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PWL#101 - Grab the offer!, Happy New Year!, New Handbook, Substituting Solders, Selecting Al-Mg Fill January 01, 2012 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. 2 January 2012 PWL#101 - Urgent call: Grab the Offer!, Happy New Year!, New ASM Handbook Volume 6A, Substitution of lead based with lead free solders, Filler Metals for Aluminum Magnesium Alloys, Friction Stir Welding Fundamentals, Orbital Welding, Brazing Joint Design (Revised), Microfocus Radiography, Comments on the answers to last issue Questionnaire, Welding related Articles and much more...
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However well
informed and expert you may be, Important AnnouncementFor assembling at no cost your own Encyclopedia Online, Did you miss our Questionnaire? No problem.
1 - Introduction 2 - Article - New ASM Handbook Volume 6A 3 - How to do it well: Substitution of lead based solders 4 - Filler Metals for Aluminum Magnesium Alloys 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article - Friction Stir Welding Fundamentals 8 - Site Updating: Orbital Welding, Brazing Joint Design (R) 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contributions: Microfocus Radiography 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board (Sponsored Links)
1 - Introduction Practical Welding Letter wishes all readers and their families So, after the celebrations for Issue 100, we go back to work, opening this new Year issue 101 with the presentation (2) of a heavy and weighty new Handbook that should be present on the bookshelf of all involved with welding and metallurgy because it deals with Fundamentals. It would be a pity to dismiss it as too difficult, but it should be recognized that a certain effort must be invested in reading and understanding the physics and in absorbing useful lessons. Readers willing to suggest other ways to make use of this Handbook are invited to share their views. Some considerations are suggested in a note (3) to those pressed to change the formerly accepted lead based solders with new Lead Free Alloys. In the next section (4) we report on an article explaining Readers needing more information on GTAW should not miss the first article reported in Section 5. A short article (7) introduces one of the chapters of the new Handbook shown above (2) dealing with Friction Stir Welding Fundamentals. It is amazing how well the process is performing while a complete theory on the Fundamentals is still unavailable. Nevertheless the article points to the directions of research and to the results achieved till now. Then (8) we report on new website pages. The first is on Orbital Welding, a productivity multiplier for the right class of joints, the second is a rewritten and revised page on Brazing Joint Design, with links to practical examples. Microfocus Radiography (11) is addressed briefly, explaining why it may be useful for detecting very fine discontinuities, normally blurred in regular radiography. The Questionnaire published in the last issue, generated some interesting answers from the readers. If you missed it you are urged to take this opportunity as advised before (above the TOC) and let us have your valued answers. Thanks. A short interim report (13) is instructive, although disappointing, in that the silent great majority did not bother to let their voice be heard. The other sections are at their usual place. Your comments and feedback are sought, and possibly your contributions, reflecting your knowledge and experience. Please use the Contact Us Form.
2 - Article - New ASM Handbook Volume 6A I got at last from ASM International my copy of the new, just released ASM Handbook, Volume 6A, titled Welding Fundamentals and Processes, companion to Volume 6 on Welding, Brazing and Soldering (1993). Attentive and interested readers could download the sample Chapter on Hybrid Laser Arc Welding from this volume, from the instructions published at 14.1 in the last issue, PWL#100. Whoever is interested can still do just that. Those wishing to read the Description of the book and to review its Table of Content are invited to enter the Store of www.asminternational.org and to click on the picture of the volume, featured with the Most Popular. It is not a book to be summarized in half a page. As it deals with the Fundamentals it is intended for readers who have time and inclination to study in depth complex subjects, not to those needing a quick fix for some production breakdown. Nevertheless it is essential information for all those wishing to study particular aspects of the science on which the technology is based. It is also an exercise in humility as every expert will find in the book sections or chapters likely to shed new light on insufficiently known subjects. The long list of References appended to each Chapter is an invaluable additional source of information for researchers, students and general public. Such a Handbook could only have been written by a large group of volunteer contributors, each one of them a renowned authority in a related discipline, with a personal history of study and research. Readers wishing to get a feeling for the thoroughness with which every subject is treated in this Handbook are urged to download the sample chapter as explained above. Technical Libraries are certain to procure the book, within their financial constraints, to make it available to their public. In section 7 further down this page an attempt has been made to give a pale idea of the content of one of the Chapters dealing with the Fundamentals of Friction Stir Welding. ASM Handbook, Volume 6A [Note: - Amazingly, the price of this Handbook from this distributor is less than that for Nonmembers from the Source] 3 - How to do it well: Substitution of lead based solders When confronted with the need to eliminate lead based solders from industrial processes, one knows that any replacement of filler material will be more expensive. Also the process, requiring higher temperature, will be more costly. An alternative worth checking, may be adhesive bonding, that in certain cases might be suitable, depending on the requirements, except possibly for electronic connections. One should first explore if any of the lead-free filler metals available on the market has the potential to be acceptable for the application involved. In particular filler metals including silver and/or indium in large proportions are likely to be significantly more expensive. Apart from commercial publications that may be useful, interested readers are referred to a Report issued by the National Institute of Standards and Technology (NIST) for critical evaluation of mechanical property data of lead free solders. See: Users ready to consider silver containing soldering filler metal for the substitute process, have to deal with higher temperatures. More energy must be supplied and more time will it take to heat uniformly the parts, than was needed for the original soldering. The flux has to be examined if its action is adequate and if its elimination after use can be performed properly enough that will not cause corrosion. Finally to evaluate the new process and materials against the former, the mechanical properties should be compared, assuming acceptable discontinuities. Tables of published mechanical properties, if available, may be difficult to find, and the data may not be readily applicable. 4 - Filler Metals for Aluminum Magnesium Alloys As observed repeatedly in this publication, unobtrusive articles are often the most helpful to solve production problems like satisfying qualification requirements. This is especially true when the quoted author is Tony Anderson, a renowned authority specializing in Aluminum Alloy Welding. The article in question was published in the December 2011 issue of the Welding Journal at page 14 under the disguise of a Questions & Answer Column. The question was originated by someone working in the boat and shipbuilding industry who was interested in making sense of the applicability of each one of the four most used filler metals for welding applications involving seven different base metals, all of the Aluminum-magnesium series, used for marine applications. The author clarifies the function of the alloying element magnesium, by explaining that base material strength is directly related to the amount of magnesium in the alloy. However a practical limit had to be introduced, well below the maximum solubility value, because definite intermetallic compounds precipitating at certain temperatures risk to cause intergranular cracking and stress corrosion. After explaining that all these alloys are not heat treatable, the author remarks that whatever higher strength level was developed by work hardening, it is reduced to the annealed condition value by welding. The differences in basic strength offered by the various base materials should be understood, as well as the contribution of the filler metals to the final joint strength. The author alerts that the natural variance of composition between different batches of the same filler metal generally complying with specifications can introduce uncertainty. Besides the general recommendation reported in the article, to use a given table as a help in selecting the recommended type, users are advised to perform their qualification tests even when they believe that a former qualification should still be valid. Readers confronting this kind of problems are urged to look for the original article indicated above. 5 - Online Press: recent Welding related Articles Juggling the variables
of GTAW It Takes Two (LBW & EBW) ESAB Introduces ICE Submerged Arc Welding Technology See the last issue of Fusion Line, TWI Connect - Download Sept-Oct and Nov-Dic 11 Issues - from 6 - Terms and Definitions Reminder High Frequency Seam Welding is a resistance seam welding process in which high frequency welding current is supplied through the electrodes into the workpieces. See High Frequency Resistance Welding.
Induction Soldering is a process where the heat for soldering is obtained from the resistance of the workpiece to the passage of induced electric currents. See Soldering. Laser Beam Drilling is used to machine very small holes, unusual-shaped holes, blind holes, and precisely tapered holes. Also for drilling holes at steep angles, and to process difficult-to-machine materials. See Laser Drilling. Oxyacetylene Cutting is an oxyfuel gas cutting process variation where acetylene is the fuel gas. See Cutting. Resistance Welding Control is a microprocessor driven electronic device, that determines the welding sequence and the timing of critical actions relative to welding current
pattern and electrode pressure and motion, with some form of adaptive feedback control. See Welding Control. Spool is a form of package to be mounted on feeders for holding and supplying filler welding wire coiled on a cylinder flanged at both ends. Torch is a general term to be further defined in relation to the specific process it is designed to handle. Being held in the operator's hand or fixed to a mechanical support, it provides a device for holding electrodes, electrical contacts, power supply, cooling capacity, shielding or active gases in a compact assembly, easy to dismantle for inspection and maintenance. It is designed to guide and to direct the arc, heat or flame precisely where and when they are needed to perform their intended job. Welding Wire is a form of continuous filler metal supplied in coils or spools, for feeding material into the weld pool. Depending on the process it may or may not transmit electric current. 7 - Article - Friction Stir Welding Fundamentals FSW was briefly introduced in this publication in issue 47 of July 2007 (PWL#047), where a link was given to a previous issue PWL#032, summarizing (in Section 11) three articles on the subject from the Welding Journal. A website page on Friction Welding Processes, added in 2008, explains their essential elements. Here we report on the article dedicated to the Fundamentals of the process, as published at page 186, in the new Handbook, Vol. 6A introduced in Section 2 above. It is explained that the rotating and advancing tool introducing friction and deformation heat, causes the plasticization of the base metals, that intermixing perform the welding. Surprisingly it is affirmed in the article that the "Control of the FSW Process is currently thought in terms of process parameters and is not related directly to fundamental deformation mechanisms". It seems a severe judgement on the theoretical, analytical and numerical research reported there in some length, implying that the huge intellectual efforts invested in fundamental research did not yet contribute to practical solutions. Maybe it will, in future. Many studies were devoted to the Thermal Aspects of the process, experimentally trying to measure the temperature distribution around the joint. It was consistently confirmed that the maximum temperature reached with all materials remains constantly well below their Solidus. Heat source estimation and plastic material flow appear to be still topics of active research. Several approaches were suggested, analytical and numerical, following different assumptions, but it seems that, for the time being, no theory is yet considered complete and acceptable. A large part of the studies is devoted to understanding the origin of defects in the joints, to provide better means to control processing parameters. In particular efforts were done to map the defects against parameter changes, to obtain empirical guidelines conducive to successful welds. The important process parameters determining friction stir welding quality and absence of defects are listed as "Tool rotational rate, tool traverse speed, axial pressure, tool tilt angle, tool geometry and gap between plates". Results reported show how the parameter changes influenced welding outcome. The article then summarizes research aimed to develop theoretical models of defect formation. It points out however that, despite the large amount of experimental and theoretical data available, "the exact nature of material flow is not known due to the complex nature of thermomechanical conditions during welding", precluding in the meantime proper understanding of defect formation. Different attempts are reported intending to describe the strain and strain rate undergone by deformed material, necessary to understand the microstructural evolution, but it is recognized that the estimates proposed involve considerable simplifications and assumptions, which may explain the difference from reported values. Further work is needed before better models will be available. The last part of the article describes the microstructure of Friction Stir welds and its dependence on many factors. Three different zones are singled out in a typical cross section. The central stir region known as weld nugget, a thermomechanically affected zone (TMAZ) and a heat affected zone (HAZ) are defined. Recrystallization, grain growth and precipitate distribution depend on the amount of deformation incurred in the different zones and on the time at temperature. General observations are reported from a few research papers. The nugget is the most worked zone, generally fine grained but not uniform, and consisting of subdomains. In the TMAZ recrystallization does not occur because of insufficient deformation, but it contains grain subboundaries. The HAZ grain structure is quite similar to that of the original base metal. The conclusion seems to be that the practical results of FSW process applications are largely in advance of satisfactory understanding of Fundamentals. Upon reaching more complete knowledge, the determination of initial parameters will probably become easier and adaptive automatic process control will be feasible. Until then more complex and difficult applications will continue to be developed as before, by trial and error. 8 - Site Updating: Orbital Welding, Brazing Joint Design (R) The Pages of this Month add some information that may be useful to readers needing it. The first introduces Orbital Welding, a mechanized process with a long history of successful applications, capable to improve productivity and to reduce the number of skilled welders needed for the job. Expert welders though are not made superfluous, they become responsible for setting up, for supervising and for troubleshooting the regular operation of the process. While not new, it is a most successful process for applications requiring several identical joints in tubes or pipes, to be welded to demanding requirements. The new page can be visited at Orbital Welding. The other page is an older one remade, edited and updated. The same revision is probably needed for several other pages that were written long ago and never critically examined again. The program is to dedicate time and effort to make most of the website pages interesting and useful. Anyhow the page on Brazing Joint Design was practically written anew. It is explained that joint geometry is only one of the critical factors responsible for successful brazing, and that design must take into account fabrication methods and service conditions. Links are provided for publications showing examples of good design. Experience is achieved by following good suggestions and by studying the outcome of both successes and failures. Find the revised page at Brazing Joint Design. New and revised pages are listed in the Site Map and in the Index Page, that may help in finding the subjects sought. As they are published, they appear in the Blog page. When looking for information, also the Search facility appearing in almost every page may become handy. Send us your needs, wishes and feedback by using the Contact Us Form. 9 - Short Items 9.1 - Air-hardening Steel contains sufficient carbon and other alloying elements to fully harden to untempered martensite structure even in large sections, upon cooling slowly in air from a temperature above its transformation range. See Tool Steel Welding. 9.2 - Blasting or Blast Cleaning is a process for cleaning or finishing metal objects by removing dirt, rust, paint and other soil by the impingement of suitable abrasive particles on the workpiece surface. See Abrasive Blast Cleaning. 9.3 - Consumable Electrode Remelting is a metals refining process in which an electrode made of the metal to be refined is molten drop by drop by the heat of an electric arc and solidifies as an ingot of refined metal, in a water-cooled mold. Refining occurs from interaction of molten drops as they fall through atmosphere, vacuum, or molten slag. 9.4 - Enantiotropy is the relation of different crystal forms of the same substance in which one form is stable above a certain temperature and the other form is stable below that temperature. Ferrite and
austenite are enantiotropic in ferrous alloys. See Welding Metallurgy. 9.5 - Metallograph is a special purpose optical microscope for the observation of opaque metallic specimens suitably prepared. Variable magnification ranges from about 25x to 2000x. Illuminators provide high intensity white or color filtered light, bright-field, dark-field, polarized light, phase contrast, oblique illumination. Digital photography, image enhancement and application of quantitative metallographic techniques are usually available in modern instruments. See Digital Imaging (7) at PWL#091. 9.6 - Reactive Metals like titanium, zirconium, and beryllium readily combine with oxygen at elevated temperatures to form very stable oxides. They also become embrittled
by the interstitial absorption of oxygen, hydrogen, and nitrogen. See Titanium Welding. 10 - Explorations: beyond the Welder Does the “Goddamn” Higgs Particle Portend the End of Physics? Marc Andreessen: Predictions for 2012 (and beyond) A real flying car in 2012? Are Cyber Threats A Mere Nuisance? SBI! Does it work? See the Proof 11 - Contributions: Microfocus Radiography It was long known in the history of development of radiographic (X-Ray) non destructive examination, used for inspection of weldments, that the Focal-Spot Size has a major influence on the radiographic definition of the smallest discontinuity discernable in a photographic plate. Definition depends, besides on focal spot size, also on geometric relationship between source to image distance and object to image distance. Ideally the highest definition could be attained by a point source of zero focal spot size. In practice, in a normal X-Ray vacuum tube for industrial use, the focal spot is a well defined region, measurable in a few square millimeters, called the Target of the anode, usually made of water cooled Tungsten. There X-Rays are generated by stopping a stream of accelerated electrons impinging on it. Because of the size of the focal spot, areas of interest, representing the projection of discontinuities, which are the purpose of radiographic inspection, result partially blurred by unobstructed radiation from other parts of the same focal spot. The degree of Geometric Unsharpness is the size of the area of partial shadow (penumbra). To reduce it to a practical minimum, as needed for the evaluation of the smallest detectable discontinuity, the focal spot size had to become as small as possible and still produce an acceptable amount of suitable x-radiation. The size of useful focal spots for high definition radiographic inspection is now measured in microns (thousandth of a millimeter), say one to five microns, where from comes the name of this nondestructive inspection technique. Microfocus Radiography is used for evaluating weldments in critical, relatively thin tubings or parts. In particular it is used for examining welds in high pressure hydraulic lines, in tube to plate welds of heat exchangers and wherever fine discontinuities must be detected (such as in ceramic parts). In the electronics industry where miniaturization has reduced the size of applications and multiplied production, small joints must be inspected to assure the increased reliability required. Microfocus Radiography, combined with digital image enhancement, is used for process control and for failure analysis to pinpoint the tiniest discontinuities. Film processing is by now obsolete by the development of digital imaging, that permits evaluation in real time, reporting, storing and transmission of images. Combined with computer tomography (that permits to view sliced sections of objects), with magnification systems (radiography at microscopic level) which depends on the sample position between the X-ray source and the intensifier, and with real time recording of reactions or processes, Microfocus Radiography has reached maturity unknown of only a few years ago. Experimental applications now strive to achieve even higher resolutions by reducing still more the already small size of the focal spot to nano dimensions, for more advanced applications and uses. 12 - Testimonials Date: 01 Dec 2011, 07:31:49 PM Name: Jim Bauer Questions and Feedback : I am a retired exec and a hobby welder puttering
around my shop and boat with stick and MIG. Then I call in a pro..... Thanks for the knowledge Jim Bauer
From: Abi Joseph Dear Elia Levi, I am an avid reader of your mails and [it] is indeed quite informative. I am the Executive Director of [...], where we manufacture various kinds of Ferro Alloys and Base Metals. [...] [...] With Kind Regards, Abi Joseph
13 - Correspondence: a few Comments The answers to last issue Questionnaire I got from nine Countries were highly positive. It is unfortunate though that only a tiny minority of the recipients of Practical Welding Letter took the trouble to answer at all. To all of them I repeat my sincere thanks. It was most encouraging to find that all the correspondents asked to continue publishing the newsletter, sometimes with warm expressions. Also the links to online resources were kindly acknowledged as useful, and the question on how to improve this publication was largely considered redundant. I know it is not exactly so, but readers' contributions are hard to come by. The question if readers would be ready to contribute from their own experience got mixed answers, as about half of them declined (they undervalue their capability), while the rest affirmed their availability but did not attach any note nor any specific promise: I am glad that they feel inclined to write and I can only repeat my invitation to just do it. It would be nice to have some sort of dialog with all readers who feel they can share ideas, opinions, wishes and proposals, to enhance the usefulness of this publication. But I don't quite believe in the Forum format, at least for technical questions. What do you think? Send your feedback. Almost all correspondents assured that they got occasionally some practical help from their reading. Unless they only try to be kind to me, without a real reason, this is the best reward I can get from my readership for the work I do here. I would appreciate if readers could quote the specific piece of information that helped them overcome their difficulty. I think I should repeat some sort of Questionnaire at least once a year and I should probably offer some sort of tangible reward for those who are so kind to answer. I appreciate your involvement. Those who missed the Questionnaire but are now ready to answer will find the link just above the TOC. If I continue to write and publish, will you continue to read? 14 - Bulletin Board 14.1 - SSPC 2012 Greencoat. 14.2 - The Manufacturing Expo. 14.3 - FABTECH Canada 2012. 14.4 - Tube 2012, Int’l Tube and Pipe Trade Fair. 14.5 - AWS Welding Buyers Guide 14.6 - Two Filler Metal Specifications Updated, Revised editions have been released: ANSI/AWS A5.14/A5.14M:2011
AWS A5.23/A5.23M:2011 14.7 - Questions about SBI Business?
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