Pulsed MIG Welding

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<p>Pulsed MIG Welding.</p> <p>MIG Weld Equipment and Pulsed MIG Weld Reality.As this site is updated frequently pleaserefresh each page before you start.</p> <p>If you want to read how pulsed MIG caused weld cracks on Fordaxles, continue to pulsed section 2 which is at the bottom of this page.</p> <p>2013: PULSED MIG, IT'S A DIFFERENT PROCESS WHEN USED WITH AUTOMATION: It's important that the weld industry understands the reasons why the pulsed MIG process when used with automation such as mechanized pipe welds or robots will typically produce superior weld quality than when pulsed MIG is used as a manual weld process.</p> <p>As many in the oil and energy industries are aware, when X-Rays are applied to "manual" all position, pulsed MIG pipe welds, lack of weld fusion is a common defect. In contrast when we see pulsed MIG used with costly, mechanized, sub sea pipe welds, or oil pipe lines, the process can attain exceptional pipe weld quality and productivity.</p> <p>When dealing with mechanized, pulsed MIG pipe weld equipment as found with oil industry pipe applications, you will often find multi-gun units with sophisticated pulsed weld eqipment and controls. The pulsed equipment will provide dedicated pulsed MIG weld programs suited to the unique requirements necessary for the pipe weld roots, fill and cap passes.</p> <p>IN THE PAST, TRADITIONAL CONSTANT VOLTAGE (CV) MIG EQUIPMENT FROM ONE MIG EQUIP MANUFACTURE WAS VERY SIMILAR TO THE CV MIG POWER SOURCES AVAILABLE FROM JUST ABOUT EVERY OTHER GLOBAL MIG EQUIPMENT MANUFACTURER. WITH CV EQUIPMENT, LIFE WAS SIMPLE, DEPENDING ON THE WELD PARAMETERS SELECTED, YOU ATTAINED EITHER SHORT CIRCUIT, GLOBULAR OR SPRAY TRANSFER.</p> <p>SINCE IT'S INTRODUCTION IN THE EIGHTIES, I HAVE BEEN EVALUATING THE PULSED EQUIPMENT FROM GLOBAL MIG EQUIPMENT MANUFACTURERS. IN THE TESTS OVER 25 YEARS AGO, I SAW THAT THE ELECTRONIC DIFFERENCES AND RESULTING PULSED ARC CHARACTERISTICS BETWEEN ONE PULSED MIG EQUIPMENT MANUFACTURER AND ANOTHER MANUFACTURER, WERE EXTENSIVE. IN 2013 LITTLE HAS CHANGED.</p> <p>Ref pulsed MIG pipe welding concens:API. 5.2.3 states that the Pulsed Gas Metal Arc Welding (GMAW-P) process may be used for any material thickness. However whenever the welding system is changed or the settings on existing equipment are"significantly altered",the fabricator should verify the reesulting weld properties. The extent of verification or testing should be as agreed between the purchaser and fabricator.Response from Ed's MIG WELD REALITY. In contrast to the traditiona, two control, MIG or flux cored weld process, there are many weld essential variables that can be readily changed with the pulsed MIG mode. While the API code engineers warn against a "SIGNIFICANT change in a pulsed settings", the real world weld decision maker needs to be aware that an insignificant parameter change with the highly sensitive pulsed MIG mode, will have a significant influence on the weld fusion, and that weld fusion will in most instances will be marginal or lacking.</p> <p>While on the subject of pulsed MIG, the API code does not discuss the mechanized versus manual pulsed welding inconsistencies. When a code body stipulates that a fusion sensitive process is OK for any pipe thickness, the code is sending the message that this process is acceptable for both manual and mechanized welds.With automated pulsed MIG pipe line welds, electronic power source features such as volt or current energy spikes can be applied to the weld weave dwell times. These increased energy spikes will impprove the pipe side wall weld fusion. Also the controlled pulsed MIG weld speeds, controlled mechanized weld weaves and constant wire stick out will have a lot to do with success of the mechanized pulsed MIG process when used for pipe line welds.Without these controls, for three decades the manual pulsed MIG weld process has proven that the attainment of 100% X-Ray all position pipe weld quality is a challenge, and this is a challenge that weld shops in 2013 do not have to face when they can use the far superior TiP TiG process.</p> <p>Pipes and weld process choices..</p> <p>Ten years ago STICK and FCAW were most common processes for pipe welds.</p> <p>PULSED MIG AND PIPE PROJECTS: Large pipe projects especially in the oil industry will today often use a mechanized, multi-torch, pulsed MIG unit for the pipe welds. The pulsed MIG equipment may or may not have a level of electronic sophistication way beyond that available in standard pulsed equipment sold for manual pulsed weld applications.</p> <p>For mechanized pipe root welds, either the MIG CMT - STT - RMD modes will typically be selected, and for the pipe fill - cap pass welds, the more conventional pulse mode will be selected. Apart from the dedicated pulsed programs for the pipe fill and cap passes with the pulsed equipment, you will also find the pulsed equipment and controls may enable unique pipe weld attributes. For example the equipment may have the capability to provide a current or volt spike during the weld dwell time in the weld weave cycle.</p> <p>Vee and J groove pipe welds have simple weld requirements. Moderate MIG weld energy is required across the hot groove weld surface, and higher weld energy with dwell times is beneficial when applied to the Vee or J groove side walls, (the thicker the pipe the higher the side wall energy required). The weave dwell energy spike from this unique pulsed process can overcome the common pulsed MIG side wall (lack of weld fusion) weld issues, (a sophistication at this time not possible with manual pulsed pipe applications). Most large automated pipe applications will enable multi-MIG guns which also add more weld heat into the groove welds again improving the weld fusion potential. Mechanized pipe welds also provide Constant MIG Wire Stick Out and Constant Weld Travel Rates which enable improved weld process control and bring a weld quality uniformity and consistency to the automated weld that again is not be possible with the manual pulsed MIG pipe welds.</p> <p>2103: LETS GET BACK TO WELD REALITY. AFTER TWENTY FIVE YEARS OF PAINFUL, MANUAL PULSED MIG EQUIPMENT EVOLUTION, DEPENDING ON WHO'S PULSED MIG EQUIPMENT WAS PURCHASED, MANY WELD SHOPS WILL HAVE PROCESS THAT CAN CAUSE MORE WELD ISSUES THAN IT RESOLVES:</p> <p>In 2013 we now have in North America, a few pulsed MIG power sources that actually work in a consistent manner and may possibly get through their 36 month warranty period without circuit board or electronic issues. The question that needs to be asked when selecting pulsed for manual steel and alloy steel applications was the purchase of this sensitive process justified in contrast to the lower cost CV MIG equipment.</p> <p>There are obvious weld benefits attained for pulsed MIG aluminum welds (alum require less weld energy than spray) and for specific MIG stainless welds that benefit from an open arc mode that enables lower weld heat than spray to possibly reduce distortion. Remember the key benefit of a MIG weld mode is the ability to provide consistent weld fusion, and on most weld applications, spray transfer will provide superior weld fusion than pulsed. Alway remember that Pulsed MIG is a process which spends 50% of its time at a back ground weld current of usually less than 100 amps. The pulsed process is also a good subsitute (in most instances not necessary) for the gague welds that are typically welded with short circuit, or when welding alloys that have poor weld transfer characteristics with conventional short circuit or spray transfer.</p> <p>As many pipe welds shops have found out, ypically when pulsed MIG is used for "manual" pipe welds that require "100% X-Rays", a combination of variables and factors will come together and lack of weld fusion may become a common weld defect. In contrast to SMAW and TIG used for pipe welds, each hour pulsed MIG will typically provides at least 10 times more weld and is therefore considered a high deposition process. When it comes to MIG weld defects that high weld deposition rate takes a large part of the blame.</p> <p>Fig. The outside appearence was irrelevant.</p> <p>If you provide what you think is an optimum pulsed MIG fillet weld on 3/8 (9.6mm) steel plates and then provide a macro section of the fillet weld, you will often see either marginal or lack of side wall weld fusion. After the macro weld evaluation you may come away with the impression that with pulsed MIG, you have a weld process that provides a poor ratio of weld energy to the weld deposition - mass and the weld speeds provided. Also with manual pulsed MIG welds the weld energy is influenced and the weld transfer is disrupted by the manual wire stick out variations and the many different weld techniques that each welder brings to the pulsed weld.</p> <p>THE RATIO OF THE WELD ENERGY DELIVERED AND THE WELD MASS AND WELD SPEEDS THAT RESULT IS ALSO AN ISSUE WITH MIG SPRAY TRANSFER, HOWEVER THE WELD SHOP NEEDS TO REMEMBER THAT WITH PULSED MIG THE WELD SPENDS 50% OF IT'S TIME WITH A BACK GROUND CURRENT &lt; 100 AMPS.</p> <p>WELD PROCESS EXPERTISE CAN OFTEN OVERCOME POOR WELD EQUIPMENT TECHNOLOGY. IN THE 1990s, I SET OPTIMUM PULSED WELDS ON THE WORLD'S MOST COMPLICATED ROBOT WELDS.</p> <p>Fig.. The most complex welds are small pipe and tubes, that have difficult acces and 100% X-Ray</p> <p>THE EASIEST PIPE WELDS TO MAKE ARE LARGE DIAMETER PIPES (EASIER TO FOLLOW THE RADIUS AND MORE TIME TO REACT). IN CONTRAST THE MOST COMPLEX PIPE WELDS ARE SMALL DIAMETER PIPES AND TUBES.</p> <p>I remember in the 1990's, when the management team at one of the world's largest engineering companies decided to purchase a seven axis robot to weld it's boiler tubes to headers. The above picture is not the parts welded but similar and the tubers were slightly larger. The boiler head pipes were approx. 8 - 10 diameter, typically 20 to 40 feet long with the 2 - 3 inch diameter thinner wall tubes. The robot traversed on a track placed on the other side of the header. These complex ASME welds were typically carried out by the highest skilled manual TIG welders. I won't go into why the management should not have selected a costly robot for these welds, however I would like to tell you about the pulsed MIG welds I produced on this robot application.</p> <p>For each boiler tube to head weld, two robot pulsed MIG weld layers were required to fill the grooves and produce the fillet around the header. The pulsed MIG welds had to pass 100 X-Ray as per the ASME requirements. As the robot could not go 360 degrees around the tubes each of the two weld layers was made with four passes so four weld start - stops was required for one layer, with a total of 8 start - stops for the completed 2 weld layers, by the way no grinding or human involvement was allowed for the weld layers.</p> <p>THE PULSED TECHNOLOGY WAS ONLY 10 YEARS OLD. THE ELECTRONICS WERE STONE AGE AND NOT UP TO THE TASK SO I USED PROCESS EXPERTISE TO ACHIEVE THE ASME PIPE WELD QUALITY:Can you remember how poor computers were in the early 1990s? well I want you to try and imagine how bad the global electronic pulsed MIG equipment was at that time. I had a sophisticated robot attached to to an inconsistent - erratic pulsed power source and had to provide optimum weld quality with vertical up, tube to header welds on two very different part thicknesses. In those small circular welds we had 8 weld starts and 8 weld stops that required perfect weld tie-ins to get past the X-Rays.</p> <p>REMEMBER WITH SMALL DIAMETER MIG WELDED APPLICATIONS AND WITH SMALL WELD LENGTHS, THE WELD ARC ON TIMES MAY BE MEASURED IN A FEW SECONDS AND YOU NEED TO RELY ON THE WELD EQUIPMENT AND CONTROLS TO GO FROM WELD START DATA TO THE WELD DATA AND TO THE WELD END DATA IN THOSE FEW SECONDS. THE REALITY IS 2013 FEW AUTOMATED UNITS ARE GOOD AT PROVIDING THIS FUNCTION, SO IMAGINE WHAT WE HAD TO WORK WITH IN THE 1990s.</p> <p>All the tube to header welds needed was one poor weld tie or lack of fusion and the ASME, 100% X-Rays would mark the weld as a failure. I used all my MIG weld process control expertise to make these robot welds work and produce an eight hour weld quality with better weld productivity and no more weld rework than that attained from the manual TIG welders. How did i solve the weld fusion - weld tie in issues?. For the side wall weld fusion I used robot weave dwell times and kept the pulsed MIG weld mass as thin as possible. For the weld start - stop tie-ins, with the robot weld end - start data, I used low wire feed than the weld with higher weld voltage which with carefullly selected dwell time provided good tie ins, (creating a dwell time energy spike) which is similar to what is today, &gt;17 years later being used by oil companies and there much more conntrolled, sophisticated, pulsed MIG equipment. I trained a technician to make those robot welds and soon after he quit and I believe the robot was eventually put out to pasture. In 2013 the tube to header welds would still be a high risk robot application especially when you can now do these welds with the easy to use TiP TiG process. www.tiptigusa.com.</p> <p>1990s.. Ed (left - right) comparing MIG short circuit versus the STT and RMD MIG weld modes on Imperial oil, nat gas pipe.</p> <p>WELD CODES, CONFUSION OR INADEQUATE INFOMATION.When it comes to MIG and flux cored welding, rather than providing weld process resolutions, most codes relevant to pipe welding will provide inadequate information or the information they provide simply adds to the global weld process myths and confusion.</p> <p>Welding decision makers often look codes such as AWS - API and - ASME to provide practical, pipe welding advice and recommendations. Those individuals that that put all their faith in the codes that are governing the specific weld applications they are working on, need to be aware of a little weld reality, The weld information in these codes has too frequently been written and influenced by code committee individuals who lacked MIG / Flux Cored weld process controls &amp; best practices / application expertise.</p> <p>50 YEARS AFTER THE INTRODUCTION OF THE "MIG PROCESS",AND 35 YEARS AFTER THE INTRODUCTION OF FLUX CORED ELECTRODES, THE PRIMARY WELD CODES WHEN ADVISING ON THESE PROCESSES STILL CREATE CONFUSION AND TOO MANY QUESTIONS.API. 5.2.3 Pulsed Gas Metal Arc Welding (GMAW-P. This code states that the pulsed process may be used for any material thickness and whenever the welding system is changed or the settings on existing equipment are"significantly altered"then the fabricator should verify the weld properties. The extent of verification or testing should be as agreed between the purchaser and fabricator.</p> <p>In a world in which engineering standards should apply, what the hell does significantly altered mean.In contrast to the traditionaL, two control, MIG or flux cored weld process, there are many weld essential variables that can be readily changed when utilizing the pulsed MIG mode. While the API code warns against a "SIGNIFICANT CHANGE" in a pulsed settings", the real world weld deci...</p>