Grinding Flashcards
week 12 (36 cards)
when is abrasive machining used
final finishing of materials also reduces the thickness of work piece
what is abrasive machining
Material removal by action of hard, abrasive particles usually in the form of a bonded whee
what is grinding
Material removal process in which abrasive particles are contained in a bonded grinding wheel that operates at very high surface speeds
what does a grinding wheel consist of
- Abrasive particles accomplish cutting
- Bonding material holds particles in place
and establishes shape and structure of
wheel
what is friability
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)
for soft material u can use ____ grain size
large
for hard material u need ____ grain size
smaller
large grit number meains ______ grain size
small (more number of grains per unit area, causing small grain size)
what must the bonding material be able to do
- with stanf centrigual forces and high temp
- resist shatterinf during shock loading of wheel
- must hold material AND dislodge to expose new sharp grains
what does wheel structure refer to
relative spacing of abrasive grains in whee
Volumetric proportions of grains, bond
material, and pores can be expressed as:
Pg + Pb + Pp= 1.0
grains, bond, pores
what does an open structure mean (Pp)
a lot of pores (pores used to remove the chip), but fewer grains
- high material removal rate
what does a dense structure mean
less pores, but a lot of grains
- good surface finish
- low MRR
soft wheels provide ______ surface finish
good (because they have good friability)
whats the difference betweeen soft and hard wheels
- 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
how can u get a good surface energy
- Small grain sizes
- Higher wheel speeds
- Denser wheel structure = more grits per wheel area
is specific energy in grinding high or low?
high
(10 times more than conventional machining)
what are the rake angles in grinding
rake angle is negative ->needing more cutting force
how to reduce grinding temperature
- 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
Forces must be kept below the …
holding strength of the grain in the bonding material
What are the 3 causes of wheel wear
- grain fracture - when a portion of the grain breaks off, but the rest remains bonded in the wheel
- Attritious wear - dulling of individual grains, resulting in flat spots and rounded edges
- Bond fracture - the individual grains are pulled out of the bonding material (bc grain becomes dull and cutting force becomes a lot)
dressing the wheel is accomplished by…
rotating disk,
abrasive stick, or another grinding wheel
held against the wheel being dressed as it
rotates
what is the purpose of dressing the wheel
- 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)
what is truing the wheel
use of a diamond-pointed tool fed slowly
and precisely across the wheel as it rotates
(restores shape of wheel)
