GRINDING AND OTHER ABRASIVE PROCESSES SME Video – Machining Processes Basics Of Grinding (vts_22) Grinding Related Abrasive Process In-class Assignment ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Abrasive Machining Material removal hard, abrasive particles bonded wheel Finishing operations Grinding Honing 0.025 m (1 -in) finish Close tolerances ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Honing Engine Blocks ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

The Grinding Wheel Balanced wheels Bonding material with abrasive particles Grain size Wheel grade Wheel structure High hardness Wear resistance Toughness Friability ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Abrasive Materials Aluminum oxide (Al2O3) Application for steel Silicon carbide (SiC) ‑ harder than Al2O3 Application for aluminum and brass Cubic boron nitride (CBN) – very expensive Application for hardened tool steels Diamond – harder, very expensive Occur naturally and also made synthetically Application for ceramics and glass ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Grain Size and Bonding Material Small grit sizes produce better finishes Larger grit sizes for high material removal Harder work materials require small grains Bonding material Centrifugal forces High temperatures Resist shattering during shock loading Hold abrasive grains rigidly Allow worn grains to be dislodged ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Wheel Structure Grinding wheel Open structure Pp is relatively large Pg is relatively small Dense structure Pp is relatively small Pg is larger Pg + Pb + Pp = 1 ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Wheel Grade Indicates bond strength in retaining abrasive Depends on amount of bonding material Wheel structure (Pb) “Soft” wheels lose grains readily Low material removal rates and hard work Hard wheels retain grains High stock removal rates and soft work Abrasive type, grit size, grade, structure, bond Example: A-46-H-6-V ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Standard Grinding Wheel Shapes straight recessed two sides metal wheel frame cutoff wheel cylinder wheel straight cup wheel flaring cup wheel ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Grain Actions in Grinding Cutting Plowing Rubbing ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Grinding Equations v=DN v=surface speed of wheel D=wheel diameter N=spindle speed lc= (Dd)0.5 lc=length of chip d=depth of cut RMR = vwwd RMR=material removal rate vw=speed of work w=width or crossfeed nc=vwC nc=number of chips formed per unit time C=number of grits per unit area v=speed of wheel U=Fcv/RMR U=specific energy Fc=cutting force ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

In-class Example In a surface grinding operation the wheel diameter = 150 mm and the infeed = 0.07 mm. The wheel speed = 1450 m/min, work speed = 0.25 m/s, and the cross‑feed = 5 mm. The number of active grits per area of wheel surface = 0.75 grits/mm2. Determine (a) average length per chip, (b) metal removal rate, and (c) number of chips formed per unit time for the portion of the operation when the wheel is engaged in the work. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

SME Video ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

In-class Assignment The following conditions and settings are used in a certain surface grinding operation: wheel diameter = 6.0 in, infeed = 0.003 in, wheel speed = 4750 ft/min, work speed = 50 ft/min, and cross‑feed = 0.20 in. The number of active grits per square inch of wheel surface = 500. Determine (a) the average length per chip, (b) the metal removal rate, and (c) the number of chips formed per unit time for the portion of the operation when the wheel is engaged in the work. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Extra Credit – hand in before test 3 An 8‑in diameter grinding wheel, 1.0 in wide, is used in a certain surface grinding job performed on a flat piece of heat‑treated 4340 steel. The wheel is rotating to achieve a surface speed of 5000 ft/min, with a depth of cut (infeed) = 0.002 in per pass and a cross‑feed = 0.15 in. The reciprocating speed of the work is 20 ft/min, and the operation is performed dry. (a) What is the length of contact between the wheel and the work? (b) What is the volume rate of metal removed? (c) If there are 300 active grits/in2 of wheel surface, estimate the number of chips formed per unit time. (d) What is the average volume per chip? (e) If the tangential cutting force on the workpiece = 10 lbs, what is the specific energy calculated for this job? ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Additive Manufacturing ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Time Permitting Content ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Temperatures at Work Surface Grinding is characterized by high temperatures and high friction Energy remains in the ground surface Resulting in high work surface temperatures Damaging effects include: Surface burns and cracks Metallurgical damage immediately beneath the surface Softening of the work surface if heat treated Residual stresses in the work surface ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

How to Reduce Grinding Temperatures Decrease infeed (depth of cut) d Reduce wheel speed v Reduce number of active grits per square inch on the grinding wheel C Increase work speed vw Use a grinding fluid ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Causes of Wheel Wear Grain fracture Portion of grain breaks off Attritious wear Dulling of individual grains Bond fracture Grains pulled out of bonding material Dressing - accomplished by rotating disk Break off dulled grits to expose new ones Remove chips clogged in wheel ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Truing the Wheel Truing - use of a diamond‑pointed tool fed slowly and precisely across wheel as it rotates Very light depth is taken (0.025 mm or less) against the wheel Sharpens wheel Restores cylindrical shape and insures straightness across outside perimeter Dressing sharpens but does not guarantee the shape of the wheel ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Application Guidelines To optimize surface finish, select Small grit size and dense wheel structure Use higher wheel speeds (v) and lower work speeds (vw) Smaller depths of cut (d) and larger wheel diameters (D) will also help To maximize material removal rate, select Large grit size More open wheel structure Vitrified bond ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Application Guidelines For steel and most cast irons, use Aluminum oxide as the abrasive For most nonferrous metals, use Silicon carbide as the abrasive For hardened tool steels and certain aerospace alloys, use Cubic boron nitride as the abrasive For hard abrasive materials (e.g., ceramics, cemented carbides, and glass) use Diamond as the abrasive ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Application Guidelines For soft metals, use Large grit size and harder grade wheel For hard metals, use Small grit size and softer grade wheel ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Analysis of Grinding Grinding ratio and surface speed as a function of wheel speed Typical wear curve of a grinding wheel ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Four Types of Surface Grinding Type (a) grinder (most common grinder) (a) horizontal spindle with reciprocating worktable (b) horizontal spindle with rotating worktable (c) vertical spindle with reciprocating worktable (d) vertical spindle with rotating worktable ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Cylindrical Grinding External Internal (a) Traverse feed (b) Plunge cut ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

External centerless grinding Internal centerless grinding ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Creep Feed Grinding Conventional surface grinding Creep feed grinding ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Disc Grinding and Belt Grinding Disc grinder Abrasive belt grinder ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Honing Finish the bores of internal combustion engines Surface finishes of 0.12 m (5 -in) or better Cross‑hatched surface that retains lubrication (a) honing tool used for internal bore surface (b) cross‑hatched surface pattern ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Lapping and Superfinishing Lapping process in lens‑making Superfinishing on an external cylindrical surface ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e