Case study: CV joint outer races (1) Established within the GROWTH project GRD "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 outer race Die geometry: Cold forging die for a CV joint outer race Die material: Hot-working steel Prestressing system: ID 150 mm, OD 350 mm Axisymmetric model of the die prestressed by STRECON E + : Stripwinding and casing, E=205 GPa =0.3, elastic Carbide winding core, E=540GPa =0.23, elastic Die: Hot-working steel 50 / 54 / 56 HRc E=220GPa, =0.3 elastic-plastic Load distribution: 1500 – 2500 MPa

Case study: CV joint outer races (2) Established within the GROWTH project GRD "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 How to determine the optimum combination of material hardness and prestressing conditions Circumferential stress distribution at max. process load: risk of axial cracks MPa Prestressed by conventional stress ring at 0.6% interference, die steel 50 HRc MPa -70 MPa 300 MPa Circumferential stress distribution at max. process load: Prestressed by STRECON E + at 0.6% interference, die steel 56 HRc

Case study: CV joint outer races (3) Established within the GROWTH project GRD "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 Tangential stress-strain responses in critical area (for two load cycles) Design A: Prestressing by conventional stress ring at 0.6% interference, hardness of the die 50 / 54 / 56 HRc  risk of early crack initiation due to high tensile stresses and cyclic plastic strains  = 1735 MPa  pl = 0.30 % 56 HRc  = 1730 MPa  pl = 0.30 % 54 HRc  = 1500 MPa  pl = 0.53 % 50 HRc

Case study: CV joint outer races (4) Established within the GROWTH project GRD "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  = 1640 MPa  pl = 0.05 %  = 1675 MPa  pl < 0.01 % Tangential stress-strain responses in critical area (for two load cycles) Design B: Prestressing by a STRECON ® E + container at 0.6% interference, hardness of the die 50 / 54 / 56 HRc  no tensile stresses, minimized cyclic plastic strains for 56 HRc 56 HRc54 HRc 50 HRc  = 1515 MPa  pl = 0.16 % 50 HRc

Case study: CV joint outer races (5) Established within the GROWTH project GRD "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 warm forging of outer races Recommended die material: High-performance hot-working steel at high hardness provides an excellent fatigue strength In case of prestressing by a stiff STRECON ® E + container, the hardness can be increased from 50 to HRc Recommended prestressing system: STRECON ® E + reduces the stresses and cyclic plastic strains in circumferential direction, leads to improved fatigue life  important: right combination of die material and prestressing system!