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Presentation On CNC Machines Presented To:- Presented By:- Mr. Pawan Kamboj Chetan Gosain (Lect. In Mechanical Department) Roll No:-10512 4 th Year, 7 th Sem.

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Aim To Discuss The CNC Machines.

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CONTENTS 1. WORKING PRINCIPLE OF CNC 2. CONSTRUCTIONAL FEATURES OF CNC 3. KEYS OF CNC 4. TYPES OF CNC 5. SAFETY CHECKING ON CNC 6. PROGRAMMING OF CNC 7. FUNDEMENTALS OF CNC PROGRAM 8. PROGRAM STRUCTURE 9. EXAMPLE OF CNC PROGRAMMING 10. CO-ORDINATE SYSTEM 11. ADVANTAGES OF CNC MACHINES

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INTRODUCTION Computer numerical control machine is a numerical control system that utilizes a dedicated, stored program computer to perform some or all of the basic numerical control functions. The external appearance of a CNC machine is very similar to that of a conventional NC machines. PART PROGRAM~> PUNCHED TAPE READER OR ANY OTHER SIMILAR DEVICE~> STORED IN COMPUTER PROGRAM.

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WORKING PRINCIPLE OF CNC By controlling the relative movements between the tool and the work piece geometrical shapes are machined. Control of these relative movements through coded letters numbers is known as Numerical Control of machine tools.

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Constructional features of CNC machine tools CNC machine tools differ from conventional machine tool in a number of respects. The special constructional features of CNC machine include: 1.)Rigid structural design. 2.)Infinitely variables spindle and feed drive. 3.)Slide ways fitted with plastic inserts. 4.)Linear bearings for axis drive. 5.)Automatic tool changers.

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KEYS OF CNC

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MACHINE STRUCTURE To meet the requirements of high efficiency the numerically controlled machine tools should have a structure that is correctly designed to withstand normal weight distribution. BECAUSE The higher cutting speeds and feeds in CNC machine results in rapid acceleration and deceleration of the slides and the machines are subjected to fluctuating and variables forces during the machining operation. Also the machine structure design should be such that removal of chips do not on the slide ways.

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Linear motion bearings The sliding friction due to direct metal to metal contact between the slides and slide ways is replaced with rolling friction by the use of antifriction ball or bearings. Rolling element when applied to reciprocating motion has followed advantages. Reduce the drive power to be used. Stick slip problem is completely eliminated. Require only small amount of lubricant. Absorb the machine vibration.

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Hydrostatic slide ways Hydrostatic slide ~> Oil pumped~>Cavities or Pockets~>Carriage on slides contact with Slide way with continous supply of thin film of fluid. The hydrostatic slide way provides almost a frictionless condition for the movement of the slide. For efficient operation it is very important that the fluid and slide ways are kept clean. Also the hydrostatic slide ways need a very large surface area to provide adequate support.

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Measuring systems In CNC machines the electronic measuring systems are used on each controlled axis and to monitor movement and compare the position of the slide and the spindle. To Measuring system used in the CNC machines are of two types To measure the position of the slide (linear measurement ) measure the spindle speed (rotary measurement) A linear scale is used as a linear measuring device which is used very often. In this method linear displacement is measured directly at the slide. The measuring device is fixed on to the moving machine element, which detect the actual distance traveled by the machine slide. One of the rotary measuring devices is an incremental rotary encoder. Incremental measurement means measurement by counting. The out put signal of incremental rotary encoders is fed to an electronic counter which provides the corresponding values.

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Work holding device and tooling The CNC machines are capable of performing a number of operations using different tools, on different faces of the component in a single setting. This requires that the component should be accessible from different sides without changing of clamps or repositioning of components. The multidirectional cutting forces to reduce the clamping and unclamping time. A work holding devices for a CNC application should have the following function. It should restrict the linear and rotary motion of the component. The component should not distort or deflect due to cutting forces process. It should facilitate quick loading and unloading of the component. It should not interfere with the cutting tools. It should provide easy removal of chips. It should be safe.

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Automatic tool changers The CNC machines are designed to perform a number of operations in a single setting of the work-piece. To reduce the down time in change over from one operation to the next, the CNC machines are equipped with automatic tool changing facility.

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WORKING PRINCIPLE OF CNC MACHINES WORKING PRINCIPLE OF CNC MACHINES Types of CNC machines TYPES OF CNC MACHINES There are mainly two types of CNC machine : (1) Machining centers There are very important types of CNC machine and are multi-functioning machine equipped with automatic tool changes and are capable to carrying out, milling, and drilling, reaming, taping, boring, counter boring. In this type of machines there are three types of axis X axis, Y axis, Z axis. Here the tools are rotated clockwise or anticlockwise the works still fixed. (2)Turning centers/ CNC lathes CNC lathes have only two axes X and Z, X axis for longitudinal movement and Z axis for crosswise movement. Tools are arranged in turret with a number of stations some lathes have rotating tools in the turret to facilitate off-axis machining such as drilling, milling etc These machines have additional controller for spindle rotation such machines are known as turning centers

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Safety check on the CNC machine Check the main pressure of the hydraulic and pneumatic system. Check the clamping pressure of the hydraulic and pneumatic system. Check the sliding movement. Check the tool position with respect to the program Check the program control levels try to cut job in a single block. Do not use compressed air for cleaning. Check the coolant supply by pressing appropriate switch manually. Check the speed over the ride position.

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PROGRAMMING OF CNC MACHINES CNC programming is a term that refers to the methods for generating the instruction that drive the CNC machine tool. Part program is a set of instructions which instructs the machine tool about the processing step to be performed for the manufacture of a component. There are two distinct techniques adopted for creating CNC programs. i.) Manual programming ii.) Computer assisted programming

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Manual programming 1). Positioning A dimensional instruction that move and position the tools or work pieces to produces the required work 2.) Motion The relative velocity of the tool with respect to the work piece is to be controlled, in both spindle drive and positioning drive 3.) Switching function: - The auxiliary function of the machine such as coolant, tool changes and program stop. The following should take into account when writing a part program. The machine features and capacity. The size if the component. The material to be machined. Machine co-ordinates. The sequence of operation. The tooling to be used. Component holding and location.

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Computer Aided part programming CNC machines of complex 3 dimensional components require thousands of instructions and with out computer assistance it would be impractical to write part programs for the production of such components. NC part programming languages and the processors and post processors that translate the language instruction into NC programs. There are several NC languages in use. Some of them are v APT v ADAPT v EXAPT v UNIPAT v SPLIT v PROMPT

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FUNDAMENTALS OF PART PROGRAMMING A program is a set of encoded information giving coordinate values and other details to indicate how a tool should be moved in relation to a work-piece in order to achieve a desired machining form.

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A part programmer has to do the following while write a program Study the drawing of component thoroughly. Identify the type of material to be used. Determine the specification and functions of machine to be used. Decide the dimensioning units metric or inch. Determine the cutting parameters for the job/tool combination. Establish the sequence of machining operation.

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PROGRAM STRUCTURE In manual part programming the programmer has to determine the machining parameters and the sequence of operations to be performed. Based upon this sequence, the tool path is calculated and program is written. The basic unit of a program input to the control is called a block. The term block structure of format refers to the rules for writing a program block. A block contains any or all of the following. Sequence or block number ( N) Preparatory function(G) Dimensional information (XYZ etc) Decimal point (.) Feed rate(F) Spindle speed (S) Tool number (T) Tool offset function(D) Miscellaneous function(M) End of block(EOB/*)

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Example of CNC Programming What Must Be Done To Drill A Hole On A CNC Vertical Milling Machine

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Top View Front View Tool Home 1.) X & Y Rapid To Hole Position

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Top View Front View 2.) Z Axis Rapid Move Just Above Hole 3.) Turn On Coolant 4.) Turn On Spindle.100

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Top View Front View 5.) Z Axis Feed Move to Drill Hole

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Top View Front View 6.) Rapid Z Axis Move Out Of Hole

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Top View Front View 9.) X&Y Axis Rapid Move Home 7.) Turn Off Spindle 8.) Turn Off Coolant

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Top View Front View Tool At Home O0001 N005 G54 G90 S600 M03 N010 G00 X1.0 Y1.0 N015 G43 H01 Z.1 M08 N020 G01 Z-.75 F3.5 N030 G91 G28 X0 Y0 Z0 N035 M30 N025 G00 Z.1 M09 Heres The CNC Program!

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Top View Front View Tool At Home O0001 Number Assigned to this program

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Top View Front View Tool At Home O0001 N005 G54 G90 S600 M03 N005 Sequence Number G54 Fixture Offset G90 Absolute Programming Mode S600 Spindle Speed set to 600 RPM M03 Spindle on in a Clockwise Direction

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Top View Front View O0001 N005 G54 G90 S600 M03 N010 G00 X1.0 Y1.0 G00Rapid Motion X1.0X Coordinate 1.0 in. from Zero Y1.0Y Coordinate 1.0 in. from Zero

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Top View Front View O0001 N005 G54 G90 S600 M03 N010 G00 X1.0 Y1.0 N015 G43 H01 Z.1 M08 G43Tool Length Compensation H01Specifies Tool length compensation Z.1 Z Coordinate.1 in. from Zero M08Flood Coolant On

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Top View Front View O0001 N005 G54 G90 S600 M03 N010 G00 X1.0 Y1.0 N015 G43 H01 Z.1 M08 N020 G01 Z-.75 F3.5 G01Straight Line Cutting Motion Z-.75Z Coordinate -.75 in. from Zero F3.5Feed Rate set to 3.5 in./min.

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Top View Front View O0001 N005 G54 G90 S600 M03 N010 G00 X1.0 Y1.0 N015 G43 H01 Z.1 M08 N020 G01 Z-.75 F3.5 G00Rapid Motion Z.1Z Coordinate.1 in. from Zero M09Coolant Off N025 G00 Z.1 M09

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Top View Front View O0001 N005 G54 G90 S600 M03 N010 G00 X1.0 Y1.0 N015 G43 H01 Z.1 M08 N020 G01 Z-.75 F3.5 N030 G91 G28 X0 Y0 Z0 G91Incremental Programming Mode G28Zero Return Command X0, Y0, Z0 X,Y,& Z Coordinates at Zero N025 G00 Z.1 M09

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Top View Front View O0001 N005 G54 G90 S600 M03 N010 G00 X1.0 Y1.0 N015 G43 H01 Z.1 M08 N020 G01 Z-.75 F3.5 N035 M30 N030 G91 G28 X0 Y0 Z0 N025 G00 Z.1 M09 M30End of Program

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FunctionMeaning G00Point to point positioning G01Leaner interpolation G02Circular interpolation G03Circular interpolation (Anti clockwise) G70Dimensioning in inch G71Dimensioning in mm G90Absolute dimensioning G91Incremental dimensioning G96Constant surface speed G97Spindle speed Preparatory function (G-words ) They are the commands, which prepare the machine for different modes of movement like positioning, contouring, thread cutting etc and for presetting the machine.

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FunctionMeaning M00Program stop M01Optional stop MO5Spindle stop MO6Tool turret index M09Coolant off M10Clamp work piece M11Release work piece M30End of program Miscellaneous function The miscellaneous function word is used to specify certain miscellaneous or auxiliary functions which do not relate to the dimensional movements of the machine. The miscellaneous functions may be spindle start, spindle stop, coolant ON/OFF, etc.

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METHODS OF LISTING THE COORDINATES OF POINTS The coordinate systems are used to define and control the position of the tool in relation to the work piece. Each system has its own applications and the coordinate systems may be used indecently or may be mixed, within a CNC part program according to the machining requirements of the component. The co- ordinate systems used in CNC machines are as follows. a) Absolute co-ordinates b) Incremental co-ordinates

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Absolute co-ordinates In the absolute co-ordinate system the co-ordinates of a point are always referred with reference to the same datum. The datum position in X axis and Y-axis and Z axis are defined by the program before starting the operation of the machine. A major advantage of this system is that it is very easy to check and correct a program written is made in the value of any dimension in a particular block.

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Incremental co-ordinate In the incremental co-ordinate system the co- ordinates of the any point are calculated with reference to the previous point i.e., the point at which the cutting tool is positioned is taken as a datum point for calculating the co-ordinates of the next point to which movement is to be made. It is difficult to check a part program written in incremental dimension in a particular block, it will affect subsequent blocks.

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Advantages of Computer Numerical Control Machines Accuracy and repeatability is very high as compared to the NC machines. Reduced scrap and rework. Reduced inspection time. Reduced material handling. Easy of inter changeability of machine parts. Complicated shapes and curves are easily manufactured with quality assurance and better production. Reduced skilled operators can work in CNC machines. It can work 24 hours a day because the resting times are very low. Time taken to complete the works is minimum as compared to manual machines. Program editing at the machine site.

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