2.Operation_Programming - Chapter 2 Contents Contents CNC Machine Axes CNC Coordinate System Absolute Programming Incremental Programming Word Address

2.Operation_Programming - Chapter 2 Contents Contents CNC...

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Unformatted text preview: Chapter 2 Contents Contents CNC Machine Axes CNC Coordinate System Absolute Programming Incremental Programming Word Address Programming G Code M Code Other Code Developing Part Program Programming Procedure Turning Center Cutters Turning Calculating Milling Calculating Drilling Calculating CNC Machine Axes CNC CNC equipment executes machining operations by CNC performing a linear and rotary motion. performing The machines automatically knows how to move in The response to an axis command, therefore the programmer need not be concerned whether it is the spindle or table that moves. spindle The machine axis will be defined in term of spindle The movement. movement. CNC machine can perform simultaneously along their CNC axis axis CNC Milling vs. CNC Lathe CNC CNC Coordinate System CNC Coordinate system Cartesian Polar Coordinate System Absolute Programming Absolute Absolute programming specifies a position or an end Absolute point from the workpiece coordinate zero (datum) point Incremental Programming Incremental Incremental programming specifies the movement or Incremental distance from the point where currently located. Incremental specify distance and direction of the machine to move. Word Address Programming The word address format for numerical control The programming precisely controls machine movement and function through the use of short sentence. i.e. function use i.e. commands commands A series of command blocks that execute motions and series machine functions in order to manufacture a part. machine These commands consists of addresses, words and These characters. characters. Letter Address Commands Letter N Line number or sequence number G Preparatory functions, which set up the mode in Preparatory which the rest of the operations are to be executed executed F Feed rate of controlled axis S Spindle speed setting T Latter address for a tool call M Miscellaneous function H and D Auxiliary letter address code used for tool offset Auxiliary storage storage N0010 G00 X-1.00 Y-1.00; (point 1) N0010 N0020 G01 X-.25 Y-.25 F10.0; (point 2) N0030 G01 Y3.25; (point 3) N0040 G01 X4.25; (point 4) N0050 G01 Y-.25; (point 5) N0060 G01 X-.50; (point 6) Part Datum Location – feature of the part from which Part the majority of the dimensions of the part are located. the Sequence Number (Nxxxx) – Identifying blocks of Sequence information within the program. information Preparatory Function (G-Codes) – Used to set the Preparatory control for various machine movements. control Spindle Control Functions (S) – Spindle speeds are Spindle controlled with an S followed by digits. controlled Miscellaneous Function (M-Codes) – Perform Miscellaneous miscellaneous machine function such as tool changes, coolant control and spindle operations. changes, Tool Calls – Start with a T and then the tool number. Tool G Code Code Code G0/G00 G1/G01 G2/G02 G3/G03 G4/G04 G17X,Y G18X,Z G19Y,Z G28 G40 G41 G42 G43 G44 G49 Meaning Non-Linear Rapid moves Linear Interpolation CW Interpolation CCW Interpolation Dwell Plane of Interpolation Plane of Interpolation Plane of Interpolation Return to Machine zero CRC cancel CRC left CRC right Tool length comp. + Tool length comp. Tool Length comp. Cancel G44 G44 G49 G50 G54-G59 G70 G71 G73 G80 G81 G82 G83 G85 G90 G91 G92 G94 G95 G97 G98 G99 Tool length comp. Tool Length comp. Cancel Set Program Zero Set Local Coordinate Systems Rough turning canned cycle Finishing turning canned cycle Drill CHPBRKR Canned Cycle cancel Spot Drilling Cycle Drill/Counterbore Peck Drilling Cycle Bore Absolute Programming Incremental Programming Set Program Zero IPM Programming IPR Programming Direct Spindle Speed Programming Return to initial level Return to R level M Code Code Code Meaning M0/M00 Program stop M1/M01 Optional stop M2/M02 Program stop M3/M03 Spindle normal rotation M4/M04 Spindle reverse rotation M5/M05 Spindle off M6/M06 Tool change M8/M08 Coolant on M9/M09 Coolant off M30 Program reset/tape rewind M98 Sub-Program call M99 Return to previous program Other Codes Other Code A,B,C Meaning Auxiliary Axis, *A supported D F Offset CRCEIPR Feedrate IPM/IPR Feedrate H I,J,K Tool length offset call Arc center location N O Sequence Numbers Program Numbers P Q Dwell time Peck Depth R R Rapid level Arc center radius S T Spindle speed Tool number U,V,W X,Y,Z Incremental Move in X, Y, Z Absolute Move in X, Y, Z Part Program Manuscript Part Developing Part Program Developing Steps involved in developing part program: 1. Process Planning 2. Axes Selection 3. Tool selection 4. Cutting process parameters planning 5. Job and tool setup planning 6. Machining path planning 7. Part program writing 8. Part program validation 9. Documentation for NC Programming Procedures Programming 1. 2. 3. 4. 5. 6. 7. Startup or preliminary procedure Tool call Workpiece location block Spindle speed control Tool motion block Home return Program end procedure Process Planning Process Consists of: Machine tool used Fixtures required Sequence of operation Requirement for each operation in form of cutting tools Requirement and process parameters and Axes Selection Axes CNC machine tools rely on the axes system to CNC describe the tool/axes motion describe To have all positive coordinate value, use the lower To left corner as datum left Z-axis datum is normally set at top surface of the part. Z-axis All +ve Z coordinate value keep the tool away from the part (to avoid collision). the The zero Z coordinate can be easily set by touching The the tool tip to the top surface during the tool setup. the Set the datum geometric center of the part if all Set geometry is symmetrical. geometry Tools Selection Tools The largest size of the end mill should be chosen for The better surface finish and high mrr. The max. tool radius of the curvature being generated. radius End mill always approach the work piece from the End side. Slot drill can approach from the side or the top of the work piece. top Tooling for Machining Centers Tooling Cutting Tools Cutting Most machining centers Most use some form of HSS or carbide insert endmill as the basic cutting tool. cutting Insert endmills cut Insert many times faster than HSS, but the HSS endmills leave a better finish when side cutting. finish Cutting Tools Cutting Facemills flatten large Facemills surfaces quickly and with an excellent finish. with Notice the engine block being finished in one pass with a large cutter. pass Cutting Tools Ball endmills (both HSS Ball and insert) are used for a variety of profiling operations such as the mold shown in the picture. shown Slitting and side cutters Slitting are used when deep, narrow slots must be cut. narrow Calculations for Speed and Feed Turning Center Cutters Turning What types of cutters are used on CNC turning Centers? Carbide (and other hard materials) insert turning and boring Carbide tools tools High Speed Steel (HSS) drills and taps High Where to find information for calculating RPM and feed Where rates? rates? Cutting tool manufacturer (first choice) Machining Data Handbook Machinery’s Handbook Standard Insert Shapes Standard V – used for profiling, weakest insert, used 2 edges per side. edges D – somewhat stronger, used for somewhat profiling when the angle allows it, 2 edges per side. edges T – commonly used for turning commonly because it has 3 edges per side. because C – popular insert because the same popular holder can be used for turning and facing. 2 edges per side. facing. W – newest shape. Can turn and face newest like the C, but 3 edges per side. like S – Very strong, but mostly used for Very chamfering because it won’t cut a square shoulder. 4 edges per side. square R – strongest insert but least strongest commonly used. commonly Typical Turning, Typical Threading, and Parting Tools Tool Holder Hand Tool For most CNC turning For centers, the cutter is on the back side of the part and is upside down. upside Right Hand tool then turns Right towards the chuck. towards Left Hand tool then turns Left towards the tailstock. towards If the cutter is symmetrical If with the shank, it is called NEUTRAL HAND. NEUTRAL Tooling Considerations Tooling Tooling choices depend on the type of workpiece, the Tooling machine, and the desired surface finish. machine, Harder workpieces require harder cutters. Modern cutters require the turning center to have high Modern spindle speeds and powerful motors. spindle Cutting process parameters planning Cutting Recommended procedure for machining are as follows Face mill top surface Rough machine the profile of the part Rough bore Drill and tap Finish profile surfaces Finish bore Finish reaming Cutting Speed Cutting What is cutting speed? Not RPM Relative speed of the work and cutter Units in feet/minute (fpm) or Units meter/minute (mpm) meter/minute Usually designated as V, cs, or S Tabulated in the book based on material, Tabulated cutter type, and type of cut (roughing or finishing) finishing) Needed to calculate RPM Calculating Turning RPM Calculating The formula for calculating RPM is : 12 × v N = RPM = π ×D Where Where V = cutting speed to be looked up in the handbook cutting D = diameter being cut do this: 12 × V ÷ π ÷ D = Note the difference between this and the actual Note formula. formula. Types of Cuts Types Roughing – primary considerations: Just removing metal, surface finish does Just not matter. not Requires a strong cutter. Generally have deep depth of cuts and fast Generally feed rates. feed The cutting speed is generally adjusted The slower to keep heat down. slower Types of Cuts Types Finishing – primary considerations: Must meet required surface finish and size Must specifications. specifications. Requires a hard cutter to hold its shape well. Generally have small depth of cuts and slow Generally feed rates. feed The cutting speed is generally adjusted The upward to give a better surface finish. upward Surface Finish Requirements She surface finish depends on urface T The the feed rate and on the cutter nose radius. nose Generally, a large nose radius Generally, and a slow feed rate coupled with high cutting speed gives the best finish. the However, too large of a nose However, radius induces chatter ruining the finish and the size. the Most inserts use a 1/32” nose Most radius as a good compromise. radius General Feed and Depth of Cut Recommendations Recommendations Roughing: 0.1” to 0.25” depth of cut (radial) 0.012 inches per revolution (ipr) to 0.018 ipr feed rate Finishing: 0.03” to 0.05” depth of cut (radial) 0.006 ipr to 0.010 ipr feed rate Note 1: the depth of cut should not be less than the Note tool nose radius unless special finishing inserts are being used. being Note 2: smaller feed rates can be used if special Note finishing inserts are being used. finishing Calculating RPM for Turning Operations with Hard Cutters Use this procedure for carbide, ceramic, and cermet Use inserts. inserts. We will adjust the cutting speed based on the desired We depth of cut and feed rate. depth Calculating Turning RPM Calculating Six step process: 1. 2. 3. 4. 4. 5. 5. 6. Select depth of cut - as deep as possible. Select feed - appropriate for roughing or finishing. Find the original cutting speed in the tables. Find Find the feed and depth of cut factors Find Modify the original cutting speed based on step 4. Calculate the RPM. Note: All data will be found in the “Machining” Note: thumb tab in the Machinery’s Handbook. Machinery’s Calculating Turning RPM Calculating Example: Take 0.250 depth of cut, 0.012 feed in quenched and Take tempered 8620 steel with a Brinell hardness of 300, hard coated carbide cutter, 2.5” diameter part. coated Step 1: Depth of cut given at 0.25”. Step 2: Feed rate given as 0.012 ipr. Calculating Turning RPM (continued) Step 3: From Table 1, page 1029, locate cutting parameters for this material Calculating Turning RPM Calculating Step 3: From Table 1, page 1029, we find Vopt = 585 fpm ipr Vavg = 790 fpm Fopt = 0.017 Note that the table lists cutting speed as S rather than V as Note used everywhere else. Note that the feed rates are given in 0.001 ipr, so the 17 listed for Fopt is actually 0.017 ipr. 0.001 Calculating Turning RPM Calculating Step 4: Once located the optimum and average cutting speeds and Once the optimum feed, we finish our calculation using the data and process described in Table 5A, page 1035. and Calculating Turning RPM Calculating Calculating Turning RPM Calculating Step 4: For this example following the steps in 5a: Calculate the following ratios: And From Table 5a, page 1035, find Ff = 1.22 and Fd = From 0.87 0.87 Calculating Turning RPM Calculating Step 5: As shown at the bottom of Table 5a, V = Vopt Ff Fd Where V = cutting speed to be used (fpm) Vopt = optimum cutting speed from the table based on material hardness and type of cutter hardness Ff = feed factor from Table 5a Fd = depth of cut factor from Table 5a For this example, V = (585)(1.22)(0.87) = 621 fpm Calculating Turning RPM Calculating Step 6: Finally, calculate the RPM with For this example: RPM = 12 x 621 / p / 2.5 = 949 RPM Speed and Feed Calculations for Milling Speed Calculating RPM for Milling Calculating Operations with HSS Cutters Use the same basic formula as for turning, except D is Use now the cutter diameter: now Tables 10 through 16 list milling data. Table 6 must be Tables used for copper alloys. used Example Milling RPM Calculation Example Mill 4140 steel with a Brinell hardness of 200 with a ½” Mill HSS endmill. HSS From Table , given V = 75 fpm, so: RPM =12X 75 /p / 0.5 = 573 RPM =12X 0.5 Feed Rates for Milling Feed Feed for milling cutters is usually tabulated as inches per Feed tooth (ipt), but feed rates on milling machines are programmed in inches per minute (ipm). The equation on page 1041 in the Handbook is given as is fm = ft nt N Where fm is the feed rate in ipm we want to set the mill at. ft is the feed rate in inches per tooth, ipt. nt is the number of teeth on the cutter we are going to use. N is the RPM we already calculated. Example Milling Feed Rate Calculation Calculation Mill 4140 steel with a Brinell hardness of 200 with a ½” 4 Mill flute HSS endmill and a ¼” depth of cut. flute Already calculated the RPM at 573, From Table ft = 0.001“ fm = 0.001 x 4 x 573 = 2.3 IPM Feed Rate Concerns Feed Feed rates for facemill and slotting cutters vary Feed widely. widely. Slow feed rates give a better finish, but sometimes Slow this actually dulls the cutter faster than a more rapid feed rate. feed Data for carbide insert milling cutters should be Data obtained from the insert manufacturer. Unlike lathe cutters which are fairly standard, milling cutters vary widely between manufacturers, so use your manufacturer’s data. manufacturer’s Milling Feed Direction Milling Remember, all CNC machines are Remember, equipped with ball screws to minimize slop when changing feed directions. The other advantage to directions The ball screws is they allow climb milling instead of conventional milling as done on most manual machines. machines. Climb milling has many advantages Climb including better surface finish, longer tool life, and the cutter deflects away from the work rather than into it. than Always climb mill on a CNC Always machining center! machining Calculating RPM for Drilling Calculating Operations with HSS Cutters The RPM formula for drilling is the same as for turning The and milling, except D is now the drill diameter. and Note: deeper holes require slower cutting speeds because Note: the coolant cannot reach the cutting edge effectively. the Feed rates for drilling are given in a paragraph on page Feed 1060. Note that the values are given in inches/revolution (ipr). If you need ipm, multiply ipr by RPM. (ipr). Drilling RPM and Drilling Feed Calculation Example Drill cold drawn free cutting brass, C36000, with a 1” Drill drill. From Table, given V = 175 fpm, so: drill. RPM =12X175 /p /1 = 668 RPM =12X175 From page 1060, the feed would be between 0.007 and From 0.015 ipr. 0.015 To find ipm, use ipm = Feed x RPM = 0.015 x 668 = 10 To ipm ipm Drills, Taps, and Reamers Drills, Common HSS tools such as Common drills, taps, and reamers are commonly used on CNC machining centers. machining Note that a spot drill is used Note instead of a centerdrill. Also, spiral point or gun taps are used for through holes and spiral flute for blind holes. Rarely are hand taps used on a machining center. machining Job and tool setup planning Job Clamp the workpiece on the fixture firmly and adjust the cutting tool to correct position Machining path planning Machining To ensure the requisite manufacturing specifications are To achieved at lowest cost. (exp. Zigzag, one way, etc achieved Use the canned cycles to simplify the program Part program writing Part Writing program manually will require knowledge of the Writing format and syntax of the program or format It can be generated automatically by various CAM It software (MasterCAM, Edge CAM, etc.) software Part program validation (verify) (verify) Part program should be verified before it can be Part loaded into the CNC machine loaded Check the following: Tool collision The dimension of the machined features To see how the tool path is programmed To see how the material is being removed from the To workpiece workpiece It can be done by backplotting or dynamically simulating It the actual sized tool through the work material the Documentation for NC Documentation Keep the component drawing, process plan sheet, Keep programming sheet etc. as a record. It is essential for updating the drawing or recall the previous drawing whenever it is required whenever Manual Part Programming Machine tool controllers are able to interpret a series of simple standard Machine command codes in order to control the table and spindle movements and all auxiliary functions. The prime code is the G-code, which can be used, for example, to define fast traverse motion (G00), linear (G01) and circular (G02 and G03) tool motion under controlled feed rates, millimeter and inch motion (G20 and G21), tool length compensation (G43), and preprogrammed function calls (G65). Other codes include feedrate F-codes, cutting speed S-codes, tool selection T-codes and auxiliary functions, such as spindle start and stop, M-codes. These machine codes, which are outlined below, are collectively referred to as G-codes. The program for producing a part is arranged in the form of coded blocks or The lines of information. Each block contains a group of commands sufficient for one individual machining operation. A typical block is given as follows: N200 G01 X120.0 Y100.0 Z80.0 F150; and is interpreted that in block 200 the tool should move from its present and position in a straight line to X = 120 mm, Y = 100 mm and Z = 80 mm at a feedrate of 150 mm/min. Some typical beginning and end sequences for CNC part programs are given in Table 2.1. Each program should have an identifying number, in this case O006. It is good practice to start the program with a return home (G91 G28) instruction so that all subsequent programming is from a known datum. This home datum point is determined by the machine tool manufacturer and is normally at Xmax, Ymax and Zmax. For safety the Z axis is usually returned to the home position first. The G92 X250.0 Y125.0 Z75.0 instruction establishes the position of the workpiece in relation to the home position. The tool defined in storage location T18 is inserted in the spindle with the M06 instruction, and the tool in storage location T19 is positioned on standby. Absolute coordinates, millimeter measurements and tool length compensation are selected with G90, G21 and G43, respectively. The cutter is moved with rapid traverse to the position Z = 100 mm and then to the position X = 0 mm, Y = 0 mm (or to any other starting position). A spindle speed of 2000 rpm is selected with S2000 and the spindle turned on with M03. Table 2.1 Table Tool Holders Tool All cutting tools must be held in ...
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