MET 33800 Manufacturing Processes Chapter 26 Abrasive Machining Processes Before you begin: Turn on the sound on your computer. There is audio to accompany this presentation. Materials Processing Chapters 11-13 Chapters 20-27 Chapters 15-17 Chapters 30-33 Chapter 26-2 ABRASIVE MACHINING Abrasive Machining Interaction of abrasive grits and workpiece at high speeds and shallow penetration. Chip Removal Process Chips are formed like other material removal processes. Chapter 26-3 1
ABRASIVE MACHINING Abrasive Categories: Free - Lapping, sand blasting. Coated - Mounted in resin on a belt. Bonded - Grinding wheel. Chapter 26-4 ABRASIVE MACHINING Unique aspects: Depth of cut small - 0.002 to 0.005 inch. Cutting edges very small. Several cutting edges can cut simultaneously. Very hard materials can be machined. Grinding wheels are self-sharpening. Chapter 26-5 ABRASIVE MACHINING Chapter 26-6 2
ABRASIVE MACHINING Chapter 26-7 GRINDING METHODS Abrasive Machining very rapid metal removal. Aggressive grinding with hard wheels. Results in residual stresses, surface cracking, over tempered martensite (steels). Conventional Grinding lower feed rates. Soft grinding wheels. Lower surface stress and no hardness change Snagging rough manual grinding Used for casting clean-up Crush Grinding form crushed into the grinding wheel during dressing. Chapter 26-8 ABRASIVES Natural Materials: Sand - free abrasive. Sandstone - 1 st abrasive wheels. Emery - mixture alumina and magnetite used in coated products. Corundum - aluminum oxide. Diamond - used as free abrasive, truing wheels, and on bonded wheels. Quartz Sand - coated and free abrasive. Garnets - off-color diamonds. Chapter 26-9 3
ABRASIVES Artificial Materials: Diamonds - used to grind carbide and ceramics (superabrasive). Silicon Carbide (SiC) - very hard and friable, used for brittle materials (ceramics) and low strength materials (aluminum, brass, copper, bronze). (continued on next slide) Chapter 26-10 ABRASIVES Artificial Materials (continued): Aluminum oxide (Al 2 O 3 ) - softer than SiC but better general purpose abrasive, used for hard high-strength materials (tool steels). Cubic boron nitride (CBN) - 2 nd hardest substance (superabrasive), used for hard high-strength materials (tool steels, die steel, stainless). Chapter 26-11 ABRASIVE CHARACTERISTICS Hardness: ability to resist penetration measured by Knoop hardness (kg/mm 2 ). Chapter 26-12 4
ABRASIVE CHARACTERISTICS Attrition: abrasive wear action of grits resulting in dull edges. Friability: fracture of grits to expose new edges. Chapter 26-13 ABRASIVE CHARACTERISTICS Grain Size: based on #openings/in 2 grain can pass through: Coarse: 4 24 Medium: 30 60 Fine: 70 600 (240 600 known as flour sizes) Chapter 26-14 ABRASIVE CHARACTERISTICS CBN Diamond Chapter 26-15 5
ABRASIVE CHARACTERISTICS Grain Size: Affects MRR and surface finish. Chapter 26-16 ABRASIVE CHARACTERISTICS Grain Shape: determines tool geometry. Cutting: 95-98% of heat goes into chip. Plowing: large negative rake angles, high percentage of heat goes into work. Rubbing: rounded edges, high percentage of heat goes into work. Chapter 26-17 ABRASIVE CHARACTERISTICS Chapter 26-18 6
ABRASIVE CHARACTERISTICS Chapter 26-19 ABRASIVE CHARACTERISTICS Chapter 26-20 GRINDING WHEELS Structure - spacing of abrasive: Close structure - densely packed, little room for chips, more cutting edges. Open structure - widely spaced, larger chip cavities, fewer cutting edges. Chapter 26-21 7
GRINDING WHEELS Chapter 26-22 GRINDING WHEELS Grade: how strongly grits are held in wheel: Hard - dislodging force high. Soft - dislodging force low. Grinding Ratio (G Ratio): in 3 stock removed : in 3 wheel lost typically 20:1 to 80:1 Chapter 26-23 GRINDING WHEELS Bonding Materials: Vitrified (clays & ceramics): porous, strong, and rigid. Resinoid or Phenolic Resins (plastics): some flexibility. Silicate (waterglass): brittle, soft. Shellac: thin wheels with some elasticity. Rubber: high speed with flexibility: Electroplating: superabrasives plated or impregnated on steel blank. Chapter 26-24 8
GRINDING WHEEL IDENTIFICATION Chapter 26-25 GRINDING WHEEL IDENTIFICATION Chapter 26-26 GRINDING WHEELS Wheel Geometry Chapter 26-27 9
GRINDING WHEELS Wheel Geometry Chapter 26-28 GRINDING WHEELS Dressing and Truing: cleans wheel and trues shape. Chapter 26-29 GRINDING WHEELS Dressing attachments incorporating a template can generate a shape which mirrors desired part profile. Chapter 26-30 10
GRINDING WHEELS Crush Dressing: form crushed into grinding wheel. Chapter 26-31 GRINDING WHEELS Crush Dressing Chapter 26-32 GRINDING SAFETY Accident causes: Wrong speed: grinding wheels are speed rated. Cracked wheels: fracture. Grinding on side of wheel: some wheels are rated for side grinding. Improper or removed guarding. Results: Fragments leaving the wheel at high speed or the wheel disintegrating much like a hand grenade. Chapter 26-33 11
CUTTING FLUIDS Used for same reasons as other chip removal processes: Coolant, Lubricity Chip removal. Chapter 26-34 SURFACE FINISH Non-Abrasive Processes Chapter 26-35 SURFACE FINISH Abrasive Processes Chapter 26-36 12
GRINDING MACHINES Chapter 26-37 CYLINDRICAL GRINDING Chapter 26-38 CYLINDRICAL GRINDING Chapter 26-39 13
CYLINDRICAL GRINDING 1. Cylindrical between centers Wheel and work revolve in opposite directions: Plain Center-Type cylindrical shapes only. Universal wheel can be rotated. Dead Centers Used to increase accuracy compared to live centers. Chapter 26-40 CYLINDRICAL GRINDING Chapter 26-41 CYLINDRICAL GRINDING Chapter 26-42 14
CYLINDRICAL GRINDING 2. Cylindrical chucking type: both internal and external surfaces. Chapter 26-43 CYLINDRICAL GRINDING Chapter 26-44 CYLINDRICAL I.D. GRINDING Chapter 26-45 15
CYLINDRICAL GRINDING 3. Cylindrical Centerless: Grinding wheel - larger, uses usual wheel speed Regulating wheel - rubber coated, angled, lower speed. Work-rest - blade to support work. Internal grinding possible. Chapter 26-46 CYLINDRICAL GRINDING 3. Cylindrical Centerless: Through-feed - workpiece is fed through the grinding wheels completely, entering on one side and exiting on the opposite. End-feed - workpiece is fed into the machine, comes to rest against a stop and then the workpiece is fed in the opposite direction to exit the machine In-feed - used to grind workpieces with relatively complex shapes. Workpiece is loaded manually into the grinding machine and the regulating wheel moved into place. Chapter 26-47 CYLINDRICAL GRINDING Chapter 26-48 16
CYLINDRICAL GRINDING Chapter 26-49 CYLINDRICAL GRINDING Chapter 26-50 CYLINDRICAL GRINDING Chapter 26-51 17
CYLINDRICAL GRINDING 4. Tool post grinders Lathe attachment. Mounts on the tool post. Chapter 26-52 SURFACE GRINDING 5. Surface Grinding: Horizontal spindle/reciprocating table. Vertical spindle/reciprocating table. Horizontal spindle/rotary table. Vertical spindle/rotary table. Chapter 26-53 SURFACE GRINDING Chapter 26-54 18
SURFACE GRINDING Horizontal Spindle/Reciprocating Chapter 26-55 SURFACE GRINDING Horizontal Spindle/Rotary Table Chapter 26-56 SURFACE GRINDING Vertical Spindle/Rotary Table Chapter 26-57 19
SURFACE GRINDING 227" Blanchard Grinder Largest in the nation with 80" height capacity, vacuum chuck, 400 HP, AC, main spindle motor and 200" table. Chapter 26-58 CREEP FEED GRINDING 6. Creep feed grinding - Single pass, very slow feed and large depth of cut. Frequently used with profile grinding operations. Chapter 26-59 CREEP FEED GRINDING Chapter 26-60 20
CREEP FEED GRINDING CDCF Continuous Dress Creep Feed Chapter 26-61 TOOL GRINDING 7. Tool grinding: special machines, universal tool and cutter grinders. Chapter 26-62 OTHER PROCESSES 8. Off-hand grinding: bench and pedestal grinders. Chapter 26-63 21
OTHER PROCESSES 9. Disk grinders: two large wheels, grinding on two surfaces Chapter 26-64 OTHER PROCESSES 10. Jig grinders: high precision, vertical spindle machines. Similar application to jig bores. Chapter 26-65 OTHER PROCESSES 11. Hand grinders: Electric or pneumatic. Deburring and mold work. Mounted wheels and points. Chapter 26-66 22
OTHER PROCESSES 12. Gear Grinding: Chapter 26-67 OTHER PROCESSES 13. Thread Grinding: Chapter 26-68 OTHER PROCESSES 14. Profile Cylindrical Grinding Chapter 26-69 23
COATED ABRASIVES Abrasive glued to cloth or backing paper. Available in sheets, rolls, endless belts, disks. Chapter 26-70 COATED ABRASIVES Chapter 26-71 COATED ABRASIVES Chapter 26-72 24
HONING PROCESS Fine abrasive stones. Very small amount of material removed. Used for truing, sizing and lay patterns. Chapter 26-73 HONING PROCESS Chapter 26-74 HONING PROCESS Chapter 26-75 25
HONING MACHINES Chapter 26-76 HONING MACHINES Chapter 26-77 FREE ABRASIVE PROCESSES Lapping: Free particles (diamond) allowed to become embedded in softer material that is used to remove very small amounts of stock from workpiece. Chapter 26-78 26
LAPPING MACHINES Chapter 26-79 FREE ABRASIVE PROCESSES Processes Ultrasonic Machining uses abrasive slurry or bonded abrasives with ultrasonic vibrations. Waterjet Cutting/Hydrodynamic Machining highvelocity jet (3000 ft/sec) at high pressure (60,000 psi) Abrasive Waterjet Cutting addition of abrasives. Abrasive Jet Machining inert gas rather than water. Abrasive Flow Machining semisolid liquid or gel with abrasives for finishing. Chapter 26-80 FREE ABRASIVE PROCESSES Chapter 26-81 27
ULTRASONIC: FREE ABRASIVE Chapter 26-82 ULTRASONIC: BONDED ABRASIVE Ultrasonic Machining - Tooling Chapter 26-83 ULTRASONIC: BONDED ABRASIVE Ultrasonic Machining Chapter 26-84 28
ULTRASONIC: BONDED ABRASIVE Ultrasonic Machining Example Parts Chapter 26-85 ULTRASONIC: BONDED ABRASIVE Ultrasonic Machining Example Parts Chapter 26-86 WATERJET PROCESS Chapter 26-87 29
WATERJET PROCESS Chapter 26-88 ABRASIVE WATERJET Abrasive Waterjet: Multi-point cutting or erosion as material removal process. Chapter 26-89 ABRASIVE WATERJET Abrasive Waterjet Cutting Chapter 26-90 30
ABRASIVE WATERJET Waterjet Cutting Chapter 26-91 ABRASIVE WATERJET Waterjet Cutting Chapter 26-92 ABRASIVE WATERJET Chapter 26-93 31
ABRASIVE JET MACHINING Abrasive Jet Machining Uses inert gas rather than water as medium for abrasive. Chapter 26-94 ABRASIVE FLOW Chapter 26-95 The End See Oncourse for Videos Chapter 26-96 32