Key Engineering Materials Vols. 504-506

Abstract: Nanoindentation test is one of the most commonly used methods for the strength investigation of the nanomaterials. Information provided from such test gives the possibility to obtain a knowledge about fracture development under the spot hitting tool. However, nano dimensions of the coatings obtained by the deposition method creates problems with exact investigation of this test. Costs of experimental study are very often excessive due to very specialized laboratory equipment. The numerical simulations can be a support for mentioned experimental research as they give possibility of fast and efficient investigation on behavior of different nanolayers dimensions and alignments. The main aim of this work is focused on taking into account real morphology of microstructure of ceramic TiN layers deposited on the metallic Ti layers during nanoindentation test. This combination of layers is widely used in medicine for improvement mechanical properties and biocompatibility behavior of bio elements. Particular attention during numerical simulation is put on influence of columnar structure of these layers on fracture development. Results obtained from the extended finite element model (XFEM) for various nanolayers alignments is discussed according to the fracture initiation and propagation.

Abstract: AeroEngines main components made by nickel super alloys are mainly obtained by machining of large forged components. The work piece machining process generates some distortions that may also be relevant. In this contest, in many cases the removed volume in the machining operations represents a large percentage of the forged component in order to obtain the thin-walled wanted geometry. Due to this reason, the residual bulk stresses induced by the process history can lead to significant 3D geometric distortions in the machined component with unacceptable dimensions and shapes of the obtained product for comparison with the wanted geometry. Moreover, it is a matter of fact how, the final component distortions depend by the cutting strategy adopted in the machining process. The experimental study of such cutting strategies on real components are particularly time consuming and costly and for this reason the chance to study the problem using reliable numerical models it is particularly welcome. In the present work authors reports the numerical model development of the forging and machining processes needed for the production of a aircraft engine component and the comparison of the obtained results with the ones physically measured. The objective is to develop and validate a modeling method able to predicts the shape and the magnitude of the distortion induced by the machining operation on the considered component and to establish a possible strategy to suggest machining working steps able to improve the quality of the manufactured component reducing the needed production time.

Abstract: This paper reports the results of an experimental study of the tool wear and cutting forces in turning of Inconel 718 with coated carbide inserts. Inconel 718 is a difficult-to-cut nickel-based super-alloy commonly used in aerospace industry. The effects of cutting speed, feed rate and cutting tool geometry on tool wear have been widely analyzed in literature. Turning operations on complex components such as aircraft engines casings require the insert replacement at the end of each geometric feature manufacturing, independently from the actual tool wear level. For this reason, it is important to preserve tool integrity mainly in the most critical phase of operation (i.e., when the tool engages the workpiece). In fact, if the tool is damaged in this stage the quality of the whole operation is compromised. The attention has been focused on engage cutting conditions because the phenomenon that appears in this critical step plays a wide influence on tool integrity and, consequently, on the quality of the operation. For this purpose a nickel-based super alloy ring-workpiece, (Inconel 718), has been machined in lubricated cutting conditions by using a CNC lathe with carbide coated tools. Two variables have been investigated in this study: the Depth Of Cut (DOC) and the approaching Engage angle (En). In the studied working conditions Speed (S), Feed-rate (F) and removed volume (Vrim) were kept constant. Both tool wear and cutting forces evolution during cutting have been analyzed.

Abstract: This work reports on the results of a study of different macro-geometrical deviation parameters, such as Straightness (SD), Parallelism (PD) and Circularity (CD) as a function of cutting speed (v) and feed (f) of dry turned UNS A92024 (Al-Cu) cylindrical bars. The results obtained have allowed establishing exponentials parametric model for predicting these deviations as a function of those cutting parameters. As a consequence of that, geometrical surfaces SD(f,v), PD(f,v) and CD(f,v) have been developed for this alloy. These surfaces allows determining marginal curves for specific v and f values, respectively, out the parameter ranges employed. So, macro-geometrical deviations can be predicted through this model for v and f values out of those considered in the study for each alloys.

Abstract: Machinability is the one of the criteria in determining the life of the cutting tool. In this experiment, hard and difficult to cut materials like hard AISI 440 C stainless steel and hard SCM 440 alloy steels were discussed. However, machinability of the material is considered to be poor due to its inherent characteristics. The machinability studies on AISI 440 C stainless steel and SCM 440 alloy steels had not been carried out by researchers. Machinability indices used in such cases have the characteristics such as cutting force, surface roughness, tool wear etc. In the case of high-speed machining of said materials machinability indices such as chip thickness (RC), shear angle (Ф), surface integrity, and chip analysis are of prime importance. Most of the researchers have not given due consideration to these vital machinability indices necessary for understanding of high-speed cutting of said materials. In this work, an experimental investigation was carried out to understand the behavior of difficult to cut materials, when machined with Cubic Boron Nitride (CBN) insert tool. The results and analysis of this work indicated that the above-mentioned machinability indices are important and necessary to assess the machinability of said materials effectively. The operating parameters used were cutting velocity 100, 125, 150, 175 and 200 m/min with feed rate of 0.10, 0.20 and 0.30 mm rev-1 with constant depth of cut of 1.0 mm. The length of turning was 150 mm and 300 mm. Machinability of both materials and tool was evaluated in terms of roughness, flank wear, cutting force, chip thickness ratio and shear angle.

Abstract: Machining of materials is to produce desired shape and size with smooth surfaces for the performance. Machining is carried out using various cutting tools starting high speed steel to recently developed tools like CBN and PCBN etc. These tools are used to machine difficult to cut materials like high strength alloy steels, stainless steel, Inconel 718, Titanium etc. The inserts used are thrown out or no longer required for finish machining. It can be used for rough machining where smooth surface is not primary important and subjected to subsequent machining using fresh inserts. The used inserts can be used subsequently by subjecting them cryogenic treatment at – 196◦ C in a closed chamber. It is longer process for more than 30 hours in a liquid nitrogen chamber. This treatment gives additional strength to cutting inserts to improve the cutting ability and wear resistance. The components used in high strength applications like an aerospace, automobile industries are treated with cryogenic process to improve wear strength. The operating parameters are cutting velocity, feed rate and constant depth of cut. In this research, CBN inserts after turning for 750 mm length was cryogenically treated and again used with same operating parameters as previous machining conditions. Each inserts were measured for flank wear by Scanning Electron Microscope (SEM) after treatment and re-used with same turning conditions as before. Performances of all inserts used were producing the same results or results near to same. The treated inserts were acting as fresh cutting edges. The results showed that cryogenically processed CBN inserts performed very close to previous results.

Abstract: The forces involved in a cutting process are related, for example, with the power consumption, with the final quality of the workpiece and with the chip geometry obtained, since these forces determine the compression experimented by the chip and therefore its final geometry. The orthogonal cutting process assisted with a High Speed Filmation (HSF) permit obtains a digital filmation of the process with high magnification. This filmation permits to obtain a measurement of the longitudinal changes produced in the chip. This deforms are related with the Shrinkage Factor, ζ. And in this case the Stabler hypothesis is enabled, by that using the shear angle and the rake angle is possible obtain a value of the Shrinkage Factor in a different conditions.

Abstract: This paper presents a study of the influence of cutting conditions on the finished surface obtained after an hard turning process, in particular a case study is presented where AISI 52100 bearing steel is machined under different cutting conditions. An analysis carried out using Surface Response Methodology has been developed in order to study the influence of the main cutting parameters such as cutting speed, feed rate and workpiece initial hardness on white (WL) and dark layer (DL) thickness. The whole experimental campaign has been performed using a chamfered PCBN tool inserts without any cutting fluid. Results show an evident influence of cutting speed and feed rate on both white and dark layer thickness while less relevant is the contribute given from the workpiece hardness on defining WL and DL depth. Finally, a model to find the optimal process conditions to minimize white and dark layer thickness is developed.

Abstract: This study is focused on developing and testing a calorimeter to measure the chip heat in drilling of C45EN. Inside the calorimeter, the cut chips fall into a fluid with known heat capacity. Its temperature is measured continuously with thermocouples. Based on calorimeter designs found in the literature, the principal assembly of the calorimeter was adapted to be used in drilling and to minimize heat losses. A modular design with measuring box, process box and top cover was developed. This allows a smooth handling of the calorimeter during experiments as well as the use of the calorimeter to analyze further processes like milling. A horizontal configuration of workpiece and tool was chosen to optimize the chip fall into the fluid, which is a basic requirement for measuring the exact temperature of the chips. The temperature is measured by three thermocouples at different positions of the calorimeter to quantify the temperature distribution in the fluid. To accelerate the process of thermal balance between chip and fluid, the system was dynamically stimulated by jerky movements of the machine axes. This aims to a uniform distribution of the chips within the calorimeter. First experimental tests validated the functionality of the calorimeter and demonstrated that dynamic axes movements accelerate the heat transfer from chip to the fluid substantially.

Abstract: Low plasticity burnishing (LPB) is a new method of surface improvement, which raises the burnishing to the next level of sophistication. LPB can provide deep compression for improved surface characteristics. The study focuses on the surface roughness, micro-hardness and surface integrity aspects on soft AISI 420 STAVAX ESR martensitic stainless steel AISI 420 material. This material is pronounced as difficult to cut materials like titanium, Inconel 718 etc. The investigation of surface integrity was done on this materials in terms of operating parameters like sliding speed, feed rate and depth of penetration (DOP) identifying the predominant factors among the selected parameters. The steel balls used were cryogenically treated at sub zero temperature of -176 degrees. Sub-surface micro-hardness study were also done to asses the depth of compression altered zone, surface roughness and surface hardness. The process can be applied to critical components effectively as the LPB process has cycle time advantages and also low investment cost. This can be also realized by introducing on high speed machines. This process was studied by using cryogenically treated different ball diameters at various operating parameters. This also improved on concentricity of work material. More the depth of compression produced low surface roughness at low sliding speed, feed rate with larger ball diameter. The DOP also helps to improve on surface and sub-surface hardness and close roundness. There are limitations on DOP beyond which the surface deteriorated.