Materials Science Forum Vols. 836-837

Abstract: With the development of advanced automation degree industries, the requirements of network management for workshop tool become more and more urgent. A very important part in network management system is identification technology of the tool. In this paper, 2D (two-dimensional) barcode identification technology is applied in the tool information in real-time query to realize network management. The 2D barcode reading device, which is combined with the local computer decoding software, could achieve communication between production line and the server. By using 2D barcode identification technology, it could achieve network management for workshop tool, improve production efficiency and reduce the artificial error.

Abstract: PID parameters of machine tool for micro-defect mitigation of KDP crystal had been optimized, after which the velocity fluctuation frequency and amplitude variation of motion axis under different spindle speeds were studied. It is evident that the stability and following errors of the system run better under the velocity&acceleration feed forward PID control algorithm and Notch filters. The velocity fluctuation frequency of motion axis varies with spindle speeds significantly when the tool system is stable, while the fluctuation amplitude variation is slightly changed. To be conclude, the optimal working spindle speed is verified to be 4.78×104 rpm based on comparative experiments, at which damage pits can be mitigated by micro-machining successfully with roughness value of 34.4nm.

Abstract: Thin-walled workpieces are widely used in the aerospace manufacturing industry in order to reduce the weight of structure and improve working efficiency. However, vibration is easy to occur in machining of thin-walled structures due to its low stiffness. Machining vibration will result in lower machining accuracy as well as machining efficiency. In order to reduce the machining vibrations of thin-wall workpieces, commonly used method is to select proper machining parameters according to the chatter stability lobes, which is generated according to the machining system parameters. However, this method requires exact system parameters to be determined, which are always changing in the machining process. In this paper, a special designed fixture with damping materials for the thin-walled workpiece is presented based on the machining vibration control theory, and analysis of the effect of vibration suppressing is obtained through the contrast of vibration tests of milling the thin-walled workpiece on the damping clamp. The damping material is used to consume vibration energy and provide support for thin-walled structure. Machining test was carried out for thin-walled structure machining to validate the effectiveness of the proposed method.

Abstract: During high-speed machining, the vibration will result in poor workpiece surface and damage the cutting tool as well as the machine tool. It will limit the productivity and lower the quality of thin-wall titanium alloy components. Moreover, vibration occurrence is strongly affected by the dynamic response of the whole system, particularly the stiffness of workpiece-fixture system. Improper fixture layout is prone to generate vibration, especially for the flexible workpiece. Hence, it’s necessary to suppress the vibration and improve the fixture design. In this work, a finite element model of the workpiece-fixture system is built. Based on this model, the laws of the natural frequency and vibration modals under different fixturing methods are obtained, which can be used to refine fixture design. With several additional auxiliary supports, the stiffness of the workpiece-fixture system is improved and the result showed that, the natural frequencies of thin-wall titanium alloy components can be improved to a level which is too high to be reached by tool’s excitation. The result of this study is helpful to design the optimum fixture scheme of thin-wall titanium alloy components.

Abstract: Instantaneous speed (IS) is of great significance of fault diagnosis and condition monitoring of the high speed spindle. In this paper, we propose a novel zoom synchrosqueezing transform (ZST) for IS estimation of the high speed spindle. Due to the limitation of the Heisenberg uncertainty principle, the conventional time-frequency analysis (TFA) methods cannot provide both good time and frequency resolution at the whole frequency region. Moreover, in most cases, the interested frequency component of a signal only locates in a narrow frequency region, so there is no need to analyze the signal in the whole frequency region. Different from conventional TFA methods, the proposed method arms to analyze the signal in a specific frequency region with both excellent time and frequency resolution so as to obtain accurate instantaneous frequency (IF) estimation results. The proposed ZST is an improvement of the synchrosqueezing wavelet transform (SWT) and consists of two steps, i.e., the frequency-shift operation and the partial zoom synchrosqueezing operation. The frequency-shift operation is to shift the interested frequency component from the lower frequency region to the higher frequency to obtain better time resolution. The partial zoom synchrosqueezing operation is conducted to analyze the shifted signal with excellent frequency resolution in a considered frequency region. Compared with SWT, the proposed method can provide satisfactory energy concentrated time-frequency representation (TFR) and accurate IF estimation results. Additionally, an application of the proposed ZST to the IS fluctuation estimation of a motorized spindle was conducted, and the result showed that the IS estimated by the proposed ZST can be used to detect the quality of the finished workpiece surface.

Abstract: In order to achieve the high efficiency machining of titanium, the cutting force model is verified through the cutting experimental platform in machining cant and curved surface with ball end milling. And then the influence of cutting parameters and surface curvature on cutting force and tool wear are investigated. Finally, the prediction model of tool wear is established based on the orthogonal test and the least square method. This study proposes that the tool wear and each tooth feeding have a major impact on cutting force and that the convex surface from a small curvature to larger and the concave surface from a large curvature to smaller can effectively improve the life of tool in machining curved surface.

Abstract: From the perspective of statics, the deformation of welded beam under the action of gravity and cutting force was studied in the paper. During the actual machining process, vibration of welded beam and even the machine can be caused due to the change of cutting condition and interference from the outside. To avoid the natural frequency, and prevent the occurrence of resonance phenomena, welded beam modal was further analyzed; the first six natural frequencies and mode shapes of the beam were achieved. Statics and modal analysis are the basis of lightweight design of the welded beam based on topology optimization. The topology optimization model of maximum stiffness design and eigenvalue problem structural dynamics was established. Finite element model of beam and its components was established in hypermesh, and the optimization objective function, constraint function and boundary conditions were also set. Compared with the structure before optimization, the weight of the beam was reduced 10%, the lightweight design of the welded beam was achieved and the comprehensive performance of the beam was significantly improved.

Abstract: Carbon fiber reinforced plastics (CFRP), which are widely used in the aerospace and some other new-tech industries, are considered very difficult to machine due to the material anisotropic and inhomogeneous features. Chemical vapor deposition (CVD) diamond films are suitable as protective coatings on cutting tools for machining advanced composite materials, owing to their extremely high hardness, favorable wear resistance, low friction coefficient and high thermal conductivity. Among different types of diamond films, the fine grained diamond (FGD) film can provide much more favorable environment for machining CFRP due to the small grain size, low surface roughness and the retentivity for the sharpness of the cutting edge. In the present study, aiming at drilling CFRP, FGD films of different thicknesses are deposited on Φ3 mm drills by controlling the growth time, adopting the common-used hot filament CVD (HFCVD) technology. It can be directly proved by deposition experiments that overlong growth time can induce spontaneous film delamination and removal before the cooling stage, probably as a result of the excessive residual stress concentrated on the complicated surfaces. As demonstrated by the cutting tests, with increasing the growth time, the main failure mode of the FGD coated drill changes from film delamination to flank wear/tipping to film delamination, and the maximum tool life exists when the growth time is moderate, because the flimsy film cannot provide sufficient protective effects on the film-substrate interface and even hasn’t totally cover the substrate, while there’s relatively higher residual stress in the film that is too thick, and such the residual stress can significantly deteriorate the film-substrate adhesion. Moreover, during the life cycle of each FGD film, relatively shorter growth time often means the slightly better hole quality, attributed to the retentivity of the initial shape of the uncoated drill that is optimal designed for machining CFRP, especially the weaker passivation of the cutting edge.

Abstract: Machining technology has undergone an extensive evolution throughout the last decades in its capability to machine hard-to-cut material. This paper will discuss about the next generation insert with cooling feature coupled with forced coolant in machining Inconel 718. The geometry of the insert was changed in a way which has enlarged the surface area approximately 12% compared to regular insert named as nusselt insert. The idea applied in “nusselt insert” was the relation of increase in surface area to heat dissipation. Forced coolant application has become a way to improve existing metal cutting concepts and improve their current material removal rates without any need for a reengineered machining process.Experiments conducted on the inserts is that the first experiment of its kind in machining technology together with forced coolant and tested in four different inserts. The primary focus of the work was the investigation of the relation between the heat dissipation with an increase in surface area/mass ratio in the cutting interface based on its influence on tool wear. The experimental results showed the nusselt insert have better ability for heat dissipation which has led to significant reduce in tool wear and successfully facing Inconel 718 at v_c 105 m/min, f 0.3 mm/rev and a_p 1 mm where the regular insert had a catastrophic failure at v_c 90 m/min, f 0.1 mm/rev and a_p 1 mm. Nusselt insert has shown to increase MRR significantly compared to regular insert.

Abstract: Dynamic characteristics of numerical control (NC) machine tools, such as natural frequency and vibration property, directly affect machining efficiency and finished surface quality. In general, low-order natural frequencies of critical components have significant influences on machine tool’s performances. The headstock is the most important component of the machine tool. The reliability, cutting stability, and machining accuracy of a machining center largely depend on the structure and dynamic characteristics of the headstock. First, in order to obtain the natural frequencies and vibration characteristics of the headstock of a vertical machining center, modal test and vibration test in free running and cutting conditions were carried out by means of the dynamic signal collection and analysis system. According to the modal test, the first six natural frequencies of the headstock were obtained, which can not only guide the working speed, but also act as the reference of structural optimization aiming at frequency-shift. Secondly, by means of the vibration test, the vibration characteristics of the headstock were obtained and the main vibration sources were found out. Finally the corresponding vibration reduction plans were proposed in this paper. That provides the reference for improving the performance of the overall unit.