Wednesday, December 10, 2008

ELECTRICAL-DISCHARGE MACHINING (EDM) WIRE


 

OBJECTIVE              : To illustrate the Non-Traditional Machining (NTM) process

using EDM Wire Cut, the machine features, process

capabilities and limitation.

 

 

INTRODUCTION:

 

EDM is a nontraditional 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 process is accomplished by establishing a large potential (voltage) difference between the workpiece to be machined and an electrode. A large burst (spark) of electrons travels from the electrode to the workpiece, workpiece material is eroded away. Thus the machining is accomplished by electrical spark erosion. This phenomenon has been known since the discovery of electricity, it was not until the 1940s that a machining process based on this principal was developed. The EDM process has become one of the most important and widely used production technologies in manufacturing. There are many types of nontraditional machining processes are the following;

 

I   )       Electron beam machining (EBM)

ii  )       Electrolytic grinding (ELG)

iii )        Electrochemical machining and deburring (ECM, ECDB)

iv )       Ultrasonic machining

v  )       Hydrojet machining

vi )       Plasma beam machining

vii)        Laser machining

 

 

 

 

 

 

 

 

 

 

 

APPARATUS:

 

Electrical Discharge Machining Wire Cutting (EDM – WC) or wire EDM machine.

 

 

 

 

               

 

 

 

 

 

 

 

 

   Figure 1:EDM Wire-Cut Machine

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                                    Figure2: EDM –Wire Cut Wiring System

 

 

 

 

 

 

 

 

 

 

 

 

THEORY        :

 

            Wire EDM, or electrical-discharge wire cutting is a variation of EDM. In this process, which is similar to contour cutting with a band saw, a slowly moving wire travels along a prescribed path, cutting the workpiece, with the discharge sparks acting like cutting teeth. This process is used to cut plates as thick as 300 mm (12 in.), and for making punches, tools, and dies from hard metals. It can also cut intricate components for the electronics industry.

In Electrical-Discharge Machining (EDM) Wire Cut a very thin wire serves as the electrode. Special brass wires are typically used, the wire is slowly fed through the material and the electrical discharges actually cut the workpiece. In Electrical-Discharge Machining (EDM) Wire Cut is usually performed in a bath of water. If observe in Electrical-Discharge Machining (EDM) Wire Cut process under a microscope, 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. In the case of the Electrical-Discharge Machining (EDM) Wire Cut process, the required shape is generated by using a wire electrode. The wire is passed through the part much like a cheese cutter through cheese. The wire is almost always copper and since copper wears rapidly the wire is fed on reels. The wire also usually made of brass, copper, or tungsten; zinc- or brass-coated and multi-coated wires are also used. This gives the part being machined a fresh electrode at all times.

The movement of the wire is computer controlled in two axis (and sometimes more). This is exactly like any other CNC controlled process but in CNC EDM the shape is generated independently by guiding the wire. In the case of complicated shapes requiring cuts or angled, conical, or other unusual surfaces, the upper and lower wire guide systems carry out differing movements accordingly.

 

 

 

PROCEDURE           :

1)      The conductive work piece is mounted to the machine and the work piece is secured to the table in such way that the electrode can make the desired cut path without interference either from the work piece, or the work holding device.

 

2)      The material needs to be removed and the part should be tightly fastened to table to ensure that it remains in place during the process.

 

3)      The work piece must be aligned relative to the machine axis that consists of X, Y, Z, U and V axes.

 

4)      The ball indicator is usually attached and the work piece is adjusted until it is vertical and parallel within the desired tolerance.

 

5)      The machine coordinate system has to be set to the appropriate position after the work piece is secured to the machine table and aligned to machine axes.

 

6)      The Wire electrode is positioned to work piece.

 

7)      The brass electrode while being spooled off and under tension is brought within a close proximity of the work piece edge.

 

8)      The edge position command and designate is executed to the appropriate axis.

 

9)      The process for the cutting had been program using G and M codes.

 

 

 

 

RESULT         :

 

In the process of using Electrical-Discharge Machining (EDM) Wire Cut machine, we are using Brass wire of 0.2mm diameter to cut Aluminium plate which has thickness of 6mm. At the end of the process, we got the end product with the desire shape which is the shape of a leaf. The process to cut the workpiece took about 10 minutes.

 

 

 

 

 

 

 

 

 

 

DISCUSSION            :

 

1.Brief process of EDM-Wire Cut

 

Because EDM Wire-cut uses a constantly-moving wire as   the cutting tool, it is also called traveling-wire EDM. The wire is threaded around the machine and though the material.

In EDM wire-cut, the sides of the wire acts like a band saw to cut through the workpiece material. Once the machine starts, the wire is in continuous motion so that the cutting is actually being done by a new electrode all the time, thus solving the problem of electrode wear. The used wire is then discarded.

Wire-cut EDM is used with computer numerical control (CNC), and machines frequently operate unattended (non-operator). Today's computers with sophisticated software packages have cut programming time and extended geometric capabilities. Hardware advances allow automatic rethreading for machines that work unattended.

A wire-cut EDM system is composed of a power supply, an electrode, a dielectric coolant and ancillary equipment. Like vertical EDM, technology is rapidly improving the systems' capabilities. Wire-cut EDM equipment can cut at speeds in excess of 20 square inches per hour. The workpiece typically is mounted on a table with two degrees of freedom. The movement of the table and wire are controlled by a computer that can compensate for overcut, wire thickness, and known errors in the workpiece.

Wire-cut EDM is efficient because the wire erodes a thin line around the perimeter of the required cut rather than the full volume of the cavity as with vertical EDM.

 

 

 

 

 

 

 

 

 

 

 

 

 

Click to view larger JPEG.                                                                                 Pic.2: The role of the brass wire.

 

 

 

 

                                                                                

 

 

   Pic.3: Principle work of EDM Wire-Cut                         Pic.4: Cutting process.

 

 

 

 

 

 

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Pic.5: Basic working principle of EDM wire-cut.

 

 

 

 

 

 

 

 

 

 

 

2. Products or applications of EDM-Wire Cut

 

            Examples of product made by EDM-Wire Cut are punches, turbine blades, aerospace parts, electronics parts, gears, tools, dies, etc.

Figure 5:Independent UV • Die inserts • Mold Inserts • Small Hole EDM • Small Wire EDM Medical Components • Extrusion Dies • Advanced Taper - 2-axis • 4-axis Twists • Independent UV • Die inserts • Mold Inserts • Small Hole EDM • Small Wire EDM Based

           

 

3. Advantages and Disadvantages of EDM-Wire Cut.

EDM-Wire Cut also has its own particular advantages. The machine capability is cutting materials regardless of its hardness. EDM-Wire Cut is much faster than EDM. It can cuts intricate shapes, narrow slots, etc. Furthermore no burrs generated during the process. The wire electrodes used are much cheaper than shaped electrodes in EDM. Nowadays, EDM-Wire Cut cables to cut tapered shape products. Electrical Discharge Machining or EDM is a highly accurate method of part production. Wire EDM technology is essential for higher tolerance parts and repeatable tooling. Tolerances are held to ±.0002" in our temperature controlled facility. Achieving high accuracy and tighter tolerances is essential for many industries such as aerospace, medical, injection molding and tool and die. With Electrical Discharge Machining we can produce and repeat the required specifications with ease

           

 

 

 

Beside that, EDM-Wire Cut also has disadvantages. The EDM-Wire Cut Machine more expansive than other machine. High skills are required to handle the machine. The work piece only conductors can be machine. EDM-wire cut have slow material removal rate (MRR) and less flexible compared others machine.  

 

4. Safety issues when handling EDM-Wire Cut

            The safety issues of when handling EDM-Cut are pre-machining condition. Such safety issues are like the set up of the machine must be right such the clamp of the workpiece is tighten securely and firmly. Since the machine is supplied by high current therefore carelessness will result to injury or worst fatality. If the machine suddenly hanged or running awkwardly press the emergency button to stop it immediately and shut down the power supply. Report to the technician.

 

 

5. Differences between EDM and EDM-Wire Cut

In EDM the electrodes used are shaped electrodes which are mirror image of the workpiece. This type of electrodes can be used many times. The machine can make fine blind holes. The dielectric used can be paraffin oil or kerosene, light oil.

However in wire EDM or EDM-Wire Cut it uses only a very thin wire as its electrodes. In contrast to EDM, the wire can only be used once at one time. The machine cannot make blind holes but only through holes. It uses deionized water as it dielectric.

 

 

6. Recommendation to purchase an EDM-Wire Cut

            One of the most important recommendations to buy EDM-Wire Cut is that due to the ability to cut any material regardless of its hardness but only conductor materials. Besides that, the absence of all-mechanical forces makes it possible to machine fragile parts without distortion. It is so recommended due to its high accuracy thus producing a high quality product. Less labour is required to operate but must be well trained. This will reduce overall production cost and increase profit of the company.

 

 

CONCLUSION          :

 

It can be concluded that:-

 

  1. Wire EDM, or electrical-discharge wire cutting process is based on the principal energy mode is thermal with the electrical discharge. It is also similar to contour cutting with a band saw, a slowly moving wire travels along a prescribed path, cutting the workpiece, with the discharge sparks acting like cutting teeth.
  2. This process is used to cut plates as thick as 300 mm (12 in.), and for making punches, tools, and dies from hard metals. It can also cut intricate components for the electronics industry.
  3. Special brass wires are typically used and usually performed in a bath of water.
  4. As technology advances in speed, workpiece size and geometry complexity, accuracy, ease of use, unattended operation, industry education and affordability. In the case of complicated shapes requiring cuts or angled, conical, or other unusual surfaces, the upper and lower wire guide systems carry out differing movements accordingly.

 

 

 

 

 

6 comments:

  1. Wow, great article, I really appreciate your thought process and having it explained properly, thank you!
    Wire cut edm

    ReplyDelete
  2. I am looking your website first time, your blog is better than other Electrical Discharge Machining (EDM)blog.

    EDM Singapore

    ReplyDelete
  3. Hi Today I have read your blog posting. It is very informative for us. We like it and it is really nice information about Sinker EDM Machine. we are also same in this field. Thanks for this nice and great information.

    ReplyDelete
  4. Useful information here about EDM tooling system. I was looking for such a blog that can provide useful information about
    EDM Tooling System
    . Thanks for sharing this blog with us.

    ReplyDelete
  5. While CNC machining has been the way to go for decades at this point, replacing many instances of manual labor, 5-axis CNC machining has been revolutionary. It takes the base concept of CNC machining and adds several layers to bring intricate designs to life.
    MD Design and Automation are providing CNC prototyping, Precision machining cnc and manual, Short run machining, cnc machining wisconsin, machining, EDM Machining Wisconsin,4 and 5 axis machining and electrical discharge machining at their facilities in Wisconsin.

    ReplyDelete