3D modeling of recrystallized layer depth and residual stress in dry machining of nickel-based alloy

Abstract

Surface integrity is one of the important requirements of engineers, and it should be controlled for manufacturing of different components. Among different indications of surface integrity, metallurgical aspects including microstructure changes and residual stresses are remarkably effective on performance and service life of the products. Machining process of Inconel 718 alloy is widely used in advanced industries, and therefore, surface integrity of machined workpieces is essential task. Since experimental investigation in this subject is really difficult and time-consuming, finite element modeling of machining processes is used as beneficial method. In this paper, 3D analysis of machining process of Inconel 718 alloy was carried out to evaluate surface integrity in terms of depth of the recrystallized layer and residual stress. At first section, experimental tests were conducted at different machining process to use them as the benchmark for evaluation of recrystallized layer depth in machining simulation. Using the critical strain criterion, the numerical results of recrystallized layer depth was calculated and successfully verified with corresponding experiments. To improve precision of the numerical results, the user subroutine was implemented in FE code to employ hardness-based flow stress and also cutting tool geometry was precisely measured. At the second section, residual stress distribution in the machined surface was firstly predicted using the elastic-plastic analysis and verified with experimental test. After that, the effect of testing conditions was evaluated and discussed on different indications of residual stress profile. Finally, there is reasonable hope that utilized strategy can be extended efficiently for other manufacturing processes.

Experimental Evaluation of Surface Alterations Induced in Machining of Ti-6Al-4V Alloy

“…It seems that with increasing cutting speed, shorter time will be available for heat exchange between the cutting zone and environment, and also friction is increased. As a result of these events, the maximum machining temperature is increased [3]. In contrast, the increment of cutting speed from a specific range does not affect the temperature of the cutting region and the temperature decreases.…”

“…More in detail, at 0.065 mm/rev feed rate, microhardness at top layer of sample was 341.7 HV and at 0.261 mm/rev feed rate, hardness was 322 HV. It seems that at higher feed rates, the temperature in machining region becomes higher and the thermal softening effect prevails and, subsequently, hardness decreases [3]. Figure 2 (b) represents the microhardness variations for different depths of cut.…”

“…The microhardness variations in the subsurface layers also had a similar trend to the surface layers. In fact, with increase of depth of cut, the machining forces increase and the mechanical strain hardening occurs at the surface, resulting in the enhancement of hardness of surface layers [3]. Figure 2 (c) demonstrates the microhardness changes by variation of cutting speed.…”

“…Despite the mentioned properties, due to the existence of a hard phase in the Ti-6Al-4V alloy, there are numerous problems in the machining of this material. Owing to the sensitivity of machined workpieces and generation of severe thermal-mechanical loads during operation, machining in inappropriate conditions causes important damage, including microcracks in the material [2,3]. In recent years, hard machining has been employed in industry due to its countless benefits.…”

“…These changes cause preformation of work hardening and microstructural changes, and thereby, affect the efficiency and service quality of parts. Thus, controlling the quality of machined part of the final product is a key issue for proper operation [3,5].…”