Journal of Manufacturing and Materials Processing — Open Access Journal

Mechanical surface treatments, e.g., deep rolling, are widely spread finishing processes due to their ability to enhance the fatigue strength of the treated materials with means of cold working and inducement of favorable compressive residual stresses. Despite of the clear advantages of deep rolling, the controlled generation of compressive residual stresses is still a challenging task, as the process can be influenced by the pre-machining stress state of the treated material. Additionally, the exact characterization of the induced residual stress field is impacted by the specific characteristics of the applied measurement technique. Therefore, this paper is focused on the X-ray diffraction residual stress analysis of deep rolled specimens, pre-machined to achieve rough or polished surface. The deep rolling process was realized as a single-trace to avoid the influence of the other process parameters and the resulted residual stress field on the surface and in depth was investigated. Additionally, the surface residual stress profiles were determined using two different measuring devices to analyze the impact of the different measurement conditions. Full article

It is well known that stress-induced phase transformation in dual-phase steel leads to the degradation of bulk corrosion resistance properties. Predicting this behaviour in high carbon steel is imperative for designing this grade of steel for more advanced applications. Dual-phase high carbon steel consists of a martensitic structure with metastable retained austenite which can be transformed to martensite when the required energy is attained, and its usage has increased in the past decade. In this study, insight into the influence of deformed microstructures on corrosion behaviour of dual-phase high carbon steel was investigated. The generation of strain-induced martensite formation (SIMF) by residual stress through plastic deformation, misorientation and substructure formation was comprehensively conducted by EBSD and SEM. Tafel and EIS methods were used to determine corrosion intensity and the effect of corrosion behaviour on hardness properties. As a result of the static compression load, the retained austenite transformed into martensite, which lowered its corrosion rate by 5.79% and increased the dislocation density and the length of high-angle grain boundaries. This study demonstrates that balancing the fraction of the martensite phase in structure and dislocation density, including the length of high-angle grain boundaries, will result in an increase in the corrosion rate in parallel with the applied compression load. Full article

Root pass manufacturing in automated welding is still a challenge when the backing plate is not feasible. Using the concept of bead formation in an original way, the GMAW (Gas Metal Arc Welding) switchback technique was assessed against linear movement as a means of facing this challenge. Experimental work was applied, keeping the process parametrization and joint configuration, so that only the switchback parameters were modified, i.e., the stroke lengths and speeds. Thermography was used to estimate the effect of the switchback parameters on bead formation. The results showed the potential of the switchback technique as a means of favoring weld pool control. Surprisingly, the operational gap range is not necessarily larger when switchback is applied. The strong influence of stroke lengths and speeds on the process performance was characterized. In general, the results showed that linear movement leads to larger pools and deeper penetrations, more adequate for gaps with no clearances. Shorter stroke lengths and slower stroke speeds (intermediate pool size) better suit root gaps that are not too wide, while longer stroke lengths and faster stroke speeds (smaller pool size, more easily sustainable) are applicable to larger root gaps. Full article

This work presents an analysis of relationships between the non-linear vibrations in machining and the machined surface quality from an analytical model based on a predictive machining theory. In order to examine the influences of tool oscillations, several non-linear mechanisms were considered. Additionally, to solve the non-linear problem, a new computational strategy was developed. The resolution algorithm significantly reduces the computational times and makes the iterative approach more stable. In the present approach, the coupling between the tool oscillations and (i) the regenerative effect due to the variation of the uncut chip thickness between two successive passes and/or when the tool leaves the work (i.e., the tool disengagement from the cut), (ii) the friction conditions at the tool–chip interface, and (iii) the tool rake angle was considered. A parametric study was presented. The correlation between the surface quality, the cutting speed, the tool rake angle, and the friction coefficient was analyzed. The results show that, during tool vibrations, the arithmetic mean deviation of the waviness profile is highly non-linear with respect to the cutting conditions, and the model can be useful for selecting optimal cutting conditions. Full article

Additive Manufacturing (AM) is the forefront of advanced manufacturing technologies and has the potential to revolutionize manufacturing, with a dramatic change in the design and project paradigms. A comprehensive review of existent metal AM processes, processable materials, respective defects and inspection methods (destructive and non-destructive) is presented in a succinct manner. Particularly, the AM design optimization methodologies are reviewed and their threats and constraints discussed. Finally, an aerospace industry case study is presented and several cost-effective examples are enumerated. Full article

The quality and reliability in additive manufacturing is an emerging area. To ensure process quality and reliability, the influence of all process parameters and conditions needs to be understood. The product quality and reliability characteristics, i.e., dimensional accuracy, precision, repeatability, and reproducibility are mostly affected by inherent and systematic manufacturing process variations. This paper presents research on dimensional quality and distortion analysis of AlSi10Mg thin-walled parts developed by a selective laser melting technique. The input process parameters were fixed, and the impact of inherent process variation on dimensional accuracy and precision was studied. The process stability and variability were examined under repeatability and reproducibility conditions. The sample length (horizontal dimension) results revealed a 0.05 mm maximum dimensional error, 0.0197 mm repeatability, and 0.0169 mm reproducibility. Similarly, in sample height (vertical dimension) results, 0.258 mm maximum dimensional error, 0.0237 mm repeatability, and 0.0863 mm reproducibility were observed. The effect of varying design thickness on thickness accuracy was analyzed, and regression analysis performed. The maximum 0.038 mm error and 0.018 mm standard deviation was observed for the 1 mm thickness sample, which significantly decreased for sample thickness ≥2 mm. The % error decreased exponentially with increasing sample thickness. The distortion analysis was performed to explore the effect of sample thickness on part distortion. The 0.5 mm thickness sample shows a very high distortion comparatively, and it is reduced significantly for >0.5 mm thickness samples. The study is further extended to examine the effect of solution heat treatment and artificial aging on the accuracy, precision, and distortion; however, it did not improve the results. Conclusively, the sample dimensions, i.e., length and height, have shown fluctuations due to inherent process characteristics under repeatability and reproducibility conditions. The ANOVA results revealed that sample length means are not statistically significantly different, whereas sample height means are significantly different. The horizontal dimensions in the xy-plane have better accuracy and precision compared to the vertical dimension in the z-axis. The accuracy and precision increased, whereas part distortion decreased with increasing thickness. Full article

In this work, we introduce an analytical expression for approximating the transient melting radius during powder melting in Selective Laser Melting (SLM) assumed with a stationary laser heat source. The purpose of this work is to evaluate the suggested analytical approach in determining the melt pool geometry during laser processing, by considering heat transfer and phase change effects. This will allow for the rendering of the first findings on the way to a quasi-real time calculation of the melt pool during laser melting, which will contribute significantly to the process design and control, especially when new powders are applied. Initially, we consider the heat transfer process associated with a point heat source, releasing a continuous and constant power (in a semi-infinite powder bed. On the point of the heat source the temperature is infinite, and the material starts to melt spherically outwards, creating an interface that separates the solid from the molten material; we assume different properties between the two phases. Unlike the cases of the cartesian and cylindrical coordinates, (in a cartesian coordinate the heat source is over a plane, i.e., W/m², and in cylindrical along a line, i.e., W/m), where the melting process is proportional to the square root of time, in spherical coordinates the melting stops at a finite radius, i.e., a maximum radius, which depends only on the heat source, the conductivity of the solid and the difference between the far-field temperature and the melting temperature of the material. Here we should also point out that to achieve continuous melting in spherical coordinates the power of the source must increase with the square root of the time. The obtained analytical expression for the maximum melting radius and the approximate expression for its dependence on the time compare well with the numerical results obtained by a finite element analysis. Full article

Laser Powder Bed Fusion (LPBF) is a predominant Additive Manufacturing (AM) process. While metallic LPBF is gaining popularity, one of the barriers facing its wider industrial use is the current relatively limited knowledge with respect to its dimensional and geometrical performance, as well as the inability to predict it. This paper presents an experimental investigation of the geometrical and dimensional deviations of selected LPBF-manufactured components according to the ASME Y14.5 (2009) standard. In this study, two types of axisymmetric parts (cylinder and cylindrical pyramid) were designed with three different levels of material concentration, and replicated at three different scales for a total of 18 test artifacts. These parts were manufactured from AlSi10Mg powder using an EOSINT M280 printer, subjected to stress relief annealing at 300 °C for two hours, removed from the platform and finished by micro shot peening. A complete statistical analysis was carried out on the artifacts before and after each post-processing step. The results of this investigation allowed for the quantification of the intra- (same part) and inter- (different parts) scale effects, as well as of the material concentration, stress relief, part removal and micro shot peening effects on the overall three-dimensional (3D) profile deviations and on the dimensional deviations of some selected features (e.g., diameter, thickness). For example, cylindrical pyramid parts showed the following average deviations of their outside diameters: a −63 µm shrinkage of the as-built part diameter as compared to its computer-assisted design (CAD) value, a +20 µm expansion after stress relief annealing as compared to the precedent step, a −18 µm shrinkage after part removal and, finally, a −50 µm shrinkage after micro shot peening. Full article

Producing metallic bipolar plates for Proton Exchange Membrane (PEM) fuel cells by forming is still a topic of research. So far, it has mainly been applied for small batches, but it offers substantial advantages regarding both costs and installation space compared to the established graphite based solutions. One new possibility for an efficient manufacturing process of these metallic bipolar plates is the forming by rolling. For the first time, this technology was used for relevant industrial scale channel geometries. By the use of an experimental rolling mill, 0.1 mm thick 316L (1.4404) stainless steel foils were roll-formed to achieve previously designed channel geometries within one rolling pass. The conducted experiments show promising results regarding the forming accuracy and the shape of the channel cross-sections. With the aim for a proof of concept in the beginning and a subsequent optimization of the process, a numerical simulation was set up prior to the real experiments and later calibrated with the experimental forming results. This calibrated model was used for further improvements of the process with the objective at reducing wrinkles and distortion. The investigation of this new process method for the manufacturing of metallic bipolar plates shows enormous potential and can lead to a more efficient and cheaper production. Full article

The tribological behavior of electrical contacts, especially separable type electrical connectors at low contact loads, are considered. The reliability of these connectors has been a major concern due to the fretting phenomenon that can lead to an unacceptable increase in contact resistance. This study analyzes various aspects of the fretting mechanism from a tribological perspective where friction and wear are the primary cause of degradation in electrical components. With the use of precise tribological equipment (high data acquisition rate of 5000 Hz), the electrical contact resistance and coefficient of friction at the contact interface are measured. The measurements were made in-situ for a simulated fretting environment under various constant loading conditions. It was observed that low contact loads (1 N) and low fretting frequency (1 Hz) leads to a high degree of fluctuation in the coefficient of friction. However, for the same conditions, the lowest wear rate and electrical contact resistance were observed. The reason behind this could be due to the lack of continuous electrical contact and a high degree of fretting frequency under low contact loads, ultimately leading to extended periods of an open circuit. Experimental analysis indicates the existence of an optimum loading condition at which the fretting wear effect is at its minimum. Detailed analysis of post fretting surface roughness, coating wear, and wear debris is conducted, as well as transfer film formations to explain the mechanism of fretting observed. Full article

Resistance spot welding of aluminum (Al5754) to magnesium (AZ31B) alloys results in the formation of a variety of solidification microstructures and intermetallic compounds that may affect the in-service performance of the weld. This study evaluates the relationship between the welding parameters and the properties of the weld nugget that is formed, and clarifies the morphological and microstructural evolutions within the weld regions during the low-current “small-scale” resistance spot welding of Al5754 to AZ31B. The investigations included a combination of microstructural characterization and thermodynamic analysis of the weld region. The results show that the welding time and clamping force parameters have significant effects on the properties of the nugget formed. The optimal welding parameters were found to be 300 ms welding time and 800 N clamping force. Weld nuggets formed with lower welding time and clamping force were undersized and contained extensive porosity. Meanwhile, a clamping force above 800 N caused gross deformation of the test samples and the expulsion of the molten metal during the welding process. The most significant microstructural changes occurred at the weld/base metal interfaces due to the formation of Al₁₇Mg₁₂ and MgAl₂O₄ intermetallic compounds as well as significant compositional variation across the weld pool. The thermal gradient across the weld pool facilitated the formation of several microstructural transitions between equiaxed and columnar dendrites. Full article

Machining processes, including turning, are a critical capability for discrete part production. One limitation to high material removal rates and reduced cost in these processes is chatter, or unstable spindle speed-chip width combinations that exhibit a self-excited vibration. In this paper, an artificial neural network (ANN)—a data learning model—is applied to model turning stability. The novel approach is to use a physics-based process model—the analytical stability limit—to generate a (synthetic) data set that trains the ANN. This enables the process physics to be combined with data learning in a hybrid approach. As anticipated, it is observed that the number and distribution of training points influences the ability of the ANN model to capture the smaller, more closely spaced lobes that occur at lower spindle speeds. Overall, the ANN is successful (>90% accuracy) at predicting the stability behavior after appropriate training. Full article

The effect of micro patterning of cemented carbide surface using nanosecond diode pumped solid-state pulsed laser on the strength of induction brazed carbide and steel joints has been investigated. Surface patterns increase the total surface area of the joint and, for an originally hydrophilic surface, increase the wettability of a liquid on a solid surface such that, instead of building droplets, the liquid spreads and flows on the surface. Microcomputed tomography (µ-CT) was used to observe the filler/carbide interface after brazing and to analyze the presence of porosity or remnant flux in the joint. Microstructures of the brazed joints with various surface patterns were analyzed using scanning electron microscopy. The strength of the joints was measured using shear tests. Results have shown that the groove pattern on the surface of carbide increases the joint strength by 70–80%, whereas, surface patterns of bi-directional grooves (grid) reduced the joint strength drastically. Dimples on the carbide surface did not show any improvement in the strength of the brazed joints compared to samples with no surface pattern. Full article

Selective laser melting (SLM) is well suited for the efficient manufacturing of complex structures because of its manufacturing methodology. The optimized process parameters for each alloy has been a cause for debate in recent years. In this study, the hatch angle and build orientation were investigated. 304L stainless steel samples were manufactured using three hatch angles (0°, 67°, and 105°) in three build orientations (x-, y-, and z-direction) and tested in compression. Analysis of variance and Tukey’s test were used to evaluate the obtained results. Results showed that the measured compressive yield strength and plastic flow stress varied when the hatch angle and build orientation changed. Samples built in the y-direction exhibited the highest yield strength irrespective of the hatch angle; although, samples manufactured using a hatch angle of 0° exhibited the lowest yield strength. Samples manufactured with a hatch angle of 0° flowed at the lowest stress at 35% plastic strain. Samples manufactured with hatch angles of 67° and 105° flowed at statistically the same flow stress at 35% plastic strain. However, samples manufactured with a 67° hatch angle deformed non-uniformly. Therefore, it can be concluded that 304L stainless steel parts manufactured using a hatch angle of 105° in the y-direction exhibited the best overall compressive behavior. Full article

Friction stir welding (FSW) provides users with many advantages over fusion welding techniques. Nevertheless, it is not widely employed in current industry mainly due to high equipment costs and royalties. To overcome these issues, a low-cost FSW technique operated at a right angle, called RAFSW, has recently been developed by our research team. To make the RAFSW technique reliable for potential users, we are going to analyze the effect of various post-weld heat treatments (PWHT) on the mechanical and physical properties of the RAFSW joints. To this end, optimized process parameters are used to weld butt joints of an AA6061-T6 alloy. The joints were characterized using a tensile test, a micro-hardness test, and metallography techniques. The most efficient aging time was obtained for various aging temperatures. Moreover, it was found that artificial aging at 220 °C for 30 min could be used as a fast and cost-effective artificial aging PWHT for the industrial sector. In addition, the repeatability of the PWHTs were demonstrated by studying the effect of waiting time prior to the artificial aging. Finally, it was revealed that a single fast artificial aging process is more beneficial than solubilizing followed by an artificial aging process in terms of tensile properties, consumed time, and cost. Full article

The efficiency of laser beam processes basically depends on the efficiency of the laser beam source and the efficiency of the irradiated material’s energy absorption. This absorptivity can be influenced by the surface condition. Besides coating or boundary layers, the surface topography is decisive. In this study, the effects of various time–temperature distributions on the absorptivity changes of steel sheets were investigated. For this purpose, three steels were chosen, namely, a stainless steel, a spring steel, and a hot work tool steel. Pre- and post-process characterizations of the absorptivity and surface topography were performed. Controlled heating with a laser beam was carried out using temperatures between 700 and 1200 °C and durations between 2 and 34 s. In order to compare the influences of these heating procedures on the absorptivity, a characteristic value, the temperature‑compensated time, was introduced. It is shown that the surface roughness was influenced by laser irradiation but inadequately describes the increase of absorptivity. The changes in absorptivity are attributed to oxidation, which had an influence on the topography in a sub‑micrometer range. Moreover, a saturation effect is observed for intense heatings. Furthermore, it is shown that the temperature‑compensated time is a suitable value to describe absorptivity changes caused by short‑term heating. Full article

This paper presents a prediction model for ground surfaces that uses the actual grinding wheel topography to perform a grinding simulation. Precise knowledge of expected machined surfaces plays an important role in process planning. Here, the main criterion is the achievement of the components’ function after manufacturing. Therefore, it is essential to consider the surface roughness to enable a function-orientated workpiece surface. The presented approach uses a real grinding tool topography, which is measured by a 3D laser triangulation sensor in the machine tool. After a data processing step, the measured topography is imported into a material removal simulation. A kinematic simulation of the realistic ground surface enables the data-based confirmation of the envelope profile theory for the first time. Full article

Prediction of weld bead geometry is critical for any welding process, since several mechanical properties of the weldment depend on this. Researchers have used artificial neural networks (ANNs) to predict the bead geometry based on the input parameters for a welding process; however, the number of hidden layers used in these ANNs are limited to one due to the small amount of data usually available through experiments. This results in a reduction in the accuracy of prediction. Such ANNs are also incapable of capturing sudden changes in the input–output trends; for example, where a wide range of heat inputs results in flat crown (zero crown height), but any further reduction in the current sharply increases the crown height. In this study, it was found that above mentioned issues can be resolved on using a two-stage algorithm consisting of support vector machine (SVM) and an ANN. The two-stage SVM–ANN algorithm significantly improved the accuracy of prediction and could be used as a replacement for the multiple hidden layer ANN, without requiring additional data for training. The improvement in prediction was evident near regions of sudden changes in the input–output correlation and can lead to a better prediction of mechanical properties. Full article

T-welded joints are commonly seen in various industrial assemblies. An effort is made to check the applicability of friction stir welding for producing T-joints made of AA6063-T6 using a developed fixture. Quality T-joints were produced free from any surface defects. The effects of three parameters, such as the speed of rotation of the tool, axial force, and travel speed were analyzed. Correspondingly, mechanical characteristics such as tensile strength, hardness in three zones (thermal heat affected zone, heat affected zone, and nugget zone) and temperature distribution were measured. The full factorial analysis was performed with various combinations of parameters generated using factorial design and responses. Evident changes in the strength, hardness, and temperature profile were noticed for each combination of parameters. The three main parameters were significant in every response with p-values less than 0.05, indicating their importance in the friction stir welding process. Mathematical models developed for investigated responses were satisfactory with high R-sq and least percentage error. Full article