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CNC Lathe

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This presentation comprises of the following:1. About CNC Lathe

2. Types of CNC lathe

3. CNC Turning Machine

4. General flow of operations of CNC machine tool

5. Coordinate system specified by CNC coordinate system

6. Types of programming

7. Important functions used in programming8. Program configuration

9. Codes used in the program in CNC system

10. Types of Coordinate system

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INTRODUCTIONAlathe is a machine tool which rotates the work piece

on its axis to perform various operations such ascutting, knurling, drilling, or deformation with toolsthat are applied to the work piece to create the desiredproduct.

http://en.wikipedia.org/wiki/Machine_toolhttp://en.wikipedia.org/wiki/Axishttp://en.wikipedia.org/wiki/Cuttinghttp://en.wikipedia.org/wiki/Knurlinghttp://en.wikipedia.org/wiki/Drillinghttp://en.wikipedia.org/wiki/Deformation_(engineering)http://en.wikipedia.org/wiki/Deformation_(engineering)http://en.wikipedia.org/wiki/Drillinghttp://en.wikipedia.org/wiki/Knurlinghttp://en.wikipedia.org/wiki/Cuttinghttp://en.wikipedia.org/wiki/Axishttp://en.wikipedia.org/wiki/Machine_tool

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WHAT IS CNC LATHE?

Computerized Numerically Controlled Lathe

The machine is controlled electronically via a computermenu style interface.

The tool paths are programmed by CAD/CAM process.

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CNC turningmachine

CNCmillingmachine

CNCGrindingmachine

Types of CNC Lathe Machines

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CNC Turning

Cutting tool is fed into the rotating job at varietyof angles and many tool shapes can be used.

Provides an economical way to make parts that arecommonly symmetrical about single axis ofrevolution.

It can be combined with CNC milling and other

processes to make more diverse shapes.

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CNC Turning can shape most rigid materials such as

Aluminium

Copper

Stainless steel Nylon

Brass

Titanium

Bronze

Steel

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Parts made by CNC Turning include Robot parts

Motorcycle parts

Pulleys Toy parts

Shafts

Flywheels

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Pros and Cons of CNC Turning machinePros

Reduces Complexity

Amount of material removed is minimized.

Reduces time consumption.

Cons

weak shapes such as long thin structures can be

difficult to machine. bored holes become difficult when the depth to

diameter is high.

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Pulleycnc turning CNC turned and milled part

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GENERAL FLOW OF

OPERATION OF CNCMACHINE TOOL

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Part Drawing Part programming

CNC SystemFinal Product

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Machining Plan

Determination of work pieces machining range.

Method of mounting work pieces on the machine tool.

Machining sequence in every cutting process.

Cutting tools and cutting conditions.

Here , we decide the cutting method in every cutting process.

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CNC Turning Machine

Programmingarea

Turret

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Turret Index able tool holder.

Multiple cutting operations can be performed each

with a different cutting tool in rapid succession. Tool path is controlled by the machine.

Two movements namely diametrical movement andlengthwise movement.

Has stations(slots) for holding the tools.

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Programming Area Screen which is a computer menu style interface.

Consists of buttons for MDI(Manual Data Input) and

certain functional buttons. Tool path is programmed by giving preparatory

functions known as G codes.

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Functional Buttons Cycle Start

Jog Button

Chuck ID-ODJob clamp LED

SPDL CW

SPDL CCW

Cycle Stop

Reference Return

Auto

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X

Program zero point

Z

X-axis : Diametrical movement of the turret.

Z-axis : Length-wise movement of the turret.

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The coordinate system is prepared on the actual tool.This can be achieved by programming the distance fromthe current position of the tool to the zero point of the

coordinate system to be set.

The tool moves on the coordinate system specified by thecnc in accordance with the command program generated

w.r.t coordinate system on the part drawing and cuts thejob into the shape on the drawing.

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The tool position is represented by coordinates in a coordinatesystem.

X-axis and Y-axis are called program axes.

Coordinates are specified as:X_Z_

Types of coordinate systems are:

1. Machine coordinate system

2. Work piece coordinate system

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MACHINE COORDINATE SYSTEM The point which is specific to a machine and serves as the

reference of the machine is called Machine zero point.

Machine zero point is set for each machine.

A coordinate system with a machine zero point set as its origin iscalled machine coordinate system.

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WORK PIECE COORDINATE SYSTEM ACoordinate system used for machining the work piece is called

work piece coordinate system.

A work piece coordinate system is set so that the tool tip is at

specified coordinates. A set work piece coordinate system can be changed by shifting its

origin.

Work piece coordinate system is set by the following method:

Method using G50 It is set by specifying a value after G50 in the program.

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ABSOLUTE COORDINATES The tool moves to a point at the distance from zero point of the

coordinate values.

Let the command be X30.0Z70.0;

The above command brings the tool at 70 mm length of the work pieceof 30 mm diameter.

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INCREMENTAL COMMANDS Here we specify the distance from the previous tool

position to the next tool position.

Distance and direction for movement along each axis is

given in the program. Instead of X and Z ,here we use U and W.

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CUTTING SPEED-SPINDLE

SPEED FUNCTION

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Cutting speed Relative motion between the cutting tool and the work piece is

called cutting speed.

UNIT : mm/min

In CNC ,the cutting speed is specified by two digit number. N = 1000v/3.14D

When a work piece 200 mm in dia should be machined at acutting speed of 300 mm/min then from above formula we get

the spindle speed approximately as 478 rpm . S 478;

Commands related to spindle speed are known as Spindle speedfunction.

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FEED-FEED FUNCTION Movement of tool at a specified speed for cutting a work

piece is called feed.

Feed rates are specified by actual numerics.

F 2.0

The above command is used to feed the tool 2 mm whilethe work piece makes one turn.

The function of deciding the feed rate is called feedfunction.

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TOOL FUNCTION We select the tool used for various machining using the tool

function.

When a number is assigned to each tool and the number is

specified in the program , the corresponding tool is selected. When a tool is stored at location 01 of the turret , then the tool

can be selected by specifying T0101

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TOOL LENGTH COMPENSATION Length of each tool used for machining must be measured

in advance.

Difference between the length of standard tool and tool

used in CNC is set in the tool offset. The above function which is set is called tool length

compensation.

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PROGRAM CONFIGURATION

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BLOCK

BLOCK

BLOCK

Program

Tool movement sequence

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BLOCKN G X Z M S T ;

Sequence No. Preparatory Dimension Word Misc. function Spindle Tool function

function function

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G-CODES AND M-CODESG-CodesG-codes are preparatory

functions.

Involves the function of the tooland its movement on the work

piece.

Usage depends on the job formachining.

M-CodesM-codes are miscellaneous

functions.

Involves function of specifying onoff operations of the

components of the machine.

Usage depends on the componentsof machine.

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G-CODESG-Code Function

G00

G01

G28

G96

G97

Positioning(Rapid traverse)

Linear interpolation

Return to Reference position

Constant surface speed control

Constant surface speed control cancel

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M-CODESM codes Function

M02

M03

M04

M07

M09

M30

Program stop

Spindle(clockwise)

Spindle(counter clockwise)

Coolant ON

Coolant OFF

Program reset and rewind

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POSITIONING G00 (Rapid Traverse Rate) The G00 command moves the tool to the position in the

work piece system at a rapid traverse rate.

In rapid traverse the next block is executed after the

specified feedrate becomes zero and the motor reaches acertain range set by the machine builder.

A rapid traverse rate is set for each axis independently bythe machine tool builder.

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LINEAR INTERPOLATION G01 The G01 command moves the tool along a line to the

specified position at a feedrate specified in F.

The feedrate is measured along the tool path.

The feedrate specified in F is effective until a new value isspecified.

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