The application of milling process has expanded rapidly
as CNC technology advanced. Traditionally, constant
spindle speed and feedrate has been widely adopted in
milling, which are conservative cutting conditions, in
order to prevent machine, workpiece and cutting tool
failure. This method ensures the stability and
reliabilty of the milling process, but on the other hand
prevents engineers to further improve machining
efficiency. However, through adaptive cutting force
control system, it's possible to increase machining
efficiency through adjusting feedrate during machining
process.
Although there are plenty of researches regarding
adaptive cutting force control, those researches focus
on design of controller and their computational
algorithm, few of them discuss the relation between
control signals, surface roughness and tool wear. This
research will establish the relation between feed rate,
spindle current and tool wear. The relation can serve as
a reference when setting machining parameters and tool
wear monitoring in adaptive cutting force control.
This research proposes a method to set machining
parameters in constant cutter load machining: feedrate
upper limit, feedrate lower limit, spindle current.
Feedrate upper limit and spindle current is set to
sustain cutting force under tool strength and surface
roughness under specification. Feedrate lower limit is
set to provide tool wear information that can sustain
tool wear condition within certain range to prevent
severe and unstable tool wear. Experiment results show
that machining parameters setting method proposed in
this research are able to keep tool wear within the
setting value when feedrate decrease to feedrate lower
limit, preventing potential risk of tool failure. The
machining parameters setting method can be adapted to
slot milling, end milling and the combination of both
milling methods. In comparison with constant feedrate
machining, the constant cutter load machining parameters
proposed in this research have better performance in
both tool life and material removal rate.
Keywords:
constant cutting force control, spindle current, tool
wear
