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Unformatted text preview: ENGR3190U: Manufacturing and Production Processes Lecture 12 Circular Interpolation, Feeds and Speeds 1. Circular Interpolation (G02, G03)
Circular interpolation allows programmer to move cutting tool in a circular path – arc. G02 – cuts arc clockwise G03 – cut arc counter clockwise Two methods to cut arcs: (1) Radius method - R (2) Arc Modifiers - I, J, K R-method (G02 or G03) (End Point: X,Y) (radius: R or R- ) (Feed Rate: F) If cut 0 < arc ≤ 180o use R, eg. R3.0 If cut 180 < arc ≤ 360o use R-, eg. R-3.0 Example 1 Write the statement to cut the following arc. Use absolute programming. Start point = X2.0 Y4.0, Centre point = X2.0 Y1.0, End point = X2.0 Y-2.0 N10 G90 G02 Y-2.0 R3.0 F3.0 (not need to repeat X2.0 because it is unchanged) I,J,K – method If X-Y plane (G17) is selected then use I and J. If Y-Z plane (G19) is selected then use J and K If Z-X plane (G18) is selected then use I and K We use X-Y plane in this course. (G02 or G03) (End Point: X,Y) (Modifiers: I, J) (Feed Rate: F) 1 I = incremental distance from the start of arc to centre of arc in “X” J = incremental distance from the start of arc to centre of arc in “Y” When I or J =0, you can leave it out. Write the statement to cut the arc in example 1 using I,J method. Use absolute programming. N10 G90 G02 Y-2.0 J-3.0 F3.0 (not need to put I0) 2. Calculating Feeds (F) and Speeds (S)
Spindle Speed How to calculate rotational or spindle speed S used in G-code program? Eg. N90 G00 G54 G90 X3.0 Y5.0 S1800 M03 From Chapter 22 Milling: N = v πD N or RPM = rotational speed or spindle speed, rev/min v = cutting speed (mm/min, inch/min) D = diameter of tool (mm, in) 2 Table of Cutting Speeds v (ft/min) Manufacture of tool usually provides you with this info Drill Milling - Roughing Material HSS CARB HSS CARB Aluminum 200 350 240 500 Brass (soft) 145 350 150 400 Mild steel 95 200 60 180 Tool steel 40 80 50 175 Stainless 55 110 40 200 N = 12* Cutting Speed values in table/(π*Diameter of tool) Simplified RPM formula: N = 4* Cutting Speed values in table/Diameter of tool Feed rate for milling How to calculate feed rate F used in G-code program? eg. From Chapter 22 Milling: fr = Nntf fr = feed rate,( mm/min, inch/min) f = chip load (mm/tooth, in/tooth) – recommended value from chart nt = # of teeth on the cutter Table of feed per tooth value f (inch/tooth) Face Mills 1” End Mill (*) Material HSS CARB HSS CARB Aluminum .011 .015 .005 .006 Brass/Bronze .007 .008 .003 .006 Mild steel .006 .008 .003 .004 Tool steel .005 .007 .002 .003 Stainless .003 .005 .002 .003 * if tool is smaller than 1”, then values will be smaller • Form Mills HSS .003 .002 .002 .002 .003 CARB .004 .003 .003 .003 .002 N120 G01 Z-.10 F3.0 • Milling – Finishing HSS CARB 300 1000 200 600 80 240 80 350 60 400 Chart will be bit different for different tool companies due to slightly differences in tool material. The above calculations is an approximate value. Factors that affect feed rate: 1. 2. 3. 4. 5. 6. 7. Old vs new machine Power of machine Sharpness of tool (wear out or not) Coolant amount used Length of tool (shorter = stronger) Material of part Material of tool 3 Example Consider a 3/8” – Two Flute HSS end mill used to cut (roughing) an aluminum part. Calculate the feeds and speeds. Use simplified formula for N. Notes • Usually round feed values to 1 decimal place, eg. F10.24 round to F10.2 Exception is tapping, need exact feed rate for that. • End mill feed rate for down feed = 30% of calculated F value. Always use a slower speed when cutting down into material since the end mill is flat at bottom and not pointed like a drill. Solution CS-value from table = 240. D = 3/8” = 0.375” N = 4*240/.375 = 2560 therefore set S2560 in program Feed per tooth: 0.005/1” = f/.375 -> f=(0.005)(.375)/1 = .001875. # of tooth = 2 = nt fr = Nntf = (2560)(2)(.001875) = 9.6 set F9.6 in program Down feed = 30%*9.6 = 2.88 so round up and set F2.9 in program when milling down. Example Suppose the calculated feed rate = 10.0 for an end mill. You want to rapid to point A, mill 0.2” into point A, then mill to point B. Use Absolute programming N10 G00 G90 X1.0 Y1.0 N20 Z2.0 N30 Z0.1 N40 G01 Z-0.2 F3.0 (30% of feed rate) N50 X3.0 F10.0 4 ...
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- Fall '10