February 2020 Volume 2

FORGING RESEARCH

Table 5: Summary of friction factor values for nitrided steel inserts measured at room temperatures with and without lubrication.

Figure 12: Change in friction factor for a series of tests using i-Kote coated steel inserts in the un-lubricated condition at room temperature. However, as shown in Table 7, a second set of H13 steel inserts were also coated with i-Kote and tested at room temperature without lubricant. The friction factor for this second set of i-Kote samples was higher than the original set (0.51 versus 0.35). The reason for this difference is unknown at present, but would obviously need to be evaluated in a future study, but either condition appears to be a significant improvement in friction factor over uncoated dies or the other coatings tested here. Table 7: Friction factor values for second i-Kote coated steel inserts measured at room temperature without lubrication. Figure 13 shows the surface of the insert coated with DLC after the forging of three rings, showing build-up of aluminum on the surface of the insert. This is typical of many of the inserts examined in this study, both with and without coatings. However, the amount of build-up on the surface of inserts coating with i-Kote is significantly lower (see Figure 14). The amount of aluminum buildup on the surface of the i-Kote samples did increase after a series of eleven forging trials (see Figure 15), but this did not result in an increase in the friction factor (as shown in Figure 12).

Figure 11: Change in friction factor for a series of tests using nitrided steel inserts in the unlubricated condition at room temperature. PVDCoated Inserts Measured friction factors for PVD coated inserts tested at room temperature without lubricants are listed in Table 6. Two of the PVD coatings, i-Kote and Super MoS 2 , exhibited friction factors significantly lower than un-coated steel inserts (data listed in Table 2). As summarized in Appendix 1, these two PVD coatings are nanocomposite thin-film coatings containing lubricious particles, and so it is likely that the lubricious particles are responsible for the lower friction factors. The change in friction factor for a series eleven forgings with the i-Kote coating in the unlubricated condition is shown in Figure 12, showing that the friction factor did not change appreciably during the production of the eleven forged rings. The four other PVD coatings listed in Table 6 (TiCN, AlCrTiN, SiC andDLC) all exhibited similar friction factors (0.87-1.00) to the un-coated steel inserts, indicating that these coatings do not appear to be useful for reducing friction during forging. Table 6: Summary of friction factor values for PVD coated steel inserts measured at room temperature without lubrication.

Figure 13: Aluminum build-up on steel insert with diamond-like-carbon (DLC) coating after three forging trials.

FIA MAGAZINE | FEBRUARY 2020 58