CNC APPLICATIONS

From the start of the NC milling machine, there have been many applications for NC technology,ranging from milling, turning, electric discharge machine(EDM), punching and nibbling, forming, bending, inspection and robotics.

Although aerospace is still one of the principal industries that require and use NC technology extensively, other industries have also used it. Because of the continuing advances and affordability of computers, the cost of NC technology has been dropping rapidly to the point where even small machine shops and small specialty industries have come to require it. Today you can find NC products in trade areas like metal working, automotive, electronics, appliances, and furniture manufacturing.

ADVANTAGES OF CNC

CNC has grown to an ever increasing rate, and its use will continue to grow because of the many advantages that it has to offer industry. Some of the most important advantages of CNC are the following;

1. Greater operator safety- CNC system are generally operated from console away from the machining area, which is enclosed on most machines. Therefore the operator is exposed less tom moving machine parts or to the cutting tool.


2. Greator operator efficiency- A CNC machine does not require as much attention as a conventional machine allowing the operator to perform other jobs while it's running.


3. Reduction of scrap because of the the high degree of accuracy of CNC systems, Scrap has been drastically reduced.


4. Reduced lead time for production- The program prepation and setup for computer numerically controlled machines is usually short. Many jigs and fixtures formerly required are not necessary.


5. Reduction of human error- The CNC program reduces of eliminates the need for an operator to take trial cuts, make trial measurements, make positioning movements, or change tools.


6. High degree of accuracy- CNC ensures that all parts produced will be accurate and uniform quality.


7. Complex machining operations- Complex operations can be performed quickly and accurately with CNC and electronic measuring equipment.


8. Lower tooling costs- CNC machines generally use simple holding fixtures, which reduce the cost of tooling by as much as 70 percent. Standard turning and milling tools eliminate the need the need for special form tools.


9. Increase productivity- Because the CNC system controls all machine fuctions, parts are produced faster and with less setup and lead time.


10. Reduced parts inventory- A large inventory of spare parts is no longer necessary since additional parts can be made to the same accuracy when the same program is used again.


11. Greater machine tool safety- The damage to machine tools as a result of operator error is virtually eliminated since there is less operator intervention.


12. Less inspection required- CNC machines produce parts of uniform quality, less inspection time is required.


13. Greater machine use- Production rates could increase as much as 80 percent because less time is required for setup and operator adjustments.
14. Reduced space requirements- A CNC system requires fewer jigs and fixtures, and therefore less storage space

Types of CNC Machine Tools

There are many different types of CNC machine tools used in industry, such as;

1. Mills and Machining Centers
   
2. Lathes and Turning Centers
   
3. Drilling Machines
   
4. EDM Machines
   
5. Flame and Laser Cutting Machines
   
6. Water Jet Profilers

CNC MACHINING CENTERS

Machining Center is the latest development in CNC technology. These systems come equiped with automatic tool changer capability of changing many tools. Some machining centers are also fitted with movable rectangular worktables called pallets. The pallets are used to automatically load and unload work pieces. At a single setup, machining centers can perform such operations as milling, drilling, tapping, boring, counter boring and so on. Additionally by utilizing indexing heads, some centers are capable of executing these tasks on many different faces of a part and at specified angles. Machining centers save production time and cost by reducing the need for moving a part from one machine to another.

CNC TURNING CENTERS

Turning center with increased capacity of tool change is also making a strong appearance in modern production shop. These CNC machines are capable of executing many different of lathe cutting operations simultaneously on a rotating part.


CNC EDM MACHINES

In addition to machining center and turning center, CNC technology has also been applied to many other types of manufacturing equipment. Among these are wire electrical discharge machines (Wire EDM) and laser cutting machines.

Wire EDM machine utilizes a very thin wire (0.0008 to 0.012 in) as electrode. The wire is stretched between diamond guides and carbides that conduct the current to the wire and cuts the part like a band saw. Material is removed by the erosion caused caused by a spark that moves horizontal with the wire. CNC is used to control horizontal table movements. Wire EDM machines are very useful for producing mold insert, extrusion and trim dies, as well as formed tools.

CNC LASER CUTTING MACHINES

Laser cutting CNC machines utilize an intense beam of focused laser light to cut the part. Material under the laser beam undergoes a rapid rise in temperature and is vaporized. If the beam power is high enough, it will penetrate through the material. Because no mechanical cutting forces are involved, laser cut part with a minimum of distortion. They have been very effective in machining slot and drilling holes.

Advantages of CNC Compared with NC

Computer Numerical Control opens up new possibilities and advantages not offered by older NC machines. Some of those are as following ;

1. Reduction in hardware necessary to add a machine function.
2. The CNC program can be written, stored, and executed directly at the CNC machine.
3. Any portion of CNC program can be played back and edited at will.
4. Many different CNC programs can be stored in the MCU
5. Several CNC machines can be linked together to a main computer. Programs written via the main computer can be downloaded to any CNC machine in the network. This is known as Direct Numerical control or DNC
6. Several DNC systems can be networked to form a large distributive numerical control system
7. The CNC programs can be input from zip or floppy disks or downloaded from local area network

Computer Numercal Control and its Components

A computer Numerical Control (CNC) machine is an NC machine with the added feature of an on-board computer. The on-board computer is often referred to as the Machine Control Unit or MCU. Control units for CNC machines are usually hard wired. This means that all machine functions are controlled by the physical electronic elements that are built into the controller. The on-board computer, on the other hand, is "Soft" wired. Thus the machine fuctions are encoded into the computer at the time of manufacture. They will not be erased when the machine is truned off. Computer memory that holds such information is known as ROM or read-only memory. The MCU has usually alphanumerical keyboard for direct or manual data input (MDI) for all part programs. Such programs are stored in RAM or Random Access Memory portion of the computer. They can be played back, edited and processed by the control. All programs residing in RAM, however, are lost when the CNC machine turned off. These programs can be saved on auxiliary storage device such as punched tape or magnetic disk. Newer MCU units have graphic screens that can display not only the CNC program but the cutter paths generated and any errors in the program.

CNC comprises on following main components;

Machine Control Unit

A small, powerful computer that controls and operates a CNC machine.It generates, stores, processes CNC programs. The machine control unit also contains the machine motion control in the form of an executive software program.

NC Machine

Responds the programmed signal from the machine control unit and manufactures the part.

Numerical Control definition (Concepts and Advantages)

Numerical control has been used in industry for more than 50 years. Simply put Numerical control is a method of automatic operating a manufacturing machine based on code of letters, neumbers and characteristics. A complete set of coded instruction for executing an operation is called a program. The program is translated into corresponding electrical signals for input to motors that run the machine. Numerical control machine can be program manually.

Traditionally, numerical control systems have been composed of the following components.

Tape Punch- Converts written instructions into a corresponding whole pattern. The hole is punched into a tape, which pass through this device. Much older units used a type writer device called flexowriter. Later devices included a microcomputer coupled with a tape punch unit.

Tape Reader- Read the whole pattern on the tape and converts the pattern to a corresponding electrical signal code.

Controller- Receives the electrical signals from the tape reader and subsequently causes the NC machine to respond.

NC Machine- Responded the programmed signals from the controller. Accordingly, the machine executes the required motions to manufacturing a part (Spindle rotation on/off or spindle movement along programmed axis direction etc.)


Advantages of NC system over manual methods of production

NC system offers some of the following advantages over manual methods of production

1. Better control of tool motion under optimum cutting conditions





2. Improved part quality and repeatability





3. Reduced time to manufacture parts





4. Reuced scrap





5. Better production planning and placement of machining operations in the hands of engineers
   

THE EVOLUTION OF NC

It was in 1947 when numerical control was born. It began when john C. Parsons of the parsons corporation Traverse city Michigan (a manufacturer of helicopter rotor blades) could not make his templates fast enough so he invented a way of coupling computer equipment with a jig borer. Mr. Parsons used punched cards to operate his digit Ron system.

1949 was the year of another "Urgent need". The US Air Material Command realized that parts for its planes and missiles were becoming more complex. Also as the design were constantly improved, changes in the drawing were frequently made. Thus in their search for methods of faster production, an air force study contract was awarded to the Parsons Corporation. The servo mechanisms laboratory of the Massachusetts Institute of Technology (MIT) was the subcontractor.

In 1951, MIT took over the complete job, and in 1952 the prototype of today's NC machine, a modified Cincinnati Hydrtel Milling Machine, was successfully demonstrated. The term numerical control was originated at MIT.