Finite Element Investigation of Friction Condition in a Backward Extrusion of Aluminum Alloy

Abstract

Finite element simulations are being widely used to increase the efficiency and effectiveness of design of bulk metal forming processes. In such simulations, proper consideration of friction condition is important in obtaining reliable results. For this purpose, the shear friction factor is widely used for bulk deformation analyses. In the earlier work, it was found that a radial tip was formed on the extruded end of the workpiece and that the radial tip distance had a linear relationship with the forming load in the tip test. In order to characterize the global average shear friction factor, a linear relationship between the nondimensionalized radial tip distance and shear friction factor was numerically determined in this study for AL6061-O for various lubrication conditions. The global average friction condition at the bottom die interface was determined to be about 60 percent of the one at the punch in the backward extrusion under the present conditions.

Characterization of Frictional Behavior in Cold Forging

“…Measurement of the dimension of the specimen with vernier calipers (Mitutoyo CD-15CPX) reduced a size irregularity, and the tolerance of specimens was maintained to be less than ±0.02 mm. In earlier works [5][6][7], the diameter and height of the specimen used in experiments were 30 and 15 mm, respectively.…”

“…2 based on the result from reference [6]. Thus, the x value was quantitatively determined by matching the slope of the numerically calculated nondimensional load versus tip distance graph with the experimentally determined one in parallel depending on the deforming material and given surface and processing conditions.…”

“…Recently, Im et al [5,6] proposed a tip test based on a hybrid of simple compression and backward extrusion in which a radial tip was formed on the extruded end of the specimen to evaluate the friction and lubrication more accurately. A cylindrical specimen, whose diameter was larger than the diameter of the punch and smaller than the diameter of the cylindrical die including the counter punch as shown in Fig.…”

“…Also, the friction condition at the container was assumed to be the same as the one at the counter punch in numerical simulations [6,7].…”

Evaluation of rheological behavior and interfacial friction under the adhesive condition by upsetting method

“…Some parameter estimation approaches, such as direct method and inverse method [16,17], were developed to analyze rheological behavior and interfacial friction; meanwhile, many test methods, such as forward extrusion [18], forward-backward extrusion [19], ring upsetting [20][21][22], cylinder upsetting [23,24], multi-layered upsetting test [3], double-cup extrusion [25][26][27], upsetting-sliding [28], backward extrusion [29], and T-shape compression test [30], were presented to analyze rheological behavior and interfacial friction. Of all the test methods, ring and cylinder upsetting test easily applied is the most well-known test method widely so far [31].…”