Spoiled for 3D Printing Choice: Polyjet, SLA, SLS, FDM

The most recent addition to Prototype Projects portfolio of 3D printing capabilities is Polyjet 3D printing.

Its main benefit is its ability to produce parts comprised of two or three different materials on the same machine, with varying degrees of rigidity including very close match to rubber characteristics.

To quote our Polyjet service page: “PolyJet is a 3D printing process used for rapid prototyping and low volume additive manufacturing. It is a highly versatile, cost-effective and fast way to achieve aesthetically appealing prototype pre-production parts and short-run additive manufacturing of production parts”.

As a description of 3D printing, you’d be forgiven for saying that it’s hard to tell how Polyjet differs from other technologies.

But Polyjet is different. In this article we’ll take a look at the benefits it offers and draw a few comparisons with the most popular 3D printing service, SLA.

What is Polyjet 3D Printing?

First some history: Polyjet is also sometimes referred to as “Objet” printing, for the name of the company that introduced Polyjet to the world in the early 21^st century.

Fast forward a few years, and the Objet organisation became part of Stratasys – who now retain the Objet name as part of their product range of 3D printers.

The process today known as “Polyjet 3D printing” is unique among 3D printing technologies for its ability to produce parts with rubber-like properties using multiple materials simultaneously to build a single part (known as dual or triple 3D printing. In some cases materials are blended during the build to produce specific material properties.

View information on our other 3D printing technologies SLA, SLS and FDM

At Prototype Projects we use a Stratasys Objet 260 Connex 3 multi-material 3D Printer, a machine that offers triple-jetting technology capable of producing a huge range of properties and finishes.

Polyjet capabilities

To summarise then, Polyjet can produce parts which:

Have rubber-like characteristics
Are comprised of more than one material
Exhibit an identical look and feel to the target production part
Have an extremely smoothly textured finish
Are laid down in very thin layers with as little as 16-micron thickness
Require great precision, including complex shape, detail and moving components
Ready for use with little or no finishing
Offer a very cost effective price point for small part runs

The range of part properties possible with Polyjet is not limited to rubber-like characteristics though. In fact Polyjet is equally capable of producing rigid parts as well as more flexible ones. Other properties achievable with Polyjet 3D printing include

Thermal resistance
Feature complexity
Surface finish smoothness
Ultra-thin layering for overprinting
Range of finishing options including drilling, tapping, sanding and painting

We have a range of delivery and finishing options of our PolyJet service.

Comparison of Polyjet 3D Printing and SLA processes

It is not always helpful to compare 3D printing processes with each other, because each one has its own merits which make it the optimum process for a specific requirement.

However because SLA is by far the most popular and widely used of all 3D printing technologies, it’s worth taking a look at how it compares with Polyjet.

As mentioned, all the 3D printing technologies are excellent for producing rapid prototype parts fast, simple, high quality parts at relatively low cost. The processes are capable of 3D printing of complex parts with complex geometries and thin vertical sections.

Materials

In 90% of cases where a close match with rubber-like properties is required, Polyjet is far and away the best process and really comes into its own.

When the specified part requires more than one material, perhaps because materials with different mechanical properties are to be used in the same part, Polyjet is the solution.

SLA, SLS and FDM cannot deliver parts with the same rubber-like characteristics.

Finishing

Depending on the exact requirement, and due to the fact that most builds typically require a support structure, SLA parts will usually require some form of finishing. The most common finishing techniques for this are sanding and blasting, which, once complete, allow the part to be painted to a very high standard.

On the other hand, Polyjet by its nature produces much smoother parts with limited requirement for support structures. These structures are easily removed, so sanding may not be needed unless an exceptionally fine and smooth finish is required.

Fine detail

The Polyjet process can produce a layer thickness between 16 and 30µm. The ultrathin build layers make for both fine detail and a very smooth finish.

This ultra fine level of detail may not be possible with an SLA due to the different build process.

Mechanical properties

Both SLA and Polyjet 3D printers can use a wide range of materials, typically resins with a range of mechanical properties.

Polyjet resins have rubber-like (or rigid) opaque and transparent properties.

Dual printing

Whereas most 3D printers can only print parts using a single material, Polyjet printers can dynamically mix 2 or 3 resins during the printing process.

This means that parts can be produced with different materials for different levels of flexibility or transparency without the need for multi-part assembly.

Despite the vast range of materials available for SLA, FDM and SLS production, parts always consist of a single material.

Medical/Bio compatibility

Medical and bio-compatibility in 3D printing depends on the availability of suitably certified materials, and the conditions in which the prototype parts are manufactured and finished.

All 3D printing processes have at least one material available that complies with bio-compatibility regulations.

Summary

Property	SLA	Polyjet	SLS	FDM
Material choice	Wide range of photosensitive resins	Photopolymers	Nylon	ABS
Surface texture	Smooth	Smooth Matte/gloss	Rough	Rough
Opacity	Opaque & translucent	Opaque and translucent	Opaque	Opaque
Mechanical properties	Strong, brittle, flexible	Strong, brittle, flexible	Strong, flexible	Strong
Finishing	Sanding, polishing, blasting, painting	Sanding, polishing, blasting, painting	Smoothing, painting, dying	Limited
Biocompatible	Yes, with certified materials	Yes, with certified materials	Yes, with certified materials	Yes, with certified materials
Speed	Next day possible	Next day possible	Next day possible	Next day possible