Seam Gap Research Articles

Calculation of dynamic assembly and tensioning loads at multiple points of prefabricated structure

Prefabricated underground station structure is rapidly assembled on site with modular components manufactured in factory. The longitudinal assembly accuracy of the components along the station’s longitudinal direction determines the construction quality of the station. In order to solve the problems encountered in the longitudinal pre-tensioning and assembly of structural components for a prefabricated station, such as low efficiency of manual operation, difficulty in determining the dynamic tensioning load, and insufficient accuracy of assembly control, a dynamic pre-tensioning load calculation method is proposed. The method, also referred to as centroid tracking pre-tensioning load algorithm, is based on controlling the dynamic relationship among the geometric centroid of rubber gasket, the centroid of multipoint tensioning load and the centroid of the elastic reaction force of rubber gasket. By using the dynamic correspondence between the compression reaction force distribution of the rubber gasket and the seam width under multipoint tensioning load, a loading control strategy is established to realize the balanced compression of the seam width of the prefabricated structure by controlling the load at each tensioning point. Thus, the centroid of the tensioning load continues to track the symmetry point of the centroid of the rubber gasket’s elastic reaction force with the geometric centroid of the rubber gasket as the reference. In this way, the tension value at each point can be precisely configured to improve the assembly accuracy of the components and realize seam width control. Based on the proposed algorithm, a set of tensioning and assembly equipment and control systems for prefabricated components of underground prefabricated structures are developed to carry out the automatic configuration of multipoint tensioning loads. The assembly tests show that the seam gap of assembled components is less than 1 mm. The proposed method demonstrates that the fast and high-precision automated assembly can be achieved and is conducive to improving the construction quality of prefabricated stations.

Influence of Industrial Washing and Cyclic Fatigue on Slippage of Linen Fabric Threads along the Seam

All seams of garments shall withstand the established force effect in the longitudinal and transverse directions. Resistance to thread slippage along the seam is a major property of fabrics that is regulated by strict guidelines. In many research works, lining fabrics are chosen as the object of research as thread slippage is the most typical of them. What concerns the reports exploring slippage of linen fabric threads along the seam, just very few papers are available. Studies dealing with the influence made by industrial washing and cyclic load on the defect under investigation, thereby taking into account operational properties of garments are not readily available at all. The objective of the paper is to define the influence of industrial washing and cyclic tensile on slippage of linen fabric threads along the seam. For the research, five 100 % linen fabrics of plain weave have been selected. Control test specimens, unwashed and processed with different washing methods, have been analysed. Cyclic tensile of the test specimens has been carried out by a tensile machine “Tinius Olsen” at tensile force P = 20 N, tensile speed of 12.55 mm/s, number of cycles of 100. The carried-out testing has demonstrated that industrial washing decreased resistance of linen fabrics to thread slippage along the seam in the most cases. Analysis of the results obtained has shown that cyclic tensile led to particularly significant increase in the seam gap. DOI: http://dx.doi.org/10.5755/j01.ms.20.1.2486

An image acquisition system for real-time seam tracking

Gas metal arc welding (GMAW) process is one of the most widespread welding processes used in industries for their excellent quality, reliability, productivity, and cost-effectiveness. To develop an automatic GMAW system, vision capability in the system is a necessary component supplying real-time information about weld pool and seam tracking. In this research work, an automatic seam tracking system is presented, where the automatic tracking of welding path and torch positioning are performed by a newly developed image acquisition system. The system aims to add a vision capability to the GMAW system. A CCD camera is configured with a welding torch to acquire real-time images. The acquired images are processed through newly developed software for real-time detection of welding seam location and characteristics. The software encapsulates the acquired image input facility, image filtering technique, strategy to measure the seam gap, strategy to position torch at the starting point of welding, user interface for automatic guide, and the strategy to correct the torch movements. The seam recognition accuracy was verified during several welding experiments on linear weld seam. Real-time measurements of the seam gap and the seam tracking have achieved a high accuracy.

A Seam Measurement Method Based on Micro Depth of Field for Laser Welding

For the seam feature measurement of the tight butt joint without misalignment in laser welding, current vision sensor cannot obtain the seam gap width and seam position stably and reliably. In this paper, a seam measurement method based on the micro depth of field is proposed. A four times optical magnification lens, a CCD/CMOS camera and an external LED lighting unit are used to constitute the measure system, which can be used for the tight butt joint for laser welding. Experiment indicated that it can obtain the seam gap width and seam position stably and correctly. With the method, seam surface normal vector also can be measured. The measurement accuracy for the seam gap width and seam position is 5 µm and 6 µm, respectively. Furthermore, the narrowest welding seam gap that can be measured by this method is 0.02 mm, which is fully satisfied the demand of the seam measurement in laser welding.

Mixed logical dynamical model of the pulsed gas tungsten arc welding process with varied gap

The modelling and control of the welding process are crucial and challenging issues in automated welding. However, many uncertainties are encountered during welding that will change the seam state, such as the existence of a seam gap. The seam gap is one of the most important measurable parameters that influence the dynamic process of welding. Benefitting from research on hybrid systems, the present study proposes a kind of mixed logic dynamical (MLD) model to describe the interrelationship between process parameters and seam gap in pulsed gas tungsten arc welding (GTAW). Random experiments have been designed to excite the dynamics of the GTAW process for different gap widths and the effectiveness of the MLD model is illustrated by evaluating the back-side width of the weld seam. Finally, the stability and reliability of the MLD model are tested against an experiment with proportional—integral—differential control.

Seam gap bridging of laser based processes for the welding of aluminium sheets for industrial applications

Laser welding has a large potential for the production of tailor welded blanks in the automotive industry, due to the low heat input and deep penetration. However, due to the small laser spot and melt pool, laser-based welding processes in general have a low tolerance for seam gaps. In this paper, five laser-based welding techniques are compared for their gap bridging capabilities: single-spot laser welding, twin-spot laser welding, single-spot laser welding with cold wire feeding, twin-spot laser welding with cold wire feeding and laser/GMA hybrid welding. Welding experiments were performed on 1.1- and 2.1-mm-thick AA5182 aluminium sheets. The resulting welds were evaluated using visual inspection, cross sectional analysis with optical microscopy, tensile tests and Erichsen Cupping tests. The results show that the use of a filler wire is indispensable to increase the gap tolerance. A proper alignment of this wire with the laser spot(s) is crucial. With the single spot laser welding with cold wire feeding, a gap up to 0.6 mm could be bridged as opposed to a maximum allowable gap width of 0.2 mm for single-spot laser welding without filler wire. For 2.1-mm-thick sheets, the laser/GMA hybrid welding process can bridge even gaps up to 1.0 mm. Most welds had a high tensile strength. However, during Erichsen Cupping tests, the deformation of the welds is significantly lower as compared to the base material

Arc welding robot system with seam tracking and weld pool control based on passive vision

The automatic control in square-wave alternating current (AC) gas tungsten arc welding (GTAW) is significant for a “teach and playback” robot to overcome the variation of the seam trajectory and the seam gap in the welding process. This paper presents a welding robot system based on the real-time visual measurement in the different levels of the welding current. The primary objective is to measure the offset of the torch to the seam center and the size of seam gap by passive vision, track the seam and control the weld pool in real time. A novel visual image analysis algorithm was developed for seam tracking and seam gap measuring, free from robot calibration. The control algorithm based on the knowledge base was established to control the weld formation by regulating the welding current and wire feed rate. The welding practice for the rocket storage tank demonstrates the efficiency of the proposed system.

Research on weld pool control of welding robot with computer vision

PurposeThe control of weld penetration in gas tungsten arc welding (GTAW) is required for a “teach and playback” robot to overcome the gap variation in the welding process. This paper aims to investigate this subject.Design/methodology/approachThis paper presents a robotic system based on the real‐time vision measurement. The primary objective has been to demonstrate the feasibility of using vision‐based image processing to measure the seam gap in real‐time and adjust welding current and wire‐feed rate to realize the penetration control during the robot‐welding process.FindingsThe paper finds that vision‐based measurement of the seam gap can be used in the welding robot, in real‐time, to control weld penetration. It helps the “teach and playback” robot to adjust the welding procedures according to the gap variation.Research limitations/implicationsThe system requires that the seam edges can be accurately identified using a correlation method.Practical implicationsThe system is applicable to storage tank welding of a rocket.Originality/valueThe control algorithm based on the knowledge base has been set up for continuous GTAW. A novel visual image analysis method has been developed in the study for a welding robot.

Technical note - effects of seaming conditions on external and internal double-seam characteristics in round metal cans

Canning is the major packaging technology for fully preserved food products. To obtain safe canned foods with extended shelf-life, the closed cans have to be hermetic. The consistency and quality of the seaming process are crucial to food safety. This note investigates the effects of different seaming conditions (base-plate pressure and seaming-roller pressure) on external (seam thickness, seam height) and internal (body hook length, overlap, lid hook length, seam gap and body hook butting) double-seam characteristics in round metal cans. External double-seam characteristics were significantly affected by the seaming-roller pressure during the final closure of the cans. Generally, there were small effects of base-plate pressure on the external double-seam characteristics. In contrast, all the investigated double-seam characteristics were affected significantly by the seaming-roller pressure, whereas only body hook length and seam gap were significantly affected by the base-plate pressure. This note illustrates the importance of close control and optimization of the seaming conditions during production of canned foods as a means to reduce the processing induced variability in double-seam characteristics, and subsequently to obtain safe and high-quality canned products. Copyright © 2005 John Wiley & Sons, Ltd.

An analysis of the geometry of light-striping vision systems for feedrate control in robot welding and other industrial processes

Light-stripping, whereby a laser or other source of a stripe of light in conjunction with a single camera can provide three-dimensional information of a scene, can be used to estimate the volume of a seam gap for welding, filling, or gluing robots, and thus provide automated feedrate control. The geometry of light-striping systems is analyzed to yield an efficient method to map the locations of stripe pixels in the image to three-dimensional coordinates. Methods are discussed to determine fill-points by recognizing the pattern produced by seam walls despite noise. Combined with computation of areas and volumes, the steps simplify to an effective algorithm for microprocessor implementation.