NC, CNC, DNC MACHINESOutline of presentation :1. Introduction to NC Machine tools. 2. Introduction to CNC Machine tools. 3. Introduction to DNC Machine tools. 4. Difference Between NC, CNC and DNC machine tools. Numerical Control (NC) Defined NC (numerical control) machine tools are the machine tool, of which the various functions are controlled by : letters , numbers and symbols. The NC machine tool runs on a program fed to it; without human operator. The NC program consist of a set of instruction or statement for controlling the motion of the drives of the machine tools as well as the motion of the cutting tool. NC machine tools . one or more of the following function may be automatic : i. . iv.Controlling the spindle speed. iii.Changing the tools. ii. Starting and stopping of the machine tool spindle.Controlling the feed rate.Positioning the tool at the desired location and guiding it along the desired path by automatic control of the motion of slides. and v. . Part program: Using the part drawing and the cutting parameters.Components of NC machine tool system 1. 2. Method use for part programming Manual part programming Computer-aided part programming . part program is written. The part program is a set of step by instruction to the machine tool for carrying out the operation. the 1. The program is entered on the tape in the form of punched holes. Vasandia (130454119006) . Program Tape: The part program is entered on the program tape.2. Machine Control Unit(MCU): The program tape is read by the tape reader. 4. Machine Tool: The machine tool is operated by the controller of the machine control unit. 3. The holes are punched with the help of punching machine. The controller takes input from the tape reader. NC Coordinate Systems For flat and prismatic (block-like) parts: Milling and drilling operations Conventional Cartesian coordinate system Rotational axes about each linear axis . and z-axes Presented by :. For rotational parts: Turning operations Only x.Nilrajsinh Vasandia . .Nilrajsinh Vasandia . Point-to-Point systems Also called position systems System moves to a location and performs an operation at that location (e.Motion Control Systems 1.g. drilling) Also applicable in robotics Presented by :. Motion Control Systems 2. milling and turning) Presented by :. Continuous path systems Also called contouring systems in machining System performs an operation during movement (e.g..Nilrajsinh Vasandia . Nilrajsinh Vasandia . y = 50 Incremental positioning Move is: x = 20. Incremental Positioning Absolute positioning Move is: x = 40. Presented by :. y = 30.Absolute vs. Advantages of NC machine tool Cycle time reduction Complex machining operation High degree of accuracy Less inspection required Reduction of scrap and wastage Increasing productivity Lower tooling cost Reduction of human error Greater operation safety Greater operation efficiency Reduction space required Operator skill-level reduced Presented by :.Nilrajsinh Vasandia . Nilrajsinh Vasandia .Limitation of NC machine tool High investment cost High maintenance effort Need for skilled programmers High utilization required Presented by :. a dedicated computer is used to perform the most of basic NC machine functions. The machining cycle for each component is controlled by the program contained in the computer memory. The stored part program listing can be used for future production also.Introduction to CNC Machine Tools In CNC (Computer Numerical Control) machines. Presented by :. The entire program is entered and stored in computer memory. CNC (Computer Numerical Control) machine is a NC machine which uses a dedicated computer as the machine control unit.Nilrajsinh Vasandia . Machine Tool.Nilrajsinh Vasandia . 6.Microprocessor Based control unit.Components of CNC machine tool system The main components of CNC machine tools are as follows : 1.Input / Output Console. 4.Interfaces. 3. 2. 5. Presented by :.Memory.Feedback unit. Nilrajsinh Vasandia .Input / Output Devices Memory (ROM) Control program for : Z Slide X Slide Feed Back Unit Memory (RAM) Part Program Machine Tool Presented by :. Feedback unit : The feedback unit takes input from machine tool and transfers it to control unit for necessary corrections. Feedback from feedback unit and actuates the drives as well as the tool of the machine tool. Machine tool : Machine tool is operated by the control unit. Presented by :. Memory : It consists of RAM & ROM. The RAM stores part program. It basically consists of monitor and Keyboard.Nilrajsinh Vasandia . while ROM stores the programs for machine control.Input / Output Console : It is the unit through which part program is fed to the CNC machine tool system and required output is taken out. Microprocessor : This controller takes input from Input / Output device. Interfaces : They are the connections between the different components of the CNC machine tool system. 2. 2. Presented by :.Open loop type CNC machine.CNC turning centre. (e) According to axis & type of operations (b) According to type of tool motion control 1. 2. (c) According methods to program 1.Straight controller CNC systems.Continuous path control CNC machines. 4.Hybrid controller CNC systems.CNC vertical machining centre.Finite positioning control CNC machines. 1.CNC milling centre. 2. 3. 1.CNC horizontal machining centre.Incremental Programming CNC machine systems.Nilrajsinh Vasandia . 2.Classification of CNC Machine tool systems (a) According to Feedback systems type of (d) According to type of controller 1.Absolute Programming CNC machine systems.Closed loop type CNC machine. which is needed to be compared with input for better control & correction of drive system. Presented by :.Classification based on type of feedback systems It does not have any feedback mechanism. It only has motion control but do not have any provision for feedback.Nilrajsinh Vasandia . It has the motion control with a provision of feedback of feedback.Classification based on type of feedback systems It has a feedback mechanism.Nilrajsinh Vasandia . Which can be used for accurately controlling the drive system by comparing it with the input information until the required or desired position is achived. Presented by :. Commonly used in drilling & punching operations.According to type of tool motion control: In point to point CNC machines. Straight cut line control mode is the extension version of point to point method. pocket milling and step turning operations. while the path along which this tool moves is irrelevant.Nilrajsinh Vasandia . straight cut is obtained controlling the movement of tool with controlled feed rate in one of the axis direction at a time. Commonly used in Face milling. the movement of cutting tool from one predefined position to another predefined position is important. Presented by :. Multi axis countering. simultaneous & coordinated motions of cutting tool & work piece along different axes. 3 axis. Presented by :. 2 ½ axis. Types : 2 axis.According to type of tool motion control: The continuous path control system is used for continuous. Such motion enables machining of different contoured profiles & curved surfaces.Nilrajsinh Vasandia . According to programming Methods X Y 0 0 0 4 2 4 2 5 4 6 4 7 6 6 8 8 8 4 5 4 In Cartesian coordinate geometry system using absolute measurement. each point is always specified using same zero established for a given coordinate system. Presented by :.Nilrajsinh Vasandia . Presented by :. So in such programming . controller must store and process additional path measurement.According to programming Methods X Y 0 0 0 4 2 0 0 1 2 1 0 1 2 -1 2 2 0 -4 - - In Cartesian coordinate geometry system using incremental measurement . each point is specified using the path differential from the preceding point position.Nilrajsinh Vasandia . Hard wired logic circuits : It performs those functions for which they are best suited.Nilrajsinh Vasandia . such as feed rate generation and interpolation. 2. Presented by :.According to type of controllers Minicomputer Interface Feedback Hard-Wired logic Circuits 1. Soft wired computer : The computer performs the remaining control functions plus other duties not normally associated with a conventional hard-wired controller. The interpolation. feed rate generation and all other functions are performed by the computer with the help of software. The only hard-wired elements are those required to interface the computer with machine tool and operator’s console.Nilrajsinh Vasandia .According to type of controllers Minicomputer Interface Feedback It uses a computer to perform all the functions. Presented by :. Automatic tool compensation. Presented by :. Change in system of units. Multiple program storage. Higher investment cost. Use of advanced interpolation. Auto generation of part program for existing components.Advantages & Limitations of CNC machine tools Advantages Limitations Ease of program input. Online part programming and Requires specialised operators.Nilrajsinh Vasandia . Higher maintenance cost. editing. defined by EIA as: DNC is a system connecting a set of NC machines to a common memory for part program or machine program storage with provision for on.Nilrajsinh Vasandia . Presented by :. Also. The tape reader is omitted. Involves data connection and processing from the machine tool back to the computer.connection and in real time.Introduction DNC DNC is a manufacturing system in which a number of machines are controlled by a computer through direct.demand distribution of data to machines. 3. Presented by :. Bulk memory which stores the NC part programs. Telecommunication lines 4.Nilrajsinh Vasandia .Components 1. Machine Tools. Central computer 2. Nilrajsinh Vasandia .Principle Presented by :. Nilrajsinh Vasandia .A central computer connected to a number of machine tools and control them Part program of all machine tools are stored in the memory of the central computer and transmitted on direct transmission lines on demand Two way information flow take place in real time Various machine tools can communicate with the computer in real time Programs in full or segment can be transferred to NC machines Computer can be used for program editing No tape readers are used No limitation for the number or size of programs stored Presented by :. Nilrajsinh Vasandia . DNC system without satellite computer. 2. Each satellites controls several machine tools. Satellite computers are minicomputers and they serve to take some of the burden off central computer. Presented by :. DNC system with satellite computer.The configuration of the DNC system can be divided into: 1. Nilrajsinh Vasandia .DNC system without satellite computer Presented by :. Nilrajsinh Vasandia .DNC system with satellite computer Presented by :. Data collection. Communication Presented by :. 2. NC without punched tape. 4.Nilrajsinh Vasandia . 3. NC part program storage.Functions of DNC The functions which a DNC system is designed to perform: 1. and reporting. processing. Nilrajsinh Vasandia .Advantages of DNC System Elimination of punched tapes and tape readers Convenient storage of NC part programs in computer files Greater computational capability and flexibility Reporting of shop performance. Convenient editing and diagnostic features. Presented by :. Same part program can be run on different machines at the same time. In CNC machine tool system. It can not import CAD files. tape reader is a part of machine control unit. The microprocessor or minicomputer forms the machine control unit. The system is software driven. 3. 3838Presented by :. 7. 1. In NC machine tool system.Comparison between NC. 6. 3. System can import CAD files and convert it to part program. 4. The data can be processed using the MIS software so as to effectively carry out the Production planning and scheduling. The part program is fed to the machine through the Main computer 2. In order to modify the program. 7. CNC and DNC machine tools 1. in which part program can be stored. 2.Nilrajsinh Vasandia . 2. The programs can be easily modified with the help of computer. They are not software driven. 4. the tapes have to be changed. It has memory storage ability. The system can use feedback system. 4. 5. System has no memory storage and each time it is run using the tape. single computer is used 3. The CNC machine does not need tape reader. In order to modify the program. 6. 1. 5. It can not use feedback system. Large memory of DNC allows it to store a large amount of part program. The part program is fed to the machine through the tapes or other such media. 5. the program is fed to the machine through the computer.