Comprehensive Study Notes on Manufacturing Science and Science and Processes and Resource Guide for Manufacturing Science

Introduction to Manufacturing Science

• Definition of Manufacturing Science: It is a branch of science and engineering that studies how raw materials are transformed into finished goods using machines, tools, energy, and human skills.

• Process Flow: Raw Material → Process → Finished Product.

• Objective of Manufacturing:

  • Increase efficiency.

  • Improve product quality.

  • Improve productivity.

  • Optimize the use of material and energy.

• Simple Explanation: It is the science behind making products, understanding processes, machines, materials, and production systems.

• Classification of Manufacturing Processes:

  • Primary Manufacturing: Converting raw material into shape and size (e.g., Casting).

  • Secondary Manufacturing: Further processing involving:

    • Metal Forming: Forging, Rolling, Extrusion, Bending, Drawing (Sheet Metal).

    • Machining (Material Removal): Turning, Drilling, Grinding.

    • Joining Processes: Welding, Brazing, Soldering.

    • Surface Finishing: Polishing, Lapping, Electroplating, Coating, Painting. This improves surface quality and appearance.

Metal Casting Process

• Casting Definition: The oldest manufacturing technique where molten metal is poured into a mould cavity of the desired shape and allowed to solidify. The solidified part is then removed.

• Steps in the Casting Process:

  1. Pattern Making: Creating a physical model of the part. The pattern is slightly larger than the final part to account for metal shrinkage.

  2. Core Making: Required if the casting needs to be hollow (e.g., a pipe). Cores are separate sand parts made of high-strength sand mixed with resin.

  3. Moulding (Creating the Cavity): The pattern is placed inside a flask, and moulding sand is packed tightly around it. The pattern is carefully removed, leaving a cavity. The core is then inserted if needed.

  4. Melting and Pouring: Metal is melted in a furnace to the correct pouring temperature and poured into the mould through a gating system.

  5. Solidification: The mould is left to cool until the metal solidifies completely.

  6. Removal (Shake Out): The sand mould is broken to remove the casting.

  7. Cleaning, Fettling, and Inspection: Rough edges and unwanted metal (from gates/risers) are removed using grinders (fettling). The final product is checked for defects like cracks.

• Advantages of Casting:

  • Complex Geometry: It can create complex internal and external shapes in a single step.

  • Material Versatility: Any metal that can be melted can be cast.

  • Size Range: Produces items ranging from small jewelry to large ship propellers.

  • Isotropic Properties: Cast parts have uniform properties in all directions.

• Disadvantages and Limitations:

  • Surface Finish: Generally rougher compared to machining or forging.

  • Accuracy: Lower dimensional accuracy and tolerance.

  • Defects: Susceptible to internal defects like porosity, shrinkage cavities, and blowholes, which are hard to detect.

  • Safety Hazards: Handling molten metal involves high risks of burns and accidents.

  • Mechanical Properties: Cast parts often have lower fatigue strength compared to forged parts due to their grain structure.

Casting Terminology and Components

• Pattern: A replica of the final object with modifications.

• Moulding Flask: A container that holds the sand mould. It is made of wood (temporary) or metal (long-term use).

  • Cope: The upper part of the moulding flask.

  • Drag: The lower part of the moulding flask.

• Parting Line: The dividing line between the cope and the drag.

• Pouring Basin: A small funnel-shaped cavity at the top of the mould where molten metal is introduced.

• Sprue: The passage through which molten metal flows from the pouring basin to the runner.

• Runner: The horizontal passage through which molten metal is regulated before reaching the cavity.

• Gate: The actual entry point where molten metal enters the mould cavity.

• Riser: A reservoir of molten metal that feeds back into the mould cavity to compensate for volume reduction during solidification.

• Core: Used to create hollow cavities within the casting.

• Chaplet: Supports the core inside the mould cavity.

• Moulding Sand: A freshly prepared refractory material made of silica, clay, and moisture in appropriate proportions.

  • Facing Sand: A small amount of sand applied to the internal surface of the cavity for a better surface finish.

  • Backing Sand: The bulk of the sand used to fill the flask behind the facing sand.

Solidification and Shrinkage

• Shrinkage Types:

  1. Liquid Shrinkage: Occurs in the liquid state from pouring temperature ($T_p$) to freezing temperature ($T_f$).

  2. Solidification Shrinkage: Occurs during the phase transformation from liquid to solid.

  3. Solid Shrinkage: Occurs in the solid state from the freezing temperature to the ambient temperature ($T_a$).

• Compensation Rule:

  • Liquid and Solidification shrinkage can be compensated by providing a Riser. Values are expressed as a percentage of volume ($\%$ shrinkage).

  • Solid shrinkage is compensated by increasing the Pattern size. Values are expressed in linear dimensions.

Pattern Allowances and Materials

• Types of Allowances:

  1. Shrinkage or Contraction Allowance: Compels the pattern to be larger than the final part.

  2. Draft or Taper Allowance: Vertical phases of the pattern are tapered to reduce mould damage during removal. Inner surfaces require higher drafts than outer surfaces. It is always provided as extra metal.

  3. Machining or Finish Allowance: Provided on the surface to ensure enough material exists for secondary machining to reach final dimensions.

  4. Distortion or Camber Allowance: Provided to overcome potential warping due to differences in shrinkage rates.

  5. Shake or Rapping Allowance: Accounts for the slight increase in cavity size when the pattern is rapped/shaken for removal.

• Pattern Materials:

  • Wood: Easy to make but not dimensionally stable.

  • Metal: Expensive but more stable and durable (e.g., Cast Iron, Brass, Aluminum).

  • Wax: Used in investment casting.

  • Plastic.

• Selection Criteria: Depends on casting size, complexity, number of castings produced, reusability, future demand, and cost.

Moulding Sand Properties

• Porosity (Permeability): The ability of the sand to allow gases and steam to pass through during pouring. Depends on particle shape, size, clay amount, and moisture.

• Cohesiveness: The strength of the sand to hold particles together. Improved by clay and Bentonite.

• Adhesiveness: The property that allows sand to stick to the sides of the moulding box.

• Plasticity/Flowability: The ability of the sand to flow into all corners and acquire the shape under ramming.

• Collapsibility: The property of the sand mould to disintegrate easily after solidification to allow the casting to be removed with minimal force.

• Refractoriness: The ability of the sand to withstand high temperatures without fusion.

Casting Defects and Pattern Types

• Common Defects:

  • Misruns: The metal solidifies before completely filling the cavity (due to low fluidity or temperature).

  • Cold Shut: Two streams of metal meet but fail to fuse due to premature freezing.

  • Cold Shot: Solid globules of metal formed by splashing during pouring that become trapped in the casting.

  • Shrinkage Cavity: Internal or surface depression caused by restricted molten metal flow during final freezing.

  • Micro-porosity: Network of small voids caused by localized solidification shrinkage in dendritic structures.

  • Hot Tearing (Hot Cracking): Cracks caused by the casting being strained during early cooling stages.

• Types of Patterns:

  • Solid (Single Piece): For simple shapes.

  • Split Piece: Pattern split into two or more parts along a symmetrical axis for easy removal.

  • Loose Piece: For patterns with internal projections that would otherwise be trapped.

  • Match Plate: Gating elements are integral to the plate; used for high production.

  • Sweep Pattern: Uses a 2D plane to generate 3D symmetric shapes like bells or cylinders.

  • Segmental Pattern: Similar to sweep but involves rotation in segments.

Chvorinov's Rule and Solidification Time

• Chvorinov's Rule: States that solidification time ($t$) is proportional to the square of the ratio of volume ($V$) to surface area ($A$).

• Equation: $t = B \times \left(\frac{V}{A}\right)^n$

  • Where $t$ = total solidification time.

  • $V$ = volume of casting ($cm^3$).

  • $A$ = surface area ($cm^2$).

  • $n$ = exponent (usually taken as $2$).

  • $B$ = mould constant ($s/cm^2$).

• Numerical Example 1: A cube of $10\,mm$ side solidifies in $2\,min$. Calculate time for a $20\,mm$ cube.

  • $t_1 = 2\,min$, $side_1 = 10\,mm$.

  • $t_2 = t_1 \times \left(\frac{side_2}{side_1}\right)^2 = 2 \times (2)^2 = 8\,min$.

• Gating Design: A good design ensures proper distribution of metal without excessive temperature loss, turbulence, or gas entrapment.

Machining Process Mechanics

• Definition: A manufacturing process where a sharp cutting tool removes excess material from a workpiece as chips to achieve a desired geometry.

• Orthogonal Cutting Parameters:

  • $t_1$: Uncut chip thickness.

  • $t_2$: Chip thickness.

  • $\alpha$: Rake angle.

  • $\phi$: Shear angle.

  • $r$: Cutting ratio (or thickness ratio) = $\frac{t_1}{t_2} = \frac{\sin(\phi)}{\cos(\phi - \alpha)}$.

• Equations:

  • $\tan(\phi) = \frac{r \cos(\alpha)}{1 - r \sin(\alpha)}$

  • Shear strain ($\gamma$): $\gamma = \cot(\phi) + \tan(\phi - \alpha)$.

• Example Calculation: $\alpha = 10^{\circ}$, $t_1 = 0.15\,mm$, $t_2 = 0.4\,mm$.

  • $r = \frac{0.15}{0.4} = 0.375$.

  • $\tan(\phi) = \frac{0.375 \cos(10^{\circ})}{1 - 0.375 \sin(10^{\circ})} \Rightarrow \phi = 21.554^{\circ}$.

  • $\gamma = \cot(21.554^{\circ}) + \tan(21.554^{\circ} - 10^{\circ}) = 2.735$.

Tool Life and Taylor's Equation

• Tool Life: The period for which a tool can be used effectively.

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

  • $V$ = cutting speed ($m/min$).

  • $T$ = tool life ($min$).

  • $n$ = tool life exponent (depends on material; e.g., HSS vs. Carbide).

  • $C$ = constant.

• Friction and Forces:

  • Coefficient of friction ($\mu$): $\mu = \frac{F}{N} = \tan(\beta)$, where $F$ is friction force and $N$ is normal force.

  • Merchant’s Circle relations convert cutting force ($F_c$) and thrust force ($F_t$) into shear force ($F_s$) and normal force ($F_n$).

Metal Forming Processes

• Classification based on Mass:

  • Primary Processes: Casting.

  • Zero Manufacturing (+ve): Joining (welding, soldering, brazing) where mass increases.

  • Secondary/Removing (-ve): Machining (turning, drilling, milling) where mass decreases.

  • Forming: Mass remains constant; shape is obtained through plastic deformation.

• Forming Conditions: Stress induced must be higher than Yield Strength ($\sigma_y$) but lower than Fracture Strength.

• Temperature Classification:

  • Cold Working: Deformation below recrystallization temperature (T < 0.4 T_m). Results in high strength but low ductility.

  • Warm Working: Intermediate temperature ($0.3 T_m$ to $0.5 T_m$).

  • Hot Working: Deformation above recrystallization temperature (T > 0.6 T_m). Results in high ductility and low force required, but poor surface finish (oxidation/scaling).

Engineering vs. True Stress and Strain

• Engineering Stress ($\sigma$): $\sigma = \frac{F}{A_0}$.

• Engineering Strain ($\epsilon$): $\epsilon = \frac{\Delta l}{l_0}$.

• True Stress ($\sigma_T$): $\sigma_T = \sigma (1 + \epsilon)$.

• True Strain ($\epsilon_T$): $\epsilon_T = \ln(1 + \epsilon) = \ln(\frac{A_0}{A_f})$.

• Flow Stress: The stress required to sustain plastic deformation at a specific strain. Represented by $\sigma_f = K \epsilon_T^n$.

  • $K$ = strength coefficient ($MPa$).

  • $n$ = strain hardening exponent ($0.1$ to $0.5$).

Rolling Process

• Description: A process where a workpiece is drawn through a set of rolls. Friction and compressive force reduce the thickness.

• Key Terms:

  • Draft ($\Delta h$): $\Delta h = h_i - h_f$.

  • Maximum Draft: $\Delta h_{max} = \mu^2 R$, where $R$ is roll radius.

  • Angle of Bite ($\theta$): $\tan(\theta) = \sqrt{\frac{\Delta h}{R}}$. Condition for self-entry is $\mu \ge \tan(\theta)$.

  • Neutral Plane: The plane where the roll velocity equals the material velocity.

  • Lagging Zone: Material velocity is less than roll velocity (backward slip).

  • Leading Zone: Material velocity is greater than roll velocity (forward slip).

• Example Calculation: Rolling a plate from $25\,mm$ to $20\,mm$ with $D = 600\,mm$.

  • $R = 300\,mm$, $\Delta h = 5\,mm$.

  • Contact length ($L$) = $\sqrt{R \times \Delta h} = \sqrt{300 \times 5} = 38.73\,mm$.

Wire Drawing and Forging

• Wire Drawing: Cold working process pushing/pulling rod through a die. Subjected to tensile and shear stresses.

  • Components: Bell section, Approach (plastic deformation), Die land (final size), Relief.

  • Lubricants: Solid (Graphite, $MoS_2$) or Wet (Emulsions).

• Forging: Compression of a workpiece between two dies using gradual pressure or impact.

  • Types:

    • Open Die Forging: Large objects, simple shapes. Causes "Barrelling Effect" due to friction at die-billet interface.

    • Closed Die Forging (Impression Die): Complex shapes; uses gutters to collect "Flash," ensuring complete die cavity filling.

  • Forging Steps: Fullering (thinning), Edging (gathering), Bending, Blocking, Finishing, Trimming flesh.

Extrusion Processes

• Definition: Forcing a metal billet through a die opening under high pressure.

• Types:

  • Direct (Forward): Metal flow is in the same direction as ram movement. High friction between billet and container.

  • Indirect (Backward): Metal flow is opposite to ram movement. No friction between billet and container wall, requiring less force.

  • Hydrostatic Extrusion: Billet is surrounded by fluid to eliminate friction.

• Key Metrics:

  • Extrusion Ratio ($R$): $R = \frac{A_0}{A_f}$.

  • True Strain: $\epsilon = \ln(R)$.

Sheet Metal Operations

• Shearing: Cutting along a straight line between two cutting edges.

• Punching vs. Blanking:

  • Blanking: The piece punched out is the desired part (the "Blank").

  • Punching: The piece punched out is scrap; the remaining sheet is the part.

• Clearance ($C$): Provided to ease removal and prevent fracture. $C = 0.0032 t \sqrt{\tau}$.