Introduction to Computer Numerical control

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 • 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 (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