Course Number: Ipe-116

Course number: IPE-116

Date: 09-04-09

Seminar on "Working principle and applications of EDM & ECM "

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Introduction: Most of the processes for molding, forming, joining, and cutting materials have been around for many years. Newer techniques that have been developed are called nontraditional or non-conventional machining. For these kind of machining there is a group including some machining process, such as- electrochemical machining (ECM), electrical discharge machining (EDM), electrodischarge grindig (EDG), electron beam machining (EBM) etc. Here we are going to describe about ECM & EDM process

Electric discharge machining: Electrical Discharge Machining, (EDM) is one of the most accurate manufacturing processes available for creating complex or simple shapes and geometries within parts and assemblies. EDM works by eroding material in the path of electrical discharges that form an arc between an electrode tool and the work piece. EDM manufacturing is quite affordable and a very desirable manufacturing process when low counts or high accuracy is required. Turn around time can be fast and depends on manufacturer back log.

[1] Working principle: The EDM system consists of a shaped tool or wire electrode, and the part. The part is connected to a power supply. Sometimes to create a potential difference between the work piece and tool, the work piece is immersed in a dielectric (electrically nonconducting) fluid which is circulated to flush away debris. The cutting pattern is usually CNC controlled. Many EDM machine electrodes can rotate about two-three axis allowing for cutting of internal cavities. This makes EDM a highly capable manufacturing process. EDM comes in two basic types: wire and probe (die sinker). Wire EDM is used primarily for shapes cut shapes through a selected part or assembly. With a wire EDM machine, if a cutout needs to be created, an initial hole must first be drilled in the material, then the

wire can be fed through the hole to complete the machining. Sinker (diesinking) EDMs are generally used for complex geometries where the EDM machine uses a machined graphite or copper electrode to erode the desired shape into the part or assembly. Sinker EDM can cut a hole into the part without having a hole pre-drilled for the electrode.

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Applications of Electric discharge machining: • • • • • • • • •

Accuracy up to .005mm can be obtained. By this method a deep hole as small as .1mm in diameter can be made. Stepped cavities can be produced by thus method. Nozzle holes can be made by this process. By this process very thin sections can also be machined.

Advantages: Some of the advantages of EDM include machining of: •

complex shapes that would be difficult to produce with conventional cutting tools.

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extremely hard material to very close tolerances.

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very small work pieces where conventional cutting tools may damage the part from excess cutting tool pressure

Disadvantages: Some of the disadvantages of EDM include: •

The inability to machine non-conductive materials.

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The slow rate of material removal.

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Reproducing sharp corners on the workpiece is difficult due to electrode wear.

Electro-chemical machining: Electrochemical Machining (ECM) is a non-traditional machining (NTM) process belonging to electrochemical category. ECM is opposite of electrochemical or galvanic coating or deposition process. Thus ECM can be thought of a controlled anodic dissolution at atomic level of the work piece that is electrically conductive by a shaped tool due to flow of high current at relatively low potential difference through an electrolyte which is quite often water based neutral salt solution. Fig. 1 schematically shows the basic principle of ECM. In ECM, the workpiece is connected to the positive terminal of a low voltage high current DC generator or power source. The tool is shaped and shape of the tool is transferred to the workpiece. The tool is connected to the negative terminal. Machining takes place due to anodic dissolution at atomic level of the work material due to electrochemical reaction. A gap between the tool and the workpiece is required to be maintained to proceed with steady state machining.

[3] Objectives:  Identify electro-chemical machining (ECM) as a particular type of non-tradition processes  Describe the basic working principle of ECM process  Descrive the principle of ECM process

Working principle of Electrochemical process: Electrochemical machining is founded on the principles outlined. As shown in Figure 3, the workpiece and tool are the anode and cathode, respectively, of an electrolytic cell, and a constant potential difference, usually at about 10 V, is applied across them. A suitable electrolyte, for example, aqueous sodium chloride (table salt) solution, is chosen so that the cathode shape remains unchanged during electrolysis. The electrolyte is also pumped at a rate 3 to 30 meter/second, through the gap between the electrodes to remove the products of machining and to diminish unwanted effects, such as those that arise with cathodic gas generation and electrical heating. The rate at which metal is then removed from the anode is approximately in inverse proportion to the distance between the electrodes. As machining proceeds, and with the simultaneous movement of the cathode at a typical rate, for example, 0.02 millimeter/second toward the anode, the gap width along the electrode length will gradually tend to a steady-state value. Under these conditions, a shape, roughly complementary to that of the cathode, will be reproduced on the anode. A typical gap width then should be about 0.4 millimeter. Being understood the characteristics and working principles of ECM, its advantages should be stated in short before going further through machining processes:

• the rate of metal machining does not depend on the hardness of the material, • complicated shapes can be machined on hard metals, • there is no tool wear.

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Equation: MRR= m/tP =IA/ fρv Where, I = current ρ= density of the material F = Faraday’s constant Applications: 

 It is a production process for machining conducting materials and gives the highest chip removal rates with reasonable surface finish on repetitive work  By this process even hardest possible material can be machined  This process is ideally suited for the production of deep holes and profiled cavities in electrically conducting materials  Examples of application of this process include air craft engine parts, turbine blades, grinding of carbide tools and dies, gun drilling etc.

Advantages of electrochemical machining:

 There is no tool wear during electrochemical machining.  Non-rigid and open work pieces can be machined easily as there is no contact between the tool and workpiece.  Complex geometrical shapes can be machined repeatedly and accurately  Electrochemical machining is a time saving process when compared with conventional machining  During drilling, deep holes can be made or several holes at once.  ECM deburring can debur difficult to access areas of parts.  Fragile parts which cannot take more loads and also brittle material which tend to develop cracks during machining can be machined easily through Electrochemical machining  Surface finishes of 25 µ in. can be achieved during Electrochemical machining

DISADVANTAGES  Tools are more difficult to design.  Special fixtures are required to withstand the high electrolyte flow.  The cost of the basic equipment is several times that for EDM.  The most common electrolyte, sodium chloride, is corrosive to equipment, tooling, fixtures, and work material.

Conclusion: Now a days with the development of modern technology, different kind of delicate machining is needed for many parts of different machines. By using ECM & EDM process machinist can now perform many sophisticated machining that is impossible using conventional machines. So, it is the need of present age to included these machines in the workshops and manufacturing industries.

Reference: [1]- en. Wikipedia.org [2]- http://betsa.fr [3] turbinemachining.com [4] & [5]-(http://electrochem.cwru.edu/ed/encycl/