1. Introduction to Computer Numerical control

2. Types of CNC Milling Machines can divide in to three categories:
By number of axes - Two , three or more
By the orientation of axes- Vertical or Horizontal
By presence or absence of tool changer

3. Types of CNC Plasma Spring forming Laser Cutting machine
Flame cutting machine
Electric Discharge Machine
Water Jet
Welding
CNC Punch Press

4. Types of Control System
Point to point Tool Movement
Point to point control system causes the tool to move to a point on the part and execute an operation at the point only
Continues path tool Movement
Continues path controller are named because they cause the tool to maintain continues contact with the part as the tool cuts a contour shape

5. Machine tool Axes
Numerical machines can also be classified on the number of axes, or direction of motion.
Machine centers usually have two-and – half, three, four, or five axis with three or four axis are more common
Lathes and turning centers generally have between two and four axes

6. Loop System
Loop system send electrical signal to drive motor controllers and receives feedback. One of the important factor that determine the tolerances to which a part can be cut is the loop system type.
Open Loop System
An open loop system utilizes stepping motors to create machine movement by electrical signals. the motor connected to Acme lead screw
The lead screws used in this system generates friction and backlash. Backlash can cause positioning Error

7. Close Loop System
Special motors called servos are used for executing machine movements in closed loop system.
Motor type can be
AC servos,
DC servos,
Hydraulic servos.
The speed depend on amount of current or hydraulic fluid passing through it.
Servos are connected to the spindle and they are connected to the machine table through the ball lead screw

8. Ball Lead Screw
Ball lead screw is the hart of the drive system
Advantages of ball lead screw over Acme lead screw are:
1. Precise position and repeatability
2. High Speed capability,
3. Less Wear
4. longer life

9. Position loop is closed by a device called an ENCODER.
An encoder is a disk with three rings around it
1000 slits in the first ring,
1000 slits in the second ring,
Only one slit in the third
There are three light receiver on the other side of the disk
Encoder passes the light to the receiver when the slits line up with the light and receiver. This create pulses
The CNC control knows there are 1000 pulses per revolution so by counting the pulses it knows the encoder’s position exactly

10. Homing moves axes to a known position where each axes is initialized
Homing (ZRN)
Homing moves axes to a known position where each axes is initialized

11. Cartesian coordinate system
Any point on a machine part, such as a hole to be drilled, can be described in terms of its position.
the system that allows us to do this is Cartesian coordinate

12. Machine axes
Machine axes are established according to the industry standard report EIA RS - 267A

13. Axes configuration
X axes moves from right to left as you face the machine
Y axes move toward and away from you
The Z axes is the spindle movement up and down spindle .
A move toward work is Z(-Z)
A move away from work is Z(+ Z)

14. Types of tool positioning
Incremental Positioning

15. Absolute Positioning

16. End of presentation