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GENERAL-METAL-WORK-OBJ (TYPE A)
01-10: CCCDBCBACC
11-20: DCCADACBCC
21-30: BBDBCBDCCC
31-40: CACCADDAAD
COMPLETED
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INSTRUCTION: ANSWER (5) QUESTION ONLY
(1i)
(i) Arc welding uses an electric arc between an electrode and the base metal as its heat source, whereas gas welding utilizes the heat produced by the combustion of a fuel gas and oxygen flame.
(ii) Arc welding generates significantly higher temperatures up to 6000° or more while gas welding reaches a maximum temperature of approximately 3100°C to 3500°C.
(iii) The arc welding process is generally faster and more efficient for joining materials, whereas gas welding is a slower, less concentrated heating process.
(iv) Arc welding is suitable for a wide range of material thicknesses, including heavy plates, while gas welding is typically restricted to welding thinner sections (under 5mm).
(v) Gas welding equipment is highly portable, requiring only cylinders and a torch, whereas arc welding requires a power source and machine, which can limit mobility in certain scenarios.
(1ii)
(Draw the diagram)
(1iii)
(i) Produces cleaner welds because the molten pool is better protected and slag flows neatly behind the flame.
(ii) Gives better visibility of the weld area, making control of the molten pool easier.
(iii) Suitable for thin metals because it provides better heat distribution and reduces the risk of burn-through.
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(2a)
(i) Actual Size: This is the measured size of a manufactured part after production. It is the real dimension obtained with instruments such as a micrometer or vernier caliper, not the theoretical or nominal size.
(ii) Upper Limit: The maximum allowable size a part can have based on its specified tolerance. It is the highest acceptable dimension without rejecting the part.
(iii) Lower Limit: The minimum allowable size a part can have based on the specified tolerance. It is the smallest acceptable dimension that is still considered within specification.
(iv) Unilateral Dimension: A dimensioning system in which the tolerance is allowed in one direction only from the nominal size, either all above or all below the basic size, but not both.
(2b)
A force fit is a type of fit where the shaft is slightly larger than the hole, so the two parts can only be assembled using force, pressure, or heating. It produces a tight, permanent joint with high strength and no relative movement between parts.
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(3ai)
(i) Scriber
(ii) Try square
(iii) Surface plate
(iv) Marking gauge
(v) Punch (centre punch / dot punch)
(vi) Divider
(3aii)
SCRIBER USES:
(i) To mark precise lines on metal surfaces before cutting or machining.
(ii) To transfer measurements from a rule or gauge onto a workpiece.
(iii) To trace patterns or outlines for drilling, sawing, or filing.
TRY SQUARE USES:
(i) To check and mark accurate right angles (90°) on metal or wood surfaces.
(ii) To verify the squareness of edges and corners on a workpiece.
(iii) To serve as a straightedge for marking parallel or perpendicular lines.
(3b)
(Draw the diagram)
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(4ai)
(i) By Tailstock Set Over: The tailstock is slightly offset to create a taper along the workpiece.
(ii) By Compound Rest: The compound slide is set at an angle to the workpiece axis to cut a taper.
(iii) By Taper Turning Attachment: A special attachment guides the tool automatically along a taper.
(4aii)
(i) By Measuring the Diameter of the Workpiece: Using a vernier caliper, micrometer, or external gauge.
(ii) By Using the Lathe’s Dials and Feed Gear Settings: Reading the tool movement on the carriage or cross-slide scales.
(4b)
(i) Three-Jaw (Self-Centering) Chuck
(ii) Four-Jaw (Independent) Chuck
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(5ai)
Heat treatment is the process of heating and cooling metals in a controlled manner to alter their physical and mechanical properties, such as hardness, strength, toughness, and ductility, without changing their shape.
(5aii)
(i) Annealing
(ii) Hardening
(iii) Tempering
(5b)
Case hardening is a heat treatment process in which the surface layer of low-carbon steel is made hard while the core remains soft and tough. The process involves heating the workpiece in a carbon-rich environment so that carbon diffuses into the surface. After quenching in water or oil, the outer layer becomes hard and wear-resistant, while the inner core stays ductile and shock-absorbing. Case hardening is commonly used for tools, gears, shafts, and other machine parts that require a hard surface and a strong, tough core.
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(6a)
(i) Upsetting increases the thickness of a metal by compressing its length, whereas drawing down reduces the thickness by stretching or elongating it.
(ii) In upsetting, the metal becomes shorter and thicker, while in drawing down, it becomes longer and thinner.
(iii) Upsetting is usually done at the ends of bars or rods, whereas drawing down is done along the entire length of the workpiece.
(iv) Upsetting is commonly used for making bolt heads or rivets, while drawing down is used for making wires, rods, or tapered sections.
(6bi)
(Draw the diagram)
Uses:
(i) To deliver heavy blows to forge or shape metal.
(ii) To upset or draw out large pieces.
(6bii)
(Draw the diagram)
Uses:
(i) To smooth the surface of hot metal.
(ii) To even out irregularities after forging
(6biii)
(Draw the diagram)
Uses:
(i) To spread metal and create grooves.
(ii) To draw out the metal in specific sections.
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(7ai)
Vernier Caliper;
(i) Measures external dimensions of a workpiece.
(ii) Measures internal dimensions such as holes or slots.
(iii) Measures depths of grooves or steps.
(7aii)
Micrometer Screw Gauge;
(i) Measures small external dimensions with high accuracy.
(ii) Measures diameters of rods, wires, or shafts.
(iii) Measures thickness of small parts.
(7aiii)
Steel Rule;
(i) Measures straight lengths or distances.
(ii) Marks out lines on workpieces.
(iii) Provides quick, approximate measurement.
(7aiv)
Depth Gauge;
(i) Measures depth of holes, slots, or recesses.
(ii) Checks step differences on surfaces.
(iii) Marks accurate depths for machining.
(7b)
(Draw the diagram)
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