Wojciech Jamrozik

Contextual reliability discounting in welding process diagnostic based on DSmT

The monitoring and diagnosing of the welding process is an important task in assuring the quality of welded joints. Observation of such a dynamic process is often performed by measuring various signals of different modality. The main problem is how to use several of the possible signals simultaneously. Many techniques that can deal with this kind of task were elaborated and introduced in practical application. One of these is decision fusion, with a group of methods based on belief function theories: Dempster-Shafer and Dezert-Smarandache DSmT. In this paper, extended fusion scheme for assessment of welding process condition, with contextual discounting of evidence sources reliability in DSmT framework, is presented. Discounting operation was used to distinguish the objective ability of each evidence source, to give a correct assessment of process condition. To validate this method, several series of welded joints representing different process conditions that result in various joint quality were made. On the basis of performed research, it was proven that contextual reliability discounting leads to increase of the condition recognition accuracy.

Welding process evaluation on the basis of video and thermal images

The progress of the welding process has a decisive impact on the quality of weld joints. Obtaining welded joints of high quality, both in terms of their mechanical and aesthetic properties, requires selection of appropriate welding process parameters and, most importantly, maintaining their stability during joint formation. While the choice of welding parameters is not a problem for an experienced welder, ensuring stability of the process is not an easy task. The stability of the welding process is affected by many interfering, often random factors, such as disruption of stability of filler feed, dirt and inaccuracy of edge preparation of the joined materials, deformation of the joined elements due to thermal expansion of the material. These factors cause welding unconformities, such as excessive melting, lack of penetration, cracks, burns, too large risers or depressions in the face of the weld, presence of bubbles, and other factors. Ensuring that high quality of welded joints is possible by controlling the welding parameters. The method of controlling welding parameters can be based on the measurement of welding parameters (e.g. current, arc voltage, and shielding gas flow). Another way to control the welding process and the welded joints is the use of visual inspection of the welding process, based on recording images of the formed welds in the visible spectrum, as well as in the nearand far-infrared spectrum, and their subsequent analysis and diagnosis. This approach is mentioned in the literature as one of the most promising ways of assessing the welding process and the welded joints. The most important aspect of using visual methods is that their use in volume production enables rapid identification of disturbances in the welding process parameters, errors in positioning of the joined elements and limiting the number of unconformities that appear throughout the series of manufactured components. Visual welding process control clearly provides increased joint quality and reduced production losses.

Application of fused visual and thermal images in monitoring and evaluation of welding processes

This article presents the application results of different methods of merging images recorded using vision cameras and thermal imaging cameras. The images were recorded during the evaluation of a welding process. The object of observation was the welding arc and the welded joint during its cooling phase. Images recorded during GMA welding on two different welding stations have been taken into account. The observations have been conducted using cameras equipped with different optics systems. This article presents an analysis of the influence of different parameters of the optics systems on the resulting fused images. The analysis also considers the pre-processing method to ensure correct matching of images. The study shows that the fused image contains aggregated information useful in online monitoring and quality evaluation of the welding process.

Concept of Database Architecture Dedicated to Data Fusion Based Condition Monitoring Systems

In the paper a concept of object-relational database dedicated to monitoring and diagnostics systems is presented. Important feature of proposed solution is the treatment of database as an integral sub-system dedicated to collect, manage and share data required for configuration and correct operation of the diagnostic system. It was assumed that diagnostic system has a modular structure, what determined the database architecture. Each module of the monitoring system and all operations performed in the system are reflected in the database by instances of designed objects connected with relations (references). In order to limit amount of stored data the database will collect only primary data like e.g. raw signals, configuration constants and meta data (rules of data management and parameters of data processing implemented in the diagnostic system). The concept of proposed database was implemented in limited form in commercial database system Oracle 12c using object-oriented features introduced in the SQL:1999 dialect.

Importance Discounting as a Technique of Expert Knowledge Incorporation into Diagnostic Decision-Making Process

In the paper the possibility of the use of importance discounting as a method of taking into account preferences of experts in a diagnostic system based on Desert-Smarandache theory is discussed. Reliability discounting is a well-known technique for belief assignments conditioning, having regard to objective properties of source of evidence. Indeed, in real applications, it is needed to differentiate between objective properties and subjective preferences of experts having proper knowledge, experience or intuition connected with the machine or the process being diagnosed. Way of importance discounting incorporation into a diagnostic system, considering gathering of expert’s opinions and the conversion from opinions to values of discounting factors is described. Theoretical reflections are supported by a practical example.

Application of Time-Frequency Methods for Assessment of Gas Metal Arc Welding Condition

Gas Metal Arc Welding (GMAW) is a popular method of material joining, widely used for a variety of critical industrial structures. Assuring high quality of joints is than a vital task. Welding is a highly dynamic and non-linear process, thus an application of time-domain or frequency-domain methods is often not suitable for evaluation of welded joints quality. To fully describe the correspondence between the geometry of welding arc, parameters that express the quality of joint, and the welding arc current, being the most important steerable parameter of a GMAW, time-frequency methods (TFM) of signal analysis should be applied. In the paper application of ensemble of STFT and EMD (Empirical Mode Decomposition)-based estimators to evaluate the stability of a GMAW process, that results in the quality of joint. Proposed method of feature extraction was applied on the real data taken during several GMAW realizations with different conditions (changes in welding current, arc voltage, shield gas flow, wire feed speed, etc.). In the active experiment process parameters were acquired. Performed investigations revealed that in comparison to traditional as well as separately used TFM, ensemble of TF estimators gave better performance in a GMAW condition assessment.

The heat treatment influence on the structure and mechanical properties of Ti6Al4V alloy manufactured by SLM technology

Titanium alloy can be processed via advanced powder manufacturing routes such as selective laser melting (SLM). This field is receiving increased attention from various manufacturing sectors including medical device sectors. These advanced manufacturing techniques associated advantages include: design flexibility, reduced production cost, reduced waste, and the opportunity to more easily manufacture complex or custom-shaped implants. Unfortunately, this production technique is characterized by high temperature gradients, which results in the build-up of thermal stresses. This is the reason why heat treatments have to be used. In this research, the effect of several heat treatments on the microstructure and mechanical properties of Ti6Al4V alloy processed by SLM are studied.

Image Processing Method for the Improvement of Visibility of Adhesive Path Defects

The increase of interest in adhesive joints is strongly connected with simple joint creation, high joint strength and its flexibility. Due to this, assurance of high-quality joints in many responsible applications is now a vital task. Because of the automatization of joint creation, autonomous vision systems are sometimes used for the control of adhesive path quality. There is a number of environmental obstacles that limit the applicability of simple off-the-shelf systems. The aim of the research is to develop an image processing method which could be applied for the enhancement of visibility of adhesive path features for further application in an adhesive path quality control algorithm implemented in a robot vision system. The solution of the posed problem requires not only identification of adhesive path edges, but also detection of bonded part edges and suppression of different light conditions influences. To achieve appropriate image quality, a series of image processing operations like sharpening filtration, edge detection, background detection and removal, binarization and morphological operations were applied. Obtained results prove that the presented approach of image processing and analysis can be used in a robotized adhesive path quality control system.

Application of Active Thermography for Detection of Soft-Soldered Lap Joints Inner Defects

Soft soldiering is a joining technique commonly used in many areas of industry. It is especially useful for joining components susceptible to damage caused by high temperature. One of the vital issues associated with this type of joining is the possibility of the formation of hidden defects, like: cracks, lack of connection, gas voids etc. In the paper, a study of active thermography application for detection of common defects in soft-soldered lap joints is presented. Lap joints of thin copper, aluminum and high-alloy steel palates were made using solder paste in a soldering oven. Internal defects were intentionally introduced into the joints. To reveal defects, an active lock-in thermography method was applied. Various heating parameters, IR images acquisition, and processing methods were tested. In order to compare the obtained defect detection results with a benchmark, tested samples were radiographically analyzed. Results prove that active thermography methods can be applied for the detection of defects in soft-soldered lap joints. Based on the research performed, the size of defects that can be detected was estimated.

Diversity Measures in Classifier Ensembles Used for Rotating Machinery Fault Diagnosis

Recent progress in computational intelligence, sensor technology and soft computing methods permit the use of complex systems to achieve diagnostic process goal. Among many, machine learning and pattern recognition techniques are often applied. When dealing with complex machinery use of one classifier is often insufficient. It is known that classifier ensembles (combined prediction from several classifiers) have the capability to outperform single classifier, because ensemble results are less dependent on peculiarities of a single training set. Additionally a combination of multiple classifiers may learn a more expressive class. In the paper a comparative study of different diversity measures for the rotating machine common faults detection and isolation. The main premise was to investigate if there is a link between diversity measure and classification accuracy. Although in several cases the connection between diversity and fault detection as well as isolation performance was revealed, the generalization of the diversity measuring concept cannot be clearly formulated.