C.U. Shah College of Engineering & Technology ,

Wadhwan city.

Importance of NC & CNC systems as a part of CAM.

Prepared by: MEMAN MAHAMMADRAFIK J. Enrolment No.: 120440119032 Roll No.: 39

Guided by: Asstt. Prof. Y.A. DARJI. Mech.Engg.Dept. C.C.E.T.

Year:2015-16

Agenda: Introduction. About NC Machine Tool. Elements of NC machine tool system. Classification of NC machine tool systems. Advantages & Disadvantages of NC machine

tools. About CNC Machine Tool. Elements of CNC machine tool system. Classification of CNC machine tool systems. Advantages & Disadvantages of CNC machine

tools. NC v/s CNC. Adaptive Control system.

Introduction:

The NC, CNC and DNC are machine tools systems which reduce the non-productive time in machining operation by reducing time elements like workpiece handling time,job set-up time,tool changing time, etc.

What is NC Machine Tool…?

NC-Numerical Control machine tools are the machine tools which controls the various operations during machining by some specified letters ,numbers and symbols.

The NC machine tool runs on the given program to it without human operator.

The NC program consists a set of instructions for controlling the motion of the drives in machine tool as well as the motion of cutting tool.

In NC machine tools , following operations may be automatic:

I. Automatic starting and stopping of the spindle;

II. Controlling the spindle speed;III. Automatic positioning the

cutting tool by controlling the motion of slides;

IV. Controlling the feed rate; andV. Changing the cutting tools.

Elements of NC Machine Tool System:

Types of program tapes:

Punched Paper Tape Punched Plastic Tape

Magnetic Cassettes , Floppy discs, CD’s Keyboard

Components of NC machine tool:

Classification of NC machine Systems:

According to control loop feedback systems:

Open-Loop type NC Machine

Close-Loop Type NC Machine

According to type of tool motion control:

Point to PointNC machine.

Straight cutNC machine.

Continuous path controlNC machine.

According to programming methods:

Absolute programmingNC Machine systems.

Incremental programmingNC Machine Systems.

According to type of controllers:

NC Controller System.

CNC Controller System.

Advantages of NC Machine Tools:

1. Reduced lead time for production.

2. Increased Productivity.3. Reduction of human error.4. High degree of accuracy.5. Less inspection required.6. Greater machine tool safety.7. Greater operator safety.

Limitations of NC Machine Tools:

1. High initial cost.2. High maintenance cost.3. High operational cost.4. Limited life of tapes.5. Time consuming punched tape

operation.

What is CNC Machine Tool…?

In CNC-Computer Numerical Control machine in which computer is used to perform the most of basic NC machine functions.

In CNC machines the entire program is entered and stored in computer memory.

The machining of each workpiece controlled by the program which is contained in computer.

The stored program of part we can also use in future.

Elements of CNC Machine Tool System:

Classification of CNC Systems:

1. According to control loop feedback systems:

a. Open-loop type CNC machines. b. Close-loop type CNC machines.2. According to type of tool motions: a. Point to point CNC machines. b. Straight cut CNC machines. c. Continuous Path control CNC machines.3. According to Programming methods: a. Absolute programming CNC machines. b. Incremental programming CNC

machines.

4. According to Type of Controllers:

Hybrid Controller CNC system.

Straight Controller CNC System.

Advantages of CNC machine tools:

1. Easy to program input.2. Multiple program storage.3. Online part programming and

editing possible.4. Greater flexibility of system.5.Change in system of units possible.6.Use of Advanced interpolation.7. Automatic tool dimension

adjustment.

Limitations of CNC machine tools:

1. Higher investment cost.2.Higher maintenance cost.3. Required skilled operators.4. For continuous production ,

proper planning is needed.

NC v/s CNC1. In NC , Computer is

not needed.2.Part Program is

entered on the Program tape.

3.Here each part program requires separate program tape.

4.Modifying the program is difficult.

1. In CNC, Computer is needed.

2. Part program is entered and stored in the computer.

3. Here only one computer is one for different part program.

4. Modification of any program is very easy.

AC-Adaptive Control System:

AC machining is developed by Bendix Research Laboratories, USA for US Air Force.

AC is a control system which measures output process variables and uses these to control the speed and feed of the spindle.

Some of the process variables used in AC are: spindle deflection, force, torque, cutting temperature, vibration amplitude and power requirement.

AC is mainly used to reduced the effectively process time.

Any Questions…..???