ADDITIVE MANUFACTURING
(SLA). The system functioned by curing, or hardening, successive layers of photosensitive resin one on top of another to gradually build-up an object. A similar patent application had been submitted a few weeks ahead of Hull’s by a team of French inventors led by Alain Le Mehaute. Surprisingly, however, their application was ultimately abandoned because a long-term viable use for the technology could not be identified. Other methods of AM
explored and developed in the 1980s included: selective laser sintering, which was invented by University of Texas student Carl Deckard; direct metal laser sintering, which was invented
“AM can be used to dramatically shorten the supply chain, enabling parts to be produced locally and quickly”
by German Company EOS; and fused deposition modelling (FDM), invented by S. Scott Crump. Stratasys, the company that Crump later co-founded with his wife Lisa, has remained a leading producer of FDM printers since. The former two processes, together with others described below, rely heavily on the use of lasers to work.
Types of laser-based AM
Powder bed fusion Laser-based powder bed fusion (PBF) can be broadly broken down into two varieties; those that melt a material to create a part and those that sinter material to achieve the same aim. The difference between melting and sintering is quite simple: melting involves moving a material from a solid to a liquid state using a high-temperature heat source; sintering does not allow the material to reach a completely liquid state because the temperature of the heat source is not high enough. In the case of sintering metal, the
metal particles are agglomerated together, but the result is typically a weaker part than can be achieved through melting. The strengths of the parts obtained using these processes, however, is comparable to those obtained by casting or machining techniques. Metals and alloys, such as stainless steel, cobalt-chromium, aluminium and titanium are most often processed using PBF processes. PBF incorporates direct metal
laser sintering, selective laser melting, and selective laser sintering. Direct metal laser sintering
(DMLS) was first commercialised in 1995 and works by sintering a metal or metal-alloy powder with a high-powered laser beam. The laser beam traces out the cross- section of each layer, causing the metal particles to agglomerate together. After each layer, the print bed moves down, and another layer of metal powder is applied. While printing, the DMLS build chamber is filled with inert gas to prevent oxidation. The process produces parts with complex geometries to tight tolerances, and it is compatible with a wide range of metals. Selective laser melting (SLM) is
a very similar process to DMLS, but higher-powered lasers are employed. It is therefore much quicker, but SLM machines can be very expensive. Further, owing to the higher temperatures employed, it has the potential to create internal stresses within parts if caution is not taken. Selective laser sintering (SLS) enables objects to be created from powders, typically plastics such as polyamide (PA) or polyetheretherketone (PEEK), without the need for a support or an intermediate binder. Using the process, a hopper containing the powder and the construction area are heated to below the melting temperature of the powder. The first layer of powder is deposited onto the construction platform. Then, a laser selectively sinters the powder particles together in the desired shape. When a layer is complete, the construction platform moves downward to
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Flexible 3D workpiece processing
Precise processing of parts in three dimensions requires highly dynamic positioning of the laser focus along the optical z-axis. With the addition of focusing units, xy scan systems can be easily transformed into 3D beam deflection systems. In this way, the laser focus can be guided along the exact contour of the workpiece being processed.
The varioSCAN product line is ideal for applications requiring f-theta lenses, as well as applications for which these costly lenses are unavailable. In the second case, the focusing system provides a plane focusing surface in addition to z-adjustment of the focus. Besides the processing of three-dimensional surfaces, classic fields of application requiring z-axis manipulation include additive manufacturing (3D printing) and laser cutting. In many of these applications, there is a trend towards higher laser powers, the use of ultrashort pulse lasers and the demand for improved image quality and positioning accuracy.
When developing the new varioSCAN II, the focus was on these exact requirements. The configuration of the optics is tailored to the individual customer requirements.
More information:
https://www.scanlab.de/en/products/z-axes-3d-add-ons/ varioscan-ii
allow for the surface to be re- coated. The process is repeated until the entire part is complete.
Directed-energy deposition Directed-energy deposition (DED) is a relatively complex AM process commonly used to repair, or add material to, existing components. A typical DED machine features a nozzle that is mounted on a multi-axis arm and deposits material onto a specified surface, where it is melted with a laser beam and solidifies. The process is similar in principle to extrusion, but the nozzle can move in multiple directions and is not fixed to a specific axis. The process can be used to process polymers and
ceramics, but is typically used with metals, in the form of either powder or wire.
Stereolithography Stereolithography (SLA) belongs to the vat photopolymerisation family of AM processes. It creates objects by selectively curing a polymer resin, layer by layer, using an ultraviolet (UV) laser beam. The materials used in SLA are photosensitive thermoset polymers that come in a liquid form. Using SLA, a build platform is positioned in a tank of liquid photopolymer, at a distance of one layer-height from the surface of the liquid. A UV laser creates the next layer by
g THE 2023 GUIDE TO LASER SYSTEMS LASER SYSTEMS EUROPE 35
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