Proceedings of the Institution of Mechanical Engineers,Part B: Journal of Engineering Manufacture

Based on the Z-map model of a workpiece and the dynamic cutting forces model of peripheral milling in which the regenerative effect of tool radial runout and axial drift are considered, a model for the prediction of surface topography in peripheral milling operations is presented. According to the stability lobe diagram obtained by the zero-order analytical method, the relationship between spindle speed and surface topography, the tool radial runout, and the axial drift following the chatter are studied. The results show that a stable cutting status but a poor surface finish is obtained at the spindle speeds at which the dominant frequency of the milling system is integral multiples of the selected machining frequency, and a stable cutting status with a good surface finish can be obtained near and on the left side of the resonant spindle speeds determined by the predicted stability lobe diagram. The motion equations of any tooth end mill for peripheral milling are established, and these equations are based on the transformation matrix and the vector operation principle of motion-homogeneous coordinates. In addition, the simulation algorithm and the system of surface topography generated in peripheral milling are given based on the Z-map model. Cutting tests are carried out, and good agreement between the measured surface topographies and the topographies predicted by the model in this study is found in terms of their shape, magnitude, feed mark, profile height of cross-section, and surface roughness. The simulation results show that the milling surface roughness increases with the increase in feed per tooth, which further shows that this simulation system has high credibility. Thus, the simulation and experimental results can provide some practical instructions for the actual peripheral milling in determining the optimal machining conditions.

Dimensional accuracy in additive manufacturing and especially for parts produced via material extrusion has been actively investigated in an effort to proceed from a prototyping process to a mature technology capable of manufacturing functional parts. Typically, accuracy in material extrusion is not the same along the different printing directions or it may vary according to the geometric feature that is fabricated. Therefore, it is considered as a problem with multiple responses and is typically tackled with multiple-objective optimization strategies in order to achieve optimal parameter settings that simultaneously satisfy contradicting requirements. In this work, response surface methodology is applied on the part, in order to obtain feature-specific models that predict dimensional accuracy. According to the proposed methodology, dimensional accuracy on every included feature and along the different printing directions is separately optimized with enhanced flexibility regarding the derived optimal solution. Optimal settings are fed directly to the material extrusion system as modified machine instructions. Different parameter settings for different regions of the same layer, or even varying material extrusion rate and feed rate along continuous trajectory, are validated. A specific part is used for demonstration purposes. The efficiency of this novel approach is compared with multiple-objective optimization based on the desirability method. The results exhibit enhanced dimensional accuracy of the part when adaptive settings are adopted for every feature.

As a new polishing method, bonnet polishing is suitable for polishing the curved surface due to its advantages in flexibility and adaptability of the polishing tool. In the polishing process, the contact state between the bonnet and the curved surface always changes. The traditional polishing tool path with equal interval will inevitably lead to over-polished areas and unpolished areas. In this article, a new tool path for bonnet polishing, which is called the revised Archimedes spiral polishing path, is proposed to ensure the physical uniform coverage of the curved surface in bonnet polishing. The path generation method is based on the modified tool–workpiece contact model and the pointwise searching algorithm. To prove the effectiveness of the revised path, two aspheric workpieces were polished along the traditional Archimedes spiral polishing path and the revised path, respectively. The roughnesses of the two workpieces are 10.94 and 10 nm, and the profile tolerances are 0.4097 and 0.2037 μm, respectively. The experimental results show that the revised path achieves lower roughness and surface tolerance than the traditional Archimedes path, which indicates that the revised path can achieve uniform physical coverage on the surface.

The objective of this work is to investigate the influences of three machining factors (burnishing speed V, feed rate f, and depth of penetration a) on the improved rate of arithmetic average roughness ΔR_a, improved rate of maximum height roughness ΔR_y, and improved rates of surface hardness ΔSH. The internal roller burnishing experiments were conducted with the aid of the computer numerical control machining center and Box–Behnken experimental design. The Kriging models were used to render the highly nonlinear relationships between inputs and outputs. An integrative approach combining a Non-dominated Sorting Genetic Algorithm II and Technique for Order Preference by Similarity to Ideal Solution was adopted to generate a set of feasible optimal solutions and determine the best machining conditions. The scanning electron microscopy images were depicted to investigate the surface morphology at the different conditions. The X-ray diffraction was applied to measure the compressive stresses at the external surface. The results showed that the predicted values of the objectives have good agreement with the experimental ones. High surface quality is characterized by an improved average roughness of 95.80%, an enhancement in the maximum roughness of 91.98%, and an improvement in surface hardness of 45.44%, compared to pre-machined surfaces. The selection of optimum process parameters could help the burnishing operators to save the machining costs and time. The combination of Kriging model, Non-dominated Sorting Genetic Algorithm II, and Technique for Order Preference by Similarity to Ideal Solution is considered as an intelligent approach for modeling and optimization of burnishing processes.

Magnetic field assisted powder mixed electrical discharge machining is a hybrid machining process with suitable modification in electrical discharge machining combining the use of magnetic field and fine powder in the dielectric fluid. Aluminum 6061 alloy has found highly significance for the advanced industries like automotive, aerospace, electrical, marine, food processing and chemical due to good corrosion resistance, high strength-to-weight ratio, ease of weldability. In this present work, magnetic field assisted powder mixed electrical discharge machining setup was fabricated and experiments were performed using one factor at a time approach for aluminum 6061 alloy. The individual effect of machining parameters namely, peak current, pulse on time, pulse off time, powder concentration and magnetic field on material removal rate and tool wear rate was investigated. The effect of peak current was found to be dominant on material removal rate and tool wear rate followed by pulse on time, powder concentration and magnetic field. Increase in material removal rate and tool wear rate was observed with increase in peak current, pulse on time and a decrease in pulse off time, whereas, for material removal rate increases and tool wear rate decreases up to the certain value and follow the reverse trend with an increase in powder concentration. Material removal rate was increased and tool wear rate was decreased with increase in magnetic field.

To solve these problems (i.e. the accuracy rate and stability of the centering) of enabling secondary machining of micro-holes with a size of 0.1 to 1 mm in high-performance metal alloy parts, a non-standard nested circle-fitting least-square method, with a linear constraint passing through the center (least square method with linear constraint [LSLC]), is proposed in this article. The experimental results show that the center of the circle is fitted with a maximum deviation of ±1.5 µm and good fitting precision, compared to other existing approaches. At the same time, the accuracy rate is increased by at least 20%, delivering a result of more than 99%, so the accuracy of the fitting and the stability of the centering are significantly improved. Finally, the new method is applied in actual micro-hole electrochemical deburring study. With the overall goal of ensuring centering, a rough-and-fine deburring process has been explored. On the premise that the hole is not expanded, the burrs have been quickly and completely removed, and machined surface roughness, R_a, has also reduced from 1.2 to 0.52 µm. The experiment has provided concrete validation of the feasibility of the nested circle-fitting method we have proposed.

The residual stress of multi-rivet structures is related with the riveting sequence, the rivet pattern, and the pitch due to the deformation interaction of different rivets. The stress amplitude of riveted structures subjected to the cyclic loads is affected by the residual stress, which increases the difficulty in the prediction of fatigue life. In this article, the riveting processes for single-row and triple-row riveted lap joints with various riveting sequences, rivet patterns, and pitches are studied numerically and experimentally. The residual stresses for both types of riveted structures are verified by the testing data. Significant difference appears in the residual stress field for riveted lap joints with various riveting sequences and rivet patterns. The decrease in the rivet pitch increases the compressive residual stress at the edge of the rivet hole. Furthermore, the fatigue life prediction model is developed for multi-rivet structures, in which the coupling effect of residual stress and cyclic load is considered. The fatigue experiments are conducted for riveted lap joints with various riveting sequences, rivet patterns, and pitches. The accuracies of the numerical results obtained from the Homan model and the developed model are compared with the experimental data. The proposed fatigue model shows better performance to predict fatigue life for multiple rivet structures.

Sufficient preload in a bolted joint is key to ensuring the reliability of mechanical products; however, under vibration, preload decrease often occurs. The mechanism of preload decrease has not yet been fully clarified. In this study, finite element models of bolted joints with and without helix angles were constructed to study the mechanism of preload decrease under transversal vibration. Based on the finite element analysis results, a new cause of preload decrease, denoted as stress release and redistribution, was discovered and explained in detail. The mechanism of preload decrease caused by stress release and redistribution, cyclic plasticity deformation and rotation loosening is studied systematically, and the typical mode of preload decrease is proposed. Based on the preload decrease curve, more comprehensive evaluation criteria are established, quantified using three parameters to represent the locking behavior of bolted joints. Finally, experiments were conducted to verify the reliability of the preload decrease results.

Dynamic vibrations of air bearing motor spindles have significant influence on the surface quality in ultra-precision machining. In this article, the influence of the vibration caused by the unbalanced magnetic force on the diamond turning is investigated on the basis of the theoretical and experimental method. A permanent magnet motor model (10 poles and 12 slots) is built and then simulated to gain a periodic unbalanced magnetic force. The effects of unbalanced magnetic force on the inclination of the spindle shaft is analyzed, which would affect the surface quality of the workpiece, and the surface topography of the workpiece is predicted during an unbalanced magnetic force acting on air bearing motor spindle. The theoretical analysis and experimental turning results validate that the angle between the direction of unbalanced magnetic force and the feed direction has a certain relationship with the profile of the machined surface. Also, under different turning speeds and directions, the surface topography of the machined workpiece shows a 10-cycle-per-revolution pattern, which has good agreement with the simulations of periodic unbalanced magnetic force. This research work provides a theoretical foundation for the fault diagnosis of air bearing motor spindle caused by motor rotor eccentricity and its effect on surface generation in turning.

A blisk is one of the key parts of an aero-engine, whose surface processing quality directly affects aero-engine performance. Different degrees of vibration occur during the process of new open belt grinding which seriously affect the precision of the dimensions and the surface quality of the entire blade profile. With the aim of addressing this problem, this study constructed a physical model of blisk belt grinding, analysed the low-rigidity characteristics of the grinding system, and researched the vibratory mechanism of the blisk belt grinding system based on a dynamic analysis method. In addition, the factors affecting the stability of the grinding process and the stability conditions of the grinding were considered. Then, the belt grinding process of a blade surface was simulated through a numerical method. The technological parameters were quantified for different conditions of the blisk belt grinding vibration. The optimal combination of process parameters was obtained. Finally, the optimised process parameters were validated experimentally. The research demonstrates that vibration from blisk belt grinding is related to the process parameters as follows, in the order of the greatest influence: the grinding pressure, belt velocity, feed speed, and contact wheel hardness. After optimisation, the cross-sectional profile is 0.031–0.041 mm and the surface roughness is 0.1–0.2 μm; the surface is smoother and has better consistency.

This article presents a new type of bi-material coin with a polymer centre and a metal ring. The polymer-metal coin is fabricated by combination of coin minting and joining by forming in a single die stroke. The design of the coin is based on an analytical model built upon plasticity theory and plastic instability of circular plates under uniform radial edge compression. The analytical model and the bi-material coin concept are supported and validated by means of finite element modelling and experimentation. Destructive tests for pushing the polymer centre out of the metal ring demonstrate the effectiveness of the mechanical joint resulting from the interface contact pressure between the polymer and the metal. The new bi-material coin was developed to obtain new aesthetic effects for the collection market, and its polymer core can additionally be used for other applications such as the incorporation of advanced security features in high-denomination coins.