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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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