3D printing turns 40 – but which process is best suited to your requirements?

In 1981, Japanese inventor Hideo Kodama created a first-of-its-kind rapid-prototyping device that used UV lights to harden polymers and create three-dimensional forms reports Jennifer Johnson.

Kodama’s technology was never properly commercialised, although the US inventor Chuck Hull used similar principles in a process he called “stereolithography”. He coined the term – meaning a method of creating solid objects by printing layers of the ultraviolet curable material one on top of the other – in his 1984 US patent application. Two years later, the patent was granted and Hull went on to establish 3D Systems, the firm behind the world’s first commercially available 3D printer, the SLA-1 stereolithography printer. The machine uses a laser to cure a liquid photopolymer resin to make an object from a digital file. The automotive industry was among the first to take an interest in the SLA-1, which it used for the rapid prototyping of parts. The machines were also used to make medical models for surgical planning, and have famously been deployed in dentistry, too.

Today’s engineers prize SLA printers for their ability to create detailed, watertight objects – useful when working on problems of air and fluid flow in the car industry.

Magnificent seven
Additive manufacturing technologies have evolved significantly since Hull’s SLA machines became available. The ISO/ASTM 52900 standard, created in 2015 to standardise terminology in additive manufacturing, identifies seven distinct types of 3D printing process: Material extrusion, vat photopolymerisation, binder jetting, material jetting, powder bed fusion, sheet lamination and directed energy deposition. But knowing which is best suited to a given application isn’t always straightforward.

Joris Laarman’s 3D printed stainless steel bridge in Amsterdam is a 12 metre pedestrian bridge located in the red-light district. The bridge was constructed using robotic printers and was made from 4 500 kilograms of stainless steel

Generally, additive manufacturing is appropriate for products that are geometrically complicated and do not need to be made in large volumes. However, there are a plethora of other factors – including budget, desired appearance and mechanical requirements – that must be considered when selecting a 3D printing process. When most people think of a 3D printer, they’ll picture a fused deposition modelling machine, through which a material is melted and extruded layer on layer until it cools and forms an object. Sometimes called fused filament fabrication, material extrusion is the most popular 3D printing process for hobbyists.

Powder bed fusion
In the world of manufacturing, material extrusion can be used to make non-functional prototypes, as the resulting objects are brittle and not suitable for mechanical parts. Organisations looking for durability may wish to utilise a metal 3D printing method, the most common of which is powder bed fusion. In this process, a thermal energy source is applied to selectively induce fusion between metal powder particles to form an object. GE Aviation used electron beam melting machines – part of the powder bed fusion family – to produce titanium aluminide blades for its GE9X aircraft engine.

Its curving S-shaped form and balustrades with lattice-style perforations were designed using parametric modelling software. Laarman had the idea for the bridge after combining robotic arms with welding machines to create a machine capable of printing furniture. “By adding small amounts of molten metal at a time, we are able to print lines in mid-air,” explained Laarman at the time

Wire arc additive manufacturing (WAAM), a type of direct energy deposition technology, is a less common method of metal 3D printing. It works by melting metal wire with an electric arc. The whole process is controlled by a robotic arm and the object is built upon a substrate material that it can be cut out of once it’s finished.

The world’s first 3D printed steel bridge, installed in Amsterdam over the summer, was created using WAAM. Developers feel that WAAM could have novel future applications in construction.