Effect of die pressure on the lubricating regimes achieved in wire drawing
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PRODUCTION PROCESS
Effect of die pressure on the lubricating regimes achieved in wire drawing Umberto Prisco1 · Gustavo Aristides Santana Martinez2 · Leonardo Kyo Kabayama3 Received: 7 May 2020 / Accepted: 15 September 2020 © German Academic Society for Production Engineering (WGP) 2020
Abstract An experimental campaign of wire drawing was carried out under different conditions of average die pressure. Experiments were carried out measuring the drawing force and the temperature at the exit of the deformation zone with the use of a thermocouple closely located to the wire-die interface. Dies of three different semi-angles (6°, 7° and 9°), were employed to obtain different values of die pressure, while different lubrication regimes were achieved varying the drawing speed in the range 1–22 m/s. It was demonstrated that lubricating regimes of lower friction coefficient are achieved at smaller values of the drawing speed with increasing the die pressure. Likewise, the hydrodynamic regime arises at lower drawing speeds by increasing the die semi-angle. For example, it was observed that the hydrodynamic regimes developed at 19 m/s for the 6° die but at 15 m/s for the 9° die. This behaviour was correlated to the response of the lubricant viscosity to the die pressure by means of the Hersey analysis. The consequences of this finding on the problem of optimizing the die angle with the objective to reduce the drawing stress are discussed. On this basis, it is shown that the optimum die angle decreases as the drawing speed increases, other things being equal. Keywords Wire drawing · Drawing speed · Die pressure · Lubricant · Viscosity · Hersey number
1 Introduction Within wire drawing industry the requirements for a more reliable, zero defect and low cost production have been lately coupled with pressing demands for higher productivity [1]. This has pushed this manufacturing sector toward the adoption of ever-increasing drawing speeds, for example exceeding 25 m/s in modern multi-stage drawing machines [2]. However, high speeds can bring about high values of * Umberto Prisco [email protected] Gustavo Aristides Santana Martinez [email protected] Leonardo Kyo Kabayama [email protected] 1
Department of Chemical, Materials and Production Engineering, University of Napoli Federico II, Piazzale Tecchio 80, 80125 Naples, Italy
2
Engineering School of Lorena, University of São Paulo-USP, Lorena 12602‑810, Brazil
3
Institute of Mechanical Engineering, Federal University of Itajubá-UNIFEI, Itajubá 37500‑903, Brazil
drawing stress and of temperature induced into the wire with end effects on the lubrication regime experienced into the die and consequently on the friction at the wire-die interface [3, 4]. Historically the lubricating mechanism and the friction phenomena experienced by the wire into the deformation zone has been condensed into one parameter: the coefficient of friction μ, which is the ratio of the average frictional stress to the average die pressure [5]. Several authors have exploi
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