Lecture 2

Introduction of CNC lathe machine
and
its operation
(Module 2)
Presented by: Mr. Dinesh Kumar
(AP/UCER)
Department of Mechanical Engineering

Session 2
Explanation of Integration of
CAD/CAM and advance automatic
machines

CAD+CAM=PRODUCT
• CAD= CREATION + ANALYSIS
CREATION= DRAFTING + MODELING
DRAFTING:- DEFINE AN OBJECT
MODELING:- RELATE DIFFERENT FEATURES
ANALYSIS= MODIFICATION+ OPTIMIZATION
(STRESS, DEFLECTION AND SIMULATION=FEM)
• CAM:- MANUFACTURING
3

COMPUTER AIDED DESIGN(CAD )
Integrated use of computer systems to assist
in the creation, modification, analysis or
optimization of a design.
Potencialities:
• Increase productivity
• quality improvement
• Varity of possible geometries
• Reduced design time
4

SOFTWARE USED FOR CAD
• Auto CAD
• Autodesk Inventor
• Solid works
• Creo
• CATIA etc
5

COMPUTER AIDED MANUFACTURING
(CAM)
Use of software to control machine tool and
related ones in the manufacturing of work
piece.
Software: Cut Viewer, CAM works etc
6

COMPUTER NUMERICAL CONTROL
(CNC )
LATHE MACHINE

Computer Numeric Control (CNC)
11

ROLE OF CNC MACHINE
CNC revolution is only beginning, and with each
year manufacturers develop new, more effective
ways to use this technology.
At present, experts are focused on ways to integrate
CNC machines with the robots used to move
and pack finished goods.
 Doing so will streamline the manufacturing process,
reducing waste and increasing simplicity.
 A single control panel may one day be enough
to direct an entire manufacturing
operation
13

Future of engineering Automation
17

Central Processing Unit/ Machine Control Unit
 The CPU is the heart of a CNC system.
 It accepts the information stored in the memory as part program.
 This data is decoded and transformed into specific position control and velocity
signals.
 It also oversees the movement of the control axis or spindle and whenever this
does not match with the programmed values, a corrective action as taken.
24

Machine Tool
 Most are made from high speed steel (HSS), tungsten carbide or ceramics.
 Some tools need coolant such as oil to protect the tool and work.
25

Driving System
 The requirement is that the driving system has to response accurately according
to the programmed instructions.
 The motor is coupled either directly or through a gear box to the machine lead
screw to moves the machine slide or the spindle.
Three types of electrical motors are commonly used:
1. DC Servo motor
2. AC Servo motor
3. Stepping motor as explained ahead.
26

CNC and Additive Manufacturing
30

Raw Material to Finished Product
31

Programming Key Letters
N - Sequence number (Used for line identification)
G - Preparatory function
X - X axis designation
Y - Y axis designation
Z - Z axis designation
R - Radius designation
F – Feed rate designation
S - Spindle speed designation
H - Tool length offset designation
D - Tool radius offset designation
T - Tool Designation
M - Miscellaneous function
45

Table of Important G Codes
G00 Rapid Transverse
G01 Linear Interpolation
G02 Circular Interpolation, CW
G03 Circular Interpolation, CCW
G17 XY Plane, G18 XZ Plane,G19 YZ Plane
G20/G70 Inch units
G21/G71 Metric Units
G40 Cutter compensation cancel
G41 Cutter compensation left
G42 Cutter compensation right
G codes are instructions describing machine tool movement
46

G43 Tool length compensation (plus)
G44 Tool length compensation (minus)
G49 Tool length compensation cancel
G80 Cancel canned cycles
G81 Drilling cycle
G82 Counter boring cycle
G83 Deep hole drilling cycle
G90 Absolute positioning
G91 Incremental positioning
47

Table of Important M codes
M Codes are instructions
describing miscellaneous
functions like calling the
tool, spindle rotation,
coolant on/off etc.,
48

Open Loop Systems
Open loop systems have no access to the real time data about the performance of the
system and therefore no immediate corrective action can be taken in case of system
disturbance.
Block Diagram of an Open Loop System.
49

Close Loop Systems
In a close loop system, feed back devices closely monitor the output and any
disturbance will be corrected in the first instance. Therefore high system accuracy
is achievable.
Block Diagram of a Close Loop System
51

1. Point-To-Point Control in CNC Drilling of Three Holes in Flat Plate
Motion Control Systems
 System moves to a location and performs an operation at that location (e.g.,
drilling)
 Also applicable in robotics
53

2. Continuous Path Control in CNC Profile Milling of Part
Outline
 Also called contouring systems in machining
 System performs an operation during movement (e.g.,
milling and turning)
54

Feedback Devices
Two types of feed back devices normally used are:
1. Positional Feed Back Devices
1.1 Linear Transducers - a device mounted on the machine table to measure the
actual displacement of the slide in such a way that backlash of screws; motors etc
would not cause any error in the feed back data.
55

1.2 Rotary Encoders: a device to measure the angular displacement. It cannot
measure linear displacement directly so that error may occur due to the backlash of
screw and motor etc.
56

2. Velocity Feedback Device
 The actual speed of the motor can be measured in terms of voltage generated
from a tachometer mounted at the end of the motor shaft.
 The voltage generated by the DC tachometer is compared with the command
voltage corresponding to the desired speed.
 The difference of the voltages is used to actuate the motor to eliminate the error.
57

Display Unit
 Interface between the machine and the operator.
The Display Unit displays:
 position of the machine slide
 spindle RPM
 feed rate
 part programs
 graphics simulation of the tool path.
58

Machine axes
Machine axes are established according to the industry standard report EIA RS -
267A
59

Axes configuration
 X axes moves from right to left as you face the machine
 Y axes move toward and away from you
 The Z axes is the spindle movement up and down spindle .
60

Lecture 2

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Lecture 2