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USING A COMPLEXITY


FACTOR TO CALCULATE COST BENEFITS OF 3-D SAND PRINTING


A part complexity-based cost metric has been developed to analyze decisions for economically viable implementation of 3-D sand printing.


E. ALMAGHARIZ, B. CONNER, L. LENNER, R. GULLAPALLI, AND G. MANOGHARAN, T


Bounding box volume Part volume


Surface area of part Number of cores Volume of core


Thickness of part, min and max Draw depth


YOUNGSTOWN STATE UNIVERSITY, YOUNGSTOWN, OHIO; B. LAMONCHA, HUMTOWN PRODUCTS, COLUMBIANA, OHIO; M. FANG, PURDUE UNIVERSITY, WEST LAFAYETTE, INDIANA


hree-dimensional sand printing provides a means to fab- ricate molds and cores without the need to make patterns and coreboxes. Metalcasters and end-users would benefi t from learning more about when to use this evolving ad- vanced technology over conventional patternmaking. To know more, researchers examined the cost of molds


and cores as a function of part design complexity quanti- fi ed by a complexity factor. Two case studies illustrate how the complexity of the castings is systematically varied by changing the geometry


and number of cores. Tooling costs and fabrication costs are estimated for both 3-D sand printing and conventional patternmaking to calculate the break-even points for the two methods. Integral aspects of every sand casting process involve tooling associated with mold making. T is includes the fabrication of patterns used to make the molds and the production of coreboxes to make cores. Some of the major limitations in moldmaking using traditional techniques include constraints such as limitations on minimum wall thickness, elimination of sharp corners, and undercuts resulting in higher draft angles leading to increased fabrication costs. T is is further ampli-


Table 1. Geometric Attributes Used as Inputs for the Complexity Factor Model Part dimensions (length, width, height)


L, W, H Vb Vp Ap Nc


Vc, i Tmin Dd


and Tmax


fi ed in the case of tooling for parts with higher complexity. For example, an expensive core and/ or set of cores are required for parts with complex internal geometry such as an engine block. In some cases, part design modifi cation is required to facilitate pat- tern removal prior to pour during sand casting. Often this leads to nonfunctional part design modifi cation and/or addi- tional processing steps after casting. Additive manufacturing in the


form of 3-D sand printing is comple- mentary to the traditional approach of moldmaking in sand casting. 3-D sand printers can directly print a mold from computer-aided design (CAD) models of the desired part design in a matter of a few hours without the need for patterns or coreboxes. 3-D sand printing provides unique


advantages in moldmaking such as signifi cantly reduced leadtime and fl exibility without the need for tooling. It also off ers additional geometric free- dom to produce complex designs not otherwise feasible or aff ordable using the traditional approach.


Tooling and Fabrication Cost T e sequential processing steps of


conventional sand casting are outlined Nov/Dec 2016 | METAL CASTING DESIGN & PURCHASING | 25


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