During the last decade, researchers have developed Rapid Prototyping (RP) techniques to meet the urgent need of making prototypes of complex three-dimensional parts in a reduced time. Various kinds of RP techniques have been commercialized: stereolithgraphy (SLA), fused deposition modeling (FDM), selective laser sintering (SLS), laminated object manufacturing (LOM), and so forth. In all the RP techniques, the computer-aided design (CAD) model of a three-dimensional part is sliced into horizontal layers of uniform, but not necessarily constant, thickness along a building direction. Each cross sectional layer is successively deposited and, at the same time, attached onto the previous layer. The stacked layers form a physical part of the model. RP techniques, however, have inherent disadvantages caused by their working principles: stair-stepped surface of parts due to layer-by-layer stacking of layers, low build speed caused by line-by-line solidification to finish one layer, and post processing to improve surface finish, etc.
The objective of this study is to propose a new RP technique, variable deposition manufacturing (VDM), which can make up for the disadvantages of the existing RP techniques, and to develop an apparatus to implement the technique. The apparatus consists of a variable deposition nozzle, a transfer table, and a controller. VDM enables the fabrication of complex parts faster and more accurately than conventional RP techniques by using a variable deposition nozzle. Unlike the extrusion head in FDM process, the variable deposition nozzle in VDM is introduced to extrude molten material in the form of a "strip", bonding the strip to the adjacent and previously deposited strips to complete each layer. In addition, the width of each strip is controlled in the process and, the slopes of both sides of the strip should be also controlled. Thus, the proposed process can greatly reduce the building time and improve the surface finish of parts generated. To improve the dimensional accuracy of parts, VDM is combined with rolling and filling as post processing.
The experiments are carried out to obtain the range of temperature of molten material to maintain its fluidity and to investigate the effect of gas cooling on the preservation of the slopes. Based on the results, some simple shapes such as a line-shape, an S-shape, and a circle-shape were fabricated from Ethylene Vinyl Acetatecopolymer (EVA). In order to examine the applicability of VDM to more general shapes, a tensile specimen and a yo-yo shape were manufactured by the proposed RP method using EVA material as the first trial approach.
As compared with the LOM process for a tensile specimen, the build-up time has been found to be greatly reduced. The present basic study has shown the possibility of a practicable utilization of the proposed VDM process to prototyping of a general three-dimensional shape.
