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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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
OUTLINE
Die lifetime is a major concern in the forging industry Wear Gross cracking or plastic deformation Mechanical or thermal fatigue
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
INTRODUCTION
At the very end, designers are expecting a comprehensive response
INTRODUCTION
DIE WEAR MODELING
CASE STUDY#1 : CONSTANT VELOCITY JOINT
DIE STRESS ANALYSIS
CASE STUDY#2 : HEAVY FORGING CRANKSHAFT
CONCLUSION
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
DIE WEAR MODELING
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
CASE STUDY#1 : CONSTANT VELOCITY JOINT
• DIE WEAR -> ARCHARD MODEL -> STEADY-STATE TEMPERATURE
DIE STRESS ANALYSIS CASE STUDY#2 : HEAVY FORGING CRANKSHAFT CONCLUSION
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
OUTLINE
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
CASE STUDY#1 : CONSTANT VELOCITY JOINT
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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 …
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
CASE STUDY#1 : CONSTANT VELOCITY JOINT
DIE STRESS ANALYSIS
CASE STUDY#2 : HEAVY FORGING CRANKSHAFT
CONCLUSION
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
OUTLINE
Different types of analysis are available Rigid die analysis Decoupled analysis Fully coupled analysis (with or without steady-state approach)
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
OUTLINE
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
CASE STUDY#2 : HEAVY FORGING CRANKSHAFT
• 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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
DIE LIFETIME PREDICTION – MODELING
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
SIMULATION VS. EXPERIMENT Other example – with courtesy of RWTH-IBF Aachen
INTRODUCTION
DIE WEAR MODELING
CASE STUDY#1 : CONSTANT VELOCITY JOINT
DIE STRESS ANALYSIS
CASE STUDY#2 : HEAVY FORGING CRANKSHAFT
CONCLUSION
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
OUTLINE
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014
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
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Parc de Haute Technologie 06255 Mougins cedex - France
CONTACT: +33 (0)4 9292 4200 +33 (0)4 9292 4201
[email protected] www.transvalor.com
5th Asia Forge Meeting - Kaohsiung (Taiwan) - November 3-6, 2014