Cnc Lathe Machine Project xvx

CNC LATHE MACHINE INTRODUCTION TO CNC MACHINE: CNC stands for computer numeric controlled. It refers to any machine tool (i.e. mill, lathe, drill press, etc.) which uses a computer to electronically control the motion of one or more axis on the machine. • The development of NC machine tools started from a task ed by the US Air Force in the early 1950’s, involving MIT and several machine-tool manufacturing companies. The need was recognized for machines to be able to manufacture complex jet aircraft parts. • As computer technology evolved, computers replaced the more inflexible controllers found on the NC machines; hence the dawn of the CNC era. • CNC machine tools use software programs to provide the instructions necessary to control the axis motions, spindle speeds, tool changes and so on. • CNC machine tools allow multiple axes of motion simultaneously, resulting in 2D and 3D contouring ability. • CNC technology also increases productivity and quality control by allowing multiple parts to be produced using the same program and tooling.

TYPES OF CNC MACHINES: There are many types of CNC machines used in the industries, such as,      

Mills and Machining Centers Lathes and Turning Centers Drilling Machines EDM Sinker and wire cut Machines Flame and Laser-Cutting Machines Water Jet Profilers

ELEMENTS OF A CNC MACHINE

ELEMENTS OF A CNC MACHINE: The various units are as follows:  INPUT UINIT: It receives all the commands from the operator interface (operation station containing all switches, push buttons, displays required to operate and monitor machine activities) and or status of machine in the form of a.c, d.c, analog signals, or by digitally. Different ways of data input are:    

MDI: Manual Data Input PROGRAM PREPARATION WITH CAD CAM PROGRAM DATA TRANSFER FROM PC TO CNC M/C PROGRAM DATA TRANSFER FROM PC TO DNC OPERATIONS

 CONTROL UNIT: It takes instructions from the memory unit and interprets them one at a time. It processes information received from the operator and machine interface. These informations are then interpreted and manipulated with hardware logic and computer programmes. It sends appropriate instructions to other units to cause instruction execution. It turns on and off machine outputs and controls motion via machine interface. TYPES OF CNC MACHINE CONTROL UNITS:

 FANUC CONTROLL  SIEMENS  GSK  MECH3  MEMORY UNIT: It stores instructions and data received from the input. It also stores the results of arithmetic operations and supply information to output unit. Part programs are usually stored in a Random Access Memory, which provide immediate access to any storage location point in memory.  ARITHMATIC UNIT: It performs calculations and makes decisions. Its results are stored in memory unit.  OUTPUT UNIT: it receives data from the memory at the command of control unit. The signals are made compatible with output devices so that commands issued by output unit can be obeyed by them.  OPERATOR AND MACHINE INTERFACE: operator stations forms a major operator interface. It is used to initiate automatic operation, to input data, and to monitor activities using display devices. A host computer also serves as operator interface, when a part is made on this machine the host computer modifies the part programme, while it is running by making corrections based on the error table, to obtain improved accuracy on the part.

OPERATIONAL FEATURES of CNC MACHINES:

CNC OPEN LOOP AND CLOSE LOOP SYSTEM: The open and closed loop system describes the two

primary types of CNC control systems. Open and closed loop describes the control process of a system. Open loop refers to a system where the communication between the controller system and the motor is one way. OPEN LOOP SYSTEM: Refers to a system using a stepper motor, where the communication

between the controller system and motor is one way. The process is fairly simple. The machinist will decide what he/she wants to accomplish and will generate the G-code and the software will create the necessary steps and direction signals to perform the desired task. The computer will relay this information to the controller which then energizes the motor. What distinguishes open looped from a close looped system is after the motor moves to the desired position; there is no to the controller system to the action. CLOSE LOOP SYSTEM:

The closed-loop system has a subsystem to monitor the actual output and correct any discrepancy from the programmed input. The system could be either analog or digital. The analog systems measure the variation of physical variables such as position and velocity in of voltage levels. Digital systems monitor output variations by means of electrical pulses.

Closed-loop systems are very powerful and accurate because they are capable of monitoring operating conditions through subsystems and automatically compensating for any variations in real-time. Most modern closed-loop CNC systems are able to provide very close resolution of 0.0001 of an inch. Closed-looped systems would, naturally, require more control devices and circuitry in order for them to implement both position and velocity control. This, obviously, makes them more complex and more expensive than the open-loop system.

If the motor does not operate as instructed there is no way for the system to know that this is occurring. The controller system will continue performing the next task or step as if there is no problem until a limit switch is tripped or the operator resets the machine. Open loop systems run the risk overloading the machine and losing steps which can ruin the work piece or cause harm to the machine. These are the drawbacks of open loop system.

CNC COORDINATE SYSTEM: In order to shape metal by machine tools, the cutting tool should move in with the work piece at certain specific points, while the work piece or cutting tool is rotating. Coordinate system is required to define the movement on the machine. Basically there are two common Coordinate systems:  CARTESIAN COORDINATE SYSTEM  POLAR COORDINATE SYSTEM

2D Cartesian coordinate system: When dealing with 2 dimensions (2D), the twodimensional coordinate system is used.

3D CARTESIAN COORDINATE SYSTEM: When dealing with three dimensions (3D), the three dimensional coordinates system is used; Three – Axis Milling machine: In a Three – Axis Vertical Milling Machine:

  

X is the direction of the Table travel Y is the direction of the Cross travel Z the Spindle travel up – down

6 AXIS MILLING MACHINE

Polar Coordinate System: The point is located by its distance (radius r) to the point of origin and its angle (alpha α) to a specified axis.

The angle is positive if it is measured in counterclockwise direction starting from positive X-axis

CNC Lathe (turning) Machine’s coordinate system:  Machine Zero Point (M): The origin of the coordinate system. It is defined by the manufacturer and cannot be changed. In general, the machine zero point M is located in the center of the work spindle nose for cnc lathe.

The work piece’s zero point (W) it is the origin of the work part-based coordinate system. Its location is specified by the programmer.

CNC PROGRAMMING:     

Offline programming linked to CAD programs. Conversational programming by the operator. MDI ~ Manual Data Input. Manual Control using jog buttons or `electronic hand wheel'. Word-Address Coding using standard G-codes and M-codes.

Basics of NC Part Programming: During secondary motion, either the tool moves relative to the work piece or the work piece moves relative to the tool. In NC programming, it is always assumed that the tool moves relative to the work piece no matter what the real situation is. The position of the tool is described by using a Cartesian coordinate system. If (0, 0, 0) position can be described by the operator, then it is called floating zero. In defining the motion of the tool from one point to another, either absolute positioning mode or incremental positioning mode can be used.

 Absolute positioning: In this mode, the desired target position of the tool for a particular move is given relative to the origin point of the program.  Incremental positioning: In this mode, the next target position for the tool is given relative to the current tool position.

Structure of an NC Part Program: Commands are input into the controller in units called blocks or statements.

 Fixed sequential format  Tab sequential format  Word address format-----sample block N135 G01 X1.0 Y1.0 Z0.125 F5 Programming Key Letters:  O- Program number (Used for program identification)  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 Table of Important G codes:           

G00 G01 G02 G03 G17 G18 G19 G20/G70 G21/G71 G42 G43

Rapid Transverse Linear Interpolation Circular Interpolation, CW Circular Interpolation, CCW XY Plane XZ Plane YZ Plane Inch units Metric Units Cutter compensation right Tool length compensation(plus)

 G44  G49      

G80 G81 G82 G83 G90 G91

Tool length compensation (minus) Tool length compensation cancel Cancel canned cycles Drilling cycle Counter boring cycle Deep hole drilling cycle Absolute positioning Incremental positioning

LIST OF IMPORTANT M CODES: M06 Tool change M00 Program stop.

M06

TOOL CHANGE

M08 Coolant on M01 Optional program stop

M08

COOLANT ON

M09 Coolant off M02 Program end

M09

COOLANT OFF

M10 Clamps on M03 Spindle on clockwise

M10

CLAMPS ON

M11

CLAMPS OFF

M30

PROGRAM STOP.

M11 Clamps off M04 Spindle on counterclockwise M30 Program stop, reset to start M05 Spindle stops.

PROGRAMMING EXAMPLE: