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The grinding morphology of metal materials is mainly determined by the geometric interference of abrasive particles, which means the machining marks left by the manufacturing process are the key components of the surface structure. However, few researches have been focused on the spatial structure of the grinding morphology. A general form of areal autocorrelative function (AACF) was proposed to characterize the conventional and ultrasonic-assisted grinding surfaces. Firstly, the 3D surfaces under different machining conditions including the axial ultrasonic-assisted grinding, vertical ultrasonic-assisted grinding, and elliptical ultrasonic-assisted grinding were simulated based on the grinding kinematics analysis. Subsequently, the features of the corresponding autocorrelation functions were analyzed and the expression form was given. Finally, the conventional grinding and axial ultrasonic-assisted grinding tests were performed to validate the AACF form. The results showed that the expression form was generally consistent with both the AACFs of the simulated and measured surfaces. The AACF family proposed in this study may serve as an effective and novel way to describe the spatial characteristics of the grinding especially the ultrasonic-assisted grinding surfaces. [ABSTRACT FROM AUTHOR]

A three-dimensional unified model is proposed to simulate the weld pool dynamic behavior in swing arc narrow gap vertical GMA welding with allowing for swing feature of arc heat source and joint configuration. Both the moving direction of arc and its inclination are considered by transformation of coordinate system. The model can simulate the weld pool sagging process reasonably. Based on the calculated and experimental results, the mechanism of weld formation in swing arc vertical-up welding is studied. The weld pool size and the peak temperature of liquid metal are reduced largely in the case of swing arc, which leads to the faster solidification of weld pool and is the major factor responsible for suppression of weld pool sagging. Meanwhile, upward component of arc force and the enhanced support force from solidified metal bulge benefits the weakness of downward flow of liquid metal. With increasing the swing frequency, weld cross section geometry tends to be symmetrical and weld bead surface becomes smoother. When the swing frequency is higher than 0.6 Hz, the satisfied weld formation can be obtained. [ABSTRACT FROM AUTHOR]

The aim of this work was to investigate the impact of nanosecond pulse laser drilling on the quality of carbon fiber reinforced polymer (CFRP). The effects of laser parameters, including laser power, scan speed, pulse width and laser frequency on micro-hole quality and the thermal damage generated during the drilling process were analyzed. 0.4 mm diameter micro-holes were drilling using a 1064 nm fiber laser, using univariate and orthogonal experimental method. The results indicate that pumping at the entrance leads to a significant increase in hole diameter and heat-affected zone (HAZ) width at both the entrance and exit, as laser power, pulse width and frequency increase, and scanning speed decrease. The width of the HAZ at the exit is dependent on whether the energy reaches the carbon fiber ablation threshold. The holes were tapered and the hole taper was closely related to the change in laser parameters at the entrance and exit of the hole. A taper of approximately 0.3 was achieved with a combination of 99 W, 50 mm/s, 13 ns and 1500 kHz. The experiments indicate that laser power and pulse width are crucial factors that affect the quality of micro-hole processing. However, nanosecond laser drilling can result in thermal damage defects, including striations, micro-cracks, delamination, voids and surface fiber 'fish scale' peeling. [ABSTRACT FROM AUTHOR]

Magnesium alloy shows good ductility and formability in a suitable temperature range, but the spinning of revolution surface workpiece with curved generatrix of magnesium alloy is a complicated problem; multi-pass spinning is low efficiency and needs multiple sets of die, and shear spinning is unsuitable for the formation of curved generatrix revolution surface since the strong thinning may lead to material damage. In this paper, one-pass hot spinning process for magnesium alloy AZ31 sheet is designed and investigated; the effect of the process parameters on the quality of the formed workpiece are analyzed; the minimal wall thickness and the maximal ovality of spun workpiece are taken as evaluating indexes; the process parameters are optimized by orthogonal experimental design based on the finite element simulation on the spinning process. The optimizing results of process parameters have been obtained: diameter-to-thickness ratio of sheet blank is 18, spinning temperature is 300 °C, feed rate is 1.0 mm/r, and swivel angle is 35°. Finally, the validity of the orthogonal experimental design results is demonstrated by one-pass hot spinning experiments. [ABSTRACT FROM AUTHOR]

The increase in port scale and business complexity has led to an increased demand for comprehensive and lean control on ports. The current operation mode is facing the bottleneck of the increasingly significant production efficiency and performance. Digital twin (DT) technology realizes holographic visual management and control patterns using cyber-physical fusion and promotes the transformation of a port to an intelligent operation mode. In this paper, the framework of a digital twin application system is proposed based on the analysis of business characteristics of large-scale comprehensive ports. Construction methods and technologies such as digital twin modeling, global ubiquitous perception, data mapping, and model fusion are analyzed. With regard to the construction needs of Qingdao Port's digital twin system, this paper presents a case study and illustrates the overall design process and function of the digital twin system for typical terminals. The system realizes the intelligent operation of the port with the core functions of three-dimensional visual monitoring and optimal dispatching based on real-time perception data. This paper serves as a feasible reference for future intelligent development of large ports and the application of digital twin technology. [ABSTRACT FROM AUTHOR]

Soft abrasive flow (SAF) finishing has advantages in precise processing for titaniferous alloy parts with large-area surfaces. However, the processing efficiency and surface quality of current SAF methods require to be improved. To address the issues, a novel gas–liquid-solid three-phase rotary abrasive flow polishing method (RGLSP) is proposed based on the microbubble cavitation effect. Referring to the energy conservation principles of bubbles group movement, an improved realizable k-ε turbulence model is set up. Based on the above model, a mechanical dynamic model of the machining apparatus is established to obtain the flow field distribution of different structural parameters. The simulated results show that the pitch-down angle determines the distribution of the rotary flow field, and an optimized processing apparatus is developed. The machining experiments show that the proposed RGLSP method can improve the machining efficiency by 60%, and the surface roughness can reach Ra 0.1 μm with lower surface defects. The RGLSP can provide an important reference direction for low-carbon emission processing. [ABSTRACT FROM AUTHOR]

In this note, we consider a single-machine scheduling problem with truncated sum-of-processing-times-based learning considerations. We show that even with the introduction of the proposed model to job processing times, several single-machine problems remain polynomially solvable. For the following objective functions, the discounted total weighted completion time, the maximum lateness, we present heuristics according to the corresponding problems without learning effect. We also analyze the worst-case bound of our heuristics. [ABSTRACT FROM AUTHOR]

During laser cleaving of brittle materials, with the controlled fracture technique, thermal stresses are generated which induce the crack and extend it along the cutting path, subsequently causing material separation. One of the problems in laser cutting of glass with this technique is the cut path deviation at the leading and the trailing edges of the glass sheet. Previous work with a continuous beam diode laser has shown the deviation to be partly due the high magnitudes of thermal stresses generated near the edges of the sheet. This paper reports on the effects of using a pulsed diode laser to cut soda lime glass. The effect of pulse parameters and cutting speed on the quality output variables such as cut deviation angle and surface finish are studied. Finite element modelling is also used to simulate the effects of the moving beam on stress generations to facilitate the understanding of the process mechanisms, and the results are compared with the experimental data. This work shows how to minimise the cut path deviation at the edges by reducing thermal stresses using optimum pulsed diode laser parameters and providing additional flexibility to the process. [ABSTRACT FROM AUTHOR]

This study used statistical control charts as an efficient tool for improving and monitoring the quality of manufacturing processes. Under the normality assumption, when a process variable is within control limits, the process is treated as being in-control. Sometimes, the process acts as an in-control process for short periods; however, once the data show that the production process is out-of-control, a lot of defective products will have already been produced, especially when the process exhibits an apparent normal trend behavior or if the change is only slight. In this paper, we explore the application of grey forecasting models for predicting and monitoring production processes. The performance of control charts based on grey predictors for detecting process changes is investigated. The average run length (ARL) is used to measure the effectiveness when a mean shift exists. When a mean shift occurs, the grey predictors are found to be superior to the sample mean, especially if the number of subgroups used to compute the grey predictors is small. The grey predictor is also found to be very sensitive to the number of subgroups. [ABSTRACT FROM AUTHOR]

The machinability of Ti-6Al-4V alloy has been a constant challenge in the industry, although the material is widely used in the aerospace and medical industries due to its mechanical properties, particularly its strength-to-weight ratio. The current research presents a hybrid laser- and ultrasonic-assisted machining (LUAM) technique to improve the machinability of Ti-6Al-4V alloy in a turning process. This is compared with ultrasonic-assisted machining (UAM), laser-assisted machining (LAM), and convectional turning (CT). The results reveal that UAM and LAM can reduce the cutting forces and surface roughness (Ra) compared to the CT. However, these are achieved mainly at the lowest range of cutting speeds. The hybrid LUAM process demonstrates process improvement with wider range of cutting speeds and depths of cut, which is achieved due to the combined force reduction and thermal softening effect by the hybrid process. [ABSTRACT FROM AUTHOR]

Machining chatter has detrimental effects on surface quality, tool life, and machining efficiency. Therefore, it is of vital significance to predict and avoid this undesirable phenomenon. This paper presents an Adams-Moulton-based method for the stability prediction of milling operations. Generally, delay differential equations with time-periodic coefficients are applied to model the milling dynamics that include the regenerative effect. To begin with, the tooth-passing period is divided into free vibration time period and forced vibration time period. Subsequently, the Adams-Moulton method is utilized to construct the transition matrix over one period through dividing the forced vibration time period equally into small time intervals. Finally, the milling stability can be obtained by examining the eigenvalues of the transition matrix based on Floquet theory. A comparison with the first-order semi-discretization method and the Simpson-based method is conducted to evaluate the convergence rate and the computation efficiency of the proposed algorithm. The results verify that the proposed method is highly accurate and efficient; thus, it is practical for workshop technicians to select chatter-free machining parameters. [ABSTRACT FROM AUTHOR]

Development of flexible forming is crucial for manufacturing three-dimensional sheet metal parts. In this paper, continuous roll forming (CRF) is investigated to improve the forming results, especially for doubly curved parts. The CRF process employs an upper flexible roll and a lower flexible roll as a forming tool, and the different forming shapes are achieved by controlling and adjusting the distribution of the roll gap between two rolls. This paper is focused on analysis of the longitudinal bending deformation in CRF process, the plane assumption for longitudinal bending analysis is discussed, and the formulation to calculate the longitudinal strain distributed over the cross-section is derived. Through a series of numerical simulation on CRF processes, the validity of the plane assumption and the other theoretical models to analyze the deformation in CRF are confirmed; the relationship between longitudinal elongation distribution and longitudinal bending deformation is discussed and the strain distribution in transverse, longitudinal, and thickness directions is presented. In addition, the CRF experiments on saddle-shaped and torus-shaped parts were carried out, and the theoretical analysis and simulation results are verified by experiments. [ABSTRACT FROM AUTHOR]

Residual stresses induced by machining coupled with the initial stresses can significantly impact mechanical properties of workpieces such as distortion, corrosion resistance, and dimensional stability. The redistribution pattern of residual stresses is extremely complex. The stress relieving can seriously deform the workpieces and reduce the fatigue life. Therefore, deflection prediction is critical for design, control, analysis, and management of machining. In this paper, an integrated modeling method is introduced to predict the deflection caused by milling residual stresses, to be more exact, to map the relationship between the deflections and the cutting parameters. Response surface design (RSD) is utilized to develop a new mathematical model which can predict the residual stress profiles of the workpieces along the cutting direction based on different cutting parameters. Then, the deflections are derived based on the estimated stress profiles and mechanics of materials theory. A finite element analysis model (FEM)-based simulation experiment using aluminum alloy 6061 as a case study has been implemented. The results from experiments indicate that the proposed approach could precisely estimate the residual stress profiles for given cutting parameters and effectively predict the deflections of the workpieces caused by residual stress. [ABSTRACT FROM AUTHOR]

The development of sustainability assessment for machining process is considered as one of the crucial strategies to realize sustainable design and manufacturing, while existing methods focusing on environmental assessment have limits due to neglect economic and social impacts. This paper proposes an assessment approach for evaluating sustainability performance of machining process with respect to a consistent set of environmental, economic, and social criteria in order to select a machining strategy from sustainable manufacturing viewpoint. Sustainability assessment criteria are identified to compare different machining parameter alternatives; cutting noise, especially, is defined as an important criterion of social impact, and energy, lubricant oil, and cutting fluids consumption are identified as criteria of environmental impact. Additionally, the weights of criteria are determined using entropy weight approach with the advantage of objective evaluation by exploiting the useful information of data to a maximum extent. Furthermore, sustainability performance of machining process is calculated based on extension theory through utilizing correlation function between evaluated matter-element and classical field matter-element. Face milling test conducted on CNC vertical machining center not only illustrates validity of the proposed method for assisting the engineers or designers to define sustainability performance of machining process, but also proves the relationship between cutting parameters and cutting noise. [ABSTRACT FROM AUTHOR]

This paper presents single and dual assist gas jet effects in the single-pass laser cutting of dry pine wood. The laser wood cutting process is influenced by the assisting gas jet(s) applied. Therefore, it is important to understand their roles in the removal of fumes and combusted materials from the cutting kerf. A computational fluid dynamic model is developed to investigate the effect of single and dual gas jets in the laser wood cutting process. In order to obtain a close approximation of the actual process, a three-dimensional model was considered. Results obtained in the simulations were compared with experimental data collected from a multifactor experiment analysing the laser cutting process of dry pine wood. A high brightness, 1 kW IPG single-mode, continuous-wave Ytterbium fibre laser was employed to cut cubic wood samples parallel to the wood fibre direction. It has been found that shear stresses produced by the gas jet(s) on the kerf walls have an important correlation with the yield and cut quality. [ABSTRACT FROM AUTHOR]

Challenges in dissimilar materials welding are the differences of physical and chemical properties between welding materials and the formation of intermetallic brittle phases resulting in the degradation of mechanical properties of welds. However, dissimilar materials welding is increasingly demanded from the industry as it can effectively reduce material costs and improve the design. In aerospace applications, Ti-6Al-4V titanium alloy and Inconel 718 nickel alloy have been widely used because of their superior corrosion resistance and mechanical properties. In this study, a single-mode continuous-wave fibre laser was used in butt welding of Ti-6Al-4V to Inconel 718. Investigations including metallurgical and mechanical examinations were carried out by means of varying processing parameters, such as laser power, welding speed and the laser beam offset position from the interface of the metals. Simple analytical modelling analysis was undertaken to explain the phenomena that occurred in this process. Results showed that the formation of intermetallic brittle phases and welding defects could be effectively restricted at welding conditions produced by the combination of higher laser power, higher welding speed and shifting the laser beam from the interface to the Inconel 718 alloy side. The amount of heat input and position of laser beam to improve the Ti-6Al-4V/Inconel 718 weld quality are suggested. [ABSTRACT FROM AUTHOR]

This paper presents a statistical analysis of the performance of an Ytterbium fibre laser utilising single and dual gas jets in a single pass to blind cut dry pine wood. Cutting wood with lasers is a multi-factor process and a proper combination of the parameters involved is needed to achieve high quality and optimum process efficiency. This study employs design of experiments and statistical modelling approach to investigate the significant process parameters along with their interactions. A high brightness, 1 kW IPG single mode Ytterbium-doped fibre laser was employed to produce blind cuts on samples of dry pine wood. The experiments were performed parallel to the direction of the wood fibre. The parameters investigated include laser power, focal plane position, traverse speed, gas pressure and single and dual gas jets. Results were compared using a number of process responses which define the efficiency of the cut in terms of kerf depth, mass removal and energy consumption as well as quality of the cut section considering the heat-affected zone, kerf width and roughness of the edge of the surface. It has been found that application of an additional gas jet produced a surface finish superior to the single jet. [ABSTRACT FROM AUTHOR]

The present study investigates the effects of four controllable variables on the metallurgy and drilling velocity of laser percussion drilled acute (30° to surface) blind holes in 2 mm thick flat pieces of nickel superalloy—CMSX-4 material. Design of experiment and statistical modelling were used in the experimental study to understand parameter interactions. Pulse energy, pulse width, pulse frequency and gas pressure were chosen as the independent process variables. The response surface method was used to develop the models for each of the responses: physical characteristics of wall and bottom recast layer and drilling velocity (function of material removal rate). A central composite design was chosen as it offered the most economical number of experiments for the required information. The significant process factors in each model were identified based on the analysis of variance and the models were checked by complete residual analysis. It was found that high pulse energy and short pulse width gave the maximum drilling velocity and lowest recast layer thickness at the hole bottom, whereas low pulse energy and short pulse width minimised the wall recast layer thickness. [ABSTRACT FROM AUTHOR]

A three-dimensional transient model is proposed to investigate the weld formation during laser + metal inert gas (MIG) hybrid welding of aluminum alloy for horizontal fillet joint, which considers the coupling of keyhole, droplet, and liquid metal pool as well as the influence of joint geometry feature and welding position. An asymmetrical double-elliptic heat source is utilized to model the arc heat input and a conic heat source with increased peak heat density is used to describe the laser energy. The coordinate rotation is used to take into account the inclination of heat source and the related forces. According to the experimental and simulated results, weld formation mechanism of horizontal fillet joint is studied. At a lower laser power, the fluid flow pattern in hybrid welding is similar to that in MIG welding and a strong downward flow caused by both gravity and arc pressure occurs at the liquid metal zone of the vertical plate, leading to the accumulation of molten metal at the horizontal plate and the resultant weld asymmetry. At high laser power, a clockwise vortex appears above the keyhole. In this case, the sagging of liquid metal near weld pool surface due to effect of gravity is an important factor responsible for the asymmetry of fillet weld. Besides, with increasing laser power, the tendency of weld pool free surface sagging is enhanced to some extent and weld bead surface becomes concave. [ABSTRACT FROM AUTHOR]

Narrow gap (or groove) laser welding involves multiple layer additive manufacture for the joining of thick-section metallic components. Typical defects include porosity, cracking, lack of fusion to sidewalls, and between layers, and component distortion including the closure of the groove. This study aimed to understand the defect formation mechanisms and factors affecting them, and to develop appropriate welding procedures and parameters for joining ferritic steel sheets of 30 mm in thickness. High-quality welded joints in 30-mm-thick Grade 43 ferritic steel sheets have been achieved by multi-pass defocused laser beam welding with filler wire addition. The microstructure and the microhardness of the multi-pass welded joint were found to be affected by the tempering of the subsequent multi-pass welding layers. Post-weld heat treatment on the welded joints were required since, although the strength of the welded joints were higher than that of base metal, the ductility was much lower than that of base metal. [ABSTRACT FROM AUTHOR]

S960 and S700 are two new high strength steels recently developed by Tata Steel, UK. Due to the high power densities that can be achieved, small component distortion, and fast welding speeds, laser welding of thick section steels has been widely used in offshore construction and shipbuilding. However, the penetration depth is typically limited in single pass welding to 1-2 mm/kW laser power. Melt sagging is a typical defect for single pass autogenous laser welding of thick section materials. Multi-pass narrow gap laser welding techniques become more attractive because they can weld thicker sections of material with a moderate laser power and suppress the melt sagging problem. In addition, this approach requires less filler material, and the cumulative heat input to the material is reduced when compared with traditional arc welding techniques. However, there are many variables involved in this narrow gap laser welding technique, which makes this process more complicated than single pass autogenous laser welding. In this study, the effects of multi-pass ultra-narrow gap laser welding parameter interactions (i.e. laser power, welding speed and wire feed rate) on laser weld quality and the welding efficiency for S960 high strength steel plates were investigated. Moderate laser powers of 1 to 2 kW were used to weld S960 high strength steel plates with a very narrow parallel groove (1.2 mm). Statistical design of experiments was carried out to assess the process parameter interactions and to optimise the ultra-narrow gap laser welding parameters. Validation experiments indicate that the proposed models predict the responses adequately within the range of welding parameters that were used. Defect-free welds in 6 mm thick S960 steel were obtained with only two passes, using the optimised welding parameters, and these optimised parameters were successfully transferred to the welding of 8 mm thick S960 steel. In addition, they were also successfully transferred to the welding of 13 mm thick S700 steel with a small modification. The optimised narrow gap laser welded joints show almost the same tensile properties as the base material, with failures occurring in the base material away from the weld. [ABSTRACT FROM AUTHOR]