1. 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 gear Cold forged bevel gearsSTRECON ® E + prestressed constainer for bevel gear dies

2. 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 mode bevel gear cracks along the fillets die insert strip- winding casing winding core

3. 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 system winding core (carbide) windings and casing die A)conventional container with a double ring 0.6% interference B)STRECON ® Basic, 1.0% interference C)STRECON ® E +, 0.6% interference

4. 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% interference Circumferential stresses at max. load  Risk of early crack initiation due to tensile stresses and large plastic strains Tangential stress-strain response Tangential stress in MPa Total strain in % 1500 MPa 1500 1000 500 0 -500 -1000 -1500 -2000 -2500 -3000 MPa Die life in production: 400

5. 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 STRECON ® Basic at 1.0% interference Circumferential stresses at max. loadTangential stress-strain response 650 MPa  Reduced max. tensile stress, but still tensile stresses and plastic strains Tangential stress in MPa Total strain in % 1500 1000 500 0 -500 -1000 -1500 -2000 -2500 -3000 MPa Die life in production: 4.700

6. 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 STRECON ® E + at 0.6% interference  Improved fatigue life: no tensile stresses, reduced stress range and cyclic plastic strains Circumferential stresses at max. loadTangential stress-strain response 0 MPa 1500 1000 500 0 -500 -1000 -1500 -2000 -2500 -3000 MPa Tangential stress in MPa Total strain in % Die life in production: >70.000

7. 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 for 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