Case study: starter pinions (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 starter pinionsCase study: Cold forging of starter pinionsfor automotive startersfor automotive starters

Cold forged starter pinions

Case study: starter pinions (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 mode in the lower die insertTypical failure mode in the lower die insert

Vertical and horizontalfatigue cracks in the lower die insert

Case study: starter pinions (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

Tooling system for improved radial and axial prestressingTooling system for improved radial and axial prestressing(STRECON(STRECON®® E E++ Axi-Fit) Axi-Fit)

Case study: starter pinions (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

FE analysis of the tooling systemFE analysis of the tooling systemwith regard to the vertical crack initiationwith regard to the vertical crack initiation

Assumed process pressure distribution2D FE model of the cross-section with the gear profile

Case study: starter pinions (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

Stress response in the prestressed conditionStress response in the prestressed condition

Because of its higher stiffness, prestressing by the STRECON® E+ leads - despite the lower nominal interference - to a similar prestress level

Case study: starter pinions (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

Stress response in the condition at max. process loadStress response in the condition at max. process load

Prestressing by the STRECON® E + reduces thetensile stress in the fillets at maximum process load

Case study: starter pinions (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

FE analysis of the tooling systemFE analysis of the tooling systemwith regard to the horizontal crack initiationwith regard to the horizontal crack initiation

Contact area

Case study: starter pinions (8)

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

Contact stresses between upper and lower die insertContact stresses between upper and lower die insertin the prestressed conditionin the prestressed condition

By reducing the plane contact area, the maximum contact stress becomes higher and gets closer to the inner bore of the die

Case study: starter pinions (9)

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

Axial stresses in the upper and lower die insertAxial stresses in the upper and lower die insertin the prestressed conditionin the prestressed condition

By reducing the plane contact area, the axial prestress in the shoulder (where the cracks actually occur) is increased

Case study: starter pinions (10)

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

Axial prestress during assemblyAxial prestress during assembly

Case study: starter pinions (11)

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 designRecommendations for the designof dies for the cold forging of tripods and cross-jointsof dies for the cold forging of tripods and cross-joints

Recommended tooling system:

• STRECON® E+ Axi-Fitprovides high stiffnessand combines improved radial and axial prestressing

Result:

• Die life for starter pinion dies improved by factor 2-3(depending on the type of starter pinion)