About this previous year paper
Course: B.Tech (Mechanical Engineering)
Subject Code: NME402
Subject Title: Manufacturing Science & Technology – I
Exam Type: Theory (Semester IV, 2016–17)
Duration: 3 Hours
Maximum Marks: 100
SECTION – A (10 × 2 = 20 Marks)
Short questions testing conceptual fundamentals.
| No. | Question | Concept Summary |
|---|---|---|
| (a) | Classification of Manufacturing Process | Primary (casting, forming), Secondary (machining, joining), Tertiary (finishing, inspection). |
| (b) | Recrystallization | Replacement of deformed grains with new, strain-free ones upon heating (removes work hardening). |
| (c) | Forgeability | Ability of a material to undergo deformation without cracking. |
| (d) | Plane Stress vs Plane Strain | Plane stress: σz=0 (thin sheets); Plane strain: εz=0 (thick bodies). |
| (e) | Angle of Bite & Neutral Plane | Angle between roll radius and contact arc; Neutral plane = point where velocity of roll = metal. |
| (f) | Pattern Allowances | Shrinkage, draft, machining, distortion, shake/rapping. |
| (g) | Notching & Nibbling | Notching removes metal from edges; nibbling cuts contour by small successive notches. |
| (h) | Curing in Plastics | Polymer cross-linking process that hardens thermosetting plastics. |
| (i) | Steps in Casting | Pattern → Mould → Melting → Pouring → Solidification → Fettling. |
| (j) | Hot vs Cold Working | Hot: above recrystallization temperature; Cold: below it (increases strength, hardness). |
SECTION – B (5 × 10 = 50 Marks)
Medium-length analytical questions combining theory and practical understanding.
(a) Open vs Closed Die Forging
| Aspect | Open Die | Closed Die |
|---|---|---|
| Flow of Metal | Free (no complete confinement) | Confined within die cavity |
| Accuracy | Low | High |
| Cost | Cheap | Expensive |
| Examples | Shafts, rings | Bolts, gears |
Rolling Defects:
Wavy edges (uneven deformation)
Edge cracks (excessive tensile stress)
Zipper cracks (centerline tension)
Alligatoring (non-uniform flow)
(b) Jigs and Fixtures
Jig: Holds and guides tool (e.g., drill jig).
Fixture: Holds workpiece (e.g., milling fixture).
Types of Jigs: Plate, box, channel, sandwich, and indexing types.
(c) Punching vs Blanking & Force Relation
F=τs×Area=τsπdtF = \tau_s \times \text{Area} = \tau_s \pi d tF=τs×Area=τsπdt
If punch face has shear (s):
F=τsπdt1+stF = \frac{\tau_s \pi d t}{1 + \frac{s}{t}}F=1+tsτsπdt
where ddd = diameter, ttt = thickness.
Thus, shear reduces cutting force and tool wear.
(d) Design Considerations in Powder Metallurgy
Uniform pressure distribution during compaction.
Control of particle size, shape, and distribution.
Proper die design and lubrication.
Sintering temperature control to ensure bonding.
(e) Tresca & Von Mises Criteria
Tresca: σ1−σ3=2k\sigma_1 - \sigma_3 = 2kσ1−σ3=2k
Von Mises:
- (σ1−σ2)2+(σ2−σ3)2+(σ3−σ1)2=6k2(\sigma_1 - \sigma_2)^2 + (\sigma_2 - \sigma_3)^2 + (\sigma_3 - \sigma_1)^2 = 6k^2(σ1−σ2)2+(σ2−σ3)2+(σ3−σ1)2=6k2
Used to predict yielding in metals under complex loading.
(f) Types of Dies
Simple Die: One operation per stroke.
Compound Die: Two or more operations at one station.
Progressive Die: Operations at successive stations.
Combination Die: Cutting and forming together.
(g) Gating System
Consists of:
Pouring Basin
Sprue
Runner
Ingate
Riser
Ensures smooth metal flow and minimizes turbulence.
(h) Rolling Process
Principle:
Thickness reduced by compressive forces from rotating rolls.
Maximum Draft:
δmax=R(1−cosα)≈Rα22\delta_{max} = R(1 - \cos\alpha) \approx \frac{R\alpha^2}{2}δmax=R(1−cosα)≈2Rα2
where RRR = roll radius, α\alphaα = angle of bite.
SECTION – C (2 × 15 = 30 Marks)
Derivation and numerical problems testing applied concepts.
Q3. Wire Extrusion with Friction
Derive:
σ=Kln(DBDa)(1+B)\sigma = K \ln\left(\frac{D_B}{D_a}\right)(1 + B)σ=Kln(DaDB)(1+B)
where
DBD_BDB = inlet diameter,
DaD_aDa = outlet diameter,
μ\muμ = coefficient of friction,
α\alphaα = die half-angle,
B=μcotαB = \mu \cot \alphaB=μcotα,
KKK = shear yield stress.
Q4. Rolling Defects & Calculation
(i) Defects: Wavy edges, edge cracks, alligatoring, zipper cracks.
(ii) Calculation:
Given:
h1=15 mm,h2=12 mm,R=200 mmh_1 = 15 \, \text{mm}, h_2 = 12 \, \text{mm}, R = 200 \, \text{mm}h1=15mm,h2=12mm,R=200mm
α=h1−h2R=3200=0.122 rad≈7°\alpha = \sqrt{\frac{h_1 - h_2}{R}} = \sqrt{\frac{3}{200}} = 0.122 \, \text{rad} \approx 7°α=Rh1−h2=2003=0.122rad≈7°
Q5. Radial Stress in Deep Drawing
Derivation:
σr=Krlnrmr\sigma_r = \frac{K}{r} \ln \frac{r_m}{r}σr=rKlnrrm
where
KKK = strength coefficient, rmr_mrm = blank radius, rrr = instantaneous radius.
Summary
This NME402 – Manufacturing Science & Technology I paper comprehensively tests:
Metal forming fundamentals (rolling, extrusion, drawing, forging)
Casting design and allowances
Sheet metal operations (punching, blanking, deep drawing)
Powder metallurgy & plastic deformation theories