APPLICATION OF THE GWPS FOR MACHINING OF A TRANSMISSION HOUSING

One component of a modern machining system that has remained virtually unchanged, since time immemorial, is part location. The fundamental basis of current methods of part location is the concept of a physical datum surface, which is created in the first machining operation and conducting all the further machining operations with reference to this physical surface. Current workpiece positioning practice utilizes physical contacts between the fixture and workpiece for location. Due to contact feature variations, the positioning is inconsistent and variable for sequential machining set-ups. Consequently, geometric errors are induced in machined features. This paper proposes a novel concept, the Global Workpiece Positioning System (GWPS), for datum establishment. Precision artifacts are strategically located on the rough workpiece and a part reference frame is defined, with respect to these artifacts, at a qualification station. This part specific information now travels with the part to the machining station. At the machining station a probe is used to locate the artifacts on the part and determine their location with reference to the machine tool's reference frame. Since the part reference frame is known with respect to the artifacts, its location can be derived with respect to the machine tool's reference frame. The part program can then be modified to reflect the actual location of the part and the machining of the features carried out with a greater degree of accuracy and precision. A prototype system using the GWPS concept is implemented and presented. Experimental results validate the GWPS concept. A three-hole pattern is drilled and bored in an aircraft transmission housing component in a two set up operation. The GWPS located workpieces retained a hole center location accuracy within the required drawing specification without the use of the traditional location fixtures that are typically used for the two operational set-ups.