Production Engineering - 1 - Mechanical Engineering MCQ

Chaplets are used to support the core inside the mould cavity. Chaplet also takes care of its own weight and overcomes the metallostatic forces.

Shot peening is a process specifically designed to enhance the fatigue strength of components which are subjected to high alternating stress. In shot peening, small spherical shots bombards the surface of the part to be finished.

Cold Shut or fold: A small crack at the corners and at right angles to the forged surface.

Cause: improper design of the die or due to less corner radius provided.

In powder metallurgy, by varying the compaction force the density of the product can be varied. That’s why the powder metallurgy is superior to casting.

There are various types of the resistance welding processes like spot welding, seam welding, projection welding, flash welding, percussion welding, upset butt welding etc.

Projections are little projected raised points which offer resistance during passage of current and thus generating heat at those points. These projections collapse under heated conditions and pressure leading to the welding of two parts on cooling. The operation is performed on a press welding machine and components are put between water cooled copper platens under pressure.

Gear hobbing is a multi point machining process in which gear teeth are progressively generated by a series of cuts with a hob. Both the hob and the work piece revolve constantly as the hob is fed across the face width of the gear blank.

Gear milling is a multi point machining process in which individual tooth spacing are created by a rotating multi edge cutter having a cross-section similar to that of the generated teeth (in volute). After cutting each space, the gear is returned to its original position, and the gear blank is indexed for the next cut.

So hobbing is faster than milling because several teeth cut at a time.

50H₇g₆ means basic size is 50 mm and the tolerance grade for the hole is 7 and for the shaft is 6.

Basic Size: The size with reference to which the limits of size are fixed.

Actual Size: Actual measured dimension of the part.

Here 50 is the basic size, not actual size.

Heat generated H = I² Rt

Where I is the current supply

R is the resistance

t is the time for which the current is supplied

H = (5500)² × 250 × 10^-6 × 0.15

= 1134 J

for Maximum production rate or Minimum production time,

A tap cuts or forms a thread on the inside surface of a hole, creating a female surface which functions like a nut.

A die cuts an external thread on cylindrical material, such as a rod, which creates a male threaded piece which functions like a bolt.

Twist drill is a rotating cutting tool, used for cutting holes in rigid materials.

End mills are tools which have cutting teeth at one end, as well as on the sides, they are used for a variety of things including facing an edge and cutting slots or channels. A drill bit can only cut in the axial direction, but a milling bit can generally cut in all directions.

Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. The process is called anodizing because the part to be treated forms the anode electrode of an electrical circuit. Anodic films are most commonly applied to protect aluminium alloys, although processes also exist for titanium, zinc, magnesium, zirconium etc.

Chromium in steel Increases strength, hardness, hardenability, and toughness, as well as creep resistance and strength at elevated temperatures.
It improves machinability and resistance to corrosion and it intensifies the effects of other alloying elements.
In hot-work steels and high speed steels,
it increases red-hardness properties

Flame or induction hardening are processes in which the surface of the steel is heated very rapidly to high temperatures (by direct application of an oxy-gas flame, or by induction heating) then cooled rapidly, generally using water; this creates a "case" of martensite on the surface.

Carburizing is a process used to case-harden steel with a carbon content between 0.1 and 0.3 wt% C. In this process steel is introduced to a carbon rich environment and elevated temperatures for a certain amount of time, and then quenched so that the carbon is locked in the structure.

Nitriding heats the steel part to 482-621°C (900-1,150°F) in an atmosphere of ammonia gas and dissociated ammonia. The time the part spends in this environment dictates the depth of the case. No quenching is done after nitriding.

Pig iron is the most basic form of iron used for making varieties of cast irons and steels. It is the crude form of iron extracted from iron ores by their smelting and reduction in the blast furnace.

Carbon percentage varies from 3.5 to 4.5% in pig iron. Carbon present in pig iron is either in free graphite form or in the form of iron carbide.

Tool signatures have 7 elements in both systems.

American Standards System (ASA) system ⇒ Back rake angle - side rake angle - end relief angle (ERA) - side relief angle - end cutting Edge angle - side Cutting Edge Angle - Nose Radius

Orthogonal Rake system (ORS) or International system ⇒ i (inclination angle) - α_n (Normal rake angle) - Side relief angle - end relief angle, end cutting edge angle - Approach angle - Nose radius

Best wire size in t

wo wire method

Where P = pitch

α = included angle

= 1.5 sec (30) = 1.732 mm

• The most common chrome steels contain from 0.5 to 2% chromium and 0.1 to 1.5% carbon. The chrome steel is used for balls, rollers and races for bearings.
• A Nickel-Chrome steel containing 3.25% nickel, 1.5% chromium and 0.25% carbon is much used for armour plates.
• Chrome nickel steel is extensively used for motor car crank shafts, axles and gears requiring great strength and hardness.

Diameter of cup (d) = 25 mm

Height (h) = 15 mm