A Guide to 3D Printing Mar. 30, 2015

Introduction

3D PRINTING, alias additive manufacturing (AM) or direct digital manufacturing (DDM), makes it possible to create an object by creating a digital file and printing it at home or sending it to one of a growing number of online 3D print services. 3D printing is achieved using an additive process, where successive layers of material are laid down in different shapes. 3D printing is also considered distinct from traditional machining techniques, which mostly rely on the removal of material by methods such as cutting or drilling (subtractive processes).


Why is it called printing?

If you look closely (with a microscope) at a page of text from your home printer, you’ll see the letters don’t just stain the paper, they’re actually sitting slightly on top of the surface of the page.

In theory, if you printed over that same page a few thousand times, eventually the ink would build up enough layers on top of each other to create a solid 3D model of each letter. That idea of building a physical form out of tiny layers is how the first 3D printers worked.


How does 3D Printing work?

It all starts with making a virtual design of the object you want to create. This virtual design is made in a CAD (Computer Aided Design) file using a 3D modeling program (for the creation of a totally new object) ór with the use of a 3D scanner (to copy an existing object). This scanner makes a 3D digital copy of an object and puts it into a 3D modeling program.

To prepare the digital file created in a 3D modeling program for printing, the software slices the final model into hundreds or thousands of horizontal layers. When this prepared file is uploaded in the 3D printer, the printer creates the object layer by layer. The 3D printer reads every slice (or 2D image) and proceeds to create the object blending each layer together with no sign of the layering visible, resulting in one three dimensional object.


Technologies of 3D Printing

We only regard in this article a Fused Filament Fabrication technology (FFF), also known as Fused Deposition Modelling (FDM) or Molten Polymer Deposition (MPD). The reason is simply that FFF printers are by far the most common 3D printer type used for home 3D printing, i.e. desktop 3D printers. If you are considering to buy your own 3D printer, a FFF is most likely the 3D printing technology that you will end up using. Note that FFF is a synonym of Fused Deposition Modelling (FDM) - both terms describe exactly the same technique.


What is Fused Filament Fabrication (FFF)?

Fused Filament Fabrication is nothing but a fancy word to describe a process by which a machine deposits a filament (picture something like a small string) of a certain material (normally thermoplastics, wax or similar products) on top or next to the same material, in order to create a joint by heat and/or adhesion. Thermoplastics are plastics which become semi-liquid above a specific temperature and return to a solid state when cooling down. A FFF printer prints a 3-dimensional object by extruding a stream of heated or melted thermoplastic material, which is carefully positioned into layer upon layer, working from the bottom up. Just imagine a heated print head that is oozing out a permanent flow of molten plastic onto a surface in order to form, through multiple layers, the virtual object you chose to print. By adding layer upon layer, which will almost immediately harden upon leaving the hot print head, you will see the object that you chose to create materialize right in front of you.

The following illustration gives you a clear understanding of FFF, as well as of a 3D printer's basic mechanism.


The Four 3D Printer’s Essentials

1. Extruder

Contrary to what you might think, the word extruder does not necessarily refer to the part of your 3D printer that squirts out the molten plastic. The extruder is actually the part that is responsible for feeding the filament into the so-called "hot-end". Extruders are the part where some of the biggest differences between 3D printers exist and where we are still likely to see some of the biggest developments in the future. Some 3D printers models use extruders which integrate the "filament driver" as well as the hot-end in one single piece. Illustration above already gave a brief overview of such an "integrated extruder".

Dual Extruder

Some 3D printers feature a Dual Extruder. This means that the printer has two filament drivers as well as two hot-ends.

The advantage of this particular feature is that you can feed two different filaments for one print, enabling you thereby to either print in dual colour or even with two different materials. Why two materials? Well, 3D printers print from the ground up. But some prints are impossible to realize, as the printer cannot print on air; that’s why you need “support structures” or support, in short. The parts of your print which would be floating on air are called “overhang“.

Basically, the limits of your print are the laws of physics. In order to overcome this problem, you can choose (or, depending on your software, these parts are automatically detected) where to print a support structure.

If your are printing with ABS or PLA (filament materials for 3D printers, described here later), you need to know that the plastic will get pretty stiff after cooling down – so cleaning the support structure can take quite some time. Also, you need to pay attention not to damage your print, especially if you use a knife or a power tool.

An easier way to get around this is printing with PVA on the second extruder. PVA, short for polyvinyl acetate/alcohol, is a special water-soluble thermoplastic. PLA is used to print your object and PVA is used to print only the support structure. Once your print is finished, just put it into water or Limonene for some time and the PVA support structure will dissolve itself (as shown in the picture to the right). Voila, you have a perfect print without the hassle or time loss for cleaning up your object.


2. Hot End

The hot end is usually made up of a block of aluminium (squared or barrel-shaped), which is heated up to temperatures up to 250° Celsius (482° Fahrenheit). These high temperatures are the reason why the hot end needs to be thermally insulated from the rest of the setup.

The hot end is also comprised of a print nozzle (a.k.a. extrusion end) and some sort of temperature sensor. The typical print nozzle's opening diameter may range in size between 0,2 to 0,5 millimetres and plays an important role in the print resolution of your object. The smaller the nozzle, the finer the print, but the longer it will take to complete. The presence of the temperature sensor is important, as different sort of plastics may need different temperatures to print with.


3. Printbed (Print-Plates)

The printbed (we’ll call it - print-plate) is the surface upon which the printed part sits on while being built. The most common print-plates are made out of Plexiglass (acrylic), aluminium or glass. When buying a 3D printer, you should always check out what the exact print-plate size is, as it plays a determining factor in the maximum size of your future printed objects. Also, you need to differentiate between simple (non-heated) print-plates and heated print-plates.

Non-heated print-plates normally need to be covered in build tape (painters tape) or even Kapton tape (i.e. polyimide tape - very heat resistant) in order to make the print stick to the printbed. The tape helps with initial adhesion of the thermoplastic and keeps everything in place during the print. The object needs to be firmly fixed to the print-plate, as the slightest movement of the printed object itself will most probably result in a botched-up print. As the adhesion factor of the blue tape wears out quickly, it needs to be replaced regularly. Instead of blue tape, some people recommend using glue, hair spray, sanding down the Kapton tape, etc. The biggest disadvantage of using a non-heated print-plate is that you may experience warping or cracking of your prints.

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4. Filament

Filament is the consumable for your 3D printer. Just as the inkjet printers need ink cartridges to work, a 3D printer needs filament in order to be able to print. Filament is usually bundled in spools, but some is also sold by the meter (ideal for test prints). Before making any purchase of filament, you need to know what filament diameter your printer works with. It will be either 1,75mm or 3mm, which are the two standard sizes.

Filament is generally sold at its weight price. You can find spools on our site in four standard weight sizes:

  1. ‘S’ (or Small spool) - 0.5lb or 220g (0.22kg),

  2. ‘L’ (or Large spool) - 2lb or 900g (0.9kg),

  3. ‘XL’ spool - 5lb or 2.26kg and

  4. ‘XXL’ spool - 10lb or 4.53kg.

There also exist many different filaments materials, but the two most common are acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA). Each material has its own physical and chemical properties, which means that each filament type needs its own specific set-up within your printing software. While some materials can be extruded at temperatures around 180°C, others need to be heated up to 250°C or more, before being ready for printing. Beginners especially need to pay attention to the fact that a specific printer may not be able to print with a certain type of material.


Materials. ABS vs PLA vs PVA


ABS (Acrylonitrile Butadiene Styrene)

ABS is used in a very large variety of applications in the industry nowadays. Examples include, among many others, the manufacturing of pipes (like drain, waste or vent pipes), automotive components, electronic assemblies, protective headgear (ABS has good shock absorbing properties), kitchen appliances, music instruments, protective carrying cases and toys, among which the most notable are the famous Lego bricks.

ABS is generally very durable and strong, slightly flexible and quite resistant to heat. Printers able to process ABS plastics normally operate with a hot end at a temperature around 210-250°C. Therefore, a 3D printer able to process ABS is necessarily equipped with a heated print-plate (the surface that the 3D prints are built on), in order to prevent warping or cracking of the printed materials.

 

3D Printed shoes


China printed house

 

Considering cost, ABS is a cheaper plastic of the filament types analysed and until recently was the favourite material of the 3D printing communities. The material is suitable for a very large variety of purposes, especially as it can easily be sanded (to smooth the printed objects and removed jagged edges) and painted. Printed or broken parts can simply be glued together with ABS glue and it is easily soluble in acetone (i.e. nail polish remover).

But ABS also has some drawbacks. First of all, it is a petroleum-based non-biodegradable plastic, but which fortunately can be recycled. Another problem is that ABS does create (mild) fumes which may irritate more sensitive persons – an installation of the printer in a well ventilated area or even a specific fume hood may be necessary. ABS can also deteriorate by prolonged exposure to sunlight.

If you are not using your ABS spool over a longer time, you should store it properly in an airtight container.


PLA (Polylactic Acid)

PLA is a biodegradable thermoplastic which is derived from renewable resources, such as cornstarch, sugar cane, tapioca roots or even potato starch. This makes of PLA the most environmentally friendly solution in the domain of 3D printing. PLA is used for example in medical suturing as well as surgical implants, as it possesses the ability to degrade into inoffensive lactic acid in the body. But PLA is also used in food packaging, bags, disposable tableware, upholstery, disposable garments, hygiene products and even diapers. PLA is therefore considered as pretty safe. For those wanting to print PLA drinking cups or other recipients destined for food or drink, a word of caution though: do not forget that the coloring pigments in the filament may not be as harmless as the PLA itself.

 

3D printed cup

PLA is tough, but a little brittle, once it has cooled down. Its temperature threshold is lower than the one of ABS, as PLA is normally extruded around 160°C-220°C. A heated print-plate is not mandatory, but it may (at temperatures around 50-60°C) be beneficial to the quality of the printed object. PLA is quite slow to cool – experts recommend sometimes to install a fan pointed at the extruded material in order to speed up the cooling process. Once it is heated, PLA does emit a slight odor, best described as sweet corn, pancakes or maple syrup – but it does not emit fumes like heated ABS. No fume hood will be necessary and you may safely print with PLA in-house.

PLA can be sanded down and may be painted over with acrylic paint, but some people recommend using a primer. Glueing PLA is however not as easy as glueing ABS. Most people seem to get some results with cyanoacrylate (i.e. super glue), but this does have some disadvantages of its own (use of safety glasses and gloves, extreme stickiness to fingers and other body parts, very quick hardening, etc.).

PLA has been becoming a very popular choice in the 3D printing communities, considering its low toxicity and its better environmental friendliness, compared to all the petroleum-based plastics.

Its main drawbacks are that it cannot stand too much heat, as standard PLA becomes soft around 50°C (i.e. you can re-heat your printed object with a hot air gun, for example). On the other hand, one may consider this an advantage in order to easily repair, bend or weld printed parts.

But PLA is generally considered the easiest material to work with, when you first start printing. It has been becoming more and more readily available and probably will overtake ABS as the preferred choice.

In case you are just starting out, it is certainly recommend that you begin with printing in PLA as this filament makes it easier to get good results and is more forgiving than ABS.

PVA (Polyvinyl Acetate/Alcohol)

PVA is a special plastic that is water-soluble. It is most commonly used as paper adhesive, as thickener, as packaging film, in feminine hygiene and adult incontinence products, as mold release agent or in children’s play putty or slime. Another wide use is in freshwater sport fishing, where PVA bags filled with bait are thrown into the water. The bag rapidly dissolves, releasing the bait, in order to attract the fish.

In 3D printing, PVA is sometimes used in printers with dual or multiple-extruders, in order to provide a support structure to an object with overhang issues. Some complex prints involving lots of overhangs (areas where there is no support under the upper layers) can be realised only by printing such a support structure. Otherwise, the printed structure would warp or simply collapse. The finished object can be put into water until the PVA has completely dissolved, freeing the object of the support structure, without the need of any pesky manual post-printing curing.

PVA is normally extruded at temperature of 190°C, but is not very easy to use, as it attracts water so much. Ambient air moisture will deteriorate the filament very quickly. PVA needs to be stored in a sealed box or container together with a desiccant and may need to be dried before use.

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