IES 1996

MillingBy S K Mondal1VideoMillingMilling machines of various types are widely used for the following purposes using proper cutting tools called milling cutters:Flat surface in vertical, horizontal and inclined planesMaking slots or ribs of various sectionsSlitting or partingOften producing surfaces of revolutionMaking helical grooves like flutes of the drillsLong thread milling on large lead screws, power screws, worms etc and short thread milling for small size fastening screws, bolts etc.3Milling2-D contouring like cam profiles, clutches etc and 3-D contouring like die or mould cavitiesCutting teeth in piece or batch production of spur gears, straight toothed bevel gears, worm wheels, sprockets, clutches etc.Producing some salient features like grooves, flutes, gushing and profiles in various cutting tools, e.g., drills, taps, reamers, hobs, gear shaping cutters etc.4

Up milling and down milling

Video-1: Down milling

Video-2: down millingUp milling and down millingIn down milling, though the cut starts with a full chip thickness, the cut gradually reduces to zero. This helps in eliminating the feed marks present in the case of up milling and consequently better surface finish. Climb milling also allows greater feeds per tooth and longer cutting life between regrinds than the conventional milling.Up milling needs stronger holding of the job and down milling needs backlash free screw-nut systems for feeding.The basic function of milling machines is to produce flat surfaces in any orientation as well as surfaces of revolution, helical surfaces and contoured surfaces of various configurations. Such functions are accomplished by slowly feeding the workpiece into the equispaced multiedge circular cutting tool rotating at moderately high speed as indicated in Fig.shown in below. 7Advantages of Down Milling1. Suited to machine thin and hard-to-hold parts since the workpiece is forced against the table or holding device by the cutter.2. Work need not be clamped as tightly.3. Consistent parallelism and size may be maintained, particularly on thin parts.4. It may be used where breakout at the edge of the workpiece could not be tolerated.5. It requires upto 20% less power to cut by this method.6. It may be used when cutting off stock or when milling deep, thin slots.

8Disadvantages of Down Milling1. It cannot be used unless the machine has a backlash eliminator and the table jibs have been tightened.2. It cannot be used for machining castings or hot rolled steel, since the hard outer scale will damage the cutter.

9IES - 2007What is the process of removing metal by a milling cutter which is rotated against the direction of travel of the work piece, called?(a)Down milling(b)Up milling(c)End milling(d)Face milling

Ans. (b) just to remember: Up milling means after cutting, tool tooth with chip goes down

10IES - 1997Consider the following statements:In Up milling process,1.The cutter starts the cut from the machined surface and proceeds upwards.2.The cutter starts the cut from the top surface and proceeds downwards.3.The job is fed in a direction opposite to that of cutter rotation.4.The job is fed in the same direction as that of cutter rotation.Of these statements correct are:(a)1 and 3 (b)1 and 4 (c)2 and 3 (d)2 and 4

Ans. (a)11IES 2010 Assertion (A): Climb or down milling operation ensures smoother operation of the machine tool and longer tool life as compared to the conventional up milling operation.Reason (R): In climb or down milling operation, the rotational motion of the cutter as well as the feed motion of the work-piece are in the same direction, and the depth of cut is maximum at the entry point as the cutter engages the workpiece.(a) Both A and R are individually true and R is the correct explanation of A(b) Both A and R are individually true but R is NOT the correct explanation of A(c) A is true but R is false(d) A is false but R is true

Ans. (b)12IAS-2009 mainDefine the term feed in milling. [2-Marks]Classification of milling machines(a) According to nature of purposes of use:General purposeSingle purposeSpecial purpose(b) According to configuration and motion of the work-holding table / bedKnee typeBed typePlaner typeRotary table type

(a) According to nature of purposes of use: General purpose most versatile commonly used mainly for piece or small lot production Single purpose e.g., thread milling machines, cam milling machines and slitting machine which are generally used for batch or lot production. Special purpose these are used for lot or mass production, e.g., duplicating mills, die sinkers, short thread milling etc.

(b) According to configuration and motion of the work-holding table / bedKnee type: typically in such small and medium duty machines the table with the job/work travels over the bed (guides) in horizontal (X) and transverse (Y) directions and the bed with the table and job on it moves vertically (Z) up and down. Bed typePlaner typeRotary table type

14Classification of milling machines(c) According to the orientation of the spindle(s).Plain horizontal knee typeHorizontal axis (spindle) and swiveling bed typeVertical spindle typeUniversal head milling machine(d) According to mechanization / automation and production rateHand mill (milling machine)Planer and rotary table type vertical axis milling machinesTracer controlled copy milling machine,Milling machines for short thread millingComputer Numerical Controlled (CNC) milling machine

(c) According to the orientation of the spindle(s).Plain horizontal knee typeHorizontal axis (spindle) and swiveling bed typeVertical spindle typeUniversal head milling machine

(d) According to mechanization / automation and production rateHand mill (milling machine)Planer and rotary table type vertical axis milling machinesTracer controlled copy milling machine,Milling machines for short thread millingComputer Numerical Controlled (CNC) milling machine

15Classifications of milling cutters(a) Profile sharpened cutters where the geometry of the machined surfaces are not related with the tool shape, viz;i.Slab or plain milling cutter: straight or helical flutedii.Side milling cutters single side or both sided typeiii.Slotting cutteriv.Slitting or parting toolsv.End milling cutters with straight or taper shankvi.Face milling cutters.

16Classifications of milling cutters(b) Form relieved cutters where the job profile becomes the replica of theTool-form, e.g., viz.;i.Form cuttersii.Gear (teeth) milling cuttersiii.Spline shaft cuttersiv.Tool form cuttersv.T-slot cuttersvi.Thread milling cutter

17VideoSlab or Plain milling cutters

Slab or Plain milling cutters: -Plain milling cutters are hollow straight HSS cylinder of 40 to 80 mm outer diameter having 4 to 16 straight or helical equi-spaced flutes or cutting edges and are used in horizontal arbour to machine flat surface as shown in Fig. below.

19Side and slot milling cutters

Side and slot milling cuttersThese arbour mounted disc type cutters have a large number of cutting teeth at equal spacing on the periphery. Each tooth has a peripheral cutting edge and another cutting edge on one face in case of single side cutter and two more cutting edges on both the faces leading to double sided cutter. One sided cutters are used to produce one flat surface or steps comprising two flat surfaces at right angle as shown in Fig. below. Both sided cutters are used for making rectangular slots bounded by three flat surfaces. Slotting is also done by another similar cutter having only one straight peripheral cutting on each tooth. These cutters may be made from a single piece of HSS or its teeth may be of carbide blades brazed on the periphery or clamped type uncoated or coated carbide inserts for high production machining.

20Slitting saw or parting tool

Slitting saw or parting tool (Fig. shown in below)These milling cutters are very similar to the slotting cutters having only one peripheral cutting edge on each tooth. However, the slitting saws Are larger in diameter and much thin possess large number of cutting teeth but of small size Used only for slitting or parting.

21End milling cutters or End mills

The shape and the common applications of end milling cutters (profile sharpened type) are shown in Fig. below. The common features and characteristics of such cutters are: Mostly made of HSS 4 to 12 straight or helical teeth on the periphery and face Diameter ranges from about 1 mm to 40 mm Very versatile and widely used in vertical spindle type milling machines End milling cutters requiring larger diameter are made as a separate cutter body which is fitted in the spindle through a taper shank arbour as shown in the same figure.

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Face milling cuttersFace milling cuttersThe shape, geometry and typical use of face milling cutters are shown in Fig. below.The main features are:Usually large in diameter (80 to 800 mm) and heavy Used only for machining flat surfaces in different orientationsMounted directly in the vertical and / or horizontal spindlesCoated or uncoated carbide inserts are clamped at the outer edge of the carbon steel body as shownGenerally used for high production machining of large jobs.

23Use of form relieved cutters (milling)

Use of form relieved cutters (milling)The distinguishing characteristics of such cutters, in contrast to profile sharpened cutters, are;Form of the tool is exactly replica of the job-profile to be made.Clearance or flank surfaces of the teeth are of archemedian spiral shaped instead of flat.Teeth are sharpened by grinding the rake surface only.Used for making 2-D and 3-D contour surfaces.The configurations and applications of several form relieved type milling cutters of common use are briefly presented. Form cuttersSuch disc type HSS cutters are generally used for making grooves or slots of various profiles as indicated in Fig. below.Form cutters may be also end mill type like T-slot cutter as shown in Fig. below.

24Tool form cutters

Form milling type cutters are also used widely for cutting slots or flutes of different cross section e.g. the flutes of twist drills (Fig. shown in below), milling cutters, reamers etc., and gushing of hobs, tabs, short thread milling cutters etc.

25T- slot cutter

26Gear teeth milling cutters

Gear milling cutters are made of HSS and available mostly in disc form like slot milling cutters and also in the form of end mill for producing teeth of large module gears. The form of these tools conforms to the shape of the gear tooth-gaps bounded by two involutes as shown in Fig. below. Such form relieved cutters can be used for producing teeth of straight and helical toothed external spur gears and worm wheels as well as straight toothed bevel gears.

27Spline shaft cutters

Spline shaft cuttersThese disc type HSS form relieved cutters are used for cutting the slots of external spline shafts having 4 to 8 straight axial teeth Fig. shown in below.

28Straddle milling

Straddle millingFor faster and accurate machining two parallel vertical surfaces at a definite distance on the horizontal milling arbour as shown in Fig. shown in below.

29IES 1995, ISRO-2010In a milling operation two side milling cutters are mounted with a desired distance between them so that both sides of a work piece can be milled simultaneously. This set up is called.(a)Gang milling(b)Straddle milling (c)String milling (d)Side milling. Ans. (b)30Gang milling

Gang millingIn gang milling, being employed, where feasible, for quick production of complex contours comprising a number of parallel flat or curved surfaces a proper combination of several cutters are mounted tightly on the same horizontal milling arbour as indicated in Fig. shown in below.31IAS-2009 MainWith a sketch, explain the principle of working and variations of bed-type milling machine.[9-marks]IES - 2006Gang milling is a(a)Milling process for generating hexagonal surfaces(b)Process of cutting gears(c)Process in which two or more cutters are used simultaneously(d)Milling operation combined with turning

Ans. (c)

33IES - 2009For machining, which one of the following gang milling operations is employed?(a)Threads(b)Bores(c)Grooves(d)Steps on prismatic parts

Ans. (d)

34Turning by rotary tools (milling cutters)

Turning by rotary tools (milling cutters)During turning like operations in large heavy and odd shaped jobs, its speed (rpm) is essentially kept low. For enhancing productivity and better cutting fluid action rotary tools like milling cutters are used as shown in Fig. below.35VideoIndexing

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Simple or Plain IndexingPlain indexing is the name given to the indexing method carried out using any of the indexing plates in conjunction with the worm. 38

VideoIndexing start at 2.08 min39ExampleIndexing 28 divisions40

ExampleIndexing 62 divisions

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IES 2004, ISRO-2011One brand of milling machine has the following two index plates supplied along with the indexing head:Plate 1: 15, 16, 17, 18, 19, 20 hole circlesPlate 2: 21, 23, 27, 29, 31, 33 hole circlesIt is proposed to mill a spur gear of 28 teeth using simple indexing method. Which one of the following combinations of index plate and number of revolutions is correct?(a)Plate 1: 1 revolution and 9 holes in 18 hole circles(b)Plate 2: 1 revolution and 9 holes in 21 hole circles(c)Plate 2: 1 revolution and 9 holes In 33 hole circles(d)Plate 1: 1 revolution and 9 holes In 15 hole circlesAns. (b)42IES - 2000One of the index plates of a milling machine dividing head has the following hole circles: 15; 16; 17; 18; 19; 20A gear wheel of 34 teeth has to be milled by simple indexing method. To machine each tooth, the index crank has to be rotated through(a)17 holes in the 20-hole circle(b)18 holes in the 20-hole circle(c)1 revolution and 3 holes in 17-hole circle(d)1 revolution and 2 holes in 18-hole circleAns. (c)43IAS - 1994A standard dividing head is equipped with the following index plates1.Plate with 12, 16, 17, 18, 19, 20 holes circles2.Plate with 21, 23, 27, 29, 31, 33 holes circles3.Plate with 37, 39, 41,43,47,49 holes circlesFor obtaining 24 divisions on a work piece by simple indexing(a)Hole plate 2 alone can be used (b)Hole plates 1 and 2 can be used(c)Hole plates 1 and 3 can be used (d)Any of the three hole plates can be used

Ans. (d)

Number of turns in simple indexing = 44

Milling VelocityThe cutting speed in milling is the surface speed of the milling cutter.

Where, V = cutting speed (surface), m/minD = diameter of the milling cutter, mmN = rotational speed of the milling cutter, rpm

45Milling TimeTime for one pass = minutes

Approach distance,

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ExampleA C50 steel flat surface of dimensions 100 mm 250 mm is to be produced on a horizontal axis milling machine. An HSS slab mill with a 100 mm diameter and 150 mm width is to be used for the purpose. The milling cutter has 8 teeth. Calculate the machining time assuming that entire stock can be removed in one depth of 2 mm.Given,Feed, f = 0.13 mm/tooth, Cutting speed, V = 20 m/min.

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4.11 mind

MRR in MillingConsidering the parameters defined in the discussion of speeds and feeds, etc, the MRR is given below,Where,MRR = where, w = width of cut,d = depth of cut

48Video49Some Formulae for Milling

GATE - 1995List-I List- II(Manufacturing Processes)(Condition)(A)Finish turning 1.Backlash eliminator (B)Forming 2.Zero rake(C)Thread cutting 3.Nose radius(D)Down milling 4.Low speedCodes:ABCDABCD(a) 2341(b)3412(c)1234(d)4123Ans. (a)52GATE - 1993A milling cutter having 8 teeth is rotating at 150 rpm. If the feed per tooth is 0.1 mm, the table speed in mm per minute is(a)120 (b)187 (c)125 (d)70

Ans. (a)

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IES - 2003In milling machine, the cutting tool is held in position by(a)Chuck (b)Spindle(c)Arbor (d)Tool holderAns. (c)54IES - 2009The arbor of a milling machine is used to hold which one of the following?(a)Spindle(b)Over-arm(c)Cutting tool(d)Mandrel

Ans. (c)

55IES - 1994Consider the following operations:1.Cutting key ways on shafts2.Cutting external screw threads.3.Cutting teeth of spur gears4.Cutting external splines.Those which can be performed with milling cutters would include(a)1 and 2 (b)2,3 and 4 (c)1 and 3 (d)1,2,3 and 4 .

Ans. (d) Cutting external screw threads cant be possible with milling. 56IES - 1992A set of eight form relieved milling cutters for each module is provided to enable cutting of gears of different(a)Materials(b) Types e.g. spur, helical, etc.(c)Number of teeth(d)Width of gears

Ans. (c)

57GATE - 1992In horizontal milling process. (up/down) milling provides better surface finish and.. (up-down) milling provides longer tool life.

Ans. down, down

58IES - 1995Assertion (A): Up milling or climb milling is commonly used for machining castings and forgings.Reason (R): Up milling can be done on universal milling machines.(a)Both A and R are individually true and R is the correct explanation of A(b)Both A and R are individually true but R is not the correct explanation of A (c)A is true but R is false(d)A is false but R is true

Ans. (d)59IES - 2005Which one of the following statements is correct?In up-milling operation, the undeformed chip thickness,Is zero at the start of the cut and increases to a maximum value just before the tooth disengages the workpiece.Increases to the maximum value at the centre of the travel and decreases towards the end of tooth engagement.Has a maximum value just after the cut is started and drops to zero at the end of the cut.Remains unchanged.

Ans. (a)60IES - 1993Climb milling is chosen while machining because(a)The chip thickness increases gradually(b)It enables the cutter to dig in and depth of cut(c)The specific power consumption is reduced(d)Better surface finish can be obtainedAns. (d) The main advantage of climb milling is better surface finish61IES - 2002Assertion (A): Virtually all modern milling machines are capable of doing down-milling.Reason (R): In down-milling the cutter tends to push the work along and lift it upward from the table. This action tends to eliminate any effect in looseness in the feed screw and nut of the milling machine table and results in smooth cut.(a)Both A and R are individually true and R is the correct explanation of A (b)Both A and R are individually true but R is not the correct explanation of A (c)A is true but R is false(d)A is false but R is true

Ans. (c)62IES - 2004The cutting speed of a milling cutter while cutting brass is:(a)45 to 60 m/min(b)30 to 40 m/min(c)25 to 35 m/min(d)15 to 20 m/min

Ans. (a)63IES - 1999A straight teeth slab milling cutter of 100 mm diameter and 10 teeth rotating at 200 r.p.m. is used to remove a layer of 3 mm thickness from a steel bar. If the table feed is 400 mm/minute, the feed per tooth in this operation will be(a)0.2 mm (b)0.4 mm (c)0.5 mm (d)0.6 mm

Ans. (a) Table feed = feed/teeth x No. of teeth x rpm

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IES - 2002A side and face cutter 125 mm diameter has 10 teeth. It operates at a cutting speed of 14 m/min with a table traverse 100 mm/min. The feed per tooth of the cutter is (a)10 mm (b)2.86 mm(c)0.286 mm (d)0.8 mm

Ans. (c)65GATE 2012 (PI) Common Data S1Data for a plain milling operation are given below.Length of workpiece 200 mmCutter diameter100 mmNo. of teeth 4Cutter speed 100 rpmFeed 200 mm/minDepth of cut 2 mmTotal clearance (entry and exit) 5 mmMean undeformed chip thickness (in microns) is(a) 142 (b) 100 (c) 71 (d) 50

Ans. (c)66GATE 2012 (PI) Common Data S2Data for a plain milling operation are given below.Length of workpiece 200 mmCutter diameter100 mmNo. of teeth 4Cutter speed 100 rpmFeed 200 mm/minDepth of cut 2 mmTotal clearance (entry and exit) 5 mmMachining time for a single pass (in seconds) is(a) 60 (b) 66 (c) 126 (d) 150Ans. (b)67IES - 2004Match List I (Milling problem) with List II (Probable causes) and select the correct answer using the codes given below the Lists:List IList IIA.Chatter 1.Too high feedB.Poor surface finish 2.Lack of rigidity in machine fixtures, bar or workpieceC.Loss of accuracy3.High cutting loadD.Cutter burrs4.Radial relief too great5.Not enough lubricantCodes:ABCDAB CD(a) 2 1 5 3 (b) 2 1 3 5(c) 4 5 2 3 (d) 4 2 3 5

Ans. (b)68IAS - 2001Which one of the following statements are correct in respect of up-milling and down-milling?1.In up-milling the cutter rotates in a direction opposite to that of workpiece travel whereas in down-milling the cutter rotates in a direction similar to that of workpiece travel.2.In down-milling chip will be thin at the beginning and increase to a maximum at the end of the cut and reverse will be the case for a chip formed by up-milling.3.Down-milling is desirable with milling cutters having a high radial rake angle when compared to up-milling.4.Down-milling forces the work-piece against the milling table to exert more pressure while up-milling tends to lift the workpiece from the table.Select the correct answer using the codes given below:Codes:(a)1, 2 and 3(b)1, 2 and 4(c)3 and 4(d) 1, 3 and 4

Ans. (d)69IAS - 1998Which of the following statements are true of face milling?1.Face milling cutter is held on an arbor.2.It has two rake angles axial rake and radial rake.3.The maximum chip thickness equals the feed per tooth.4.The chip thickness varies from a minimum at the start of cut to a maximum at the end of cut.Select the correct answer using the codes given below:Codes :(a)1 and 2(b)2 and 3(c)2 and 4(d)3 and 4

Ans. (b)70IAS - 2001Which of the following mechanisms are suitable for indexing the table of rotary transfer line?1.Rack and pinion2.Ratchet and pawl3.Lead screw4.Geneva mechanismSelect the correct answer by using the codes given below:Codes:(a)1, 2 and 3(b)2, 3 and 4(c)1, 3 and 4(d)1, 2 and 4

Ans. (d)71IAS - 2000Consider the following mechanisms:1.Geneva gearing 2.Rack and pinion3.Ratchet and pawlWhich of these mechanisms are used to index the work table on a transfer machine?(a)1 and 2(b)2 and 3(c)1 and 3 (d)1, 2 and 3

Ans. (d)72IAS - 2003A milling cutter of 70 mm diameter with 12 teeth is operating at a cutting speed of 22 m/min and a feed of 0.05 mm/tooth. The feed per minute is(a)110 m/min (b)35 mm/min(c)6 mm/min (d)60 mm/min

Ans (d)

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IES-1994Which one of the following operations is carried out at the minimum cutting velocity if the machines are equally rigid and the tool work materials are the same?(a)Turning(b)Grinding(c)Boring (d)MillingAns. (d) Minimum cutting velocity is in milling.74IES - 2012Statement (I): Vibrations in milling are induced due to interrupted cutting operation.Statement (II):Vibrations can be suppressed to a large extent by using equal spacing of teeth along the periphery of the cutters.(a) Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)(b) Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)(c) Statement (I) is true but Statement (II) is false(d) Statement (I) is false but Statement (II) is true

Ans. (*)75IES 2011Match List I with List II and select the correct answer using the code given below the lists :

CodesA B C D A B C D(a)2413(b)3412(c) 2 1 4 3(d) 3 1 4 2

List I List IIA. Lathe1. FluteB. Shaper2. Universal indexingC. Drilling machine3. LeadscrewD. Milling machine4. Rocker armAns. (b)76IES- 2002Match List I with List II and select the correct answer:List I (Machine tools) List II (Machine tool parts)A.Lathe 1.Lead strewB.Milling machine 2.Rocker armC.Shaper 3.Universal indexingD.Drilling machine 4.FluteCodes:ABC DAB CD(a) 4 2 3 1 (b) 1 3 2 4(c) 4 3 2 1 (d) 1 2 3 4

Ans. (b)

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Ch-7: MillingQ NoOptionQ. NoOption1B7D2B8D3D9A4A10D5C11C6D12D79