November 2020 Volume 2

FORGING RESEARCH AND TECHNOLOGY

Comparing the shape change at each orientation, it can be deduced from the metal flow trends that maximum metal flow occurs in the path of least resistance. Because of this, the metal tends to flowmore along the longitudinal axis when oriented parallel to the lay and more in the transverse direction when oriented perpendicular to the lay. Plots of true strain values also showed an interesting result. The most effect on both strains occurred for platen Ra values between 0.25 and 1.25 µm whereas the effect of orientation can be seen at all roughness levels in Figure 10.

(a)

(b)

Figure 11. Spread ratios for 6061 aluminum as a function of orientation angle and platen roughness for (a) Boron Nitride and (b) high temperature vegetable oil at platen temperatures of 149 degrees °C. Steel - A significant difference can be noted between the outlines of aluminum and steel workpieces in that aluminum is more influenced by the platen lay, whereas steel showed a different effect. Comparing the shape of the steel cigar specimens at each orientation shows that the overall shape did not change significantly with increasing angle and this can be seen in Figure 12. While the overall shape is generally the same for each orientation, there are some small differences between the workpieces. The workpieces oriented parallel (0°) to the platen lay tended to show more convex curvature at the ends parallel to the long transverse axis of the workpiece. For the workpieces whose orientation was perpendicular (90°) to the platen lay showed more convex curvature on the sides parallel to the longitudinal axis and almost none on ends parallel to the long transverse axis. 13 Figure 11. Spread ratios for 606 roughne s for (a) r itride and (b) hig temperatu e veg tabl oil at platen tem eratures of 149 degrees °C. Steel - A significant difference can be noted between the outlines of aluminum and steel workpieces in that aluminum is more influenced by the platen lay, whereas steel showed a different effect. Comparing the shape of the steel cigar specimens at each orientation shows that the overall shape did not change significantly with increasing inum as a function f orientation angle and platen

Figure 10. Plot of longitudinal and width strains as a function of lay and surface roughness for AA6061 using high temperature vegetable oil at a platen temperature of 194 °C In order to better illustrate the effect of unidirectional lay and platen roughness on metal flow, three-dimensional plots were made where the spread ratio was used as the dependent variable (Figure 11). The spread ratio, which is commonly used in open die forging, is defined here as the ratio of the width and longitudinal strains. A reduced spread ratio indicates that flow is increased in the longitudinal direction, whereas a larger value would indicate an increase in flow in the width direction. The shape along the roughness axis coincides with the changes in lubrication regimes discussed previously. The effect of the orientation angle is readily apparent and has the largest effect at typical die finishes, though the effect is still present but somewhat reduced at the highest roughness values.

FIA MAGAZINE | NOVEMBER 2020 48