Grinding

Question 1

when is abrasive machining used

Answer 1

final finishing of materials also reduces the thickness of work piece

Question 2

what is abrasive machining

Answer 2

Material removal by action of hard, abrasive particles usually in the form of a bonded whee

Question 3

what is grinding

Answer 3

Material removal process in which abrasive particles are contained in a bonded grinding wheel that operates at very high surface speeds

Question 4

what does a grinding wheel consist of

Answer 4

1. Abrasive particles accomplish cutting
2. Bonding material holds particles in place
   and establishes shape and structure of
   wheel

Question 5

what is friability

Answer 5

ability to fracture when cutting edge dulls, so a new sharp edge is exposed

poor friability causes poor cutting and more heat (needing more cutting force)

Question 6

for soft material u can use ____ grain size

Answer 6

large

Question 7

for hard material u need ____ grain size

Answer 7

smaller

Question 8

large grit number meains ______ grain size

Answer 8

small (more number of grains per unit area, causing small grain size)

Question 9

what must the bonding material be able to do

Answer 9

• with stanf centrigual forces and high temp
• resist shatterinf during shock loading of wheel
• must hold material AND dislodge to expose new sharp grains

Question 10

what does wheel structure refer to

Answer 10

relative spacing of abrasive grains in whee

Question 11

Volumetric proportions of grains, bond
material, and pores can be expressed as:

Answer 11

Pg + Pb + Pp= 1.0
grains, bond, pores

Question 12

what does an open structure mean (Pp)

Answer 12

a lot of pores (pores used to remove the chip), but fewer grains
- high material removal rate

Question 13

what does a dense structure mean

Answer 13

less pores, but a lot of grains
- good surface finish
- low MRR

Question 14

soft wheels provide ______ surface finish

Answer 14

good (because they have good friability)

Question 15

whats the difference betweeen soft and hard wheels

Answer 15

• Soft wheels lose grains readily - used for
  low material removal rates and hard work
  materials
• Hard wheels retain grains - used for high
  stock removal rates and soft work materials

Question 16

how can u get a good surface energy

Answer 16

• Small grain sizes
• Higher wheel speeds
• Denser wheel structure = more grits per wheel area

Question 17

is specific energy in grinding high or low?

Answer 17

high
(10 times more than conventional machining)

Question 18

what are the rake angles in grinding

Answer 18

rake angle is negative ->needing more cutting force

Question 19

how to reduce grinding temperature

Answer 19

• Decrease infeed (depth of cut) d
• Reduce wheel speed v
• Reduce the number of active grits per square inch on the grinding wheel C
• Increase work speed vw
• Use a grinding fluid

Question 20

Forces must be kept below the …

Answer 20

holding strength of the grain in the bonding material

Question 21

What are the 3 causes of wheel wear

Answer 21

1. grain fracture - when a portion of the grain breaks off, but the rest remains bonded in the wheel
2. Attritious wear - dulling of individual grains, resulting in flat spots and rounded edges
3. Bond fracture - the individual grains are pulled out of the bonding material (bc grain becomes dull and cutting force becomes a lot)

Question 22

dressing the wheel is accomplished by…

Answer 22

rotating disk,
abrasive stick, or another grinding wheel
held against the wheel being dressed as it
rotates

Question 23

what is the purpose of dressing the wheel

Answer 23

• Break off dulled grits to expose new
  sharp grains
• Remove chips clogged in wheel
• Required when wheel is in third region of
  wear curve
  (doesn’t restore shape of wheel)

Question 24

what is truing the wheel

Answer 24

use of a diamond-pointed tool fed slowly
and precisely across the wheel as it rotates
(restores shape of wheel)

Question 25

to optimize surface finish

Answer 25

 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 hel

Question 26

to maximize the material removal rate

Answer 26

 Large grit size
 More open wheel structure
 Vitrified bond

Question 27

Does creep feed provide good surface finish and accuracy?

Answer 27

no

Question 28

what is honing

Answer 28

In honing a set of abrasive sticks is used to remove machining marks.

Question 29

deos honing provide good surface finish?

Answer 29

yes, resulting in higher number of grains

Question 30

what is lapping

Answer 30

Uses fluid suspension of very small abrasive particles between workpiece and lap (tool)

Question 31

what is superfinishing

Answer 31

Similar to honing - uses bonded abrasive stick pressed against surface and reciprocating motion, gives a much better surface finish

Question 32

what are the differences of superfinishing with honing

Answer 32

• Shorter strokes
• Higher frequencies
• Lower pressures between tool and surface
• Smaller grit sizes

Question 33

what is polishing and buffing used for

Answer 33

to improve the visual appearance of the workpiece

Question 34

how is polishing and buffing done

Answer 34

an abrasive is suspended in a compounf or wax and applied with a cloth/leather/felt

Question 35

purpose of cutting fluid in grinding

Answer 35

• washes away chips
• keeps wheel from becoming clogged
• controls dust
• reduces temperature

Question 36

Enviornmental concerns for grinding

Answer 36

the dmsll size of the grinding particles:
- Shorter strokes
- Higher frequencies
 Lower pressures between tool and surface
 Smaller grit sizes