Cnc lecture1

10/12/2016 1 Numerical Control Machines

CNC-MDP471

Design and Production Engineering Department,

Faculty of Engineering,

Ain Shams University.

Lecture 1

DR. AMR SHAABAN

10/12/2016 2

•Introduction

•CNC classification

•Control unit

•Control system

•Interpolation

•Designation of machine axes

•Local coordinate system

•Absolute and incremental

•Introduction to part Program

10/12/2016 Dr.Amr Shaaban-Numerical Control Machines 3

INTRODUCTION

PROBLEM DEFINITION

CONCEPTUAL DESIGN

EMBODIMENT DESIGN

DETAIL DESIGN

MANUFACTURE

Scope of CAD/CAM/CNC

Specifications

Concepts

Layouts

Analysis/ Drafting

Product

DESIGN PROCESS


CAD CNC

CAM

INTRODUCTION


CONTROL UNIT

NC – Punched Tape •The control is hard wired, and therefore any

modification needs many changes in the

controller.

•The part program punched into paper tape

on a separate punching machine

•Read and executed one line of code at a

time from a part program

•When the entire program was executed, the

tape reader would rewind back to the

beginning of the program. The machine has

no means of storing or editing of loaded

programs.


CONTROL UNIT

Computerized

Numerical Control •Developments in electronics industry has led to use

the computer in place of conventional dedicated

controller.

•No punched tapes; instead, all information flows from

a computer which interfaced with machine control

unit. A typical system for instance can store programs

equivalent to about 700 m of punched tape

•Minimum of electronic hardware is used, as some of

the hard ware modules is replaced by software.

•MCU functions of data decoding, control, buffering,

feed rate control, interpolation and position control.


CONTROL UNIT

Direct Numerical Control

DNC

•Utilize a single large frame computer to

control several machines through a data

transmission lines. A minimum of 5 to 10

machine tools is considered necessary to

make the system economically justifiable.

•It allows machining processes to be fully

integrated with other automation systems,

with data files, and with management

information system.


CONTROL SYSTEM

Open Loop System •Operates without verifying that the actual

position is equal to the specified position.

•Usually stepper motors are used.

•Stepper motor is an electric motor that

rotates a set amount every time it receives

an electronic pulse from the MCU.

•The displacement value is controlled by

controlling the number of pulses sent to

the stepping motor while the feed rate is

controlled by controlling the rate of pulse.


CONTROL SYSTEM

Closed Loop System

•Use feedback system to verify that the actual

position is equal to the specified one.

•Use an error detector that returns a signal

which is proportional to the difference between

input and feedback.

•Usually servo motors are used with feedback

loops.

•Tachometers are attached to motors and drives

for velocity feedback loop, while encoders are

attached to sliding parts for position feedback

loop.

•Sensors used for the feedback system make it

more expensive.


INTERPOLATION

P-Type

•Position type or point to point control.

•There is no control on the path followed to reach that

position. Only axial path or 45 degree are provided.

•When point-to-point is used for a certain axis, the

cutter or work table moves in rapid positioning mode

(maximum feed rate). Hence, no machining can

occur using P-type controlled axis.

•If the tool is at A (X5, Y5) , and the absolute

coordinates (X20, Y30) are input, the movement will

take place simultaneously at an angle of 45 degrees

on both the X and Y axes until the tool reaches B

(X20, Y20), and then will continue on the Y axis only

until the tool is at C (X20,Y30).


INTERPOLATION

L-Type •Line type control.

•The main difference between this system and p-system is that it is

possible for the rate of movement to be programmed to suit the

machining conditions. This permits machining to be carried out

during the movements.

•A line motion control system can be used to produce a wide range

of work by milling shapes that are composed of lines at 90 degrees

and 45 degrees, and can also be used on turning centers for the

production of stepped shafts


INTERPOLATION

C-Type •Contour type control.

•Different rate of movement can occur at the same time on different

axes.

•There may be from two to eight controllable axes; movement can

take place on a number of axes simultaneously, all at different feed

rates if necessary.


INTERPOLATION

NOTE Commonly, machines have different modes of control on

different axes. Frequently the control system provides circular

interpolation on any two axes and linear interpolation on the

remaining third axis. This type of control system is referred to

as 2CL. Similarly, 2PL indicates point-to-point control on two

axes and line motion control on a third axis; 5C is a machine

which has contouring on five axes.

Punching CNC machines Drilling CNC machines VMC


MACHINE AXES

RIGHT HAND ROLE

•Z is always the axis of rotation.

•Negative Z is the direction in which the cutter

approaches the work piece.

•X axis is the axis of the long path.

•Using RHR, the 3 axes and their signs can be determined.

•A, B, and C are the axes of rotation about X, Y, and Z

respectively.

•U, V, and W are three auxiliary axes corresponding to X,

Y, and Z respectively.


MACHINE AXES


MACHINE AXES

X Y

Z

B

U

C A


MACHINE AXES


COORDINATE SYSTEM

Machine Zero Programming Zero Floating Zero


ABSOLUTE & INCREMENTAL

G90

Example

G91


PART PROGRAM

•Part program is a series of coded instructions required to produce a part.


PART PROGRAM

N5 G90 G20

N10 T0101

N15 M03

N20 G00 X2 Z0.1 M08

N35 G71 P40 Q55 U0.05 W0.05 D625

F0.012

N40 G01 X0 Z0

N45 G03 X0.5 Z-0.25 I0 K-0.25

N50 G01 X1.75 Z-1.0

N55 X2.1

N50 T0100 G00 X4 Z3

N65 T0202

N70 G00 X2 Z0.1

N75 G70 P40 Q55 F0.006

N80 G00 X4 Z3 M09

N85 T0200 M05

N90 M30

Turning parts


PART PROGRAM

Milling parts

N5N5 G90 G80 G20 G99

N10 M06 T6

N15 M03 S1300

N20 G00 X1 Y1

N25 Z0.5

N30 G81 Z-0.25 R0.125 F5 N35 X2

N40 X3

N45 Y2

N50 X2

N55 X1

N60 G80 G00 Z1

N65 X0 Y0

N70 M05

N75 M30

10/12/2016 CNC - Part programming 23

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