In order to extend the life of the tool or improve its working
efficiency, it is particularly important to improve the surface friction
conditions. Therefore, more and more applications of high-efficiency
cutting materials have emerged. The cvd thin coating and pvd coating
have greatly improved the performance of the tool surface, and this
effect is far from being exhausted until now. Using modern analysis
technology, the microstructure of the tool surface can be clearly
observed, and it can better optimize. The surface structure of the tool
is achieved through a predetermined process program, and now the
functional design can be performed according to the optimized tool
performance.
The most commonly used surface modification treatment method
is the surface coating of the material. Through the combination of
carbides, nitrides and oxides of high-hardness metals, the performance
of individual compounds can be adjusted, especially in terms of the
ability to improve abrasion resistance, oxidation wear, diffusion wear
and bond wear. Of course, introducing other materials into the surface
(such as through the injection method) can also have a lasting effect on
the surface properties of the material.
In addition to mechanical bite, the adhesion mechanism
between chips and tools is mainly represented by friction. Through a
material modification treatment method-depositing a soft coating on the
tool surface-one can effectively improve the friction performance.
In addition, the surface morphology can be modified, such as
by polishing or purposely roughening (in order to form a lubricating oil
groove). Polishing is a traditional method to reduce friction by
mechanical means, especially for cutting tools without adding lubricant
to the cutting area. Polishing is an effective method to reduce friction
in most cases.
Periodic surface structures can be formed by polishing.
Structural elements of a certain shape can also be obtained by
lithography or laser. Compared with sheet metal processing, these
methods are currently not common in cutting. A theoretical basis of this
method is that microstructuring can reduce the heat transfer between
chips and tools, and reduce the thermal load of the tool.
Pvd coating polishing. The polishing process belongs to the
modification of surface morphology. There are various polishing methods
for ground or coated surfaces. In addition to the Troyes polishing
method used for high-volume parts, there are the brush method and sand
blasting method commonly used in tool production. These methods are not
novel and have been used for many years in the production of cutting
inserts, such as cauliflower-like surface structures for polishing cvd
thick coatings. The polished cutting insert showed very uniform wear
after 6 minutes of cutting. The unpolished blades show parallel
microscopic cracks, which will cause the wear zone to widen quickly and
cause the tool to fail prematurely.
These polishing methods are now often used for PVD coatings.
For example, on the surface of a pvd-coated hole machining blade, a
structure called "droplet" in the pvdarc method can be seen. These
droplets act like stones in the river bed, hindering the process of chip
removal, which is particularly disadvantageous in hole processing. If
the chips can be removed quickly and with less friction, the contact
time between the chips and the tool is reduced, and the heat transfer to
the tool is also reduced. The unobstructed chip removal makes the
cutting force smaller, and prevents the chip from biting and blocking in
the drill bit and milling cutter groove. The quality of polishing
depends on the choice of polishing method and the adjustment of process
parameters.
The polishing process can extend the life of the tool. Take a
twist drill as an example. A measuring instrument developed for final
inspection to determine the friction in the chip flute. The reduction in
friction is related to the surface condition. The friction coefficient
of the polished bit groove is only 25% of the unpolished. The treated
drill bit allows higher cutting volume and drilling depth.
