3D Printing: An Overview

With the recent boom in the consumer 3D printing market, it is perhaps easy to forget that early attempts at the technology were made as far back as the 1980s. Indeed, the patent application for the material extrusion technology used in most consumer machines today, namely Fused Deposition Modelling (granted as US 5,121,329), was filed in this period. 3D printing may have started off as a fanciful idea, but it would quickly turn into an effective option for small-scale manufacturing.

A breakthrough was made in 1999 when scientists succeeded in printing a human bladder. By 2008, advances in materials science and printing techniques were sufficient to allow the first 3D-printed prosthetic limb to be made. 3D printing now has widespread applications in medicine, ranging from hearing aids to stents to titanium implants.

The aerospace industry was another early adopter of 3D printing. Manufacturers have been able to replace multiple parts in a large assembly with a single 3D-printed part, thereby reducing weight and fuel consumption. The latest serial-production jet engines, for example, can contain hundreds of 3D-printed parts.

Cutting-edge manufacturing aside, since the mid-2000s, low-cost 3D printing has become increasingly prevalent and has sustained a growing hobbyist community. It has also enabled rapid prototyping, dramatically cutting tooling costs and increasing speed for product development.

Decades of rapid development has resulted in a dizzying array of technologies. In very broad terms, the most common technologies can be grouped into five main categories below.

• Material extrusion is the most common process employed in consumer machines. In this process, the printer builds the object from bottom up, depositing one layer of melted polymer filament at a time on top the solidified layer below. Its popularity is due in part to low cost and a wide range of usable materials. However, mechanical performance is limited and a smooth finish requires significant post-processing.
• In vat photopolymerisation, the 3D object is formed upside-down on a build platform as it is being pulled upwards from a vat of liquid photopolymer resin which solidifies on exposure to light. Light is selectively focused on the solid-liquid interface to build one cross-sectional layer at a time. In comparison with material extrusion, smooth finish and fine details can be readily achieved, although mechanical performance is also limited.
• In powder bed fusion, the 3D object is built from bottom up in layers. Each layer us formed by spreading fresh powder across the entire build area, then selectively applying heat (from a laser or electron beam) to fuse the powder together to form a solid cross-section. At the end of the process, the loose powder encasing the 3D object is removed. Both metal and plastic parts can be made this way. Functional parts with fine details and high mechanical performance can be produced. However, due to high costs, this process is largely limited to applications such as aerospace, automotive and medicine.
• Binder jetting is similar to powder bed fusion, except the powder is bound together by selectively depositing a binder in each layer instead of using heat. Sand and metal objects can be made using this process. Mechanical performance is not as good as powder bed fusion, but metal objects made this way can be strengthened by first burning off the binder, then allowing bronze to fill the voids left behind by the binder.
• Material jetting is similar to standard inkjet printing in that tiny droplets are ejected, except a photopolymer or wax is used instead of ink to build up layers of solid material. This process gives a high qualify surface finish and can produce parts in full colour and/or with multiple materials. As mechanical performance tend to be poor, this process is usually used in model making or as part of a mould-making process.

The undeniable importance of 3D printing in medicine and industry has led to an unprecedented amount of innovation in the field, and a growing number of patent applications. According to official statistics, close to 16,800 3D printing-related patent applications were filed at the EPO between 2010 to 2018, 47% of which originated in Europe, followed by 35% from the US. In terms of sectors, the health sector accounted for nearly a quarter of these applications, followed by energy and transportation.

While it may seem far-fetched to think that everyone will someday manufacture their own gadgets using their 3D printers at home, it does not seem unreasonable to expect that many aspects of our daily lives will soon benefit from 3D printing in one way or another.