Abrasive Cutting Technical Overview

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Introduction

The first step in preparing a specimen for metallographic or microstructural analysis is to locate the area of interest. Sectioning or cutting is the most common technique for obtaining this area. Proper sectioning has the following characteristics:

Desirable Effects:

• Flat and cut close to the area of interest
• Minimal microstructural damage

Undesirable Effects:

• Smeared (plastically deformed) metal
• Heat affected zones (burning during cutting)
• Excessive subsurface damage (cracking in ceramics)
• Damage to secondary phases (e.g., graphite flakes, nodules, or grain pull-out)

The goal of any cutting operation is to maximize the desirable effects, while minimizing the undesirable effects.

Sectioning can be categorized as either abrasive cutting and precision wafer cutting. Abrasive cutting is generally used for metal specimens and is accomplished with silicon carbide or alumina abrasives in either a resin or resin-rubber bond. Proper blade selection is required to minimize burning and heat generation during cutting, which degrades both the specimen surface as well as the abrasive blades cutting efficiency. Wafer cutting is achieved with very thin precision blades. The most common wafering blades are rim-pressed abrasive blades, in which the abrasive is located along the edge or rim of the blade. Precision wafering blades most commonly use diamond abrasives, however cubic boron nitride (CBN) is also used for cutting samples that react to dull diamond (e.g. high carbon, heat treated steels cut more effectively with CBN as compared to diamond). Wafer cutting is especially useful for cutting electronic materials, ceramics and minerals, bone, composites and even some metallic materials.

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Abrasive Blade Selection Guidelines

Selecting the correct abrasive blade depends on the design of the cut-off machine and, to a large extent, operator preference. Abrasive blades are generally characterized by their abrasive type, bond type, and hardness. Determining the correct blade depends on the material or metal hardness and whether it is ferrous or nonferrous. In practice, it often comes down to odor and blade life. Resin/rubber blades smell more because the rubber will burn slightly during cutting; however, resin/rubber blades do not wear as fast and therefore last longer. On the other hand, resin blades are more versatile and do not produce a burnt rubber odor, but they do break down faster. Resin blades also provide a modestly better cut because the cutting abrasive is continually renewed, producing a cleaner cut.

Note that the traditional "older" technology for producing abrasive blades resulted in very specialized resin/rubber blades. Finding the proper resin/rubber hardness, abrasive size, and blade thickness to match the sample properties and the cutting machine parameters required a lot of testing and experimentation. In the past, resin/rubber blades were more popular in the US market. However, in recent years, as resins have improved, there has been a trend towards resin bonded abrasives. Conversely, resin bonded blades have typically been more widely used in the European and Asian markets for quite some time.

Summary:

• Resin bonded blades - less smell, higher wear, less sample burning, more versatile
• Resin-rubber bonded blades - longer life, burnt rubber smell, more likely to burn the sample, more difficult to find the correct blade

Material	Composition	Recommended Blade	Blade Image
Soft non-ferrous metals (aluminum, brass, zinc, etc.)	Alumina/resin bonded	MAX-E
Hard non-ferrous metals (titanium, zirconium, etc.)	Silicon carbide/resin-rubber bond	MAX-C
Soft steels	Alumina/resin bonded	MAX-E
Hard and case hardened steels	Alumina/resin bonded	MAX-VHS
General purpose blade for steels and ferrous metals	Alumina/resin bonded	MAX-D
Universal thin resin/rubber blade	Alumina/resin-rubber bond	MAX-A
Industrial general purpose thin blade	Alumina/resin-rubber bond	MAX-I

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Abrasive Blade Thickness

Blade Thickness (inches)	10-inch	12-inch	14-inch	16-inch
MAX-A	0.039	0.055	0.063	0.090
MAX-C	0.059	0.078	0.078	0.100
MAX-D	0.059	0.078	0.078	0.100
MAX-E	0.059	0.078	0.078	0.100
MAX-I	0.059	0.078	0.078	0.100
MAX-VHS	0.075	0.078	0.098	0.100
DMAX	0.059	0.060	0.060	0.075

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Abrasive Blade Maximum Operating Speed (MOS)

Maximum Speed (rpm)	10-inch	12-inch	14-inch	16-inch
MAX-A	3820	3185	2730	2860
MAX-C	3440	3185	3460	2390
MAX-D	4585	3820	3275	3800
MAX-E	4500	3800	3200	3800
MAX-I	4500	3800	3200	3800
MAX-VHS	3055	2500	2220	1925
DMAX	6100	5000	4350	3800

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Abrasive Cutting Process Description

Abrasive sectioning has primarily been used for sectioning ductile materials. Examples include metals, plastics, polymer matrix composites, metal matrix composites, plastics, and rubbers. The proper selection of an abrasive blade requires an understanding of the relationship between the abrasive particle, abrasive bonding, and the specimen properties.

Abrasive Type

Today's high-performance abrasive blades use alumina or silicon carbide abrasives. Alumina is a moderately hard and relatively tough abrasive, making it ideal for cutting ferrous metals. Silicon carbide is a very hard abrasive that fractures and cleaves easily, making it a self-sharpening abrasive more commonly used for cutting nonferrous metals.

Bonding Material

The hardness and wear characteristics of the sample determine which resin system is best suited for abrasive cutting. In general, the optimum bonding material breaks down at the same rate as the abrasive dulls, exposing new abrasives for the most efficient and effective cutting operation.

Abrasive Cutter Speed

Variable speed saws allow the user to better control the abrasive cutting process by matching the cutting speed with the hardness of the blade to minimize damage while maximizing the cutting speed. Typically, softer metals are cut at slower speeds to reduce the cutting burr or smearing of the metal. Harder samples are cut at medium to high speeds to break down the wheel bond and expose new, sharp abrasives. Note that for hardened steels, the recommended cutting speed for the MAX-VHS blades is approximately 50% of the maximum MOS to prevent overheating and burning at the specimen surface.

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Recommended Abrasive Cutting Procedures

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Cutting Fluids

Lubrication and swarf removal during abrasive cutting and diamond wafer cutting are required in order to minimize damage to the specimen. For some older abrasive cutters, the proper cutting fluid can also have the added benefit of coating cast iron bases and the fixtures in order to reduce or eliminate corrosion.

TIP: Most abrasive cutters have a hood, which can produce a corrosive humidity chamber when not in use. In order to reduce these corrosive effects, keep the hood open when not in use.

Abrasive Cutting Fluid - The ideal cutting fluid for abrasive cutting is one that removes the cutting swarf and degraded abrasive blade material. It should have a relatively high flash point because of the sparks produced during abrasive sectioning.

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Abrasive Sectioning Troubleshooting

Symptom	Cause	Action
Chipped or broken blade	-Secure sample properly- -Reduce cutting force	-Secure sample properly -Reduce cutting force
Bluish burnt color on specimen	-Incorrect cutting fluid -Improper blade or excessive force	-Use proper cutting fluid -Consult applications guideline or use a blade with a softer resin

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Abrasive Blade Product Descriptions

Abrasive Blades (32 mm / 1.25-inch arbor) (Qty 10 per package)

Description	10-inch	12-inch	14-inch	16-inch
Soft non-ferrous materials (aluminum, brass, zinc, etc.)	MAX-E250	MAX-E300	MAX-E350	MAX-E400
Hard non-ferrous materials (titanium, zirconium, etc.)	MAX-C250	MAX-C300	MAX-C350	MAX-C400
Soft steels	MAX-E250	MAX-E300	MAX-E350	MAX-E400
Hard and case hardened steels	MAX-VHS250	MAX-VHS300	MAX-VHS350	MAX-VHS400
General steels and ferrous metals	MAX-D250T	MAX-D300	MAX-D350	MAX-D400
Universal Thin Blade	MAX-A250	MAX-A300	MAX-A350	MAX-A400
Industrial general purpose thin blade	MAX-I250	MAX-I300	MAX-I350	MAX-I400

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Abrasive Cutting Fluid

Description	Quantity	Part No.	Product
MAXCUT Cutting Fluid (32 oz)	32 oz	MAXCUT-1000-32
MAXCUT Cutting Fluid (1/2 gallon)	1/2 gallon	MAXCUT-1000-64
MAXCUT Cutting Fluid (1 gallon)	1 gallon	MAXCUT-1000-128
MAXCUT Cutting Fluid (5 gallons)	5 gallons	MAXCUT-1000-5G

Description	Quantity	Part No.	Product
MAXCUT 2 Cutting Fluid (with corrosion inhibitor) (32 oz)	32 oz	MAXCUT2-1000-32
MAXCUT 2 Cutting Fluid (with corrosion inhibitor) (1/2 gallon)	1/2 gallon	MAXCUT2-1000-64
MAXCUT 2 Cutting Fluid (with corrosion inhibitor) (1 gallon)	1 gallon	MAXCUT2-1000-128
MAXCUT 2 Cutting Fluid (with corrosion inhibitor) (5 gallons)	5 gallons	MAXCUT2-1000-5G

Description	Quantity	Part No.	Product
MAXCUT OL1000 Water Soluble Emulsion Cutting Fluid (32 oz)	32 oz	MAXCUT-OL-1000-32
MAXCUT OL1000 Water Soluble Emulsion Cutting Fluid (1/2 gallon)	1/2 gallon	MAXCUT-OL-1000-64
MAXCUT OL1000 Water Soluble Emulsion Cutting Fluid (1 gallon)	1 gallon	MAXCUT-OL-1000-128
MAXCUT OL1000 Water Soluble Emulsion Cutting Fluid (5 gallons)	5 gallons	MAXCUT-OL-1000-5G