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Table 2. Comparison of the Capabilities of Various Sand Casting Processes Case


study 1.0


1.1


1.2 1.3 1.4 1.5 1.6 1.7 1.8


Volume (in3


) Vp 209.16


Surface area (in2


Ap 229.77


162.49 319.56 144.47 383.45 131.76 421.96 123.11


481.40 513.95


) # of cores Nc


0 1


2 3


120.01 460.38 113.83 105.66


103.43 525.19


446.35 4 5 6 7 8


pecially true for low quantity produc- tion that would occur during product development. T e motivation of this study was to develop a model based on part design complexity, production volume and tooling-fabrication costs of coreboxes. T e developed model can be applied to evaluate the economic feasibility of traditional sand casting methods and 3-D sand printing for varied combinations of part designs and production volume.


The Complexity Factor T e methodology employed in this


study involves: • T e creation of CAD models for each casting design for evaluation.


• Quantifi cation of part design complexity in cast parts using a cri- terion adopted from a prior study.


• Estimation of fabrication costs associated with conventionally produced molds and cores and


¦ Cores volume (in3


) Nc 0


46.67 64.69 77.40 86.05 89.15 95.33


103.50 105.74


Min


thickness (in) Tmin


0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12


Max


thickness (in) Tmax


8.24 8.24 8.24 8.24 8.24 8.24 8.24 8.24 8.24


• Analysis of fabrication costs as a function of part complexity fac- tor values.


3-D sand printing for varied production volume.


• Estimation of breakeven costs between traditional and 3-D sand printing to determine levels of part complexity where 3-D sand printing is more cost-eff ective.


• Examination of the eff ects of changing the costs of 3D sand printing.


T e criterion for measuring part


design complexity used in this study was adopted from a prior study focused on quantifi cation of part complexity of cast parts for traditional processes. Key geometric attributes that can be determined from the CAD model of the desired part as- sociated using this complexity model are presented in Table 1. T e tooling cost is infl uenced by tool design and


Length (in) L


8.24 8.24 8.24 8.24 8.24 8.24 8.24 8.24 8.24


Width (in) W


6.36 6.36 6.36 6.36 6.36 6.36 6.36 6.36 6.36


Height (in) H


5.16 5.16 5.16 5.16 5.16 5.16 5.16 5.16 5.16


Draw depth (in) Dd


2.95 2.95 2.95 2.95 2.95 2.95 2.95 2.95 2.95


Complexity factor CF


19.7 41.3 50.1 55.4 58.9 60.9 63.1


65.6 66.7


complexity which is dictated by the part design complexity. For example, the mold for a complex part design such as a train air brake may require multiple cores. Alternatively, a simpler casting might be a solid uniform cross- sectioned part without the need for a single core. Designers and tool makers observed that the tooling cost depends on the number of cores, volume and surface area of part, core volume, draw depth (i.e., the depth of tooling) and variation in section thickness. For a given part design, the cost of moldmaking for both pattern and 3-D sand printing was conducted. For con- ventional pattern making, tooling costs were generated using an Internet-based cost generator. T e bounding box of the part, the number of cores and the num- ber of part features are required to gener- ate the tooling costs. Fabrication costs of molds and cores were estimated by industry quotation method based on the


Figure 4. Tooling costs (i.e., patterns and coreboxes) as a function of complexity are shown for Case Study 1.


Figure 5. Fabrication costs for Case Study 1 for 3-D sand printing costs and conventional patternmaking is shown.


Nov/Dec 2016 | METAL CASTING DESIGN & PURCHASING | 27


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