Archives For Arc Welding

Reciprocating wire feed gas metal arc welding (RWF-GMAW) is a low heat input, precisely controlled variation of the GMAW process.  With the RWF-GMAW process the wire is reciprocated in and out of the weld pool.  The wire motion is synchronized with the current waveform to produce a weld that is characterized as having minimal if any spatter, and very controlled heat input, bead placement, and base metal dilution.  Manufacturers of RWF-GMAW equipment include Jetline Engineering (Controlled Short Circuit (CSC)), Fronius (Cold Metal Transfer (CMT)), SKS Systems (micro-Mig), and Panasonic (Active Wire Process (AWP)).  The purpose of this article is to describe the reciprocating wire feed gas metal arc welding (RWF-GMAW) process and to provide examples of applications where this variation of the GMAW process may be advantageous.

The gas metal arc welding (GMAW) process is a fusion welding process that produces coalescence of metal using the heat from an arc between a continuously fed consumable electrode wire and the base metal.  An illustration of the GMAW process is shown in Figure 1.  Electrical contact is made to the consumable electrode wire at the contact tip.  A stream of shielding gas is fed through the nozzle and displaces the atmosphere in the vicinity of the arc and the weld pool.  In addition to preventing atmospheric contamination of the weld pool and the heated consumable electrode wire, the shielding gas also provides the medium for current flow (i.e. the arc).

Figure 1 Illustration of the GMAW Process

Figure 1.  Illustration of the GMAW process

For conventional GMAW there are four primary modes of metal transfer: short-circuit transfer, globular transfer, spray transfer, and pulse spray transfer.  Short-circuit transfer has historically been the GMAW mode used for applications requiring low heat input, low distortion, and/or small weld size.  With the short-circuit mode the current level is not sufficient to maintain an arc or to enable transfer of droplets across the arc.  The droplet forms on the end of the wire and is transferred to the weld pool when the wire with molten droplet come into contact with the weld pool.  When the wire with molten droplet comes into contact with the weld pool, an electrical short is created and the current spikes.  The combination of surface tension forces and the magnetic pinch force created by the current spike cause the droplet to transfer to the weld pool and the arc is reestablished.  This process repeats itself about 100 times per second.  The short-circuit mode can be used to produce relatively low heat input welds, with lower distortion levels than that achievable with other GMAW modes.  The process uses conventional GMAW equipment and has a limited number of controls, making it very user friendly.  However, because of the violent nature of the short-circuiting event, the process mode is characterized as having high spatter levels.  The short-circuit mode also has a tendency for incomplete fusion discontinuities when welding thicker materials and is not allowed by several codes.

Figure 2 HSV image of a short circuit transfer weld made with conventional GMAW equipment

Figure 2.  High speed video image of a short-circuit transfer weld made with conventional GMAW equipment

Several manufacturers have advanced versions of the short-circuit mode that enable more controlled droplet transfer, more precise bead placement, and reduced spatter levels.  These advanced versions control the current waveform throughout the stages of the short circuit transfer cycle.  Specifically, when the wire with molten droplet is in contact with the weld pool, the current increase that occurs is controlled so that spatter resulting from the clearing of the short circuit is reduced.  These advanced short circuit transfer modes are deployed for many applications including those that have historically used short-circuit transfer GMAW but desire lower spatter levels, and root pass welding in the pipeline industry.  Both the conventional and advanced short circuit modes are most often deployed semi-automatically.  The advanced short circuit modes are insensitive to changes in the contact tip-to-work (CTWD) distance making them ideally suited for semi-automatic operation.

With RWF-GMAW the wire is reciprocated in and out of the weld pool in synchronization with the current waveform.  This process is an even more controlled variation of the GMAW process because of the synchronization between the wire feed and the current waveform.  Plots of wire feed speed, current, and voltage verses time for a weld made with Fronius’s CMT mode are shown in Figure 3, while high speed video images of a CMT weld are shown in Figure 4.  During the arcing phase a droplet is formed on the end of the wire.  The wire is retracted and then moved toward the weld pool.  The shorting phase begins when the wire and molten droplet come into contact with the weld pool.  The current first increases slightly, and then reduces to a minimum value.  The retraction of the wire, in combination with the surface tension forces cause the droplet to detach.  After the droplet detaches an arc is formed and the cycle repeats itself.  Similar wire feed speed, current, and voltage waveforms are expected for RWF-GMAW welds made with other manufacturer’s equipment.  With the RWF-GMAW process there is no current spike when the wire and molten droplet come into contact with the weld pool.  With both the conventional and advanced short circuit modes droplet transfer is achieved through the combination of the pinch force imposed by an increased current level and surface tension forces.  With the RWF-GMAW mode the current isn’t used to transfer the droplet, rather the droplet is transferred through the combination of surface tension forces and the mechanical retraction of the wire.

Figure 3 WFS, current, and voltage verses time for a weld made with the Fronius CMT system

Figure 3.  WFS, current, and voltage verses time for a weld made with a Fronius CMT system (numbers in parenthesis correspond to images shown in Figure 4)

Figure 4

Figure 4.  High speed images of a t-joint fillet weld made with a Fronius CMT system (image numbers correspond to the waveform location in Figure 3)

The RWF-GMAW process has very low spatter levels when setup correctly.  For many applications the RWF-GMAW process will produce no visually observable spatter.  The process is capable of heat input levels ranging from less than 1-kJ/in up to heat input levels approaching that of the GMAW-P mode.  WFS settings commonly range from 35-in/min up to several hundred inches per minute.  In addition to its low heat input and low spatter characteristics, the RWF-GMAW process is capable of producing low dilution levels and precise bead placement.  The RWF-GMAW process is more complex than the conventional and advanced short-circuit modes.  A given wire feed speed setting can have 11 or more parameters associated with it.  Many equipment manufacturer’s offer pre-canned programs that enable synergic control of the welding program.  These pre-canned programs can be used in the as-received condition, or the background parameters can be tailored for the specific application.  Modification of the background parameters is often required for difficult applications.  The RWF-GMAW process is most commonly applied as a mechanized or automated process rather than a semi-automatic process.  RWF-GMAW equipment is also more expensive than the equipment required for the conventional and advanced short-circuit modes.

Due to the added complexity and cost, the RWF-GMAW process is most often utilized for applications that warrant its positive attributes.  For the majority of the applications that EWI has applied this process for, the reasons for evaluating the RWF-GMAW process were due to one or more of the following process characteristics: 1) low heat input, 2) low and controlled base metal dilution, and/or 3) precise bead placement.

The RWF-GMAW process has been applied for automotive applications where it’s low spatter and low heat input characteristics result in less spatter and distortion.  The RWF-GMAW process was evaluated as an alternative to GTAW for titanium sheet metal applications because the RWF-GMAW process has adequate arc stability and spatter characteristics with much lower heat input and distortion levels.  EWI has also applied the RWF-GMAW process as an alternative to shielded metal arc welding (SMAW) for the fabrication of thick section weldments made from crack sensitive steels.  Procedures were developed for the RWF-GMAW process that produced welds that met the ASME Section IX qualification criteria while providing increased travel speed (and production rates) and crack-free heat affected zones.  EWI applied the RWF-GMAW process to the wheel to shaft joint illustrated on the left in Figure 5.  This application utilized a partial penetration, narrow joint configuration.  The weld was required to penetrate to the root of the joint, have complete sidewall fusion, withstand a torque of 1680-N/m, and due to an o-ring on the backside of the wheel, the maximum temperature on the backside of the wheel was limited to 100-deg C at any time.  EWI developed RWF-GMAW procedures that met these requirements.

Figure 5a Illustration of the wheel to shaft jointFigure 5b Macrograph from the wheel to shaft joint

Figure 5.  Illustration of the wheel to shaft weld joint (left) and a macrograph of the welded joint (right)

EWI has applied the RWF-GMAW process for numerous other applications that are proprietary to the project sponsors.  Many of these applications have involved non-ferrous high alloy materials that are sensitive to heat input and dilution and require precise bead placement with no spatter.  The RWF-GMAW process can produce welds with quality comparable to that of the GTAW process, at production rates characteristic of the GMAW process.  The ability to produce welds with low and controlled heat input has enabled this process to be successfully used to weld crack-sensitive materials.  The RWF-GMAW process should be considered for applications that require one or more of the following attributes: low and/or controlled heat input, low and/or controlled base metal dilution, precise bead placement, and spatter free welds.

For more information on the RWF-GMAW process, contact Nick Kapustka at 614-688-5175 or nkapustka@ewi.org

Marc on bike

If you are following EWI Associate Marc Purslow’s cross-country, solo bike trek to raise money for ASAS (After-School All Stars), you’ll know that he’s relentless in achieving his goal. Since he embarked on his journey from Maine on July 3rd, he has left New England, crossed New York State, and made his way through Ohio. For news about his adventures and challenges, be sure to follow his blog. To find out where Marc is at this very moment. click here.

Ride on, Marc — we’re proud of you!

EWI won the latest EWI-MDK Bike to Work Challenge by a score of 60 to 48. The Challenge started  Monday, June 2, 2014 and ended Friday, June 13, 2014.  The scoring was one point per day of commuting to work by bicycle during the work week, regardless of distance (you didn’t need to ride the full distance).  Tracking of rides was done on RideNet | Home.  Our challenger is a locally-based law firm, Home : Manley Deas Kochalski, LLC (employer of Blake McAllister’s sister and Jim Tighe’s sister-in-law).  Several of us from each team met for a Happy Hour last week to celebrate (or lick our wounds, as the case may be).

On a larger scale, Thursday, May 1 was the start of the National Bike Challenge.  This covers all types of riding and will continue until the end of September.  EWI has a team in this event.  Information can be found at Home | National | National Bike Challenge.

A bit of history:  The first Central Ohio Bike to Work Week was held in 2008.  Five EWI Associates participated that year and Team MDK won the 100 to 499 employee division.  I looked at the numbers and realized that we could have won if we doubled our score.  With a bit of a push in 2009, EWI had 17 riders and won our division. Team MDK was second. The photo below shows most of our team that year, including Jim Tighe holding our trophy.

2009 Bike to Work Week Victors

The third year of the local Bike to Work Challenge, Jim’s sister-in-law said in an email “You may also want to spread the word around your office that the bike to work week cheating that costs us our title last year will not be tolerated.  God sees all, and I’m going to give you the benefit of the doubt and believe that you had nothing to do with it.  Prepare to be schooled in the correct way to win.  Let me be your guide.”  With this extra motivation, we had 33 people (nearly 25% of our workforce) ride at least once and won our division a second time.  Team MDK was second. The end results were the same for the top two of our division in 2011, the last year of the local challenge.

EWI and MDK have held our own Bike to Work Challenge the past two years.  EWI has continued to prevail.  The power of innovation…

 

 

Marc Purslow is passionate about helping disadvantaged kids succeed. That’s why the EWI Applications Engineer (arc welding) is taking time this summer to raise money for After School All Stars, a program that provides free afternoon programs that keep at-risk children safe and help them achieve in school and life.

Marc and kids

But if you know Marc, you know he doesn’t do things half-way. He’s made a commitment to ride his bicycle solo across the country to raise $50,000 for the ASAS program! Marc starts his journey in coastal Maine on July 3rd, and plans to end in San Francisco some 4-5 weeks later.

We at EWI are incredibly proud of Marc, and are thrilled to support his ASAS Cycle America Challenge. We’ll be keeping up with his adventures and reporting on his cross-country progress throughout the summer. If you want to “join the ride,” you can check “Latest News” at ewi.org, where we’ll post Marc’s regular reports from the road.

You can learn more about ASAS and support Marc’s goal, by clicking here. All donations from his ride will benefit ASAS Ohio.

Go, Marc!


Challenge map

Marc on bike

 

 

 

jesse-header

On May 7-8, EWI participated in the 9th annual National Center for Defense Manufacturing and Machining (NCDMM) Summit in Blairsville, PA. The event, which included a full day of panel discussions, allowed for an open forum and information exchange, as well as the opportunity to learn about capabilities of other attendees. An exhibit area in the presentation hall showcased about 30 participant companies, as well.

The meeting agenda covered technologies relevant to manufacturing, the mission and status of the new National Network of Manufacturing Innovation institutes (including EWI-founded ALMMII), a session on the roles that primary and secondary education providers need to play in the success of the NNMI, and the renewed culture of manufacturing innovation in the United States.

The day led off with a great introduction by Ralph Resnick, President and Executive Director of NCDMM, and a keynote presentation and address by Adele Ratcliff from the Office of the Secretary of Defense (OSD). The presentation focused on the importance of the institutes in delivering meaningful results, their relevance to the President’s efforts to return the United States to a position of excellence in manufacturing, and what we can do as individuals to assist in this effort. It was impossible to not feel a strong sense of community, commitment, and national pride afterward, a great way to kick off the event.
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The rest of the day was equally informative and inspiring. Being able to see and speak with such a diverse set of contacts in one day are what make attendance at events like the NCDMM Summit so relevant, and easy to justify. We will definitely be at the Summit next year.

Arc-welding robots have been around for decades and are used in many industries, including heavy manufacturing, automotive, aerospace, and ship building.  Historically, the knowledge and skill required to implement arc-welding robots has been substantial and may have discouraged first-time robot users.  In recent years, however, robotic welding equipment manufacturers and integrators have advanced the level of control and ease of use.

The development of offline programming (OLP) software has been one such advancement.  By incorporating a 3D part model into the OLP software, which contains a model of the real equipment, the user has the ability to create a weld path without using the actual robot.  Using a robot and a teach pendant to create a weld path can take hours, if not days, depending on the part size, configuration, or complexity.  Using OLP can drastically reduce the programming time required and also eliminates the need to shut down production to program the robot.

 

 

Additionally, modern robotics systems that incorporate the use of OLP offer a variety of useful features to make implementation much easier. Some of these features include:

  • Ability to perform reach studies
  • Simulation videos
  • Collision detection
  • Cycle time estimation
  • Multi-bead, multi-layer welds
  • Searching joints to account for joint variations
  • Calculated adaptive fill

If you are interested in learning more about the different offline programming options for robotic arc welding, please feel free to contact Adam Uziel at auziel@ewi.org, or Steve Massey, at smassey@ewi.org.

 

Desert

Mil-E-24403/1 and AWS A5.20 specifications (“D” and “Q” designators) have their requirements on low and high heat inputs to qualify a FCAW wire in addition to the control of pre-heat and inter-pass temperatures. A specified heat input is an average heat input for all passes in a test assembly. AWS A5.20 / 17.2 even applies heat input limits on individual passes during the welding of a whole test assembly. However, it still won’t be able to prevent one creative interpretation and practice from manipulating the heat input to qualify FCAW consumables.

During the qualification welding, a targeted heat input should be kept as stable as possible to weld a pass from the beginning to the end. According to the layout of the test assembly illustrated in AWS and Military specifications, usually, about half of the test assembly is used to machine out a tensile specimen for the tension test, and the rest is used for Charpy “V”-notch (CVN) impact samples. This layout provides an unintended advantage of allowing improper manipulation on the heat input in welding.

When a high heat input is used to weld a test assembly, 3G welding is usually adopted for the consumable qualification. For a certain E71T-1 type product as an example, if a consistent heat input is used to weld a pass from the bottom to top by using a 0.052” (or other diameters) FCAW wire, it is very likely that the yield strength falls out the specified strength range, or the CVN impact toughness fails. A “smart” solution is to weld the bottom half by a low heat input with a fast travel speed and weld the top half by a high heat input with a slow travel speed. The whole test assembly is effectively separated into two parts that are welded with two different heat inputs. After the welding, a “smart” move is followed by averaging the low and high heat inputs to satisfy the average heat input required by specifications. By doing that, both the yield strength and impact toughness can be reported to be satisfactory.

Due to the resultant unevenness of mechanical properties on the whole weld assembly, the “smart” move shall not be considered to be legitimate (or decent) from the engineering practice, nor shall be deemed by the welding consumable community. On the other hand, the layout of the test assembly for welding consumables qualification shall be revised to prevent those “smart” moves.

Last week EWI had the first EWI ShipIt! Days. Employees were given 24-hours to do anything they wanted that wasn’t related to their regular job. The catch? You have to deliver something at the end of the 24-hours. This commercial about EWI is what my team delivered. Enjoy!!

 

 

If you are not familiar with the original Dollar Shave Club video, check it out.

Buffalo BuildingNew York State has confirmed its investment plans for the new advanced manufacturing institute to be operated by EWI in Buffalo. The announcement to dedicate  $45 million for the new center was made last week. This allocation will fund facilities, equipment, and start-up operations for the first five years, after which the institute will be self-sustaining.

Activities will focus on four areas of manufacturing innovation: flexible automation and controls, advanced materials and testing, additive manufacturing, and advanced fabrication.

The facility, located downtown Buffalo, NY, is set to open in stages with some operations starting up this summer. About half of the space will function as laboraties, with meeting rooms and offices in the other half.

For more details about EWI and the launch of the advanced manufacturing institute in Western New York, click here.

ewi-related-postsBuffalo Billion logo

Buffalo Billion logo                                    western_new_york

Excitement is building in Western New York as state and local officials, businesses, and community leaders get ready to welcome EWI to downtown Buffalo. EWI will launch the new advanced manufacturing institute at the end of February as part of the Buffalo Billion Investment Development Plan.

Here’s what we’re hearing from New York…

Governor Andrew Cuomo:
“As operator of the Institute, EWI will bring a proven record of helping the industry tackle and solve manufacturing and production issues. Under this partnership, EWI will make Western New York more competitive and position the region as a leader in manufacturing technology and innovation, which will help spur new economic opportunities for years to come.”

Chris Sansone, President of Buffalo Niagara Manufacturing Alliance:
“I’m excited about [EWI] opening up shop. Their forte is bridging the gap between government-funded research and the commercialization of those technologies.”

Buffalo Mayor Byron Brown:
“EWI’s selection to provide Buffalo’s advanced manufacturing sector with the tools needed to be highly competitive continues the great momentum that’s underway in Buffalo.”

Erie Community College President Jack Quinn on the relationship between ECC and EWI:
“We’ll be working together, and they’re a world-class operation.”

To read the latest from Buffalo Business First, click here.