November 2020 Volume 2

The spread ratio was also calculated and plotted for steel and is shown below in Figure 16 for three different platen temperatures. cigar specimens at 149 ºC (300 °F) (d – f) and aluminum cigar specimens at 20 ºC (68 °F) (g – i). Steel specimens were compressed at platen temperatures of 149 ºC (300 °F) using a graphite lubricant and aluminum specimens were compressed at platen temperatures of 149 ºC (300 °F) using high temperature vegetable oil as a lubricant. The spread ratio was also calcul ted nd plotted for steel and is shown below i Figure 16 for three different platen temperatures. (g) R a 0.51 µm (20 µin) (i) R a 1.52 µm (60 µin) Figure 15. Comparison of steel cigar specimens at 1010 ºC (1850 °F) (a – c), aluminum (h) R a 1.02 µm (40 µin)

FORGING RESEARCH AND TECHNOLOGY

Conclusions Based on the specimen shapes and friction factors calculated from ring testing, it can be concluded that: • Due to the unidirectional platen surface lay, the friction factors for aluminum and steel rings is significantly higher along the direction that is perpendicular to the platen lay. • For aluminum ring specimens compressed with either high temperature vegetable oil or boron nitride lubricant, the friction factor generally increased with surface roughness from Ra 0.25 – 6.1 µm (10 – 240 µin). A deviation was noted at a platen roughness of Ra 1.02 µm (40 µin) which was similar to that of the aluminum workpiece prior to compression. It is thought that, due to the similar surface roughnesses of the platen and workpiece, this resulted in a mixed lubrication condition. • Steel ring specimens showed a similar trend to those of aluminum as friction factor generally increased with platen surface roughness from Ra 0.25 – 6.1 µm (10 – 240 µin). A local maximum friction factor is seen at a platen surface roughness of Ra 1.52 µm (60 µin) due to similar workpiece and platen surface roughnesses and the high flow stress of the steel workpieces. It is hypothesized that interlocking of asperities occurs at the interface thus leading to an increase in friction factor. In order to study the effects of lay directionality on metal flow, rectangular shaped workpieces were side pressed (a.k.a. cigar test). Based on an analysis of the deformed workpieces and true strains, it was concluded that: • For aluminum and steel cigar workpieces, as the workpiece orientation increases relative to the platen lay, the workpiece length decreases and the width increases. The shape of the aluminum workpiece is more affected by the platen lay when compared to steel due to its lower flow stress which caused sliding in the parallel direction but shearing in the perpendicular direction. In the case of steel, sliding likely predominated in both directions. • For both steel and aluminum cigar workpieces, the average length true strain decreased, and the average width true strain increased, with an increase in workpiece orientation. The only deviation to this trend was seen at lower platen roughnesses when steel workpieces were used. It is hypothesized that this is due to the increased real area of contact at low platen roughnesses. Bibliography: 1. Matcha, Andrew, R., “Investigation of Surface Topology Effects on Metal Flow of Aluminum and Steel During Hot Compression”, M.S. Thesis, Department of Mechanical Engineering, Marquette University, 2019. ■ Joseph Domblesky Marquette University Department of Mechanical Engineering joseph.domblesky@marquette.edu

(a)

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(b)

Figure 16. Spread ratios for AISI 1018 steel as a function of orientation angle and platen roughness for surface temperatures of (a) 149, (b) 176, and (c) 204 degrees C. (c) Figure 16. Spread ratios for AISI 1018 steel as a function of orientation angle and platen roughness for surface temperatures of (a) 149, (b) 176, and (c) 204 degrees C. Conclusions Based on the specimen shapes and friction factors calculated from ring testing, it can be concluded that:

FIA MAGAZINE | NOVEMBER 2020 51