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Research Papers

Effect of Thermal Deformation on Part Errors in Metal Powder Based Additive Manufacturing Processes

[+] Author and Article Information
Ratnadeep Paul

Center for Global Design and Manufacturing,
School of Dynamic Systems,
Mechanical Engineering Program,
University of Cincinnati,
Cincinnati, OH 45221
e-mail: paulrp@ucmail.uc.edu

Sam Anand

Center for Global Design and Manufacturing,
School of Dynamic Systems,
Mechanical Engineering Program,
University of Cincinnati,
Cincinnati, OH 45221
e-mail: sam.anand@uc.edu

Frank Gerner

Microscale Heat Transfer Lab,
School of Dynamic Systems,
Mechanical Engineering Program,
University of Cincinnati,
Cincinnati, OH 45221
e-mail: frank.gerner@uc.edu

1Corresponding author.

Manuscript received May 1, 2013; final manuscript received January 16, 2014; published online March 26, 2014. Assoc. Editor: Yung Shin.

J. Manuf. Sci. Eng 136(3), 031009 (Mar 26, 2014) (12 pages) Paper No: MANU-13-1211; doi: 10.1115/1.4026524 History: Received May 01, 2013; Revised January 16, 2014

In metal additive manufacturing (AM) processes, parts are manufactured in layers by sintering or melting metal or metal alloy powder under the effect of a powerful laser or an electron beam. As the laser/electron beam scans the powder bed, it melts the powder in successive tracks which overlap each other. This overlap, called the hatch overlap, results in a continuous cycle of rapid melting and resolidification of the metal. The melting of the metal from powder to liquid and subsequent solidification causes anisotropic shrinkage in the layers. The thermal strains caused by the thermal gradients existing between the different layers and between the layers and the substrate leads to considerable thermal stresses in the part. As a result, stress gradients develop in the different directions of the part which lead to distortion and warpage in AM parts. The deformations due to shrinkage and thermal stresses have a significant effect on the dimensional inaccuracies of the final part. A three-dimensional thermomechanical finite element (FE) model has been developed in this paper which calculates the thermal deformation in AM parts based on slice thickness, part orientation, scanning speed, and material properties. The FE model has been validated and benchmarked with results already available in literature. The thermal deformation model is then superimposed with a geometric virtual manufacturing model of the AM process to calculate the form and runout errors in AM parts. Finally, the errors in the critical features of the AM parts calculated using the combined thermal deformation and geometric model are correlated with part orientation and slice thickness.

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Figures

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Fig. 1

Overall methodology for thermal distortion based error modeling

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Fig. 3

3D Schematic of the thermomechanical model

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Fig. 5

Thermal boundary condition

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Fig. 6

(a) Structural boundary condition during deposition of layers, (b) structural boundary condition after deposition of all layers: first case and (c) structural boundary condition after deposition of all layers: second case

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Fig. 7

Schematic for validating FEA model

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Fig. 8

Geometric virtual manufacturing model

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Fig. 9

Error in surface point location due to thermal deformation

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Fig. 11

Cylindricity error

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Fig. 12

Circularity error evaluation

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Fig. 13

Total runout error evaluation

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Fig. 14

Circular runout error evaluation

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Fig. 17

FEA result: deformed shape of (a) test part 1 and (b) test part 2

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Fig. 18

Vertical nodal displacement (mm) map for test part 1, (a) 0 deg part orientation, (b) 30 deg orientation, and (c) 45 deg orientation

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Fig. 19

Vertical nodal displacement (mm) map for test part 2, (a) 0 deg part orientation, (b) 45 deg orientation, and (c) 60 deg orientation

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Fig. 20

(a) Virtually manufactured geometry of test part 1 at 45 deg orientation, (b) points sampled from cylindrical feature, C2, and (c) points sampled from planar feature, F2

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Fig. 21

(a) Virtually manufactured geometry of test part 2 at 45 deg orientation, (b) points sampled from cylindrical feature, C2, and (c) points sampled from planar feature, F2

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Fig. 22

Flatness error for test part 1

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Fig. 23

Flatness error for test part 2

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Fig. 24

Cylindricity error for test part 1

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Fig. 25

Cylindricity error for test part 2

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Fig. 26

Circularity error at different locations from the base of the feature, test part 1

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Fig. 27

Circularity error at different locations from the base of the feature, test part 2

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Fig. 28

Circular runout error at different locations from the base of the feature, test part 1

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Fig. 29

Circular runout error at different locations from the base of the feature, test part 2

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Fig. 30

Runout error for test parts 1 and 2

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