Abrasive Cutting

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

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