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Manufacturing Rounded Shapes II

Manufacturing Rounded Shapes II. Manufacturing Processes. Outline. Specialized Turning Operations High-Speed Machining Ultraprecision Machining Hard Turning Cutting Screw Threads Knurling Boring and Boring Machines Drilling and Drills Reaming and Reamers Tapping and Taps

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Manufacturing Rounded Shapes II

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  1. ManufacturingRounded Shapes II Manufacturing Processes

  2. Outline • Specialized Turning Operations • High-Speed Machining • Ultraprecision Machining • Hard Turning • Cutting Screw Threads • Knurling • Boring and Boring Machines • Drilling and Drills • Reaming and Reamers • Tapping and Taps • Chip Collection

  3. High-Speed Machining Decreases cutting time by increasing cutting speed Approximate Range of Cutting Speeds: • High Speed: 2000-6000 ft/min • Very High Speed: 6000-60000 ft/min • Ultrahigh Speed: >60000 ft/min Decreases total energy required: - Power for high-speed machining ≈ .004 W/rpm • Power for normal machining ≈ .2-.4 W/rpm Most important when cutting time is a significant part of the manufacturing time

  4. High-Speed Machining Factors: • Stiffness of the machine tools • Stiffness of tool holders and workpiece holders • Proper spindle for high speeds and power • Sufficiently fast feed drives • Automation • A proper cutting tool for high cutting speeds • Ability to hold the piece in fixtures at high speed

  5. UltraprecisionMachining Used for very small surface finish tolerances in the range of .01 µm The depth of cut is in the range of nanometers Machine tools must be made with high stiffness

  6. UltraprecisionMachining Factors: • Stiffness, damping, and geometric accuracy of machine tools • Accurate linear and rotational motion control • Proper spindle technology • Thermal expansion of machine tools, compensation thereof, and control of the machine tool environment • Correct selection and application of cutting tools • Machining parameters • Performance and tool-condition monitoring in real time, and control thereof

  7. Hard Turning Used for relatively hard, brittle materials Produces parts with good dimensional accuracy, smooth surface finish, and surface integrity May be used as an alternative to grinding

  8. Hard TurningProcedure

  9. Hard TurningStatistics Heat dissipated by chips Tool forces: radial force is greatest

  10. Hard TurningChip Formation Brittle materials form segmented chips, which cause a large force against the cutting edge

  11. Hard Turning Advantages (as an alternative to grinding) • Lower cost of machine tools • Ability to machine complex parts in a single setup • Ability to create various part styles or small part numbers efficiently • Less industrial waste • Ability to cut without fluids (eliminates grinding sludge) • Easily automated

  12. Hard TurningSurface Finish NOYES A hard journal bearing surface should have a surface with deep valleys and low peaks

  13. Cutting Screw Threads Cutting threads on a lathe is slower than newer methods • Die-Head Chasers used to increase production rate of threading on a lathe • Solid Threading Dies used for cutting straight or tapered threads on the ends of pipes or tubing

  14. Cutting Screw Threads

  15. Cutting Screw Threads

  16. Die-Head Chasers and Solid Threading Dies Straight chaser cutting die (top) Circular chaser cutting die (bottom left) Solid threading die (bottom right)

  17. Screw Machine

  18. Screw Machine

  19. Cutting Screw Threads Design Considerations: • Threads should not be required to reach a shoulder • Avoid shallow blind tapped holes • Chamfer the ends of threaded sections to reduce burrs • Do not interrupt threaded sections with slots, holes etc. • Use standard thread tools and inserts as much as possible • The walls of the part should be thick enough to withstand clamping and cutting forces • Design the part so that cutting operations can be completed in a single setup

  20. Knurling Used to create a uniform roughness pattern on cylindrical surfaces Performed on parts where friction is desired (knobs, grip bars etc.) Types: • Angular Knurls create a pattern of diamond-shaped ridges • Straight Knurls create a pattern of straight longitudinal ridges

  21. Knurling Results

  22. Knurling Operation

  23. Boring andBoring Machines Boring produces circular internal profiles Small pieces can be bored on a lathe; boring mills are used for larger workpieces

  24. Boring Operation

  25. Boring Operation

  26. Boring andBoring Machines Design Considerations: • Avoid blind holes when possible • A higher ratio of the length to the bore diameter will cause more variations in dimensions because the boring bar will deflect more • Avoid interrupted internal surfaces

  27. Drilling and Drills Types of drill • Twist drill (most common) • Gun drill • Trepanner Pilot Holes Sometimes, when drilling large-diameter holes, it is necessary to drill a smaller hole first to guide the large drill

  28. Types of Drillsand Drilling Operations

  29. Drill Terminology

  30. Drill Point Angle Point Angle 118° Standard 135° Harder Materials stainless steel, titanium Minimizes burring 90° Softer Materials plastic

  31. Trepanners

  32. Drills and Drilling Deep Holes Complications may occur when drilling a hole longer than 3 times the drill diameter Problems • Chip removal • Coolant dispensing to the cutting edge • Tool deflection

  33. Drills and Drilling Small Holes Small drills .0059-.04 in Microdrilling .0001-.02 in

  34. Microdrills

  35. Pilot Holes

  36. Drills and Drilling Forces and Torque Thrust force: acts perpendicular to the axis of the hole; large forces can cause the drill to bend or break Torque: the torque acting to turn the drill These values are difficult to calculate

  37. Drill Feedand Speed V = πDN/12 V = cutting speed in ft/min; Velocity at which the drill edge moves along the workpiece surface D = diameter of the drill N = RPM of the drill Feeds for drills are listed as in/rev or m/rev. Multiply these by the RPM to obtain the feed in in/min or m/min. The feed cannot be controlled accurately on a drill press fed by hand.

  38. Drill Feedand Speed

  39. Drill Feedand Speed Example: Work Material: Aluminum Tool Material: High Speed Steel Drill Diameter: .5 in Recommended Cutting Speed: 200-300 ft/min (from table) N = 12V/πD N=12*(200-300)/(π*.5) =1528-2293 RPM Recommended Feed for aluminum, .5in = .006-.01 in/rev (from table) f = (.006-.01)*1528 RPM = 9.2-15.2 in/min

  40. Drilling MaterialRemoval Rate Material Removal Rate MRR = (πD2/4)f N D = drill diameter f = feed, in/rev or mm/rev N = RPM

  41. Drilling MaterialRemoval Rate Example: Drill Diameter: .5 in Feed: .006 in/rev RPM: 1528 RPM MRR = (πD2/4)f N = (π(.5)2/4).006*1528 = 1.8 in3/min

  42. Drilling Operation

  43. Reaming and Reamers Used to improve the dimensional accuracy or surface finish of an existing hole Types of reamers • Hand reamers • Rose reamers • Fluted reamers • Shell reamers • Expansion reamers • Adjustable reamers

  44. Types of Reamers

  45. Reamer Terminology

  46. Tapping and Taps Used to make internal threads in workpiece holes Types of taps • Tapered taps • Bottoming taps • Collapsible taps

  47. Tap Terminology

  48. Drilling, Reamingand Tapping Design Considerations: • Holes should be drilled on flat surfaces perpendicular to the hole axis to prevent drill deflection • Avoid interrupted hole surfaces • The bottoms of blind holes should match standard drill point angles • Avoid blind holes when possible; if large diameter holes are to be included, make a pre-existing hole in fabrication • Design the workpiece so as to minimize fixturing and repositioning during drilling • Provide extra hole depth for reaming or tapping blind or intersecting holes

  49. Summary Specialized cutting procedures exist for unusual materials and requirements Proper procedure, securing of the workpiece, and feeds and speeds must be considered to prevent damage and injuries

  50. T h e E n d

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