Laser-Based Powder Bed Fusion: History
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Nader Asnafi

Laser-based powder Bed Fusion (L-PBF), formerly SLM, is one of the seven Additive Manufacturing basic process categories in the new standards. 

  • rapid tooling
  • additive manufacturing (AM)
  • laser-based powder bed fusion (L-PBF)
  • production tools
  • cold working
  • hot working
  • injection molding

1. Introduction

During the past 15 years, layered manufacturing has been subject to further research studies, standardization and industrialization. According to the developed standards, the technology is named Additive Manufacturing (AM). Laser-based powder Bed Fusion (L-PBF), formerly SLM (Figure 1b), is one of the seven AM basic process categories in the new standards [1][2][3][4]. For a detailed description of L-PBF, see [5][6][7][8][9].

Table 1 displays the features of the current (2020) machines for AM by L-PBF. This table, which is based on the machine makers specifications, shows that the maximum object size that can be 3D-printed today is 600 × 600 × 600 mm3 (although the largest height is 850 mm in one of the other machines). This size has more than doubled compared to that in the 1995 machine for selective laser sintering. In addition to higher laser power, some of the current machines have more than one laser and therefore a much higher productivity.

Due to the complexity of L-PBF, the manufacturers of metal AM systems have developed sets of optimized processing conditions for some existing powder metals. The machine manufacturer sets the process parameters for one or some specific powder metals as the default values for additive manufacturing based on the customer preferences before machine delivery and installation, Table 2. The number of these powder metals is much larger than those in 1995. However, this number is still very small, compared to the number of existing materials made and used conventionally.

Table 1. The features of the current L-PBF machines [10][11][12][13][14][15][16].

Manufacturer Model Number and Type of Lasers Laser Power
(per Laser)
(W)		 Build Volume
(l × w × h)
(mm3)		 Build
Rate (cm3/hr)		 Layer
Thickness
(μm)		 Scan Speed (m/s)
3D Systems DMP Factory 500 Printer Module 3 fiber 500 500 × 500 × 500 1 - 2–200, Typical: 30, 60 & 90 -
DMP Factory/Flex 350 1 fiber 500 275 × 275 × 420 - 5–200, Typical: 30, 60 & 90 -
DMP Flex 100 1 fiber 100 100 × 100 × 90 - 10–100 -
ProX DMP 300 1 fiber 500 250 × 250 × 330 - 10–100, preset: 40 -
ProX DMP 200 1 fiber 300 140 × 140 × 115 - 10–100, preset: 30 -
Additive
Industries		 MetalFAB1 1 to 4 Yb fiber 500 420 × 420 × 400 - 20–100 -
Concept Laser X Line 2000R 2 (cw) fibre 1000 800 × 400 × 500 - - -
M Line Factory 4 fiber 1000 500 × 500 × 400 - - -
M2 Multilaser 2 (cw) fiber 400 250 × 250 × 350 - - -
EOS EOS M 400-4 4 Yb-fiber 400 400 × 400 × 400 1 100 80 7
EOS M 400 1 Yb-fiber 400 400 × 400 × 400 1 50 - 7
EOS M 300-4 4 Yb-fiber 400 300 × 300 × 400 10 - 7
EOS M 290 1 Yb-fiber 400 250 × 250 × 325 1 - - 7
EOS M 100 1 Yb-fiber 200 f100 × 95 1 & 2 - - 7
SLM Solutions SLM®NXG XII 600 12 1000 600 × 600 × 600 1000 - -
SLM®800 4 400 or 700 500 × 280 × 850 1 Up to 171 20–90 10
SLM®500 4 IPG fiber 700 500 × 280 × 365 1 Up to 171 20–75 10
SLM®280 1, 2, 3 or dual 400, 700, or 700 & 1000 280 × 280 × 365 1 Up to 113 20–90 10
SLM®125 1 IPF fiber 400 125 × 125 × 125 1 Up to 25 20–75 10
Renishaw RenAM 500Q/S 1 or 4 Yb-fiber 500 250 × 250 × 350 1 Up to 150 20–100 10
RenAM 500E 1 Yb-fiber 500 250 × 250 × 350 1 Up to 150 20–100 10
RenAM 500M 1 Yb-fiber 500 250 × 250 × 350 1 Up to 150 20–100 10
AM 400 1 400 250 × 250 × 300 1 - - -
AM 250 is now replaced by AM 400 250 × 250 × 300 1 - - -
Trumpf TruPrint 1000 1 fiber 200 f100 × 100 1 & 2 2–18 10–50 -
TruPrint 2000 1 fiber 300 f200 × 200 2 - 20–100 -
TruPrint 3000 1 fiber 500 f300 × 400 2 5–60 20–150 -
TruPrint 5000 3 fiber 500 f300 × 400 2 5–180 30–150 -
1 Height includes the thickness of the substrate/building plate. 2 Diameter × height.

Table 2. Materials the current machines L-PBF machines can be set in for upon installation [10][11][12][13][14][15][16].

Manu-
facturer		 Model Powder Metals Based on…
Al Co Cu Fe Ni Ti W
3D
Systems		 DMP Factory 500 Printer Module By request Nickel alloys By request
DMP Factory/Flex 350 AlSi7Mg0.6, AlSi10Mg CoCrF75 - Maraging Steel, 17-4PH, 316L Ni625, Ni718 Ti Gr1, Ti Gr5, Ti Gr23 -
DMP Flex 100 - CoCr - 17-4PH, 316L - - -
ProX DMP 300 AlSi12 CoCr - Maraging steel, 17-4PH - - -
ProX DMP 200 AlSi12 CoCr - Maraging steel, 17-4PH, 316 L - - -
Additive Industries MetalFAB1 AlSi10Mg, ScalmAlloy© - - Tool steel 1.2709, 316L IN718 Ti6Al4V -
Concept Laser X Line 2000R AlSi10Mg—Balanced & Productivity - - - Nickel 718 Ti6AL4V Grade 23 -
M Line Factory A205 CoCrMo - - Nickel 718 CL - -
M2 Multilaser AlSi10Mg, AlSi7Mg CoCrMo - Maraging M300, 316L, 17-4PH Nickel 625, Nickel 718 Ti6AL4V Grade 23 -
EOS EOS M 400-4 AlSi10Mg - - MS1, 316L HX, IN718 Ti64, TiCP Grade 2 -
EOS M 400 AlSi10Mg - - MS1 IN718 Ti64, Ti64ELI -
EOS M 300-4 AlSi10Mg - - MS1 IN718 Ti64 -
EOS M 290 AlSi10Mg MP1 - MS1, CX, PH1, 17-4PH, 316L HX, IN625, IN718 Ti64, Ti64ELI, TiCP Grade 2 -
EOS M 100 - SP2 - 316L - Ti64 W1
SLM Solutions SLM®NXG XII 600 ALSi10Mg (No limitations) No limitations IN718 (No limit.) No limitations
SLM®800 AlSi10Mg, AlSi7Mg0.6, AlSi9Cu3 CoCr28Mo6, SLM® MediDent CuSn10, CuNi2SiCr Maraging 1.2709, 316L (1.4404), 15-5PH (1.4545), 17-4PH (1.4542), H13 (1.2344), Invar 36® HX, IN625, IN718, IN939 Ti6Al4V ELI (Grade 23), TA15, and Ti (Grade 2) -
SLM®500
SLM®280
SLM®125
Renishaw RenAM 500Q/S AlSi10Mg CoCr - Maraging M300, 316L IN625, IN718 Ti6Al4ELI -
RenAM 500E
RenAM 500M
AM 400
AM 250
Trumpf TruPrint 1000 Yes to all except W + precious metal alloys + amorphous metals
TruPrint 2000 Yes to all except Cu and W + amorphous metals
TruPrint 3000 Yes to all except Co, Cu and W
TruPrint 5000 Yes to all except Co, Cu and W

2. Tool Design for Metal Additive Manufacturing by L-PBF

Additive manufacturing provides significantly larger design freedom (compared to conventional manufacturing), the benefits of which can be maximized by the emerging computer-aided design (CAD) technologies like generative design (GD). It is now possible to:
(1) Generate a wide range of design alternatives by artificial intelligence-based algorithms (GD software) after setting the part/object design space, constraints, criteria and objectives. The designer reviews the different design options and chooses the best-suited for the application [17][18].
(2) Topology optimize the selected design alternative, the purpose of which is to remove unnecessary material while meeting (or exceeding) the performance criteria. The goal is to optimize a part properly (weight, stiffness, frequency …) while respecting a certain set of constraints. The topology optimization process uses various mathematical algorithms and methods (each having several versions) [19][20][21][22].
(3) Optimize the internal lattice and surface structure of the topology optimized object by creating an internal mesh while meeting (or exceeding) the performance criteria [23][24][25][26].
(4) Produce this complex object by L-PBF (and post-processing).
During the past two decades, different new design methodologies have emerged, among them the Design for X (DfX). X represents a particular perspective to improve during the product design as well as the design process [27][28]. DfX applied to the Additive Manufacturing process is named DfAM. It aims at using the full potential of the AM technologies for design, for which there are two methods [18][29][30].
A new detailed DfAM process has been proposed including the available design support (methods, design rules, guidelines and software tools), the tools and methods that are best suited at different stages of the design process are specified, and the possibility to achieve a more automated DfAM is indicated [31].
As far as the L-PBF process design (i.e., the preparation of the L-PBF process) is concerned, the part orientation, support structures, overhangs and part supporting angles, channels and holes, wall thickness, tolerances and offsets are addressed in [32][33][34]. VDI 3405 Part 2, [32], addresses the qualification, quality assurance and post processing. The procedure described in this standard is applied to DIN 1.2709 in a VDI inter-laboratory test. The obtained properties in this inter-laboratory test are accounted for in [32].
The angle between the building platform and the building direction is also of great significance for the properties of the as-built object. In other words, the properties of the as-built object are anisotropic due to the layered manufacturing, the loading direction etc. Table 11 and Figure 7 display 7 different configurations, in which tensile specimens in 316L (1.4404) were built with an oversize of 0.4 mm in width and thickness. After milling to final shape, the specimens were tested. Table 12 displays the tensile properties of these specimens. The maximum strength is obtained at a 45° layer versus loading offset [35].
Figure 7. The tensile samples in 1.4404 (316L) on the building platform: overview of the positioning, building angles and arrangement (configurations). See also Table 11 and Table 12. The figure is from [35].
Table 11. The tested configurations. See also Figure 7 and Table 12. The table is from [35].
Config. Polar Angle Φ; αXY (°) Azimuth Angle Θ; αX (°) Total Runtime (h)
(a) 0 0 -
(b) 0 90 39.5
(c) 15 0 -
(d) 45 0 -
(e) 75 0 86.5
(f) 90 0 -
(g) 90 90 -

Table 12. The tensile properties of 1.4404 (316L) in different building configurations. See also Table 11 and Figure 7. The specimens were built with an oversize of 0.4 mm in width and thickness and milled to final shape before tensile testing. The table is from [35].

Config. Young’s Modulus Yield Strength Ultimate Tensile Elongation at Poisson’s Ratio
E (GPa) Rp0.2 (MPa) Strength Rm (MPa) Failure At (%) ν (-)
Average STDEV Average STDEV Average STDEV Average STDEV Average STDEV
(a) 151.01 25.56 516.51 7.16 634.43 7.39 33.24 0.57 0.444 0.031
(b) 207.57 24.22 539.47 3.29 643.67 3.25 42.74 0.82 0.155 0.014
(c) 147.87 23.59 501.32 7.70 624.65 4.36 34.09 1.12 0.479 0.058
(d) 227.35 25.12 589.89 11.86 698.98 23.65 32.56 10.17 0.203 0.024
(e) 151.43 18.80 485.65 11.93 571.23 18.63 22.84 7.27 0.558 0.020
(f) 137.78 14.25 438.60 9.69 511.99 17.95 11.76 5.38 0.453 0.005
(g) 137.83 16.25 457.21 17.29 530.22 8.09 17.46 4.42 0.170 0.085

Design demands knowledge of the precise material properties. These properties are anisotropic and the component orientation on the build platform needs therefore to be considered [35]. (Post L-PBF heat treatment affects also these properties. See the properties of 316L (1.4404) before and after heat treatment in Table 7.)

It is possible to achieve ±0.2% in tolerance, with the minimal value being 0.2 mm. It is also possible to achieve a wall thickness of 0.5 mm. However, the wall shape is dependent upon the orientation, its height (in relation to the thickness), and the possibility to have support if needed. As far as gaps (between walls or solid portions) are concerned, the minimum gap width should be larger than at least the melt pool width. It is also important to add an allowance of 0.3–0.5 mm to the locations and surfaces that require post-processing by machining to reach the required tolerance and surface roughness [24][32].

This entry is adapted from the peer-reviewed paper 10.3390/met11030458

References

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  2. ISO. International Standard ISO 52900, 2016—Additive manufacturing—General principles—Terminology (ISO/ASTM 52900, 2015, IDT); ISO: Geneva, Switzerland, 2016.
  3. ISO. International Standard ISO 17296-2, 2016—Additive manufacturing—General principles—Part 2, Overview of process categories and feedstock (ISO 17296-2, 2015); ISO: Geneva, Switzerland, 2016.
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  10. 3D Systems, Printers and Materials Specifications. Available online: (accessed on 27 November 2020).
  11. Additive Industries, Printers and Materials Specifications. Available online: (accessed on 27 November 2020).
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  13. EOS (Electro Optical Systems), Printers and Materials Specifications. Available online: (accessed on 27 November 2020).
  14. SLM Solutions, Printers and Materials Specifications. Available online: (accessed on 27 November 2020).
  15. Renishaw, Printers and Materials Specifications. Available online: (accessed on 27 November 2020).
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  19. Bendsoe, M.P.; Sigmund, O. Topology Optimization: Theory, Methods and Applications; Springer: Berlin/Heidelberg, Germany, 2004.
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  21. Zhao, F. A nodal variable ESO (BESO) method for structural topology optimization. Finite Elem. Anal. Des. 2014, 86, 34–40.
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