Piston Slipper Assembly : Forming and fatigue analysis · 7 Piston Slipper Assembly, forming and...

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


Hydraulic pump working principleIntroduction

Source: Emmanuel Viennet (LMB)


Presentation overviewIntroduction

Introduction

Simulation of the forming process

Assembly fatigue calculation

Assembly fatigue calculation with forming process

Conclusion


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


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


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.


ResultsForming Process

Stress (von Mises)



Typical bad results

Force too large,

important

remaining strain

Strain Gap

0

<

Contact pressure



Typical good results

Strain GapContact

pressure

Capability to model / support the forming process for new piston-slippers


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


ModelsFatigue Analysis

Contacts

Augmented Lagrange

Offset corresponding to clearance

4 calculations

corresponding part and contacts

deselected using APDL


~20 iterations, 30 min (6 cores,

cluster)


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


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


BackgroundFatigue and Forming Analysis

Residual compressive stress following

2D forming analysis


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


~1100 iterations, 36h (6 cores, cluster)


ResultsFatigue and Forming Analysis

Stress (von Mises), after forming,

under high pressure load


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.


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

Piston Slipper Assembly : Forming and fatigue analysis · 7 Piston Slipper Assembly, forming and...

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