August 2020 Volume 2

FORGING RESEARCH

same temperature as the lower insert). A contact thermocouple probe was used to monitor the cooling of the preheated inserts, and once at the appropriate temperature (100°C/212°F or 200°C/392°F), the press was activated and the testing performed. The rings were forged to a final height of approximately 0.1-inches (a maximum of 70% reduction). The dimensions of the aluminum rings were measured after the forging process using digital calipers. The friction factor for each test condition was estimated using the type of calibration curve shown in Figure 1b. The steel inserts were initially tested at room temperature without lubrication, and the measured friction factors are shown in Figure 3a and 3b. The friction factors varied between 0.60 and 1.0 (slightly dependent upon height reduction), with the average friction factor being about 0.80. As shown in Figure 3a and 3b, when lubricated with either Molykote or graphite, the room temperature friction factor for the un-coated steel inserts was significantly reduced, with the average friction factor with Molykote being 0.12 and 0.30 with graphite. The impact on the friction factor of testing steel inserts at elevated temperatures with lubrication is shown in Figure 3b, 3c, and 3d. These data show that the friction factors for both Molykote and graphite lubricants are similar at 100°C (212°F) as for room temperature testing, but for both lubricants the friction factors increased significantly when tested at 200°C (392°F). As summarized in Figure 3b, for Molykote, the friction factor at 200°C (392°F) increased to 0.38, and for graphite increased to 0.80, the latter being similar to the friction factor for the un-lubricated steel inserts at room temperature. This study has identified and validated a laboratory test, the ring compression test, that simulates the forging process and can discriminate between different lubrication conditions at both room temperature and elevated temperatures. The dies designed for this test allow for the evaluation of friction conditions for aluminum forging as a function of lubricant, die surface condition (such as different PVD coatings), temperature, and other controllable test parameters such as strain rate. This laboratory test, therefore, can be used in future research to identify effective lubricants and perhaps die coatings that minimize friction during the forging operation and so should allow for quantitative studies of lubricants and die coatings that may allow for a reduced amount of conventional lubricants to be used in the forging process.

References 1. K.D. Clarke & C.J. Van Tyne, “Lubrication and Wear in Forging”, ASMHandbook, Vol. 18, Friction, Lubrication, andWear Technology, 2017, 798-807. 2. Forging Industry Technology Roadmap, 2016 Revision, April 30, 2016, Pub: Forging Industry Education and Research Foundation. 3. Vision of the Future, www.forging.org/producers-and suppliers/technology/vision-of-the-future. 4. George E. Dieter, Mechanical Metallurgy, 2nd Edition, McGraw-Hill, 1976, p. 539-549. 5. R. Kohser, PhDDissertation, Lehigh University, 1975. 6. S. Goodchild, “Forging Lubricants, Graphite or Synthetics?”, Forge Magazine, August 7, 2015. Accessed October 19, 2019 online: https://www.forgemag.com/ articles/84386-forging-die-lubricants-graphite-or synthetics. 7. A.T. Male & M.G. Cockcroft, “A Method for the Determination of the Coefficient of Friction of Metals under Conditions of Bulk Plastic Deformation”, J. Inst. Metals, 93, 1964-65, 38. ■

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