MULTIPLE REGRESSION AND COMMITTEE NEURAL NETWORK FORCE PREDICTION MODELS IN MILLING FRP

This work utilizes the mechanistic modeling approach for predicting cutting forces and simulating the milling process of fiber-reinforced polymers (FRP) with a straight cutting edge. Specific energy functions were developed by multiple regression analysis (MR) and committee neural network approximation (CN) of milling force data and a cutting model was developed based on these energies and the cutting geometry. It is shown that both MR and CN models are capable of predicting the cutting forces in milling of unidirectional and multidirectional composites. Model predictions were compared with experimental data and were found to be in good agreement over the entire range of fiber orientations from 0 to 180°. Furthermore, CN model predictions were found to greatly outperform MR model predictions.     

Modelling the effects of machine breakdowns in the generalized cell formation problem

Machines are key elements in manufacturing systems and their breakdowns can dramatically affect system performance measures. This paper proposes a new multi-objective pure integer linear programming approach for the cell formation problem with alternative process routings and machine reliability consideration. The model minimizes total cost and maximizes system reliability simultaneously. Traditional reliability evaluation approaches attempt to model the reliability of the manufacturing system as a function of its elements. These approaches have some negative aspects; therefore, instead of modeling the system reliability as an explicit objective function, we use an approach to model the effects of the machine unreliability in terms of cost and time-based effects. Using the ?-constraint method as an optimization tool for multi-objective programming, a numerical example is solved to demonstrate the capability of the proposed model in evaluating various effects of the reliability consideration.     

Seismic evaluation and analysis of high-voltage substation disconnect switches

Disconnect switches are one of the components of an electrical substation that are vulnerable to the effects of earthquake shaking. Three vertical-break and two horizontal-break 230 kV switches of porcelain and composite construction were tested on a triaxial earthquake simulator in various configurations. Three-pole switches were mounted on a stiff, low-profile frame and tested according to the industry standard IEEE-693-1997. The vulnerable components of the switches were the aluminum spacers at the base of the switch posts and the welded post-blade connections and the bolted connections at the base of the posts. Single-degree-of-freedom models of the switch insulator posts were developed using experimental data to establish the amplification of seismic demand on the switches when mounted on frames of different heights and stiffness.     

Weld defect formation in FSWed coppers

This work was undertaken to explore the formation of weld defects in FSWed copper metals via both numerical and experimental approaches. The 4 mm-thick copper sheets were friction stir welded at a tool rotational speed of 710 rpm and tool translational speed of 40 mm/min. Microstructural evaluations were performed on the welded specimens. Also a 3D arbitrary Lagrangian Eulerian numerical model was developed to obtain temperature and material velocity profiles. To this aim, DEFORM-3D was implemented for developing the numerical simulation. Numerical results for temperature values showed good agreement with the recorded experimental data. They also suggest that on the advancing side (AS) of the trailing side, the pin velocity has the minimum amount (zero), and this is the main reason for the formation of tunneling cavity. Experimental results show that a force is created between the reminder of material at the joint and the rim of AS. This force causes a prong of surface material from the AS rim to penetrate into lower parts of weld. It seems that the inadequate pressure (low values of the plunge depth), inadequate surface materials, and the trapped air are the main causes for the formation of the weld defects.     

Integrating cell formation with cellular layout and operations scheduling

Designing a cellular manufacturing (CM) system involves three major decisions: cell formation (CF), cellular layout (CL), and cellular scheduling (CS). The integrated design of CM systems is investigated in this paper by proposing two mathematical models. The first model integrates cellular layout problem with cell formation problem to determine optimal cell configuration and the layout of machines and cells in order to minimize the total movement costs. The second model takes also the cellular scheduling into consideration with the objective of minimizing the total completion time of parts. Two genetic algorithms are developed to solve the real-sized problems. The proposed models are formulated as mixed integer linear programming, and two numerical examples are solved in order to investigate the effects of integration in the CM systems design. The results show that considering CF, CL, and CS decisions in a simultaneous manner can significantly improve the performance of the CM systems.