Papers by Keyword: Machinability

Abstract: 2.25Cr-1Mo-0.25V steel is the material of key parts of major equipment in petroleum and chemical field. Aiming at its unworkability and low heavy cutting tool life, at first, the tool life comparative experiment of cutting 42CrMo steel, 2.25Cr-1Mo-0.25Vsteel and 45 steel was carried out. It was found that process ability of 2.25Cr-1Mo-0.25Vsteel was the worst, the second was 42CrMo steel. And the tool life of cutting 45 steel was 2 times more than that of 2.25Cr-1Mo-0.25Vsteel. Then the comparative experiment of different tool life of cutting 2.25Cr-1Mo-0.25Vsteel was made under the condition of heavy cutting. The service life of heavy cutting tool XF8 was significantly higher than that of YT15. At last, the factors affecting the service life of heavy cutting tool were analyzed, in order to provide basis for improving heavy cutting tool life of 2.25Cr-1Mo-0.25V steel.

Abstract: The paper presents a new environmentally friendly lead-free free-machining structural steel AVTs19KhGN containing bismuth and calcium. The following quality characteristics of the new steel (in as-cast and forged condition) are determined: mechanical properties; austenite grain size; amount of non-metallic inclusions; surface quality. In forged rods (square 20 mm) a tendency towards an increase of bismuth content is observed from bottom to top of the ingot. Calcium distribution along the billet is uniform. Surface quality of billets in heats following the test heats is comparable to that of analog steels. Austenite grain size does not exceed ASTM number 6. Austenite grain is refined with increasing bismuth content. Mechanical properties are at the same level as for the steel without bismuth and calcium.

Abstract: In order to develop high-performance lead-free brasses, the effect of magnesium content on the machinability of lead-free brass alloys was carefully studied in the present work. The ingots of the Cu-Zn-Bi-Sb alloy were fabricated in terms of different magnesium contents of 1.0, 2.0, 3.0 and 4.0 wt%. The difference in the machinability of the Cu-Zn-Bi-Sb alloy ingots was discussed in terms of their microstructure, mechanical properties and chip morphologies. X-ray diffraction analysis indicated that α phase (0~38 Zn by atom %), β phase (45~49 Zn by atom %), CuMgSb and CuMgZn existed in the Cu-Zn-Bi-Sb alloys with the different magnesium contents. With increasing the content of magnesium, the machinability of the present lead-free brass alloys was markedly improved, which is mainly attributed to the formation of intermetallic compounds such as CuMgSb and CuMgZn.

Abstract: The paper describes the properties of two new medium-carbon free-machining alloy structural steels. These steels are environmentally friendly since lead in them is replaced with much less harmful elements bismuth and calcium. Bismuth and calcium are rather uniformly distributed in the ingot, though there are two zones of bismuth heterogeneity in the bottom and in the head part of the ingot. Mechanical properties of steels are at the same level as for steels without bismuth and calcium. Non-metallic inclusion content is typical for structural steels melted in open electric arc furnaces with basic lining and is not changed by the presence of bismuth and calcium. Machinability of the steels with bismuth and calcium is at the same or higher level than that of lead-bearing steels. Melting, casting, forging and rolling of steel containing bismuth and calcium is not associated with working area air-pollution with harmful substances in amounts exceeding maximum permissible concentrations. During rolling of the lead-free steels harmful emissions are almost absent, unlike the lead-bearing steels.

Abstract: The paper presents the results of comparative studies of working area air pollution during the production of three alloy steels containing bismuth and calcium as machinability-enhancing additives: AVTs40Kh13 (0.4 %C + 13 %Cr + Bi + Ca), AVTs14Kh17N2 (0.14 %C + 17 %Cr + 2 %Ni + Bi + Ca) and AVTs19KhGN (0.19 %C + 0.9 %Mn + 0.9 %Cr + 0.9 %Ni + Bi + Ca). Experimental studies were performed in industrial conditions at Zlatoust Electrometallurgical Plant, Ltd. According to the technology developed and used at the enterprise, bismuth was introduced in the form of shot to the steel stream during casting of 0.5 t ingots at a special casting site. Air samples (of statistically reliable volume) were taken using standard techniques in the working areas at principal moments of technological processes. Bismuth content in air samples was then determined by polarography method. The results demonstrate that bismuth introduction to the steel stream during top casting results in bismuth concentration in the air of the working areas exceeding the maximum permissible concentration of 0.5 mg/m³ only in the first 10 min after casting start. Bottom casting and hot forming of free-machining steels containing bismuth and calcium is not accompanied by pollution of the air in the working area with harmful substances in amounts exceeding maximum permissible concentration, unlike leaded free-machining steels.

Abstract: Fcc-TiBCN powder synthesized by boronizing of Ti was pressured into monolithic block by hot pressing (HP) method. Then the block material was machined by wire-cut EDM. The machinability and the material removal mechanisms were discussed of Fcc-TiBCN block in wire-cut EDM. Results show that the machinability of Fcc-TiBCN is satisfying. The discharge current has little relationship on surface roughness in the range of factory-adjusted optimum settings. The discharge duration and pulse interval time play an important role on the quality of machined surface and EDM machining efficiency. In order to obtain excellent quality of the machined surface, the number of power tube turned on can not exceed 6, and the pulse interval time must be as long as possible. The mini roughness of machined surface is 0.4μm～0.6μm as the number of power tube turned on is 5, the pulse interval time and discharge duration is set in the range of 20～22μs and 65～75μm, respectively. There are three material removal mechanisms of TiBCN conductive ceramic in the EDM machining process: spalling, melting and evaporation. Spalling is the main mechanism resulted by thermal stress superposing.

Abstract: Carbon fiber reinforced plastic (CFRP) are used for various aircraft structural components because of their superior mechanical and physical properties such as high specific strength, high specific stiffness, etc. In order for CFRP materials to be used in aircraft structures or machine elements, high quality holes must be created on them efficiently. However, it is difficult for conventional methods such as drilling, helical milling and so on to meet the requirements. Therefore, this study proposes a novel method for creating holes on CFRP products. This method is just performed by tilting the workpiece at a certain angle on the basis of conventional helical milling (CHM) and hence called tilt helical milling (THM). In this paper, the processing principle of the THM is described in detail at first. An experimental apparatus is then constructed by installing a work holding unit produced in house onto a CNC milling machine. Finally, experiments are carried out on the apparatus. The obtained experimental results demonstrated that the THM is capable of creating holes on CFRP with lower burrs and chippings formation compared with those by CHM. By this new method, high quality holes could be obtained with high efficiency compared with conventional methods.

Abstract: As a new type of material, Ti₂AlNb based alloy has a broad application prospects in aerospace field due to its excellent properties such as low density, high specific strength at elevated temperature, excellent oxide and creep resistance. Many studies involving its material composition and structural properties have been published. However, there are relatively few literatures available on the machinability of Ti₂AlNb based alloy. In this work, the turning experiment of Ti₂AlNb based alloy was carried out with coated cemented carbide tools. The machinability of Ti₂AlNb based alloy was investigated through the cutting force, cutting temperature, tool wear and surface roughness. The result shows that the cutting force is lower and surface quality is better under condition of higher cutting velocity, lower feed rate and smaller depth of cut. The life of tool is longer when they were cutting under the high cutting velocity, low feed rate and small depth of cut. The research could provide some instructive information and basic data for the turning process parameters optimization of Ti₂AlNb based alloy.

Abstract: Based on the cutting performance parameter of hardened steel 7CrSiMnMoV and the application of fuzzy synthetic evaluation principle, the essay establishes a two-level fuzzy synthetic evaluation model of the machinability of 7CrSiMnMoV. Choosing cutting force, cutting temperature and surface roughness of the workpiece produced during machining process as the evaluation index, data are measured through experiment and a synthetic evaluation of the machinability of hardened steel 7CrSiMnMoV is conducted. The result shows that it is reasonable to use cutting force, cutting temperature and surface roughness of the workpiece as evaluation index to evaluate the material machinability. And it also provides guidance to the selection of tools and the technological parameters during the process of cutting 7CrSiMnMoV.

Abstract: Hard turning is recent upcoming technology through which surface quality of machined components can be enhanced while comparing with the traditional grinding method. Since the absence of metal cutting fluids during this process, numerous harmful effects on shop floor operators and possible negative impacts on environment can be eliminated. Normally some of the vital machinability aspects such as surface integrity of machined parts has been influenced by magnitude of cutting temperature which evolved in metal cutting interface. Therefore in this experimental investigation, the influence of various process control parameters on tool-chip interface temperature was evaluated during hard turning of AISI D3 tool steel in dry condition. The machining trials were conducted as per the L₉ Taguchi DOE approach and subsequent experimental data were analysed with the use of Design-Expert® V7 statistical software. This experiment results revealed that feed rate is having predominant influence in determining the magnitude of cutting temperature followed by depth of cut and cutting speed whereas the influence of cutting tool nose radius is insignificant.