Advance Machine Design (ME-702 (D)) - Unit 2 Short Notes

1.0 Fundamentals of Energy Systems

1.1 Energy Sources: Classification & Inter-convertibility

• Primary Energy Sources: Naturally occurring, unused form (e.g., coal, crude oil, natural gas, solar, wind, uranium, hydro potential).

• Secondary Energy Sources: Derived from primary sources after conversion (e.g., electricity, petrol, diesel, LPG, hydrogen).

• Inter-convertibility: Energy can be converted from one form to another (e.g., chemical → thermal → mechanical → electrical in a thermal power plant). No conversion is 100% efficient; each step incurs losses (typically governed by the Second Law of Thermodynamics).

[!TIP] Exam often asks for classification with examples. Remember: Electricity is always a secondary source.

2.0 Renewable Energy Systems (Indian Context Focus)

2.1 Solar Energy

• Factors Affecting Solar Intensity:

  • Latitude: Lower latitude (near equator) receives higher intensity.

  • Season & Day Length: Summer solstice > winter solstice.

  • Atmospheric Conditions: Cloud cover, humidity, dust, pollution.

  • Surface Orientation & Tracking: Tilt angle, azimuth, single/dual-axis tracking.

• Advantages for India: Abundant (5-7 kWh/m²/day in most regions), decentralized, low operating cost, no fuel cost, reduces carbon footprint.

• Limitations for India: Intermittency (day/night, monsoon), high initial capital cost, large land requirement for utility-scale plants, low efficiency (~15-22% for PV), storage challenge.

• Comparison with Wind Energy:

  | Feature | Solar PV | Wind Energy | | :--- | :--- | :--- | | Primary Resource | Solar Radiation | Wind Velocity | | Capacity Factor (India) | 15-20% | 25-35% | | Land Use | High (but can be co-located) | Very High (spacing between turbines) | | Intermittency Pattern | Diurnal & seasonal | Variable, often stronger at night/seasonal | | Maturity in India | Rapidly growing, rooftop potential | Mature, onshore dominant |

2.2 Wind Energy

• Factors Affecting Wind Velocity:

  • Geographic/Topographic: Coastal areas, mountain passes, open plains (low surface roughness).

  • Altitude: Wind speed increases with height (logarithmic profile).

  • Diurnal & Seasonal Variation: Land-sea breeze cycles, monsoon patterns.

• Limitations for India: Grid integration challenges (remote windy sites), land acquisition issues, turbine noise & avian impact, low-wind-speed sites require taller towers/special turbines, initial cost.

2.3 Hybrid Energy Systems

• Definition & Concept: Integration of two or more renewable energy sources (e.g., solar + wind, solar + hydro, solar + biomass) with or without energy storage (batteries) and/or conventional backup (diesel genset) to improve reliability, reduce variability, and optimize cost.

• Feasible Options for India:

  1. Solar-Wind Hybrid: Complementary generation profiles (wind stronger at night/winter, solar day/summer).

  2. Solar-Wind-Hydro: Hydro provides storage & quick ramping.

  3. Solar-Biomass: Biomass provides base load, solar peaks during day.

  4. Solar-Wind-Diesel: For remote off-grid/mini-grid applications.

2.4 Micro & Pico Hydro Machines

• Comparison:

  | Parameter | Micro Hydro | Pico Hydro | | :--- | :--- | :--- | | Capacity | 100 kW - 10 MW | < 100 kW (often < 10 kW) | | Head (m) | Medium to High (10-500m) | Low to Medium (1-30m) | | Flow (m³/s) | Moderate | Very Low | | Technology | More conventional (Pelton, Francis) | Often specialized low-head turbines (Crossflow, Kaplan) or propeller | | Application | Village/micro-grid, small industry | Individual homes, small communities, very remote areas | | Civil Works | Significant (dam, penstock) | Minimal (weir, canal) |

• Applications & Suitability: Ideal for hilly/riverine remote areas with perennial streams. Provides reliable, 24x7 power for rural electrification, reducing diesel dependence.

3.0 Thermal Power Plant Systems

3.1 Coal Handling System

• Elements & Components:

  1. Wagon Unloading: Track hopper, rotary wagon tippler.

  2. Crushing: Primary & secondary crushers (jaw, hammer).

  3. Screening & Grading: Vibrating screens.

  4. Storage: Coal yard (stacker-reclaimer system).

  5. Conveying: Belt conveyors (with magnetic separators, metal detectors).

  6. Boiler Feeding: Coal feeders (gravimetric/volumetric) → pulverizers (ball mill, bowl mill) → coal pipes → burners.

• Schematic:

  DiagramCANVAS: Show flow from wagon tippler -> crusher -> conveyor -> stacker/reclaimer in coal yard -> reclaim conveyor -> bunkers -> pulverizer -> coal pipes -> boiler furnace burners.

3.2 Fuel Burning Systems

• Overfeed vs. Underfeed Principle of Firing:

  • Overfeed Stoker: Coal fed above the grate. Grate moves slowly, ash falls through. Advantage: Good for low-volatile coals, better combustion control. Disadvantage: Higher height requirement, more flying dust.

  • Underfeed Stoker: Coal fed below the grate. Grate pushes coal upward. Advantage: Compact, suitable for high-volatile coals. Disadvantage: Poor air distribution, not suitable for low-volatile coals.

3.3 Steam Cycle Improvements: Reheating

• Concept: In a simple open-cycle gas turbine (Brayton cycle), exhaust gases are hot (~500-600°C). Reheating involves passing the partially expanded working fluid (gas) from the high-pressure turbine back to the combustion chamber for second-stage combustion before expanding in a low-pressure turbine.

• Impact on Thermal Efficiency:

  • Increases: Mean temperature of heat addition increases → higher cycle efficiency (approaches Carnot).

  • Increases: Net work output for same turbine inlet temperature.

  • Trade-off: Slightly higher compressor work (due to higher pressure ratio), increased complexity and capital cost.

  • Equation: Efficiency improvement depends on pressure ratio and maximum temperature. For ideal Brayton cycle with reheating, net work output increases, but thermal efficiency gain is significant only at higher pressure ratios.

3.4 Fluidized Bed Combustion (FBC)

• System Description:

  DiagramCANVAS: Sketch of circulating FBC (CFBC). Show: Air distributor plate at bottom, bed material (sand, limestone), fuel feed point, cyclone separator, return leg, boiler tubes immersed in bed, exhaust flue gas exit.

  1. Bed: Solid particles (fuel + inert bed material like sand) suspended by upward air flow (fluidization).

  2. Combustion: Occurs at relatively low temperature (800-900°C) within the bed.

  3. Limestone (CaCO₃) Addition: In-bed for in-situ desulfurization (SO₂ capture).

  4. Circulating (CFBC): High velocity carries fine particles to cyclone; collected particles recirculated.

• Advantages over Conventional (Pulverized Fuel) Combustion:

  • Fuel Flexibility: Can burn low-grade coals, biomass, waste.

  • In-situ SO₂/NOₓ Control: Lower temperature reduces thermal NOₓ; limestone captures SO₂.

  • Higher Heat Transfer: Better heat transfer coefficients → smaller boiler size.

  • Lower Ash Sintering: Lower combustion temperature reduces slagging/fouling.

3.5 Feed Water Treatment

• Elements of Feed Water Treatment Plant:

  1. Screening & Filtration: Remove suspended solids.

  2. Softening: Lime-soda process or ion exchange to remove hardness (Ca²⁺, Mg²⁺).

  3. Deaeration: Remove dissolved gases (O₂, CO₂) using steam stripping in deaerator.

  4. Chemical Treatment: Phosphate (for high-pressure boilers) or All-Volatile Treatment (AVT - ammonia + hydrazine/oxygen scavenger) to control pH and remove residual oxygen.

  5. Polishing: Mixed-bed ion exchange or membrane filtration (for ultra-pure water in supercritical plants).

3.6 Plant Heat Balance

• Concept: Quantitative account of energy input (fuel LHV), useful output (electricity), and all losses (stack, radiation, blowdown, condenser) for a power plant. Basis: 1 kg of fuel or 1 kWh output.

• Example (Fossil Fuel Plant):

  • Input: 100% = LHV of fuel.

  • Outputs/Losses:

    • Boiler Efficiency (~88-90%): Steam energy output.

    • Turbine Efficiency (~40-45%): Electrical output (overall plant efficiency ~33-38%).

    • Condenser Losses (~50% of heat input): Largest loss.

    • Stack Losses (~6-8%): Unburnt carbon, sensible heat in flue gas.

    • Auxiliary Consumption (~5-8%): Parasitic loads (pumps, fans).

    • Radiation & Blowdown (<1%).

  • Heat Rate: Inverse of efficiency. Typical Indian coal plant: 2200-2400 kcal/kWh.

3.7 Boiler Trends

• Recent Trends:

  • Size: Increase in capacity (660 MW, 800 MW, 1000 MW+ units).

  • Selection: Preference for supercritical (SC) and ultra-supercritical (USC) parameters (e.g., 25 MPa, 600°C/600°C) for higher efficiency (>45%) and lower emissions.

  • Operation: Once-through boilers for SC/USC. Advanced control systems (DCS, AI/ML for optimization). Use of low-NOₓ burners, OFA (Over Fire Air), FGD (Flue Gas Desulfurization), SCR (Selective Catalytic Reduction).

4.0 Nuclear Power Plant Systems

4.1 Nuclear Fission Phenomenon

• Process: Absorption of a slow (thermal) neutron by a fissile nucleus (e.g., U-235, Pu-239) → nucleus becomes unstable → splits into two lighter fission fragments + 2-3 fast neutrons + ~200 MeV energy.

• Chain Reaction: Neutrons from fission cause further fissions. Controlled by moderator (slows neutrons) and control rods (absorb neutrons).

• Energy Distribution: Kinetic energy of fission fragments (~85%), fast neutrons (~5%), gamma rays (~5%), fission products (~5%).

4.2 Reactor Types & Characteristics

4.2.1 Pressurized Heavy Water Reactor (PHWR) – Working & Sketch

• Working Principle:

  DiagramCANVAS: Sketch of PHWR (CANDU type). Show: Pressure tubes (contain fuel & heavy water coolant) running through a large vessel (calandria) containing heavy water moderator. Separate systems: Primary coolant (high-pressure D₂O) circulates through pressure tubes to steam generators. Moderator (low-pressure D₂O) in calandria. Control rods (adjustable) inserted into calandria.

  1. Fuel: Natural Uranium (0.7% U-235).

  2. Moderator & Coolant: Heavy Water (D₂O). Both functions separate.

  3. Pressure: High pressure in coolant channels (pressure tube design) to prevent boiling; low pressure in moderator tank (calandria).

  4. On-power Refueling: Unique feature; fuel bundles can be changed while reactor is critical.

• Characteristics: High neutron economy (can use natural uranium), good fuel utilization, flexible design, heavy water expensive but can be recovered.

4.2.2 Advanced Gas-Cooled Reactor (AGR) – Features

• Generation: Second generation of UK's Magnox reactors.

• Fuel: Enriched Uranium (2.5-3.5% U-235).

• Moderator: Graphite.

• Coolant: Carbon Dioxide (CO₂) at high pressure (~40 bar).

• Core: Graphite moderator blocks with fuel channels. Fuel is uranium oxide pellets in stainless steel cladding.

• Key Feature: Higher operating temperature (~650°C) than Magnox → higher thermal efficiency (~40%).

• Status: UK's AGR fleet is being phased out.

4.2.3 Thermal vs. Fast Breeder Reactors – Comparison

4.3 Moderators

• Functions: Slow down fast fission neutrons to thermal energies (0.025 eV) where fission probability in U-235 is highest. Must have low neutron absorption cross-section.

• Types & Characteristics:

  | Moderator | Light Water (H₂O) | Heavy Water (D₂O) | Graphite | Beryllium | | :--- | :--- | :--- | :--- | :--- | | Absorption Cross-Section | High (~0.66 barn) | Very Low (~0.0005 barn) | Low (~0.0035 barn) | Very Low (~0.009 barn) | | Scattering Power | Good | Good | Good | Excellent | | State | Liquid | Liquid | Solid | Solid | | Use With | Requires Enriched Uranium | Can use Natural Uranium | Can use Natural/LEU | Can use Natural/LEU (often with BeO) | | Examples | PWR, BWR | PHWR (CANDU) | RBMK (Chernobyl), AGR | Some research/early reactors |

4.4 Reliability & Control Features

4.4.1 Reliability Features for Nuclear Plants

• Multiple Physical Barriers: Fuel pellet → Zirconium cladding → Reactor pressure vessel → Containment building (steel + concrete).

• Redundant & Diverse Safety Systems: Multiple independent shutdown systems (SCRAM), emergency core cooling systems (ECCS), backup power (diesel generators, batteries).

• Defense-in-Depth: Hierarchical layers of safety (prevent accidents, control accidents, mitigate consequences).

• High-Quality Components & Rigorous QA: Stringent manufacturing, testing, and inspection protocols.

• Seismic Design & Safety Analysis: Probabilistic Safety Assessment (PSA), design basis accidents.

4.4.2 Principles of Reactor Control

1. Reactivity Control: Adjusting neutron multiplication factor (k_eff).

2. Control Rods: Primary method. Boron, Cadmium, Hafnium rods inserted/withdrawn to absorb neutrons.

3. Chemical Shim: Dissolving neutron absorber (e.g., boric acid) in coolant/moderator (PWR).

4. Burnable Absorbers: Temporary absorbers (Gd₂O₃, B₄C) in fuel to control initial excess reactivity.

5. Moderator Temperature Coefficient: Negative feedback (increase temp → density ↓ → moderation ↓ → power ↓).

6. Doppler Coefficient (Fuel Temp): Negative feedback (fuel temp ↑ → resonance absorption ↑ → power ↓).

5.0 Hydraulic Power Plant Systems

5.1 Hydraulic Turbines

• Classification & Specific Characteristics:

  | Type | Impulse (Pelton) | Reaction (Francis) | Reaction Axial Flow (Kaplan) | | :--- | :--- | :--- | :--- | | Energy Transfer | Kinetic energy of jet | Pressure + Kinetic (in casing & runner) | Pressure + Kinetic (axial flow) | | Head (H) | High (>300m) | Medium (30-300m) | Low (<30m) | | Flow (Q) | Low | Medium | High | | Specific Speed (Ns) | Low (10-60) | Medium (60-300) | High (300-1000+) | | Runner | Bucket-shaped, open | Closed, radial flow | Propeller blades, adjustable | | Efficiency | Very High (>90%) | High (90-94%) | High (90-93%) | | Casing | Not required (open) | Spiral casing (volute) | Tubular/simple casing |

• Selection Factors for Hydel Plants:

  1. Net Head (H): Primary determinant.

  2. Design Discharge (Q): Flow availability.

  3. Load Factor & Operation: Base load vs. peak load.

  4. Site Constraints: Size, geology, tailrace conditions.

  5. Specific Speed (Ns): Computed from H & Q → selects turbine type.

  6. Cost & Efficiency: Capital cost vs. operational efficiency trade-off.

5.2 Site Selection Criteria

• Parameters for Hydraulic Power Plant:

  1. Water Availability: Perennial river, high average flow, low seasonal variation.

  2. Head: Natural fall (waterfall, gorge) or feasible dam height.

  3. Storage: Possibility of reservoir for seasonal storage & flood control.

  4. Geology & Foundation: Strong rock for dam, powerhouse, underground caverns.

  5. Accessibility: Proximity to load centers, transport for materials.

  6. Environmental Impact: Minimal displacement, submergence, ecological sensitivity.

  7. Seismic Stability: Low earthquake zone.

• Comparison: Fossil vs. Hydro vs. Renewable Plants:

  | Parameter | Fossil Fuel (Coal/Gas) | Hydro | Solar/Wind (Renewable) | | :--- | :--- | :--- | :--- | | Fuel Cost | High, variable, dominant O&M cost | Zero (but high capital) | Zero | | Capital Cost | Medium | Very High (dam, civil) | Medium-High (panels/turbines) | | Lead Time | 4-6 years | 8-12 years | 1-3 years | | Efficiency | 33-45% | 85-95% (turbine) | 15-45% (conversion) | | Capacity Factor | 60-85% | 40-60% (storage) | Solar 15-25%, Wind 25-40% | | Flexibility | Good (ramp up/down) | Excellent (storage, quick start) | Intermittent, needs backup/storage | | Environmental | Air pollution, CO₂, ash | Land use, displacement, ecology | Land use, intermittency |

6.0 Power Plant Economics & Operation

6.1 Key Performance Definitions

• Maximum Demand (MD): Highest instantaneous load (kW or MW) on the plant during a given period (usually a year).

• Load Factor (LF): Ratio of average load to maximum demand over a specified period.

$$\text{Load Factor} = \frac{\text{Average Load}}{\text{Maximum Demand}} = \frac{\text{Energy (kWh)}}{\text{MD} \times \text{Time (h)}}$$

*   Indicates how uniformly the plant is loaded. Higher LF → better utilization, lower cost per unit.

• Diversity Factor (DF): Ratio of sum of individual maximum demands of consumers to the maximum demand of the system.

$$\text{Diversity Factor} = \frac{\sum \text{Individual Peak Loads}}{\text{System Peak Load}}$$

*   DF > 1. Reflects that all consumers do not peak simultaneously.

• Plant Factor (PF) / Capacity Factor: Ratio of actual energy produced to the energy that would have been produced if operated at full capacity continuously.

$$\text{Plant Factor} = \frac{\text{Actual Annual Energy Output (kWh)}}{\text{Rated Capacity (kW)} \times 8760 \text{ h}}$$

*   Indicates how much of the installed capacity is actually used. PF ≤ LF (since MD ≤ Rated Capacity).

6.2 Numerical Problems

6.2.1 Calculation of Maximum Demand & Annual Energy

• Given: Diversity Factor (DF), Load Factor (LF), Individual Peak Loads.

• Steps:

  1. System Maximum Demand (MD) = $$\displaystyle \frac{\sum \text{Individual Peaks}}{\text{Diversity Factor}} $$

  2. Average Load = MD × LF

  3. Annual Energy = Average Load × 8760 hours = MD × LF × 8760

• Example from Paper: Peaks = 10, 5, 8, 7 MW. DF = 1.5, LF = 0.6.

  • MD = (10+5+8+7) / 1.5 = 30 / 1.5 = 20 MW

  • Annual Energy = 20 × 0.6 × 8760 = 105,120 MWh = 105.12 GWh

6.2.2 Depreciation Methods

• Straight Line Method (SLM): Equal depreciation every year.

$$D = \frac{P - S}{n}$$

Where, P = Initial cost, S = Salvage value, n = life (years). Annual depreciation (D) constant.

• Sinking Fund Method (SFM): Depreciation increases over time. Annual deposit (A) into a fund earning interest (i) to accumulate to (P-S).

$$A = (P - S) \cdot \frac{i}{(1+i)^n - 1}$$

*   **Boxed Formula for Annual Sinking Fund Deposit:**

$$\boxed{A = (P - S) \cdot \frac{i}{(1+i)^n - 1}}$$

*   Depreciation in year t = A × (1+i)^(t-1). Total depreciation sum = P-S.

6.3 Load & Duration Analysis

• Load Duration Curve (LDC): Loads arranged in descending order vs. time percentage. Shows how often a certain load level is exceeded. Area under curve = total energy. Used for capacity planning, demand-side management.

• Flow Duration Curve (FDC): Similar to LDC but for river/stream discharge (m³/s) vs. % time. Crucial for hydro plant feasibility and firm power calculation.

6.4 Auxiliary Systems: Cooling Towers

• Types & Principles:

  1. Natural Draft: Hyperbolic shape creates chimney effect. Large, low cost, no power. Used in large thermal/hydro plants.

  2. Mechanical Draft: Fans force/induce air.

     • Forced Draft: Fan on air inlet → positive pressure.

     • Induced Draft: Fan on air outlet → negative pressure (more common).

     • Induced vs. Forced: Induced draft allows better air distribution, easier plume control.

  3. Principle: Hot water from condenser sprayed → heat exchanged with air → part evaporates → cooled water collected. Approach = (Cold water temp - Wet bulb temp).

6.5 Tariff Structures

• Types:

  1. Flat Rate: Fixed charge per kWh, independent of load/usage.

  2. Block Rate: Different rates for different consumption blocks (slab system).

  3. Two-Part Tariff: Fixed Charge (based on MD or connected load) + Energy Charge (per kWh). Most common for industrial/commercial.

  4. Power Factor Tariff: Incentive/penalty based on PF (kWh charge varies with PF).

  5. Time-of-Day (TOD) Tariff: Different rates for peak, normal, off-peak hours.

7.0 Special/Alternative Conversion Systems

7.1 MagnetoHydroDynamic (MHD) Converter

• Working Principle:

  DiagramCANVAS: Sketch of open-cycle MHD generator. Show: Combustor (air + fuel + seed) → nozzle → electrode walls (cathode top, anode bottom) in magnetic field (B) → hot ionized gas (plasma) flows perpendicular to B → electrodes collect DC current → diffuser → steam turbine.

  1. Ionization: Combustion gases (air + fuel) seeded with alkali metal (e.g., potassium carbonate) → ionized at high T (~2500°C).

  2. Seeded Gas flows through a channel with perpendicular magnetic field (B).

  3. Hall Effect: Charged particles (ions/electrons) experience Lorentz force → separate to electrodes → DC power extracted.

  4. Exhaust still hot (~2000°C) → used in bottoming steam cycle (combined cycle).

• Factors Limiting Commercial Use:

  • Material Challenge: Electrode & channel materials must withstand ~2500°C, corrosive/erosive plasma.

  • Seed Recovery: Potassium seed must be recovered from slag/ash (complex, costly).

  • Low Electrical Efficiency: Seed ionization incomplete, electrode voltage drop, Hall parameter limitations.

  • High Capital Cost: Special materials, magnets, seed recovery system.

  • Environmental: Seed handling, slag disposal.

7.2 Fuel Cells

• Definition: Electrochemical device that converts chemical energy of a fuel (H₂, hydrocarbon) and oxidant (O₂) directly into electricity and heat, bypassing Carnot cycle limitations.

• Working Principle (Proton Exchange Membrane Fuel Cell - PEMFC):

  1. Anode: H₂ → 2H⁺ + 2e⁻ (oxidation).

  2. Electrolyte: Proton exchange membrane (Nafion) → H⁺ ions migrate to cathode.

  3. Cathode: ½O₂ + 2H⁺ + 2e⁻ → H₂O (reduction).

  4. Overall: H₂ + ½O₂ → H₂O + Electricity + Heat.

  • Thermodynamic Equations:

    • Reversible Voltage: $$\displaystyle E^0 = \frac{-\Delta G}{nF} $$ (ΔG = Gibbs free energy change, n=2, F=Faraday).

    • For H₂/O₂ at 25°C, 1 atm: $$\displaystyle E^0 \approx 1.23 $$ V.

    • Actual cell voltage: $$\displaystyle V = E^0 - \eta_{activation} - \eta_{ohmic} - \eta_{concentration} $$.

• Applications: Transportation (fuel cell vehicles - Toyota Mirai), stationary power (backup, remote), portable electronics, space (NASA).

8.0 Advanced Non-Traditional Machining Processes

8.1 Ultrasonic Machining (USM)

• Mechanism of Metal Removal:

  DiagramCANVAS: Sketch of USM. Show: Tool (sonotrode) vibrating at 20 kHz axially, abrasive slurry (water + SiC/B₄C) flowing in gap between tool and workpiece. Tool impacts abrasive grains → grains impact workpiece → micro-chipping.

  1. Tool (usually soft metal like titanium) vibrates at high frequency (15-25 kHz) and low amplitude (10-50 µm).

  2. Abrasive Slurry (water + hard, sharp abrasives like SiC, B₄C) flows in the tool-workpiece gap.

  3. Micro-chipping: Vibrating tool impacts abrasive grains → grains hammer into workpiece surface → brittle fracture/chipping of workpiece material.

  4. No Chemical Reaction: Purely mechanical erosion. Suitable for brittle, hard, fragile materials (ceramics, glass, silicon, carbides, gems).

• MRR: Proportional to frequency², amplitude², abrasive concentration, tool area. Inversely proportional to hardness of workpiece.

8.2 Electrical Discharge Machining (EDM)

• Working Principle:

  DiagramCANVAS: Sketch of EDM. Show: Dielectric fluid (kerosene) in tank. Tool electrode (copper/graphite) and workpiece connected to DC pulse generator. Gap filled with dielectric. Voltage rise → dielectric breakdown → spark → localized melting/vaporization → plasma channel collapses → dielectric flushes debris.

  1. Tool & Workpiece immersed in dielectric fluid (hydrocarbon oil, deionized water).

  2. Small gap (10-100 µm). Pulsed DC voltage applied.

  3. When voltage exceeds dielectric strength → spark occurs in gap → intense heat (10,000°C) → localized melting & vaporization of workpiece & tool.

  4. Material Removal: Each spark removes a tiny crater. Flushing (dielectric circulation) removes debris.

  5. Tool Wear: Tool also erodes (graphite lower wear than copper).

• Types of Errors in Material Matching/Process:

  1. Tool Wear Error: Tool shape changes → inaccuracies in cavity/profile.

  2. Corner Error/Overcut: At sharp corners, dielectric flushing poor → reduced MRR → undercutting.

  3. Spark Gap Error: Actual gap larger than programmed → dimensional inaccuracy.

  4. Thermal Stresses: Heat-affected zone (HAZ) → micro-cracks, recast layer.

  5. Electrode Misalignment: Poor setup → taper/angularity errors.

8.2.3 Wire EDM – Working Principle & Applications

• Working Principle:

  DiagramCANVAS: Sketch of Wire EDM. Show: Thin brass wire (0.05-0.3 mm) fed from spool, guided by upper/lower diamond guides. Workpiece on CNC table. Wire and workpiece in deionized water bath. Pulse generator between wire and workpiece. Wire continuously feeds, sparking occurs along wire length, cuts workpiece like a bandsaw.

  • Wire acts as continuously moving tool electrode.

  • No tool wear (wire constantly renewed).

  • CNC Control: X-Y axes + possibly U-V (taper) or rotary table.

  • Flushing: Deionized water pumped through workpiece (often with slots).

• Applications (4+):

  1. Die & Mold Making: Complex 2D/2.5D cavities, extrusion dies, forging dies.

  2. Prototype Manufacturing: Intricate shapes from hard materials.

  3. Aerospace: Turbine blades, gears, nozzles from superalloys.

  4. Medical: Surgical tools, implants (complex contours).

  5. Tooling: Forming tools, punches, gauges.

  6. Micro-Machining: Micro-gears, holes (<0.1 mm).

8.3 Laser Beam Machining (LBM)

• Principle: High-intensity, coherent, monochromatic laser beam (CO₂, Nd:YAG, fiber) focused to a small spot (~0.025 mm) on workpiece. Material removal via:

  • Melting & Vaporization (most common).

  • Thermal Stress Fracture (brittle materials).

  • Photochemical (excimer lasers, UV).

• Effect of 'Focusing' on Performance:

  • Spot Size: Smaller focal spot → higher power density (W/cm²) → deeper penetration, finer features, higher aspect ratio.

  • Depth of Focus (DOF): Smaller spot → shorter DOF → requires precise Z-axis control, sensitive to workpiece surface flatness.

  • Beam Quality (M²): Low M² (close to 1) → can be focused to smaller spot → better precision, edge quality.

  • Trade-off: Very small spot → less energy per unit area along depth → may reduce cutting speed for thick materials.

8.4 Electrochemical Machining/Honing

8.4.1 Electrochemical Honing – Concept

• Hybrid Process: Combines ECM (anodic dissolution) with mechanical honing (abrasive stones).

• Process: Workpiece (anode) and tool (cathode) with electrolyte flow. Low voltage DC (5-20 V) applied. Abrasive stones (insulated) on tool face oscillate/rotate.

• Advantage: ECM removes bulk material fast, honing stones break down passive oxide film on workpiece → maintains high dissolution rate, improves surface finish (Ra ~0.2-0.6 µm) and geometric accuracy. Used for finishing hard-to-machine gears, camshafts, internal surfaces.

8.4.2 Etch Factor – Definition & Significance

• Definition: Ratio of undercut (u) to depth of cut (d) in ECM/ECG.

$$\text{Etch Factor} = \frac{u}{d}$$

• Significance:

  • Measures the lateral extent of anodic dissolution beyond the tool edge.

  • Lower Etch Factor (closer to 0) is desirable → indicates better dimensional accuracy (less undercut).

  • Depends on: Electrolyte (conductivity, flow), current density, workpiece material, tool shape, pulse parameters (in pulsed ECM).

  • Goal: Minimize undercut by controlling current density distribution (tool design, insulation).

8.4.3 Mechanism of Machining Rate

• Faraday's Law: Material removal is governed by anodic dissolution.

$$\text{MRR} = \frac{I \cdot M}{n \cdot F \cdot \rho}$$

Where:

*   I = Current (A)

*   M = Atomic mass (g/mol)

*   n = Valency (number of electrons exchanged)

*   F = Faraday's constant (96485 C/mol)

*   ρ = Density (g/cm³)

• Key Points:

  • MRR ∝ Current (I). Primary control parameter.

  • No tool-workpiece contact → no mechanical forces, no tool wear.

  • No Heat Affected Zone (dissolution is at atomic level).

  • Limitations: Requires conductive workpiece, electrolyte handling, sludge disposal, passivation issues.

9.0 Rapid Prototyping (RP) & Additive Manufacturing

9.1 Fundamentals

• Definition: Additive Manufacturing (AM) is the process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive (machining) or formative (casting) technologies.

• Significance in Product Development:

  • Design Freedom: Complex geometries (lattices, internal channels) impossible with conventional methods.

  • Reduced Lead Time: From CAD to physical part in hours/days.

  • Cost-Effective for Low Volume: No tooling/mold costs.

  • Customization & Personalization: Ideal for medical implants, dental, bespoke parts.

  • Concurrent Engineering: Design, analysis, prototyping happen in parallel.

  • Functionality Testing: Fit, form, and limited function testing early.

• Basic Types of Starting Materials:

  1. Liquid: Photopolymer (SLA), thermoplastics (Material Jetting), binder + powder (Binder Jetting).

  2. Solid (Powder): Thermoplastics (SLS), metals (DMLS/SLM), ceramics.

  3. Solid (Filament/Sheet): Thermoplastics (FDM), paper/laminate (LOM).

9.2 Principles & Technologies

9.2.1 3D Printing – Principles & Working

• General Principle: Layer-by-layer material addition from a digital 3D model (STL file).

• Working Steps:

  1. Pre-processing: 3D CAD model → sliced into thin 2D layers (slicer software) → generate toolpaths.

  2. Production: Machine reads toolpath, deposits/joins material layer by layer.

  3. Post-processing: Support removal, surface finishing, heat treatment, infiltration.

• Common Technologies:

  • FDM (Fused Deposition Modeling): Thermoplastic filament extruded through heated nozzle.

  • SLA (Stereolithography): UV laser cures photopolymer resin vat.

  • SLS (Selective Laser Sintering): Laser sinters powder bed (nylon, metal).

  • DMLS/SLM (Direct Metal Laser Sintering/Melting): Laser fully melts metal powder.

9.2.2 Stratified Wire

• Concept: Likely refers to Laminated Object Manufacturing (LOM) or similar sheet lamination.

• Working: Thin sheets of material (paper coated with thermoplastic, metal foil, ceramic tape) are cut to shape (using CO₂ laser or knife) and bonded together layer by layer using heat/pressure. Unbonded material is removed as waste.

• Characteristics: Fast build rate for large parts, low cost, but limited strength (anisotropic), poor surface finish, limited material choice (paper, composites).

9.3 Application & Implementation Issues

• Application Issues in Rapid Prototyping:

  1. Material Limitations: Fewer engineering-grade materials compared to conventional processes. Properties (strength, thermal, UV stability) often inferior.

  2. Surface Finish & Accuracy: Layer lines visible, stair-stepping effect. Tolerances typically ±0.1-0.5 mm, not suitable for precision mating parts without machining.

  3. Build Size: Machine build envelope limits part size.

  4. Build Time & Cost: Can be slow for large/complex parts; cost per part high for volume production.

  5. Support Structures: Required for overhangs → waste material, post-processing needed.

  6. Anisotropy: Properties vary with build direction (weak inter-layer bonding).

  7. Intellectual Property & File Security: Digital files easy to copy/share.

  8. Operator Skill: Requires knowledge of materials, machine parameters, post-processing.

10.0 Micro-Fabrication & Microsystems

10.1 Microsystem Devices

• Basic Types & Discussion:

  1. MEMS (Micro-Electro-Mechanical Systems): Integration of mechanical elements (cantilevers, gears, membranes), sensors, actuators, and electronics on a single silicon chip.

     • Examples: Accelerometers (airbags), pressure sensors, inkjet printer heads, micro-mirrors (DLP), gyroscopes.

  2. Microsensors: Transduce physical/chemical parameters to electrical signals.

     • Examples: Pressure, temperature, flow, biosensors (glucose), gas sensors.

  3. Microactuators: Convert electrical/thermal/magnetic energy to mechanical motion.

     • Examples: Piezoelectric stacks, thermal bimorphs, electrostatic comb drives, micro-valves.

  4. Microfluidics: Devices that handle/process small fluid volumes (nL-µL).

     • Examples: Lab-on-a-Chip (LOC), micro-TAS (Total Analysis Systems), DNA chips, drug delivery systems.

10.2 Micro-Fabrication Processes

10.2.1 LIGA Process – Explanation

• Acronym: LIthographie (Lithography), Galvanoformung (Electroforming), Abformung (Molding).

• Process Steps:

  1. Lithography: Deep X-ray Lithography using synchrotron radiation. Thick photoresist (PMMA, 100 µm - few mm) exposed through mask → creates high-aspect-ratio structures.

  2. Electroforming: The resist pattern acts as mold. Electroplating (Ni, Cu, Au) fills the cavities → creates a metallic master (tool).

  3. Molding: The metallic master used as mold in injection molding (plastics) or hot embossing to mass-produce microstructures.

• Key Feature: Produces high-aspect-ratio (>100:1), smooth, vertical sidewall microstructures. Used for micro-optics, microfluidic channels, precision molds.

10.2.2 Industrial Applications of Micro-Fabrication

1. Semiconductor & Electronics: IC fabrication (photolithography, etching, deposition), MEMS chips.

2. Automotive: Pressure sensors (tire, engine), accelerometers, fuel injectors.

3. Healthcare & Medical: Lab-on-a-chip diagnostics, drug delivery micropumps, neural implants, stents.

4. Optics & Photonics: Micro-lenses, optical waveguides, diffraction gratings, displays (DLP).

5. Aerospace & Defense: Inertial navigation systems (gyros), pressure monitoring, micro-propulsion.

6. Consumer Electronics: Inkjet printheads, microphones, hard disk read/write heads.

7. Energy: Micro-turbines, fuel cells, solar cells (texturing).

8. Metrology & Instrumentation: Micro-probes, calibration standards.