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\clearpage
\section{Test B---Preset Workpiece Temperature} \label{sec:results_test_B}

This section presents the resulting cutting forces and AE signals generated during the
preset work temperature tests described in Section~\ref{sec:procedure_test_B}. The
first part shows the variation of the cutting forces with preset temperature, while the
second part shows the variation of AE with preset temperature.

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\subsection{Cutting Forces}

\begin{figure}[h]
   \center{\includegraphics{[temp_var][080A15][forces].eps}}
   \caption[Variation of cutting forces with workpiece surface
   temperature; work material 080A15.]
   {Variation of cutting forces with workpiece surface
   temperature;
   work material 080A15, \mbox{$t_1 = 0.1$ mm$/$rev}.
   (a)~\mbox{$V = 75$ m$/$min}. (b)~\mbox{$V = 200$ m$/$min}.}
   \label{fig:[temp_var][080A15][forces]}
\end{figure}
\begin{figure}[h]
   \center{\includegraphics{[temp_var][080M40][forces].eps}}
   \caption[Variation of cutting forces with workpiece surface
   temperature; work material 080M40.]
   {Variation of cutting forces with workpiece surface
   temperature; work material 080M40, \mbox{$V = 200$ m$/$min},
   \mbox{$t_1 = 0.1$ mm$/$rev}.}
   \label{fig:[temp_var][080M40][forces]}
\end{figure}
\begin{figure}[h]
   \center{\includegraphics{[temp_var][304S15][forces].eps}}
   \caption[Variation of cutting forces with workpiece surface
   temperature; work material 304S15.]
   {Variation of cutting forces with workpiece surface
   temperature; work material 304S15, \mbox{$V = 200$ m$/$min},
   \mbox{$t_1 = 0.1$ mm$/$rev}.}
   \label{fig:[temp_var][304S15][forces]}
\end{figure}
\begin{figure}[h]
   \center{\includegraphics{[temp_var][6082-T6][forces].eps}}
   \caption[Variation of cutting forces with workpiece surface
   temperature; work material \mbox{6082-T6}.]
   {Variation of cutting forces with workpiece surface
   temperature; work material \mbox{6082-T6}, \mbox{$V = 200$ m$/$min},
   \mbox{$t_1 = 0.1$ mm$/$rev}.}
   \label{fig:[temp_var][6082-T6][forces]}
\end{figure}
The plots shown in
Figures~\mbox{\ref{fig:[temp_var][080A15][forces]}--\ref{fig:[temp_var][6082-T6][forces]}}
present the variation of $F_\mr{X}$ and $F_\mr{Y}$ with workpiece surface temperature
($T_\mr{WS}$) measured before each run
(Tables~\ref{tab:temperature1}--\ref{tab:temperature4}). Firstly, for each $T_\mr{WS}$
value, the mean of the values of $F_\mr{X}$ and $F_\mr{Y}$ acquired during each 500~ms
interval was computed. Thereafter, the mean of all the 500~ms means obtained along the
whole cutting length was computed, resulting in the points shown on the plots (the
length of the error bars correspond to two standard deviations).

In the majority of the cases, it can be observed that the cutting forces vary slightly
with $T_\mr{WS}$. However, as this trend was not exactly observed in all cases, it was
decided to describe each one individually:
\begin{description}

   \item [080A15 (Figure~\ref{fig:[temp_var][080A15][forces]}a)]
   Both cutting forces remain more or less constant with
   increasing $T_\mr{WS}$.

   \item [080A15 (Figure~\ref{fig:[temp_var][080A15][forces]}b)]
   The cutting forces remain more or less invariant with
   $T_\mr{WS}$.

   \item [080M40 (Figure~\ref{fig:[temp_var][080A15][forces]})]
   Bellow approximately 170$^\circ$C, $F_\mr{X}$ and $F_\mr{Y}$
   decrease slightly with increasing $T_\mr{WS}$. However,
   above this temperature, the cutting forces fall abruptly down
   until $T_\mr{WS}$ approaches 220$^\circ$C\@. From this point,
   $F_\mr{X}$ and $F_\mr{Y}$ rise abruptly until
   $T_\mr{WS}$ reaches approximately 240$^\circ$C\@. Above
   240$^\circ$C the cutting forces start to fall again with increasing
   $T_\mr{WS}$.

   \item [304S15 (Figure~\ref{fig:[temp_var][304S15][forces]})]
   Both cutting forces remain more or less constant with
   $T_\mr{WS}$.

   \item [6082-T6 (Figure~\ref{fig:[temp_var][6082-T6][forces]})]
   Both $F_\mr{X}$ and $F_\mr{Y}$ fall almost linearly
   with increasing  $T_\mr{WS}$.

\end{description}

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\subsection{Acoustic Emission}

\begin{figure}[h]
   \center{\includegraphics{[temp_var][080A15][mode].eps}}
   \caption[Variation of AE level with workpiece surface
   temperature; work material 080A15.]
   {Variation of AE level with workpiece surface
   temperature;
   work material 080A15 and \mbox{$t_1 = 0.1$ mm$/$rev}.
   (a)~\mbox{$V = 75$ m$/$min}. (b)~\mbox{$V = 200$ m$/$min}.}
   \label{fig:[temp_var][080A15][mode]}
\end{figure}
\begin{figure}[h]
   \center{\includegraphics{[temp_var][080M40][mode].eps}}
   \caption[Variation of AE level with workpiece surface
   temperature; work material 080M40.]
   {Variation of AE level with workpiece surface
   temperature; work material 080M40, \mbox{$V = 200$ m$/$min},
   and \mbox{$t_1 = 0.1$ mm$/$rev}.}
   \label{fig:[temp_var][080M40][mode]}
\end{figure}
\begin{figure}[h]
   \center{\includegraphics{[temp_var][304S15][mode].eps}}
   \caption[Variation of AE level with workpiece surface
   temperature; work material 304S15.]
   {Variation of AE level with workpiece surface
   temperature; work material 304S15, \mbox{$V = 200$ m$/$min},
   and \mbox{$t_1 = 0.1$ mm$/$rev}.}
   \label{fig:[temp_var][304S15][mode]}
\end{figure}
\begin{figure}[h]
   \center{\includegraphics{[temp_var][6082-T6][mode].eps}}
   \caption[Variation of AE level with workpiece surface
   temperature; work material \mbox{6082-T6}.]
   {Variation of AE level with workpiece surface
   temperature; work material \mbox{6082-T6}, \mbox{$V = 200$ m$/$min},
   and \mbox{$t_1 = 0.1$ mm$/$rev}.}
   \label{fig:[temp_var][6082-T6][mode]}
\end{figure}
The plots shown in
Figures~\mbox{\ref{fig:[temp_var][080A15][mode]}--\ref{fig:[temp_var][6082-T6][mode]}}
present the variation of AE with $T_\mr{WS}$ for both AE sensors (\mbox{MICRO 80S} and
\mbox{PICO}). In order to process the AE data, for each $T_\mr{WS}$ value, the value of
the $I_\mr{mode}$ was calculated for each set of 65536 AE data points that were
acquired at every 500~ms (the low-pass cut-off frequency applied to the full-wave
rectified data was 1000~Hz). Afterwards, the mean of all the $I_\mr{mode}$ values was
computed, resulting in the points shown on the plots (the length of the error bars
correspond to two standard deviations).

From the observation of the plots, it can be affirmed that the value of $I_\mr{mode}$
decreases as $T_\mr{WS}$ increases. This trend is more or less visible in all plots,
being less visible in Figure~\ref{fig:[temp_var][080A15][mode]}b, where, especially for
the MICRO~80S data, $I_\mr{mode}$ seems to change very little with varying $T_\mr{WS}$.
