% !TeX root = ../dissertation.tex

\chapter{Process Charcterization}
\label{cha:process_charcterization}

Induction heating, despite all its positive aspects, is a difficult process to control due to it's multi-physical nature.

Annika Eggbauer described in her PhD\cite{eggbauer2018inductive} the influence of heating speed on the resulting quenched microstructure, on top of austenitization temperature, hold time, and quenching parameters.
This influence of the full heating curve compounds with the fact that every the heat generation of an induction setup are unique to each pairing of material and inductor geometry.

As such, heavy instrumentation would be required to collect adequate physical data as input for a full process simulation:
Precise voltage or current measurements for the electro-magnetic simulation of heat generation, as well as detailed termaertaure measurements at several key points of the volume to easily verify the simulation.
Many industrial induction ovens are however not instrumented beyond a power meter, and even that will not record information about the transformer's efficiency and output waveform.

For this reason, the \emph{Material Center Leoben} (MCL) commissioned an induction heating teat rig equipped with a bank of thermocouple endpoints.
This machine has a maximum power of <??>, supplied by a <??> transformer, and can be run in constant-voltage, constant-current, and constant-power mode.

A series of induction experiments was conducted by our research group to obtain data on a induction hardening procedure, whose temperature curve closely imitated that of the industrial prcess we aimed to simulate in part~\ref{part:crankshaft}.

The material chosen for these experiments was 50CrMo4 steel whose chemical composition is close to that of the proprietary C38p Steel used in the crankshafts of part~\ref{part:crankshaft}.
The experiments on rod samples done on the MCL in-house induction test rig were well instrumented and published under J\'aszfi \emph{et al.}\cite{jaszfi2019influence, jaszfi2022indirect, jaszfi2022residual}

The induction test rig was configured to approximate a linear temperature increase up to the assumed maximum of \qty{1050}{\degreeCelsius}?? which was held for \qty{10}{\s}, after which quenching fluid was injected in between the induction coil to achieve a cooling coefficient of $\lambda = 0.1$ or \qtyrange{500}{300}{\degreeCelsius} in \qty{10}{\s}??.

The rod samples had holes drilled for thermocouples at center height of the coil at \qtylist{0.5;10.5}{\mm} depth.

A procedure for characterizing the electrical signal that drives the induction coil is given in appendix~\ref{apx:pub1}.
That article defines a cutoff up to which harmonic solutions to the electromagnitc simulation (see section~\ref{sec:the_finite_element_method}) are viable.


