Date of Award

Fall 1997

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering - (M.S.)

Department

Mechanical Engineering

First Advisor

M. C. Leu

Second Advisor

Zhiming Ji

Third Advisor

Donald H. Sebastian

Abstract

The curl distortions in rapid prototyping using 3-D laser stereo lithography occur as the top layers shrink after being drawn and attaching to the bottom layers. The amount of curl is dependent upon the how much shrinkage the layer has finished prior to adhesion. It is also dependent on how deep the cure of the top layer amounts to as it adheres into the bottom layer. This thesis investigated the effect of build parameters on the distortions associated with the diagnostic 'Letter-H' shaped test part. The same parameters were also considered in a time optimization study, using calculated, predicted results rather than empirical data. The build parameters varied for this study were layer thickness, border overcure, hatch overcure, fill cure depth, fill spacing, and hatch spacing. The material used to build the part was Ciba-Geigy Resin SL 5170 and the apparatus was a 3D Systems Corporation SLA-250 rapid prototyping system.

Experimental measurements confirm that layer thickness, hatch overcure, and hatch spacing are the three dominant parameters that affect part accuracy and account for 80 - 90 percent contribution for the distortions at the positions measured. The magnitude of distortion is dependent on the amount of resin surface area that has been cured. The smallest values of distortion occur when less than 100% of the surface has been cured. By using Taguchi orthogonal arrays an optimization study showed that smaller layer thicknesses combined with smaller hatch overcures and larger hatch spacings produced smaller distortions. Smaller layer thicknesses also produced quicker build scan times.

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