Abstract
Lubrication and friction conditions vary with deformation during metal forming processes. Significant macro-variations can be observed when a threshold of deformation is reached. This study shows that during the cold compression processing of #45 (AISI 1045) steel rings, the magnitude of friction and surface roughness (Ra) changes significantly upon reaching a 45% reduction in ring height. For example, the Ra of compressed ring specimens increased by approximately 55% immediately before and after reaching this threshold, compared to an 18% or 25%variation over a 35%-45% or a 45%-55% reduction in height, respectively. The ring compression test conducted by this study indicates that the Coulomb friction coefficient μ and Tresca friction factor m are 0.105 and 0.22, respectively, when the reduction in height is less than 45%; and 0.11 and 0.24, respectively, when the reduction in height is greater than 45%.
Highlights
Friction has a significant influence on metal forming processes
A cold ring compression test was conducted on medium carbon steel and the friction conditions were evaluated to a low error (0.5%)
The compressed ring specimens for specific height reductions were selected according to variations in friction conditions and their surface topography was measured
Summary
Friction has a significant influence on metal forming processes. Classic models, such as the Coulomb (Eq (1)) and Tresca (or constant shear friction) (Eq (2)) friction models are often used to describe the friction that occurs at a die-workpiece interface: p (1). To determine the magnitude of or m, experimental data from the measurement of changes to the inner diameter of compressed rings are compared with friction calibration curves. This provides estimates of their value under various friction conditions. Pioneering experimental work by Male and Cockcroft [6] to determine these curves in the 1960s was followed by the implementation of several theoretical approaches, such as the slab method [20, 21] and the upper-bound method [22] to elaborate friction calibration curves for ring compression tests These curves did not consider the influence of material and compression conditions on metal forming processes. The magnitude of friction was observed to change significantly immediately before and after this threshold
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