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An Introduction to 3D Printing with Plastics

Ever since Chuck Hull printed his first prototype at home more than 30 years ago, plastics have been the material type most associated with the field of additive manufacturing. 3D printing with plastics allows for the quick creation of quality prototypes, but with recent advances in printing materials and technology, also offers opportunities for the creation of functional parts, suitable for mass production. In this short tutorial, we will look closely at some of the options currently available for printing with plastics, their respective advantages/disadvantages, and some of the key things you should consider before selecting a material for your project.

 

The evolution of plastic materials for additive manufacturing

 

The number of materials available for additive manufacturing projects has broadened considerably over the years, which means a range of options now fall under the umbrella of ‘plastics’. It’s therefore important to consider your options carefully for each project before making the decision as to what to print with. Your options include:

 

  • ABS (Acrylonitrile Butadiene Styrene). ABS is used for a wide range of functional parts nowadays, ranging from drainpipes to car parts, and even LEGO bricks! ABS is highly versatile, being particularly strong, durable, and suitable for post-processing techniques, such as sanding or gluing. However, the material is non-biodegradable, and must be stored in an airtight container when not in use, as it can absorb moisture and be affected by prolonged exposure to sunlight — both of which will lower the quality of your printed parts. Also, the fumes it produces can prove irritating, which means ventilation is required during printing (although certain printers incorporate filters to compensate for this).
  • PLA (Polylactic Acid). PLA is a biodegradable material created from renewable sources. This means it is especially suitable for printing disposable items, or any part when environmental factors are a serious concern. It has even been used in medical applications, to create sutures and surgical parts that simply degrade into harmless lactic acid once the patient heals. It can be sanded and painted in the same way as ABS, although gluing it is slightly harder and it does not withstand heat quite as well. It also requires careful storage, as with ABS, as the absorption of moisture can affect the printed results.
  • PVA (Polyvinyl Alcohol). This is a special water-soluble plastic that is often used to create support structures for parts during the printing process that can simply be dissolved later. This can speed up the post-processing stage, but it is only achievable using printers with multiple extruders. It is also quite expensive and requires air-tight storage at all times.
  • PC (Polycarbonate). This is a highly strong, resistant thermoplastic that’s often used for making compact discs, bullet-proof glass, and other products where durability is a key factor. It has a high impact strength, and a transparent look that’s highly attractive to many users. As with ABS though, it requires ventilation during printing, as it produces a lot of fine particles that can irritate users’ eyes and clog printer heads if they are not properly maintained. It is also more prone to warping than other materials.
  • HDPE (High-density polyethylene). HDPE is a petroleum-based thermoplastic, often used to create recyclable parts, such as bottles. Its principal disadvantage is that it is quite difficult to bond to other materials and can be quite difficult to work with compared to other options. However, it is a highly attractive option for companies keen to adopt a sustainable, environmentally-friendly approach to manufacturing.
  • HIPS (High-impact polystyrene). This is another soluble support material, similar to PVA, although it dissolves in limonene rather than water, and has similar material properties to ABS when printed. This is a relatively new material that is still establishing itself among additive manufacturing companies.
  • PA (Nylon). Nylon is a relatively recent addition to the family of 3D printing materials that offers incredible versatility when it comes to finishing and colour options. It is also a low-friction material, which makes it a highly attractive option for printing machine parts, such as gears. It is strong, durable and flexible, although bear in mind that it must be dried before printing and can prove prone to warping if it is allowed to cool too fast. When printing with nylon, the printing temperature is typically higher than other materials, so make sure your printer can accommodate this.
  • PEEK (Polyetheretherketone). This is a thermoplastic polymer, commonly used in the medical field for the creation of surgical implants, thanks to its chemically inert, biocompatible and sterilisable nature. Research is also underway to determine its potential applications in the automotive industry, thanks to its excellent hardness and abrasion properties. However, in spite of its considerable versatility, PEEK can be challenging to print, so a specialist printer, with an enclosed chamber and heat bed capable of reaching temperatures of up to 400°C will be required.
  • TPE (ThermoPlastic Elastomer). TPE is a versatile, non-toxic, rubber-like material that is widely used for printing flexible parts (springs, phone cases etc.). However, it is not suitable for use in all printers, as the filament has been known to create blockages in certain types of extruder.
  • TPU (ThermoPlastic Polyurethane). TPU is similar to TPE in terms of its mechanical properties, but is slightly easier to print more suitable for working parts, thanks to its higher resistance to abrasion, solvents, oils and grease. It also retains its elasticity at colder temperatures.
  • PMMA (Polymethyl Methacrylate). Also known as acrylic plastic, PMMA is a rigid, transparent plastic that is ideal for smaller prints with lots of fine detail. This makes it an extremely attractive choice for creative applications, such as miniatures or sculptures, or any parts requiring light diffusion. It is unsuitable for any parts that will be subjected to heat or stress, and while the level of achievable detail is very high, individual layers will be slightly more visible than with other materials, so this should be factored into your 3D model. Also, printing with PMMA may require fine-tuning of the nozzle and heat bed, on a printer with an enclosed chamber to minimise shrinkage during the cooling process.

 

Recently, a number of plastic-based materials have been introduced that incorporate metallic elements, allowing objects to printed with some of the qualities of metal parts without the added complexity of 3D printing with metal.

 

The key points to consider when choosing a plastic

 

  1. What material properties do you require from your final printed part? This should be completely clear before any decision is made. Consider what it will eventually be used for; is it intended to be a prototype, or a functional product that will see intensive day-to-day use?
  2. Check the filament diameter to ensure it will be compatible with your printers. While certain printers can accept multiple diameters, it is still worth checking in advance before making a purchase.
  3. Check the minimum/maximum wall thickness that will be printable and ensure your 3D model accommodates this.
  4. Consider whether any supports or overhangs will be required during printing and ensure these are factored into your model to ensure its stability. If your printer allows it, you may want to consider a dedicated support material.
  5. Make sure the right storage methods are used. As you will have seen above, many of the commonly used plastic 3D printing materials require special storage methods to ensure quality results. Make sure to follow the supplied instructions when storing your filaments between projects.
  6. Make sure your printer can operate at the right extrusion temperature for the chosen material and that an appropriate heating bed is used. The wrong temperature will lead to sub-optimal results.