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PWL#042 - MFDC, Welding Aluminum Castings, New Lead-free solder, Surf. Impact Treatm., Tony Anderson January 31, 2007 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. PWL#042 - MFDC Power Supplies for Resistance Spot Welders, Weld repairing of Aluminum Castings, A New Lead-free Solder, Surface Impact Treatments to enhance Fatigue and Stress Corrosion Resistance, Welding Resources, Interview with Tony Anderson 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.
You are urged to pass-along this publication to your friends, if you like it, and if you want to 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.
1 - Introduction 2 - Article: MFDC Power Supplies 3 - How to do it well: Weld repair of Aluminum Castings 4 - Filler Metal: A new Lead-Free Solder Alloy 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article - Surface Impact Treatments 8 - Site Updating: Welding Resources 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contribution: Interview with Tony Anderson 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board
1 - Introduction This new issue of PWL for February 2007 opens with a subject that may not be familiar to those readers that do not deal intensively with power supplies for Resistance Spot Welding. This important market is driving an evolution of technology that one cannot afford to ignore. Weld repairing of Aluminum Castings is the subject of our next item. It is a kind of reminder for anyone who might occasionally need to express an opinion or give a helpful hand to solve a production problem. Lead-free solders are recently a hit in the electronic industry, following the ban emitted by environmental agencies on the old Sn/Pb eutectic solder. In the filler material section we introduce a new material, recently tested, that seems to display most of the characteristics sought for by innovative world renowned companies. Another article reviews some of the techniques used to impart favorable subsurface compressive residual stresses to metal parts subject to fatigue damage or to stress corrosion, in order to improve their resistance. Our Page of the Month is the recently announced hub of Welding Resources, grouping in an easy to find location, right from the Navigation Bar, the scattered information of our Mid Month Bulletins. It should become a useful reference for whoever looks for additional information. We are glad to be able to offer to our readers an informative Interview with a professional Welding Expert, Tony Anderson, who was ready to share with our readership his views on the many ways of building a successful welding career. We hope that young people will find in this Interview encouragement and support in their search. The other departments of this newsletter are at their usual place. Should we repeat once more that we would like to have your comments and feedback? Click on Contact Us.
2 - Article: MFDC Power Supplies Medium Frequency Direct Current Power Supplies for Resistance Spot Welding machines evolved in recent times to include the technology developed for inverters in arc welding machines. Among the advantages that MFDC offers is a greater flexibility to weld a variety of gauges and materials within a small and light unit. This capability is mostly welcome within the automotive industry. MFDC systems can weld both aluminum and steel components in the same robotic welding cell with limited downtime during changeover. Conventional welding power sources use transformers operating from the line frequency (50 or 60 Hz). It is possible to reduce substantially the size and the weight of transformers by operating at a much higher frequency, because the amount of iron core required is inversely proportional to the applied frequency. The power from a three phase supply is first rectified to Direct Current by a full wave rectifier, smoothing out the line ripples. Direct Current applied to the inverter is transformed into high frequency square wave alternating current using solid state devices called IGBT (Insulated [or Integrated] Gate Bipolar Transistor) switches. The power to the welding transformer is controlled by the time the IGBTs are left on, determining the pulse width. This is called Time Ratio Control (TRC) and also Pulse Width Modulation (PWM). MFDC transformers for Resistance Welding use frequency pulses of 400 to 2,000 Hz. Therefore their iron core mass can be reduced to a fraction of that needed for line frequency transformers. The transformed low voltage, high alternating current output is finally rectified to Direct Current for welding. An additional advantage of this technology is that low weight transformers can be placed much closer to the welding tool, on the arms of welding robots, thus reducing the transmission losses in long cables. Short pulses of direct current are especially suitable to Resistance Spot Welding of aluminum alloys, whose electrical and thermal conductivity requires 2.5 to 3 times the current, but only one third of the weld time used for steel of the same thickness.
3 - How to do it well: Weld repair of Aluminum Castings Aluminum Alloy castings scrapped in the foundry because of surface defects and lack of dimensional integrity can be salvaged by welding except if they present massive porosity. Gas tungsten arc welding (GTAW) with high frequency stabilized Alternating Current is normally used to repair sound castings. Inclusions should be prevented by taking care to avoid touching the surface with the pure tungsten electrode. Argon with or without helium can be used as a shield. Helium helps generating a hotter arc if necessary. To prepare for welding one should remove defects, especially cracks, by dry chipping with a rounded tool or by hand milling, to obtain a smooth area. One should never attempt to weld on the original casting external rough surface without first removing the thick oxidized layer. Removal of oil and grease is performed using vapor degreasing or clean solvents. Use of acid etch is not recommended. If impregnation was applied, it should be removed before welding. A clean stainless steel wire brush should be used to remove thick oxide layers just before welding. Filler material alloy is usually the same as that of the casting. Preheating is needed only in exceptional cases to overcome difficulties. On suitably prepared surfaces of sound castings, with oxide layers thoroughly removed, one should be able to weld as easily as on wrought alloys. It would be good practice to look for cracks in the weld by using penetrant inspection. Radiographic inspection may be required by contract in certain cases. If the original castings are to be heat treated, also the repaired ones should follow the same process. Weld repairing of heat treated casting would impair their mechanical properties. The feasibility of repair of aluminum alloy castings that were already heat treated and machined is questionable because of stresses and deformations likely to develop during welding. An example of such a repair performed by developing a special procedure with electron beam welding is reported in our page on Frequently asked Questions. An article on Filler Metal for repairing Aluminum Castings was published in issue No. 39 of Practical Welding Letter for October 2006. To see the article click on PWL#039.
4 - Filler Metal: A new Lead-Free Solder Alloy It is well known that Lead has been banned from solder alloys because of serious concerns about its negative impact on environment due mainly to improper disposal of Printed Circuit Boards (PCB) containing soldered electronic components. Until recently the most common solder alloy was the eutectic Sn/Pb (63% Tin - 37% Lead). The Restriction of Hazardous Substances Directive (RoHS), adopted in February 2003 by the European Union, took effect on July 1, 2006. It requires that all equipment put on sale in Europe be Lead free. A small company called IKA INDUSTRIAL CONSULTING LTD. started developing a new lead-free solder in 1999. They looked for new ways to modify the Sn/Zn eutectic which had been found to show problems of zinc oxidation. The new approach consisted in microalloying the solder with minute amounts of Manganese. It was found that this approach was successful in that it overcame the problems that restricted a wider application of the original eutectic and permitted them to obtain an international patent (PCT) on the new solder, designated IKALLOY. This alloy has melting temperature of 1990C which is lower than that of the competing tin-silver-copper alloy Sn-3.9Ag-0.6Cu (217–2200C) although 16 degrees higher than that of Sn-37Pb (1830C). The additional advantage on the competing solder is its lower material price. It was reported that International Companies, Manufacturers of electronic components for consumers goods, have thoroughly tested the new material with encouraging results. For more details see
5 - Online Press: recent Welding related Articles Laser braze aluminium to steel without flux From the Fabricator: From TWI: Welding Consumables Part 4 - Gas shielded Consumables The complete Issue 5 - September 2006 (in pdf format) of
6 - Terms and Definitions Reminder Cylinder Manifold is a distribution system used to connect multiple gas sources to users at their location. Flash is the material expelled from the joint while upsetting in a flash welding process. Intergranular Penetration in welding or brazing is the penetration of a filler metal along the grain boundaries of a base metal. Joint Root is the part of the joint to be welded where the two elements are at the least distance between them. Overaging (heat treatment) is performed by exceeding on purpose optimal time and temperature, to obtain a condition better suited to special requirements (i.e. corrosion resistance), even at the expense of degrading somewhat the mechanical properties. Scarf Joint is a form of brazing butt joint where the separation of the members is inclined relative to the surface, to increase the area of contact. Thermal Stress is generated by nonuniform heating. Workpiece Connection is the connection between workpiece and workpiece lead.
7 - Article - Surface Impact Treatments Peening processes are used to impart residual compressive stresses on the surface of metallic bodies and weld beads when required. The purpose is to improve the resistance to fatigue failures to parts subject to alternating or periodic loading. Items sensitive to stress corrosion cracking improve their resistance if shot peened. Traditional impact treatment is performed with metallic, ceramic or glass shots thrown with force through directional nozzles upon the surfaces to be treated. Shots are controlled per applicable specifications as to shape, size distribution and hardness. Powders must be removed from the process. To be effective, peening processes have to be controlled as to intensity, coverage and time. Control is performed with Almen strips, whose measured deformation upon peening is indication of the intensity of the treatment. A different process called Laser Shock Wave Peening was developed by the Lawrence Livermore National Laboratory for aerospace applications. It enjoyed substantial success after being commercialized, although it is claimed to be slow and expensive. The surface to be processed is first covered with an ablative layer of laser absorbing material. The laser pulse passes through a flowing water region and strikes the opaque layer causing it to vaporize. The vapor absorbing the laser energy produces a rapidly expanding high pressure plasma. The expanding plasma induces a high-pressure shock wave that propagates into the material leaving it plastically deformed or cold worked. The Compressive residual stresses so generated extend below the surface and approach the yield strength of the material. Aircraft engines applications include titanium alloy fan blades, laser treated to limit foreign object damage, and additional rotating titanium components. An article on the above application was published (page 65) in the August 2003 issue of Advanced Materials & Processes, an ASM International publication. An article titled "Laser Shock Peening improves Fatigue Life of Lightweight Alloys" was published (page28) in the October 2006 issue of the AWS Welding Journal. Another process, called Cavitation Peening, was investigated to provide less expensive surface enhancement. It is a process which generates a cloud of cavitation bubbles in a water flow at ultra high pressure. No additional shot is used besides the air bubbles. The peening effect is achieved by the bubbles collapsing on the metallic surface and generating compressive shock waves that produce the sought after deep residing stresses. Special equipment was built and used to test extent and amount of the compressive stresses generated in the materials. Results are reported to be positive and further testing was planned. For more information see:
8 - Site Updating: Welding Resources As announced previously, the Page of this Month displays in an easy way, from the Weld Resource button of the Navigation Bar of every page of the Website, the past Mid Month Bulletin Pages that list online addresses of important information. We plan to update regularly this page to have it always displaying the most recent collection of online welding resources. It is going to become a rich source of more detailed information for interested readers wanting to research the subjects of their concern. To see the page click on the Weld Resources button on the Navigation Bar from any page of the Website (www.welding-advisers.com). To find all the subjects click on the Site Map.
9 - Short Items 9.1 - Anvil is a large, heavy steel block that holds the stationary die of a forging hammer. It is also the steel block on which blacksmith forgings are made. In ultrasonic welding it is the massive fixed machine base unto which the parts to be joined are placed, kept in compression under the sonotrode or horn. 9.2 - Barrel Plating is performed by placing parts in a rotating container, usually a perforated cylinder that operates at least partially submerged in a plating solution while a suitable direct current is applied. 9.3 - Core in Casting is a specially formed material inserted in a mold to shape the interior or hollow portions of the cast part. In case hardening heat treatment of a ferrous alloy, it is the portion of the material unaffected by the surface treatment. In Flux Cored Arc Welding, it is the flux contained in the hollow electrode. 9.4 - Deoxidizing of molten metals is the removal of oxygen by the use of a suitable deoxidizer. In welding of copper alloys it is the function performed by certain elements included in proper filler metals to reduce copper oxide. In metal finishing it is the removal of oxide films from metal surfaces by chemical or electrochemical reaction. 9.5 - Firecracker Welding is called a variation of the shielded metal arc welding process in which a length of covered electrode, connected to a power supply, is placed along the joint in contact with the workpiece, and an arc is struck between the electrode end and the workpiece. During the welding operation, the stationary electrode is consumed as the arc travels the length of the electrode. 9.6 - Permeability is the measure of fluid flow (gas or liquid) through a porous material or the diffusion (or rate of passage) of a gas, vapor, liquid, or solid through a material. In Magnetism it is either "absolute permeability," which is a change in magnetic induction divided by the corresponding change in magnetizing force, or "specific (relative) permeability," the ratio of the absolute permeability to the permeability of free space. In metal casting, it denotes the characteristics of molding materials that permit gases to pass outside through them without being trapped as porosity in the castings.
10 - Explorations: beyond the Welder MIT - Tech Talk The car-trike combo: Twike Dark Energy Videos of How Things Are Made A Magazine for Artists and Writers
11 - Contribution: Interview with Tony Anderson
PWL: Meet Tony Anderson. If a Welding Professional of world renown like Tony is ready to share with you his knowledge and experience, you should not skip this gift.
We are grateful and obliged to Mr. Tony Anderson for having graciously agreed to let us publish this interview.
Tony Anderson is Corporate Technical Training Manager for ESAB North America.
Prior to his current position he was the Technical Director for AlcoTec Wire Corporation.
Question: How would you invite young people to consider welding as their career?
Answer: A career in welding can be as extensive and exciting as you personally would like to make it. So many opportunities are available within the welding industry. An individual who enters the field of welding has access to many associated disciplines in which they can become involved and here are just some examples:
One choice is the qualified welder. I was one for a number of years in the 1970’s. At the beginning of my career, I worked as an Admiralty Certified Welder on pressure hulls of nuclear submarines for the British Navy in the UK.
At the highest level, welding is often recognized as an art rather than a craft.
Depositing sound weld metal in accordance with stringent procedures, and welding safety critical joints that require scrutiny by sophisticated testing techniques (such as radiography and ultrasonic testing) can be very challenging and rewarding. Taking pride in producing top quality welds that perform successfully under many adverse conditions is for many a gratifying career.
There are many other opportunities within the welding industry; many good welders choose to move from welding into welding management. They become welding foremen, welding supervisors and welding managers.
This avenue can provide satisfaction from duties such as the design and implementation of systems and procedures for improving welding productivity, and generally controlling the welding activities within an organization.
In the 1980’s I worked as a welding manager responsible for the welding activities on the construction of large power stations in Africa; I had 300+ welders and many welding supervisors reporting to me.
A welder may choose to select a career in quality control. Welding inspection is an option I chose after welding. Initially I worked as a welding inspector on pipelines in Africa in the 1980’s, then inspected irrigation equipment in the Middle East in the 1990’s and finally wrote a column on welding inspection for an American magazine in 2001-2002, welding inspection has always been of a personal interest to me throughout my career and I believe that it can open many doors to career advancement.
There are internationally recognized qualifications for welding inspection. One of the most widely recognized programs is the American Welding Society Certified Welding Inspector (AWS CWI).
Another sector of the welding industry that can provide many opportunities for interesting career advancement is in the quality control environment, which involves testing of weldments. Destructive testing of welding samples often involves working within a testing laboratory and using various types of testing equipment to evaluate the mechanical and physical properties of weldments.
Non-destructive testing (NDT) is the testing of weldments with methods such as radiographic, ultrasonic and various other crack detection processes. I chose NDT, early in my career. In my late twenties, I became an NDT manager on a large power station construction project in Africa where I evaluated hundreds of radiographs daily and was responsible for the health and safety of a number of NDT technicians working with radioactive isotopes.
There are many opportunities within this sector of the welding industry and again there are internationally recognized qualifications available for the weld testing processes, at levels I, II and III, that range from NDT operator/technician to NDT manager or consultant requirements.
If your interest is within quality systems, there is also Quality Assurance. Much of the welding fabrication industry is associated with the quality systems as prescribed by the ISO 9000 quality system requirements. Welding, generally accepted as being a special process, must be controlled in the manufacturing environment.
I specialized in this area for 6 years. I was employed by the Southern African Institute of Welding in Johannesburg South Africa as a Consultant in Welding Quality Management. In this position, I assisted many welding manufacturer’s design and introduced quality systems for welding. Producing a quality system for welding involves the design, development and introduction of welding procedures, welder testing and qualification, and welding inspection criteria.
Training is another area within the welding industry that offers a variety of opportunities. There are many areas and levels of training. There is both practical and theoretical training of welders, welding inspectors, NDT personnel and welding engineers. This training is conducted in many environments.
Examples include in-house training by manufacturers as well as training conducted by technical institutions such as colleges and universities. I have worked within many training environments, from teaching hands on welding at a manufacturing facility to lecturing Bachelor and Master of Science Welding Engineering students. Again there are formal qualifications available for welder training, the AWS have the Certified Welding Educator (CWE) qualification available for persons who work in this field.
Welding equipment and consumable sales is yet another job opportunity. Many welders move into this field and work for either a manufacturer or distributor of these products. A competent welder has a distinct advantage in the welding equipment sales field.
Another area is formal training and qualification as a welding technician or engineer, and registration as a Professional Engineer or Technician. I am registered as a Chartered Engineer through my professional institute, the TWI in the UK, with the British Engineering Council.
There are similar associations in the United States for professional engineering registration that can help to give credibility to your professional standing. Good welding engineers are in high demand and can command very competitive salaries.
In the last 38 years I have spent in the welding industry, I have worked on many interesting projects, in many places around the world, and within many areas of the welding industry.
I can honestly say that I have seldom been bored and have always seen opportunities within this industry. I would therefore invite young people to consider welding as their career because there are so many challenging and rewarding opportunities available within this industry.
Q: Which should be the main personality traits of a good welder?
A: In my experience, having worked with hundreds of welders, over many years, on many projects, I would say that the main personality trait of a good welder is to be conscientious. To be conscientious about their work in all respects, this includes all areas from time keeping to going that extra mile to ensure that the quality of their work is the best that they are capable of providing.
I have had some brilliantly talented welders work for me who I could trust with the most critical welds and never worry that the weld would fail x-ray, however, unfortunately they could not be relied upon to appear at work on time, or at all, on a Monday morning.
The most talented welder in the world is a liability unless they have integrity, good work ethics and can be trusted. Many welded constructions are of a safety critical nature, peoples lives may depend on the integrity of the weld and a good weld may often depend on the integrity of the welder.
Q: What should be the first steps of a promising career and what advice would you offer to a young person just starting a welding career?
A: If you do decide to enter the welding industry as a welder (as I did), try to find employment within a company who is willing to provide you with training. If you want to advance within your industry training and education are paramount. Take whatever opportunities are available to further your education and enhance your knowledge within the welding industry.
If the company you are working for is reluctant to provide you with training, find one that will. If you have the opportunity, enroll in a formal welding education program, this may be at a local technical school or at a university, Ferris State University in Michigan for instance offer both 2 year associate degrees and 4 year bachelor degrees in Welding Engineering Technology.
Beginning your career with such a degree under your belt is a distinct advantage. Don't be afraid to move on to another company if you truly believe that the move will enhance your career, sometimes the only way to obtain experience is to make a move.
If you decide to remain in one place and specialize in a particular field that’s also fine, however, don't become complacent, continue to remain informed about the many changes and new technology within our industry. Become involved with the American Welding Society.
Become a member of the AWS and join your local chapter and attend the local meetings, there is often a lot to be learned from these older guys who attend these meetings. Try to attend welding trade shows if you can and always attend welding seminars and technical presentations if the chance should arise.
Q: Which goals and achievements should stand firmly in one's mind?
A: I would recommend that if you start as a welder and intend to advance within the welding industry that you set goals and achievements based on further education and formal qualification. These would depend on your interests and opportunities and may involve attending college or university to obtain a particular diploma or degree.
It may also involve attending training courses in preparation for certification examinations to become a Certified Welding Inspector, a Certified NDT Technician or a Certified Welding Supervisor. If you decide you want a career as a Welding Inspector, Head of a Welding Inspection Department, Welding Manager, NDT Technician, NDT Manager, Welding Engineer, or any other position within the welding industry, it can happen, but only you can make it happen.
Q: Which welding processes or developing technology is likely to become a challenging and rewarding field of action for ambitious young people?
A: I have just recently returned from a visit to the British Welding Institute (TWI) in Cambridge England. I have also within the last few years presented papers, with many others from around the world, at the International Welding Institute – International Congress.
From my exposure to the current technology I can only say that there are fascinating developments within most areas of the welding industry. The British Welding Institute (TWI) which is the largest welding research center in the world is expanding their facilities and becoming more involved globally.
The Edison Welding Institute (EWI) which is the TWI counterpart in the USA is also seriously involved with welding research and development for both commercial and military projects.
The welding industry in general has very interesting developing technology, from new materials, new welding processes, new welding equipment, testing methods and NDT techniques.
Tony Anderson CEng SenMWeldI
PWL: Thank you, Tony Anderson
12 - Testimonials From: Patrick Frisbie (e-mail removed for security) Thank you Sir! Patrick T. Frisbie
Date: 22 Jan 2007, 11:15:13 AM Questions and Feedback : I receive your newsletter regularly and enjoy the vast amount of knowledge I gain from it. My sincere appreciation to you and those involved in developing the website. [...]
13 - Correspondence: a few Comments A correspondent noted a puzzling characteristic in a publication regarding a commercial plasma cutter: "The capacity 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?" Upon our asking the manufacturer on the above observation we got the following answer: "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." We report what we learnt for the benefit of curious and interested readers.
14 - Bulletin Board 14.1 - TMS 2007 136th Annual Meeting and Expo 14.2 - World Trade Fair for Industrial Technology 14.3 - From SiteSell
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