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In the aerospace industry, high-precision components like impellers and blisks present considerable challenges in machining due to their intricate geometries and the need for reliable performance. Blades, often classified as thin-walled parts with complex, free-form surfaces, are crucial in ensuring the efficiency and safety of aircraft engines. Their geometries and materials require strict control over cutting parameters, such as tool path and orientation, to avoid deformation and maintain surface integrity. This study investigates the impact of tilt angle variation during ball end milling of Ti6Al4V thin-walled parts. Four different tilt angles (15°, 30°, 45°, and 60°) were analysed to evaluate their effect on dimensional accuracy and surface roughness. The results show that tilt angle significantly influences surface quality and dimensional precision. A tilt angle of 30° achieved the best balance between surface finish and dimensional tolerances, with flatness values ranging from 0.038 mm at 30° to 0.101 mm at 60°, representing a 152.5% increase in flatness. The findings provide practical guidelines for optimizing ball end milling of thin-walled components, emphasizing the importance of tool orientation in reducing deformation and enhancing surface quality. [ABSTRACT FROM AUTHOR]

This article analyses the influence of tool orientation on the geometry and surface finish obtained during the machining of thin-walled curved freeform surface parts on multitasking machining centre. These complex surfaces parts have direct application in blade manufacturing for the aeronautical sector, which has very high quality standards and are difficult to achieve. In addition, the material used is Ti6Al4V which adds a challenge due to its difficult machinability. Tool orientation has a significant effect on the accuracy of multi-axis machining reducing the theoretical force in a 6.17 % have achieved a dimensional improvement of a 7.84 %. [ABSTRACT FROM AUTHOR]

High-aspect-ratio vortex curved thin wall is widely used in electronics, precision instruments, aerospace, and other fields. It is a typical flexible geometrical structure with varying curvature making it very difficult to be fabricated with high quality due to burrs, dimensional errors, tool marks, and other defects in the machining process. In order to improve the machining quality of vortex curved thin walls, a new micromilling process with large cutting depth and slow feed is proposed. Firstly, through the single factor finite element simulation and micromilling experiment, the influences of radial depth of cut ae and feed per tooth fz on milling forces are analyzed under the condition of large axial depth of cut ap. Then, under the guidance from the results of single-factor experiments, the orthogonal experiments are conducted selecting surface roughness Ra, dimensional error △w, and burr height h as the evaluation indexes of machining quality. The influences of key milling parameters (feed per tooth fz, axial depth of cut ap, radial depth of cut ae, and spindle speed n) on machining quality are explored. By comprehensively analyzing the key milling parameters and their effects, an optimum combination of cutting parameters is identified. Finally, the new micromilling process is validated for the fabrication of high quality vortex curved thin walls. [ABSTRACT FROM AUTHOR]

Thermally induced error has proven to be the major source of machining error for the machine tool working in a non-temperature-controlled workshop. Current research on thermal error modeling and compensation is implemented based on the measured thermal deformation of machine tool, and the data is obtained referring to spindle idling rather than metal cutting condition, resulting in the disadvantages of the established model with low adaptability to varying conditions. In this paper, a modeling and compensation method based on the dimensional error of the machined parts is proposed to address the issue and verified through machine tools in an automatic production line. Compared with the modeling based on thermal deformation, the method formulates a more direct relations between temperature rise and machining error. The thermal error modeling is carried out by measuring the dimension deviation of the inner hole diameter of the motor end cover and the screened representative temperature variables. Meantime, considering the temperature coefficient in model is difficult to converge when modeling with the single-day data, the unified modeling with the multi-day data is realized by improving the conventional multiple linear regression model. Finally, the generalized model used for thermal error compensation in x direction of the machine tool is obtained. The real-time compensation of the thermal error based on the established model is realized with the machine tool machining in mass production. The verification results show that this error modeling and compensation method can reduce the machining error of the end cover by more than 52%, irrespective of experiencing various complicated working conditions. Stability and robustness of the modeling are also validated through application on the other machine tool with the same configuration and real machining over seven days. • Dimensional error of machined parts represents thermal effect of machine tool more directly. • Thermal error modeling with real cutting condition guarantees strong robustness. • A generalized error model arises from processing multiday data obtained on production line. • Thermal error model is duplicable to other machine tool and has stability of prediction accuracy. [ABSTRACT FROM AUTHOR]

In the biomedical industry, tricalcium phosphate is a bioceramic substance that is frequently employed in the fabrication of scaffolds and bone structures. Fabrication of porous ceramic structures using conventional manufacturing techniques is very challenging because of the brittle nature of the ceramics, which has led to a newly adapted direct ink writing additive manufacturing method. This work investigates the rheology and extrudability of TCP inks to produce near-net-shape structures. Viscosity and extrudability tests found that stable TCP: Pluronic ink of 50 vol.% was more reliable compared to other tested inks prepared from a functional polymer group polyvinyl alcohol. A line study was carried out to identify the printing parameters suitable for printing structures from the selected ink with lesser dimensional error. Printing speed 5 mm/s and extrusion pressure 3 bar was found suitable to print a scaffold through a nozzle of 0.6 mm, keeping the stand-off distance equal to the nozzle diameter. The printed scaffold was further investigated for its physical and morphological structure of the green body. A suitable drying behavior was studied to remove the green body without cracking and wrapping before the sintering of the scaffold. [ABSTRACT FROM AUTHOR]

Dimensional error of workpiece is an important index that indicts the grinding accuracy of machine tools. Conventional error compensation strategies focus on modeling one or several error factors for a particular CNC machining type, which are time consuming and costly. Based on data-driven sliding mode terminal iterative learning control, a new dimensional error compensation method is proposed in this paper. The compensation algorithm based on an iterative sliding surface and an objective function is established using the terminal experimental data. A modified NC program is fed to the machine tool to push the workpiece dimension towards desired. The theoretical analysis and experimental results show the proposed compensation method can effectively improve the batch grinding accuracy of the machine tool, which shows good perspective in manufacturing industry. [ABSTRACT FROM AUTHOR]

A comprehensive dynamic model is introduced try to further reduce dimensional errors of micromilled micro straight thin walls based on an in-process cutting parameter compensation device. First, a mathematical model is established to predict the dynamic elastic deformation of the thin walls in the micromilling process. Next, the radial deformation and the runout of the cutter are modeled. Then, the comprehensive in-process parametric compensation model and strategy are established. Finally, a real-time in-process cutting force measurement and cutting parameter compensation device is applied to the micromilling system and thin wall fabrication experiments have been conducted. It shows that the comprehensive dimensional error model and iterative compensation method are effective, and the dimension and shape precision of the micro straight thin wall has been obviously improved after the compensation of the radial cutting depth. The average relative errors have been reduced from 6.86% to 1.10%∼1.70%. The in-process compensation method introduced in this study is efficient and convenient as long as compensation strategies are integrated in the controlling unit for a specific micromilling process.

The boundary dimension of ring forgings is an important factor to ensure the machining quality. However, point cloud models of ring forgings obtained by three-dimensional laser scanner have a large amount of data and many redundant points, resulting in dimensional errors in the simplification processing of three-dimensional point cloud models of ring forgings. Therefore, this paper proposes an improved point cloud data simplification method of single median error metric based on firefly algorithm. Firstly, the point cloud data are preliminarily simplified by the improved farthest sampling method to improve the efficiency of the subsequent simplification process. Secondly, the triangle collapse algorithm is improved by using the proposed single median error metric. The single median error of the triangle is regarded as the objective function by the firefly algorithm, and the optimal solution of the single median error function is solved by using the mutual attraction relationship between fireflies. Finally, through the simplification experiment of the point cloud model of ring forging, it is verified that the algorithm can reduce the amount of point cloud data of annular forging and the dimensional error between the forging and the original model. The simplification method proposed is feasible according to the experimental results. [ABSTRACT FROM AUTHOR]

In order to further reduce the machining errors of microstraight thin walls caused by the elastic deformation in micromilling process, the deformation mechanism has been studied, and a compensation method is proposed to reduce the machining errors. Firstly, conventional micromilling experiments have been conducted. It shows that large dimensional errors exist in finished thin walls. Second, a mathematical model is established to calculate the thin wall deformation based on Rayleigh–Ritz theory. The deformation values are determined by calculating the selected discrete measurement points. Based on the deformation of measurement points, the thin wall deformation of any position can be calculated by numerical method. Finally, the thin wall dimensional errors are reduced by compensating the deformation according to the analysis based on the introduced mathematical model. The high machining quality of the thin wall is realized. The experimental results show that the dimensional errors of the thin wall have been significantly reduced after the deformation compensation. The average relative dimensional errors have been reduced from 6.86 to 1.11 ~ 2.69%. Also, the fabricated thin walls keep good shape accuracy. The experimental results show that the introduced device and the compensation method can effectively improve micromilling quality of thin walls. [ABSTRACT FROM AUTHOR]

In order to satisfy the increasing fabrication quality requirements of micro curved thin wall structures, deformation, burrs height and dimensional errors in micro-milling processes of curved thin walls are studied. At first, the finite element analysis of curved thin wall deformation is carried out, it shows that complex elastic-plastic deformation and recutting occur in each micro-milling layer. Appropriate radial depth of cut, smaller spindle speed and axial depth of cut are beneficial to reduce deformation. Then, the influence of key process parameters in micro-milling as the speed of spindle n , feed engagement f z , radial depth of cut a e and axial depth of cut a p on milling force (F n), burrs height (H) and dimensional errors (△ w) are analyzed using the response surface method (RSM). To facilitate the quantitative analyses, mathematical models of burrs height and dimensional errors are established considering the interactions and quadratic effects of key parameters. It shows that the interactions among key parameters cannot be ignored. Therefore, cutting parameters should be delicately selected. The multi-objective particle swarm optimization (MOPSO) experiments are carried out based on the established prediction model. The results show that the combination of the optimized parameters identified by this method can effectively reduce the burr height and the dimensional error. Finally, under the guidance of this method, high-quality curved thin wall parts are fabricated. • The method to solve the deformation in curved thin wall micro-milling. • An optimal micro-milling parameter identification method for curved thin walls. • Multi-objective optimization for reducing dimensional errors and burr height. • The interactions and quadratic effects of key parameters are considered. • The method proposed provides a guidance for curved thin wall fabrications. [ABSTRACT FROM AUTHOR]

In order to further improve the dimensional accuracy of micromilled thin walls with high aspect ratios, the machining process should be actively controlled. A device for active cutting force measurement and cutting parameter compensation is developed to realize the real-time measurement of radial cutting forces and compensation of radial cutting parameters in thin wall cutting process. Firstly, a mathematical model is established to calculate the deformation and cutting force of thin walls based on the cantilever beam deformation theory. The thin wall deformation in the cutting process is estimated by measuring the cutting force. Then, the obtained incremental thin wall deformation is to be compared with the compensation threshold, which is set at 0.5 μm. If the value of the incremental deformation is less than 0.5 μm, compensation will not be processed. Otherwise, the incremental deformation is used as the compensation value for iterative compensation, until the incremental deformation of the thin wall is less than 0.5 μm. At last, a contrast experiment is carried out. The experimental results show that the introduced device and compensation method are feasible. Machining quality of the thin wall has been obviously improved in dimension precision after the cutting parameter compensations. [ABSTRACT FROM AUTHOR]

In die-mold manufacturing and aircraft industry, many components that have thin-walled features are produced by turning operation. The major problem encountered during internal or external turning is cutting force induced deflection of workpiece along the periphery as well as axial length of a component. The present research work aims to develop a mathematical model for estimating dimensional and geometric errors during turning of thin-walled hollow cylinder qualitatively and quantitatively. In the proposed model, a mechanistic approach which is semi-analytical in nature is followed to achieve accuracy of the predicting results. First of all, process geometry model for thin-wall turning is developed based on process geometry variables such as uncut chip thickness, actual feed per revolution, actual depth of cut, peripheral cutting speed, effective cutting area etc. Using these process geometry variables and mechanistic cutting constants, a force model of turning is developed to estimate the tangential and radial force components. Later on, based on the predicted forces, tool-workpiece combined deflection model is developed to estimate radial, diametric and various geometric errors of the turned surface. The developed models are able to predict radial, diametric and various geometric errors such as straightness, circularly and cylindricity errors without conducting expensive actual machining operation. Hence, the present study will be helpful to take care of precautionary measures for controlling of dimensional and geometric errors more efficiently and reliably. Therefore, an attempt has been made to provide a basic platform to machining practitioners and process planners for in-depth comprehension and characterization of dimensional and geometric errors of the entire turned surface for varying machining conditions. [Display omitted] • Asymmetrical part in thin-wall turning • Peripheral thinning is prominent in thin-wall turning. • Diametric is not double of radial error for thin-walled part. • Geometrical shape change prominent in thin-wall turning. [ABSTRACT FROM AUTHOR]

Dimensional error of workpiece is an important index that indicts the grinding accuracy of machine tools. Conventional error compensation strategies focus on modeling one or several error factors for a particular CNC machining type, which are time consuming and costly. Based on data-driven sliding mode terminal iterative learning control, a new dimensional error compensation method is proposed in this paper. The compensation algorithm based on an iterative sliding surface and an objective function is established using the terminal experimental data. A modified NC program is fed to the machine tool to push the workpiece dimension towards desired. The theoretical analysis and experimental results show the proposed compensation method can effectively improve the batch grinding accuracy of the machine tool, which shows good perspective in manufacturing industry.

The vertical surface is a common and typical characteristic structure among Nomex honeycomb core components. However, the conventional high-speed milling and ultrasonic cutting struggle to meet the high-quality machining requirements of a vertical surface. In this study, an ultrasonic trepanning method is proposed and a special ultrasonic trepanning tool is developed, aiming to improve the machining quality of the vertical surface. The trepanning quality of the vertical surface is further studied from the aspects of dimensional error and trepanning incision quality. Based on the kinematic characteristics of ultrasonic trepanning, a theoretical model of dimensional error in trepanning is established. Meanwhile, the influence of ultrasonic vibration on the trepanning process is analyzed, and the result shows that ultrasonic vibration significantly improves the equivalent elastic constant of the honeycomb core material. The theoretical model is proposed to predict the trepanning dimensional error, which is verified by experiment. The effectiveness of the ultrasonic vibration on the incision quality is verified by several experiments, and the quantitative analysis results demonstrate that ultrasonic vibration significantly improves the trepanning quality of the vertical surface. [ABSTRACT FROM AUTHOR]

Since manufacturing errors significantly affect the dynamic performance of the deployable mechanism, the length of links must be adjusted in assembly. To ensure the assembly quality and shorten the adjustment period, this paper presents an efficient assembly optimizer with machine learning for the deployable mechanism. Considering the assembly dimensions, a numerical iterative algorithm is firstly proposed to analyze ultimately deployed angles of joints after link adjustment. For more effective inference, an agent model with neural network is trained to predict the dynamic performance. The training datasets are obtained after calculating amounts of locked angles for joints in different dimensional errors, and a BP network with two hidden layers is constructed based on optimal brain surgeon. Experiments demonstrate that our method can accurately predict whether the adjusted mechanism meets the requirement of assembly quality in about 0.3 s. [ABSTRACT FROM AUTHOR]

Bolted joints are the most common form of union of the components in an airplane, with drilling being the most used process in obtaining the holes. However, this process can cause several defects, so the parts produced can go to the assembly line with some defects. Aim of this manuscript was to analyze the influence of spindle speed and the feed in the power consumption and system vibration, during the drilling process of the composite of furfuryl resin/Carbon Nanotube/Carbon fiber, as well as the quality of the hole, the dimensional error, and the tool wear. Spindle speed of 1000 and 2000 rpm and feeds of 0.025, 0.05, 0.1, 0.2 and 0.3 mm/rev were used. The drills used are carbide coated with Balinit Helica®, 6.5 mm in diameter. Concluded that the feed influences on the power, vibration and in the quality of the holes. The addition of nanotubes does not inhibit dimensional error but causes it to be smaller. Helica coating is not ideal for drilling composites reinforced with carbon fiber. [ABSTRACT FROM AUTHOR]

The utilization of components fabricated by directed energy deposition (DED) faces certain limitations that hinder its widespread application. These critical challenges primarily include significant errors in dimension accuracy caused by the unreliable build-up of flowing powder and low surface quality arising from the interlayer cumulative effect and powder adhesion. The present study aims to comprehensively investigate the impact of process parameters and deposition height on the geometrical errors observed in the thin-walled structures fabricated by DED. By establishing a rational relationship between the dimensional error and the sample height, the mechanism underlying the influence of deposition height on printing stability and sustainability is elucidated. Furthermore, an innovative building strategy incorporating a variable speed is proposed to eliminate protrusions at the end of the components. The study also examines the surface roughness of inclined thin walls, revealing a correlation between roughness and both position and angle. The presence of adhering powder on the front side of the parts and the formation of a molten oxide layer on the backside result in a diminished impact of angle on roughness. Ultimately, the findings of this study are validated through the fabrication of a thin-walled axisymmetric curved structure, providing a guide for the printing of large special-shaped parts. [ABSTRACT FROM AUTHOR]

Due to the complexity of machine tool structure and the cutting process, the dynamics of machining processes are still not completely understood. This is especially true for high-speed machining processes. To model and control these complex processes, new approaches, which can represent complex phenomenon combined with learning ability, are needed. The combined neural-fuzzy approach appears ideally suited for this purpose. To illustrate the approach, the recently developed fuzzy adaptive networks are used to model dimensional error in turning operations. The fuzzy adaptive network has both the learning ability of a neural network and the linguistic representation of a complex, not well understood or vague phenomenon. An approximate model representing the influences of machining parameters on dimensional error is first established. This model is then improved by learning with the given training data. The improved models are verified by the use of test data, which are obtained by the use of actual experiments. [ABSTRACT FROM AUTHOR]

Distribution of contact pressure between the bipolar plate and gas diffusion layer considerably affect the performance of proton exchange membrane fuel cell. In this regard, an adaptive neuro-fuzzy inference system (ANFIS) is developed to predict the contact pressure distribution on the gas diffusion layer due to dimensional errors of the bipolar plate ribs in a proton exchange membrane fuel cell. Firstly, the main data set of input/output vectors for training and testing of the ANFIS is prepared based on a finite element simulation of the contact between bipolar plate and gas diffusion layer. An experimental procedure is used to validate the simulation results. Then, the ANFIS is developed and validated using the randomly selected data series for network testing. The applied ANFIS model has ten inputs made up of the dimensional errors of the bipolar plate ribs (e1 … e10). The standard deviation of contact pressure distribution (Pstd) on the gas diffusion layer is the unique output of the ANFIS model. To select the best ANFIS model, the average errors of various architectures two different data series of training and testing of the main data set are calculated. Results indicated that the developed ANFIS has an acceptable performance in predicting the contact pressure distribution for the cited fuel cell model. The proposed integrated prediction model is feasible and effective for the dimensional tolerances considered. This method can reduce computing time and cost considering the acceptable accuracy of the obtaining results, and can be used to analyze the effects of dimensional errors of bipolar plate on the performance of proton exchange membrane fuel cell.

At present, laser cutting is currently employed to cut metallic plates, due to their good finish and dimensional quality, as well as because of the flexibility of the process to obtain different shapes. In the present paper, surface roughness, dimensional accuracy, and burr thickness of thin plates of 0.8 mm are studied as functions of different process parameters: pulse frequency, pulse width, and speed. Eight different experiments were performed according to a full 23 factorial design, with two replicates each. Square specimens of 10 mm × 10 mm were cut. Arithmetical mean roughness Ra was measured with a contact roughness meter, and the dimensions and burr thickness with a micrometer. Ra values ranged between 1.89 and 3.86 µm, dimensional error values between 0.22 and 0.93%, and burr thickness between 2 and 34 µm. Regression analysis was performed, and linear models were obtained for each response. Results showed that roughness depends mainly on frequency, on the interaction of frequency and pulse width and on pulse width. Dimensional error depends on pulse width, frequency, and the interaction between pulse width and speed. Burr thickness is influenced by frequency, pulse width, and the interaction between frequency and speed. Multi-objective optimization showed that, in order to simultaneously minimize the three responses, it is recommended to use high frequency (80 Hz), high pulse width (0.6 ms), and high speed (140 mm/min). The present study will help to select appropriate laser cutting conditions in thin plates, in order to favor good surface finish and dimensional accuracy, as well as low burr thickness.

In order to improve the machining quality and reduce the dimensional errors of micro high-aspect-ratio straight thin walls, the on-line cutting parameter compensation device has been introduced and corresponding micromilling processes have been investigated. Layered milling strategies for the micromilling of thin walls have been modeled and simulated for thin walls with different thicknesses based on the finite element method. The radial cutting parameters compensation method is adopted to compensate the thin wall deformation by raising the radial cutting parameters since the thin wall deformation make the actual radial cutting parameters smaller than nominal ones. The experimental results show that the dimensional errors of the thin wall have been significantly reduced after the radial cutting parameter compensation. The average relative dimensional error is reduced from 6.9% to 2.0%. Moreover, the fabricated thin walls keep good shape formation. The reduction of the thin wall dimensional error shows that the simulation results are reliable, which has important guiding significance for the improvement of thin wall machining quality, especially the improvement of dimensional accuracy. The experimental results show that the developed device and the machining strategy can effectively improve the micromilling quality of thin walls.

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Abstract Thin wall fabrication is a long lasting hot research topic in the precision manufacturing fields. There is still a lack of studies in key machining parameters and qualities for thin wall fabrications. In this paper, micromilling parameters and processes are comprehensively studied for thin walls fabrications considering the dimensional errors and surface quality. First, the influences of key process parameters in micromilling as the feed engagement f z , radial depth of cut a e and axial depth of cut a p on milling forces, surface roughness and dimensional errors of thin walls are analyzed by single-factor finite element simulations and experiments. The reasonable micromilling parameters are identified by the single-factor studies. Second, contrast experiments have been conducted to evaluate the effects of multi-axial feed engagement on dimensional errors. It turns out that there exists the appropriate feed times for achieving smaller dimensional errors of thin walls with the same height. Then, thin wall fabrication experiments have been conducted. The suitable feed times identified by the study are 2 and 3 for thin walls made of the material brass H59 with the width of 50 μm, height of 300 μm and 900 μm, respectively. The correspondingly dimensional errors are 0.73 μm and 5.95 μm, respectively. The study indicates that both micromilling parameters and feed times need to be separately optimized for the fabrication of thin walls with good dimensional accuracies. Highlights • The influences of key parameters on milling force, surface roughness and dimensional error are revealed. • Cutting forces have nonlinear effects on surface roughness and dimensional errors of thin walls. • The feed times (axial depth of cut) has effect on the dimensional error. • There exists appropriate feed times for achieving smaller dimensional errors of thins walls with the same height. • The suitable axial feed times are 2 and 3 for thin walls made of material brass H59 with aspect ratio of 6 and 18. [ABSTRACT FROM AUTHOR]

The vertical surface is a common and typical characteristic structure among Nomex honeycomb core components. However, the conventional high-speed milling and ultrasonic cutting struggle to meet the high-quality machining requirements of a vertical surface. In this study, an ultrasonic trepanning method is proposed and a special ultrasonic trepanning tool is developed, aiming to improve the machining quality of the vertical surface. The trepanning quality of the vertical surface is further studied from the aspects of dimensional error and trepanning incision quality. Based on the kinematic characteristics of ultrasonic trepanning, a theoretical model of dimensional error in trepanning is established. Meanwhile, the influence of ultrasonic vibration on the trepanning process is analyzed, and the result shows that ultrasonic vibration significantly improves the equivalent elastic constant of the honeycomb core material. The theoretical model is proposed to predict the trepanning dimensional error, which is verified by experiment. The effectiveness of the ultrasonic vibration on the incision quality is verified by several experiments, and the quantitative analysis results demonstrate that ultrasonic vibration significantly improves the trepanning quality of the vertical surface.

The influence of the pulse energy in electrical discharge machining (EDM) of deep holes in 40Х steel workpieces is studied. The factors considered are the change in steel microstructure within the machining zone and the change in dimensions, shape, and surface roughness of the hole under the action of the current pulses. The depth of the defective layer in finishing and precision machining is no more than 1 mm. However, increase in pulse energy in the electrical discharge machining of 40Х steel is associated with increase in microhardness in the white layer and strengthening and increase in width in the tempering zone. Minimum pulse energy is associated with maximum precision and minimum surface roughness. [ABSTRACT FROM AUTHOR]

Due to the complexities of calculations based on different representations of constituent parts in an assembly, the combined improvement of efficiency and precision for the riveting has seldom been studied by the sequence planning or dimensional engineering. This article develops an assembly sequence optimization method that simultaneously minimizes the path length and overall dimensional error for the solid riveting. The sequence is denoted by the order of classifications for the nodes around the rivet holes in the finite element model for the assembly. Ant colony algorithm is applied on the optimization by integrating two calculations, that is, the length calculation of riveting path and the calculation of the dimensional error related to rivet upsetting directions and assembly sequence. Results for three assemblies are presented which show a good degree of optimization in performance for different scales of assemblies with different numbers of rivets that share the same solid riveting process. [ABSTRACT FROM AUTHOR]

This study offers an efficient method to improve manufacturing technique of metallic bipolar plates (BPPs) so as to simultaneously reduce contact resistance (CR) and maximize power density in proton exchange membrane fuel cell (PEMFC). CR plays an important role in the energy conversion in the cell and can be normally reduced by coating on the BPP surface. Nevertheless, the effect of fabrication process on the CR has not been revealed, especially for the welding and forming characteristics. In this paper, a comprehensive three-dimensional finite element model of BPP/gas diffusion layer (GDL) assembly was established to investigate the influences of coating, weld and dimensional error on the CR, which are produced during the fabrication process of metallic BPPs. Experiments were carried out to validate the accuracy of the model. The results indicate that direction and distribution of the current in the cell change significantly with altering the weld path of metallic BPPs, which are different from graphite BPPs. 47% CR reduction is observed for the case of dense weld arrangement. For the coating process, it is found that the necessity of coating on both sides of single BPP is quite low if channel number is less than 20. Statistic simulation was conducted to investigate the effect of dimensional error on CR. Specially, 14.5% increment in CR is found when the dimensional error exceeds 30 μm. The methodology developed is beneficial to the fabrication management of metallic BPPs and the efficiency improvement of PEMFC. [ABSTRACT FROM AUTHOR]

This paper presents a comparative experimental investigation of the dimensional accuracies of two widely used rapid prototyping (RP) processes: stereolithography (SLA) and powder binder printing (PBP). Four replicates of a purpose-designed component using each RP process were fabricated, and the measurements of the internal and external features of all surfaces were performed using a general-purpose coordinate measurement machine. The results showed that in both cases, the main cause of dimensional variations was the volumetric change inherent in the process. The precision of SLA was far better than that of PBP. The dimensional accuracy of SLA was better in the z direction, whereas PBP produced better dimensional accuracy in the x- y plane. In both RP processes, the height error consisted of two components: constant error and cumulative error. The constant error component was equal to the datum surface error. SLA yielded an average datum surface error that was 68 % higher than in PBP. The height error of SLA improved with the increase in nominal height, whereas it deteriorated in PBP. [ABSTRACT FROM AUTHOR]

In recent years, fused deposition modelling (FDM) is gaining more popularity due to its distinct advantages in terms of cost-effectiveness, lower build times, and flexibility. Compared to other 3-D printing processes such as SLS, this process does not use any kind of high-intensity laser power to build functional parts out of CAD models and, hence, makes the process much simpler, cheaper, and adaptable. Past studies reveal that productivity of the FDM process can be further increased by effectively controlling its process parameters such as layer thickness, part orientation, extrusion temperature, and so on. In this regard, many authors have investigated the optimal parameter settings for improving part strength, surface finish, wear, and fatigue properties of FDM made prototypes. However, warping performance behavior has got very recent attention due to complex heat transfer mechanism involved during this process. Experimental investigations are necessary to understand the deformation behavior of prototypes. In addition, the quantification and optimization of warp deformation along with dimensional error poses a challenging multi-objective optimization problem. Therefore, this work proposes an evolutionary system identification (SI) approach to explicitly quantify the warp deformation and dimensional error based on the four inputs such as line width compensation, extrusion velocity, filling velocity, and layer thickness of FDM prototypes. The two models' performance analysis comprising of error metrics evaluation, cross-validation, and hypothesis tests is performed to validate its robustness. The analysis concluded that the layer thickness and extrusion velocity influence the warp deformation and, while filling velocity and line width compensation, influences the dimensional error the most. [ABSTRACT FROM AUTHOR]

This paper is an experimental investigation into the dimensional error of the rapid prototyping additive process of powder-binder three-dimensional printing. Ten replicates of a purpose-designed part were produced using a three-dimensional printer, and measurements of the internal and external features of all surfaces were made using a general purpose coordinate measuring machine. The results reveal that the bases of all replicates (nominally flat) have a concave curvature, producing a flatness error of the primary datum. This is in contrast to findings regarding other three-dimensional printing processes, widely reported in the literature, where a convex curvature was observed. All external surfaces investigated in this study showed positive deviation from nominal values, especially in the z-axis. The z-axis error consisted of a consistent positive cumulative error and a different constant error in different replicates. By compensating for datum surface error, the average total height error of the test parts can be reduced by 25.52 %. All the dimensional errors are hypothesised to be explained by expansion and the subsequent distortion caused by layer interaction during and after the printing process. [ABSTRACT FROM AUTHOR]

This paper aims to present a computer-based prediction and compensation method for dimensional errors in batch manufacture without additional hardware requirements. Indexable insert grinding is introduced as the instance for batch manufacture. The least square polynomial fitting is applied to predict the dimensional error trend for batch manufacture. The polynomial fitting estimates the workpiece dimensional error with a good accuracy. A low-pass filter is introduced to determine the compensation for the next workpiece processing. Error correction is realized via grinding workpieces with a modified CNC part program. The simulation and experimental results verify the effectiveness of error prediction and intelligent soft pre-compensation method, and the dimensional accuracy has been improved significantly. [ABSTRACT FROM AUTHOR]

The problem of error compensation in manufacturing industry becomes important since the product quality is the manufactures' competition. This paper presents an intelligent self-learning method for dimensional error pre-compensation in CNC grinding. Measurements of the system output obtained from the previous runs are used to compute the correction for the current run without in-process sensing and measurement, which is attractive for applications lacking in situ measurements. A modified NC program is fed to the machine tool to push the system output towards target. The simulation results and the real system input and output responses show the feasibility and effectiveness of this intelligent self-learning method. [ABSTRACT FROM AUTHOR]