<p>U disertaciji se prikazuje razvoj sistema za<br />projektovanje i optimizaciju konstrukcije pribora za<br />ma&scaron;insku obradu. Analizirani su različiti prilazi u<br />projektovanu pribora. Prikazana je koncepcija i<br />funkcionisanje razvijenog sistema. Validacija sistema<br />je izvr&scaron;ena na konkternim radnim predmetima za<br />operacije obrade bu&scaron;enja i glodanja. Na kraju su dati<br />odgovarajući zaključci i mogući pravci budućih<br />istraživanja</p> / <p> The dissertation shows the development of<br /> system for fixture design and layout<br /> optimization for machining processi. Different<br /> approaches were analyzed in fixture design.<br /> The concept and functioning of the developed<br /> system is presented. Validation of the system<br /> is made with specific workpieces for drilling<br /> and milling process operations. At the end the<br /> appropriate conclusions and possible<br /> directions for future research are given.</p>

<p>U doktorskoj disertaciji je prikazana nova metodologija za projektovanje<br />i optimizaciju konstrukcije elemenata pribora. Projektovani su i<br />realizovani uređaji koji omogućavaju ispitivanje nosivosti i<br />popustljivosti kontakta između elemenata pribora i radnog predmeta u<br />statičkim i dinamičkim uslovima opterećenja. U istraživanjima je<br />simuliran proces stezanja elementima sa specijalno projektovanim<br />završetkom i praćena je nosivost i popustljivost spoja između<br />elemenata pribora i radnog predmeta. Utvrđeno je da standardni<br />elementi za stezanje sa ravnim čelom u odnosu na specijano<br />projektovane elemente imaju značajno manju nosivost i popustljivost.<br />Pozitivni efekti primene elemenata za stezanje sa specijalno<br />projektovanim završetkom ogledaju se u povećanju pouzdanosti, tačnosti<br />i produktivnosti mašinske obrade.</p> / <p>Presented in this doctoral dissertation is a new methodology for the design and<br />optimization of fixture elements. Special device is designed and manufactured<br />to test load capacity and interface compliance between fixture elements and<br />workpiece under static and dynamic loads during machining. The research<br />process is simulated by specially designed clamping elements and monitored<br />for load capacity and interface compliance between fixture elements and<br />workpiece. It was found that the standard clamping elements with flat clamping<br />surface have a significantly lower load capacity and interface compliance in<br />comparison with the specially designed clamping elements. Application of the<br />specially designed clamping elements results in increased reliability, accuracy<br />and machining productivity.</p>

This thesis focuses on the application of case based reasoning (CBR) to welding fixtures in a computer aided design (CAD) environment. Modular fixtures have become more popular in previous years due to the creation of flexible manufacturing systems. Modular fixtures, since they are composed of many standardized parts, require much iteration to produce a full fixture design. This process is made more complicated when it is applied to more complex parts such as welding assemblies. In an effort to simplify fixture design for such complicated parts, researchers have been working on integrating fixture design into CAD packages. These efforts, generally known as computer aided fixture design (CAFD), do not focus on the transition of experience from more experienced designers but only provide a structure and a virtual environment to create fixtures. The research presented in this thesis will apply to this area. Case based reasoning (CBR) is a method of using previous cases to help aid the development of solutions to new problems. Applied to CAFD, this method is reduced to the application of a database and a retrieval and adaptation system. Current research on CAFD and CBR is limited to only proposing systems for machining fixtures. This thesis presents a methodology of a CAFD and CBR system that is dedicated to welding assemblies and fixtures. The focus is on creating an indexing system that adequately represents the workpiece and fixture, a retrieval system that accurately recovers the previous cases, and a method that integrates designer feedback in each process. The results of this thesis will be shown in a case study using an automobile muffler fixture assembly to define each idea of the methodology and to provide an example.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: error proofing; foolproofing; poka-yoke; free-form surfaces; fixture. Includes bibliographical references (p. 76-78).

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Fixture stiffness matrix; Jacobian matrix; kinetic model; geometric model; fixture design verification; stability analysis; tolerance analysis; tolerance assignment. Includes bibliographical references (p. 92-97).

Dissertation (Ph.D.) -- Worcester Polytechnic Institute. / Keywords: Computer-aided fixture design; Finite element analysis; Fixture Stiffness. Includes bibliographical references (p. 140-148).

With growing demands on improved product quality and shorter time to market, there is need for rigorous but practical tools to support the fixture design and analysis process. Computer-aided fixture design (CAFD), with predictable fixture stiffness, becomes a means to provide an appropriate solution in fixture design. The effectiveness of previous CAFD systems is not fully satisfactory partially because analysis of fixture stiffness has not kept pace with the development of CAFD. The dissertation research provides a model of fixture unit stiffness analysis and an experimental method of identifying contact stiffness parameters. The model and the method offer the potential for a more realistic analysis of fixture stiffness properties of a fixture-workpiece system, based on a fixture unit description. An FEA model of fixture unit stiffness is developed with contact elements for solving contact problems encountered in the study of fixture unit stiffness. The penalty function method is used to model the contact conditions in the energy equation of the general FEA and to describe the nonlinearity of connection shown in previous experiments. The contact and friction conditions are represented mathematically in the FEA model. The FEA model and the analysis procedure are validated by numerical simulation. An experimental study on contact parameters is carried out to identify contact stiffness, including normal contact stiffness and tangential contact stiffness, by both static and dynamic approaches. For normal contact stiffness, a static identification procedure is developed to estimate the contact parameters, using experimental data. Four factors - testing environment, contact area, surface finish of the specimen, and normal loads, - are examined to see how they affect the behavior of the contact interface. A dynamic method is also used to identify normal contact stiffness. A scheme of eigenvalue analysis is developed to test the contact structure to estimate contact stiffness. The dynamic test results are compared with the results of static test under the same experimental condition and a reliable correspondence is presented. Similar to methods devised to identify normal contact stiffness, a frequency-domain identification system is developed to estimate tangential contact stiffness, using FEA and experimental data. A simulation study on vibration data from tangential contact model is presented in this study. The experimental study is carried out and tangential contact stiffness is estimated based on numerical simulation and experimental data. This research establishes the finite element model of fixture unit stiffness and develops the experimental approaches to identify contact stiffness. Based on this study, the database of fixture stiffness can be built up, and further used in CAFD

This study presents Computer-Aided Fixture Design Verification (CAFDV) - the methods and implementations to define, measure and optimize the quality of fixture designs. CAFDV verifies a fixture for its locating performance, machining surface accuracy, stability, and surface accessibility. CAFDV also optimizes a fixture for its locator layout design, initial clamping forces, and tolerance specification. The demand for CAFDV came from both fixture design engineers and today's supply chain managers. They need such a tool to inform them the quality of a fixture design, and to find potential problems before it is actually manufactured. For supply chain managers, they will also be able to quantitatively measure and control the product quality from vendors, with even little fixture design knowledge. CAFDV uses two models - one geometric and one kinetic - to represent, verify and optimize fixture designs. The geometric model uses the Jacobian Matrix to establish the relationship between workpiece-fixture displacements, and the kinetic model uses the Fixture Stiffness Matrix to link external forces with fixture deformation and workpiece displacement. Computer software for CAFDV has also been developed and integrated with CAD package I-DEAS TM. CAD integration and a friendly graphic user interface allows the user to have easy interactions with 3D models and visual feedback from analysis results.

The objectives of Sensor Based Fixture Design and Verification (SFDV) research are to provide the means for detecting contact failure of the workpiece with fixture locators and for preventing incorrect loading of the workpiece in a fixture. The fixtures that involve complex free-form surfaces especially in the aerospace industries face problems caused by the contact failure of the workpiece with locators. In batch and mass production defects often occur due to incorrect loading of the workpiece in a fixture by an operator due to fatigue or inadvertence. The current fixturing research is focussed on improving the fixture quality and other aspects and do not address these issues. This research is focussed on three areas, to generate algorithms for automatically foolproofing the fixtures, to build locators with embedded sensors that could be used to verify the contact and foolproof the existing fixtures, and to design and experimentally validate fixtures for free-form surfaces with sensors to verify the location. In foolproofing, workpieces were classified into different categories to identify the existence of a solution and the geometry was simplified and used to search for a solution based on symmetry/asymmetry to discover a foolproofing location. The algorithms were implemented in a CAD software and the solutions were verified in 3D space. The locators with inbuilt sensors were designed for foolproofing and location verification purposes and the sensors were used in case studies to establish credibility. A sensor based fixture design method is created for the part location of free-form surfaces using fiber optic sensors. An experimental fixture with sensors incorporated in the locators was used to determine the effects of surface curvature on the sensitivity of the sensors. A new theory on best locations for the sensor based locators by utilizing surface curvature is proposed based on the experimental results. The SFDV implementation may help realize the dream for any manufacturing sys­tem aspiring to move beyond the six sigma levels of quality and achieve zero defects.

Assembling of the compliant parts used in aviation industry is a challenging process. Assembly fixtures are quite important tools in this effort and widely used in industry. In fixturing of easily deformable sheet metal parts, besides restraining the rigid body motion of the parts, the possible deformations that may occur during the assembly process and the spring-back effect on the final product need to be taken in to consideration. In order to guarantee a successful assembling, in other words, to obtain the final product within specified tolerances, a systematic approach to the fixture design problem is required. The designer should predict the correlation between the input variations and the final assembly variation, especially, for the complex assemblies. This study proposes a design and analysis approach in fixturing of sheet metal assemblies for helicopter components. The design of an assembly fixture for a particular tail cone has been completed convenient to the existing locating principles. Finite Element Analysis (FEA) has been realized in simulating the assembling process in order to predict the possible variation of the interested feature on a complex assembly due to deformations.