الفهرس 
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Abstract
Wire electrical machining is a special form of traditional electrical discharge machining where in the electrode is a continuously moving conductive wire. Wire electrical discharge machining (WEDM), is also known as electrical discharge wire cutting (EDWC). Material removal by WEDM is effected as a result of spark erosion as the wire electrode is fed (from a spool) through the workpiece . In most cases, horizontal movement of the worktable, controlled by computer numerical control (CNC) on modern machines, determines the path of the cut. With wire EDM technology, complicated cutouts two-and tree-dimensional shapes can be made through difficult to machine components.
To obtain a better machining performance of WEDM, the machining parameters and cutting conditions should be properly chosen. The selection of the appropriate machining parameters for WEDM is difficult and relies heavily on the operators` technologies and experience, in addition to machining parameters tables and catalogues provided by the machine-tool manufacturer.
The overall aim of the present thesis is to design a new electrical discharge machining knowledge-based system, which allows the making of decisions to optimize the wire EDM operation, minimize the production costs and improve the overall performance of the WEDM process by functioning as a diagnostic tool. For this purpose , four categories of workpiece materials were selected to be machined. Tool steel 2714 (55Ni Cr Mo V7) being the first category, while for the second one, two types of cast iron were used in the third category. For the fourth category, seven types of conductive composites were selected.
The experiments were performed on a high precision 5 axis CNC wire electrical discharge machine. The wire used was hard brass with a 0.25 mm diameter. Two types of surface finish were selected for this work.
The proposed WEDM knowledge-based system was based on the production rule system of representing knowledge. This system was built in the ”clips 6.05” shell software. The designed knowledge-based system consisted of four main modules, namely: machining parameters, wire EDM machine settings, machine technology database and problem diagnosis.
The machining parameters module includes the required workpiece information such as type of workpiece material to be machined, height of the workpiece, and the desired final machining quality (surface finish and precision class). The wire EDM machine settings module includes the required parameters for operating the machine such as pulse frequency, average machining voltage, injection flushing flow, wire speed, spark gap value and wire tension. The third module contains a database for recording and organizing the heuristic knowledge of the WEDM process. The machining technology data for various wire/workpiece combinations has been stored in the form of facts. In such a way, fast retrieval of information was realized. Moreover, changes can be easily made and data can be readily appended. The problem diagnosis module was designed for the purpose of diagnosis errors and advising operators while the WED machine. The program diagnosis module suggests the possible faults and recommend the operators with the possible actions that must be taken.
Results showed that the knowledge based system for wire electrical discharge machining proved to be a powerful tool for improving the performance of the process. The CLIPS software was characterized by fast retrieval of information, where changes could be easily made and data could be readily appended. The designed system has the ability to determine WED machining parameters such as cutting speed and material removal rate in addition to the determination of WED machine settings such as pulse frequency, average machining voltage, injection flushing pressure, wire speed, wire tension and spark gap size.
Using the WEDM fault diagnostic tool advises the operators and leads to minimize the process dead time. The operators are expected to consult the system when the WEDM operation fails in one way or another, or when problems occur.
WEDM cutting speed and material removed rate values surface roughness (Ra=3.2µm) were higher than those values at (Ra = 1.8µm) for any workpiece thickness value. Also, cutting speed and material removal rate values increased directly with the increase of thickness for all surface roughness conditions.
Pulse frequency and spark gap values were directly proportional to workpiece height at roughing conditions. With finishing conditions, the pulse frequency value was set at a maximum value of 250 khz. Average machining voltage values were inversely proportional to workpiece height at finishing conditions whereas for roughing conditions, the average machining voltage were almost constant.
Cutting speed and material removal rate values decreased with the increase of the SiC% value for the composite materials.