1. INTRODUCTION TO CNC MACHINING

CNC stands for Computer Numerical Control. It is in practice in

since 1970s. Till that time the controlling system used for Machine tools is Numerical

Control which involved use of programmed tapes for controlling the Machine tools.

CNC machining stands for Computer Numerical Control machining.

In this a computer controller reads code and instructions (in the form of a program) and

drives a machining tool in order to make a product according to specific requirements. It is

a union of the field s of Software and Manufacturing that gives very effective and useful

outputs. Before there was CNC machining, there was NC machining. NC stands for

numerically controlled machining. This kind of machining does not use the aid of

computers and can not be reprogrammed to suit the manufacturer’s or customer’s needs.

Making products was very straight cut and inflexible in Numerical Control Machining.

1.1 Advantages of CNC machining:

Setup time reduction:

Modular fixturing, standardised tooling, fixed locators, automatic

tool changing, pallets, and other advanced features make setup time in CNC

machining more efficient.

Lead time reduction:

Once a part program is written and is found to give the correct

output, then it is ready to be used again in future. So though the lead time is

comparatively more for first time, the lead time for second and subsequent

production of the same component is less or virtually nil. Any engineering

modification can be obtained by just modifying the program.

1

Accuracy and repeatability:

The accuracy of the CNC machining is very high. It is of the order

of 0.005. In CNC machining the same product can be obtained any number of

times.

Contouring of complex shapes:

CNC lathes and machining centres are capable of contouring a large

variety of different shapes without making a prototype or model of that component.

Consistent cutting time:

Cutting time is known as “cycle time” in CNC machining

terminology. It is always consistent, i.e. a CNC machine takes same amount of time

for producing each unit of same component.

Easy way of updating:

The CNC machines can be easily updated by just improving the

software used to drive the machine.

Single user can supervise more than one machine simultaneously:

One person can supervise many CNC machines as once they are

programmed they can usually be left to work by themselves. Sometimes only the

cutting tools need replacing occasionally.

Excellent surface finish:

The surface finish of the component that is produced by CNC

machining is very high.

Reduction of Human error:

The use of computer program eliminates the need for an operator to

take trial cuts, make trial measurements, and make positioning movements or

change tools. This reduces the human error in obtaining the desired component.

2

Lower tooling cost:

CNC machines generally use simple holding fixtures, which reduce

the cost of tooling by as much as 70 percent. Standard turning and milling tools

eliminate the need the need for special form tools.

Greater machine tool safety:

As there is less intervention of the operator the operator error is

eliminated resulting in greater machine tool safety.

Simplified tooling:

Non-standard and operator machined tooling are used in a

conventional machine, which can be eliminated by using standard tooling, specially

designed for computer numerical control applications. Multi-step tools such as pilot

drills, step drills, combination tools, counter borers and others, are replaced with

several individual standard tools in the case of CNC machines. These tools are

often cheaper and easier to replace than special and non-standard tools.

Simplified work holding:

Fixtures and work holding devices used for CNC machines have

only one major purpose, to hold the part rigidly and in the same position. Fixtures

designed for CNC work do not normally require special jigs, pilot holes and other

hole-locating aids.

3

1.2 Applications of CNC machining:

In industries for removing metal:

The metal removing industries remove the metal from the raw

material to give it the desired shape as per the requirements. These can be the

automotive industries for making the shafts, gears, and many other parts. These can

be manufacturing industries for making the various rounded, square, rectangular,

threaded and other jobs. All these metal removal works are performed by different

machine tools like lathe, milling machine, drilling machine, boring machine,

shaping machine, reamer, etc. Traditionally these machines are operated by the

operators, but the CNC versions of all these machines are now used extensively.

In industries for fabricating metals:

In many industries thin plates like steel plates are required for

various purposes, in fabrications industry the machining operations are performed

on such plates. In these industries the CNC machines are used for various

machining operations like shearing, flame or plasma cutting, punching, laser

cutting, forming, and welding and many other applications. To bring the plates to

their final shape CNC lasers and CNC plasma cutters are used commonly. To punch

the holes in the plates of all sizes CNC turret punch presses are used. And if you

want to bend the plate so as to give it a final shape, you can use CNC press brakes.

In some cases the CNC back gages are coupled with the shearing machines, this

enables controlling the length of the plate to be sheared as for different applications.

Electrical Discharge Machining (EDM) industry:

The EDM machines remove the metal by creating the sparks that

burn the metal. There are two types of EDM with the CNC automation – Vertical

EDM and Wire EDM. The Vertical EDM needs an electrode of the shape and size

of the cavity that is be made in the job. Wire EDM is used to make the punch and

die combinations for the dies set that are used in the industries where fabrication is

done.

CNC metal spinning:

4

It involves a lathe set with a blank that rotates at high speeds while a

metal spinning roller shapes the work piece into a desired shape.

Surface finishing with CNC machines:

Ultra finished surfaces are obtained by using a Computer Numerical

Controlled grinding machine. Normally the surface grinding machine is used for

final machining process to the work piece which has been machined by other

method to get high accuracy in dimension of the work piece.

Other industries where CNC machines are used:

CNC machines are also used extensively in the wood working

industries to perform various operations like routing and drilling. CNC technology

is also used in number of lettering and engraving systems. There are also CNC

machines for the electrical industry such as CNC coil winders, and CNC terminal

location and soldering machines.

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2. COORDINATE GEOMETRY

2.1 Description:

One of the first and foremost steps towards basic understanding of

CNC principles and geometrical concepts is thorough understanding of a subject known in

mathematics as the system of coordinates. System of coordinates is founded on a number

of mathematical principles dating back over four hundred years. The most important of

these principles are those that can be applied to CNC technology of today. In various

publications on mathematics and geometry, these principles are often listed under the

headings such as the real number system and the rectangular coordinates.

2.2 Rectangular coordinate system:

Basic system:

Rectangular coordinate system is a concept used to define a planar 2D

point (two dimensions), using the XY coordinates, or a spatial 3D point (three dimensions),

using the XYZ coordinates. It is also called as the Cartesian coordinate system.

Fig. 2.1 Rectangular Coordinates Fig. 2.2 Origin and axes

A given point can be mathematically defined on a plane or in space.

The definition of one point is relative to another point as a distance parallel with one of

three axes that are perpendicular to each other. In a plane, only two axes are required, in

space, all three axes must be specified. In programming, point represents an exact location.

If such a location is on a plane, the point is defined as a 2D point, along two axes. If the

6

location is in space, the point is defined as a 3D point, along three axes. The intersection of

two points is called Origin. It refers to the point (0, 0) in 2D coordinate system and (0, 0, 0)

in 3D coordinate system.

Quadrants:

Viewing the two intersecting axes and the new plane, four distinct

areas can be clearly identified. Each area is bounded by two axes. These areas are called

quadrants. A quadrant is any one of the four parts of the plane formed by the system of

rectangular coordinates.

Fig. 2.3 Quadrants

Right hand coordinate system:

In the right-hand coordinate system, the positive axis starts at origin

and is directed towards the right for X-axis, upwards for Y-axis and towards the

perpendicular viewpoint for Z-axis. Opposite directions are always negative.

Machine geometry:

Machine geometry defines the relationship of distances and

dimensions between fixed point of the machine and selectable point of the part. Typical

geometry of CNC machines uses the right hand coordinate system.

Absolute Coordinate System:

CNC machines are normally programmed using the absolute

coordinate system, which is based on the point of origin being (0,0,0). This absolute

programming method follows very strictly the rules of rectangular coordinate geometry.

7

User Coordinate System:

A CNC machine of any type can be designed with one or more

additional axes, normally designated as the secondary - or parallel - axes using the U, V

and W letters. These axes are normally parallel to the primary X, Y and Z axes

respectively.

3D Coordinate representation:

Fig. 2.4 3D-Coordinate System

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3. TYPES OF CNC MACHINE TOOLS

3.1 Description:

Different types of CNC machines cover rather large variety. Number of

installations is rapidly increasing, and the technology development advances at a rapid

pace. It is impossible to identify all possible applications, they would make along list. Here

is a brief list of some of the groups CNC machines can be part of:

Mills and Machining centres

Lathes and Turning centres

Drilling machines

Boring mills and Profilers

EDM wire machines

Punch presses and Shears

Flame cutting machines

Routers

Water jet and Laser profilers

Cylindrical grinders

Welding machines

Benders, Winding and Spinning machines, etc.

CNC machining centers and lathes dominate the number of installations in an

industry. These two groups are the most prominent of the types of CNC machine tools.

Some industries may have a higher need for a particular type of machines, depending on

their needs. There are many models of lathes and machining canters available. However,

the programming process for a vertical machine is similar to the one for a horizontal

machine or even a simple CNC mill, for example. Even between different machine groups,

there is a great amount of general applications, while the programming process is generally

unchanged. For example, a contour milled with an end mill has a lot in common with a

contour cut with a wire on an EDM machine.

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3.2 Mills and Machining Centers:

CNC mills, also called CNC milling machines are usually small, simple

machines, without a tool changer or other automatic features. Their power rating is often

low. In industry, they are used for tool room work, maintenance purposes, or small part

production. They are usually designed for simple contouring, unlike CNC drills. Minimum

number of axes on a milling machine is three (X, Y and Z axes). Part set on a milling

machine is always stationary, mounted on a moving machine table. The cutting tool

rotates, it can move up and down but it does not physically follow the tool path.

CNC machining centers are far more efficient than CNC drills and CNC mills

mainly in case of their flexibility. The main benefit users get out of a CNC machining

center is the ability to group several diverse operations into a single setup. For example,

drilling, boring, counter boring, tapping, spot facing and contour milling can be

incorporated into a single CNC program operation. In addition, the flexibility is enhanced

by automatic tool changing, using pallets to minimize idle time, indexing to a different face

of the part, using a rotary movement of additional axes, and number of other time saving

features. CNC machining center scan be equipped with special software that controls

cutting speeds and feeds, life of the cutting tool, automatic in-process gauging, broken tool

detection, offset adjustment and other production enhancing and time saving devices.

There are two basic designs of a typical CNC machining center. They are

vertical and horizontal machining centers .The major difference between the two types is

the nature of work that can be done on them efficiently. For a vertical CNC machining

center, the most suitable type of work are flat parts, either mounted to the table fixture, or

held in a vise or a chuck. The work that requires machining on two or more faces (sides) in

a single setup is more desirable to be done on a CNC horizontal machining center .A good

example is pump housing and other cubic-like shapes, often irregular. Some multi-face

machining of small parts can also be done on a CNC vertical machining center equipped

with a rotary table.

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3.3 Lathes and Turning Centers:

A CNC lathe in its basic form is a machine tool with two axes, vertical X axis

and horizontal Z axis. The main feature of a lathe that distinguishes it from a mill is that

the part is rotating about the machine center line. In addition, the cutting tool is normally

stationary, mounted in a sliding turret. Cutting tool follows the contour of the programmed

tool path.

A CNC lathe can be horizontal or vertical one. Horizontal type is far more

common than vertical type, but both designs have their purpose in manufacturing. Several

different designs exist for either group. For example, a typical CNC lathe of the horizontal

group can be designed with a flat bed or a slant bed, as a bar type, chucker type or a

universal type. Added to these combinations are many accessories that make a CNC lathe

an extremely flexible machine tool. Accessories such as tailstock, steady rests or follow-up

rests, part catchers, pullout fingers and a third axis milling attachment are popular

components of CNC lathes. A CNC lathe can be very versatile - so versatile in fact, that it

is often called a CNC Turning Center.

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4. CNC TURNING CENTRE

4.1 Introduction:

Conventional engine lathe or a turret lathe is a common machine in

just about every machine shop. A lathe is used for machining cylindrical or conical work,

such as shafts, rings, wheels, bores, threads, etc. A lathe can also be used for internal

operations such as boring, as well as for facing, grooving, threading, etc., if a proper

cutting tool is used. Turret lathes are usually weaker in machining power than engine

lathes, but they do have a special holder that stores several mounted cutting tools. An

engine lathe has often only one or two cutting tools mounted at a time, but it has more

machining power.

The term 'turning centre' is an overall description of a CNC lathe that

can be used for a great number of machining operations during single setup. For example,

in addition to the standard lathe operations such as turning and boring, CNC lathe can be

used for drilling, grooving, threading, knurling and even burnishing. It can also be used in

different modes, such as chuck and collets work, bar feeder, or between centers. Many

other combinations also exist. CNC lathes are designed to hold several tools in special

turrets, they can have a milling attachment (live tooling), chuck with indexing, a sub

spindle, tailstock, steady rest and many other features not always associated with a

convention all a the design. The tools possess changeable special “inserts”.

4.2 Lokesh CNC turning centre – TL 30 ER:

Fig. 4.1 Overview of the LOKESH-TL30ER turning centre

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Specifications:

Table 4.1 Specifications of TL30ER turning centre

I

II

III

Capacity:

Bed

Swing over saddle

Max. turning dia.(overall length)

Max. turning length(without chuck)

Max. turning length(with chuck)

Distance between centers

Component loading height

Distance from Guard to spindle centre

Spindle:

Spindle nose

Front bearing size

Bearing accuracy class

Bore through spindle

Spindle ID taper

Spindle power

Spindle speed

Full power range

Bar capacity

Tailstock:

Quill dia.

Quill stroke

Quill taper

Base travel

mm

mm

mm

mm

mm

mm

mm

No.

mm

ISO

mm

No.

KW

rpm

rpm

rpm

mm

mm

No.

mm

30º to Horizontal

Ø500

Ø340

510

460

620

1000

400

A2 -6

100

P4

56

MT-6

11/15

50-5000

1250-5000

40

90

120

MT-4

395

13

IV

V

VI

VII

VIII

Chuck:

Model

Size

Gripping range

Through hole

Chucking Cylinder:

Model

Max. pulling force

Piston stroke

Through hole

Z-axis:

Stroke

Rapid traverse

Motor type

Motor max. speed

X-axis:

Stroke

Rapid traverse

Motor (Built in brake)

Motor max. speed

Turret:

Model

No. of stations

Tool shank size

Max. boring bar dia.

Index time (30º)

Index time (180º)

No.

mm

mm

mm

No.

Kgf.

mm

mm

mm

m/min

rpm

mm

m/min

rpm

No.

mm

mm

sec

sec

sec

B- 208 (Kitagawa)

Ø210

Ø13-Ø210

Ø52

S 1552 (Kitagawa)

5710

22

Ø52

510+(15 Safety on each side)

30

Alpha 12/3000i

3000

260(170+90)+2x15 Safety

30

Alpha 8/3000i

3000

SMH 20 (Diplomatic)

12

25x25

Ø40

0.31

0.82

14

IX

X

XI

Accuracies:

Position accuracy

Repeatability

Turret indexing accuracy

Turret repeatability

Coolant system:

Coolant tank capacity

Coolant pump capacity

Machine physical parameters:

Total connected power

Overall sizes without chip conveyor (LxBxH)

Machine weight

mm

mm

I

Ipm

KVA

mm

Kg

0.01

±0.005

±4”

±1.6”

140

120

43

2600x2700x1730

4500

15

4.3 Constructional features of Lokesh TL 30 ER turning centre:

Fig. 4.2 Various parts inside a turning centre’s cabin

Bed:

The turning centre has a robust rear type slant bed. It is 300 to the

horizontal. The entire machine is based on the bed.

Casing and doors:

This is the outer protective cover that compactly encloses the internal

machinery of the turning centre and the doors give access to the interior of the cabin of

turning centre when opened and prevents the coolant from splashing outside when closed.

Hydraulic chuck:

The function of the hydraulic chuck is to clamp and unclamp the job.

It has three jaws that hold the job in between them. The jaws vary for different sizes of the

jobs that are to be held. The jaws can be removed and changed according to the

requirement. The clamping and unclamping of job is entirely a hydraulic mechanism.

Fig 4.3 Hydraulic chuck of the turning centre.

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Tailstock:

Its purpose is same to that as in conventional lathe. The tailstock is

used to support long jobs at both ends, that is one end in chuck and the other end is

supported by the tailstock. The movement of quill is controlled by hydraulic mechanism.

Fig. 4.4 Tailstock of a turning centre.

Turret:

The turning centre has a twelve station, bidirectional indexing turret.

The turret is designed to hold twelve different tools simultaneously. During the CNC

machining process the turret automatically rotates to bring the right tool, to right position,

at right time of the process. The motion of the turret is controlled by hydraulic mechanism.

Fig. 4.5 The turret of a turning centre.

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Lubricating system:

A centralised lubrication system is incorporated in the machine. The

lubricant is pumped to all the required regions in the machine along pipelines. The

lubricant used is servo way32 lubricating oil. The lubrication unit supplies the lubrication

oil to side ways of the X-axis and Z-axis at an interval of 30 minutes. Also the lubricant is

pumped once as and when the CNC ON button is pushed in the control panel. The

lubrication unit is preset with pressure setting relief valve. However it should be reset if the

viscosity of the oil changed.

Chip evacuation system:

The chip evacuation system employed in this machine is an automatic

chip conveyor. The conveyor takes away the chip in the cabin that falls on it to outside of

the machine and dumps the chip in the chip collection bin. All this process takes place

when the chip conveyor button on the control panel is in on position.

Stabilizer:

The CNC turning centre is supplied with 3-pahse input power by an

Exelon stabilizer. The rating of the stabilizer is 20 KVA. The input frequency is 5o Hz.

The input voltage to the stabilizer is 295V-465V and the output of the stabilizer is 415V.

Operation panel:

The entire machining and other operations of the CNC turning centre

are controlled by the various functions that are present on the operation panel. It has

various functions like mode selection, rapid over ride, program edit lock, CNC on-off,

coolant on-off, start and stop operation, spindle speed, automatic feed etc.

Fig. 4.6 The operation panel of a turning centre.

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Control panel:

The control panel has two main components- keypad and a display

screen. The display screen shows the program that is fed into the control system and other

operational features like feed, speed of spindle, coordinates of tool and work piece etc.

Fig. 4.7 The control panel of a turning centre.

Cooling system:

A continuous supply of coolant is pumped to the part that is machined.

The coolant used is Servo-S coolant oil (Servo 68 oil). The control panel is cooled by an

air cooler to keep it at desired room temperature.

Hydraulic system:

The motion of the quill, turret, clamping and unclamping of chuck are

all controlled by the high pressure hydraulic system. Especially the motion of the turret is

controlled by hydraulic mechanism in conjunction with telescopic covers.

Fig. 4.8 Telescopic covers

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4.4 Coordinate system of a turning centre:

A typical CNC turning centre is designed with two standard axes - one

axis is the X-axis, the other axis is the Z-axis. Both axes are perpendicular to each other

and represent the typical two-axis turning centre’s motions. X-axis also represents cross

travel of the cutting tool, Z-axis represents its longitudinal motion. All varieties of cutting

tools are mounted in a turret. Because of this design, a turret loaded with all cutting tools

moves along both X and Z axes, which means all tools are in the work area at all times.

Fig. 4.9 Coordinates of a turning centre.

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5. CNC MILLING CENTRE

5.1 Introduction:

CNC milling machines vary in size, features, suitability for certain work, but they all have

one common denominator, that is , their primary axes are X and Y axes and for this

reason, they are called the XY machines. Milling machine is a machine capable of a

simultaneous cutting motion, using an end mill as the primary cutting tool, along at least two axes

at the same time. It even performs more operations than milling.

5.2 General specifications of a vertical milling machine:

Table 5.1 General specifications of CNC vertical milling machine

Sl. No. Description Specification

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Number of axes

Table dimensions

No. of tools

Max. travel of X-axis

Max. travel of Y-axis

Max. travel of Z-axis

Spindle speed

Spindle output

Spindle nose to table distance Z-axis

Spindle centre to column distance Y-axis

Spindle taper

Tool shank size

Feed rate range

Rapid traverse range

Tool selection

Max. tool diameter

Max. tool length

Tool change time (chip to chip)

3 axes (XYZ)

780 x 400 mm

20

575 mm

380 mm

470 mm

60-8000 rpm

AC 7.5/5/5 KW

150-625 mm

430 mm

No. 40

CAT 50

2-10000 mm/min

40000 mm/min (XY)

35000 mm/min (Z)

Random memory

80 mm (150w/ empty pockets)

300 mm

2.5 seconds

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5.3 Construction of a CNC vertical milling machine:

Fig. 5.1 Vertical CNC milling machine

Bed:

The vertical milling machine has a robust rear type slant bed. It is 300

to the horizontal. The entire machine is based on the bed.

Casing and doors:

This is the outer protective cover that compactly encloses the internal

machinery of the turning centre and the doors give access to the interior of the cabin of

turning centre when opened and prevents the coolant from splashing outside when closed.

Clamping system:

The job is clamped on the machine table using a solid heel clamp on

the table. The screw is loosened and the job is placed between the table surface and the

clamp. Then the screw is tightened.

Fig. 5.2 Clamping of work piece on table.

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ATC:

ATC stands for automatic tool changer. It has a tool magazine and a

gripper. The tool magazine carries all the tools that are required. The gripper replaces the

current tool with the required tool. The capacity of the tool magazine in the CNC milling

machine’s ATC is 20 tools.

Fig. 5.3 ATC

Telescopic covers: The motion of the table is controlled by hydraulic mechanism

in conjunction with telescopic covers.

Fig. 5.4 Telescopic covers

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Lubricating system:

A centralised lubrication system is incorporated in the machine. The

lubricant is pumped to all the required regions in the machine along pipelines. The

lubricant used is servo way32 lubricating oil. The lubrication unit supplies the lubrication

oil at an interval of 30 minutes. Also the lubricant is pumped once as and when the CNC

ON button is pushed in the control panel. The lubrication unit is preset with pressure

setting relief valve. However it should be reset if the viscosity of the oil changed.

Stabilizer:

The CNC milling machine is supplied with 3-pahse input power by an

Exelon stabilizer. The rating of the stabilizer is 20 KVA. The input frequency is 5o Hz.

The input voltage to the stabilizer is 295V-465V and the output of the stabilizer is 415V.

Operation panel:

The entire machining and other operations of the CNC turning centre

are controlled by the various functions that are present on the operation panel. It has

various functions like mode selection, rapid over ride, program edit lock, CNC on-off,

coolant on-off, start and stop operation, spindle speed, automatic feed etc.

Fig. 5.5 The operation panel of a CNC milling machine.

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Control panel:

The control panel has two main components- keypad and a display

screen. The display screen shows the program that is fed into the control system and other

operational features like feed speed of spindle, coordinates of tool and work piece etc. The

key pad is useful for manipulating the data entry.

Fig. 5.6 The control panel of a CNC milling machine.

Cooling system:

A continuous supply of coolant is pumped to the part that is machined.

The coolant used is Servo-S coolant oil (Servo 68 oil). The control panel is cooled by an

air cooler to keep it at desired room temperature.

5.4 Coordinate system of a vertical CNC milling machine:

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Fig. 5.7 Coordinate system of a CNC milling machine.

A typical vertical machining centre has three mutually perpendicular

controlled axes, defined as X-axis, Y-axis, and Z-axis. X-axis is parallel to the longest

dimension of machine table, Y-axis is parallel to the shortest dimension of the table and Z-

axis is the spindle movement. So the X and Y directions specify the table movement, while

the Z-direction specifies the tool movement.

6. CONTROL SYSTEM OF A CNC MACHINE

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6.1 GENERAL DESCRIPTION:

A CNC machine is equipped with a computerized numerical control

system. In an analogy of the machine tool being the body of a CNC machine system, the

control unit is its brain. All machine speeds, feeds, axes motions and hundreds of other

tasks are programmed by a CNC programmer and controlled by a computer that is major

part of the CNC unit.

Any control unit has two basic components - one is the operation

panel, full of rotary switches, toggle switches and push buttons and the other component is

the display screen with a keyboard or a keypad. CNC programmer has to use either the

operation panel or the display screen. The control unit of a CNC system contains features

that work in conjunction with the program. Some features can be used only if the program

supports them. All switches and buttons and keys are used by the machine operator, to

exercise control over program execution and machining process.

Fig. 6.1 Operation panel of a CNC machine.

Features of operation panel:

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Table 6.1 Features of operation panel

Sl.

No.

Feature Description

1

2

3

4

5

6

7

8

9

10

On/Off switch

Cycle start

Emergency stop

Free hold

Single block

Optional stop

Block skip

Dry run

Spindle over ride

Feed rate over ride

Power and control switch for the main power

and control unit.

Starts program execution or MDI command.

Stops all machine activity and turns off power to

control unit.

Temporarily stops motion of all axes.

Allows program to run one block at a time (one

block is executed each time start cycle is

pressed).

Temporarily stops program execution (M01

required in program).

Ignores blocks preceded with a forward slash

(/) in the program.

Enables program testing at fast feed rates

(without a mounted part).

Overrides programmed spindle speed, usually

within 50-120% range.

Overrides programmed feed rate, usually within

28

11

12

13

14

15

16

17

18

19

20

21

22

Chuck clamp

Table clamp

Coolant switch

Gear selection

Spindle rotation

Spindle orientation

Tool change

Reference position

Handle (MPG)

Tailstock switch

Indexing table switch

MDI mode

0-200% range.

Shows current status of the chuck clamping

(Outside / Inside clamping).

Table Clamp Shows current status of table

clamping.

Coolant control ON / OFF / AUTO.

Shows current status of working gear range

selection.

Indicates spindle rotation direction (clockwise

or counter clockwise).

Manual orientation of the spindle.

Tool Change Switch allowing a manual tool

change.

Switches and lights relating to setup of machine,

from reference position.

Manual Pulse Generator (MPG), used for

selection of and handling increment switches.

Tailstock and/or quill switch to manually

position the tailstock.

Manually indexes machine table during setup.

Mode Manual Data Input mode.

29

23

24

25

26

27

28

29

30

31

Auto mode

Memory mode

Tape / Ext or DNC mode

Edit mode

Manual mode

Jog mode

Rapid mode

Memory access mode

Error lights

Allows automatic operations.

Allows program execution from memory of the

CNC unit.

Allows program execution from an external

device, such as a desktop computer (Direct

Numerical Control) or a punched tape.

Allows changes to be made to a program stored

in CNC memory.

Allows manual operations during setup.

Selects jog mode for setup. In this mode the

coordinates can be set using X, Y, Z, buttons

quickly.

Selects rapid motion mode for setup. The

motion is faster than the initial speed for which

program is written.

Key (switch) to allow program editing.

Red light indicates an error in corresponding

field.

Control panel:

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Fig. 6.2 The control panel of a CNC machine.

The control panel has two main components- keypad and a display

screen. The display screen shows the program that is fed into the control system and other

operational features like feed, speed of spindle, coordinates of tool and work piece etc. The

key pad is useful for manipulating, entering and deleting the data on the screen and other

data entry related functions.

7. INSPECTION

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7.1 Definitions:

Quality:

Quality in manufacturing context can be defined as the degree to

which a product or its components conform to certain standards that have been specified by

the designer.

Inspection:

The process of checking the quality of a product or a component is

called as inspection. The inspection process enquires into the deviations of a component

from standard specifications. These deviations are known as defects.

Manual inspection:

The process of manual inspection is done by:

1. Visual inspection.

2. Using instruments.

In visual inspection the parts or components are observed and defects

are identified. It is the basic method of inspection. The operators of machines usually

segregate the defective parts.

Using instruments like micrometer, vernier calipers, depth gauge

various dimensions of the parts or components are checked. Another way of inspection is

using the limit gauges. Using go and no-go gauges the components are checked for any

deviation. Go gauge corresponds to the maximum metal limit and no-go gauge corresponds

to minimum metal limit of the component.

If the go gauge passes through a component and no-go gauge doesn’t

pass then the part is within the standard limits. If both the gauges doesn’t pass it means that

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the hole is of under size or the shaft is of over size. If both gauges pass then it means that

the hole is of over size or the shaft is of under size.

7.2 Tesa microhite plus M 600 (Inspecting machine):

Tessa microhite plus M 600 is a height gauge used to check the

deviation of the dimensions of a part or a component from its standard design dimensions.

It has a robust base, a magnetic V-block that holds the job, a display unit that shows the

mode of the system and the measurement of the deviation. This microhite enables 2D

measurement that is measurement in two directions.

First a standard is placed on the base of the microhite and then the

microhite probe is adjusted to the height of the probe. Then the job that is to be checked is

positioned in required manner in the magnetic V-block. Then the reference point is set.

Then various dimensions (up to the tip of the probe) are obtained with respect to reference

point . The obtained values are verified for allowable deviation.

Fig. 7.1 Tesa microhite 600 plus M.

8. CONCLUSION

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After studying and analysing the processes of CNC machining and

inspection it was found out that Computer Numerical Control machining is more efficient

and economical than conventional machining process. It saves time, cost of production,

increases productivity and accuracy, and gives the products a very high degree of surface

finish. Considering all these benefits CNC machines make an essential part of a machine

shop of any manufacturing industry.

Inspection is a very important process in any industry. The efficiency

of the process of inspection determines the quality of the products or components

manufactured by an industry.

It is also observed that if the inspection process is integrated with the

CNC machining (instead of a separate inspection process) a lot of time, resources and

material can be saved.

BIBILOGRAPHY

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1) CNC programming hand book by Peter Smid

2) www.google.com

3) www.cnczone.com

4) www.wikipedia.com

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