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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