Better Be Running! Tools to Drive Design Success (part 3)

This is the third in our series of excerpts from “Better Be Running! Tools to Drive Design Success” by Dr. Ronald Hollis, President, CEO, and Co-founder of Quickparts.com (Atlanta, GA). Written for business managers, the book focuses on manufacturing processes, tooling choices, and production strategies that can help companies bring products to market faster. To order the book, go to www.betterberunning.com.

Selective Laser Sintering: Powder to the People

Background

Selective Laser Sintering (SLS) creates solid 3D objects by fusing or sintering particles of powdered material with a hot CO2 laser. A thin layer of powdered thermoplastic material is rolled onto a heated build platform. The laser beam directs cross-sectioned CAD data onto the surface of the powder bed. The heat laser then traces each layer, melting plastic particles to the previous plastic layer. After each cross section is scanned, the powder bed is lowered by one layer thickness, then a new layer of material is applied on top. The process is repeated until the part is complete.

Borderline magic, SLS turns powder into parts in a matter of hours, typically building at a rate of one cubic inch per hour. While SLS began as a way to build prototype parts early in the design cycle, it is now being used in low-volume manufacturing to produce strong, fully functional parts with an accuracy of 0.005 inch (five thousandths).

Originated by DTM Corporation, SLS was acquired by 3D Systems, Inc., in 2001. 3D Systems, based in Rockhill, South Carolina, now manufactures and sells SLS systems and materials worldwide.

Another major player in SLS equipment is EOS (Electro Optical System) GmbH of Munich, Germany. While technically better, EOS leads SLS sales only in Europe. 3D Systems has benefited from replicating many features of the EOS system.

Step by Step with SLS

First, an operator converts your CAD file to a Standard Tessellation Language (STL) file, then the SLS system software processes the file and orients the part for optimum build. Next, the SLS software slices the STL file into electronic layers and sends it as instructions to direct the operation.

Thermoplastic powder is spread by a roller over the surface of a build cylinder. The piston in the cylinder moves down one layer thickness to accommodate each new layer of powder. The powder delivery system is similar in function to the build cylinder. Here, a piston moves upward incrementally to supply a measured quantity of powder for each layer.

A laser beam is then traced over the surface of this compacted powder to selectively melt and bond it to form a thin layer of the object. The fabrication chamber is maintained at a temperature just below the melting point of the powder so that heat from the laser raises the temperature slightly to cause sintering. A nitrogen atmosphere inside the fabrication chamber prevents the material from burning. The process is repeated until the entire object is fabricated.