Additive Manufacturing: Selective Laser Melting

This post was originally created in January 2017.

With all the buzz about Additive Manufacturing, or 3D Printing, in the manufacturing world today, there is a lot of mystery and confusion surrounding the common practices and techniques. So, this week’s blog post will address a common type of 3D printing known as Selective Laser Melting (SLM).

What is Selective Laser Melting?

It is actually part of a broader category, commonly referred to as a Granular Based Technique. All granular based additive manufacturing techniques start with a bed of a powdered material. A laser beam or bonding agent joins the material in a cross-section of the part. Then the platform beneath the bed of material is lowered, and a fresh layer of material is brushed over the top of the cross-section. The process is then repeated until a complete part is produced. The first commercialized technique of this category is known as Selective Laser Sintering.

The Selective Laser Sintering Technique was developed in the mid-1980s by Dr. Carl Deckard and Dr. Joseph Beaman and the University of Texas at Austin, under DARPA sponsorship. As a result of this, Deckard and Beaman established the DTM Corporation with the explicit purpose of manufacturing SLS machines; in 2001, DTM was purchased by their largest competitor, 3D Systems.

SLM is a similar process to SLS, though there are some important differences. Instead of the substrate being sintered, it is melted to fuse layers together. This is typically done in a chamber with an inert gas (usually Nitrogen or Argon), with incredibly low levels of oxygen (below 500 parts per million). This is to prevent any unwanted chemical reactions when the material changes its physical state. This technique yields higher density parts than any sintering process.

What Are the Advantages of this Process?

SLM is quick; it is one of the fastest rapid prototyping techniques (hough, relatively speaking, most techniques are fast). In addition, it can potentially be one of the most accurate rapid prototyping processes, the major limiting factor being the particle size of the powdered material.

As mentioned previously, this technique yields higher density parts than other additive manufacturing techniques, making for a much stronger part.

Another advantage of the material bed is the ability to stack multiple parts into the build envelope. This can greatly increase the throughput of a DMLS machine.

What Are the Disadvantages of this Process?

Of the commercially available rapid prototyping machines, those that use the Selective Laser Melting technique tend to have the largest price tag. This is usually due to the scale production these machines are designed for, making them much larger than others.

SLM can be very messy. The material used is a bed of powdered material and, if not properly contained, will get EVERYWHERE. In addition, breathing in powdered metals can potentially be very hazardous to one’s health. Though most machines account for this, it is certainly something to be cognizant of when manufacturing.

Unlike other manufacturing processes, SLM limits each part to a single material. This means parts printed on SLM machines will be limited to those with uniform material properties throughout.

In Conclusion

There are quite a few different ways to 3D print a part, with unique advantages and disadvantages of each process. This post is part of a series, discussing the different techniques. Thanks for reading!

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