JJ 104 WORKSHOP TECHNOLOGY 1MILING MACHINE

INTRODUCTION Milling is the machining process of using

rotary cutters to remove material from a workpiece advancing (or feeding) in a direction at an angle with the axis of the tool. It covers a wide variety of different operations and machines, on scales from small individual parts to large, heavy-duty gang milling operations. It is one of the most commonly used processes in industry and machine shops today for machining parts to precise sizes and shapes.

TYPES OF MILLING MACHINE• Mill orientation is the primary

classification for milling machines. The two basic configurations are vertical and horizontal. However, there are alternate classifications according to method of control, size, purpose and power source.

PARTS OF MILLING MACHINE

Vertical Milling Machine

1.Face milling cutter

2.Spindle

3.Spindle head

4.Column

5.Table ( X-Axis )

6.Saddle (Z-Axis )

7.Knee ( Y-Axis )

8.Base

9.Spindle switch

10.Spindle speed gear lever

11.Spindle speed control lever

12.Oil tank

13.Table manual wheel

14.Table lock bar

15.Saddle automatic moving bar

16.Saddle automatic moving control dial

17.Saddle manual wheel

18.Knee manual wheel

19.Quick button

Horizontal Milling Machine

1.Base2.Column3.Console4.Transversal Carriage5.Table6.Bridge7.Axis tool

1. Base: It gives support and rigidity to the machine and also acts as a reservoir for the cutting fluids.

2. Column: The column is the main supporting frame mounted vertically on the base. The column is box shaped, heavily ribbed inside and houses all the driving mechanisms for the spindle and table feed.

3. Knee: The knee is a rigid casting mounted on the front face of the column. The knee moves vertically along the guide ways and this movement enables to adjust the distance between the cutter and the job mounted on the table. The adjustment is obtained manually or automatically by operating the elevating screw provided below the knee.

4. Saddle: The saddle rests on the knee and constitutes the intermediate part between the knee and the table. The saddle moves transversely, i.e., crosswise (in or out) on guide ways provided on the knee.

5. Table: The table rests on guide ways in the saddle and provides support to the work. The table is made of cast iron, its top surface is accurately machined and carriers T-slots which accommodate the clamping bolt for fixing the work. The worktable and hence the job fitted on it is given motions in three directions:

a). Vertical (up and down) movement provided by raising or lowering the knee.b). Cross (in or out) or transverse motion provided by moving the saddle in relation to knee.c). Longitudinal (back and forth) motion provided by hand wheel fitted on the side of feed screw.In addition to the above motions, the table of a universal milling machine can be swiveled 45° to either side of the centre line and thus fed at an angle to the spindle.

6. Overarm: The Overarm is mounted at the top of the column and is guided in perfect alignment by the machined surfaces. The Overarm is the support for the arbor.

7. Arbor support: The arbor support is fitted to the Overarm and can be clamped at any location on the Overarm. Its function is to align and support various arbors. The arbor is a machined shaft that holds and drives the cutters.

8. Elevating screw: The upward and downward movement to the knee and the table is given by the elevating screw that is operated by hand or an automatic feed.

PRINCIPAL OF MILLING MACHINE

In milling machine, the metal is cut by means of a rotating cutter having multiple cutting edges.

For cutting operation, the workpiece is fed against the rotary cutter. As the workpiece moves against the cutting edges of milling cutter, metal is removed in form chips.

Machined (dimesin) surface is formed in one or more passes of the work. The work to be machined is held in a vice, a rotary table, a three jaw chuck, an index head, between centers, in a special fixture or bolted to machine table.

The rotatory speed of the cutting tool and the feed rate of the workpiece depend upon the type of material being machined.

During the machining process, the work piece can be moved up and down (Y-axis), left and right (X-axis) and also back and front (Z-axis)

METHOD OF UP CUT AND DOWN CUT OF MILLING MACHINE

Method to be used will depend on the machine and the face mill cutter that has been selected. Generally down cut machining offers longer tool life than up cut milling.

the metal is removed in form of small chips by a cutter rotating against the direction of travel of the workpiece.

In this type, the chip thickness is minimum at the start of the cut and maximum at the end of cut.

As a result the cutting force also varies from zero to the maximum value per tooth movement of the milling cutter.

The major disadvantages of up-milling process are the tendency of cutting force to lift the work from the fixtures and poor surface finish obtained. But being a safer process, it is commonly used method of milling.

Down milling is also known as climb milling. In this method, the metal is removed by a cutter rotating in the same direction of feed of the workpiece.

The effect of this is that the teeth cut downward instead of upwards. Chip thickness is maximum at the start of the cut and minimum in the end.

In this method, it is claimed that there is less friction involved and consequently (seterusnya) less heat is generated on the contact surface of the cutter and workpiece.

TYPES OF MILLING CUTTERMilling cutters are cutting tools typically used in milling machines or machining centres to perform milling operations . They remove material by their movement within the machine or directly from the cutter's shape

Side Milling Cutters - Straight Teeth

For slotting and light duty side milling.

These cutters can be ganged or used as

straddle mills.

Milling Cutters Concave

For milling male half circles.

Milling Cutters ConvexFor milling female half

circles.

Milling Cutters Plain - Light Duty

For light milling or finishing cuts.

Plain - Heavy DutyFor heavy stock

removal furnished with 45 degree left hand

helix.

Helical Plain Milling CutterFor slab or face milling

mild steels ideal for light to intermittent cut on thin parts.

These can be run at high speeds and produce smooth finishes without

leaving feed marks.

Single Angle Milling CuttersSingle Angle Cutters

are utilized for milling ratchet teeth or

dovetails.

Double Angle Milling CuttersDouble Angle Cutters are used for milling notches, grooves,

serrations or threads. Double Angle Cutters are available in 45, 60

or 90 degree.

Shank Type Milling Cutters - Concave

Shank Type Concave Milling Cutter with

weldon shank.To be used in manual or NC

Machining Centers. For Milling Male Half

Circles.

Shank Type Milling Cutters - Convex

Shank Type Convex Milling Cutter with

Weldon Shank. To be used in manual or NC Machning Centers. For

Milling Female Half Circles.

Single Angle for Angular Milling

Single Angle Milling Cutter for Chamfers and other angular milling operations.

Double Angle for Angular MillingFor Notches, V-Grooves

and other angular milling operations.

Corner Rounding Milling CuttersArbor Type. Available in Right Hand or Left

Hand Cutters. Specifically designed

to mill radii on various materials.

Woodruff Key Seat Cutters

1/2" diameter Straight Shank. Ideal for cutting standard

and woodruff keyways in steel and

other ferrous materials.

Staggered Tooth Woodruff Key Seat Cutters

Arbor Type. Staggered Tooth

Woodruff Key Seat Cutters. High Speed

Steel.

Corner Rounding End Mills

Use for rounding corners and adapting many screw machine applications as end

forming tools to form a specific radius.

CUTTING TOOL HOLDER

Solid collet

◦Has a precision ground shank that fits the spindle on the milling machine

Split collet

◦Widely used to hold cutters◦Effective cutter holding devices

Work piece holder

Work tableThe simplest method of holding a workpiece

for milling is to clamp it directly to the worktable.

Adequate tee slots are provided for this purpose.

Care should be taken to avoid machining the table – if necessary, the workpiece should be raised on a pair of parallels.

Vice

A vice is the most versatile piece of equipment for holding workpieces.

It must be positioned,to ensure accurate alignment with machine movements.

Rotary table

A rotary table is used where part of the surface being machined is of a circular nature. In this case, the table is moved to bring the workpiece in the correct position under the cutter.

The workpiece is then rotated past the cutter to produce a circular profile.

The circular table is provided with tee slots, to enable clamping of the workpiece.

A central hole enables setting of the workpiece about the centre of rotation and enables the rotary table to be set central with the machine spindle.

Concentric circles on the table surface are provided to aid the initial setting of the workpiece roughly central.

RPM,Feed rate, cutting time

RPM

Feed Rate

Safety procedures

Safety proceduresProper dress

All machine guards should be in place prior to starting up a milling machine.

Report any unsafe or dangerous practices by those around you to the person in charge.

Be careful when handling tools or sharp-

edged workpiece to avoid getting cut; use shop towel to protect your hands.

The cutting tools need to be securely fastened in the machine spindle to prevent any movement during the cutting operation. Excessive feed rates can break the cutting tool.

Never leave a running machine unattended.

Indexing

Indexing is the operation of dividing the periphery of a piece of work into any number of equal parts.

Used to divide circumference of workpiece into equally spaced divisions when milling gear teeth, squares, hexagons, and octagons

Indexing is accomplished by using a special attachment known as dividing head or index head as shown in Fig.

the indexing calculation to machine a square is :

Index crank turns = 40/N = 40/4 = 10

Where N is the required number of divisions.

The available index plate has 8 circles of 24, 25, 28, 30, 34, 37, 38 and 39 holes. Three of these hole circles, (24, 30, and 39) can be divided by this lowest common denominator of 3.

To operate the index head1. Unlock the spindle and pull back the crank pin

plunger.2. Rotate the crank the required number of turns

plus the fraction of a turn.3. Set the sector arms to keep track of the additional

holes beyond the full turn of the crank.4. Bring the crank pin around until it just drops into

the required hole. 5. If you overshoot the position, back off well past

required hole and come up to it once again. This will eliminate any backlash in worm and worm gear assembly.

Plain or Simple Dividing Head The plain dividing head comprises a cylindrical spindle housed

on a frame, and a base bolted to the machine table. The index crank is connected to the tail end of the spindle directly, and the crank and the spindle rotate as one unit. The

index plate is mounted on the spindle and rotates with it. The spindle may be rotated through the desired angle and

then clamped by inserting the clamping lever pin into anyone of

the equally spaced holes or slots cut on the periphery of the index plate.

This type of dividing head is used for handling large number of workpieces, which require a very small number of divisions on the periphery.

1. Swiveling block 2. Live centre3. Index crank 4. Index plate.