EXAM PAPER ON DESIGN OF MACHINE TOOLS Answer FIVE questions, taking ANY TWO from Group A, ANY TWO from Group Band All from Group C. Figures Figures in the bracket bracket indicate full marks. marks. Group A Q. 1 (a) Basic definition wise how is 'Machine tool' different from 'Mechanism' and 'Machine'? (4) 'Machine'? (4) (b)How is a centre lathe specified? specified? (4) (c) Name (c) Name the various various mechanisms mechanisms that are used to convert rotary motion motion into linear linear or translatory motion and give examples of application of those different mechanisms in machine tools. (10) (d) Why are almost all the lathes made horizontal and their Centre height from the floor is also more or less same and is around 1.0 metre. (2) Q. 2 (a) Why are Centre lathes provided with a speed gearbox and a feed gearbox? (4) (b)Draw a feasible Ray diagram and the corresponding gear layout for a speed gearbox to be used in a Centre lathe having 12 spindle speeds ranging from 20 rpm to 900 rpm. (12) (c) Show by a block diagram the major procedural steps that are followed in sequence while designing a machine tool. (4) Q. 3 (a) Draw schematically the kinematic diagram of a Centre lathe or a milling machine and briefly state the working principle of that machine tool (12) (b) Why and how the stroke length of a shaping machine is varied (or adjusted)? (4) (c) Why is lathe spindle made hollow'? (4) Q. 4 (a) What factors need to be considered during designing the body or structure of any machine tool? (4) (b)Why (b)Why is grey cast-iron preferably used to make lathe beds? (4) beds? (4) (c) Draw a cross sectional view of the bed of a medium duty Centre lathe and state the functions or purposes of the different features (surfaces) shown in that cross sectional view of the lathe bed. (8) (d)How is the table-feed controlled in a grinding machine having hydraulically driven worktable? (4) Group B Q. 5 (a) Sketch a centre lathe spindle showing its mounting in two bearings at its two ends and three gears of different size being rigidly mounted on that spindle. (b)What (b)What factors need to be considered while designing a lathe spindle for strength? (4) (c) Why and how the friction in between the worktable (slide) and the bed (guide) is reduced in heavy-duty machine tools. (4) tools. (4)
(d)State the working principle and the relative advantages of recirculating balls type feed screws being used in modern machine tools like CNC milling machines. (4) Q. 6 (a) What are the effects and possible causes of vibration in machine tools? (8) (b)What does machine tool chatter mean? How such chatter develops and can be controlled? (4) (c) State the purposes of mounting machine tools on proper foundations. (4) (d)What features and characteristics of a machine tool are checked and measured during its: (i) Geometrical test, (ii) Kinematic test, (iii) Idle run and (iv) Full load-running test? (4) Q. 7 (a) How can vibration in centre lathes be reduced without sacrificing productivity and product quality? (4) (b)Compare flexible automation with fixed automation with respect to their basic working principle in machine tools, advantages, limitations and applications. (8) (c) Usually when, where and by whom machine tools are thoroughly tested? (4) (d)What are the differences between Machine tool inspection and Machine tool testing?' (4) Q. 8 (a) With the help of a suitable sketch briefly describe the working principle of hydraulic copying lathe or copy milling machines. (8) (b)State the purposes of incorporating automation in machine tools. (4) 2009 DESIGN OF MACHINE TOOl.S (MC-424) Q. 1. ( a ) Ex plain how the machine tools are classified. Derive the expr ession for the machining time of any operation in the machine tools. Discuss the general requir ements of machine tool design. (8) ( b) What do you mean by o ptimum design criterion? Discuss the same considering two simple- su pported beams of mild steel and cast ir on of length l , br eadth b and depth d sub jected to a centr al concentric load P satisfying the following conditions: (8) (c) What ar e the advantages of all gear ed headstock ? Mention the r equir ements to be 'satisfied for ideal all gear drive. (4) Q. 2. (a) W hat is the function o f pressure valves? Draw a neat sket ch of a ball-ty pe pre ssure val ve and explain its principle o f o perat ion. ( 6 ) (b) Find the speed steps arranged in geometric pr ogression for the following conditions: 11min = 12 rpm, 11max = 510 rpm, and z = 8. (5) (c) Draw the cr oss-sectional view of the bed of a commonly used Centre lathe and state the functions of its important features. ( 4)
( d) Explain how the· sel ect ion of electric motor i s mad e on t he con sideration of overloading and heating. ( 5 ) Q. 3.(a) Draw the neat sketch of a rotary hydraulic dr ive and discuss its principle of operation. ( 4) ( b) Draw the cross- section o f milling machine column. Find out the t otal deflection at t he top of t he millin g machine column al ong wit h their limiting val ue. ( 6 ) ( c ) Discuss the k inematic advant ages of geometric pr ogr e ssion ( GP ) series. ( 6 ) ( d) Discuss how the module of the gear i s determined in machine t ool s. ( 4 ) Q. 4. (a) Ex plain in brief , with sketches, different gear transmi ssion s y st em s , u sed for tran smitt ing rotary motion. ( 4 ) (b) What d o you mean b y d ynamic stiffne s s and magni ficat ion fact or ? M ake the anal y sis when the (i) amplitud e o f the e xcit in g for ce i s independent of the excitin g frequenc y, and ( ii) amplitud e of the excitin g force depends upon the excit ing frequenc y. ( 6 ) ( c ) Make the analysis and design of tailstock assembly using the pr o por tions of tailstock as given by Nicolson and Smith. (6) (d) Discu ss the ad vanta ges of cone pulle y drive in machine tools. What ar e its limitations? (4) Group B Q. 5. ( a ) Discuss, with neat sketches, various types of sleeve bear ing used in a lathe. (4) (b) Discuss the slideways with hydraulic relief . What are its char acteristics? (5) ( c ) Dr aw a neat sk etch of t he cam- cont roll ed aut omat ic s y stem u sed in machine tools. E x plain it s working principle. ( 5) (d) Descr ibe t he acceptance tests for l athe s. (6) Q. 6. (a) Explain in brief, with sk etches, various methods used for adjustment of clear ances in slideways. (5) (b) Draw a neat sketch of the s peed changing mechanism of a jig boring machine and ex plain its principle of operation. (5) (c) Di scuss in brief the effect of vibration on the cuttin g condit ions. (5) (d) Expl ain var iou s instrument s r equired for accept ance te sts. (5 ) Q. 7. (a) What do you mean by aerostatic slideways? Discuss br iefly its o perating pr inciple along with its design aspects. (6) ( b) Der ive an e xpression to find out the diameter of the· s pindle subjected t o combined bending and twisting. (6) (c) Explain briefly the design pr inciples of push buttons with a sketch. (4) (d) What are the variou s source s o f vibr ation s? Ex plain any two of them brie fly. (4) Q. 8. (a) Ex plain in brief the importance of adaptive control system.
Draw a block diagram of a pr ocess o ptimization adaptive control system and explain its pr inciple of operation. (6) ( b) Explain briefl y the stick slip mot ion in guide s and its effect on the performance of machine tools. How is the stick slip motion minimized? ( 6 ) . (c) Discuss in brief, with sketches, the design principles of toggles. (4) (d) Discuss the hydrodynamic slideways. Find out me hydrodynamic force and maximum load carrying capacity in a wedge of infinity width. (4) Group C Q. 9. (A) Match the following: Machine Tool Common Ratio, (i) Heavy duty machine tools and automats (a) 1·26 (ii) Large- to- medium size general- purpose machine tools and automats (b) 1 ·41 iii) For milling machines, the drive and feed· motions are: (i) The coefficient of efficiency of belt drive with flat belt is (a) 0·98 (b) 0·96 (c)0·95 ( d) 0·90. (ii) The piston pumps in hydraulic transmission system is used for pressures up to (a) 250 N/cm2 (b) 1000 N/cm2 (c) 1400 N/cm2 (d) 1800N/cm2. ᶲ
List II (a) Generatrix (b) Grey cast iron as spheroidal graphite iron (c) Directrix (d) C-1045 steel (1 x6) Cutting motion Hollow-heavy duty spindles (iii) Tapered roller bearings (iv) (v) List I (1) Cylindrical roller bearings (ii) Feed motion (e) Both radial and axial loads (vi) Normal accuracy spindles (j) Radial loads only. (C) Choose the correct answer for the following: (1 x 10)
(iv) Medium- to-small size general- (d) 1·12. purpose machine tools (B) Match the following: Common Ratio, rp (a) 1·26 (a) rotary motion of the cutter and translatory motion of the workpiece, respectively. (b) rotary and translatory motion of the cutter, respectively (c) rotary motion of the workpiece and translatory motion of the cutting tool in the axial/ radial direction, respectively. (d) reciprocating motion of the cutting tool and intermittent translatory motion of the workpiece, respectively. (iv) The maximum spindle speed (in r.p.m) in turning is dependent on (a) the maximum possible diameter of the workpiece that can be admitted. (b) the miniumum required cutting speed for turning. (c) both the maximum possible diameter of the workpiece that can be admitted and the minimum required cutting speed for turning. (d) both the minimum economical diameter of the workpiece and the greatest possible cutting speed. (v) It is always desirable that the ratio between two corresponding steps, q>, should be Group A 1. (a) State the essential requirements of machine tools. Outline various factors affecting the selection of materials for machine tools. (b) What are the important elements of mechanical transmission? Explain each one of them briefly? 2.(a) How do you select range of speeds in the design of gear boxes? (b) What is support-drive? Explain. 3. (a) Discuss advantages .and disadvantages .of hydraulic regulation of machine tool drives. Describe the working of a hydraulic drive unit for rotary motions. (b) What is the effect of stiffness arrangement on the bending and torsional stiffness of box-type structure? 4. (a) What are the aspects to be considered while selecting welded vs. cast structure. What is the importance of combination of guide and guideway materials? (b) Define stress concentration factor. State the methods to reduce effect of stress concentration.
Group B 5. (a) Sketch and explain the tandem arrangement of spindle bearing of a horizontal boring machine? (b) What do you understand by the term 'stick-slip vibration' in machine tools? What is the purpose of scraping the cast iron guide and guideways after finish grinding operation. 6. (a) Why is preloading of spindle support bearing done? State the method of preloading radial ball bearing. (b) State the procedure for selecting ball bearing from manufacturer's catalogue. 7. (a) List the applications of hydraulic and pneumatic actuators and controls in machine tools. (b) Distinguish between steady load and cyclic load. Mention applications where these loads are occurred. 8. Write short notes on the following: (a) Ergonomics applied to machine tools (b) Acceptance tests of machine toots Group C 9. Write the answer for the following in brief: (i) Classify design work. (ii) Discuss basic requirements of a good machine tool design. (iii) What are the factors to be considered in the selection of the axis feed drive of a machine tool ? (iv) Name four mechanical stepless drivers. (v) Mention any three mechanisms that can convert rotary motion into translation. (vi) What are the requirements of a machine tool structure? (vii) How do you express life of bearing? (viii) What are the slideway profiles? (ix) What is meant by dynamic rigidity in terms of machine tool design? (x) What are the feed rate-dependent errors?
Group A 3 (a) Discuss various methods of increasing rigidity of 1 machine elements. (b) Differentiate between connection diagram and flow diagram for a gear box having four output speeds. Differentiate between the following: 4x5 (a) Static and dynamic stiffness (b) Stepped and step less drive
(c) Goodman's diagram and modified Goodman's diagram (d) Guideways and slideways. · Group B 5. (a) Discuss design of machine tool spindle subjected to combined bending and twisting. (b) Explain the following : (i) Stick slip motion in guides (ii) Chatter in machine tools 6. (a) Discuss objects and procedure for acceptance tests for machine tools and explain any two instruments used for it. (b) Describe various elements of control systems for machine tools. 7. (a) Explain standard acceptance test charts for a lathe. (b) Describe aesthetic and ergonomics as applied to machine tools with suitable examples. 8. (a) Discuss the effect of vibration on machine tools. (b) Explain the force analysis of lathe guideways. Group C 9. Explain the following in brief: (i) What is kinematic structure of machine tool? (ii). Explain speed structure-analysis. (iii) Differentiate between rigidity and. compliance of a machine tool. (iv) For what type of loads bearings are· designed? Explain. (v) Explain the application of hydrostatic bearings. (vi) What is ray diagram? (vii) Explain waviness meter. (viii) What is modular design? (ix) Describe the purpose of machine tool spindle," (x) Name the sources of machine tool vibrations. MC 424/PR414 (i50'9) DESIGN OF MACHINE TOOLS Group A 1. ( a) Classify working motions ~ a machine tool with neat sketches. (b) Explain important elementary transmissions being used in machine tools for transforming rotary motion into translator motion. 2. (a) Explain general requirements of a machine tool design in detail.
(b) Write· the. layout formulae and sketch the 'layout for shaping, planning, drilling and br oaching machines. 3·(a) Design a nine s peed gear box having minimum and maximum s peed of 100 rpm and 630 rpm, respectively; Assume motor speed= 1400 rpm; The design should include structural diagram, s peed chart; gearing diagram and· number of gear teeth. (b) . Explain the electrical ste pless r egulation of speed and feed rates; 4. (a) Mention the factor s aff ecting stiffness of a machine tool structure and explain the methods of impr oving it ( b) Compare welded and cast structur e with r espect to the ap plication in machine tool structures. 5. (a) Discuss the phenomenon of deflection of spindle axis due to com pliance of s pindle su p ports. ( b) · Explain the methods of pr e-loading cylindrical and taper -roller bearing. 6. (a) Classify the guides used in machine tools. ( b) Explain the design pr ocedure of slideways based on Stiffness 7. (a) Explain the method of determining the 'dynamic character istics 'of a machine tool structure using exper imentation. (b) Discuss the eff ects of forced vibration on the performance of a machine tool. 8. (a ) Explain the im portance of aesthetics and er gonomics on the design of machine tools. (b) Discuss various static measurements carried out for the acce ptance tests of machine tools. Group· C 9. · Answer the following in br ief : · (i) Classification of machine tools (ii) Required properties of mater ials for machine tools (iii) Elements of hydraulic transmission (iv) Aim of feed rate regulation (v) Choice of different sections of machine tools structures (vi) Functions of machine tools control systems (vii) Standardization of machine tools (viii).Chatter in machine tools (ix ) Factor influencing the dynamic stability of machine tools (x) Advantages of modular design.
