Casting

1. Q: What is casting in manufacturing?

A: A process where solid metal is melted, poured into a mold, and solidified into a desired shape in one step.

2. Q: What is a foundry?

A: A factory equipped for making molds, melting metal, casting, and finishing parts, staffed by foundrymen.

3. Q: What are the five basic steps of the casting process?

A: (1) Make mold, (2) Melt metal, (3) Pour into mold, (4) Solidify, (5) Remove from mold.

4. Q: Name two advantages of casting.

A: Can create complex geometries and has no size limit.

5. Q: What is a common disadvantage of sand casting?

A: Poor dimensional accuracy and surface finish.

6. Q: Give an example of a large part made by casting.

A: Engine block for automotive vehicles.

#### Casting Processes

7. Q: What distinguishes expendable mold processes?

A: The mold is destroyed after casting (e.g., sand, plaster).

8. Q: What material is typically used for permanent molds?

A: Metal (or sometimes ceramic refractory material).

9. Q: Which casting process is more economical for high production?

A: Permanent mold processes.

#### Fundamentals of Casting

10. Q: What are the six basic requirements for casting?

A: Mold cavity, melting process, pouring technique, solidification process, mold removal, finishing/inspection.

11. Q: What is the cope in a mold?

A: The upper half of the mold.

12. Q: Why is the mold cavity made oversized?

A: To account for shrinkage during solidification and cooling.

13. Q: What is the purpose of a riser in casting?

A: To supply molten metal to compensate for shrinkage during solidification.

14. Q: What is draft in casting?

A: A taper on patterns or cavities to allow easy removal from the mold.

#### Heating and Pouring

15. Q: What three types of heat are needed to melt metal for casting?

A: Heat to reach melting point, heat of fusion, and heat to superheat for pouring.

16. Q: What factors determine successful pouring?

A: Pouring temperature, pouring rate, and turbulence control.

17. Q: What is fluidity in casting?

A: The ability of molten metal to flow and fill a mold before freezing.

18. Q: How does high surface tension affect fluidity?

A: It reduces fluidity.

#### Solidification and Cooling

19. Q: How does a pure metal solidify differently from an alloy?

A: Pure metals solidify at a constant temperature; alloys freeze over a temperature range.

20. Q: What is the chill zone in a casting?

A: A layer of fine equiaxed grains formed by rapid cooling near the mold wall.

21. Q: What is Chvorinov’s Rule used to calculate?

A: Total solidification time (TST = Cm (V/A)^n).

22. Q: Which shape solidifies fastest: sphere, cube, or cylinder (same volume)?

A: Cube (highest surface area-to-volume ratio).

23. Q: What are the three stages of shrinkage in casting?

A: (1) Liquid contraction, (2) Solidification shrinkage, (3) Solid metal contraction.

24. Q: What is directional solidification?

A: A process where remote areas freeze first, progressing toward risers to minimize shrinkage voids.

25. Q: What causes gas porosity in castings?

A: Entrapped gases rejected during cooling due to lower solubility in solid metal.

#### Design and Engineering

26. Q: Why must a riser’s V/A ratio be higher than the casting’s?

A: To ensure the riser solidifies after the casting, feeding shrinkage.

27. Q: What does Bernoulli’s Theorem describe in casting?

A: The conservation of energy (pressure, kinetic, head) in fluid flow, used to calculate pouring velocity.

28. Q: How can aspiration in a sprue be prevented?

A: By tapering the sprue so the cross-sectional area adjusts with height.

29. Q: What is a general design rule for casting gates?

A: Gates should feed into thick sections of the casting.

30. Q: Why should casting designs avoid hot spots?

A: Hot spots (uneven sections) solidify last, causing shrinkage cavities.

Introduction and General Casting Processes

Q: What are the two main categories of casting processes?
A: Expendable mold processes and permanent mold processes.
Q: What is an advantage of expendable mold processes?
A: Ability to create more complex shapes.
Q: What is a disadvantage of permanent mold processes?
A: Geometries are limited by the need to open the mold.
Q: What is ingot casting used for?
A: Producing large metal blocks (ingots) for subsequent processing like rolling.
Q: How does continuous casting differ from ingot casting?
A: It produces a continuous strand of metal with uniform properties at a lower cost.

Sand Casting

Q: What is the most widely used casting process?
A: Sand casting.
Q: Name two metals that can be sand casted.
A: Steel and aluminum.
Q: What are three key properties of foundry sand?
A: Cohesiveness, strength, and permeability.
Q: What does "green" mean in green-sand molds?
A: The mold contains moisture at the time of pouring.
Q: What is the typical sand mixture for sand casting?
A: 90% sand, 3% water, 7% clay.
Q: What is a common pattern material for sand casting?
A: Wood.
Q: What is the purpose of a riser in sand casting?
A: To supply molten metal and prevent shrinkage during solidification.
Q: What are the five main steps in the sand casting process?
A: (1) Pour metal, (2) Solidify, (3) Break mold, (4) Clean/inspect, (5) Heat treat if needed.
Q: What is a sand casting defect caused by gas release?
A: Sand blow.
Q: What causes a mold shift defect in sand casting?
A: Sidewise displacement of cope and drag.

Other Expendable Mold Casting Processes

Q: What binds the sand in shell molding?
A: Thermosetting resin binder.
Q: What is an advantage of shell molding over sand casting?
A: Better surface finish and dimensional accuracy.
Q: What holds the sand together in vacuum molding?
A: Vacuum pressure, not a chemical binder.
Q: What is the pattern material in the expanded polystyrene process?
A: Polystyrene foam.
Q: What happens to the foam pattern in lost-foam casting?
A: It vaporizes when molten metal is poured.
Q: What is another name for investment casting?
A: Lost-wax process.
Q: What is the first step in investment casting?
A: Producing wax patterns by injection molding.
Q: Why is investment casting considered a precision process?
A: It produces high accuracy and intricate details.
Q: What material is used for the mold in plaster mold casting?
A: Plaster of Paris (gypsum).
Q: What limits plaster mold casting to low-melting-point metals?
A: Plaster cannot withstand high temperatures.
Q: What advantage does ceramic mold casting have over plaster mold casting?
A: It can cast high-temperature alloys like steel.

Permanent Mold Casting Processes

Q: What material is typically used for permanent molds?
A: Cast iron or steel.
Q: What is an advantage of permanent mold casting over sand casting?
A: Better dimensional control and surface finish.
Q: What distinguishes die casting from other permanent mold processes?
A: Molten metal is injected under high pressure.
Q: What type of die casting uses a piston to inject low-melting-point metals?
A: Hot-chamber die casting.
Q: What metals are commonly cast in hot-chamber die casting?
A: Zinc, tin, lead, and magnesium.
Q: How does cold-chamber die casting differ from hot-chamber?
A: Molten metal is poured into an unheated chamber before injection.
Q: What is slush casting used to produce?
A: Hollow ornamental objects like candlesticks.
Q: What force distributes metal in centrifugal casting?
A: Centrifugal force from mold rotation.
Q: What is produced by true centrifugal casting?
A: Tubular parts like pipes and tubes.
Q: What is an example of a part made by semicentrifugal casting?
A: Wheels.
Q: How does centrifuge casting differ from true centrifugal casting?
A: Part cavities are located away from the axis, not requiring radial symmetry.

Casting Quality and Defects

Q: What is a misrun defect in casting?
A: The casting solidifies before completely filling the mold cavity.
Q: What causes a cold shut defect?
A: Lack of fusion between two metal flows due to premature freezing.
Q: What is a shrinkage cavity defect?
A: A depression or void caused by solidification shrinkage.
Q: How can microporosity be reduced in castings?
A: By flushing with inert gas or melting in a vacuum.
Q: What inspection method detects obvious casting defects?
A: Visual inspection.

Product Design Considerations

Q: Why should sharp corners be avoided in casting design?
A: They cause stress concentrations and may lead to hot tearing.
Q: What is the typical draft angle for sand casting?
A: 1 degree.
Q: What is the purpose of a machining allowance in sand casting?
A: To provide extra material for machining to achieve required dimensions.
Q: Why should large flat areas be avoided in casting design?
A: They can warp during cooling and cause uneven metal flow.
Q: How does simplifying part geometry improve castability?
A: It reduces the need for cores and simplifies mold-making.
Q: What is the recommended draft angle for permanent mold casting?
A: 2 to 3 degrees.
Q: Why is a “flattest” parting line preferred in casting design?
A: It simplifies mold separation and reduces defects.
Q: Which casting process offers the best dimensional accuracy?
A: Die casting.

General Bulk Deformation

Q: What are bulk deformation processes?
A: Metal forming operations causing significant shape change by plastic flow of bulk forms like bars, billets, or slabs.
Q: Name the four basic bulk deformation processes.
A: Rolling, forging, extrusion, wire and bar drawing.
Q: What is a key benefit of hot working in bulk deformation?
A: Allows significant shape change due to reduced strength and increased ductility.
Q: How does cold working enhance bulk deformation parts?
A: Increases strength through strain hardening.
Q: What does "near net shape" mean in bulk deformation?
A: Parts require little or no subsequent machining.
Q: What are typical starting forms for bulk deformation?
A: Cylindrical bars, billets, rectangular billets, and slabs.

Rolling

Q: What is rolling in metalworking?
A: A process where slab or plate thickness is reduced by compressive forces between opposing rolls.
Q: What percentage of deformed materials undergo rolling?
A: Over 90%.
Q: What is flat rolling used for?
A: Reducing thickness of a rectangular cross section.
Q: What is shape rolling?
A: Forming a square cross section into shapes like I-beams or rails.
Q: What is the purpose of backing rolls in a four-high rolling mill?
A: To support smaller work rolls and reduce deflection.
Q: How does a tandem rolling mill operate?
A: Uses a sequence of two-high mills for continuous reduction.
Q: What is a common defect in flat rolling due to high friction?
A: Wavy edges.
Q: What causes alligatoring in rolling?
A: Excessive deformation or sticking leading to surface splitting.
Q: What is the role of camber in rolling mills?
A: Compensates for roll bending to ensure uniform strip thickness.
Q: Why is hot rolling more common than cold rolling?
A: It allows large deformations due to lower material strength.
Q: What improves in cold-rolled sheet compared to hot-rolled?
A: Surface finish and dimensional tolerances.
Q: What is thread rolling?
A: A cold working process to form threads on cylindrical parts using dies.
Q: What is an advantage of thread rolling over machining?
A: Stronger threads due to work hardening.
Q: What does ring rolling produce?
A: Thin-walled rings of larger diameter from thick-walled rings.

Rolling-Related Processes

Q: What is roll piercing used for?
A: Creating seamless tubes by exploiting internal cracks in a compressed bar.
Q: What controls the hole size in roll piercing?
A: A mandrel.
Q: What is roll forging also known as?
A: Cross-rolling.
Q: What are examples of roll-forged products?
A: Tapered leaf springs and knives.
Q: What happens in ball rolling?
A: Steel balls are formed by skew-rolling or upsetting for bearings.

Forging

Q: What is forging?
A: Controlled plastic deformation of metal into a predefined shape by pressure or impact.
Q: How old is the forging process?
A: Dates back to about 5000 BC.
Q: What is an advantage of forging over casting?
A: Work hardening increases strength.
Q: What are the three main types of forging dies?
A: Open-die, impression-die, flashless.
Q: What is open-die forging also called?
A: Upsetting or upset forging.
Q: What causes barreling in open-die forging?
A: Friction between work and die surfaces.
Q: What is the role of flash in impression-die forging?
A: Constrains metal flow to fill the die cavity.
Q: Why is impression-die forging often manual?
A: Requires skilled operators under adverse conditions.
Q: What is a limitation of impression-die forging?
A: Not capable of close tolerances; machining is often needed.
Q: How does flashless forging differ from impression-die forging?
A: No excess flash is created; the work is fully constrained.
Q: What is coining in forging?
A: A flashless process to mint coins with sharp details.
Q: What is upsetting used for?
A: Forming heads on nails, bolts, and similar hardware.
Q: What is swaging?
A: A process using rotating dies to taper a workpiece radially.
Q: What is a typical swaged product?
A: Tapered rods or tubes.
Q: What equipment applies an impact load in forging?
A: Drop hammers (gravity or power).

Forging Equipment and Economics

Q: What is the speed range of a hydraulic forging press?
A: 0.06-0.30 m/s.
Q: Which forging equipment has the highest speed range?
A: Counterblow hammer (4.5-9.0 m/s).
Q: Why are hydraulic presses expensive in forging?
A: High initial cost, though easier to maintain.
Q: When is forging more economical than casting for a connecting rod?
A: For large quantities.
Q: What reduces setup and tooling costs in forging?
A: Increasing the number of pieces forged with the same die.

Extrusion

Q: What is extrusion?
A: A process forcing metal through a die opening to form a uniform cross-sectional shape.
Q: What are the two basic types of extrusion?
A: Direct (forward) and indirect (backward/reverse).
Q: What is the "butt" in direct extrusion?
A: The small portion of billet that cannot be forced through the die.
Q: Why is indirect extrusion limited?
A: Lower rigidity of the hollow ram and difficulty supporting the extruded product.
Q: What enhances grain structure in cold extrusion?
A: Work hardening.
Q: What is a disadvantage of cold extrusion?
A: High stresses on machinery and die wear without lubrication.
Q: What defect can occur in extrusion with high friction?
A: Pipe (extrusion) defect.
Q: What is impact extrusion?
A: High-speed cold extrusion, often for collapsible tubes.
Q: What should be avoided in extruded cross-section design?
A: Sharp corners and non-uniform thicknesses.

Wire and Bar Drawing

Q: How does wire drawing differ from extrusion?
A: Work is pulled through the die instead of pushed.
Q: What is the typical cross-sectional shape in wire drawing?
A: Circular.
Q: What distinguishes wire drawing from bar drawing?
A: Wire drawing uses smaller diameter stock (down to 0.03 mm).
Q: What limits the maximum reduction per pass in drawing?
A: Draw stress exceeding the yield strength causes elongation instead of reduction.
Q: What is the purpose of annealing in wire drawing?
A: Relieves work hardening between dies.
Q: What is a common product of bar drawing?
A: Metal bars for machining or forging.