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Piston Slipper Assembly : Forming and fatigue analysisPascal Pelloquin (Liebherr Machines Bulle SA) 2017-09-06
Liebherr GroupIntroduction
9/11/2017Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)2
Workforce: 42’000
Companies worldwide > 130
Turnover: 9 billion €
Liebherr ComponentsIntroduction
9/11/2017Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)3
Diesel engine
Splitter box
Hydraulic
motors
Founded: 1978
Employees: 1,060
/ Bulle portfolio
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)4 9/11/2017
Typical applicationsIntroduction
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)5 9/11/2017
Hydraulic pump working principleIntroduction
Source: Emmanuel Viennet (LMB)
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)6 9/11/2017
Presentation overviewIntroduction
Introduction
Simulation of the forming process
Assembly fatigue calculation
Assembly fatigue calculation with forming process
Conclusion
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)7 9/11/2017
Types of piston slipperIntroduction
Slipper in brass
+ Easy to produce (punch)
+ Cheaper variant
- Lower load capability
Only sliding surface in brass
+ larger angle possible
+ steel-steel contact resistant to
foreign particles
- Difficult manufacturing
- Expensive
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)8 9/11/2017
ChallengesForming Process
Find the right forming matrix
Find the right pressing force
Material limits
Lateral angle (product performance)
Axial clearance
Min value
friction
no locking
Max value
leakage
backlash
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)9 9/11/2017
Calculation ProcedureForming Process
Axi-symmetrical model
Material model : bi-linear
Boundary conditions
Find contacts
Touch matrix
Pressing force / Forming
Release
Contact
Normal Lagrange
Total of 150 substeps
~500 iterations, 5 min
0
0
0
1.
- x
-x
- X - x
2. 3. 4.
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)10 9/11/2017
ResultsForming Process
Stress (von Mises)
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)11 9/11/2017
ResultsForming Process
Typical bad results
Force too large,
important
remaining strain
Strain Gap
0
<
Contact pressure
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)12 9/11/2017
ResultsForming Process
Typical good results
Strain GapContact
pressure
Capability to model / support the forming process for new piston-slippers
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)13 9/11/2017
ModelsFatigue Analysis
Copyrig
ht
Lie
bherr
Confid
entia
l–
do n
ot
pass t
o3
rdpart
ies.
Half symmetric model
4 models mandatory:
2 for the piston
Swash plate angle +/-
Cylinder can rotate
freely
2 for the slipper
Swash plate angle +/-
Slipper can rotate
freely
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)14 9/11/2017
ModelsFatigue Analysis
Contacts
Augmented Lagrange
Offset corresponding to clearance
4 calculations
corresponding part and contacts
deselected using APDL
Total of 20 substeps
~20 iterations, 30 min (6 cores,
cluster)
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)15 9/11/2017
ResultsFatigue Analysis
Results combined with FEMFAT
(ECS Software), considering :
Surface finish
Material properties dispersion
Survival probability
Piston results too good
Past experience showed
margin is sufficient, but not
extreme
Very high cycle fatigue
Piston with very high cycle
fatigue leads to realistic value
s
Nk N
log(S
tre
ss A
mp
litu
de)
log(Load Cycles)
sa
Infinite Life
Very High Cycle Fatigue
(VHCF)
HCF
106
Slope k
Borderline
Good
Bad
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)16 9/11/2017
ResultsFatigue Analysis
Results combined with FEMFAT
(ECS Software), considering :
Surface finish
Material properties dispersion
Survival probability
Slipper results pessimistic with very
high cycle fatigue
Very high cycle fatigue concept
applicable ?
Known to work well in serial
production
Influence of production needs to
be considered
Borderline
Good
Bad
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)17 9/11/2017
BackgroundFatigue and Forming Analysis
Residual compressive stress following
2D forming analysis
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)18 9/11/2017
ModellingFatigue and Forming Analysis
3D because of loading under angle
Normal Lagrange contacts
Boundary conditions
Find contacts
Touch matrix
Pressing force / Forming
Release
Load axially
Load in one direction
Release
Load in other direction
Total of 250 substeps
~1100 iterations, 36h (6 cores, cluster)
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)19 9/11/2017
ResultsFatigue and Forming Analysis
Stress (von Mises), after forming,
under high pressure load
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)20 9/11/2017
ResultsFatigue and Forming Analysis
FEMFAT Results
Very high cycle fatigue applicable ?!
Borderline for HCF Pessimistic for VHCF
Copyrig
ht
Lie
bherr
Confid
entia
l–
do n
ot
pass t
o3
rdpart
ies.
Piston Slipper Assembly, forming and fatigue, Pelloquin Pascal (LMB)21 9/11/2017
Summary Next StepsConclusion
Good methodology for forming
process
Good methodology for piston fatigue
Incomplete methodology for slipper
fatigue
high cycle fatigue approach too
conservative
high cycle fatigue with forming
approach realistic but
cumbersome
very high cycle fatigue with
forming approach too
conservative and cumbersome
Material modelisation as
multilinear
Material characterization of
Brass
Stress-Strain behavior
Very high cycle fatigue
behavior
Test the new ANSYS Explicit
STR solution coming along
Mechanical Enterprise license
for 3D forming process.
Liebherr Components
Liebherr Components
System-engineered components
Thank you for your attention
Available for any questions
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