Diamond / CBN Wafering Blades cut-off wheel, continuous rim. The body of the wheel is metal and the rim is a bond of metal or bakelite with diamond or CBN. The wear is very low, caused by cutting and dressing. Diamond / CBN Wafering Blades cut-off wheels are usually made with a metal body and the abrasive with the bond is placed around the periphery of the body. The abrasive / bond layer can be a continuous layer around the periphery of continuous rim or in segments. The metal body allows for very thin wheels, down to 0.15 mm - 0.006 inches - suited for precision cutting. In cutting wheels with electroplated abrasives, the abrasives are placed in a band along the periphery of a metal body and covered with a metal layer. These wheels only have a thin layer of abrasive; they are less expensive than the wheels described above and their lifetime is shorter.
Truing and Dressing
Because the slow consumable wheels have a very stable bond, the abrasive grain does not readily break away even when very worn. Also, the edge of the wheel may clog up with abraded material that stops the cutting action. Therefore, truing or dressing must be done. Dressing is important, because it exposes new abrasive grains in the edge by removing bond material and to a certain degree removes worn down grains. Dressing is done with a dressing stick made from hard materials such as sintered Al2O3 and SiC that is held against the edge of the wheel for 5–10 seconds.
Attention: Dressing should not be overdone because it wears down the relatively expensive wheel.
Diamond / CBN Wafering wheels are used frequently when consumable wheels are not suitable. Cut-off in general: For cutting of ferrous metals with hardness higher than approximately HV 500–700 and up to HV 1400, CBN wheels are used. For sintered carbides, ceramics, and other very hard materials, diamond wheels are used. Tough ductile materials like sintered carbides are cut with a bakelite bond and most hard and brittle materials with a metal bond.
This operation, done on precision cut-off machines often calls for very thin wheels below a thickness of 0.5 mm / 0.02 inches; therefore, slow consumable wheels are used. Normally, when cutting hard materials and composites, metal bond is used with either high or low diamond concentration. High concentrations are used for the softer materials and low concentrations for the hardest materials like ceramics. At low concentrations the cutting action is high because of the fewer abrasive grains, creating a higher force on each grain. If possible, ductile materials, like most metals, should not be cut with slow consumable wheels. The ductile metal will constantly clog up the edge of the wheel, the cutting action will be very low, and the wheel will “wear” its way through the work piece. When cutting most metals on a precision cut-off machine, a thin resin bonded consumable wheel should be used if a thickness of 0.5 mm_0.02 in_ can be allowed.
The wheel speed should be approximately 25 m/s / 4900 fpm. This can be established with most precision machines, but often the heavier machines for general cutting will not be able to accommodate this relatively low wheel velocity. At low speed cutting with small precision cutters, very low wheel speeds in the range of 2 m/s at 395 fpm are used.
Slow consumable wheels for general use are available in diameters from 200–400 mm 8 to 16 inches. Thickness from 1 to 2.2 mm / 0.04–0.09 inches. Shaft diameter the arbor is normally 32 mm or 1.25 inch.
Wheels for precision cutting wafering are available in diameters from 75–200 mm / 3–8 inches. Thickness varies from 0.15–0.9 mm / 0.006–0.035 inches. Shaft arbor is normally 12.7 or 22 mm /0.5 or 0.87 inches.