Additive Manufacturing: what is it and what advantages does it bring?

In recent years there has been increasing talk of Additive Manufacturing, an industrial process that, using specific technologies, is able to fabricate parts, and semi-finished and finished products characterised by high precision, while optimising manufacturing costs.  

What is Additive Manufacturing?

How did the definition of Additive Manufacturing originate? Quite simply, the process takes place by addition, i.e. the object is built by adding material until it is complete.

In order to better understand the core characteristics of additive manufacturing, it is necessary to clarify a few other concepts. Firstly,  this process is the opposite of traditional manufacturing, which is based on the subtractive principle, i.e. a product that is made by removing material.  

Examples of traditional techniques include milling and turning, in which objects are obtained by removing material from an initial block. 

Additive Manufacturing is also known as 3D printing as it produces products starting from a digital design file.

Starting from the mid-1980s, 3D printing technology was initially used for fast prototyping; recently, its spread has been favoured by a decrease in the cost of the machines, the ability to produce larger objects more quickly and the identification of mass production opportunities using the vast range of materials and filaments available.

What impact does additive manufacturing have on manufacturing processes?

Examples of additive manufacturing can be found in the production of parts used in the aeronautical sector, as well as in the automotive and motor sports, medical and construction industries, where it has replaced traditional manufacturing technologies. 

The various additive manufacturing technologies are used for highly customised serial production, for the creation of objects for just-in-time-oriented systems, and to respond to emergencies resulting from a shortage of components for in-line production.  

Presentation of the utilisation process

In order to produce objects using additive manufacturing technologies it is necessary to follow a series of preset steps. This file can be optimised using CAE (Computer Aided Engineering) techniques. 

Once the final CAD file has been obtained, it is possible to proceed with production using a 3D printer that melts the material by laser or deposits it by means of a nozzle that may be attached to a robotic arm.

The software installed in the printer processes the CAD file, splitting it into a series of layers and creating a process to be followed for the production of the object. The material used for manufacture can be in the form of filaments, power or liquid resin, depending on the technology used.

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Types of Additive Manufacturing

There are different types of Additive Manufacturing, including Selective Laser Melting (SLM), stereolithography (SLA) and Fused Deposition Modelling (FDM).  

Each of these technologies has specific processes and techniques. Once the 3D printing is complete, it is possible to proceed with further processing, for example mechanical processing, such as CNC and heat treatments, and the cutting, polishing or coating of the objects. 

Fused Deposition Modelling

Fused Deposition Modelling (FDM) or Fused Filament Fabrication (FFF) uses filaments of polymer (PLA, ABS, Nylon, PET, PEEK) gathered in reels and melted by one or more extruders.

The extruders, i.e. heated nozzles or tips, fluidify the filaments and move them according to the software coordinates that define the outer and inner perimeters, the filling and all the other details provided for by the file.

The position of the extruder can be controlled by different mechanisms such as gantries, core XYs, polars, deltas or anthropomorphic robotic arms through a specific extruder installed on the printhead. Once the layer has been completed, the surface on which the object rests remains immobile and the extruder moves upwards to start the next layer. Once printing is complete, the object is allowed to cool before being extracted, ready for use. 

Stereolithography

Stereolithography technologies consist in three methods for printing three-dimensional objects.  

The first, known as laser stereolithograph, consists in creating a printed object using only light sources (photopolymerisation of the material using a laser beam or UV rays) 

For the creation of the object, the technology uses a perforated plate at the bottom of a vat containing liquid resin. Here, a laser beam is projected and modulated to create the image of the first layer of the object. The plate descends for each subsequent scan until the object is complete. The printed object is then exposed to ultraviolet light inside an oven. The machines must not be installed in environments with inadequate ventilation, due to the toxicity of the liquid resin. 

The second method is Digital Light Processing (DLP) stereolithography, which uses a light source projected at a minimal distance from the resin to ensure better resolution. In this process, the polymer sets layer by layer in contact with light. 

The third method consists in Liquid Crystal Display (LCD) stereolithography, which utilises backlit liquid crystal screens as ultraviolet sources to create three-dimensional objects.  

Selective Laser Sintering (SLS) 

Selective Laser Sintering or SLS  produces a single object by solidifying (sintering) layers of powder using a laser.  

At the end of this process the piece is freed of the excess powder and placed in an oven for variable times depending on the characteristics of the object to be created. 

Selective Laser Melting is a 3D printing technology that was invented in Germany in the mid-1990s. Its particularity lies in the fact that instead of sintering it melts the metal powder into an even, solid mass, using a high-power laser, following a previously created 3D design.   

This method involves the use of materials and results very similar to those obtained with traditional techniques in terms of aesthetics and performance. 
 
Manufacturers who use this technology ensure the fabricated objects greater material purity and better performance. 

Selective Laser Melting (SLM)

Selective Laser Melting is a 3D printing technology that was invented in Germany in the mid-1990s. Its particularity lies in the fact that instead of sintering it melts the metal powder into an even, solid mass, using a high-power laser, following a previously created 3D design.  

This method involves the use of materials and results very similar to those obtained with traditional techniques in terms of aesthetics and performance. 
 
Manufacturers who use this technology ensure the fabricated objects greater material purity and better performance. 

Multi Jet Fusion (MJF)

Multi Jet Fusion (MJF) is the term given to an extremely reliable and efficient 3D printing process, a powder-bed 3D printer developed by HP. 

It is the ideal technology to replace CNC machining or injection moulding. 

Its advantages include the ability to fabricate very high-quality prototypes very quickly, save time and avoid design errors, and create parts with the required characteristics at very competitive costs. 

Binder Jetting (BJ)

Binder Jetting (BJ)  is an additive manufacturing technology that uses a bed of powders made to adhere by means of a binder deposited by a printhead.   

In Binder Jetting, the powders are distributed over a printing surface by a spatula or a roller, with a variable thickness that determines the print resolution in the z-direction.  

A printhead, similar to those used in ordinary inkjet printers, releases tiny drops of binder able to define the resolution on the x-y plane. At the end of the process, the print surface moves down then releases another layer of powder on which a new layer is printed. This operation is repeated until all the layers required to fabricate the object have been deposited. 

Direct Energy Deposition (DED)

Direct Energy Deposition (DED) is normally used in additive manufacturing processes to perform repairs or to add material to existing parts. Although it is possible to fabricate completely new pieces using this technology, it is mainly used for specific industrial applications, such as repairing damaged turbine blades or propellers. 

DED, like other powder bed fusion (PBF) technologies such as LPBF or EBM, uses a concentrated energy source, for instance a laser or electron beam, to melt the material. However, this takes place at the same time as the deposition of the material by means of a nozzle. In a certain sense, this technology is half-way between material extrusion and powder bed fusion. 

It should be pointed out that this process is often defined with other names, such as Laser Engineered Net Shaping (LENS) and Direct Metal Deposition (DMD), depending on the specific technology or the method used.  

Advantages deriving from the use of additive manufacturing

Additive Manufacturing allows highly customised production, in both prototype form and serial production.

The success of this evolution is based on the potential for fabricating lightweight precision parts starting from the data included in the design file, thus reducing, first and foremost, material consumption. 

In addition, this type of production consists of a single step, which allows significant savings in prototyping and variant design costs. 

The ability to fabricate multipart objects with integrated functions simplifies assembly, reduces the processes and limits the use of human resources. 

Additive manufacturing can also be utilised to repair parts, thereby extending the service life of the object or system, while decreasing the environmental impact. 

The materials used in most Additive Manufacturing processes are recyclable, as in the case of filaments, or reusable, as in the case of powders.  

There is another aspect to be emphasised. Additive Manufacturing allows the creation of highly customised and complex objects, items that it would be difficult, if not impossible, to fabricate using other manufacturing methods. 

Made-to-measure objects suited to the specific requirements of customers. Since each product can be created starting only from a 3D model, the manufacturing process can be easily customised to satisfy increasingly specific requirements.