Influência das propriedades mecânicas das ligas de alumínio na usinabilidade foco no grau de recalque, na dimensão da zona de fluxo e na microdureza dos cavacos

Abstract

The machinability of materials are strongly dependent on their properties and can be measured by several parameters, including tool life, machining forces, cutting temperature, surface roughness among others. In a previous work1 developed at LEPU2 the machinability of several aluminum alloys was studied considering the cutting temperature, machining force, power consumption, and surface roughness, correlating them with the mechanical properties (hardness, tensile strength and elongation) and the cutting conditions (cutting speed, feed rate and depth of cut). Others variables related to the chips are also important to the machining process. The chip thickness ratio (or the shear angle), the microhardness of the chips and the flow zone are three of these important variables. The main objective of the present work is to experimentally determine the correlation among the mechanical properties (hardness, tensile strength, elongation and necking) of several aluminum alloys and the cutting conditions (cutting speed, feed rate and depth of cut) with the characteristics of the chips collected during cylindrical turning. The chip forms were also studied. The following alloys were considered: 3030 O, 6262 T4, 6351 T4, 7075T73 e 7075 T6, what allowed models that correlates the output (chip thickness ratio, flow zone dimensions and microhardness of the chips) with the input parameters (properties of the aluminum alloys and the cutting conditions) to be generated, through multiple regression analysis. The chip thickness ratio and the flow zone dimensions were optimized using surface response method SRM and classical optimization techniques (global utility function and differential evolution). The microhardness was also measured in chip roots samples obtained in quick stop tests for a set of cutting conditions. The 2011 T4 alloy was used to validate the models linear regression. The generated models showed small errors indicating great coherence and adequacy for the machinability characteristics considered. This stresses the importance of the use of statistical tools in the experimental studies of machinability. The cutting conditions and the mechanical properties of the alloys showed significant influences on the responses (output parameters) as expected. When using Global Utility Function the best values found for the degree of repression Rc = 1.84 and the size (thickness) of the flow zone Dz = 19.1 μm, were to vc = 284 m /min, ap = 2.18 mm, f = 0.23 mm /rot, D = 140 HV, σR = 420 MPa and Z = 27%. At high speeds best values for Rc =1.7 and Dz = 16.3 μm were for: vc = 401 m/min, ap = 2.81 mm, f = 0.20 mm/rev, D = 132 HV, σR = 500 MPa and Z = 25%.