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PWL#109 - Oxy-Fuel Flame Safety, Developing Laser Welding Procedures, Filler Metals for Active Metal August 30, 2012 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. PWL#109 PWL#109 - Safety with Oxy-acetylene Flames, How to develop a Laser Welding Procedure, Filler Metals for Active Brazing, Clad Brazing Materials, Corrosion Protection under Insulation in Steel Piping for Petrochemical Industry, Brazing Graphite, Hardness Test and much more...
September 2012 - Practical Welding Letter - Issue No.109
It can be found however either in the Welding Resources page, or by clicking directly on Bulletin 76. DON'T USE REPLY to send your messages! Use Contact Us instead.
You are urged to pass-along this publication to your friends, if 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 - Safety with Oxy-acetylene flames 3 - How to do it well: How to develop a laser welding procedure 4 - Filler Metals for Active Brazing 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article: Clad Brazing Materials 8 - Site Updating: Brazing Graphite (R), Hardness Test (R) 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contributions: Corrosion Protection 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board 1 - Introduction Hoping that you all enjoyed pleasurable and refreshing vacations, this new back to work Issue 109 of Practical Welding Letter for September 2012 opens with a call to Safety when using oxy-fuel flames. Serious attention should be devoted to equipment, people, training and discipline. An innocent question asking just for a complete laser welding procedure, is answered by exposing the development program required to obtain the essential parameters by trial and error. The same lengthy and laborious preparation work may be required also for other processes. Active brazing is not new: reference to a serious and expensive practical project reported in the note in Section 4, may cast some light on how to deal with demanding applications. Similar basic attitudes should be considered also for simpler endeavors. Integral brazing material clad upon base metals may simplify assembly operations and reduce costs: it should be considered, when available, as a suitable solution for mass produced brazed items. A practical application of thermal spray to prevent corrosion under insulation in steel piping for Petrochemical industry installations, is universally claimed as being satisfactory and economic. An article referred to in Section 7 explains how investing in people, procedures and training can realize hefty maintenance gains if performed consistently with due care to all details. The website pages of this month are reviewed and updated old versions. One deals with Brazing Graphite, the other with Hardness Testing. Requests and feedback from readers could contribute to make the information collected here more practical and useful. DON'T USE REPLY for letting us have your comments, click on Contact Us instead. Other common columns are found where you would expect them. To remain updated with new pages, browse regularly through the Site Map, the Index Page or subscribe to our RSS service just below the NavBar in every page, to be advised on new and revised pages. 2 - Article - Safety with Oxy-acetylene flames It is never redundant to review from time to time the essential safety rules to be always applied when working with oxyfuel flames, especially when it is wrongly assumed that all is known and self evident. It is the consistent and thorough application of the rules that must be enforced and verified on all involved, as expression of responsible behavior. A nice presentation is offered in the recent publication of an article on this subject that can be seen at page 48 of the August 2012 issue of the Welding Journal. Although the article is from the manager of a commercial firm, the insights are applicable to handling of equipment of any manufacturer, and should be rehearsed periodically. Readers for whom the information may be useful, are urged to seek the original publication quoted above, and to review the application of the exposed principles in their routine work. Furthermore this commercial company offers a no cost instructive video DVD, and additional documents including checklists for best practices, a guide on how to conduct a successful seminar, and more. To request a free copy, contact a Victor Technologies district manager at Reference to this source can be found also in our Bulletin 39 page at Resources on Training DVD and Video. 3 - How to do it well: How to develop a laser welding procedure. Question: I have a small 11.5 gauge T-304 SS Tubing and need to weld a clean solid bead all the way around to a 17-4 SS Insert with a 100W Co2 Laser. Answer: Unfortunately the question above cannot be answered to give a real, practical procedure applicable to the set-up indicated above, or for that matter to any set-up at all. It should be noted that the joint configuration is not described in sufficient detail and that no requirements are spelled out to convey the important elements for quality evaluation of results. The request of specific parameter values for process variables, as if a single solution was possible, ignores the fact that the actual selections influence each other in subtle ways: it indicates that the inquirer is not alert to the practical aspects of the development process. Even if a numerical simulation program was available providing tentative settings for starting trials, nonetheless physical test runs would be required to permit refinement and fine tuning of the real values. One should be aware of the empiric fact that different combinations of independent process variables or welding parameters may be found to give acceptable results. A thorough development program should explore most of the possible procedures, among which the most suitable would then be selected. Also one should examine if Laser Beam Welding (LBW) is indeed the most suitable process for the job or if the choice was only dictated by the availability of this equipment. The right way to find a suitable answer to the question above is to set a development program to be carried out on scrap material, and to be prepared to change the parameters by small amounts, in sequence, until an acceptable weld is obtained. A thorough treatment of this subject can be found at page 556 of ASM Handbook Volume 6A under the title "Laser Beam Welding". The article above (14 pages) can be purchased online from ASM: The first parameter to be selected is the actual power density, depending not only on the equipment output, but also on beam diameter and its spatial distribution. Also position and depth of focus relative to the workpiece surface affect the value obtained. The equipment may provide pulsed or continuous wave laser. Depending on the welding results, the tentative selection of a definite mode may indicate which one seems to be more promising. Previous experience with the equipment could help in selecting a tentative power value (maybe around half of the maximum power available) that will give an acceptable static or low speed weld bead without too much spatter and without burning through. Interaction time describes the time a certain spot of the workpiece is under the laser beam. The speed selected affects this time, the weld profile and the depth of beam penetration. The interplay between power and speed determines weld shape, penetration and microstructure, that will be evaluated by performing metallographic examinations of cross sections through the weld. During this exercise one could play around with focal spot and beam diameter, to find suitable starting parameters. Power could then be raised gradually until acceptable values are found. Then the total heat input can be decreased if desired, by introducing pulse-width modulation. If filler metal is required, type 308L could be selected and preplaced on the joint. Preliminary welding tests can be performed in air. Production welds can be protected from discoloration by a stream of low pressure flowing argon directed to cover the weld area. Once the visual results indicate that a suitable procedure is reached, one should perform and check if all requirements are met. The outcome of the tests may require further refinements of the procedure. 4 - Filler Metals for Active Brazing A short note on this subject was published (4) in issue 97 of Practical Welding Letter for September 2011. Click on PWL#097 to read it. Active Brazing was dealt with also in the Mid August 2011 Bulletin 64 on Ceramic Brazing, published in the second part of PWL#096. Our Website Pages on Brazing Graphite, on Brazing Ceramic and on Brazing Titanium provide basic information on the issues confronting those who need to employ these technologies. A recent article published at page 25 in the August 2012 issue of Advanced Materials and Processes, an ASM International publication, reports on a complex project involving manufacturing of a special item made by brazing titanium to graphite. Although the application was for fundamental research on elementary particles known as neutrinos, the basic lessons learned during process development confirm that the technology used for brazing titanium to graphite with active filler metals is mature and suitable for industrial projects. It appears however that despite the considerable experience of the company involved, many tests had to be performed to come up with satisfactory solutions. Testing should therefore be considered as an essential part of any development program. Interested readers are urged to seek the original article indicated above. 5 - Online Press: recent Welding related Articles Welding Equipment and Consumables for the Power Industry Laser welding process devised for large-area protective layers EWI (Edison Welding Institute) sparks innovative approach to training welders Pushing the Productivity Envelope with Strip Cladding High Deposition Welding for Shipbuilding 6 - Terms and Definitions Reminder Electrode Force is that applied in resistance welding to the workpiece by the electrodes in order to make spot-, seam- or projection-welding. It is an important schedule parameter to be specified for any specific job. Follow Up in resistance projection welding describes the ability of the upper (movable) electrode, to maintain contact with the deforming workpiece, to assure a sound weld. Gouging, a Thermal cutting process, is used to remove partially or totally a weld (typically defective), by melting or burning it, to form a bevel or groove for further welding. Hammering, in resistance spot welding, is the workpiece surface condition resulting, at the start of the welding cycle, by excessive electrode impact. Initial current, in pulse welding, is that applied at start, but before establishment of high level pulse welding current. Laser Beam Diameter is the dimension of a laser beam circular cross section at a specified position along its axis. Metal Bath Dip Brazing is a variation where brazing is performed by dipping workpieces in a bath of molten filler metal that usually contains a floating layer of flux to prevent oxidation. Procedure is the detailed description of the elements of a process or method to be employed in a given job to obtain the specified results. 7 - Article: Clad Brazing Materials For certain mass production fabrications by furnace or dip brazing, it is advantageous to have the brazing material already in place, as a thin layer clad on the base metal. This is true especially for complex assemblies like heat exchangers featuring a large number of similar joints. Using Clad Brazing Materials when applicable, one reduces part count (by eliminating filler metal preforms) and one simplifies assembly. Typical are aluminum brazing alloy (of the series BAlSi) clad to brazeable aluminum sheet or strip by roll bonding, (dip brazing is common in a molten flux bath) and also copper clad stainless steel sheet. See Roll Welding. The metallurgical bond between the clad layer and the base metal assures protection from oxidation and contributes to the success of the brazing process. These Clad Brazing Materials can be formed by usual cold forming processes, cleaned and assembled for brazing without additional brazing filler metal. Flux may or may not be needed depending on the actual materials and on the furnace atmosphere. Among the advantages listed for the use of Clad Brazing Materials when applicable, one remarks the following:
These benefits are especially valuable when product design is centered on the use of clad materials. In this case tighter tolerances can be prescribed and the process becomes more reliable. Readers with first hand experience with application of clad materials are invited to write a short note on he subject, to be published in a later issue of this letter. 8 - Site Updating: Brazing Graphite (R), Hardness Test (R) The Pages of this Month are updated versions of older publications, dealing with the issues indicated in the title. Although no major changes are introduced, links and references are checked again and verified. As mentioned briefly in section 4 above, Brazing Graphite may be the preferred joining process for demanding applications. The revised page provides an overview of the problems and of the methods to overcome them. See the revised page at Brazing Graphite. The new page on Hardness Test reviews briefly the main hardness testing methods used in the metal industry and explains why it is important to know the hardness of whatever one needs to weld. Of course a more complete treatment can be found in my book on Practical Hardness Testing Made Simple, available at no cost by subscription. Nevertheless the page represents a concise summary of essential facts, and now it provides links to a few Videos that show how hardness testing is performed in practice. For searching the Welding Advisers Website, besides using a search engine, one may use the Site Map and follow updates by subscribing to the RSS service under the Navigation bar on the left side of every website page. 9 - Short Items 9.1 - Strain Aging is a microscopic mechanism related to solid-solution strengthening that shows changes in ductility, hardness, yield point, and tensile strength occurring when a metal or alloy that has been cold worked is stored for some time. In steel, strain aging is characterized by a loss of ductility and a corresponding increase in hardness, yield point, and tensile strength. 9.2 - Tolerance Limits are the extreme values (upper and lower) defining the range of permissible variation in size or other quality characteristic of a part. 9.3 - Ultra High Strength Steels designation is arbitrary because no universally accepted strength level for the term has been established. Nevertheless this class of Structural steels is usually intended to include those with minimum yield strengths of 1380 MPa (200 ksi). 9.4 - Vibratory finishing is a deburring process where the parts to be treated are vibrated in a container including also an abrasive compound. 9.5 - Wrinkling is the waviness produced in formed or deep drawn sheet metal parts, between the edge of the flange and the draw radius, due to unbalanced compressive forces. 9.6 - Yield is evidence of plastic metal deformation. It is also the percentage of acceptable product items from a given production run relative to the quantity produced. In foundry practice it is the ratio of casting weight to that of all the material poured in the mold. 10 - Explorations: beyond the Welder Lifelike, cost-effective robotic Sandia Hand (with Video) Microwave laser fulfills 60 years of promise (with Podcast) A Dash of Color Creates Camouflage for Spineless Robots (with Video) Has the Time Come to Try Geoengineering? Black Holes to the Rescue 11 - Contributions: Corrosion Protection Petrochemical industry installations confront severe corrosion issues especially for items under insulation. Although the problems develop after years of operation, the need to shut down equipment for maintenance increases costs and limits availability. Long time experience all over the world demonstrated that properly conducted Thermal Sprayed Aluminum (TSA) on carbon steel assures suitable corrosion protection, provided it is correctly applied on clean surfaces. An article published at page 46 in the August 2012 issue of Advanced Materials and Processes, an ASM International publication, in the International Thermal Spray & Surface Engineering supplement, mentions the applicable international standards and advises on investing in people and equipment. Due attention has to be paid to quality control and to safety procedures. Correct application of TSA is likely to reduce maintenance costs. Interested readers are urged to seek the original article indicated above to gain the most from the author's experience. 12 - Testimonials On Sat Jul 28 07:57:55 2012, the following results were submitted from the "Form 5" on welding-advisers.com: Name: Nick Wilder 13 - Correspondence: a few Comments It is a good thing that readers ask Welding Advisers their questions. Unfortunately not always the questions are such that a short answer is all the inquirer needs. I get requests for help on spare parts and operating instructions on some equipment from obscure manufacturers. Other than trying to locate the manufacturer there is not much I can be helpful about. Sad to say, most readers will not follow up informing me if my help was useful. The question asking for parameters for laser welding was also unsuitable for a straight answer. It was dealt with in Section 3 above. Another reader asks for "the maximum allowable convexity in the cap pass (final pass) in submerged arc welding of pressure vessels according to ASME Sec VIII" without giving a clue if it is an hypothetical question or if it refers to a production problem. Readers who browse even occasionally in my website should know that I don't sell equipment. Nevertheless I receive a seven pages specification for a complete system including setup, acceptance and training... Informative answers can only be given to practical and detailed questions. 14 - Bulletin Board 14.1 - 2012 International Conf. on Advances in Materials Science and Engineering. 14.2 - Sheet Metal Welding Conf. XV. 14.3 - AWS/GSI Conf. on U.S. and European Welding Standards: 14.4 - Explore the best overall introduction to SBI! 14.5 - Visit Now the BlockBuilder 2 Page Get Ready for a New Start!
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