15879_ecm, cm, edm, pvd, cvd

78
CHEMICAL AND PHOTO-CHEMICAL MACHINING

Upload: amit-dev

Post on 04-Oct-2015

225 views

Category:

Documents


0 download

DESCRIPTION

ecm

TRANSCRIPT

  • CHEMICAL AND PHOTO-CHEMICAL MACHINING

  • Chemical Machining (CHM)Chemical Machining (CHM) was developed based on the observation that chemicals attack metals and etch them by using chemical dissolutions.

    Chemical machining (CHM) is the controlled chemical dissolution (CD) of the work piece material by contact with a strong reagent.

    Special coatings called maskants protect areas from which the metal is not to be removed.

    The work piece is either immersed in or exposed to a spray of chemical reagent.

    The process is the oldest of nontraditional machining processes, and has been used to engrave metals and hard stones and to remove materials from parts having a high strength-to-weight ratio.Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Steps in CHMCleaningMaskingScribingEtchingDemaskingName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Principle of CHMName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Contour, Taper and Step Cut by CHMName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • MaskantsMaskants are generally used to protect parts of the work piece where CD action is not needed. Synthetic or rubber base materials are frequently used. Maskants should, however, possess the following properties:

    Be tough enough to withstand handlingAdhere well to the work piece surfaceScribe easilyBe inert to the chemical reagent usedBe able to withstand the heat generated by etchingBe removed easily and inexpensively after etchingName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Types of maskants used in CHMCut and Peel masksScreen resist masksPhoto resist masks

    Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • EtchantsEtchants are acid or alkaline solutions maintained within a controlled range of chemical composition and temperature. Their main technical goals are to achieve the following:

    Good surface finishUniformity of metal removalMaintenance of personal safetyMaintenance of air quality and avoidance of possible environmental problemsLow cost per unit weight dissolvedAbility to regenerate the etchant solution and/or readily neutralize and dispose of its waste productsName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Maskant and Etchant CharacteristicsName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Scribing Templates Scribing templates are used to define the areas for exposure to the chemical machining action.The most common work piece scribing method is to cut the mask with a sharp knife followed by careful peeling of the mask from the selected areas.

    Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • AdvantagesSimultaneous material removal, from all surfaces, improves productivityNo burrs are formedNo stress is introduced to the work piece, which minimizes the part distortionThe capital cost of equipment, used for machining large components, is relatively low.The good surface quality in addition to the absence of burrs eliminates the need for finishing operationsTooling costs are minorName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • DisadvantagesHandling and disposal of chemicals can be troublesomeDifficult to get sharp cornerDifficult to chemically machine thick materialsScribing accuracy is limited, causing less dimensional accuracyWelded areas frequently etch at rates that differ from the base metal.

    Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • ApplicationsHigh Precision Partsand Decorative ItemsGasketsWashers Sensors NameplatesJewelry Microprocessor Chips

    CHM is used to thin out walls, webs, and ribs of parts that have been produced by forging, casting, or sheet metal forming

    Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Photochemical machining (PCM)Photochemical machining (PCM) is a variation of chemical machining (CHM) where the chemically resistant mask is applied to the work piece by photographic techniques.CHM is usually used on three dimensional parts originally formed by another manufacturing process, such as forging and casting of irregular shapes.Photochemical machining, creates new parts from thin materials, rather than simply smoothing or altering parts formed by other manufacturing methods.Sometimes photochemical machining is used to surface etch components with lettering or graphics where the etchant works its way to only a certain depth in the material.

    Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Flow Chart for Photochemical machiningName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Steps in PCMName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Electrochemical Machining (ECM)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.

    Electrical energy is used to produce a chemical reaction, therefore, the machining process based on this principle is known as Electrochemical machining (ECM). This process works on the principle of Faradays laws of electrolysis.

    Michael Faraday discovered that if the two electrodes are placed in a bath containing a conductive liquid and DC potential (5-25V) is applied across them, metal can be depleted from the anode and plated on the cathode This principle was in use for long time. ECM is the reverse of the electroplating.Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Schematic of ProcessName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Chemistry of processName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Electrochemical Drilling UnitName of Discipline Mechanical Engineering*Power supply

    Electrolyte supply and cleaning system

    Tool and tool feed system

    Work piece and Work holding system.

    Name of Discipline Mechanical Engineering

  • Power SupplyDuring ECM, a high value of direct current ( may be as high as 40000 A) and a low value of electric potential ( in range of 5-25 V) across IEG( Interelectrode gap) is desirable.

    The highest current density achieved so far is around 20,000 A/cm2.

    Hence , with the help of a rectifier and a transformer, three phase AC is converted to a low voltage, high current DC.

    Silicon controlled rectifier (SCRs) are used both for rectification as well as for voltage regulation because of their rapid response to the changes in the process load and their compactness.Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Electrolyte supply and Cleaning systemThe electrolyte supply and cleaning system consisting of a pump, filter, pipings, control valves, heating or cooling coils, pressure gauges, and a storage tank ( or reservoir).

    Electrolyte supply ports may be made in the tool, work or fixture, depending upon the requirement of the mode of electrolyte flow.Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Tool and Tool Feed systemUse of anti corrosive material for tools and fixtures is important because they are required for a long period of time to operate in the corrosive environment of electrolyte.

    High thermal conductivity are main requirements.

    Aluminum, Brass, Bronze, copper, carbon, stainless steel and monel are a few of the material used for this purpose.Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Work piece and work holding systemOnly electrically conductive material can be machined by this process, The chemical properties of anode ( work) material largely govern the material removal rate (MRR).

    Work holding devices are made of electrically non conductive materials having good thermal stability, and low moisture absorption properties.

    For Example, graphite fibres reinforced plastics, plastics, Perspex,etc., are the materials used for fabricating the work holding device.Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • ApplicationsName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Electrochemical GrindingElectrochemical grindingis a process that removes electrically conductive material by grinding with anegatively chargedabrasive grinding wheel, anelectrolytefluid, and a positively charged work piece.Electrochemical grinding andelectrochemical machiningare similar but a wheel is used instead of a tool shaped like the contour of the work piece.Process characteristicsThe wheels and work piece are electrically conductive.Wheels used last for many grindings - typically 90% of the metal is removed byelectrolysisand 10% from the abrasive grinding wheel.Capable of producing smooth edges without the burrs caused by mechanical grinding.Does not produce appreciable heat that would distort work piece.Decomposes the work piece and deposits them into the electrolyte solution. The most common electrolytes aresodium chlorideandsodium nitrate.

    Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Electrochemical GrindingName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • UsesProduction of tungsten carbide cutting tools.Burr-free sharpening of hypodermic needlesGrinding of super alloy turbine bladesForm grinding of aerospace honeycomb metalsName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Electrodischarge MachiningThe history of electrodischarge machining (EDM) dates back to the days of World Wars I and II.The evolution of wire EDM in the 1970s was due to the powerful generators, new wire tool electrodes, improved machine intelligence, and better flushing.Recently, the machining speed has gone up by 20 times, which has decreased machining costs by at least 30 percent and improved the surface finish by a factor of 15.Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Advantages1. Cavities with thin walls and fine features can be produced.2. Difficult geometry is possible.3. The use of EDM is not affected by the hardness of the work material.4. The process is burr-free.Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Machining System

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Characteristics of EDM

    (a) The process can be used to machine any work material if it is electrically conductive (b) Material removal depends on mainly thermal properties of the work material rather than its strength, hardness etc (c) In EDM there is a physical tool and geometry of the tool is the positive impression of the hole or geometric feature machined (d) The tool has to be electrically conductive as well. The tool wear once again depends on the thermal properties of the tool material (e) Though the local temperature rise is rather high, still due to very small pulse on time, there is not enough time for the heat to diffuse and thus almost no increase in bulk temperature takes place. Thus the heat affected zone is limited to 2 4 m of the spark crater (f) However rapid heating and cooling and local high temperature leads to surface hardening which may be desirable in some applications (g) Though there is a possibility of taper cut and overcut in EDM, they can be controlled and compensated.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    The open circuit voltage - Vo The working voltage - Vw The maximum current - Io The pulse on time the duration for which the voltage pulse is applied - ton The pulse off time - toff The gap between the workpiece and the tool spark gap - The polarity straight polarity tool (-ve) The dielectric medium External flushing through the spark gap. Process parameters

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*PulseOnTime(tepulsedurationins)The duration of time(s)the current is allowed to flow per cycle.Material removal(MRR) is directly proportional to the amount of energy applied during this on-timeThis energy is really controlled by the peak current and the length of the on-time

    PulseOff-Time(tointervaltimeins)The duration of time(s) between the sparksThis time allows the molten to solidify and to be wash out of the arc gapThis parameter is to affect the speed and the stability of the cutIf the off-time is too short ,it will cause sparks to be unstable

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Uimachining voltage (v)ie peak currenttdignition delay time (s)te pulse duration (s)to interval time (s)

    (b) Non-electrical parameters:-Flushing-Types of dielectric medium (kerosene, dielectric, etc)

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Spark gapThe distance between the electrode and the part during the process of EDM

    Duty cycleIt is a percentage of the on-time relative to the total cycle timeThis parameter is calculated by dividing the on-time by the total cycle time( on time + off-time)The result is multiplied by 100 for the percentage of efficiency or the so called duty cycle

    IntensityPoints out the different levels of power that can be supplied by the generator of the EDM machine.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Effect of pulse current (energy) on MRR & surface roughness.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Effect of pulse on-time (energy) on MRR & surface roughness.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Common electrodes used such as brass,tungsten,copper-tungsten,silver-tungsten,copper,graphiteandetc.Copper have been used primarily in resistance capacitance circuit where higher voltage are employed.

    Graphite commonly used in application to get fine surface,low cost and high material removal rate. Other type of electrodes are copper tungsten, brass, steel, cast iron, zinc based alloys.Electrodes of EDM

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Flushing is important because it removes eroded particle from the gap between tool and work piece while machining.

    Methods: a)Vacuum (suction) through electrode b)Suction through work piece c)Pressure through hole flushing (injection flushing) d)Pressure through work piece e)Outside flushing (fluid injection, side flushing)

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    MRR (cm3/min) = (Wb -Wa) / (*t)

    Wa = Weight after machiningWb= Weight before machining= Densityt = Machining time.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Applications of EDM

    a)Sinking of two connecting rods with electrode.b)Sinking of extrusion insert plate of motor anchor with single electrode.c)Machining of embossing die.d)Machining of forging die.e)Sinking of injection mold insert for light alloys

    Name of Discipline Mechanical Engineering

  • LASER BEAM MACHININGName of Discipline Mechanical Engineering*Laser is the abbreviation of light amplification by stimulated emission of radiation. A highly collimated, monochromatic, and coherent light beam is generated and focused to a small spot. High power densities (1000000 W/mm2) are then obtained. A large variety of lasers are available in the market including solid-state, ion, and molecular types in either continuous wave (CW) or pulsed mode (PM) of operation.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Electron Beam MachiningName of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Chemical Vapour Deposition

    Name of Discipline Mechanical Engineering*Chemical Vapour DepositionIntroductionChemical vapour deposition or CVD is a generic name for a group of processes that involve depositing a solid material from a gaseous phase.Microfabrication processes widely use CVD to deposit materials in various forms, including: monocrystalline, polycrystalline, amorphous, and epitaxial. These materials include: silicon, carbon fiber, carbon nanofibers, filaments, carbon nanotubes, SiO2, silicon-germanium, tungsten, silicon carbide, silicon nitride, silicon oxynitride and titanium nitride. CVD process is also used to produce synthetic diamonds.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Working Concept

    Chemical vapor deposition (CVD) results from the chemical reaction of gaseous precursor(s) at a heated substrate to yield a fully dense deposit. Thermodynamics and kinetics drive both precursor generation and decomposition. Control of thermodynamics and kinetics through temperature, pressure, and concentrations yields the desired deposit. A simplified concept diagram is shown as Fig Metal deposition metal halide (g) metal(s) + byproduct (g)Ceramic deposition metal halide (g) + oxygen/carbon/nitrogen/boron source (g) ceramic(s) + byproduct (g) g- gas; s-solid

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*A basic CVD process consists of the following steps: a predefined mix of reactant gases and diluent inert gases are introduced at a specified flow rate into the reaction chamber; the gas species move to the substrate; the reactants get adsorbed on the surface of the substrate; the reactants undergo chemical reactions with the substrate to form the film; andthe gaseous by-products of the reactions are desorbed and evacuated from the reaction chamber.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*During the process of chemical vapor deposition, the reactant gases not only react with the substrate material at the wafer surface (or very close to it), but also in gas phase in the reactor's atmosphere. Reactions that take place at the substrate surface are known as heterogeneous reactions, and are selectively occurring on the heated surface of the wafer where they create good-quality films. Reactions that take place in the gas phase are known as homogeneous reactions. Homogeneous reactions form gas phase aggregates of the depositing material, which adhere to the surface poorly and at the same time form low-density films with lots of defects. In short, heterogeneous reactions are much more desirable than homogeneous reactions during chemical vapor deposition.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*A typical CVD system consists of the following parts: sources of and feed lines for gases; mass flow controllers for metering the gases into the system; a reaction chamber or reactor; a system for heating up the wafer on which the film is to be deposited; and temperature sensors.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*

    Name of Discipline Mechanical Engineering

  • Types of CVDName of Discipline Mechanical Engineering*

    Classified by operating pressure:

    Atmospheric pressure CVD(APCVD) CVD at atmospheric pressure.

    Low-pressure CVD(LPCVD) CVD at sub-atmospheric pressures. Reduced pressures tend to reduce unwanted gas-phase reactions and improve film uniformity across the wafer.

    Ultrahigh vacuum CVD(UHVCVD) CVD at very low pressure, typically below 106Pa(~108torr). Note that in other fields, a lower division between high andultra-high vacuumis common, often 107Pa.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Classified by physical characteristics of vapor:

    Aerosol assisted CVD(AACVD) CVD in which the precursors are transported to the substrate by means of a liquid/gas aerosol, which can be generated ultrasonically. This technique is suitable for use with non-volatile precursors.

    Direct liquid injection CVD(DLICVD) CVD in which the precursors are in liquid form (liquid or solid dissolved in a convenient solvent). Liquid solutions are injected in a vaporization chamber towards injectors (typically car injectors). The precursor vapors are then transported to the substrate as in classical CVD. This technique is suitable for use on liquid or solid precursors. High growth rates can be reached using this technique.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Plasma methods Plasma Enhanced CVD(PECVD) CVD that utilizesplasmato enhance chemical reaction rates of the precursors.PECVD processing allows deposition at lower temperatures, which is often critical in the manufacture of semiconductors. The lower temperatures also allow for the deposition of organic coatings, such as plasma polymers, that have been used for nanoparticle surface functionalization.Remote plasma-enhanced CVD(RPECVD) Similar to PECVD except that the wafer substrate is not directly in the plasma discharge region. Removing the wafer from the plasma region allows processing temperatures down to room temperature. Combustion CVD (CCVD) Combustion Chemical Vapor Deposition or flame pyrolysis is an open-atmosphere, flame-based technique for depositing high-quality thin films and nanomaterials. Rapid thermal CVD(RTCVD) This CVD process uses heating lamps or other methods to rapidly heat the wafer substrate. Heating only the substrate rather than the gas or chamber walls helps reduce unwanted gas-phase reactions that can lead toparticleformation. Photo-initiated CVD(PICVD) This process uses UV light to stimulate chemical reactions. It is similar to plasma processing, given that plasmas are strong emitters of UV radiation. Under certain conditions, PICVD can be operated at or near atmospheric pressure

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*APCVD, LPCVD, and PECVD Comparison

    CVD ProcessAdvantagesDisadvantagesApplicationsAPCVDSimple, Fast Deposition,Low Temperature Poor Step Coverage,ContaminationLow-temperature OxidesLPCVDExcellent Purity,Excellent Uniformity,Good Step Coverage,Large Wafer CapacityHigh Temperature,Slow DepositionHigh-temperature Oxides, Silicon Nitride, Poly-Si, W, WSi2PECVDLow Temperature,Good Step CoverageChemical and Particle ContaminationLow-temperature Insulators over Metals, Nitride Passivation

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Advantages of CVDCan be used for a wide range of metals and ceramicsCan be used for coatings or freestanding structuresFabricates net or near-net complex shapesIs self-cleaningextremely high purity deposits (>99.995% purity)Conforms homogeneously to contours of substrate surfaceHas near-theoretical as-deposited densityHas controllable thickness and morphologyForms alloysInfiltrates fiber preforms and foam structuresCoats internal passages with high length-to-diameter ratiosCan simultaneously coat multiple componentsCoats powders

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*ApplicationsCVD processes are used on a surprisingly wide range of industrial components, from aircraft and land gas turbine blades, timing chain pins for the automotive industry, radiant grills for gas cookers and items of chemical plant, to resist various attacks by carbon, oxygen and sulphur.Some important applications are listed below.Surface modification to prevent or promote adhesion Photoresist adhesion for semiconductor wafers Silane/substrate adhesion for microarrays (DNA, gene, protein, antibody, tissue) MEMS coating to reduce stiction BioMEMS and biosensor coating to reduce "drift" in device performancePromote biocompatibility between natural and synthetic materials Copper capping Anti-corrosive coating

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Physical Vapour Deposition(PVD) Introduction 1.Physical vapour deposition (PVD) is fundamentally a vaporisation coating technique, involving transfer of material on an atomic level. It is an alternative process to electroplating 2.The process is similar to chemical vapour deposition (CVD) except that the raw materials/precursors, i.e. the material that is going to be deposited starts out in solid form, whereas in CVD, the precursors are introduced to the reaction chamber in the gaseous state. Working Concept PVD processes are carried out under vacuum conditions. The process involved four steps: 1.Evaporation 2.Transportation 3.Reaction 4.Deposition

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Evaporation During this stage, a target, consisting of the material to be deposited is bombarded by a high energy source such as a beam of electrons or ions. This dislodges atoms from the surface of the target, vaporising them.Transport This process simply consists of the movement of vaporised atoms from the target to the substrate to be coated and will generally be a straight line affair.ReactionIn some cases coatings will consist of metal oxides, nitrides, carbides and other such materials. In these cases, the target will consist of the metal. The atoms of metal will then react with the appropriate gas during the transport stage. For the above examples, the reactive gases may be oxygen, nitrogen and methane. In instances where the coating consists of the target material alone, this step would not be part of the process.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Deposition This is the process of coating build up on the substrate surface. Depending on the actual process, some reactions between target materials and the reactive gases may also take place at the substrate surface simultaneously with the deposition process. Fig. shows a schematic diagram of the principles behind one common PVD method. The component that is to be coated is placed in a vacuum chamber. The coating material is evaporated by intense heat from, for example, a tungsten filament. An alternative method is to evaporate the coating material by a complex ion bombardment technique. The coating is then formed by atoms of the coating material being deposited onto the surface of the component being treated.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*The vacuum evaporation PVD process

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering* Variants of PVD include, in order of increasing novelty: Evaporative Deposition: In which the material to be deposited is heated to a high vapor pressure by electrically resistive heating in "high" vacuum. Electron Beam Physical Vapor Deposition: In which the material to be deposited is heated to a high vapor pressure by electron bombardment in "high" vacuum. Sputter Deposition: In which a glow plasma discharge (usually localized around the "target" by a magnet) bombards the material sputtering some away as a vapor. Cathodic Arc Deposition: In which a high power arc directed at the target material blasts away some into a vapor. Pulsed Laser Deposition: In which a high power laser ablates material from the target into a vapor.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Summary of Merits and Demerits of evaporation methods

    MethodMeritsDemeritsE-Beam Evaporation1. high temp materials 2. good for liftoff 3. highest purity 1. some CMOS processes sensitive to radiation 2. alloys difficult 3. poor step coverageFilament Evaporation1. simple to implement 2. good for liftoff1. limited source material (no high temp) 2. alloys difficult 3. poor step coverageSputter Deposition1. better step coverage 2. alloys 3. high temp materials 4. less radiation damage 1. possible grainy films 2. porous films 3. plasma damage/contamination

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Importance of PVD CoatingsPVD coatings are deposited for numerous reasons. Some of the main ones are:Improved hardness and wear resistanceReduced frictionImproved oxidation resistanceThe use of such coatings is aimed at improving efficiency through improved performance and longer component life. They may also allow coated components to operate in environments that the uncoated component would not otherwise have been able to perform.

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*AdvantagesMaterials can be deposited with improved properties compared to the substrate materialAlmost any type of inorganic material can be used as well as some kinds of organic materialsThe process is more environmentally friendly than processes such as electroplatingDisadvantagesIt is a line of sight technique meaning that it is extremely difficult to coat undercuts and similar surface featuresHigh capital costSome processes operate at high vacuums and temperatures requiring skilled operatorsProcesses requiring large amounts of heat require appropriate cooling systemsThe rate of coating deposition is usually quite slow

    Name of Discipline Mechanical Engineering

  • Name of Discipline Mechanical Engineering*Applications PVD coatings are generally used to improve hardness, wear resistance and oxidation resistance. Thus, such coatings use in a wide range of applications such as:AerospaceAutomotiveSurgical/MedicalDies and moulds for all manner of material processingCutting toolsFire arms **

    Name of Discipline Mechanical Engineering