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CAD/CAM

KESHAVAMURTHY.Y.C

DEPARTMENT OF MECHANICAL ENGINEERING,

RVCE

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UNIT-II

CONTENTS

� NC, CNC, DNC Technology: Basic components of

NC system, NC procedure, Coordinate system, NC

motion control system, problem with conventional

NC system, NC control technology, Computer

numerical control, Direct numerical control systemnumerical control, Direct numerical control system

� CNC tooling: Cutting tool materials, turning tool

geometry, milling tool system, tool presetting,

automatic tool changer, work holding, selection

and applications of turning tools.

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CUTTING TOOL MATERIALS

� Various cutting-tool materials have been used in

the industry for different applications

� High speed steel

� Cemented carbides

� Coated carbides

� Ceramics� Ceramics

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HIGH SPEED STEEL

� HSS tool materials have significant quantities of

tungsten, molybdenum, chromium and vanadium.

� Complex carbides of tungsten, molybdenum and

chromium distributed through out the metal matrix

provides very good hot hardness and abrasion

resistance.

� Major alloying elements, which contributes to the � Major alloying elements, which contributes to the

hardness is tungsten and molybdenum.

� Main advantages of high-speed steels is their high

hardness, hot hardness, good wear resistance, high

toughness and reasonable cost.

� Physical coating process (PVD) allows the HSS tools to

be coated with hard nitrides of titanium and

Aluminium.

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HIGH SPEED STEEL

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HIGH SPEED STEEL

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CEMENTED CARBIDES� Cemented carbides are produced by the cold compaction of the tungsten carbide powder in a binder such as cobalt, followed by liquid phase sintering.

� Cobalt content increases, toughness and impact strength of cemented carbide increase while hardness, Young’s modulus and thermal conductivity decrease.

� Since tungsten and cobalt are expensive, some special cemented carbides having predominantly tantalum cemented carbides having predominantly tantalum carbides with Ni and Mo as binder have been developed.

� Cemented carbides being expensive are available in insert form in different shapes such as triangle, square, diamond and round.

� Each of the edge would act as a cutting edge. After all the edges as utilized, the tools are thrown out and a new bit is used in the tool holder (throwaway bits).

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CEMENTED CARBIDES

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CEMENTED CARBIDES

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COATED CARBIDES

� Tool life of the coated tools is often two to three

times that of the uncoated, also these tools can be

used at higher cutting speeds, thus increasing

productivity.

� To accomplish the same, thin coating of TiN has

been used on cemented carbide tools.been used on cemented carbide tools.

� Coatings such as titanium carbide, titanium

nitride, Aluminium oxide, hafnium nitride and

hafnium carbide or multiple coatings of the above,

are deposited generally on the carbide tool bits by

the Chemical Vapour Deposition (CVD) process.

� Coated carbides are being increasingly used in the

industry in comparison to the uncoated varieties.

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CERAMICS� Ceramics are alumina-based high refractory materials introduced specifically for high speed machining of materials which are difficult to machine such as cast iron.

� Ceramics can withstand very high temperatures, are chemically more stable and have higher wear resistance than the other cutting tool materials.

� Main problems of ceramic tools are their low strength, � Main problems of ceramic tools are their low strength, poor thermal characteristics and the tendency to chipping.

� Apart from the pure alumina based ceramics, sometimes other materials such as titanium carbide are added to enhance the transverse rupture strength.

� Ceramic tools can be used with very high cutting speeds on steels. Ceramic tools are used for machining work pieces, which have high hardness such as castings, case hardened and hardened steels.

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CERAMICS

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Summary of applications for various

cutting tool materialsTool

materialWork materials Remarks

Carbon

steels

Low strength, softer

materials, non ferrous

alloys, plastics

Low cutting speeds, low strength

materials

Low/mediu

m alloy

steels

Low strength, softer

materials, non ferrous

alloys, plastics

Low cutting speeds, low strength

materials

All materials of low and

HSS

All materials of low and

medium strength and

hardness

Low to medium cut-ting speeds, low

to medium strength materials

Cemented

carbides

All materials up to medium

strength and hard-ness

Not suitable for low

speed application

Coated

carbides

Cast iron, alloy steels,

stainless steels, super alloys

Not for Titanium alloys, not for non-

ferrous alloys as the coated grades

do not offer additional benefits over

uncoated.

Ceramics

Cast iron, Ni-base super

alloys, non ferrous alloys,

plastics

Not for low speed operation or

interrupted cutting. Not for

machining Al, Ti alloys.

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TURNING TOOL GEOMETRY� Since the cost of the CNC machine tool is high, it is necessary to use (actual time and material removal capacity) the machine to fullest extent possible.

� In the respect appropriate cutting tool and the process parameters make a lot of difference.

� Since CNC machine tools have adequate rigidity as well as high spindle speed, it is necessary to use either cemented carbide or ceramic tool according to cemented carbide or ceramic tool according to situations.

� As of now a majority of the tools used are of the cemented carbide type with indexable insert type.

� Therefore it becomes necessary to understand the ISO coding systems for these, to be able to easily make the selection.

� The actual selection of the tools for a particular application has to carefully match the geometry.

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TURNING TOOL GEOMETRY

ISO coding system for tungsten carbide inserts used in turning

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TURNING TOOL GEOMETRY

ISO coding system for tungsten carbide turning-too holders used in external

turning (SCEA- Side cutting edge angle, ECEA- end cutting edge angle)

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TURNING TOOL GEOMETRY

Typical contour capability of external turning tools

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TURNING TOOL GEOMETRY

Typical contour capability of internal turning tools

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MODULAR TOOLING SYSTEMS FOR TURNING

� In view of variety of machining needs, the tooling

systems used in CNC turning centers makes use of

different shank sizes and shapes which required

different tool holders for clamping them securely in the

tool turret.

� This makes the tool change function as well as the

design of storage magazine a difficult one.design of storage magazine a difficult one.

� This is changed by adopting a modular tooling system

such that all the tools have the same type of holding

method used, whether it is external or internal turning.

� In these tool modules the clamping end remains the

same, whatever is the type of tool.

� In these systems the tool change takes only a few

seconds, thus increasing the available productive time

in the machine tool and also stability is very high.

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MODULAR TOOLING SYSTEMS FOR TURNING

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CLAMPING SYSTEM USED IN MODULAR

TOOLING FOR TURNING TOOLS

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MILLING TOOL SYSTEM� Milling tool to be used in CNC machine tool is an

assembly of a number of parts besides the actual

cutting tool.

� Assembly consists of the adopter to suit the spindle

taper, a collet for holding the straight shank of the end

mill, a retention knob which is used by the hydraulic

draw bar in the spindle housing for retaining or draw bar in the spindle housing for retaining or

releasing the tool from the spindle, besides the actual

cutting tool, the end mill.

� CNC machine tools are versatile, they need to use a

large variety of tools to accomplish the range of

machining tasks they are capable of.

� There are number of shapes of the adopter depending

on the machine tool standard followed by the machine

tool builder.

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TOOL ASSEMBLY

Complete tool assembly as used in a CNC machining center

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RETENTION KNOB

Retention knob as used in the top of tool assembly for clamping

and releasing purpose as used in a CNC machining center.

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TOOL PRESETTING� Generation of actual geometry is taken care of by the

CNC part program, which is essentially the coordinates

through which the cutting tool tip moves, it is

important to know the actual dimensions of the tool

when it is placed in spindle.

� Relationship of the tool with reference to the tool-

holding mechanism requires a special attention during holding mechanism requires a special attention during

CNC machining process.

� The actual point to be programmed in a CNC part

program is the tip of the tool where the axes will be

moving with respect to a known point in the spindle.

� Therefore it becomes necessary to know precisely the

deviation of the tool tip from the gauge point on the

spindle. Hence tool setting equipment is generally

used.

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TOOL PRESETTING� A simple mechanical type tool setting device is used for

tool setting.

� In this system, the base is provided with the exact tape

as used in the actual machine tool.

� The assembled tool is therefore placed in the spindle

taper.

� The measurement is done with the help of a � The measurement is done with the help of a

micrometer head, which is attached to a U-clamp.

� The U-clamp can be moved manually on a post, which

has precise location slots that are separated by an

exact distance.

� The length of the tool can therefore be measured by the

measurement of the micrometer plus the slots along

the post.

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TOOL PRESETTING

� A similar tool-setting device which can measure

the length as well as the diameter of a spindle

tooling.

� The tool-measuring probe moves on two precise

axes to measure both the length and the diameter

of a spindle tooling unit.

� The display is shown digitally so that there is no

error in measurement.

� Further, they are provided with a serial port for

outputting the measured values directly into any

tool management system for the purpose of

generating the tool offset values.

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TOOL PRESETTING

Typical Tool Setting system useful for machining center tooling

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TOOL PRESETTING

Typical tool setter integrated with a CNC turning centre

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TOOL PRESETTING

Typical digital tool-setting system for machining center tooling

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AUTOMATIC TOOL CHANGER

� During the operation of a machine too, a

considerable amount of time is spent in idle

movement of tools such as tool engagement and

disengagement, tool change and tool setup.

� To improve the machine utilization, it is necessary to

minimize these idle motions.

� To that extent automatic tool changers or ATC, plays � To that extent automatic tool changers or ATC, plays

a very important role.

� ATC are particularly useful in machining

applications where a number of tools are to be used

for finishing the job.

� ATC is single factor which makes a CNC machine

tool more autonomous with little operator

intervention.

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AUTOMATIC TOOL CHANGER

� For the automatic tool changer to operate, it is

necessary to have the following:

a) A tool magazine where sufficient number of tools

can be stored.

b) The tool adopter that has a provision for pick-up

by the tool change arm.by the tool change arm.

c) The ability in the control to perform the tool

change function.

d) Tool change procedure

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TOOL MAGAZINES� Tool magazines to be used have to be considered in

terms of the following attributes.

� Storage capacity

� Type and shape

� Tool change procedure

� Simplest type of tool magazine is a turret. This

method combines tool storage with the tool change method combines tool storage with the tool change

procedure, without the need for a tool change arm.

� Turret simply indexes to bring the tool into the

position of machining, since the spindle is combined

with the tool turret.

� The next type of tool magazine found in most of the

machine tools with lower tooling requirements is the

drum or disc type magazine.

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TOOL MAGAZINES� In drum type tool magazine, drum rotates for the

purpose of tool change to bring the required tool to

the tool change arm.

� The diameter of the disc is indicative of the number of

tools it can hold.

� As the number of tools in the magazine increases, its

diameter becomes too large to be practical.diameter becomes too large to be practical.

� For storing large number of tools, a chain type tool

magazine provides the necessary flexibility.

� In chain type, the tools are attached to the pockets

which are in turn attached to the chain which is

moving on appropriate sprockets.

� The chain allows for a very large variety of

arrangements.

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TOOL MAGAZINES

TYPICAL TOOL TURRET USED IN CNC DRILL/MILLING MACHINES

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TOOL MAGAZINES

CNC drilling machine using a tool turret

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TOOL MAGAZINES

CNC machining center with a drum type tool magazine

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TOOL MAGAZINES

A chain type tool magazine for holding larger number of

spindle tooling used in CNC machining centers.

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TOOL MAGAZINES

Variations of chain type tool magazines.

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TOOL MAGAZINES

An example of a chain type tool magazine with a capacity of 100 tools

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TOOL CHANGING

� In case of turret, the tool changing is

relatively simple, because of the turret

indexing.

� In case of other tool magazines, it is

necessary to have a tool changing arm which

can provide the necessary tool transfer.can provide the necessary tool transfer.

� The tool magazine is placed close to the

spindle such that the actual tool transfer

does not consume a lot of time.

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TOOL CHANGING� The tool change activity requires the following motions:

i. Stopping the spindle at the correct orientation for the tool change arm to pick the tool from the spindle.

ii. Tool change arm to move to the spindle.

iii. Tool change arm to pick the tool from the spindle.

iv. Tool change arm to index to reach the tool magazine.

v. Tool magazine to index into the correct position where the v. Tool magazine to index into the correct position where the tool from the spindle is to be placed.

vi. Place the tool in the tool magazine.

vii. Indexing the tool magazine to bring the required tool to the tool change position.

viii.Tool change arm to pick the tool from the tool magazine.

ix. Tool change arm to index to reach the spindle.

x. New tool is placed in the spindle.

xi. Tool change arm moves into its parking position.

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TOOL MAGAZINES

One common type of tool-change arm used for tool changing with a double gripper

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TOOL CHANGING SEQUENCE

� Sequence of tool changing in case of a double gripper.

i. Tool magazine to index into the correct position where

the tool from the spindle is to be placed.

ii. Stopping the spindle at the correct orientation for the

tool change arm to pick the tool from the spindle. (a)

iii. Tool change arm to index to reach the tool magazine.

iv. Tool change arm to pick the tool from the spindle and

the tool magazine simultaneously (b)

v. Tool change arm to index to reach the tool magazine. (c)

vi. New tool is placed in the spindle and the tool

magazine.(d)

vii. Tool change arm moves into its parking position.

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TOOL CHANGE PROCEDURE

Tool change procedure with a tool change arm having a double gripper

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TOOL CHANGE PROCEDURE

Tool change procedure with a tool change arm having a double gripper

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WORK HOLDING

� Work holding in CNC machine tools is more

important since the conventional work holding

devices such as vices or chucks are rarely used

except for very simple components.

� For complex shapes of the work pieces, it become

necessary to use some special fixtures for quick necessary to use some special fixtures for quick

set up of the work pieces.

� Modular fixturing systems, which are in trend for

conventional machine tools have been refined and

are widely used for holding the work pieces in

CNC machine tools.

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WORK HOLDING

� Grid plates are generally used as one of the

fixturing bases.

� The grid plates are provided with precisely drilled

and tapped holes to facilitate the clamping

operation.

� Since the holes on these grid plates are made at � Since the holes on these grid plates are made at

precise positions, the operator would know the

exact location of the component depending upon

clamping.

� In addition to these standard fixture bases, a

large number of fixture elements such as angle

blocks and base elements are used to quickly

clamp the work pieces in position.

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WORK HOLDING

Grid plate with holes which can be used as a machine table.

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WORK HOLDING

Tombstone for mounting multiple components on different places

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WORK HOLDING

Modular fixture elements used for supporting complex work pieces.