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PWL#043 - Huge Savings, Thickness of Cutters, Brazing Aluminum/Steel, Incompatible Materials, more.. March 01, 2007 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. PWL#043 - Huge Savings in repairing expensive Scrap Parts, Thickness Range of a Plasma Cutter, Brazing Aluminum to Steel, Joining incompatible Material Combinations, Cold Welding, Contribution: Welder Shortage, Comments and more...
This publication brings to the readers practical answers to welding problems in an informal setting designed to be helpful and informative. We actively seek feedback to make it ever more useful and up to date. We encourage you to comment and to contribute your experience, if you think it may be useful to your fellow readers. Click on Contact Us
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1 - Introduction 2 - Article: Huge Savings in Repairing expensive Scrap Parts 3 - How to do it well: Thickness Range of a Plasma Cutter. 4 - Filler Metal for brazing Aluminum to Steel 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article - Joining incompatible Material Combinations 8 - Site Updating: Cold Welding 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contribution: Welder Shortage 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board
1 - Introduction This is our 43th issue of this newsletter. The voluntary task to publish once a month the Practical Welding Letter is both challenging and rewarding. We learn and enjoy by researching the current literature and by finding interesting news in technology and in materials and applications to report. We start the present publication by presenting a new way of salvaging expensive items that cannot be repaired by current techniques, too aggressive to be useful. The new technology may be expensive but at half the cost of new parts the repair may still be not only affordable but really economic. Then we offer a manufacturer's answer on a practical question regarding the operation range of plasma cutters. In the filler metal department we are talking of innovative technologies, not only of materials, for brazing aluminum and steel together, a challenging task researched by automotive manufacturers. Then we continue with the general problem of welding incompatible material combinations. One should first recognize the problem and then study the ways out of it, either by a change of materials or by process substitution. The Page of this Month brings you a classic process, Cold Welding, which can be quite successful for suitable applications. In the Contribution we report on a growing concern for many expanding industries, Welder Shortage, and on what is being done to mitigate its impact. Other departments can be found at their usual place. Is this PWL interesting and useful to you, our reader? Please take a few minutes to comment, let us have your feedback by e-mail. Click on Contact Us. Don't miss..., at the bottom of this page, the 3 minutes SBI! TV Show.
2 - Article: Huge Savings in repairing expensive Scrap Parts Hold on! Don't put the Red Tag on that part! Don't throw it yet to the junk yard heap! Next time you have an expensive part to scrap, mismachined or just worn out, wait a moment: it might be salvaged with the technology presented here. Laser power sources are used to fuse deposited metal powders for Near Net Shape freeform fabrication, for repair of worn out expensive metallic components and for cladding of wear resistant alloys upon common material substrates. The introduction of optical fibers for laser beam transmission greatly simplified the construction of the special heads built to perform this kind of operations. The integration of numerical control based positioning machines realized the means of performing the process. Development programs originating from initial experiments made by the Sandia National Laboratories were conducted with federal funding by teams that included commercial companies and other agencies. The deposited material, fused by very low heat input, is bonded metallurgically, entails minimum dilution and distortion, causes a thin heat affected zone and, due to the high cooling rates, produces very fine grain structures that exhibit remarkable mechanical properties. Current equipment is used in the power ranges from 0.4 to 3 kW, with laser spot sizes from 1 to 4 mm. Powder utilization percentage and deposition rates vary widely depending on the actual parameters employed. Stainless steels, nickel and copper alloys, titanium alloys and hardfacing materials are successfully deposited with this technology. Only aluminum and copper, due to their high reflectivity, cannot be deposited efficiently. A recent review published in the Welding Journal of January 2007 at page 44 reports on numerous successful repair applications. In particular delicate surfaces of bearing housings and labyrinth seals of gas turbine engines could be salvaged from their scrap condition (nonrepairable by conventional techniques), at half the cost of a new part. The article lists also at least two commercial firms accepting repair jobs from the outside. By the use of improved filler metal powders one can obtain, in the repaired portion of the item, higher hardness and better wear resistance properties than those of the original part. The technology, originally developed for aerospace industry and for defense projects, is slowly spreading out to commercial industries. It is often necessary to perform suitable qualification work to demonstrate the adequacy of the proposed repair procedure. It is affirmed in the above mentioned article, that important savings could be introduced also in primary manufacturing by simplifying forgings or castings and by reducing the material required, if the laser technology is used to add freeform appendages only where needed. Could this be of practical interest for you? Would you explore the technology for your applications? Let us have your comments. Write a short note and send it by e-mail. Click on the Contact Us button in the Navigation Bar on any page of our website (www.welding-advisers.com). An article on Laser Beam Welding was published in Issue No. 13 of Practical Welding Letter for September 2004. Click on PWL#013 to read it. The Mid Month Bulletin for September 2006 offers a great number of online resources on Laser Technologies. Click on PWL#037B to read the Bulletin. For the complete collection of online welding and material information click on Weld Resources.
3 - How to do it well: Thickness Range of a Plasma Cutter Q: The capacity of a certain cutter is noted as 1 1/2" Manual and 3/4" mechanized. Why would the performance be cut in half when using a machine torch rather than a hand torch? A: Plasma machines that can handle both manual and mechanized tasks usually have a lower thickness rating for mechanized cutting rather than manual. This is for several reasons. Starting and ending the cut on materials close to the maximum thickness properly requires some operator technique that is easy for a human operator but difficult or impossible to program into a machine. Hence a lower rating for satisfactory cuts. Mechanized cutting requires piercing in most cases rather than edge starts. A machine generally can not pierce successfully as thick as it can cut. Customers using a machine in an automated set up would generally find the cut speeds on the thickest materials too slow to be acceptable for mechanized operation. Note: This answer was supplied by B. Fernicola from ESAB, USA.
4 - Filler Metal for brazing Aluminum to Steel Aluminum and Steel are incompatible materials, when it comes to fusion welding them together. The main reasons are:
Furthermore the significant differences in thermal expansion, thermal conductivities, and specific heats are expected to generate important welding stresses that compromise the soundness of the welds. The two materials can be joined successfully by solid state processes (friction-, ultrasonic-, magnetic pulse-, explosion-welding), by brazing, by high energy process and by adhesive joining (besides mechanical fastening). Two Companies that promote process development for automotive manufacturing, were engaged in research for practical means to obtain suitable joints between sheets of aluminum and steel. They published the success obtained with their efforts. However they did not disclose much of the technical details. Nevertheless we publish hereafter the reference to their work so that interested readers might be able to contact them if they wish and to explore if their approach could solve their own specific problems. The first Company is FRONIUS International GmbH from Austria, (www.fronius.com) originators of a process they call "Cold Metal Transfer". Type "CMT" in their search box in order to get links to their publications on this subject. The second Company is CORUS Automotive We will publish updates on this interesting subject when available.
5 - Online Press: recent Welding related Articles From AWS: From Lincoln Electric: From TWI: Novel technologies for repair and refurbishment From Olympus:
6 - Terms and Definitions Reminder Direct Current Electrode Negative (DCEN) describes the connection of a direct current welding power source, where the electrode is in contact with the lead joined to the negative pole. Direct Current Electrode Positive (DCEP) describes the connection of a direct current welding power source, where the electrode is in contact with the lead joined to the positive pole. Edge Joint is the configuration where two or more parallel components touch at the edge, while being placed from the same part of a plane running on the common edge and perpendicular to the interface. Furnace Brazing is a brazing process, generally using a protecting atmosphere, where parts to be brazed, with preplaced filler metal, are heated in a furnace to the brazing temperature and then cooled to room temperature. Groove is the space to be filled with a weld between components arranged for a butt joint. Impulse in resistance welding is the complete succession of current pulses included in the heating portion of a welding cycle. Oxyacetylene Welding is a process utilizing the heat of a flame issuing from a welding torch where oxygen and acetylene gases are mixed in the correct combustion proportion, for melting base and filler metal to create coalescence of the welded parts. Transferred Arc in plasma arc welding is the plasma arc struck between the electrode and the workpiece, which completes the electrical circuit.
7 - Article - Joining incompatible Material Combinations On the subject of (compatible) dissimilar welding we published a few articles now available in our FAQ Page, where indications are given on how to proceed for obtaining best properties. When it comes to dissimilar metals welding however, there are some combinations that, no matter which procedure is used, they simply will not stick together. If we have to confront such a situation we should just stop a moment to consider the problem. Two elements concur to generate the difficulties:
In other words, if the combination of materials cannot be changed, then we may have to look for a more favorable process. If it is the process that cannot be changed, then we should explore the possibility of changing at least one of the materials or to insert in-between a third material whose presence is acceptable to both the given materials. We should examine both issues to find out the solution for the problem at hand. An example of such a problem and of particular solutions, was discussed above in Section 4. But here we are considering the general case. 1- Materials If we know that our problem would be solved by substituting one of the two materials with another one more favorable to the process, we should seriously consider the possibility of implementing the change. Otherwise we should study if by interposing a third material, acceptable by both the present ones, more favorable combinations are achieved. The transition can be done by buttering (covering) the surface of one of the materials to be welded with a special electrode. That clad surface is then welded to the other material. As an example, welding mild steel to stainless steel can be done by buttering the mild steel with a suitable stainless that will not cause dilution problems. The covered surface will then be readily welded to the austenitic stainless steel. 2 - Processes Most of the problems are generated by fusion welding processes, because the metallurgy of the original material combination may not allow the production of sound joints. Such problems arise when there is a great difference between the melting temperature of the two materials, when there is no appreciable solubility of either metal in the other in the solid state and when brittle intermetallic compounds are likely to form. Difficulties are quite probable also when there is a wide difference between thermal expansion coefficients, thermal conductivity and specific heat of the two materials respectively, because of development of significant stresses in the weld. We should be ready to consider if adopting another more suitable process for the material combination in cause would give an acceptable joint with the required properties. Joining processes capable of permitting connections of adequate mechanical properties and sufficient resistance to service conditions should be looked for within the following list:
Sometimes a mixed solution is preferred as in the following example. If a copper tube has to be welded to an aluminum tube, a bimetallic transition part is procured, half made of aluminum and half of copper, friction welded together. This transition part is then arc welded twice, so that the copper side faces the copper tube and the aluminum side faces the aluminum tube. The same considerations apply when aluminum is to be joined to steel or stainless steel. If applicable, solid state processes should be preferred, taking into account special joint requirements (i.e. overlap, when needed) for each one of those listed above.
8 - Site Updating: Cold Welding This time the Page of the Month deals with a quite special process that is used in particular industries. It is a mechanical type of joining using high pressure and ductile deformation of materials to obtain a metallurgically sound joint without using electrical energy or heat. Although looking technologically not sophisticated it can be the perfect process for suitable applications. See the new page at Cold Welding. Website pages are regularly updated with new information when available. See the Site Map when looking for answers to your problems. Visit the Weld Resources if you have not yet seen them. They present a wealth of information readily available online. Let us have your comments and feedback by clicking on Contact Us.
9 - Short Items Contact Fatigue is the damage, appearing as cracking and pitting, occurring on surfaces subjected to alternating pressure stresses such as those produced under rolling and/or sliding contact in rolling element bearings or in gears. Controlled Atmosphere is a specified inert gas or mixture of gases of a given composition and properties at a predetermined temperature in which certain processes take place. Heat Sink is a material that absorbs or transfers heat away from a critical element or part to protect it from damage. Impurities are elements or compounds whose presence in a material is unwanted and possibly harmful. These minor constituents or components are tolerated if less than some established level. Optical Emission Spectroscopy is an analytical technique that measures spectra emitted by excited atoms and ions with optical transitions in the optical wavelength range from ultraviolet, visible light and near infra-red. Permanent Set is the residual deformation remaining after an elastic material has been stressed mechanically and then released.
10 - Explorations: beyond the Welder Global Warming River Renewal MyLifeBits Project http://research.microsoft.com/barc/MediaPresence/MyLifeBits.aspx Tweel - Airless Tire
Isla de Vieques,
11 - Contribution: Welder Shortage The Editorial in the Welding Journal Issue of January 2007, written by AWS President Gerald D. Uttrachi, raises a pressing problem for industry in the USA, and probably in the whole world. It addresses the Welder Shortage already felt, and the prediction than huge numbers of qualified workers will be missing in a few years from now, as it appears that far fewer welding students take the training to prepare themselves to replace the aging people that go into retirement. But the industry expansion makes the mere replacement inadequate to assure the required workforce needed for future growth. Various organizations are taking initiatives to set up new schools and to advertise the new careers they propose to the young and unaware students that look into promising opportunities. Such enterprises should be multiplied and encouraged if fabricators are to attain tangible results in a few years time. One untapped source of suitable prospect students has been identified by the observation that only 5% of welders in the USA are women. Many more women could probably be recruited by dedicating concerted efforts to promote this issue. The high demand situation is encouraging in that it may assure better paid jobs and the continuing need for the next level of competence and expertise. The career of ambitious welders, who may wish to become robotic welding technicians, inspectors or specialists in other disciplines, is therefore expected to grow and prosper. AWS initiated in 1989 an Education Foundation that yearly provides hundreds of scholarships to welding students. To increase the offer of trained welders, many more scholarships should be made available for distribution. Caring fabricators and concerned industry leaders could help improving the strength of the welding workforce by joining in and by donating liberally to the AWS Foundation or to similar initiatives.
12 - Testimonials From: marlon alajas (email address removed for security) Feb.05,2007 Thanks,
From: Eliezer Kiselnik (email address removed for security) Thanks for the answer, It will be a pleasure to use your knowledge if needed. REGARDS 13 - Correspondence: a few Comments It is well known to the readers of this newsletter that I encourage the visitors of my Website (www.welding-advisers.com) to ask questions on welding problems. I enjoy this correspondence and I try to supply useful answers that often may be already available in the website, but the reader did not bother to look for the information. In this case I just point out where in the site the explanation can be found. Occasionally the question is so large or unfocused that a welding encyclopedia would be needed to answer it. But sometimes the question is very specific, illustrating a manufacturing process that somehow is failing to perform correctly, resulting in defects and in rejects. It is clear that time is lost, production is slowing down, and good money is funneled down the drain. As I always say to my readers, I am ready to provide help at no cost to individuals, to students, to owners of small welding shops. But when it comes to industrial operations, those asking for help should be ready to pay for consultation fees. They would not dream of asking their doctor or their lawyer for free advice, would they? And then an amazing case is developing. As long as the advice was freely available, it was sought for and accepted, at times even gratefully. But once a request for a fee is made, the interest dwindles to nothing, they simply switch off without a pretext. I just cannot understand, if they asked for help it means the problem was real and urgent. It is not a question of lack of confidence, otherwise they would raise the problem. The price is not an obstacle as they do not object to it. No matter that the fault is expensive and that the loss is sizeable. It is evident that by working on the problem an expert could solve it providing a return that would improve the bottom line. The gain is likely to be worth many times the expense of the consultation fees. And the time saved may be even more important. In principle managers should be supposed to be logical people, striving with all their capability to improve the economic results of their administration. In practice it is often not so. There is no logical explanation to this occurrence. Only psychological drives or fears seem to produce such an irrational behavior. Well, it is their choice, also if it looks quite strange. This is the recent comment of a reader who asked for help, speaking of the managers of his company: Do you know why is it so? If you like to comment I would be glad to read your feedback, especially if you know what I mean from your experience. Click on the Contact Us button from the NavBar in the website (www.welding-advisers.com).
14 - Bulletin Board 14.1 - 14th Int'l Conf. on the Joining of Materials (JOM-14) and 14.2 - International Trade Fair - Joining Cutting Surfacing May 28-31, 2007 - Moscow - Russia www.schweissen-schneiden-russia.com 14.3 - Click on the following image to watch the SBI! TV Show!
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