selective laser sintering

selective laser sintering
Name	Selective Laser Sintering
Caption	Schematic of a typical SLS system
Other names	SLS
Classification	Additive manufacturing, Rapid prototyping
Inventor	Carl Deckard, Joseph Beaman
Invention year	1980s
Organization	University of Texas at Austin
Related technologies	Selective laser melting, Direct metal laser sintering, Binder jetting

Selective laser sintering is an additive manufacturing technique that uses a high-power laser to fuse small particles of polymer, metal, ceramic, or glass powders into a mass representing a three-dimensional object. The process is guided by a digital model, typically an STL file, and is conducted layer-by-layer within a build chamber filled with an inert atmosphere, often nitrogen or argon. Developed at the University of Texas at Austin, it is a foundational technology within the broader field of rapid prototyping and industrial production.

Overview

The technique operates on the principle of using thermal energy from a carbon dioxide laser or fiber laser to selectively fuse powdered material. A key characteristic is that unsintered powder remains in place to support the structure during the build, eliminating the need for dedicated support structures common in other methods like stereolithography. This allows for the creation of complex geometric shapes, including internal channels and lattice structures, that would be impossible with traditional subtractive manufacturing. The process is governed by parameters such as laser power, scan speed, and layer thickness, which are optimized for specific materials and desired part properties.

Process

The build cycle begins with a thin layer of powder being spread across the build platform by a recoater blade or roller. The laser then scans the cross-section of the part, sintering the powder particles together. Following each scan, the build platform lowers by one layer thickness, and a new layer of powder is applied. This sequence repeats until the part is complete. After cooling, the entire build chamber is removed, and the fabricated part is excavated from the loose powder, which can often be recycled for subsequent builds. Post-processing typically involves media blasting, such as with glass beads, to remove excess powder and may include secondary operations like infiltration with epoxy or metal to enhance strength.

Materials

A wide variety of materials can be processed, with polyamide powders, such as PA 11 and PA 12 (Nylon 12), being the most common for plastic parts. For metal components, common powders include stainless steel (e.g., 17-4 PH), titanium alloys (e.g., Ti-6Al-4V), cobalt-chrome, and aluminum. Advanced composites and engineered materials, such as carbon fiber-filled PEEK or sand cores for investment casting, are also utilized. The powder characteristics, including particle size distribution and flowability, are critical to achieving consistent results.

Applications

Primary applications span from functional prototyping and concept modeling to end-use part production in sectors like aerospace, automotive, and medical device manufacturing. In the medical industry, it is used to create patient-specific surgical guides and bone implants. The consumer goods sector employs it for producing complex jigs and fixtures and customized products. Its ability to produce durable parts directly from digital files makes it integral to digital inventory and on-demand manufacturing strategies adopted by companies like BMW and Airbus.

Advantages and limitations

Significant advantages include design freedom for complex geometries, high material utilization with powder recycling, and good mechanical properties in finished parts. It does not require support structures, which simplifies post-processing. Key limitations involve relatively high equipment and material costs, a rough surface finish often requiring secondary finishing, and inherent porosity in parts that can affect mechanical strength. The process also requires careful handling of fine powders and management of the inert build atmosphere to prevent oxidation or explosion risks.

History and development

The fundamental patents for the technology were filed in the mid-1980s by graduate student Carl Deckard and his advisor Joseph Beaman at the University of Texas at Austin, under sponsorship from the Defense Advanced Research Projects Agency (DARPA). Commercialization began in the late 1980s through the company DTM Corporation, which was later acquired by 3D Systems. Parallel and subsequent developments led to related processes like selective laser melting for fully dense metals. The expiration of key patents in the 2010s spurred a significant expansion in the availability of both industrial and desktop SLS machines from various manufacturers worldwide.

Category:Additive manufacturing Category:Industrial processes