Kristin L. Wood

Surface Characterization of Polycarbonate Parts from Selective Laser Sintering

Surfaces of polycarbonate Selective Laser Sintering parts are investigated to determine the characteristics aaecting part quality. Surfaces are obtained from experiments by varying four factors, namely, layer thickness, laser power, part orientation, and build angle. First, spatial modes on SLS surfaces are decomposed using a qualitative spectral analysis in an attempt to nd their origins. Thermal modes on the top surfaces of polycarbonate SLS parts result in the other modes being obscured; melting and part curl are concluded to be the dominant modes on these surfaces. Furthermore, surface modes resulting from building the part at an angle to the powder bed are identiied and modeled. Then, mathematical measures are computed for the surfaces to determine surface precision quantitatively. An analysis-of-variance study is performed to reveal the trends in surface precision with respect to control factors. Surface precision is shown to change signiicantly with laser power and part orientation, and trade-oos with part strength are presented.

Variant Constraint Satisfaction: Associativity in Product Realization

Constraint representation and constraint satisfaction are central to engineering design (Sussman and Steele, 1980; Popplestone, 1984, 1985, 1987; Serrano, 1987). Almost all product design is subject to limitations of various types such as performance, cost, and manufacturing technology. In each stage of the product development process, from conceptual design through manufacture, the design team experiences many iterations of first understanding what the constraints are (problem clarification), generating proposed solutions (synthesis), and assessing whether the proposed solutions satisfy the constraints (evaluation). Product design always involves compromise among the many competing requirements and limitations that are present in any design problem. Many engineers are drawn to the profession by the satisfaction felt in finding the solution that best fits the limitations imposed by the problem. It is not surprising then that we, as engineers, should be concerned with constraint management in direct engineering. Constraint management is a core enabling technology for direct engineering.