MANUFACTURING TECHNOLOGY (ME-405) - Unit 1 Short Notes

I. Fundamentals of Machining

Single Point Cutting Tool Nomenclature and Tool Signature

• Tool Signature: Standardized code (ASA system) specifying tool geometry angles in the order: A-A, B-B, C-C, D-D, E-E (back rake, side rake, end relief, side relief, end cutting edge angle).

• Example: 8-7-5-5-10-0-0 indicates back rake 8°, side rake 7°, end relief 5°, side relief 5°, end cutting edge 10°, side cutting edge 0°, nose radius 0.

• Nomenclature: Key angles include rake (α), relief (γ), cutting edge (ε), nose radius (r). Rake influences chip flow and tool strength; relief prevents flank wear.

[!TIP]

Exam Focus: Tool signature is frequently asked. Remember ASA order and that angles are measured from tool reference planes.

Orthogonal vs. Oblique Cutting Mechanics

• Orthogonal Cutting:

  • Cutting edge ⟂ to feed direction.

  • Forces: Tangential cutting force (Fc), Thrust force (Ft), Feed force (Ff).

  • Shear plane angle φ, shear force Fs.

  • Force relationships:

$$ F_c = F_s \cos(\phi - \alpha) + F_{te} \sin(\phi - \alpha) \\ F_t = F_s \sin(\phi - \alpha) - F_{te} \cos(\phi - \alpha) $$

where α = rake angle, $$\displaystyle F_{te} $$ = friction force on tool face.

• Sketch: Show tool, workpiece, shear plane, forces Fc, Ft, Fs.

• Oblique Cutting:

  • Cutting edge inclined at angle λ to feed direction.

  • Forces have lateral component; 3D force system.

  • More realistic for turning, milling.

  • Forces resolved into orthogonal components for analysis.

[!TIP]

Common Pitfall: In orthogonal cutting, Ff is often neglected in power calculations; in oblique, all three forces matter.

Specific Cutting Energy and Cutting Power

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

$$ U = \frac{F_c}{A} = \frac{F_c}{d \cdot f} $$

where $d$ = depth of cut (mm), $f$ = feed (mm/rev), $$\displaystyle F_c $$ in N, $U$ in J/mm³ or J/m³.

• Cutting Power (Pc):

$$ P_c = F_c \cdot V_c $$

where $$\displaystyle V_c $$ = cutting velocity (m/min). Convert units appropriately.

[!BOX]

Key Formula:

$$ > \boxed{U = \frac{F_c}{d \cdot f} \quad \text{and} \quad P_c = F_c \cdot V_c} > $$

Tool Life Equations and Taylor's Tool Life Equation

• Taylor's Equation:

$$ V T^n = C $$

where $V$ = cutting speed (m/min), $T$ = tool life (min), $n$ = tool life exponent (0.1–0.8), $C$ = constant.

• Interpretation:

  • $n$ indicates sensitivity: higher $n$ → tool life more sensitive to speed changes.

  • $C$ depends on tool-workpiece material and cutting conditions.

• Comparison of Tool Materials:

  | Material | n (typical) | C (typical) | Remarks | |----------|-------------|-------------|---------| | HSS | 0.1–0.3 | 60–100 | Low n, less speed-sensitive | | Carbide | 0.5–0.7 | 1000–3000 | High n, more speed-sensitive | | Ceramics | 0.6–0.9 | 5000–10000 | Very high n, high speed |

[!TIP]

Exam Trick: For comparing tools, rearrange: $$\displaystyle T_1/T_2 = (V_2/V_1)^{1/n} $$. Higher n gives greater life difference for same speed change.

Cutting Fluids

• Types:

  1. Coolants: Water-based emulsions, oils (cooling).

  2. Lubricants: Oils, fatty substances (reduce friction).

  3. Semi-synthetics: Emulsions with additives.

  4. Gases: Air, CO₂, nitrogen (minimal cooling).

• Mechanisms of Effectiveness:

  • Cooling: Reduce temperature, prevent thermal softening.

  • Lubrication: Form film, reduce friction and built-up edge.

  • Cleaning: Flush chips, prevent smearing.

  • Corrosion Prevention: Additives protect machine/workpiece.

• Applications:

  • High-speed machining, deep cuts, difficult materials (stainless steel, aluminum).

  • Grinding (to prevent burning).

  • Tapping, threading (lubrication critical).

[!TIP]

Common Error: Confusing cooling vs. lubrication. Water-based coolants excel at cooling; oils at lubrication.

II. Conventional Machining Processes

Grinding Processes – Surface Grinding

• Specifications: Workpiece size, wheel size (diameter × width), spindle speed, table travel.

• Construction:

  • Wheel (abrasive), work table (reciprocating/rotary), wheel head (cross-feed), base.

  • DiagramSEARCH: surface grinding machine diagram

• Applications: Flat surfaces, precision slots, tool and die making.

• Advantages: High accuracy (±0.002 mm), good surface finish (Ra 0.1–0.8 μm), hard materials.

• Limitations: Slow material removal, wheel wear, thermal damage risk.

Centreless Grinding

• Principle: Workpiece supported by two wheels (grinding and regulating) and a work rest blade; no centers or chucks.

• Construction:

  • Grinding wheel (high speed, cuts), Regulating wheel (low speed, controls feed), Work rest blade (supports).

  • Through-feed, in-feed, end-feed types.

  • DiagramSEARCH: centreless grinding machine diagram

• Applications: Mass production of cylindrical parts (pins, rollers, bearings).

• Advantages: High productivity, no workpiece deformation, automation-friendly.

• Limitations: Limited to cylindrical parts, setup critical, not for complex shapes.

[!TIP]

Exam Focus: Centreless grinding is frequently asked. Distinguish through-feed (continuous) vs. in-feed (stepped).

Grinding Wheel Specifications

• Grain Size: Grit number (10–600); higher number = finer grit (e.g., 60 = coarse, 220 = fine).

• Grade: Hardness (A–Z); A = soft, Z = hard. Soft grade for hard materials (to avoid glazing), hard grade for soft materials.

• Structure: Density of grains (0–12); open structure for soft materials/continuous cutting, dense for hard materials.

• Bond Type:

  • Vitrified (V): ceramic, strong, porous.

  • Resinoid (B): flexible, high speed.

  • Rubber (R): flexible, fine finish.

  • Metal (M): for superabrasives.

Wheel Dressing vs. Truing

• Dressing: Exposes fresh, sharp grains; restores cutting ability; uses coarse diamond tool; done frequently.

• Truing: Restores wheel geometry (roundness, concentricity); uses precise diamond tool; done after mounting or if wheel out-of-round.

• Key Difference: Dressing = sharpness; Truing = shape.

Broaching

• Cutting Action: Multiple teeth, each progressively higher; each tooth removes chip; one stroke completes operation.

• Continuous Surface Broaching Machine:

  • Workpiece clamped on table, broach stationary or moving.

  • Used for external surfaces: slots, keyways, contours.

  • DiagramSEARCH: continuous surface broaching machine diagram

• Suitable Components:

  • Internal: keyways, splines, gears (internal).

  • External: flat surfaces, contours, turbine blades.

Sawing Processes

• Band Saw:

  • Continuous blade, guides, wheels.

  • Applications: curved cuts, large stock, metal fabrication.

  • Advantages: versatile, kerf loss low.

  • Limitations: blade breakage, slower for straight cuts.

• Circular Saw:

  • Rotating disc, high speed.

  • Applications: straight cuts, bar stock, sheet metal.

  • Advantages: fast, accurate.

  • Limitations: limited to straight lines, vibration.

• Power Hacksaw:

  • Reciprocating blade, automatic feed.

  • Applications: large diameter bars, pipes.

  • Advantages: robust, low cost.

  • Limitations: slow, rough finish.

III. Tool Wear and Failure

Four Mechanisms with Sketches:

1. Flank Wear: Gradual wear on flank (rake face) due to abrasion.

   DiagramCANVAS: flank wear on tool flank

2. Crater Wear: on rake face, due to diffusion/adhesion at high temp.

   DiagramCANVAS: crater wear on rake face

3. Chipping: Small fragments break from edge (mechanical shock).

   DiagramCANVAS: chipping at cutting edge

4. Fracture: Catastrophic breakage (brittle tools, excessive load).

   DiagramCANVAS: tool fracture

5. Plastic Deformation: Edge rounds due to high temperature (soft tools).

   DiagramCANVAS: deformed cutting edge

[!TIP]

Exam Pattern: Always sketch and label. Flank and crater wear are most common; chipping/fracture for interrupted cuts.

IV. Finishing and Superfinishing Processes

• Honing:

  • Abrasive stones (honing sticks) rotate and reciprocate.

  • Applications: cylinder bores, bearing races.

  • Advantages: improves geometry, cross-hatch pattern.

  • Limitations: slow, manual loading.

• Lapping:

  • Loose abrasives in carrier, between workpiece and lap (flat/cylindrical).

  • Applications: high-precision flat/cylindrical surfaces (gauge blocks).

  • Advantages: extreme accuracy (μm), low roughness.

  • Limitations: very slow, size limited.

• Electro-polishing:

  • Electrochemical anodic dissolution; peaks dissolve faster than valleys.

  • Applications: stainless steel parts, medical devices, decorative finish.

  • Advantages: burr-free, bright finish, no stress.

  • Limitations: only conductive materials, electrolyte handling.

• Buffing:

  • Soft wheel (cloth) with fine abrasive (paste).

  • Applications: final luster on metals, plastics.

  • Advantages: high gloss, removes minor scratches.

  • Limitations: not for dimensional correction.

• Superfinishing:

  • Very fine abrasives (0.01–0.1 μm) with light pressure, oscillating motion.

  • Applications: bearing races, shafts, gears.

  • Advantages: ultra-low roughness (Ra < 0.025 μm), improves fatigue life.

V. Gear Manufacturing Technology

Gear Terminology and Elements

• Pitch Circle: Imaginary circle where teeth mesh.

• Addendum: Height above pitch circle.

• Dedendum: Depth below pitch circle.

• Module (m): Pitch diameter / number of teeth.

• Diametral Pitch (DP): Teeth per inch of pitch diameter.

• Pressure Angle (φ): Angle between line of action and tangent (usually 20°).

• Diagram:

  DiagramCANVAS: gear tooth terminology diagram showing pitch circle, addendum, dedendum, base circle, tooth thickness

Gear Production vs. Gear Generation

Gear Hobbing

• Working Principle:

  • Hob (threaded tool) rotates and feeds into gear blank.

  • Hob and blank rotate in synchronous ratio (like gear meshing).

  • Continuous indexing; each hob tooth cuts a gear tooth space.

  • DiagramSEARCH: gear hobbing machine diagram

• Advantages: Fast, high production, good accuracy, no index error.

• Limitations: Cannot cut internal gears, limited to 12–14 teeth minimum (unless modified), hob wear critical.

Gear Shaping

• Principle:

  • Cutter (pinion-shaped) reciprocates across gear blank.

  • Blank rotates and indexes after each stroke.

  • Simulates two gears meshing.

• Advantages: Can cut internal gears, any number of teeth, idler gears.

• Limitations: Slower than hobbing, limited to medium-sized gears.

Gear Finishing Methods

1. Shaving: Skiving with rotary cutter; removes small errors.

2. Honing: Abrasive stones; improves surface, corrects minor errors.

3. Lapping: Loose abrasives; high precision, low noise.

4. Grinding: Form grinding or generating; for hardened gears.

5. Burnishing: Plastic deformation with rollers; improves surface.

DP Cutters for Involute Gear Cutting

• Characteristics:

  • Designed for specific Diametral Pitch (DP); not interchangeable.

  • Standardized tooth profile (involute) for given DP.

  • Made of high-speed steel or carbide.

  • Used in gear shapers or mills for production gears.

  • Limited to gears with same DP; must match gear blank DP.

VI. Unconventional Machining Processes (UMP)

Introduction and Need for UMP

• Need:

  • Machine hard, brittle materials (ceramics, carbides).

  • Complex shapes (internal profiles, micro-features).

  • No tool-work contact → no tool wear, no residual stress.

  • High precision, minimal thermal damage.

• Vs. Conventional: Conventional relies on sharp tool, mechanical force; UMP uses thermal, chemical, electrochemical energy.

Electrical Discharge Machining (EDM)

• Working Principle:

  • Tool (electrode) and workpiece immersed in dielectric fluid.

  • Pulsed DC spark erodes workpiece material.

  • Dielectric flushes debris.

  • DiagramSEARCH: EDM machine diagram

• Advantages:

  • Any conductive material, regardless of hardness.

  • Complex shapes, internal corners, sharp edges.

  • No mechanical force → delicate parts.

• Disadvantages:

  • Slow material removal rate.

  • Electrode wear, recast layer, thermal damage.

  • Only conductive materials.

Electron Beam Machining (EBM)

• Characteristics:

  • Focused electron beam in vacuum (10⁻⁵ torr).

  • Beam melts/vaporizes material instantaneously.

  • CNC controlled for precision.

• Advantages:

  • Extremely precise (μm), no tool wear.

  • High aspect ratio holes, slots.

  • No mechanical stress.

• Limitations:

  • Vacuum required → large, expensive.

  • Only conductive materials (for electrical focusing).

  • Safety hazards (X-rays).

Abrasive Water Jet Machining (AWJM)

• Working Principle:

  • High-pressure water (2000–4000 bar) mixed with abrasives (garnet, Al₂O₃).

  • Jet exits nozzle, erodes material by micro-cutting.

  • DiagramSEARCH: AWJM nozzle diagram

• Abrasive Selection Factors:

  • Hardness: harder than workpiece.

  • Shape: angular for cutting, round for polishing.

  • Size: finer for smooth finish, coarser for MRR.

  • Flow rate: affects cutting power and taper.

• Advantages:

  • Cold process → no thermal damage.

  • Any material (metal, ceramic, composite).

  • Environmentally friendly (water).

• Limitations:

  • Taper in cut, slow for thick materials.

  • Abrasive cost, nozzle wear.

Electrochemical Machining (ECM)

• Logical Diagram:

  DiagramCANVAS: ECM diagram showing tool cathode, workpiece anode, electrolyte flow, power supply

• Procedure:

  1. Tool (cathode) shaped as inverse of workpiece.

  2. Electrolyte (NaCl, NaNO₃) flows at high pressure.

  3. DC current applied; anode (workpiece) dissolves.

  4. Gap maintained (0.1–0.5 mm).

• Working: Anodic dissolution: Metal → ions + electrons. No tool wear.

• Advantages:

  • No tool wear, high MRR for hard materials.

  • Smooth surface, no burrs.

  • Complex shapes (turbine blades).

• Limitations:

  • Only conductive materials.

  • Electrolyte handling, corrosion.

  • Accuracy limited by gap control.

Ultrasonic Machining (USM)

• Construction:

  • Ultrasonic transducer (piezoelectric/magnetostrictive).

  • Tool (sonotrode) vibrates at 20 kHz.

  • Abrasive slurry (SiC, B₄C) between tool and workpiece.

  • DiagramSEARCH: USM machine diagram

• Working:

  • Tool vibrates, abrasives impact workpiece → micro-chipping.

  • Brittle materials (glass, ceramics) ideal.

• Advantages:

  • No thermal damage, no chemical reaction.

  • Complex shapes in brittle materials.

• Limitations:

  • Slow MRR, tool wear (soft metals).

  • Only brittle/soft materials.

Plasma Arc Machining (PAM)

• Construction:

  • Plasma torch with tungsten electrode, orifice, shielding gas.

  • DC power supply, high current (100–1000 A).

  • DiagramSEARCH: plasma arc cutting diagram

• Working:

  • Gas (N₂, Ar, H₂) ionized → plasma jet (20,000°C).

  • Melts and blows away material.

• Applications: Cutting thick steel plates (up to 200 mm), stainless steel, aluminum.

• Advantages: Fast cutting, no electrode wear (non-transferred arc).

• Limitations: High power, fume/UV radiation, only conductive materials.

Laser Beam Machining (LBM)

• Short Note:

  • Focused laser beam (CO₂, Nd:YAG) melts/vaporizes material.

  • CNC controlled.

  • Applications: cutting, drilling, welding of metals, plastics, ceramics.

  • Advantages: non-contact, high precision, automation.

  • Limitations: High cost, reflective materials problematic, thermal affected zone.

Comparative Analysis

• EDM vs. EBM:

  | Feature | EDM | EBM | |-------------------|--------------------------|--------------------------| | Medium | Dielectric fluid | Vacuum | | Energy Source | Electrical sparks | Electron beam | | Materials | Conductive only | Conductive (mostly) | | Precision | ±0.01 mm | ±0.001 mm | | MRR | Low | High | | Cost | Lower | Very high |

• EDM vs. Plasma:

  • EDM: spark erosion, any shape, slower. Plasma: thermal cutting, straight cuts, faster for thick plates.

VII. Numerical Control and CNC Technology

NC vs. CNC Machines

NC Machine Tool Construction and Components

1. Drive System: Servo motors, ball screws, drives axes.

2. Machine Tool: Lathe, mill, grinder with rigid structure.

3. Control Unit: NC/CNC processor, reads part program.

4. Feedback System: Encoders/resolvers for position/speed.

5. Magnetic Tape/Punch Reader: Input media (older NC).

6. Coolant System: For machining.

7. Safety Guards: Enclosures, interlocks.

Coordinate Systems in NC Machines

• Cartesian (Rectangular): X, Y, Z linear axes. Right-hand rule.

• Polar: Radius and angle (for rotary tables).

• Spherical: Radius, θ, φ.

• Machine Zero: Reference point on machine.

• Workpiece Zero: Program origin (chosen by programmer).

NC Part Programming

• Manual Programming:

  • Write G-codes/M-codes by hand.

  • For simple geometries (2–3 axes).

  • Error-prone, time-consuming.

• Computer-Assisted Programming (CAD/CAM):

  • CAD model → CAM software → tool paths → post-processor → G-code.

  • Diagram:

    DiagramCANVAS: CAD/CAM flowchart: design → tool path simulation → post-processing → machine

• Advantages of CNC: Complex shapes, high accuracy, repeatability, easy modification.

• Limitations: High initial cost, skilled operators needed.

G-codes and M-codes

• G-codes (Preparatory):

  • 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.

• M-codes (Miscellaneous):

  • M00: Program stop.

  • M03/M04/M05: Spindle on CW/CCW/stop.

  • M06: Tool change.

  • M08/M09: Coolant on/off.

  • M30: Program end.

[!TIP]

Common Codes: G00, G01, G02, G03, M03, M05, M06 are most used.

Adaptive Control of NC Machines

• Definition: Real-time adjustment of cutting parameters (speed, feed, depth) based on sensor feedback (force, temperature, vibration).

• Purpose: Optimize MRR, prevent tool breakage, maintain quality.

• Types:

  • Adaptive Control with Constraint (AC with C): Adjust to keep force/torque within limit.

  • Adaptive Control with Optimization (AC with O): Maximize MRR subject to constraints.

• Implementation: Sensors → controller → adjust servo drives.

Motion Control Statements (Computer-Assisted)

1. G00 (Rapid Traverse): Non-cutting move at max speed.

2. G01 (Linear Interpolation): Straight line at programmed feed.

3. G02/G03 (Circular Interpolation): CW/CCW arc; specify I, J, K or R.

4. G04 (Dwell): Pause for specified time.

5. G28/G29: Return to reference point/from reference point.

6. G90/G91: Absolute/incremental programming.

7. G41/G42: Cutter radius compensation left/right.

VIII. Metal Forming Processes

Extrusion

• Principle: Push billet through die to produce long product of constant cross-section.

• Types:

  • Direct Extrusion: Billet and ram move same direction; friction at die.

  • Indirect Extrusion: Die moves with billet; less friction.

  • Hydrostatic Extrusion: Billet surrounded by fluid; high pressure.

  • Tube Extrusion: With mandrel (fixed or floating).

    DiagramSEARCH: tube extrusion with mandrel diagram

• Metal Flow Types:

  1. Homogeneous Flow: Uniform deformation.

  2. Plug Flow: Dead metal zone near die.

  3. Fracture Flow: Center fractures (low friction).

  4. Banding Flow: Laminar separation (inhomogeneous).

  • Importance: Affects product quality, defects, die design.

• Applications: Aluminum windows, pipes, rods, structural shapes.

• Advantages: Good surface finish, continuous, complex sections.

• Disadvantages: High force, die wear, residual stresses.

Hot vs. Cold Extrusion

Forging – Pressure Distribution Derivation

For rectangular block (width $w$, height $h$, length $b$) with sliding friction (coefficient $\mu$), shear strength $K$:

• Consider equilibrium of element at distance $x$ from center.

• Pressure $p$ varies exponentially:

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

• Derivation Sketch:

  DiagramCANVAS: forging pressure distribution derivation free-body diagram

Rolling – Defects in Rolled Parts

1. Centerline Cracking: In compression, center yields first.

2. Edge Cracking: Due to tensile stresses at edges.

3. Alligatoring: Surface cracks due to poor temperature control.

4. Scale Pits: Oxide scales entrained.

5. Uneven Thickness: Roll deflection, improper setup.

6. Residual Stresses: Non-uniform cooling.

Drawing – Classification and Types

• Wire Drawing: Bar through die; diameter reduction.

  DiagramSEARCH: wire drawing machine diagram

• Tube Drawing:

  • With Mandrel: Fixed or floating mandrel inside tube.

  • Without Mandrel: Sinking (wall thickness increases).

• Sheet Drawing: Cup drawing (deep drawing), stretch drawing.

Other Forming Processes

• Stretch Forming: Sheet stretched over form die; no wrinkle. Applications: aircraft skins, automotive panels.

• Peen Forming: Shot peening induces compressive stress → curvature. Applications: aircraft wing panels.

• Superplasticity on Sheet Metals:

  • At high temperature (0.5–0.7 Tm) and low strain rate (10⁻⁴ s⁻¹), materials exhibit huge elongation (200–500%).

  • Applications: complex shapes (blow forming, SPF).

IX. Polymer Processing and Plastic Manufacturing

Types of Plastics

• Thermoplastics: Soften on heating, harden on cooling; recyclable (PE, PP, PS, PVC).

• Thermosets: Set permanently on heating; cannot reheat (epoxy, phenolic, melamine).

Plastic Additives

1. Plasticizers: Increase flexibility, reduce brittleness (e.g., phthalates in PVC).

2. Fillers: Reduce cost, improve strength/rigidity (calcium carbonate, glass fibers).

3. Stabilizers: Prevent degradation (UV, thermal, oxidation); e.g., antioxidants, UV absorbers.

4. Colorants: Pigments/dyes.

5. Lubricants: Ease processing (internal/external).

6. Flame Retardants: Reduce flammability.

Injection Molding

• Mold Types:

  1. Two-Plate Mold: Simple, single parting line.

  2. Three-Plate Mold: Separate runner system; automatic ejection.

  3. Hot Runner Mold: Heated runner; no sprue waste.

• Benefits: High production, complex shapes, good surface finish, automatic.

• Applications: Automotive parts, containers, toys, electronics.

Transfer Molding vs. Extrusion Molding

Blow Molding

• Process:

  1. Extrusion Blow: Parison extruded, captured in mold, blown.

  2. Injection Blow: Preform injected, then blown.

  3. Stretch Blow: Axial stretch (PET bottles).

  DiagramSEARCH: blow molding process diagram

• Advantages: Fast, hollow parts, thin walls.

• Defects:

  • Flash: Excess material at mold line.

  • Weak Joint: Incomplete welding.

  • Sink Marks: Thick sections sink.

  • Air Traps: Bubbles.

Compression Molding

• Process:

  1. Preform (measured charge) placed in heated open mold.

  2. Mold closes, pressure applied, heat cures (thermosets).

  3. Cool, open, eject.

  DiagramSEARCH: compression molding diagram

• Applications: Electrical insulators, automotive parts, composites.

Calendaring

• Process:

  • Plastic passed through series of heated rollers (3–7).

  • Thickness reduced, surface smoothed.

  • Final sheet/film wound.

  DiagramSEARCH: calendaring machine diagram

• Applications: PVC sheets, films, coated fabrics.

Film Blowing

• Process:

  1. Extruded tube (bubble) through annular die.

  2. Inflated with air, cooled by air ring.

  3. Collapsed, wound.

• Applications: Polyethylene bags, agricultural films.

Thermoforming

• Process:

  1. Sheet heated to rubbery state.

  2. Formed over mold by vacuum, pressure, or mechanical means.

  3. Cool, trim.

• Types: Vacuum forming, pressure forming, twin-sheet forming.

• Applications: Packaging, trays, automotive interiors.

Welding of Plastics

• Methods:

  1. Heated Tool Welding: Hot plate contacts surfaces, then pressed.

  2. Ultrasonic Welding: High-frequency vibration at interface.

  3. Friction Welding: Rotary or linear motion generates heat.

  4. Spin Welding: Rotational friction (cylindrical parts).

  5. Hot Gas Welding: Hot air softens, then pressed (like soldering).

  6. Induction Welding: Electromagnetic heating of inserts.

  7. Laser Welding: Focused laser beam.

• Advantages:

  • Lightweight, corrosion-resistant, complex shapes.

  • No fasteners, airtight/watertight joints.

• Limitations:

  • Thermal degradation, limited to compatible plastics.

  • Joint strength lower than base material, surface preparation critical.

X. Casting Processes

Pattern Making

• Types:

  1. Solid Pattern: Single piece, simple shapes.

  2. Split Pattern: Two or more pieces, for complex shapes with cores.

  3. Match Plate Pattern: Pattern mounted on plate with core prints.

  4. Loose Piece Pattern: Removable pieces for undercuts.

  5. Sweep Pattern: For rotationally symmetric parts.

• Allowances:

  • Draft: Taper on vertical faces for easy removal.

  • Machining: Extra material for finish.

  • Shaking: Taper on parting plane for core removal.

  • Distortion: Opposite taper for warpage control.

  • Sketches: Show draft angle, machining allowance on pattern.

Gating System

• Elements:

  1. Sprue: Vertical channel from pouring cup to runner.

  2. Runner: Horizontal channel distributing metal.

  3. Gate: Constriction controlling flow into mold cavity.

  4. Riser: Reservoir to compensate shrinkage.

  5. Core Prints: Hold cores in position.

• Design Principles:

  • Sprue: conical to reduce turbulence.

  • Runner: balanced, smooth flow.

  • Gate: location at thick section, minimize turbulence.

Centrifugal Casting

• Technique:

  • Mold rotated at high speed (300–3000 rpm).

  • Molten metal poured, centrifugal force pushes against mold wall.

  • Types:

    • Horizontal: for long cylindrical parts (pipes, tubes).

    • Vertical: for rings, disks.

  • DiagramSEARCH: centrifugal casting machine diagram

• Advantages:

  • Dense, fine-grained structure (no porosity).

  • No riser needed, cylindrical bore accurate.

• Limitations:

  • Limited to cylindrical parts.

  • Inner diameter control difficult, non-uniform wall thickness if speed low.

Die Casting

• Technique:

  1. Molten metal injected under high pressure (700–1400 bar) into permanent steel die.

  2. Rapid solidification, die opens, ejector pins push out.

  3. Cycle time seconds.

  DiagramSEARCH: die casting machine diagram

• Advantages:

  • High production rate, excellent surface finish, dimensional accuracy.

  • Thin walls possible, smooth surfaces.

• Limitations:

  • High die cost, porosity (air entrapment), limited to low-melting alloys (Al, Zn, Mg).

  • Not for heat-treatable alloys (porosity causes blistering).

XI. Welding Processes (for Metals)

Tungsten Inert Gas (TIG) Welding

• Components:

  • Tungsten electrode (non-consumable).

  • Inert gas (Ar/He) shield.

  • Power supply (DC for steel, AC for Al).

  • Filler rod (optional).

  • Water-cooled torch.

• Process: Arc between tungsten and workpiece; gas shield prevents contamination. Filler added manually.

• Applications: Aerospace, stainless steel, thin sections, critical welds.

Heat Affected Zone (HAZ)

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

• Sketch:

  DiagramCANVAS: weld cross-section showing fusion zone, HAZ, base metal

• Characteristics:

  • Coarse-grained HAZ: near fusion line, high temp → coarse grains, brittle.

  • Fine-grained HAZ: lower temp → fine grains, tougher.

  • Partially Transformed HAZ: mixed phases.

• Effect: Reduced toughness, residual stresses, distortion.

Weldability

• Definition: Ability of a material to be welded without defects and with desired properties.

• Influencing Factors:

  1. Material Composition: Carbon content (steel), alloying elements.

  2. Thermal Conductivity: Affects heat input.

  3. Shrinkage/Expansion: Residual stresses.

  4. Joint Design: Fit-up, accessibility.

  5. Welding Process: Heat input, speed.

  6. Environment: Preheating, post-weld heat treatment.

Welding Safety Precautions

• Fumes/Gases: Ventilation, respirators.

• Radiation: UV/IR protection (face shield, gloves).

• Electric Shock: Grounding, dry conditions.

• Fire: Remove flammables, fire watch.

• Compressed Gases: Secure cylinders, check leaks.

Friction Welding

• Construction:

  • One part rotated (spindle), other fixed (tailstock).

  • Axial force applied during and after rotation.

  • DiagramSEARCH: friction welding machine diagram

• Working:

  1. Parts brought together with force, one rotated.

  2. Friction heats interface to plastic state.

  3. Rotation stopped, forge pressure applied → solid-state weld.

• Advantages: No filler, clean, high strength, automation.

• Limitations: Limited to cylindrical parts, flash removal needed.

Brazing

• Description:

  • Filler metal (melting point > 450°C but below base metal) melts and flows by capillary action.

  • Base metal not melted.

  • Flux used to prevent oxidation.

• Advantages:

  • Joints stronger than soldering, minimal base metal alteration.

  • Can join dissimilar metals, thin sections.

• Limitations:

  • Lower strength than welding, flux residues corrosive.

  • Not for high-temperature service.

XII. Press Tool and Sheet Metal Operations

Compound Dies vs. Progressive Dies

• Compound Die:

  DiagramCANVAS: compound die cross-section showing multiple cutting edges in one station

• Progressive Die:

  DiagramCANVAS: progressive die strip layout with stations

Punching Calculations

• Shear Force (F):

$$ F = \tau \cdot A = \tau \cdot (perimeter \times thickness) $$

where $\tau$ = shear strength (MPa), $A$ = shear area (mm²).

• Clearance (c):

  • Typically 5–10% of thickness for precision.

  • For punching: clearance on punch side? Actually, clearance is total between punch and die.

  • Punch diameter $$\displaystyle d_p = d - 2c $$, die diameter $$\displaystyle d_d = d + 2c $$, where $d$ = hole diameter.

• Shear Angle (θ):

  • To reduce force, shear angle provided on punch:

$$ F_{reduced} = F \cdot \frac{\theta}{90^\circ} \quad \text{(approx)} $$

• Or: $$\displaystyle F = \tau \cdot A / \sin\theta $$ for single shear.

• Press Capacity: Must exceed maximum shear force with factor of safety (2–3).

[!TIP]

Example Problem: Given hole diameter, thickness, shear strength, clearance, calculate punch/die sizes and shear force. Always check press capacity.

XIII. Material Science in Manufacturing

Yield Criteria for Ductile Materials

• Tresca (Maximum Shear Stress):

  Yield when max shear stress reaches critical value:

$$ \tau_{max} = \frac{\sigma_1 - \sigma_3}{2} = \frac{\sigma_y}{2} $$

where $$\displaystyle \sigma_1 $$, $$\displaystyle \sigma_3 $$ = max/min principal stresses, $$\displaystyle \sigma_y $$ = yield strength.

• Von Mises (Distortion Energy):

  Yield when distortion energy reaches critical value:

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

For 2D (plane stress):

$$ \sigma_{eq} = \sqrt{\sigma_x^2 + \sigma_y^2 - \sigma_x\sigma_y + 3\tau_{xy}^2} $$

Relation between Von Mises and Tresca

• Von Mises criterion is more accurate for ductile metals.

• For pure shear: Tresca predicts $$\displaystyle \tau_y = \sigma_y/2 $$; Von Mises predicts $$\displaystyle \tau_y = \sigma_y/\sqrt{3} \approx 0.577\sigma_y $$.

• Von Mises ellipse is 15% larger than Tresca hexagon in principal stress space.

• For most metals, Von Mises agrees better with experiments.

XIV. Non-Destructive Testing (NDT) Methods

[!TIP]

Exam Focus: Match method to defect type (surface vs. subsurface) and material (ferrous vs. non-ferrous).