CNC AND ITS COMPONENTS
- 1. CNC Machine & Its Components
- 2. Numerical Control Machine(NC) Form of programmable automation. Mechanical actions of machine tool are controlled by program. The program is in form of alphanumeric data. After a job is finished the program of instructions can be changed to process a new job.
- 3. Numerical Control Machine(NC) Advantages Reduces non productive time Reduces manufacturing lead time Greater manufacturing flexibility Improves quality control Reduced inventory Disadvantages High investment cost High maintenance effort. Part programming Higher utilization of NC equipments
- 4. CNC Machines To overcome the shortcomings of the NC machines CNC machines evolved. CNC machines are the NC machines whose MCU is based on the micro computer rather than the hardwired controller. Elements of CNC machines are Part program Machine Control Unit Machine tool Features of CNC machines are: Storage of more than one part program In-process compensation Improved programming and operating features Adaptive control adjustments
- 5. Common types of CNC machines CNC Lathe machine CNC Milling machine CNC Drilling machine CNC Grinding machine CNC Laser cutting machine Water jet cutting machine Electro discharge machine
- 6. Advantages Higher accuracy Reduce lead time Higher flexibility Reduce scrap rate Reliable operation Consistent quality Reduced manpower Increased productivity Reduced non productive time
- 7. Applications • Parts needed in a hurry • Parts with complicated contours • Parts requiring expensive jigs and fixtures • Parts those have several engineering changes • Cases where human errors can be extremely costly • Parts requiring close tolerance or good repeatability
- 8. Components of CNC Electrical components Mechanical components
- 11. Dc brushless motor Digital pulse is converted into rotary motion. It is an open loop system
- 12. Operating principle A stepper motor is a type of DC motor which has a full rotation divided in an equal number of steps. There is stator winding and a permanent magnet at the centre of windings. When electric current is passed through winding it starts acting as an electromagnet and the permanent magnet moves. The position of the rotor is controlled by the attractive and repulsive forces.
- 14. Advantages Control is achieved at low cost High torque at startup and low speed Simple construction Can operate in open loop control system Low maintenance
- 15. Disadvantage Low torque at high speed Requires a dedicated control circuit Should not be used for high performance or high load applications.
- 16. Servo Motor
- 17. Servo Motors A servomotor is a simple electrical motor controlled with the help of servomechanism. Servo motors are functional with the sensor feedback. The input to its control is signal either in the analog or digital form Servo motors are primarily used where speed, power , noise level as well as velocity and positional accuracy.
- 18. Servo motors DC brush servo motor AC servo motors
- 19. DC Brush Servo motors: The brush refers to the brushes which passes the electric current to the rotor , the rotating part of the motor. In DC Servo motor each coil is angularly displaced from one another so when the torque drops off from one coil it automatically switches to the another coil as to produce the maximum torque. This switching is done by the brushes and a commutator present in the motor. AC Servo motors: Its physical construction is similar to that of the DC Servo motor but there are no magnets in the AC Servo motor. But both the rotor and the stator are constructed from coils. These are capable of delivering very high torque at very high speed. There are no brushes in this type of motors which means they are maintenance free.
- 20. Working Principle Motor is controlled by a feedback signal generated by comparing output signal and the reference input signal. Reference input signal is applied to the system and compared with output signal of the system and thus a third signal is generated by feedback system. This third signal acts as input signal to the device. This input signal to the device is present as long as there is a logical difference between reference input signal and output signal of the system. After achieving the desired output there will be no longer logical difference between the input signal and the output signal of the system. Now the feedback signal is not enough to produce further output until the next reference input signal is provided.
- 21. Advantages Low Cost Smooth rotations High speed attainable Wide variety is available High peak torque available Disadvantages Thermally inefficient Require maintenance Can be demagnetised DC Servo motors
- 22. AC servo motors Advantages High Performance Maintenance Free High torque available Cannot be demagnetised Accurate position information Disadvantages Expensive Added feedback component Increased control complexity
- 23. Encoders An encoder is a device, circuit, transducer, software program, algorithm that converts information from one format or code to another, for the purposes of standardization.
- 25. Mechanical components Recirculating ball screw Planetary roller screws Recirculating roller screws:
- 27. The recirculating ball steering mechanism contains a worm gear inside a block with a threaded hole in it. This block has gear teeth cut into the outside to engage the shaft. They convert sliding friction into rolling friction.
- 28. Advantages wear will be reduced reliability of the system will be increased the efficiency of ball screws may reach up to 90%.
- 30. Roller screw This type of screw provide backlash-free movement Their efficiency is same as that of ball screws. These are capable of providing more accurate position control. Cost of the roller screws are more compared to ball screws. The thread form is triangular with an included angle of 90 degrees.
- 33. These are capable of transmitting high load at fast speed. There is no axial movement of the rollers relative to the nut. The rollers are threaded with a single start thread.
- 35. The rollers in this case are not threaded. The rollers are provided with a circular groove and are positioned circumferentially by a cage. Recirculating roller screws are slower in operation. They are capable of transmitting high loads with greater accuracy
Editor's Notes
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