Ajex Diamond & CBN grinding wheels are high efficiency tools which if correctly selected and adopted to particular application help to provide optimum economical solutions to various grinding problems.

Cubic Boron Nitride (CBN) is an abrasive with remarkable properties for the wet and dry grinding of high alloy steels. CBN is an abrasive which bridges the gap between conventional abrasives and diamond. It is equally suitable for machining materials such as high speed tools steels, hot and cold working steels, stainless and high-temperature structural steels as well as Nickel, Chromium and Titanium alloys.

The following table gives recommendations regarding materials to be ground either with Diamond or with CBN Wheels.

Wheel Shape:

This catalogue offers a wide range of standard wheels for your various grinding problems. These wheel shapes and sizes confirm to the FEPA (Federation European of Product Abrasive) standard which in itself is the result of decades of international experience and standardizing efforts. These standard products are supplemented by a range of special wheel shapes designed to particular machine or workpiece requirements.

Next to Diamond and CBN grit types and their concentration in the matrix the bond ranks second in importance for the performance and life of a grinding wheel. It is the particle retention capability of the bond which governs the practical behaviour of an abrasive tool. A suitable bond assures high stock removal efficiency and at the same time low wheel wear (high G-ratio).

The stock removal rate of a grinding wheel is defined by

The grinding ratio G-ratio describes the wear resistance and as such the life time characteristics of a grinding wheel. It is calculated from

Grinding costs per cm³ workpiece material removed are given by the following equation:

where

Ks   =  price of grinding wheel in Rs

Vs   =  consumable rim volume of the grinding wheel in cm³

Ku   =  time costs (machine plus labour plus overheads) in Rs/h

Zeff  =  effective grinding time

Resin Bonds

Resin Bond grinding wheels give very good removal rates, are particularly free cutting and cause only very little workpiece damage even at high removal rates. they are normally used for grinding TC, high alloy steels and other metals.

Metal Bonds

Metal Bond diamond and CBN grinding wheels because of higher mechanical strength of the bond material itself and of the tougher, blocky grit types normal for these bond systems are considerably more wear resistant and less sensible to impact forces than resin bond tools. They do, however, not allow for the high removal rates like their resin bond counterparts. Metal bond grinding wheels therefore are preferred for machining non-metallic materials such as ceramics, glass, etc.

Electroplated Bonds

Compared to resin and impregnated metal matrices electroplated bonds are noted for relatively large diamond or CBN grit protrusion. This results in very free cutting properties and in high stock removal capability. However, with difficult-to-grind, short-ship materials single layer electroplated tools are unable to retain their performance over long periods of grinding by self-sharpening effects.

Besides in the grinding of TC, electroplated diamond tools also achieve excellent results in machining green (presintered) carbides, duro plastics, glass fibre, reinforced plastics, graphite, artificial coal, ferrites, ceramics, hollow glass, laboratory glass.

Electroplated CBN-tools are preferred for grinding bores on internal and coordinate grinding machines, the workpiece materials being hardened steels of >58HRC particularly of high alloy tool steel and HSS qualities.

This bond type allows Special Shapes and profile tools to be made at short notice. The necessary steel blanks can either be manufactured by ourselves according to drawings or are supplied by the customer.

Diamond Concentration

The basis for defining concentrations is 100=4.4 cts/cm³ rim volume. This concentration value is equivalent to a Diamond or CBN grit content of 25 percent of the total matrix volume with a density of 3.52 g/cm³ for diamond and 3.42 g/cm³ for CBN respectively. Frequently used concentration values are:

High concentrations of 75 to 150 are typical for coarse grits in peripheral wheels, profile wheels of small contact area and small rim width.

Low concentrations of 50 are used with fine grits for wheels of large rim width as well as for face grinding with cup wheels.

We guarantee that the diamond and CBN grit content of Ajex Diamond and CBN grinding wheels corresponds to these concentration values.

Grit Sizes

For optimum stock removal capability it is generally of advantage to use the largest grit size allowing surface quality requirements.

Ajex Diamond and CBN grit sizes confirm to the FEPA standard. This standard prescribes the most precise test sieve specifications for abrasive grits under consideration of the latest technological developments.

We recommend the following grit sizes:

Truing a Wheel Rim

Excessive axial and radial run-out of Diamond and CBN grinding wheels must be reduced and if possible eliminated by truing. There are four different truing methods.

2. Truing on a Soft Block (En 9)

4. Truing with Loose SiC

After exact geometric accuracy of a wheel rim has been achieved by truing according to methods 1 and 3 it is absolutely necessary to sharpen a diamond and CBN grinding wheel with the help of a Ajex dressing stick before it is put to use. By sharpening a wheel rim not only debris adhering to the active wheel surface is removed, it can also help to overcome clogging problems when the wheel has been used under wrong conditions. Normally Ajex Diamond and CBN wheels regenerate their sharpness automatically during grinding provided they are operated under appropriate conditions.

Wheel peripheral speed is very influential on the performance and life of Diamond and CBN wheels as well as on the quality aspect of the grinding operation. We therefore strongly recommend to select wheel diameter and spindle speed in accordance with the correct wheel peripheral speed which is fundamental for the economy of a grinding job.

Lower speed values quoted in this table are valid for larger, higher values for smaller wheel/workpiece contact areas.