computer numerical control

by Lalrin Muani,
Christian Medical College

1. Presented by Miss lalrin muani k. 3 rd yr bpo Cmc vellore

2. Introduction CNC is the acronym for computer numerical control . It is an outgrowth of the older term "NC", which stands for just " numerical control ". Numeric control is a programmable automation in which process is controlled by numbers, letters and symbols. (Computer + NC=CNC) CNC refers to the idea of controlling machine tools programmatically via computer . With the older "NC" term, A computer need not be involved. The machine might be controlled using, for example, punched tape.

3. Introduction This means a computer converts the design produced by Computer Aided Design Software (CAD), into numbers . The numbers can be considered to be the coordinates of a graph and they control the movement of the cutter. In this way the computer controls the cutting and shaping of the material. CNC can control the motions of the work piece or tool, the input parameters such as feed, Depth of cut, speed, and the functions such as turning spindle on/off, turning coolant on/off.

4. Applications The applications of CNC include both for machine tool as well as non-machine tool areas . Some are as follows: lathe , drill press, milling machine, Grinding unit, laser, sheet-metal press working machine, tube bending machine etc.

5. welding machines (arc and resistance), Measuring machine, electronic assembly, tape laying and filament winding machines for Composites etc. This Technology is applied to Prosthetics and Orthotics field as well.

6. History The first NC machines were built in the 1940s and 1950s by Prof. John T Parson. Conceived method of using punched cards containing coordinate position data to control the machine tool. In 1948, Parson demonstrated his concept to U.S Air Force Fig: punched card which contains command to control automated machinery

7. History CNC machine came to existence after evolution of computer around 1980. Modern CNC Machine are improving further as the technology is changing with variety of functions according to applications. 1959 CNC Machine: Milwaukee- Matic -II was first machine with a tool changer...

8. Computer numerical control Advantages Easier to program Easy storage of existing programs Easy to change program Avoid human error CNC machines are safe to operate Complex geometry is produced as cheaply as simple ones disadvantages Costly setup than manually operated machines. Skilled operators Computers, programming knowledge required Maintenance is difficult.

9. Computer numerical control Advantages Short production time Greater manufacturing flexibility Contour machining (2 to 5 axis machining) disadvantages

10. Direct numerical control advantages Greater computation and flexibility. Eliminates use of punched tapes. Convenient storage of NC Part Programme in computer file. Direct conversion of data from CAD to NC program. Increases Productivity Save time. disadvantages  The only disadvantage of the DNC is if the computers breaks down, but the computer is so reliable that this is unlikely to occur.. Some type like Terminal-based DNC system and Network-based DND system are expensive.

11. numerical control advantages Higher productivity- reduction in time of set up, work piece handling time, tool changing time. Reduced non-productive time. Reduced fixturing. Greater accuracy and repeatability Reduced inventory Reduced floor requirements. Operator skill level reduced NC machine are safer to operate. disadvantages  high investment cost. High maintenance effort. Need for skilled programmers. High utilization required.

12. Elements of cnc machine A CNC machine consists of following 6 major elements: Input device Machine control unit Machine tool Driving system Feedback devices Display unit

13. Input devices Floppy disk device Serial communication USB flash drive

14. Machine control unit ( mcu ) the machine control unit is the heart od CNC system. There are two sub-units in the machine control unit: Data Processing Unit(DPU) Control Loop Unit(CLU)

15. Machine tool This can be any type of machine tool or equipment.

16. Driver system The driving system is an important component of CNC machine as the accuracy and repeatability depend very much on the characteristics and performance of the driving system. The driving system is classified as Spindle drives and feed drives. The spindle drives are used to provide angular motion to the work piece or cutting tool. Feed drives are used to drive the slide or a table.

17. Feedback devices

18. Display unit