(PDF) Investigation on the Electric Arc Light Emission in TIG Welding

Abstract: It has been presented the results of investigation spectrum of the electric arc light. The main goal of these researches was to check that welding arc light can be seen as a signal carrying essential information about the welding process and exploiting in the Designed and made experimental stati on. The advanced spectrophotometer was used to data acquisition of spectrum of arc light. The investigations were conducted on the automated TIG welding station. For each welding parameter indicate that the welding arc light emission contains a lot of information concerning the course of the welding process. That signal is much more sensitive than the signals recorded in th e electric circuit of the welding arc to the changes of welding conditions and s hould be used as a tool for monitoring and CCD array with 1028 elements (pixels) in the visible spectral range of 340 to 860 nm. It is an expensive instrument and that can be used only as a are indicative of the next steps of researches on the welding arc radiation phenomenon and the possibilities of using this signal for online sensing of the welding process on fully automated and robotised stands. This monitoring system will be particularly attractive for welded - structures manufacturing industry because it could significantly re and repairs. Quite new approach to monitoring of welding processes replaces 'trough the arc methods' of monitoring by non-conventional methods. Three means to simulate the spectrum distribution of the electric arc light. The mathematical-physical model of the arc light emission and neural networks Reference to this paper should be made as follows: W 'Investigation on the electric arc light emission in TIG welding', He studied according to an individual programme of studies 'Quality Control of Automated Welding Techniques'. In 2001 he studied in the Department of Mechanical Engineering at the Horsens Polytechnic in Denmark. From 2003 to date he is employed as a Research A ssistant in the Institute of Welding in

visual testing VT1, VT2 and radiogra phic testing RT1, RT2 course. He has Many signals, having their source in the welding arc, may be used to investigate the stability of the arc burning. Indirectly they can be also used to test the stability of the welding process. In many cases, based on the assessment concerning the stability of the welding arc, the quality of the joint can be evaluated. Upto now the stability of arc burning was mostly assessed based on the signals of the welding voltage and the welding current (Luksa, 2003, 2006; Kuo and Wu, 2002; Wang and Chen, 2002; Wikle et al., 1999), recorded during the welding process. As the appearance of many kinds of welding imperfections are not accompanied by any dis tinct changes of the welding parameters. For this reason these parameters may not be used to estimate the stability of the welding process and the quality of the joint. Arc light radiation is a fundamental phenomenon associated with the arc welding process, and in the most cases it can be obser ved directly, being a hazard for the welder's eyes (Kennebeck, 1994). It may be also considered to be one of the signals emitted in the course of welding and utilised as a carrier of information about the welding process Infrared sensing techniques for penetrati on depth control of the submerged arc welding process (Wikle et al., 2001) is also a very useful technique to monitoring of The intensity of radiation produced by the welding arc is a function of the welding process itself and of the welding variables. For example, less ultraviolet and visible energy is radiated at comparable current levels during shielding metal-arc and flux-cored arc welding than during gas metal-arc welding. The sources of visible radiation in the welding arc are the following: the arc column, the regions close to the electrodes, the liquid metal transported across the welding arc, the molten pool, the heated region of base material around the molten pool and the heated end of the electrode wire. Hot slag may be also a source of radiation. The range of length of the emitted light waves and their spectral composition depend on the weld ing parameters, the atmosphere in which the arc glows, the kind of the base and consum able material as well as on several other Measurements and the analysis of the arc li ght emission are used in investigations of the welding process (TIG). During the inves tigations the following characteristics were specified: the temperature distribution in the arc (Fan and Ravala, 2003), the conductivity of the arc columns, the temperature and the emissivity of the tungsten electrodes, the temperature of the drops of the liquid metal, the amount of hydrogen in the gaseous shield of the welding arc and also the temperature of the weld pool. The investigations were also conducted to calculate the mean temperature of the welding arc (Handdad and Farmer, 1985). The analysis of the arc light emission may help to develop the technique of taking photographs of the welding arc. Investigations on the visible radiation of the MIG/MAG method helps also to monitor the way in which the metal is transferred

During the investigations the spectrophotometer, designed for the remote fibre spectroscopy in the range from 340 to 860 nm was used. The investigated light is introduced to the spectrometer via a standa was controlled by the PC computer equipped with special control program. During the experimental procedure the follo the arc burns between the thoriated tungsten electrode (cathode) and a copper plate the range of 30 300 A). It was assumed that the arc length is equal to the distance between the electrode tip and the surface of the welded me was changed in the range from 1 to 6 mm. Figure 3 shows the arc spectrum obtained in the range of 340 welding current of 200 A, arc length in range of 1 6 mm and 100% Ar as the shielding gas. Figure 4 shows the arc spectrum obtained in the range of 340 same welding parameters, Figure 5 in the range of 480 700 nm and Figure 6 in the Figure 3 Effect of the arc length on the arc light spectrum. The welding current 200 A, the arc length in the range of 1 6 mm, Ar as the shielding gas, wavelength in the The entire arc column will be analysed as a single object. Disclosure of the ro les of the light will be the main objective of the research. The spectrum of the arc is composed of a continuous background spectrum that follows the blackbody radiation law with th The shape of the discrete lines is modified by two major causes, namely collision line

Figure 17 shows the influence of arc length on the visible light intensity and arc voltage for the welding currents in the range of 50 300 A. It can be seen that considerable changes of the arc length are followed by substantial changes of radiation intensity of the welding arc (wave length 698 nm) and only by small changes of the arc On the basis of the collected test data and Equation (6) (Li and Zhang, 2001b) a and the welding current intensity ( ) can be determined. The arc length is in the range of By using a computer program, coefficients have been calculated on the basis of accumulated data for an arc length in the range of 2 The Equation (7) is satisfied for the wave length of 698 nm and the welding current not greater than 150 A at the arc length 2 3.3 The use of artificial neural networ To find a relation between the visible arc radiation with the welding current in a wider range (30 220 A) and the arc length in the range of 2 neural networks have been applied. With the use of the automatic net creator from the neural network software the neural net has been bu ilt. The welding current values in the range of 30 220 A and the intensity values of the visible radiation (wave length 698.6 nm) in the range of 0.06-8.35 i.u. were int roduced to the neural network as the input values by the automatic creator (W glowski and Mikno, 2005), while the quantity of the learning subset was 78, validation subset - 28 and testing subset - 6. As the result All results obtained by application of the artificial neuron network and by using the welding arc model (Equation (7)) are compared and shown in Figure 19. The welding current values in the range of 30 220 A and the arc length in the range

the relationship between the welding arc length and the intensity of arc radiation and and the real ones indicate a very good f The experience gained during these investiga on the welding arc radiation phenomenon. Obtaining knowledge increases the possibilities of using the signal for online monitorin g of the welding process on automated and robotised stands. The analysis of the spectrum of the radiation of the welding arc helps in development of new vision sensor in arc welding. The author would like to thank The Ministry of Education and Science in Poland for financing the research, which was done within the framework of the research project Agapiou, G. and Kasiouras, C. (1999) 'A de tailed analysis of the MIG spectrum for the process in the presence of plate inclination angle', Kennebeck, M. (1994) 'Eye damage from radiati on in arc welding. Recognition, evaluation and Li, P.J. and Zhang, Y.M. (2000) 'Analysis of an arc light mechanism and its application in sensing Li, P.J. and Zhang, Y.M. (2001a ) 'Precision sensing of arc length in GTAW based on arc light Proceedings of 12th International Scientific Conference on Achievements in Mechanical and Wang, Q.L. and Li, P.J. (1997) 'A rc light sensing of droplet transfer and its analysis in pulsed

Are there different CWI's for different industries like; shipyard, structure, oilfields?

The Certified Welding Inspector certification is more than a rewarding career. It involves great responsibility and remarkable skill demonstration. The CWI is widely recognized, both nationally and internationally, and successful companies have come to rely on this AWS certification when ensuring the highest level of quality workmanship. The American Welding Society (AWS) offers three certification levels for welding inspectors: certified associate welding inspector, certified welding inspector and senior certified welding inspector (aws.org). All candidates must meet basic education and work experience requirements in order to be eligible for certification. Certified Associate Welding Inspector (CAWI) Certified associate welding inspector (CAWI) candidates must pass a written and practical test. Topics covered on the test include welding processes, quality assurance and mathematics. Candidates need at least two years of experience in a welding-related job. Certified associate welding inspectors can only hold their level of certification for three years, after which they may take the test to qualify for the certified welding inspector credential. CAWI certification is not eligible for renewal. Certified Welding Inspector (CWI) Like the CAWI certification, the CWI requires individuals to successfully complete a written and practical test. The practical test includes plastic replicas of welds, inspection tools and a codebook. The first knowledge test is a closed-book 150-question exam, while the second knowledge test, taken after the practical exam, is a 46-60 question test in a welding specialization chosen by the applicant. Certification must generally be renewed every three years. Senior Certified Welding Inspector (SCWI) Senior certification for welding inspectors calls for at least six years as a CWI and a minimum of 15 years in a welding-related profession. Candidates must pass an eye examination and written test. Certification must be renewed every three years. A 9-year recertification cycle is available for CWIs and SCWIs by examination or by completing continuing education courses. Job Duties Welding inspectors check the quality of the metal-joining work done by other welders. Specific job duties depend upon qualification levels and are determined by the employer. In general, certified associate welding inspectors perform inspections under the supervision of CWIs and SCWIs, according to the AWS. Certified Welding Inspectors review various welds to ensure that the join between the two pieces does not break, mark defective welds for repair and observe welders in metal shops, according to job listings on Monster.com in Nov. 2011. Step 2: Earn a Postsecondary Education Formal training through a community college or vocational school is not required, but some employers seek welding inspectors with postsecondary education. Technical programs in welding typically last 1-2 years and result in a welding diploma or certificate. Topics generally include blueprint reading, metallurgy, fabrication and arc welding. Students also might consider 2-year associate's degree programs in welding technology. Step 3: Gain Work Experience Welders work in a variety of industries, including construction, aerospace and machinery manufacturing. Before moving into the role of inspector, welders might perform entry-level work, such as cleaning and degreasing parts; checking grooves, angles and dimensions for accuracy; inspecting equipment; and mixing and applying protective coatings. As new hires gain experience, they might advance to reading blueprints and using their knowledge and skills in metallurgy and welding to join, bind and fuse two or more metals together. Skilled welders might move on to even more complex tasks, such as welding difficult angles or materials, like titanium or steel. Advanced welders also might develop templates and models, estimate parts and labor costs, and examine work for defects. Promotion to welding inspector might lead to duties like writing inspection reports; ensuring that equipment complies with engineering, welding and testing standards; and training other welding staff. Step 4: Pass Welding Inspector Certification Exam Welders who have attained a high school diploma or a postsecondary degree and completed three years of documented work experience may apply to become Certified Welding Inspectors (CWIs). The certification exam covers three areas, including welding fundamentals, practical applications and welding code application. Certifications generally last three years; however, CWIs can take additional exams or courses in order to prolong recertification for up to nine years.