REFERENCE FREE PART ENCAPSULATION - A NEW UNIVERSAL FIXTURING CONCEPT

Fixturing is an essential prerequisite to machining a three-dimensiona l component. With traditional techniques, the range of fixturable shap es is limited, and the identification of suitable fixtures in a given setup involves complex reasoning. As a result, automated fixture plann ing systems tend to be slow and conservative, and they remain a major stumbling block in the development of computer-aided process planning systems. This paper presents a new universal fixturing technique calle d Reference Free Part Encapsulation (RFPE), which solves the problems of immobilization, location, and support of the component independentl y of its shape. At first glance, RFPE closely resembles other phase-ch ange techniques in that it first relies on encapsulating the workpiece in a low melting point filler matrix for immobilization and support. The subtle difference arises, however, in the manner in which RFPE sol ves the traditional problems of loss of locational information when a setup change is effected. In RFPE, the filler block is machined to a k nown shape like a cube. After machining features in any setup, the blo ck is refilled and restored to its original shape. The faces of the fi ller block are now used as locational cues in refixturing the block in a new setup. The fact that RFPE is independent of the shape of the co mponent makes planning easier, expands the range of machinable parts, and makes it an ideal component for rapid prototyping by machining. So me technological aspects of RFPE and their implications on design and process planning are discussed. Finally, schemes for integrating RFPE- based fixturing into the functionality of an open architecture machine tool are presented.