Finite Element Simulation of Induction
Hardening in Saw Blades for Food Processing
H. Torres1, F.A. Pérez-González1,, N.F. Garza-Montes-deOca1,, O. Zapata-Hernández1, I.
Felde2, T. Réti2, M. Réger2 and R. Colás1
1Universidad Autónoma de Nuevo León
2 Obuda University, Hungary.
• Introduction
• Introducción
• Experimental procedure
• Model preparation
• Results
• Procedimiento
experimental
• Preparación de modelo
• Resultados
• Conclusiones
• Referencias
• Conclusions
• References
INTRODUCTION
Optimization of induction hardening process by FEM. SISAMEX, UANL, GH
Induction.
Induction hardening patterns prediction by FEM. SISAMEX.
Abstract
Resumen
Saws for food are expected to have a good
resistance wear during service; these are
components that are subjected to induction
hardening process. This process offers good
industrial advantages since heating is done at
specific regions during very short times without
heating al l volume.
Las sierras de corte para alimentos son
componentes los cuales se espera tengan una
buena resistencia al desgaste durante su servicio,
estas son sometidas al proceso de endurecimiento
por inducción. Este proceso ofrece grandes
ventajas
industriales
desde
realizar
el
calentamiento en zonas especificas durante
tiempos muy cortos sin calentar todo el volumen.
The scope of this work is to simulate induction
hardening processing using Finite Element Method
(FEM) to solve heat transfer problem, and
Boundary Element Method (BEM) to solve
electromagnetic
problem.
A
coupled
electromagnetic-thermal-structural model was
created in DEFORM 3D to model heating and
quenching
stages
considering
phase
transformation. Altogether to the finite element
simulation, experimental tests were made to the
aim to use the same conditions and validate the
results from FEA and experimental process.
Samples characterisation was carried out by SEM
and micro-hardness.
EL alcance de este trabajo es realizar la simulación
del proceso de calentamiento por inducción
utilizando el Metodo de Elemento Finito para
resolver el problema de transferencia de calor, y el
Metodo de Elemento Frontera para solucionar el
problema
electromagnetico.
Un
modelo
electromagnetico-térmico-estructural acoplado fue
creado in DEFORM 3D para modelar las etapas de
calentamiento y enfriamiento considerando la
transformación de fase.
La caracterización de muestras fue realizada por
microscopia electronica de barrido (SEM) y
microdureza.
Introduction
High carbon steels are used in the manufacture of cutting tools due to its capacity to
develop a high hardness structure made of tempered martensite. Respect to the
heat treatment, as well-known, the hardening and tempering process of the steel
consists of the steps of austenitizing, quenching and tempering: the first two are
characterised by the formation of austenite and its full transformation to hard
martensite, while the third is performed to restore toughness.
Figure 1. Saw blade for food processing.
Figure 2. CCT diagram for 0.44 % carbon steel
*Source: After "Einführung in die Werkstoffwissenschaften"; ed. W.
Schatt, 7th edition 1991.
Introduction
Induction hardening
• Some of the advantages of
induction hardening are: heating
is very fast, it is a very efficient
process, and it has the ability of
heating locally.
Endurecimiento por inducción
• Algunas de las ventajas del
endurecimiento por inducción
respecto a los tratamientos
térmicos
tradicionales
son:
calentamiento rápido, proceso
eficiente, tratamiento localizado,
entre otras.
Figure 3. Induction heating applications
Introduction
Saw blades in food processing are tools that are used to
cut meat and bones, and they are found in butcheries,
slaughter houses, and super markets.
Bone
Induction
hardened zone
Figure 4. Saw blades during cut of meat with bones.
Specifications:
• Polished high carbon steel
• Hardened, ground teeth
• Laser-etched blade for easy identification
Meat types:
• Meat with bones or boneless,
thawed or frozen
• Fish
Objective
Objetivo
• Simular
el
proceso
de
endurecimento por inducción de
sierras de corte para alimentos
mediante el metodo de elementos
finitos y metodo de condiciones de
frontera, con el fin de resolver
problemas de transferencia de
calor
y
electromagneticos,
respectivamente.
• Simulate induction hardening
processing of saw blades using
Finite Element Method (FEM) to
solve heat transfer problem, and
Boundary Element Method
(BEM) to solve electromagnetic
problem.
FEM
Physical
System
Validation
Model
Modify of
system
Prediction
Experimental procedure
A company of cutting tools for industrial food
applications provided saws of commercial high
carbon steels. To the aim to improve a good
induction heat treatment and increase the
mechanical behaviour of the saw, in specific
the teeth’s was design and manufacture an
induction coil as can be appreciated in Figure
5, where is observed the coil and the saw
modelled in a CAD program.
The parameters used for this study are the
same in the simulation and experimental
process (voltage was considered to be 8 kV
and frequency has a value of 27 MHz,
processing time is 13.5 ms) in order to
validate the simulation with experimental
values.
Tooth
Figure 5. Coil and saw system.
Model preparation (FEM)
The geometry of the saw was simplified
since heat only concentrates on the tooth. A
height of 5.6 mm, which is 10 times the
thickness of the sheet, was considered.
General purpose commercial finite elements
programs are used very frequently to model
induction hardening processes. These kind
of programs offer high capability of handling
complex geometries and deal with very
complex phenomena. Therefore, computer
simulation was used to obtain the
temperature distributions on the saw during
induction hardening process. This was done
using DEFORM 3D software, as can be
observe in Figure 6.
Figure 6. Finite element mesh of the system.
*Note. The total number of elements was 47692
and 13389 for saw and coil, respectively
Model preparation (FEM)
Boundary conditions are show in Figure 7. The base of
the saw was fixed and a translational velocity of 1.3
m/s was assigned to the coil. It is important to notice
that in the real process the coil is fixed. Assigning this
velocity to the saw will require a very high
computational time for the calculation because of the
Lagrangian formulation for the elements of the saw.
The initial temperature of the saw is 20 °C.
Thermal properties for austenite and martensite
phases were considered to be temperature dependent
and they are shown in Figure 8, where thermal
conductivity and specific heat capacity are plot
respect to the temperature for each phase.
Figure 8. a) Thermal conductivity, b) Specific heat of steel.
Figure 7. Boundary conditions.
Model preparation (FEM)
Electromagnetic properties for austenite and
martensite phases were considered the same.
Electrical resistivity is shown in Figure 9.
For the coil the electrical resistivity and the
relative
magnetic
permeability
were
-6
considered to be 2.5x10 W-m, and 1,
respectively. Thermal expansion coefficient was
not assigned in this model since there was no
calculation of thermal stresses due to phase
transformation although usually are developed
during quenching.
Figure 9. Electrical resistivity of steel.
Results
In this figure is possible to observe the temperature distribution on the saw. The
maximum temperature is localized in the tip of tooth (1200 °C), where is
mandatory to promote the phase transformation.
1200
Figure 10. Temperature distribution in the saw.
Results
Measurement of temperatures during this process is very difficult since in the real process
the saw is moving. In this simulation velocity boundary condition was applied to the coil to
reduce computational time.
4
3
2
1
Figure 11. Temperature evolution during simulation in different regions of the saw.
Results
Micrograph of the saw blade after the surface hardening, in this figure is possible to observe a
typically gap or layer of phase transformation, where this layer is a fine-grain martensitic on
specific areas of the saw.
Figure 12. Microstructure evolution after heat treatment of the master material.
Results
Micro-hardness test were carried out on different samples to the aim to measure the
mechanical properties on the induction-hardening zone of the saw.
Figure 13. Hardness evolution on the saw
Results
Phase transformation using the specialized software and micrograph by SEM. In this figure is
possible to observe that the layer or gap of phase transformation on software and micrograph
is similar, because the layer of fine martensite on tooth are the same for both analyses, but in
small zones this layer by FEM is different respect to micrograph .
~860 µm
~840 µm
Figure 14. a) Finite element simulation of martensite transformation, b) Metallographic examination of the saw.
Conclusions
• A coupled electromagnetic-thermal-structural with phase transformation models
packages was successfully implemented. The gap or layer of full phase transformation to
martensite in the material was very similar for both, Finite Element and micrographic
analyses. Using Finite Element Analysis is possible to obtain the optimal parameter to
do a good heat treatment, respect to the deep of tempering on the material.
• Distance between coil and sample has to be considered in the design of the process, to
the aim to have an uniformity of the temperature in the material or study zone.
Otherwise, the geometry and orientation of the coil respect to the work specimen is very
important too, due to these variables have a high consequence in the surface hardening
process.
Current process
Optimized Process
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