京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21757号 / 工博第4574号 / 新制||工||1713(附属図書館) / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 西脇 眞二, 教授 髙田 滋, 教授 鈴木 基史 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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The thesis work investigates the possibility of replacing the Body-In-White (BIW) sections used in a physical test with a fixture. Volvo-cars perform several sub-system tests on its car components taken from various car models for different issues. Squeak and Rattle in Cockpits is one such important phenomenon investigated through its sub-system tests. Currently, the Body-in-White (BIW) sections taken from car body are used in holding the cockpits for Squeak and Rattle physical testing on a vibrating rig, the idea is to design a fixture that can replace these BIW sections for the test. Additionally, it is ensured that the fixture is designed to accommodate a variety of cockpits through the flexibility in its structure. Models from two different car segments were considered for performing the thesis. The development process started by researching the theory behind squeak and rattle along with investigating the important design parameters which would determine the requirements on the fixture. This is followed up with benchmarking the parameters and a physical test which would help later in comparison and evaluation of fixture performance against the BIW. The result from benchmarking were then used for topology optimization in obtaining a material layout to provide a basis for fixture design. Then, a basic CAD model is generated which is adapted to provide flexibility using Aluflexmechanisms. The final design comprises of a sufficiently rigid main structure made of hollow steel beams upon which Aluflex mechanisms are attached to provide flexibility in accommodating a variety of cockpit models. The fixture is analyzed and evaluated by comparing with benchmarked data. With the thesis, a fixture with generic (flexible) features which is manufacturable has been designed. It was concluded that at its current stage it cannot completely replace the BIW since the fixture is performing better than BIW in some respects and failing to conform to the requirements in others. The possible reason for the fixture failing to meet the requirements in the few aspects has been explored. As future work, it was proposed to explore into stiffness varying mechanisms (spring mechanisms) that could alter the stiffness requirements on the fixture as per the cockpit used for testing. It was also suggested to look for alternatives to Aluflex which would provide better stiffness at the connection points. Further, it was suggested to look for alternatives in the design concept which would avoid the connection part in extending too much away from the main structure thereby retaining high stiffness at the connection point.

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Topology Optimization has been proven to be a useful tool in discovering non-intuitive optimal designs subject to certain design constraints. The results of Topology Optimization are either represented as a tessellation object composed of thousands of triangular surfaces, or as a point cloud. In either case, the results of Topology Optimization are not suited for use in subsequent steps of the design process which require 3D parametric CAD (Computer Aided Design) models. Converting Topology Optimization results into parametric CAD geometry by hand is an extremely tedious and time consuming process which is highly subjective. This thesis presents a shape recognition algorithm that uses a feature by feature CAD-centric approach to convert Topology Optimization results into parametric CAD geometry. This is accomplished by fitting 2D cross section geometry to various parts of a given feature through the use of Shape Templates and then constructing 3D surfaces through the set of 2D cross sections. This algorithm aids in measuring the geometric approximation error of the generated geometry as compared to the optimal model, and standardizes the process through automation techniques. It also aids the designer / engineer in managing the direct tradeoff between closeness of geometric approximation (measured by volumetric comparison) and model complexity (measured by the number of parameters required to represent the geometry).

In collaboration with Kongsberg Automotive, the thesis focuses on material selection and redesigning the shift fork for additive manufacturing using topology optimization. The shift fork is a component in the gear shifting mechanism in the automotive industry. The current shift fork at Kongsberg is manufactured from aluminum using die-casting. This design and material do not withstand huge dynamic loads in commercial vehicles. The material to withstand the loading conditions and is widely available across powder manufacturers is selected using the weighted properties method. The topology optimization of the design resulted in a 50 % reduction in mass. The shift fork's two legs undergo uneven load distribution due to eccentricity. The optimized models are simulated using Finite Element Analysis to validate the design. The optimized design is obtained such that the difference in displacement between both legs is within 50 %. Numerous metal powder manufacturers and 3D printing service providers were contacted to understand the current additive manufacturing market.