Today we will walk you through the production process of this technology. PolyJet works in a similar way to inkjet printing as used by conventional 2D printers on paper, but instead of injecting droplets, they inject layers of liquid photopolymer into a tray that harden when exposed to ultraviolet rays.
This technology has many advantages as mentioned in the previous post, such as excellent resolution (up to 0.016 mm), flat surfaces (no staircase effect, unlike FDM printed objects) and a wide choice of materials and colours for a relatively low cost and printing time.
The manufacturing process can be divided into 3 steps:
Pre-processing
Design – creation of the 3D model
As with other AF technologies, the process begins with the creation of a CAD (Computer-Assisted Design) model. This step involves creating, modifying and analysing three-dimensional (also two-dimensional) representations of physical objects using computer software.
Cutting the part – .STL format
Once the model is created, it is converted to .STL format (or .AMF / .3MF, more recent formats), which is a triangulated representation of a 3D CAD model.
Production
The orientation of the machine or construction needs to be defined and whether there will be support structures (which may be necessary for the deposition of layers in near horizontal orientations).
Next, the manufacturing sequence is detailed. These actions are also carried out with specific software that is often determined by each printer and technology.
Once the process has started, the liquid resin is heated to 30-60°C to obtain the right viscosity for printing. The print head, much like an inkjet printer, then projects hundreds of micro-droplets of UV-sensitive photopolymer resin. This is integrated into the printhead and hardens the material to form the first layer. This technology is based on the principle of photopolymerisation. Multimaterial and polychromatic printing is possible because the printhead holder has many nozzles capable of “spraying” several materials simultaneously. The printer prints and cures the liquid photopolymer droplets instantly by means of ultraviolet light. Thin layers build up on the tray to create a precise model or 3D part.
If there are protrusions or complex shapes that require supports, the 3D printer injects a support material that can be removed later. After receipt of the material and verification (if necessary) of the key feature certificates (defined in the applicable standard or in the technical specification of the purchase), the raw material is loaded into the printer.
- First stage, injection of photo-reactive polymers in a liquid state: in this first stage, the material is injected through multiple nozzles into the areas of the platform where it is needed for the construction of the part including support structures. By using multiple nozzles, each one of them can selectively deposit a different type of material, which is an advantage of these technologies compared to others: the possibility of giving the parts different properties in each area, making it possible to create heterogeneous products in terms of stiffness, colour, roughness, etc.
- Second stage, solidification of the material using UV light: in this second stage, while the material is being deposited in a liquid state, lamps emitting UV light proceed to its photopolymerisation to bring it to a solid state.
The precision achieved by this technology can range from 0.05 to 0.15 mm depending on the machine used, with some having a manufacturing volume of up to 500 x 400 x 200 mm3.
Post-production
To finish the production of the structure, the support material is removed by hand, with water or in a solution bath. Subsequently, the models and parts are ready for use and handling when removed from the manufacturing process, without the need for further hardening.
