Case study: CV joint outer races (1) Established within the GROWTH project GRD1-1999-10748...

Case study: CV joint outer races (1)

Established within the GROWTH project GRD1-1999-10748 "Improvement of Service Life and Reliability of Cold Forging Tools with respect to Fatigue Damage due to Cyclic Plasticity (COLT)", funded by the European Community.

COLT Design Manual for Cold Forging Dies

Case study: Cold forging of outer raceCase study: Cold forging of outer race

• Die geometry:Cold forging die for a CV joint outer race

• Die material: Hot-working steel

• Prestressing system: ID 150 mm, OD 350 mm

Axisymmetric model of the die prestressed by STRECON E+:

Stripwinding and casing, E=205 GPa=0.3, elastic

Carbide winding core, E=540GPa =0.23, elastic

Die: Hot-working steel50 / 54 / 56 HRc E=220GPa, =0.3elastic-plastic

Load distribution:1500 – 2500 MPa




How to determine the optimum combination of How to determine the optimum combination of material hardness and prestressing conditionsmaterial hardness and prestressing conditions

Circumferential stress distributionat max. process load:

450

300

150

0

-150

-300

-450

-600

-750

-900

-1050

risk of axial cracks

MPa

Prestressed by conventional stress ring

at 0.6% interference, die steel 50 HRc

450

300

150

0

-150

-300

-450

-600

-750

-900

-1050

MPa

-70MPa

300MPa

Circumferential stress distributionat max. process load:

Prestressed by STRECON E+ at 0.6% interference, die steel 56 HRc




-2000

-1500

-1000

-500

0

500

-1 -0.5 0 0.5 1

Total strain in %

Str

es

s in

MP

a

Tangential stress-strain responses in critical area (for two load cycles)

Design A: Prestressing by conventional stress ring Design A: Prestressing by conventional stress ring at 0.6% interference, hardness of the die 50 / 54 / 56 HRc at 0.6% interference, hardness of the die 50 / 54 / 56 HRc

risk of early crack initiation due to high tensile stresses and cyclic plastic strains

=1735 MPa

pl=0.30

%

56 HRc-2000

-1500

-1000

-500

0

500

-1 -0.5 0 0.5 1

Total strain in %

Str

es

s in

MP

a =1730 MPa

pl=0.30

%

54 HRc-2000

-1500

-1000

-500

0

500

-1 -0,5 0 0,5 1

Total strain in %

Str

ess

in M

Pa

=1500 MPa

pl=0.53

%

50 HRc




-2000

-1500

-1000

-500

0

500

-1 -0.5 0 0.5 1

Total strain in %

Str

es

s in

MP

a

-2000

-1500

-1000

-500

0

500

-1 -0.5 0 0.5 1

Total strain in %

Str

es

s in

MP

a

=1640 MPa

pl=0.05

% =1675 MPa

pl<0.01

%

Tangential stress-strain responses in critical area (for two load cycles)

Design B: Prestressing by a STRECONDesign B: Prestressing by a STRECON®® E E++ container container at 0.6% interference, hardness of the die 50 / 54 / 56 HRc at 0.6% interference, hardness of the die 50 / 54 / 56 HRc

no tensile stresses, minimized cyclic plastic strains for 56 HRc

56 HRc54 HRc

50 HRc-2000

-1500

-1000

-500

0

500

-1 -0,5 0 0,5 1

Total strain in %

Str

ess

in M

Pa

=1515 MPa

pl=0.16

%

50 HRc




Recommendations for the designRecommendations for the designof dies for the warm forging of outer racesof dies for the warm forging of outer races

Recommended die material:

• High-performance hot-working steel at high hardnessprovides an excellent fatigue strength

• In case of prestressing by a stiff STRECON® E+ container,the hardness can be increased from 50 to 54-56 HRc

Recommended prestressing system:

• STRECON® E+

reduces the stresses and cyclic plastic strains in circumferential direction, leads to improved fatigue life

important: right combination of die material and prestressing system!

Case study: CV joint outer races (1) Established within the GROWTH project GRD1-1999-10748...

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