TOPICS TOPICS COVERED COVERED – (2014-15) (2014-15) 1.
MACHINE TOOLS –
LATHE LATHE,, SHAPER SHAPER,, PLANER PLANER,, SLOTT SLOTTER, ER, DRILL DRILLING ING,, MILLIN MILLING, G, BROACH BROACHING ING,, GRIND GRINDING ING,, SUPER SUPER FINIS FINISHIN HING, G, THREA THREAD D MFG, MFG, GEAR MFG, JIGS & FIXTURES, NON-TRADITIONAL MACHINING, NC, CNC, DNC, NC PART ART PROGRAMMING. 2. WELDING ING –
CLAS CLASSI SIFI FICA CATI TION ON,, WELD WELDAB ABIL ILIT ITY Y OF COMM COMMON ON MET METALS, ALS, METALLURGY OF WELDS, TYPES OF JOINTS, 30 DIFFERENT WELDING PROCESSES, DEFECTS, DESIGN CONSIDERATIONS, WELD SPECIFICATIONS
D G R C PRADEEP
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MACHINE TOOLS INTRODUCTION: The The proc proceess of meta metall cutt cuttin ing g in whi which chi chip p is for form med is effe effect cted ed by a rela relativ tivee mom momen entt b/w the the work work pie piece ce and and the the hard edge of the cutting tool. The relative motion is produced by a combination of rotary and translatory moments moments of either work piece (or) tool (or) both. Eg:
Machine Tool Lathe Shaper, Planer Drilling Milling Surface Grinding Cylindrical Grinding
Relative Motion Work Tool R T T T Fixed R&T T R T R R&T R
MACHINE TOOLS INTRODUCTION: The The proc proceess of meta metall cutt cuttin ing g in whi which chi chip p is for form med is effe effect cted ed by a rela relativ tivee mom momen entt b/w the the work work pie piece ce and and the the hard edge of the cutting tool. The relative motion is produced by a combination of rotary and translatory moments moments of either work piece (or) tool (or) both. Eg:
Machine Tool Lathe Shaper, Planer Drilling Milling Surface Grinding Cylindrical Grinding
Relative Motion Work Tool R T T T Fixed R&T T R T R R&T R
LATHE LATHE – MAIN PAR PARTS TS
Dr G. R. C. PRADEEP
Email:
CARRIAGE CARRI AGE ASSEMBL ASS EMBLY Y
SLIDE
Video 1,2
SLIDE
SPECIFICATIONS OF LATHE 1) Height Height of centers centers over over bed U.K. spec. 2) Maximum Maximum swing swing over bed USA spec. 3) Maximum Maximum swing swing over carriage 4) Maximum Maximum swing swing over Gap 5) Maximum Maximum distance distance b/w centers 6) Length Length of of bed 7) No. of speeds and feeds etc.
EARLY LATHES
EARLY LATHES
EARLY LATHES
EARLY LATHES
TYPES OF LATHES 1) Bench lathe: It is a very small lathe mounted on separately prepared bench or cabinet and used for small, precision works.
2) Speed lathe: They do not have provision for power feed and have no gear box, carriage, lead screw etc. Two or three spindle speeds are available by cone pulley arrangement. They are used for wood turning, polishing, metal spinning etc
3) Engine lathe: In olden days lathe was driven by a steam engine. Hence the name is still in existence even after modern lathes are provided with motor drive.
4) Tool Room Lathe: It is nothing but the engine lathe equipped with some extra attachments for accurate and precision work like taper turning attachment, follower rest, collets, chucks etc. The bed is relatively small.
5) Capstan & Turret lathes: These are semi automatic type machines very useful for mass production (small lot sizes). Less skill is required for operator and wide range of operations can be performed. They carry special mechanisms for indexing their tool heads. They are provided with a front tool post which can hold 4 turning related tools and rear tool post which can hold 2 to 4 turning related tools. The turrets can hold only drilling related tools. The turning tools used in the rear tool post are reverse tools with reverse geometry.
Video 3,4
Turret Indexing Movement of turret during return stroke
Turret Indexing in Capstan and Turret Lathes
Just before indexing at the end of the return stroke, the locking pin is withdrawn by the lever which is lifted at its other end by gradually riding against the hinged wedge as shown. Further backward travel of the turret slide causes rotation of the free head by the indexing pin and lever as shown. Rotation of the turret head by exact angle is accomplished by insertion of the locking pin in the next hole of the six equi-spaced holes.
Turret Lathe
Turret Lathe Layout
Capstan Lathe
Capstan Lathe Layout
Turret Lathe Capstan lathe 1. Turret head (square (or) 1. Turret head (round (or) square hexagonal) is mounted on (or) hexagonal) is mounted on saddle auxiliary slide that moves on guide ways provided on saddle 2. The above arrangement gives 2. Less rigidity, vibrations occur, rigidity as forces are hence suitable for lighter and transferred to bed. Hence smaller jobs (up to 60mm) and capable of handling heavy precision work. jobs (up to 200mm) and severe cutting conditions.
3 Tool travel is along entire bed 3. length 4. Tool feeding is slow and 4. causes fatigue to operator hands 5. No tail stock 5.
Tool travel is limited because of auxiliary slide traverse limitation. Tool feeding is fast and causes less fatigue to operator hands. No tail stock
6) Automatic lathes: These are designed so that all the working and Job handling movements of the complete Manufacturing process for a job are done automatically. No participation of the operator is required during the operation. They fall in the category of heavy duty, high speed lathes employed in mass production(large lot sizes). Geneva mechanism is used for indexing the turret. Video 5,6,7,8
Types of automatic lathe: 1) According to type of stock material Bar automatics; Chucking automatics 2) According to No. of spindles Single spindle; Multiple spindle 3) According to the directions of the axis of m/c spindles Horizontal; Vertical
The general purpose single spindle automatic lathes are widely used for quantity or mass production (by machining) of high quality fasteners; bolts, screws, studs, bushings, pins, shafts, rollers, handles and similar small metallic parts from long bars or tubes of regular section and also often from separate small blanks. Unlike the semiautomatic lathes, single spindle automats are : • used always for producing jobs of rod, tubular or ring type and of relatively smaller size. • run fully automatically, including bar feeding and tool indexing, and continuously over a long duration repeating the same machining cycle for each product • provided with up to five radial tool slides which are moved by cams mounted on a cam shaft • of relatively smaller size and power but have higher spindle speeds
Swiss type automatic lathe The characteristics and applications of these single spindle automatic lathes are : In respect of application: Used for precision machining of thin slender rod or tubular jobs, like components of small clocks and wrist watches in mass production. Job size ⎯ Diameter range – 2 to 12 mm; ⎯ Length range – 3 to 30 mm. Dimensional accuracy and surface finish – almost as good as provided by grinding In respect of configuration and operation: There is no tailstock or turret High spindle speed (2000 – 10,000 rpm) for small job diameter •
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The headstock travels enabling axial feed of the bar stock against the cutting tools as shown The cutting tools (up to five in number including two on the rocker arm) are fed radially Drilling and threading tools, if required, are moved axially using swivelling device(s) The cylindrical blanks are prefinished by grinding and are moved through a carbide guide bush Video 9,10
7) Special – purpose lathes: These are designed to perform certain specified operations only. Video Eg: Facing lathe, vertical lathe, crank shaft lathe
11,12,13,14
WORK HOLDING DEVICES 1) Chucks ---a) 3 Jaw – Self centering, smaller in size, used for round cross sections b) 4 jaw – Not self centering, medium in size, used for round, square, rectangular cross sections.
c) Collets– Fixed size. They are air operated or hand operated. Used in – Tool Room lathes, Bar Automatic Lathes, Vertical Milling m/c to hold end mills.
d) Pneumatic Chucks – In chucking Automatics Note: In bar automatics the component is parted of from the bar and in chucking automatics, the component is released from the chuck and another blank is loaded from the magazine. e) Magnetic – Used for ferrous metals in Lathe, Milling, Surface Grinding machines for light works and also where Distortion is not permitted like in aerospace components. f) Vacuum – Similar to above and used for non ferrous metals
2) Face plate – Used for large size work pieces of round, square, rectangular, and also very complex geometries not possible in any other devices.
3) Carriers and catch plates – Used for supporting shafts, mandrels for imparting rotation. 4) Centers – For supporting a) Live centre – used with face plate b) Dead centre – used in tail stock
5) Mandrel – Used to support the work pieces and also for holding hollow parts to meet concentricity requirements Live Centre
Work piece
Dead Centre
Face Plate Mandrel Carrier Dog
6) Steady rest – mounted on bed, used for long heavy jobs that deflect centrally by self weight 7) Follower rest – mounted on carriage and moves with tool, used for long thin jobs that deflect laterally by cutting force.
TOOL POST
Tool Setting on Lathe 1. Setting the tool below the centre decreases the effective rake angle and increases the effective clearance angle. This increases the cutting forces. 2. Setting the tool above the centre increases the effective rake angle and decreases the effective clearance angle. This increases rubbing with flank surface. Effective Rake is the apparent Rake angle w.r.t tool and work position and not the actual rake angle provided on the tool.
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TOOL HOLDERS HSS Tool Holders
Brazed Carbide tip Tool Holders (Can be grinded)
Throw away Carbide Tip Tool holders (Can not be Grinded)
Box Tool Holders – Used in turret lathes to apply heavy cuts & act as travelling steadies.
OPERATIONS 1) Straight turning: Here the work rotating about lathe axis, tool is fed parallel to it, depth of cut is perpendicular to it, thus producing a straight cylindrical surface. Here Diameter is effected but Length is not effected. 2) Shoulder / Step turning: Same as above except that diameter is reduced only up to certain length.
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Video 13
3) Facing:- Here the tool is fed perpendicular to the lathe axis and depth of cut is parallel to the lathe axis and thus producing a flat surface. Here Length (in Shafts) / thickness (in plates) is effected, but Diameter is not effected. 4) Knurling:- Process of embossing a diamond shaped pattern on work surface which is used for gripping purpose. Video 15,16
