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Week 1 mill 1


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Week 1 mill 1

  1. 1. Milling Processes
  2. 2. ObjectivesThe students are able to identify: Various Types of Milling Machine & Layout Industrial Applications Milling Tools Operation Factors - Speed, Feed, ... Milling Methods Planning & Setup Procedures Practices
  3. 3. Classification of Machining Processes
  4. 4. Milling Process Milling is a machining operation in which a workpiece is fed past a rotating cylindrical tool with multiple cutting edge. Multi-points cutting process Cutting Direction Chips are cut off by the Tooth rotating cutter Workpiece is fed in linear motion Milling Tool with one cutting edge is Cutter called fly-cutter (rarely used) Workpiece Feed Direction
  5. 5. Basic Milling Processes Two types of milling processes  Up milling or conventional milling process  Down milling or Climb milling process
  6. 6. Up Milling (Conventional Milling) The metal is removed in form of small chips The chip thickness is minimum at the start of the cut and maximum at the end. Cutting force varies from zero to the maximum value Advantages of Up Milling  It does not require backlash eliminator  It is safer in operation ( the cutter does not climb on the workpiece)  Loads on the teeth are acting gradually  Built-up-edge (BUE) fragments are absent from the machined surface  The cutter is not affected by the sandy surfaces of the workpiece Disadvantage of Up Milling  The tendency of cutting force to lift the work piece from the fixtures and  poor surface finish obtained
  7. 7. Up Cut FEED
  8. 8. Up Cut FEED
  9. 9. Up Cut FEED
  10. 10. Up Cut FEED
  11. 11. Up Cut FEED
  12. 12. Up Cut FEED
  13. 13. Up Cut FEED
  14. 14. Up Cut FEED
  15. 15. Up Cut FEED
  16. 16. Up Cut FEED
  17. 17. Up Cut FEED
  18. 18. Up Cut Cutter rotates in a direction opposite to the table feed CUTTER FEED
  19. 19. Down Milling (Climb Milling) A cutter rotating in the same directions of the feed of the workpiece. Chip thickness is maximum at the start of the cut and minimum in the end. There is less friction involved and consequently less heat is generated on the contact surface of the cutter and workpiece Advantages  Fixtures are simpler and less costly, as cutting forces are acting downward  Flat workpiece (that cannot be firmly held) can be machined by down-milling  Cutter with higher rake angles can be used, which decreases the power requirements  Tool blunting is less likely  Better surface finish  It is characterized by less tendencies of chattering and vibration
  20. 20. Down Cut FEED
  21. 21. Down Cut FEED
  22. 22. Down Cut FEED
  23. 23. Down Cut FEED
  24. 24. Down Cut FEED
  25. 25. Down Cut FEED
  26. 26. Down Cut FEED
  27. 27. Down Cut FEED
  28. 28. Down Cut FEED
  29. 29. Down Cut FEED
  30. 30. Down Cut FEED
  31. 31. Down Cut Cutter rotates in the same direction as the table feed FEED CUTTER
  32. 32. Up Cut Vs Down Cut Up Cutting  Down Cutting  Will not cause the  Better surface finishing table to a step  Not suitable for motion conventional machine  Recommended for  Suitable for CNC machine conventional or the machine equipped machine with BACKLASH ELIMINATOR
  33. 33. Types of Milling Cutters
  34. 34. Type of Milling Cutter
  35. 35. Type of Milling Operations Two basic type of milling operations  Peripheral milling (Plain Milling)  Axis of the tool is parallel to the surface being machined.  Face milling
  36. 36. Example of Peripheral Milling (a) Slab milling; (b) Slot Milling; (c) Side Milling (d) Straddle Milling (e) Form Milling
  37. 37. Peripheral Milling Direction of Cutter Rotation  Two form of milling  Up milling and down milling Up milling (Conventional milling): the direction of motion of the cutter teeth is opposite the feed direction when teeth cut into the workpiece.  It is milling “ against the feed” Down Milling (Climb Milling): the direction of cutter motion is the same as the feed direction when teeth cut into the workpiece.  It is milling “ with the feed”
  38. 38. Face Milling The axis of the cutter is perpendicular the surface being milled. Various forms of face milling  (a) Conventional face milling; (b) Partial face milling; (c) End Milling; (d) Profile Milling; (e) Pocket Milling; (f) surface contouring Milling
  39. 39. Milling Method• Plain Milling  End Milling  Cutter axis perpendicular to the – Cutter axis parallel to the machined surface machined surface  Peripheral & end cutting edges – Peripheral cutting edges  Vertical milling normally – Horizontal milling normally PLAIN MILLING END MILLING
  40. 40. Milling Machines  It has a horizontal spindle and well suited for performing the peripheral milling (e.g. slab milling, slotting milling, side milling and straddle milling)  It has a vertical spindle and well suited for performing the face milling (e.g. end milling, surface contouring milling)
  41. 41. Horizontal Milling Machine Spindle arbor rotates parallel to the table Machine table moves along the 3 axes - X,Y, & Z Cutter being used: x  Slab milling cutter y  Side & face cutter  Slitting saw z
  42. 42. Cutters for Horizontal Milling Machine SLITTING SAWSLAB MILLING CUTTER SIDE & FACE CUTTER
  43. 43. Vertical Milling Machine  Spindle rotates perpendicular to the table normally  Milling Head can be adjusted in different angle  Cutter being used :  End mill  Face milling cutter
  44. 44. Cutters for Vertical Milling Machine END MILL FACE MILLING CUTTER
  45. 45. Type of Milling Machines Special purposes milling machine
  46. 46. Knee and Column Milling Machine
  47. 47. Planer Type Milling Machine
  48. 48. Rotary Table Milling Machine
  49. 49. Surface Finishing Cylindrical marks are left on surface by end milling Parallel marks are left on surface by plain milling Roughness of milling is directly END MILLING proportional to the feed rate & depth of cut Finishing measurement (Roughness Value) in milling Ra = 6.3 ~ 0.8 m PLAIN MILLING
  50. 50. Tool Life Tool life is defined as the length of cutting time that the tool can be used. Operating the tool until final catastrophic failure is also defined as tool life. Taylor Tool Life Equation is expressed as VT n C Where, V cutting speed (m/min);T tool life (min); n and C are parameters whose values depend on feed, depth of cut, work materials, tooling and tool life criterion used. Milling cutter is a Multi-point cutting tool  Ground by special grinding machine  Precision cutting angles Cutter re-shape is very time consumable Tool life can be increased by  Correct spindle speed & feed rate  Apply cutting fluid  Correct cutting method
  51. 51. Tool Material High Speed Steel  An alloy of iron, chromium, nickel, cobalt & some molybdenum etc..  High resistance to wear, loss hardness at 600°C  Two basic types:  Tungsten –type (T-grades by AISI)  Molybdenum –type (M-grades by AISI) Carbide  Widely apply in modern industry  Suitable for very higher cutting speed, hard material, & high accuracy  Smooth surface Ceramic & Diamond cutting tool
  52. 52. Cutting Speed Cutting Speed of milling is defined by the movement of each cutting edge per minute (m/min) TOOL HIGH SPEED CARBIDE MATERIAL STEEL Cutting Cutting Feed Feed MATERIAL Speed Speed mm/Tooth mm/Tooth m / min. m / min. MILD STEEL 25 0.08 100 0.15 ALUMINUM 100 0.15 500 0.3 HARDEN STEEL 50 0.1
  53. 53. Machining Variables and Relationships Formula DN Cutting Speed V 1000 Feed rate F f r nt N Cutting Time T L/ F Material Removal Rate MRR Wc dF Power, hp (cutter) HP Cutter HPu MRR HP (actual)=HP (tare) + HP (actual)/EmCutting Speed,V m/min; Workpiece Diameter or tooldiameter, D mm,N rpm, F mm/min, f r mm/rev;nt number of cutter tee MRR th, mm3 /minL Piece Length Lead Length Pretraveland Overtravel Depth of cut d ; ;Length of Lead, for Face/end milling, l D (mm) 2for slab/slot milling, l R2 R d d D dHP(tare) horsepower(kW) to run machine (cutting air)Em Motor efficiency
  54. 54. Example An end mill is used to put a 25-mm slot with a depth of 5 mm in a cast iron block with a high- speed cutter. The block is 50 mm wide, 20 mm tall, and 100 mm long. The cutter, a high-speed cutter with a diameter of 25 mm, has four teeth. The pretravel and overtravel combine to a total length of 5 mm. The cut will be made at a feed rate of 0.130 mm/tooth and a cutting speed of 40 m/min. The unit kilowatt power is 0.005 kW/mm3/min, the tare horsepower is 75 kW and the motor efficiency is 80 %. Figure indicates the final shape to be produced. (1) What is the RPM used? (2) What is the length of the lead? (3) What is the cutting time? (4) What is the metal removal rate? (5) What is the power (kW) required at the cutter? (6) What is the motor horsepower requirements?
  55. 55. Sample Calculation Data Given Width of cut, Wc = 25 mm Depth of cut, d = 5 mm Diameter of cutter, D = 25 mm Number of teeth , nt = 4 Pretravel and Overtravel = 5 mm Feed , fr = 0.130 mm/tooth Unit horsepower, HPu = 0.005 kW/mm3/min Tare horsepower, Hptare = 75 kW Motor efficiency, Em= 80% = 0.8
  56. 56. (1) Cutting speed: DN 1000 V 1000 (40) V N 510 rpm 1000 D (25)(2) Length of Lead for end milling, l = D = 25 mm(3) Cutting time, T= L/F Length of Lead, L = Piece length+ Lead length + pretravel and Overtravel L = 100+25+5 = 130 mm Feed rate, F f r nt N 0.130 4 510 265 mm/min L 130 The cutting time, T 0.49 min F 265(4) Material removal rate: MRR Wc dF 25 5 265 33125 mm 3 /min(5) Power HP cutter HPu MRR 0.005 33125 mm 3 /min 155 kW(6) Motor power requirement HP ( Actual ) HP ( Tare ) HP cutter / Em 0.005 33125 mm 3 /min 75 kW 155 kW/0.8 268 .75 kW
  57. 57. Cutting Fluid Cooling the workpiece & the cutting tool  Maintain hardness of cutting tool Provide lubrication  Reduce fraction between workpiece & cutting tool Wash away the chips  Prolong tool life Soluble oil is widely use in our workshop  5 ~ 20 % soluble oil mixed with water
  58. 58. SAFETY Consult Staff Where are the Dangerous Points Familiar with the Controls Stop the Machine in Emergency Only One Man Operates One Machine Suitable & Safety Protection of Yourself Dont Leave the Machine when it is Running Dont Touch the Work while it is Running Dont Operate the Machine Without Staff Supervised
  59. 59. End