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ECM.pptx

Apr 03, 2018

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    UNIT-3

    ELECTR0-CHEMICAL PROCESSES

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    Electro-chemical Machining

    Latest and potentially available methodMichael faraday Electroplating

    ECM Reverse of Electroplating

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    Chemistry of Electroplating

    Metal to be plated by metal negative charge- cathode

    Metal used plate positive Charge Anode

    Put in the same solution

    Electrons flow from + to where the metal to beplated is being reduced and the metal being used inthe process is being oxidized.

    The positive ions from the salt solution and the metalbeing used to plate "stick" onto the object being plated

    since it has a negative charge. The thickness of themetal plating depends on how long you leave it in thesolution, and the flow of electrons.

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    ECM Reverse of Electroplating

    ECM uses a shaped tool or Electrode

    Tool Cathode Work piece Anode

    Electrolyte is pumped

    Chemical properties of the electrolytes

    Constituents go into the electrolyte

    By proper design the cavity or hole which is

    exactly produced reproduces the tool shape.

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    Shaped tool is connected to negative terminal(cathode)

    Tool should be made up of materials have enoughthermal and electrical conductivity, high Chemical

    resistance to electrolyte.Stainless steel, titanium, Brass, copper,

    Reinforced plastics.

    Shaping the tool is not a problem, Easy tomachine

    Cold forging, electroforming Favorablemethods.

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    No restriction except to be a good conductorof electricity

    Chemical characteristics of the work material

    affect MRR. MRR atomic weight and 1/ to the valency

    of the work material.

    Fixtures should be of insulating material.Epoxy resin 0r glass fibres

    For cheapest purpose Perspex , PVC

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    Low voltages 2 to 20v

    Rare time 30v

    Current 800 amp/cm

    2

    three phase 440v, ACpower supply converted by a step down

    transformer, Rectifier

    Protective circuits is given Mishandling,Incorrect fitting.

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    Electrolyte

    completing the electric circuit between thetool and the work piece

    Allowing desirable machining reactions tooccur

    Carrying away heat generated during the

    chemical reactionCarrying away products of reaction from the

    zone of machining

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    Commonly used electrolyte

    Most application-sodium chloride in water isused

    Corrosive is a problem

    Sodium nitrate solution less corrosive innature

    Potassium nitrate, sodium chromate, sodium

    hydroxide, sodium fluoride and potassiumchloride.

    Mixture of two or more is efficient

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    Working life of the

    electrolyte

    Composition of the electrolyte changes duringuse

    Main changes are

    Loss of hydrogen Reduces the electricalconductivity of the electrolyte

    Loss of water due to evaporation

    Precipitate formation

    Salt absorption by the precipitate

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    Temperature and pressure

    Difference in temperature is an important factor

    Kubeth & Heitmann recorded 45C Decreases the specific resistance of the electrolyte

    Precautions taken to overheating of the electrolyte

    An increase in temperature speed up theelectrode reactions, reduces the over voltages

    required

    Voltage required is reduces with increase intemperature

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    In order to obtain good results

    Remove the contaminated electrolyte from the

    working Gap

    Minimize polarization.

    Limit the rise in temperature of the electrolyte.

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    Working of ECM

    Is a method of removing metal particles by an

    electrochemical process instead of standard

    machining methods.

    First introduction of ECM in 1929 by Gusseff, its

    industrial applications

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    The workpiece is made anode of the setup and

    material is removed by anodic dissolution.Tool is made cathode and kept in close proximity

    to the workpiece and current is passed throughthe circuit.

    Both electrodes are immersed into the electrolytesolution.

    This works on the basis of Faradays law ofelectrolysis. The cavity machined is the mirror

    image of the tool. MRR in this process can easily be calculatedaccording to Faradays law.

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    Mechanism of Electrolysis

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    First Law The quantity of a substance

    produced by electrolysis is proportional to the

    quantity of electricity used.

    Second Law For a given quantity of electricity

    the quantity of substance produced is

    proportional to its weight.

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    13/05/2002 23 AUC - MENG

    Advantages

    There is no cutting forces therefore clamping

    is not required except for controlled motion of

    the work piece.

    There is no heat affected zone.

    Very accurate.

    Relatively fast

    Can machine harder metals than the tool.

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    Disadvantages

    More expensive than conventional machining.

    Need more area for installation.

    Electrolytes may destroy the equipment.

    Not environmentally friendly (sludge and

    other waste)

    High energy consumption.

    Material has to be electrically conductive.

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    Applications

    The most common application of ECM is highaccuracy duplication. Because there is no tool wear,it can be used repeatedly with a high degree ofaccuracy.

    It is also used to make cavities and holes in variousproducts.

    It is commonly used on thin walled, easilydeformable and brittle material because they wouldprobably develop cracks with conventionalmachining.

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    Economics

    The process is economical when a largenumber of complex identical products need tobe made (at least 50 units)

    Several tools could be connected to a cassetteto make many cavities simultaneously. (i.e.cylinder cavities in engines)

    Large cavities are more economical on ECMand can be processed in 1/10 the time ofEDM.

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    Products

    The two most common products of ECM areturbine/compressor blades and rifle barrels. Each of thoseparts require machining of extremely hard metals with certainmechanical specifications that would be really difficult to

    perform on conventional machines. Some of these mechanical characteristics achieved by ECM

    are:

    Stress free grooves.

    Any groove geometry.

    Any conductive metal can be machined. Repeatable accuracy of 0.0005.

    High surface finish.

    Fast cycle time.

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    Safety Considerations

    Several sensors are used to control short circuit, turbulence,passivation, contact and overcurrent sensors. In case ofcontact, immense heat would be generated melting the tool,evaporating the electrolyte and cause a fire.

    The worker must be insulated to prevent electrocution. The tool and the work piece must be grounded before any

    handling is performed.

    Hydrogen gas emitted is very flammable, so it should bedisposed of properly and fire precautions should be taken.

    The waste material is very dangerous and environmentallyunfriendly (metal sludge) so it must be recycle or disposed of

    properly.

    Electrolyte is highly pressurized and worker must check for

    minor cracks in piping before operating