ADVANCED MECHANICAL ENGINEERING CRAFT PRACTICE ANSWERS
SECTION A: ANSWER ALL QUESTIONS
Oxidation is a chemical process where a substance reacts with oxygen. When metal comes into contact with oxygen and moisture, it undergoes oxidation, resulting in the formation of rust. This is commonly seen with iron or steel. The oxygen in the air combines with the metal atoms, causing them to lose electrons. This process weakens the metal and leads to the formation of reddish-brown rust.
(PICK ANY FOUR)
(i) Wear appropriate protective gear, such as safety glasses, gloves, and hearing protection, to safeguard yourself from potential hazards.
(ii) Ensure that the machine is properly guarded with safety shields or barriers to prevent accidental contact with moving parts.
(iii) Before operating the machine, inspect it thoroughly for any signs of damage or malfunction. Report any issues to the appropriate personnel and do not use the machine until it has been repaired or replaced.
(iv) Follow proper lockout/tagout procedures when performing maintenance or repairs on the machine. This involves isolating the power source and securing it to prevent unexpected startup.
(v) Never wear loose clothing, jewelry, or long hair that could get caught in the machine’s moving parts. Keep a safe distance and avoid reaching into the machine while it is in operation.
(vi) Familiarize yourself with the machine’s operating manual and follow the manufacturer’s instructions for safe operation. If you’re unsure about anything, seek guidance from a qualified supervisor or trainer.
(PICK ANY TWO)
(iii) Wear Resistance
(iv) Heat Resistance
(v) Corrosive Resistance
(vi) Cost effectiveness
The term boring refers to a machining process used to enlarge or refine an existing hole or cylindrical opening. It involves using a cutting tool called a boring bar to remove material from the inner diameter of a workpiece, creating a more precise and accurate hole.
Boring is often used when a hole needs to be resized, straightened, or made smoother. It can also be used to create internal features such as grooves or threads. This process is commonly used in industries like automotive, aerospace, and manufacturing.
(PICK ANY TWO)
(i) Risk of Falling Objects:
The primary concern is the risk of falling objects. If the suspended machine or any components of it were to fail or become dislodged, there is a danger of heavy parts, tools, or materials falling from a height. This can cause serious injury or even be fatal to anyone standing underneath.
(ii) Equipment Failure:
Machines and equipment are subject to wear and tear, and they may fail unexpectedly. Components such as bolts, fasteners, or structural elements could give way, leading to a sudden collapse. Being under a suspended machine increases the likelihood of injury in the event of equipment failure.
(iii) Accidental Activation:
Some machines may have the potential for accidental activation or unexpected movement, especially during maintenance, testing, or malfunction. Standing underneath such a machine exposes individuals to the risk of being caught in moving parts or machinery unexpectedly starting.
(iv) Safety Regulations and Standards:
Occupational safety regulations and standards typically prohibit individuals from standing under suspended loads or machinery. Adherence to these guidelines is crucial to maintaining a safe working environment. Ignoring these regulations can result in legal consequences and, more importantly, poses a serious threat to personal safety.
(PICK ANY TWO)
(i) Ease of Assembly:
Studs simplify the assembly process compared to bolts.
(ii) Improved Alignment:
Studs help in maintaining accurate alignment between two components.
(iii) Reduced Risk of Cross-Threaded Fasteners:
Cross-threading, which occurs when the threads of a bolt or nut become misaligned and damaged during tightening, is less likely to happen with studs.
(iv) Easier Maintenance and Disassembly:
Studs can simplify maintenance and disassembly processes.
(PICK ANY FOUR)
(i) Reliability: It functions consistently and accurately, ensuring dependable performance.
(ii) Durability: It is built to withstand the demands of a workshop environment and has a long lifespan.
(iii) Precision: It provides accurate and precise measurements or outputs, allowing for precise work.
(iv) Efficiency: It is designed to maximize productivity and minimize waste of time and resources.
(v) Safety: It incorporates safety features and adheres to safety standards to protect users from harm.
(vi) Versatility: It can be used for various tasks and is adaptable to different workshop needs.
(i) Thermoplastic Material:
A thermoplastic material is a type of polymer that can be melted and reshaped multiple times without undergoing significant chemical degradation. When heated, thermoplastics soften and become more pliable, allowing them to be molded into different shapes. The molecular chains in thermoplastic polymers are not cross-linked, which means the material retains its ability to flow and reshape upon heating. Common examples of thermoplastics include polyethylene, polypropylene, polystyrene, and PVC (polyvinyl chloride). These materials are widely used in various applications, such as packaging, consumer goods, automotive components, and medical devices.
(ii) Thermosetting Material:
A thermosetting material is a type of polymer that, once cured or set, undergoes a chemical reaction that irreversibly hardens the material. Once formed, thermosetting plastics cannot be melted and reshaped. The curing process involves the formation of cross-links between polymer chains, creating a three-dimensional network structure. Thermosetting materials exhibit high strength, durability, and resistance to heat and chemicals due to their cross-linked structure. Common examples of thermosetting plastics include epoxy resins, phenolic resins, and melamine formaldehyde. These materials are often used in applications where high mechanical strength and dimensional stability are essential, such as in electrical components, adhesives, and composite materials.
(PICK ANY FOUR)
(i) Excellent Castability
(ii) High Wear Resistance
(iii) Good Machinability
(iv) Cost effectiveness
(v) Thermal conductivity
(vi) High Compressive Strength
The function of a brake in a system is to slow down or stop the motion of a machine or vehicle. It helps control the speed and ensure safety by providing friction or resistance against the moving parts. Brakes are commonly used in vehicles, machinery, and various mechanical systems to prevent accidents and allow for better control and maneuverability.
SECTION B: ANSWER FIVE(5) QUESTIONS ONLY
(i) Increased Efficiency: Fixtures help improve production efficiency by providing a secure and precise setup for the workpiece. This reduces setup time and allows for faster and more accurate machining.
(ii) Enhanced Quality: By securely holding the workpiece in place, fixtures help maintain consistency and accuracy during manufacturing. This leads to higher quality products and reduces the likelihood of errors or defects.
(i) Cost: Designing and manufacturing fixtures can be costly, especially for complex or specialized applications. The initial investment in fixtures may require careful consideration of the overall production costs.
(ii) Limited Flexibility: Fixtures are designed for specific parts or processes, which means they may not be easily adaptable to different workpieces or production requirements. This lack of flexibility can be a disadvantage if frequent changes or customization are needed.
(i) Material Selection: Choosing the right material for the jig is crucial. Factors such as strength, durability, and resistance to wear should be considered based on the specific application and expected usage of the jig.
(ii) Design Optimization: Before finalizing the jig, it’s important to consider factors such as weight, size, and ease of use. Optimizing the design can help ensure efficient operation, minimize operator fatigue, and improve overall productivity.
Material testing is necessary for several reasons:
(i) Quality Assurance: Material testing ensures that the materials used meet the required standards and specifications. This is essential to guarantee the quality and reliability of the final product.
(ii) Safety: Testing materials help identify their mechanical properties and behaviors under different conditions. This information is critical for ensuring the safety of structures, machinery, and products.
(iii) Performance Assessment: Material testing provides insights into how materials perform under various stress, temperature, and environmental conditions. This information helps engineers and designers select materials that will perform optimally in specific applications.
(iv) Research and Development: Material testing is a fundamental aspect of research and development, allowing scientists and engineers to explore new materials and improve existing ones. Understanding material properties is essential for innovation and progress in various industries.
(v) Cost Efficiency: By testing materials, manufacturers can identify the most cost-effective options without compromising on quality. This can lead to optimized production processes and reduced costs.
(vi) Compliance with Regulations: Many industries have strict regulations and standards regarding the materials used in their products. Material testing ensures that these standards are met, helping companies comply with legal requirements.
(i) Tensile test: A tensile test is a type of material testing that measures the strength and behavior of a material when subjected to tension or pulling forces. It involves applying a gradually increasing load to a sample until it reaches its breaking point.
(ii) Impact test: An impact test is a type of material testing that measures the ability of a material to withstand sudden loading or impact forces. It involves striking a standardized specimen with a pendulum or hammer to simulate real-world impact conditions.
(i) Low friction
(ii) High Hardness (iii) Good wear Resistance
(iv) High Load carrying Capacity
The material commonly used in the manufacture of ball bearings is chrome steel. Chrome steel is a high-carbon alloy steel that contains chromium, which contributes to its hardness, wear resistance, and corrosion resistance. It is well-suited for ball bearings due to its combination of strength and durability.
The purpose of a bearing on a machine is to support and facilitate the smooth rotation or movement of a shaft or component. Bearings reduce friction and allow for efficient transfer of loads, ensuring proper alignment and minimizing wear and tear on the machine’s moving parts.
(i) A file without handle:
Using a file without a handle is not advisable because it can compromise the user’s safety. A file handle provides a secure grip and control over the tool. Without a handle, there is an increased risk of the file slipping from the user’s hand, leading to potential injuries. Additionally, a handle allows for better maneuverability and precision during filing.
(ii) Hammer with mushroom surface:
A hammer with a mushroomed surface (a deformed or flattened striking face) is not suitable for use because it poses safety risks. The mushroomed surface can cause metal splinters or fragments to break off during use, posing a hazard to the user and others in the vicinity. It can also result in less effective striking due to the deformed surface, leading to inefficient and unsafe work.
If a hacksaw blade is broken while cutting, it is not advisable to continue cutting in the same spot after fixing another blade because the broken blade may have caused damage to the material being cut. Continuing in the same spot can result in an uneven or compromised cut, and it may also put excessive strain on the new blade, leading to further breakage. It is recommended to start cutting from a fresh spot to ensure a clean and effective cut.
(i) Choose a tap that is specifically designed for cutting M10 threads. Ensure that the tap is in good condition and has the correct thread pitch.
(ii) Secure the workpiece in a suitable holding device such as a vise to prevent movement during the tapping process.
(iii) Use a drill bit that corresponds to the recommended drill size for M10 threads to drill a pilot hole in the workpiece. The hole should be centered and straight.
(iv) Place the tap into the tap wrench or a tapping handle. Ensure that the tap is aligned with the drilled pilot hole.
(v) Apply cutting fluid to the tap to lubricate the cutting edges and reduce friction.
(vi) Slowly and steadily turn the tap clockwise (right-hand thread) into the pilot hole.
(vii) While tapping, periodically rotate the tap counterclockwise to break the chips and prevent the tap from binding.
(viii) Use a depth gauge to check the depth of the tapped hole and ensure it corresponds to the required depth for M10 threads.
(ix) After completing the tapping process, use a thread chaser or a thread gauge to clean and verify the threads.
(i) A tapping guide or tapping fixture can be used to guide the tap perpendicular to the workpiece. This helps maintain the squareness of the tapped hole.
(ii) Ensure that the pilot hole is drilled accurately and perpendicular to the workpiece surface. A properly drilled pilot hole provides a starting point for the tap, ensuring the threads are cut perpendicular to the surface.
(iii) Before tapping, check the runout of the workpiece using a dial indicator. Minimize runout to ensure the tap enters the hole squarely.
(iv) While tapping, visually inspect the alignment of the tap to ensure it remains perpendicular to the workpiece. Adjust as needed to maintain squareness.
(v) Use precision tapping equipment, such as tapping heads or CNC tapping machines, that are designed to maintain the perpendicularity of the tap to the workpiece.
(vi) After tapping, use measurement tools such as a square or a coordinate measuring machine (CMM) to verify the squareness of the tapped hole.
The function of a micrometer screw gauge is to measure small distances or thicknesses with high precision. It consists of a calibrated screw and a thimble that allows for accurate measurements in increments as small as 0.01mm. It is commonly used in engineering, manufacturing, and scientific applications where precise measurements are required.
The function of valves used in engineering machines is to control the flow of fluids (liquids or gases) within a system. Valves can open, close, or partially obstruct the flow, allowing for regulation and control of the fluid. They are crucial components in various machines and systems, such as pipelines, engines, pumps, and hydraulic systems.
– Lapping is a process of rubbing two surfaces together with an abrasive slurry between them.
– It is primarily used to achieve a high degree of flatness, smoothness, and tight tolerances on surfaces.
– Lapping is commonly used in the manufacturing of precision parts, such as bearings, valves, and sealing surfaces.
– Honing is a process of using abrasive stones or tools to remove material from the surface of a workpiece.
– It is primarily used to improve the surface finish, size, and shape of cylindrical holes or bores.
– Honing creates a cross-hatch pattern on the surface, which aids in lubrication and improves the performance of components like cylinders, engine blocks, and hydraulic cylinders.
(i) Spirit Level:
Working Principle: A spirit level consists of a sealed tube partially filled with liquid (usually alcohol) and an air bubble. The tube is mounted with the bubble in the center. When the level is placed on a surface, the bubble moves to the highest point, indicating whether the surface is level.
Working Principle: A clinometer, also known as an inclinometer, measures the angle of slope or inclination of a surface. It typically consists of a protractor or a graduated scale and a leveling mechanism. By aligning the instrument with the slope, the angle of inclination can be read directly.
(iii) Engineer’s Block:
Working Principle: An engineer’s block, also known as a gauge block, is a precision measuring tool. It consists of a set of standardized metal or ceramic blocks of known dimensions. The principle involves stacking these blocks to achieve a specific height, allowing for precise measurements in various applications.
(iv) Straight Edge:
Working Principle: A straight edge is a tool used to check the straightness of surfaces. It is a flat, straight piece of material with accurately machined edges. When placed against a surface, any gaps or light visible between the straight edge and the surface indicate deviations from straightness.
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