cause and effect - manufacturing midterm 1

Restricting dislocation motion: cause, effect, fix?

CAUSE: Obstacles (grain boundaries, solute atoms, tangles, precipitates)

EFFECT: Stronger and harder, but less ductile and tough

FIX / USE: Use only as far as the part needs; anneal if ductility must be restored

Strain hardening (cold work): cause, effect, fix?

CAUSE: Dislocations multiply and tangle (traffic jam)

EFFECT: Strength up, ductility down, anisotropy, residual stress

FIX / USE: Anneal (recovery, recrystallization, grain growth) to reset

Annealing: recovery: cause, effect, fix?

CAUSE: Heat after cold work

EFFECT: Stored stress released, dislocations move to lower energy and some annihilate

FIX / USE: Stage 1 of 3

Annealing: recrystallization: cause, effect, fix?

CAUSE: More heat

EFFECT: Elongated grains replaced by new equiaxed (spherical) grains, ductility restored

FIX / USE: Stage 2 of 3

Annealing: grain growth: cause, effect, fix?

CAUSE: Continued heat/time

EFFECT: New grains get larger, strength drops further

FIX / USE: Stage 3 of 3; stop early if you want to keep strength

Anisotropic vs isotropic: cause, effect, fix?

CAUSE: Elongated, aligned grains (anisotropic) vs random grains (isotropic)

EFFECT: Properties vary with direction vs the same in all directions

FIX / USE: Advantage if you need strength in one direction (pipe hoop stress); disadvantage if uneven (sheet warping)

Why processes are done in compression: cause, effect, fix?

CAUSE: Tension reduces cross-section as the part deforms

EFFECT: Necking: load drops and deformation becomes non-uniform

FIX / USE: Work in compression to stay uniform

Uniform plastic deformation window: cause, effect, fix?

CAUSE: Need permanent shape change without necking

EFFECT: Between yield strength and ultimate tensile strength

FIX / USE: Stress above yield (to deform) and below UTS (no necking)

Designer vs manufacturer view of yield: cause, effect, fix?

CAUSE: Designer wants no permanent deformation in service; manufacturer wants to change shape | EFFECT: Designer stays below yield; manufacturer works above it | FIX / USE: Manufacturer wants LOW strength to cut forming force

Springback (elastic recovery): cause, effect, fix?

CAUSE: Elastic part of strain is released when load is removed | EFFECT: Part changes shape (stamped bracket opens up) | FIX / USE: Overform: dies are not built to final dimensions. Total strain = plastic + elastic recovery

Weakening a material (annealing) to reduce corrosion: cause, effect, fix?

CAUSE: Dislocations and grain boundaries store energy and internal stress | EFFECT: Stress points crack and expose the part to the environment | FIX / USE: Anneal: fewer dislocations, bigger grains, less stored energy. Also weaken when you need easier manufacturing

Ways to change grain size: cause, effect, fix?

CAUSE: Solidification rate, additives, deformation then anneal | EFFECT: Fine grains = stronger | FIX / USE: Faster cooling, add inoculants (nucleation sites), or deform then anneal

Amorphous metal (metallic glass): cause, effect, fix?

CAUSE: Extremely fast cooling | EFFECT: Bypasses crystalline solidification, no grains | FIX / USE: Cool extremely fast

Creep: cause, effect, fix?

CAUSE: Constant load at high temperature | EFFECT: Slow deformation over time, worse at grain boundaries where atoms move across | FIX / USE: Directionally solidified (columnar) or single-crystal blades

Pure metal vs alloy solidification: cause, effect, fix?

CAUSE: Pure metal freezes at one temperature; alloy freezes over a range (liquidus to solidus) | EFFECT: Pure: planar front, chill zone then columnar then equiaxed. Alloy: mushy zone with dendrites | FIX / USE: Alloys are more prone to microporosity because interlocking dendrites trap liquid

Dendrites trap liquid (microporosity): cause, effect, fix?

CAUSE: Dendrite arms interlock in the mushy zone | EFFECT: Interdendritic micro-porosity | FIX / USE: Increase convection (vibrate the mold), finer grains

Coarse vs fine structure: cause, effect, fix?

CAUSE: Slow cooling vs fast cooling | EFFECT: Slow: coarse dendrites, wide arm spacing. Fast: fine structure | FIX / USE: Control cooling rate, add inoculants (e.g. TiB2 in aluminum) for heterogeneous nucleation and more equiaxed zone

Grain growth direction: cause, effect, fix?

CAUSE: Grains grow opposite to heat flow | EFFECT: Columnar grains point toward the heat source | FIX / USE: Chill plate at one end or a goose-neck/corkscrew constriction gives single direction or single crystal

Fluidity: cause, effect, fix?

CAUSE: Ability of liquid metal to fill the mold | EFFECT: Low fluidity gives misruns and cold shuts (metal freezes early) | FIX / USE: Raise superheat, pour faster, preheat the mold, lower-conductivity or smoother mold, narrower freezing-range alloy

Fluidity factors you cannot change: cause, effect, fix?

CAUSE: Viscosity, surface tension (oxide films), inclusions, solidification pattern | EFFECT: Wide freezing range and dendrites lower fluidity | FIX / USE: Can change: mold design, mold material, superheat, pour rate, heat transfer

Cost of raising superheat or preheating mold: cause, effect, fix?

CAUSE: Hotter metal or mold | EFFECT: More dissolved gas, coarser weaker grains, more shrinkage, longer cooling | FIX / USE: Balance against fill; hotter mold can reduce cracking

Shrinkage void: cause, effect, fix?

CAUSE: Thick or last-to-freeze section cut off from riser | EFFECT: Void or cavity (macro-porosity), weaker, lower thermal and electrical properties | FIX / USE: Chills (external or internal), better riser size or placement, vented runners, lower superheat

Gas porosity (round pores): cause, effect, fix?

CAUSE: Dissolved gas expelled during solidification | EFFECT: Small round pores throughout, weaker part | FIX / USE: Flush melt with inert gas, vacuum pour, dry mold, lower superheat, better venting

Open blow (spherical or elongated surface cavities): cause, effect, fix?

CAUSE: Moisture in mold turns to steam and rises to the surface | EFFECT: Cavities on the casting surface | FIX / USE: Use a dry mold

Last part to solidify: cause, effect, fix?

CAUSE: Thick sections hold more heat and lose it slowly | EFFECT: Shrinkage voids if not fed | FIX / USE: Place riser on the thick section, use chills to direct solidification toward riser

Normal segregation: cause, effect, fix?

CAUSE: Planar front, non-equilibrium cooling | EFFECT: Lower-melting alloy pushed to the center | FIX / USE: Know it ends in the CENTER

Inverse segregation: cause, effect, fix?

CAUSE: Dendritic non-equilibrium cooling | EFFECT: Lower-melting material trapped in dendrite arms at the SURFACE | FIX / USE: Know it ends at the SURFACE

Gravity segregation: cause, effect, fix?

CAUSE: Density differences in the melt | EFFECT: Heavy elements sink, light elements float | FIX / USE: Stir or control cooling

Micro vs macrosegregation: cause, effect, fix?

CAUSE: Cored dendrites (micro) vs whole-casting variation (macro) | EFFECT: Micro: composition varies within a grain. Macro: varies across the casting | FIX / USE: Homogenize by heat treatment (micro)

Sprue taper: cause, effect, fix?

CAUSE: Straight sprue walls would pull air in | EFFECT: Air entrained in the metal stream | FIX / USE: Tapered sprue stays full and in contact with the metal

Gating system with a bend or cavity: cause, effect, fix?

CAUSE: Oxides and inclusions in the melt | EFFECT: Contaminants trapped on walls (like a U-bend in a sink) | FIX / USE: Properly designed gating, pouring basin on top of sprue

Gating parts matching: cause, effect, fix?

CAUSE: Pouring basin=cup on top; sprue=tapered funnel; runner=horizontal feed; riser=extra metal reservoir; core=insert for hollow cavity; chill=heat sink for thick areas | EFFECT: Each part has one job | FIX / USE: Memorize the 7 pairs

Sand casting: cause, effect, fix?

CAUSE: Need big size, any metal, low volume, low cost | EFFECT: Cheap tooling, almost any shape/size/metal, but rough finish and poor accuracy | FIX / USE: Use for propellers, prototypes, large low-volume parts; expect machining after

Investment (lost wax) casting: cause, effect, fix?

CAUSE: Need intricate shape and best finish, no parting line | EFFECT: Excellent accuracy, almost any metal, but expensive patterns and labor, small parts | FIX / USE: Jet turbine blades, complex small parts

Die casting: cause, effect, fix?

CAUSE: High volume, need finish and fine grains | EFFECT: Good finish, fast, low porosity, but high die cost, mostly non-ferrous, limited size | FIX / USE: Transmission cases, high volume. Fast fill can trap gas: improve venting, injection speed, gating

Shell mold casting: cause, effect, fix?

CAUSE: Need better tolerance than sand at higher rate | EFFECT: Finer finish and tighter tolerance than sand, but expensive equipment | FIX / USE: Small high-precision housings

Slush casting: cause, effect, fix?

CAUSE: Need hollow thin-walled part without cores | EFFECT: Hollow part with good outer skin, poor wall control and internal finish | FIX / USE: Decorative zinc toys

Permanent mold vs sand: cause, effect, fix?

CAUSE: Reusable metal mold | EFFECT: Better finish, accuracy, faster, but higher tooling cost | FIX / USE: Worth it at high volume

Continuous casting: cause, effect, fix?

CAUSE: Metal poured through tundish into cooled mold, starter bar withdraws strand | EFFECT: More uniform microstructure, fine grains, less porosity, lower cost than ingot | FIX / USE: Feed into rolling to close porosity

Cost per piece vs volume: cause, effect, fix?

CAUSE: Expensive tooling spread over parts | EFFECT: High-tooling processes (die casting) start high and drop fast; sand is cheaper at low volume | FIX / USE: Choose process by production volume

Directional or single-crystal blades: cause, effect, fix?

CAUSE: Need creep resistance | EFFECT: No transverse grain boundaries (DS) or no boundaries at all (single crystal); very expensive process | FIX / USE: Water-cooled chill plate lowered slowly; corkscrew selects one crystal

Why cast instead of machine a complex part: cause, effect, fix?

CAUSE: Complex geometry from a block wastes material and time | EFFECT: Casting gives near-net shape with little waste | FIX / USE: Cast, then finish as needed

Hot working: cause, effect, fix?

CAUSE: Heat lowers yield strength and raises ductility | EFFECT: Large deformation with low force, recrystallization prevents work hardening, but poorer finish and dimensional control, oxidation | FIX / USE: Use for large reductions

Cold working advantages: cause, effect, fix?

CAUSE: No heating | EFFECT: Better finish, dimensional control, strength, fatigue and wear, no thermal stresses | FIX / USE: Use for precision small parts

Cold working disadvantages: cause, effect, fix?

CAUSE: Material is hardened | EFFECT: Higher force and heavier equipment, less ductility, surface must be cleaned, anisotropy, residual stress | FIX / USE: Intermediate anneals

Residual stress from cold work: cause, effect, fix?

CAUSE: Non-uniform deformation stores energy | EFFECT: Early cracking, shorter fatigue life, more corrosion | FIX / USE: Anneal (extra process step)

Higher temperature: cause, effect, fix?

CAUSE: Atoms move more easily | EFFECT: Lower yield strength, higher ductility, but thermal expansion and dimension change on cooling, oxidation, grain growth | FIX / USE: Raise temperature when cracking or high force is a problem

Higher strain rate: cause, effect, fix?

CAUSE: Working faster | EFFECT: Higher strength, lower ductility, more force, more heat generated | FIX / USE: Slow the process (e.g. slower rollers) if you need more ductility

Independent variables: cause, effect, fix?

CAUSE: Things you choose | EFFECT: Starting material and geometry, die geometry, lubrication, starting temperature, speed, amount of deformation | FIX / USE: Change these to control the dependents

Dependent variables: cause, effect, fix?

CAUSE: Result of the independent ones | EFFECT: Force, final properties, exit temperature, surface finish and tolerance, material flow | FIX / USE: Predict direction of change when you alter an independent variable

Cooler billet plus faster line: cause, effect, fix?

CAUSE: Colder metal is stronger, faster rate raises flow stress | EFFECT: More force, more cracking risk, more die wear, chilled surface, higher exit temperature from speed | FIX / USE: Keep billet hot or change lubrication and die design; do not change both at once

Lubrication purposes: cause, effect, fix?

CAUSE: Beyond reducing friction | EFFECT: Coolant, thermal barrier, corrosion inhibitor, parting agent | FIX / USE: Choose type and amount by temperature, pressure, tolerable friction

Friction in rolling vs extrusion: cause, effect, fix?

CAUSE: Rolls need grip to pull stock; extrusion friction just adds pressure | EFFECT: Rolling: some friction required. Extrusion: friction is bad | FIX / USE: Light lubrication in rolling, heavy lubrication in extrusion

Annealing after cold work: cause, effect, fix?

CAUSE: Work hardening has used up ductility | EFFECT: Restores ductility and lowers yield strength | FIX / USE: Anneal so you can keep cold working or restore ductility; spheroidizing fully resets

Rolling needs more ductility: cause, effect, fix?

CAUSE: Cold or fast rolling | EFFECT: Low ductility | FIX / USE: Raise material temperature or slow the rollers

Hydraulic vs mechanical press: cause, effect, fix?

CAUSE: Hydraulic: more capability. Mechanical: faster, cheaper | EFFECT: Mechanical suits high production or lower upfront cost | FIX / USE: Choose mechanical for volume and cost

What forging does: cause, effect, fix?

CAUSE: Compression of heated metal | EFFECT: Improves microstructure, directional grain flow, eliminates porosity, near-net shape discrete parts | FIX / USE: Use for fatigue-critical parts (connecting rods, landing gear, gears); about 20% better strength-to-weight than cast or machined

Forgeability: cause, effect, fix?

CAUSE: Material's ability to be shaped without cracking | EFFECT: Increases with temperature | FIX / USE: Test with upsetting and hot twist

Upsetting test: cause, effect, fix?

CAUSE: Compression of a specimen | EFFECT: Vary temperature and strain rate to find optimal forging conditions | FIX / USE: Open-die compression

Hot twist test: cause, effect, fix?

CAUSE: Twist heated specimen to failure | EFFECT: Most turns before failure marks the best forging temperature | FIX / USE: Torsion test

Forging temperature too low: cause, effect, fix?

CAUSE: Low ductility, high flow stress | EFFECT: Cracks form | FIX / USE: Heat more, but not so high that it melts, oxidizes, or grows grain

Barreling: cause, effect, fix?

CAUSE: Die friction holds back surface spread and cold dies chill the workpiece surface | EFFECT: Middle bulges larger than ends | FIX / USE: Lubricate, ultrasonic vibration of dies, heat dies (isothermal forging)

Isothermal forging: cause, effect, fix?

CAUSE: Die and workpiece at similar temperatures | EFFECT: Lower yield strength, higher ductility, less barreling | FIX / USE: Use for materials with limited forgeability. Too-hot dies: lower strength, die damage, lost tolerance

Open-die forging: cause, effect, fix?

CAUSE: Simple, very large shapes | EFFECT: No size or weight limit, low die cost, high skilled labor, rough finish | FIX / USE: Large shafts, eccentric shafts, stock for later machining

Impression-die forging: cause, effect, fix?

CAUSE: Shaped dies, thousands of parts | EFFECT: Better dimensions than open die, makes flash | FIX / USE: Wrenches, crankshafts

Flash: cause, effect, fix?

CAUSE: Dies never fully close, excess metal squeezed out | EFFECT: Thin flash cools fast, builds pressure and friction, plugs gap and forces metal into cavity. Wastes 20 to 40 percent material, must be trimmed | FIX / USE: Why impression-die works; not used in closed-die

Non-uniform strength in impression-die: cause, effect, fix?

CAUSE: Different strain, strain rate and temperature at each location | EFFECT: Varying cold work, residual stress | FIX / USE: Anneal or hot work to homogenize

Closed-die forging: cause, effect, fix?

CAUSE: Need fine finish and little machining, high volume | EFFECT: Flashless, exact volume needed, high skill, most expensive dies, high wear | FIX / USE: Use when machining labor is limited and finish matters (coins)

Closed-die undersized billet: cause, effect, fix?

CAUSE: Not enough material | EFFECT: Unfilled corners, pockets, holes | FIX / USE: Control billet volume tightly

Closed-die oversized billet: cause, effect, fix?

CAUSE: Too much material with no flash escape | EFFECT: Die cracks, press jams, premature die failure | FIX / USE: Control billet volume tightly

Blocker vs conventional vs precision: cause, effect, fix?

CAUSE: Tolerance class | EFFECT: Blocker: rough shape, cheap dies. Conventional: closer. Precision: near final, expensive dies | FIX / USE: Precision pays off for large batches (500,000 links) by cutting machining

Forging vs casting choice: cause, effect, fix?

CAUSE: Strength and fatigue vs complexity and cost | EFFECT: Forge for grain flow and density; cast for complex shapes (octopus table, housings) | FIX / USE: Cast low-volume or complex; forge fatigue-critical and high-volume

Non-homogeneous properties after forging: cause, effect, fix?

CAUSE: Uneven deformation | EFFECT: Properties vary through part | FIX / USE: Hot work or anneal