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FEATURE MATERIALS IN DESIGN & PROTOTYPING


FDM OR POLYJET? The choice is yours...


3D printing is truly transformational, even at this early stage in its ongoing evolution. There are, however, many factors to consider when purchasing a 3D printer, as Laser Lines explains


W


hen purchasing a 3D printer, it is important to understand the


difference between Fused Deposition Modelling (FDM) and Polyjet. FDM heats a thermoplastic filament –


effectively a coil of fine thermoplastic wound on a spool – and extrudes it in a continuous bead of semi-molten material. Once deposited, it cools and solidifies to form a new layer. According to Mark Tyrtania, sales


director at Laser Lines, the result can often be stronger and more dimensionally stable than a Polyjet model. Not only that, but FDM models are more robust and, depending on the choice of material, can be made to withstand high temperatures and more demanding working conditions. However, the layer thickness used by


an FDM 3D printer isn’t as fine as with Polyjet printer. So, where Polyjet allows for smoother surfaces on curves, slopes and gradients, an FDM model will sometimes have visible layers. Polyjet’s finer layer resolution is


made possible through its use of liquid polymers, which are jetted in liquid form and then cured through exposure to ultraviolet light. The technology’s focus is on final product realism, smooth surfaces and fine feature detail. Depending on the material, Polyjet parts can have a range or combination of properties from rigid to flexible; full colour to clear; or even be medically compatible. As a result, Polyjet is often used for concept


and form models where the finished appearance is important, such as consumer products and electronics.


MATERIAL CHOICES With Polyjet, there are over 1000 materials and the option to blend multiple digital materials within the printing process. In fact with the latest Polyjet J750, six model materials can be loaded simultaneously; and so mixed material parts, mixed material builds or full colour parts are easily achievable. Materials used across the range also enable modelling of transparent parts (or semi-transparent through mixing), producing fully flexible models with a scale of rigidity that can match anything from a soft gasket to a vehicle tyre. Yet while FDM isn’t capable of producing


flexible parts, its output is often more durable. Parts can be built using heat- and flame-retardant materials and from ABS, ASA, PC-ABS and Polycarbonate. As such, end use parts or finished jigs, fixtures and tools can be produced for immediate use. Where required, either technology can be used in the production of medical equipment, food packaging and kitchen utensils, when supplied with consumables that conform to ISO 10993 ratings.


COST, SIZE AND COMPLEXITY The purchase cost of raw consumables is broadly the same. However, the more rigid build of an FDM-model, and the fact it is constructed from material that’s already semi- solid at the point of deposition, means it’s much better at supporting itself. It therefore requires fewer support structures than a Polyjet part, using less raw material. Furthermore, while FDM printers require an ongoing supply of


38 NOVEMBER 2016 | DESIGN SOLUTIONS


build trays and extrusion nozzles, Polyjet devices may need to have their print heads replaced after every 2000 hours of use, which represents a higher running cost. While Polyjet is the more complex


option from a technological standpoint, it’s no more difficult to use than FDM. All 3D parts, regardless of the process used to create them, are sent to the printer as an STL (STereoLithography) file, or as a VRML file with the new J750 VRML machine, and can be in production after a few mouse clicks. In addition, the print size for each tops out at around 1000 x 800 x 500mm. However, the relative simplicity of the FDM process means that the printer itself is often a little more compact. If the majority of the models that you plan to produce are no more than 240mm along the longest size, a capable FDM device may be able to sit on the end of a regular desk.


POST PROCESSING


It is possible to print products ranging from robot arms to trainers


It’s common for models produced using either technology to require some support structure during the build process – although FDM often needs fewer. Depending on the material used to build a model, the support scaffold on an FDM part can simply be snapped off or, if printed using one of the soluble support materials, dissolved in a wash tank. However, an equivalent wash process is now available for Polyjet, with a two-step soak and


rinse now able to remove SUP706 polymer in a similar


fashion to soluble FDM supports.


With Polyjet printers, the finer layer resolution is made possible through its use of liquid polymers, which are jetted in liquid form and then cured through exposure to ultraviolet light


CHOOSING THE RIGHT PRINTER There are many factors to consider when buying a 3D printer, from the required applications and choice of materials to its overall running cost. In many ways, the initial capital investment is a secondary consideration. Tyrtania concluded: “You might find that a single 3D printer won’t do everything your company needs. But in our experience it’s often the case that one technology will cover at least 80% of any firm’s requirements. The remaining 20% can then be satisfied by using bureau services like the one offered by Laser Lines.”


Laser Lines http://3dprinting.co.uk


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