Laser-sintering has evolved significantly since its commercial introduction in the 1980s. Born out of the rise of rapid prototyping technology, laser-sintering is now the design-driven catalyst for global innovation in such industries as aerospace, medical device design, automotive and consumer.
Simply said, laser-sintering removes the constraints of traditional manufacturing methods, such as machining, molding or casting, and concurrently allows for conceptualizing, designing and manufacturing certified, three-dimensional parts directly from CAD data. The process is no longer one-directional where, for so long, manufacturing requirements dictated, and thus restricted and controlled, design. Equipment and Process Laser-sintering builds parts additively and automatically from plastic or metal powder. A 3D CAD file is divided into cross sections by control software, which causes the laser-sintering system to deposit a layer of finely powdered plastic or metal onto a build platform. A focused laser then moves across the powder, sintering it into a cross section of the part. The platform lowers itself exactly the thickness of the first layer and the process repeats layer-by-layer until a three-dimensional part emerges. This production method creates parts with complex geometries, and sometimes integrates into a single part what would have been several if manufactured by traditional means.
Plastics laser-sintering equipment employs:
- 30-50-Watt CO2 laser with two 50-Watt lasers in larger P 730 and P 800 series machines.
- build size range from 200 mm x 250 mm x 330 mm (7.9 × 9.8 × 13 in) in the FORMIGA to 700 mm × 380 mm × 580 mm (27.6 × 15 × 22.9 in) in the P 730.
- laser scan speed of up to 5-6 meters/second (twice that in models with twin lasers).
- variable build layer thickness, depending on the material, from 0.1 mm to 0.15 mm (0.004 - 0.006 in.).
- nitrogen-filled build chamber, typically.
Direct metal laser-sintering (DMLS) equipment employs:
- 200-Watt ytterbium-fiber laser.
- effective build platform of 250 mm x 250 mm × 215 mm (9.85 × 9.85 × 8.5 in.).
- scan speed of up to 7 meters/second.
- variable laser focus diameter of 100 - 500 m (0.004 - 0.02 in.), controlled by the software as it moves across the powder.
- build-layer thickness from 20 - 40 m (0.0008 - 0.0015 in.), depending on the material and the application.
- nitrogen-filled chamber except when building in titanium, which requires argon to ensure an impurity-free final part.
The variety of available plastic and metal materials has expanded considerably in the past few years, with an emphasis on materials for manufacturing rather than prototyping.
With few exceptions, available plastic material for laser-sintering is based on PA 12 or PA 11 polyamide. The fine powder is resistant to most chemicals and, when laser-sintered, produces functional prototypes and manufactured parts with a highend finish easily capable of withstanding high mechanical and thermal loads.
Particular requirements of different applications call for variants of this material, such as filling the polyamide with aluminum, glass or carbon fiber. Another polyamide variant is PA 2210 FR, containing a chemical flame retardant that produces a UL 94 V-0 flammability rating and is free of halogens. Also, PrimePart DC, a new high-impact polyamide, offers an elongation at break of 50 percent, about twice as high as that of previously available materials. PrimePart DC has a tensile strength of 48 MPa and a Young’s modulus of 1550 MPa, with its other mechanical properties similar to those of PA 2200 series polyamides.
In addition to these polyamide offerings, PrimeCast 101 is a polystyrene used to produce lost patterns for plaster casting and master patterns for vacuum casting. And, with the recent introduction of PEEK HP3, the first high-performance, high-temperature thermoplastic polymer available for laser-sintering, the medical industry is exploring this material for its biocompatibility, sterilizability, tensile strength and conductivity. PEEK HP3 end-products achieve tensile strengths of up to 95 MPa (13.78 KSI) and a Young’s modulus of 4,400 MPa (640 KSI). Its excellent chemical resistance makes PEEK impervious to numerous chemicals except corrosive acids. In applications where light weight and flame resistance are critical, PEEK is a popular replacement for metal, including stainless steel and titanium.
The number of metal materials available for use with DMLS is driven in part by the medical and aerospace industries, which continue finding expanded uses for stainless steel, cobalt chrome and titanium, in particular. Toolmaking applications, as well, have driven the addition of a maraging steel.
The Near Future
Advances in commercial laser-sintering and material offerings will continue to provide improved flexibility, manufacturing rates and greater standardization of processes.
The development of PEEK HP3 suggests other plastics besides polyamides are candidates for laser-sintering. And, in theory, practically any metal that can be welded and can be delivered as a suitable powder could be considered for laser-sintering. Examination and production of these materials will be application-, industry-, and customer-driven.
Leading manufacturers are demonstrating continuing commitment to laser-sintering. In Europe, for example, a consortium of companies including Boeing, EOS, Evonik Industries and MCP HEK Tooling – joined more recently by Siemens, Stratasys, Stükerjürgen and JetAviation – is presently exploring advancements in the technology at the Direct Manufacturing Research Center (DMRC) at the University of Paderborn in Germany.
The DMRC analyzes current laser-sintering systems and the present generation of materials to establish their state of performance for build speed, powder size, uniformity and final product quality. The DMRC will move toward developing industry requirements for materials, training, and standards. These activities will strengthen and expand the adoption of laser-sintering by providing established, exacting documentation and quality requirements to global manufacturing industries, such as aerospace and medical.
The greatest future advances in laser-sintering will surface, not from new materials or improved equipment, but from the users themselves as they become accustomed to design-driven manufacturing. The freedom to create parts of practically any shape, without regard to the rules and restrictions of older manufacturing processes, is just beginning to be explored by designers who have gained expertise with laser-sintering.