1. Case study: tripods and cross-joints (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 tripods and cross-joints Die material: ASP 23, 60 HRc Prestressing system: ID 85 mm, OD 280 mm Cold forged tripods and cross-joints

2. Case study: tripods and cross-joints (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 Fatigue cracks in a tripod dieFatigue cracks in a cross-joint die

3. Case study: tripods and cross-joints (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 analysis of the tooling system winding core windings and casing die A)conventional container with a double ring 0.6% interference B)STRECON ® Basic, 0.8% interference C)STRECON ® E +, 0.6% interference

4. Case study: tripods and cross-joints (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 A) Prestressing by a double stress ring at 0.6% interference Circumferential stress distribution at max. process load  risk of early crack initiation due to tensile stresses and large plastic strains 400 200 0 -200 -400 -600 -800 -1000 -1200 -1400 -1600 MPa Tangential stress-strain response in the critical area (5 load cycles) 330 MPa

5. Case study: tripods and cross-joints (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 B) Prestressing by STRECON ® Basic at 0.8% interference Circumferential stress distribution at max. process load  Reduced max. tensile stress, but still considerable plastic strains 400 200 0 -200 -400 -600 -800 -1000 -1200 -1400 -1600 MPa Tangential stress-strain response in the critical area (5 load cycles) 60 MPa Tangential stress in MPa

6. Case study: tripods and cross-joints (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 C) Prestressing by a STRECON ® E + at 0.6% interference Circumferential stress distribution at max. process load  Improved fatigue life: no tensile stresses, reduced stress range and cyclic plastic strains 400 200 0 -200 -400 -600 -800 -1000 -1200 -1400 -1600 MPa Tangential stress-strain response in the critical area (5 load cycles) -320 MPa Tangential stress in MPa

7. Case study: tripods and cross-joints (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 for the cold forging of tripods and cross-joints 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 - the outer diameter of the die insert should be close to the inner contour (better effectivity of the carbide winding core) STRECON ® Basic in case of long-legged parts (especially cross-joints), where a carbide winding core would not be that effective