A diamond tool is a cutting tool with diamond grains spread randomly throughout a matrix of bonded hard material, such as metal, high temperature resin or ceramics. The diamond grains are exposed at the surface of the tool as the matrix wears away during use.[1] The diamonds used in these tools are synthetic or natural industrial diamond of different grain sizes and shapes. Diamond is especially suited to cut highly abrasive materials, such as ceramics, concrete and natural stone.
Metal matrices are silver soldered or brazed onto a backing plate or tool holder that fits different types of machines.
Metal matrix bonds are usually a sintered segment with diamond grit mixed into a metal powder, which is blended to get just the right alloy that will wear according to the use of the finished diamond tool. For metal-bonded diamond tools, the matrix bond is one of the prime factors when selecting which tool to use for cutting or grinding a specific material, depending on how hard, or abrasive, the material is. The bond used is what dictates the rate at which the metallic powders wear down and expose new diamond crystals at the surface to maintain what would be considered a abrasive surface.
Different bond strengths are achieved but the metallic powders chosen, (alloy mix) and how much heat and pressure are applied to the sintered segment.
Hard bonds are best for soft materials and soft bonds for hard materials. This may seem counterintuitive, but it is because particles of the material being cut or polished provide the wear medium the wears away the bond to expose the diamond grit. Diamond grit is usually not worn out but simply lost when the bond releases them. The more particles the more wear.
For example, when sawing hard materials, a diamond blade with a soft bond would be needed. This means the bonded metallic powders in the segments (teeth) of the diamond blade will wear fast enough to expose diamond crystals and to replace lost grit, exposing new diamond on the cutting edge allowing the tool to continue cutting efficiently. Inversely, to cut a soft abrasive material like asphalt or freshly poured "green" concrete, you would need to use a diamond blade with a hard bond so that the segments do not wear down prematurely releasing the diamond grit without doing enough cutting work, putting the blade to waste.
Resin matrix diamond tools are usually poured into molds with the diamond grains in suspension. The mold shape becomes the tool itself. After removal from the mold, the tools are bonded to a backer. Some have velcro applied to the back of the tool, allowing it to be attached to any hook and loop surface such as concrete grinders.
Diamond dressers consist of single-point or multipoint tools brazed to a steel shank and are used for trueing and dressing of grinding wheels. The tools come in several types, including: grit impregnated, blade type, crown type, and disc type. The advantages of multipoint over single point tools are:
Many diamond tools don’t cut like a knife or saw blade, instead they grind. They usually have segments, or teeth, welded to the “cutting” edge of the tool which contain exposed diamond crystals for grinding.
For example, with a diamond blade, the saw operator will push the blade through the material. The blade will begin to cut through the material and the material being cut will begin the wearing process of the diamond blade, at the rate of which the blade advances or the depth at which is being cut. The exposed diamonds will break into smaller pieces when cutting. Hard, dense materials will fracture the diamonds faster. As this happens, the material being cut also wears down the metal bond through abrasion. Highly abrasive materials will wear the bond faster, exposing new diamond crystals to continue cutting.
Polycrystalline diamond (PCD) is formed in a large High Temperature-High Pressure (HT-HP) press, as either a diamond wafer on a backing of carbide, or forming a 'vein' of diamond within a carbide wafer or rod.
Most wafers are polished to a mirror finish, then cut with an Electric Discharge Machine (EDM) into smaller workable segments that are then brazed onto the sawblade, reamer, drill or other tool. Often they are EDM machined and/or ground an additional time to expose the vein of diamond along the cutting edge. Today these tools are mostly used for machining of nonmetallic and nonferrous materials.
The grinding operation is combined with EDM for several reasons. For example, according to Modern Machine Shop, the combination allows a higher material removal rate and is therefore more cost effective. Also, the EDM process slightly affects the surface finish. Grinding is used on the affected zone to remove the affected area and provide a finer final surface. Along the same lines, Beijing Institute of Electro-Machining attributes a finer shaping and surface geometry to the combination of the two processes into one.
The process itself is accomplished by combining the two elements each individual process into one wheel. The diamond graphite wheel accomplishes the task of grinding while the graphite ring around the existing wheel serves as the EDM portion. However, since diamond is not a conductive material, the bonding in the PCD work piece must be ample enough to generate the conductivity necessary for the EDG process to work.
Diamond pastes are used for polishing materials that require a mirror finish. They are often used in metallurgical specimens, carbide dies, carbide seals, spectacle glass industry, and for polishing diamonds.
Diamond powder deposited through electroplating is used in the form of files (including nail files) or small grinding applications.
Single point diamond turning (SPDT) utilizes a solid, flawless diamond as the cutting edge. The single crystalline diamond can be natural or synthetic, and is sharpened to the desired dimensions by mechanical grinding and polishing. The cutting edge of most diamond tools is sharp to tens of nanometers, making it very effective for cutting non-ferrous materials to high resolution. SPDT is a very accurate machining process used to create finished aspherical and irregular optics without the need for further polishing after completion. The most accurate machine tool in the world, the LODTM at Lawrence Livermore National Labs, has a profile accuracy estimated at 23 nanometers, while most machines seek a roughness within that deviation.
PCD tools are used extensively in automotive and aerospace industries. They are ideal for speed (9000+ SFM) machining in tough and abrasive aluminum alloys, and high abrasion processes such as carbon fiber drilling, and ceramics. The diamond cutting edges make them last for extended periods before replacement is needed. High volume processes, tight tolerances, and highly abrasive processes are ideal for diamond tooling.
SPDT is used for optics, and for flat surfaces where both surface finish and irregularly high dimensional accuracy are required and when lapping would be uneconomical or impractical.
The grinding method is ideal for materials that do not cut but are ground: stone, cement, carbides are all difficult to process normally, often making a diamond abrasion method necessary.
Uses
In medicine, the Venezuelan scientist Humberto Fernandez Moran invented the diamond scalpel for applications in delicate surgeries. In industry, they are commonly used for cutting a wide variety of very hard construction materials, including reinforced and cured concrete, all types of brick and cinder blocks, dense metals, rebar, asphalt, granite, marble, travertine, porcelain, and many other materials which cannot be cut with ordinary cutting tools.
Diamonds should not be used for cutting steel or iron, as carbon will dissolve into the workpiece and lead to tool wear and work hardening. Three other materials are better than diamond for cutting steels are cubic boron nitride (CBN), aluminum oxide, and silicon nitride.[citation needed]