fem simulation of surface hardening techniques - applications to ...

FEM SIMULATION OF SURFACE HARDENING TECHNIQUES - APPLICATIONS TO GEAR COMPONENTS -

R.DUCLOUX 1 , S. ANDRIETTI 1 , J. BARLIER 1

1 TRANSVALOR SA - FRANCE

5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014

INTRODUCTION

SURFACE HARDENING TECHNIQUES

CASE STUDY#1 : HEAT TREATMENT OF A BEVEL GEAR

CASE STUDY#2 : INDUCTION HARDENING OF A SPUR GEAR

CONCLUSION & PERSPECTIVES


OUTLINE


INTRODUCTION

Standard goals of forming process simulations

- Understand material flow : underfilling, folds & laps

- Determine optimum forming sequence : reduce design cycle

- Predict material properties : grain flow, microstructure

- Extend die life : stress analysis, wear, load, …

Productivity, Quality, Innovation & Savings


INTRODUCTION

Recent challenges - Predict the ‘in-use’ properties of the forgings

- Simulate the entire manufacturing process including all pre & post-forming operations (from initial heating to final heat treatment) Today’s presentation - Illustrate a wide range of heat treatment simulations - Application to surface hardening on forged components

INTRODUCTION






OUTLINE



Goal of surface (or case) hardening - Increase wear resistance and surface hardness - Keep inner metal softer - Applicable to low carbon & alloy steel - Followed by heat treatment to get desired hardness - Typical parts are : pinion, camshaft, gear, …

Among the most common techniques - Carburizing - Nitriding, other diffusion processes - Induction hardening - Shot peening



Application of surface hardening on gear components Very located and non-constant contact area

Need to increase hardness on the surface

Need to maintain ductility in the core of the component

Source : http://science.howstuffworks.com/transport/engines-equipment/gear4.htm

Source : http://www.yourdictionary.com/bevel-gear

Source : http://science.howstuffworks.com/transport/engines-equipment/gear2.htm

INTRODUCTION



• CARBURIZING -> QUENCHING -> TEMPERING




OUTLINE


CASE STUDY#1 : AUTOMOTIVE BEVEL GEAR

Complete forming sequence description Two warm forging stages

Piercing-Flash trimming, Machining

Heat treatment operations (carburizing-quenching-tempering)


CASE STUDY#1 : PROCESS DATA • Automotive bevel gear

– Max outer diameter ~ 52 mm

– Weight ~ 180 g

– Low carbon steel for carburizing (e.g. 20MnCr5)

• Carburizing conditions

– Process : 2h40 at 850°C

– Initial carbon rate in the part : 0.20%

– Atmosphere enriched in carbon : 0.8%

• Quenching

– Oil bath : 20°C during 2min

– HTC : 5500 W/°C.m2

• Tempering

– To relieve internal stresses : 200°C during 40min


CASE STUDY#1 : CARBURIZING STAGE

Objectives of the carburizing stage Increase of carbon concentration on surface

Increase quenchability for low carbon steel

0.20% carbon

~

Low

quenchability

0.80% carbon

~

High

quenchability

Isothermal diagram is shifted according to the carbon rate

from 0.20% to 0.8% of C


CASE STUDY#1 : CARBURIZING RESULTS

Carbon concentration (%)

after carburizing

Carburizing


CASE STUDY#1 : QUENCHING RESULTS

Phase distribution after oil quenching

(martensite-bainite-pearlite-ferrite) Residual stress distribution

(1st principal stress)


CASE STUDY#1 : PART DISTORTION

Distortion observed on the component after quenching due to plastic deformation

(magnification x10)

Quenching


CASE STUDY#1 : TEMPERING RESULTS

Effective stress relieving due to tempering

- before (left) & after (right) -

Von Mises stress (MPa)

Tempering

INTRODUCTION




• LOCAL HEATING BY INDUCTION -> QUENCHING



OUTLINE


CASE STUDY#2 : STRAIGHT-CUT OR SPUR GEAR

Typical ‘in-use’ conditions with loading / unloading sequence

Alternative ‘compression vs. tension’ mode at the root of the teeth


CASE STUDY#2 : STRAIGHT-CUT OR SPUR GEAR

How to increase the resistance to fatigue loading for contact fatigue : increase local hardness

for bending fatigue : increase compressive residual stress

Objective : delay cracks propagation

Material characteristics

Resisting torque = 1000 N.m

Yield stress = 600 Mpa

Ultimate stress = 800 Mpa

Elongation at break = 5 %

Pressure distribution

Red => compression

Blue => tension


CASE STUDY#2 : HEAT TREATEMENT SEQUENCE

Heating (induction) Tempering (induction) Quenching (water jets)


INDUCTION HEATING : FEM SOLVERS

Heating

Electro magnetic solver FORGE® Solver Heating source

Temperature

Air

Inductor

Workpiece Only workpiece


INDUCTION HEATING : GLOBAL MESHING TECHNIQUE

Heating

Generation of a unique ‘global’ FEM mesh

Inductor & Part : import from CAD

Air : defined via box or cylindrical area around the inductor

The global mesh gathers all entities (air+inductor+part)


CASE STUDY#2 : PROCESS DATA

Heating (induction)

Quenching (water jets)

• Spur gear

– Diameter : 100mm (outer) – 84mm (inner)

– Thickness : 10mm

– Alloy steel : 34CrNiMo6 (DIN 1.6582 – AISI 9480)

• Induction heating

– Current intensity : 4000 A

– Current frequency : from 5KHz to 20 KHz

– Heating time : from 2 to 10 sec

• Quenching

– HTC : 2600 W/°C.m2

– Media temperature : room temperature

– Time : 15min


CASE STUDY#2 : RESULTS

Heating (induction)

Heat power (W/m3) Magnetic field (A/m)



Heating (induction)

Temperature (deg C) Austenite rate



Heating (induction)

Low frequency High frequency Heating time is longer Heating time is shorter

Preferential heating zone: tooth base Preferential heating zone: tooth tip

𝑰𝒓𝒎𝒔= 4000 A

f = 5 kHz

Heating time = 10 sec

Austenite distribution Austenite distribution

Dual frequency ? 𝑰𝒓𝒎𝒔= 4000 A

f = 20 kHz

Heating time = 2 sec


CASE STUDY#2 : RESULTS Heating (induction) Quenching (water jets)

Martensite rate Temperature (deg C)


CASE STUDY#2 : RESULTS Heating (induction) Quenching (water jets)

Martensite distribution - Frequency = 20000 Hz

Depth

-400

-300

-200

-100

0

100

200

300

0 0,5 1 1,5 2 2,5 3

Depth

Residual stresses (Mpa) 𝒕𝒆𝒏𝒔𝒊𝒐𝒏

𝒄𝒐𝒎𝒑𝒓𝒆𝒔𝒔𝒊𝒐𝒏

0

100

200

300

400

500

600

700

800

0 0,5 1 1,5 2 2,5 3

Hardness (HV)

Depth

Final material properties by the quenching end

INTRODUCTION






OUTLINE



Process simulation is the key-solution : - Simulate the complete manufacturing process. - Associate Heat treatment & Forming operations. - Predict the final ‘in-use’ properties of component. ‘State of the art’ surface hardening techniques can be simulated : - Carburizing + Quenching + Tempering. - Impact of carbon rate on IT diagram for martensitic transformation. - Induction hardening (heating + quenching). - Right compromise for process parameters.



Extensive capabilities in FORGE® NxT : - Forming process & heat treatment simulations - Heat treatment capabilities : austenitisation, hydrogen diffusion, carburizing, quenching, tempering, … - Unique electro-magnetic solver for induction heating, hardening, heat treating, …

Keep increasing our competitive advantages with : - Enhanced phase transformation models - Complementary surface treatment : nitriding, carbonitriding - Precipitate prediction incl. coupling with strain & stress

THANK YOU FOR YOUR ATTENTION

ADDRESS: 694, av du Dr. Maurice Donat

Parc de Haute Technologie 06255 Mougins cedex

France

CONTACT: +33 (0)4 9292 4200 +33 (0)4 9292 4201

[email protected] http://www.transvalor.com/


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