Final Heat Treatment as a Possible Solution for the Improvement of Machinability of Pb-Free Brass Alloys

In today's unmanned productions systems, it is very important that the manufacturing processes are carried out efficiently and smoothly. Therefore, controlling chip formation becomes an essential issue to be dealt with. It can be said that the material removal from a workpiece using machining is based on the degradation of material cohesion made in a controlled manner. The aim of the study was to understand the chip formation mechanisms that can, during uncontrolled processes, result in the formation and propagation of microcracks on the machined surface and, as such, cause failure of a component during its operation. This article addresses some aspects of chip formation in the orthogonal and oblique slow-rate machining of EN 16MnCr5 steel. In order to avoid chip root deformation and its thermal influence on sample acquisition, that could cause the changes in the microstructure of material, a new reliable method for sample acquisition has been developed in this research. The results of the experiments have been statistically processed. The obtained dependencies have uncovered how the cutting tool geometry and cutting conditions influence a chip shape, temperature in cutting area, or microhardness according to Vickers in the area of shear angle.

Section: State Of the Artmentioning

confidence: 99%

Comparative Study of Chip Formation in Orthogonal and Oblique Slow-Rate Machining of EN 16MnCr5 Steel

Monková

Monka

Sekerakova

et al. 2019

“…Chip curl is also influenced to a large extent by the nose configuration and its effect is dependent on the relationship between the nose radius and process parameters selected [21]. Chip segmentation is of pivotal importance, since it facilitates the machining ergonomics and scrap removal without damaging workpiece surface quality and ensuring the safety of the working personnel [22].…”

Section: State Of the Artmentioning

confidence: 99%

“…Using the software MATLAB, the following regression functions, (22) and (23), were defined for both types of machining, while their reliabilities R 2 were 0.91 and 0.93, respectively: a) for orthogonal cutting: On the first cut of the sample chip root, the built-up edge was not noticeable, but according to the shape of the outgoing chip, the rake angle appeared negative, while the rake angle of the straight roughing tool was positive, at γ = 3 • . The cutting angle Φ was 36 • .…”

Section: A Chip Root Of En 16mncr5 Steel Observationmentioning

confidence: 99%

“…The experimentally obtained values of the shear angle Φ, as well as the encoded matrix of individual cutting condition parameters, are shown in Table 7. Using the software MATLAB, the following regression functions, (22) and (23), were defined for both types of machining, while their reliabilities R 2 were 0.91 and 0.93, respectively: (a) for orthogonal cutting:…”

Section: A Chip Root Of En 16mncr5 Steel Observationmentioning

confidence: 99%

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Research on Chip Shear Angle and Built-Up Edge of Slow-Rate Machining EN C45 and EN 16MnCr5 Steels

Monková

Monka

Sekerakova

et al. 2019

One of the phenomena that accompanies metal cutting is extensive plastic deformation and fracture. The excess material is plastically deformed, fractured, and removed from the workpiece in the form of chips, the formation of which depends on the type of crack and their propagation. Even in case of the so-called 'continuous' chip formation there still has to be a fracture, as the cutting process involves the separation of a chip from the workpiece. Controlling the chip separation and its patterning in a suitable form is the most important problem of the current industrial processes, which should be highly automated to achieve maximal production efficiency. The article deals with the chip root evaluation of two EN C45 and EN 16MnCr5 steels, focusing on the shear angle measuring and built-up edge observation as important factors influencing the machining process, because a repeated formation and dislodgement of built-up edge unfavorably affects changes in the rake angle, causing fluctuation in cutting forces, and thus inducing vibration, which is harmful to the cutting tool. Consequently, this leads to surface finish deterioration. The planing was selected as a slow-rate machining operation, within which orthogonal and oblique cutting has been used for the comparative chips' root study. The planned experiment was implemented at three levels (lower, basic, and upper) for the test preparation and the statistical method, and regression function was used for the data evaluation. The mutual connections among the four considered factors (cutting speed, cutting depth, tool cutting edge inclination, and rake angle) and investigated by the shear angle were plotted in the form of graphical dependencies. Finally, chips obtained from both steels types and within both cutting methods were systematically processed from the microscopic (chip root) and macroscopic (chip pattern) points of view.Metals 2019, 9, 956 2 of 27 of a machined surface are in many cases not achievable by mechanical working or casting processes, because the surfaces of the parts are adversely affected. This is why machining is needed.[3] Controlling the chip separation and its patterning in a suitable form is the most important problem of the current industrial processes, which should be highly automated to achieve maximal production efficiency.One of the phenomena that accompanies metal cutting is extensive plastic deformation and fracture. The excess material is plastically deformed, fractured, and removed from the workpiece in the form of chips, the formation of which depends on the type of crack and their propagation. Even in the case of so-called 'continuous' chip formation there still has to be a fracture, as the cutting process involves the separation of a chip from the workpiece. Chips at the machining are formed due to tearing and shearing, the workpiece material adjacent to the tool face is compressed and a crack runs ahead of the cutting tool and towards the body of the workpiece. Cutting takes place intermittently and there is no movement of the w...

“…Such studies were mainly focused in the optimization of various machining criteria under certain machining process parameters variation, using parametric and non-parametric studies, e.g., design of experiments (DOE) and analysis of variance (ANOVA) approaches (see relevant Ref. [9][10][11]).…”

Section: Introductionmentioning

confidence: 99%

A Comprehensive CFD Model for Dual-Phase Brass Indirect Extrusion Based on Constitutive Laws: Assessment of Hot-Zone Formation and Failure Prognosis

Pashos¹,

Pantazopoulos²,

Contopoulos³

2018

Self Cite

A numerical method for the precise calculation of temperature, velocity and pressure profiles of the α-β brass indirect hot extrusion process is presented. The method solves the Navier-Stokes equations for non-Newtonian liquids with strain-rate and temperature-dependent viscosity that is formulated using established constitutive laws based on the Zener-Hollomon type equation for plastic flow stress. The method can be implemented with standard computational fluid dynamics (CFD) software, has relatively low computational cost, and avoids the numerical artifacts associated with other methods commonly used for such processes. A response surface technique is also implemented, and it is thus possible to build a reduced order model that approximately maps the process with respect to all combinations of its parameters, including the extrusion speed and brass phase constitution. The reduced order model can be a very useful tool for production, because it instantaneously provides important quantities, such as the average pressure or the temperature of hot-spots that are formed due to the combined effect of die/billet friction and the generation of heat from plastic deformation (adiabatic shear deformation heating). This approach can assist in the preliminary evaluation of the metal flow pattern, and in the prediction and prevention of critical extrusion failures, thus leading to subsequent process and product quality improvements.