Essay on the Selective Laser Melting (SLM)

Selective Laser Melting (SLM), also directed as laser powder bed fusion (LPBF) or natural metal laser melting (DMLM); exists an Additive Manufacturing (AM) strategy developed to melt and fuse metallic powders via a high power-density laser. The principle of the Selective Laser Melting procedure starts with a construction platform applied with very thin layers of metallic powders; which stand melted later by the thermal energy generated by one or several laser beams. The cross-section area of the developed 3D part stands built by selectively melting and re-solidifying metallic powders per layer.

Here is the article to explain, How to define Selective Laser Melting (SLM)?

The construction platform exists then lowered by a small length and a new layer of powders stands deposited and leveled by a re-coater. The laser beam(s) can exist handled and focused through a computer-generated pattern by carefully prepared scanner optics. Therefore, the powder particles can exist selectively melted in the powder bed and create the build of 3D things according to the Computer-Aided Design (CAD) layout. What does mean Rapid Prototyping (RP)?

A considerable variety of metal powders has existed displayed in the Selective Laser Melting (SLM) procedure, including aluminum, titanium, copper, chromium, cobalt-chromium, stainless steel, tool steel, and superalloys. Although most of the unused powders can stand reclaimed for further Additive Manufacturing (AM) techniques; the necessity to fill the build volume in the SLM working compartment is problematic and inefficient especially when large details need to produce.

Some level of fabric loss occurs when the powders exist contaminated or oxidized in the melting procedure and hence become non-recyclable. The SLM procedure also has some limitations for building arbitrarily designed shapes. It is currently challenging to produce overhanging geometries or horizontal struts; mainly due to the poor heat conduction in the powder bed immediately below the newly solidified layers of exposed powders.

Essay;

Most of the saleable Selective Laser Melting (SLM) systems generally utilize powders with particle sizes ranging from 20 to 50 µm and a specific layer thickness of 20–100 µm. The analysis and development to climb down the conventional SLM for advanced quality resolution exist mainly focused on three factors: powder particle size, laser beam diameter, and layer thickness. Both CW and pulsed lasers have existed utilized in micro SLM systems.

The laser spot size ranging from 20 to 30 µm has existed utilized for micro SLM systems; and, the corresponding quality resolution could stand reduced to a similar level of the spot size. Compared to the direct writing techniques that exist more commonly used for micro applications, micro SLM shows several attractive benefits, including simpler procedure setup, faster cycle time, and larger material diversity. Micro SLM has recently found increasing applications in the fabrication of precision components and lattice structures in several fields, including microfluidic devices, MEMS, dentistry, etc.

The properties of metallic Microlattice exist governed by strut build angle, and micro SLM cannot build horizontal strut so far. It has existed demonstrated as a faster procedure to avoid wastage of material, even though it is relatively expensive. Current state-of-the-art micro SLM systems have successfully achieved a part density of more than 99% with a minimum surface roughness of 1 µm and a minimum quality resolution of 15 µm.

SLM Knowledge or Background;

Selective laser melting device stood first introduced by Fockele and Schwarze (F&S) of Germany in 1999 with the support of the Fraunhofer Institute of laser technology which stood a steel powder-based SLM machine. Later in 2004 first SLM device named Realizer, 250 SLM existed released commercially after F&S coped up with MTT and in 2005 high-resolution device named SLM Realizer 100 stood released.

Since the release of the MCP Realizer SLM, other manufacturers such as Concept laser and EOS released machines with a different procedure named Laser curing and Direct metal laser sintering respectively. Concept laser (GmbH) first released M3 Liner and M1 Cushing in 2001, later they released another device named M2 Cushing to produce reactive materials like titanium and aluminum alloys. EOS released the device named EOSINT M 270 DMLS in 2003 and termed as the most common device for direct metal fabrication. In 2008 MTT and 3D systems proclaimed a distribution agreement for the rights to distribute SLM machines in the Americas and Japan. In 2008-09 new version of SLM existed released by MTT named SLM 250 and SLM 125.

Basic Principles of Selective Laser Melting (SLM);

SLM is a powder-based additive manufacturing procedure that permits attaining 3D functional parts from CAD data. SLM follows the same procedure route as SLS, where complete melting of powder occurs instead of sintering or partial melting. The procedure begins with the deposition of a thin layer of powder thickness ranging from 50µm to 75µm across a substrate platform. A high-power fiber laser scans the powder surface, the generated heat melts the powder particles and forms a molten pool.

Once the layer has existed scanned, the platform drops down by single-layer thickness in the z-axis; and the fresh layer of powder stands deposited and the procedure exists repeated until the entire building is complete. Loose powders remove once the fully dense part is complete. SLM parts must exist completed in the inert gas atmosphere such as argon to remove oxygen from the building chamber. Supports like thin teeth shaped needed to secure hanging features due to shrinkage of material solidification. The substrate removes from the build chamber once the procedure gets complete and supports removed carefully.

SLM is termed as the most viable technique for the direct fabrication of complex featured parts of metals. SLM can permit the design optimization and production of complex functionalities beyond the capabilities of traditional techniques; which is possible because of accuracy, versatility, and the laser beam spot size.

More things;

The small laser spot size minimizes the area to exist melted enabling the manufacturing of the part of high resolution. However, to positioned SLM in the RM category as a general method to achieve greater recognition in companies, methods and development need to change to perform and prove themselves as being reliable, repeatable, and cost-effective production processes.

SLM is also known as the freeform fabrication procedure and is capable to build thin wall complex features models of high resolution; and extends its capabilities than the conventional processes; such as customized medical implants especially dental crown and bridge framework, tooling inserts with conformal cooling channel and functional models.

SLM concerns primarily turn around the application of high powered fiber laser to generate high temperature to completely melt the powder, surface roughness is the main concern of SLM; because high heat input causes material vaporization and generation of spatter that stands subjected by melting and re-solidifying. But SLM parts cover committed microstructure parts and material properties that make possible this technique for the application.

Benefits of Selective Laser Melting (SLM):

• Parts produced in this procedure are nearly 100% dense and have the same mechanical strength as the original material.
• Almost no powder material waste, the loose powders which were not solidified can reuse.
• SLM offers minimum time to market, exact shape generation without an expansive mold, procedure flexibility, and great utilization of material.
• SLM powder bed technology allows reasonable and speedy powder metallurgy. The alloys to tested can utilize straightly within the prototyping apparatus; and alloys can smoothly accustomed to the evolution of the elemental balance of powders.

Drawbacks of Selective Laser Melting (SLM):

• SLM consider as the increase-temperature gradient; which causes thermal stress build-up and quick solidification so coarse to grainy surface finished parts created.
• The inadequate availability of some materials in powder form restricts the range of materials for processing. The procedure should optimized for available material.

Advantages and Disadvantages of Selective Laser Melting (SLM);

SLM technology enables the manufacturing of geometries that include complex elements that are not possible; with traditional manufacturing techniques such as casting, powder metallurgy, forging, and extrusion. Like other AM and RP techniques, the manufacturing of biomedical devices by SLM has an economic impact; as it allows short production runs without significant cost penalties. In particular, compared to conventional manufacturing techniques; SLM stands suited for biomedical device manufacturing because of the following capabilities:

• It allows the manufacturing of prototype device features, for design validation objectives before mass production runs.
• SLM technology enables low-volume production elements, especially during the initial formatting deployments, which allows rapid implementation of any design modifications.
• This technology like other AM techniques results in a quicker product life cycle through flexible production stages; which ensure shorter time-to-market of the manufactured machines.
• There practically no constraints in the imagination of any difficult-shaped geometries via SLM technology. Biomedical machine elements that are not technically feasible to fabricate with other conventional methods; for example, involved porous scaffolds and components with prepared porosities, can precisely manufactured by SLM.
• Fabrication of biomedical machines by SLM does not require any additional expensive tooling or extensive assembly needs; thus directly reducing the production expenses.
• SLM technology allows the complexity and customization of biomedical machines for free.
• Optimization of different processing parameters of SLM results in part densities up to 99.98% for Ti alloys, permitting mechanical properties of the fabricated parts; their corrosion manners, and procedure accuracies to fulfill needs for medical or dental parts manufacturing.

The key advantages of biomedical machine manufacturing by SLM over traditional manufacturing techniques.