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diameter circle and a nine-layer diam- eter circle, the CLI outputs confirmed that the slicing algorithm was indeed method C and an egg-shape distortion was present in the CLI file center and right-most image in Figure 5. For a layer thickness value of 0.011 in. (0.28 mm) a four-layer circle diameter would be 0.044 in. (1.12 mm).


Fig. 4. Screen distribution results of rounded silica sand are shown.


Selection of Test Diameters Diameters of 3/8, 1/2, 3/4, and 1


in. (9.525, 12.7, 19.05, 25.4 mm) were selected for testing. Tese values were rounded down to the closest full layer value possible, as shown in Table 1. Tese rounded down final values were used for testing. Te test geometry was positioned


Fig. 5. The initial determination of slicing method is shown. One the left is a three-layer diameter circle (orange), and right is a pre-cut three-layer diameter circle (orange). The middle circle is an example of the four-layered output, and right most circle is an example of a nine-layer output.


used in testing was 0.011 in. (0.28 mm). Te binder system used was a furan system. Te binder is a furfuryl alcohol with zero nitrogen and zero water. Te activator was a toluene sulfonic acid (TSA).


Determination of Slicing Method


Before the test geometry could be created, the exact method of slicing needed to be determined. Te com- mercial software supplied by the printer manufacturer was used to determine the slic- ing method employed. Tis software allowed the ability to view the CLI file with a dimensional overlay to confirm if the pre-cut model matched to a traditional model. Previously conducted


research determined that the printer only prints in full lay- ers. Te normal circle (NOR) was an STL output with no modifications (orange) and


Fig. 6. Measurement locations are indicated with proportionally equivalent upper and lower line segments.


the pre-cut circle (PRE) was designed to follow method C (cyan) left image as shown in Figure 5. When this technique was applied to a four-layer


vertically and horizontally to determine the outcome of the different print head resolutions on the 3-D sand printer and the influence of slicing on the final geometry shape. Each test geometry contained five samples. Te Y resolution was fixed at 0.0039


in. (0.1 mm). Te Z resolution has a range of 0.011-0.0197 in. (0.28- 0.5mm). However, the Z resolution was fixed for this testing at 0.011 in. (0.28 mm). Te X-resolution is selected based upon desired transverse or tensile strength. Te X-resolution has a range of 0.0004-0.006 in. (0.01- 0.16mm); the value of 0.0039 in. (0.10 mm) was selected to match the Y-resolution. Te test orientations selected were the YZ and XY plane. Te test samples were sectioned vertically between the NOR samples and the PRE samples for evaluation.


Positioning of


Measurement Points Te location of the mea-


surement points were selected to provide more data points in the lower and upper one-third of the circles. Te purpose of a denser data selection in these locations was to determine if the slope of the circle, when it was the shallowest, would cause more distortion in the printed circles. Te Y values


June 2017 MODERN CASTING | 37


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