Grinding with Superabrasives Tools - COMEGUI
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Grinding with Superabrasives Tools
Influences on grinding processes
workpiece material
grinding tool process
vR
dressing machine
lubricant
dressing tool vcc
cooling
environment
vfa
processing results
safety aspects
Design of diamond and CBN tools
relatively thin layer
attached to bodies made out of
aluminium
steel
resin
ceramic
composite materials
adhered by
glueing
sintering
shrinkage
electro plating
Contents of grinding layers
all sintered electro
bond types resin vitrified
bond types metal plated
abrasives
- natural dt.
- synthetic dt.
- CBN
filler
- SiC, TiC, B4C,
- Al2O3, SiO2 ,
- metals
- lubricants
Abrasives are a grinding tool best friends
Most
important
factor in
a layer
are ...
... the .
abrasives !
And not
the bond !
Lattice structures of graphite and boron nitride,
diamond and cubic boron nitride
HIGH
PRESSURE
–
HIGH
TEMPERATURE
SYNTHESIS
C - graphite C - diamond
BN - boron nitride cBN - cubic boron nitride
hexagonal lattice structure cubic lattice structure
How a High-Pressure - High-Temperature
Synthesis works ...
synthesis
parameters
diamonds:
ϑ ≈ 1.750 K
p ≈ 5,4 M Pa
ϑ t ≈ 4 .. 8 h
t preliminary
condition:
p p catalysators like
Fe, Ni, Co, Mn
in order to get
carbon out of
the graphite
Features of diamond and CBN crystals
To use abrasives at their best it is
necessary to know details about
grit size and mean distribution
grit shape
surface roughness
coating
inclusions
fracture strength
toughness index
heat diversion
International standardization of
grit sizes for diamond and CBN
International standardization of grit sizes for diamond and cubic boron nitrid
Nomenclature of sieved grit sizes fine grit sizes *)
DIAMOND CBN DIAMOND + CBN mesh width diamond CBN grit
FEPA - Standard FEPA - Standard US - Standard acc. ISO6106, marking marking size
narrow | wide narrow | wide narrow | wide 1DIN848-11 SGA SGA µm
grit sizes recommended
by SGA
*) similar to FEPA Standard
FEPA: Federation Europeenne
des Fabricants de
Produits Abrasifs
Mean distribution of grit sizes
As closer the size of crystals
per grit size is as better the
grinding result will be superfines, low quality
main
distribution
peak
fines coarse
tail tail on size, high quality
super over-
occurence
fines size
grit size oversize, low qualitycBN and diamond crystals
Mean distribution of grit sizes – example
Exemplary for grit size B151
superfines, low quality
B151
7 % < 127 µm 7% > 165 µm
0,5% < 90 µm 0,1% > 227 µm
on size, high quality
accumulation
main
super fines coarse over-
distribution
fines tail tail size
peak
grit size oversize, low quality
© Saint-Gobain 2007Geometrical shapes of
diamond and CBN crystals
octahedral tetrahedral
cubic
octo-
hedralSurface roughness of
diamond and CBN crystals
The surface roughness of diamond
or CBN grits is an indicator for
the retaining behaviour inside
the bond and/or the coating
the breakdown behaviour
the shaping of cutting edges
and the cutting behaviourCoatings for diamond and CBN crystals
tasks of coatings are
increase of mechanical clamping
heat diversion
coatings can be made out of
Ag – coating
Cr – spikes
Cu – coating
Ni – coating
Ni/P – coating
Ti – coating
glass – coating
guarantor for best use is the adaption of
bond
coating
grit shape
grit toughnessInclusions inside of
diamond and CBN crystals
moderate very little Inclusions
inclusions inclusions
may cause
the break-
down of
hardly abrasives
inclusions during a
little grinding
inclusions
process
very much much
inclusions inclusionsBreakdown behaviour of diamond and CBN crystals monocrystalline breakdown microcrystalline breakdown
Properties of abrasives
thermal conductivity
diamond 500 - 2.000 W / (mK)
CBN 200 - 700 W / (mK)
Cu 393 W / (mK)
X12 Cr Ni Mo 18 8 10 W / (mK)
hardness thermal stability
diamond 7.000 N/mm2 diamond 600 ... 700 °C
CBN 4.600 N/mm2 CBN > 1.000 °C
SiC 2.580 N/mm2 SiC 700 °C
Al2O3 2.000 N/mm2 Al2O3 2.050 °C
density modulus of elasticity
diamond 3,52 kg / dm3 diamond 890 kN / mm2
CBN 3,48 kg / dm3 CBN 590 kN / mm2
SiC 3,22 kg / dm3 SiC 470 kN / mm2
Al2O3 3,90 kg / dm3 Al2O3 390 kN / mm2Where to use CBN and diamonds
metals non metals
iron metals nonferrous metals inorganic organic
materials materials
unalloyed (soft) aluminium alloy ceramics rubber (soft)
low-alloyed (soft) copper alloy cermets rubber (hard)
high-alloyed (soft) magnesium based alloy ferrites plastics
nickel based alloy glass wood
low-alloyed (hard)
titanium alloy semi cond. mat.
high-alloyed (hard)
carbide stones
chilled cast iron
CBN DIAMONDContents of grinding layers
all sintered electro
resin vitrified
bond types metal plated
abrasives powder powder powder powder
- natural dt. - epoxy resin - Ag, Co, Cu, - vitreous frits - Ag salt
- synthetic dt. - melanin - Fe, Ni, Sn, - ceramics - Au salt
- CBN - phenolics - bronzes - metal oxyds - Co salt
- polyimides - etc. ... - nitrate - Cu salt
- waxes - Ni salt
filler liquids liquids liquids
- SiC, TiC, B4C, - epoxy resin -binder - acids
- Al2O3, SiO2 , - glues - leaches
- metals - phenolics - additives
- lubricantsBond systems for grinding wheels
resin sinter metal vitrified electro plated
• phenolic resin • bronze • basis silicate • chemical
• polyimide • brass - vitreous • electrolytical
- cristaline
• carbide
multiple resp. volume layer single layerTasks of bonds retaining of the abrasives, as long as grit edges are sharp abrasives releasing of the abrasives, after the grit edges become dull or flaten resistance against abrasion, to ensure a high profile accuracy warranty of „own“ wear, bond to get the necessary grit protrusion heat transfer, to avoid grit damages body good properties for easy profiling, to avoid needless secondary processing time
Knowledge about bond components
Bonds and their properties
will be influenced strongly by the
bronze powder (89:11) -- 50 µm --
structure
purity
surface copper powder -- 10 µm --
grit size
particle size distribution
of each single component silver powder -- 10 µm --You can also read
