3D PRINTING - PART 3

How Long Is a Piece of Filament?

A Guide to Fused Deposition Modelling - FDM Using UPBOX 3+

One of Walt Disney’s legendary quotes seems particularly appropriate for this topic: “If you can dream it, you can do it”. Now, when we’re told this as children, it is supposed to inspire us to never give up and be optimistic for the future where anything is possible, but if you can think back to a time before the digital revolution, there were obvious problems with this mantra.

If I recall correctly, there were things that were just impossible to make, not because of lack of imagination or communicating an idea, rather it was lack of technology to do so. Now of course, every child has access to a 3D printer, every child’s bedroom has an UPBOX+ (okay, maybe that’s an exaggeration, but give it a few years), they are able to take an idea they have from a drawing they made in class and turn it into a physical object to hold in their hands.

As you already discovered by now through the previous chapters on 3D printing, not all 3D printers are the same, nor are the techniques used to create the objects. Depending on the size, complexity, and material constraints, there are different approaches to 3D printing.

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As discussed in the previous chapters, you’re now familiar with the terms SLA (Stereolithography), and CJP (ColourJet Printing), but the most popular and probably the most affordable is FDM (Fused Deposition Modelling). The UPBOX + uses fused deposition modeling process to melt and extrude ABS and/or PLA plastic onto additive layers. The ABS/PLA filament is first fed into a heated printer nozzle where it melts into a liquid. Subsequently, the printer nozzle extrude plastic onto the print bed over the areas of the print object. The print bed is then lowered and the process is repeated until the object is fully printed.

  1. The filament is fed into the FDM 3D printer.
  2. The thermoplastic is heated past their transition temperature inside the hot end.
  3. The filament is extruded and deposited by an extrusion head onto a build platform where it cools.
  4. The process is continuous, building up layers to create the model.
  5. The build platform lowers gradually as the model takes shape.

It can be confusing when deciding on the most appropriate method to use for prototyping – particularly for 3D printing and just as important as it is to choose the right technology, consideration should be taken onto the choice of material as well (Grenda, 2006). So far we have briefly discussed the types of materials employed by SLA and CJP, including strength, flexibility, accuracy, and special conditions the material may require in order to print properly and accurately. With the UPBOX+ ABS and PLA are the two types of materials currently in use, but the differences between the two aren’t immediately apparent. What’s the difference?

First, let’s define what exactly the two materials are. Both ABS and PLA are thermoplastics. Wohler’s and Caffrey (2014, p. 29) describe thermoplastics as becoming malleable when superheated, thus allowing you to mold and sculpt them into different shapes prior to cooling” (p.29). It is worth noting that the UPBOX+ currently in use within the Prototyping Laboratory only use ABS for print jobs, with PLA implemented only for particular requests or needs of a project. That being said, below is a quick glance at the merits of each thermoplastic in case you’re wondering why the distinction exists to begin with:

ABS

ABS, short for Acylonitrile Butadiene Styrene, is an oil-based plastic. It is a strong, sturdy material that manufacturers use for constructing products such as plastic car parts, musical instruments, and the ever-popular Lego building blocks. ABS has a high melting point, and can experience warping if cooled while printing (Wohler’s & Caffrey 2014). As a result, ABS objects must be printed on a heated surface, which is absent in many household 3D printers. In addition, ABS also requires ventilation when in use, as the fumes can be unpleasant. The aforementioned factors make ABS printing difficult for hobbyist printers, though, it’s the preferred material for professional applications (Wohler’s & Caffrey 2014).

PLA

PLA, or Poly Lactic Acid, is made from organic material – cornstarch and sugarcane to be exact. This affords the material to be much safer to use with a surface finish that’s smooth and shiny. The fumes generated are less harsh and sweet when heated as a result of it being a sugar based material when compared to the harsh smell often associated with ABS. However, while PLA might seem like a better overall choice at first glance, it features a far lower melting point than ABS. This means that using printed parts for mechanical operations, or even storing them in high-temperature locations, can result in the part warping, cracking, or melting (Wohler’s & Caffrey 2014).The material is also weaker than ABS, though, it can achieve a superior level of print detail and is less prone to errors while printing.

  • ABS – better structural integrity and will be more suited to mechanical use given the material can better withstand the elements.
  • PLA – more precise prints, better aesthetic quality, if you can do without the strength and resilience of ABS.

UPBOX+ A CLOSER LOOK

Precision and Smoothness

With FDM, the resolution of printed parts relies heavily on the size of the print nozzle and the precision of the extruder movements (X/Y axis). Other factors that influence printed parts are the bonding force between the layers as well as the weight of upper layers, which may squeeze the layers below. This process inevitably leads to issues such as warping, misalignment of layers, shifting of layers, shrinking of the lower parts, etc. It is often the case that quick concept models are printed on an UPBOX+ to prove a concept works before a more refined model will sometimes be sent to an SLA printer. Please refer to the section on finishing parts for an understanding on model preparation and post processing.

Removal After 3D printing

Removal of printed objects is usually quite simple, wearing protective gloves and glasses, added pressure by hand to pry the part off the platform or a palette knife inserted at the base of the part and leveraged. Plastic support filament will stick to the platform clogging the small holes in which case a sharp flat chisel is needed to scrap the surface of the platform, clearing it of any support structure.

Post Processing

After completing a part on an UPBOX+ printer, support material (if the model has overhangs) and excess plastic needs to be removed with appropriate cutting tools. Sanding helps to obtain a smoother surface and removes any imperfections on the part. Fillers are also used during this stage to bring the part up to a high quality model before painting is applied.

If precision, accuracy, smooth finish and money is no object, the use of an SLA printer is the best option. However if cost is of high priority, as well as speed, low finish level and detailing, the use of an FDM printer is the most appropriate choice. The UPBOX+ uses a standard filament roll that are available in size (diameter: 1.75mm) from various sources. Filament rolls are available in a range of colours, however the Prototyping Laboratory stocks black, white, green and clear as standard options. The overall build platform area is W255 x D205 x H205mm.

When to use FDM

  • Rapid prototyping
  • Low-cost models
  • For experimenting
  • When precision and surface finish are not crucial

When to use SLA

  • When intricate details are required
  • When a very smooth surface finish is crucial
  • When strength and durability of the model is not crucial
  • For creating molds for casting to facilitate mass-production
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