The difference between 3D printing and additive manufacturing: explained

Materials World magazine
,
1 Sep 2016

Frustrated with the confusion surrounding additive manufacturing and 3D printing, Emma Ryan and Adam Scott explain how, like fingers and thumbs, the latter is a subset of the former. 

Lots of people are getting the relationship between additive manufacturing (AM) and 3D printing wrong, particularly the media. Claims are regularly made that human tissue, bridges, buildings, clothing and electrical circuits have been 3D printed – and it is a term that is easily recognised by the general public. However, 3D printing is a specific AM process and many of the applications reported refer to different AM processes.

What is additive manufacturing? 

AM refers to processes that deposit a material to make objects from a 3D computer model, layer upon layer. AM is different to many conventional manufacturing methods as there is little or no removal of material. There are many different types of AM and there are general benefits to most, such as reduction in waste and the ability to make complicated geometries that would be impossible by conventional means. 

Because of its benefits, AM has applications in many industries, such as medicine, aerospace, automotive, and even fashion. It is favourable for the medical industry because of the individuality it affords. A CAD file can be based on a 3D scan of each patient to manufacture specialised implants easily and quickly. Additionally, parts of the patient can even be manufactured from scans to enable surgeons to practice tricky operations before the real thing. It is attractive to the aerospace and automotive industries because there can be significant mass reductions made by using topological optimisation to generate manufacturable, organic structures. 

According to BSI standards, the Additive Manufacture – General Principles – Terminology (BS ENISO 52900) – AM can be divided into seven different categories, as seen in the table above. 

The AM categories appear somewhat arbitrary. The division of categories is not consistent as the same feature has not been used to define the different techniques like material used, deposition technique or joining process. More development is required to establish accuracy and clarity of the standard, with input from end users.

It is difficult to write standards, as AM is a relatively new, complicated set of processes. There are considered to be more than 150 variables for each technique, such as wire feed speed for wire and arc AM or powder particle size for powder bed fusion processes. It is important to have a concise set of standards for AM to avoid any confusion in the field, such as the difference between 3D printing and other AM processes.

Selected AM processes

3D printing
The original patent for 3D printing, dating back to 1995, was created by a team from MIT, USA. It refers specifically to the use of a binder material to join the layers of powder. Powder is deposited into a chamber and a nozzle or print head like a conventional ink jet printer selectively deposits binder to join the material together. The binder material is an adhesive that sets very quickly after being deposited and holds the powder together. 

Fused filament fabrication (FFF)
This process – also known as fused deposition modeling, (FDM) – is the process most commonly confused with 3D printing. Many so-called 3D printers use FFF, but ‘3D printer’ is a much catchier name than ‘AM machine that uses the FFF process’. FFF is a material extrusion technique that works in a similar way to a glue gun – thermoplastic material is melted then extruded through a nozzle along a pre-programmed path. Unlike 3D printing, it does not use powder or binder material. 

Laser metal powder bed fusion (LMPBF)
LMPBF has been chosen in this case to describe one of the most common metal AM processes. There are trade names for certain types of LMPBF, such as selective laser sintering (patented by 3D Systems Corporation), and direct metal laser sintering (patented by EOS GmbH). Sintering in this case is a recognised misnomer, as the powder is actually melted. Powder is deposited in layers in an enclosed chamber. Lasers selectively melt the powder on the surface to form a layer, the platform then lowers, a new layer of powder is deposited and the process repeats until the part is completely encased in powder, which is then removed. 

Wire and arc AM (WAAM)
This is a directed energy deposition process. WAAM typically uses the metal inert gas welding process to deposit beads of feedstock wire layer by layer onto a substrate and then subsequent layers. It is different to other AM processes as parts do not have to be built in a single build direction – no support is required.

Final thoughts

3D printing, FFF, LMPBF and WAAM are common AM processes, but there are many more. All have their advantages, disadvantages and applications. One process is not better than another – they all have different uses. Although the terminology for AM has not been fully developed yet, understanding the basic differences between the processes is useful. 

AM is an exciting area of manufacture but, despite the obvious potential of all the different processes, there are still issues. Education is a critical problem, even within the industry, because of a current lack of experience, underdeveloped standards and the hype associated with AM. 

There is also currently a misunderstanding of suitable applications for the different AM processes and the advantages and disadvantages of each of the processes – such as build volume or material used – need to be considered when building AM parts. For example, WAAM could build a large primary structure but for small, high-fidelity parts LMPBF would be a better choice. 

AM is still in development, so it pays to be sceptical when reading an article on how a car or liver has been 3D-printed because, firstly, it is probably a prototype, not a functioning part and, secondly, it probably has not been 3D-printed but additively manufactured using a different process.