Plastic 3D Printing

When it comes to 3D printing, plastic is king. Though materials like metals and ceramics are increasingly compatible with the technology, plastic 3D printing – which covers numerous thermoplastics and elastomers – is most common.

At the cheaper end of the scale, consumer-grade plastics like PLA and ABS are often used for making toys and models, while industrial-grade polymers allow for the production of plastic molds, prototypes, and even end-use parts.

This article looks at the development of plastic 3D printing, the different materials and technologies available, and selected use cases in production today.

 

The “thermoplastic pyramid” is a common categorization of the range of plastics available in manufacturing. At the bottom of the pyramid are low-cost materials ideal for non-critical applications. Such standard plastics in this range include ABS (acrylonitrile butadiene styrene) and PLA (polylactic acid). Moving up the pyramid are more expensive engineering plastics, better for general-purpose bearing and wear. These include acrylics and nylon.

At the top of the pyramid are the highest performing and most expensive plastics, better for high-temperature applications and with good wear resistance. In this range can be found PEEK (polyether ether ketone) and the highest performing of all thermoplastics, PBI (polybenzimidazole).

It is important to note that not all of these thermoplastics are ideal for 3D printing. For instance, PVC (polyvinyl chloride) is perhaps the most common of all thermoplastic polymers, with excellent properties in durability and cost. However, it is not common in 3D printing; melting this plastic can pose serious health risks and requires elaborate air filtration systems. Similarly, PBI isn’t compatible with mainstream 3D printing applications, though some are conducting research in that area.

PLA is by far the most customary in consumer-grade plastic 3D printing, popular for its ease of use and affordability. This makes it a great material for learning and experimenting, although its mechanical properties are limited. PLA parts can’t withstand much weight or impact. As such, users mainly print toys, decorative items, and non-functional prototypes with it.

ABS is a more functional material than PLA. It is commonly found in household items, from laptop keys to LEGOS. ABS has high strength, low flexibility, and is also very durable.

Nylon (from the polyamide family, PA) is a popular 3D printing alternative to PLA and ABS, with even better engineering properties. This material produces durable and flexible plastic parts. Nylon has a range of usages, from prosthetics to cases and enclosures.

A less common 3D printing plastic, but one with increasing availability, is PP (polypropylene). PP is found in many household objects, from milk jugs to pill bottles. It is automakers’ material of choice for car bumpers. It can be difficult to print due to issues with shrinkage and warping.

TPU (thermoplastic polyurethane) is another innovative plastic 3D printing option, ideal for printing flexible plastic parts. TPU materials combine the properties of thermoplastic with those of rubber. They are practical for medical devices, phone cases, and sporting goods, such as New Balance’s 3D printed midsole.

PEEK is one of the highest-performing 3D printing plastics, boasting an extremely high strength-to-weight ratio and great chemical, water, fire, and corrosion resistance. However, its highly crystalline nature makes it very challenging to print.

 

Plastic 3D printing technologies mostly fall into three categories: material extrusion (e.g. FFF, FDM), vat polymerization (e.g. SLA, DLP), and powder bed fusion (e.g. SLS, MJF). FFF and SLA are readily available in consumer and professional desktop machines, while powder bed fusion (PBF) is best for industrial use.

The most common type of plastic 3D printing technology is Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF). The FDM name is trademarked by the Stratasys company, whose founder Scott Crump invented the technology. In this process, a heated nozzle melts and extrudes thermoplastic filament onto a build plate.

Some material extrusion printers can 3D print plastic pellets instead of filament. Pellets are touted to reduce print times and, as they are mass-produced for conventional manufacturing methods like injection molding, drastically lower costs.

Stereolithography (SLA) printers are also quite popular for plastic 3D printing. They have become very affordable in recent years, with some models available for under $200. SLA printing is a vat polymerization process: a laser or light source polymerizes (solidifies) a vat (tank) of resin.

SLA photopolymer materials encompass a range of different thermal and mechanical properties. Options include brittle materials to more durable polycarbonate-, polypropylene-, and ABS-like materials.

Selective Laser Sintering (SLS) is a PBF process that produces high-quality 3D plastic parts suitable for functional prototypes and even small production runs. In SLS, a laser sinters powder particles together. This technology can produce very complex geometries as well as moving parts that do not require assembly. One downside to this technology, and the reason why SLS is not suitable for consumer use, is that parts require tedious, time-consuming post-processing.

Plastic 3D printing is an exploding ecosystem. The 3D printing marketplace was valued at $12 billion in 2020 and is expected to be worth over $51 billion by 2030. Any industry with a projected decade-long 15% growth rate is one that will offer numerous opportunities and benefits to society, such as reinforcing supply chains.

3D printing plastic also unlocks enormous potential for innovation in general, and not only in terms of design freedom. The accessibility of plastic 3D printing, due to its low costs, allows startups all over the world to bring customized products to market with just a couple of printers.

The COVID-19 pandemic has accelerated the utility of 3D printing, demonstrating its ability to provide a huge lift to overtaxed supply chains reliant on traditional manufacturing. When personal protective equipment (PPE) supply chains ran out of materials in 2020 in the US, additive manufacturing stepped up. According to a US government report, between February and July of 2020, companies printed over 50 million parts including face shields, nasal swabs, ear savers, and mask and ventilator components.

Beyond the pandemic, plastic 3D printing is also promising in the field of prosthetics. It makes it possible to customize devices according to a patient’s body shape, and even to their gait. Furthermore, complex internal geometries (e.g., honeycomb and lattice structures) can significantly reduce a device’s weight of solid parts. Weight reduction is crucial to patients wearing an object 24 hours a day. 

In the automotive field, Michelin and Goodyear tires are exploring the use of 3D printing to create non-pneumatic (airless) tires. They leverage the unique geometries of plastic 3D printing to create alternative internal structures which are puncture-proof.

IKEA is also working with 3D printing to make its furniture more handicapped-accessible. The company launched its ThisAbles initiative in 2019, providing free 3D printable designs to bolt onto existing furniture. Such modifications include making knobs larger and creating 3D printed platforms to elevate sofas or chairs higher off the ground.

The examples above merely hint at the possibilities that plastic 3D printing offers. As thermoplastics become more functional and affordable, the range of usages will only increase. The diversity and flexibility of plastic 3D printing will continue to expand, too, with manufacturers developing composites filled with metals, ceramics, wood, carbon fiber, and more.