Additive Manufacturing (3D Printing) Inspection Applications and Light Microscopy Techniques

The Additive Manufacturing (AM) industry has been exploding over the last several years with new materials and processes to produce more complex and reliable parts for critical applications.

Due to this rapidly growing field with new developments and needs, it becomes extremely important to be able to understand the materials characteristics along with the process variations which can impact the final product.

From incoming inspection of raw materials to final inspection of the product, there are several points along the way for Light Microscopy to be a valuable tool in understanding how the process is working.

Additionally, Light Microscopy is also extremely useful in the development of new processes or in failure analysis investigation.

We will look at several applications in Light Microscopy for use in Powder Bed Fusion which is one process widely used in metals. This method provides some challenges but also some distinct advantages. 

Motic Compound light microscopes and Stereo microscopes can provide the tools to improve the end AM product from start to finish. 

Fundamentally, the AM process known as Powder Bed Fusion, discussed here, consists of several insertion points along the way from powder to the final product where microscopy can provide valuable insight.

Below are several of these insertion points:

#1 POWDER MATERIAL ANALYSIS

For the metal powder bed fusion process, incoming powders of various metals and exotic alloys need to be inspected for size, shape, density and defects. Size distribution(s) needs to be checked to ensure proper operation of equipment.

The shape is considered to be best when spherical which leads to maximum powder bed density and flowability. Bed density is how well the particles fit tightly together. If all powder particles are of the same size there will be gaps between them.

Oftentimes two or three-size particles (bimodal or trimodal) are used to fill gaps when melting, to create flows to fill the smallest gaps for fully dense material. 

• Light microscopy can provide powder size distribution and shape (sphericity / roundness) through use of image analysis. This is usually for powder sizes =/> 5micron (ISO/ASTM 52907) in brightfield transmitted light. Transmitted light is blocked by the particles and produces a shadow like image of high contrast for analysis. See below.
• Brightfield reflected light allows observation of powder particle’s surfaces for inspection of powder defects such as surface voids, contaminants, etc.  

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