Case study: bevel gears (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 bevel gearCase study: Cold forging of bevel gear

Cold forged bevel gears STRECON® E+ prestressed constainer for bevel gear dies

Case study: bevel gears (2)

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

Typical failure modeTypical failure mode

bevel gear

cracks along the fillets

die insert

strip-winding

casing

windingcore

Case study: bevel gears (3)

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

FE model of the tooling systemFE model of the tooling system

winding core(carbide)

windingsand casing

die

A) conventional container with a double ring0.6% interference

B) STRECON® Basic, 1.0% interference

C) STRECON® E+, 0.6% interference

Case study: bevel gears (4)

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

Prestressing by a double stress ring at 0.6% interferencePrestressing by a double stress ring at 0.6% interference

-3000

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

-1.5 -1.0 -0.5 0.0 0.5 1.0

Circumferential stresses at max. load

Risk of early crack initiation due to tensile stresses and large plastic strains

Tangential stress-strain response

Tan

gent

ial s

tres

s in

MP

a

Total strain in %

1500 MPa

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

MPa

Die life in production: 400

Case study: bevel gears (5)

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

Prestressing by STRECONPrestressing by STRECON®® Basic at 1.0% interference Basic at 1.0% interference

Circumferential stresses at max. load Tangential stress-strain response

650 MPa

-3000

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

-1.5 -1.0 -0.5 0.0 0.5 1.0

Reduced max. tensile stress, but still tensile stresses and plastic strainsT

ange

ntia

l str

ess

in M

Pa

Total strain in %

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

MPa

Die life in production: 4.700

Case study: bevel gears (6)

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

Prestressing by a STRECONPrestressing by a STRECON®® E E+ + at 0.6% interferenceat 0.6% interference

Improved fatigue life: no tensile stresses, reduced stress range and cyclic plastic strains

-3000

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

-1.5 -1.0 -0.5 0.0 0.5 1.0

Circumferential stresses at max. load Tangential stress-strain response

0MPa

1500

1000

500

0

-500

-1000

-1500

-2000

-2500

-3000

MPa

Tan

gent

ial s

tres

s in

MP

a

Total strain in %Die life in production: >70.000

Case study: bevel gears (7)

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

Recommendations for the design of dies Recommendations for the design of dies for the cold forging of bevel gearsfor the cold forging of bevel gears

Recommended die material:

• Power-metallurgical tool steel (instead of carbide),provides an excellent fatigue strength

Recommended prestressing system:

• STRECON® E+

reduces the stresses and cyclic plastic strains,leads to improved fatigue life,improves the accuracy by reducing the elastic expansion

Example for very successful die life improvement:

• Die life improved by a factor of more than 10

• Costs per part reduced by a factor of 9