1MACHINE TOOLS LATHE: 1) Estimate the machining time to turn MS Rod from 4 cm dia to 3.5 cm dia for a length of 15 cm in a single cut. Assume cutting speed 30 m/min. feed 0.4 mm/ rev. Ans. 1.58 min 2) Find the time required to turn a 60mm dia rod into the dimensions shown, take cutting speed as 20 m/ min. f = 1.2 mm/ rev. All cuts are 3mm deep. Ans. 3.23 min 3) Find the time for threading on 3 cm spindle of M.S for length of 15 cm. The no. of threads to be cut are 3 / cm. The lathe runs at 88 rpm. Assume Approach and over travel are 0.5 cm each and no. of cuts for M.S. are 7. Ans. 3.85 min 4) Estimate the boring time to enlarge a spindle bore from diameter 30 mm to diameter 40 mm for a length of 100 mm taking cutting speed as 30 m/min, feed 0.01 cm/rev. All cuts are 2mm deep. a) 3.2 min b) 10.7 min c) 3.7 min d) 4.2 min Ans: B 5) A through hole of diameter 20 mm has to be drilled in a lathe in a rectangular plate of size 500 x 400 x 50 mm. Drills of diameter 10 mm and 20 mm are available. Assuming that the cutting speed is 10 m/min and the feed for drill is 0.2 mm/rev, calculate the drilling time. Neglect approach and over travel. Maximum material cut at a time cannot exceed 10 mm. a) 1.6 min b) 13 min c) 16 min d) 2.4 min Ans: D 6) A round plate of diameter 500 mm has to be faced on both sides to reduce it thickness from 30 mm to 20 mm. Depth of cut is 3 mm. Estimate the machining time. Cross feed is 0.05 cm/rev and plate rotates at 500 rpm. a) 1 min b) 2 min c) 4 min d) 3 min Ans: C 7) A square plate of size 300 x 300 mm has to be faced on both sides to reduce it thickness from 50mm to 40mm in two cuts per side. Cross feed is 0.05 cm/rev, plate rotates at 200 rpm. a) Estimate the machining time a neglecting corner lengths a) 1.5 min b) 6 min c) 3 min d) 9 min Ans: B b) Estimate the machining time including corner lengths a) 8.5 min b) 2.1 min c) 4.3 min d) 12.7 min Ans: A 8) The roughing speed and finishing speed for turning a job are 30 m/min and 60 m/min. The respective feeds are 0.24 mm/rev and 0.1mm/rev. The max depth of cut is 2 mm and min depth of cut is 0.75 mm. Take material constant is 1600 N/mm2. Calculate the power required for roughing and finishing in watts. Ans. Roughing Power = 384 W, Finishing Power = 120 W PREVIOUS QUESTIONS: 9. For cutting double start screw threads of pitch 2mm on a lathe, the thread cutting tool should have a feed of _______ Ans. 4 mm/rev Dr. G. R. C. PRADEEP Email:
[email protected] 2 10. Determine the transformation ratio (TR) of the gear train connecting the spindle and lead screw of 4 TPI required to cut 1mm pitch screw threads on a centre lathe. Ans. 20/127 11. Calculate a simple gear train to cut right hand threads of 1mm pitch on a lathe with lead screw of 3mm pitch. Ans. 20/60 with one idler 12. A non standard thread of pitch 3.175mm is cut on a lathe having lead screw of pitch 6mm. A change gear set is provided with lathe having following teeth: 20, 30, 40, 50, 60, 70, 80, 90,100, 110, 120, 127. The correct pairs of change gears (a/b x c/d) is ______ Ans. a/b x c/d = 127/40 x 20/120 13. Find the angle at which the compound rest should be set to turn a taper on a work piece having a length of 200 mm, diameters, 45 mm and 35 mm. Ans. 1.50 14. Find the amount of offset of tail stock required to turn a taper of length 400 mm when the diameters at the ends are 60 and 40 respectively. Ans. 10 mm 15. A medium carbon steel work piece is turned on a lathe at 50 m/min cutting speed, 0.8mm/rev feed and 1.5 mm depth of cut. What is MRR. Ans. 60000mm3/min 16. A shaft of length 90 mm has a tapered portion of length 55 mm. The diameter of the taper is 80 mm at one end and 65 mm at the other. If the taper is made by tailstock set over method, the taper angle and the set over respectively are. (a) 15032′ & 12.16mm (b) 18 032′ & 15.66mm (c) 11022′ & 10.26mm (d) 10032′ & 14.46mm Ans. (a) SHAPER: 1) In a shaper work, the length of the stroke is 200 mm. No. of double strokes per min. is 30 and ratio of return time to cutting time is 2:3 find the cutting speed. Ans. 10 m/min 2) Find the time required for taking a complete cut on a plate 600 x 900 mm, if the cutting speed is 9 m / min. The return time to cutting time ratio is 1:4, feed is 3mm, clearance at each end is 75mm. Ans. 31.25 min 3) Also find for the above problem Time required by cutting stroke, Return stroke time, and No. of double strokes required to complete the job. Ans. Time required by cutting stroke = 0.083 min Return stroke time = 0.021 min No. of double strokes required to complete the job = 300 4) Calculate the power in shaping a steel plate with a depth of cut 2.8 mm, cutting speed 65 m /min. Feed rate is 0.4mm and constant for HP conversion is 79 x 10-6 Ans. 5.75 H.P PREVIOUS QUESTIONS: 5. If the number of double strokes per minute in a shaper is calculated by (0.643 x Cutting speed in m/min) per length of stroke in m, the return speed is faster than cutting speed by _____ Ans. Faster by 40% Dr. G. R. C. PRADEEP Email:
[email protected] 3 6. The quick return mechanism used in a shaper has a rocker arm drive of length 200mm. If the crank radius is 50 mm and the offset between crank centre and rocker arm pivot is 20 mm, length of the stroke is __________ Ans. 1m 7. A 600 symmetrical V tool is used in shaping a work piece with a depth of cut of 0.1 mm and feed of 0.1 mm/stroke. The theoretical peak to valley height, in mm, of the surface produced is ___ a) 0.043 b) 0.067 c) 0.086 d) None Ans: C 8. A work piece of 2000 mm length and 300 mm width was machined by a planning operation with the feed set at 0.3 mm/stroke. If the machine tool executes 10 double strokes / min, the planning time for a single pass will be _______ a) 50 min b) 100 min c) 200 min d) 220 min Ans: B 9. A cast iron block of 200 mm length is being shaped in a shaping machine with a depth of cut of 4 mm, feed 0.25 mm/stroke, and the tool principal cutting edge angle of 300. Number of cutting strokes per minute is 60. Using specific energy for cutting as 1.49 J/mm3, the average power consumption in watts is _____ Ans. 298 W DRILLING: 1) At what speed a 20mm dia drill will run for cutting steel at 25 m /min surface speed? Ans. 398 RPM 2) A hole of 40mm dia and 50mm depth is to be drilled in a M.S. component. The cutting speed is 65m /min. feed rate is 0.25 mm /rev. Calculate a) Machining time b) material removal rate. Assume approach and O.T. = 3mm. Ans. a) 0.5 min b )163.4 cm3.min 3) Blind holes of dia 10 mm are to be drilled up to a depth of 50 mm at a speed of 600 rpm and feed 0.2 mm/rev. Point angle of drill is 1200. Machining time per hole is ____ Ans. 0.44 min. PREVIOUS QUESTIONS: 4. A drilling machine has to be designed with 8 spindle speeds ranging between 120 to 1200 rpm. The 5th spindle speed is ________ Ans N5 = 447 rpm 5. A component requires a hole which must be with in the two limits of 25.03 and 25.04 mm diameter. Which of the following statements about reamer size are correct? 1. Reamer size cannot be below 25.03mm 2. Reamer size cannot be above 25.04mm 3. Reamer size can be 25.04mm 4. Reamer size can be 25.03mm Ans. 1&2 6. A hole of 30 mm dia is to be produced by reaming. The min, dia. Possible is 30.00mm and max. dia. possible is 30.05mm. Which of the statement are correct? 1. The min. dia. of the reamer can be less than 30mm 2. The min. dia. of the reamer cannot be less than 30mm 3. The max. dia. of the reamer can be more than 30.05mm 4. The max. dia. of the reamer must be less than 30.05mm Ans. 2 & 4 Dr. G. R. C. PRADEEP Email:
[email protected] 4 MILLING: 1) Estimate the time required to prepare a square prism on a milling machine from a round block 90 mm in length and 40mm in dia, feed 25 mm / minute. Set up & Indexing time is 15 min. Added table travel = 10 mm. Ans. 31 min 2) Estimate the milling time to cut 60 teeth on a gear blank of 60 mm thick, feed 35 mm / minute and take set up time as 10 min. Assume table travel = 10 mm. Ans. 130 min 3) A slot is to be made on a milling machine with the help of a peripheral cutter, revolving at 120 rpm. Find the time required to prepare the slot in two cuts, if it is 2 cm deep and 10 cm long with a cutter of 8 cm dia. Assume feed as 0.5mm/rev. Neglect Over travel and assume clearance at exit is 0.5 cm. Ans. 4.38 min 4) A 20x5 cm. C.I. surface is to be faced on a milling machine with a face cutter having a dia of 10 cm. and 16 teeth. The cutting speed and feed are 50 m / min. and 5 cm / min. Determine the milling time for a roughing cut, rpm of cutter and feed per tooth. Ans. Time taken = 4.135 min.; RPM, N = 159 rpm; ft = 0.002 cm / tooth 5) A CNC vertical milling machine has to cut a straight slot of 10 mm width, 2mm depth b/w (0,0) and (100,100) on XY plane (Dimensions in mm) with a cutter of dia 10mm. Feed rate is 50 mm/min. Milling time in seconds is __________. Ans. 175.7 sec PRACTICE PROBLEMS: 6) A hexagonal prism is to be made in a milling machine from a round bar of diameter 60 mm and 100 mm length. The feed is 30 mm/min and set up time is 2 min per face. Estimate the machining time. Assume added table travel 10 mm. a) 24 min b) 20 min c) 32 min d) 34 min Ans: D 7) A splined shaft having 5 splines is to be produced in horizontal milling m/c. The spline slot dimensions are 100 x 15 x 3 mm. If feed is 25 mm/min, estimate the machining time assuming setup time is 15 min. Neglect over travel. Cutter dia is 15mm a) 21.2 min b) 36.2 min c) 20 min d) None Ans: B 8) A work piece of 100 x 50 x 25 mm has to be machined using a face milling cutter of diameter 60 mm and 20 teeth to reduce the thickness to 15 mm. The feed per tooth is 0.03 mm/tooth. The cutter rotates at 150 rpm. The depth of cut cannot exceed 5 mm. a) 2.52 min b) 1.26 min c) 1.1 min d) None Ans: A 9) A work piece of 200x150x50mm is to be machined using a face milling cutter of Ф 50 mm and 20 teeth to reduce the thickness to 45mm. The depth of cut cannot exceed 5 mm. Added table travel is 10mm. The feed per tooth is 0.02mm/tooth. The cutting speed is 50 m/min a) Determine the RPM of the cutter a) 1000 b) 320 c) 250 d) None Ans: B b) Determine the milling time. a) 5 min b) 1.7 min c) 3.4 min d) None Ans: A 10) Data for a slab milling operation are given below: Length of WP = 200 mm, Cutter Dia = 100 mm Dr. G. R. C. PRADEEP Email:
[email protected] 5 No. of teeth = 4, Cutter speed = 100 rpm Feed = 200 mm / min, Depth of cut = 2 mm Total clearance at entry and exit = 5mm. Neglect over travel. a) Mean undeformed chip thickness is _____________ b) Machining time for single pass in sec is __________ Ans. a) tavg = 71 µm b) T = 66 sec 11) A side and face cutter of 125 dia has 10 teeth. It operates at cutting speed 14m/min with table traverse 100 mm/min. Feed per tooth of cutter is _____________ Ans. ft = 0.28 mm 12) One brand of milling m/c has following index plates. Plate 1:- 15, 16, 17, 18, 19, 20, hole circles; Plate 2:- 21, 23, 27, 29, 31, 33, hole circles To make 28 teeth by simple indexing, what plate is suitable? Ans. Plate 2:- 1 full revolution + 9 holes in 21 hole circle. NTM: PREVIOUS QUESTIONS: (ECM) 1) During the electrochemical machining (ECM) of iron (atomic weight = 56, valency = 2) at current of 1000A with 90% current efficiency, the MRR was observed to be 0.26 gm/s. If Titanium (atomic weight = 48, valency = 3) is machined by the ECM process at the current of 2000A with 90% current efficiency, the expected MRR in gm/s will be ----- Ans.0.2984 gm/s 2) Electrochemical machining is performed to remove material from an iron surface of 20 mm x 20 mm under the following conditions: Inter electrode gap = 0.2 mm; Supply voltage (DC) = 12 V; Atomic weight of iron = 55.85, Valency of iron = 2; Specific resistance of electrolyte = 2 ohm-cm; Faraday’s constant = 96540 coulombs; the MRR in gm/s will be -- Ans. 0.3471 g/sec. 3) While removing material from iron (atomic weight = 56, valency = 2, density = 7.8 g/cc) by ECM, a MRR of 2 cc/min is desired. The current required for achieving this MRR is ------ Ans. 896.07 Amp 4) A researcher conducts ECM on a binary alloy (Density= 6000 kg/m3) of iron (atomic weight = 56, valency = 2) and metal P (atomic weight = 24, valency = 4). Faradays constant = 96500 coulombs /mole. Volumetric MRR of the alloy is 50 mm3/sec at a current of 2000A. The percentage of metal P in the alloy is -------- Ans. 25.48 % 5) Estimate the MRR (in cc/s) of an alloy containing 18% cobalt, 62% Nickel, 20% Chromium during ECM with a current of 500A. Density of alloy is 8.28 g/cc. The following data is available: Metal Gram Atomic Weight Valency Co 58.93 2 Ni 58.71 2 Cr 51.99 6 Ans. MRR = 1.24 x 10-2 cc/s PRACTICE PROBLEMS: (ECM) Dr. G. R. C. PRADEEP Email:
[email protected] 6 6) Calculate the MRR and electrode feed rate in the ECM of an iron surface that is 25mm x 25mm in cross section using Nacl in water as electrolyte. The gap between tool and work piece is 0.25 mm. Supply voltage is 12V DC. Specific resistance of electrolyte is 3 Ω-cm Valency of iron =2, Atomic weight = 55.85, Density = 7860 kg/m3. Ans. a) Metal Removal Rate = 0.0368 cm3/sec. b) Electrode feed rate = 3.53 mm/min 7) In ECM operation of pure iron, an equilibrium gap of 2 mm is kept. Determine the supply voltage, if the over voltage is 2.5V, resistivity of electrolyte is 50 Ω-mm, Set feed rate is 0.25mm/min. Z = 2, A = 56, Density = 7860 kg/m3. Ans. 13.78V PRACTICE QUESTIONS: (EDM) 1. In a RC type generator in EDM, the maximum charging voltage is 80 V and the charging capacitor is 100 µF. Determine spark energy. Ans. 0.32 J/cycle 2. If in a RC type generator in EDM, to get an idle time of 500 µs for open circuit voltage of 100 V and maximum charging voltage of 70 V, determine charging resistance. Assume C = 100 µF. Ans. R = 4.15 Ω 3. For a RC type generator in EDM to get maximum power dissipation during charging Vc = Vs x 0.716. Determine idle time for R = 10 Ω and C = 200 μF Ans. 2.51 milli sec 4. Determine on time or discharge time in EDM if Supply voltage = 100 V and Discharge voltage= 15 V, Spark energy = 0.5 J. Generator is expected for maximum power during charging. Machine resistance = 0.5 Ω. Ans. 0.15 milli sec PREVIOUS QUESTIONS: (EDM) 5. A titanium sheet of 5.0mm thickness is cut by a wire edm process using a wire of 1mm dia. A uniform spark gap of 0.5 mm on both sides is maintained during the cutting operation. If the feed rate of the wire in to the sheet is 20mm/min, the MRR in mm3/min is _______ Ans. MRR = 200 mm3/min 6. In EDM process using RC relaxation circuit, a 12 mm dia through hole is made in steel plate of 50 mm thickness using a graphite tool and kerosene as dielectric. Assume discharge time is negligible. Machining is carried under following conditions. Resistance = 40Ω. Capacitance = 20 µF, Supply voltage = 220 V, Discharge voltage = 110 V. a) The time for one cycle in milli sec is __________ b) Average power input in KW is _____________ Ans. a) Cycle Time = 0.55 milli sec b) Average power Input = 0.22 KW. NC MACHINES: 1. In a point to point control of NC machine, the slides are positioned by an integrally mounted stepper motor drive. If the specification of the motor is 1 deg/pulse and pitch of the lead screw is 3.6 mm, what is the expected positional accuracy. Ans. 10 µm. 2. A cylinder of 155 mm dia is to be reduced to 150mm dia in one turning cut with a feed of 0.15 mm/rev and cutting speed of 150 m/min on a NC lathe. What are the programmed feed rate and MRR. Ans. Programmed feed rate = 46.2 mm/min; MRR = 56250 mm3/min Dr. G. R. C. PRADEEP Email:
[email protected] 7 3. A DC servo motor is directly driving an NC table. The pitch of the lead screw of the table is 5mm. The motor rotates at 100 rpm for an applied voltage of 10V. If the voltage speed characteristic of the motor is linear, the applied voltage for a table speed of 3 m/min is _____. Ans. 60V 4. In a CNC feed drive, a stepper motor with step angle of 1.80 drives a lead screw with pitch of 2 mm. The BLU for this drive is _____. Ans. 10 µm 5. A stepper motor has 150 steps. The output shaft of the motor is directly coupled to a lead screw of pitch 4 mm which drives the table. If the frequency of pulse supply to the motor is 200Hz, the speed of the table (mm/min) is ______ Ans. 320 mm/min 6. The total angular movement (in degrees) of a lead screw with a pitch of 5 mm to drive the work table by a distance of 200 mm in a NC machine is _______ Ans. 144000 7. For a 3-axes CNC table, the slide along the vertical axis of the table is driven by a DC servo motor, via lead screw nut mechanism. The lead screw has a pitch of 5 mm. This lead screw is fitted with a relative (incremental) encoder. The BLU of the slide along the vertical axis of the table is 0.005mm. When the table moves along the vertical axis by 9mm, the corresponding number of pulses generated by the encoder is _______ Ans. 1800 pulses 8. A DC servo motor is coupled directly to a lead screw which drives an NC table. A digital encoder which emits 500 pulses per revolution is mounted on the other end of the lead screw. If the pitch of the lead screw is 5mm and the motor rotates at 600 rpm, calculate a) Linear velocity of the table b) BLU of the NC system c) The frequency of pulses transmitted by the encoder. Ans. a) 3 m/min b) 10 µm c) 5000 Hz NC PART PROGRAMMING: 1) A work piece shown in the figure has to be drilled with 3 holes at different places as shown. The depth of hole is 10mm and the cutting tool is positioned above the work surface. The feed rate is 200 mm/ min and spindle rotates at 1000 rpm. 2) A work piece shown in figure has to be machined along AB & BC in milling taking depth of cut as 5 mm. The feed rate is 200 mm/min spindle speed is 2000 rpm, cutter dia 10 mm. Dr. G. R. C. PRADEEP Email:
[email protected] 8 3) Prepare a part program for machining a rectangular contour of 200 mm x 150 mm size from a suitable blank of 5mm thickness. Also a reamed hole of ϕ16 mm has to be made centrally in the rectangular contour. Take feed and speed arbitrarily. 4. In finish machining of an island on a casting with CNC milling machine, an end mill of 10mm dia is used. The corner points of the island are (0, 0), (0, 30), (50, 30), (50, 0). By applying cutter radius compensation, the trajectory of cutter will be____ Ans. (-5, -5) (55, -5) (55, 35), (-5, 35) (-5, -5) 5) Make a program in Apt for the part shown in the figure. 6) Make a part program for the part shown using both tools of mill & drill. Assume plate thickness of 15mm and set point at (0, 20, 0) and Z = 0 at the surface of job. Dr. G. R. C. PRADEEP Email:
[email protected] 9 7) Make a program in Apt for the part shown in the figure. Assume suitable data. 8) Make a program in Apt for the part shown on the left in the figure. Assume suitable data. Assume thickness of work piece is 6 mm. Dr. G. R. C. PRADEEP Email:
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