Mgr inż. RYSZARD JASTRZĘBSKI, Prezes Zarządu  Technolkonstrzębski Co Sp.  z o.o. w Krakowie,   Mgr inż. MARIAN GODNIAK, Huta im. T. Sendzimira, egzaminator spawaczy w Technolkonstrzębski Co sp. z o.o. , Mgr TOMASZ SKAKUJ, Zakład Psychologii Ogólnej, Uniwersytet Jagielloński, Mgr ANNA STENCEL, psycholog, Instytut Łączenia Metali w Krakowie,  Dr Inż. ANDRZEJ TROJNACKI, Zakład PKM, Politechnika Krakowska

Användandet av kognitiv psykologi och muskelrörelsers biomekanik vid träning av svetsare  

Sammanfattning

Bristen av tillräckligt snabba datorer på  äåö åttiotalet som behövdes vid tillämpningen av biocybernetiska metoder fick författarna av denna artikel att påborja programmering av svetsarens hjärna (den snabbaste och mest kapabla datorn i världen) i samarbete med psykologer. Denna artikel är den första i en serie av publicerade artiklar angående intellegenta biocybernetiska datorprogram som används vid svetsning. Författarna av artikeln har på basis av erfarenheter hämtade från polska svetsingenjörer isärskiljt inlärningsprocessen av svetsning och förhöjning av svetsarens kvalifikationer under tiden denne arbetar till följande element; musklernas fysiska uppbyggnad, intensiviteten och tiden av inlärning, svetsträning, erfarenhet, rollen av skolning vid kurs, igenkänningsprocesser, kognitiva teorier vid igenkänning av bilder, mekanismen av igenkänning och behärskning av svetstekniken samt inflytandet av observationsmekanismer på kvaliteen av svetsningen. Denna grundliga analys av temat har lett till bearbetning och införning av metoder som möjligör snabbare och bättre skolning av svetsare. Nämda metoder kan användas vid skapande av datorprogram som har till uppgift att styra industrirobotar. Dagens kognitiva psykologi använder det som polska fackmän inom biocybernetik kommit fram till när det gäller förklaringen av psykologiska lagar i samband med hjärnans uppbyggnad.

  1.       Inledning

       Hard konkurrens bland svetstraningskurser organiserade i Krakow i borjan av nittiotalet tvingade forfattarna av denna artikel att forbattra kvaliteen pa de kurser som anordnades. Maknaden ar dominerad av privata foretag som kravde nyskolade svetsfackman som med sina nyinlarda kunskaper mojliggjorde att de kunde utfora arbeten som var bestallda av vasteuropeiska foretag. Efterfragan pa den Tyska marknaden skyndade pa processen for att hitta nya losningar inom omraden som aldrig tidigare anvants i sammanhang med svetsning.

          2.       Forskningsprogram

For nuvarande finns det ingen applicerbar svetsteknologi som mojliggor att en industri-     robot med optiska sensorer kan producera en rorfog pa basis av en bild analys, om fogen ar lagd pa ett felaktigt satt, samt om svetsfogen ar forberred pa ett inkorrekt satt (skiftad kant, andrad (ang. sill) storlek and spricka.

Detta maste utforas av en valtranad svetsare.

For att intensifiera svetsarens traning och gora den mer effektiv sa forsokte vi fordela de faktorer som ansvarar for kvaliteen av svetsning. Foljande faktorer har valts:  fysisk traning, visuell kontroll och koordinationen av rorelser och observationer.

Fysisk traning

One could easily assume that the relationship between a welding training’s participant and the welding supervisor was similar to that between an athlete and his or her coach. In such a case it would suffice to teach a physically fit person how to weld, and let him supervise the welding process. The research done in co-operation with the movement mechanics’ specialists aimed at identifying the influence of muscle development on welding efficiency. The aim was to develop alternative training methods for the muscles vital in the welding process.

As a result following tasks have been assigned for the welders’ physical training:

¨       development and training of muscles, including wrist muscles, teaching the technique of the right grip and grip movements,

¨       reflex consolidation for greater stability of welding and proper welding bead formation.

2.2. Kognitiv process

It turns out that the physical training variables alone are not sufficient for correct prediction of changes in the welding quality, which occur during a regular training. A joint effort of engineers and psychologists, which resulted in the above division of the factors determining welding quality, proved the usefulness of cognitive psychology, as if predestined for this task. Visual control and co-ordination of movements and observation are both problems, the solutions to which are to be found within the field of this most modern branch of psychology. Cognitive psychology interprets knowledge about the human psyche in terms of data processing mechanisms. Knowledge of these mechanisms at the training level could optimize the teaching process itself, and improve the skills of a chief welder, enabling him of correcting welders’ movements.

2.2.1. Svetsprocessen och ingenjorer’s forvantningar

The following tasks for a psychologist were formulated with the new possibilities in mind:

¨       to collect the available information concerning the means of perception and filtration of an image by the perceptive apparatus, especially in a case when a vital part of an image finds itself not in the figure (the bright elements of an image), as usual, but in the background (the obscure, barely visible elements). (“Figure” and “(back)ground” are technical, perceptive terms drawn from the Gestalt psychology),

¨       to consider the possibility of gaining the information about a welding process phenomena on the unconscious level of data processing,

¨       to collect information concerning the studies on learning the skills (praxis) based on the feedback between eyesight and muscles movements,

¨       to prepare methods of theoretical training.

2.2.2. Kognitivistiska metoder av bild identifikation[1]

Cognitivistic theories of image identification may add vital information to the characteristics of cognitive processes actively participating in the welding operation. The rapidly developing cognitive psychology enables us to grasp these characteristics, and may therefore be employed in welding. Three models of image identification systems have been analyzed:

¨       a system of comparison with the original pattern (the simplest model – the key term is “original pattern”: the representation which is being identified. The identification is based on matching the outside signal with the inner original pattern. To find a pattern which matches the signal better than the others means to identify the signal),

¨       the so called Pandemonium (this system consists of succeeding demons working on an received image, each of them performing a separate task. The first demon team – image demons, has the simplest task: they record the original image of an outside signal. Then the image is analyzed by characteristics demons, each of which looks for a certain characteristics in the image: a specific line or angle, a unique curve or outline. Cognitive demons observe the characteristics demons’ reactions. Each cognitive demon is responsible for identification of a certain pattern of characteristics. The last stage consists of decisive demons which judge the intensity of the reactions of individual cognitive demons. The Pandemonium System describes the stages in image characteristics analysis.)

¨       a model of analysis by means of synthesis (the sensory data interpretation is based on the knowledge of what the signal should be. This knowledge is provided by a context of a sensory incident, which is described as a huge load of information stored and usually automatically used for explaining the incidents. This context-based information evokes expectations which focus our attention on certain stimuli and are responsible for their selective reception. This model has an ability of self-teaching).

The three models differ in the way they deal with difficulties created by the problem tasks concerning sensory data processing, at the end of which process the image is identified. This theory employed in context of processing the information gathered during an intentional act of welding, the contents and form of which has been registered, is presented below on the bases of experiences acquired during the welding training.

  2.2.3. Forskningsprogram for svetsprocess ingenjorer

The research began with the task given to the welding engineers running the welding courses. They were asked to gather experience and to perform certain experiments. The knowledge was provided by nearly a hundred expert welders, giving lectures during “Engineering Supervision and Inspection of Welding Courses” organized by Technolkonstrzębski Co Sp. z o.o. in Kraków. The experiments and observation tasks were performed in training centers of renowned companies and in welding laboratories of technical colleges in Poland. In the laboratories welders were taught practical skills of correcting the welder’s movements, which was part of the above-mentioned courses.

The main aim of the research was:

¨       a study of the elements and phenomena of a welding pool observed by a welder during work, and registered in the subconscious,

¨       a training in noticing the less visible elements of the pool, which are important for the welding and forming of the welding bead (the ability of filtering the image of the welding pool).

  Kognitiv process och larandet av svetsteknik

  The process of welding learning usually begins when a trainee accidentally produces a correct weld and registers in the subconscious the image of the welding pool. After many trials he learns how to stabilize the process and achieve the recorded image of the pool. That is why, when welding with the use of MAG method after the welding material is heated and the weld seam widens, the welder shortens the welding arc, regulating the welding machine voltage instead of the current in a wire feeder.

In order to teach a trainee how to make a smooth face, it is better to make him “lead an edge of a weld pool along an upper surface of a former bead”, than to “move each new bead half the width of a former one”, since division of the distance into two equal parts is imprecise. A similar technique is used when teaching forming filling beads without sticking or undercuts. Further training consolidates the newly created connections in the brain.

The decisive factors in fast and efficient learning of welding are: eyesight, sense of hearing, knowledge and the way of perception, physical fitness, intensity of training and its duration, experience and training in welding. 

  Den traditionella traningen for svetsare

  Traditionally, the training consists of welding tasks that gradually become more and more difficult. Since the processes in a welding pool and algorithms of welder’s movements automatics are still insufficiently researched, an instructor will try to show the process in practice rather than explain it (in many cases he may not realize why he actually did something in that particular way).

According to the Polish regulation PN-87/M-69900 there are elementary and qualification courses. According to the EU regulation PN-EN 287-1 there are qualification courses for a fillet welder, a sheet welder and a pipe welder. In both cases the total time of a pipe welder’s training consists of about 400 practice hours.

Many experienced welders cannot explain why the welds they make are correct, while those of other welders are faulty. That is why even the welders certified by the Office of Technical Inspection (UDT) instead of teaching their sons themselves would rather entrust them to welding centers’ instructors.

  Influence of perception mechanisms on welding quality

Each candidate for a welder has his eyesight examined. Certain welding difficulties were noticed with those, who had problems distinguishing the shades of red corresponding with the color of liquid slag and metal.

Some of them could learn welding in easily accessible places after a long training, but could not cope with welding in more difficult circumstances. Amongst the most experienced welders there were some who would use their sense of hearing rather then eyesight. This would come out when working in a hardly accessible and dark place, where such an expert would produce a weld next to a weld groove.

As a rule, during construction works in difficult conditions, when the well-practiced motions are distorted, it is eyesight that decides about the quality of a joint (movements’ correction). The ability to observe is necessary for the learning process. The intensity of an electric ark during welding makes a trainee at first overlook the vital elements in welding: the previous bead, liquid metal pool and liquid slag pool. Only after a long period of training a trainee stops paying attention to the arc, and concentrates on the more important elements.

According to a research conducted by Institute for Joining of Metals in the welders’ training center of Technolkonstrzębski Company, a thorough analysis of pictures showing the welding place shortens the time required by the welder to learn to observe the weld pool. The same mechanism lets us identify the familiar faces in the crowd rather than those we barely know.

Frequently, after a long practice a trainee would not follow given instructions. But when an instructor pointed at a liquid metal pool and liquid slag, the learning process would become very fast. This shows that a trainee has initial problems identifying the less visible liquid metal pool, a former bead and a welding groove against a bright welding arc.

The participants of “ Engineering Supervision and Inspection of Welding Course” were repeatedly and over a long period of time shown the mechanisms of weld forming, elaborated by Institute for Joining of Metals, as well as the way of directing the heat source and the technique of feeding the weld metal. The relationship between process dynamics and an observed image was also revised. As a result trainees who had never before held a welding gun were able at the first attempt to make a correct weld penetration and weld face using MAG and TIG methods.

Thus we can conclude that eyesight and the ability to distinguish between liquid slag and liquid metal against a very bright electric arc and a dark image of the previous bead and welding groove is important in the welding process control. It should be emphasized, however, that even more important are the style and technique of observation and perception of the welding process.

  6.     The importance of the sense of hearing in welders’ training

  A skillful welder will be able to control the glowing of a welding arc and the creation of a proper bead basing on the sense of hearing. It lessens the eyestrain and decreases the welders’ fatigue. A characteristic sound in the pipe means the granite layer (called penetration) has been made correctly. With the use of the sense of hearing one can also control the proper glowing of a welding arc. One can then concentrate on watching the weld pool.

An experiment was held, during which some trainees could only rely on their sense of hearing (no observation allowed) while they listened to the noises accompanying welding of course samples. These trainees achieved better course results as compared with the other trainees.

  Physical development

A long training experience showed that tall, well-built and athletic people had more difficulties learning the practical skills of welding than those slender and unfit. They usually had problems with firm and precise gun-leading.

At first it looked as though there was no correlation. Painstaking research showed, however, that the muscles responsible for a firm grip are wrist muscles, not biceps.

What also proved important are habits and learned patterns of behavior. Those welders who used to work with covered electrode and switched to MAG welding with granite layer still try, out of a habit, to weld with weaving with a gap of 1.5 mm and they have problems with weld penetration. TIG welders who used to do gas welding before are less efficient and produce low quality granite layers. Gas welding habits also hinder the production of the first layer with no undercuts.

People motioning the whole arm had problems with welding. The welders who only moved their wrists and fingers performed much better. Many instructors insist, that the training should finish only when a trainee stops thinking about welding and leads the gun automatically, without any conscious control. The conscious control is like a patch, which slows down the whole computer program.

People with dysequilibrium are unable to learn welding.

      8.       Intensity and duration of a course

Too many course hours a day are tiresome for trainees, and make them persist in bed habits. Also breaks during a training period that are too long negatively influence the efficiency of training.

An experiment was conducted:

-          a more advanced trainee trained 12 hours a day

-          a beginner trainee trained 4 hours a day

      The trainee who trained less but systematically, learned welding faster and better.

The course time is the time for developing muscles. Experience shows that a course cannot last less than 20 working days. All longer breaks negatively affect the training.

Bearing in mind the difference in efficiency, a TIG welder and a gas-method welder would produce equal number of 200 welds on pipes f 75 x 3.2 mm, that is 1200 running meters of pipeline during a course. Similarly, teaching MAG welding and covered electrode welding requires the same number of welds of the same width. The low efficiency is caused by the necessary breaks made by a trainee after every 50 mm of new bead in order to asses the results.

The conclusion is that EU regulations setting the required number of hours, not days, do not allow for the above mentioned and obvious aspects of practice in learning welding, and are therefore slightly inaccurate.

9.       Achieving welding proficiency

  9.1. Welding training

     Once the technique is acquired, it is the training that decides about welder’s reliability. Pressure vessel welders coming back after a longer leave produce a few incorrect joints at first. The same results may be caused by too much intensive work or training.

    Stamina is also very important in long-term welding. Those welders with the proper leading and gripping technique do not get tired easily. Intensive welding requires a 2-3 days’ rest. A longer break might negatively influence the quality of welding. On the first day after a longer break one should not work on important welded joints.

    9.2. Experience

Quite frequently it happens that older welders who wear glasses and whose hands shake make important joints better than their younger and fitter colleagues with only a few years of experience. The decisive factors are: the knowledge of the experienced welders, who got to know the subject thoroughly, care in preparing and putting together the edges of a groove, maintaining a welding machine in working order and mental strength.

It is often said that a young welder finishing a course is like an inexperienced athlete, who, unlike the elder    ones, cannot mentally endure the tension during an important sports event.

An experienced welder works not only subconsciously, but also consciously – mental processing means a better gun leading and weld metal feeding in non-standard conditions.

  9.3. The role of course training in acquiring welding mastery

At times the so called “self-taught welders” enroll for a course. They have many years’ experience, and are regarded specialists by their managers, engineers with building authorization for weldments. They are expected to pass a qualification test without any additional training. It is only when they are shown the requirements and skills possessed by other, trained, specialists that they become less ambitious and decide to prolong the training period before the exam. During the course it turns out that the time is further prolonged, and as a result a self-taught welder needs 50% more time than a complete novice. It is partly due to the instructors’ reluctance to train the conceited “specialists”, and also due to the fact that the latter do not immediately notice the necessity of getting rid of bad habits, which itself is far from easy. In welding it is clear that mastery requires knowledge and experience of a few generations, without which an amateur is rather helpless. The level of proficiency attained by a welder depends on proficiency of his instructor and his colleagues, who share their experience with him, on how responsible the tasks are and on the skills of the chief welder, who supervises the work.

  System of welders’ training in Poland

   The table below shows the division into 5 proficiency levels, based on entries in welder’s book at various times. The highest ranking are the chromium-molybdenum-vanadium (CrMoV) steels welders, who work with steam pipes of high dynamic load, where the pressure is above 100 Mpa, and which are at risk of being blown out by minute leaks caused by radiologically undetectable stickings, small tube bubbles and defective beginnings and endings of beads. In practice defects of this kind can cause a break-down of a power plant within a few days’ time.

A model training center, established within the Welding Institute, prepares for exams in accordance with the European building standards. There are also other welders’ training centers in Poland, preparing skilled labor to work abroad or for the best home companies. This experience led to creation of such training methods that allow to train expert welders in respective fields, according to European and American standards. The majority of  those training centers are certified by UDT.

Big companies’ policy makes it impossible for welders from other companies to be trained in training centers of those companies.

A Table

Symbol explanation:

P – elementary range of approval

B – qualification-test range of approval

R – qualification-test range of approval for pipe welding

1 – low-carbon steel

2.1 – low-alloy steel with alloying elements’ content of 3%

2.2  - low-alloy steel with alloying elements’ content of 3 to 5%

11.    Conclusions

       Following conclusions have been drawn:

       Course training teaches the skills based on experience of many generations and is therefore indispensable in gaining high professional skills,

¨       Practical training, performing demanding tasks under supervision of a welding engineer, is vital,

¨       Use of the cognitive psychology based methods facilitating the welders’ training, such as repetitive display of over-exaggerated weld-pool pictures, can reduce the training to 4 hours a day, but the total number of training days must remain at least 20 for TIG and MAG welding (for butt welds in vertical upwards position) and 40 days for gas and covered electrode welding (for butt welds in vertical upwards and horizontal positions and for upward welding, pipe axis inclined at an angle of 45%, fixed pipe);

¨       Knowledge of cognitive psychology and mechanisms of visual data processing helps the chief welder to achieve better welding movements’ correction;

¨       European norms which set the total number of training hours, and not days and welds, are inaccurate,

¨       Teaching gas welding before TIG training, and covered electrode welding before MAG training may facilitate the first stage, but may prove harmful for the final results of the training,

¨       Better results are achieved when teaching the TIG method before gas welding, and the MAG method before the covered electrode welding,

¨       An experienced welder has a greater mental strength as compared with a beginner, and thus he is more reliable when making demanding welds.  

  [1] “Cognitivism” is a technical term describing the cognitive psychology paradigm. The term