Induction heat treatment of automotive parts

Induction Heat
Treatment of
Automotive Parts
Dr. Valentin Nemkov
Director of Research
Fluxtrol, Inc., USA
Webinar
April 20, 2016

Dr. Valentin Nemkov April 20, 2016
Outline
 Induction heat treating of automotive parts
 Basics of Induction heating and heat treating
 Magnetic flux control in induction coils
 Computer simulation and optimization
 Advanced design of processes and coils
 Induction coil manufacturing
 Examples of induction heat treating
• Crankshaft hardening
• Axle shaft heat treating
• Stresses and distortions
 Conclusions
2

Dr. Valentin Nemkov April 20, 2016 3
Benefits of Induction Heating
• Favorable for production environment: in-line heating, no
pollution, “push button” performance
• Good controllability and repeatability
• Better metallurgical results due to fast and clear heating
• Predictable and well controllable residual stresses
• Less and better predictable distortions
• Short heating cycles and high production rates
• Energy saving due to selective and efficient heating
• Minimum surface oxidation or decarburization
• Small equipment footprints
Some results can be achieved only by induction method.

More than 50% of all mechanical parts are subject to induction hardening!
Courtesy GH Induction

• High liability and therefore a need of strong quality control
• Strong global competition
• Permanent demand for improvements and savings
• Very high production rate (68 000 000 passenger cars in 2015
with 21 000 000 in China)
• High demand for the coil lifespan (hundred thousands cycles)
• Evolution of car design and industry in general, e.g. introduction
of electric cars.
How can induction technology meet these challenges?
Challenges in Induction Heat Treating
of Automotive Parts

Designed for Induction Heating (DFIH)
6
• Selection of steel type
• Steel quality, grain size
• Part shape and geometry
• Hardness specifications
• Sequence of operations
• Account for treatment stresses

Induction Heating Phenomenon
7Dr. Valentin Nemkov April 20, 2016

Basics of Induction Heating
8
Induction heating is a contactless method,
based on energy absorption from the
alternating magnetic field, generated by
induction coil.
Induction heating is based on two tightly
coupled phenomena: Electro Magnetism
and Heat Transfer with their well-
developed theories and fundamental
equations of Maxwell and Fourier. There
are multiple related phenomena and
multiphysics programs of different level
that can treat tasks of induction heating.
To use them, the user must understand
well physics of induction heating. Scan hardening, Interpower Induction
Scrap melting in induction furnace

Induction Heating Physics
Simple rules that all induction people must know:
1. All currents flow in closed loops. We need to provide
path for the coil current and imagine closed loops in
the part for induced (eddy) currents to flow
2. Inductor’s ampere-turns IN are the source of magnetic
field. Lines of magnetic field go around the conductors
that carry current and are always closed
3. Part of generated magnetic field “penetrates” into the
part. Variation of this field in time generates electric field (voltage U) in the
part according to a Law of Induction of M. Faraday
U = 6.28 f Φ, with f – frequency and Φ - magnetic flux value.
4. Generated voltage causes eddy currents in the part, which heat it.
We can control heating by the coil design, frequency and power (via the coil
current).
It looks very simple!
9

Skin-Effect in Induction Heating
Source of photo:
www.denkikogyo.co.jp
F, kHz 2.5 10 20 50 100
δ, mm 10 5 3.5 2.2 1.6
δ, mil 400 200 140 87 63
Frequency selection is very important!
A good initial approach for fast and efficient heating
is to have a reference depth equal to 1.5-2 hardness
depths. Example: Hd = 4 mm, fopt = 3-5 kHz
Magnetic field penetrates into the part and
attenuates. Measure of attenuation called
Reference, Penetration or Skin Depth δ (delta).
Delta δ depends upon field frequency, material
resistivity and magnetic permeability.
For hot steel (non-magnetic state)
δ = 500/ 𝒇, mm = 20/ 𝒇, in.
10

Power Density and Temperature
Distribution during Rod Heating
Program Elta 6
Hd
Frequency 3 kHz, Hot reference depth is 9 mm, Hd – expected hardness depth 4 mm
Hd
11

A unique feature of induction heating is that the coil parameters depend on the
load/part conditions: dimensions, cracks, off-center, temperature, etc.
Corresponding frequency, current and voltage sensors are widely used for process
monitoring and control.
Modern power supplies may be set for operation at constant or programmed
variation of voltage, current or generator power.
Control of Induction Hardening

Magnetic Flux Control
Magnetic flux control is modification of magnetic flux value and distribution in the
induction system by placing “magnetic controllers” in the coil magnetic circuit.
Controllers can provide concentration, redistribution or shielding of magnetic flux.
They can also increase the coil efficiency and power factor.
Magnetic field lines and temperature colour maps
for flat coil (top) and internal coil (right) without
and with magnetic controllers

Effect of magnetic concentrator
Color map and isolines of temperature
generated by Elta program
Robotic scan heating of water-cooled plate
demonstrating effect of magnetic
concentrator

Materials for Magnetic Flux Control
Heating by coil with lamination, SMS
Elotherm
Machined SMC core for internal
inductor, Fluxtrol, Inc.
1. Traditional material – sheets of electrical steel (laminations)
2. Newer materials – Soft Magnetic Composites (SMC). They have excellent
machinability, good saturation and ability to work well in 3D magnetic
field at any frequency used in induction heating
3. Ferrites – almost not used in heating automotive parts.

Induction Hardening Installations
Example of a single-platform induction hardening installation,
Water
cooling
system
Power
supply
Heat
station
Coil
Quench
system
Machine
control
Machine
Induction installations
may be:
• Distributed
• Mounted on a single
platform
• Built in line
16

Examples of Power
Supplies
Sinac power supply,
Power up to 320 kW, 10-25
kHz , EFD Induction
Minac Twin power
supply, 2x 40 kW, 10-35
kHz , EFD Induction

Induction Hardening of Tulips and CVJs

Hub Unit Hardening Machine
Source: Denki Kogyo Co. brochure

Computer Simulation

Modeling of Induction Hardening
Loading
21

Frequency 50 kHz; gear modulus 5 mm.
Maximum current density is in root area near the tooth end.
Gear Heating Simulation Using Flux 3D

2D Simulation of Axle Shaft Hardening
Temperature distribution and magnetic field lines at the end of dwell
Flux 2D program
Traditional two-turn coil Optimized coil

Process Design:
Heat Treating of the Shaft End
Pin diameter 40 mm
Hardness depth Hd = 4 mm
Hardened length 60 mm
Steel 1040

Example: In-Line Heat Treating of Pin
Load/Unload
Austenitizing
Quenching
Tempering
Cooling
AUS
TENI
TIZI
NG
QUENCH
COOLING
TEMPERING
t
Simulation showed that minimum
time for austenitizing heating is
slightly under 4 sec at optimal
frequency of 3 kHz.
This time was selected as a base
for other stages:
• Austenization 4sec
• Quenching 8 sec
• Tempering 4 + 4 sec
• Final cooling 8 sec
• Transportation time 1 sec
Rotary table machine has 8
positions with 2 positions used for
tempering

Temperature Color Map and T Isolines
QuenchingHeating Tempering Final cooling
R
A
D
I
U
S
Program Elta 6
Surface
At Hd
Center
26

Induction Coils

Good coil must:
• Meet specifications to temperature distribution
• Have a satisfactory life time
• Provide desired production rate
• Have good electrical efficiency
• Have favorable parameters for power supply (matching)
• Meet special requirements (quenchant supply, atmosphere, material
handling, incorporation into the machine, etc.)
• Have reasonable cost
In many cases magnetic flux controllers are required to achieve these goals
Old coil master, 1958: “ It is difficult to make a coil that does not heat at all”
Requirements to Induction Coils

29
Traditional Coil Manufacturing
Copper tube bending Brazing of machined and bent parts.
Application of concentrators

Coil for Camshaft Heating
Coil for heating multiple cams. Magnetic shields prevent mutual influence of
individual positions and improve heat pattern
30

Coils with Machined Copper Body
SharP-C inductor, courtesy of Inductoheat Inc.
31
Machined copper body
benefits:
• high accuracy
• high mechanical strength
• reliable performance
Side shields play three roles:
• crankshaft web shielding
• heat pattern control
• coil efficiency improvement

New Technologies of Coil Manufacturing
Wax modeling by 3D printing then
microfusion using silver or silver alloy
3D printed (3DP) coils on the
working plate of a EBM machine
Additive Manufacturing Microfusion
Advantages: - Repeatability due to Improved accuracy
- Increased lifespan due to optimal cooling and absence of flaws
- Consistent quality
Courtesy of GH Induction Atmospheres

Combined Induction Coil
Courtesy of GH Induction Atmospheres
Microfusion coils in the end
zones of a long inductor for
single-shot heating of shaft

Coil Life Time
Concentrator
Flux 2D program
Optimized coil
with improved
water path and
concentrator
Copper erosion due to overheating
Simulated
temperature
pattern
What to do to provide long life time:
1. Good coil design!!!
2. High quality materials:
 Pure oxygen free copper
 Concentrator material when required
 Insulation and coating when required
3. Best manufacturing technique
 Tube bending
 Accurate brazing (not soldering!)
 Machining
 Special
4. Setting
 Mechanical protection
5. Maintenance
 Water cooling (pressure, temperature,
flow rate, quality, build-up control)
 Cleaning and repair when required

Temperature map of scanning
system . Temperature scales are
different for a coil and a work piece
Prediction of Coil Temperature
35
Coil heating is caused by its current,
by magnetic losses in concentrator
and by heat transfer from the hot
part.
Computer simulation can take into
account all these factors and predict
the coil components temperature,
which is the main factor of the coil
life time.

Crankshaft Hardening

Lines for induction hardening of
crankshafts; system TOCCO,
Remscheid, Germany (1938)
Initial design of TOCCO inductor, 1933
Modern clam-shell coil with side
magnetic shields for hardening small
crankshafts
TOCCO Clam-shell Method

First test inductor of Elotherm
system (1941)
Modern inductor (Fluxtrol, Inc.) and hardness pattern
Rotational Crankshaft Hardening
Source: website of Alfing company
Multi-position hardening of
Large crankshaft

Non-Rotational Contactless Method
39
Modern contactless Inductor, InductoheatPrinciple of Contactless Inductor,
VNIITVCh, Russia, 1960s
Two station machine for
hardening and tempering
crankshafts, Inductoheat

Axle Shaft Hardening

Optimization of Coil and Process
Magnetic filed lines and temperature color
map at the end of dwelling stage
Full assembly of a two-turn axle
scan coil with quench body
Traditional two-turn coil
41

Optimization of Coil and Process
A
B
C
H
R
C
Position A
Original
Design
Optimized
Design
Case depth 10 mm 10 mm
Scan speed
9.5
mm/sec
10.7
mm/sec
Position B
Case depth 13.5 mm 11 mm
Position C
Case depth 4.5 mm 6.5 mm
Dwell time 10 sec 8 sec
Both cases: 170 kW, 1 kHz
NewOld

Virtual Prototyping of Axle Shaft Heat
Treatment
Steps of simulation:
1. Simulation of Hardening Process
- Electromagnetic and Thermal, Flux 2D
program
- Structures, Stress and Deformation,
Dante program
- Induction coil loading and temperature,
Flux 2D
2. Tempering: simulation of stresses and
deformation, Dante program
3. Torque Loading test: simulation of
stresses and strains, Dante program.

Influence of Residual Stresses on Shaft
Performance
Axial stresses after hardening,
Stresses can be controlled by
temperature distribution and
severity of quenching
Stresses for torque 6 kNm ,
no account for residual
stresses
Program Dante
Stresses for torque 6 kNm, with
account for residual stresses

Influence of Residual Stresses on Failure
Overload crack
in spline zone
Simulated principal stresses vs. applied
torque with and without account for RS.
Red line shows overload failure

Conclusions
• Induction heat treating of automotive parts is a special field of
induction technology due to its specifics
• Many improvements in this technique and corresponding
equipment have been made during last 15 years
• Computer simulation helps to achieve optimal results much
faster and more secure than trial-and-test method
• The most effective way of optimization is Virtual Prototyping
based on multi-physics simulation of a chain of processes that
includes induction heat treatment
• Advanced coil design and manufacturing is a critical point for
effective use of induction heat treatment.

About Axle Shaft Induction Hardening

Thank you!
www.fluxtrol.com, e-mail vsnemkov@fluxtrol.com , Ph. +1 248 393 2000

49
Selected References
• ASM Handbook, Volume 4C, Induction Heating and Heat Treatment,
ASM International, 2014, 820 p.
• Handbook of Thermal Process Modeling Steels, CRC Press, 2008, 712 p.
• R. Haimbaugh, Practical Induction Heat Treating, ASM International,
2001, 332 p.
• www.fluxtrol.com

Induction heat treatment of automotive parts

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