Educational Section

Table of Contents

Diamond Blade Basics
Diamond Tools & Technology
Factors that Affect Cutting Performance
Diamonds - Key to Successful Cutting
Cutting Depth Chart
Operating Speed Chart
Do's and Dont's

Diamonds - Key to Successful Cutting

Diamond crystals can be grown in a wide range of sizes. The size of the diamond crystals used in a cutting tool determines the amount of diamond exposed above the tool's cutting surface. The exposure, or height, of diamond protrusion influences the depth of cut of each crystal, and subsequently, the material removal rate for the cutting tool. Larger crystals and greater diamond protrusion will result in a potentially faster material removal rate.
In general, larger crystals are used for cutting softer materials and smaller crystals are used for harder materials.

The mesh size of the diamond also determines the number of crystals per carat. As the mesh increases, the pieces per carat increase. Mesh size is a measure of the size of a diamond; larger diamonds have smaller mesh numbers. This is similar to grit size in sand paper. The larger the grit numbers the smaller the size of the abrasive particle.

Selection of the mesh size is critical for tool performance since the number of crystals on the surface of a cutting tool affects the tool's life and power requirements. For instance, changing to a finer mesh size to increase the number of crystals on the cutting edge of a low concentration tool generally increases tool life and power requirements.

In addition to the crystal size, the concentration of diamond used in the cutting segment also determines the number of crystals on the cutting surface. Mesh size and concentration must be balanced for the best performance. Concentration is a measure of the number of diamond particles in a cubic inch of segment and is measured in one of two ways: 100 con = 72 carats/cubic inch or 125 con = 75 carats/cubic inch. The two methods of measurement for diamond concentration were established years ago in Europe and the United States. No single measurement standard has ever been agreed upon by the industry.

Shape

Diamond crystal shapes can vary from the well-structured crystals to partially-grown, irregular shapes to fragments. When crystals grow together in clusters they are called polycrystalline agglomerates.

A definite relationship exists between the shape and performance of the diamond crystal. A high proportion of irregularly shaped, angular crystals are desirable for less severe applications.
As the shape of the crystals becomes blockier, the diamond product becomes more suited for applications of greater severity.

Experience has shown the optimum diamond product for applications with severe crystal loads is one that contains predominantly block-shaped crystals. This shape offers the greatest resistance to fracturing with a maximum number of points or edges and a minimum surface contact. The result is lower machine power requirements and longer tool life. The ideal diamond shape for sawing and drilling applications is a shape called ''cubo-octahedron."

Inclusions

Inclusions are foreign material trapped in the diamond crystal during its growth. They can vary by type and amount, by location, and distribution throughout the crystal. Inclusions can be either metallic or nonmetallic. They affect the performance of a diamond product by influencing how the crystals break down.
The cutting process is dynamic. The crystal loading fluctuates significantly from high-energy impact to a varying continuous load even within a single cut. Severity of the cutting application determines the amount and type of loading on the crystal. The inclusions within the crystal are an important factor in determining how the crystal withstands the loading.

Impact Strength

The impact strength of a diamond product is a measure of the ability of the population of crystals to withstand impact loads. The impact strength is influenced by crystal shape, size, inclusions, and the distribution of these crystal properties within the population.
Factors that must be considered in selecting a diamond product include the tool's design, properties of the bond and of the work piece material, available machine power, removal rates, and the economics of the system. Selecting the right grade of diamond will lead to the best performance at minimum cost
Generally, the tougher the material being cut, the greater the impact strength required from the diamond product Studies also indicate that there is a minimum impact strength needed for a given application. Using a diamond product with impact characteristics above the minimum required for the application may not significantly improve tool performance. As the severity of the application increases, the minimum impact strength requirement for the diamond product increases. A measure of the impact strength of diamond is known as the Toughness Index (TI).
Impact loading is not the only loading considered for selection of a grade of diamond. Diamond crystals are also subjected to very high temperatures during the cutting process. The measure of a diamond crystal to withstand thermal cycling is known as the Thermal Toughness Index (TTI). This index is determined by measuring the toughness of a sample of diamond crystals, subjecting them to a high temperature, then allowing them to return to ambient temperature and measure the change in toughness.

Bond Characteristics

Diamond does not act alone, but in combination with its bond system. This system plays several important roles in the performance of the tool:

• Disperses and supports the diamond
• Provides controlled wear while allowing crystal protrusion
• Prevents crystal pull-out
• Acts as a heat sink
• Distributes impact and load as the diamond attacks the work piece

Optimum performance of a diamond tool is achieved through the proper choice of diamond grade, bond system, and machine parameters. Low temperature bonds (less than 900° C, 1652° F) preserve diamond crystal properties best. Such bonds are usually made from cobalt, nickel iron, bronze or a combination of these metals.