Four types of bonds are generally used for diamond and CBN grinding tools:
Sintered metal bonds
The different types of bonds are classified in bond groups
which are in turn allocated to certain bonding tasks. Resin
bonds are subclassified according to their bond hardness.
In contrast to the hardness of a ceramic bond grinding tool,
which is a measure of resistance to penetration, the hardness
of a resin bond for diamond or CBN grinding tools describes
the effective hardness and grinding behavior of these tools.
However, in the case of sintered metal bonds, resistance to
wear is generally referred to in a somewhat modified form.
The bond decisively influences both the grinding behavior and the service life of the grinding tool.
The bond must adhere to the grains as long as possible while
simultaneously wearing in such a way that the tips of the
abrasive grains can cut freely in the course of the metal
cutting process. This process is called the "self-sharpening
effect". It results from the combined effect of the bond,
the grain size and the concentration on the one hand, and
from the bond wear caused by chip formation on the other hand.
The optimal bond is the one that offers the most cost-effective
balance between the stock removal rate on the workpiece and
the wear of the abrasive layer.
In order to accomplish a wider variety of grinding tasks,
a wide variety of bonds must be made available.
The resin bond is a very versatile type of bond. Its range of application covers far more than half of all the machining tasks for which diamond and CBN grinding tools can be used.
The outstanding features of a resin bond are that it enables large cutting volumes as well as soft and cool grinding.
However, its rate of wear is higher than that of sintered metal bonds.
Sintered metal bonds
Sintered metal bonds can be divided into two main groups:
bronze bonds and steel bonds.
In special cases, bonds made
of hard materials are also used.
The higher mechanical stability and thermal load capacity of sintered metal bonds gives them a greater resistance to wear than offered by resin bonds. This is utilized especially in connection with grinding tools for profile grinding jobs and in the machining of materials which exhibit a strong abrading effect, such as glass, ceramics, etc.
With the exception of brittle bronze bonds, sintered metal bonds yield lower material removal rates than resin bonds do.
In the electroplated bond, the grain-on-grain abrading medium is embedded on a substrate by a metallic deposit in a galvanic bath.
As a rule a single-layer coating is used, however, a multilayer coating is also possible where feasible.
In the case of the single-layer coating, the abrasive grains protrude out of the bond by
approx. 1/3 of their size.
The main characteristic features of diamond and CBN grinding tools with electroplated
- Exceptional gripping capacity,
- High cutting capacity,
- Manufacture of complex profiles,
- Manufacture of tools with micro dimensions,
- Repeated use of substrates.
Ceramic bonds are used for diamond and grinding tools only
in isolated cases.
CBN grinding tools usually attain good results with ceramic
bonds when used to machine long-chipping materials such as
ball bearing steels.