The approach of laminate object manufacturing(LOM) process

• Main Authors: Yun-Yao Chiu, 邱雲堯
• Other Authors: Y.S. Liao
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/05969406194384034868

博士 === 國立臺灣大學 === 機械工程學研究所 === 88 === The purpose of this study is to explore innovative approaches regarding the slicing method, the crosshatch determination and the waste material removal in the process of Laminated Object Manufacturing (LOM). With respect to the slicing method, the current slicing rule of LOM system is unable to ensure unilateral tolerance on the whole prototype and therefore the occurrence of over-cut and under-cut in the same part. This drawback leads to unsatisfactory precision of the part in the post processing. To solve the problem, a new uniform slicing method is proposed in this paper. Based on the geometry information provided by the STL file, an algorithm is developed. The new slicing rule is decided according to the inner product of the normal vector and working direction of the part, together with the function of the part to be manufactured. The STL file is cut into 2D section and the accurate contour is calculated. After computation based on the slicing rule, a proper working path is produced. The rules proposed in this paper are also verified. It can not only be applied to the improvement of slicing rules in existing LOM system, but also to the rapid prototyping (RP) systems using uniform thickness slicing. It tremendously increases the manufacturing efficiency and ensures the presence of accurate working tolerance. With respect to the waste material removal process so-called “de-cubing” of LOM, the traditional uniform crosshatch setting is a labor intensive and time-consuming task. An adaptive crosshatch approach is developed to improve working efficiency and to alleviate the effort involved in de-cubing process. The working region is divided into two sub-divisions, the inner region and the outer region, by the proposed rectangle and original contour offset approaches. The fine crosshatch pattern is designated for the inner region based on the shape of the cross-section contour, and the rules for selecting crosshatches for different shapes are given. The outer region has a coarse crosshatch pattern, whose size is an integer multiple of that of the inner region. The brick-layered effect in the overlap zone of the waste material is eliminated by the projection method. Experiment shows that the adaptive crosshatch approach brings four major advantages: reduced laser power consumption, protection of the part from damage, improved machining and de-cubing efficiencies. To further improve the efficiency of de-cubing process, the laser path planning of burn-out rule is proposed. The algorithm of part’s threshold inclined slope is developed based on the parameters of laser energy, working velocity, layer thickness and laser diameter. If the inclined surface of the slicing part is smaller than the threshold value, the compact laser path is processed in the overlap zone because the larger zone adheres to the waste. The optimal distance between laser paths is calculated according to the thermo-model of laser cut, whose binder behind the layer is burn out. The rule is proved effective in facilitating the de-cubing process.