| This research is aimed at developing a scientific basis for the design of fixtures for machining prismatic or box shaped workpieces. To ensure that the workpiece is produced according to the specified shape, dimensions, and tolerances, it is essential that it is appropriately located and clamped on the machine tool. This work involves the systematic organization of previously intuitive knowledge, and a correlation of that knowledge with established engineering methods in fixture design. Towards that aim, there are three key aspects of this work: (1) Planning the sequence of machining operations in terms of workpiece setups; (2) developing a locating and clamping scheme, i.e., designing a fixture for each setup; and (3) performing a kinematic and dynamic analysis of the proposed designs.; Tolerance and precedence relationships between "manufacturing" features are taken into account in order to group the features into setups. The sequence of setups from the initial setup to the final setup is also obtained. Rules are defined for locator and clamp placement based on these and a number of other commonly accepted machining practices. A fixture configuration is produced for every setup. Next, an entire approach is developed to evaluate all fixture designs by kinematic and dynamic analyses.; Kinematic analysis reveals the deficiencies in restraint for a given locating and clamping arrangement. Using a representation based on the theory of screws, suitable alterations in the locating and clamping arrangement are suggested, if necessary, to obtain total restraint.; In dynamic analysis, a physical model of the fixture workpiece system is developed. A machining operation is simulated and the performance of the fixture studied. Results are reported on the effect of locator placement, clamp placement, clamp forces, clamping sequence, etc., on the dimensional stability of the workpiece. |
