"Tool material, improper selection of geometric parameters, tool wear and other factors will affect the surface roughness."
1. The choice of tool materials
When the tool material has a large affinity with the metal molecules of the material to be processed, the material to be processed
is easily bonded to the tool. Therefore, if the bonding is severe and the friction is severe, the surface roughness is large, and vice
versa. The same processing of gray cast iron parts, traditional carbide inserts are difficult to achieve the surface roughness of
Ra1.6, even if it is achieved, its tool life is greatly reduced, and BNK30 CBN grade tools due to low friction coefficient of the tool
material, excellent high temperature heat Stability and wear resistance, the surface roughness of Ra1.6 can be easily processed
under the condition that the cutting speed is several times higher than that of traditional carbide. At the same time, the tool life is
several times that of trditional carbide tool, and the surface brightness is improved by one magnitude.
Surface roughness after processing of traditional carbide tool processing
Surface roughness after processing of BNK30 CBN grade inserts from Halnn
2, The choice of tool geometry parameters
The major influences on the surface roughness in the tool geometry are the main declination Kr, the minor declination Kr,' and
tool nose radius Re. When the primary and secondary declination are small, the height of the residual area of the machined
surface isalso small, so the surface roughness can be reduced; the smaller the secondary declination, the lower the surface
roughness,but the reduction of the secondary declination is likely to cause vibration, so it is reduced. The secondary declination
depends on therigidity of the machine tool. The effect of tool nose radius Re on the surface roughness: When Re increases,
the surface roughness will decrease, and increasing Re is a good method to reduce the surface roughness. Therefore, reducing
the maindeclination Kr,the minor declination Kr', and increasing tool nose radius Re of the blade edge can reduce the height of
the residual area,thereby reducing the surface roughness.
Halnn engineer said, "The choice of the arc angle of the tool tip is based on the rigidity and roughness requirements of the
machined workpiece. If the rigidity is good, try to choose a large arc angle, which not only improves the machining efficiency,
but also improves the machining efficiency. Improve the surface finish of the machine; However, when boring or cutting an
elongated shaft or a thin-walled part, a small blade radius is often used because of the poor rigidity of the system.
3,Tool wear
Tool wear is divided into three phases: initial wear, normal wear and severe wear. When the tool enters the stage of severe wear,
the wear rate of the flank of the tool rises sharply, the system tends to be unstable, the vibration increases, and the variation of
the surface roughness also rises sharply.
In the field of gray cast iron, many parts are mass-produced, which requires high consistency of product quality and high
production efficiency. Therefore, many machining companies choose to change the tool in the third stage without the sharp wear
of the tool.
Tool change, machining companies will repeatedly test the tool to determine a critical point, in the case of ensuring the surface
roughness requirements and dimensional accuracy of gray cast iron, without affecting the overall production efficiency.