11-10-2012, 05:10 PM
Optimization of the In-line Induction Heating Process for Hot Forging in Terms of Saving Operating Energy
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Introduction
Energy-savings considerations in manufacturing processes have
been drawing a great attention to the designers and manufactures
because of the ecological issues, cost-saving pressure, and new
environmental legislations.1 Manufacturing companies have been
trying to “produce more with less”,2 so the improvement of
machining and process efficiency for manufacturing is one of the
promising solutions.3,4 Induction heating process has been
considered as a high productivity, repeatable quality, and green
heating technology compared to fuel-fired furnaces. This is the
reason why the induction heating, a best available heating
technology, is preferred in the forging industry.5,6 Induction heating
prior to hot forging, namely induction through heating, requires a
huge amount of electrical energy for heating a steel workpiece with
large volume from the ambient temperature to approximate
1150~1250°C. Therefore, the increase in the electrical efficiency of
the heating system significantly saves the consumed energy.
State of the research
Within the International Collaborative R&D Program
“Development of information technology-based manufacturing
process system for energy savings” hosted by KITECH, we have
been carrying out the sub-project “Holistic process
Research methodology and systematic procedure for optimizing the heating process
To save the experimental costs, the numerical simulation
method was used instead of performing a set of expensive physical
experiments. In addition, it is impossible to measure the
temperature distribution inside the heated workpiece by a pyrometer
while the workpiece moves continuously. In the case of induction
through-heating, the accuracy of the simulation result is very high
when the material properties and the simulation modeling are welldefined.
16,17 Therefore, numerical simulation is an appropriate
choice for studying the behavior of the induction heating system in
this work.
Mathematical and numerical modeling of the induction heating process
Induction heating is a complex electromagnetic and heattransfer
process because of the temperature dependency of
electromagnetic, electrical, and thermal properties of material as
well as skin effect. The temperature profile of the heated workpiece
and the energy consumption are complicated functions of the
current density, frequency, material properties, coil design, the
coupling between coils and workpiece, and the characteristic of the
power supply. The layout of the induction heating system and its
principle are depicted in Fig. 5. In the physical aspect,
electromagnetic field and heat-transfer are complicated, and the
transient simulation takes a long computational time.
Heating strategy and energy efficiency analysis
Flexible manufacturing requires the induction heating systems
to have an ability of adapting to the change of the throughput while
keeping a reasonable energy efficiency. In addition, the energy
efficiency depends on the heating pattern along the heating line as
previously mentioned in the research hypothesis in Section 2.
Therefore, the seven heaters are divided into three groups with the
strategy described in Fig. 7. The group 1, including two heaters,
heats the billet below and around the Curie’s temperature. The
group 2 with three heaters is responsible for heating above Curie’s
temperature and gives a large portion of heat energy that transfers
from the surface of the billet to the center (through heating). The
group 3, including two heaters, just gives a small remaining portion
of energy to heat the billet up to the target temperature and mainly
compensates the heat loss caused by convection and radiation at the
hot billet’s surface at the final heating stage.