By far the most widely used sectioning devices in metallographic laboratories
are abrasive cutoff machines. They range from small, thin-sectioning machines
employing abrasive or diamond-rimmed wheels approximately 4 inch in diameter
and a few mils thick to large floor-model machines employing abrasive or
diamond-rimmed wheels up to 12 inch in diameter and 1/16 inch thick. An advanced design of automatic cutoff machine for laboratory use employs abrasive wheels 6 to 12 inch in diameter.
Abrasive-wheel cutting may produce deformation damage to a depth as great as
0.04 inch. Deformation damage can be minimized by using thin cutoff wheels.
A hard wheel is usually best for cutting soft stocks, whereas a soft wheel
is preferred for cutting hard materials. A good general purpose cutoff wheel
is a medium-hard silicon carbide abrasive wheel.
All abrasive-wheel sectioning should be done wet. An ample flow of water or
water soluble oil coolant should be directed onto cut. Some laboratory
cutoff machines provide for submerged wet cutting. Wet cutting will produce
a smooth surface finish and, most important, will guard against excessive
surface damage cused by overheating.
Abrasive Blade Selection Guidelines Chart
Materials (alloys) |
Classification |
Abrasive/Bond |
Aluminum, brass, zinc, etc. |
Soft non-ferrous |
SiC/Rolled rubber |
Heat treated alloys |
Hard non-ferrous |
Alumina/Rubber resin |
< Rc 45 steel |
Soft ferrous |
Alumina/Rubber resin |
> Rc 45 steel |
Hard ferrous |
Alumina/Rubber resin |
Superalloys |
High Ni-Cr alloys |
SiC/Rolled rubber
|
Diamond Wafer Blade Selection Guidelines
Material |
Characteristic |
Speed (rpm) |
Load (grams) |
Blade (grit/conc.) |
Silicon substrate |
soft/brittle |
< 300 |
< 100 |
Fine/low |
Gallium arsenide |
soft/brittle |
< 200 |
< 100 |
Fine/low |
Boron composites |
very brittle |
500 |
250 |
Fine/low |
Ceramic fiber composites |
very brittle |
500 |
250 |
Fine/low |