February 2020 Volume 2
FORGING RESEARCH
Figure 7: Simulation of the stresses developed in the test die during forging of aluminum rings. For testing at room temperature, the aluminum rings were simply placed onto inserts pre-loaded into the holders on the hydraulic press. For lubricated tests, two types of lubricants were used – an aerosol graphite spray (CNC brand) and a molybdenum-based grease called Molykote. The lubricants were applied directly to the aluminum rings, rather than to the steel die inserts. For elevated temperature testing, the steel inserts were loaded into an electric resistance box furnace pre-heated to a temperature approximately 50°C hotter than the test temperature (furnace temperature of about 250°C for a test temperature of 200°C, and a furnace temperature of about 150°C for a test temperature of 100°C). The inserts were heated in the furnace for about two hours prior to testing. Once the inserts were preheated to the required temperature, they were removed from the furnace, inserted into the holders, and a room temperature aluminum ring placed onto the lower insert (previous testing has shown that the aluminum rings would heat within seconds to 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 or 200°C) the press was activated and the testing performed. The rings were forged to final heights down to 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 was estimated using the type of calibration curve shown in Figure 2. Results Results from the various testing conditions are summarized below. Un-coated Steel Inserts The first series of tests were performed using un-coated steel inserts. The un-coated inserts were initially tested at room temperature without lubrication, and the measured friction factors are shown in Figure 8 and are summarized in Table 2. As shown in Figure 8, the friction factors varied between 0.60 and 1.0 (slightly dependent upon height reduction), with the average friction factor being about 0.80.
Figure 4: Schematic drawing of the upper and lower forging dies, incorporating the hardened H13 steel inserts.
Figure 5: Photograph of the steel holders containing a set of hardened steel inserts. Additional sets of inserts are also shown.
Figure 6: Drawings of the upper insert (left) and lower insert (right). Dimensions in inches. A tube of 6061 aluminum was purchased for the testing. The tube had an OD of 1.0-inches and an ID of 0.5-inches. Samples 0.33-inches long were cut from the rod for testing. After saw-cutting the aluminum rings, the saw cut surfaces were ground flat, and their final dimensions measured using digital calipers. As shown in Figure 7, modeling of the steel forging die and insert was performed usingDEFORMsimulation software, which showed that the highest stress generated was only 32.8 ksi, well below the yield strength of hardened H13 steel. Therefore, the researchers were confident that plastic deformation of the H13 steel inserts would not occur during testing.
FIA MAGAZINE | FEBRUARY 2020 56
Made with FlippingBook - professional solution for displaying marketing and sales documents online