X. Ai

Wear patterns and mechanisms of cutting tools in high-speed face milling

Abstract High-speed machining has received important interest because it leads to an increase of productivity and a better workpiece surface quality. However, at high cutting speeds, the tool wear increases dramatically due to the high temperature at the tool–workpiece interface. Tool wear impairs the surface finish and hence the tool life is reduced. That is why an important objective of metal cutting research has been the assessment of tool wear patterns and mechanisms. In this paper, the wear performances of PCBN tool, ceramic tool, coated carbide tool and fine-grained carbide tool in high-speed face milling are presented when cutting cast iron, 45# tempered carbon steel and 45# hardened carbon steel. The tool wear patterns were examined through a toolmaker’s microscope. The research results show that the tool wear types differed in various matching of materials between the cutting tool and the workpiece. The dominant wear patterns observed were rake face wear, flank wear, chipping, fracture and breakage. The main wear mechanisms were mechanical friction, adhesion, diffusion and chemical wear promoted by cutting forces and high cutting temperature. Hence, the important considerations of high-speed cutting tool materials are high heat-resistance and wear-resistance, and chemical stability as well as resistance to the failure of coatings. The research results will be of great benefit in the design and the selection of tool materials and in the control of tool wear in high-speed machining processes.

A study on the prediction of the mechanical properties of a ceramic tool based on an artificial neural network

Abstract A new type of ceramic tool material is usually developed with the “trial-and-error” method which wastes a lot of time and effort. With the advancement of computers and ceramic material science, ceramic material design can be carried out based on known knowledge and experience of the fabricated materials, with the aid of the computer. The compositions and contents of the ceramic tool materials to be developed may be designed and simulated in accordance with the requirement for the mechanical properties. The development process of a new ceramic tool material can be carried out based on the simulated information of the material composition and content. In this paper, the characteristics of the artificial neural network (ANN) and it’s applications in the design of ceramic tool materials are introduced. The non-linear mapping relationship between the component, the composition content of raw material, the flexural strength, and the fracture toughness of the composite ceramic tool is investigated. The model for predicting the mechanical properties of the alumina matrix ceramic tool is established by means of an ANN. On the basis of the neural network toolbox in MATLAB (MATrix LABoratoryMA software), the neural network model for predicting the mechanical properties of the ceramic tool is trained to be reliable and the required programs are compiled. The mechanical properties of two-phase and three-phase composite ceramic tools such as Al 2 O 3 –(W, Ti)C and Al 2 O 3 –TiC–ZrO 2 are predicted to verify the proposed model. It is found from the research results that the established model based on the ANN are available and effective in simulating the composition content and predicting the mechanical properties of the ceramic tool.

Relationship between the thermal shock behavior and the cutting performance of a functionally gradient ceramic tool

Abstract Based on a deep understanding of the requirements of cutting conditions on ceramic tools, a design model for functionally gradient ceramic tool materials with symmetrical composition distribution is presented in this paper, according to which an Al2O3–TiC functionally gradient ceramic tool material FG-1 was synthesized by a powder-laminating and uniaxially hot-pressing technique. The thermal shock resistance of the Al2O3–TiC functionally gradient ceramics FG-1 was evaluated by water quenching and subsequent three-point bending tests of flexural strength diminution. Comparisons were made with results from parallel experiments conducted using a homogeneous Al2O3–TiC ceramics. The functionally gradient ceramics exhibited higher retained strength under all thermal shock temperature differences compared to the homogeneous ceramics, indicating their higher thermal shock resistance. The experimental results were supported by the calculation of the transient thermal stress field. The cutting performance of the Al2O3–TiC functionally gradient ceramic tool FG-1 was also investigated in the rough turning of the cylindrical surface of an exhaust valve of a diesel engine in comparison with that of a common Al2O3–TiC ceramic tool LT55. The results indicated that the tool life of FG-1 increased by 50% over that of LT55. The tool life of LT55 was mainly controlled by thermal shock cracking which was accompanied by mechanical shock, whilst tool life of FG-1 was mainly controlled by mechanical fatigue crack extension rather than thermal shock cracking, revealing the less thermal shock susceptibility of functionally gradient ceramics than that of common ceramics.

Case representation and similarity in high-speed machining

Applying case-based reasoning in high-speed machining can utilize previous cases and experience in machining a new work piece. This is helpful in overcoming the shortage of available high-speed machining data, and has significance for extending the application of HSM technology. For case representation, a model of case in HSM with relational data mode is proposed in the paper. With analysis of the characteristics of attributes and domain knowledge of HSM, the local similarities of case attributes are sorted into four classes: the numerical type, the enumerative type, the independent type, and the dependent type. The global similarity of cases is calculated by a composite similarity measure.

A study on the development of a composite ceramic tool ZrO2/(W, Ti)C and its cutting performance

Abstract An experimental investigation is carried out to fabricate a new ceramic tool ZrO2/(W, Ti)C by the hot pressing method and to study the effects of (W, Ti)C on the microphotograph of crystal particles, the phase transition and the mechanical properties of the new ceramic tool. Scanning electron microscope (SEM) observation reveals that the densification degree of the material ZrO2/(W, Ti)C may be improved and that the microstructure of the new ceramic tool material is more homogeneous as a result of the proper addition of the powder (W, Ti)C. Tests of the mechanical properties and wear resistance in machining are conducted. It is found that the fracture toughness of the developed ceramic tool is the highest when the content of powder (W, Ti)C is 45% in terms of volume due to the highest content of tetragonal zirconia. It is also shown that when machining a carbon tool steel the new tool material can increase the tool-life as compared to other ceramic tool materials that have the same matrix but were fabricated without (W, Ti)C, while the fracture toughness is improved by up to 38.8%. When compared with a conventional ceramic tool, the new ceramic tool material exhibit superior ability in maintaining wear resistance during the entire tool-life.

A theoretical model of surface roughness in ultrasonic vibration assisted electrical discharge machining in gas

A new machining method, named Ultrasonic vibration assisted electrical discharge machining (UEDM) in a gas environment is proposed in this paper. It is shown that ultrasonic assisted electrical discharge machining can be achieved well in a gas medium. The tool electrode is made of a thin-walled pipe, and the high pressure gas medium is supplied from inside. During machining, ultrasonic vibration of the workpiece can improve the machining process. A theoretical model to estimate the roughness of the finished surface has been developed. AISI 1045 steel and copper are selected as the workpiece material and electrode material respectively. Experiments have been carried out, and the results show that the roughness of finished surface increases with an increase in the discharge voltage (Ue), the discharge current (Ie) and the pulse duration (tS ).

Study on Residual Stresses in Milling Aluminium Alloy 7050-T7451

The machining residual stresses can have significant effects on component life by influencing fatigue strength, creep, and stress-corrosion-cracking resistance. This paper studies the residual stresses induced in milling of aluminum alloy 7050-T7451. Particular attention is paid to the influence of cutting parameters, such as the cutting speed and feed rate. In the experiments, the residual stresses at the surface of the workpiece and in depth were measured by using X-ray diffraction technique in combination with electro-polishing technique. In order to correlate the residual stresses with the thermal and mechanical phenomena developed during milling, the orthogonal components of the cutting forces were measured using a Kistler 9257A type three-component piezoelectric dynamometer. The temperature fields of the machined workpiece surface were obtained with the combination of infrared thermal imaging system and finite element method. At last, the formation of the residual stresses can be explained by thermo-mechanical coupling effects.

Prediction of Dynamic Stability Limit of Time-Variable Parameters System in Thin-Walled Workpiece High-Speed Milling Processes

A method for predicting dynamic stability limit of thin-walled workpiece high-speed milling process is described. The proposed approach takes into account the variations of dynamic characteristics of workpiece with the tool position (or machining time). A dedicated thin-walled workpiece representative of a typical industrial application is designed and modeled by finite element method. The curvilinear equation of modal characteristics changing with tool position is regressed. A specific dynamic stability lobe diagram is then elaborated by scanning the dynamic properties of workpiece along the machined direction throughout the machining process. The results show that, during thin-walled workpiece milling process, material removing plays an important part on the change of dynamic characteristics of system, and the stability limit curves are dynamic curves with time-variable. In practical machining, some suggestion is interpreted in order to avoid the vibrations. Then investigations are compared and verified by high speed milling experiments with thin-walled workpiece.

Method of stability prediction for milling processes including process damping

Semi-discretization method is expanded to determine the stability charts of NFDE for milling processes including process damping. The method is based on a special kind of discretization technique with respect to the past effect only. The convergence of approximate method is investigated by the example of delayed Mathieu equation, and stability charts of the damped and neutral delayed Mathieu equation for different time-period/time delay ratios are determined. The results show that, semi-discretization method can be employed to predict the stability of milling processes including process damping.

Predicting the Effect of Vibration on Machining Distortion in High-Speed Milling Aerospace Monolithic Components

Based on the stability lobe diagram of two degrees of freedom milling system obtained by using the numerical method, two kinds of cutting conditions (stable and unstable) are selected to perform the cutting tests of aeronautical monolithic components. Cutting distortion and secular distortion are measured and analyzed by using the MISTRAL 775 coordinate measuring machine (CMM), respectively. Influences of chatter on machining distortion are investigated. It is shown that, both machining distortion and secular distortion are smaller in stable case; in unstable case, machining distortion is also smaller, while secular distortion is very large, and torsion occurs in the workpiece end with larger box. Therefore, workpiece need be machined in stable conditions for subsequent assembly work, especially aeronautical monolithic components.Copyright