How SEM helps to detect additive manufacturing defects in a 3D-printed object

By Karl Kersten - October 11, 2018

3D printing, or additive manufacturing (AM), refers to processes that are used to make 3D printed objects. In order to achieve this, successive layers of material are formed under computer control to create an object. The objects can have almost any shape or geometry and are produced using digital data from a 3D model or other electronic data source.

But successive layers formed under computer control can result in structural interruptions or defects that negatively affect the reliability of an 3D printed object. And these undesirable defects  should not go undetected; something we discuss in this blog later on. But first, more about 3D printing.

What is 3D printing, or additive manufacturing?

The term "3D printing" describes processes that deposit a binder material, layer by layer, onto a powder bed using inkjet printer heads. There are several categories of additive manufacturing processes available: binder jetting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet lamination, and vat photopolymerization. The additive manufacturing production of metal products began in 1971 by means of lasers.

Additive manufacturing for laser sintering of metallic powders

Additive manufacturing methods are used for sintering a wide spectrum of metallic powders e.g. light alloys, titanium alloys, steel alloys as well as polymer materials (e.g. polyamide) or ceramic and composite materials.

Direct Metal Laser Sintering (DLMS) is the latest technology used for the production of complex shapes, using the selective melting of metallic powders method. Thanks to DMLS technology, it is possible to repeat the strength parameters of elements. The advantage of this technology is that it enables complex shapes to be produced that would otherwise be impossible to make - even when employing casting methods.

DMLS machines operate in the following way: on a layer of precisely-composed metallic powder, successive layers of an element are fabricated via selective sintering using a near-infrared laser beam.

Additive manufacturing & SEM

In 2016, Walczak et al. (Applied Computer Science, vol. 12, no.3, pp 29-36) published a study on the characteristics of products made of 17-4PH steel by means of 3D printing method. The results stated that a SEM analysis of the surface after laser sintering indicated defects in the form of structural interruptions in the area of the welded surface.

Such additive manufacturing defects are undesirable because the structural discontinuities in the upper layer can act as so-called micro-notches. Furthermore, as a result of stress concentration, these micro-notches can compromise the reliability of the object being printed.

3D printing SEM.png              3D printing.png

Fig. 1 SEM image of micro-rabbits  (no defects are visible at this magnification)                    

Fig. 2 SEM image of micro-rabbit at a higher magnification showing the defects in the surface structure.

Regarding material surfaces: how well would you be able to recognize these if viewed with a SEM? If you would like to test your knowledge, we have a fun SEM images quiz for you.

It shows samples that are magnified more than a hundred or a thousand times, and your challenge is to guess what the materials in the images are. Are you a SEM Starter, Star or Superstar? Take the quiz and find out.

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About the author

Karl Kersten is head of the Thermo Scientific Phenom Desktop SEM Application Team at Thermo Fisher Scientific. He is passionate about the Phenom Desktop SEM product and likes converting customer requirements into product or feature specifications so customers can achieve their goals.

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