COMPUTER-AIDED MODULAR FIXTURE DESIGN AND ASSEMBLY

Abstract

Fixtures are holding devices used in machining, assembly, inspection, and other manufacturing operations. The function of such devices is to establish and secure the desired position and orientation of a workpiece according to manufacturing requirements. Recently, the rapid development in automated manufacturing systems such as Flexible Manufacturing Systems (FMS) has created a requirement for flexible and cost effective fixtures. Traditional fixtures (dedicated fixtures), which have been used for many years, cannot meet the requirements because of lack of flexibility. The concept of replacing dedicated fixtures by modular and flexible fixtures is becoming more important in automated manufacturing, due to smaller batch production sizes. Modular fixtures are constructed from standard modular fixturing elements such as baseplates, locators, clamps, etc., and these elements can be re-used after they are disassembled. The main advantages of using modular fixtures are their flexibility and the reduction of fixture design time and cost required for the intended manufacturing operations. On the other hand, with the increased use of CAD/CAM systems, modular fixtures provide a workpiece-holding solution that is well suited for computer-aided fixture design and assembly (CAFDA). The design of fixtures is a highly complex and intuitive process. With the aid of CAD/CAM technologies, it becomes feasible to automate fixture design, especially the modular fixture design and assembly. This thesis describes an approach to Computer Aided Modular Fixture Design and Assembly (CAMFD). It emphasizes the generation of standard fixture element databases, modular fixture tower databases (MFTD), fixture configurations, and assembly strategies. The system includes five modules, i.e. fixturing database generation, fixture planning and assembly, and input and output modules. The input module was developed to transfer input information to ICAD and in fact, this is achieved by the integration between ICAD and UG. The inputs to the system are: 3-D workpiece, faces for locating, supporting and clamping positions, and the machining envelope defined by the tool path. Based on input information, the fixture planning module is used to select a suitable baseplate and standard element category to which other fixture elements belong. The modular fixture tower database (MFTD) is used for selecting the suitable towers (i.e. the attributes of each tower) from the MFTD, positioning and orientating the workpiece with respect to the base-plate, determining the points for supporting, locating and clamping, as well as interference checking. The assembly module is used to determine the assembly points (i.e. the points on the baseplate upon which the datum point of the tower will be attached to), the tower orientation and the assembly sequence. The output module is used to display the 3-D fixture assembly, sequence of assembly and a bill of material. The system was developed using the knowledge-based engineering (KBE) system, ICAD, and interfacing with UG for modelling a workpiece. By using ICAD functions, the fixturing database can be effectively created and is easy for use in fixture assembly. The modular fixture tower database (MFTD) is used to represent the sub-assembly of fixtures. This will simplify the fixture design and assembly process. A built-in interference checking routine is used in the planning stage to ensure a collision-free fixture design. Modular fixture design examples generated by the system are also provided to illustrate the development.