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PAPERS: Process Planning Considerations for AM

Build Direction Effects on Microchannel Tolerance and Surface Roughness

[+] Author and Article Information
Jacob C. Snyder

Department of Mechanical
and Nuclear Engineering,
Penn State University,
START Lab,
3127 Research Drive,
State College, PA 16801
e-mail: jacob.snyder@psu.edu

Curtis K. Stimpson

Department of Mechanical
and Nuclear Engineering,
Penn State University,
START Lab,
3127 Research Drive,
State College, PA 16801
e-mail: curtis.stimpson@psu.edu

Karen A. Thole

Department of Mechanical
and Nuclear Engineering,
Penn State University,
136 Reber Building, University Park, PA 16802
e-mail: kthole@psu.edu

Dominic J. Mongillo

Pratt and Whitney,
400 Main Street,
East Hartford, CT 06118

Contributed by the Design for Manufacturing Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received March 4, 2015; final manuscript received July 7, 2015; published online October 12, 2015. Assoc. Editor: Christopher Williams.

J. Mech. Des 137(11), 111411 (Oct 12, 2015) (7 pages) Paper No: MD-15-1190; doi: 10.1115/1.4031071 History: Received March 04, 2015; Revised July 07, 2015

With the advance of additive manufacturing (AM) processes, complex designs can be created with engineering metals. One specific advantage of this greater design space is the ability to create small internal channels and passageways for cooling high heat flux or temperature applications such as electronics and gas turbine airfoils. These applications can have complex shapes, which when coupled with the required small channel sizes, make traditional finishing processes a challenge for additively manufactured parts. Therefore, it is desirable for designers to be able to use AM parts with small internal channels that are as-built. To achieve this goal, however, designers must know how the AM process affects internal channel tolerances and roughness levels, since both impact the amount of cooling that can be achieved in actual applications. In this study, the direct metal laser sintering (DMLS) process, more generically referred to as selective laser melting (SLM), was used to additively manufacture test coupons. The AM build direction was varied to study its effect on small microsized, circular channels. Specifically, X-ray computed tomography (CT-scan) was used to nondestructively inspect the interior of the test coupons. Using the data from the CT-scans, internal surface roughness, geometric tolerances, and deviations from the computer-aided design (CAD) model were calculated. In comparing the data, significant differences were seen between the three different build directions.

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Figures

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Fig. 1

Designed dimensions, shape, and channel spacing of the test coupons

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Fig. 2

Coupon orientation and support structures (shown in red/darker gray) for the (a) vertical, (b) horizontal, and (c) diagonal build directions

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Fig. 3

Geometric tolerance definitions for (a) concentricity, (b) circularity, and (c) total runout

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Fig. 4

A slice taken along the channel axis showing the roughness features and surface fit for one plane of the vertically built channel surface

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Fig. 5

Comparison of surface roughness contours from (a) an optical profilometer and (b) a CT scanner showing features missing in CT scan data

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Fig. 6

Distribution of the difference between the coupon surface points and the CAD model for the three different build directions

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Fig. 7

Three-dimensional surfaces representing the internal channel topology of a single channel for the (a) vertical, (b) horizontal, and (c) diagonal build directions

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Fig. 8

Axial slices at various streamwise locations of (a) vertically, (b) horizontally, and (c) diagonally built channels

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