Exploring Polyjet 3D Printing

Pioneered by Stratasys in 2007, polyjet 3D printing — while less widely used than SLS or SLA — is an effective tool for printed parts that require a high level of surface detail (0.1mm details are achievable) and a smooth, high-quality finish. Its applications include:

• Highly detailed display models that require multiple colours, such as medical models.
• Prototyping stages where a large number of iterations of a part are expected. Polyjet’s printing speed makes it ideal for this.
• Limited-run non-functional parts, such as decorations for luxury cars.
• Generating moulds and patterns for injection moulding, sand casting and similar technologies.

How does it work?

Polyjet printing could be thought of as a close relative of fused deposition modelling. Like FDM, it works by using an extruder head to print parts one layer at a time. However, rather than using a filament to deposit material on the printing bed, polyjet works in a manner closer to 2D inkjet printing. The extruder deposits tiny droplets of the selected photopolymer material on the printing bed, after which they are cured with ultraviolet light.

Polyjet 3D printing delivers a naturally smooth surface quality, which means additional sanding or polishing during post-processing is unnecessary. On the other hand, polyjet parts can be dyed and painted in the same way as SLS parts, which provides lots of options when it comes to creating a unique finish. Polyjet parts can also be glued when required, which provides you with the option of printing larger parts as separate components, then fixing them together.

What materials can be printed with polyjet?

Polyjet printing generally utilises resin, rather than the plastics utilised in other 3D printing methods. The most basic polyjet printers can only use one resin at a time, but more sophisticated ones can combine multiple resin’s during printing, providing a lot of flexibility when it comes to creating unique looks for parts, or even to provide different areas of the same part with separate material qualities.

Polyjet resins are available with a wide range of colours, feels and material qualities. Stiffness ranges from flexible and rubber-like (26-28 Shore D) materials like Objet TangoPlus, to more rigid ones (83-86 Shore D), like Objet VeroClear. In addition, overmold materials, which add a layer of rubber-like material to more rigid parts, are also available. Visual qualities can range from opaque to transparent, and plain black or white. Composites of different resins are also available, to deliver specific material qualities. This allows polyjet to provide a close approximation of various production materials during the prototyping stage, should this ever be required.

Designing polyjet parts

Here are a few useful guidelines to bear in mind when designing your polyjet parts:

• • Consider your support structures. Polyjet prints will require support structures for all overhangs, although these can be printed using a special dissolvable material, which dramatically speeds up their removal during post-processing.
  • Balance layer thickness with speed. While polyjet can print in layers as thin as as 0.00063 inches, this will significantly slow down the speed of printing. Aim to strike a sensible balance between the part’s level of detail and the necessary production time.
  • Plan for your material costs. Polyjet resins are quite dense compared to other 3D printing materials, which means you will need more of them to successfully print a part. Also, be sure to factor in the cost of your support material.
  • Consider the purpose of your part. At the time of writing, polyjet materials are not suitable for functional production parts, although as noted above, the technology excels at creating moulds and patterns for other manufacturing technologies. If you are looking to create functional production parts, another 3D printing method may serve you better, but look for ways polyjet printing could be used to streamline the whole process. You may be surprised at what can be achieved.

• Which file format will best suit you? Coloured polyjet parts are typically captured in either the familiar STL file format, or Virtual Reality Modeling Language (VRML) format. With STL files, colours are expressed as RGD codes, while for VRML files offer a number of sophisticated ways to apply colour, such as texture modelling. While VRML files are less common in additive manufacturing, the level of flexibility the offer for full-colour printing make them a useful enhancement for polyjet printing.

While polyjet 3D printing is still less established than other methods, it is very hard to beat when it comes to delivering parts where the aesthetic quality and level of detail is the top priority. With a little creativity, its potential is enormous, so be bold and don’t be afraid to experiment!