Machine tools and their applications Unit – I Machine tools and their applications

Syllabus Drilling machine: Types of drills and operations. Twist drill geometry, Types of drilling machine, Tool holder, Calculation of machining time for Drilling Process Milling machine: Types of milling machines, Cutter-types and geometry and their applications. Universal dividing head, Methods of Indexing: Simple, Compound, Differential. Numericals based on indexing. Calculation of machining time for Milling processes(Numericals) Broaching: Introduction to broaching, Broach tool geometry, Types of broaching machines and operations.Planner and Boring Machines.(Introduction and types)

Milling machine

University Questions Write short note on : i. Thread Milling ii. Helical Slot Milling iii. Cam Milling Operation iv. Universal Dividing Head v. Milling Cutter Geometry (5 mks each) Explain with neat sketch the following Milling Operations: i. Form Milling ii. Plain Milling (6 mks) Describe compound indexing with suitable example. (6 mks)

University Questions 4. Explain the procedure to cut a spur gear on Milling Machine (7 mks) 5. Write a short note on work holding devices in Milling Machine 6. With figure explain mechanism of knee type milling machine (8 mks) 7. Differentiate : i. Up milling and Down milling ii. Gang milling and straddle milling (8 mks)

MILLING Milling: is a metal cutting operation in which the excess material from the work piece is removed by rotating multipoint cutting tool called milling cutter. Milling machine: is a power operated machine tool in which work piece mounted on a moving table is machined to various shapes when moved under a slow revolving serrated cutter.

PRINCIPLE OF MILLING The milling process: Typically uses a multi-tooth cutter Work is fed into the rotating cutter Capable of high MRR Well suited for mass production applications Cutting tools for this process are called milling cutters

COMPARISON BETWEEN UP MILLING & DOWN MILLING SL. NO. UP MILLING (CONVENTIONAL MILLING) DOWN MILLING (CLIMB MILLING) 01 Work piece fed in the opposite direction that of the cutter. Work piece fed in the same direction that of the cutter. 02 Chips are progressively thicker. Chips are progressively thinner. 03 Strong clamping is required since the cutting force is directed upwards & tends to lift the work piece. Strong clamping is not required since the cutting force is directed downwards & keep the work piece pressed to the table. 04 Gives poor surface finish, since chips gets accumulated at the cutting zone. Gives good surface finish, since the chips are thrown away during cutting. 05 Used for hard materials. Used for soft materials and finishing operations.

CLASSIFICATION OF MILLING MACHINES 1. Column and knee milling machines a. Plain column & knee type milling machine - Horizontal spindle type - Vertical spindle type 2. Bed type milling machine 3. Planer type milling machine 4. Special purpose milling machine a. Tracer controlled milling machine b. Thread milling machine c. CNC milling machine

HORIZONTAL MILLING MACHINE MAJOR PARTS : BASE COLUMN SPINDLE OVERARM KNEE SADDLE WORKTABLE FIG. HORIZONTAL MILLING MACHINE

VERTICAL MILLING MACHINE MAJOR PARTS : BASE COLUMN SPINDLE SPINDLE HEAD KNEE SADDLE WORKTABLE FIG. VERTICAL MILLING MACHINE

DIFFERENCES BETWEEN HORIZONTAL & VERTICAL MILLING MACHINES SL. NO. HORIZONTAL MILLING MACHINE VERTICAL MILLING MACHINE 01 Spindle is horizontal & parallel to the worktable. Spindle is vertical & perpendicular to the worktable. 02 Cutter cannot be moved up & down. Cutter can be moved up & down. 03 Cutter is mounted on the arbor. Cutter is directly mounted on the spindle. 04 Spindle cannot be tilted. Spindle can be tilted for angular cutting. 05 Operations such as plain milling, gear cutting, form milling, straddle milling, gang milling etc., can be performed. Operations such as slot milling, T-slot milling, angular milling, flat milling etc., can be performed and also drilling, boring and reaming can be carried out.

MILLING OPERATIONS Plain or slab milling Face milling End milling Slot milling Angular milling Form milling Straddle milling Gang milling Slitting or saw milling Gear cutting

PLAIN/SURFACE/ SLAB MILLING Plain Milling: Process to get the flat surface on the work piece in which the cutter axis and work piece axis are parallel. Cutter: Plain/ Slab milling cutter. Machine: Horizontal Milling m/c. FIG. PLAIN MILLING

FACE MILLING Face Milling: Operation carried out for producing a flat surface, which is perpendicular to the axis of rotating cutter. Cutter: Face milling cutter. Machine: Vertical Milling Machine FIG. FACE MILLING

END MILLING End Milling: Operation performed for producing flat surfaces, slots, grooves or finishing the edges of the work piece. Cutter: End milling cutter. Machine: Vertical Milling Machine FIG. END MILLING

SLOT MILLING SLOT Milling: Operation of producing slots like T-slots, plain slots, dovetail slots etc., Cutter: End milling cutter, T-slot cutter, dovetail cutter or side milling cutter Machine: Vertical Milling Machine FIG. T-SLOT MILLING FIG. DOVE TAIL SLOT MILLING

ANGULAR MILLING Angular Milling: Operation of producing all types of angular cuts like V-notches and grooves, serrations and angular surfaces. Cutter: Double angle cutter. Machine: Horizontal Milling Machine FIG. ANGULAR MILLING

FORM MILLING End Milling: Operation of producing all types of angular cuts like V-notches and grooves, serrations and angular surfaces. Cutter: Double angle cutter. Machine: Horizontal Milling Machine FIG. FORM MILLING

STRADDLE MILLING Straddle Milling: Operation of machining two parallel surfaces simultaneously on a work piece. Cutter: 2 or more side & face milling cutters Machine: Horizontal Milling Machine FIG. STRADDLE MILLING

GANG MILLING Gang Milling: Process to get different profiles on the work piece simultaneously with two or more cutters at one stretch. Cutter: Different cutters as required. Machine: Horizontal Milling Machine FIG. GANG MILLING

SPECIFICATIONS OF MILLING MACHINE Size of the work table: expressed in length x width Eg: 1500 x 30mm. Longitudinal movement: Total movement of table in mm(X-direction). Eg:800mm Transverse movement: Total movement of saddle along with table in mm(Y-direction). Eg:200mm Vertical movement: Total movement of table, saddle & knee in mm mm(Z-direction). Eg:380mm Range of the speed: Speed variation in the gear box in RPM. Eg: 45 to 200 rpm. Power capacity of the motor in HP. Eg: 2 HP

Milling Cutters

More Milling Cutters

Formed Cutters Concave Convex Gear Tooth Metal-Slitting Saws

Cutting Tool Material Choices Carbon and medium alloy steels High Speed Steels Cast-cobalt alloys Carbides (or cemented or sintered carbides) Coated tools Alumina based ceramics Cubic boron nitride Diamond

Plain Milling Cutter Geometry Used for peripheral or slab milling Fig : Tool geometry elements of an 18‑tooth plain milling cutter

Indexing Methods It is a division of Job periphery into a desired number of equal divisions It is followed by the controlled movement of the crank such that , the workpiece rotates through a definite angle after each cut is over

Methods of Indexing Direct Simple or Plain Compound Differential Angular

Indexing (Dividing) Head One of the most important attachments for milling machine Used to divide circumference of workpiece into equally spaced divisions when milling gear teeth, squares, hexagons, and octagons Also used to rotate workpiece at predetermined ratio to table feed rate

Indexing Devices Universal Dividing Head

Direct Indexing Simplest form of indexing Used for quick indexing of workpiece when cutting flutes, hexagons, squares, etc. Plain Dividing Head

Direct Indexing Divisions Direct indexing plate usually contains three sets of hole circles or slots: 24, 30, and 36 Number of divisions possible to index limited to numbers that are factors of 24, 30, 36   Slots Direct indexing divisions 24 2 3 4 _ 6 8 _ __ 12 __ __ 24 __ __ 30 2 3 _ 5 6 _ _ 10 __ 15 __ __ 30 __ 36 2 3 4 _ 6 _ 9 __ 12 __ 18 __ __ 36

Example: Direct Indexing What direct indexing is necessary to mill eight flutes on a reamer blank? Since the 24-hole circle is the only one divisible by 8 (the required number of divisions), it is the only circle that can be used in this case. Slots Direct indexing divisions 24 2 3 4 _ 6 8 _ __ 12 __ __ 24 __ __ 30 2 3 _ 5 6 _ _ 10 __ 15 __ __ 30 __ 36 2 3 4 _ 6 _ 9 __ 12 __ 18 __ __ 36 Never count the hole or slot in which the index pin is engaged.

Simple Indexing Calculating the indexing or number of turns of crank for most divisions, simply divide 40 by number of divisions to be cut or,

Index Plate and Sector Arms Circular plate provided with series of equally spaced holes into which index crank pin engages Sector arms Fit on front of plate and may be set to any portion of a complete turn

Index Head Parts

Simple Indexing The indexing required to cut eight flutes: The indexing required to cut seven flutes: The five-sevenths turn involves use of an index plate and sector arms.

Index-plate hole circles Brown & Sharpe Plate 1 15-16-17-18-19-20 Plate 2 21-23-27-29-31-33 Plate 3 37-39-41-43-47-49 Cincinnati Standard Plate One side 24-25-28-30-34-37-38-39-41-42-43 Other side 46-47-49-51-53-54-57-58-59-62-66

Brown & Sharpe dividing head : Index Plate 1

Compound Indexing Two separate movements of index crank in two different hole circles of one index plate to obtain crank movement not obtainable by simple indexing Two movements One of index crank as in simple indexing Second of index plate – after locking the plate with plunger

Compound Indexing

First movement – crank pin is rotated through required number of spaces in one of the hole circles of index plate and crank pin is engaged Second movement – Removing rear lock pin and rotating plate together with index crank – forward or backward through calculated number of spaces of another hole circle and then lock pin is engaged

Rule for compound indexing

N – No of divisions required N1 - hole circle used by crank pin N2- hole circle used by lock pin n1 – hole spaces moved by crank pin in N1 hole circle n2 - hole spaces moved by lock pin in N2 hole circle

Numerical : Index 69 divisions by compound indexing = 𝑋 𝑎 ± 𝑋 𝑏 Assumption : Index plates of 23 and 27 hole circles are selected

Solution Step 1: factorize the no of required divisions ( A ) 69= 3 x 23 Step 2: factorize the standard number 40 ( B ) 40 = 10 x 4 Step 3: factorize the difference of selected hole circles i.e. 23 and 27 ( C ) Difference = 27 – 23 = 4 therefore , 4 = 2 x 2

Solution Step 4: factorize the no of holes of one circle and the other ( D ) 23 = 23 and 27 = 3 x 9 Step 5: substitute in the relation : 𝐴 ∗ 𝐶 𝐵 ∗ 𝐷 = 3 𝑥 23 𝑥 4 10 𝑥 4 𝑥 23 𝑥 ( 9 𝑥 3 ) = 1 90 The required indexing movements are obtained by , = 𝑋 𝑎 - 𝑋 𝑏 = 90 23 − 90 27 = 3 21 23 - 3 9 27

Solution It means crank is moved 21 holes on 23 holes circle and the plate and crank 9 holes on 27 hole circle in the opposite direction Applying second check, Crank movement = 21 23 - 9 27 = 40 69 So obtained movements are correct

Differential indexing Required division is obtained by combination of two movements Movement of index similar to simple indexing 2. Simultaneous movement of index plate when crank is turned

Differential indexing set up using Simple Gear Train A Gear train is used (simple or compound), which connects dividing head spindle to worm spindle, to move index plate

Differential indexing set up using compound Gear Train

Movement of index plate may be added or subtracted according to direction of rotation of plate Change gears – 24, 28 , 32 , 40, 44, 48 , 56 ,64 , 72 , 86 ,100

Rule for differential indexing Gear ratio, indexing movement of crank and number of idlers Gear ratio N = required number of divisions to be indexed A = selected number which can be indexed by plain indexing and number is approximately equal to N In gear ratio so calculated, numerators of fraction indicates driving gears on index head spindle and denominator indicates driven gears on index plate

Index crank movement = 40 𝐴 Index crank will have to be moved by an amount (40/A) for N number of complete division of work Index crank should move in same direction or opposite to each other depending on type of gearing ratio and selected number A chosen If (A-N) is positive plate must rotate in same direction as crank and if (A-N) is negative the index plate must rotate in direction opposite to that of a crank

To achieve these conditions number of idlers used depends upon : a. If gear train is simple and ( A-N) is positive , only one idle gear is used b. If gear train is compound and (A-N) is positive, no idle gear is used c. If gear train is simple and (A-N) is negative, two idler are used d. If gear train is compound and (A-N) is negative , only one idle is used.

Index 83 divisions First find out whether index crank can be indexed by plain indexing or not Index crank movement in plain indexing = 40/N = 40/83 since there is no plate with 83 number of holes number can not be indexed by plain indexing

Assume A - let us take A = 86 ( 86 is near to 83 and can be indexed by plain indexing)

Gear ratio

Therefore, driver gears = 72,40 driven gears = 24,86 Index crank movement For complete indexing , index crank will be have to be moved by 20 holes in 43 circle hole As ( A- N) i.e. (86-83) = 3 , is positive and gearing ratio is compound , no idler is required