UNIT 2: MANUFACTURING TECHNOLOGY - SHORT NOTES

I. CASTING PROCESSES

Pattern Making

Pattern: A replica of the final casting with allowances, used to form the mould cavity.

Exam Tip: Distinguish between pattern (for mould) and core (for hollows).

Types of Patterns:

Pattern Allowances (with Sketches):

Allowances are extra material added to pattern for:

1. Shrinkage/Contraction Allowance: Compensates for solidification & cooling shrinkage. Largest allowance (1-2%).

   Material-specific: Cast Iron ~1.0%, Steel ~1.5-2.0%, Al ~1.3%.

2. Machining (Finish) Allowance: Extra material for subsequent machining. Depends on casting size & method.

3. Draft (Taper) Allowance: Taper on vertical faces for easy pattern removal. 1°-3° for external, 3°-8° for internal.

4. Distortion Allowance: For long, thin sections (e.g., "camber" upward for U-bends).

5. Rapping (Shake) Allowance: Extra dimension to account for rapping pattern to loosen it (~0.5-1.0 mm).

Gating System

Purpose: To control molten metal flow into mould cavity, ensuring complete filling without turbulence or erosion. Elements:

1. Pouring Basin: Receives molten metal from ladle.

2. Sprue: Vertical channel connecting pouring basin to runner. Acts as a reservoir and regulates flow.

   Sprue Purpose: Controls flow rate, traps dross (impurities).

3. Runner: Horizontal channel distributing metal to multiple gates.

4. Gate: Constricted opening through which metal enters the cavity. Controls flow direction and rate.

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

Special Casting Techniques

Centrifugal Casting

Process: Molten metal is poured into a rotating mould (horizontal or vertical axis). Centrifugal force drives metal against mould wall. Working:

1. Mould is rotated at high speed.

2. Metal is poured while rotating.

3. Solidification starts from outer wall inward.

4. After solidification, mould stops, and casting is removed. Applications: Cylindrical parts (pipes, tubes, cylinders, bushings, wheels). Advantages: Dense, fine-grained structure, no core needed for hollows, good surface finish. Disadvantages: Limited to symmetrical shapes, requires precise speed control, inner diameter may be less accurate.

Die Casting

Process: Molten metal (non-ferrous: Al, Zn, Mg) forced under high pressure (7-700 MPa) into a steel die (mould) at high speed. Working:

1. Two die halves clamped together.

2. Molten metal injected under high pressure.

3. Rapid solidification due to cold die.

4. Die opens, ejector pins push out casting. Applications: Thin-walled, complex, high-volume parts (automotive components, housings, toys). Advantages: High production rate, excellent dimensional accuracy & surface finish, thin sections possible. Disadvantages: High die cost, limited to low-melting non-ferrous metals, porosity possible.

II. WELDING AND JOINING PROCESSES

Arc Welding: Tungsten Inert Gas (TIG) Welding

Process: Non-consumable tungsten electrode creates arc in inert gas shield (Ar/He). Filler rod may be added separately. Components:

1. Power Source: DC (most common) or AC (for Al).

2. Electrode Holder: Holds non-consumable tungsten electrode.

3. Tungsten Electrode: Pure or alloyed (Thoriated, Ceriated).

4. Inert Gas Cylinder & Regulator: Provides shielding gas.

5. Liquid-Cooled Torch: Conducts current, gas, and water (if cooled).

6. Filler Rod: Optional, added manually.

7. Workpiece & Ground Clamp. Applications: Aerospace, thin sections, reactive metals (Al, Mg, Ti), critical welds. Advantages: Clean weld, no filler metal contamination, precise control. Disadvantages: Slow, requires skill, expensive.

Heat Affected Zone (HAZ)

Definition: The region of base metal adjacent to the weld that has undergone microstructural changes due to heat, but not melted. Characteristics: Altered mechanical properties (often reduced toughness, hardness changes). Width depends on heat input, material, and welding process. Sketch: Shows Fusion Zone (melted) -> HAZ (microstructure changed) -> Base Metal (unaffected).

Safety Precautions in Welding

1. Protective Clothing: Flame-resistant apron, gloves, shoes.

2. Eye Protection: Welding helmet with appropriate shade filter (to prevent "arc eye").

3. Ventilation: Remove fumes and gases (use exhaust fans or respirators).

4. Fire Prevention: Remove flammable materials, have fire extinguisher ready.

5. Electrical Safety: Proper grounding, check cables, avoid moisture.

6. Gas Safety: Secure cylinders, check for leaks (soap test), proper storage.

Friction Welding (FW)

Construction & Working (Rotary FW):

1. One workpiece rotated, other held stationary.

2. Workpieces brought into contact under axial pressure (forge force).

3. Friction at interface generates heat.

4. When temperature reaches welding range, rotation stops.

5. Upset (forging) pressure applied briefly to consolidate weld. Applications: Similar metals (steels, Al, Ti), tubes, rods, aerospace, automotive (axles, valves). Advantages: No external heat/consumables, clean, fast, can weld dissimilar metals. Disadvantages: Limited to round/symmetric sections, requires rigid machine.

Welding of Plastics

Process: Joining thermoplastic or thermoset plastics using heat (and sometimes pressure). Methods:

• Hot Gas Welding: Hot air softens surfaces, pressed together (like soldering).

• Heated Tool Welding: Heated tool melts surfaces, tool removed, surfaces pressed.

• Ultrasonic Welding: High-frequency vibration generates heat at interface.

• Friction Welding: Relative motion generates heat.

• Laser Welding: Focused laser beam melts joint. Advantages: Can join complex shapes, good strength, no fasteners. Limitations: Limited to thermoplastics (some thermosets), joint design critical, surface preparation needed, equipment cost.

Weldability

Definition: The capacity of a material to be welded under given conditions into a specific, designed structure, and to perform satisfactorily in service. Influencing Factors:

1. Material Composition: Carbon content in steel (↑C ↓weldability), alloying elements.

2. Thermal Properties: Thermal conductivity, expansion coefficient.

3. Metallurgical Factors: Phase transformations, hardenability, susceptibility to cracking (hot/cold).

4. Service Requirements: Load type, environment (corrosion, temperature).

5. Welding Process & Conditions: Heat input, preheat/post-heat.

Brazing

Process: Joining by melting a filler metal (brazing alloy) with melting point above 450°C but below base metal's melting point. Capillary action draws filler into joint. Flux used to prevent oxidation. Steps: Clean surfaces → Apply flux → Heat assembly → Filler melts & flows → Cool → Clean flux residue. Applications: HVAC, electrical, jewelry, aerospace (high-strength joints). Advantages: Joins dissimilar metals, minimal base metal distortion, good strength. Disadvantages: Not for high-temperature service, flux residue may be corrosive.

Non-Destructive Testing (NDT)

III. METAL FORMING PROCESSES

Hot Working vs Cold Working

Classification of Forming Processes

Primary Processes:

1. Rolling: Reducing thickness/length by passing between rolls.

2. Forging: Shaping by localized compressive forces (hammer/press).

3. Extrusion: Forcing material through die opening.

4. Drawing: Reducing cross-section by pulling through die.

5. Sheet Metal Forming: Bending, deep drawing, stretch forming.

Drawing and its Classification:

Drawing: Tensile force pulls material through a die to reduce cross-section. Classification:

• Wire Drawing: Cylindrical bar to wire.

• Tube Drawing: Over mandrel or sinker (without mandrel).

• Sheet Metal Drawing (Deep Drawing): Forming cup-shaped parts from sheet.

Defects in Formed Products

Defects in Rolled Parts:

• Centerline Crack (Alligatoring): Longitudinal crack at center due to high tensile stress.

• Edge Cracking: Due to shear stresses at edges.

• Wavy Edges: From uneven compression or roll misalignment.

• Zipper Cracks: Longitudinal surface cracks from inclusions.

• Roll Marks: Surface imprints from roll imperfections.

Defects in Forgings:

• Cold Shuts: Folds due to incomplete filling or improper die design.

• Cracks: From high tensile stresses, improper temperature, or sharp corners.

• Laps/Flaps: Surface irregularities from metal folding.

• Scale Pit: Surface depression from oxidized scale not removed.

• Misrun: Incomplete filling.

• Buckling: In upsetting due to instability.

Special Forming Processes

Stretch Forming

Operation: Sheet metal strip clamped at ends and stretched over a form block while under tension. Plastic deformation occurs. Sketch: Shows sheet, form block (contour), and pulling clamps. Applications: Large, smooth-curved panels (aircraft skins, car doors, architectural panels). Advantages: Good surface finish, low springback, suitable for low-quantity. Disadvantages: High force required, limited to simple curves.

Peen Forming

Process: Surface of sheet metal is impacted by small shot particles (peening) in a controlled manner. Induced compressive residual stresses cause the sheet to bend or form into a curved shape. Sketch: Shows shot peening gun impacting one side of a flat sheet, causing it to curve. Applications: Forming aircraft wing skins, compressor blades, complex double-curvature parts. Advantages: No tooling contact, forms complex shapes, beneficial residual stress. Disadvantages: Slow, process control critical, surface roughness increases.

Superplasticity of Metals

Definition: Ability of some fine-grained metals/alloys to exhibit very high tensile elongations (200-1000%) before fracture, at elevated temperatures (0.5-0.7 Tm) and low strain rates (10⁻⁴ to 10⁻² s⁻¹). Sheet Metal Processing: Used for Superplastic Forming (SPF). Sheet is clamped over a die, heated, and gas pressure (or vacuum) slowly pushes sheet into die cavity. Applications: Complex, single-piece components (aircraft panels, automotive body panels). Advantages: Near-net-shape, no welds/joins, complex shapes. Disadvantages: Very slow, expensive dies, limited material selection (Al-Li, Ti-Al, Zn alloys).

Extrusion (Metal)

Working Principle: A billet (slug) is forced to flow through a die opening by a ram under high pressure, producing long products of constant cross-section. Applications: Rods, tubes, complex sections (window frames, structural shapes). Advantages: Good surface finish, can produce complex cross-sections, continuous process. Disadvantages: High force, poor surface on extruded tube ID, limited to simple-to-moderate complexity.

Hot Extrusion vs Cold Extrusion:

Tube Extrusion Process

Direct (Forward) Tube Extrusion:

1. Billet (with hollow or solid) placed in container.

2. Mandrel (fixed to ram) pierces solid billet or supports hollow.

3. Ram pushes metal through die, forming tube. Sketch: Shows ram, mandrel, die, container, and extruded tube. Indirect (Backward) Tube Extrusion: Die moves with ram, billet stationary. Reduces friction.

Types of Metal Flow & Importance:

1. Uniform Flow: Desirable. Material flows evenly through die.

2. Non-Uniform Flow (Dead Metal Zone): Occurs near die corners due to high friction. Causes defects, uneven grain structure.

3. Flow Defects: Fins (excess metal), Seams (laps), Centerline Burst (tensile stress center). Importance: Understanding flow helps in die design (fillet radii, angle), predicting defects, and controlling grain structure.

Pressure Distribution Derivation for Rectangular Block Forging

For a rectangular block (width w, height h, length b) under flat dies with sliding friction (μ):

Assumptions: Homogeneous, incompressible, constant shear strength K, Coulomb friction. Result: Pressure p varies exponentially from centerline (x=0) to edge (x=b/2):

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

Simplified for typical case:

$$ \boxed{\frac{p}{2K} = \frac{1}{1 - e^{-\frac{2\mu b}{h}}} \cdot e^{-\frac{2\mu x}{h}}} $$

Where x is distance from centerline. Pressure is maximum at center, drops toward edges.

Sheet Metal Operations: Compound Die vs Progressive Die

Punching Calculations

Hole Punching (Blanking):

• Punch Force (F): $$\displaystyle F = \tau_u \cdot A_s = \tau_u \cdot (\pi d t) $$

  Where $$\displaystyle \tau_u $$ = ultimate shear strength, d = hole diameter, t = thickness.

• Shear Angle (ψ): Provided on punch to reduce force and wear.

$$F_{actual} = F \cdot \frac{1}{\cos\psi}$$

Where $$\displaystyle \psi = \tan^{-1}\left(\frac{\text{clearance}}{\text{thickness}}\right) $$.

• Press Capacity: Must exceed calculated force with safety factor (1.5-2).

• Die Clearance (C): Typically 5-10% of thickness t for shearing. C = k \cdot t, k=0.05 to 0.1.

  Punch diameter = Hole diameter - 2C

  Die diameter = Hole diameter + 2C

Example (from Jun 2023):

Hole d=100mm, t=5.6mm, $$\displaystyle \tau_u $$=550 MPa, clearance=10%, cutting at 40% penetration.

• Punch Force (F): $$\displaystyle F = 550 \times 10^6 \times \pi \times 0.1 \times 5.6 \times 10^{-3} = 966,000 $$ N ≈ 966 kN.

• Die & Punch Size: Clearance C = 0.1 × 5.6 = 0.56 mm.

  • Punch Ø = 100 - 2×0.56 = 98.88 mm.

  • Die Ø = 100 + 2×0.56 = 101.12 mm.

• Shear Angle (ψ): $$\displaystyle \tan\psi = \frac{C}{t} = \frac{0.56}{5.6} = 0.1 $$ → $$\displaystyle \psi = \tan^{-1}(0.1) = 5.71° $$.

• Force at 40% Penetration: Force ∝ depth. At 40% penetration, force ≈ 0.4 × F = 386.4 kN. With shear angle: $$\displaystyle F_{shear} = \frac{386.4}{\cos 5.71°} = 388.8 $$ kN ≈ 39 tonnes (since 1 tonne ≈ 9.81 kN). Shop press (30 tonnes) is insufficient.

Forging Processes: Pressure Derivation

For upsetting a cylindrical billet (height h₀, diameter d₀) between flat dies with friction:

Assumptions: Homogeneous, constant flow stress $$\displaystyle \sigma_f $$, Coulomb friction $\mu$, no barreling. Result: Average forging pressure $$\displaystyle P_{avg} $$:

$$ \boxed{P_{avg} = \sigma_f \left( 1 + \frac{\mu d_0}{3h_0} \right)} $$

Where $$\displaystyle \sigma_f $$ is average flow stress. Pressure increases as height decreases ($$\displaystyle h_0 $$ ↓ → P ↑).

IV. CONVENTIONAL MACHINING PROCESSES

Single Point Cutting Tool: Nomenclature & Tool Signature

Nomenclature:

• Rake Face: Surface from which chip flows.

• Rake Angle (α): Angle of rake face w.r.t. cutting edge. (+ve for easier cutting).

• Clearance (Relief) Face: Surface behind cutting edge.

• Clearance Angle (γ): Angle of clearance face w.r.t. workpiece. Prevents rubbing.

• Cutting Edge: Intersection of rake & clearance faces.

• Nose Radius (r): Radius on cutting tip for finish.

• Side Cutting Edge Angle (ψ): Angle between side cutting edge & tool axis.

• End Cutting Edge Angle (φ): Angle between end cutting edge & tool axis.

• Shank: Tool body.

Tool Signature (ISO System):

α_o - α_r - ε_r - ε_s - C

Example: 8-8-5-5-1 means:

• Back rake α_o = 8°

• Side rake α_r = 8°

• End clearance ε_r = 5°

• Side clearance ε_s = 5°

• Side cutting edge angle = 1°

Mechanics of Machining

Orthogonal Cutting

• Cutting edge is perpendicular to direction of cut.

• Tool face is vertical (no side cutting edge angle).

• Chip flows straight ahead.

• Simplified force system: 2D (Tangential F_t, Thrust F_th).

Oblique Cutting

• Cutting edge is inclined to direction of cut (ψ > 0).

• Chip flows at an angle (chip flow angle φ).

• Force system: 3D (Tangential F_t, Feed F_f, Radial F_r).

• More realistic for turning, milling.

Cutting Forces, Specific Cutting Energy, and Force Calculations

• Forces: $$\displaystyle F_t $$ (tangential, major), $$\displaystyle F_f $$ (feed), $$\displaystyle F_r $$ (radial).

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

$$U = \frac{P}{MRR} = \frac{F_t \cdot V_c}{A_c \cdot V_c} = \frac{F_t}{A_c}$$

Where $$\displaystyle A_c = d \cdot f $$ (depth × feed). Units: J/mm³ or N/mm².

> **Example (Jun 2025):** Given $$\displaystyle U = 1 \times 10^3 $$ J/m³ = $$\displaystyle 1 \times 10^{-3} $$ N/mm², d=4mm, f=0.25mm/rev, Vc=120 m/min.

*   $$\displaystyle A_c = 4 \times 0.25 = 1 $$ mm².

*   $$\displaystyle F_t = U \cdot A_c = (1 \times 10^{-3}) \times 1 = 0.001 $$ N? **Wait, unit error!**

*   **Correction:** $$\displaystyle U = 1 \times 10^3 $$ J/m³ = $$\displaystyle 1 \times 10^3 $$ N·m / m³ = $$\displaystyle 1 \times 10^{-3} $$ N/mm².

*   $$\displaystyle F_t = U \times A_c = 0.001 \times 1 = 0.001 $$ N? That's too small. Check: 1 J/m³ = 1 N·m/m³ = 1 N/m² = 10⁻³ N/mm². So 1000 J/m³ = 1 N/mm².

*   **Correct:** $$\displaystyle U = 1000 $$ J/m³ = **1 N/mm²**.

*   $$\displaystyle F_t = 1 \times 1 = 1 $$ N? Still small. **Re-exam:** $$\displaystyle A_c $$ in mm², U in N/mm² gives F_t in N. But typical U for steel is ~2-4 N/mm². Given U=1000 J/m³ = 0.001 N/mm² is too low. Likely typo in question? Assume U = $$\displaystyle 1 \times 10^3 $$ **N/mm³**? No.

*   **Standard Approach:** $$\displaystyle F_t = U \times A_c $$. If U=1e3 J/m³ = 1e-3 N/mm², A_c=1 mm² → F_t=0.001 N. Impossible. **Most likely U = 1e3 N/mm²?** But that's huge.

*   **Interpretation from past:** They likely meant $$\displaystyle 1 \times 10^3 $$ **N/mm²**? Or $$\displaystyle 1 \times 10^9 $$ J/m³? Let's use given: $$\displaystyle U = 1 \times 10^3 $$ J/m³. Convert: 1 J/m³ = 10⁻⁶ N/mm²? Wait:

    1 J = 1 N·m, so 1 J/m³ = 1 N·m / m³ = 1 N / m² = 10⁻³ N/mm².

    So $$\displaystyle 10^3 $$ J/m³ = 1 N/mm².

    $$\displaystyle A_c = 4 \times 0.25 = 1 $$ mm².

    $$\displaystyle F_t = 1 \times 1 = 1 $$ N. **This is unrealistic.** Possibly feed is 0.25 mm/rev, depth 4 mm, but MRR = Vc * f * d = (120 m/min = 2000 mm/s) * 0.25 * 4 = 2000 mm³/s. Power P = U * MRR = 1000 * 2000 = 2e6 J/s = 2 MW! Impossible.

*   **Conclusion:** There is likely a unit error in the question as presented. In typical problems, U is in N/mm². If U=1000 N/mm², F_t=1000 N. But 1000 N/mm² is too high (steel ~2-4 N/mm²). Perhaps U=1.0? Let's assume they meant $$\displaystyle 1 \times 10^3 $$ **N/mm²** is a mistake and use $$\displaystyle U = 1 \times 10^3 $$ **J/cm³**? 1 J/cm³ = 10^6 J/m³ = 1000 N/mm²? Messy.

*   **For exam:** Use formula $$\displaystyle F_t = U \cdot d \cdot f $$. Ensure units consistent. If U in N/mm², d,f in mm → F_t in N. In the given problem, if we take U=1000 N/mm², F_t=1000*4*0.25=1000 N. That's plausible for small cut? But 1000 N is small for 100mm dia turning. Likely U is around 2 N/mm² → F_t=2*4*0.25=2 N? Still small.

*   **Actual calculation from past papers:** They often give U in J/mm³ or N/mm². Let's re-read: "specific cutting energy of the work material is $$\displaystyle 1\\times10^{3}\\ \\mathrm{\\frac{J}{m^{3}}} $$." That is 1000 J/m³ = 0.001 N/mm². That is impossibly low. **It must be a typo.** In similar problems, U is ~2000 J/mm³? No, 2000 J/mm³ = 2e12 J/m³.

*   **Best guess:** They meant $$\displaystyle 1 \times 10^3 $$ **N/mm²**? Or $$\displaystyle 1 \times 10^3 $$ **J/mm³**? 1 J/mm³ = 1e9 J/m³.

*   **For your notes:** Write formula: $$\displaystyle F_t = U \cdot (d \cdot f) $$. Emphasize unit consistency. In exam, if given U in J/m³, convert: 1 J/m³ = 10⁻⁶ N/mm²? Actually: 1 J/m³ = 1 N·m / m³ = 1 N / m² = 10⁻³ N/mm². So 1000 J/m³ = 1 N/mm². Then F_t = 1 * 4 * 0.25 = 1 N. That seems wrong. Possibly they meant $$\displaystyle 1 \times 10^3 $$ **N/mm²**? But that's 1000 times too high.

*   **Alternative:** Maybe they meant $$\displaystyle 1 \times 10^3 $$ **J/cm³**? 1 J/cm³ = 10^6 J/m³ = 1000 N/mm²? 1 J/cm³ = 1 N·m / (0.01 m)^3 = 1e6 N/m² = 1 N/mm²? Confusing.

*   **Decision:** In your notes, state: $$\displaystyle F_t = U \cdot A_c $$, with U in N/mm², A_c in mm². For the example, if U=1 N/mm², F_t=1 N. But note that typical U for steel is 2-4 N/mm². **Perhaps the given U is 1e3 J/mm³?** 1 J/mm³ = 1e9 J/m³ = 1e6 N/mm²? No.

*   **Let's calculate from power:** Cutting power P = F_t * Vc. Vc=120 m/min=2 m/s. If F_t=1000 N, P=2000 W=2 kW. That's plausible. So F_t should be around 1000 N. Then U = F_t / A_c = 1000 / (4*0.25) = 1000 N/mm²? That's 1000 MPa, which is flow stress? Flow stress for steel ~500-1000 MPa. So U ≈ flow stress. So likely U = 1000 N/mm² = 1000 MPa. But they wrote J/m³. 1000 MPa = 1000 N/mm² = 10^9 N/m² = 10^9 J/m³? Because 1 N/m² = 1 J/m³? Yes: 1 Pa = 1 N/m² = 1 J/m³. So 1000 MPa = 10^9 J/m³. So they likely meant $$\displaystyle 1 \times 10^9 $$ J/m³, but wrote $$\displaystyle 10^3 $$. **So in your notes, clarify: Specific cutting energy U has units of pressure (N/mm² or Pa). 1 Pa = 1 J/m³.**

*   **Final for example:** Assume U = 1000 MPa = 1000 N/mm²? But then F_t = 1000 * 1 = 1000 N. That's small for 100mm dia? MRR = π*100*0.25*4 = 314 mm³/rev. At 120 m/min = 2000 mm/s, spindle speed N = Vc/(πD) = 2000/(π*100) ≈ 6.37 rev/s. MRR = 314 * 6.37 ≈ 2000 mm³/s. Power = U*MRR = 1000 N/mm² * 2000 mm³/s = 2e6 N·mm/s = 2000 W = 2 kW. That's reasonable. So U=1000 N/mm² is plausible. But they wrote $$\displaystyle 10^3 $$ J/m³. So **in your notes, write: U = 1e9 J/m³ = 1000 MPa.** And for the problem, F_t = U * d * f = 1000 * 4 * 0.25 = 1000 N. **But wait: d=100mm diameter? In orthogonal cutting, depth of cut is radial depth. For turning 100mm dia, depth of cut is 4mm, so A_c = d * f = 4 * 0.25 = 1 mm². So F_t = 1000 N.**

*   **Conclusion:** The given U is likely $$\displaystyle 1 \times 10^9 $$ J/m³ (1000 MPa). But they wrote $$\displaystyle 10^3 $$. **In your answer box, write:** $$\displaystyle F_t = U \cdot d \cdot f = (1 \times 10^9 \ \mathrm{J/m^3}) \times (4 \times 10^{-3} \ \mathrm{m}) \times (0.25 \times 10^{-3} \ \mathrm{m}) = 1000 \ \mathrm{N} $$. Or in mm: U=1000 N/mm², d=4mm, f=0.25mm → F_t=1000 N.

To avoid confusion, in notes:

Specific Cutting Energy (U): Energy per unit volume removed. $$\displaystyle U = \frac{P}{MRR} = \frac{F_t}{d \cdot f} $$. Units: J/m³ or N/mm² (1 N/mm² = 10^9 J/m³). For steel, U ≈ 2-4 N/mm².

Tool Life and Taylor's Equation

Taylor's Tool Life Equation: $$\displaystyle V T^n = C $$

• V = cutting speed (m/min)

• T = tool life (min)

• n = exponent (0.1-0.5, tool material dependent)

• C = constant (depends on tool-workpiece material, environment)

Comparing Tools (e.g., Carbide vs HSS):

Given: $$\displaystyle V_1 T_1^{n_1} = C_1 $$, $$\displaystyle V_2 T_2^{n_2} = C_2 $$.

For same tool life ($$\displaystyle T_1=T_2=T $$): $$\displaystyle \frac{V_1}{V_2} = \left( \frac{C_1}{C_2} \right)^{1/n_1} $$? Not directly.

Better: For given V, find T for each. Or find V where $$\displaystyle T_{carbide} > T_{HSS} $$. Example (Dec 2024, Jun 2022):

Carbide: $$\displaystyle V T^{1.6} = 3000 $$ → $$\displaystyle T_c = (3000/V)^{1/1.6} $$

HSS: $$\displaystyle V T^{0.6} = 200 $$ → $$\displaystyle T_h = (200/V)^{1/0.6} $$

Set $$\displaystyle T_c > T_h $$: $$\displaystyle (3000/V)^{0.625} > (200/V)^{1.6667} $$ $$\displaystyle 3000^{0.625} \cdot V^{-0.625} > 200^{1.6667} \cdot V^{-1.6667} $$ $$\displaystyle 3000^{0.625} > 200^{1.6667} \cdot V^{-1.0} $$ $$\displaystyle V > \frac{200^{1.6667}}{3000^{0.625}} $$

Calculate: 200^{5/3} = (200^5)^{1/3} = (3.2e11)^{1/3} ≈ 684. (200^{1.6667} ≈ 200^{5/3} = (200^5)^{1/3} = 3200000000000^{1/3}? Better: 200^{1.6667} = 200^{5/3} = (200^{1/3})^5. 200^{1/3}≈5.848, ^5≈5.848^5≈7000? Let's compute numerically: 200^{1.6667} = exp(1.6667 * ln200) = exp(1.66675.2983) = exp(8.8305) ≈ 6700. 3000^{0.625} = 3000^{5/8} = (3000^{1/8})^5. 3000^{0.625} = exp(0.625ln3000)=exp(0.625*8.006)=exp(5.00375)≈149.

So V > 6700 / 149 ≈ 45 m/min. Thus, for V > 45 m/min, carbide gives higher tool life.

Determining Cutting Speed for Higher Tool Life:

From Taylor's: $$\displaystyle V \propto T^{-1/n} $$. To double tool life, new speed $$\displaystyle V_2 = V_1 \cdot (T_2/T_1)^{-1/n} = V_1 \cdot (2)^{-1/n} $$.

Tool Failure Modes

1. Abrasive Wear: Gradual wear on flank & rake face due to hard particles in workpiece. Sketch: Shows flank wear land.

2. Adhesive Wear: Welding and tearing of tool material at high contact pressure. Sketch: Shows built-up edge on tool.

3. Diffusive Wear (Crater Wear): High temperature causes diffusion of tool elements into chip. Occurs on rake face. Sketch: Shows crater near cutting edge on rake face.

4. Mechanical Failure (Breakage/Chipping): Due to excessive force, vibration, or thermal shock. Sketch: Shows chipped edge or broken tool.

Cutting Fluids

Types:

1. Coolants (Liquid): Mineral oils (straight, soluble), water-based emulsions.

2. Aerosols (MQL): Minimal quantity lubrication.

3. Gases: Air, CO₂, nitrogen (for specific materials).

4. Solid Lubricants: Graphite, MoS₂ (for difficult-to-cut materials).

Mechanisms for Effectiveness:

1. Cooling: Reduces temperature in cutting zone → reduces tool wear, thermal damage to workpiece.

2. Lubrication: Reduces friction at tool-chip interface → lowers cutting forces, improves surface finish, reduces built-up edge.

3. Chip Control: Flushes chips away, prevents re-cutting.

4. Corrosion Protection: Prevents rust on machine/workpiece.

Uses & Applications:

• High-speed steel tools: Need good lubrication (oils).

• Carbide tools: Need good cooling (water-based).

• Aluminum: Use soluble oils to prevent welding.

• Grinding: Need abundant cooling (water-based emulsions).

Broaching

Cutting Action:

• Broach: Multi-tooth tool, each tooth progressively taller.

• Stroke: Broach pushed/pulled through/over workpiece.

• Each tooth removes small chip.

• Rise per tooth: Height difference between successive teeth.

• Finish teeth: Same height for final sizing.

Continuous Surface Broaching Machine:

• Construction: Horizontal or vertical machine. Workpiece clamped on table. Broach mounted on ram (pull type) or broach stationary, workpiece moved (push type).

• Useful Component Surfaces: Internal surfaces (keyways, splines, gears), external surfaces (flat, contoured), surfaces requiring high precision and finish in one stroke.

• Applications: Internal splines, turbine blade fir-tree roots, automotive transmission parts.

Sawing Processes

Band Saw

• Sketch: Continuous toothed band running on two wheels (idler & drive). Workpiece fed into moving band.

• Description: Can cut curves, straight lines, various materials. Vertical or horizontal. Used for rough/finish cutting, contouring.

Circular Saw

• Sketch: Rotating circular disc with teeth on periphery. Workpiece fed into rotating disc.

• Description: High speed, straight cuts only. Used for bar stock, sheet, plate cutting.

Power Hacksaw

• Short Note: Reciprocating motion. Blade tensioned, guided. Slow speed, high torque. Used for cutting large bars, pipes, structural sections. Often automatic feed.

V. GRINDING PROCESSES

Surface Grinding

Constructional Features:

• Base: Supports column & table.

• Column: Supports wheel head & table.

• Table: Reciprocates (hydraulic), has magnetic chuck for workpiece.

• Wheel Head: Mounts grinding wheel, can traverse (cross-feed) and swivel (for taper).

• Wheel: Abrasive wheel (Al₂O₃, SiC, CBN).

• Reciprocating Mechanism: For cross-feed. Working: Wheel rotates at high speed. Workpiece on magnetic table moves back-and-forth under wheel (reciprocates). Incremental down-feed (vertical) after each pass. Applications: Flat surfaces, parallel surfaces, squaring, surface preparation. Advantages: High accuracy (0.001-0.005 mm), good finish, hard materials. Limitations: Heat generation (burn), wheel wear, not for very large parts.

Centerless Grinding

Working Principle:

• Through-feed: Workpiece supported on work rest blade, between regulating wheel (rotates slowly, controls speed) and grinding wheel (rotates fast, cuts). No centers. Workpiece fed axially.

• In-feed: Workpiece stopped, wheel head fed radially for grinding diameter.

• End-feed: For tapered parts. Sketch: Shows grinding wheel, regulating wheel, work rest blade, workpiece. Applications: Mass production of cylindrical parts (pins, rollers, bearings, shafts). Advantages: No workpiece clamping, high productivity, can grind delicate parts. Limitations: Setup complex, limited to cylindrical surfaces, not for parts with projections.

Grinding Wheel Specifications

Parameters (Wheel Marking: e.g., 32-A-36-M-V):

1. Abrasive Type: A=Al₂O₃, C=SiC, D=Diamond, CBN.

2. Grain Size: Number (8-240). Coarse (8-24) for fast removal, fine (80-240) for finish.

3. Grade (Hardness): A (soft) to Z (hard). Softer grade for hard workpiece (to expose new grains), harder for soft workpiece.

4. Structure: Open (high porosity) for coolant/wheel loading, dense for precision.

5. Bond Type: V=Vitrified, B=Resinoid, S=Silicate, M=Metallic.

6. Manufacturer's Symbol.

7. Wheel Dimensions: Diameter, width, bore.

Significance: Selection determines material removal rate, surface finish, wheel life, and power required.

Wheel Maintenance: Dressing vs Truing

VI. GEAR MANUFACTURING

Gear Elements and Nomenclature

• Pitch Circle: Imaginary circle where gear tooth thickness equals space width.

• Addendum: Radial height from pitch circle to tooth tip.

• Dedendum: Radial depth from pitch circle to tooth root.

• Circular Pitch (p): Distance along pitch circle from one tooth to next.

• Diametral Pitch (P_d): Number of teeth per inch of pitch diameter. $$\displaystyle P_d = \frac{N}{D} $$.

• Module (m): Pitch diameter per tooth (mm). $$\displaystyle m = \frac{D}{N} $$.

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

• Base Circle: Circle from which involute profile is generated.

• Root Circle: Circle at tooth root.

• Tooth Thickness & Space Width.

Gear Production vs Gear Generation

Gear Machining Processes

Gear Hobbing

Working: Hob (helical toothed cutter) and gear blank rotate in synchronism (speed ratio = number of hob threads : gear teeth). Hob feeds axially, generating teeth by continuous indexing. Sketch: Shows hob, gear blank, relative rotation and axial feed. Advantages: High production rate, good accuracy, versatile (can cut worms, splines). Limitations: Not for internal gears, requires separate setup for each module, lower accuracy than grinding.

Gear Shaping

Principle: Shaper cutter (pinion-shaped) reciprocates (cutting stroke) and rotates (indexing). Workpiece rotates in sync. Generating action. Advantages: Can cut internal gears, idler gears, racks. Good for small batches, repair. Limitations: Slower than hobbing, lower accuracy, requires precise kinematic chain.

Gear Shaving

Principle: Finishing process. Shaving cutter (rack-like or helical) meshes with gear under light pressure. Small chips removed by scraping action. Relative sliding motion. Applications: Improve accuracy, surface finish, and reduce noise after heat treatment. Advantages: High precision (up to AGMA Q12), good surface finish. Disadvantages: Requires hardened gear, expensive cutter, not for large corrections.

Gear Finishing Methods (Explain Any Four)

1. Gear Shaving: As above.

2. Gear Honing: Similar to shaving but with abrasive stones. For hard gears. Improves surface, corrects minor errors.

3. Gear Lapping: Abrasive paste between two gears rotated under light pressure. Very high precision (AGMA Q14), used for instrument gears.

4. Grinding (Form & Generating):

   • Form Grinding: Wheel dressed to exact gear shape.

   • Generating Grinding: Worm wheel (abrasive) generates profile like hobbing. High precision for hardened gears.

5. Burnishing: Plastic deformation by rolling to improve surface finish and fatigue strength.

6. Shot Peening: Induces compressive residual stress.

Special Cutters: DP Cutter for Involute Gear Cutting

DP Cutter (Double-Path Cutter):

• Characteristics:

  1. Two cutting edges (paths) diametrically opposite.

  2. Cutter rotates, workpiece translates (like rack cutter).

  3. Each tooth space cut by two passes (one from each edge), balancing radial forces.

  4. Produces high-precision involute gears with good surface finish.

  5. Used for medium production of medium-sized gears.

• Advantage: Force balance → less machine deflection → better accuracy than single-path rack cutter.

VII. SUPER FINISHING PROCESSES

Overview & Purpose: Ultra-fine finishing operations to achieve extremely low surface roughness (<0.1 µm Ra), high precision, and improve fatigue life. Remove minimal material (microns).

Honing

Process: Abrasive stones (honing sticks) mounted on a mandrel rotate and oscillate in the hole (or on surface) under light pressure. Loose abrasive slurry used. Sketch: Shows honing tool with stones, workpiece (cylinder), rotation and oscillation. Applications: Finishing cylinder bores (engines, hydraulic), bearing races, internal cylindrical surfaces. Advantages: Improves geometry (roundness, straightness), cross-hatch pattern for oil retention. Limitations: Slow, limited to internal/external cylindrical surfaces.

Lapping

Process: Workpiece and lapping plate (or two workpieces) rubbed together with abrasive slurry (loose grains). Can be manual or machine. Sketch: Shows lapping plate, workpiece, abrasive slurry. Applications: Extremely high precision flat surfaces (valve seats, gauge blocks), spherical surfaces (ball bearings), sealing surfaces. Advantages: Very high accuracy (microns), excellent surface finish, can correct minor geometry errors. Disadvantages: Very slow, size may increase (if lapping plate wears), requires skilled operator.

Electro Polishing

Process: Electrochemical finishing. Workpiece is anode in electrolyte bath. Current passed, metal dissolves preferentially from micro-peaks → smooth surface. Principle: Anodic dissolution. Micropeaks dissolve faster due to higher current density. Applications: Stainless steel, Al, Cu parts for medical, food, aerospace (deburring, brightening, corrosion resistance). Advantages: No mechanical stress, can finish complex shapes, burr removal, improves corrosion resistance. Disadvantages: Requires conductive material, dimensional control difficult, waste disposal.

Buffing

Process: Polishing with rotating buff wheel (soft cloth/leather) and abrasive compound (fine grit, loose). Low pressure, high speed. Sketch: Shows buff wheel, compound, workpiece. Applications: Final decorative finish, mirror finish, removing minor scratches. Advantages: Very high luster, smooth surface. Disadvantages: Only surface finish, no dimensional correction, labor-intensive.

VIII. UNCONVENTIONAL MACHINING PROCESSES

Introduction: Need for Unconventional Processes

Reasons over Conventional:

1. Machining Hard/Brittle Materials: Ceramics, carbides, glass, diamonds.

2. Complex Shapes: Intricate cavities, micro-features.

3. No Tool-Workpiece Contact: Avoids mechanical stress, distortion.

4. High Precision & Finish: Micromachining, no burrs.

5. Material Removal by Energy: Thermal, chemical, electrochemical, abrasive.

6. Low Tool Wear: Tool not in mechanical contact (EDM, ECM, LBM).

7. Automation & Flexibility: CNC compatible.

Electrical Discharge Machining (EDM)

Working Principle: Material removal by controlled spark erosion between electrode (tool) and workpiece immersed in dielectric fluid. Voltage creates spark gap, spark vaporizes/ melts material, dielectric flushes debris. Sketch: Shows electrode, workpiece, dielectric tank, pump, spark gap. Advantages: No mechanical force, any hard conductive material, complex shapes, good finish. Disadvantages: Only conductive materials, slow MRR, electrode wear, thermal damage (recast layer).

Electrochemical Machining (ECM)

Logical Diagram: DC power supply → Anode (workpiece), Cathode (tool), Electrolyte (NaCl, NaNO₃) flowing at high pressure. Procedure:

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

2. Workpiece (anode) and tool maintained at small gap (0.1-0.5 mm).

3. Electrolyte pumped at high pressure (10-30 m/s).

4. DC voltage applied (5-25 V, 5000-50000 A).

5. Anodic dissolution occurs → material removed as ions → flushed away. Working Principle: Faraday's law: $$\displaystyle m = \frac{I \cdot t \cdot M}{n \cdot F} $$. Material removal rate controlled by current density. Advantages: No tool wear, no thermal stress, high MRR for hard metals, burr-free. Disadvantages: Only conductive materials, electrolyte handling, poor accuracy (gap control), hydrogen gas evolution.

Abrasive Water Jet Machining (AWJM)

Principle: High-velocity jet of water (200-900 m/s) mixed with abrasive particles (Al₂O₃, SiC) erodes material. Sketch: Shows high-pressure pump, abrasive feeder, mixing tube, focusing nozzle, workpiece. Factors for Abrasive Selection:

1. Hardness: Must be harder than workpiece.

2. Shape: Angular grains for sharp cutting edges.

3. Size: Smaller for finer finish, larger for faster cut.

4. Toughness: Must withstand impact without breaking.

5. Purity: Avoid contamination.

6. Flow Rate: Affects cutting speed and kerf width.

Ultrasonic Machining (USM)

Working: Tool (sonotrode) vibrates at ultrasonic frequency (20 kHz) against workpiece in abrasive slurry. Abrasive grains impact and erode workpiece. Important Elements:

1. Power Supply & Generator: Converts AC to high-frequency AC.

2. Transducer: Converts electrical to mechanical vibration (magnetostrictive or piezoelectric).

3. Amplifier (Booster): Increases amplitude.

4. Sonotrode (Tool): Transmits vibration to abrasive grains.

5. Abrasive Slurry: Water + abrasive (SiC, B₄C, diamond).

6. Workpiece & Fixture. Applications: Brittle, hard materials (glass, ceramics, semiconductors, carbides). Advantages: No thermal damage, complex shapes, no tool wear (tool is soft metal). Disadvantages: Slow, limited to small depths, slurry handling.

Electron Beam Machining (EBM)

Characteristics:

• High-velocity electron beam focused in vacuum (10⁻⁴ Pa).

• Material removal by melting/vaporization from kinetic energy of electrons.

• No tool wear, no contact.

• High precision (microns), high aspect ratio holes.

• Only conductive materials (for vacuum).

• Requires vacuum chamber. Advantages: Extremely small features, high speed, no tool wear. Disadvantages: Expensive, vacuum required, only conductive, X-ray hazard, recast layer.

Plasma Arc Machining (PAM)

Construction:

• Plasma Torch: Tungsten electrode, orifice, cooling, gas supply (Ar, N₂, H₂, air).

• Power Supply: DC high current.

• Gas Supply & Control.

• Workpiece & Ground. Working: Gas ionized by arc → plasma jet (10,000-50,000°C) melts/vaporizes material, high-velocity jet blows away molten metal. Applications: Cutting thick plates (steel, Al, Cu), gouging, welding (plasma arc welding). Advantages: High speed, cuts thick materials, clean cut. Disadvantages: High noise, UV radiation, fumes, thermal distortion.

Laser Beam Machining (LBM)

Short Note:

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

• Applications: Cutting, drilling, welding, marking. Metals, plastics, ceramics.

• Advantages: Non-contact, high speed, precision, can cut complex shapes.

• Disadvantages: High cost, low efficiency, reflective materials problematic, thermal damage zone.

Process Comparisons

EDM vs EBM

Plasma Arc Cutting vs Wire Cut EDM

IX. NUMERICAL CONTROL (NC) AND COMPUTER NUMERICAL CONTROL (CNC)

NC Machine Construction: Features & Functions

1. Part Program: Set of instructions (G/M codes) for machine.

2. Machine Control Unit (MCU): "Brain" - reads program, decodes, generates pulses.

3. Drive System: Servo-motors, ball screws, amplifiers - convert pulses to motion.

4. Feedback System: Transducers (encoders, resolvers) measure position/speed → closed-loop control.

5. Machine Tool: Lathe, mill, etc. - performs machining.

6. Input/Output Devices: Tape reader, keyboard, display, communication ports.

NC vs CNC

Coordinate Systems in NC Machines

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

• Polar: Radius, angle.

• Spherical: Radius, two angles.

• Machine-Specific:

  • Lathe: Z (axial), X (radial).

  • Milling: X, Y (table), Z (spindle).

  • Cylindrical: X, Z, C (rotary around Z).

  • 5-axis: Adds rotational axes (A, B, C).

NC Part Programming

Working of NC Machine Tool with Diagram:

1. Part program (instructions) input to MCU.

2. MCU interprets (decodes) each block.

3. Generates command pulses for axes.

4. Drive system (servo) moves axes.

5. Feedback system verifies position → closed loop.

6. Machine tool executes cut.

7. Repeat for next block.

Manual vs Computer-Assisted Programming:

• Manual: Write G-code by hand (calculator, reference books). For simple parts. Error-prone.

• Computer-Assisted (CAD/CAM): Use software (Mastercam, NX, Fusion 360). Geometry from CAD, tool paths generated, post-processor outputs G-code. For complex parts.

Advantages of NC Machines:

• High accuracy & repeatability.

• Complex geometries possible.

• Reduced setup time, non-productive time.

• Less skilled operator needed.

• Easy modification, part program storage.

• Consistent quality.

Limitations:

• High initial cost.

• Maintenance requires skilled staff.

• Program preparation time for complex parts.

• Vulnerability to software/hardware failure.

Part Program for Machining Center (Milling):

Given geometry (e.g., rectangle with pocket, holes). Use:

• G90 (absolute), G54 (work coordinate).

• G00 (rapid traverse), G01 (linear interpolation).

• G02/G03 (circular interpolation).

• M06 (tool change), M03/M05 (spindle on/off).

• G81 (drilling cycle), G82 (counterboring), G83 (peck drilling).

Example (simplified):

O1000 (PROGRAM)

G90 G54 (Absolute, Work Coords)

G00 X0 Y0 Z50 (Rapid to safe)

S800 M03 (Spindle 800 rpm CW)

G00 X10 Y10 Z5 (Rapid above hole1)

G01 Z-5 F100 (Drill to depth)

G00 Z50 (Retract)

... (other holes)

G00 X0 Y0

M30 (End)

Programming Statements (Five Motion Control)

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

2. G01 - Linear Interpolation: Straight line cutting at feed rate. Modal.

3. G02/G03 - Circular Interpolation: CW/CCW arc. Requires I, J (center from start) or R (radius).

4. G04 - Dwell: Pause for specified time (P) or revolutions (X). Non-modal.

5. G28 - Return to Machine Zero: Via intermediate point (X, Y, Z). For tool change position.

Control Codes: G & M Codes

• G-Codes (Preparatory): Define motion, mode, coordinate system.

  • G00, G01, G02, G03, G04, G20/G21 (inch/mm), G40/G41/G42 (cutter comp), G90/G91 (abs/inc), G94/G95 (feed/rev).

• M-Codes (Miscellaneous): Control machine functions.

  • M00 (stop), M01 (optional stop), M02/M30 (program end), M03/M04/M05 (spindle CW/CCW/stop), M06 (tool change), M08/M09 (coolant on/off).

Control Systems in NC

1. Point-to-Point: Control only end points (e.g., drilling, EDM). Path not controlled.

2. Straight Line: Control along straight lines between points. Only one axis moves at a time or coordinated for 45°.

3. Contouring (Continuous Path): Simultaneous control of two or more axes. Follows any path (arcs, curves). Used in milling, turning.

Adaptive Control of NC Machines

Concept: Real-time adjustment of cutting parameters (speed, feed) based on sensor feedback (force, temperature, vibration) to optimize performance. Objectives:

• Maximize MRR while preventing tool breakage.

• Maintain constant cutting force.

• Compensate for tool wear.

• Improve surface finish. Types: Adaptive control with constraint (AC-AC), adaptive control optimization (ACO). Example: If force sensor detects increase (tool wear), system automatically reduces feed to maintain force within limit.

X. PLASTICS MANUFACTURING PROCESSES

Plastics Basics

Types:

1. Thermoplastics: Soften on heating, harden on cooling. Reversible. (PE, PP, PS, PVC, Nylon).

2. Thermosets: Undergo irreversible chemical change (curing) during first heating. Once set, cannot remelt. (Phenolic, Epoxy, Polyester, Melamine).

Purpose of Additives:

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

2. Fillers: Reduce cost, improve strength/stiffness, reduce shrinkage (e.g., CaCO₃, wood flour).

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

4. Colorants: Pigments/dyes for color.

5. Reinforcements: Fibers (glass, carbon) for strength.

6. Lubricants: Ease mould release.

7. Flame Retardants: Reduce flammability.

Molding Processes

Injection Molding

Process: Plastic pellets melted in barrel, injected under high pressure into closed mould, cooled, ejected. Types of Molds:

• Two-Plate (Cold Runner): Simple, single parting line.

• Three-Plate (Hot Runner): Separate runner plate, hot manifold keeps runners molten → no runner scrap.

• Hot Runner: Manifold with heated channels → direct melt to cavities. Benefits: High production rate, excellent surface finish, complex shapes, automatic. Applications: Automotive parts, containers, toys, housings.

Blow Molding

Process for Bottles:

1. Extrusion Blow Molding: Parison (tube) extruded, captured in mould, air blown to expand.

2. Injection Blow Molding: Preform (injection moulded) placed in mould, blown.

3. Stretch Blow Molding: Preform stretched axially and radially (for PET bottles). Advantages: Low cost for hollow parts, fast, good strength-to-weight. Defects: Flash, sink marks, warpage, uneven wall thickness, stress cracking.

Transfer Molding vs Extrusion Molding

Compression Molding

Process: Pre-measured charge (powder/granule) placed in heated open mould. Mould closed, heat & pressure applied, cure, open, eject. Sketch: Shows open mould, charge, closed mould with force. Applications: Thermosets (phenolic, epoxy), composites (SMC), large flat parts (trays, panels). Advantages: Low pressure, good for large parts, low cost tooling. Disadvantages: Slow cycle, flash, manual charging, poor finish.

Calendaring Process

Process: Plastic compound passed through series of heated rotating rolls (calender) to form sheet/film. Sketch: Shows 3-7 rolls in L or inverted L arrangement, nip points, sheet emerging. Applications: PVC sheets, films, coated fabrics, leathercloth. Advantages: Good surface finish, uniform thickness. Disadvantages: Limited to sheet/film, edge effects, roll wear.

Film Blowing

Process: Extruded tube (bubble) of thermoplastic, inflated with air, cooled, collapsed, wound. Sketch: Shows extruder, annular die, air ring, bubble, cooling rings, collapsing frame, winder. Applications: Polyethylene bags, packaging films. Advantages: High production, biaxial orientation → strength. Disadvantages: Thickness control, edge effects.

Thermoforming

Process: Heating plastic sheet, forming over mould by vacuum, pressure, or mechanical means. Types: Vacuum forming, pressure forming, twin-sheet forming. Sketch: Shows sheet clamped, heater, mould, vacuum/air. Applications: Packaging (blisters), trays, automotive interior, bathtubs. Advantages: Low tool cost, large parts, quick changeover. Disadvantages: Limited to thin sheets, wall thickness variation, scrap.

END OF UNIT 2 NOTES