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CNC Machines and its Components

- Numerical Control Machines - Computer Numerical Control Machines - CNC Components

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CNC MACHINESCNC MACHINES AND ITSAND ITS
COMPONENTSCOMPONENTS
( Mechanical Engineering / Special Machines / Unit 5)( Mechanical Engineering / Special Machines / Unit 5)
v CNC Machines
vComponents of CNC machine
Prepared by
Dr.S.Cartigueyen, M.Tech., Ph.D.
v CNC MACHINES
o  Modern  manufacturing  systems  are  advanced  automation  systems.  The  numerical 
control (NC) and computer numerical control (CNC) machines are an integral part of 
the automation systems.
o CNC machining is capable of meeting the tightest tolerances, and producing the most 
accurate, precise products over and over again. First ‘CNC Machining’ means :
Machining : Process of removing metal with the assistance of mechanical machines.
NC – Numerical Control : Governing  the  machines  automatically  through  a  set  of 
instructions (letters, numbers, symbols).
CNC – Computer Numerical Control : Process by which an operator can write, adjust 
and implement instructions using a computer comfort.
q Numerical Control (NC)
o  NC  is  defined  as  control  of  machine  slide  movements    and  various  functions  by 
means of letters, numbers and symbols
o Letters, numbers and symbols forming some sequence is called Part Program.
o  The  part  program  is  arranged  in  the  form  of  blocks  of  information.  Each  block 
contains the alphanumerical data required to produce one segment of the work piece. 
o  The  part  program  is  translated  into  the  appropriate  electrical  signals  for  input  to 
motors that run the machine.
2Dr.S.Cartigueyen
q Components of NC System
o Three basic components are 1. Program of instructions 2. Machine control 
unit (MCU) and 3. Machine tool.
o The coded instructions are to cause the machine to perform a specific series 
of operations. Basically, it is control of machine tools by numbers.  
 Functions automated by NC system
- Starting and stopping of machine tool spindle.
- Controlling the spindle speed.
- Positioning the tool tip
- Guiding the tool in desired paths
Advantages
• Reduces non productive time
• Reduces manufacturing lead time
• Greater manufacturing flexibility
• Improves quality control
• Reduced inventory
Disadvantages
• High investment cost
• High maintenance effort.
• Part programming
• Higher utilization of NC equipmentsBasic Components of NC System
3Dr.S.Cartigueyen
q CNC System
o To overcome the shortcomings of the NC systems, CNC systems are evolved.
o CNC machines are the NC machines whose MCU is based on the microcomputer 
rather than the hardwired controller.
o  A CNC system consist of the following
1. Input device        2. Machine control unit (MCU)  3. Machine tool  
4. Driving system   5. Feedback devices                     6. Display unit
Schematic diagram of a CNC System
4Dr.S.Cartigueyen
q Working Principle of a CNC System
o  In  CNC  systems  the  part  program  is  fed  into  the  computer.  Then  the 
instructions are read and interrupted by the controller to convert it into signals 
that activate the machine tool. 
o  The  signals  are  sent  to  the  servo  control  system.  This  servo  control  system 
control the machine tool for performing different operations.
o The feed back transducer checks the actual position of the machine tool  slide 
and passes it to CPU. 
o If there is any difference between given input and actual position achieved, the 
CPU  takes  corrective  action  to  achieve  the  given  input  values  by  suitable 
instructions to the machine tool.
o Closed loop CNC system has both velocity and position control loops.
o Software of CNC system has three major programs
Part Program: It has part dimensions, Spindle speed, Feed rate, etc.
Service Program: Used to check , edit, correct the part program.
Control Program: Accepts the part program as a input data to produce
 signals to drive the axes of motion.
5Dr.S.Cartigueyen
Machine Control Unit (MCU)
o It consists of programmable logic controller (PLC), processor, memory devices. PLC 
controls the spindle ON/OFF, coolant ON/OFF, tool path, speed, feed and tool changes.
o It converts the program commands into signals.
Operator Control Panel
o It provides the interaction between user & CNC system. Also it consists of monitor, 
feather touch keyboard, machine control panel.
q Schematic diagram of a CNC machine tool
6Dr.S.Cartigueyen
Working Principle of a CNC System …
Servo Control Unit & Drives
o PLC gives command signal to servo drives , this command signal values are 
converted into actual movement on the machine by servo drives.
Feedback Devices
o  PLC  receives  feedback  signal  about  actual  movement  of  the  machine  tool 
through  feedback  devices.  Feedback  devices  are  transducers  &  encoders.  This 
feedback signals are compared with the Input signals and error correction is done.
q Features of CNC Machines
1. Storage of more than one part program
    - CNC machine can store multiple programs.  It can be used again and again.
2. Various forms of program input
    - Multiple data entry capabilities such as magnetic tape, floppy discs, manual 
data input, communication ports,  etc. 
3. Program editing at the machine tool
    - Helps in testing and correcting a program entirely at the machine tool. 
    - Output can be viewed without doing actual machining
7Dr.S.Cartigueyen
Features of CNC Machines…
4. Fixed cycles and programming sub-routines
   - Fixed cycle : Frequently used machining cycle as Macros, stored in memory and can 
be called into every other programs.
5. Interpolation
    - Helical, parabolic and cubic interpolations are executed only through CNC (as a 
stored program algorithm)
6. Positioning features for set up
    - Position set feature (software option) in CNC is used to set the work piece or fixture 
with respect to the machine tool axes. 
7. Cutter length and size compensation
    - Compensations like tool nose radius, cutter radius etc are automatically made in the 
computed tool path.
8. Acceleration and deceleration calculations
    - Feed rate is smoothly decelerated and then accelerated back after direction change.
9. Communications interface
    -  Machine can be linked to other computers &  computer-driven devices (like robots)
10. Diagnostics
    - On-line diagnostics capability to detect mal-functions / system breakdowns etc.
8Dr.S.Cartigueyen
q Difference between NC and CNC Machines
9Dr.S.Cartigueyen
Advantages of CNC Machines
q Higher accuracy
q Reduce lead time
q Higher flexibility
q Reduce scrap rate
q Reliable operation
q Consistent quality
q Reduced manpower
q Increased productivity
q Reduced non productive time
q Shorter cycle time
q JIT Manufacture
q Lesser floor space
q Increased operational safety
q Machining advanced materials
Disadvantages of CNC Machines
§ High machine cost
§ Complicated maintenance
§ Parts are imported from abroad
§ High tool cost
§ Temperature, humidity and dust must
   be controlled
Applications of CNC System
• Parts needed in a hurry
• Parts with complicated contours
• Parts requiring expensive jigs and fixtures
• Parts those have several engineering changes
• Cases where human errors can be extremely 
   costly
• Parts requiring close tolerance or good 
  repeatability
10Dr.S.Cartigueyen
q CNC Turning Centre / CNC Lathe
- CNC Turning centre is a machine tool capable of performing various  turning and 
related operations in one setup under CNC system.
- CNC turning centers are designed mainly for machining shaft-type work pieces 
which  are  supported  by  a  chuck.  It  is  capable  of  producing  cylindrical  parts  in 
greater volume with high accuracy.
- Main parts of the CNC turning centre are bed, head stock, tailstock, turrets, servo 
system and MCU. 
-  The  various  work  holding  devices  are,    self-centering  chuck  ,  collect  chuck, 
counter centrifugal chuck. 
 - CNC turning centre tool turret have the capacity of 8, 12 or 16 tools.
Two axis control  
Z axis - Parallel to spindle axis,  
X axis - Perpendicular to spindle axis
Types
(a) Horizontal spindle turning centre    
(b) Vertical spindle turning centre
11Dr.S.Cartigueyen
(a) Horizontal Spindle Turning Centre
- CNC chucking centre is designed to machine most work that is held in a chuck.
- Chucking machines usually have shorter beds and a single saddle with single 
drum type turret or two independent saddles with turret as shown in the figure. 
Special Features
- Checking the dimensions of 
work piece after machining.
- Sensing the tool whether is 
worn-out or not.
-  Automatic  tool  changing 
when tools have broken.
-  Automatic  work  piece 
changer at the completion of 
work piece.
12Dr.S.Cartigueyen
Horizontal Spindle Turning Centre
Horizontal Spindle Turning Centre
13Dr.S.Cartigueyen
(b) Vertical Spindle Turning Centre
- Vertical CNC lathes widely used for machine heavy components.
- Some of these machines can also be used for milling operations. Such machines 
are sometimes known as turn -mill centers.
- The tool turret is placed in a plane above the spindle.
Rotary Table Vertical Spindle Turning Centre
14Dr.S.Cartigueyen
Machine Axes Convention
q Machining Centre / Milling Centre
-  A  machining  centre  (MC)  is  capable  of  performing  multiple  operations  like 
milling, drilling, reaming, tapping, boring and allied operations.
Special features
Automatic tool changer, 
Automatic work piece positioning  and 
Automatic pallet changer.
 Five axis control
X axis, Y axis, Z axis - Linear movements. 
A axis - Spindle Tilt  and 
B axis - Table rotation.
Types
(a) Horizontal spindle machining centre  
(b) Vertical spindle machining centre 
(c) Universal machining centre
-  Main  parts  of  CNC  machining  centre  are  bed,  column,  spindle,  table,  servo 
mechanism,  tool  magazine,  automatic  tool  changer  (ATC)  and  automatic  pallet 
changer (APC).
15Dr.S.Cartigueyen
(a) Horizontal Spindle Machining Centre
- HMC is a machining center with its spindle in a horizontal orientation.
- X axis - Table longitudinal movement
- Y axis - Spindle up and down movement
- Z axis - Table movements towards spindle
- HMC have rotary table with axis parallel to Y axis and is called B axis
- Generally these are single spindle machines with ATC & APC
16Dr.S.Cartigueyen
Machine Axes Convention
Horizontal Spindle Machining Centre (HMC)…
- This machining center design favours uninterrupted production work. 
- One reason for this is that the horizontal orientation encourages chips to fall away, 
so they don't have to be cleared from the table.
- Horizontal design allows a two-pallet work changer which saves time. 
-  Work  can  be  loaded  on  one  pallet  of  an  horizontal  machining  center  while 
machining occurs on the other pallet.
- Used for heavier work piece with large metal removal.
17Dr.S.Cartigueyen
Horizontal Spindle Machining Centre
(b) Vertical Spindle Machining Centre (VMC)
• VMC has its spindle on vertical axis.
• Used for heavier work piece with large
metal removal
• X axis - Table longitudinal movement
• Y axis - Table cross wise movement
• Z axis - Spindle up & down movement
• VMC have rotary table with axis parallel 
to X axis & is called A axis
•Tool magazine have up to 60 tools
• Generally these are single spindle with 
ATC or multi spindle with turret head.
(c) Universal Machining Centre (UMC)  
- Having both vertical and horizontal spindles
- Capable of machining vertical, horizontal and diagonal surfaces.
- Changing the spindle configuration from horizontal to vertical and vice versa is 
done automatically.
18Dr.S.Cartigueyen
Vertical Spindle Machining Centre
q Machine Axes Conventions – Co-ordinate System
• Each ‘axis of motion’ has a separate driving device ( stepper motor / servo motor)
• Z axis is always  in rotating ‘ Spindle’.
• Three main axes of motion will be referred to as the X, Y and Z axes.
• Thumb – X axis ;  Index finger – Y axis ;  Middle finger – Z axis
19Dr.S.Cartigueyen
q Turning Centre Axes Conventions qMachining Centre Axes Conventions
o Basically CNC turning centre has two axes namely X and Z axis.
o CNC Machining centre has three linear axes namely X, Y and Z.
o Axis designation appear with positive (+) or negative (-) signs for direction of travel.
20Dr.S.Cartigueyen
q Co-ordinate Measuring Machine (CMM)
v CMM is an electro mechanical system designated to measure several features of 
a work piece using ‘ Probe (Sensor) ’ as given below:
o to locate a surface 
o to locate the centre of a hole, cylindrical shafts 
o to locate geometric centre of a pocket/spigot
o to measure angles
o to measure a series of coordinate points relative to a given axis
21Dr.S.Cartigueyen
Various Parts of Bridge type CMM
Co-ordinate Measuring Machine (CMM)…
o  CMMs are built rigidly and very precise. They are equipped with digital read-out 
or can be linked to computers for online inspection of parts.
o CMM consists of a measuring table to hold the work piece. The probe can be 
moved in three directions and brought into contact with the surface to be measured.
o CMM records even complex profiles with high sensitivity and speed. 
o Probe can be position to a resolution of 1 micron. 
CMM Components
1. Probe head and probe
2. Mechanical structure  
and displacement 
transducers
3. Drive system and 
control
4. Digital computer with 
software
22Dr.S.Cartigueyen
Bridge type CMM
q Construction of Coordinate Measuring Machine (CMM)
o Based on the construction & mechanical structure of CMM, it can be classified as  
23Dr.S.Cartigueyen
Coordinate Measuring Machine (CMM)...
Specifications of CMM
- Measuring range (X, Y & Z axis)
- Resolution 
- Accuracy
- Axis guide method (air bearing)
- Drive speed
- Maximum measuring speed 
- Maximum measuring acceleration
- Maximum work piece length 
- Maximum work piece weight
- Temperature range 
- Temperature variation
- Probe type
- Table design
Benefits of CMM
- Flexibility
- High production rate
- Less man power required (automated)
- High precision
- Reduced operator errors
-  High integrity with FMS
Disadvantages of CMM
-Table and probe may not be in perfect 
alignment
- Probe may have run out.
- Probe moving in Z-axis may have some 
perpendicular errors.
- Probe will move X and Y direction but not 
be square to each other.
- Chances of errors in digital system 
24Dr.S.Cartigueyen
Bridge type CMM Cantilever type CMM
25Dr.S.Cartigueyen
v COMPONENTS OF CNC MACHINE
o The major components of a CNC machine are controller, drives and mechanical 
elements.
Drives Primary function of drives is to cause motion of the spindle and slide ways 
as per the command.
Types of Drives (i) Electrical drives   (ii) Hydraulic drives
1. Spindle drives (constant power) – AC/DC motors  
2. Feed drives (constant torque) – AC/DC Servo motors, Stepper motors , Linear 
motors
Spindle (constant power) drive Feed (constant torque) drive
26Dr.S.Cartigueyen
q Slide Movement Elements
Slide Ways
o  Precise  positioning  and  repeatability  of  machine  tool,  slides  are  the  major 
functional requirements of CNC machines. 
o The inaccuracies that caused are mainly due to the stick slip motion when plain 
slide ways (metal to metal contact) are used. 
o To eliminate  stick-slip,  there are different  slide ways systems such of rolling 
friction slide ways and slide ways with low friction are required. 
Requirement of Good Slide Ways
• High accuracy
• Low wear
• Negligible stick-slip
• High rigidity
• Low price
• Low co-efficient of friction properties
• Good surface finish on slide way surface
• High Stiffness at the sliding joint
• Good damping capacity
Types of Slide ways
1. Friction type slide ways
      - V/flat/round/dove tail slide ways
- Plastic coated slide ways , 
2. Antifriction slide ways
      - Linear motion bearings (ball, roller) 
- Recirlculating ball screw and nut
27Dr.S.Cartigueyen
q Friction Slide Ways
- Removes ‘stick-slip’ and  reduces frictional resistance between sliding parts.
- To improve load bearing properties, hardened steel inserts are used. 
- Flat slide ways have better load bearing capabilities than other guide ways.
q Plastic Coated Slide Ways
- Plastic or non metallic inserts are mostly used. 
- Polymer composite inserts are used. 
- Inserts are thermoplastics or thermosetting types. 
-  These  inserts  reduce  coefficient  of  friction, 
increase strength, wear resistance and load bearing 
capacity. They also have self-lubricating property. 
-  The  worn-out  strip  can  be  replaced    easily 
without the need for any machining of bed ways. 
28Dr.S.Cartigueyen
Plastic Coated Slide Way
q Antifriction Slide ways
- It involves intermediate rolling member (balls or rollers) between the sliding members, 
thus reducing the friction.
- Less wear, low friction, no stick slip, high load capacity but low damping capacity.
(a) Linear motion bearings
- Balls  or    rollers  are  used  to  get  antifriction  linear  motion  in  slide  ways.  The  unit 
consists of a bearing block and rail. 
- The unit is constructed in such a manner that each of the rows of balls, rolling over the 
rail comes into contact with the race-way at an angle of 45 degree. 
- The race is in line contact rather than the conventional point contact. 
- The system is capable of withstanding equal load in any direction. 
29Dr.S.Cartigueyen
Linear Ball Bearing Linear Roller Bearing
Antifriction Slide ways..
(b) Recirculating ball screw and nut
- Balls rotate between the screw and nut.
- It converts the sliding friction into rolling friction.
- Ball screws are primarily employed in feed mechanism of CNC machine tools.
- The balls provide only physical contact between the nut and the lead screw. The 
balls are re-circulated from one end to the other by return tubes. 
- The connection between the screw and nut is achieved by an endless stream of 
recirculating steel balls.
30Dr.S.Cartigueyen
Recirculating ball screw and nut
(b) Recirculating ball screw and nut…
Advantages
§ Low co-efficient of friction
§ Less wear and long life
§ Requires less power
§ No stick-slip effect
§ No backlash
§ High efficiency (90%)
§ Used for heavier loads at 
faster speeds.
Elimination of Backlash
o Backlash is the sum of the axial clearance and deformation caused by axial or 
thrust loading.
o By making the carriage movement accurately in both the direction, backlash 
between screw and nut can be avoided.
o Backlash can be avoided by preloading. It is achieved by fitting two nuts.
31Dr.S.Cartigueyen
Recirculating ball screw and nut
qTool Magazines
-The  system  of  arrangement  which  holds  large  number  of  tools  is  called  tool 
magazine. It is used in CNC turning centres and machining centres. 
- It is specified by storage capacity and shape. 
- Storage capacity ranges from 12 - 200 tools.
- It keeps the tools clean and free from damage.  Also it keeps track of which tools 
are there by coding.
Types   1. Tool turret  2. Drum/Disc type  3. Chain type
(1) Tool Turret
o It is the simplest form of tool magazine
o It consists of tool storage without tool changer
o Turret is indexed in required position for 
desired operation
o Tool can be easily identified
o Tool change time is more
32Dr.S.Cartigueyen
Tool Turret
Tool Magazines…
(2) Drum/Disc type
o It is the rotates to get the desired tool in  position 
with tool change arm
o  It carries 12 - 50 tools
o If diameter of the disc is large, more number of 
tools can be hold
o It have pockets where the tools can be inserted
33Dr.S.Cartigueyen
Drum/Disc Type MagazineTool Turret type Magazine
Tool Magazines…
(3) Chain type Tool Magazine
o It is capable of storing more number of tools.
o Used in machining centre.
o Tools are inserted into their pockets which are 
attached to the chain.
o Chain moving on sprocket and sprockets are 
driven by motors.
34Dr.S.Cartigueyen
Chain type Tool Magazine
q Automatic Tool Changer (ATC)
- All  CNC  machining  centers  should  have  the  capability  of  changing  the  tools 
automatically.
- The device used to pick up a tool from tool magazine and replace it with the tool 
in the spindle with in 3 to 7 seconds, is called ATC.
- ATC reduce the idle time during tool changing operations.
Types of ATC
1. Turret head      
2. 180º rotation  
3. Pivot insertion  
4. Multi-axis  
5. Spindle direct 
q 180º Automatic Tool Changer
- Simplest ATC
- Upon receiving a tool change command:
- MCU sends the spindle to its fixed tool 
change coordinates.
- At the same time, the tool magazine is 
indexed to the proper position.
35Dr.S.Cartigueyen
180º Automatic Tool Changer
q Working of 180º Automatic Tool Changer
36Dr.S.Cartigueyen
Working of 180º Automatic Tool Changer…
Working
1. ATC arm rotates through 90º from the rest position.
2. One end grips tool in the magazine & another end grips tool in the spindle.
3. Both tools are pulled  out.
4. ATC arm rotates through 180º.
5. It inserts new tool to the spindle & old tool to the magazine.
6. ATC arm rotates through 90º and goes to the rest position.
Characteristic of Tool Magazines
o Tools magazine has to be compact and as simple as possible. 
o Interchange of tools should not interfere with the work piece space and tool space 
o Easier & safer manual exchange of tools in tool magazine during loading/ unloading. 
o All preparatory works for tool exchange should be made during machining. 
o Capable of holding enough tools needed for machining.
Advantages
• Simplicity
• Minimal motion involved
• Fast tool changes
Disadvantages
• Tools must be stored in a plane parallel to the spindle
• Chances of getting chips, coolants on the tool holders.
37Dr.S.Cartigueyen
q Feed Back Devices
oThe electronic devices such as Transducer and Encoders used for giving the 
position and velocity of the machine elements are called feedback devices.
o Feed back is required to close the loop. 
o Based on feedback control the systems are classified as
Types
1. Open Loop Control System  
2. Closed Loop Control System
(1) Open Loop Control System
o  In  this  control  system,  there  is  no feed back devices to  compare  the  actual 
position of the cutting tool or work piece with the input signals are called open loop 
control systems.
38Dr.S.Cartigueyen
Open Loop Control System
Feed Back Devices…
(2) Closed Loop Control System
o The machine tool control system in which there are feed back devices to compare the 
actual position of the cutting tool or work piece with the input signals are called open 
loop control systems.
Types  1. Velocity feed back  2. Position feed back
(1) Position Feed Back
- Measuring the slide movement by linear transducer.
(2) Velocity Feed Back
- Tacho-generator gives voltage output proportional to its speed. Output voltage is used 
as feed back to monitor the motor speed. It can be done by rotary transducer. 
39Dr.S.Cartigueyen
Closed Loop Control System
Feed Back Devices…
Open Loop Control System Vs Closed Loop Control System
Open Loop Control
Advantages
-Low cost
- Less maintenance
Disadvantages
-Less accuracy
Closed Loop Control
Advantages
-Accuracy is more
Disadvantages
- More cost
40Dr.S.Cartigueyen
q Transducer
- A device that converts energy from form to another (normally into an electrical 
signal) is called Transducer. They are used for converting the physical quantities 
like speed, feed, velocity, displacement into electronic signals and vice versa.
(1) Rotary Transducer
- It is used to measure the angular rotation of the lead screw.
- Disc is made up uniform alternate transparent and dark regions.
- When the disc rotates with lead screw, photocell senses the light and dark area 
alternatively.  Photocell gives wave signal to the control unit (as pulses).
- It calculates the slide positions by knowing the pitch value of the lead screw.  
-The direction of rotation of lead screw can be sensed by putting a second photocell. 
41Dr.S.Cartigueyen
Rotary Transducer
(2) Linear Transducer
- It is used to measure the displacement of machine slide. 
- Linear grating scale is fixed to the moving table.
- Linear scale is engraved with alternate transparent and dark parallel lines.
- Photocell gives pulses to control unit. 
- From  the  known  number  of  engraved  lines  per  unit  length  on  the  scale  and 
counting the number of pulses, the control unit measures the slide position. 
42Dr.S.Cartigueyen
Linear Transducer
q Encoders
o Encoders are devices used to give positioning feedback to the control unit and 
also change the signal or data into a coded form.
Types
Based on movement : 1.  Rotary Encoders   2. Linear Encoders
Based on datum reference : 1. Incremental Encoders    2. Absolute Encoders 
Incremental - The current position is determined by stating a previous position as datum. 
Absolute  - The position of the slide is measured from a single datum at starting. 
A rotary encoder is a type of sensor that when mounted to the shaft of the motor can
detect its angular position. Its is made from light source, optical sensor, disc with 
small slits cut into it like spokes. Linear encoder is used to detect linear movements.
Linear EncoderRotary Encoder
43Dr.S.Cartigueyen
q In-Process Probing (Process Inspection)
-The process of inspection is called Probing and the device used for inspection is 
called  Inspection Probe. Probes (Sensors) may be contact type & non-contact type.
-The process of performing the inspection procedure during manufacturing 
operation using probes is called In-process probing. Here manufacturing as well as 
inspection are done simultaneously.
Types of Probes 1. Single tip probe  2. Multiple tip probe 3. Touch trigger probe
Advantages
• Loading / unloading time and inspection time will be reduced.
• Costly inspection equipment / devices will be eliminated.
• Over processing of defective components will be eliminated.
• Component quality and process control will be improved.
44Dr.S.Cartigueyen
q Tool Materials
- Various cutting tool materials have been used in the industry for different applications.
- The cutting tools can be classified on the basis of the following :
1. On the basis of setting up of cutting tool
(a) Preset tools (b) Qualified tools  (c) Semi qualified tools 
2. On the basis of cutting tool construction
(a) Solid tools  (b) Brazed tools  (c) Inserted bit tools 
3. On the basis of cutting tool material
(a) High speed steel (HSS)  (b) High carbon tool steel (HCS) 
(c) Cast alloy  (d) Cemented carbide  (e) Ceramics 
(f) Boron nitride  (g) Diamond  (h) Sialon 
High Speed Steel (HSS)
- 18:4:1 steel :18% Tungsten , 4% Molybdenum, 1% Vanadium.
- Good hot hardness, abrasion resistance, high toughness. It can be used up to 600ºC.
Cemented Carbide
- Tungsten carbide powder + Cobalt (as binder) + Sintering
- Improved toughness, impact strength. Available in different shapes.
45Dr.S.Cartigueyen
Tool Materials…
Coated Carbides
- Cemented carbide + Coating materials
- Coating materials : 5 micron of tin, titanium carbide,  aluminium oxides, etc.
- Life of the coated tool is 2 to 3 times the life of uncoated tools.
Ceramics
- Alumina based high refractory materials. Used for high speed.
- It can withstand high temperature, chemically more stable & high wear resistance.
q Tool Life
v  50% increase in cutting speed results 90% decrease in tool life
v  50% increase in feed rate results in 60 % decrease in tool life
v 100 % increase in depth of cut results in 25% decrease in tool life.
v For longer tool life , the tool material should have 
- Hot hardness , wear and abrasion resistance, increased thermal conductivity
- High impact and toughness, lower coefficient of thermal expansion
- Easy to form, grind and sharpen to the required geometry.
46Dr.S.Cartigueyen
q Tool Inserts
- CNC Tools are very costly. They cannot be re-sharpened frequently.
- So, Tool Tips called Tool Inserts are produced by powder metallurgy process.
- Tool inserts are available in various shapes.
- Tool inserts can not be re-sharpened but they have multiple cutting edges.
- Tool inserts are used in CNC to minimize the tool change and tool setting time.
- Mechanically clamped tool tips are known as “ Indexable Inserts”.
- Inserts with built-in chip breakers can be used by the way of clamping arrangements.
47Dr.S.Cartigueyen
Shapes of Inserts Tool Inserts Clamping Tool Inserts
Dr.S.Cartigueyen
scartigueyen@rediffmail.com
48Dr.S.Cartigueyen

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CNC Machines and its Components

  • 1. CNC MACHINESCNC MACHINES AND ITSAND ITS COMPONENTSCOMPONENTS ( Mechanical Engineering / Special Machines / Unit 5)( Mechanical Engineering / Special Machines / Unit 5) v CNC Machines vComponents of CNC machine Prepared by Dr.S.Cartigueyen, M.Tech., Ph.D.
  • 2. v CNC MACHINES o  Modern  manufacturing  systems  are  advanced  automation  systems.  The  numerical  control (NC) and computer numerical control (CNC) machines are an integral part of  the automation systems. o CNC machining is capable of meeting the tightest tolerances, and producing the most  accurate, precise products over and over again. First ‘CNC Machining’ means : Machining : Process of removing metal with the assistance of mechanical machines. NC – Numerical Control : Governing  the  machines  automatically  through  a  set  of  instructions (letters, numbers, symbols). CNC – Computer Numerical Control : Process by which an operator can write, adjust  and implement instructions using a computer comfort. q Numerical Control (NC) o  NC  is  defined  as  control  of  machine  slide  movements    and  various  functions  by  means of letters, numbers and symbols o Letters, numbers and symbols forming some sequence is called Part Program. o  The  part  program  is  arranged  in  the  form  of  blocks  of  information.  Each  block  contains the alphanumerical data required to produce one segment of the work piece.  o  The  part  program  is  translated  into  the  appropriate  electrical  signals  for  input  to  motors that run the machine. 2Dr.S.Cartigueyen
  • 3. q Components of NC System o Three basic components are 1. Program of instructions 2. Machine control  unit (MCU) and 3. Machine tool. o The coded instructions are to cause the machine to perform a specific series  of operations. Basically, it is control of machine tools by numbers.    Functions automated by NC system - Starting and stopping of machine tool spindle. - Controlling the spindle speed. - Positioning the tool tip - Guiding the tool in desired paths Advantages • Reduces non productive time • Reduces manufacturing lead time • Greater manufacturing flexibility • Improves quality control • Reduced inventory Disadvantages • High investment cost • High maintenance effort. • Part programming • Higher utilization of NC equipmentsBasic Components of NC System 3Dr.S.Cartigueyen
  • 5. q Working Principle of a CNC System o  In  CNC  systems  the  part  program  is  fed  into  the  computer.  Then  the  instructions are read and interrupted by the controller to convert it into signals  that activate the machine tool.  o  The  signals  are  sent  to  the  servo  control  system.  This  servo  control  system  control the machine tool for performing different operations. o The feed back transducer checks the actual position of the machine tool  slide  and passes it to CPU.  o If there is any difference between given input and actual position achieved, the  CPU  takes  corrective  action  to  achieve  the  given  input  values  by  suitable  instructions to the machine tool. o Closed loop CNC system has both velocity and position control loops. o Software of CNC system has three major programs Part Program: It has part dimensions, Spindle speed, Feed rate, etc. Service Program: Used to check , edit, correct the part program. Control Program: Accepts the part program as a input data to produce  signals to drive the axes of motion. 5Dr.S.Cartigueyen
  • 6. Machine Control Unit (MCU) o It consists of programmable logic controller (PLC), processor, memory devices. PLC  controls the spindle ON/OFF, coolant ON/OFF, tool path, speed, feed and tool changes. o It converts the program commands into signals. Operator Control Panel o It provides the interaction between user & CNC system. Also it consists of monitor,  feather touch keyboard, machine control panel. q Schematic diagram of a CNC machine tool 6Dr.S.Cartigueyen
  • 7. Working Principle of a CNC System … Servo Control Unit & Drives o PLC gives command signal to servo drives , this command signal values are  converted into actual movement on the machine by servo drives. Feedback Devices o  PLC  receives  feedback  signal  about  actual  movement  of  the  machine  tool  through  feedback  devices.  Feedback  devices  are  transducers  &  encoders.  This  feedback signals are compared with the Input signals and error correction is done. q Features of CNC Machines 1. Storage of more than one part program     - CNC machine can store multiple programs.  It can be used again and again. 2. Various forms of program input     - Multiple data entry capabilities such as magnetic tape, floppy discs, manual  data input, communication ports,  etc.  3. Program editing at the machine tool     - Helps in testing and correcting a program entirely at the machine tool.      - Output can be viewed without doing actual machining 7Dr.S.Cartigueyen
  • 8. Features of CNC Machines… 4. Fixed cycles and programming sub-routines    - Fixed cycle : Frequently used machining cycle as Macros, stored in memory and can  be called into every other programs. 5. Interpolation     - Helical, parabolic and cubic interpolations are executed only through CNC (as a  stored program algorithm) 6. Positioning features for set up     - Position set feature (software option) in CNC is used to set the work piece or fixture  with respect to the machine tool axes.  7. Cutter length and size compensation     - Compensations like tool nose radius, cutter radius etc are automatically made in the  computed tool path. 8. Acceleration and deceleration calculations     - Feed rate is smoothly decelerated and then accelerated back after direction change. 9. Communications interface     -  Machine can be linked to other computers &  computer-driven devices (like robots) 10. Diagnostics     - On-line diagnostics capability to detect mal-functions / system breakdowns etc. 8Dr.S.Cartigueyen
  • 9. q Difference between NC and CNC Machines 9Dr.S.Cartigueyen
  • 10. Advantages of CNC Machines q Higher accuracy q Reduce lead time q Higher flexibility q Reduce scrap rate q Reliable operation q Consistent quality q Reduced manpower q Increased productivity q Reduced non productive time q Shorter cycle time q JIT Manufacture q Lesser floor space q Increased operational safety q Machining advanced materials Disadvantages of CNC Machines § High machine cost § Complicated maintenance § Parts are imported from abroad § High tool cost § Temperature, humidity and dust must    be controlled Applications of CNC System • Parts needed in a hurry • Parts with complicated contours • Parts requiring expensive jigs and fixtures • Parts those have several engineering changes • Cases where human errors can be extremely     costly • Parts requiring close tolerance or good    repeatability 10Dr.S.Cartigueyen
  • 11. q CNC Turning Centre / CNC Lathe - CNC Turning centre is a machine tool capable of performing various  turning and  related operations in one setup under CNC system. - CNC turning centers are designed mainly for machining shaft-type work pieces  which  are  supported  by  a  chuck.  It  is  capable  of  producing  cylindrical  parts  in  greater volume with high accuracy. - Main parts of the CNC turning centre are bed, head stock, tailstock, turrets, servo  system and MCU.  -  The  various  work  holding  devices  are,    self-centering  chuck  ,  collect  chuck,  counter centrifugal chuck.   - CNC turning centre tool turret have the capacity of 8, 12 or 16 tools. Two axis control   Z axis - Parallel to spindle axis,   X axis - Perpendicular to spindle axis Types (a) Horizontal spindle turning centre     (b) Vertical spindle turning centre 11Dr.S.Cartigueyen
  • 12. (a) Horizontal Spindle Turning Centre - CNC chucking centre is designed to machine most work that is held in a chuck. - Chucking machines usually have shorter beds and a single saddle with single  drum type turret or two independent saddles with turret as shown in the figure.  Special Features - Checking the dimensions of  work piece after machining. - Sensing the tool whether is  worn-out or not. -  Automatic  tool  changing  when tools have broken. -  Automatic  work  piece  changer at the completion of  work piece. 12Dr.S.Cartigueyen Horizontal Spindle Turning Centre
  • 13. Horizontal Spindle Turning Centre 13Dr.S.Cartigueyen
  • 14. (b) Vertical Spindle Turning Centre - Vertical CNC lathes widely used for machine heavy components. - Some of these machines can also be used for milling operations. Such machines  are sometimes known as turn -mill centers. - The tool turret is placed in a plane above the spindle. Rotary Table Vertical Spindle Turning Centre 14Dr.S.Cartigueyen Machine Axes Convention
  • 15. q Machining Centre / Milling Centre -  A  machining  centre  (MC)  is  capable  of  performing  multiple  operations  like  milling, drilling, reaming, tapping, boring and allied operations. Special features Automatic tool changer,  Automatic work piece positioning  and  Automatic pallet changer.  Five axis control X axis, Y axis, Z axis - Linear movements.  A axis - Spindle Tilt  and  B axis - Table rotation. Types (a) Horizontal spindle machining centre   (b) Vertical spindle machining centre  (c) Universal machining centre -  Main  parts  of  CNC  machining  centre  are  bed,  column,  spindle,  table,  servo  mechanism,  tool  magazine,  automatic  tool  changer  (ATC)  and  automatic  pallet  changer (APC). 15Dr.S.Cartigueyen
  • 16. (a) Horizontal Spindle Machining Centre - HMC is a machining center with its spindle in a horizontal orientation. - X axis - Table longitudinal movement - Y axis - Spindle up and down movement - Z axis - Table movements towards spindle - HMC have rotary table with axis parallel to Y axis and is called B axis - Generally these are single spindle machines with ATC & APC 16Dr.S.Cartigueyen Machine Axes Convention
  • 17. Horizontal Spindle Machining Centre (HMC)… - This machining center design favours uninterrupted production work.  - One reason for this is that the horizontal orientation encourages chips to fall away,  so they don't have to be cleared from the table. - Horizontal design allows a two-pallet work changer which saves time.  -  Work  can  be  loaded  on  one  pallet  of  an  horizontal  machining  center  while  machining occurs on the other pallet. - Used for heavier work piece with large metal removal. 17Dr.S.Cartigueyen Horizontal Spindle Machining Centre
  • 18. (b) Vertical Spindle Machining Centre (VMC) • VMC has its spindle on vertical axis. • Used for heavier work piece with large metal removal • X axis - Table longitudinal movement • Y axis - Table cross wise movement • Z axis - Spindle up & down movement • VMC have rotary table with axis parallel  to X axis & is called A axis •Tool magazine have up to 60 tools • Generally these are single spindle with  ATC or multi spindle with turret head. (c) Universal Machining Centre (UMC)   - Having both vertical and horizontal spindles - Capable of machining vertical, horizontal and diagonal surfaces. - Changing the spindle configuration from horizontal to vertical and vice versa is  done automatically. 18Dr.S.Cartigueyen Vertical Spindle Machining Centre
  • 19. q Machine Axes Conventions – Co-ordinate System • Each ‘axis of motion’ has a separate driving device ( stepper motor / servo motor) • Z axis is always  in rotating ‘ Spindle’. • Three main axes of motion will be referred to as the X, Y and Z axes. • Thumb – X axis ;  Index finger – Y axis ;  Middle finger – Z axis 19Dr.S.Cartigueyen
  • 20. q Turning Centre Axes Conventions qMachining Centre Axes Conventions o Basically CNC turning centre has two axes namely X and Z axis. o CNC Machining centre has three linear axes namely X, Y and Z. o Axis designation appear with positive (+) or negative (-) signs for direction of travel. 20Dr.S.Cartigueyen
  • 21. q Co-ordinate Measuring Machine (CMM) v CMM is an electro mechanical system designated to measure several features of  a work piece using ‘ Probe (Sensor) ’ as given below: o to locate a surface  o to locate the centre of a hole, cylindrical shafts  o to locate geometric centre of a pocket/spigot o to measure angles o to measure a series of coordinate points relative to a given axis 21Dr.S.Cartigueyen Various Parts of Bridge type CMM
  • 22. Co-ordinate Measuring Machine (CMM)… o  CMMs are built rigidly and very precise. They are equipped with digital read-out  or can be linked to computers for online inspection of parts. o CMM consists of a measuring table to hold the work piece. The probe can be  moved in three directions and brought into contact with the surface to be measured. o CMM records even complex profiles with high sensitivity and speed.  o Probe can be position to a resolution of 1 micron.  CMM Components 1. Probe head and probe 2. Mechanical structure   and displacement  transducers 3. Drive system and  control 4. Digital computer with  software 22Dr.S.Cartigueyen Bridge type CMM
  • 23. q Construction of Coordinate Measuring Machine (CMM) o Based on the construction & mechanical structure of CMM, it can be classified as   23Dr.S.Cartigueyen
  • 24. Coordinate Measuring Machine (CMM)... Specifications of CMM - Measuring range (X, Y & Z axis) - Resolution  - Accuracy - Axis guide method (air bearing) - Drive speed - Maximum measuring speed  - Maximum measuring acceleration - Maximum work piece length  - Maximum work piece weight - Temperature range  - Temperature variation - Probe type - Table design Benefits of CMM - Flexibility - High production rate - Less man power required (automated) - High precision - Reduced operator errors -  High integrity with FMS Disadvantages of CMM -Table and probe may not be in perfect  alignment - Probe may have run out. - Probe moving in Z-axis may have some  perpendicular errors. - Probe will move X and Y direction but not  be square to each other. - Chances of errors in digital system  24Dr.S.Cartigueyen
  • 25. Bridge type CMM Cantilever type CMM 25Dr.S.Cartigueyen
  • 26. v COMPONENTS OF CNC MACHINE o The major components of a CNC machine are controller, drives and mechanical  elements. Drives Primary function of drives is to cause motion of the spindle and slide ways  as per the command. Types of Drives (i) Electrical drives   (ii) Hydraulic drives 1. Spindle drives (constant power) – AC/DC motors   2. Feed drives (constant torque) – AC/DC Servo motors, Stepper motors , Linear  motors Spindle (constant power) drive Feed (constant torque) drive 26Dr.S.Cartigueyen
  • 27. q Slide Movement Elements Slide Ways o  Precise  positioning  and  repeatability  of  machine  tool,  slides  are  the  major  functional requirements of CNC machines.  o The inaccuracies that caused are mainly due to the stick slip motion when plain  slide ways (metal to metal contact) are used.  o To eliminate  stick-slip,  there are different  slide ways systems such of rolling  friction slide ways and slide ways with low friction are required.  Requirement of Good Slide Ways • High accuracy • Low wear • Negligible stick-slip • High rigidity • Low price • Low co-efficient of friction properties • Good surface finish on slide way surface • High Stiffness at the sliding joint • Good damping capacity Types of Slide ways 1. Friction type slide ways       - V/flat/round/dove tail slide ways - Plastic coated slide ways ,  2. Antifriction slide ways       - Linear motion bearings (ball, roller)  - Recirlculating ball screw and nut 27Dr.S.Cartigueyen
  • 28. q Friction Slide Ways - Removes ‘stick-slip’ and  reduces frictional resistance between sliding parts. - To improve load bearing properties, hardened steel inserts are used.  - Flat slide ways have better load bearing capabilities than other guide ways. q Plastic Coated Slide Ways - Plastic or non metallic inserts are mostly used.  - Polymer composite inserts are used.  - Inserts are thermoplastics or thermosetting types.  -  These  inserts  reduce  coefficient  of  friction,  increase strength, wear resistance and load bearing  capacity. They also have self-lubricating property.  -  The  worn-out  strip  can  be  replaced    easily  without the need for any machining of bed ways.  28Dr.S.Cartigueyen Plastic Coated Slide Way
  • 29. q Antifriction Slide ways - It involves intermediate rolling member (balls or rollers) between the sliding members,  thus reducing the friction. - Less wear, low friction, no stick slip, high load capacity but low damping capacity. (a) Linear motion bearings - Balls  or    rollers  are  used  to  get  antifriction  linear  motion  in  slide  ways.  The  unit  consists of a bearing block and rail.  - The unit is constructed in such a manner that each of the rows of balls, rolling over the  rail comes into contact with the race-way at an angle of 45 degree.  - The race is in line contact rather than the conventional point contact.  - The system is capable of withstanding equal load in any direction.  29Dr.S.Cartigueyen Linear Ball Bearing Linear Roller Bearing
  • 30. Antifriction Slide ways.. (b) Recirculating ball screw and nut - Balls rotate between the screw and nut. - It converts the sliding friction into rolling friction. - Ball screws are primarily employed in feed mechanism of CNC machine tools. - The balls provide only physical contact between the nut and the lead screw. The  balls are re-circulated from one end to the other by return tubes.  - The connection between the screw and nut is achieved by an endless stream of  recirculating steel balls. 30Dr.S.Cartigueyen Recirculating ball screw and nut
  • 31. (b) Recirculating ball screw and nut… Advantages § Low co-efficient of friction § Less wear and long life § Requires less power § No stick-slip effect § No backlash § High efficiency (90%) § Used for heavier loads at  faster speeds. Elimination of Backlash o Backlash is the sum of the axial clearance and deformation caused by axial or  thrust loading. o By making the carriage movement accurately in both the direction, backlash  between screw and nut can be avoided. o Backlash can be avoided by preloading. It is achieved by fitting two nuts. 31Dr.S.Cartigueyen Recirculating ball screw and nut
  • 32. qTool Magazines -The  system  of  arrangement  which  holds  large  number  of  tools  is  called  tool  magazine. It is used in CNC turning centres and machining centres.  - It is specified by storage capacity and shape.  - Storage capacity ranges from 12 - 200 tools. - It keeps the tools clean and free from damage.  Also it keeps track of which tools  are there by coding. Types   1. Tool turret  2. Drum/Disc type  3. Chain type (1) Tool Turret o It is the simplest form of tool magazine o It consists of tool storage without tool changer o Turret is indexed in required position for  desired operation o Tool can be easily identified o Tool change time is more 32Dr.S.Cartigueyen Tool Turret
  • 33. Tool Magazines… (2) Drum/Disc type o It is the rotates to get the desired tool in  position  with tool change arm o  It carries 12 - 50 tools o If diameter of the disc is large, more number of  tools can be hold o It have pockets where the tools can be inserted 33Dr.S.Cartigueyen Drum/Disc Type MagazineTool Turret type Magazine
  • 34. Tool Magazines… (3) Chain type Tool Magazine o It is capable of storing more number of tools. o Used in machining centre. o Tools are inserted into their pockets which are  attached to the chain. o Chain moving on sprocket and sprockets are  driven by motors. 34Dr.S.Cartigueyen Chain type Tool Magazine
  • 35. q Automatic Tool Changer (ATC) - All  CNC  machining  centers  should  have  the  capability  of  changing  the  tools  automatically. - The device used to pick up a tool from tool magazine and replace it with the tool  in the spindle with in 3 to 7 seconds, is called ATC. - ATC reduce the idle time during tool changing operations. Types of ATC 1. Turret head       2. 180º rotation   3. Pivot insertion   4. Multi-axis   5. Spindle direct  q 180º Automatic Tool Changer - Simplest ATC - Upon receiving a tool change command: - MCU sends the spindle to its fixed tool  change coordinates. - At the same time, the tool magazine is  indexed to the proper position. 35Dr.S.Cartigueyen 180º Automatic Tool Changer
  • 36. q Working of 180º Automatic Tool Changer 36Dr.S.Cartigueyen
  • 37. Working of 180º Automatic Tool Changer… Working 1. ATC arm rotates through 90º from the rest position. 2. One end grips tool in the magazine & another end grips tool in the spindle. 3. Both tools are pulled  out. 4. ATC arm rotates through 180º. 5. It inserts new tool to the spindle & old tool to the magazine. 6. ATC arm rotates through 90º and goes to the rest position. Characteristic of Tool Magazines o Tools magazine has to be compact and as simple as possible.  o Interchange of tools should not interfere with the work piece space and tool space  o Easier & safer manual exchange of tools in tool magazine during loading/ unloading.  o All preparatory works for tool exchange should be made during machining.  o Capable of holding enough tools needed for machining. Advantages • Simplicity • Minimal motion involved • Fast tool changes Disadvantages • Tools must be stored in a plane parallel to the spindle • Chances of getting chips, coolants on the tool holders. 37Dr.S.Cartigueyen
  • 38. q Feed Back Devices oThe electronic devices such as Transducer and Encoders used for giving the  position and velocity of the machine elements are called feedback devices. o Feed back is required to close the loop.  o Based on feedback control the systems are classified as Types 1. Open Loop Control System   2. Closed Loop Control System (1) Open Loop Control System o  In  this  control  system,  there  is  no feed back devices to  compare  the  actual  position of the cutting tool or work piece with the input signals are called open loop  control systems. 38Dr.S.Cartigueyen Open Loop Control System
  • 39. Feed Back Devices… (2) Closed Loop Control System o The machine tool control system in which there are feed back devices to compare the  actual position of the cutting tool or work piece with the input signals are called open  loop control systems. Types  1. Velocity feed back  2. Position feed back (1) Position Feed Back - Measuring the slide movement by linear transducer. (2) Velocity Feed Back - Tacho-generator gives voltage output proportional to its speed. Output voltage is used  as feed back to monitor the motor speed. It can be done by rotary transducer.  39Dr.S.Cartigueyen Closed Loop Control System
  • 40. Feed Back Devices… Open Loop Control System Vs Closed Loop Control System Open Loop Control Advantages -Low cost - Less maintenance Disadvantages -Less accuracy Closed Loop Control Advantages -Accuracy is more Disadvantages - More cost 40Dr.S.Cartigueyen
  • 41. q Transducer - A device that converts energy from form to another (normally into an electrical  signal) is called Transducer. They are used for converting the physical quantities  like speed, feed, velocity, displacement into electronic signals and vice versa. (1) Rotary Transducer - It is used to measure the angular rotation of the lead screw. - Disc is made up uniform alternate transparent and dark regions. - When the disc rotates with lead screw, photocell senses the light and dark area  alternatively.  Photocell gives wave signal to the control unit (as pulses). - It calculates the slide positions by knowing the pitch value of the lead screw.   -The direction of rotation of lead screw can be sensed by putting a second photocell.  41Dr.S.Cartigueyen Rotary Transducer
  • 42. (2) Linear Transducer - It is used to measure the displacement of machine slide.  - Linear grating scale is fixed to the moving table. - Linear scale is engraved with alternate transparent and dark parallel lines. - Photocell gives pulses to control unit.  - From  the  known  number  of  engraved  lines  per  unit  length  on  the  scale  and  counting the number of pulses, the control unit measures the slide position.  42Dr.S.Cartigueyen Linear Transducer
  • 43. q Encoders o Encoders are devices used to give positioning feedback to the control unit and  also change the signal or data into a coded form. Types Based on movement : 1.  Rotary Encoders   2. Linear Encoders Based on datum reference : 1. Incremental Encoders    2. Absolute Encoders  Incremental - The current position is determined by stating a previous position as datum.  Absolute  - The position of the slide is measured from a single datum at starting.  A rotary encoder is a type of sensor that when mounted to the shaft of the motor can detect its angular position. Its is made from light source, optical sensor, disc with  small slits cut into it like spokes. Linear encoder is used to detect linear movements. Linear EncoderRotary Encoder 43Dr.S.Cartigueyen
  • 44. q In-Process Probing (Process Inspection) -The process of inspection is called Probing and the device used for inspection is  called  Inspection Probe. Probes (Sensors) may be contact type & non-contact type. -The process of performing the inspection procedure during manufacturing  operation using probes is called In-process probing. Here manufacturing as well as  inspection are done simultaneously. Types of Probes 1. Single tip probe  2. Multiple tip probe 3. Touch trigger probe Advantages • Loading / unloading time and inspection time will be reduced. • Costly inspection equipment / devices will be eliminated. • Over processing of defective components will be eliminated. • Component quality and process control will be improved. 44Dr.S.Cartigueyen
  • 45. q Tool Materials - Various cutting tool materials have been used in the industry for different applications. - The cutting tools can be classified on the basis of the following : 1. On the basis of setting up of cutting tool (a) Preset tools (b) Qualified tools  (c) Semi qualified tools  2. On the basis of cutting tool construction (a) Solid tools  (b) Brazed tools  (c) Inserted bit tools  3. On the basis of cutting tool material (a) High speed steel (HSS)  (b) High carbon tool steel (HCS)  (c) Cast alloy  (d) Cemented carbide  (e) Ceramics  (f) Boron nitride  (g) Diamond  (h) Sialon  High Speed Steel (HSS) - 18:4:1 steel :18% Tungsten , 4% Molybdenum, 1% Vanadium. - Good hot hardness, abrasion resistance, high toughness. It can be used up to 600ºC. Cemented Carbide - Tungsten carbide powder + Cobalt (as binder) + Sintering - Improved toughness, impact strength. Available in different shapes. 45Dr.S.Cartigueyen
  • 46. Tool Materials… Coated Carbides - Cemented carbide + Coating materials - Coating materials : 5 micron of tin, titanium carbide,  aluminium oxides, etc. - Life of the coated tool is 2 to 3 times the life of uncoated tools. Ceramics - Alumina based high refractory materials. Used for high speed. - It can withstand high temperature, chemically more stable & high wear resistance. q Tool Life v  50% increase in cutting speed results 90% decrease in tool life v  50% increase in feed rate results in 60 % decrease in tool life v 100 % increase in depth of cut results in 25% decrease in tool life. v For longer tool life , the tool material should have  - Hot hardness , wear and abrasion resistance, increased thermal conductivity - High impact and toughness, lower coefficient of thermal expansion - Easy to form, grind and sharpen to the required geometry. 46Dr.S.Cartigueyen
  • 47. q Tool Inserts - CNC Tools are very costly. They cannot be re-sharpened frequently. - So, Tool Tips called Tool Inserts are produced by powder metallurgy process. - Tool inserts are available in various shapes. - Tool inserts can not be re-sharpened but they have multiple cutting edges. - Tool inserts are used in CNC to minimize the tool change and tool setting time. - Mechanically clamped tool tips are known as “ Indexable Inserts”. - Inserts with built-in chip breakers can be used by the way of clamping arrangements. 47Dr.S.Cartigueyen Shapes of Inserts Tool Inserts Clamping Tool Inserts