November 2020 Volume 2

workpieces was Fe2O3 scale removal prior to testing. This was accomplished by heating the samples to working temperature and then knocking the scale off with vigorous tapping. While this removed 70% of the oxide, complete scale removal was achieved by coating the samples with a cutting fluid and then reheating for 10 minutes. As the cutting fluid burned off, an expanding gas was created beneath the oxide scale, separating it from the surface. Figure 2 shows typical steel workpieces before and after the scale is removed. All ring test specimens were cut from round bar stock, drilled, reamed, and then ground flat to achieve a 6:3:2 (OD:ID:Height) ratio. The side pressing specimens were cut from 6.35 mm (0.25 in) square bar stock and then ground to length. A billet ratio of 8:1 (length:width) was chosen for side pressing, as this is representative of values used in many commercial forging processes. All 1018 steel and 6061-T6 aluminum test pieces were heated in a resistance type box furnace for a minimum of 30 minutes to achieve temperature equilibration prior to testing. One of the challenges in using steel workpieces was Fe 2 O 3 scale removal prior to testing. This was accomplished by heating the samples to working temperature and then knocking the scale off with vigorous tapping. While this removed 70% of the oxide, complete scale removal was achieved by coating the samples with a cutting fluid and then reheating for 10 minutes. As the cutting fluid burned off, an expanding gas was created beneath the oxide scale, separating it from the surface. Figure 2 shows typical steel workpieces before and after the scale is removed. FORGING RESEARCH AND TECHNOLOGY Figure 2. AISI 1018 side-pressing sample prior to scale removal (left) and post oxide scale removal after being coated with a cutting fluid (right). Initially it was intended to replicate hot forging conditions for both materials but, due to heat losses during transfer and die chilling, maintaining a controlledworkpiece temperature over 1093 °C (2000 °F) was not possible for the steel tests. Consequently, warm forging conditions (900 °C) were used for steel as these could be consistently maintained in the lab. For the steel workpieces, a 1:8 graphite-water based forging lubricant, (Bonderite L-FG; Henkel AG & Co.), was manually applied to the platens using an atomizing spray device to ensure that an even, thin layer of lubricant was applied to the surface of each platen. For the aluminum samples, both high-temperature vegetable oil and boron nitride were used, and each was applied using an aerosol container. Ring testing was conducted according to standard test procedures. For the cigar test, some discussion is warranted. In order to study the effect of directionality, three different workpiece orientations were used (0˚, 45˚, and 90˚) where the longitudinal axis was placed at an angle relative to the lay direction as depicted in Figure 3. In order to ensure consistent alignment of the workpieces relative to the lay direction, orientation was confirmed using a laser pointer mounted on a magnetic base. Using this location method, alignment was held to within ± 5˚. 4

HRC 50-55 to develop a protective oxide layer and inhibit abrasive wear. A 4-post Superior die set was used to mount the platens and instrumentation package (Figure 1) on the press. Kiss blocks were also used to achieve a consistent height reduction. A purpose-built control system that enabled the platen temperature to be controlled to within ±4 °C was used during each run.

Figure 1. Photograph showing the die setup with instrumentation components. Workpiece Material & Preparation - Both AISI 1018 cold rolled steel and AA 6061-T6 aluminum were used as workpiece materials. Experimental conditions used for each material are given below in Table 1. A vibratory bowl was used to achieve a uniform, non directional surface roughness on all specimens to ensure the workpiece surface did not influence the test results. The non directional (isotropic) surface roughness for all workpieces was Ra 0.89 µm (35 µin) and was confirmed by averaging profilometer measurements made along three different directions.

Table 1. Summary of test conditions used in the study.

All ring test specimens were cut from round bar stock, drilled, reamed, and then ground flat to achieve a 6:3:2 (OD:ID:Height) ratio. The side pressing specimens were cut from 6.35 mm (0.25 in) square bar stock and then ground to length. A billet ratio of 8:1 (length:width) was chosen for side pressing, as this is representative of values used in many commercial forging processes. All 1018 steel and 6061-T6 aluminum test pieces were heated in a resistance type box furnace for a minimum of 30 minutes to achieve temperature equilibration prior to testing. One of the challenges in using steel All ring test cimens were cut from round bar stock, drilled, reamed, and then ground flat to chieve a 6:3:2 (OD:ID:Height) rat o. The side pressing specimens were cut from 6.35 mm (0.25 in) square bar stock and then ground to length. A billet ratio of 8:1 (length:width) was chosen for side pressing, as this is representative of values used in many commercial forging processes. All 1018 steel and 6061-T6 aluminum test pieces were heated in a resistance type box furnace for a minimum of 30 minutes to achieve temperature equilibration prior to testing. One of the challenges in using steel workpieces was Fe 2 O 3 scale removal prior to testing. This was accomplished by heating the samples to working temperature and then knocking the scale off with vigorous tapping. While this removed 70% of the oxide, complete scale removal was achieved by coating the samples with a cutting fluid and then reheating for 10 minutes. As the cutting fluid burned off, an expanding gas was created beneath the oxide scale, separating it from the surface. Figure 2 shows typical steel workpieces before and after the scale is removed.

Figure 3. Specimen orientation used in side-pressing tests. After side pressing, the length, width and height of each workpiece was measured and recorded. While the deformed height was consistent throughout, workpiece length and width varied along these directions due to friction and corner effects. Due to the curved

FIA MAGAZINE | NOVEMBER 2020 45