Papers by Keyword: Turning

Abstract: In the paper the detailed structural changes in the cutting zone were determined using metallography. Accurate determination of parameters such as shear angle, slip angle, chip thickness, cutting ratio, chip separation point, etc. required metallographic analysis on a relatively complex sampling of the cutting area. We performed the analysis on an orthogonal cutting. We achieved orthogonal cutting by turning a thin-walled Inconel 718 and C45 alloy tubes and setting the lath bit cutting edge perpendicular to the tube axis. In real state, the shapes in the cutting zone are more complicated therefore the chip thickness was determined using quantitative metallography from the equality of areas and the resulting point of transition between the chip and the machined surface. The shear angle starts from this point and is a tangent to the cutting edge, the direction of which was determined using the Thales circle. The distance between this point and the machined surface which represents a layer which is not separated from the machined material but is planar deformed was determined too. The depth of the deformed layer and the value of deformation on the machined surface was determined by quantitative metallography. A much simpler numerical simulation was performed with the same parameters using Deform 2D/3D software package. Numerical simulation could not fully replace metallographic analysis, but to some extent numerical simulation can be used instead of metallographic analysis.

Abstract: Austenitic stainless steels (ASSs) are characteristic with a combination of good mechanical and corrosion properties. Therefore, they are used in the primary circuits of nuclear power plants. Under the influence of a corrosive environment containing chloride ions and mechanical loading, the phenomenon of stress corrosion cracking occurs in ASSs. SCC can also be initiated by the surface condition of ASSs. Machining is usually the last stage of production, during which a significant deformed zone with high residual tensile stresses can be created, which can accelerate the initiation of stress corrosion cracking. Research is focused on analyzing the influence of final turning on microstructural changes of the surface-machined layer caused by various turning parameters (e.g.: cutting speed, feed, depth of cut, cutting tool geometry). No significant microstructure changes were observed between the samples by light microscopy, so we focused on transmission electron microscopy (TEM) on thin lamellas prepared using the focus ion beam (FIB) technique. TEM observation confirmed the presence of a deformed zone and a passivation layer. In the case of the sample that was turned with a higher feed and cutting speed, the passivation layer was discontinuous. Such a microstructural change can significantly affect the corrosion resistance of ASS.

Abstract: During metal machining, under certain conditions, vibrations occur, both at the cutting tool, at the workpiece and at the machine tool. The appearance of vibrations during the cutting process is troublesome, because vibrations reduce the durability of cutting tools (especially in tools with inserts). It also increases machine tool wear and worsens the quality of the machined surface (roughness). The problem of vibration is vast and will represent a permanent research topic for tool makers, machine tool builders and process engineers. This paper presents the study and finite element analysis of the vibrations of a cutting tool, a tool used in the longitudinal turning process, both for deburring and finishing operations. The behavior of the tool, the natural frequencies and the elastic deformations that lead to the impairment of the processing precision and the quality of the surface obtained after processing were demined by calculation. We believe that this study is useful both to the manufacturers of cutting tools, but especially to the technological engineers, for the optimization of the process, by avoiding the cutting parameters that lead to resonance with the tool's own frequencies.

Abstract: Tools applied in various cutting processes are constantly exposed not only to thermal, mechanical but also chemical stresses, which has a significant impact on the wear of the cutting tool, but also on the cutting performance itself. By measuring the components of the cutting force, we can predict the wear or suitability of the cutting tool for machining given types of materials. The present study investigates the effect of changing the shape of the tool geometry on the magnitude of cutting forces in turning tool steels. The measurement of cutting forces was carried out on a conventional lathe with a Dynamometer attachment, interchangeable cutting inserts of DNMG and WNMG type were used as tools, tool steels produced by PM and conventional metallurgy were used as the machined material. The cutting tools were selected regarding their common use in engineering production, the tool steels were selected with regard to their application in industry in the production of rotary tools.

Abstract: It is well known that the surface roughness in turning consists of the theoretical roughness, vibration in the depth of cut direction, and overcutting by adhered work material. Some of authors had already proposed the method to calculate surface roughness components. In this method, the approximate arc was used as a representative tool contour of the tool contour to dividing roughness curve into each feed marks. The arc was defined by the height of the intersection of the measured tool contours set at feed intervals horizontally. However, when the boundary wear occurred in the finished surface formation area, the arc defined by the height of the intersection sometimes didn’t agree with theoretical roughness obtained by the measured tool contours set at feed intervals horizontally. As a result, there was concern that the difference affected the prediction reliability of tool edge contour position during cutting. Therefore, both of theoretical roughness and approximate arc of the measured tool contour were defined by the peak point of the measured tool contours set at feed intervals horizontally. Additionally, the representative tool contour was also defined by the different arcs to adopt the asymmetry of tool wear. Using the newly representative tool contour, the reliable roughness components could be calculated regardless of the tool pattern.

Abstract: In this article, technological parameters such as cutting speed, feed rate and depth of cut and their relationships with average power are investigated and modelled using statistical design of experiments. This allows a quantitative and qualitative description of the relationship between average power and process parameters. The analytical knowledge gained from the tests provides the conditions for optimising the energy consumption of the turning process.

Abstract: The occurrence of chatter during machining processes is a serious problem because of an excessive vibration that consequently dropped the quality of the machined surface. Especially on the turning process of tube shaped workpieces e.g. steel pipe that has relatively low stability limit represented by low critical depth of cut due to the naturally low dynamic stiffness of steel pipe. A cheap and simple method to increase the stability limits during the turning process of steel pipe has been developed in this research by using “Sand” as granular damper material to dissipate the elevated vibration energy. An experimental research is performed to investigate the performance of the sand damper by doing the cutting process of two different diameter the steel pipe that is filled up by sand. The result of the experiment shows that the 3 inch nominal diameter with fully filled of Sand can increase the stability limits from the critical depth of cut 0.68 mm (empty or without sand) up to 3.27 mm (full) or elevate by 4.8 times (almost fivefold). On the other hand, the 2.5 inch nominal diameter by filling with full of sand can improve stability limits from the critical depth of cut 0.95 mm (without sand) up to 3.05 mm or increase by 3.2 times. In simple words, the result of this research can be concluded that the increasing of the stability limits means also the elevated of the quantitative performance or the production rate of the turning process of Steel pipe almost up to fivefold. Keywords: Stability limits, chatter, sand damper, turning, steel pipe, vibration.

Abstract: Machining is a complex process which uses cutting tool for finshing the workpiece material. A sequence of machining tests costs a lot of expense and effort to complete. It's critical to avoid time-consuming runs and put technology first. Surface roughness (Ra) has been used to signal quality of product in the turning process as part of an automated monitoring system deployed in-process. This research uses machine learning models to estimate surface roughness while machining AISI 304 stainless steel rods. The key elements impacting surface quality are the input variables of turning, namely feed rate, depth of cut, and spindle speed. Four machine learning (ML)-based algorithms were used to predict surface roughness in this study: Gradient Boosting Regression (GBR), Decision Tree Regression (DTR), Extreme Gradient Boosting Regression (XGB), and Random Forest (RF) of Surface Roughness (Ra). The baseline models' predictive ability was measured using error measures such as Root Mean Square Error (RMSE), mean squared error (MSE), and coefficient of determination (R²). Overall, the XGB and GBR models appear to have the most accuracy in predicting surface roughness (Ra).

Abstract: In recent years, hybrid manufacturing combining additive and subtractive processes is gaining increasingly importance in the industry. One of the issues related to this association of processes concerns the use of cutting fluids, important to optimize the machining part, but that can strongly affect the additive part by generating pores in the laser metal deposition. The present work deals with the performance of a new ecological cutting fluid that dries just as water, eliminating the need for a cleaning step between the machining and the laser metal deposition. This lubricant is an emulsion mainly composed of water and alkylphosphonic acids known to allow creating a low-friction tribofilm on metals. This study is carried out by comparing the machining performance of this new cutting fluid with two more classical lubricants, a straight oil and a soluble oil. It was found that machining forces and surface roughness were not very affected by the change of the lubrication mode, while the tool wear showed a significant difference between the dry and the lubricated cases. Considering that the performance of all the cutting fluids was very close, it was concluded that the new lubricant has a great potential for machining applications, since it is ecologically more friendly, non-harmful to the operator and does not need a degreasing step.

Abstract: Numerical simulation of the temperature field and parameters of the turning process of workpieces made of 45 and 12Kh18N10T steels is performed. The front angle of the cutter, as well as the coefficients of chip friction on the front surface of the tool μ₁, the flank surface on the workpiece μ₂, and the coefficient of friction on the yield stress μ were selected as variable parameters. The degree of influence of the variable parameters on the tangential component of the cutting force, the friction force on the front and flank surfaces of the cutting tool, the power of heat sources, contact temperatures and the average temperature of the workpiece is estimated.