Francho Garza Güell 27/12/2012
PRODUCT DESIGN AND MANUFACTURING PROCESS
1. EDM (Electrical discharges machine ) and WEDM ( Wire Electrical discharges machine). • Fundamentals of process;
Principles of EDM Electrical Discharge Machining (EDM) is a controlled metal-removal process that is used to remove metal by means of electric spark erosion. In this process an electric spark is used as the cutting tool to cut (erode) the workpiece to produce the finished part to the desired shape. The metal-removal process is performed by applying a pulsating (ON/OFF) electrical charge of high-frequency current through the electrode to the workpiece. This removes (erodes) very tiny pieces of metal from the workpiece at a controlled rate.
EDM (electrical discharge machining) is a machining method primarily used for hard metals or those that would be impossible to machine with traditional techniques as milling, drilling, etc. One important limitation, however, is that EDM only works with materials that are electrically conductive. EDM can cut small or odd-shaped angles, intricate contours or cavities in extremely hard steel and exotic metals such as iconel, hastelloy, kovar, titanium and carbide. Sometimes referred to as spark eroding or spark machining, EDM is a method of removing material by a series of rapidly recurring electric arcing discharges between an electrode (the cutting tool) and the work piece, in the presence of an energetic electric field. The EDM cutting tool is guided along the desired path very close to the work but it doesn't touch the piece. Rapidly occurring consecutive sparks produce a series of micro-craters on the work piece and remove material along the cutting path by melting and vaporization. The constantly flushing dielectric fluid washes away the particles.
Wire EDM machining (Electrical Discharge Machining) is an electro thermal production process in which a thin single-strand metal wire serves as the electrode (Special brass wires are typically used) in a de-ionized water (used to conduct electricity) that allows the wire to cut through metal by the use of heat from electrical sparks. The wire itself does not actually touch the metal to be cut; the electrical discharges actually remove small amounts of material and allow the wire to be moved through the workpiece. The path of the wire is typically controlled by a computer, which allows extremely complex shapes to be produced. To stop the sparking process from shorting out, a non conductive ﬂuid or dielectric is also applied. The wastematerial is removed by the dielectric, and the process continues.
• Advantages & Disadvantages;
Advantages of EDM: • • • • • • Complex shapes that would otherwise be difﬁcult to produce with conventional cutting tools. Extremely hard material to very close tolerances. Very small work pieces where conventional cutting tools may damage the part from excess cutting tool pressure. There is no direct contact between tool and work piece. Therefore delicate sections and weak materials can be machined without any distortion. A good surface ﬁnish can be obtained. Very ﬁne holes can be easily drilled.
Disadvantages of EDM: • • • • • • • • The slow rate of material removal. The additional time and cost used for creating electrodes for ram/sinker EDM. Reproducing sharp corners on the workpiece is difﬁcult due to electrode wear. Very high speciﬁc power consumption. High power consumption. "Overcut" is formed. Excessive tool wear occurs during machining. Electrically non-conductive materials can be machined only with speciﬁc set-up of the process. 2
Prototype production The EDM process is most widely used by the mold-making tool and die industries, but is becoming a common method of making prototype and production parts, especially in the aerospace, automobile and electronics industries in which production quantities are relatively low. In sinker EDM, a graphite,...
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