Research On Key Techniques Of Agile Fixture Design

A fixture is a device which directly affects product quality and lead-time. Many firms are running a single piece, small path or customized production in current aeronautical industry. In such a production mode, a mass of work should be done for fixture design and manufacture. It happens once in a while to delay production caused by not preparing fixture in time and also the workpiece deformation caused by a poor fixture setup. This leads to a huge economic loss. Therefore, the method of rapid fixture optimization design is urgently required. Based on the analysis of structure and process of an agile fixture design system, some researches have been done deeply in agile fixture design. They are concurrency of design, flexible resource management, variation of design, fixture optimization, rapid fixture assembly and so on. The main works in this paper are concluded as follows:A concurrent integration structure of an agile fixture design is created based on product data management (PDM). The feature-based workpiece integration model is developed. Fixturing feature model, feature information pick-up process, feature identifying and feature mapping method are analyzed. In order to meet the demand of information integration in different platforms, XML is used to describe the workpiece integration information. In order to extend the data management function of PDM, some integration functions, such as fixture structure management, configuration management and process management are analyzed and developed.Aiming at the flexible management and effective sharing of fixture design resources, a fixture model is created based on fixture structure tree and feature net and design recourse model, which supports the entire process of fixture design is established. SML (tabular layouts of article characteristics) are used to describe characteristics of the key design resources, such as fixture element, component and fixture. The automatic modeling method of part, component and fixture are studied in detail. Based on fixture element modeling, automatic driving and automatic geometry modeling for fixture component and fixture are accomplished.The issue of using case-based reasoning (CBR) in the entire process of fixture design is proposed. The strategy of reusing design is applied in the different stage of design, such as scheme design, optimization design, detail design, assembly design and other stage. Hierarchical index rule, reasoning rule, modification rule and instance storage strategy are analyzed. In order to solve the difficulty of instance modification, key points such as fixture template constructing, variation classification based on the template, expression of variation knowledge, and variation flow are studied. As a result, the variations of component specification and component position are realized.Fixture optimization design is the main point of agile fixture design for high-precision thin-walled workpiece. The optimizing model of fixture layout and clamping forces simultaneously is developed with objective of reducing machining deformation and increasing the distributing uniformity of deformation. The fixture multi-objective synchronization optimization design process is realized based on genetic algorithm and finite element method. When establishing finite element model, the influences of the contact force, friction force, cutting force, clamping force, and scraps, are all taken into account to make the model more reasonable and more close to reality. A method using dynamic clamping forces on the basis of optimized fixture layout, to reduce workpiece deformation, is presented. The solution model and method of dynamic clamping force based on finite element method and genetic algorithm are studied. An example is given to illustrate that the fixture layout and clamping force multi-objective optimization and alterable clamping force optimization can reduce workpiece deformation.In order to reduce the model complexity, the idea of dividing assembly model into node layer and feature layer is proposed. The effective path is introduced into node layer while effective feature face and effective effect-distance are introduced into feature layer, which make the assembly model more rational. This paper also researches on assembly strategy based on effective path and assembly feature face and implements fixture assembly rapidly.Finally, an agile fixture design prototype system is developed based on GS-PDM and SolidWorks platform. Software packages such as SolidWorks, MATLAB and ANSYS are effectively integrated. The system integrates all function modules including design module, analysis module, management module and so on. Some modules of this prototype system have applied well.