Intro to 3D Printing + Materials Part 2

Image courtesy of Hubs.com

This is part 2 of my post exploring common 3D printing technologies and materials. As we continue our survey we will be looking at SLS - Selective Laser Sintering and Binder Jetting 3D printing.

SLS - Selective Laser Sintering
Selective Laser Sintering
or SLS is a unique 3D printing technology where a laser is used to heat and fuse a powder material to generate a highly detailed 3D form. SLS printing was developed in the 1980's by Dr. Carl Deckard and Dr. Joe Beaman at the University of Texas at Austin. SLS along with SLA are among the very first 3D printing technologies developed.

In the SLS process a thermoplastic powder, usually nylon is used. This powder is made up of very small, smooth particles less than 100 microns (.100mm) in diameter. This powder is contained in a reservoir and is heated via an infrared lamp or heating coils just below its melting temperature.

After the powder is heated, a powder blade or roller dispenses a smooth, uniform layer onto a build plate adjacent to the reservoir. Next a laser moves horizontally across the powder layer selectively fusing particles together, the laser melts or sinters the powder particles together, hence the process name.

The build plate lowers slightly with each pass of the laser slowly forming the desired 3D shape. Once complete, un-sintered powder encases the part so no support structures or post processing is needed.

SLS printing like in SLA yields strong, functional parts with good isotropic mechanical properties that can be used for detailed prototyping or  low volume, end-use production.

SLS Materials
The most popular material used in SLS is Nylon PA12 which accounts for over 90% of the market. Balancing strength and detail, Nylon PA12  is a highly capable material for both functional prototyping and end-use production of complex assemblies and durable parts with high environmental stability.

TPU (Thermoplastic Polyurethane) is also a popular SLS material combining the properties of both plastic and rubber - TPU can produce elastic, highly durable parts that can be easily bent, twisted or compressed.

DMLS - Direct Metal Laser Sintering
Metals such as titanium, stainless steel or special alloys like Inconel can be also 3D printed via laser sintering. The process is essentially the same as in SLS - after the metal part is printed, an additional heating process is employed to harden it and fully realize its physical characteristics. The last step entails light sanding and polishing. These highly specialized prints are typically used for tools, dental and aerospace components.

SLS Brands
Popular SLS brands include Formlabs, Sintratec, Sinterit, and Stratasys. This technique is commonly used in commercial and industrial applications - currently SLS 3D printers are still too expensive for the everyday consumer.

Back Story
While in graduate school at RISD I had worked on the redesign of a “Talking Book” player - basically a mini-tape deck with speaker that plays audio books for the visually impaired. That year the National Library Service for the Blind and Physically Handicapped had sponsored a competition to redesign the player and I jumped on the opportunity.

After going through a rigorous design process I had my final 3D design modeled in Solidworks. Instead of realizing my final model in conventional wood or Strux foam, I opted to 3D print my design. This was somewhat of a provocative move in our ID studio. At that time 3D printing was not a common thing industrial design students leveraged in their projects as it was very expensive.

However, I was completely fascinated by the new tech and had to try it. I wanted my submission to be exactly they way I had designed it in Solidworks and the only way to achieve that precision was to get it 3D printed. I sent my CAD file away and after a few days I had not one by two models in my hand - submissions were not returned so I had to print two!

I proudly displayed the remaining 3D printed model on my desk in studio and for the next several days whenever someone asked about it, I simply said, “O this? Ya it's a Z Corp binder jet print…” - pretending I like I knew what I was talking about...

talking book concept sketches

Muse Talking Book Concept

Upright - 'Talking' position

Z Corp Binder Jet 3D Print

Binder Jetting
Back then I didn’t fully understand the process, but today I do. My design was printed using a technique called Binder Jetting. This process was developed in 1990's at MIT and was the first to be officially recognized and labeled as 3D Printing.

Binder Jetting is a non-heat process, very similar to inkjet printing. Instead of melting or sintering material particles together via lasers, a liquid binder or glue is used to fuse and build up the 3D form.

Similar to SLS, a build plate supplies a thin layer of material powder. However, instead of a laser, a print head moving in the X and Y direction lays down a liquid binder onto the powder selectively fusing or glueing  the material.

After the print head completes its pass, the powder layer is exposed to an incandescent light to evaporate solvent in the binder. The plate then lowers and a new layer of powder is spread onto the plate - the process repeats, progressively building the part.

After the part is printed, it is combined with another material in a heat process called infiltration - this finishes and makes the part stronger and more resistant to failure.

Binder jetting is used with a variety of materials including plaster, polymers, ceramics and metals. The nature of this 3D printing process allows for binder jetting parts to be printed in full color and any unused powder can be recycled and used for future prints.

Binder Jetting Brands
In my research, binder jetting is not as popular as some of the other process we covered. That being said, there are a handful of companies that utilize this approach, among them are: EXOne, Voxel Jet and Desktop Metal.

I hope this brief survey of 3D printing technologies and materials was helpful and I hope that with this knowledge you can better understand and approach your next 3D printing project.

Thank you, until next time! - Andreu O.

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