Seam Quality Research Articles

Design and analysis of welding inspection robot

Periodic inspection, commonly performed by a technician, of weld seam quality is important for assessing equipment reliability. To save labor costs and improve efficiency, an autonomous navigation and inspection robot is developed. The development process involves the design of chassis damping, target detection mechanism, control system, and algorithms. For performing weld inspection in complex, outdoor, environments, an algorithm is developed for the robot to avoid any obstacles. This algorithm for planning the inspection route is based on an improved timed-elastic-band (TEB) algorithm. The developed robot is capable of conducting inspection tasks in complex and dangerous environments efficiently and autonomously.

A systematic analysis of maximum tolerable tool wear in friction stir welding

Friction stir welding (FSW) is a solid-state joining process with a wide range of applications in the E-mobility, automotive, aerospace and energy industries. However, FSW is subjected to specific challenges including comparatively high process forces and high requirements on the clamping technique as well as tool wear resulting from the tool-workpiece interaction and thermo-mechanical stresses. Geometric-related tool wear can cause premature tool failure, process instabilities or weld seam irregularities. Therefore, tool wear in general, wear limits and tool life are essential factors for the efficient and sustainable implementation of friction stir welding. Against this background, this study analysed areas of significant tool wear on the shoulder and probe as a function of process temperature, weld seam length and weld seam quality. This provided functional correlations for determining limiting conditions on maximum tolerable tool wear. Geometrical deviations of the tool, induced by wear, were detected experimentally at different measuring points on the probe and shoulder and varying weld seam length. The investigations were carried out using a force-controlled robotized welding setup in which AA-6060-T66 sheets with a thickness of 5 mm were joined by weld seams up to 500 m in length. To identify the maximum tolerable tool wear, the weld seam properties were determined by visual and metallographic inspections and by tensile tests at 50-m intervals on the weld seam. It was shown that a 50% reduction in rotational speed (lower temperatures) resulted in less wear and thus in an increase of tool life of up to 150%. In addition, it was shown that the shoulder, like the probe, was also subject to significant wear. These results can be incorporated into FSW maintenance schedules to maximize tool life and minimize scrap rates.

Enabling laser transmission welding of additively manufactured thermoplastic parts using an expert system based on neural networks

In order to use laser transmission welding (LTW) for additively manufactured parts such as prototypes, small series, or one-off products, an enhanced process knowledge is needed to overcome the difficulties in the part composition resulting from the additive manufacturing process itself. In comparison to an injection molding process for thermoplastic parts, the additive manufacturing process fused deposition modeling leads to an inhomogeneous structure with trapped air inside the volume. In this paper, a neural network-based expert system is presented that provides the user with process knowledge in order to improve the weld seam quality of laser welded additively manufactured parts. Both additive manufacturing and LTW process are assisted by the expert system. First, the designed expert system supports the user in setting up the additive manufacturing process to increase the transmissivity. During welding, the additive manufacturing and LTW process parameters are used to predict the weld seam strength. To create the database for the expert system, specimens of transparent and black polylactide are additively manufactured. In order to change the transmissivity at an emission wavelength of 940 nm of the diode laser used, the manufacturing parameters for the transparent parts are varied. The transmissivity of the parts is measured with a spectroscope. The transparent samples are welded to the black samples with laser powers between 8 and 14 W in the overlap configuration and shear tensile tests are performed. In this work, the predictions of the transmissivity and the shear tensile force are demonstrated with an accuracy of more than 88.1% of the neural networks used for the expert system.

Effects of Needle Size and Sewing Thread on Seam Quality of Traditional Fabrics

The role of fabric properties in sewing performance and seam quality is essential, therefore, it is crucial to understand the effect of diferent parameters on traditional fabrics’ sewability properties. This study aimed to evaluate the seam quality of traditional fabrics produced from silk, cotton and linen fibres and their blends in terms of seam strength, seam efficiency and fabric sewability. The samples were sewn using two different sewing needle size (75 Nm and 90 Nm) and sewing thread (100% mercerised cotton and 100% polyester corespun). Based on the obtained results, it can be concluded that sewing thread and fabric type had significant effect on seam strength and seam efficiency. The samples sewn with polyester corespun sewing thread had higher seam strength than other. The sewing needle significantly affected the needle penetration force values and the silk fabric had lowest sewability values both in warp and weft direction.

Maximization of Sewing Strength and Minimization of Seam Pucker for Denim Fabrics Using Taguchi Method

Seams provide the shape of the garments and support the fabric pieces together. The seam quality is important for the serviceability of any garment. In general, the seam quality depends on various factors such as fabric weight, sewing thread type, and stitches per unit area. In this research, three different levels of fabric types with the same construction and different weights, which are mostly used in the production of denim products, were examined. For this purpose, each fabric was sewn in the warp direction with three different levels of sewing threads and three different levels of stitch densities. Then, the values of seam strength, and the seam pucker values were obtained with three replications for each combination of levels. In this study, it is aimed to obtain the optimum levels of fabric weight, sewing thread type, and stitch density of denim fabrics by using the Taguchi method. Custom Taguchi Design is employed to observe the efficiency of factor levels on seam strength and seam pucker, and existence of interactions among fabric weight, sewing thread type, and stitch density.

Investigations on laser beam welding of thin foils of copper and aluminum regarding weld seam quality using different laser beam sources

Nowadays, there is a strong and growing ambition to switch from combustion technology to battery-electric drives, and energy storage is spotlighted. Laser beam welding is an appropriate and favorable welding technology in battery production. Due to the high welding speed, the local heat input, the contact freeness efficient, and automatable processes can be established. Materials used in batteries for electrodes that have to be connected are commonly copper and aluminum. Specifically, copper is highly reflective for widely used infrared laser beam wavelengths. Furthermore, the thickness in the area of 10 μm is quite challenging to deal with, in terms of gap free clamping and avoidance of damage to the material as well as distortion during welding. There is a fine line regarding energy input between burning the material and generating a lack of fusion. In the presented research, welding approaches with different laser beam sources emitting laser beams with infrared wavelengths, various beam shapes, and welding modes (continuous and pulsed) are studied. A total of 40 copper foils with a thickness of 10 μm and 40 aluminum foils with a thickness of 15 μm are welded to similar sheet metals. Aim of the process development are welds with high quality and high connection widths to provide the best electric conductivity.

A new characterization approach for heat sealing of polymer packaging films identifying optimum sealing parameters using Pareto‐based trade‐off analysis

AbstractThis paper presents a new approach for characterizing heat sealing processes in packaging machines, which identifies all appropriate and optimum sealing parameters subject to given quality criteria. The presented approach is distinct from established methods, such as heat seal curves or response surface plots, in three aspects: It provides an easy‐to‐read chart indicating optimum and appropriate settings of sealing temperature and dwell time, as well as process robustness for each parameter set. The data points of the charts are generated directly from experiments without using any regression model. The design of experiments features a determinate sequence of tests and no iterative loops are necessary. The approach stems from a ‘trade‐off’ model of heat sealing and a specific multi‐objective optimization method. This trade‐off model states that improving seam quality, reducing sealing temperature, reducing dwell time, and increasing process robustness are conflicting objectives. This hypothesis is deduced from a literature review and verified by experiments. The optimization method claims that all optimum sealing parameters are part of the solution of a multi‐objective optimization problem, the Pareto‐frontier. This hypothesis is elaborated into a design of experiments using the normal‐boundary‐intersection method, and is verified using a peelable seam and tear seam scenario.

Influence of superimposed intensity distributions on weld seam quality and spatter behavior during laser beam welding of copper with green laser radiation

With the increasing demand for copper connections in the field of renewable energies, e.g., for electric vehicle applications, various approaches were pursued to reduce the challenging spatter and melt ejection susceptibility in laser beam welding of copper materials. One is the use of adjustable intensity profiles of multi-mode beam sources with a combination of a core and ring beam in order to affect a modification of the flow field in the melt pool surrounding the highly dynamic keyhole in the deep penetration welding process. This should favor a reduction of spattering and melt pool ejections, especially at low weld speeds and high penetration depths in pure copper, therefore enabling a more stable deep penetration welding process. In this work, the influence of different superimposed intensity distribution ratios for green laser radiation with summarized power up to 3 kW on the generation of process imperfections was investigated conducting welding experiments on Cu-ETP using high-speed imaging for enhanced process understanding. In addition, the effects of different power distribution conditions and welding speeds on the seam dimensions were analyzed. It was found that a significant amount of laser power in the ring beam leads to a widening of the melt pool in the area near the sample top-surface, which effectively reduces spatter behavior. The associated change in process zone morphology in laser beam direction was furthermore observed via sandwich analysis, allowing a detailed view into the laser–matter interaction area through a borosilicate glass sheet clamped in front of a processed sample. This setup was found to be a cost-effective method for obtaining further information about the keyhole formation mechanism and melt dynamics under comparative boundary conditions.

Development of a Procedure for the Assessment of Material Potentials Under Consideration of the Weld Seam Quality for Multi‐material Applications in the FDM Process

AbstractDue to the great popularity of the fused deposition modeling (FDM) process, more and more new materials become commercially available. The functionality of the FDM process allows the use of multiple materials, and this is known as multi‐material printing. By integrating different materials into one component, component properties, such as mechanical properties like tensile strength, can be influenced. The aim of this study is to develop a procedure for assessing the suitability of different materials for multi‐material printing in the FDM process. This enables the evaluation of different material combinations for the FDM process. The analysis of the material suitability for multi‐material applications in the FDM process is carried out with the help of the evaluation of the weld seam quality. In this regard, a test method as well as test specimens are used, which ensure an evaluation of the processing suitability of different materials which is independent of the machine as well as the data preparation. In addition, suitable conditions must be defined for manufacturing the test specimens using two different materials. Single‐strand test specimens are used in order to be able to draw conclusions about the weld seam quality. The weld seam quality is evaluated in relation to varying nozzle temperatures and build chamber temperatures. Finally, the suitability of the materials for multi‐material applications in the FDM process are evaluated.

Inline Weld Depth Evaluation and Control Based on OCT Keyhole Depth Measurement and Fuzzy Control

In an industrial joining process, exemplified by deep penetration laser beam welding, ensuring a high quality of welds requires a great effort. The quality cannot be fully established by testing, but can only be produced. The fundamental requirements for a high weld seam quality in laser beam welding are therefore already laid in the process, which makes the use of control systems essential in fully automated production. With the aid of process monitoring systems that can supply data inline to a production process, the foundation is laid for the efficient and cycle-time-neutral control of welding processes. In particular, if novel, direct measurement methods, such as Optical Coherence Tomography, are used for the acquisition of direct geometric quantities, e.g., the weld penetration depth, a significant control potential can be exploited. In this work, an inline weld depth control system based on an OCT keyhole depth measurement is presented. The system is capable of automatically executing an inline control of the deep penetration welding process based only on a specified target weld depth. The performance of the control system was demonstrated on various aluminum alloys and for different penetration depths. In addition, the ability of the control to respond to unforeseen external disturbances was tested. Within the scope of this work, it was thus possible to provide an outlook on future developments in the field of laser welding technology, which could develop in the direction of an intuitive manufacturing process. This objective should be accomplished through the use of intelligent algorithms and innovative measurement technology—following the example of laser beam cutting, where the processing systems themselves have been provided with the ability to select suitable process parameters for several years now.

Study of the compression properties of welded seams formed using hot wedge, hot air, ultrasonic, and high-frequency welding techniques

The compression properties of welded seams depending on welding parameters using the hot wedge and hot air welding technique, ultrasonic welding technique, and high-frequency welding technique were studied. The compression properties, expressed by parameters such as compressional energy WC, compressional resilience RC, linearity LC, and compressibility C, are important information about the welded seam quality in terms of touch, voluminosity, stiffness, and flexibility of the welded seam. KES-FB and FAST measurement systems were used to test the compression properties of the welded seams. Based on the analysis of the results obtained, the influence of the welding parameters on the compression properties of the welded seam was determined. The results of the investigation showed that improperly selected welding parameters, such as the supply or introduction of too much heat into the material to be welded or too long exposure of the material in the weld zone to heat, result in welded seams with expressive extrusion edges, which affects the quality of the welded seams. These welded seams have very low values of compressional resilience RC and very high values of compressional energy WC and compressibility C.

Comparison of penetration depth in bead-on-plate welds of thick-walled steel sheets with Laser Beam Welding in Vacuum and Electron Beam Welding

Electron Beam Welding is unchallenged concerning weld seam quality, but in case of penetration depth, the Laser Beam Welding in Vacuum (LaVa) can keep up and even outperform EBW in case of bead-on-plate welds using maximum beam power of 40 kW. The work presented here combines the advantages of reduced working pressure with modern high energy Laser beam sources and extends the recent limits of deep penetration welding to a defect-free single layer weld seam with a penetration depth of 115 mm in medium strength steel S355JR.

Automatic detection and prediction of discontinuities in laser beam butt welding utilizing deep learning

Laser beam butt welding of thin sheets of high-alloy steel can be really challenging due to the formation of joint gaps, affecting weld seam quality. Industrial approaches rely on massive clamping systems to limit joint gap formation. However, those systems have to be adapted for each individually component geometry, making them very cost-intensive and leading to a limited flexibility. In contrast, jigless welding can be a high flexible alternative to substitute conventionally used clamping systems. Based on the collaboration of different actuators, motions systems or robots, the approach allows an almost free workpiece positioning. As a result, jigless welding gives the possibility for influencing the formation of the joint gap by realizing an active position control. However, the realization of an active position control requires an early and reliable error prediction to counteract the formation of joint gaps during laser beam welding. This paper proposes different approaches to predict the formation of joint gaps and gap induced weld discontinuities in terms of lack of fusion based on optical and tactile sensor data. Our approach achieves 97.4 % accuracy for video-based weld discontinuity detection and a mean absolute error of 0.02 mm to predict the formation of joint gaps based on tactile length measurements by using inductive probes.

Investigation of Actual Phenomena and Auxiliary Ultrasonic Welding Parameters on Seam Strength of PVC-Coated Hybrid Textiles

Abstract A study of polyvinylchloride-coated woven polyester fabric welding potential was conducted using continuous ultrasonic welding machines. The effect of cooling air, anvil wheel status, anvil wheel width, material surface contact, and welding gap on seam strength was studied. Three main welding parameters with different levels were selected based on 5 and 10 mm welding widths using old and new anvil wheels with and without cooling air. A lapped type of seam was applied under full factorial design. A microstructure was captured to examine the formation of welding joints, and seam tensile properties were determined. Comparative analysis of comparable welding parameters was analyzed for a gap against pressure and amplitude against power. The actual weld phenomenon was also analyzed based on the recorded machine parameters. The results showed that auxiliary parameters had a significant effect on seam strength. A microscopic image of a welded seam indicated that cooling air reduced the number and size of holes produced. Weld seam with controlled pressure or power provided higher seam strength than that of the controlled gap or amplitude. The actual phenomenon of welding parameters was important to evaluate weld seam quality, whereby the obtained results indicated good quality at lower power and pressure.

Experimental Investigation of Temperature and Contact Pressure Influence on HFI Welded Joint Properties.

This paper presents an experimental electro-thermo-mechanical simulation of high-frequency induction (HFI) welding to investigate the effect of temperature and contact normal stress on the weld seam quality. Therefore welding experiments at different temperatures and contact pressures are performed using flat specimens of 34MnB5 steel sheet. In order to characterize the weld seam strength of the welded specimens, tensile and bending tests are performed. To obtain a relative weld seam strength, the bending specimens were additionally hardened prior to testing. With the hardened specimens, it can be shown that the weld seam strength increases with increasing temperature and contact normal stress until a kind of plateau is formed where the weld seam strength remains almost constant. In addition to mechanical testing, the influence of the investigated process parameters on the weld seam microstructure is studied metallographically using light optical microscopy, scanning electron microscopy, EBSD and hardness measurements. It is shown that the weld seam strength is related to the amount of oxides in the bonding line.

Seam pucker detection through presser foot displacement monitoring

The paper investigates the relation between seam pucker, woven fabric formability, and the presser foot displacement during stitch formation. Superimposed seams of class 1 were sewn in warp and weft direction using woven fabrics for tailored garments. The presser foot height was continuously monitored during stitch formation for different sewing machine speeds. The foot displacement during the sewing cycle was correlated with seam pucker. The obtained results showed various patterns of pressure foot displacement regarding the sewing machine speeds. It was found that at a lower machine speed there is no bouncing of the presser foot and the ratio of the height of the presser foot before and after rising and declining movement versus double thickness of the fabric (h/T1), correlates significantly with the seam pucker percentage. The fabrics having a higher h/T1 ratio showed a higher percentage of seam pucker. The obtained results suggest that online monitoring of this parameter can be a useful indication of on-seam pucker appearance, providing reliable means to obtain a quality seam.

Multicriterial optimization strategies for electron beam welding processes

The electron beam welding process is analyzed of high-strength steel type 15Cr5Mo samples with deflection oscillations along the zone of interaction. The geometries of the molten and the heat affected zones are studied in order to investigate the influence of the deflection oscillations parameters and to improve the seam quality. A robust engineering approach is implemented for the case of production conditions considering the errors in the process parameter settings. The problem of quality improvement through fulfilling pre-set technological and quality requirements is solved by scalarization of the vector criteria by implementing a reference point strategy. Other multicriterial optimization strategies are also proposed.

Seam Strength Prediction for Different Stitch Types Considering Stitch Density of Cotton Woven Fabrics

Seam strength is critical in achieving the proper and adequate quality seam, which eventually determines the overall quality of any garment. The target of this research was to investigate exactly how different stitch density affected seam strength for different stitch types. Commercially available, 100% cotton plain weave structured woven fabric with mass per unit area of 270 g/m2 was used in this analysis. Two different stitch types, such as lock stitch (ISO#301) and chain stitch (ISO#401), along with four stitch densities like 8, 10, 12 and 14 per inch were utilized. The seam strength of the prepared samples was determined using a tensile strength tester followed by the ASTM D1683 standard procedure. The impact of independent variables on superimposed seam strength was statistically analyzed using a regression correlation with the help of SPSS software to construct a regression equation to predict seam strength before the manufacturing process. The study found a non-linear relationship between seam strength and stitch density. When the stitch density is too low, the seam strength is shown low as well, because the cloth cannot be held under tensile load. In a very compact woven fabric, structural jamming or intrinsic puckering occurs if it is too high. As a result, the best stitch density should be chosen to achieve the best seam strength. This study will help the manufacturers choose a suitable SPI for lock and chain stitches from polynomial regression equations before the sewing production of cotton woven fabric, which was not predicted by any researcher before. Therefore, the optimum stitch density can be chosen using regression equations to get the best result for seam strength.

Results of implementation of mechanical logging for additional investigation of the geological structure of the Olon-Shibirskoe coal deposit

Mining coal requires detailed geological information about the structure of the coal seam and the quality of coal seams that allows to minimize the risks associated with the complicating mining and geological factors and changes in the quality characteristics of coal. The article discusses the experience of applying the mechanical logging method as an express method of operational exploration in the Olon-Shibirsk coal deposit. The mechanical logging data were compared with core sampling data and geophysical well surveys. As a result, criteria for dividing the coalbearing sequence of the deposit into lithotypes were identified. According to these criteria, it is possible to identify a general pattern for the considered coal seam: drilling speed increases with decreasing grain size, drilling speed also increases with increasing the content of organic matter in the rock, the maximum drilling speed is characterized by coal seams. The drilling speed is the determining parameter, while the other drilling parameters complement its readings in case of ambiguity in the interpretation of the graph. For coal seams, the dependence of drilling speed on ash content was determined. At the same time, the dependence is most correct for coal seams with thickness more than one meter. On the basis of operational exploration data using mechanical logging for some areas, the morphology of coal seams, as well as the complexity of their structure and ash content, which allowed to specify the reserves and quality by geological blocks. In the final comparison with the fact was confirmed an increase in the accuracy of calculations using the method of mechanical logging. Practical significance of the results of the study is to improve the quality of operational exploration in the field while reducing costs.

Hybrid laser-arc welding of laser- and plasma-cut 20-mm-thick structural steels

It is already known that the laser beam welding (LBW) or hybrid laser-arc welding (HLAW) processes are sensitive to manufacturing tolerances such as gaps and misalignment of the edges, especially at welding of thick-walled steels due to its narrow beam diameter. Therefore, the joining parts preferably have to be milled. The study deals with the influence of the edge quality, the gap and the misalignment of edges on the weld seam quality of hybrid laser-arc welded 20-mm-thick structural steel plates which were prepared by laser and plasma cutting. Single-pass welds were conducted in butt joint configuration. An AC magnet was used as a contactless backing. It was positioned under the workpiece during the welding process to prevent sagging. The profile of the edges and the gap between the workpieces were measured before welding by a profile scanner or a digital camera, respectively. With a laser beam power of just 13.7 kW, the single-pass welds could be performed. A gap bridgeability up to 1 mm at laser-cut and 2 mm at plasma-cut samples could be reached respectively. Furthermore, a misalignment of the edges up to 2 mm could be welded in a single pass. The new findings may eliminate the need for cost and time-consuming preparation of the edges.