Mechanical
Joining processes are mainly classified on the basis of which factors?
- State of parent metals and temperature used
- Type of machine and operator skill
- Color of the parent metal
- Shape of the component only
Explanation:
- Joining processes are commonly classified according to the state of the parent metals and the temperature used during joining.
- Important joining processes include welding, brazing and soldering.
- In welding, the parent metal is generally melted or brought to a plastic/molten state at the joint.
- In brazing and soldering, the parent metals are not melted; only the filler metal melts.
Which joining process uses a filler metal whose melting temperature is above 450°C but below the melting temperature of the parent metals?
- Brazing
- Soldering
- Fusion welding
- Forging
Explanation:
- In brazing, the filler metal melts at a temperature above 450°C but below the melting temperature of the parent metals.
- The parent metals remain essentially solid during the process.
- Capillary action helps distribute the molten filler metal into the joint clearance.
In soldering, the filler metal generally melts at a temperature:
- Below 450°C
- Above 450°C and below the melting point of the parent metal
- Above the melting point of the parent metal
- Equal to the melting point of the parent metal
Explanation:
- Soldering is a low-temperature joining process in which the filler metal melts below 450°C.
- The parent metals are not melted.
- Common soft solders are based on tin alloys.
Which joining process generally produces a joint by melting the parent metal?
- Welding
- Soldering
- Brazing
- Adhesive bonding
Explanation:
- Fusion welding involves melting of the parent metal at the joint, with or without additional filler metal.
- The molten metal solidifies to form the welded joint.
- Brazing and soldering do not normally melt the parent metals.
Which process relies mainly on capillary action to distribute molten filler metal between closely fitted surfaces?
- Brazing
- Forging
- Arc welding
- Rolling
Explanation:
- Capillary action is an important mechanism in brazing.
- The molten filler metal flows into the narrow clearance between the components.
- Proper joint clearance and clean surfaces are important for obtaining a sound brazed joint.
Which of the following is a major advantage of brazing?
- It can join dissimilar metals with relatively low distortion
- It always melts the parent metals
- It requires no surface cleaning
- It can only join identical metals
Explanation:
- Brazing can join many dissimilar metals and produces comparatively low distortion because the parent metals are not melted.
- It is widely used for pipes, heat exchangers, carbide tools and electrical/mechanical assemblies.
Which of the following is commonly used as a flux in soldering?
- Rosin
- Cast iron
- Graphite electrode
- Aluminium oxide only
Explanation:
- Flux removes or prevents oxide films and promotes proper wetting of the surfaces.
- Rosin-based fluxes are commonly used in electrical soldering.
- Different applications may require different flux compositions.
What is the main function of flux in brazing and soldering?
- To remove/prevent oxides and improve wetting
- To increase the hardness of the parent metal
- To increase the melting point of the filler metal
- To act as the main structural metal
Explanation:
- Oxide films interfere with wetting and filler-metal flow.
- Flux helps remove or prevent such oxides and assists the filler metal in spreading over the joint surfaces.
Which welding process uses an electric arc as the principal source of heat?
- Arc welding
- Forge welding
- Cold welding
- Roll bonding
Explanation:
- Arc welding generates heat through an electric arc between the electrode and workpiece or between electrodes.
- The heat melts the joint region and, where applicable, the filler electrode.
In shielded metal arc welding, the electrode generally serves as:
- Both an electrode and a filler metal
- Only a cooling device
- Only a shielding gas source
- Only a clamping device
Explanation:
- In conventional shielded metal arc welding (SMAW), the consumable electrode conducts current and melts to provide filler metal.
- The electrode coating produces shielding gases and slag during welding.
What is the primary purpose of shielding in arc welding?
- To protect the molten weld pool from atmospheric contamination
- To increase cutting speed
- To cool the electrode rapidly
- To increase the weight of the weld
Explanation:
- Atmospheric oxygen and nitrogen can contaminate molten weld metal and cause defects.
- Shielding gases, fluxes or slag protect the weld pool from the atmosphere.
Which welding process uses a non-consumable tungsten electrode?
- TIG welding
- MIG welding
- Submerged arc welding
- Resistance spot welding
Explanation:
- TIG stands for Tungsten Inert Gas welding and is also called Gas Tungsten Arc Welding (GTAW).
- It uses a non-consumable tungsten electrode.
- Argon or helium, or mixtures containing them, are commonly used as shielding gases.
Which characteristic is associated with TIG welding?
- High-quality and precise welds using a non-consumable tungsten electrode
- Consumable wire electrode only
- Welding without shielding
- Use of mechanical pressure only
Explanation:
- TIG provides excellent control of the welding arc and weld pool.
- It is suitable for thin materials and applications requiring high weld quality.
- Filler metal may be added separately when required.
MIG welding primarily uses which type of electrode?
- Continuously fed consumable wire electrode
- Non-consumable tungsten electrode
- Carbon block electrode only
- Ceramic electrode
Explanation:
- MIG stands for Metal Inert Gas welding and is commonly associated with Gas Metal Arc Welding (GMAW).
- A continuously fed consumable wire electrode acts as the filler metal.
- Shielding gas protects the arc and molten weld pool.
Which shielding gas is commonly used in MIG welding?
- Argon
- Oxygen as the only shielding gas
- Nitrogen as the only shielding gas for all metals
- Hydrogen as the only shielding gas
Explanation:
- Argon is widely used in MIG/GMAW, particularly for non-ferrous metals and many steel applications.
- Carbon dioxide and argon-CO2 mixtures are also commonly used, especially for steels.
What is the major difference between TIG and MIG welding?
- TIG uses a non-consumable tungsten electrode, whereas MIG uses a continuously fed consumable wire
- TIG always uses a flux-coated electrode, whereas MIG never uses shielding
- TIG is a resistance welding process, whereas MIG is a forging process
- There is no difference
Explanation:
- TIG uses a non-consumable tungsten electrode.
- MIG/GMAW uses a continuously fed consumable wire electrode.
- TIG generally provides greater control, while MIG is well suited to higher deposition rates and productivity.
Gas welding commonly uses which fuel gas with oxygen?
- Acetylene
- Nitrogen
- Carbon dioxide
- Argon
Explanation:
- Oxy-acetylene welding is one of the most widely known gas welding processes.
- Oxygen supports combustion, while acetylene provides the fuel.
- The flame can reach a sufficiently high temperature for welding many metals.
Which flame is generally preferred for welding most steels in oxy-acetylene welding?
- Neutral flame
- Strongly oxidizing flame
- Strongly carburizing flame
- Cold flame
Explanation:
- A neutral flame has approximately balanced oxygen and acetylene.
- It is commonly used for welding mild steel and many other metals.
- Carburizing and oxidizing flames are used for specific materials and applications.
Which gas welding flame contains excess acetylene?
- Carburizing flame
- Neutral flame
- Oxidizing flame
- Plasma flame
Explanation:
- A carburizing or reducing flame contains excess fuel gas, such as acetylene in oxy-acetylene welding.
- It is useful for selected materials and applications where a reducing atmosphere is beneficial.
Which gas welding flame contains excess oxygen?
- Oxidizing flame
- Neutral flame
- Carburizing flame
- Reducing flame
Explanation:
- An oxidizing flame contains excess oxygen.
- It is used for certain materials such as some copper alloys, but it is generally unsuitable for ordinary steel because excessive oxidation can occur.
Resistance welding generates heat mainly due to:
- Electrical resistance to current flow
- Chemical reaction only
- Mechanical friction only
- Steam pressure
Explanation:
- Resistance welding uses electrical resistance heating at the joint.
- The heat generated is related to I2Rt, where I is current, R is electrical resistance and t is welding time.
- Pressure is applied to hold the workpieces together.
Which of the following is a resistance welding process?
- Spot welding
- TIG welding
- MIG welding
- Oxy-acetylene welding
Explanation:
- Spot welding is a resistance welding process.
- Other resistance welding processes include seam, butt and projection welding.
- Heat is generated by electrical resistance while pressure maintains contact.
In spot welding, the weld is formed between:
- Electrodes pressing overlapping sheets together
- A rotating cutting tool and workpiece
- Two gas flames
- A milling cutter and workpiece
Explanation:
- In spot welding, two or more overlapping sheets are placed between electrodes.
- Current passes through the sheets and generates heat at the contact region.
- Electrode pressure is applied during the welding cycle.
Which resistance welding process produces a continuous or nearly continuous weld using overlapping spots?
- Seam welding
- Spot welding
- Stud welding
- TIG welding
Explanation:
- Resistance seam welding uses wheel-type electrodes to produce overlapping weld nuggets.
- It is useful for making leak-resistant joints in sheet-metal products such as tanks.
Which welding process uses pressure along with resistance heating to join components end-to-end?
- Resistance butt welding
- TIG welding
- Gas welding
- Submerged arc welding
Explanation:
- Resistance butt welding joins components by resistance heating at their contacting ends followed by pressure.
- Flash butt welding is a related resistance welding process in which flashing occurs before forging the joint.
Which welding defect is a cavity or hole caused by trapped gas in the weld metal?
- Porosity
- Undercut
- Overlap
- Crater
Explanation:
- Porosity consists of gas cavities in solidified weld metal.
- It may result from contamination, inadequate shielding, moisture or improper welding parameters.
A groove melted into the base metal adjacent to the weld toe is called:
- Undercut
- Porosity
- Slag inclusion
- Blowhole
Explanation:
- Undercut is a groove formed in the base metal near the weld toe or edge of the weld.
- It reduces the effective cross-section and can act as a stress concentration.
Which welding defect occurs when non-metallic material becomes trapped inside the weld metal?
- Slag inclusion
- Porosity
- Undercut
- Crater
Explanation:
- Slag inclusion occurs when slag becomes trapped inside the weld.
- It can result from inadequate cleaning between passes or incorrect welding technique.
Incomplete fusion in welding means:
- Failure of weld metal to properly fuse with the base metal or previous weld bead
- Formation of a gas cavity
- Excessive penetration only
- Formation of a perfect weld
Explanation:
- Incomplete fusion occurs when the weld metal does not properly fuse with the sidewall, root or preceding weld bead.
- Insufficient heat input, improper electrode angle and excessive travel speed can contribute to this defect.
Which welding defect is caused when the weld does not extend sufficiently through the joint thickness?
- Incomplete penetration
- Porosity
- Undercut
- Overlap
Explanation:
- Incomplete penetration means the weld metal does not penetrate fully to the required depth at the joint root.
- It reduces the effective load-carrying area of the joint.
Which non-destructive testing method is particularly suitable for detecting surface and near-surface defects in ferromagnetic materials?
- Magnetic particle testing
- Radiographic testing
- Ultrasonic testing only
- Compression testing
Explanation:
- Magnetic particle testing (MT) is used mainly for ferromagnetic materials.
- A magnetic field is applied and magnetic particles accumulate at leakage fields caused by discontinuities.
- It is especially effective for surface and near-surface defects.
Which NDT method uses high-frequency sound waves to detect internal defects?
- Ultrasonic testing
- Visual testing
- Dye penetrant testing
- Magnetic particle testing
Explanation:
- Ultrasonic testing (UT) uses high-frequency sound waves transmitted into the material.
- Reflections from internal discontinuities are detected and analyzed.
- UT can detect internal flaws such as cracks, inclusions and lack of fusion.
Which NDT method is commonly used to detect surface-breaking defects in non-porous materials?
- Dye penetrant testing
- Ultrasonic testing
- Radiography
- Magnetic particle testing only
Explanation:
- Dye penetrant testing, also called liquid penetrant testing, detects surface-breaking discontinuities.
- The penetrant enters the surface opening by capillary action.
- It can be used on many non-porous materials, including non-ferromagnetic metals.
Which NDT method uses X-rays or gamma rays to inspect internal defects?
- Radiographic testing
- Dye penetrant testing
- Magnetic particle testing
- Visual testing
Explanation:
- Radiographic testing uses penetrating radiation such as X-rays or gamma rays.
- Differences in material thickness and density produce variations in the radiographic image.
- It can reveal internal defects such as porosity and inclusions.
Which of the following is generally classified as a destructive test?
- Tensile test
- Ultrasonic testing
- Radiographic testing
- Dye penetrant testing
Explanation:
- In a tensile test, the specimen is loaded until deformation and usually fracture occur.
- Therefore, it is a destructive test.
- UT, radiography and dye penetrant testing are non-destructive testing methods.
Foundry work is primarily concerned with:
- Producing components by pouring molten metal into moulds
- Joining metals only by soldering
- Removing material using cutting tools only
- Rolling metal sheets only
Explanation:
- Foundry processes involve melting metal and pouring it into a mould cavity having the desired shape.
- After solidification, the casting is removed and subjected to cleaning and finishing operations.
What is the function of a pattern in casting?
- To produce the mould cavity corresponding to the desired casting shape
- To melt the metal
- To remove slag from molten metal
- To measure hardness
Explanation:
- A pattern is a replica or representation of the desired casting shape, with appropriate allowances.
- The mould cavity is formed around the pattern.
- Pattern allowances may be provided for shrinkage, machining and other requirements.
Which casting process uses a permanent metal mould?
- Die casting
- Sand casting
- Shell moulding with disposable shell
- Investment casting
Explanation:
- Die casting uses a reusable metal die as the mould.
- Molten metal is injected under pressure into the die cavity.
- It is widely used for high-volume production of non-ferrous alloy components.
Which casting process commonly uses a disposable sand mould?
- Sand casting
- Permanent mould casting
- Die casting
- Centrifugal casting only
Explanation:
- Sand casting uses a sand mould that is generally broken to remove the solidified casting.
- It is versatile and suitable for a wide range of component sizes and metals.
In investment casting, the pattern is commonly made from:
- Wax or a similar expendable pattern material
- Permanent cast iron only
- Steel plate only
- Concrete
Explanation:
- Investment casting commonly uses wax patterns.
- The pattern is surrounded by refractory material to form the mould.
- The pattern is then removed before pouring the molten metal.
Which casting process is particularly suitable for producing hollow cylindrical components without using a conventional core?
- Centrifugal casting
- Sand casting only
- Investment casting only
- Drop forging
Explanation:
- In centrifugal casting, molten metal is introduced into a rotating mould.
- Centrifugal force distributes the molten metal against the mould wall.
- The process is particularly useful for pipes, liners and other cylindrical products.
Which casting defect is caused by shrinkage of metal during solidification when adequate liquid metal is not supplied?
- Shrinkage cavity
- Cold shut
- Blowhole only
- Scab
Explanation:
- Metals generally contract during solidification.
- If the contracting region is not adequately fed with molten metal, shrinkage cavities or porosity may develop.
- Proper riser design helps compensate for solidification shrinkage.
A casting defect caused by trapped gas is commonly called:
- Blowhole
- Cold shut
- Misrun
- Hot tear
Explanation:
- Blowholes are gas-related cavities formed when gases become trapped in the casting.
- Gas may originate from the mould, moisture, molten metal or inadequate venting.
When two streams of molten metal meet but fail to fuse properly, the casting defect is called:
- Cold shut
- Blowhole
- Shrinkage cavity
- Sand inclusion
Explanation:
- A cold shut occurs when two streams of molten metal meet but do not fuse properly.
- Low pouring temperature, poor fluidity or unsuitable gating can contribute to this defect.
A casting defect caused by insufficient filling of the mould cavity is called:
- Misrun
- Blowhole
- Hot tear
- Core shift
Explanation:
- A misrun occurs when molten metal solidifies before completely filling the mould cavity.
- Low metal temperature, slow pouring, thin sections or poor fluidity can contribute to misruns.
What is the primary purpose of a riser in a casting mould?
- To supply molten metal to compensate for solidification shrinkage
- To cool the casting rapidly
- To cut the casting
- To remove machining allowance
Explanation:
- A riser acts as a reservoir of molten metal.
- It feeds the casting during solidification to compensate for shrinkage.
- A properly designed riser should solidify after the region it feeds.
Forging is a manufacturing process in which metal is primarily shaped by:
- Compressive forces
- Tensile forces only
- Electrical resistance only
- Melting and solidification
Explanation:
- Forging shapes metal by applying compressive forces through hammers or presses.
- It can improve the mechanical properties of components by producing a favorable grain flow.
Which forging process uses repeated blows from a hammer?
- Hammer forging
- Press forging
- Extrusion
- Rolling
Explanation:
- Hammer forging applies impact loads repeatedly to deform the workpiece.
- Press forging applies relatively gradual compressive force using a press.
In open-die forging, the workpiece is deformed between:
- Dies that do not completely enclose the workpiece
- Two closed mould cavities containing molten metal
- Two welding electrodes only
- A drill and a workpiece
Explanation:
- Open-die forging uses dies that do not fully enclose the workpiece.
- The workpiece can be manipulated between successive strokes or pressing operations.
- It is suitable for large and relatively simple forgings.
Closed-die forging is also commonly known as:
- Impression-die forging
- Sand casting
- Deep drawing
- Extrusion welding
Explanation:
- In impression-die forging, the dies contain impressions corresponding to the desired component shape.
- The workpiece is forced to fill the die cavity under compressive loading.
- Flash may form at the die parting line in conventional closed-die forging.
Which is a major advantage of forging compared with casting for many load-bearing components?
- Improved mechanical properties due to favorable grain flow and reduced internal defects
- Always lower manufacturing cost
- No deformation of metal
- It requires melting the entire component
Explanation:
- Forging can produce favorable grain flow and can reduce certain casting-type defects.
- Forged components are widely used where high strength and toughness are important.
Extrusion is a manufacturing process in which a billet is:
- Forced through a die opening to produce a continuous product of constant cross-section
- Poured into a mould and solidified
- Joined using an electric arc
- Ground using abrasive particles
Explanation:
- In extrusion, a billet is forced through a die.
- The resulting product has a cross-section approximately corresponding to the die opening.
- Extrusion is commonly used to produce rods, tubes, channels and complex profiles.
In direct extrusion, the billet and ram generally move:
- In the same direction
- In opposite directions only
- Perpendicular to each other
- Randomly
Explanation:
- In direct or forward extrusion, the ram pushes the billet toward and through the die.
- The extruded product flows in the direction of ram movement.
In indirect extrusion, the extruded metal generally flows:
- In the direction opposite to the movement of the ram
- In the same direction as the ram in all cases
- Only vertically upward
- Without passing through a die
Explanation:
- In indirect or backward extrusion, the die is mounted on the ram and moves into the billet.
- The metal flows through the die in the direction opposite to the ram movement.
- Indirect extrusion can reduce friction between the billet and container wall.
Which process is commonly used for producing long products having a uniform cross-section?
- Extrusion
- Spot welding
- Forging only
- Sand moulding only
Explanation:
- Extrusion is well suited for long products with constant cross-sections.
- Examples include aluminium channels, rods, tubes and structural profiles.
Which joining process generally has the lowest joining temperature among welding, brazing and soldering?
- Soldering
- Brazing
- Fusion welding
- Arc welding
Explanation:
- Soldering generally uses filler metals melting below 450°C.
- Brazing uses filler metal above 450°C but below the melting temperature of the parent metals.
- Welding generally involves much higher temperatures and may melt the parent metal.
Which joining process generally does NOT melt the parent metals?
- Brazing and soldering
- Fusion welding only
- Arc welding only
- Gas fusion welding only
Explanation:
- In brazing and soldering, the filler metal melts while the parent metals remain essentially solid.
- In fusion welding, the joint is formed by melting the parent metal, with or without filler metal.
Which welding process is particularly suitable for welding thin sheets with high control and good weld quality?
- TIG welding
- Large-scale open-die forging
- Sand casting
- Cold rolling only
Explanation:
- TIG welding provides precise control over the arc and heat input.
- It is particularly useful for thin materials and high-quality weld applications.
- However, TIG generally has a lower deposition rate than MIG/GMAW.
Which welding process is generally preferred when a high deposition rate and continuous wire feeding are desired?
- MIG/GMAW
- TIG/GTAW
- Manual brazing
- Gas soldering
Explanation:
- MIG/GMAW uses a continuously fed consumable wire electrode.
- This enables relatively high deposition rates and productivity.
- It is widely used in fabrication and production welding.