1. 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 pinions for automotive starters Cold forged starter pinions

2. 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 insert Vertical and horizontal fatigue cracks in the lower die insert

3. 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 prestressing (STRECON ® E + Axi-Fit)

4. 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 system with regard to the vertical crack initiation Assumed process pressure distribution 2D FE model of the cross-section with the gear profile

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

6. 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 load  Prestressing by the STRECON ® E + reduces the tensile stress in the fillets at maximum process load

7. 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 system with regard to the horizontal crack initiation Contact area

8. 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 insert in 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

9. 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 insert in the prestressed condition  By reducing the plane contact area, the axial prestress in the shoulder (where the cracks actually occur) is increased

10. 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 assembly

11. 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 design of dies for the cold forging of tripods and cross-joints Recommended tooling system: STRECON ® E + Axi-Fit provides high stiffness and 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)