# A Novel Digital Design Approach for Metal Additive Manufacturing to Address Local Thermal Effects

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## Abstract

**:**

## 1. Introduction

## 2. Design Approach Overview

#### 2.1. Digital Design Approach for Metal AM That Addresses Thermal Effects

#### 2.2. Design Optimization and Analysis Steps

^{6}Pa and 0.4, respectively. TFor the current study, a 3D density-based topology optimization formulation, native to the TOSCA module, was used. This gradient-based formulation uses analytic sensitivity approaches similar to most TO methods for computing the derivatives of the objective and constraints. A mesh independent filter is used for filtering the output [44]. For the current study, the objective for the topology optimization problem was to minimize the compliance of the domain. A constraint was applied to limit the volume to 50% of the original. The optimized output was then thresholded to retain only those elements that had a volume fraction of 70% or more. This process was included to reduce any partial density elements and increase the overall solidity of the structure. The thresholding process can lead to jagged surfaces which were smoothed out in this investigation by simplifying the optimized domain. To accomplish this goal, the thresholded domain was exported from Tosca in a compatible mesh format and the optimized domain was recreated using splines in a CAD environment.

#### 2.3. Process Simulation Step

#### 2.4. Lattice Introduction Step

#### 2.5. Lattice Optimization Step

## 3. Results

#### 3.1. Topology Optimization

#### 3.2. Process Simulations

#### 3.3. Lattice Introduction

^{3}and the mass being replaced was 0.19 kg which gave an effective density of the lattice region to be around 0.0041 g/mm

^{3}. The angle of the struts is critical for accurate and supportless manufacturing. Lattice-types considered for this purpose are the ‘X’, ‘W’ and ‘star’ (Table 2) as these lattice unit cells within the Netfabb suite can be modified to be manufactured without any supports.

#### 3.4. Lattice Optimization

#### 3.5. Effect of Lattice on Hotspot

## 4. Discussion

#### 4.1. Topology Optimization and CAD Generation

^{5}mm

^{3}according to the given dimensions. The optimization reduces the volume to 49.9% of the original, resulting to a volume of 3.37 × 10

^{5}mm

^{3}. Thresholding of the optimized geometry further reduces the optimum value of the volume. However, this step is required to reduce the size of the domain and to accurately define a CAD model. For this geometry, it was found that the thresholding value of 0.7 allows for a close approximation of the optimized domain. Another approach to simplify the optimized geometry would have been to use a shape optimization procedure, however, the large number of design variables would lead to a very large computational time in the Tosca environment hence a manual simplification was opted for.

#### 4.2. Lattice Optimization

#### 4.3. Process Simulations

#### 4.4. Advantages and Limitations of Proposed Methodology

## 5. Conclusions

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

- Yan, R.; Luo, D.; Huang, H.; Li, R.; Yu, N.; Liu, C.; Hu, M.; Rong, Q. Electron beam melting in the fabrication of three-dimensional mesh titanium mandibular prosthesis scaffold. Sci. Rep.
**2018**, 8, 1–10. [Google Scholar] [CrossRef][Green Version] - Zadpoor, A.A.; Malda, J. Additive Manufacturing of Biomaterials, Tissues, and Organs. Ann. Biomed. Eng.
**2016**, 45, 1–11. [Google Scholar] [CrossRef] - Orme, M.; Madera, I.; Gschweitl, M.; Ferrari, M. Topology Optimization for Additive Manufacturing as an Enabler for Light Weight Flight Hardware. Designs
**2018**, 2, 51. [Google Scholar] [CrossRef][Green Version] - Chadha, C.; Crowe, K.A.; Carmen, C.L.; Patterson, A.E. Exploring an AM-Enabled Combination-of-Functions Approach for Modular Product Design. Designs
**2018**, 2, 37. [Google Scholar] [CrossRef][Green Version] - Singamneni, S.; Lv, Y.; Hewitt, A.; Chalk, R.; Thomas, W.; Jordison, D. Additive Manufacturing for the Aircraft Industry: A Review. J. Aeronaut. Aerosp. Eng.
**2019**, 8, 1–13. [Google Scholar] [CrossRef][Green Version] - Wieding, J.; Jonitz, A.; Bader, R. The Effect of Structural Design on Mechanical Properties and Cellular Response of Additive Manufactured Titanium Scaffolds. Materials
**2012**, 5, 1336–1347. [Google Scholar] [CrossRef] - Bose, S.; Robertson, S.F.; Bandyopadhyay, A. Surface modification of biomaterials and biomedical devices using additive manufacturing. Acta Biomater.
**2018**, 66, 6–22. [Google Scholar] [CrossRef] - Gibson, L.J.; Ashby, M.F. Cellular Solids: Structure and Properties; Cambridge University Press: Cambridge, UK, 1997. [Google Scholar]
- Carroll, B.E.; Palmer, T.A.; Beese, A.M. Anisotropic tensile behavior of Ti-6Al-4V components fabricated with directed energy deposition additive manufacturing. Acta Mater.
**2015**, 87, 309–320. [Google Scholar] [CrossRef] - Evans, A.; Hutchinson, J.; Ashby, M. Multifunctionality of cellular metal systems. Prog. Mater. Sci.
**1998**, 43, 171–221. [Google Scholar] [CrossRef] - Wauthle, R.; Vrancken, B.; Beynaerts, B.; Jorissen, K.; Schrooten, J.; Kruth, J.-P.; Van Humbeeck, J. Effects of build orientation and heat treatment on the microstructure and mechanical properties of selective laser melted Ti6Al4V lattice structures. Addit. Manuf.
**2015**, 5, 77–84. [Google Scholar] [CrossRef] - DebRoy, T.; Wei, H.L.; Zuback, J.S.; Mukherjee, T.; Elmer, J.W.; Milewski, J.O.; Beese, A.M.; Wilson-Heid, A.; De, A.; Zhang, W. Additive manufacturing of metallic components–Process, structure and properties. Prog. Mater. Sci.
**2018**, 92, 112–224. [Google Scholar] [CrossRef] - Murr, L.; Gaytan, S.M.; Ramirez, D.A.; Martinez, E.; Hernandez, J.; Amato, K.N.; Shindo, P.W.; Medina, F.R.; Wicker, R.B. Metal Fabrication by Additive Manufacturing Using Laser and Electron Beam Melting Technologies. J. Mater. Sci. Technol.
**2012**, 28, 1–14. [Google Scholar] [CrossRef] - Calignano, F. Investigation of the accuracy and roughness in the laser powder bed fusion process. Virtual Phys. Prototyp.
**2018**, 13, 97–104. [Google Scholar] [CrossRef] - Saboori, A.; Aversa, A.; Marchese, G.; Biamino, S.; Lombardi, M.; Fino, P. Microstructure and Mechanical Properties of AISI 316L Produced by Directed Energy Deposition-Based Additive Manufacturing: A Review. Appl. Sci.
**2020**, 10, 3310. [Google Scholar] [CrossRef] - Beese, A.M.; Carroll, B.E. Review of Mechanical Properties of Ti-6Al-4V Made by Laser-Based Additive Manufacturing Using Powder Feedstock. JOM
**2015**, 68, 724–734. [Google Scholar] [CrossRef] - Gaynor, A.T.; Guest, J.K. Topology optimization considering overhang constraints: Eliminating sacrificial support material in additive manufacturing through design. Struct. Multidiscip. Optim.
**2016**, 54, 1157–1172. [Google Scholar] [CrossRef] - Langelaar, M. An additive manufacturing filter for topology optimization of print-ready designs. Struct. Multidiscip. Optim.
**2016**, 55, 871–883. [Google Scholar] [CrossRef][Green Version] - Wang, C.; Qian, X. Simultaneous optimization of build orientation and topology for additive manufacturing. Addit. Manuf.
**2020**, 34. [Google Scholar] [CrossRef] - Han, Y.; Xu, B.; Zhao, L.; Xie, Y.M. Topology optimization of continuum structures under hybrid additive-subtractive manufacturing constraints. Struct. Multidiscip. Optim.
**2019**, 60, 2571–2595. [Google Scholar] [CrossRef] - Manogharan, G.; Wysk, R.; Harrysson, O.; Aman, R. AIMS-A Metal Additive-hybrid Manufacturing System: System Architecture and Attributes. Procedia Manuf.
**2015**, 1, 273–286. [Google Scholar] [CrossRef][Green Version] - Panesar, A.; Abdi, M.; Hickman, D.; Ashcroft, I. Strategies for functionally graded lattice structures derived using topology optimisation for Additive Manufacturing. Addit. Manuf.
**2018**, 19, 81–94. [Google Scholar] [CrossRef] - Echeta, I.; Feng, X.; Dutton, B.; Leach, R.; Piano, S. Review of defects in lattice structures manufactured by powder bed fusion. Int. J. Adv. Manuf. Technol.
**2019**, 106, 2649–2668. [Google Scholar] [CrossRef][Green Version] - Pasini, D.; Guest, J.K. Imperfect architected materials: Mechanics and topology optimization. MRS Bull.
**2019**, 44, 766–772. [Google Scholar] [CrossRef] - Miki, T.; Yamada, T. Topology optimization for considering distortion in additive manufacturing. Struct. Multidiscip. Optim.
**2020**. [Google Scholar] [CrossRef] - Liu, J.; Gaynor, A.T.; Chen, S.; Kang, Z.; Suresh, K.; Takezawa, A.; Li, L.; Kato, J.; Tang, J.; Wang, C.C.L.; et al. Current and future trends in topology optimization for additive manufacturing. Struct. Multidiscip. Optim.
**2018**, 57, 2457–2483. [Google Scholar] [CrossRef][Green Version] - Li, C.; Liu, Z.; Fang, X.; Guo, Y.B. Residual Stress in Metal Additive Manufacturing. Procedia CIRP
**2018**, 71, 348–353. [Google Scholar] [CrossRef] - Simson, T.; Emmel, A.; Dwars, A.; Böhm, J. Residual stress measurements on AISI 316L samples manufactured by selective laser melting. Addit. Manuf.
**2017**, 17, 183–189. [Google Scholar] [CrossRef] - Baufeld, B.; Biest, O.; Gault, R. Additive manufacturing of Ti-6Al-4V components by shaped metal deposition: Microstructure and mechanical properties. Mater. Des.
**2010**, 31, S106–S111. [Google Scholar] [CrossRef] - Shao, J.; Yu, G.; He, X.; Li, S.; Chen, R.; Zhao, Y. Grain size evolution under different cooling rate in laser additive manufacturing of superalloy. Opt. Laser Technol.
**2019**, 119. [Google Scholar] [CrossRef][Green Version] - Gockel, J.; Beuth, J.; Taminger, K. Integrated control of solidification microstructure and melt pool dimensions in electron beam wire feed additive manufacturing of Ti-6Al-4V. Addit. Manuf.
**2014**, 1, 119–126. [Google Scholar] [CrossRef] - Monkova, K.; Monka, P. Qualitative parameters of complex part produced by additive approach. In Proceedings of the 2017 8th International Conference on Mechanical and Aerospace Engineering (ICMAE), Prague, Czech Republic, 22–25 July 2017; Institute of Electrical and Electronics Engineers (IEEE): Prague, Czech Republic, 2017; pp. 691–694. [Google Scholar]
- Gouge, M.; Denlinger, E.; Irwin, J.; Li, C.; Michaleris, P. Experimental validation of thermo-mechanical part-scale modeling for laser powder bed fusion processes. Addit. Manuf.
**2019**, 29, 100771. [Google Scholar] [CrossRef] - Cheng, L.; To, A.C. Part-scale build orientation optimization for minimizing residual stress and support volume for metal additive manufacturing: Theory and experimental validation. Comput. Des.
**2019**, 113, 1–23. [Google Scholar] [CrossRef] - Choo, H.; Sham, K.-L.; Bohling, J.; Ngo, A.; Xiao, X.; Ren, Y.; Depond, P.; Matthews, M.J.; Garlea, E. Effect of laser power on defect, texture, and microstructure of a laser powder bed fusion processed 316L stainless steel. Mater. Des.
**2019**, 164, 107534. [Google Scholar] [CrossRef] - Zhang, B.; Meng, W.J.; Shamsaei, N.; Phan, N.; Shamsaei, N. Effect of heat treatments on pore morphology and microstructure of laser additive manufactured parts. Mater. Des. Process. Commun.
**2019**, 1, e29. [Google Scholar] [CrossRef][Green Version] - Bobbio, L.D.; Qin, S.; Dunbar, A.; Michaleris, P.; Beese, A.M. Characterization of the strength of support structures used in powder bed fusion additive manufacturing of Ti-6Al-4V. Addit. Manuf.
**2017**, 14, 60–68. [Google Scholar] [CrossRef] - Ranjan, R.; Yang, Y.; Ayas, C.; Langelaar, M.; Van Keulen, F. Controlling local overheating in topology optimization for additive manufacturing. In Proceedings of the Euspen Special Interest Group Meeting: Additive Manufacturing, Leuven, Belgium, 10–11 October 2017. [Google Scholar]
- Son, K.N.; Weibel, J.A.; Kumaresan, V.; Garimella, S.V. Design of multifunctional lattice-frame materials for compact heat exchangers. Int. J. Heat Mass Transf.
**2017**, 115, 619–629. [Google Scholar] [CrossRef][Green Version] - Cheng, L.; Liu, J.; Liang, X.; To, A.C. Coupling lattice structure topology optimization with design-dependent feature evolution for additive manufactured heat conduction design. Comput. Methods Appl. Mech. Eng.
**2018**, 332, 408–439. [Google Scholar] [CrossRef] - Lynch, M.E.; Mordasky, M.; Cheng, L.; To, A. Design, testing, and mechanical behavior of additively manufactured casing with optimized lattice structure. Addit. Manuf.
**2018**, 22, 462–471. [Google Scholar] [CrossRef] - Sidambe, A.T. Biocompatibility of Advanced Manufactured Titanium Implants-A Review. Materials
**2014**, 7, 8168–8188. [Google Scholar] [CrossRef][Green Version] - Najafi, A.R.; Safdari, M.; Tortorelli, D.A.; Geubelle, P. Shape optimization using a NURBS-based interface-enriched generalized FEM. Int. J. Numer. Methods Eng.
**2017**, 111, 927–954. [Google Scholar] [CrossRef] - Zuo, Z.H.; Xie, Y. A simple and compact Python code for complex 3D topology optimization. Adv. Eng. Softw.
**2015**, 85, 1–11. [Google Scholar] [CrossRef] - Cheng, B.; Shrestha, S.; Chou, Y.K. Stress and Deformation Evaluations of Scanning Strategy Effect in Selective Laser Melting. Processing
**2016**, 12. [Google Scholar] [CrossRef] - Dunbar, A.J.; Denlinger, E.R.; Gouge, M.F.; Michaleris, P. Experimental validation of finite element modeling for laser powder bed fusion deformation. Addit. Manuf.
**2016**, 12, 108–120. [Google Scholar] [CrossRef] - Denlinger, E.R.; Gouge, M.; Irwin, J.; Michaleris, P. Thermomechanical model development and in situ experimental validation of the Laser Powder-Bed Fusion process. Addit. Manuf.
**2017**, 16, 73–80. [Google Scholar] [CrossRef] - Brown, W.F.; Mindlin, H.; Ho, C.Y. Aerospace Structural Metals Handbook; CINDAS/Purdue University: West Lafayette, IN, USA, 1995. [Google Scholar]
- Xiao, H. 11.5.2.1 Thermal Evaporation. In Introduction to Semiconductor Manufacturing Technology; Society of Photo-Optical Instrumentation Engineers (SPIE): Bellingham, WA, USA, 2012; p. 485. [Google Scholar]
- Zhang, G.; Chen, J.; Zheng, M.; Yan, Z.; Lu, X.; Lin, X.; Huang, W. Element Vaporization of Ti-6Al-4V Alloy during Selective Laser Melting. Metals
**2020**, 10, 435. [Google Scholar] [CrossRef][Green Version] - Rai, R.; Elmer, J.W.; Palmer, T.A.; Debroy, T. Heat transfer and fluid flow during keyhole mode laser welding of tantalum, Ti-6Al-4V, 304L stainless steel and vanadium. J. Phys. D Appl. Phys.
**2007**, 40, 5753–5766. [Google Scholar] [CrossRef][Green Version] - Hooper, P. Melt pool temperature and cooling rates in laser powder bed fusion. Addit. Manuf.
**2018**, 22, 548–559. [Google Scholar] [CrossRef] - Cheng, L.; Liu, J.; To, A.C. Concurrent lattice infill with feature evolution optimization for additive manufactured heat conduction design. Struct. Multidiscip. Optim.
**2018**, 58, 511–535. [Google Scholar] [CrossRef]

**Figure 1.**Proposed digital design approach for metal additive manufacturing to address thermal effects.

**Figure 3.**The isometric and planar views of the ‘X’ lattice (

**left**), ‘W’ lattice (

**center**) and the ‘Star’ lattice (

**right**). The overhang angles for the members are ensured to be more than 45 degrees from the horizontal to ensure supportless printing.

**Figure 4.**(

**a**) Evolution of the design domain using topology optimization and (

**b**) the history plot of the compliance and volume for the optimization process.

**Figure 5.**(

**a**) Domain simplification methodology by using the output from topology optimization, thresholding the mesh to a user-specified partial density, designing a simplified CAD geometry using splines for introduction of lattices. (

**bottom**) Static analysis plot shown the von Mises stress for (

**b**) the original design domain and (

**c**) the topology optimized output.

**Figure 6.**Hot spot contour plot from a process simulation of the optimized geometry. The inset shows the region with the highest thermal accumulations in terms of the percentage of finite element volume.

**Figure 7.**Identification of region for lattice introduction by using: (

**a**) the isolines of the hotspot volume in printing, (

**b**) the von Mises stress buildup in the part during printing, (

**c**) the von Mises stress experienced by the optimized cantilever part during static loading and (

**d**) the manufacturing constraints of minimum overhang angle and clearance from the base to create (

**e**) the partitioned domain. The dotted arrows indicate the region to be considered for lattice introduction. Continuous black lines are fixed. Dotted black lines can be adjusted to accommodate the changing parameters for a given setup (e.g., varying hotspot buildup (a) for the same part using different process parameters or different allowable overhang angles for different selective laser melting (SLM) machines (d)).

**Figure 8.**Lattice optimization iterations and the evolution of the lattice thickness in iterations 1, 10 and 49 shown in (

**a**), (

**b**) and (

**c**) respectively; (

**d**) the convergence history of the optimization.

**Figure 9.**Comparing the hotspot observed in (

**a**) the optimized domain and (

**b**) the ‘X’ lattice introduced optimized domain. The inset in (a) shows the regions affected by the hotspot and in (b) the effect of lattice introduction

**Figure 10.**Comparing the hotspot observed in the optimized domain and the lattice introduced optimized domains using the ‘X’, ‘W’ and ‘Star’ lattices. The insets in

**(X)**,

**(W)**and

**(Star)**shows the effect of the different lattices on the hotspots.

Parameters | Value |
---|---|

SLM Printer model | EOS M 290 |

Laser Power (Watts) | 250 |

Heat source absorption efficiency (%) | 40 |

Laser beam diameter (mm) | 0.15 |

Travel speed (mm/s) | 1000 |

Layer thickness (mm) | 0.04 |

Hatch spacing (mm) | 0.15 |

Interlayer rotation angle | 67° |

Lattice Parameters | Value |
---|---|

Unit cell | X/W/Star |

Unit cell dimension (mm) | 15 × 10 × 10 |

Min. beam radius (mm) | 1 |

Max. beam radius (mm) | 4 |

Parameters | Topology Optimized Beam | TO Beam with X Lattice | TO Beam with W Lattice | TO Beam with Star Lattice |
---|---|---|---|---|

Part Volume (cm^{3}) | 307.75 | 267.73 | 272.21 | 269.85 |

Support Volume (cm^{3}) | 8.16 | 8.95 | 8.94 | 8.96 |

Build time (hhh:mm:ss) | 84:21:59 | 76:30:55 | 77:24:51 | 77:47:56 |

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## Share and Cite

**MDPI and ACS Style**

I. Perumal, V.; R. Najafi, A.; Kontsos, A. A Novel Digital Design Approach for Metal Additive Manufacturing to Address Local Thermal Effects. *Designs* **2020**, *4*, 41.
https://doi.org/10.3390/designs4040041

**AMA Style**

I. Perumal V, R. Najafi A, Kontsos A. A Novel Digital Design Approach for Metal Additive Manufacturing to Address Local Thermal Effects. *Designs*. 2020; 4(4):41.
https://doi.org/10.3390/designs4040041

**Chicago/Turabian Style**

I. Perumal, Vignesh, Ahmad R. Najafi, and Antonios Kontsos. 2020. "A Novel Digital Design Approach for Metal Additive Manufacturing to Address Local Thermal Effects" *Designs* 4, no. 4: 41.
https://doi.org/10.3390/designs4040041