THERMO MECHANICAL FATIGUE ANALYSIS ON s/Asia Forge... · PDF filethermo-mechanical...

THERMO-MECHANICAL FATIGUE ANALYSIS ON FORGING TOOLS

STÉPHANE ANDRIETTI DIRECTOR OF SOFTWARE PRODUCTION DEPARTMENT

TRANSVALOR SA - FRANCE

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

INTRODUCTION

DIE WEAR MODELING

CASE STUDY#1 : CONSTANT VELOCITY JOINT

DIE STRESS ANALYSIS

CASE STUDY#2 : HEAVY FORGING CRANKSHAFT

CONCLUSION


OUTLINE

Die lifetime is a major concern in the forging industry Wear Gross cracking or plastic deformation Mechanical or thermal fatigue


INTRODUCTION

Premature cracks due to mechanical fatigue

Courtesy of:

Thermal fatigue cracking

Gross cracking

Cost of tooling remains high Up to 15% of the final price is due to die works Challenge is to : extend die life by increasing the number of parts per tool set reduce production costs (maintenance & resink – tool changing)

Environmental matters : fewer tool manufacturing goes green

How process simulation can help ? Understand die failure mechanism Provide efficient modeling for die wear & die stress analysis Consider thermo-mechanical fatigue phenomena


INTRODUCTION

At the very end, designers are expecting a comprehensive response

INTRODUCTION

DIE WEAR MODELING


DIE STRESS ANALYSIS


CONCLUSION


OUTLINE

Standard basic model Based on normal stress & interface velocity

Does not depend on temperature

Applicable with simple rigid die analysis

Provide a qualitative response for abrasion wear

The Archard’s model Dependent on :

normal stress & interface velocity

hardness (temperature dependent)

tooling properties

Applicable with fully coupled analysis

Provide a quantitative response


DIE WEAR MODELING


DIE WEAR MODELING

Abrasion wear on die

Based upon standard basic model

Qualitative approach : red areas show where

the abrasion is the largest

Abrasion wear on lower die

by the end of forging

INTRODUCTION

DIE WEAR MODELING


• DIE WEAR -> ARCHARD MODEL -> STEADY-STATE TEMPERATURE

DIE STRESS ANALYSIS CASE STUDY#2 : HEAVY FORGING CRANKSHAFT CONCLUSION


OUTLINE



Automotive CV Joint

Material : 38MnSV4 steel grade

Warm forging : ~ 800 °C

Final height : ~ 110 mm

Gross weight : ~ 1,5kg

Objectives

Abrasion wear prediction on punch

Basic wear vs Archard’s model

Impact of initial die temperature

Benefits of a temperature steady-state distribution

Initial preform

Final shape

End of forging


ABRASION WEAR : STANDARD BASIC MODEL

Conditions : Rigid die computation

Die constant temperature 200°C

Wear modeling : standard basic

10mm prior to

end of forging

6mm prior …

4mm prior …


ABRASION WEAR : ARCHARD MODEL

Conditions :

Deformable die computation

Initial die temperature 200°C

Wear modeling : Archard’s model End of forging 4mm prior … 6mm prior … 10mm prior to

end of forging

Temperature evolution on punch

Abrasion wear on punch

Kw , Kf : constant

Hv : surface hardness

σn : normal stress

∆v : tangential velocity


WEAR PREDICTION : STD BASIC VS. ARCHARD MODEL

Archard abrasion wear model is temperature dependent.

Location of maximum wear are slightly the same,

but the intensity is significantly different.

Configuration #1

No temperature dependency

Configuration #2

Temperature dependent

Punch initial temperature = 200°C

Vs.

Standard basic model

Archard model


MODELING OF STEADY-STATE TEMPERATURE

Objective : predict the ‘stabilized’ temperature distribution on the punch after several forgings

Resting

(5 sec)

Forging

Lubrication

(2 sec)

Step #1

Recording of the thermal

loading during the 1st cycle

Step #2

Apply on the punch the

recorded thermal loading

Step #3

Iterate until convergence is reached

on maximum temperature


TEMPERATURE DISTRIBUTION AFTER STEADY-STATE

Noticeable difference on temperature distribution once steady-state is reached

Temperature distribution

after one single part

Punch nose

Stabilized temperature

distribution after ~ 80 parts

Punch nose


Drastic impact of the initial temperature on the abrasion wear prediction with Archard’s model

ABRASION WEAR : IMPACT OF STEADY-STATE TEMPERATURE

Configuration#1 : Archard model - 200°C as initial temperature Configuration#2 : Archard model - steady-state temperature

Vs.

INTRODUCTION

DIE WEAR MODELING


DIE STRESS ANALYSIS


CONCLUSION


OUTLINE

Different types of analysis are available Rigid die analysis Decoupled analysis Fully coupled analysis (with or without steady-state approach)


DIE STRESS ANALYSIS

Type Description Strength Outputs Understanding

RIGID DIE

No die deflection Constant temperature on die

Quick & Easy

Contact pressure Largest compressive zones

Abrasion wear Abrasion areas

Contact time Temperature gradient

DECOUPLED ANALYSIS

Deformable dies (stress & deflection) Additional analysis on dies only Based on mechanical loading recorded during rigid die

Elastic or elasto-plastic behaviour for the die Compatible with shrink-fit dies

Displacement Deflection

Hydrostatic pressure Inner tension & compression

Effective stress Plastic deformation

1st & 3rd principal stress & vector Tensile & compression areas, crack propagation direction

FULLY COUPLED ANALYSIS

Billet & dies are modeled as deformable bodies Interaction between billet & dies Temperature & stress calculation

Same ones as decoupled analysis +

Fully coupled thermo-mechanical resolution at each time step

Displacement Deflection

Stress components Comprehensive die stress analysis

Temperature & damage criteria Thermal & mechanical cracking

Abrasion wear with advanced modeling Quantitative wear prediction

Number of cycles before cracking Die lifetime


DIE STRESS ANALYSIS

Level of understanding : Rigid vs Decoupled vs Fully coupled approach

Accuracy

CPU

Comprehension

1

1

1

2

2

2

4

3

4

rigid analysis decoupled analysis fully coupled analysis

INTRODUCTION

DIE WEAR MODELING CASE STUDY#1 : CONSTANT VELOCITY JOINT DIE STRESS ANALYSIS

CASE STUDY#2 : HEAVY FORGING CRANKSHAFT • FULLY COUPLED ANALYSIS -> THERMO-MECHANICAL FATIGUE

CONCLUSION


OUTLINE



• Crankshaft

– 4 cylinders

– Preform : 1160mm length - 150mm outer diameter

– Gross weight : ~ 160 kg

– Alloy steel : 34 CrMo4-4 (DIN 1.7341 – SAE 4130)

• Forging conditions

– Blocker stage

– Billet temperature : ~ 1150 °C

– Crank press : 8000 tons

– Water& graphite lubrication

– Final flash thickness : 8mm

Preform

End of forging

Halfway


STANDARD DIE STRESS ANALYSIS

Maximum die deflection => elastic distorsion

Effective stress => areas subject to plastic deformation

Maximum deflection (mm) Effective stress distribution (Mpa)

Results obtained on lower die


STANDARD DIE STRESS ANALYSIS

1st principal stress => areas in tension

Principal stress vector => direction of tension

1st principal stress (Mpa)

Results obtained on lower die

Zoom on critical areas

Principal stress vectors


DIE LIFETIME PREDICTION

Types of die failure Wear

Plastic deformation

Thermal & mechanical fatigue

A thermo-mechanical fatigue model for hot forging Developed by RWTH-Aachen B.-A. Behrens, A. Bouguecha, T. Hadifi, G. Hirt, M. Franzke, M. Lopez Santaella

“FEM-Simulaton der Werkzeugversagens bei Warmmassivumformprozessen infolge thermisch-mechanischer Materialermüdung”

Schmiedejournal September 2011, Industrieverband Massivumformung e.V., Hagen, Germany, Page 42-46 (ISSN 0933-8330)

etotal = emechanical + ethermal

emechanical = σ1 max / Young modulus (at die temperature)

ethermal = linear thermal expansion x ∆temperature Number of cycles until crack initiation (empirical approach)

N = −C2ε

𝑡𝑜𝑡𝑎𝑙

2𝐶1

with C1 & C2 constants depending on the tooling


DIE LIFETIME PREDICTION – MODELING


DIE LIFETIME PREDICTION - RESULTS

Deformation during blocker stage Cycles until crack initiation

(minimum ~ 1000 parts - see blue areas)

Prediction of the number of forging cycles prior to crack initiation


DIE LIFETIME PREDICTION - RESULTS Prediction of the number of forging cycles prior to crack initiation

The scale indicates the

number of parts

before crack initiation

In the blue areas,

the risk of crack initiation

due to thermo-mechanical

fatigue is maximal


SIMULATION VS. EXPERIMENT Other example – with courtesy of RWTH-IBF Aachen

INTRODUCTION

DIE WEAR MODELING


DIE STRESS ANALYSIS


CONCLUSION


OUTLINE


CONCLUSION About abrasion wear prediction … - Models must be temperature dependent and it is critical to calculate the ‘steady-state’ temperature on the die. - The Archard’s model associated with a ‘steady-state’ temperature distribution on the die provides an excellent response.

About die stress analysis … - A fully coupled approach guarantees accuracy & a large variety of output results. - An innovative model based on thermo-mechanical fatigue is now implemented into FORGE® software and it predicts the number of cycles until crack initiation.

Areas of improvement … - Consider surface treatment (nitriding, …). - Introduce self-adaptive meshing / remeshing to trap localized phenomena.

THANK YOU FOR YOUR ATTENTION

ADDRESS: 694 avenue 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] www.transvalor.com


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