Part VI — Manufacturing and Production Engineering

Chapter 6: Casting, Welding, Machining and Metrology

6.1 Casting

Casting is a manufacturing process in which molten metal is poured into a mould cavity and allowed to solidify into the desired shape. Sand casting is the most widely used and versatile casting process, using a sand mould (typically green sand — a mixture of sand, clay, and moisture) formed around a pattern. Die casting uses reusable metal moulds (dies) under pressure, suitable for high-volume production of precision parts (commonly with non-ferrous alloys like aluminium and zinc). Investment casting (lost-wax casting) uses a wax pattern coated with a ceramic shell, which is then melted out before pouring molten metal, allowing very high dimensional accuracy and intricate detail.

6.2 Welding

Welding joins materials (usually metals) through localised melting/fusion. Arc welding uses an electric arc between an electrode and the workpiece to generate heat for fusion (e.g., Shielded Metal Arc Welding/SMAW, commonly known as "stick welding"). Gas welding (e.g., oxy-acetylene welding) uses a fuel-gas flame for heat. Resistance welding (e.g., spot welding) uses electrical resistance heating at the joint interface under applied pressure, widely used in sheet-metal fabrication (e.g., automotive body assembly).

6.3 Machining Processes

Machining removes material from a workpiece to achieve the desired shape and finish, typically via a lathe (rotating the workpiece against a stationary/moving cutting tool, used for turning cylindrical parts), a milling machine (using a rotating multi-point cutter against a workpiece, suitable for flat surfaces, slots, and complex shapes), and a drilling machine (producing round holes using a rotating drill bit). Cutting speed, feed, and depth of cut are the three fundamental machining parameters governing material removal rate, surface finish, and tool life.

6.4 Metrology (Measurement)

Metrology deals with precision measurement in manufacturing. A vernier caliper measures internal, external, and depth dimensions with a typical least count of 0.02mm (0.001 inch). A micrometer (screw gauge) provides finer precision, with a typical least count of 0.01mm, commonly used for measuring small, precise dimensions like wire diameter or sheet thickness. Limits, fits, and tolerances define the acceptable variation in manufactured part dimensions to ensure proper assembly and interchangeability of mating parts.

6.5 Practice Set — Manufacturing & Production Engineering (16 MCQs)

1. Casting is a manufacturing process in which:
   (a) Material is removed from a solid block (b) Molten metal is poured into a mould and solidified (c) Two metals are joined by localised melting (d) A metal sheet is bent into shape
2. Sand casting typically uses which type of mould material?
   (a) Steel dies exclusively (b) A sand mould, often "green sand" (c) Ceramic shells exclusively (d) Only wax patterns
3. Die casting is particularly suited for:
   (a) One-off, low-volume production (b) High-volume production of precision parts, often non-ferrous alloys (c) Only ferrous metals (d) Only very large components
4. Investment casting (lost-wax casting) is valued for:
   (a) Very high dimensional accuracy and intricate detail (b) Being the cheapest process for large simple castings (c) Requiring no pattern at all (d) Using only sand moulds
5. Shielded Metal Arc Welding (SMAW), commonly known as "stick welding," generates heat via:
   (a) A gas flame (b) An electric arc between electrode and workpiece (c) Electrical resistance heating under pressure only (d) Friction alone
6. Oxy-acetylene welding is an example of:
   (a) Arc welding (b) Gas welding (c) Resistance welding (d) Friction welding
7. Resistance (spot) welding is widely used in:
   (a) Automotive body sheet-metal assembly (b) Casting large iron blocks (c) Cutting threads on bolts (d) Measuring dimensions
8. A lathe machine is primarily used for:
   (a) Producing flat surfaces and slots (b) Turning cylindrical parts by rotating the workpiece against a cutting tool (c) Producing round holes only (d) Casting molten metal
9. A milling machine uses:
   (a) A rotating multi-point cutter against a workpiece (b) A stationary tool only (c) Molten metal poured into a mould (d) An electric arc for cutting
10. A drilling machine is primarily used to:
    (a) Produce round holes using a rotating drill bit (b) Cut external threads only (c) Cast molten metal (d) Weld two plates together
11. Which of the following are the three fundamental machining parameters?
    (a) Cutting speed, feed, and depth of cut (b) Voltage, current, and resistance (c) Pressure, temperature, and volume (d) Mass, length, and time
12. A vernier caliper typically has a least count of approximately:
    (a) 0.02mm (b) 0.2mm (c) 2mm (d) 20mm
13. A micrometer (screw gauge) typically provides finer precision, with a least count of approximately:
    (a) 0.1mm (b) 0.01mm (c) 1mm (d) 10mm
14. A micrometer is commonly used to measure:
    (a) Small, precise dimensions like wire diameter or sheet thickness (b) Very large distances like building lengths (c) Fluid flow rate (d) Electrical resistance
15. Limits, fits, and tolerances in manufacturing primarily ensure:
    (a) Proper assembly and interchangeability of mating parts (b) Reduced material cost only (c) Increased casting temperature (d) Faster welding speed
16. Which casting process uses a wax pattern coated with a ceramic shell, melted out before pouring metal?
    (a) Sand casting (b) Die casting (c) Investment casting (lost-wax casting) (d) Centrifugal casting

Answer Key

1.(b)

2.(b)

3.(b)

4.(a)

5.(b)

6.(b)

7.(a)

8.(b)

9.(a)

10.(a)

11.(a)

12.(a)

13.(b)

14.(a)

15.(a) 16.(c)