selective laser melting


  • [57] SLM is often a more sustainable option due to decreased raw material use, less complex tool use, lightweight part potential, near-perfect final geometries, and on-demand

  • It is not only the Print operation and orientation that provides a change in material properties, it is also the required post processing via Hot Isostatic Pressure (HIP)
    Heat Treat and shot peen that change mechanical properties to a level of noticeable difference in comparison to equiaxed cast or wrought materials.

  • Depending on the part made and its intended use, SLM can help make more lightweight parts with complex dimensions which reduce both energy intensive post-processing machining
    such as EDM or a computer numerical control (CNC) machining and decrease part weight.

  • “[61] Metallic support structure removal and post processing of the part generated may be a time-consuming process and require the use of machining, EDM and/or grinding machines
    having the same level of accuracy provided by the RP machine.

  • [6] Process Selective laser melting is able to process a variety of alloys, allowing prototypes to be functional hardware made out of the same material as production components.

  • Additionally, wear properties are typically better as seen with the studies done on additive Inconel 718 due to surface condition; the study also demonstrated the laser power’s
    influence on density and microstructure.

  • Since the components are built layer by layer, it is possible to design complex freeform geometries, internal features and challenging internal passages that could not be
    produced using conventional manufacturing techniques such as casting or otherwise machined.

  • Defect formation Despite the large successes that SLM has provided to additive manufacturing, the process of melting a powdered medium with a concentrated laser yields various
    microstructural defects through numerous mechanisms that can detrimentally affect the overall functionality and strength of the manufactured part.

  • [52] What sets SLM apart from other 3D printing process is the ability to fully melt the powder, rather than heating it up to a specific point where the powder grains can
    fuse together, allowing the porosity of the material to be controlled[citation needed].

  • Tests by NASA’s Marshall Space Flight Center, which is experimenting with the technique to make some difficult-to-fabricate parts from nickel alloys for the J-2X and RS-25
    rocket engines, show that difficult to make parts made with the technique are somewhat weaker than forged and milled parts but often avoid the need for welds which are weak points.

  • One such example is the development of secondary phase precipitates within the bulk structure due to the repetitive heating within solidified lower layers as the laser beam
    scans across the powder bed.

  • [46] Industry applications[edit] • Aerospace – Air ducts, fixtures or mountings holding specific aeronautic instruments, laser-sintering fits both the needs of commercial
    and military aerospace • Energy – Laser-melting can be used to produce innovative pump impellers, high pressure reactors and hard-to-find spare parts • Manufacturing – Laser-sintering can serve niche markets with low volumes at competitive

  • Selective laser melting (SLM) is one of many proprietary names[1] for a metal additive manufacturing (AM) technology that uses a bed of powder with a source of heat to create
    metal parts.

  • [citation needed] Independent of the material system used, the SLM process leaves a grainy surface finish due to “powder particle size, layer-wise building sequence and [the
    spreading of the metal powder prior to sintering by the powder distribution mechanism].

  • SLM allows parts to be built additively to form near net shape components rather than by removing waste material.

  • The electric use is often the most energy intensive part of the printer, as the high power lasers, chillers, configurations, and part separation all contribute to this.

  • “[44] The 3D printing process for the SuperDraco engine dramatically reduces lead-time compared to the traditional cast parts, and “has superior strength, ductility, and fracture
    resistance, with a lower variability in materials properties.

  • [60] Constraints The aspects of size, feature details and surface finish, as well as print through dimensional error[clarification needed] in the Z axis may be factors that
    should be considered prior to the use of the technology.

  • The exception to this is in research environments where the machine is not constantly used and use is more infrequent, in this case, the embodied energy from primary processing
    and manufacturing is dominant.

  • SLM produces fully dense durable metal parts that work well as both functional prototypes or end-use production parts.

  • Ultimately, the total embodied energy considering all parts made is dependent on many factors but is almost always dominant during the printing phase and more specifically
    during long idle times and post-processing part removal through EDM.

  • Therefore, SLM can produce stronger parts because of reduced porosity and greater control over crystal structure, which helps prevent part failure[citation needed].

  • Another name for selective laser melting is direct metal laser sintering (DMLS), a name deposited by the EOS brand, however misleading on the real process because the part
    is being melted during the production, not sintered, which means the part is fully dense.

  • [34] This technology is used to manufacture direct parts for a variety of industries including aerospace, dental, medical and other industries that have small to medium size,
    highly complex parts and the tooling industry to make direct tooling inserts or those requiring short lead times.

  • The laser energy is intense and focused enough to permit full melting (fusion) of the particles to form a solid structure.

  • [32] The cellular structure is considered to be the main cause of the differences in deformation behavior, especially during the first creep stage, primarily because it limits
    the work-hardening capacity of the material.

  • The technology is used both for rapid prototyping, as it decreases development time for new products, and production manufacturing as a cost saving method to simplify assemblies
    and complex geometries.

  • [43] The ability to 3D print the complex parts was key to achieving the low-mass objective of the engine.

  • [32] Applications The types of applications most suited to the selective laser melting process are complex geometries and structures with thin walls and hidden voids or channels
    on the one hand or low lot sizes on the other hand.

  • Since the components are built layer by layer, it is possible to design internal features and passages that could not be cast or otherwise machined.

  • These defects can arise from not using a laser source with adequate power or scanning across the powdered surface too quickly, thereby melting the metal insufficiently and
    preventing a strong bonding environment for solidification.

  • Selective laser melting is very useful as a full-time materials and process engineer.

  • This advancement is very important to both material science and the industry because it can not only create custom properties but it can reduce material usage and give more
    degrees of freedom with designs that manufacturing techniques can’t achieve.

  • Cracking is another mechanical defect in which low thermal conductivity and high thermal expansion coefficients generate sufficiently high amounts of internal stresses to
    break bonds within the material, especially along grain boundaries where dislocations are present.

  • [59] Another example is the 1kg weight reduction through a hydraulic valve body which estimates a saving of 24,500L of jet fuel and 63 tons of CO2 emissions from a lightweight
    design and decreased material used compared to traditional manufacturing methods.

  • With multiple alloying elements and high aluminum/titanium fraction, these materials, when consolidated through SLM form various secondary phases, which affects the processability
    and leading to weakness within the structure.

  • First, the embodied energy that was used to make the printer, which has more than 500 parts, contributes around 124,000 MJ for a standard Renishaw AM250.

  • Advantage can be gained when producing hybrid forms where solid and partially formed or lattice type geometries can be produced together to create a single object, such as
    a hip stem or acetabular cup or other orthopedic implant where osseointegration is enhanced by the surface geometry.

  • Additionally, certain types of nanoparticles with minimized lattice misfit, similar atomic packing along matched crystallographic planes and thermodynamic stability can be
    introduced into metal powder to serve as grain refinement nucleates to achieve crack-free, equiaxed, fine-grained microstructures.

  • As a new processing technique, SLM can produce a unique microstructure that is difficult to achieve using conventional techniques.

  • The ability to quickly produce a unique part is the most obvious because no special tooling is required and parts can be built in a matter of hours.

  • [19] The future challenges are being unable to create fully dense parts due to the processing of aluminum alloys.

  • [citation needed] Laser polishing by means of shallow surface melting of SLM produced parts is able to reduce surface roughness by use of a fast-moving laser beam providing
    “just enough heat energy to cause melting of the surface peaks.

  • For production tooling, material density of a finished part or insert should be addressed prior to use.

  • For another superalloy Inconel IN718, researchers found the additively manufactured material showed large columnar grains with an orientation parallel to the building direction,
    whereas the wrought material showed a fine-grained structure with no significant texture.

  • Requests such as requiring a quick turnaround in manufacturing material or having specific applications that need complex geometries are common issues that occur in industry.

  • [citation needed] It is critical to have a full overview of the material along with its processing from print to required post-print to be able to finalize the mechanical
    properties for design use.

  • [35] Traditional high-volume manufacturing techniques have a relatively high set-up cost (e.g.

  • [8] SLM machines predominantly uses a high-powered Yb-fiber optic laser with standard laser powers ranging from 100–1000 W. Inside the build chamber area, there is a material
    dispensing platform and a build platform along with a recoater system (blade or roller) used to evenly spread new powder across the build platform.

  • [51] Potential Selective laser melting or additive manufacturing, sometimes referred to as rapid manufacturing or rapid prototyping, is in its infancy with relatively few
    users in comparison to conventional methods such as machining, casting or forging metals, although those that are using the technology have become highly proficient[weasel words].

  • [18] Material Density that is generated during the laser processing parameters can further influence crack behavior such that crack reopening post HIP process is reduced when
    density is increased.

  • Much of the pioneering work with selective laser melting technologies is on lightweight parts for aerospace[34] where traditional manufacturing constraints, such as tooling
    and physical access to surfaces for machining, restrict the design of components.

  • [56][57] Often a direct comparison can only be made by looking at parts made through two different processes.

  • Being able to print very high strength advanced alloys … was crucial to being able to create the SuperDraco engine as it is.

  • Depending on the composition of the precipitates, this effect can remove important elements from the bulk material or even embrittle the printed structure.

  • As a consequence, a wide range of effects might take place like the formation of non-equilibrium phases and changes in the microstructure.

  • However, by planning the build in the machine where most features are built in the x and y axis as the material is laid down, the feature tolerances can be managed well.

  • However, for limited quantise of bespoke customisable parts, the process remains attractive for a number or uses.

  • [citation needed] Machine components The typical components of a SLM machine include: laser source, roller, platform piston, removable build plate, supply powder, supply doses

  • [12] In order for the material to be used in the process it must exist in atomized form (powder form).

  • Laser-sintering is independent of economies of scale, thus liberating one from focusing on batch size optimization.

  • [citation needed] The ASTM International F42 standards committee has grouped selective laser melting into the category of “laser sintering”, although this is an acknowledged
    misnomer because the process fully melts the metal into a solid homogeneous fully dense mass, unlike selective laser sintering (SLS) which is a true sintering process.

  • For example, the directed laser beam can induce convection currents upon direct impact in a narrow “keyhole” zone or throughout the semi-molten metal that can impact the material’s
    overall composition.

  • [16] Additionally, industry pressure has added more superalloy powders to the available processing including AM108.

  • [37] An EADS study shows that use of the process would reduce materials and waste in aerospace applications.

  • Other factors that are negligible, yet sometimes varied, are: inert gas use, material (powder) waste, materials used, atomization, and disposal of machine components.


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Photo credit:’]