GATE Past Year Questions: Forming | Manufacturing Engineering - Mechanical Engineering PDF Download

Q1: The "Earing" phenomenon in metal forming is associated with
(a) deep drawing
(b) rolling
(c) extrusion
(d) forging
Ans: (a)
Sol: 
Fig. Earning in a drawn steel cup, caused by the planar anisotropy of the sheet metal

In deep drawing, the edges of cups may become wavy, called earing. Ears are objectionable on deep-drawn cups because they have to be trimmed off, as they serve no useful purpose, and interfere with further processing of the cup, resulting in scarp. Earing is caused by the planar anisotropy of the sheet metal, and the number of ears produced may be two, four or eight, depending on the processing history and microstructure of the material. If the sheet is stronger in the rolling direction than transverse to the rolling direction, and the strength varies uniformly with respect to orientation, then two ears will form. If the sheet has high strength at different orientations, then more ears will form.

Q2: A cylindrical billet of 100 mm diameter and 100 mm length is extruded by a direct extrusion process to produce a bar of L-section. The cross sectional dimensions of this L-section bar are shown in the figure. The total extrusion pressure (p) in MPa for the above process is related to extrusion ratio (r) as
where σ_m  is the mean flow strength of the billet material in MPa, l is the portion of the billet length remaining to be extruded in mm, d₀ is the initial diameter of the billet in mm, and K is the die shape factor.
If the mean flow strength of the billet material is 50 MPa and the die shape factor is 1.05, then the maximum force required at the start of extrusion is ________ kN (round off to one decimal place).     (2022 Set - 2)

(a) 865.3
(b) 2429.3
(c) 2145.6
(d) 1254.5
Ans: (b)
Sol: 

Extrusion pressure will be maximum at the start of extrusion process where L₀ = 100mm

Q3: A 4 mm thick aluminum sheet of width w=100mm is rolled in a two-roll mill of roll diameter 200 mm each. The workpiece is lubricated with a mineral oil, which gives a coefficient of friction, μ=0.1. The flow stress (σ) of the material in MPa is σ=207+414ε , where ε is the true strain. Assuming rolling to be a plane strain deformation process, the roll separation force (F) for maximum permissible draft (thickness reduction) is _________ kN (round off to the nearest integer).
where  is average flow stress, L is roll-workpiece contact length, and  is the average sheet thickness.    (2022 Set - 1)
(a) 0.12
(b) 0.35
(c) 0.55
(d) 0.85
Ans: (b)
Sol: 
Initial thickness h₁ =4 mm Width w=100 mm
Roll Diameter D=200mm
Roll Radius R=100mm
Coefficient of Friction μ=0.1
Flow stress is given by σ=207+414ε

We have equation for maximum possible reduction is

Stress when material is rolled to maximum possible extent

Since Strain hardening characteristics is linear the average flow stress

Q4: The thickness, width and length of a metal slab are 50 mm, 250 mm and 3600 mm, respectively. A rolling operation on this slab reduces the thickness by 10% and increases the width by 3%. The length of the rolled slab is ________mm (round off to one decimal place).     (2021 Set 2)

(a) 3254.2
(b) 2453.6
(c) 5421.3
(d) 3883.5
Ans: (d)
Sol: 

 Q5: The size distribution of the powder particles used in Powder Metallurgy process can be determined by    (2021 Set 2)
(a) Laser scattering
(b) Laser reflection
(c) Laser absorption
(d) Laser penetration
Ans: (a)
Sol: 
Particle Size, Shape, and Distribution:

Particle size is generally controlled by screening, that is, by passing the metal powder through screens (sieves) of various mesh sizes. Several other methods also are available for particle-size analysis:

1. Sedimentation, which involves measuring the rate at which particles settle in a fluid.
2. Microscopic analysis, which may include the use of transmission and scanning- electron microscopy.
3. Light scattering from a laser that illuminates a sample, consisting of particles suspended in a liquid medium; the particles cause the light to be scattered, and a detector then digitizes the signals and computes the particle-size distribution.
4. Optical methods, such as particles blocking a beam of light, in which the particle is sensed by a photocell.
5. Suspending particles in a liquid and detecting particle size and distribution by electrical sensors.

Q6: A 200 mm wide plate having a thickness of 20 mm is fed through a rolling mill with two rolls. The radius of each roll is 300 mm. The plate thickness is to be reduced to 18 mm in one pass using a roll speed of 50 rpm. The strength coefficient (K) of the work material flow curve is 300 MPa and the strain hardening exponent, n is 0.2. The coefficient of friction between the rolls and the plate is 0.1. If the friction is sufficient to permit the rolling operation then the roll force will be _____kN (round off to the nearest integer).     (2021 set-1)
(a) 780
(b) 652
(c) 365
(d) 985
Ans: (a)
Sol:
Given: Width of plate, w = 200 mm
Thickness of plate, t₀ =20mm
Radius of roller, R = 300 mm
Reduced thickness of plate in one pass,
t_f =18mm
Rollers speed, N = 50 rpm
Strength coefficient, (K) = 300 MPa
Strain hardening exponent, n = 0.2
Coefficient of friction,  μ=0.1
Find: Roll force (F)

Q7:  There are two identical shaping machines S₁ and S₂. In machine S₂, the width of the workpiece is increased by 10% and the feed is decreased by 10%, with respect to that of S₁. If all other conditions remain the same then the ratio of total time per pass in S₁ and S₂ will be __________ (round off to one decimal place).   (2020 Set - 2)
(a) 1.2
(b) 0.6
(c) 0.8
(d) 0.2
Ans: (c)
Sol: 

Q8: A slot of 25 mm x 25 mm is to be milled in a workpiece of 300 mm length using a side and face milling cutter of diameter 100 mm, width 25 mm and having 20 teeth. For a depth of cut 5 mm, feed per tooth 0.1 mm, cutting speed 35 m/min and approach and over travel distance of 5 mm each, the time required for milling the slot is_______ minutes (round off to one decimal place).   (2020 Set -1)
(a) 1.61
(b) 8.1
(c) 40.5
(d) 16.5
Ans: (b)
Sol:

Q9: A strip of thickness 40 mm is to be rolled to a thickness of 20 mm using a two-high mill having rolls of diameter 200 mm. Coefficient of friction and arc length in mm, respectively are    (2020 Set -1)
(a) 0.45 and 38.84
(b) 0.39 and 38.84
(c) 0.39 and 44.72
(d) 0.45 and 44.72
Ans: (d)
Sol: 

Q10: The cold forming process in which a hardened tool is pressed against a workpiece (when there is relative motion between the tool and the workpiece) to produce a roughened surface with a regular pattern is    (2019 Set - 2)
(a) Roll forming
(b) Strip rolling
(c) Knurling
(d) Chamfering
Ans: (c)
Sol:  Knurling is the process of producing a straight angled cross lines by rolling using lathe machine. It is done by using one or more hard rollers that contain reverse of the pattern to be imposed.