1. 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

2. 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

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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

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

11. 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

12. 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

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

14. In-class Assignment
The following conditions and settings are used in a certain surface grinding operation: wheel diameter = 6.0 in, infeed = 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

15. 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) = 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

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

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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

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

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

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

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

31. 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

32. 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