MANUFACTURING TECHNOLOGY (ME-405) - Unit 3 Short Notes

1.0 FUNDAMENTALS OF MACHINING & CUTTING TOOLS

1.1 Single-Point Cutting Tool Nomenclature & Signature

• ASA System (American Standards Association): Reference plane is machining axis. Tool signature is a 7-code sequence: -10-5-6-8-2-15-2

  Interpretation: Back rake = -10°, Side rake = -5°, End relief = 6°, Side relief = 8°, End cutting edge angle = 2°, Side cutting edge angle = 15°, Nose radius = 2/32 inch.

• ORS/ISO System: Reference plane is rake face. More common internationally.

[!TIP] ASA signature order: Back Rake, Side Rake, End Relief, Side Relief, End Cutting Edge, Side Cutting Edge, Nose Radius.

1.2 Mechanics of Machining

• Orthogonal Cutting: Cutting edge ⟂ to feed direction. Simplified 2D analysis.

• Oblique Cutting: Cutting edge inclined to feed direction. 3D chip flow.

• Cutting Forces:

  • Tangential (Fc): Primary force, major power component.

  • Feed (Ff): Along feed direction.

  • Radial (Fr): Perpendicular to workpiece surface.

• Specific Cutting Energy (u): Energy required to remove unit volume of material.

  \boxed{u = \frac{P_c}{MRR} = \frac{F_c \cdot V_c}{d \cdot f \cdot V_c} = \frac{F_c}{d \cdot f}}

  where \(d\) = depth of cut, \(f\) = feed (consistent units; if mm, \(u\) in N/mm²).

• Merchant’s Circle: Force analysis for orthogonal cutting. Shear angle \(\phi\) derived from:

  \boxed{\phi = 45^\circ + \frac{\alpha}{2} - \frac{\beta}{2}}

  where \(\alpha\) = rake angle, \(\beta\) = friction angle.

[!TIP] For power calculation: \(P_c = F_c \times V_c\). Neglect feed force if specified.

1.3 Tool Life & Wear

• Taylor’s Tool Life Equation:

  \boxed{V T^n = C}

  \(V\) = cutting speed (m/min), \(T\) = tool life (min), \(n\) and \(C\) = tool material constants.

• Tool Material Comparison:

  | Material | \(n\) range | Sensitivity to \(V\) | |----------|-------------|---------------------| | HSS | 0.1–0.2 | Low | | Carbide | 0.2–0.5 | High |

• Tool Failure Modes:

  1. Flank wear: Gradual wear on flank face (most common).

  2. Crater wear: On rake face due to diffusion/adhesion.

  3. Notching: At depth-of-cut line due to cyclic stress.

  4. Chipping/Breakage: Mechanical failure from impact or vibration.

[!TIP] Flank wear limits tool life; crater wear affects cutting geometry.

1.4 Cutting Fluids (Coolants & Lubricants)

• Types:

  • Water-based: Emulsions (oil-in-water), solutions (synthetic).

  • Oil-based: Mineral oils, fatty oils.

  • Gases: Air, CO₂, nitrogen.

  • Solid pastes: Graphite, molybdenum disulfide.

• Effectiveness Mechanisms:

  • Cooling: Reduce temperature.

  • Lubrication: Reduce friction and built-up edge.

  • Chip flushing: Remove chips from zone.

  • Corrosion prevention: Add inhibitors.

• Application Methods: Flooding, mist, jet, manual brushing.

2.0 GRINDING PROCESSES & WHEELS

2.1 Grinding Wheel Specifications & Selection

• Five parameters: Abrasive type (Al₂O₃, SiC, CBN), Grain size (grit number: lower = coarser), Grade (A–Z: A soft, Z hard), Structure (open to dense), Bond type (vitrified, resinoid, rubber).

• Wheel designation example: A-36-V-220 → Abrasive Al₂O₃, grit 36 (medium), vitrified bond, structure? (often omitted).

  DiagramSEARCH: grinding wheel specification diagram

2.2 Wheel Dressing & Truing

• Dressing: Exposes fresh grit, restores cutting ability (uses single-point diamond or multi-point tools).

• Truing: Restores true geometric shape (roundness, flatness).

• Difference: Dressing cleans/sharpen; truing corrects shape. Often done sequentially.

2.3 Centreless Grinding

• Principle: Workpiece supported on work rest blade between rotating grinding wheel (fast) and regulating wheel (slow, controls feed). No centers required.

• Types:

  • Through-feed: Continuous feed for cylindrical parts (most common).

  • In-feed: For long parts, workpiece fed axially.

  • End-feed: For short parts, workpiece fed from end.

• Components: Grinding wheel, regulating wheel, work rest blade.

• Advantages: High productivity, no chucking, good for small/delicate parts.

• Limitations: Setup complex, sensitive to vibrations, limited to cylindrical parts.

[!TIP] Through-feed is ideal for mass production of pins, shafts.

2.4 Surface Grinding

• Horizontal spindle (peripheral): Grinding wheel periphery contacts workpiece. For flat surfaces, grooves, profiles.

• Vertical spindle (face): Face of wheel contacts workpiece. For large flat surfaces, die work.

• Construction: Base, column, wheel head (vertical/horizontal), work table (reciprocating), cross feed.

3.0 GEAR MANUFACTURING PROCESSES

3.1 Gear Production vs. Gear Generation

• Production (Forming): Tool shape matches gear tooth space (e.g., milling, broaching). Lower accuracy, requires finishing.

• Generation: Tool and workpiece move in kinematic synthesis to generate tooth profile (e.g., hobbing, shaping). Higher accuracy, can correct errors.

• Comparison:

  | Feature | Production | Generation | |---------|------------|------------| | Tool | Form tool (custom) | Simple tool (hob, pinion cutter) | | Accuracy | Lower | Higher | | Flexibility | Low (one tool per gear) | High (same tool for multiple gears) | | Applications | Roughing, simple gears | Finishing, precise gears |

3.2 Gear Generation Processes

• Gear Hobbing:

  • Working principle: Hob (worm with cutting edges) rotates and feeds into gear blank. Hob and blank rotate in fixed ratio (like rack and pinion).

  • Machine types: Indexing (spur gears), differential (helical gears), progressive (worm gears).

  • Advantages: High productivity, versatile (spur/helical), good for medium batches.

  • Limitations: Cannot cut internal gears, requires finishing for high precision.

  • DiagramSEARCH: gear hobbing machine sketch

• Gear Shaping:

  • Working principle: Pinion-shaped cutter reciprocates and rotates with indexing. Cutter and blank have synchronized rotation.

  • Types: Conventional (climb), helical (cutter angled), internal (for internal gears).

  • Advantages: Can cut internal gears, idlers, small batches; no blind hole limitation.

  • Limitations: Slower than hobbing, limited to moderate sizes.

  • DiagramSEARCH: gear shaping machine sketch

3.3 Gear Finishing Methods

• Shaving: Using shaving cutter with abrasive teeth; generates improved surface and corrects errors.

• Honing: For hardened gears; abrasive stones in a honing machine.

• Lapping: For master gears; abrasive paste between two gears.

• Burnishing: Plastic deformation with rollers/balls; improves surface finish and fatigue strength.

• Detailed any four: Shaving (common for hardened gears), Honing (cylindrical gears), Lapping (high-precision gears), Burnishing (noise reduction).

3.4 Gear Elements & DP Cutters

• Basic gear terminology: Pitch circle, addendum, dedendum, module, pressure angle, base circle, tooth thickness.

• DP (Disc or Face) Cutters: Used in gear planers. Characteristics: Cutter has involute profile, indexed by diametral pitch (DP). Generates involute gears by linear reciprocating motion.

4.0 FINISHING & SUPER FINISHING PROCESSES

4.1 Honing

• Principle: Abrasive stones (honing sticks) mounted on a mandrel, rotated and reciprocated in a hole.

• Applications: Cylinder bores, bearing races, gear teeth.

• Advantages: Improves geometry (roundness, straightness) and surface finish.

• Limitations: Slow, limited to internal surfaces.

4.2 Lapping

• Principle: Loose abrasives in carrier paste between two surfaces. Relative motion causes micro-cutting.

• Types: Manual, machine, plate lapping (for flat surfaces).

• Applications: High-precision flat/round surfaces, sealing surfaces, gauge blocks.

• Advantages: Extremely high accuracy (µm level) and finish.

• Limitations: Very slow, size limitations, requires skilled operation.

4.3 Super Finishing

• Definition: Extreme surface finish (Ra < 0.1 µm) and geometry correction.

• Process characteristics: Very low speed (0.1–0.5 m/s), light pressure, abrasive stone oscillates radially.

• Used after: Grinding/honing for final precision.

4.4 Buffing & Polishing

• Buffing: Rotating buff wheel (soft) with abrasive compounds (rough → fine). Produces lustrous finish.

• Polishing: Final luster using fine abrasives (e.g., rouge) on soft cloth.

• Difference: Buffing uses abrasive on wheel; polishing uses loose abrasive.

4.5 Electro-polishing

• Principle: Anodic dissolution in electrolytic cell. Workpiece (anode) polished by selective removal of micro-peaks.

• Mechanism: Micro-current densities higher at peaks → faster dissolution.

• Applications: Decorative finishes (stainless steel), deburring, improved corrosion resistance.

• Advantages: No mechanical stress, smooth surface, burr removal.

• Limitations: Requires conductive material, electrolyte handling, shape limitations.

5.0 UNCONVENTIONAL / NON-TRADITIONAL MACHINING PROCESSES

5.1 Need & Classification

• Need: Machine hard/brittle materials, complex shapes, no tool-work contact (avoid stress), stress-free machining.

• Classification:

  • Mechanical: AJM, AWJM, USM.

  • Electro-chemical: ECM.

  • Thermal: EDM, EBM, LBM, PAM.

  • Chemical: CHM (not covered).

5.2 Abrasive Jet Machining (AJM) / Abrasive Water Jet Machining (AWJM)

• AJM: High-velocity jet of dry air + abrasive (Al₂O₃, SiC). Nozzle directs jet. Material removal by micro-chipping.

  • Applications: Cutting brittle materials, drilling, deburring, etching.

  • Abrasive selection factors: Hardness (must > workpiece), shape (angular for sharpness), size (affects finish/rate), flow rate.

• AWJM: High-pressure water (2000–4000 bar) + abrasive. Water jet accelerates abrasive.

  • DiagramSEARCH: abrasive water jet machining diagram

  • Advantages: No thermal damage, can cut thick materials (up to 300 mm).

  • Limitations: Taper, slow for thick sections, abrasive consumption.

5.3 Ultrasonic Machining (USM)

• Principle: Tool (sonotrode) vibrates at ultrasonic frequency (20 kHz) in abrasive slurry. Abrasive grains impact and erode workpiece.

• Construction: Transducer (piezoelectric/magnetostrictive), amplitude transformer, tool, slurry circulation.

• DiagramSEARCH: ultrasonic machining machine diagram

• Applications: Brittle materials (ceramics, glass, carbide), fragile shapes.

• Advantages: No thermal damage, good for intricate shapes.

• Limitations: Slow, tool wear, limited to small depths (<10 mm).

5.4 Electro-Discharge Machining (EDM)

• Principle: Spark erosion between tool electrode and workpiece in dielectric fluid. Material removed by localized melting/vaporization.

• DiagramSEARCH: EDM machine diagram

• Process parameters:

  • Peak current: Affects removal rate and electrode wear.

  • Pulse duration: Affects surface finish and depth of affected zone.

  • Gap voltage: Controls spark gap.

• Advantages: Complex shapes, hard materials, no mechanical stress.

• Disadvantages: Slow, electrode wear, thermal damage (recast layer).

• Wire-cut EDM: Uses continuous wire as electrode. For cutting 2D profiles, high precision, no electrode wear.

5.5 Electrochemical Machining (ECM)

• Principle: Anodic dissolution (Faraday’s law). Workpiece (anode) dissolves in electrolyte when current flows. Tool (cathode) shaped, gap maintained.

• Logical diagram: Power supply (DC), electrolyte system (pump, filter), tool (cathode), workpiece (anode), feed mechanism.

  DiagramSEARCH: ECM logical diagram

• Procedure: Electrolyte flows, voltage applied, tool feeds to maintain gap (0.1–0.5 mm).

• Advantages: No tool wear, no HAZ, high material removal for conductive materials.

• Limitations: Shape prediction difficult, electrolyte handling, limited to conductive materials.

5.6 Electron Beam Machining (EBM)

• Principle: Focused high-velocity electron beam in vacuum. Kinetic energy converts to thermal energy, melting/vaporizing material.

• Characteristics: High energy density (~10⁹ W/m²), vacuum required (10⁻⁵ torr), precise.

• DiagramSEARCH: electron beam machining diagram

• Advantages: Extremely small features (10 µm), no tool contact, fast for small areas.

• Limitations: High equipment cost, vacuum system, safety (X-rays), limited to conductive materials.

5.7 Laser Beam Machining (LBM)

• Principle: Focused coherent light beam (laser) melts, vaporizes, or ablates material.

• Types: Pulsed (drilling), Continuous (cutting).

• Applications: Cutting, drilling, welding, marking.

• Advantages: Non-contact, flexible, can cut various materials (metals, ceramics, polymers).

• Limitations: Thermal damage, reflectivity issues (high for metals), efficiency low (~10%).

5.8 Plasma Arc Machining (PAM)

• Principle: High-temperature plasma jet (ionized gas) melts and blows away material.

• Construction: Torch with electrode, gas (N₂, Ar, H₂), nozzle. Arc heats gas to plasma (20,000–30,000 K).

  DiagramSEARCH: plasma arc machining torch diagram

• Applications: Cutting conductive materials (metals), fast cutting (up to 500 mm/min).

• Advantages: High speed, can cut thick plates (up to 200 mm).

• Limitations: Thermal damage, fumes, limited to conductive materials.

6.0 PLASTICS MANUFACTURING PROCESSES

6.1 Plastics: Types & Additives

• Thermoplastics: Soften on heating, harden on cooling. Recyclable. E.g., PE, PP, PVC.

• Thermosets: Set permanently on heating. Not recyclable. E.g., Bakelite, epoxy, phenolic.

• Additives:

  • Plasticizers: Increase flexibility (e.g., phthalates).

  • Fillers: Reduce cost, improve strength (e.g., talc, calcium carbonate).

  • Stabilizers: Prevent degradation (UV, thermal, oxidative).

  • Colorants: Dyes (transparent) and pigments (opaque).

6.2 Moulding Processes

• Injection Moulding:

  • Principle: Plastic granules melted and injected under high pressure into closed mould.

  • Machine components: Injection unit (screw, barrel), mould (clamped by platen).

  • Mould types:

    • Cold runner: Sprue and runners solidify as waste.

    • Hot runner: Melted channels, no waste, better control.

  • Advantages: High production, complex shapes, good surface finish.

  • Limitations: High tool cost, flash possible, size limitations.

• Compression Moulding:

  • Principle: Preheated charge placed in open mould, then closed and pressure applied. Curing occurs in mould.

  • Process steps: Charging → closing → curing → opening → ejection.

  • Applications: Thermosets, composites (SMC, BMC).

  • Advantages: Low pressure, good for large parts, minimal flow marks.

  • Limitations: Slow cycle, flash, longer cure times.

• Transfer Moulding:

  • Principle: Preheated charge forced from pot into closed mould through sprue.

  • Comparison with injection: Transfer uses pot, better for thermosets and inserts; injection uses barrel, faster for thermoplastics.

• Blow Moulding:

  • Types:

    • Extrusion blow: Parison extruded, then blown in mould.

    • Injection blow: Parison injection moulded, then blown.

  • Process for bottles: Parison (tube) formed, clamped in mould, air injected, cooled, ejected.

  • Advantages: Fast, seamless containers, low scrap.

  • Defects: Flash (excess material), Pinch-off (mark at base), Waviness (uneven wall).

6.3 Welding of Plastics

• Principle: Heating interface to join, then cool to solidify.

• Methods:

  • Heated tool: Hot plate contacts surfaces.

  • Ultrasonic: Vibrations generate heat at interface.

  • Vibration: Linear or orbital friction.

  • Spin: Rotary friction.

  • Hot gas: Hot air softens surfaces (e.g., PVC welding).

• Advantages: Joining dissimilar plastics, no fasteners, clean joints.

• Limitations: Surface preparation critical, material compatibility limited.

6.4 Other Processes

• Calendaring: Plastic passed through heated rollers to form sheet/film.

  DiagramSEARCH: calendaring machine diagram
  • Applications: PVC sheets, films, coated fabrics.

• Extrusion: Continuous profile through die.

  • Applications: Pipes, rods, films, profiles.

• Film Blowing: Extruded tube inflated to form bubble, cooled, flattened.

  • Applications: Plastic bags, stretch film.

7.0 METAL FORMING: EXTRUSION

7.1 Extrusion Process Fundamentals

• Principle: Forcing billet through die to get constant cross-section.

• Types:

  • Direct (forward): Billet and ram move same direction. Simple, but friction on die.

  • Indirect (backward): Die moves with ram, billet stationary. Less friction, longer billet possible.

  • Hydrostatic: Billet under fluid pressure, used for brittle materials (e.g., powder).

  DiagramSEARCH: direct vs indirect extrusion diagram

7.2 Hot vs. Cold Extrusion

• Comparison:

  | Aspect | Hot Extrusion | Cold Extrusion | |--------|--------------|---------------| | Temperature | Above recrystallization | Room temperature | | Surface finish | Rough, scale | Excellent, smooth | | Dimensional accuracy | Low | High | | Mechanical properties | Coarse grain, lower strength | Work hardening, higher strength | | Ductility | High | Lower | | Materials | Al, Mg, Cu, steels (softened) | Pb, Sn, Al, Cu (soft metals) | | Press capacity | Lower (reduced flow stress) | Higher (increased force) | | Speed | Faster | Slower | | Applications | Long sections, large volumes (aluminum windows) | Small parts, high strength (collapsible tubes, fasteners) |

7.3 Tube Extrusion

• Process: Using hollow billet or solid billet with mandrel.

  • With mandrel: Mandrel fixed or floating. Billet extruded around mandrel to form tube.
  DiagramSEARCH: tube extrusion with mandrel diagram

• Applications: Pipes, tubes, hollow sections.

7.4 Metal Flow in Extrusion

• Types:

  • Homogeneous: Uniform flow (ideal).

  • Laminar: Layers slide, can cause transverse defects.

  • Fracture: Central fracture due to tensile stress, causes scarring.

• Importance: Affects product quality, die design, required force. Fracture flow leads to poor surface and internal defects.

8.0 NUMERICAL CONTROL (NC) & COMPUTER NUMERICAL CONTROL (CNC)

8.1 NC/CNC Machine Construction & Elements

• Basic components:

  1. Program input device: Punched tape, keyboard, CAD/CAM interface.

  2. Controller (CPU): Interprets program, generates axis commands.

  3. Drive system: Servo motors, stepper motors, ball screws.

  4. Feedback system: Transducers (encoders, resolvers) for position/speed.

  5. Machine tool: Lathe, mill, etc.

• Functions: Controller reads program → sends signals to drives → feedback ensures accuracy.

8.2 NC vs. CNC

• NC: Hardwired logic, limited flexibility, no storage, no computation.

• CNC: Software control, flexible (easy program change), large storage, can compute (interpolation, loops).

• Key difference: CNC uses microcomputer; NC uses hardwired circuits.

8.3 Coordinate Systems in NC

• Cartesian (X, Y, Z): Most common. Right-hand rule.

• Polar, Spherical: For turning with angular dimensions.

• Absolute vs. Incremental:

  • Absolute: Coordinates from fixed origin (G90).

  • Incremental: Coordinates from last point (G91).

• Points: Machine reference point (home), machine zero (fixed), work zero (part zero, e.g., G54).

[!TIP] Always define work zero (G54–G59) for part programming.

8.4 NC Part Programming

• Manual Programming: Writing G-codes (preparatory) and M-codes (miscellaneous).

  • Common G-codes:

    • G00: Rapid traverse

    • G01: Linear interpolation

    • G02/G03: Circular interpolation (CW/CCW)

    • G04: Dwell

    • G20/G21: Inch/mm

    • G40/G41/G42: Cutter compensation cancel/left/right

  • Common M-codes:

    • M00: Program stop

    • M03: Spindle on (CW)

    • M05: Spindle off

    • M06: Tool change

    • M30: End of program

• Computer-Assisted Programming (CAP): Using CAD/CAM software to generate code.

• Example (simple milling square):

  
  G21 G90 G54
  
  G00 X0 Y0
  
  G01 X10 Y0 F100
  
  G01 X10 Y10
  
  G01 X0 Y10
  
  G01 X0 Y0
  
  M30
  
  

8.5 Control Systems in NC

• Point-to-Point: Only end points matter (e.g., drilling).

• Straight-line: Linear interpolation between points (e.g., turning).

• Contouring: Continuous path control (2D/3D), interpolation for curves (milling, EDM).

8.6 Advanced CNC Features

• Adaptive Control (AC): Adjusts parameters (feed, speed) based on feedback (force, power) to optimize.

• Canned cycles: Pre-programmed cycles (e.g., G81 for drilling, G76 for threading).

• Subprograms: Reusable code blocks (e.g., M98 P1000).

• Macros: Parametric programming with variables (e.g., #1 = 10).

9.0 OTHER MACHINING & SAWING PROCESSES (Less Frequent)

9.1 Broaching

• Cutting action: Progressive teeth on broach, each tooth removes small amount. Roughing and finishing teeth.

• Continuous surface broaching machine: Workpiece moves continuously through stationary broach, or broach moves over stationary workpiece.

• Useful for: Internal surfaces (keyways, splines), external irregular shapes (turbine blades).

• Advantages: High production, good finish, precise.

• Limitations: High tool cost, dedicated to specific shape.

9.2 Power Hacksaw & Band Saw

• Power hacksaw: Reciprocating blade, rigid, for heavy cutoff of bars, pipes.

• Band saw: Continuous toothed blade, guided by wheels. Versatile, can cut curves.

• Comparison:

  • Band saw: More versatile, smoother cut, thinner kerf.

  • Hacksaw: More robust for heavy-duty, larger capacities.

10.0 INTEGRATED TOPICS FROM MULTIPLE PAPERS

10.1 Non-Destructive Testing (NDT) Methods

• Visual (VT): Surface defects, simple.

• Liquid Penetrant (PT): Surface cracks, porous materials.

• Magnetic Particle (MT): Surface/subsurface in ferromagnetic materials.

• Ultrasonic (UT): Internal defects, thickness measurement.

• Radiographic (RT): Internal defects, welds (X-ray, gamma).

• Eddy Current (ET): Surface cracks, conductivity, coating thickness.

10.2 Weldability & Factors

• Weldability: Ability of material to be welded without defects.

• Factors:

  • Material composition (carbon equivalent, alloying elements).

  • Thickness (heat input required).

  • Joint design (stress concentration, accessibility).

  • Service conditions (corrosion, temperature, loading).

10.3 Yield Criteria for Ductile Materials

• Tresca (Max Shear Stress): Yields when max shear stress reaches shear yield strength.

  \boxed{\tau_{max} = \frac{\sigma_y}{2}}

• Von Mises (Distortion Energy): Yields when distortion energy reaches critical value.

  \boxed{\sigma_{vm} = \sqrt{\frac{(\sigma_1-\sigma_2)^2 + (\sigma_2-\sigma_3)^2 + (\sigma_3-\sigma_1)^2}{2}} = \sigma_y}

• Relationship for plane strain (\(\sigma_3 = 0\)):

  Von Mises: \(\sigma_{vm} = \sqrt{\sigma_1^2 - \sigma_1\sigma_2 + \sigma_2^2}\)

  Tresca: \(\sigma_1 - \sigma_2 = \sigma_y\)

  Von Mises gives higher safety factor (more conservative).