Additive Manufacturing: Printing an Industrial Future

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Is Additive Manufacturing simply a method of producing quirky gadgets and prototypes, or can it be seen as an important new process for manufacturing products on an industrial scale?

The first article in this series explored the basics of an exciting technology known as Additive Manufacturing (AM), or 3D printing as it is commonly referred to. Whilst Additive Manufacturing processes have been used since the 1970s, they have received significant attention over the past five years. This heightened attention is most noticeable in the 2013 State of the Union Address made by Barack Obama.

Barack Obama: Next Industrial Revolution

For approximately 40 seconds of his speech, Barack Obama recognized the power of 3D printing, with the president’s words being forever immortalized by the French digital artist Gilles Azaro in a very original fashion. Gilles Azaro used his desktop 3D printer in order to generate a physical visualization of the sound waves generated from the presidential speech.

Obama Voice Sculpture: Next Industrial Revolution | Gilles AZZARO - YouTube

The piece, entitled ‘Barack Obama: Next Industrial Revolution’, features a 5 foot long 3D printed waveform which allows observers to see the points where the president raises his voice, pauses, or emphasizes a statement in the speech.

The endorsement of AM by Barack Obama was enhanced in June 2014 when the Smithsonian Institute scanned the American leader in order to produce the first-ever 3D presidential portrait. Although the process of scanning the president took around 7 minutes to be finished, the real scale bust was developed using Selective Laser Sintering (SLS) in a time of 42 hours.

The President, in 3D | The White House - YouTube

Using Metal in Additive Manufacturing

All of the methodologies reviewed in the previous article in this series made use of thermoplastics, resins, or ceramic powders as raw printing material. This represents a considerable disadvantage when trying to use AM in an industrial environment as the mechanical properties of these materials are limited when compared to metals.

However, several AM technologies that use metals are currently available. Although traditional manufacturing processes, such as milling and turning, are still preferred when manufacturing final products, AM is starting to play a significant role in the development of supplementary products such as fixtures and tools.

Prometal Printing

Prometal is a 3D printing process used to create injection tools and dies with powder-based stainless steel. The process starts when a 3D model of the part is segmented into layers. Next, a liquid binder is sprayed out in jets to the steel powder to selectively bind sections of each layer. After a layer is finished, a piston lowers the powder base to build the next layer.

Once the part is finished, the residual powder must be removed and a heat treatment process performed to sinter the metal together. The sintered material is then infiltrated with bronze to add strength and fill up the pores. However, a second surface treatment of the part is necessary for the use of the dies.

Laminated Object Manufacturing

This secondary treatment stage is not necessary when working with Laminated Object Manufacturing (LOM). This process combines additive and subtractive techniques in order to build a part layer by layer.

The material is provided in sheet form and is bound together by pressure, heat application, and by a thermal adhesive coating.

A laser cuts the material to the shape of each layer. The advantages of the process include its low cost, no post-processing being required, no phase change during the procedure, and the potential to build large parts.

The disadvantages of LOM include the waste of material, low surface definition, the part is direction-dependent for mechanical properties (Anisotropic) and complex internal cavities are very difficult to form.

Laser Engineered Net Shaping

Another AM technology used in industry is known as Laser Engineered Net Shaping (LENS). This technique builds a part by melting metal powder that is injected into a specific location. The material is melted using a high-powered laser beam before it is allowed to cool down and solidify. This process permits the use of a high variety of metals.

It is important to note that LENS is also used to repair parts that by other processes will be impossible or more expensive to do. However, one disadvantage of using the process in this way is the residual stresses caused by uneven heating and cooling, which can be significant during the repair of critical parts, such as turbine blades.

Selective Laser Sintering

Selective Laser Sintering (SLS), also known as Direct Metal Laser Sintering (DMLS), is a 3D printing process in which a powder is sintered or fused by the application of a carbon dioxide laser beam.

The laser fuses the powder at a specific location for each layer specified by a CAD model. The particles lie loosely in a bed, which is controlled by a piston that is lowered the same level of the thickness each time a layer is completed.

This process offers a great variety of materials that could be used such as plastics and metals, as well as combinations of polymers and metals. The main advantage of this technology is the wide range of materials that can be used.

However, the disadvantages of SLS are that the accuracy is limited by the particle size of the material and that oxidation needs to be avoided by using an inert gas and the process occurring at a constant temperature. The oxidation issue is addressed by relatively new technology, Electron Beam Melting (EBM). EBM is very similar to DMLS, with the difference that takes place in a high vacuum chamber to avoid oxidation.

Continuous Liquid Interface Production

However, all of these AM technologies, and their non-metallic counterparts, share two major drawbacks: the time required to produce a part and the fact that the mechanical properties change with the direction of the piece, due to the use of layers to generate the part.

This is property is referred to anisotropic and the main issue of this condition is that the structure can stand certain loads when they are applied on a direction but will shatter under the same loads if they are applied in another direction.

In order to overcome these drawbacks, researchers at the University of North Carolina developed a new 3D printing technique called Continuous Liquid Interface Production (CLIP).

Carbon3D CLIP technology demo 7X speed | 3DPrint.com - YouTube

Although this breakthrough technique uses a liquid resin as raw material, the actual process allows parts to be developed considerably faster than by using other current AM techniques. A 10-hour piece can now be made in less than 7 minutes using this technique.

The created parts are also stronger than the pieces developed in current 3D printing systems. These advantages are due to a radical difference with AM technologies. The process is not based on layers of materials but rather produces the part in a continuous fashion.

The resin is contained in a special reservoir that has an oxygen-permeable window on the floor. This leads to an oxygen-rich ‘dead zone’ which is less than 1mm thick at the bottom of the tank. The oxygen stops the resin from solidifying even when UV light is projected through it, meaning that the solidification takes place just above the ‘dead zone’.

The shape that solidifies is controlled via the light projections through the window and since there is no need to wait for the new resin to flow in, the object can be pulled upwards steadily.

The Future of Additive Manufacturing

Although Additive Manufacturing technologies are a number of years away from taking a central role in the industrial workshop, their influence can already be seen in the production of tooling and other ancillary products.

Additive Manufacturing is able to generate parts that are too complex for traditional manufacturing procedures to be able to produce and cutting-edge research is allowing AM to compete with traditional manufacturing methods.

Considering the amount of research which is being carried out in the field of AM, along with the development of new desktop systems which permit the end-user to manufacture their own innovative components, it is not difficult to see how AM technologies can be part of a new industrial revolution in the near future.

Sources and Further Reading

• Smithsonian Creates the First-ever 3D Presidential Portrait - Smithsonian Institute
• Scientists Create Terminator 2-Inspired 3D Printer - The Guardian
• EOS Manufacturing Solutions
• K. Agarwal, D. Mathur, R. Shivpuri, and J. Lembo, “Evaluation of PROMETAL technique for Application to Dies for Short Run Forgings,” 2002.
• J. O. Figueroa Cavazos, H. Siller, C. A. Rodriguez, and A. Gameros, “Rapid Prototyping for Complex Biomedical and Aerospace Components with Internal Features,” in Memorias del XIX Congreso Anual de la SOMIM, 2013, pp. 873–882.

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