The path to productivity not only involves looking at how to improve your current process, but also investigating practices that can make your business better.
Gas-shielded flux cored welding (FCAW) is a time-proven process trusted for its high deposition rates and out-of-position welding capabilities in heavy manufacturing and fabrication applications. In an industry often averse to change, many companies consider their current FCAW practices and equipment as trustworthy family members: always reliable, with no reason to change.
However, every family has secrets, and blind trust in an old FCAW procedure can significantly weaken your competitiveness, especially if your company is merely maintaining the same productivity level is was years ago.
This article showcases methods to improve productivity and quality while lowering installed costs (installed costs are the total costs, materials, time and overhead associated with manufacturing a part) by considering new electrode types, wire feeder capabilities, power source technology and welding procedures.
Flux Cored Improvements
Gas-shielded flux cored electrodes rely on a combination of the shielding gas and flux contained within the hollow, tubular electrode to shield the weld puddle from impurities that can affect weld strength and aesthetics. Different flux composition enables adjusting variables, such as creating a fast-freezing puddle for all-position welding. The slag that forms on the completed weld must be manually removed, either with a chipping hammer, air hammer, grinder, wire brush or all of the above.
One quick method of increasing productivity might be looking at the diameter and type of electrode you are using. For example, many fabricators weld 1/2-in. plates with a .045-in. AWS E71T-1 electrode, either because it's what they've always done or what was recommended. However, welding with a 1/16-in. or even a 3/32-in. electrode in the flat position might increase deposition rates and travel speeds without risking burn-through.
The classification of electrode used also affects productivity. AWS E71T-1 is an extremely popular electrode because of its all-position capabilities. It's a great feature, but it can hamper productivity if welding a lot in the flat position. In this case, an electrode designed specifically for welding in the flat position, such as an AWS E70T-1, can improve productivity. The chart in Fig. 1 provides some examples.
Dual Electrode Feeders for Versatility
If your work requires mostly FCAW but would benefit from adding another electrode, switching to a dual electrode feeder is your best option for maximizing productivity. These feeders hold two rolls of wire and feature two shielding gas lines and two guns. Some feeders automatically recognize which gun is being used as soon as the gun trigger is pulled, so changeover is fast and simple. By adding a dual feeder, you could weld with both all-position and flat position electrodes, (or with .045 and 1/16th diameter electrodes). This lets you choose the electrode most appropriate for the application to increase productivity.
Recently, the owners of The Metal Shop in Logan, Utah were picked to build the extreme "X-Scream" amusement ride perched atop the Stratosphere Hotel and Casino in Las Vegas. Such a high profile ride requires meticulous planning and several months of making countless full-penetration welds.
With thicker materials, achieving a full-penetration weld requires beveling the edges and making the root pass with short circuit GMAW, a cooler process, because FCAW would burn-through the joint. The metal deposited during the root pass then supports making subsequent passes using the hotter, more productive FCAW process. To eliminate the non-productive set up time required with a single wire system, Kevin Jepperson, co-owner of The Metal Shop, standardized on dual feeders.
"In my opinion, any shop that doesn't have a dual feeder running multiple electrode types is compromising its quality and productivity," he says. "We weld on a wide variety of material thicknesses, so the two different processes enable us to have one machine tailored to al l thicknesses and joint designs."
"There are only two other options," he adds. "Either have a guy who does nothing but weld with a solid electrode on one machine and have another guy come after him with flux cored, or have the guy weld it with solid electrode and then stop to swap out his electrode, swap out his tip, swap out his drive rolls, change gases and then weld it with flux cored." [Short circuit GMAW produces best results with a 75/25 argon/CO2 mix, while most FCAW can be done with 100 percent CO2 to lower gas costs].
Both options Jepperson describes adversely affect productivity and quality. In the first scenario, productivity depends on how fast the operator welding can complete his work. In the second scenario, downtime builds up—an extra 15 or 20 minute each time the operator stops to make the necessary equipment changes. In addition, Jepperson feels that single wire systems compromise quality because operators are prone to cheat to save time, making short FCAW welds when the procedure calls for GMAW and vice-versa.
|
|
|
Digital meters found on dual electrode feeders allow operators to precisely dial in weld parameters, ensuring consistency between weld stations and exact compliance with weld specifications.
|
Additional benefits can be found with today's dual electrode feeders. Switching to a feeder with a four drive roll system will improve feedability (improved arc performance, reduced birds nests, etc.) compared to a two drive roll system. Drive roll tension is critical, and today's systems feature dual tension controls that allow the operator to fine-tune the pressure on the electrode independently when feeding a variety of electrodes.
The greatest benefits, however, can be found in the more advanced technologies being incorporated into today's dual electrode feeders. Digital meters allow operators to precisely dial in weld parameters, ensuring consistency between weld stations and exact compliance with weld specifications.
Many feeders also feature dual scheduling programs that allow the operator to switch between two pre-set welding parameters using what's called trigger program select. With just the click of a trigger, the operator can switch, for example, between hotter parameters for welding in the flat position and cooler parameters for welding vertical up. Some dual models also allow four welding programs to be stored per side, further reducing set-up time.
Metal Cored Wire Advantages
If you've been welding with flux cored electrode for years, the idea of switching electrodes might seem like a stretch, but the benefits can improve productivity. FCAW disadvantages include high levels of smoke and fumes that can require smoke extraction equipment for your work environment. It also leaves a slag that must be removed, which can increase cycle time up to 10 percent. To address these issues, some companies are switching to metal cored electrodes.
Metal cored electrodes consist of metal sheath and a core of alloying materials occasionally mixed with fluxing oxides. They create no spatter, no slag, little to no silicon islands and drastically reduce the smoke and fumes associated with flux cored electrodes. Metal cored electrodes are popular in general fabrication, automotive, railway, shipbuilding, construction, agricultural, offshore and robotic applications, to name a few.
Many people are initially attracted to metal cored electrodes because they maintain or increases deposition rates and travel speeds while improving cycle times by eliminating the need to remove slag (a huge benefit when making multiple-pass welds).
An important concept to understand when considering metal cored electrodes (or any other productivity enhancement, for that matter) is "compensation or preparation?" Those currently using a flux cored electrode think of slag removal as preparing the part for the next step in the manufacturing process. In reality, what they are doing is compensating for the fact that the FCAW process creates an additional, time-wasting step(slag removal(that must take place before the part is ready for the next step. With a metal cored electrode, the part is already prepared for the next step (e.g., the paint shop) because no grinding is necessary.
Metal cored electrodes also help reduce or eliminate another compensation activity: rework. Metal cored electrodes are able to better bridge part gaps and weld materials at higher amperages without burn-through, two of the most common causes of rework. Instead of staffing a rework station with two operators on three shifts, it may be possible to have a rework station staffed by one operator on one shift or eliminate it altogether. More parts are welded right the first time, more parts go out the door at the end of the day, and available staff can be utilized for other productive activities. As a result, the additional "perceived cost" of metal cored electrodes compared to flux cored electrodes should be a non-issue because they significantly lower installed costs.
Pulsed MIG Combines Best Features of All Processes
If you're facing extreme pressure to lower installed costs or increase productivity without adding staff, chances are that you need the benefits of new technology, such as a dual wire feeder and metal cored electrodes, more than you think. One other way to improve productivity may also be to use pulsed GMAW.
If you tried pulsed GMAW years ago and found it too complicated or too different from short circuit, spray transfer or FCAW, it is extremely important to note that today's new pulsed GMAW technology has addressed and overcome these concerns (this is not your father's pulsed GMAW!).
 |
|
Pulsed MIG systems offer higher deposition rates, lower fumes, all-position welding, fewer rejects, reduced clean-up time and lowered installed costs.
|
This article has addressed many welding goals: higher deposition rates, lower fumes and smoke, all-position welding, fewer rejects, reduced clean-up time and lowered installed costs. Manufacturers currently using the FCAW process can achieve some or all of these goals with an advanced "multi-MIG system" capable of pulsed GMAW, as OEM Fabricators of Woodville, Wisconsin recently discovered.
In conjunction with its programs for kaizan (continuous improvement) and 5S (Sort, Simplify, Sweep/Shine, Standardize, Sustain), OEM recently standardized on one electrode, one gas and one welding system for nearly all of its mild steel weldments from 1/8-in. to unlimited thickness. Having relied in the past on short circuit GMAW and FCAW, OEM now uses one wire (.045 ER70S-6), one shielding gas (90/10 argon/CO2) and one process (Accu-Pulse™ pulsed GMAW) in most of its 28 welding stations.
The resulting change has reduced OEM's welding costs by up to $2,000 per day and paid for the entire new fleet of welding systems in about six months.
According OEM manufacturing engineer Scott Exner, many of the welding procedures given to OEM Fabricators by its customers were established 20 or 30 years ago and haven't changed since. The weldments required for the fabrication of heavy construction and agricultural equipment often include a wide variety of different materials, joint combinations and joint positions. With old technology it was often required to use 75/25 argon/CO2 shielding gas using short circuit transfer MIG welding for thin sections, then switch to an all-position flux cored electrode and a 100 percent CO2 shielding gas for thick sections in the flat and horizontal sections to complete the weldments.
"In addition to losing 15 minutes every time the operators stopped to change gas and electrodes, along with changing weld parameters, there's the clean-up time and the cost of grinding discs," says Exner. "Anytime I see a weld with grinding marks all over it, the first thing I look at is how much we paid a guy to do that. At the present time, approximately half of every manufacturing dollar is labor cost. Anytime we back up in the process, we've already spent that time once, and now the operator is doing it again, so it costs us twice. Additionally, the operator is not getting done what he should be getting done, which equates to three times the labor for a given weld section. The ease and efficiency of the pulsed MIG process over short circuit transfer and flux cored has allowed us to substantially reduce waste in our manufacturing process. I calculated that a lot of our welding cells had lost up to 2.75 hours of productivity per 10-hour shift due to the older welding technology and its inherent disadvantages."
While switching to a pulsed GMAW process may require re-qualifying the procedure, the effort of doing so is well worth it when considering the productivity increases Exner discusses.
 |
|
When welding requires both solid and flux cored electrodes the use of a dual wire feeder eliminates non-productive set up time required with a single wire system.
|
Conclusion
Everyone in the welding industry should strive to reduce installed cost. Flux cored welding is an extremely effective process and suits many applications, but new equipment and technologies can help streamline and put more parts in the bucket at the end of the day. The addition of a dual feeder, a switch to a larger flux cored electrode, using two different electrodes or adding an advanced multi-MIG system may make your life easier and reduce costs for you and your customers. But every shop is different. Armed with the topics discussed in this article, we encourage you to talk with your preferred welding supply distributor or manufacturer to see if any of these ideas are right for you. A change now might make you a hero with your boss and your customers, so don't be afraid to change.