Application and Technical Information Thread Milling System (TMS) Minimum Bore Diameters for Thread Milling

Transcription

1 Inserts Application and Technical Information Minimum Bore iameters for Thread Milling UN-ISO-BSW tpi Technical ata Accessories Vintage Cutters Widia Cutters Thread Milling Slotting ie and Mold End Mills Face Mills cutter workpiece material pitch mm cutter dia. (1) K035TM1RW050-STN K045TM1RW050-STN11N K049TM1RW037LT11S K061TM1RW06-STN16T K067TMRW075-STN K075TM1RW075-STN16T K079TM1RW075-STN16N K087TM1RW100-STN16L K10TMRW100-STN ,5 0,75 1,0 1,5 1,5,0,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 minimum bore diameter () (inches) K118TM1RW100-STN7N K146TM1RW15-STN7N K165TMRW15-STN Cutting ata Recommendation 1.38 (UN) (ISO) (BSW) cutting speed (sfm) feed rate per grade KC610M grade KC60M grade KC635M revolution carbon steels < 187 HB carbon steels 187 to 0 HB alloy steel HB alloy steel HB stainless steel, austenitic < 10 HB stainless steel, martensitic < 31 HB stainless steel, ferritic < 45 HB cast steel < 140 HB cast steel 0-30 HB titanium alloys high-temperature (nickel and iron base) high-temperature (cobalt base) cast iron malleable iron bronze/copper aluminum NOTES: All thread milling inserts are full profile or cresting type. Inserts are designed to mill full thread depth in one revolution or pass. When machining difficult materials, two passes may be desired. A 60% thread depth on the first pass, and a 40% thread depth on the second pass is recommended. Thread relief grooves in blind holes are not necessary. Applications in this area may be machined with special inserts and cutter bodies. Quoted on request. Thread milling large parts requires considerably less horsepower compared to other threading methods. Thread milling produces short chips compared to stringy chips of other threading methods. One holder is suitable for many different thread pitches. PV coated inserts provide maximum tool life for a wide variety of materials. M370

2 Understanding Thread Milling In order to perform a thread milling operation, a milling machine with three-axis control, capable of helical interpolation, is required. Helical interpolation is a CNC function producing tool movement along a helical path. This helical travel combines circular movement in one plane with a simultaneous linear motion in a plane perpendicular to the first. For example, the path from point A to point B (figure A) on the envelope of the cylinder combines a circular movement in the X and Y plane with a linear movement in the Z direction. On most CNC systems, this function can be executed in two different ways: G0: helical interpolation in a clockwise direction G03: helical interpolation in a counterclockwise direction The thread milling operation (figure B) consists of circular rotation of the tool about its own axis together with an orbiting motion along the bore or workpiece circumference. uring one such orbit, the tool will move vertically one pitch length. These movements, combined with the insert geometry, create the required thread form. Inserts Face Mills End Mills α - - P - helix angle external diameter pitch There are three acceptable ways of approaching the workpiece with the tool to initiate production of the thread: 1. along a tangential arc. radially 3. along a tangential straight line NOTE: Climb milling is preferred. ie and Mold figure A Tangential Approach (arc) figure B With this method, the tool enters and exits the workpiece smoothly. No marks are left on the workpiece and there is no vibration, even with harder materials. Although it requires slightly more complex programming than the radial approach method (see next page), this is the method recommended for machining the highest quality threads. 1 - : rapid approach - 3: tool entry along tangential arc, with simultaneous feed along Z-axis 3-4: helical movement during one full orbit (360 ) 4-5: tool exit along tangential arc, with continuing feed along the Z-axis 5-6: rapid return Slotting Thread Milling Widia Cutters Accessories Technical ata Vintage Cutters internal thread Tangential Approach (line) This method is very simple, and has all of the advantages of the tangential arc method. However, it is applicable only to external threads. external thread 1 - : radial entry with simultaneous feed along the Z-axis - 3: helical movement during one full orbit (360 ) 3-4: radial exit M371

3 Inserts Face Mills Application and Technical Information Radial Approach 1 - : radial entry - 3: helical movement during one full orbit (360 ) 3-4: radial exit This is the simplest method. There are two characteristics worth noting about the radial approach: a. A small vertical mark may be left at the entry (and exit) point. This is of no significance to the thread itself. b. When using this method with very hard materials, there may be a tendency for the tool to vibrate as it approaches the full cutting depth. NOTE: Radial feed during entry to the full profile depth should be only 1/3 of the subsequent circular feed! ie and Mold End Mills internal thread Preparing for the Thread Milling Operation external thread Slotting Thread Milling Widia Cutters Vintage Cutters Accessories Technical ata calculation of feed rates at the cutting edge calculation of program feed rate internal thread (F 1 x d 1 ) P f = F 1 - The first step is to calculate the tool feed rate at the cutting edge. F 1 = ipt x nt x rpm where: F 1 = tool feed rate at the cutting edge (in./min.) ipt = inch per tooth (feed rate) nt = number of effective inserts in cutter rpm = rotational speed (spindle rpm) On most CNC machines, the feed rate required for programming is at the centerline of the tool. When dealing with linear tool movement, the feed rate at the cutting edge and the centerline are identical. But, with where: P f = program feed rate (in./min.) = major diameter (external thread) = minor diameter (internal thread) d 1 = cutting diameter, over insert The rotational speed (rpm) is calculated by the following formula: rpm = where: sfm = cutting speed, surface feet per minute d 1 = cutter diameter, over insert π = circular tool movement this is not the case. The following equations define the relationship between feed rates at the cutting edge and at the tool centerline. external thread 1 x sfm π x d 1 (F 1 x d 1 ) P f = F 1 + M37

4 Step-by-Step Thread Milling Example thread: internal right hand 1 1 /4 x 16 UN B RH(1) material: AISI 4140 (300 HB) thread diameters: (minimum bore dia.) = 1.18 o (nominal dia.) = 1.5 inch thread length:.50 inch efine the Appropriate Cutter: For best thread quality, the cutter with the largest d 1 (cutter diameter) possible should be used. This cutter diameter can be found in the table on page M370, as a function of pitch and minimum bore diameter. The result for the above example is that any cutter diameter 1.0 inch or smaller can be utilized. A cutter with a smaller d 1 will perform the thread milling operation in less time. The smaller d 1 may result in less tool rigidity, so it should be used with caution on very tough materials. Find the appropriate normal-length shank cutter on page M368. Use the minimum bore diameter table above. Choosing Insert Size The insert IC is defined by the selected cutter (STN16). Use the appropriate insert table on pages M363-M366. Find the appropriate normal-length shank cutter diameter on page M368. pitch (tpi) pitch mm 1,0 1,5 1,5,0 cutter dia. d 1 minimum bore diameter figure B: cutter selected: K079TMIRW075STN16N outer dimensions: d 1 =.79, R t (radius of tool) = d 1 =.395 Slotting ie and Mold End Mills Face Mills Inserts b insert a internal thread inch number size inch pitch thread of IC (mm) (tpi) length teeth catalog number insert selected: STN16 16UN-I Cutting ata Recommendation workpiece material selected carbide grade: KC610M selected cutting speed: 500 sfm selected feed:.004 ipt KC610M grade external thread catalog number b inch number thread of length teeth cutting speed (sfm) feed rate per mini thread mill grade KC610M grade KC60M revolution STN10 carbon steels (< 187 HB) carbon steels (187 to 0 HB) alloy steel (00-50 HB) alloy steel (50-35 HB) stainless steel austenitic (< 10 HB) grade cutter type 3 STN16 3UN-I STN16 3UN-E STN16 8UN-I STN16 8UN-E STN16 7UN-I STN16 7UN-E /8 4 STN16 4UN-I STN16 4UN-E STN16 0UN-I STN16 0UN-E (16) 18 STN16 18UN-I STN16 18UN-E STN16 16 STN16 16UN-I.56 9 STN16 16UN-E STN16 14UN-I.57 8 STN16 14UN-E STN16 13UN-I.54 7 STN16 13UN-E STN16 1UN-I.58 7 STN16 1UN-E.58 7 stock standard non-stock standard Choose the carbide grade, define the cutting speed and select the proper feed. KC60M Technical ata Accessories Vintage Cutters Widia Cutters Thread Milling KC610M KC60M M373

5 Step-by-Step Thread Milling Example (cont d.) Technical ata Accessories Vintage Cutters Widia Cutters Thread Milling Slotting ie and Mold End Mills Face Mills Inserts Calculate the feed rates: First, find the rpm. 1 x sfm 1 x 500 rpm = = = 418 rpm π x d x.79 Next, calculate the feed rate at the insert cutting edge (F 1 ): (using the chosen feed per tooth of.004.) F 1 = ipt x nt x rpm =.004 x 1 x 418 = 9.67 in./min. Finally, calculate the feed rate at the cutter centerline (F ): F 1 x ( d 1 ) 9.67 x ( ) F = = = 3.07 in./min Select the thread milling method. [Selected method...climb milling (preferred), refer to page 71.] Calculate the radius of the tangential arc R e : (R i C L ) + R o (.591.0) +.65 R e = = R o x.65 R e = in. Calculate the angle (β): R o R e β = 90 + arc sin ( ) R e β = 90 + arc sin ( ) β = = = 95 10' Calculate the movement along the Z-axis during the entry approach from point A to point B (Zα). (NOTE: P = pitch) α.065 Zα = P(in.) x = x =.0156 in., since α = Calculate the X and Y values at the start of the entry approach. X = 0 Y = R i + C L = =.571 in. efine Z-axis location at the start of the entry approach. (NOTE: L = length of thread) Z = (L + Zα) = ( ) =.5156 in. efine the starting point. X a = 0 Y a = 0 CNC Program (Fanuc 11M) % N10G90G00G57X0.000Y0.000 N0G43H10Z0.M3S417 N30G91G00X0.Y0.Z N40G4160X0.000Y Z0. N50G03X0.650Y0.5710Z0.0156R0.5733F3.06 N60G03X0.Y0.Z0.065I 0.65J0. N70G03X 0.65Y0.5710Z0.0156R N80G00G40X0.Y Z0. N90G49G57G00Z8.0M5 N100M30 R i = % = minor diameter R o o = o = nominal diameter α = 90 M374

6 Appendix A erivation of Formulas for Internal Thread Milling Appendix B erivation of Formulas for External Thread Milling Inserts R e, β, and X can be found by a geometric analysis of the entry path. This entry path is defined by the tool traveling along a circular path, with a radius of R e about the point C. (R i C L ) + R o derivation of R e = R o Triangle OAC enables us to simply solve for R e. Note that OAC is a right angle triangle, and that: OA = R i C L CA = R e OC = R o R e Pythagoras law states: OA + OC = AC Replacing actual values, we get: (R i C L ) + (R o R e ) = R e Simplifying, we get: R e = (R i C L ) + R o R o R e, β, and X can be found by a geometric analysis of the entry path. This entry path is defined by the tool traveling along a circular path, with a radius of R e about the point C. (R o + C L ) + R i derivation of R e = R i Triangle OAC enables us to simply solve for R e. Note that OAC is a right angle triangle, and that: OA = R o + C L CA = R e OC = R e R i Pythagoras law states: OA + OC = AC Replacing actual values, we get: (R o + C L) + (R e R i) = R e Simplifying, we get: (R o + C L ) +R i R e = R i Thread Milling Slotting ie and Mold End Mills Face Mills Find the angle β. β = 90 + σ OC (R o R e ) sin σ = = CA R e Technical ata Accessories Vintage Cutters Widia Cutters R o R e σ = arc sin ( ) R e R o R e Therefore, β = 90 + arc sin ( ) R e Find the angle β. β can be easily found using the same triangle: AO (R o + C L ) sin β = = AC R e R o + C L β = arc sin ( ) R e M375

7 Inserts Application and Technical Information Thread Milling Troubleshooting problem possible cause solution Technical ata Accessories Vintage Cutters Widia Cutters Thread Milling Slotting ie and Mold End Mills Face Mills cutting speed too high Reduce cutting speed. excessive insert flank wear chip is too thin Increase feed rate. Insert Tolerance Classes insufficient coolant Increase coolant quantity/pressure. Reduce feed rate. chipping of chip is too thick Use the tangential arc method of entrance. cutting edge Increase rpm. vibration Check rigidity. material cutting speed too slow Increase cutting speed. build-up on the chip thickness too small Increase feed rate. cutting edge chatter / vibration feed rate is too high Reduce the feed. profile is too deep (coarse pitch threads) thread length is too long insufficient thread accuracy tool deflection Execute two passes, each with increased cutting depth. Execute two passes, each cutting only half the thread length. Execute two passes, each cutting only half of the thread length. Reduce feed rate. Execute a zero cut. thread designation standard designation tolerance class UN ANSI B A/B *UNJ MIL-S-8879A 3A/3B ISO R6 (IN 13) 6g/6H NPT USAS B.1 : 1968 standard NPT NPTF ANSI B standard BSW B.S. 84 : 1956, IN 59, ISO 8/1 : 198 medium class A BSPT B.S. 1 : 1985 standard BSPT *ACME ANSI B1/5 : G *PG IN standard *TR IN 103 7e/7H *NOTE: enotes thread forms quoted on request as non-stock standards (4-6 weeks delivery). M376

8 The following are a few thread milling methods (work directions). NOTE: Climb milling results in lower cutting forces, better chip development, higher thread surface quality and longer insert life. Therefore, it should be used whenever possible. But, in the case of some hardened materials or when milling certain difficult-to-machine exotic materials, conventional milling may be preferred. Methods of External Thread Milling Inserts Face Mills ie and Mold Widia Cutters Vintage Cutters Technical ata Accessories Thread Milling Slotting End Mills right-hand thread... conventional milling right-hand thread... climb milling left-hand thread... conventional milling Methods of Internal Thread Milling left-hand thread... climb milling right-hand thread... conventional milling right-hand thread... climb milling left-hand thread... conventional milling left-hand thread... climb milling M377