EFFICIENCY OF FACE FINISHING MILLING OF CAST IRON WITH VERMICULAR GRAPHITE BY TOOLS MADE OF CUBIC BORON NITRIDE AND NITRIDE CERAMICS

Abstract

The article presents the summary results of experimental studies of the influence of cutting modes and type of tool material
on tool wear, surface quality parameters, and microstructure of the machined layer of cast iron with vermicular graphite of
CGI450 grade during face finishing milling. The Box-Behnken method was used to plan the experiment and a multiple criteria
approach was applied. This made it possible to investigate the mutual influence of the main machining parameters - cutting
speed, feed per tooth and depth of cut - on the key performance criteria of the finishing face milling process.These include: tool
wear (VB), machined surface roughness (Ra), milling process productivity (MRR).
During the study, tools made of cubic boron nitride (CBN) and nitride ceramics (NC) were compared. It turned out that
BNB provides the formation of a hardened surface layer with high residual compressive stresses (up to -166.42 MPa), a crushed
matrix structure, and increased microdeformations. This indicates intensive surface hardening. The surface roughness is 0.16
< Ra ≤ 0.63 μm. Tools made of NK demonstrate slightly higher wear resistance and machining stability at high cutting speeds.
However, they have less pronounced structural strengthening and are characterized by slightly worse Ra parameters.
In addition, an economic assessment was made, which took into account the cost of the tool and the cost of machining
one kilometer of cutting path. As a result, it was found that in the finishing modes of HSS milling (cutting speed 400-800 m/min,
feed rate 0.1-0.15 mm/tooth, cutting depth 0.08-0.15 mm), the use of round-shaped cutting inserts made of nitride ceramics is
much more cost-effective than CBN inserts. Based on the analysis of the obtained results, recommendations for the choice of
tool material depending on the production priority were formulated: CBN - to achieve maximum surface quality and increased
wear resistance of the surface layer; Nitride ceramics - to ensure cost-effectiveness and process stability during serial
processing. The data presented here can be used to optimize the milling process of cast irons with vermicular graphite in critical
machine-building production.