Selective Laser Melting (SLM) refers to the additive manufacturing (AM) process that builds up a complex three-dimensional (3D) object by using a laser beam to melt powder materials [1]. SLM has been considered one of the most versatile technologies as it can process a wide variety of materials, particularly metals and alloys [2]. Its most suited applications are in the aerospace, automotive, construction, food, and jewellery industries [3].
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SLM is an additive manufacturing process in which powder materials are melted using a high-power laser and solidified in successive layers to produce a complex 3D physical model [1]. This process uses metal powders as raw materials [2]. A thin layer of the metal powder is deposited on a substrate plate, and the laser heats and melts the powder particles following a computer-aided design (CAD) [2]. SLM is also known as laser powder bed fusion (LPBF) or direct metal laser melting (DMLM) [1]. Some of SLM’s advantages and limitations include the following [4][5].
Table 1. Advantages and Limitations of the Selective Laser Melting Technology
Advantages |
Limitations |
High accuracy |
Accuracy requires longer durations in the process |
Functionality |
High surface roughness and high residual stress |
Minimal post-processing |
Anisotropic properties |
Wide variety of materials (some under development) |
Deficiency of quality on-line control |
Allows the creation of complex and unique shapes from metal powders |
High cost of equipment and materials |
Surface structuring (including micro- and nano-structuring) |
Requires an inert gas supply |
High recyclability of the raw material |
Difficulty in removing powder from small channels |
Early applications of SLM only included cast iron, titanium, and nickel. These were used mainly due to their abundance in nature, opportunities for widespread applications, and cost. Later, SLM research progressed, and other metals were included such as aluminium, copper, cobalt, tungsten, and their alloys and composites [4]. Table 2 presents an overview of some of the most common metal powders used in SLM and their applications.
Table 2. Materials for Selective Laser Melting
Materials |
Properties |
Applications |
Alloy Examples |
Steel and Iron-based alloys |
High corrosion resistance High strength (less malleable) Surface roughness Relative density (>90%) Micro-hardness |
Medical and biomedical (i.e., implants) Dental (i.e., orthodontic products) Heat exchangers Lightweight structures (i.e., honeycomb-like structures) Other application (i.e., filter elements) |
Fe-Ni Fe3Al Fe-Ni-Cr Fe-Ni-Cu-P 304L stainless steel H20 tool steel Ultra-high carbon steel |
Titanium-based alloys |
High relative density (>98%) Superior shear strength (higher or equal compared to its counterparts) Surface roughness Low porosity |
Medical and dental (i.e., body prosthesis, dental implants) Lightweight structures (i.e., scaffolds) |
CP-Ti Ti-6Al-7Nb Ti-24nb-4Zr-8Sn Ti-13Zr-Nb Ti-13Nb-13Zr |
Nickel-based alloys |
High-temperature resistance Excellent corrosion resistance Wear resistance Good weldability Relative density (near 100%) |
Aircraft engines Combustion chambers Die models for bevel gear Porous filtration media |
Chromel Nimonic 263 IN738LC MAR-M-247 Ni-Ti |
Other Metals (Aluminium, Copper, Magnesium, Cobalt-Chrome, Tungsten, Gold, Silver) |
High relative density of aluminium and cobalt-chrome (>96%) and other metals (82%-85%) High strength in aluminium (i.e., 400 MPa for AlSiMg) Increased hardness of parts when powder copper has been added
|
Biomedical and dental applications (i.e., crowns and bridges) Heat exchangers Automobile parts Jewellery |
Cu+Cu10Sn+Cu8.4P CoCr 24 Carat gold K220 CuNi15C18400 |
Ceramics |
High melting temperatures Brittle nature High surface roughness |
Medical and dental (i.e., dental restorations, bone substitution implants Thin wall structures Electrical or thermal insulation Wear resistance coating |
Silica Yttria stabilized zirconia Tri-calcium phosphate Alumina zirconia Mixture Porcelain |
The market for additive manufacturing with metal powders was at about USD 366 million in 2019. It is forecasted to grow over 18% (compound annual growth rate) between 2020 and 2026 to reach around USD 970 million by 2026. Advancements in technology would be focused on lighter and cleaner products as well as shorter processing time and cost [6].
The SLM technology generally uses powder particles sizes ranging between 20 to 50 mm and layer thicknesses between 20 to 100 mm. Recent efforts have scaled down the technology to work with particles sizes of less than 10 mm and layer thickness of less than 10 mm. This technology is known as micro SLM, and it is expected to continue to evolve and find applications in cell biology, biomedical science, and clinical diagnostics. [7].
The aerospace and automobile industries are envisioning installing devices and sensors at microscale and nanoscale resolution through precise macrostructure control.
Another industry that would continue to evolve is the jewellery industry with efforts to include more precious metals such as gold, platinum, and palladium alloys. These also involve achieving near-net shape fabrication, decreasing material waste, and increasing efficiency in the manufacturing process [7].
[1] Xu Song, Wei Zhai, Rui Huang, Jin Fu, Mingwang Fu, Feng Li, 2020, Metal-Based 3D Printed Micro Parts & Structures, Reference Module in Materials Science and Materials Engineering, Elsevier, 2020
[2] Prashanth Konda Gokuldoss, Sri Kolla, Jürgen Eckert, 2017, Additive Manufacturing Processes: Selective Laser Melting, Electron Beam Melting and Binder Jetting—Selection Guidelines, Materials, 2017 Jun 10(6): 672
[3] Prashanth Konda Gokuldoss, 2020, Selective Laser Melting; Materials and Applications, MDPI Books, Basel Switzerland
[4] Chord Yen Yap, Kai Se Chua, 2015, Review of selective laser melting: Materials and Applications, Applied Physics Reviews, 2(4), December 2015, Available, https://www.researchgate.net/publication/286497734_Review_of_selective_laser_melting_Materials_and_applications (accessed January 29, 2021)
[5] Interreg, Sudoe, Addispace, Diagnosis and Study of Opportunities of Metallic Additive Manufacturing on Sudoe Aerospatial Sector, [Online] Available: http://www.addispace.eu/gestor/recursos/uploads/imagenes/noticias/INFORME/State_of_the_art_MAM-ENGLISH_low.pdf (accessed January 29, 2021)
[6] Kunal Ahuja, Sonal Singh, 2020, Additive Manufacturing with Metal Powders Market Size, Global Marketing Insights, Report ID: GM1783, June 2020, [Online] Available: https://www.gminsights.com/industry-analysis/additive-manufacturing-with-metal-powders-market(accessed January 29, 2021)
[7] Balasubramanian Nagarajan, Zhiheng Hu, Xu Song, Wei Zhai, Jun Wei, Development of Micro Selective Laser Melting, The State of the Art and Future Perspectives, Engineering, Volume 5, Issue 4, pages 702-720, August 2019.