Thesis (PH.D.) -- Syracuse University, 2004. / "Publication number AAT 3149061."

In this dissertation, comprehensive thermal models are developed to account for the influence of grinding conditions on the temperatures generated. Various aspects of the heat transfer problem are analyzed and experimentally investigated including the fluid flow through the grinding zone, energy partition to the workpiece, heat flux distribution at the workpiece surface, cooling by the grinding fluid, transient temperatures during a grinding pass, and burn-out heat flux limits for creep-feed grinding. The work begins with an analysis of fluid flow through the grinding zone. The model predicts tangential and radial fluid velocities relative to the wheel, the depth of fluid penetration into the wheel pores, and the useful flow rate through the grinding zone. The useful flow rates predicted using the model are combined with experimental measurements for both conventional and creep-feed wheels to estimate the effective wheel porosity, which provides a measure of the ability of a wheel to pump fluid through the grinding zone. Thermal models are then developed to predict the partition of the total grinding heat to the workpiece, the fluid, and the grinding wheel. The thermal properties of the composite depend on the effective wheel porosity as described above. Results are obtained for the local partition of the total energy to the workpiece and to the composite along the grinding zone for different grinding conditions. For creep-feed grinding in the absence of fluid burn-out, the energy partition to the workpiece is typically only a few percent of the total. Inverse heat transfer methods are developed to determine the heat flux distribution to the workpiece from measured temperature distributions for regular grinding of steels with both conventional aluminum oxide wheels and CBN wheels. These results are also used to estimate the energy partition to the workpiece, as well as the wheel-workpiece contact length and convective heat transfer coefficient on the workpiece surface. A transient thermal analysis was developed. For creep-feed grinding, the temperature rise is found to be much bigger than the quasi-steady state value at the end of the cut. The transient temperature model is subsequently applied to predicting burn-out heat flux limits for creep-feed grinding. (Abstract shortened by UMI.)

Several design methodologies for automatically designing injection molds were developed to reduce warpage of injection molded parts. The part warpage was defined from warpage simulation, so as to represent various deformation behavior of the molded part. A concept for deliberately varying part wall thicknesses, within feasible dimensional tolerances to reduce the warpage, was introduced. The wall thicknesses, that minimized the effect of process fluctuation inherent to molding process, were obtained using the Taguchi method. The results of the example indicated that one can considerably reduce the warpage, and may also reduce material costs, by varying the wall thicknesses. A modified complex method was developed to optimize various domains in injection mold design. The modified complex method significantly reduced the part warpage with a moderate number of independent analysis evaluations for the proposed optimization of: part wall thicknesses; location and sizes of cooling channels; and process conditions. The runner system of multiple cavity molds was successfully balanced by adjusting the sizes of runners and gates using the iterative redesign method integrated with packing simulation in two case studies. A design technique for automatically determining the "best" gate location(s) of injection molds was presented in association with the three important parameters in gating design--the part warpage, the weld and meld line location at the critical areas, and the Izod impact strength at a specific region of the part. The difficulty in predicting accurate values of engineering property like Izod impact strength is that they vary throughout a part with respect to the thermomechanical history. Upon evaluating each gating design, the trained neural network computation predicts, regardless of part geometry, Izod impact strength by a non-parameteric modeling of the complex relation with thermomechanical processing histories. As the results, when the polymer resin and the part geometry were predetermined, the part warpage could be considerably reduced by the developed design tools for the part wall thicknesses, the mold systems including gating, runner, and cooling system, as well as the process conditions.

The objective of this investigation is to evaluate the ability of analytical and computational models to describe the momentum and heat transfer between the gas and particles in a falling-bed heat exchanger. Experimental data are presented for a test falling-bed heat exchanger. Measured temperatures, pressures, and overall heat transfer rates are compared to predicted values from analytical and computational models, and the capabilities and deficiencies of these modeling methods are discussed. In addition, the effect of the addition of a particle distributor on the performance of the falling-bed heat exchanger is measured. In the falling-bed heat exchanger, solid particles fall through a vertical column against a counterflowing gas stream flowing upward with a velocity less than the terminal velocity of the particle. Heat is exchanged between the falling particles and rising gas. This arrangement has been proposed for heat recovery and regeneration in power plants and other process applications. The ability to model and predict the heat transfer rate between the gas and particles is critical to the design of the falling-bed heat exchanger. The heat transfer between the gas and solid particles in these devices has typically been modeled by assuming steady-state and ideal, uniform, one-dimensional flow of the continuous fluid and the particle or droplets. This model, termed the uniform mixing model in this study, has been used in many instances to estimate the effective heat transfer coefficient and Nusselt number of the falling droplets and particles as a function of effective Reynolds number from experimental data. The addition of a particle distributor has been shown to increase the heat transfer effectiveness of the falling-bed heat exchanger in experiments. It has been determined that the uniform mixing model generally does not provide an accurate representation of the falling-bed heat exchanger, as it cannot account for gas and particle maldistributions such as those created by a particular particle distributor design. Computational fluid dynamics, which can permit the modeling of these spatial maldistributions, has been used to model the falling-bed heat exchanger. The predictions of the overall heat transfer rate from computational fluid dynamics are in better agreement with the measured values. However, discrepancies between the predicted and measured pressures and local temperatures indicate that the modeling of the turbulent mixing of momentum and energy is inadequate.

A numerical simulation of the injection-compression molding process is developed with the capability of predicting product quality attributes including residual stress, birefringence, and warpage. A hybrid finite element/finite difference method is employed to calculate the temperature and pressure fields of the process with a non-isothermal compressible flow model. The process simulation is coupled with viscoelastic constitutive models to predict the flow and thermally induced residual stresses. A structural finite element analysis is formulated to predict the warpage of the disc due to asymmetric thermal stress and gravity after demolding. The flow and thermally induced birefringence of injection-compression molded optical media is predicted by applying a stress-optical rule to the flow and thermally induced stresses. The resulting model considers the contributions of flow and cooling induced molecular orientation, and the transient effect of thermal stress and pressure on the birefringence. The simulation is validated by compact-disc-recordable moldings with an optical grade polycarbonate under different processing conditions.

An autonomous system has been developed for cylindrical plunge grinding to optimize the operating parameters while taking complete sets of part quality and machine related constraints into account. The system is capable of adjusting the operating parameters from part to part to minimize cycle time while satisfying part quality and machine related constraints in response to in-process and post-process measurements which characterize the processing conditions and part quality. Two important constraint models for out-of-roundness and taper have been developed analytically and verified experimentally. Existing process and constraint models have also been improved and verified experimentally. Two optimization strategies have been developed to find closed-form solutions for real-time control to minimize the grinding time and also to minimize the production time which includes optimization of the dressing interval. The system is capable of coping with the quantitative uncertainty of the process by using a newly developed predictive model for the uncertain parameters and employing parameter estimation to update the models from part to part. Modified strategies for accelerated control have also been developed to reduce transient times. Optimization strategies were first evaluated in simulation. Practical implementation and testing of the autonomous system was then performed on an internal grinder, retrofitted with electrical drives and sensors and interfaced to a personal computer for data acquisition, system identification, and machine control. The system has also been successfully applied on a production machine in industry. The results of this investigation provide the scientific and technological basis for commercial development of a new generation of grinding systems and for retrofitting of older grinders.

Design For Manufacturing (DFM) and Design For Assembly (DFA) have become important design philosophies in product design practice. Component process selection and assembly combination decisions are key issues in DFM and DFA. As philosophies, it is important and imperative to derive some general guidelines in these aspects to support product design at early design stages. Since low product cost, short time-to-market, and high product performance are the three most important goals in the development of consumer products, and since injection molding and stamping are the two most commonly used manufacturing processes in the production of consumer products, in this dissertation, we focus on the process selection of injection molding and stamping based on the comparison of product costs (including tooling cost, processing cost, material cost and assembly cost), production time periods (including tooling time period, processing time period, and assembly time period), and product performance (including strength, stiffness, corrosion resistance, aesthetics, etc.). Some general guidelines and conclusions to determine if a component should be injection molded or stamped, and if an assembly should be combined into a single component or not are generated. A hybrid evaluation method based on the Pahl-Beitz method and the Dominic method is developed for product performance evaluation. A product evaluation method based on an overall evaluation of cost, time, and performance is proposed as well. In addition, several examples with components and assemblies from real products are analyzed and evaluated by using the guidelines and the overall evaluation method to illustrate the concepts and the feasibility of the approaches introduced.

Knowledge about the design of parts for metal stamping was obtained through extensive discussions with expert metal stampers. This information was organized in a form of a relative cost model which provides a systematic approach to the analysis of the manufacturing complexity of metal stampings. The resultant Design for Stamping model permits designers to evaluate part designs in the early concept stage of the design process, and to quantitatively assess the effect of changing part attributes on relative cost. A coding and classification system and a database of cost-related information are key features of the Design for Stamping model. The relative cost model enables one to compare design options in terms of total relative cost, and to determine the relative cost savings associated with design changes.

A generalized approach to fast interpretation of objects and their features has so far eluded researchers. In manufacturing, this interpretation can be approached from a vision point of view or from a CAD data perspective. Presently, CAD systems are widely used in several aspects of manufacturing, and such systems will eventually be data driven. It is therefore more efficient to use CAD data for object reasoning in manufacturing. Components can be modelled on a CAD system using various modeling techniques. The method of representation of their geometric information however differs from one CAD system to another. The advent of Initial Graphics Exchange Specification (IGES) now makes it possible to represent CAD data in a neutral and standard manner. This research concentrates on developing an object interpretation system. This interpretation system contains an automatic form feature extractor and a product modeller which acquired the technological information, such as tolerances (including position and form tolerances) and surface finish through users' interface. This research describes a scheme for recognizing and representing features from any CAD system using a neutral graphics data interface. The scheme developed is based on Graph-based feature representation, where features are represented by a set of faces as well as their topological adjacency. Based on theories related to group and graph theory, the strategies for classifying and representing features and methods of decomposing a complicated feature into several simpler features for recognition purposes has been developed. Finally, this work concentrates on ideas related to developing a product modeller. This modeller assists the interpretation of features by providing non-geometric information obtained through the designer. Such information can not be obtained directly from current CAD systems but are nevertheless important in the final attainment of the integration of design and manufacturing systems.

Product realization is a very complex, interdisciplinary process. At early design stages, decisions must be made not only about physical attributes of the design, but also about scheduling and resource allocation for many product and manufacturing engineering activities, as well as purchasing, finance, marketing, etc. Typically, complex interdependencies exist among these disparate activities, and it is difficult to predict how decisions will affect overall organizational objectives of low cost, high quality and short time-to-market. Many decision support needs in this process seem to fall in a gap between emerging design-for-manufacture models (which evaluate design attributes for cost of a specific manufacturing activity) and management-level models (such as very abstract but comprehensive PERT-type networks). This research addresses this "gap." In the proposed model there are three distinct object representations that together define a product realization problem: product attributes, activities, and resources. In the first stage of the model, two relational matrices are used to (i) match product attributes to the required design and manufacturing activities, and (ii) then match the activities to the resources required for realization. In the second stage, an activity network is generated from the data in the relational matrices. The network is assembled from predefined "templates" of activities which have default precedence relationships (for example, sequences of prototyping and tooling activities). This activity network is then used to simulate aggregate cash flow. There are several applications envisioned for a computer tool based on this model: as a "prospectus" for new product designs to assess aggregate cost and development time within a specific organizational context; to assist managers in "concurrent" scheduling of design, tooling, and other preproduction activities; as a vehicle for budget negotiation between engineers and financial managers during the design process; and as an aid for value analysis. After reporting results of a field study and prototype computer implementation, I conclude that the model could potentially be used for decision support, but several important conceptual and implementation limitations remain to be addressed.