Hot Hydroforging for Lightweighting Presentation IDE 2015
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The document discusses the hot hydroforging process, which involves creating lightweight hybrid gears using a metal shell and a low melting core, with aims for significant weight reduction and machining efficiency. It details the objectives of crafting gears with near-net shapes, various material considerations, and the advantages of investment forging to allow hollow structures. The conclusion highlights the feasibility of this process and the effectiveness of using steel/glass as core material over steel/aluminum due to better compatibility.
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Hot Hydroforging for Lightweighting Presentation IDE 2015
- 1. 2015-IDE Conference Hot Hydroforging for Lightweighting Bulent Chavdar1, Robert Goldstein2, Xi Yang3, Jacob Butkovich4, Lynn Ferguson5 1Eaton Corporation, Southfield, MI, USA 2Fluxtrol Inc., Auburn Hills, MI, USA 3General Motors, Warren, MI,USA 4Walker Forge Inc., Clintonville, WI,USA 5DANTE Solutions Inc., Cleveland, OH, USA September 23, 2015
- 2. 2 What is Hot hydroforging? Definition: Hot forging of lightweight products from a hybrid billet of a metal shell and a low melting core. Concept: Hot hydroforging is done at temperatures where the core material is in viscous state and builds up uniform pressure thereby enabling a uniform deformation of the metal shell. Goal: Lightweight net shape forging with complex topologies Viscous core Core is squeezed out of center.
- 3. 3 Hybrid lightweight gear The outer structure is steel, the inner structure is a low melting lightweight material.
- 4. 4 Objectives • Forging light weight hybrid gears with net teeth and near net center. • The hybrid gear has all steel outer structure. • Investment forging is enabled (molten core can be emptied). • Press loads are reduced and larger gears can be forged. • 30% to 50% weight reduction per gear is targeted. • Up to 10% weight reduction per transmission is expected. • 60% to 70% reduction in machining scrap rate due to near net teeth. • Gear teeth can be induction hardened with significant energy savings.
- 5. 5 Steels and low melting point materials
- 6. 6 Structural FEA Modeling of Hybrid Gears 2.5 mm thick steel cover Out side body with Steel Inside core body with Aluminum Gear B Gear D
- 7. 7 Subassembly Deformation and Stress, All Steel Gear and Hybrid Forged Gear Deformation Hybrid-Bi-Metal forging All Steel Gear B Gear D Countershaft Gear B Gear D Countershaft Total (mm) 0.48 0.425 0.297 0.46 0.421 0.294 Angular (0) 0.31 0.31 0.31 0.3 0.3 0.3 Radial (mm) -0.063 -0.127 -0.127 -0.06 -0.122 -0.123 Axial (mm) 0.081 -0.0442 0.032 0.077 -0.043 0.031 Stress (MPa) Hybrid-Bi-Metal forging All Steel Gear B Gear D Gear B Gear D Von-Mises 825 876 761 745 Max principal 730 728.96 696 673.6 Min principal -934 -977.87 -859 -831 No stress or deflection is increased more than 8% for the bimetal gear compared to the all-steel gear
- 8. 8 Hybrid billet design for hot hydroforging Cap Tube Al bar Steel tube seamless, and w/ seam 0.25” and 0.5” wall Weld bead Electron beam welding Interference fit 0.003”, and 0.005” Factors Levels Wall thickness 0.25” (6.25 mm) 0.5” (12.5 mm) Steel tube type seamless with seam Interference fit 0.003”(0.075mm) 0.005” (0.125 mm) Forging technique Hot (solid state) Hot hydroforging
- 9. 9 Die design and simulations Weld bead Electron beam welding The pockets in the top and the bottom dies keep the weld zone of end caps under compression during busting forging. Before forging After forging Forged part Closed and split die
- 10. 10 0 100 200 300 400 500 600 700 0 20 40 60 80 100 NormalPressure(MPa) Curvilinear distance (mm) Normal Pressure on the die a b c d e e d cba Ram displacement (mm/406mm) Forge load (ton) Fill radius, d (mm) Stress at the die fillet, d (MPa) 405.90 973 1.50 2120 405.87 758 2.30 1750 405.68 552 4.25 1320 Die stress analysis Forging temperature: 1100C
- 11. 11 Interpower High Frequency Induction Power (10 kHz, 500 kW) Interpower Induction controller being built up New Interpower coil for high frequency
- 12. 12 Induction heating simulations for solid state hot forging Temperature vs. time in the radial direction Ramp HoldTransfer Al Core Steel Case 0 200 400 600 800 1000 1200 0 0.01 0.02 0.03 0.04 Temperature (C) T = 2 t = 4 t = 6 t = 8 t = 10 t = 12 t = 14 t = 16 t = 18 t = 20 t = 22 t = 24 t = 26 Al Core Steel Case Both steel and aluminum are in solid state Due to differential heating rate steel shell pulled away from the core
- 13. 13 Billet induction heating simulations for hot hydroforging, on-off control strategy Iso-temperature lines showing the temperature distribution in the radial direction from the center axis to the outer diameter of the billet at mid height of the billet as function of the heating time. The heating simulation shows the effect of on/off control strategy Heating simulation shows that aluminum core reaches 1000C in 6 on/off cycles in 60 seconds
- 14. 14 Solid state hot forging simulations Solid state forging simulations predicted folds and shrinkage gap.
- 15. 15 Steel wall thickness uniformity simulations with hot hydroforming Top surface constrained bottom surface constrained Symmetrical plane Linearly increasing hydrostatic pressure Boundary conditions
- 16. 16 Concept: Two-blow hot hydroforming simulations for uniform wall thickness 1st blow forming preform transfer to 2nd die 2nd blow forming The teeth profile is formed half way in the first die (top). The preform is indexed by half width of tooth and placed in the second die for final forging (bottom).
- 17. 17 Tooth profile wall uniformity comparison 2 blow operation with hydrostatic pressure 1 blow operation Solid state forging simulation • Non-uniformity index : largest thickness / smallest thickness. 1 means ideal uniform. • Al - steel ratio: area of the Al / area of the steel in the tooth. Non-uniformity index 1.3 6.7 Al-steel ratio 2.7 0.6 The steel wall thickness uniformity can be improved significantly with 2- blow, indexed, hot hydroforging as compared to 1-blow solid state forging
- 18. 18 Forging Trials at Walker Forge Walker’s Erie 4000 ton mechanical press Bi-Metal billets before forging Interpower Induction 10 kHz heater installed at Walker Forge Heating Transferred to the die Right after forging A few seconds after forging Forged parts
- 19. 19 Comparison of hot forging and hot hydroforging experiments Solid state hot forging Steel @1100C Al core @400C World’s 1st Hot hydroforging Steel @1100C Al core @1100C Fractured wall Incomplete fill Fold Non-uniform wall Gap due to CTE mismatch No fracture or crack Cracks Uniform wall Void due to CTE mismatch Hot hydroforging is promising if CTE mismatch is eliminated
- 20. 20 Weld zone healing in hot hydroforging Before forging Dentritic structure After busting hot hydroforging Normalized structure Dendritic structure of weld zone disappeared after hot hydroforging
- 21. 21 “Investment Forging” • Investment forging is a term coined at Eaton. • It describes a process where the molten core is evacuated from the forged part after a hot hydroforging process leaving behind a hollow part. • Investment forging provides the ultimate weight reduction up to 50% for a gear. • Investment forging can also be applied to many other forged parts. For example forged hollow engine exhaust valves can be created by investment forging. Steel eb weld Core emptied Low melting core
- 22. 22 Eliminating CTE Mismatch with Glass • Glass is identified as the core material of choice with matching CTE to that of steel, 10-12 (10-6 m/mK). • The other advantages of glass: • Low cost • Low density • Good bonding to steel • Lower elastic modulus than steel • Working temperature can be optimized • May enable and temper a through-hardened steel wall
- 23. 23 Heating/cooling simulations of hybrid billets, Displacement and gap formation in solid state Steel/Glass Steel/Aluminum No gap predicted Significant gap predicted Glass is a promising lightweight core material.
- 24. 24 Histories of temperature, radial displacements and radial gap N165 is on steel bore, and N4442 is on outer surface of core. Steel/Glass Steel/Aluminum No gap predicted Significant gap predicted * * *
- 25. 25 Conclusions • Feasibility of hot hydroforging and investment forging for lightweighting, net shape forging and waste reduction are demonstrated. • Steel/aluminum hybrid billets were prepared. Then, the billets were hot hydroforged in closed dies. • A uniform steel wall thickness was observed all around the hot hydroforged part upon cross sectioning. • Weld seams are healed (normalized) upon hot hydroforging. • Steel/glass is a more promising hybrid than steel/aluminum for hot hydroforging due to the CTE match.
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