CNC.ppt

Pankaj Chhabra CAD/CAM
NC machine tools- basic components, coordinate systems; features of NC machine
tools. Computerized Numerical Control (CNC): Tooling for NC machines - tool
presetting equipment, flexible tooling, tool length compensation, tool path graphics;
NC motion control system; Manual part programming, fixed/floating zero. Block
format and codes: Computer assisted part programming. DNC and Adaptive Control:
Direct numerical control: Adaptive control in machining system; Combined DNC/CNC
system.

1.Introduction to CNC machine
CNC = Computerized Numerical Control

History and Development of
Technology
Conventional M/C
NC M/C
(1948 US Air force, MIT 21 months )
CNC M/C
1997  1st commercial NC m/c
“CINCINNATIC HYDROTEL VERTICAL-SPINDLE MACHINE “

History and Development of
Technology

Conventional vs. CNC machine
• Machine Structure
The CNC machine tools are basically built in the
same way as conventional machine tools. The
difference lies in the fact that the machine
components relevant for turning and milling
processes are controlled by computers.

• Function

• Conventional machine
 eyes, hands, brain, skill
• CNC machine
Program Control unit Motor Motion
Measuring & Reflection Unit
No skill is required for operating CNC m/c .

Conventional machine
CNC machine

Difference between Conventional M/C
& CNC M/C
Item Conventional
machine
CNC
machine
1. Movement Acme screw Ball screw
2. Feed manual motor
3.measurement manual Linear scale

Advantages of CNC
• Flexible, high accuracy
• Short production time
• Complex shapes
• Short setting time
• No skill requirement
• Short inspection time/ high quality product
• Low cost

Disadvantages of CNC
• High machine cost
• Complicated maintenance
• Skill & training are required for programming
and maintenance.
• Parts are imported from aboard.
• High tooling cost
• Temperature, humidity & dust must be
controlled.

2. Component and Function of CNC
• 1 ) Different components related to CNC
machine tools:-
( 1.1 ) Part program:
( 1.2 ) Machine Control Unit:
( 1.3 ) Machine Tool

( 1.1 ) Part program:

Feed drive
( 1.3 ) Machine Tool

Measuring
System

Tool change facilities

( 1.2 ) Machine Control Unit:
Machine Control Unit
(MCU)
It reads and interprets the
coded instructions for coded instructions for machining a particular work piece
and generation
electric output signals. It also acts as a feedback
controller for precise positioning of machine table or spindle. MCU consists of
Data-processing unit (DPU)
reads coded instructions processes coded instructions
transmits data pertaining to the position of each transmits data pertaining to the
position of each axis to the CLU.
Control loop unit (CLU)
Control loop unit (CLU) executes linear or circular interpolations based on the
position and speed signals from the DPU on the position and speed signals from
the DPU
and generates control signals receives axis feedback signal receives axis
feedback signal implement auxiliary control function

Open and closed loop

ADAPTIVE
CONTROL
Optimization
ADAPTIVE CONTROL
With constraints (ACC)
ADAPTIVE CONTROL

Coordinate System
3.1 CNC Axes

Axes on a CNC lathe

Axes on a CNC milling machine

Zero and reference points on CNC

Zero Point of machine on a CNC lathe

Machine Zero Point and Work part zero point on
CNC milling machine

TYPES OF CNC MACHINE
There are many different types of CNC
Machines used in
industry, Such as:
•Mills and Machining Centre
•Lathes and Turning Centre
•Drilling Machines
•EDM Sinker and wire cut Machines
•Flame and Laser-Cutting Machines
•Water Jet Profilers

Steps in part program writing
Codes with explanation of use
Tool length compensation
Cutter radius compensation

CNC.ppt

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