unit ii cnc tooling
DESCRIPTION
CNC tollingTRANSCRIPT
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CAD/CAM
KESHAVAMURTHY.Y.C
DEPARTMENT OF MECHANICAL ENGINEERING,
RVCE
UNITUNITUNITUNIT----IIIIIIII
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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.