Case study: spline profiles (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 spline profiles Die material: Vanadis 23, 60 HRc Prestressing system: ID 50 mm, OD 140 mm Net-shape forged spline tap

Case study: spline profiles (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 Typical failure mode Fatigue cracks in the grounds of the spline geometry The cracks start in the fillets in axial direction and propagate on the top in radial direction.

Case study: spline profiles (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 FE model of the tooling system 2D model of the die, here prestressed by STRECON E + Stripwinding and casing E=205 GPa, =0.3, elastic Carbide winding core E=540GPa, =0.23, elastic Die, E=225GPa, =0.3 elastic-plastic process load: 1000 MPa A)conventional container with double ring 0.6% interference B)STRECON ® Basic, 0.8% interference C)STRECON ® E +, 0.5% interference

Case study: spline profiles (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 A) Prestressing by a double stress ring at 0.6% interference Tangential stress distribution at max. process load  risk of early crack initiation due to tensile stresses at maximum process load and large stress range 565 MPa  = 2850 MPa MPa Tangential stress-strain response in the fillet (for one load cycle)

Case study: spline profiles (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 B) Prestressing by STRECON ® Basic at 0.8% interference Tangential stress-strain response in the fillet (for one load cycle) 40 MPa  = 2840 MPa MPa Tangential stress distribution at max. process load  Enhanced fatigue strength due to the elimination of tensile stresses, but still the same stress range as the conventional double stress ring

Case study: spline profiles (6) 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 Risk of over-prestressing 190 MPa Condition of the die after prestressing by 0.8% and subsequent disassembly (e.g. for separate surface treatment).  If the die is prestressed by a high interference level and taken out from the prestressing system, cracks may occur in subsequent treatments. Equivalent plastic strains 0.2% % Residual stresses

Case study: spline profiles (7) 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  = 2480 MPa C) Prestressing by a STRECON ® E + at 0.5% interference -125 MPa MPa  Optimum fatigue strength due to the elimination of tensile stresses and the minimization of the stress range Tangential stress-strain response in the fillet (for one load cycle) Tangential stress distribution at max. process load

Case study: spline profiles (8) 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 Further optimization: change of the diameter ratio  The closer the carbide winding core to the inner contour of the die insert, the more effective the stiffness of the STRECON E + container. Design D: die OD ø 40 mm prestressed by STRECON E + Design C: die OD ø 50 mm prestressed by STRECON E + ø 50 ø 40

Case study: spline profiles (9) 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  = 2240 MPa Design D: Prestressing by modified STRECON ® E + container (ID reduced from 50 to 40 mm) at 0.45% interference -210 MPa MPa  Optimum fatigue strength due to the elimination of tensile stresses and the minimization of the stress range (from 2850 down to 2240 MPa) Tangential stress-strain response in the fillet (for one load cycle) Tangential stress distribution at max. process load

Case study: spline profiles (10) 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 Comparison of elastic expansion under process load  Reduced elastic expansion due to stiffness of STRECON E + container Diameter change under process loadElastic expansion under process pressure contour under prestressing contour under process load

Case study: spline profiles (11) 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 cold forging of spline profiles Recommended die material: Powder-metallurgical tool steel provides an excellent fatigue strength Recommended prestressing system: STRECON ® E + reduces the stresses and cyclic plastic strains in the fillets, leads to improved fatigue life The outer diameter of the die insert should be close to the inner contour (better effectivity of the stiff carbide winding core). For variable adjustment of the inner diameter of the die (to compensate for wear and manufacturing tolerances), a STRECON ® VARI-FIT is recommended, see case study.see case study.