ripped, resulting in one-time use and dedicated cleanup of the residue of UV glue. In this case, we want to develop an user-friendly, long-lasting and cost-effective ink vat for the FUS-printing applications.
Impact
This will allow the upcoming material scientists to quickly iterate the novel material design without wasting time on ink vat preparation each time. Our design will use mechanical mechanisms to replace the UV glue in fixing the films, using friction and forces to flatten the film and lock in place. Instead of plastic film, we also propose to utilize stiffer film with relatively thin thickness, such as polyimide. With this improved design, we aim to 1. Half the ink preparation time 2. Minimize the ink leakage and 3. Minimize the sinking of the film when the ink is loaded. This will significantly increase the repeatability of the experiment given more than dozens of parameters that need optimization. With the reliable ink vat, the FUS-printing will be able to iterate faster. It also benefits light-aided printing with replaceable vat bottoms. In the current commercial products, if there’s scratches introduced by ink loading or the vat is broken, the entire vat needs replacement. As a consumable, the film could be replaced separately to accommodate different ink without multiple vats.
Methods
The additive manufacturing methodology primarily used will be FDM printing. FDM printing will be crucial in the rapid-prototyping phase, as it will assist in the design iterations of the ink vat. As adjustments are made throughout the process and transition towards the final prototype, SLA or SLS printing will be utilized to improve quality. Since a requirement for the prototype is to be watertight, SLA and SLS printing ensures that there will be no leakage from the ink and when submerged in water. Lean manufacturing will also be implemented to ensure the amount of waste during the process will be minimized. Since FUS printing has been discovered recently, the prototype is completely new and multiple design iterations will be needed. As stated previously, the previous vat used was inefficient in terms of assembly, with the need of replacing the film after one use. With this design, a new film will be used and will not need to be replaced after each use. Because research with FUS printing is still new, there are many challenges that will need to be considered as the prototype progresses. Some considerations of these challenges are further discussed below as well as the approach for design concepts.
- Design and assemble the ink vat
The improved ink will be printed using a Bamboo 3D printer using PLA to test the tolerance and the tightening mechanism as a proof-of-concept. Two films will be tested on the vat – plastic film and polyimide film to validate the design of the vat will stretch out the film and secure it. Then, the model will be printed using SLA or SLS printing to get a better quality for long-term use.
- Ink leakage test
Once the ink vat is printed, the leakage will be tested with colored solutions. Acrylic dyes will be mixed with water and stored in the vat. After sealing with the new mechanism, the ink vat will be submerged in a water tank mimicking the environment of FUS-printing. Lastly, the ink vat will be tested with the real FUS printer which applies high frequency of ultrasound on the film and ink inside. The relationship between leakage and tolerance of fabricating will be investigated. Also, drop test will be conducted on the ink vat, where the vat containing water will be dropped on the ground from different angles to test the leakage.
- Loading and film deformation
The film deformation is also an observed issue in the previous design, which significantly impacts the precision and consistency of the FUS printing. Since the stiffness of the plastic film is too low, once the ink is loaded in the vat, there’s an obvious sink on the film. We will test the polyimide and PVC film side-by-side; also, the new design will be compared with the glued-on design to obtain quantitative measurement of the deformation. The size of the snap-in mechanism will be adjusted to get the best flatness.
Preliminary Designs
For the initial design, the material that will be used is PLA. As stated previously, the initial prototype will use FDM printing. The initial design consists of three parts: top window, bottom window, and ink cavity. The top and bottom window will have the same design as seen in figure 1. The ink cavity drawing is presented in figure 2.
The assembly of the initial design is presented in figure 3, where the pegs of the top and bottom windows are secured into the ink cavity and the surfaces will be flesh.
The design still needs to be optimized, with future implementations of a snap-fit and clamp to ensure that there is no leakage. The initial design is still in a very basic phase.
Future plan
Though we expect the proposed design will significantly improve the issues presented by the current glue-on ink vat, there are still potentials for further optimization. The vat will be printed with an FDM and SLA printer in this proposal. However, to achieve a higher fidelity and stability, a metallic frame such as aluminum will improve the long-term durability. Additionally, the vat will be attached on the x- and y- axis adopted from a desktop CNC machine, so the weight of the ink vat is critical to maintain the stability of the printhead even during printing. Therefore, the design could be optimized through topological analysis to remove unnecessary parts and minimize mass while maintaining the functionality.