increase occurred between one cube-shaped core and two cylindrical cores. For 3-D sand printing, it also was observed that at lower levels of complexity the fabrication cost was higher than that of conventional manufacturing. Unlike the previous case study, the 3-D sand printing cost does not ‘‘level out’’ because the volume of the cores is significantly increased due to the cylinders and the final core geometry. For complexity factor
Figure 8. Tooling costs as a function of complexity is shown for Case Study 2.
values greater than 51, the fabrication cost of 3-D sand printing is lower than conventional mold making. As the final three core geom- etries were approached, the 3-D sand printed cores were consolidated into a single core providing a cost advantage over conventional moldmaking. Figure 10 presents the combined ef-
fects of tooling and fabrication costs and part design complexity factor. For pro- duction volume of less than 26 castings, 3-D sand printing is more affordable than conventional patternmaking even in the case of casting without any cores. However, for production volume
greater than 26 castings, it depends on the level of part-core complex- ity. As seen in the Case Study 1, the breakeven point shifts to increasing
levels of complexity as the quantity increases. In the case of 1,000 castings, as observed in Case Study 1, the tool- ing cost per mold/set is significantly lower since fabrication costs is more significant and the scenario is very similar to Figure 9.
Future Work In order to accelerate the adop-
tion of emerging technology such as 3-D sand printing in the metalcasting industry, this study recommends future work to examine the combinations of conventional patternmaking and 3-D sand printing for a single casting. For example, the economics of using conventional patterns for molds and 3-D sand printing for complex cores
could be explored. Further, economics and fabrication time associated with using alternative additive manu- facturing technologies for patternmaking such as ma- terial extrusion (also known as fused deposition model- ing) could be explored. Tis study assumed the 3-D sand molds and cores printing provided an equivalent surface finish and sand performance with traditional pattern making for mold and core manufacturing. However, an extension to this study would focus on incorporat-
ing additional factors to incorporate such attributes. Tus, evaluation of such factors can be achieved by measuring surface finish and testing of physical and mechanical properties. Tis work will give additional evalua- tion criteria for both approaches along with estimated cost. Finally, incorporating these results
into a CAD–CAM software system would be immediately beneficial. Te end user should be able to plug in the geometric attributes of the castings as shown in Table 1 and input cost parameters such as materials, consum- ables, labor, depreciation and other costs for both patternmaking and 3-D sand printing.
Figure 9. The fabrication costs for Case Study 2 for 3-D sand printing costs and conventional patternmaking are shown.
Figure 10. This chart depicts the total costs (tooling and fab- rication) for Case Study 2 where conventional patternmaking costs are shown for quantities of 26, 100 and 1,000 units.
Nov/Dec 2016 | METAL CASTING DESIGN & PURCHASING | 29
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