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PWL#117 - Laser Roll Welding, Selecting and Maintaining GMAW Torches, Shim Filler Metal for EBW May 01, 2013 |
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PWL#117 Laser Roll Welding aluminum to steel sheet metal, Selecting and Maintaining GMAW Torches, Shim Filler Metal for Electron Beam Welding, ASME Boiler and Pressure Vessels Code, Section IX - Welding Qualifications, Advancements in Assisted Visual Inspection, Resistance Welding Tips (R), Diffusion Welding (R) and much more...
May 2013 - Practical Welding Letter - Issue No.117
The Mid April Issue of Practical Welding Letter, Bulletin 84, dealing with Resources on Welding FAQ was not distributed by e-mail but it is available at Bulletin 84 and from the Welding Resources Page.
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you like it, and if you think it may help them. If you received this from a friend and if you like what you read, please subscribe free of charge and you will also receive a bonus book on Practical HARDNESS TESTING Made Simple. The addresses reported hereafter were live and correct at the time of their publication. There is no guarantee that they will always be so, because they are administered by the sources themselves and are under their control. Note: References to articles or other documents are given here in If they are URL's (Uniform Resource Locator), which is the analogue of an address, they begin with "http://..." or "www.". These are not live and must be copied and pasted entirely into the browser (after having selected them with the mouse or otherwise). If they are long they may be displayed in two or more lines. In that case one has to care that the URL be copied completely in a single line without any space, and Enter. If the information is important to you as we hope, you may save the selected pages in a suitable folder on your Computer for easy reference. You are welcome to forward this page to those of your friends who may profit of this information.
1 - Introduction 2 - Article - Laser Roll Welding 3 - How to do it well: Selecting and Maintaining GMAW Torches 4 - Filler Metal for Electron Beam Welding 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article: CASTI Guidebook to ASME Section IX - Welding Qualifications 8 - Site Updating: Resistance Welding Tips (R), Diffusion Welding (R) 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contributions: Advancements in Assisted Visual Inspection 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board
(Sponsored Links) 1 - Introduction This 117th issue of Practical Welding Letter for May 2013 opens with a short review of Laser Roll Welding that was, only a few years ago, a curious development of a process, object of learned research, as remarked in one of our pages. Since then it was adopted in the automotive industry, but things are moving fast there, and it may be already obsolete. GMAW torches are an important tool for those who use them. To get the most out of the investment, it would pay to be receptive to advice given by manufacturers and users. A note summarizes a few hints on selection and maintenance of these implements. Electron Beam Welding is mostly performed without filler metal at all. But in a few cases the proper selection of a suitable shim may avoid cracking and save the job, allowing acceptable welding. One should know where to look for finding how to correct difficult cases. The Interpretation of Code requirements may be tricky. Especially for the Boiler and Pressure Vessel Code (BPVC) of the American Society of Mechanical Engineers (ASME). We recently got questions from puzzled readers. A link to an informed Guidebook, available online, written by a knowledgeable author, may help to clarify some issues. Readers are welcomed to provide feedback, if it is indeed of help to them. Two of the website pages were revised and updated this month. They deal with Resistance Welding Tips (R) and with Diffusion Welding (R). The work is continuing but it will take some more time until the large part of this revision is accomplished. In Section 11, some advancements are reviewed, that were researched and implemented in view of improving assisted visual inspection. There is a strong drive to limit the work charge of experienced visual inspectors to those cases that require personal judgement. Routine visual welding inspection will be more and more performed by automatic devices designed to screen most of production. Only marginal cases will be then be routed to the decision of a human inspector. The other subjects, grouped under the usual titles, can be found at their place in the page. It is hoped that, even in this publication, most of readers will find some useful information. For the items that interest you, the Search function is available in almost every page of the website Titles of Articles from Practical Welding Letters can be found in the Welding Topics page. Links to the PWL complete list is available from the Index of Past Issues of PWL. The subjects treated in the Mid Month Bulletins are listed in the Welding Resources page. Please enjoy reading, and use the Contact Us form to send your comments, feedback or questions. 2 - Article - Laser Roll Welding Laser Roll Welding is a hybrid process combining the technology described in our page on Roll Welding, with localized laser beam heating ahead of the rolling pressure, to promote coalescence of the welded materials. It is briefly mentioned in that page as a research item. This process has been used to join surfaces of dissimilar metals like aluminum and steel for applications in the automotive industry. Aluminum melts only in a very shallow layer upon making contact with the laser heated steel. The rapid cooling minimizes the formation of brittle intermetallic compounds. Laser power, roll pressure and working speed are controlled together in order to minimize the thickness of the welded interlayer. While the Fe rich intermetallic compounds are somewhat ductile, those rich in Al result much more brittle. Although their formation is unavoidable, some control of their type and amount is still possible. Therefore, the success of the method is measured in the quality of the joint products formed. It is reported that, for adequate joint strength, the mixed interface layer should be less than 10 microns thick. The roll pressure improves the contact area and increases the cooling rate, further limiting the diffusion of dangerous phases. The same purpose was recently achieved by different means as explained in the following press release: http://world.honda.com/news/2013/4130218New-Technology-Join-Steel-Aluminum/ Readers are urged to link to the above page to learn how this kind of new dissimilar joint is made. 3 - How to do it well: Selecting and Maintaining GMAW Torches Two articles on GMAW Torches, both in the April 2013 issue of the Welding Journal, include important information for welders using them in their daily work. The first, at page 34, explains basic points to consider before selection. The right selection for the job may have considerable influence on suitability for the job, on personal satisfaction and on overall cost of ownership in the long run. The gun should be rated at maximum amperage for the job and compatible with the power source. No advantage is to be expected by selecting higher then needed rating. Duty cycle has to be determined according to job requirements: in semiautomatic flux cored welding applications, a 60% duty cycle is most commonly used and should be sufficient when used with CO2 shielding gas, except that for robotic work 100% duty cycle is preferred. The shielding gas used when assessing duty cycle reported by the manufacturer should be ascertained. This is because when using argon or mixtures, the gun runs hotter. Therefore in that case the amperage rating should be reduced at a given duty cycle or the duty cycle should be reduced at the given amperage. Air or water cooled? The second type runs cooler and is lighter but costs twice as much for the same rating and duty cycle. Other recommendations suggest to select tips with flattened threads that assure extended service life, massive contact tips and harder materials, besides longer and tapered nozzles that permit easier access to tight areas, if required. The second article, at page 44, stresses the importance of routine maintenance. Attention should be paid to clogging of liners, either by overtensioning of flux cored electrodes or by dirt. Blowing out with compressed air the liner whenever changing filler metal spool is recommended. Cleaning pads as offered by manufacturers can be used but should be firmly secured. Worn liners must be replaced as soon as possible. Liner length is critical to correct operation. No void space should remain between liner and diffuser. Trimming the liner to exact length should not leave any burrs on the inside, likely to scratch the wire. Spatter should not accumulate inside the nozzle, possibly by dipping in anti-spatter compound. Discard the tip rather than damaging the orifice by trying to remove spatter. Contact tips, preferably of high quality, should be kept in plastic containers and changed frequently. Using the gun as a chipping hammer to remove spatter(!?) seems preposterous: welders should be warned not to do so. All O-rings must be inspected and replaced regularly. Worn insulators must be replaced. Cables must be kept straight as much as possible, and hanged free of knots at the end of the day. Feeder connection is to be checked regularly. Suitable and timely maintenance goes a long way in keeping costs low and weld quality high. Interested readers are urged to look for the quoted articles referred to above.
4 - Filler Metal for Electron Beam Welding Electron Beam Welding is performed, most of times, without any filler metal at all. Extra metal to fill volume in special cases, can be obtained from integral material designed to border the joint, for the purpose of being melted in place. However problems can surface in cases of difficult to weld or crack susceptible materials. Then suitable foils to be placed in the joint, may play an essential function in assuring acceptable welds. For hard steels, usually titanium foil proves advantageous in providing a more ductile metal in the joint. The same will also work as a getter to remove porosity wherever gases are evolved. Added filler metal is often required for welding heat treatable aluminum alloys of the 60xx series. For welding dissimilar material one can either use a transition piece or a suitable metal shim as reported in the literature. A few suggested combinations include filler shims as listed hereafter.
In every case joint design, fit-up and operating conditions should assure minimum joint restraint and residual stresses. It is true that this short note cannot solve all the countless cases that show up in real practice. In case of doubt, please Contact Us. Note: it was realized unfortunately, after the publication of this issue of PWL, that a similar column as this one, with the same title, was already published in the past. It can be found (4) in Issue 12 of Practical Welding Letter for August 2004, by clicking on PWL#012 to see it. We apologize for the oversight with our Readers. 5 - Online Press: recent Welding related Articles MeltView cameras provide safer welding worksites MesoCoat to Work With Nation's Top Organization for Materials Joining and Welding The impact of impact toughness Aluminum filler metals: selection, storage, operation, and equipment Times are changing for welding industry, says Kemppi CEO 6 - Terms and Definitions Reminder Arc Welding Gun is a device, used in mechanized, automatic or semiautomatic arc welding, to transmit the electric current, guide the consumable filler metal wire, and convey the flow of shielding gas. Bronze Welding is a nonstandard term used to indicate Braze Welding. Carbon Arc Brazing is performed by using heat from an arc between two carbon electrodes to melt brazing filler metal spread in the joint by capillarity. Deposition Sequence is a nonstandard term used instead of weld pass sequence. Fusion Face is the surface of the base metal to be melted while welding. Gas Torch is a nonstandard term for gas welding torch or gas cutting torch. High Vacuum Electron Beam Welding (EBW-HV), is a variation where electron beam welding is performed in a vacuum space at pressure of 10-4 to 10-1 pascal (about 10-6 to 10-3 torr). Oxyhydrogen Cutting is an oxyfuel gas cutting process variation that uses hydrogen as the fuel gas. 7 - Article: CASTI Guidebook to ASME Section IX - Welding Qualifications A few queries were recently received from readers, about interpretation of requirements specified in the document ASME Boiler and Pressure Vessel Code, Section IX. The perusal of the above Guidebook is suggested to this readership as it might help to dispel some doubts. It is recognized that the ASME Code is not an easy document to use. The Author of the above Guidebook is well entitled to give guidance, as he was for many years a member of the Subcommittee who wrote it. Section IX is considered a set of rules that must be integrated to obtain successful products. The Book aims to provide clarity and interpretations even to readers whose speciality is not welding. Section IX specifies the requirements for qualification of welders and of the Welding Procedure Specifications (WPS) employed to weld in accordance with both the above Code and with ASME B31 Code for Pressure Piping. The Guide explains that three steps are involved:
The Guide Author advises that most of the confusions among users derive when they work on any of the above documents but apply requirements relative to a different one. He advances his personal opinion that three separate Codes would prevent confusion. The Author declares that the Guide is not official interpretation of the rules. That should be ascertained by asking the Committee and by obtaining guidance from the Jurisdictional Authority involved. Published official Interpretations to the Code by the Subcommittee are not part of the Code but are accepted as a help to understand the Intent of the Code. The purpose of the Guide is indicated as an instructive reference help and to provide insight on the intent of Code requirements. The Introduction explains the scope of the information provided. With its 16 Chapters, 5 Appendixes, numerous Tables and several examples, this Guide is believed to provide essential instructions and useful help in the struggle to comply with all Code Requirements. Download your copy of: An Article on ASME IX Code Changes of Heat Input Calculation was published (11) in Issue 110 of Practical Welding Letter for October 2012, with reference links to two sources. View and download also the Brochure: Readers who find the Guide useful in their work are welcome to comment with their observations for the benefit of fellow readers. Use the Contact Us Form.
8 - Site Updating: Resistance Welding Tips (R), Diffusion Welding (R) The first of the reviewed and updated Pages of this Month deals with Resistance Welding Tips (R), a subject quite complex, as all those responsible for quality production know quite well. As with other demanding processes, constant attention is required, based on complete knowledge of a large base of information, and on experience gained with long hours of work with various equipment. Click on Resistance Welding Tips to see this page. Diffusion Welding (R) is a group of specialized processes to be selected only when an acceptable alternative is not readily available. Complex equipment and long processing times characterize them, together with difficult quality requirements that must be followed. Click on Diffusion Welding to learn the basics of this process and follow the additional links to further important information. To find the pages covering other welding related argument, see the Site Map, or type your query in the Search window appearing in almost every page of this website. Questions, comments and feedback are always welcomed. Don't use Reply, use the Contact Us form instead.
9 - Short Items 9.1 - In a Reverberatory Furnace for melting metal, flames do not impinge on the metal surface itself, but heat is reflected off the walls and roof. 9.2 - Supercooling means cooling slowly a substance below the temperature at which a change of state (freezing) would ordinarily take place, without such a change of state occurring, resulting in a metastable state. 9.3 - Tempered Martensite consists of the decomposition products that result from heating martensite below the ferrite-austenite transformation temperature. Shows higher toughness than untempered martensite. 9.4 - Ultrasonic Frequency is that greater than the highest audible frequency, higher than 20 kHz. 9.5 - Vacuum Casting is a process in which metal is melted and poured under very low atmospheric pressure. Also a form of permanent mold casting in which the mold is inserted into liquid metal, vacuum is applied, and metal is drawn up into the cavity. 9.6 - Woody Structure is the appearance of fractured surfaces of extruded aluminum alloys and of wrought iron, showing elongated features of separation similar to splintery wood. 10 - Explorations: beyond the Welder Everybody Starts Wearing Smartglasses EPA on Keystone XL: Significant Climate Impacts from Tar Sands Pipeline What Boston Showed about Human Nature Obama Praises Future Scientists at White House Science Fair We Need a New Just-War Theory, Which Aims to End War Forever
11 - Contributions: Advancements in Assisted Visual Inspection Visual inspection is the first and most important of the nondestructive evaluation methods of welded parts and of many other industrial products. Inspectors eyes are usually capable of finding visual indications by scanning selected surfaces. Under suitable illumination they can be helped by useful tools like low power lenses or microscopes, endoscopes, boroscopes and other instruments. Particularly valuable for the metallurgical laboratory are stereo macroscopes of various design. Under the pressure of developing tools for automated inspection of mass produced items like Printed Circuit Boards, requiring inspection of thousands of items and of their connections, progress was made in various types of optical instruments. Normal microscopes are generally limited in depth of focus, making them ideal for examination of polished specimens as used for metallography, but mostly useless, at higher magnification, for rough surfaces. The depth-from-defocus (DFD) method, introduced in the 1990s, helps circumventing this limitation, allowing the use of new digital microscopes for the visual examination of very rough surfaces. The method uses autofocusing technique as a means of estimating depth: it has the advantage of less computation time and fewer images to calculate depth. The principle is that, if the amount of blur can be estimated, then it is possible to recover the depth, provided the lens settings are known. Digital Image Correlation (DIC) is another technology that compares images from the same specimen before and after deformation. Without contacting the surface of the specimen, it helps measuring displacement and strain fields, providing high resolution. Another advancement in optical technology is called Electronic Speckle Pattern Interferometry (ESPI) that uses short wavelength lasers. Both DIC and ESPI, when combined with computer controlled digital microscopes, further extend Automated Optical Inspection, widely improving the capability and the productivity of inspectors. With suitable definition of subtle indications at large magnification on rough surfaces, the task of interpretation is eased to the point where, in certain cases, it can be made automatic, by positively separating acceptable from unacceptable features. The advancements reported here will help the increasing presence of modern optical examination instruments on the shop floor. See also the following article. Semi-Autonomous Visual Inspection of Vessels Assisted by an Unmanned Micro Aerial Vehicle (7 pages) 12 - Testimonials [From Spring Survey] I am astonished at the amount of material you have accrued, yet it is all well organized, concise, and linked. There is no filler here. I can tell you have both a passion and a gift when it comes to gaining, organizing, and sharing knowledge. I have no suggestions on how to do better than already being the best personal welding website on the internet. Jesse Gunn
I think PWL is good enough as it is. Christophe Delaere 13 - Correspondence: a few Comments 13.1 - You may recall that readers were invited in the last issue to take part in the Spring Survey. Unfortunately only a handful of kind and obliging correspondents took the trouble to answer, too few to allow any general conclusions. Nevertheless the same few readers expressed their satisfaction with the present publication and did not suggest to improve it in any way. From the scantiness of answers, it appears that the publication of PWL in the present form, despite the appreciation of some readers, does not command the attention of a wide readership. Any ideas on how to reach a larger diffusion? Would you be ready to advertise it to your acquaintances? 13.2 - We are prepared to ready our pages for all Devices (Desktops, Laptops and Tablets, Smartphones), to let our readers browse our pages through the devices they use and like most. But we don't know if this is a real need, or if and how many of our readers would appreciate this opportunity. So please let us know with a short note that you are indeed interested. Use the Contact Us Form. Thanks. 14 - Bulletin Board 14.1 - Pipeline Conf. 14.2 - R&D Building Workshop 2013 - Organized by TWI 14.3 - Corrosion Risk Management 14.4 - Codes and Standards Conf.
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