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  1. 1. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHCNC TURNING By   1 Mohd Sharizan Mohd Sharif
  2. 2. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHCONTENTSCHAPTER 1Introduction about CNC Turning machinesHistory about CNC Turning machinesAdvantage and disadvantageCNC Turning machines componentsTypes of CNC Turning machines componentsCNC Turning Cartesian coordinate systemCutting toolsTypes of cutting toolsCHAPTER 2Preventive maintenance and servicing of CNC Turning machines toolsReplacement parts inventoryThe level of maintenance operationsMaintenance and repairPreventive maintenance programsA typical preventive maintenance programsMachine command codesLetter address commandsCHAPTER 3Project exampleWork step to enter the programmed codeCHAPTER 4Safety rules for CNC Turning machines 2 Mohd Sharizan Mohd Sharif
  3. 3. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHCHAPTER 1INTRODUCTION OF CNC TURNING MACHINES A conventional engine lathe or turret lathe is a common machine in just aboutevery machine shop. A lathe is used for machining cylindrical or conical work such asshafts, rings, wheels, hores, threads and everything. The most common lathe operation isremoval or material from a round stock, using a turning tool for enternal cutting. A lathecan also be used for internal operations such as boring, as well as for grooving, threadingand everything if a proper cutting tool is used. Turret lathes are usually weaker in machining power than engine lathes, but theydo have a special carousel that holds several mounted cutting tool. An engine lathe hasoften only one or two cutting tools mounted at a time, but has more machining power.Typical lathe work controlled by CNC systems uses machines known in industry as theCNC Turning Centres or common the CNC lathes. The term „turning center‟ is a rather unpopular, but an accurate overall descriptionof a computerized lathe (a CNC lathe) that can be used for a great number of machiningoperations during a single setup. For example, in addition to the standard lathe operationssuch as turning and boring, a CNC lathe can be used for drilling, grooving, threading,knurling and even burnishing. It can also be used in different modes, such as chuck work, collet work, barfeeder,or between centers. Much other combination also exists, CNC lathes are designed to holdseveral tools in special turret, and they can have a milling attachment, indexable chuck, asub spindle, a tailstock, a steadyrest and many other features not always associated with aconventional lathe design. Lathe with more than four axes also common. With constantadvances in machine tool techonologies, more CNC lathes appear on the market that are 3 Mohd Sharizan Mohd Sharif
  4. 4. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHdesigned to do a number of operations in a single setup, many of them traditionallyreserved for a mill or a machining center.HISTORIAL OF CNC TURNING MACHINES Old manual engine turning and knee mills had no computer. The operator cutgood part by cranking on big shiny hand wheels, expertly coaxing the tool down thedesired path. After years of this back and dialing, the crank handles became handpolished to a mirror finish. The idea of using electric motor to do all this cranking came up during the trouble-free 1950s. The big question was whether a motor could crank as accurately as a human.An interesting solution written back in the ‟50s was recently post in the hallways of afamous engineering university. Using the dual premise of electronic control and motionfeedback, a written proposal to the cranking dilemma had long existed in academia (andthe military establishment). Apparently, this design didn‟t move into widespreadcommercial manufacturing. Most of early motorized machine tool was temperamental, expensive and hard toset up and operate. Early on, the market potential for dependable CNC machine tools wassolid. During the middle and late 1970s some exceptional computer numericallycontrolled machine tools were introduced to the world market. The factory standard use in the design and manufacture of these early CNCmachiones routinely provided years of flawless operation. A single machine in the late„70s gave the profitability to the purchase one new machine after another. Shops with afew of these mighty machines have done well to the present day. The basic design of the system which was mass marketed in the „70s bore aresemblance to the posted design from the „50s. Accurate control of electric motors was 4 Mohd Sharizan Mohd Sharif
  5. 5. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHaccomplished by closing the motion loop using early micro-processors and digital circuitsto track the command pulses going out and the motion feedback pulses coming back. First generation machoines naturally use older technology than what is sold today.Back then, the motor current for axis and spindle motion was provided by thyrister-controlled, DC (Direct Current) motor drivers. Internal computer logic and controlfunction came from an 8-bit CPU (Central Processing Unit) built on a platform ofintricate, pressed wire-trace circuit boards and all were plugged into a collector‟s itemwire wound back plane. Memory data originally resided in old magnetic-donut memoryboards, which as since been replaced by compatible, modern IC RAM (Integrated CircuitRandom Acces Memory) memories. The old 8-bit computers sense machine movement by counting signals from theprecision feedback unit mounted to each motor shaft. These units send motor direction,speed and position information. Although costly, the complete feedback units weredesigned to be replaced or exchanged. Early, CNC Turning centers could move at 300 IPM (Inch Per Minute) and holdtwo-tenths of an inch. The smallest position unit the computer displays is 1 um (OneMicron, Metric) or 1 tenth (One Ten-Thousandths, Inch). An active change of themachine position flashes over a cluster of universal seven segment displays. In concert,the displays form a some what coherent read-out for the operator to use in programmingand monitoring the machine. Machines from the seventies are still running in production today, some 20 yearslate! The best explanation for this longevity is a combination of stout, oversizemechanicals and top-quality wiring and electronics running at the typically slower speeds. The new machines of today are fast. Performance AC motors are driven at highspeed by compact vector-controlled digital inverter. But more astounding are the 5 Mohd Sharizan Mohd Sharif
  6. 6. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHcomputer improvement: the new high speed RISC (Reduced Instruction Set Computing)processors and the running of expanded software options from the open PC platforms. Machine functions previously handled mechanically are now economicalaccomplished using nifty NC software models. Industrial grade PC computers are nowupgraded with plug-in NC modules. Similar to the process of adding a modem orinstalling a new software program, an entire numerical control is plugged in andconfigured for machine. The closed CNC systems of the past are now beginning to openup. The twenty-year transition from the first generation machines to the systems of todayfrequently visited the concept of Kiazen, the study and implementation of continuousprocess improvements.ADVANTAGES AND DISADVANTAGES OF CNC TURNING MACHINES CNC Turning machines have been continually improved to increase theiraccuracy, efficiency, and productivity. Most modem CNC Turning machines are accurateto within 0.0002 inch positioning and repeatability. They are also capable of positioningthe cutter (toolholder) at a rate 700 inches per minute or greater. Additionally, CNC Turning machines can be designed with various options. Forexample, CNC Turning machines can be equipped with tool sensing sytems, with two ormore spindles, additional turrets and „live tooling‟. The tool sensing sytems is designed toquickly and accurately find and store each tool tip offset value. The dual spindle option allows turning of two parts at the same time. By addinganother tool turret it provides greater workpiece machining flexibility and reduces setuprequirements. The live tooling option allows secondary machining such as milling anddrilling operations to be performed in the same turning operation.The Following Is A List Of Advantages That Can Be Derived From CNCTurning Machines 6 Mohd Sharizan Mohd Sharif
  7. 7. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH CNC Turning machines can be used continuously 24 hours a day, 365 days a year and only need to be switched off for occasional maintenance. CNC Turning machines are programmed with a design which can then be manufactured hundreds or even thousands of times. Each manufactured product will be exactly the same. Less skilled or trained people can operate CNC‟s unlike manual turning or milling machines which need skilled engineers. CNC Turning machines can be updated by improving the software used to drive the machines Training in the use of CNC‟s is available through the use of „virtual software‟. This is software that allows the operator to practice using the CNC Turning machines on the screen of a computer. The software is similar to a computer game. CNC Turning machines can be programmed by advanced design software such as Pro/DESKTOP®, enabling the manufacture of products that cannot be made by manual machines, even those used by skilled designers or engineers. Modern design software allows the designer to simulate the manufacture of his/her idea. There is no need to make a prototype or a model. This saves time and money. One person can supervise many CNC Turning machines as once they are programmed they can usually be left to work by themselves. Sometimes only the cutting tools need replacing occasionally. A skilled engineer can make the same component many times. However, if each component is carefully studied, each one will vary slightly. A CNC Turning machines will manufacture each component as an exact match. Simple to complex operations can be executed on a single CNC Turning machines. Greater accuracy and piece-to-piece consistency. 7 Mohd Sharizan Mohd Sharif
  8. 8. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH  Finer dimensional tolerances are achieved within tight statistical process control parameters.  Automatic part loading devices can accommodate a variety of work pieces with only minimal adjustments for consistent production rates.  CNC Turning machines reduce setup time  CNC Turning machines reduce handling, which improves quality and production.  CNC Turning machines run automatically without operator intervention.  CNC Turning machines output maximum part accuracy.The Following Is a List of Disadvantages That Can Be Derived From CNCTurning Machines  CNC Turning machines are more expensive than manually operated machines, although costs are slowly coming down.  The CNC Turning machine operator only needs basic training and skills, enough to supervise several machines. In years gone by, engineers needed years of training to operate centre lathes, milling machines and other manually operated machines. This means many of the old skills are been lost.  Less workers are required to operate CNC Turning machines compared to manually operated machines. Investment in CNC Turning machines can lead to unemployment.  Many countries no longer teach pupils or students how to use manually operated turning or milling machines. Pupils or students no longer develop the detailed skills required by engineers of the past. These include mathematical and engineering skills.  Tools on CNC Turning machines do not cut metal any faster than conventional machines. 8 Mohd Sharizan Mohd Sharif
  9. 9. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH  CNC turning machines does not eliminate the need for expensive tools. There is also a greater initial cost involved with the CNC Turning machines.  CNC Turning machines will not totally eliminate errors. Operators can still fail to push the correct buttons, make incorrect alignments, and fail to locate parts properly in a fixture.  Selection and training of programmers and maintenance personnel is required.CNC TURNING MACHINES COMPONENTS CNC Turning machines and convertional turning machines each have the samebasic components, such as the main motor, the spindle, the bed, the tool turret, theheadstock, the cross-slide, the carriage and the way systems. However, CNC Turningmachines, in addition, are outfitted with a computerized control and servomotors tooperate them. Manual CNC Turning can be very versatile and productive machine tools, butwhen coupled with a CNC, they become the „high tech production turning machines‟ ofthe machine shop. Additionally, repetitive operations such as turning, facing and boringare ideal machining applications for CNC Turning machines. CNC Turning machines can also be designed to include a variety of optionalcomponents and features. These options are basically designed to reduce setup time, parthandling and cycle time. For instance, one option for minimizing part handling time is toadd a part loading magazine or a robot arm. The maximum spindle speed (RPM) of aCNC Turning machines can also very depending on the need or application. 9 Mohd Sharizan Mohd Sharif
  10. 10. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH The factors that determine the spindle speed range selected can include the type ofpart materials, the part sizes and the annual part production quantities to be machined.Another factor that influences the spindle speed range is the type of tool cutter materialthat will be used, such as HSS, coated carbide, diamond and ceramic. High-production turning machines can be designed with dual chucks that enable apart to be machined on both ends. Also, live tooling can be incorporated that allowsmilling and drilling at various angles. Other options may include a second or third turret,a bar feeder, a parts catcher, a steady rest follower and a tool setter. Picture: CNC Turning machines. 10 Mohd Sharizan Mohd Sharif
  11. 11. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHTypes Of Components CNC Turning Machines: The main components of the CNC Turning machines include the bed, theheadstock, the cross-slide, the carriage, the turret, the tailstocks, the ways, the servomotor,the ball screws, the hydraulic and lubrication systems and the machine control unit(MCU). The two primary axes of a CNC Turning center are the X-axis and the Z-axis. TheX-axis, which controls the cross-slide, moves the cutting tool to control the workpiecediameter. The Z-axis, which controls the carriage, moves the cutting tool lengthwise, tocontrol the workpiece length. Picture: CNC Turning machines components. 11 Mohd Sharizan Mohd Sharif
  12. 12. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH i. CNC Turning Control : The modern CNC Turning machine tool is software driven. The computer controlsare programmed instead of hardwired. The control panel is where the machine operationbuttons and knobs are located. The control panel typically includes the following items :  Power On/Off button.  Cycle Start button.  Axis Select knob.  Spindle Override knob.  Load meters.  Keyboard pad.  3.5-inch input disk drive.  Feed Hold button.  Emergency Stop button.  Axis Jog wheel.  Feed Override knob.  Turret Index button.  Mode select Knob.  Miscellaneous function button. ii. CRT Display : The CRT is also located on the control panel. The CRT display allows theoperator easy visual access to CNC program and machine information. On the screen ofthe CNC control, the operator can view the CNC program, active codes, tool andworkpiece offsets, machine positions, alarms, error message, spindle RPM andhorsepower. 12 Mohd Sharizan Mohd Sharif
  13. 13. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH iii. Bed : The bed is designed to support and align the X-Z axes and cutting toolcomponents of the machine. Bed is designed in two ways: they either lie flat or at a slant. Most lathes have a slant-bed design, providing the operator easy access for loadingand unloading parts and tools. It also allows the chips and coolant to fall away from thecutting area to the bottom of the chip conveyor. iv. Headstock : The headstock contains the spindle and transmission gearing or belts, whichrotate the chuck and workpiece. A variable speed motor drives the headstock spindle,which is programmed in RPM. They are typically equipped with a variety of motor sizesranging from 5 to 75 horsepower and spindle speeds from 32 to 5500 RPM. v. Chuck and Jaws : The chuck is mounted to the spindle and is equipped with a set of jaws to gripand rotate the workpiece. They are categiorized into two groups: manually operated orautomatically power operated. The chuck can be designed as a 2-jaws, 3-jaws, 4-jaws, 6-jaws or a collect jaw type. The jaws are either hardened (hard jaws) or mild steel (soft jaws) and are selecteddepending on the operation holding requirements. The hard jaws are available in variousstandard design. The soft jaws are also available in various standard design, but theyrequire a boring operation to match the diameter that they will hold. Collect jaws aredesigned to grip barstock, which can be round, square and hexagon. 13 Mohd Sharizan Mohd Sharif
  14. 14. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH Picture: The 3-Jaw chuck features. vi. Tool Turret : Tool turrets come in all styles and sizes. The basic function of the turret is tohold and quickly index the cutting tools. The CNC Turning usually is equipped with oneturret that can hold from four to twelve tools. The type and number of turrets on a CNC Turning can vary with the size of themachine and the manufacture. Most turrets are capable of bidirectional indexing and theslides on which the turrets are positioned can travel at a rapid rate of approximately 400in./min, which reduces noncutting time of the machine cycle. 14 Mohd Sharizan Mohd Sharif
  15. 15. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH Picture: Turret description. 15 Mohd Sharizan Mohd Sharif
  16. 16. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH vii. Tool Indexing : This design allows a lathe tool to be fastened in each turret station so it can beindexed automatically during the CNC program cycle. Quick tool indexing is animportant factor on CNC Turning machines used for production purposes. Therefore, theindex time is typically completed within seconds. viii. Tailstock : The tailstock is used to support workpieces that lack rigidity such as long shafts,long hollow castings and similar parts. The tailstock can be designed to operate eithermanually or by CNC program commands. The tailstock basically supports one end of theworkpiece with a center. The most common is the live center, which rotates on a bearingpack to eliminate friction. The tailstock travels on its own hardened and ground-bearingways. Picture: Tailstock and center. 16 Mohd Sharizan Mohd Sharif
  17. 17. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH Picture: Tailstock center. Picture: Tailstock setup. 17 Mohd Sharizan Mohd Sharif
  18. 18. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH ix. Ways and Way Covers : The ways are precision-hardened rails that allow the turret to travel in rapidtraverse and feed motion (X and Z axes). The way covers are a means of protecting theways from damage due to scraping from metal chips or due to dents from metal itemssuch as tools or parts. x. Way Lube System : The way lube system is designed to keep the ways lubricated, which will reducewear from friction and eliminate early machine failure. The operator and maintenancepersonnel must check the way lube system reservoir level on a daily basis. xi. Electrical Control Panel : The electrical control panel is where the main Power On/Off switch is usuallylocated. This also where all the electric components, including fuses and reset buttons, areenclosed for safety. The electrical control panel is usually locked to prevent entry byunauthorized personnel. An authorized electrician should be contacted if entry isrequired. xii. Ball Screw : The ball lead screw uses rolling motion rather than the sliding motion of anormal lead screw. Sliding motion is used on conventional acme lead screws. Unlike theball screw, the motion principle of an acme lead screw is based on friction and backlash.Below are some advantages of the ball screw versus the acme lead screw :  Less wear.  Longer life.  High speed capability. 18 Mohd Sharizan Mohd Sharif
  19. 19. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH  Precise position and repeatability. xiii. CNC Turning Tailstock Setup Description : The illustration typically setup for a workpiece, which requires a tailstock. Theworkpiece, which must be center drilled at one end before the CNC Turning machinesoperation, is held at one end with the 3-jaw chuck and supported at the other end with thetailstock. The tailstock and center are required to support it during machining operationswhen the turn tool is cutting the workpiece. xiv. Servo Drive Motors : CNC machines use electric servomotors that turn ball screws, which in turn drivethe different axes of the machine tool. The axes (X and Z) each have a separateservomotor and ball screw to control each axis independent of each other. xv. Auto Bar Feeder : This option can be added to reduce the handling time required for loading theworkpiece material into the chuck. The bar feeder can be designed as a single tube type ormagazine type. The purposes of the bar feeder is to quickly load more stock automaticallyat the end of the CNC machine cycle. xvi. Parts Catcher : The purposes of the parts catcher is to catch the part immediately after it is cutoff and avoid damage to the part, tools and machine components. This option is typicallyincluded with bar-feed-type machines. 19 Mohd Sharizan Mohd Sharif
  20. 20. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH xvii. Secondary Turret : The main turret and the secondary turret are designed to work independently ofeach other. This design of the turrets allows simultaneous cutting with two tools to reducethe cycle time. The main turret is a two-axis design. xviii. Subturret : This design of the turrets also allows simultaneous cutting with two tools toreduce the cycle time. The subturret is typically a single-axis design, which uses the B-axis travel. xix. Tool Setter : The tool setter is a sensing device on the machine that automatically refrenceseach tool in a setup. The control then automatically records the distance values in theoffset storage memory. This optional device can minimize setup downtime and improvesthe quality of the parts produced. xx. Dual Spindle/Chuck : The dual spindle and chuck design allows the CNC machine to automaticallymachine the first operation, then transfer the workpiece to the second chuck and machineit simultaneously. This produce is designed to complete all the turning operations andthus minimize lead time. xxi. Chip Conveyor : The chip conveyor is designed to remove the metal chips produced from the 20 Mohd Sharizan Mohd Sharif
  21. 21. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHworkpiece machining operations from the CNC Turning work area. When operating, thechip conveyor typically transfer and deposits the metal chips into a dumpster. This alsocontrols the handling of metal chips for recycling. xxii. Open-Loop Systems : The stepping motor is an electric motor that rotates a calculated amount everytime the motor receives an electronic pulse from the MCU. The stepping motor‟s rotarymotion is converted into the linear motion of the machine axes through the use of leadscrews. The open-loop system is simpler and rarely used for CNC machines that requireaccuracy and repeatability. xxiii. Closed-Loop Systems : Servomotors permit automatic operation of the machine and the closed-loopcontrol system verifies that the machine accurately positions the CNC programcommands. The computer makes it possible to continuously monitor the machine‟sposition and velocity while it operating.The advantages of the servomotor are increasedaccuracy and repeatability. 21 Mohd Sharizan Mohd Sharif
  22. 22. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHPicture: CNC Turning closed-loop system diagram. 22 Mohd Sharizan Mohd Sharif
  23. 23. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHCNC TURNING CARTESIAN COORDINATE SYSTEM The Cartesian coordinate system is applied to CNC machine tools in various ways.The most common application for CNC lathes is the X-axis and the Z-axis. On a CNCturning machine, the X-axis specifies the diameter coordinate movement, and the Z-axisspecifies the length coordinate movement. A coordinate position command always startwith a letter “X and/or Z” code followed by a numeric value that represents the travel tocoordinate point. Picture: Cartesian coordinate system for CNC Turning machines. 23 Mohd Sharizan Mohd Sharif
  24. 24. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH Picture: Cartesian coordinate systems for CNC Turning machines.CUTTING TOOLS The CNC operator must be thoroughly knowledgeable in machining operationsthat pertain to the type of CNC machine to be operated. The CNC tooling is directlylinked to the machining operations planning process. There is various type of holders andtools types used in CNC machining operations. The most commonly used OD cuttingtools on CNC are carbides, twist drills, boring bars, reamers and taps.Types of Cutting Tools a. Carbides indexable insert drills : Represent the latest state of the art advancements in CNC hole drilling. It can drillholes at much hinger metal removal rates than HSS twist drills. The advantage of 24 Mohd Sharizan Mohd Sharif
  25. 25. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHindexable or replaceable inserts that can save time during setup and tool changes. Thecarbides inserts also allow the tool to be driven into harder materials. Picture: Features and description of carbide drills, spade drills and holder. 25 Mohd Sharizan Mohd Sharif
  26. 26. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH b. Twist Drills : The twist drill is used to produced a hole in the center of the workpiece. The twistdrill is made from various types of materials, which includes HSS, cobalt, solid carbideand carbide tipped. c. Boring bars : Boring bars are used in situations where high accuracy or fine surface finish of hole isrequired. Boring bars typically produce better hole straightness and roundness. Picture: Features and description of boring, grooving and threading bars. 26 Mohd Sharizan Mohd Sharif
  27. 27. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH d. Reamers : Used in situations where high accuracy and fine surface finish of a hole is required.The factor that basically determines use of a reamer or a boring is the diameter size. Areamers is usually selected when the hole size is 0.125inch up to 0.625inch in diameter. Picture: Features, description and types of reamers. 27 Mohd Sharizan Mohd Sharif
  28. 28. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH e. Taps : There are various thread forms, which are machined on lathes. Some common threadforms include the „Acme‟ thread, the „buttress‟ thread, the „square‟ thread and the„unified‟ thread. Picture: Features, types and identification of taps. 28 Mohd Sharizan Mohd Sharif
  29. 29. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHCHAPTER 2PREVENTIVE MAINTENANCE AND SERVICING OF CNC TURNINGMACHINES TOOLSReplacement Parts Inventory Most CNC manufactures have list recommending the most frequently neededreplacement parts. Parts less frequently needed are normally available from themanufacture within 24 hours. Potential CNC users are already purchasing completereserve control from which parts can simply be taken as needed. This process simplifiesand accelerate repair from many point of view:  Any required part is always available.  The hardware cost for the complete control are less and then for the replacement parts.  Downtime is kept to a minimum  In the event of the significant malfunctions, damage or total brake down of the control the complete controller can be exchanged  The standby control is available for the testing purposes and for comparative research  The control can be used to train operating and maintenance personnel.The Level of Maintenance Operations a. Planned and preventive maintenance b. Repair of breakdowns The size of the firm usually has a great impact on its ability to maintain andrepair modern CNC equipment. Larger firms are more likely to have adequate number ofskilled, trained and experienced repair personnel than smaller firms. As smaller companies 29 Mohd Sharizan Mohd Sharif
  30. 30. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHhave to accept a lower level of repair capability, preventive maintenance is even moreimportant to them. Obviously the degree of repair capability by in house personnel is alsodependent on the number, complexity, and variety of machine installed. The experience oflarger CNC users in United States has shown that one technician is able to masterapproximately four different hard wired CNC system but only two different CNC systems. The first level of preventive maintenance and vital one is routine maintenance ofthe machine. The includes checking oil levels and hydraulic and pneumatic pressures andinspecting and charging oil filters. There are many ways of drawing up a simple but effective controller preventivemaintenance program, and such routine inspections should lie within the capabilities ofmost users. The required instruction and guideline for such programs are obtainable fromthe equipment manufacturer or may be worked out by the users with help of themanufacturer‟s personnel during the installation period. A checklist with the daily, weeklymonthly and yearly operations to be carried out should also be prepared along the lines ofthe proposed. c. Typical guidelines are:  If the power supply for the electronics does not always delivered a perfectly stable voltage, voltage fluctuations, noise or brief power failure can occur. Excessive voltage can caused damage especially to ICs and other electronic components. Low voltage and interference voltages are often the cause of malfunctions which appear intermittently and hard to locate. There four the power supply should be checked every three to six month and compared with the manufacturer‟s specifications. Ripple voltage or bad connections can then often be identified before they cause major breakdowns.  The so-called “clock oscillator” and other frequency generators which control feed rate and system frequencies can drift with time. This can result 30 Mohd Sharizan Mohd Sharif
  31. 31. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH in irregular machine movement or measurement deviations caused sinusoidal changes in resolver or inductosyn measuring voltages. Therefore, frequency regulation testing should also take place ever y six to twelve months. Faulty feedback signals are often a cause of positioning errors. First the tachometer voltage should be checked for uniformity and absolute value. I the brush are uneven or if the slip ring is dirty, strong voltage interference can result, and this noise is amplified even more by the control loop which, in turn can cause rough machine feeding, hard stop or triggering of safety device. It is therefore recommended that brushless tachometer be used on the original installation or as replacement parts. Defective optical encoders can also produce similar malfunction and their power supplies should be checked every three to six months for proper voltage levels. The servo amplifier is balanced for drift, amplification and machine dynamics at the time installation. This balancing procedure should be repeated every three months in order to determine whether its ratio has change in any of the axes. Drift can change data position and path precision, leading to over shoots and damage the drive components. The quarterly function check of over travel limits switches and emergency stop switch is vital. These switches should be checked for correct actuation and proper secure mounting. Malfunction for such a limit switch can lead to expensive machine damage but can avoided by performing the simple preventive maintenance check. One of the most frequent causes of failure can be avoided by routinely checking the data input devices on the CNC. This should include cleaning, lubricating and adjusting any tape readers and spoolers. Indicator lamp should be checked to ensure they light promptly to indicate danger or function status to the operator. Documentation is another important area. All malfunctions and maintenance operations should be accurately recorded in maintenance log 31 Mohd Sharizan Mohd Sharif
  32. 32. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH located in every CNC. Recurring serious areas for malfunction can than be quickly be noted. Such a log also provides a valuable maintenance history.Maintenance and Repair The CNC machine is an electromechanical installation which encompasses a widerange of technologies, including mechanical components, hydraulics, pneumatics, electrotechnology and electronics. As a result of the CNC machine demands a high standard ofknowledge and experience of the part of maintenance technicians. Training programs for the technician maintenance technicians often to go toomuch detail. A classic example will be study of the interpolator logic for linear/ circular-interpolating continuous part control. The explanation of this principle which often takeone or two days, serves only to satisfy the technical curiosity of trainers and does nothingto assist in elimination of CNC malfunctions. Caution should be exercised with respect to randomly exchanging plug inmodules; this can be costly practice. Components may be damaged during the exchangeprocess, an inventory of parts will grow containing damaged components and moredamage will be done to the machine. The systematic approach of error location is much better. In this context, CNC canbe divided into three main groups : Group 1: Machine tool: axis and spindle drives, machine components, hydraulics and pneumatics. Group2: Measuring System and Control Loops including transfer systems Group3: Electronic Control: technology for digital and data processing, logic links, input and output units. 32 Mohd Sharizan Mohd Sharif
  33. 33. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH Through intensive cross linking of these group- through control loops, measuringcircuits and interlocks.Preventive Maintenance Programs From evaluation of previous experience in preventive CNC maintenance, thefollowing guidelines are suggested:  Leave well-functioning components alone! Do not alter any setting and do not dismantle or rebuild any devices without good reasons.  Each time the system is serviced, pay special attention to sign of possible future malfunctions: corrosion, loose connections, discolored contacts and any material will may be present whose origin is unknown.  The three most important preventive maintenance function to be carried out on a timely basis are cleaning, lubricating and inspecting as prescribed by the manufacturer.  Use only as much lubricant as needed.  Diagnosis and electrical should only take place in accordance with appropriate written instructions. Deviation noted should be corrected immediately if possible.  Preventive maintenance should reduce downtime to a minimum. Therefore used available replacement parts as much as possible and repair defective parts in your shop or send them back to the manufacture once the machine is back in operation.A typical preventive maintenance programs looks like the following a. Weekly :  Run a short program and alter the feed rate override control between minimum and the maximum.  Test deficiencies and complaint operator. 33 Mohd Sharizan Mohd Sharif
  34. 34. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH  Check all fans for the operation and pay attention to good air circulation.  Check the appearance of functioning of any tape reader paying special attention to wear of drives and reeler, cleanliness of read head and alignment of channel and transport tracks.b. Monthly :  Test a part program without using a work piece and observe the axes for the stability, uniform movement, positioning behavior and so on.  Oils all fans, of applicable  Make sure that all plug in circuit are correctly positioned in the contact strips and the retainers are in the place.  Check moving cable and plugs for worn or damages wires and connections.  Remove yhe cover of each measuring system and check for dirt, cable condition, and condition of connections.  Reorder replacement parts for those which have been used.  Check maintenance logs for problems by operating personnel-especially repetitive problems.c. Semiannually :  Measure the mutual dependency of speed/tachometer voltage and following error as the function of the command voltage. Compared the measured value with value measured at the time of installation.d. Annually :  Test each circuit board for perfect seating in its contact strip.  Inspect all contact strips for damage or breakage.  Checked doors, seals and screw fitting for loose connections.  Clean console with vacuum cleaner and soft brush as necessary  Test tape reader mechanics for good working condition.  Test functioning and precision of the CNC. 34 Mohd Sharizan Mohd Sharif
  35. 35. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH  Test power supply for correct voltage output.  Complete fictional test of CNC by processing a test part program with and without a work piece.MACHINE COMMAND CODES The CNC machine receives a series of commands via the CNC program. Thesecommands are structured using letters and numbers such as G00, S2300 and M03. Eachletter and number combination gives the control a specific command. There are somecodes differences between the various machine tool and control manufacturers. Therefore,each machine and control manufacturer provides a specific manual listing all thecommands. Most CNC codes are identical, while some may vary slightly or entirely.Letter Address CommandsMost letter address codes fall into two categories : modal and nonmodal .  Nonmodal : command codes that are only active in the block in which they are specified and executed.  Modal codes : codes that once executed will remain active throughout the program until another code n the same group overrides or cancel its. a. The M codes : Perform a miscellaneous machine function such as automatic tool changes, coolantcontrol and spindle operations. b. The G codes : Set preparatory machine functions such as rapid traverse mode, feed mode andactive tool length offsets. Spindle speeds are controlled with the S code followed by up tofour digits to specify the RPM. 35 Mohd Sharizan Mohd Sharif
  36. 36. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHPicture: World address codes and description. 36 Mohd Sharizan Mohd Sharif
  37. 37. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHPicture: Preparatory function G code description. 37 Mohd Sharizan Mohd Sharif
  38. 38. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHPicture: Miscellaneous function M code description. 38 Mohd Sharizan Mohd Sharif
  39. 39. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHCHAPTER 3PROJECT EXAMPLE Picture: Project example is bottle water. 39 Mohd Sharizan Mohd Sharif
  40. 40. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHPicture: Autocad design about bottle water. 40 Mohd Sharizan Mohd Sharif
  41. 41. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHWORK STEP TO ENTER THE PROGRAMMED CODE  START PROGRAMMED :%0 5451G59 : X0, Z208G96 : V200, T0202, M03G92 : S2000, M08  FACING OBJECT :G00 : X20, Z0G01 : X-1, Z0, F0.2G00 : X20, Z2G71 : P60, Q70, I0.02, K0.02, D1, F0.2G26  SUB PROGRAMMED :N60G46G00 : X0, Z0G01 : X5, Z0G01 : X5, Z-5G01 : X18, Z-12G01 : X18, Z-22G01 : X16, Z-23G01 : X16, Z-30G01 : X18, Z-31G01 : X18, Z-48G40N70 41 Mohd Sharizan Mohd Sharif
  42. 42. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHG26  CUTTINGG96 : V200, T0101, M04G92 : S2000, M08G00 : X20, Z-49.5G01 : X14,G00 : X15,G01 : X10,G00 : X11,G01 : X6,G00 :X7,G01 : X2,G00 : X3,G01 : X0,  END PROGRAMMED :G26M05,M09M00% 42 Mohd Sharizan Mohd Sharif
  43. 43. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAHCHAPTER 4SAFETY RULES FOR CNC TURNING MACHINES These safety rules are generally applicable to most CNC machine operatingsituations. Most machine shop safety rules and safe guards for operating CNC Turningare specified and enfoerced by OSHA and ANSI guidelines are applied to safetyequipment. Therefore, it is highly recommended that people has to follow the rules whenthey get inside the worksyop. Additionally, the doors are usually hardwired with switches, which will preventthe CNC Turning spindle from operating whenever the doors are open. Another built-insafety feature prevents the CNC Turning spindle from operating whenever the chuck jawsare unclamped. An important safety feature that is built-in for CNC Turning and mostmachines alike is the „way-lube-fault‟warning. This safety feature will also prevent the spindle from operating whenever thelubricant in the way lube reservoir diminishes to a low level. The following is acategorized list of recommended safety rules that the reader is strongly advised to fullyread and understand before attempting to operate CNC Turning machines. a. Personal safeguards :  Keep long hair covered when operating or standing near lathe.  Avoid skin contact with any cutting fluids or oil.  Always report any injury and apply first aid treatment.  When the spindle is rotating, avoid standing directly in front of the chuck.  Wear safety shoes when working with heavy tools and equipment.  When ANSI-approved safety glasses with side shields at all times in the shop areas.  Wear hearing protection for noise levels that exceed OSHA specifications. 43 Mohd Sharizan Mohd Sharif
  44. 44. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH Wear an approved face mask for dust levels that exceed OSHA specifications. Do not wear jewelry or loose clothing while operating or standing near lathes. Do not operate any lathes or equipment while under the influence of drugs (prescribed or otherwise) b. Shop environment safeguards : Remove chips from the floor. Clean all liquid, oil, and grease spills immediately. Keep floors and walk aisles clean. Report any fumes or odors. c. Lathe and tool handling safeguards : Always remove hand wrenches after tightening or untightening. Always remove chuck wrenches after tightening or untightening. Store tools in their appropriate tool trays and racks. Keep tools sharp and in good working condition. Keep tools, parts and any other items off the lathe and part. Keep all electrical and mechanical panels secured in place. Check that oil levels are maintained and sufficient. Check that all safety guards and devices are in place and working before operating any lathe. Check that all compressed air equipment is in good working condition. Do not handle loose wires or electrical components. Do not used compressed air to clean chips. Never use gloves when operating a lathe or cleaning the chips. Use gloves when handling tools by their cutting edges. 44 Mohd Sharizan Mohd Sharif
  45. 45. POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH d. Safe machining practices : Do not open the electrical panel or control doors when the machine is operating. Maintain a continuous flow of coolant to the cutting tools when it is operating. Do not remove the chips with a hand when the spindle is finishing its job. Keep hands clear of all moving machines components. Keep hands away from spindle while it is rotating. In case of any emergency while operating a machines, immediately press the Emergency Stop button. Use caution to avoid inadvertently bumping any CNC control buttons. Check that all feeds and speeds do not exceed recommended values. Always consult with an authorized person if you are uncertain or unfamiliar with any operation. 45 Mohd Sharizan Mohd Sharif