Mechanical Engineering UPSC PYQ 2025

(a-i) If the power source characteristic in a Metal Inert Arc welding process is Vp = 38 – I⁄60 and the arc characteristic is Va = 3La + 27, calculate the change in arc power when arc length changes from 1 mm to 3 mm. Also find the maximum arc length sustainable when source current limit is 300 A. (a-ii) An EDM process cuts a 6 mm deep cavity in high-carbon steel using (I) copper–tungsten and (II) copper electrodes. Taking wear ratios 9 : 1 and 3 : 1 respectively, determine the required spindle movement. (b-i) In ECM a 15 mm diameter, 125 mm deep hole is to be drilled in high-carbon steel. With 45 A current and 15 % NaCl electrolyte, find the machining time. Take valency of Fe = 2, atomic weight 56, density of steel 7·8 g cm⁻³. (b-ii) Using ECM to machine Nimonic-75 alloy (composition table given) and the lowest valency of dissolution for each element (data table given), compute the material-removal rate when current is 1050 A. (c) With a line diagram explain the different flow patterns used in plant layouts. State the conditions that must be satisfied by an ideal flow pattern.27:["$","d Change in arc power for arc-length change 1 mm → 3 mm and maximum sustainable arc length with 300 A current limit. [10M] EDM cavity 6 mm deep in high-carbon steel using Cu-W and Cu electrodes; determine spindle movement given wear ratios 9 : 1 and 3 : 1. [10M] ECM drilling of 15 mm × 125 mm hole in high-carbon steel; compute machining time at 45 A with 15 % NaCl electrolyte. [10M] For ECM of Nimonic-75 with current 1050 A, use composition and data tables to calculate material-removal rate. [10M] <!--qid:MAINS_2025_Mechanical_Engineering-I_Q6-->

(a) A low carbon steel stock of thickness 25 mm is to be rolled in two stages. In the first stage, the reduction is to be from 25 mm to 15 mm and in the second stage from 15 mm to 5 mm. Determine the minimum diameter of the rolls for the two stages if the maximum angle of bite is 35° for the first stage and 25° for the second stage. Also, calculate the required coefficient of friction in both the stages. (b) In an arc welding process of steel with a potential of 15 V, current of 150 A and travel speed of 5 mm s⁻¹, the cross-sectional area of joint is 15 mm². If heat required to melt the steel is 10 J mm⁻³ and heat-transfer efficiency is 0·75, calculate the melting efficiency. (c) In an automobile manufacturing industry the demand for a specific part was 250 in April, 100 in May and 200 in June. The forecast for April was 150. Calculate the forecast for the month of July with a smoothing constant of 0·25 using first-order exponential smoothing. (d) Five different products are manufactured in a mixed-model production line. The time required for each task (in seconds) is : Product-1 Product-2 Product-3 Product-4 Product-5 Task A 5 5 – 5 5 B 6 6 6 – 6 C 6 – 6 6 – D 7 7 – – 7 E – 4 4 4 – Each product requires a set of tasks. Calculate the total number of work-stations for this mixed-model assembly line if the cycle time is 15 s. (e) For the given dimensions of mated parts, determine the allowance, hole tolerance and shaft tolerance using the basic hole system. Hole : 57·50 mm, 57·52 mm Shaft : 57·47 mm, 57·45 mm23:["$","main",null,{"className <!--qid:MAINS_2025_Mechanical_Engineering-I_Q5-->

(a) In an orthogonal machining process of medium-carbon steel using an HSS tool with 9° rake angle, the following were observed: feed 0·25 mm rev⁻¹, cutting speed 250 m min⁻¹, depth of cut 1·5 mm, chip-thickness ratio 0·30, vertical cutting force 1100 N, horizontal cutting force 600 N. Calculate (i) shear force along shear plane, (ii) normal force on shear plane, (iii) friction force along rake surface, (iv) normal force along rake surface, (v) friction angle, (vi) work done in shear, (vii) work done in friction. (b) Annual demand for an item is 2400 units, unit cost ₹ 6. A 5 % discount is offered for orders of 500 units or more. Ordering cost is ₹ 32 per order and inventory carrying cost is 16 %. Determine whether accepting the discount is economical. <!--qid:MAINS_2025_Mechanical_Engineering-I_Q7-->

(a) What are the various computer languages used for NC machines? Explain the merits and limitations of each language. (b) A small manufacturing unit produces bolts and the weight of each bolt is measured. The target weight for a bolt is 60 g. A sample of 5 bolts is taken every day for 30 days. The weight (in grams) for the first 5 days is given below: Day Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 1 59·8 60·2 60·0 60·1 59·9 2 60·1 60·3 60·2 60·0 59·8 3 59·7 60·0 60·1 59·9 60·2 4 60·0 59·8 60·2 60·1 59·9 5 60·2 60·3 60·1 60·0 59·9 Calculate the control limits for the X̄ (X-bar) chart. The constant A₂ for a sample size of 5 is 0·577. (c) A certain component can be manufactured either by welding or by forging process. The factory has an order for 5,00,000 units. The costs involved for both methods of manufacturing are as follows: Welding Forging Fixed cost ₹ 15,000 ₹ 94,000 Variable cost per unit ₹ 5 ₹ 4·25 (i) Which is the most economical method of manufacturing the component? Draw the indicative graph also for BEP. (ii) What will be the loss if a wrong choice is made?29:["$","div","MAINS_2025_Mechanical_E <!--qid:MAINS_2025_Mechanical_Engineering-I_Q8-->