Production Engineering - 2 - Mechanical Engineering MCQ

Gear finishing processes:

(1) Conventional finishing process for years:

i) Gear shaving

ii) Gear grinding

iii) Gear honing

iv) Gear lapping

v) Gear burnishing

vi) Gear skiving

(2) Advanced finishing processes for gears:

i) Gear finishing by electrochemical honing.

ii) Gear finishing by electrochemical grinding.

iii) Gear finishing by abrasive flow finishing (AFF).

Gear hobbing:

• It is the process of generating gear teeth by means of a rotating cutter referred to as a “hob”
• Hobbing can be used to produce spur, Helical, & worm gears, as well as splines in almost material (ferrous and non-ferrous metals & plastics), but not bevel or internal gears.

Helix angle is the angle between the leading edge of the land and the axis of the drill. It is also known as the spiral angle. The usual value of helix angle of a drill is 30°.

A feeler gauge is a tool used to measure gap widths. Feeler gauges are mostly used in engineering to measure the clearance between two parts.

They consist of a number of small lengths of steel of different thicknesses with measurements marked on each piece.

In thermit welding, chemical reaction takes place between Iron oxide and aluminum to produce aluminum oxide which is used as slag. Iron is produced which is used as filler material and heat is generated which is used as heat for melting of plates.

The working faces of the punch or die are ground off so that these don’t remain parallel to the horizontal plane but are inclined to it. This angle of inclination is called shear. This has the effect of reducing the area in shear at any one time and maximum force is much less. In sheet metal working, shear is provided on punches and dies so that press load is reduced.

Advantages of die casting process

1. Good grain structure

2. Low scrap cast

3. Good surface finish and better appearance

4. High dimensional accuracy

5. Repeated use of moulds

6. Rapid production rate

7. Low porosity

8. Lesser floor space required

A casting defect is an irregularity in the metal casting process that is undesired.

Classification of casting defects is given as:

For arc welding the main parameters are as follows:

Welding current: Welding current is the most influential parameter because it affects bead shape, controls the rate at which electrode is melted and therefore also controls the deposition rate, heat affected zone, the depth of penetration, and the amount of base metal melted.

Arc voltage: Welding voltage varies with the length of the arc between the electrode and molten weld metal. With the increase in arc length, the arc voltage increases.

Welding speed: Welding speed is the linear rate at which an arc is moved along the weld joint. With any combination of welding voltage and welding current, the effect of changing the welding speed confirms to a general pattern, the weld bead becomes smaller.

Electrode size: Electrode size affects the weld bead shape and the depth of penetration at fixed current.

Electrode work angle: The electrode may be held perpendicular to the workpiece or, tilted forward or backward with respect to the weld pool. As the arc stream tends to align itself along the axis of the electrode, the weld pool shape is different in each case, and so is the shape of the weld bead.

Bond commonly used in grinding wheels:

Vitrified bonded (V) wheels:

• Easy to form & compare of Clays & ceramic substances.
• Vitrified wheels are porous, strong, rigid & unaffectedly oils, water or temp. Over the ranges usually encountered in metal cutting that’s why vitrified bond is commonly used bond.

Silicate bonded (s) wheels:

• Use silicate of soda (water glass) as bond material.
• More brittle & not so strong as vitrified wheels.

Resinoid (B) wheels:

Provides shock absorption & elasticity.

Shellac bonded (E) wheels:

Used for making thin but strong wheels possessing some elasticity.

Produce high polish thus used for gridding such parts as camshafts & mill rolls.

Rubber bonded (R) wheels:

For making flexible wheels.

Operates at high speeds up to 16000 ft/mm. They are commonly used for snagging work in foundries & for thin cut off wheels.

Metallic Bonds (M):

For diamond wheels only.

Just like GTAW / TIG welding process, wherein a non-consumable electrode is used with inert gas as shielding, MIG welding employs the use of shielding gases such as Argon or Helium. MIG welding generally uses a mix of 25% Argon, 75% CO₂. Pure Argon can be used, but this mixture is cheaper.

Cast iron is used as material for base beds of heavy equipments because of its high damping capacity and compressed strength. Damping capacity is the relative ability of a material to absorb vibration.

Important G codes

G 00 – Rapid Transverse

G 01 – Linear Interpolation

G 02 – CW Circular Interpolation

G 03 – CCW Circular Interpolation

G 04 – Dwell

G – 97 – Spindle Speed

Important M codes

M 00 – Program Stop

M 03 – Spindle (CW)

M 04 – Spindle (CCW)

M 05 – Spindle Stop

M 08 – Coolant on

M 09 – Coolant off

M 10 – Clamp on

M 11 – Clamp off

M 02 or M 30 – Program stop, reset to start.

In hacksaw blade, teeth face forward. The saws are designed so the blade will cut when it’s pushed (the forward stroke) rather than when pulled.

Steel is used to make rails for railway lines. This steel must be hard wearing & resistance to crocking. These properties of steel depend upon the proportion of carbon & manganese that it contains. Carbon upto maximum of 0.82% and manganese, to a maximum of 1.7%, are needed to produce hard, wear resisting steels.

Carbon electrode works on DC. If the polarity is negative (straight) the arc will be stable, easy to maintain, uniform, and conical in shape. If the polarity is positive (reverse), the arc will be difficult to maintain and will leave a black carbon deposit on the surface of the base metal.

Crystal structure of Material

FCC: - Ni, Cu, Ag, Pt, Au, Pb, Al, Austenite or Ƴ-iron

BCC: - V, Mo, Ta, W, Ferrite or α-iron, δ-ferrite or δ-iron

HCP: - Mg, Zn,

Cobalt: - HCP < 420°C, FCC > 420°C

Chromium:- HCP < 20°C, BCC > 20°C

Glass: - Amorphous

The three different forms of iron are known as ferrite (α), stable until 910°C, austenite (γ), stable from 910° ‐ 1394°C and delta ferrite (δ), stable from1394° – 1539°C.

Electrical discharge machining (EDM) is a manufacturing process whereby a desired shape is obtained by using electrical discharges (sparks). Material is removed from the workpiece by a series of rapidly recurring current discharges between two electrodes, separated by a dielectric liquid and subject to an electric voltage. Quite often kerosene based oil is used as dielectric in EDM. The dielectric fluid is circulated through the tool at a pressure of 0.35 N/m² or less to free it from eroded metal particles. It is circulated through a filter.

Quality screw threads are produced by thread chasing.  This process is slow but can provide high quality. Multipoint chasing gives more productivity but at the cost of quality to some extent.

R = 2 mm

f = ?