MANUFACTURING TECHNOLOGY (ME-405) - Unit 5 Short Notes

UNIT 5: MANUFACTURING TECHNOLOGY

(Based on Past Exam Questions: Jun 2022 – Jun 2025)

I. FUNDAMENTALS OF MACHINING AND CUTTING TOOLS

Single Point Cutting Tool Nomenclature & Signature

• Nomenclature: Key angles and surfaces define tool geometry.

  • Back Rake Angle (α_b): Slope of tool face from cutting edge.

  • Side Rake Angle (α_s): Slope perpendicular to cutting edge.

  • End Relief Angle (γ_e): Angle between tool flank and workpiece.

  • Side Relief Angle (γ_s): Angle on flank.

  • End Cutting Edge Angle (C_e): Angle between end flank and workpiece axis.

  • Side Cutting Edge Angle (C_s): Angle between side flank and workpiece axis.

  • Nose Radius (r): Curved tip radius for finish.

• Tool Signature (ASA System): Sequence of angles in order: Back Rake / Side Rake / End Relief / Side Relief / End Cutting Edge / Side Cutting Edge / Nose Radius.

  • Example: 8-8-7-7-15-15-0.8 (all in degrees, radius in mm).

• Other Systems: ORS (Orthogonal Rake System), NRS (Normal Rake System).

[!TIP] Exam Focus: Sketch the tool and label all angles. Be ready to convert between ASA and ORS signatures.

Orthogonal vs. Oblique Cutting

Cutting Forces, Power & Specific Cutting Energy

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

$$ u = \frac{F_c}{A} = \frac{F_c}{f \times d} $$

where $$\displaystyle F_c $$ = tangential force (N), $f$ = feed (mm/rev), $d$ = depth of cut (mm). Units: J/mm³ or N/mm².

• Tangential Force Calculation (from given u):

$$ F_c = u \times f \times d $$

• Merchant's Circle (Orthogonal Cutting):

  • Forces: $$\displaystyle F_c $$ (tangential), $$\displaystyle F_t $$ (feed/thrust).

  • Resultant $$\displaystyle F = F_c / \cos(\phi - \alpha) $$, where $\phi$ = shear angle, $\alpha$ = rake angle.

  • Shear Angle (approximation):

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

    where $\beta$ = friction angle ($$\displaystyle \tan\beta = \frac{F_t}{F_c} $$).

*   **Power**: $$\displaystyle P_c = F_c \times V_c $$, where $$\displaystyle V_c $$ = cutting velocity (m/min).

[!TIP] Common Pitfall: In orthogonal cutting calculations, ensure units are consistent (convert mm to m for power in Watts).

Tool Life Equations & Material Comparison

• Taylor's Tool Life Equation:

$$ V T^n = C $$

where $V$ = cutting speed (m/min), $T$ = tool life (min), $n$ & $C$ = tool-workpiece constants.

*   **n** (exponent): 0.1 (HSS) to 0.5 (carbide). Lower n → less sensitivity to speed.

*   **C**: Speed for 1 min life. Higher C → better tool life.

• Tool Material Comparison:

  | Property | High Speed Steel (HSS) | Carbide (WC-Co) | | :--- | :--- | :--- | | Hardness | Moderate (62-68 HRC) | High (89-93 HRA) | | Hot Hardness | Up to 600°C | Up to 900-1200°C | | Toughness | Good | Brittle | | Cost | Low | High | | Application | General purpose, interrupted cuts | High-speed, continuous, hard materials |

Cutting Fluids

• Types: Oils (straight, soluble), Emulsions (oil-in-water), Semi-synthetics, Synthetics, Gases (N₂, CO₂), Pastes.

• Mechanisms of Effectiveness:

  1. Cooling: Reduces temperature, prevents thermal damage.

  2. Lubrication: Reduces friction, tool wear, improves surface finish.

  3. Chip Flushing: Removes chips, prevents built-up edge.

• Selection Criteria:

  • Operation: Grinding (cooling), Hobbing (lubrication).

  • Work Material: Steel (sulfurized oils), Aluminum (synthetics).

  • Tool Material: Carbide (more cooling needed).

II. CONVENTIONAL MACHINING PROCESSES

A. Grinding

Surface Grinding

• Machine Elements: Workpiece table, magnetic chuck, reciprocating wheel head, abrasive wheel.

• Working: Wheel rotates at high speed; workpiece moves reciprocally under wheel; depth of cut by wheel head downfeed.

• Applications: Flat surfaces, slots, profiles.

• Advantages: High accuracy (0.001-0.005 mm), good finish (Ra 0.1-0.8 μm).

• Limitations: High cost, thermal damage risk, not for soft/ductile materials.

Centerless Grinding

• Working Principle: Workpiece supported between rotating grinding wheel (drive), regulating wheel (feed control), and work rest blade. No centers required.

• Types:

  • Through-feed: For cylindrical parts (long bars). Workpiece fed axially.

  • In-feed: For stepped/dished parts. Regulating wheel retracted.

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

• Advantages: High productivity, no work holding marks, good for small parts.

• Limitations: Setup complexity, limited to cylindrical parts, not for internal surfaces.

• Applications: Bearings, piston pins, shafts.

Grinding Wheel Specifications (SELECT-A-GRIND)

1. Abrasive Type: Al₂O₃ (steel), SiC (cast iron, non-ferrous), CBN (hardened steel), Diamond (ceramics).

2. Grain Size: Gauge number (10-600). Coarse → high MRR, poor finish; Fine → opposite.

3. Bond: Holds grains. Vitrified (rigid, porous), Resinoid (flexible), Rubber (very flexible).

4. Structure: Grain spacing. Dense (low #) for hard materials; Open (high #) for soft/ductile.

5. Grade: Bond strength. Hard grade (A-Z) → grains dull slowly; Soft grade → grains release quickly.

6. Diameter: Affects surface speed & rigidity.

Wheel Dressing vs. Truing

B. Broaching

• Cutting Action: Progressive teeth on a broach. Each tooth is slightly longer than previous. Roughing teeth (large rake, high rake) remove bulk; finishing teeth (small rake, zero rake) provide final size/finish.

• Continuous Surface Broaching Machine:

  • Construction: Vertical or horizontal. Workpiece clamped on fixture; broach mounted on ram/slide.

  • Operation: Broach pulls or pushes through/over workpiece in single stroke. Return stroke is non-cutting.

  • Useful For: Internal surfaces (keyways, splines, gears), external surfaces (contours).

• Applications: Internal: Square holes, turbine blades. External: Automotive parts, machine ways.

C. Tool Failure Modes

Sketch Required: Show flank wear, crater wear, chipping, fracture on a tool insert.

III. GEAR MANUFACTURING

A. Gear Fundamentals

• Elements:

  • Pitch Circle: Imaginary circle where pure rolling occurs.

  • Module (m): $$\displaystyle m = \frac{\text{Pitch Circle Diameter (PCD)}}{\text{Number of teeth (Z)}} $$ (mm).

  • Pressure Angle (φ): Angle between line of action and tangent to pitch circle (standard: 20°).

  • Involute Profile: Curve traced by end of taut string unwinding from base circle. Property: Conjugate action maintained even with center distance variation.

B. Gear Production Methods

Gear Hobbing

• Working Principle: Hob (screw-like cutter with helical teeth) rotates and feeds axially into blank rotating in mesh. Continuous indexing.

• Hob Construction: Body, cutting teeth (with relief), gashing (flutes), pilot.

• Kinematics: Hob rotation ($$\displaystyle N_h $$) and blank rotation ($$\displaystyle N_b $$) maintain ratio: $$\displaystyle N_b / N_h = Z / K $$, where Z = teeth on blank, K = starts on hob.

• Advantages: Fast, continuous, high productivity, good accuracy.

• Limitations: Cannot cut internal gears, requires specific machine, not for very small batches.

• Sketch: Show hob, gear blank, indexing motion.

Gear Shaping

• Principle: Cutter (pinion-shaped) reciprocates (cutting stroke) and rotates with workpiece (indexing). Return stroke is non-cutting.

  • Indexing: Cutter and workpiece rotate in exact ratio (like hobbing).

  • Cutting Stroke: Downward, material removal.

  • Return Stroke: Upward, tool lifted, workpiece indexed.

• Advantages over Hobbing:

  • Can cut internal gears, clusters, arms.

  • Can cut very large gears (hob size limits).

  • Can cut keyways in same setup.

• Disadvantages: Intermittent cutting → lower productivity than hobbing.

Gear Finishing Methods

1. Shaving: Cutting with crossed-axis helical shaving cutter. Removes small error.

2. Honing: Abrasive stones in gear-shaped hone. For hard gears.

3. Lapping: Lapping wheel with abrasive slurry. For high precision.

4. Burnishing: Rolling with hardened rollers. Improves surface finish, no material removal.

C. Specialized Gear Cutting

• DP Cutter (Dedendum Plug Cutter):

  • Used in gear shaping for involute gears.

  • Characteristics: Cutter has rack tooth profile (not involute). Its addendum and dedendum are designed for specific module (m) and pressure angle (φ).

  • Purpose: Generates correct involute flank on gear by generating motion. Cutter geometry must match base pitch of gear to be cut.

IV. FINISHING AND SUPER FINISHING PROCESSES

V. UNCONVENTIONAL MACHINING PROCESSES

A. Electrical Discharge Machining (EDM)

• Working Principle: Spark erosion. Tool (electrode) & workpiece submerged in dielectric (kerosene, deionized water). Pulsed DC voltage causes sparks across gap, vaporizing/removing material. Dielectric flushes debris.

• Sketch: Show power supply, tool electrode, workpiece, dielectric tank, pump, filter.

• Advantages: No mechanical contact, machines hard/brittle materials, complex shapes, good finish.

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

• Wire EDM: Uses continuously fed conducting wire (brass) as electrode. Cuts 2D profiles. Higher precision, no electrode wear.

B. Electrochemical Machining (ECM)

• Logical Diagram:

  
  [Power Supply (+)] --> [Tool (Cathode)]
  
                            |
  
  [Electrolyte Pump] --> [Gap] --> [Workpiece (Anode)] --> [Removed Ions]
  
                            |
  
  [Electrolyte Tank/Filter]
  
  

• Procedure: Select electrolyte (NaCl, NaNO₃), set voltage/current, maintain inter-electrode gap (0.1-0.5 mm), electrolyte flow high.

• Working: Anodic dissolution. Faraday's Law: $$\displaystyle m = \frac{I \cdot t}{n \cdot F} \cdot M $$, where $m$=mass removed, $I$=current, $t$=time, $n$=valency, $F$=Faraday constant, $M$=atomic mass.

• Advantages: No thermal stress, no tool wear, burr-free, high MRR for soft metals.

• Limitations: Only conductive, electrolyte handling, shape limited by tool, hydrogen evolution.

C. Ultrasonic Machining (USM)

• Working: Tool (sonotrode) vibrates at ultrasonic frequency (20 kHz) in slurry of abrasive (SiC, Al₂O₃) & water. Abrasive grains impact & erode workpiece.

• Sketch: Show transducer (piezoelectric/magnetostrictive), horn, tool, abrasive slurry circulation.

• Elements: Frequency (~20 kHz), Amplitude (0.01-0.1 mm), Abrasive type/size, Load.

• Applications: Brittle materials (ceramics, glass, Si), small holes, intricate shapes.

D. Electron Beam Machining (EBM)

• Characteristics: High-velocity focused electron beam in vacuum (10⁻⁵ torr). Kinetic energy → thermal energy → vaporization.

• Advantages: Extremely precise (0.01-0.1 mm), high aspect ratio holes, no tool wear.

• Limitations: Very high equipment cost, vacuum required, only conductive materials, X-ray hazard, slow for large areas.

E. Abrasive Water Jet Machining (AWJM)

• Principle: High-pressure water (2000-4000 bar) accelerated through nozzle. Abrasives (garnet) entrained in mixing tube, creating high-velocity abrasive jet.

• Sketch: Pump, intensifier, abrasive feeder, mixing tube, focusing nozzle, workpiece.

• Abrasive Selection Factors:

  1. Hardness: Must be harder than workpiece.

  2. Shape: Angular grains better cutting.

  3. Size: Smaller → finer cut, lower MRR.

  4. Flow Rate: Affects cutting speed & taper.

F. Plasma Arc Machining (PAM)

• Construction: Power supply (DC), gas (N₂, Ar, H₂, air), torch (electrode, nozzle), water cooling.

• Working: Gas ionized by arc → plasma (10,000-50,000°C) → high-velocity jet melts/vaporizes metal.

• Applications: Cutting thick (up to 150 mm) conductive plates (steel, Al, Cu). Fast, but rough.

G. Laser Beam Machining (LBM)

• Principle: Focused high-energy laser beam (CO₂, Nd:YAG, fiber) melts/vaporizes material.

• Types:

  • CO₂: Infrared (10.6 μm), for non-metals, thick metals.

  • Nd:YAG: Solid-state (1.06 μm), high precision, metals.

  • Fiber: Efficient, high quality, metals.

• Applications: Cutting, drilling, welding, marking.

H. Comparisons

VI. NUMERICAL CONTROL AND COMPUTER AIDED MANUFACTURING

A. NC vs. CNC Machines

Coordinate Systems

• Absolute: All coordinates from fixed origin (work zero). G90.

• Incremental: Coordinates from previous point. G91.

• Polar: Radius & angle.

• Machine Zero (Home): Fixed machine reference point.

• Work Zero (Program Zero): User-defined origin on workpiece.

B. NC Machine Construction & Functions

• Drive System: Servo motors (DC/AC) or stepper motors with ball screws/lead screws.

• Feedback Devices: Encoders/resolvers for closed-loop control (position/speed).

• Control Unit (CPU): Reads program, interpolates, sends signals to drives.

• Functions:

  • Axis movement (X, Y, Z, A, B, C).

  • Spindle control (speed, direction).

  • Tool change (ATC).

  • Coolant, clamp control.

C. NC Part Programming

• Manual Programming: Using G-codes (preparatory) & M-codes (miscellaneous).

  • Motion Control:

    • G00 - Rapid traverse (point-to-point).

    • G01 - Linear interpolation (cutting feed).

    • G02 - Circular interpolation CW.

    • G03 - Circular interpolation CCW.

  • Other: G20/G21 (inch/mm), G40/G41/G42 (cutter compensation).

• Computer-Assisted Programming (APT, CAM):

  • Adaptive Control (AC): Real-time adjustment of feed/speed based on cutting force/torque sensors. Optimizes MRR, prevents tool breakage.

D. Control Systems

1. Point-to-Point: Moves tool to exact point (drilling, boring). No path control.

2. Straight-Line: Tool moves along straight line between points at specified feed.

3. Contouring (Continuous Path): Tool follows continuous path (2D/3D) while machining (milling, turning). Requires simultaneous axis control.

VII. METAL FORMING PROCESSES

A. Extrusion

• Hot vs. Cold Extrusion:

  | Basis | Hot Extrusion | Cold Extrusion | | :--- | :--- | :--- | | Temperature | Above recrystallization temp. | Room temp. (below recryst.) | | Surface Finish | Poor (scale) | Excellent | | Mechanical Props | Recrystallized (soft) | Strain hardened (strong) | | Material | Low-melting (Al, Mg, Cu) | High-melting (steel, Ti) | | Force | Lower (due to hot flow) | Very high (requires heavy press) | | Applications | Long sections, tubes | Bolts, cans, small parts |

• Classification:

  • Direct (Forward): Ram & billet move same direction. Simple, but friction high.

  • Indirect (Backward): Die moves with billet. Lower friction, longer die life.

  • Hydrostatic: Billet surrounded by pressurized fluid. Uniform pressure, complex shapes.

  • Impact (Cold): High-speed punch (like extrusion forging). Fast, good surface.

  • Tube Extrusion:

    • With Mandrel: Mandrel fixed/plug creates hollow. Sketch: billet, mandrel, die, ram.

    • Without Mandrel (Porthole): Billet split, rejoin around mandrel in die.

• Metal Flow in Extrusion:

  1. Homogeneous (Plug Flow): All elements move at same speed. Ideal.

  2. Laminar (Velocity Gradient): Center moves faster than periphery (friction). Causes defects.

  3. Fracture (Cracking): Severe velocity gradient → tensile stress → fracture.

  • Importance: Understanding flow prevents defects (center void, surface cracking).

B. Sheet Metal Forming

• Press Tools:

  • Compound Die: Performs multiple operations in one stroke (e.g., blanking & piercing). All operations at same station. Sketch: Show die block with multiple punches/blankers.

  • Progressive Die: Multiple stations. Strip fed progressively; different operation at each station. High production, but complex.

• Drawing:

  • Deep Drawing: Depth > diameter. Requires blankholder, careful clearance.

  • Shallow Drawing: Depth < diameter.

  • Variables: Blank diameter, thickness, die radius, punch speed, friction.

  • Defects:

    • Wrinkling (buckling): Due to compressive stress in flange. Prevent: Increase blankholder force.

    • Tearing (cracking): Due to tensile stress in wall. Prevent: Increase die radius, use proper blank size.

• Defects in Rolled Parts: Cracks (edge, surface), Warping (non-uniform cooling), Alligatoring (center split).

• Defects in Forgings: Misrun (incomplete fill), Cold shut (cold metal fold), Laps (surface fold).

• Stretch Forming: Sheet clamped at edges, stretched over form block. Applications: Aircraft skins, automotive panels.

• Peen Forming (Shot Peening): Small shots bombarded surface → compressive residual stress → improves fatigue life. Applications: Springs, gears, turbine blades.

• Super Plastic Forming: Grain-refined material (e.g., Ti, Al alloys) at high temp (0.5-0.7 Tₘ) in inert gas. Extremely slow, large strains. Applications: Complex aerospace parts.

C. Forging

• Yield Criteria (for ductile materials):

  • Tresca (Max Shear Stress): Yielding when max shear stress = shear yield stress. $$\displaystyle \tau_{max} = \frac{\sigma_y}{2} $$.

  • Von Mises (Distortion Energy): Yielding when distortion energy reaches critical value. $$\displaystyle \sigma_{eq} = \sqrt{\frac{1}{2}[(\sigma_1-\sigma_2)^2 + (\sigma_2-\sigma_3)^2 + (\sigma_3-\sigma_1)^2]} = \sigma_y $$.

  • Relation: $$\displaystyle \sigma_{y(Tresca)} = 0.5 \sigma_{y(VonMises)} $$. Von Mises is more accurate for metals.

• Pressure Distribution in Rectangular Block Forging (Sliding Friction):

$$ \frac{p}{2K} = e^{-\frac{2\mu x}{h}} \left[ 1 - e^{-\frac{2\mu b}{h}} \right] $$

where $p$ = pressure at distance $x$ from center, $K$ = shear strength, $\mu$ = friction coeff., $h$ = height, $b$ = half-width. Pressure decays exponentially from center.

D. Hot vs. Cold Working

VIII. PLASTICS MANUFACTURING PROCESSES

A. Plastics Basics

• Thermoplastics: Soften on heating, harden on cooling (reversible). Examples: PE, PP, PS, PVC, Nylon.

• Thermosets: Harden permanently on heating (chemical cross-linking). Examples: Phenolic, Epoxy, Polyester, Melamine.

• Additives:

  • Plasticizers: Increase flexibility (phthalates in PVC).

  • Fillers: Reduce cost, increase strength/stiffness (CaCO₃, glass fibers).

  • Stabilizers: Prevent degradation (heat/UV stabilizers like HALS, UV absorbers).

B. Molding Processes

Injection Molding

• Process: Plastic granules melted in barrel, injected under high pressure into closed mold, cooled, ejected.

• Mold Types:

  • Two-Plate: Simple, single parting line. Ejector on one side.

  • Three-Plate: Two parting lines. Allows automatic ejection, better gate location.

  • Hot Runner: Manifold keeps plastic molten in runners. Benefits: No runner waste, faster cycle, better control.

• Applications: Almost all plastic parts (containers, automotive, toys).

Blow Molding

• Extrusion Blow Molding (for bottles):

  1. Tube (parison) extruded downward.

  2. Parison captured in split mold.

  3. Air blown, parison expands to mold.

  4. Cool, open mold, eject.

  • Sketch: Extruder, parison, mold, air inlet.

• Advantages: Fast, low cost for hollow parts.

• Defects: Flash (excess material), Thin walls, Weld lines.

Compression Molding

• Process: Measured charge placed in open heated mold, mold closes, heat & pressure applied, cure, open, eject.

• Sketch: Show heated platens, mold cavity, charge.

• Applications: Thermosets (Bakelite), composites (SMC), large parts.

Transfer Molding vs. Extrusion Molding

C. Other Plastics Processes

• Calendaring: Plastic passed through series of heated rolls to form sheet/film. Applications: PVC sheets, films, floor coverings. Thickness controlled by roll gap.

• Film Blowing: Extruded tube (bubble) inflated with air, cooled, collapsed, wound. Applications: Polyethylene bags, agricultural films.

• Thermoforming: Sheet heated, formed over mold by vacuum (vacuum forming) or pressure (pressure forming). Applications: Trays, packaging, automotive interior.

D. Welding of Plastics

• Methods:

  • Heated Tool (Hot Plate): Heated plate contacts joint surfaces, melts, plates removed, surfaces pressed.

  • Ultrasonic: High-frequency vibration at joint → friction heat.

  • Vibration (Spin): One part rotated, pressed against stationary part.

  • Friction: Rotational/linear motion generates heat.

• Advantages: Strong joints, clean (no adhesives), fast.

• Limitations: Material-specific (thermoplastics only), joint design critical, equipment cost.

IX. CASTING PROCESSES (Nov 2022)

Patterns

• Solid Pattern: Single piece, simple shapes.

• Split Pattern: Two or more pieces (for complex shapes with cores).

• Match Plate Pattern: Pattern mounted on plate with matching cope/drag patterns. Used in machine molding.

• Sweep Pattern: Used for cylindrical cavities (swept around axis).

• Discuss any three (e.g., Solid, Split, Match Plate).

Gating System

• Sprue: Vertical channel from pouring cup to runner.

• Runner: Horizontal channel distributing metal to gates.

• Gate: Constricted opening into mold cavity. Controls flow, minimizes turbulence.

• Riser (Feeder): Reservoir of molten metal to compensate for shrinkage.

• Purpose: Control metal flow, filter dross, prevent erosion, allow air escape.

Pattern Allowances (with Sketches)

1. Draft Allowance: Taper on pattern faces for easy removal. (1-3° for external, 3-10° for internal).

2. Shrinkage Allowance: Extra size to compensate for solidification shrinkage. (1-2% for most metals).

3. Machining Allowance: Extra material for post-casting machining.

4. Distortion Allowance: For irregular shapes (e.g., "U" shape bends opposite to distortion).

Centrifugal Casting

• Horizontal: Mold rotates about horizontal axis. Used for long cylindrical parts (pipes, bushings). Dense outer surface, porous center.

• Vertical: Mold rotates about vertical axis. Used for rings, wheels. Better density distribution.

• Centrifugal Force: $$\displaystyle F_c = m \omega^2 r $$. Drives denser metal to periphery.

• Applications: Pipes, cylinder liners, flywheels, rings.

Die Casting

• Process: Molten metal injected under high pressure (700-5000 bar) into permanent steel dies (two halves). Dies are water-cooled.

• Advantages: High production rate, excellent surface finish, dimensional accuracy, thin walls possible.

• Limitations: High die cost, limited to low-melting non-ferrous (Al, Zn, Mg), porosity possible, high maintenance.

X. WELDING PROCESSES (Metal)

Tungsten Inert Gas (TIG) Welding

• Components:

  • Non-consumable tungsten electrode (pure or alloyed).

  • Inert shielding gas (Ar, He, or mix) from torch.

  • Filler rod (optional, added manually).

  • Power source (DC for steel/Al, AC for Al).

• Process: Arc between tungsten & workpiece. Shielding gas protects weld pool. High-quality, clean weld.

Heat Affected Zone (HAZ)

• Definition: Region of base metal adjacent to weld, microstructure/properties altered by heat, but not melted.

• Zones (in steel, from weld outward):

  1. Fusion Zone (weld metal).

  2. Coarse Grain HAZ: Near weld, peak temp just below melting. Grain growth → brittle.

  3. Fine Grain HAZ: Lower temp, normalizing effect.

  4. Partially Transformed HAZ (subcritical): Tempering effect.

  5. Unaffected Base Metal.

• Effects: Reduced toughness in coarse grain HAZ, residual stresses, distortion.

Welding Safety Precautions

• Fumes & Gases: Use ventilation/respirators (Zn, Mn, Cr toxic).

• Radiation: UV/IR from arc → eye/skin damage. Use proper helmet/shield.

• Fire: Remove combustibles, have fire watch.

• Electrical: Check cables, ground clamp, avoid moisture.

• Compressed Gases: Secure cylinders, proper regulators.

Brazing

• Filler Metal: Alloy (Cu-Zn, Ag-Cu) with melting point above 450°C but below base metal.

• Capillary Action: Filler drawn into joint by capillary force.

• vs. Soldering: Soldering uses filler < 450°C, weaker joints.

• Process: Clean surfaces, flux applied, heat assembly (torch, furnace), filler flows, cool, clean flux.

Friction Welding

• Principle: Solid-state welding. Heat generated by friction between rubbing surfaces under pressure. No melting.

• Process: One part rotated, other held axially. Rotational speed & pressure applied until forge temperature reached. Rotation stopped, pressure maintained for consolidation.

• Applications: Rods, tubes, dissimilar metals (Al-steel), engine valves, aerospace.

XI. MISCELLANEOUS AND SUPPORTING TOPICS

Non-Destructive Testing (NDT)

Sawing Machines

• Power Hacksaw: Reciprocating blade, automatic feed. For large stock, pipes.

• Band Saw: Continuous toothed belt. Construction: Frame, wheels, blade guides, drive. Operation: Blade runs continuously, workpiece fed manually/automatically. Applications: Contour cutting, curves, pipes.

• Circular Saw: Rotating circular blade. Construction: Arbor, blade, guard, table. Applications: Straight cuts, sheet metal, bars.

Weldability

• Factors:

  1. Material Composition: Carbon equivalent (CE) for steel. High CE → poor weldability.

  2. Thickness: Thicker → higher heat input, more distortion.

  3. Joint Design: Stress concentration, accessibility.

  4. Service Requirements: Corrosion, fatigue, temperature.

  5. Welding Process: Heat input affects HAZ.

END OF UNIT 5 NOTES
Always cross-check formulas with latest RGPV syllabus and past papers. Practice derivations (e.g., Merchant's circle, pressure in forging) and sketch-based questions.