Milling. COPYRIGHT 2008, Seco Tools AB 1/111

Transcription

1 Milling 1/111

2 2/111 Milling A simple choice!

3 Experts required? No Just follow some basic rules. 3/111

4 Face milling 4/111

5 Square shoulder milling 5/111

6 Disc milling 6/111

7 Copy milling 7/111

8 Plunge milling 8/111

9 High feed milling 9/111

10 Thread milling 10/111

11 Solid Carbide milling 11/111

12 Mini milling cutters A full range cutters from 0,004 up to diameter. 62HRc Phone Mold 12/111

13 Mill Turning Face Turnmilling Cutter off centre-line Peripheral Turnmilling (helical interpolation ramping) External Cutter on centre-line Internal 13/111

14 Cutting depth a p inch Machine Capability Insert application insert dimensions cutting conditions Power Turbo Super Turbo Micro Turbo Nano Turbo Feed f z inch/tooth (Typical example) 14/111

15 Nomenclature & Cutter Geometry 15/111

16 Milling Cutter Nomenclature 16/111

17 Cutter Geometry Milling cutter geometry Cutting forces Power Metal removal rate Cutting edge geometry Tool life Cutting forces Chip breaking geometry Chip formation Cutting forces 17/111

18 Cutter positioning Cutter Geometry Entry shock (pressure stress) Exit shock (tensile stress) 18/111

19 The difference between milling and turning Varying cutting forces (stress). Varying cutting temperatures (tension in insert). Milling has varying chip thickness. Turning has a constant chip thickness. 19/111

20 Varying Edge Temperature Chipping Thermal cracks 20/111

21 Cutter Geometry γ p κ γ f Milling cutter geometry = Positioning of the cutting edge Lead angle - κ Axial rake angle - γ p Radial rake angle - γ f 21/111

22 Cutter Geometry Positive positive Advantages/disadvantages + Smooth cutting. + Good chip removal. + Good surface smoothness. - Cutting edge strength. - Unfavorable entry contact. - Draws workpiece away from machine table. 22/111

23 Cutter Geometry Negative negative Advantages/disadvantages + Cutting edge strength. + Productivity. + Pushes the workpiece towards the machine table. - Large cutting forces. - Chip obstruction. 23/111

24 Cutter Geometry Negative vs. Positive Double negative Double positive 24/111

25 Cutter Geometry Positive negative Advantages/disadvantages + Good chip removal. + Favorable cutting forces. + Wide range of applications. 25/111

26 Insert nomenclature & cutting edge geometry. 26/111

27 Milling Insert Nomenclature OFER070405TN-ME15 T25M 27/111

28 Edge Condition and Rake Angle OFER070405TN-ME15 T25M -E -ME -M -MD 28/111

29 Ultra High Positive Rake /111

30 Milling Cutter Application. 30/111

31 Conventional Climb Conventional milling Used on older machines / unstable conditions. Unfavorable milling process. Climb milling Favorable milling process. Not recommended on older machines / unstable conditions. 31/111

32 Cutter positioning The basic problem in conventional milling is the insert entry. Cutting edge radius, rubbing the edges away not enough heat! Self-hardening materials Stainless Steel. Chip jamming/obstruction. 32/111

33 Cutter positioning Climb milling can be used for most processes. The machine must have a stable setup and spindle with no play. (Modern CNC machines) Advantages of climb milling Longer tool life. The chips land behind the cutter on the surface just milled, and will therefore not be machined again. Climb milling causes a downward pressure and therefore does not lift up the workpiece. Better surface finish. Easier chip removal. Requires less power. 33/111

34 Cutter positioning Conventional milling Central milling Combination of climb and conventional milling. Unfavorable due to varying cutting forces. Unavoidable when slot milling Climb milling 34/111

35 pitch Arc of tool engagement. Insert spacing. Arc of tool engagement. 35/111

36 Cutter Engagement Under-formed chip Undesirable, sometimes unavoidable. Thick chip Desirable, better tool life. 36/111

37 Cutter positioning Entry shock (pressure stress) Exit shock (tensile stress) If possible position the cutter as shown on the right, if you can. 37/111

38 Cutter positioning Interrupted cut milling Short tool life (cutting edge breakage). Vibration problems. This is often unavoidable! 38/111

39 Milling cutter pitch pitch : Impact of each tooth. : Vibration amplitude. Normal pitch Differential pitch Differential pitch reduces the risk of vibration. 39/111

40 Vibrations F F z F x The size and direction of the cutting force for a face milling cutter, 45 entering angle (sum of axial and radial forces perpendicular to cutting edge). 40/111

41 Vibrations F F z F x The size and direction of the cutting force for a square shoulder milling cutter, 90 entering angle. (sum of axial and radial forces perpendicular to cutting edge). 41/111

42 Vibrations n = fz = hm D ae (1 sink) fz = hm D ae Change cutter positioning Minimise tool overhang Improve stability (n π D) 12 f = ( z or k) fz v c 12 π D vf = n ( z or k) fz Decrease cutting speed Increase feed Decrease depth of cut Conventional milling Q = ae ap vf 42/111

43 Vibrations 43/111

44 Average chip thickness 44/111

45 Average chip thickness f z Chip thickness = Thickness of the undeformed chip at right angles to cutting edge.. and is constantly changing. 45/111

46 Average chip thickness f z 46/111

47 Average chip thickness f z h m Chip thickness = Thickness of the undeformed chip at right angles to cutting edge.. and is constantly changing THEREFORE average chip thickness is important. 47/111

48 Average chip thickness Calculating the average chip thickness, to achieve the correct cutting data should only be applied when Ae is LESS THAN 50% f z Dc h m Ae = 50% 48/111

49 Average chip thickness Relationship between feed and average chip thickness. Radial cutting depth - Diameter of the cutter. Cutter positioning. Entering angle. 49/111

50 Average chip thickness f z f z a e Dc Dc h m a e h m Radial cutting depth Diameter of the cutter (a e /D c ratio) What is happening to the average chip thickness as Ae reduces? 50/111

51 Average chip thickness f z Which will have the higher feed rate? 51/111

52 Average chip thickness Formula to calculate f z for square shoulder milling: f z = h m D a e 2.5 = = = legend f z = feed per tooth h m = average chip thickness D = cutter diameter a e = radial width of cut example find the f z of a Turbo mill: h m = D = 2.5 a e = /111

53 Average chip thickness v f = 21.5 v f = 25.8 v f = 48.5 v f = 64.5 v f = % engagement 50% engagement 20% engagement 10% engagement 5% engagement 53/111

54 Description a e Width of cut a p Depth of cut ( v c ) SFPM (f z ) FPT (h m ) Average Chip (n) RPM (v f ) Feed Rate IPM Slotting 100% Engagement Profiling 50% Engagement Profiling 20% Engagement Profiling 10% Engagement Profiling 5% Engagement /111

55 Average chip thickness a e Caution! 55/111

56 Average chip thickness Caution! 56/111

57 Average chip thickness a e Caution! 57/111

58 Average chip thickness 90deg 45deg h : 100% h : 70% f z : 100% f z : 100% 58/111

59 Average chip thickness h = f z x sin (ҳ ) 59/111

60 Average chip thickness Formula to calculate f z for face milling: D f = h z m a e 1 sinκ x x 1.41 = legend f z = feed per tooth h m = average chip thickness D = cutter diameter a e = radial width of cut κ = setting angle example find the f z of a Octomill face mill: h m = D = 4 a e = 0.8 κ = 43 o 60/111

61 Average chip thickness Relationship between feed and average chip thickness. Radial cutting depth - Diameter of the cutter. Small a e /D c gives larger feeds. Cutter positioning. Single sided cutting gives larger feeds. Entering angle. Smaller angle of engagement gives larger feeds. 61/111

62 Average chip thickness Feed and average chip thickness Average chip thickness. If too large broken inserts. If too small extra wear. 62/111

63 Average chip thickness For 90 lead angle cutters only 63/111

64 Average chip thickness 64/111

65 Cutting edge geometry 65/111

66 . Cutting edge geometry Difficult machining strong edges D MD SE.. AFTN -MD15 SE.. AFTN -D16 M SE.. AFTN -M14 SE.. AFTN -M15 SE.. AFTN -M16 Easy machining sharp edges ME E SE.. AFN -E07 SE.. AFTN -ME10 SE.. AFN -E12 SE.. AFTN -ME13 SE.. AFTN -ME decreasing chip thickness increasing 66/111

67 Cutting edge geometry The vertical axis specifies the degree of difficulty in the machining operation (i.e. E = Easy, M = Medium etc.) The horizontal axis denotes the application range. The numbers indicate the average chip thickness in mm, 10 meaning 0.1mm or meaning 0.13mm or etc. XOMX TR-ME13 F40M 67/111

68 Cutting edge geometry -ME06 example ME06 geometry is for medium easy machining operations h m should be kept at 0.06mm (0.002 ) under normal conditions and for average material (Seco material group 3-5) 68/111

69 Cutting edge geometry -M10 example M10 geometry is for medium machining operations h m should be kept at 0.10mm (0.004 )under normal conditions and for average material (Seco material group 3-5) 69/111

70 Cutting edge geometry To maintain maximum tool life, it is crucial to exceed or at least equal the edge protection chamfer. Cutting speed can also be increased in side milling operations thereby optimizing the application. 70/111

71 Milling methods 1. Peeling Method 2. High speed machining 3. High feed machining 4. Plunge milling 71/111

72 Peeling method Small radial cutting depth Deep cutting depth High cutting speed Spiral Cutter Roughing method which normally eliminates semi-finishing 72/111

73 Peeling method Ae=.060 Ap= MM B90A30-E05 Rpm=6630 Vf= 70 inch/min 73/111

74 High speed machining Small cutting depth Small radial cutting depth Small average chip thickness High cutting speed Sharp cutting edges in hard grades 74/111

75 High feed milling Small cutting depth Very high feed per tooth High cutting speed Good method in hardened steel and difficult material Roughing method which normally reduces the cutting depth for semi-finishing 75/111

76 High feed milling Minimaster high feed insert R high feed cutter Jabro high feed cutter 76/111

77 Plunge Milling Method mostly for long overhang or weak machines Normal cutting speed Good method for difficult material like Inconel Roughing method which normally increase productivity 77/111

78 Plunge Milling Tool 1 Tool= R V= 524 sft/min Fz= per/tooth Side step = 3/8 Tool 2 Tool= L V=524 sft/min Fz= per/tooth Side step= ½ Tool 3 Tool= R V= 524 sft/min Fz= per/tooth Side step= ¼ then /111

79 Trochoidal Milling The Trochoidal method is a fast and productive method for slotting operations. D c Step over Width 79/111

80 Surface Finish Small radius corner insert Large radius corner insert Faceted corner insert Faceted insert plus Wiper insert 80/111

81 Surface Finish Axial run-out with a non adjusted cutter. Cassettes give a better surface finish when correctly adjusted. 81/111

82 Surface finish & tool life. Tool life Tool tolerances Measured with a reference insert Modern Classic Run - out influences The tool life. The surface finish. Machining noise level. Axial/radial run-out (Typical example ) 82/111

83 Milling insert clamping Common method uses a screw though the insert. The insert is clamped in the centre, screw head below insert! This system is commonly used for modern milling cutters. This system allows the use of modern chip face geometries. 83/111

84 Maintenance Always clean the insert seating before clamping a new insert in place. Always replace damaged anvils or the tool if the insert seating is damaged. Never use re-built (welded) tools. Replace damaged screws and keys. Lubricate moving parts regularly. Always use the correct keys (dynamometric keys). Always position the insert carefully before clamping it in place. Make sure the insert fits flush against the supports. If the insert is not positioned correctly, it will not be clamped properly (insert breakage). 84/111

85 Milling 85/111