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Mechanical Engineering 2024 Paper I 50 marks Explain

Paper I — Q8

(a) Explain the principle of electric discharge machining (EDM) using suitable diagram. Describe the effect of process parameters…

(a)

Explain the principle of electric discharge machining (EDM) using suitable diagram. Describe the effect of process parameters of electric discharge machining on process performance characteristics such as material removal rate, tolerance and surface characteristics. 20 marks

(b)

XYZ corporation has given the following information on its capacity, sales and cost:

(i)

Current capacity = 100000 units

(ii)

At current level of operation, its margin of safety is 50% of its break-even point

(iii)

Contribution margin P/V ratio = 25%

(iv)

The unutilized capacity at present is 10000 units

(v)

Sales price is ₹ 40 per unit

Based on the above information, determine the break-even point in sales volume, fixed costs, variable costs per unit and margin of safety in units. 20 marks

(c)

A company is interested in locating a new facility in a target market and would like to know the most appropriate place in the target market to locate the facility. There are four supply points A, B, C and D in the locality which will provide key inputs to the new facility. A two-dimensional grid map of the target market in which we would like to locate a new facility along with the distance coordinates of four supply points is shown in the figure below. The annual supply from these four points to the proposed facility is 200, 450, 175 and 350 tons, respectively:

(Distance coordinates are in brackets)

Supply PointsCoordinates (Units)Annual Supply (tons)
A(125, 550)200
B(350, 400)450
C(450, 125)175
D(700, 300)350

Identify the most appropriate point in the grid map to locate the new facility using centre of gravity model. 10 marks

हिंदी में प्रश्न पढ़ें
(a)

उपयुक्त आरेख की सहायता से विद्युत निस्सरण मशीन (EDM) के सिद्धांत की व्याख्या कीजिए। विद्युत निस्सरण मशीन की प्रक्रिया प्राचलों (पैरामीटर्स) का इसके प्रक्रिया प्रदर्शन अभिलक्षणों, जैसे कि पदार्थ पृथक्करण दर, उपेक्ष्य त्रुटि (टॉलरेंस) तथा सतही अभिलक्षण, पर पड़ने वाले प्रभावों का वर्णन कीजिए। (20 अंक)

(b)

XYZ निगम ने अपनी क्षमता, बिक्री तथा लागत की निम्नलिखित जानकारी प्रदान की है :

(i)

मौजूदा क्षमता = 100000 इकाई

(ii)

संचालन के वर्तमान स्तर पर, इसकी सुरक्षा का मार्जिन इसके ब्रेक-ईवेन बिंदु का 50% है

(iii)

योगदान मार्जिन P/V अनुपात = 25%

(iv)

मौजूदा समय में अप्रयुक्त क्षमता 10000 इकाई है

(v)

विक्रय मूल्य ₹ 40 प्रति इकाई है

उपर्युक्त जानकारी के आधार पर, ब्रेक-ईवेन बिंदु बिक्री की मात्रा में, स्थिर लागत, परिवर्तनीय लागत प्रति इकाई तथा इकाई में सुरक्षा का मार्जिन ज्ञात कीजिए। (20 अंक)

(c)

एक कंपनी लक्षित बाजार में एक नई सुविधा (फैसिलिटी) स्थापित करने में रुचि रखती है और सुविधा का पता लगाने के लिए लक्षित बाजार में सबसे उपयुक्त स्थान जानना चाहती है। इलाके में चार आपूर्ति बिंदु हैं A, B, C और D, जो नई सुविधा के लिए मुख्य निवेश प्रदान करेंगे। लक्षित बाजार का एक दो-आयामी ग्रिड मानचित्र, जिसमें हम चार आपूर्ति बिंदुओं के दूरी निर्देशांक के साथ एक नई सुविधा का पता लगाना चाहते हैं, नीचे दिए गए चित्र में दर्शाया गया है। प्रस्तावित सुविधा के लिए इन चार बिंदुओं से वार्षिक आपूर्ति क्रमशः: 200, 450, 175 तथा 350 टन है :

(दूरी निर्देशांक कोष्ठक में हैं)

आपूर्ति बिंदुनिर्देशांक (इकाई)वार्षिक आपूर्ति (टन)
A(125, 550)200
B(350, 400)450
C(450, 125)175
D(700, 300)350

गुरुत्वाकर्षण केंद्र मॉडल का प्रयोग करके नई सुविधा का पता लगाने के लिए ग्रिड मानचित्र में सबसे उपयुक्त बिंदु की पहचान कीजिए। (10 अंक)

Q8 of the 2024 UPSC Mains Mechanical Engineering Paper I, as printed
The question as printed in the 2024 Mechanical Engineering paper
Evaluate your answer to this question → See all 2024 Mechanical Engineering questions

The figure this question refers to, in words

The question paper is a scan and the diagram did not survive as text. This is the figure as read from the original page — every component, value and label — so the question can be worked from the text below.

(b) Table with 4 columns and 11 rows. Header row: Sample, No. of Dissatisfied Customers, Sample, No. of Dissatisfied Customers. Row 1: 1, 10, 11, 6. Row 2: 2, 12, 12, 19. Row 3: 3, 8, 13, 10. Row 4: 4, 9, 14, 7. Row 5: 5, 6, 15, 8. Row 6: 6, 11, 16, 4. Row 7: 7, 13, 17, 11. Row 8: 8, 10, 18, 10. Row 9: 9, 8, 19, 6. Row 10: 10, 9, 20, 7.

(c) A two-dimensional Cartesian grid map with an X-axis and a Y-axis, both labeled 'Units'. The X-axis has tick marks at 100, 200, 300, 400, 500, 600, and 700. The Y-axis has tick marks at 100, 200, 300, 400, 500, and 600. Four points are plotted on the grid: Point A is located at coordinates (125, 550); Point B is located at coordinates (350, 400); Point C is located at coordinates (450, 125); and Point D is located at coordinates (700, 300). Each point is marked with a small circle and labeled with its corresponding letter.

Model answer

Drafted with AI by UPSC Answer Check against this question's marking rubric, to the expected length. UPSC does not publish answers for Mains — this is one way to score well, not an official key. How we build rubrics and answers.

(a) Electric discharge machining removes material by controlled thermal erosion, not by mechanical cutting. A conductive tool electrode and workpiece are held apart by a small dielectric-filled gap; a pulse generator applies short high-voltage pulses across the gap. When the dielectric breaks down, a spark discharge occurs, locally heating the workpiece to melting/vapourisation temperature. A tiny volume of metal is ejected, and the dielectric flushes debris, cools the zone and re-insulates the gap. A servo system maintains the gap by feeding the tool according to discharge conditions. In a suitable diagram, the tank contains dielectric, a pump circulates it, the pulse-generator circuit connects the tool and workpiece, and the tool-workpiece gap is shown.

Diagram: EDM schematic

How this answer will be evaluated

What earns full marks: Accurate calculations, clear diagrams, and correct application of models.

Evaluation rubric

Each sub-part is marked on its own, against the marks and word limit printed on the paper.

  1. (a) Principle of EDM with diagram; effect of process parameters on MRR, tolerance and surface characteristics. 20 marks

    explain— definition/context → points in order → small example → short close

    Must cover

    • Principle: spark erosion across dielectric gap; melting/vaporisation; flushing; servo gap control
    • Labelled diagram: pulse generator, tool, workpiece, dielectric, pump/filter, servo
    • Parameters: peak current, pulse on-time, off-time, voltage, polarity, dielectric/flushing
    • Effects: higher energy ⇒ higher MRR but rougher surface, thicker recast/HAZ, more tool wear, poorer tolerance (overcut)

    Loses marks

    • Describing it as a mechanical cutting process

    Earns more

    • RC relaxation vs transistorised generator
    • Tool materials (graphite, copper)

    Extra mark

    • Wire EDM mention
  2. (b) Break-even point, fixed cost, variable cost per unit and margin of safety for XYZ corporation. 20 marks

    calculate— given → formula → substitution → result with units → interpretation

    Must cover

    • Current sales = 100,000 − 10,000 = 90,000 units
    • MOS = 0.5 BEP and Sales = BEP + MOS ⇒ BEP = 60,000 units, MOS = 30,000 units
    • Contribution/unit = 25% × ₹40 = ₹10; VC = ₹30
    • Fixed cost = 60,000 × ₹10 = ₹6,00,000

    Loses marks

    • Taking MOS as 50% of sales

    Earns more

    • BEP in value = ₹24 lakh

    Extra mark

    • Profit at current level = ₹3 lakh
  3. (c) Centre-of-gravity location for a new facility with four supply points. 10 marks

    map— locate accurately → label → one line on why it matters

    Must cover

    • Weights 200, 450, 175, 350 (total 1175)
    • X̄ = 506,250/1175 ≈ 430.9
    • Ȳ = 416,875/1175 ≈ 354.8
    • Location ≈ (431, 355) marked on the grid

    Loses marks

    • Unweighted average of coordinates

    Earns more

    • Limitations of the CoG method

    Extra mark

    • Grid sketch with the point
What "Explain" is asking you to do

Make the working of something clear — what sets it off, what follows from what, and what it produces. Explain is the Commission's mechanism word: it dominates the technical papers and the “explain why” stems, where the marks sit in the causal chain and not in the label.

Structure that answers it

State what it is → the initiating condition → the chain of cause, step by step → an instance where it plays out → what the chain produces

Where marks are lost

Describing what something looks like instead of why it works that way. Naming the stages without linking them reads as description too.

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