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Turning Operations Lathe Turning Operations • Machine Tool – LATHE • Job (workpiece) – rotary motion • Tool – linear motions “Mother of Machine Tools “ Cylindrical and flat surfaces Some Typical Lathe Jobs Turning/Drilling/Grooving/ Threading/Knurling/Facing... The Lathe Head stock Spindle Guide ways Tool post Spindle speed selector Feed change gearbox Cross slide Dead center Tailstock quill Tailstock Handle Compound rest and slide(swivels) Bed Carriage Apron Feed rod Lead screw The Lathe Head Stock Tail Stock Bed Feed/Lead Screw Carriage Main Parts • • • • • Bed Headstock Feed and lead screws Carriage Tailstock 6 Lathe Bed • Heavy, rugged casting • Made to support working parts of lathe • On top section are machined ways – Guide and align major parts of lathe 7 Lathe Bed 8 Headstock • Clamped on left-hand end of bed • Headstock spindle – Hollow cylindrical shaft supported by bearings • Provides drive through gears to work-holding devices – Live center, faceplate, or chuck fitted to spindle nose to hold and drive work • Driven by stepped pulley or transmission gears • Feed reverse lever – Reverses rotation of feed rod and lead screw 9 Headstock 10 Headstock Back Gear arrangement Headstock belt drive 11 Quick-Change Gearbox • Contains number of different-size gears • Provides feed rod and lead-screw with various speeds for turning and thread-cutting operations – Feed rod advances carriage when automatic feed lever engaged – Lead screw advances the carriage for threadcutting operations when split-nut lever engaged 12 Quick-Change Gearbox 13 Carriage • Used to move cutting tool along lathe bed • Consists of three main parts – Saddle • H-shaped casting mounted on top of lathe ways, provides means of mounting cross-slide and apron – Cross-slide – Apron 14 Carriage < Saddle < Apron 15 Carriage 16 Carriage 17 Apron • • • • The apron attached to the front of the carriage, holds most of the control levers. These include the levers, which engage and reverse the feed lengthwise (Z-axis) or crosswise (X-axis) and the lever which engages the threading gears. The apron is fastened to the saddle, houses the gears and mechanisms required to move the carriage and cross-slide automatically. The apron hand wheel can be turned manually to move the carriage along the Lathe bed. This hand wheel is connected to a gear that meshes in a rack fastened to the Lathe bed. The automatic feed lever engages a clutch that provides the automatic feed to the carriage 18 Cross-slide • Mounted on top of saddle • Provides manual or automatic cross movement for cutting tool • Compound rest (fitted on top of cross-slide) – Used to support cutting tool – Swiveled to any angle for taper-turning – Has graduated collar that ensure accurate cutting-tool settings (.001 in.) (also crossslide) 19 Cross-slide 20 21 Top Slide (Compound slide) • • • • Fitted to top of Cross slide Carries tool post and cutting tool Can rotate to any angle Is used to turn tapers 22 Tailstock • Upper and lower tailstock castings • Adjusted for taper or parallel turning by two screws set in base • Tailstock clamp locks tailstock in any position along bed of lathe • Tailstock spindle has internal taper to receive dead center – Provides support for right-hand end of work 23 Tailstock Supports long workpieces when machining. 60 degree rotating center point. Drill Chuck Turn the tailstock handwheel to advance the ram. 24 Tailstock 25 Lead Screw and Feed Rod < Lead Screw < Feed Rod 26 Types of Lathes • Engine Lathe • Speed Lathe • Bench Lathe • Tool Room Lathe • Special Purpose Lathe • Gap Bed Lathe … Size of Lathe Workpiece Length Swing Size of Lathe .. Example: 300 - 1500 Lathe • Maximum Diameter of Workpiece that can be machined = SWING (= 300 mm) • Maximum Length of Workpiece that can be held between Centers (=1500 mm) Workholding Devices • Equipment used to hold – Workpiece – fixtures – Tool - jigs Securely HOLD or Support while machining Workholding Devices .. Chucks Three jaw Four Jaw Chucks • Used extensively for holding work for lathe machining operations – Work large or unusual shape • Most commonly used lathe chucks – Three-jaw universal – Four-jaw independent – Collet chuck 32 Three-jaw Universal Chuck • Holds round and hexagonal work • Grasps work quickly and accurate within few thousandths/inch • Three jaws move simultaneously when adjusted by chuck wrench – Caused by scroll plate into which all three jaws fit • Two sets of jaw: outside chucking and inside chucking 33 Three-jaw Universal Chuck 34 Three jaw self centering chuck 35 Four-Jaw Independent Chuck • Used to hold round, square, hexagonal, and irregularly shaped workpieces • Has four jaws – Each can be adjusted independently by chuck wrench • Jaws can be reversed to hold work by inside diameter 36 Four-Jaw Independent Chucks 37 Four-Jaw Independent Chucks • With the four jaw chuck, each jaw can be adjusted independently by rotation of the radially mounted threaded screws. • Although accurate mounting of a workpiece can be time consuming, a four-jaw chuck is often necessary for non-cylindrical workpieces. 38 Workholding Devices .. Mandrels Workpiece (job) with a hole Workpiece Mandrel Mandrels • Holds internally machined workpiece between centers so further machining operations are concentric with bore • Several types, but most common • • • • Plain mandrel Expanding mandrel Gang mandrel Stub mandrel 40 Mandrels to Hold Workpieces for Turning Figure 23.8 Various types of mandrels to hold workpieces for turning. These mandrels usually are mounted between centers on a lathe. Note that in (a), both the cylindrical and the end faces of the workpiece can be machined, whereas in (b) and (c), only the cylindrical surfaces can be machined. 41 Workholding Devices .. Rests Steady Rest Follower Rest Jaws Work Hinge Work Carriage Lathe bed guideways Jaws Steadyrest • Used to support long work held in chuck or between lathe centers – Prevent springing • Located on and aligned by ways of the lathe • Positioned at any point along lathe bed • Three jaws tipped with plastic, bronze or rollers may be adjusted to support any work diameter with steadyrest capacity 43 Steadyrest 44 Follower Rest • Mounted on saddle • Travels with carriage to prevent work from springing up and away from cutting tool – Cutting tool generally positioned just ahead of follower rest – Provide smooth bearing surface for two jaws of follower rest 45 Follower Rest 46 Operating/Cutting Conditions 1. 2. 3. Cutting Speed v Feed f Depth of Cut d Tool post Workpiece N (rev/min) Chip Tool D S peripheral speed (m/min) Operating Conditions Tool post Workpiece Chip N (rev/min) S Tool peripheral D speed (m/min) relative tool travel in 1 rotation D peripheral speed S D N Operating Conditions.. Cutting Speed D – Diameter (mm) N – Revolutions per Minute (rpm) v DN 1000 m/min The Peripheral Speed of Workpiece past the Cutting Tool =Cutting Speed Operating Conditions.. Feed f – the distance the tool advances for every rotation of workpiece (mm/rev) D1 D2 f Feed Operating Conditions.. Depth of Cut perpendicular distance between machined surface and uncut surface of the Workpiece d = (D1 – D2)/2 (mm) D1 D2 d Depth of Cut 3 Operating Conditions Cutting speed Workpiece Depth of cut (d) Machined surface N Chuck Feed (f ) Tool Chip Depth of cut Operating Conditions.. Selection of .. • • • • • • Workpiece Material Tool Material Tool signature Surface Finish Accuracy Capability of Machine Tool Operations on Lathe .. Material Removal Rate MRR Volume of material removed in one revolution MRR = D d f mm3 • Job makes N revolutions/min MRR = D d f N (mm3/min) • In terms of v MRR is given by MRR = 1000 v d f (mm3/min) Operations on Lathe .. MRR dimensional consistency by substituting the units MRR: D d f N (mm)(mm)(mm/rev)(rev/min) = mm3/min Operations on Lathe .. Operations on Lathe • • • • • Turning Facing knurling Grooving Parting • • • • Chamfering Taper turning Drilling Threading Operations on Lathe .. Turning Cylindrical job Operations on Lathe .. Turning .. Cylindrical job Cutting speed Workpiece Depth of cut (d) Machined surface N Chuck Feed Tool Chip Depth of cut Operations on Lathe .. Turning .. Excess Material is removed reduce Diameter • Cutting Tool: Turning Tool • a depth of cut of 1 mm will reduce diameter by 2 mm to Operations on Lathe .. Facing Flat Surface/Reduce length Chuck Workpiece d Machined Face Cutting speed Depth of cut Tool Feed Operations on Lathe .. Facing .. • machine end of job Flat surface or to Reduce Length of Job • Turning Tool • Feed: in direction perpendicular to workpiece axis –Length of Tool Travel = radius of workpiece • Depth of Cut: in direction parallel to workpiece axis Operations on Lathe .. Facing .. Operations on Lathe .. Eccentric Turning 4-jaw chuck Axis of job Axi Cutting speed Eccentric peg (to be turned) Operations on Lathe .. Knurling • Produce rough textured surface – For Decorative and/or Functional Purpose • Knurling Tool A Forming Process MRR~0 Operations on Lathe .. Knurling Knurled surface Cutting speed Feed Knurling tool Tool post Movement for depth Operations on Lathe .. Knurling .. Operations on Lathe .. Grooving • Produces a Groove on workpiece • Shape of tool shape of groove • Carried out using Grooving Tool A form tool • Also called Form Turning Operations on Lathe .. Grooving .. Shape produced by form tool Form tool Feed or depth of cut Groove Grooving tool Operations on Lathe .. Parting • • • • • Cutting workpiece into Two Similar to grooving Parting Tool Hogging – tool rides over – at slow feed Coolant use Operations on Lathe .. Parting .. Parting tool Feed Operations on Lathe .. Chamfering Chamfer Feed Chamfering tool Operations on Lathe .. Chamfering Beveling sharp machined edges Similar to form turning Chamfering tool – 45° To • • • Avoid Sharp Edges Make Assembly Easier Improve Aesthetics Operations on Lathe .. Taper Turning • Taper: D1 D2 tan 2L 90° D1 B A L C D2 Operations on Lathe .. Taper Turning.. Conicity D1 D2 K L Methods • • • • Form Tool Swiveling Compound Rest Taper Turning Attachment Simultaneous Longitudinal and Cross Feeds Operations on Lathe .. Taper Turning .. By Form Tool Workpiece Taper Form Straight tool cutting edge Direction of feed Operations on Lathe .. Taper Turning ,, By Compound Rest Dog Mandrel Tail stock quill Tail stock Face plate Tool post & Tool holder Cross slide Direction of feed Compound rest Slide Compound rest Hand crank Operations on Lathe .. Drilling Drill – cutting tool – held in TS – feed from TS Quill clamp Drill moving quill Tail stock Feed Tail stock clamp Operations on Lathe .. Process Sequence • How to make job from raw material 45 long x 30 dia.? 15 40 Steps: •Operations •Sequence 20 dia •Tools •Process Operations on Lathe .. Process Sequence .. Possible Sequences • • • • • • TURNING - FACING - KNURLING TURNING - KNURLING - FACING FACING - TURNING - KNURLING FACING - KNURLING - TURNING KNURLING - FACING - TURNING KNURLING - TURNING – FACING What is an Optimal Sequence? X X X X Operations on Lathe .. Machining Time Turning Time • Job length Lj mm • Feed f mm/rev • Job speed N rpm • f N mm/min t Lj f N min Operations on Lathe .. Manufacturing Time Manufacturing Time = Machining Time + Setup Time + Moving Time + Waiting Time Example A mild steel rod having 50 mm diameter and 500 mm length is to be turned on a lathe. Determine the machining time to reduce the rod to 45 mm in one pass when cutting speed is 30 m/min and a feed of 0.7 mm/rev is used. Example Given data: D = 50 mm, Lj = 500 mm v = 30 m/min, f = 0.7 mm/rev Substituting the values of v and D in v DN 1000 m/min calculate the required spindle speed as: N = 191 rpm Example Can a machine has speed of 191 rpm? Machining time: t t Lj f N min = 500 / (0.7191) = 3.74 minutes Example • Determine the angle at which the compound rest would be swiveled for cutting a taper on a workpiece having a length of 150 mm and outside diameter 80 mm. The smallest diameter on the tapered end of the rod should be 50 mm and the required length of the tapered portion is 80 mm. Example • Given data: D1 = 80 mm, D2 = 50 mm, Lj = 80 mm (with usual notations) tan = (80-50) / 280 • or = 10.620 • The compound rest should be swiveled at 10.62o Example • A 150 mm long 12 mm diameter stainless steel rod is to be reduced in diameter to 10 mm by turning on a lathe in one pass. The spindle rotates at 500 rpm, and the tool is traveling at an axial speed of 200 mm/min. Calculate the cutting speed, material removal rate and the time required for machining the steel rod. Example • Given data: Lj = 150 mm, D1 = 12 mm, D2 = 10 mm, N = 500 rpm • Using Equation (1) • v = 12500 / 1000 • = 18.85 m/min. • depth of cut = d = (12 – 10)/2 = 1 mm Example • feed rate = 200 mm/min, we get the feed f in mm/rev by dividing feed rate by spindle rpm. That is • f = 200/500 = 0.4 mm/rev • From Equation (4), • MRR = 3.142120.41500 = 7538.4 mm3/min • from Equation (8), • t = 150/(0.4500) = 0.75 min. Example • Calculate the time required to machine a workpiece 170 mm long, 60 mm diameter to 165 mm long 50 mm diameter. The workpiece rotates at 440 rpm, feed is 0.3 mm/rev and maximum depth of cut is 2 mm. Assume total approach and overtravel distance as 5 mm for turning operation. Example • Given data: Lj = 170 mm, D1 = 60 mm, D2 = 50 mm, N = 440 rpm, f = 0.3 mm/rev, d= 2 mm, • How to calculate the machining time when there is more than one operation? Example • Time for Turning: • Total length of tool travel = job length + length of approach and overtravel • L = 170 + 5 = 175 mm • Required depth to be cut = (60 – 50)/2 = 5 mm • Since maximum depth of cut is 2 mm, 5 mm cannot be cut in one pass. Therefore, we calculate number of cuts or passes required. • Number of cuts required = 5/2 = 2.5 or 3 (since cuts cannot be a fraction) • Machining time for one cut = L / (fN) • Total turning time = [L / (fN)] Number of cuts • = [175/(0.3440)] 3= 3.97 min. Example • Time for facing: • Now, the diameter of the job is reduced to 50 mm. Recall that in case of facing operations, length of tool travel is equal to half the diameter of the job. That is, l = 25 mm. Substituting in equation 8, we get • t = 25/(0.3440) • = 0.18 min. Example • Total time: • Total time for machining = Time for Turning + Time for Facing • = 3.97 + 0.18 • = 4.15 min. • The reader should find out the total machining time if first facing is done. Example • From a raw material of 100 mm length and 10 mm diameter, a component having length 100 mm and diameter 8 mm is to be produced using a cutting speed of 31.41 m/min and a feed rate of 0.7 mm/revolution. How many times we have to resharpen or regrind, if 1000 workpieces are to be produced. In the taylor’s expression use constants as n = 1.2 and C = 180 Example • Given D =10 mm , N = 1000 rpm, v = 31.41 m/minute • From Taylor’s tool life expression, we have vT n = C • Substituting the values we get, • (31.40)(T)1.2 = 180 • or T = 4.28 min Example • Machining time/piece = L / (fN) • = 100 / (0.71000) • = 0.142 minute. • Machining time for 1000 work-pieces = 1000 0.142 = 142.86 min • Number of resharpenings = 142.86/ 4.28 • = 33.37 or 33 resharpenings Example • 6: While turning a carbon steel cylinder bar of length 3 m and diameter 0.2 m at a feed rate of 0.5 mm/revolution with an HSS tool, one of the two available cutting speeds is to be selected. These two cutting speeds are 100 m/min and 57 m/min. The tool life corresponding to the speed of 100 m/min is known to be 16 minutes with n=0.5. The cost of machining time, setup time and unproductive time together is Rs.1/sec. The cost of one tool resharpening is Rs.20. • Which of the above two cutting speeds should be selected from the point of view of the total cost of producing this part? Prove your argument. Example • Given T1 = 16 minute, v1 = 100 m/minute, v2 = 57 m/minute, D = 200mm, l = 300 mm, f = 0.5 mm/rev • Consider Speed of 100 m/minute • N1 = (1000 v) / ( D) = (1000100) / (200) = 159.2 rpm • t1 = l / (fN) = 3000 / (0.5 159.2) = 37.7 minute • Tool life corresponding to speed of 100 m/minute is 16 minute. • Number of resharpening required = 37.7 / 16 = 2.35 • • or number of resharpenings = 2 Example • Total cost = • Machining cost + Cost of resharpening Number of resharpening • = 37.7601+ 202 • = Rs.2302 Example • Consider Speed of 57 m/minute • Using Taylor’s expression T2 = T1 (v1 / v2)2 with usual notations • = 16 (100/57)2 = 49 minute • Repeating the same procedure we get t2 = 66 minute, number of reshparpening=1 and total cost = Rs. 3980. • • The cost is less when speed = 100 m/minute. Hence, select 100 m/minute. Example • Write the process sequence to be used for manufacturing the component from raw material of 175 mm length and 60 mm diameter Example 20 Threading 50 40 Dia 50 40 50 20 Dia Example • To write the process sequence, first list the operations to be performed. The raw material is having size of 175 mm length and 60 mm diameter. The component shown in Figure 5.23 is having major diameter of 50 mm, step diameter of 40 mm, groove of 20 mm and threading for a length of 50 mm. The total length of job is 160 mm. Hence, the list of operations to be carried out on the job are turning, facing, thread cutting, grooving and step turning Example • A possible sequence for producing the component would be: • Turning (reducing completely to 50 mm) • Facing (to reduce the length to 160 mm) • Step turning (reducing from 50 mm to 40 mm) • Thread cutting. • Grooving
