Manufacturing Process (ME-305) - Unit 4 Short Notes

UNIT 4: MANUFACTURING PROCESSES

I. CASTING PROCESSES

A. Overview & Classification

• Sand Casting: Most versatile, uses expendable sand molds. Low cost for low/medium volume.

• Investment Casting (Lost Wax): High precision, complex shapes. Wax pattern invested in ceramic.

• Die Casting: High pressure, reusable metal dies. Thin walls, excellent surface finish. Non-ferrous alloys (Al, Zn, Mg).

• Centrifugal Casting: Molten metal poured into rotating mold. Used for cylindrical parts (pipes, bushings). Density increases radially outward.

• Continuous Casting: Molten metal solidified continuously into slabs/billets. High productivity for steel/ingots.

• Selection Criteria: Material (ferrous/non-ferrous), geometry complexity, production volume, tolerance/surface finish requirements, cost.

B. Pattern Making

1. Pattern Types

2. Pattern Allowances (High Priority)

Definition: Extra dimensions added to a pattern to compensate for post-casting changes.

Calculation Example (Shrinkage):

Final casting dimension = \( L_f \)

Pattern dimension = \( L_p = L_f \left(1 + \frac{S}{100}\right) \)

where \( S \) = linear shrinkage percentage.

Example: For a 100 mm casting with 1.5% shrinkage, pattern size = \( 100 \times (1 + 0.015) = 101.5 \) mm.

3. Pattern Design Considerations

• Material: Wood (low cost, easy to shape), Metal (durable, for high volume), Plastic (light, corrosion resistant).

• Construction: Solid, laminated, skeleton.

• Core Prints: Projections to form core seats in mold. Must have draft.

• Locators: To align pattern halves (e.g., metal pins in match plate).

4. Core Making

• Core Sand: Finer grain, higher strength (hot & cold), lower permeability than molding sand. Uses binders (e.g., oil, resin, cereal).

• Core Box: Mold for forming core. Must allow easy core removal.

• Coating (Dressing): Refractory slurry (e.g., zircon, graphite) applied to improve surface finish and prevent metal penetration.

C. Mold & Core Materials

1. Foundry Sands

2. Core Sands

• Hot Strength: Must retain shape at metal temperature.

• Friability: Easy to break out after casting.

• Low Gas Evolution: Prevent gas porosity.

• Good Collapsibility: Facilitate shake-out.

3. Binders & Additives

• Clay (Bentonite): Provides green/dry strength.

• Resins (Furan, Phenolic): High strength, used in core sand & no-bake molds.

• Oils (Linseed): Increase dry strength, improve breakdown.

• Cereals (Starch): Improve collapsibility, reduce gas.

D. Gating, Runners & Risers (High Priority)

1. Functions

• Sprue: Vertical channel connecting pouring basin to runner.

• Runner: Horizontal channel distributing metal to ingates.

• Ingate: Constricted opening controlling flow into mold cavity.

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

2. Gating System Design

• Top Gating: Metal enters from top. Simple but can cause turbulence & erosion.

• Bottom Gating: Metal enters from bottom. Reduces turbulence, better for delicate castings.

• Parting Line Gating: Gating along parting line. Common in two-piece molds.

• Design Principles: Minimize turbulence (smooth transitions, proper ingate size), avoid air entrapment, ensure directional solidification (cavity solidifies before riser).

3. Riser Design

• Open (Top) Riser: Exposed to atmosphere. Simple, easy to inspect.

• Blind (Top) Riser: Covered by mold. Better insulation, less heat loss.

• Shape: Spherical (best V/A ratio), Cylindrical (common), Top cylindrical (easy to attach).

• Placement: On heaviest section (last to solidify). Must be connected via smallest possible neck (choke) to mold cavity.

Chvorinov’s Rule:

$$ t = C \left( \frac{V}{A} \right)^n $$

where:

• \( t \) = solidification time

• \( V \) = volume of casting/riser

• \( A \) = total surface area

• \( C \) = mold constant (depends on mold material, metal)

• \( n \) = exponent (usually 2)

Application: Riser must solidify slower than casting. So, \( \left( \frac{V}{A} \right)_{riser} > \left( \frac{V}{A} \right)_{casting} \).

For cylindrical blind riser with constant volume:

Volume \( V = \frac{\pi d^2}{4} h \), Surface Area \( A = \pi d h + \frac{\pi d^2}{2} \).

For minimum solidification time (maximum V/A), differentiate \( \frac{V}{A} \) w.r.t \( d \) or \( h \). Result: \( h = \frac{d}{2} \) (height = half diameter). This gives spherical shape (optimal).

4. Impact on Quality

• Poor gating: Turbulence → oxide inclusions, erosion, cold shuts.

• Inadequate risering: Shrinkage cavities.

• Optimization: Proper riser size/placement, use of chills, exothermic pads to achieve directional solidification. Yield = (Casting weight) / (Casting + Riser + Gating weight).

E. Solidification & Defects

1. Solidification Theory

• Cooling Curve: Shows temperature vs time. Plateau at liquidus (start of solidification) and solidus (complete solidification).

• Nucleation: Formation of solid crystals (homogeneous/heterogeneous).

• Growth: Dendritic growth in most metals. Shrinkage occurs during liquid-to-solid transformation.

2. Common Casting Defects

3. Defect Elimination

• Chills: Metal/ graphite inserts to increase cooling rate locally (create hot spots).

• Chaplets: Metal supports for cores. Must be same metal as casting to avoid metallurgical issues.

• Exothermic Pads: Insulating/heat-generating material on top of riser to keep it hot longer.

• Proper Gating/Risering: As per Chvorinov, minimize turbulence.

F. Special Casting Techniques

1. Centrifugal Casting

• Principle: Mold rotates at high speed (30-3000 rpm). Centrifugal force pushes metal to periphery.

• Applications: Cylindrical parts (pipes, tubes, bushings, cylinder liners). Can be horizontal/vertical.

• Advantages: Dense, fine-grained periphery, no riser needed, good for tubular parts.

• Limitations: Limited to cylindrical shapes, inner diameter rough, non-uniform wall thickness difficult.

2. Continuous Casting

• Process: Molten metal poured into water-cooled copper mold (strand). Solidifies as it emerges, cut to length.

• Suitable Materials: Steel, aluminum, copper alloys.

• Advantages: High yield (no risers), uniform quality, automation, lower cost for long products.

• Limitations: High initial cost, limited to simple cross-sections.

3. Investment Casting

• Steps:

  1. Wax Pattern: Injection molding of wax.

  2. Tree Assembly: Patterns attached to sprue.

  3. Investing: Dipping in ceramic slurry + stucco (refractory sand).

  4. Dewaxing: Burn out wax (steam/autoclave).

  5. Mold Firing: Burn out residuals, strengthen mold.

  6. Pouring: Molten metal poured.

  7. Finishing: Knockout, cut-off, cleaning, heat treat.

• Advantages: Excellent surface finish, dimensional accuracy, complex shapes, no draft needed.

• Limitations: Expensive, size limited (<25 kg), labor intensive.

• Applications: Turbine blades, dental crowns, jewelry, aerospace parts.

4. Die Casting

• Process: Molten metal injected under high pressure (700-4500 bar) into steel die.

• Die Design: Two halves, cores for holes, ejector pins. Must withstand high pressure/temperature.

• Dimensional Tolerances: Very tight (e.g., ±0.1 mm for first 25 mm). Depends on die design, material, process control.

• Material Selection: Low melting point alloys (Al, Zn, Mg) to reduce die wear.

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

• Limitations: High die cost, limited to non-ferrous, porosity possible, size limited (<20 kg).

G. Auxiliary Elements

• Chills: External (placed on mold surface) or internal (embedded). Materials: Graphite, cast iron, copper. Used for directional solidification.

• Chaplets: Support cores. Types: Wire, solid, split. Must be same metal as casting to fuse properly.

• Core Prints & Locators: Core prints form seats for cores. Locators (pins, holes) ensure proper core/mold alignment. Draft on core prints essential.

II. WELDING PROCESSES

A. Fundamentals

• Joint Types: Butt, lap, corner, edge, T-joint.

• Fusion vs Non-Fusion: Fusion (molten base metal), Non-fusion (solid-state, e.g., friction welding).

• Heat Input: Energy per unit length. Affects HAZ size, distortion, properties.

• Penetration: Depth of weld pool. Controlled by current, voltage, travel speed.

B. Arc Welding (High Priority)

1. Manual Metal Arc Welding (MMAW / SMAW)

• Electrode: Consumable, coated with flux.

• Flux Functions:

  • Shielding: Forms gas shield (CO₂, H₂O vapor) to protect from atmosphere.

  • Deoxidizers/Alloying: Add elements to counteract oxidation.

  • Slag Formation: Protects cooling weld, shapes bead, slows cooling.

  • Arc Stabilizer: Easier ignition/stability (e.g., potassium, sodium compounds).

• AC vs DC:

  | Characteristic | AC | DC | | :--- | :--- | :--- | | Arc Stability | Less stable (zero crossing) | More stable | | Penetration | Medium | DCEN: Deep penetration (electron to work). DCEP: Shallow penetration (electron to electrode). | | Common Use | General purpose, mild steel | DCEN for thick sections, DCEP for thin sheets/fill pass. | | Equipment | Simple, no polarity switch | Requires polarity selection. |

• Electrode Polarity:

  • DC Electrode Positive (DCEP): Electron flow from work to electrode. Electrode melts faster (higher deposition rate). Shallow penetration. Used for sheet metal, root passes.

  • DC Electrode Negative (DCEN): Electron flow from electrode to work. Electrode melts slower, work heats more. Deep penetration. Used for thick sections.

2. TIG Welding (GTAW)

• Electrode: Non-consumable tungsten (pure, thoriated, ceriated).

• Shielding: Inert gas (Ar, He). Argon common for steel/Al; He for copper/Al (deeper penetration).

• Filler Rod: Optional, added manually.

• Control: Precise control of current (AC for Al, DC for steel), gas flow, arc length.

• Applications: Thin sections, reactive metals (Al, Mg, Ti), high-quality welds (aerospace, piping).

• Advantages over MMAW/MIG: No slag, clean weld, precise heat input, no spatter, all-position welding.

• Limitations: Slower, requires skill, sensitive to contamination.

3. MIG Welding (GMAW)

• Electrode: Consumable wire fed continuously.

• Shielding: Inert (Ar, He) or semi-inert (CO₂, Ar+CO₂ mixes). CO₂ cheap but more spatter.

• Operation: Semi-automatic (hand-held gun) or automatic (mechanized).

• Comparison:

  • vs TIG: Faster, higher deposition, less skill needed. But more spatter, less precise, not ideal for thin materials.

  • vs MMAW: Faster, cleaner, easier automation. But more equipment cost, sensitive to wind/gas shielding.

• Applications: High-production welding (automotive, shipbuilding).

4. Electrode & Flux Importance

• Electrode Composition: Core wire (matching base metal) + coating.

• Coating Types: Cellulosic (deep penetration), rutile (easy to use, smooth bead), iron powder (high deposition).

• Storage: Low humidity to prevent moisture (causes hydrogen porosity). Oven-drying before use.

C. Other Welding Methods

1. Gas Welding (Oxy-fuel)

• Process: Oxy-acetylene flame (temperature ~3200°C). Filler rod used.

• Defects:

  • Porosity: Caused by incorrect gas pressure, contaminated metal/filler, improper flame (carburizing/oxidizing).

  • Remedies: Correct gas pressures, clean surfaces, neutral flame, proper travel speed.

• Applications: Repair, thin sheets, non-ferrous metals, pipe welding.

2. Thermit Welding

• Chemical Reaction: \( 2Al + Fe_2O_3 \rightarrow 2Fe + Al_2O_3 + \text{Heat (2500°C)} \)

• Conditions: Preheated mold, thermit mixture ignited (magnesium ribbon), molten metal poured.

• Challenges: Control of reaction, slag inclusion, precise mold preparation, high temperature.

• Applications: Railway tracks, large sections (turbine shafts), in-situ repairs.

3. Resistance Welding (Brief)

• Spot Welding: Overlap sheets, electrodes apply pressure & current. Spot nugget forms.

• Seam Welding: Rotating wheels for continuous weld (tanks, pipes).

D. Welding Defects & Quality

1. Common Defects & Causes

2. Remedies

• Porosity: Preheat/dry electrodes/workpiece, correct gas flow, proper technique (dip technique in TIG), use low-hydrogen electrodes.

• Spatter: Optimize parameters (voltage, current), correct polarity, use anti-spatter compounds.

• Cracks: Preheating (slow cooling), post-weld heat treatment (PWHT), proper joint design (avoid sharp corners), use low-hydrogen process/electrodes.

E. Welding Calculations

1. Heat Input

Formula: \( Q = \frac{V \times I \times \eta}{v} \)

where:

• \( Q \) = heat input (J/mm or J/m)

• \( V \) = arc voltage (V)

• \( I \) = welding current (A)

• \( \eta \) = heat transfer efficiency (typical: SMAW=0.75, GMAW=0.9, GTAW=0.6-0.8)

• \( v \) = travel speed (mm/s or m/s)

Given: \( V = 20 + 1.5L \) (L in mm). So for L=4 mm, V = 20 + 1.5×4 = 26 V.

Example (Jun 2023):

\( V = 26 \) V, \( I = 400 \) A (from context), \( \eta = 0.85 \), \( v = 15 \) cm/s = 150 mm/s.

\( Q = \frac{26 \times 400 \times 0.85}{150} = 59.07 \) J/mm.

2. Weld Cross-Sectional Area

Given: Power source maintains 40 V, 400 A. Heat transfer efficiency \( \eta_h = 0.8 \), melting efficiency \( \eta_m = 0.3 \), heat to melt electrode \( H_m = 20 \) J/mm³, travel speed \( v = 4 \) mm/s.

Step 1: Heat input to work \( Q_w = \frac{V I \eta_h}{v} = \frac{40 \times 400 \times 0.8}{4} = 3200 \) J/s = 3200 J/mm (since v in mm/s, Q in J/mm? Check units: v=4 mm/s → Q in J/mm? Actually \( \frac{J/s}{mm/s} = J/mm \). Yes.)

Step 2: Heat used for melting electrode \( Q_m = \eta_m \times Q_w = 0.3 \times 3200 = 960 \) J/mm.

Step 3: Volume melted per mm length = \( \frac{Q_m}{H_m} = \frac{960}{20} = 48 \) mm³/mm.

Step 4: Cross-sectional area \( A = \frac{\text{Volume}}{\text{Length}} = 48 \) mm².

\boxed{A = 48 \text{ mm}^2}

III. FORGING PROCESSES

A. Fundamentals

1. Mechanical Working of Metals

• Significance:

  • Refines grain structure → improved mechanical properties (strength, toughness).

  • Closes porosity, reduces segregation.

  • Improves ductility in direction of working.

  • Can produce complex shapes with less scrap than machining.

2. Hot Working vs Cold Working

3. Elastic vs Plastic Deformation

• Elastic: Stress removed → full recovery (Hooke’s law: \( \sigma = E \varepsilon \)).

• Plastic: Permanent deformation after yield point. Occurs by slip/twinning.

B. Forging Operations

1. Open-Die Forging

• Process: Deformation between flat/contoured dies. Metal flows freely except at contact.

• Operations:

  • Drawing Out: Reduce cross-section, increase length.

  • Upsetting: Increase cross-section, reduce length (e.g., bolt heads).

  • Punching: Hole creation (with or without piercing).

• Applications: Large parts (shafts, discs, rings), custom forgings, preforms for closed-die.

2. Impression-Die (Closed-Die) Forging

• Process: Metal fully confined in die cavity. Flash (excess metal) forms in flash gutter.

• Steps: Upsetting → preforming → final forging → trimming flash.

• Applications: High-volume complex shapes (crankshafts, gears, tools). High strength, good surface finish.

3. Drop Forging

• Hammer Drop Forging: Gravity-driven hammer (mechanical/hydraulic). Impact load, fast. Used for medium parts.

• Press Drop Forging: Slow, continuous pressure. Better control, less vibration. Used for large, complex parts.

4. Horizontal Forging (Upsetting)

• Machine: Horizontal upsetter (multiple cavity die). Workpiece fed horizontally, gripped, end upset.

• Advantages: High production, good for long parts (bolts, screws), automatic feeding.

C. Forging Machines

• Drop Hammers: Counterblow (energy absorbed by anvil) or gravity drop. High impact, short dwell.

• Hydraulic Presses: Slow, high force, adjustable. Good for large, complex parts.

• Horizontal Upsetters: Specialized for long parts, high-speed production.

D. Forging Defects & Remedies

IV. PRESS WORKING (SHEET METAL FORMING)

A. Introduction

• Definition: Sheet metal forming using presses and dies. High-volume, accurate production.

• Press Machine Types: Mechanical (crank, eccentric), Hydraulic, Pneumatic.

B. Press Machines

1. Mechanical Presses

• Principle: Crank or eccentric converts rotary to reciprocating motion.

• Characteristics: High speed (up to 2000 spm), fixed stroke, force varies with position (max at bottom). Good for shallow drawing, blanking.

• Force Curve: Increases as crank rotates, peaks near BDC.

2. Hydraulic Presses

• Principle: Fluid pressure drives piston.

• Advantages: Adjustable force, long stroke, constant force throughout stroke. Good for deep drawing, forming.

• Disadvantages: Slower, higher cost, larger footprint.

3. Pneumatic Presses

• Principle: Compressed air.

• Applications: Light duty, assembly, clinching.

• Limitations: Lower force, less precise.

C. Press Working Operations (High Priority)

1. Shearing Operations (Cutting along a line)

Key Difference: Blanking → part is punch shape. Punching → part is sheet with hole.

2. Bending & Forming

3. Deep Drawing

• Process: Sheet drawn into cup shape by punch. Blank held by blankholder to prevent wrinkling.

• Draw Ratio: \( DR = \frac{d}{D} \) (d = punch diameter, D = blank diameter). \( DR_{max} \approx 0.6-0.7 \) for single draw.

• Defects:

  • Wrinkling: Buckling of flange due to compressive stress. Remedy: Increase blankholder force.

  • Tearing: Tensile stress in wall exceeds ductility. Remedy: Increase die radius, reduce friction, use proper draw ratio, intermediate anneals.

• Remedies: Proper die design (large die radius, smooth transitions), lubrication, blankholder force control, multi-stage drawing.

4. Other Operations

• Coining: Extreme squeezing to produce fine details (coins, medals). High pressure, small deformation.

• Curling: Rolling edge to form a hem (e.g., can tops).

D. Tooling & Dies

• Die Types:

  • Simple Die: One operation per stroke (e.g., blanking).

  • Compound Die: Multiple operations in one station at same time (e.g., blanking + piercing).

  • Progressive Die: Series of stations, part progresses through die, different operation each station. High production.

  • Combination Die: Combines forming & cutting (e.g., blanking + bending).

• Clearance for Shearing: \( c = k \times t \), where \( t \) = sheet thickness, \( k \) = 5-8% for ferrous, 8-12% for non-ferrous. Clearance on one side.

  • Effect: Too small → high forces, poor edge, tool wear. Too large → rough edge, large burr.

• Die Materials: Tool steel (D2, A2), carbide. Heat-treated for hardness/wear resistance.

E. Process Parameters & Calculations

1. Shearing Force

\( F = \tau \times t \times L \)

where:

• \( \tau \) = average shear strength (MPa)

• \( t \) = sheet thickness (mm)

• \( L \) = cut length (mm)

For blanking/punching: \( L \) = perimeter of part/punch.

Example: Blanking 100 mm × 50 mm rectangle from 2 mm thick steel (\( \tau = 300 \) MPa).

Perimeter = 2(100+50) = 300 mm.

\( F = 300 \times 2 \times 300 = 180,000 \) N = 180 kN.

2. Drawing Force & Blankholder Force

• Drawing Force (approx): \( F_d = \pi d t \sigma_u \ln\left(\frac{D}{d}\right) \)

  where \( \sigma_u \) = tensile strength, \( d \) = punch diameter, \( D \) = blank diameter.

• Blankholder Force: \( F_b = 0.5 \times F_d \) to \( 1.0 \times F_d \). Prevents wrinkling but not too high to cause tearing.

3. Stock Layout & Utilization

• Scrap Margin: Given 20% margin on each side. If component width = \( w \), then spacing between components = \( w + 0.4w = 1.4w \)? Actually "20% scrap margin on each side" means gap between components = 0.2w + 0.2w = 0.4w. So pitch = \( w + 0.4w = 1.4w \).

• Example (Jun 2023): Sheet 300 mm × 500 mm. Component width? Not given. Assume component width = \( w \), length = \( l \). But question says "rectangular components" without dimensions. Likely component size is given in problem? In Jun 2023 paper: "A manufacturing plant is performing a blanking operation on a sheet metal with a width of 300 mm and a length of 500 mm. The blanking process requires a 20% scrap margin on each side of the desired component." But component dimensions missing? Possibly component is square or given elsewhere. Let's assume component is of size \( a \times b \). Then with 20% margin on each side, effective pitch in width direction = \( a + 0.4a = 1.4a \), in length = \( b + 0.4b = 1.4b \). Number along width = \( \left\lfloor \frac{300}{1.4a} \right\rfloor \), along length = \( \left\lfloor \frac{500}{1.4b} \right\rfloor \). Total = product. Without \( a,b \), can't compute. Perhaps component is given in full problem? In provided context, it's cut off. But method is: layout with spacing = component dimension + 2×(scrap margin fraction × component dimension).

4. Material Formability

• Factors: Ductility, strain hardening exponent (n-value), anisotropy (r-value), thickness, surface quality.

• Common tests: Tensile test (n, r), Erichsen cupping test.

F. Auxiliary Equipment & Safety

• Stock Feeders: Automatically feed sheet/coil to press. Types: friction feeder, roller feeder.

• Scrap Cutters: Shear/scrap cutters to separate scrap from parts.

• Safety Devices:

  • Light Curtains: Infrared beams, stop press if broken.

  • Guards: Fixed/interlocked barriers.

  • Two-Hand Controls: Both hands required to operate, away from die.

  • Die Setting: Proper setting, use of safety blocks.

  • Maintenance: Regular inspection of dies, presses.

V. ROLLING PROCESSES

A. Rolling Fundamentals

1. Rolling Mills

2. Rolling Mechanics

• Deformation: Thickness reduction, length increase, width increase (constrained by friction).

• Slip: Difference between roll surface speed and metal speed. Friction necessary to pull metal in.

• Roll Force, Torque, Power: Complex based on flow stress, friction, geometry. Not required in detail for exam.

B. Hot Rolling vs Cold Rolling (High Priority)

C. Rolled Products

1. Structural Sections (I-beams, channels, angles)

• Process: Rolled from blooms in successive passes (breaking down → roughing → finishing). Complex roll grooves.

• Application: Construction, bridges, buildings.

2. Plates & Sheets

• Plates: Thick (>6 mm), usually hot rolled. Used for pressure vessels, ship hulls.

• Sheets: Thin (<6 mm), can be hot or cold rolled. Cold rolled for automotive, appliances (better finish/strength).

• Production: Hot rolling → pickling (remove scale) → cold rolling (tandem mills) → annealing → temper rolling.

3. Bars, Rods & Shapes

• Rods: Small diameter (<12 mm), often cold drawn.

• Bars: Larger, hot rolled. Shapes (round, square, hexagonal) from continuous casting billets.

• Finishing Passes: Final passes to achieve tight tolerances, surface finish.

D. Rolling Defects

VI. MACHINING PROCESSES (MACHINE TOOLS)

A. Lathe Machines (High Priority)

1. Main Components

• Bed: Base, guides for carriage.

• Headstock: Contains spindle (holds workpiece), speed gearbox (changes speed), motor.

• Tailstock: Supports other end, can hold drill/center.

• Carriage: Moves along bed. Contains:

  • Saddle: Supports cross-slide.

  • Cross-slide: Moves perpendicular to spindle axis (tool feed).

  • Tool Post: Holds cutting tool.

• Feed Mechanism: Controls tool movement (manual/automatic).

2. Basic Operations

3. Lathe Types

• Engine Lathe: General purpose, manual.

• Turret Lathe: Multiple tools on turret, automatic indexing. High production.

• CNC Lathe: Computer-controlled, complex shapes, high precision.

B. Shaper & Planer Machines

1. Working Principle

• Reciprocating motion of tool (shaper) or workpiece (planer).

• Quick Return Mechanism: Forward stroke (cutting, slower), return stroke (non-cutting, faster). Ratio typically 1:1.5 to 1:3.

2. Operations

• Shaper: Horizontal/vertical/contouring shaping. Small/medium parts (up to 1 m).

• Planer: Large flat surfaces (up to 10 m). Workpiece clamped on table, reciprocates.

3. Comparison

C. Milling Machines

1. Types

• Horizontal Milling: Spindle horizontal. Arbor holds multiple cutters (gang milling).

• Vertical Milling: Spindle vertical. End mills, face mills.

• Universal Milling: Table can swivel, helical milling possible.

• CNC Milling: 3-5 axes, complex contours.

2. Milling Operations

3. Milling Cutters

• End Mill: Cuts from end and periphery. Versatile.

• Face Mill: Large diameter, inserts, face cutting.

• Slab Mill: Wide, heavy peripheral cutting.

• Fly Cutter: Single-point, large flat surfaces.

D. Grinding Machines

1. Types

• Surface Grinder: Horizontal/vertical spindle. Flat surfaces.

• Cylindrical Grinder: Rotating workpiece, rotating wheel. External/internal cylindrical surfaces.

• Centerless Grinder: No centers, workpiece supported on blade and regulating wheel. High production for small parts (pins, shafts).

2. Applications in Precision Machining

• High surface finish (Ra 0.1-0.8 μm).

• Tight tolerances (±0.005 mm).

• Hard materials (HRC > 45) where conventional machining difficult.

• Final finishing after heat treatment.

3. Abrasives & Wheel Selection

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

• Grain Size: Coarse (fast removal), Fine (fine finish).

• Bond Type: Vitrified (strong, porous), Resinoid (flexible), Rubber (flexible, fine finish).

• Wheel Geometry: Shape (straight, cup, disc), grade (hard/soft), structure (dense/open).

E. Drilling Machines

1. Types

• Bench Drilling: Small, bench-mounted.

• Pillar Drilling: Floor-mounted, larger capacity.

• Radial Drilling: Arm moves radially, large workpieces.

• CNC Drilling: Multi-spindle, automated.

2. Drilling Operations

• Drilling: Making hole with twist drill.

• Reaming: Finishing hole to precise size/smoothness.

• Tapping: Internal threads.

• Boring: Enlarging/true hole (on lathe or boring machine).

3. Twist Drill Geometry

• Parts: Shank, body (flutes, margins), point (118° standard, 135° for hard materials).

• Lands & Flutes: Remove chips, coolant flow.

• Point Angle: Affects penetration, chip formation, thrust force.

4. Speeds & Feeds

• Cutting Speed: \( V_c = \frac{\pi D N}{1000} \) (m/min), D in mm, N in rpm.

• Feed: \( f \) (mm/rev).

• Material Dependent: High speed/feed for Al, low for stainless steel.

5. Drilling Time Calculation

\( T = \frac{L + A + O}{f \times N} \)

where:

• \( T \) = time (min)

• \( L \) = hole depth (mm)

• \( A \) = approach distance (mm) (drill enters full thickness)

• \( O \) = overrun/return distance (mm) (drill exits)

• \( f \) = feed (mm/rev)

• \( N \) = rpm

Example (Jun 2023): D=20 mm, thickness=40 mm, N=400 rpm, f=0.1 mm/rev, A+O = radius = 10 mm.

\( T = \frac{40 + 10}{0.1 \times 400} = \frac{50}{40} = 1.25 \) min.

\boxed{T = 1.25 \text{ min}}

VII. INTEGRATED CALCULATIONS & APPLICATIONS

A. Casting Calculations

1. Pattern Dimension from Shrinkage

\( L_p = L_f \left(1 + \frac{S}{100}\right) \)

Example (Dec 2023): \( L_f = 100 \) mm, \( S = 1.5\% \). \( L_p = 100 \times 1.015 = 101.5 \) mm.

2. Riser Solidification Time (Chvorinov)

For cylindrical riser: \( \frac{V}{A} = \frac{\pi d^2 h / 4}{\pi d h + \pi d^2 / 2} = \frac{d h / 4}{h + d/2} \)

Given constant volume \( V = \frac{\pi d^2 h}{4} = \text{const} \), maximize \( \frac{V}{A} \) → minimize solidification time.

Differentiate \( \frac{h}{4(h + d/2)} \) with \( h = \frac{4V}{\pi d^2} \). Result: \( h = \frac{d}{2} \).

Example (Jun 2023): Riser: d=6 cm, h=6 cm. \( V = \frac{\pi \times 6^2 \times 6}{4} = 169.6 \) cm³, \( A = \pi \times 6 \times 6 + \frac{\pi \times 6^2}{2} = 113.1 + 56.55 = 169.65 \) cm². \( \frac{V}{A} = 1 \). Casting: 7×10×2 cm. \( V_c = 140 \), \( A_c = 2(7×10 + 7×2 + 10×2) = 2(70+14+20)=208 \) cm². \( \left(\frac{V}{A}\right)_c = 140/208 = 0.673 \). Since \( \left(\frac{V}{A}\right)_{riser} > \left(\frac{V}{A}\right)_c \), riser solidifies slower. \( t_r = t_c \times \left( \frac{(V/A)_r}{(V/A)_c} \right)^2 = 1.36 \times \left( \frac{1}{0.673} \right)^2 = 1.36 \times 2.21 = 3.00 \) min (approx). \boxed{t_r \approx 3.0 \text{ min}}.

3. Solidification Shrinkage & Contraction

Example (Jun 2023): Cubic casting 50 mm side. Vol. shrinkage = 4%, vol. contraction = 6%. Total volumetric change = 1 - (1-0.04)(1-0.06) = 1 - 0.96×0.94 = 1 - 0.9024 = 0.0976 = 9.76% (approx). But careful: Shrinkage during solidification (liquid→solid), contraction during cooling (solid→room). Assume uniform. Final side \( L_f = L_0 (1 - \text{total linear shrinkage}) \). Total volumetric shrinkage ≈ 4%+6% = 10%? Actually sequential: After solidification, volume = \( V_0 (1-0.04) \). After cooling, volume = \( V_0 (1-0.04)(1-0.06) = V_0 \times 0.9024 \). So total volumetric reduction = 9.76%. Linear ≈ 9.76%/3 = 3.25%. Final side = \( 50 \times (1 - 0.0325) = 48.375 \) mm. But check: \( (0.9675)^3 = 0.904 \), close to 0.9024. \boxed{L_f \approx 48.4 \text{ mm}}.

B. Press Working Calculations

1. Blanking/Punching Force

\( F = \tau \times t \times L \). Example: See above (180 kN).

2. Stock Layout with Scrap Margin

Example (Jun 2023): Sheet 300×500 mm, 20% scrap margin on each side. If component size = \( a \times b \), then pitch in width = \( a + 0.4a = 1.4a \), in length = \( 1.4b \). Number along width = \( \left\lfloor \frac{300}{1.4a} \right\rfloor \), along length = \( \left\lfloor \frac{500}{1.4b} \right\rfloor \). Total = product. Without component size, cannot compute. Assume component is square of side \( x \)? Possibly from context: "rectangular components" but size not given. Might be missing. But method is key.

3. Deep Drawing Parameters

Draw Ratio: \( DR = d/D \). Max \( DR \approx 0.6-0.7 \) for single draw.

Blank Diameter: \( D = \sqrt{d^2 + 4 d h} \) for cylindrical cup (approx), where h = height.

C. Welding Calculations

1. Heat Input with Variable Voltage

Given \( V = 20 + 1.5L \) (L in mm). Compute V for given L, then \( Q = \frac{V I \eta}{v} \).

2. Weld Area from Melting Efficiency

Example (Jun 2023): \( V=40 \) V, \( I=400 \) A, \( \eta_h=0.8 \), \( \eta_m=0.3 \), \( H_m=20 \) J/mm³, \( v=4 \) mm/s.

\( Q_w = \frac{40 \times 400 \times 0.8}{4} = 3200 \) J/mm.

\( Q_m = 0.3 \times 3200 = 960 \) J/mm.

Volume melted per mm = \( 960 / 20 = 48 \) mm³/mm.

Cross-sectional area = 48 mm². \boxed{48 \text{ mm}^2}.

D. Drilling Time Calculation

Example (Jun 2023): D=20 mm, thickness=40 mm, N=400 rpm, f=0.1 mm/rev, A+O = radius = 10 mm.

\( T = \frac{40 + 10}{0.1 \times 400} = \frac{50}{40} = 1.25 \) min. \boxed{1.25 \text{ min}}.

[!TIP] Exam Focus:

• Pattern Allowances: Be ready to calculate pattern size from shrinkage, explain each allowance with example.

• Chvorinov’s Rule: Derive optimal riser shape (h = d/2), solve time problems.

• Welding: Compare AC/DC, TIG/MIG, calculate heat input with given formulas.

• Press Working: Distinguish blanking vs punching, calculate shearing force, layout with scrap margins.

• Lathe: Know all components and basic operations (turning, facing, drilling, threading).

• Drilling Time: Memorize formula \( T = \frac{L+A+O}{fN} \), note units (mm, rev, min).

• Hot vs Cold Working: Contrast temperature, properties, applications (wire drawing = cold).

• Deep Drawing Defects: Wrinkling (↑ blankholder force), tearing (↓ draw ratio, ↑ die radius).