Milling cutters

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Transcript of Milling cutters

  • 1.MillingM.V.TADVI LECTURER MED SVNIT, SURAT1

2. Figure Typical parts and shapes produced by milling. 2 3. Milling Processes Milling is one of the basic machining processes. Milling is a very versatile process capable of producing simple two dimensional flat shapes to complex three dimensional interlaced surface configurations.3 4. The Process The milling process: Typically uses a multi-tooth cutter Work is fed into the rotating cutter Capable of high MRR Well suited for mass production applications Cutting tools for this process are called milling cutters4 5. Classifications Milling operations are classified into two major categories: Peripheral (side) Generally in a plane parallel to the axis of the cutter Cross section of the milled surface corresponds to the contour of the cutterFace Generally at right angles to the axis of rotation of the cutter Milled surface is flat and has no relationship to the contour of the cutter Combined cutting action of the side and face of5 milling the 6. Peripheral Millingmilling)(horizontal6 7. Face Milling (vertical milling)7 8. Up milling Milling is another basic machining process by which surface is generated progressively by the removal of chips from a work piece as it is fed a rotating cutterAlso called conventional milling, - Wheel rotation opposite of the feed - The chip formed by each cutter tooth starts out very thin and increases its thickness - The length of the chip is relatively longer - Tool life is relatively shorter - Need more clamping force to hold the work part still.8 9. Down milling: Also called climb milling, - Wheel rotation is parallel to the feed - The chip formed by each cutter tooth starts out thick and leaves out thin - The length of the chip is relatively short - Tool life is relatively longer - Need less clamping force to hold the work part still.9 10. Peripheral Milling The axis of the cutter rotation is parallel to the work piece surface to be machined in peripheral milling. Slab milling: Cutter width extends beyond the work piece on both sides Slotting (Slot milling): Cutter width is less than the work piece width, creating a slot. If the cutter is very thin, it can be used to cut a work part into two, called saw milling. Side milling: Cutter, machines the side of the work piece. Straddle milling: Similar to side milling, but cutting takes on both sides of the work part simultaneously.10 11. Milling Types11 12. Slab Milling (peripheral milling): process where axis of cutting tool is parallel to the workpiece surface to be machined -- used to create flat surfaces or slots -- cutter may have either straight or helical teeth12 13. Slab Milling tools13 14. Milling Cutter Types14 15. Face Milling The generated surface is at right angles to the cutter axis and is the combined result of actions of the portions of the teeth located on both periphery and the face of the cutter. Most of the cutting is done by the peripheral portions of the teeth, with the face portions providing some finishing actions. Conventional face milling: Diameter of tool is larger than work parts width. Partial face milling: The cutter overhangs from one side of work part . End milling: Cutters diameter is less than the work parts width.15 16. Continue... Profile milling: Outside periphery of flat part is cut. Pocket milling: Similar to end milling, but the shape created is a shallow pockets in flat surfaces Surface contouring: A ball-nose cutter is fed back and forth across the work part to create a contoured surface perpendicular to the cutter.16 17. Face millingPocket millingProfile millingEnd milling17 18. More Examples on Face Milling18 19. Face Milling tools19 20. Milling Cutters20 21. More Milling Cutters21 22. Milling Cutter Materials Cutter Characteristics Harder than metal being machined Strong enough to withstand cutting pressures Tough to resist shock resulting from contact Resist heat and abrasion of cutting Available in various sizes and shapes 22 23. Cutting Tool Material Choices Carbon and medium alloy steels High Speed Steels Cast-cobalt alloys Carbides (or cemented or sintered carbides) Coated tools Alumina based ceramics Cubic boron nitride Diamond23 24. Cutting Tool Material Choices: Carbon and medium alloy steels -- of historical importance; but limited to low speed operations High Speed Steels -- first produced in early 1900's, -- can be hardened to various depths, have toughness and good wear resistance, and are relatively inexpensive --molybdenum(M series): contains up to 10% molybdenum with chromium, vanadium, tungsten, and cobalt alloying elements. --tungsten(T series): contains 12 to 18% tungsten with chromium, vanadium, and cobalt alloying elements. --95% of these are M series because of better abrasion resistance, less heat distortion, and less expensive than T series. -- can be coated or heat treated or case hardened to improve performance. -- accounts for the largest tonnage of tool materials used today -- used for applications such as drills, reamers, taps, gear cutters -- use is limited by cutting speed and high temperatures.24 25. Cast-cobalt alloys -- cast alloy of cobalt, chromium, and tungsten. -- good wear resistance and hardness at higher temp. than HSS -- not very commonly used -- less tough than high speed steels but can handle faster speeds. Carbides (or cemented or sintered carbides) --usually made of tungsten carbide in a cobalt bonding matrix or titanium carbide in a nickel-molybdenum alloy matrix. --have high elastic modulus, thermal conductivity, and low thermal expansion. --usually manufactured as inserts to be clamped or brazed to the tool shank. 25 26. Coated tools --common coatings include titanium nitride, titanium carbide, titanium carbonitride, and aluminum oxide. -- improve characteristics such as lower friction, higher crack resistance, longer wear, chemical stability. -- applied by chemical vapor deposition methods. Alumina based ceramics -- fine-grained high purity aluminum oxide with other agents cold pressed and into insert shaped and sintered at high temperatures. -- very high abrasion resistance and hot hardness -- chemically stable and low adherence to workpiece material -- lack toughness and subject to failure by impact or thermal fatigue. -- cermets (also called black or hot-pressed ceramics), are 70% aluminum oxide and 30% titanium carbide are slightly more expensive than the alumina-based ceramics. 26 27. Cubic boron nitride -- second hardest material presently available -- made by bonding polycrystalline cubic boron nitride to a carbide substrate by sintering under pressure. -- shock resistance with high wear and cutting edge strength -- chemically inert to nickel and iron, and resistant to oxidation. -- is sensitive to thermal and fatigue failure Diamond -- hardest known substance -- low friction, high wear resistance, good edge maintenance -- more likely used as polycrystalline diamond form which is made of very small synthetic crystals fused at high temperature and pressure. -- due to chemical affinity, not recommended for steel, titanium, nickel or cobalt based alloys, but very good with soft non-ferrous 27 and abrasive nonmetallic materials. 28. High-Speed Steel Iron with additives Carbon: hardening agent Tungsten and Molybdenum: enable steel to retain hardness up to red heat Chromium: increases toughness and wear resistance Vanadium: increases tensile strength Used for most solid milling cutters 28 29. Cemented-Carbide Higher rates of production (3-10 times faster) Must select proper type of carbide Straight tungsten carbide: cast iron, plastics Tantalum carbide: low/medium-carbon steel Tungsten-titanium carbide: high-carbon steel29 30. Milling Cutters The tool used in milling is known as a milling cutter, the cutting edges called teeth. Types of milling cutters are related to the milling operations can be classified as: Plain milling cutters: - Used in peripheral milling operations - Cylindrical or disk shaped - Have several straight or helical teeth on periphery - Used to mill flat surfaces Side milling cutters: - Similar to plain milling cutters - Teeth extend radial part way across one or both ends of cylinder toward the center - Relatively narrow30 31. Plain Milling Cutters Once widely used Cylinder of high-speed steel with teeth cut on periphery Used to produce flat surface Several types Light-duty Light-duty helical Heavy-duty High-helix 31 32. Light-Duty Plain Milling Cutter Less than in. wide, straight teeth Used for light milling operations Those over in have helix angle of 25 Too many teeth to permit chip clearance32 33. Heavy-Duty Plain Milling Cutters Have fewer teeth than light-duty type Provide for better chip clearance Helix angle varies up to 45 Produces smoother surface because of shearing action and reduced chatter Less power required33 34. High-Helix Plain Milling Cutters Have helix angles from 45 to over 60 Suited to milling of wide and intermittent surfaces on contour and profile milling Sometimes shank-mounted with pilot on end and used for milling elongated slots 34 35. Standard Shank-Type Helical Milling Cutters Called arbor-type cutters Used for Milling forms from solid metal Removing inner sections from solids Inserted through previously drilled hole and supported at outer end with type A arbor support 35 36. Side Milling Cutters Comparatively narrow cylindrical milling cutters with teeth on each side and on periphery Used for cutting slots and for face and straddle milling operations Free cutting action at high speeds and feeds Suited for milling deep, narrow slots 36 37. Half-Side Milling Cutters Used when only one side of cutter required Also make with interlocking faces so two cutter may be placed side by side for slot milling Have considerable rake Able to take heavy cuts 37 38. Face Milling Cutters Generally over 6 in. in diameter Have inserted teeth made of high-speed steel held in place by wedging devi