The Benefits of TW-GMAW for High-productivity Precision Welding Applications

Twin-wire gas metal arc welding (TW-GMAW) was recently
evaluated for use in high-productivity precision fillet welding applications by
EWI. The results show that TW-GMAW offers deep penetration, a wide and smooth underbead
profile, omni-directional deposition, process stability with variations in
CTWD, lower cost setup, and high-deposition arc-DED building capabilities.

EWI associates Michael Carney, Dennis Harwig, Nick Kapustka, and Travis Peterson have written a paper discussing this work, Twin-wire GMAW for High-productivity Precision Fillet Welds. To download this paper, free of charge, simply complete the form on this page

To learn more about this study, contact Michael Carney at [email protected]. To learn more about EWI’s capabilities in arc welding and directed energy deposition, click here.

Complete this form to download the paper:

To view the paper, please submit the form above.

To speak to an EWI expert about a project, call 614.688.5152 or click here.

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The Unique Advantages of Binder Jetting

Binder jetting offers unique material options compared to
high-energy deposition alternatives. Coupled with low running costs, binder
jetting can provide an effective method to produce finished parts at nearly
production-ready speeds. This additive manufacturing (AM) method is being
considered for applications in high-volume industries such as automotive where it
is cost-competitive to casting.

Binder jetting utilizes a liquid binding agent applied to
layers of powdered material to quicky build complex geometries and parts. In
contrast to high-energy powder bed fusion (PBF) systems, material consolidation
in binder jetting does not occur in the printer itself. Separating heat treatment from printing enables more uniform
heat application, reduces part distortion and warping, and frees up printer
time to make more parts. Once the initial print is complete, the entire
container is cured which makes the parts strong enough to be gently removed
from the powder. These “green” parts do not possess final part strength and are
still fragile.

The final processing step generally includes heat treatment
in a vacuum furnace to burn off the rest of the binder, followed by either a sintering
or infiltration process. A large industrial vacuum furnace can process
significantly more parts and reduces the bottlenecks common in high-energy PBF.
Often, manufacturing
facilities already have these furnaces in place for other heat treatment
processes. If not, the cost of purchasing a vacuum furnace is usually well
worth the overall increase in throughput.

A unique feature of binder jetting systems is the broad
application of different materials. High-energy output is not applied to the
parts, so volatile material can be used. The process is also well-suited to
materials that do not typically melt such as ceramics and composites.

Because binder jetting can accommodate a variety of materials, can print parts quickly, and can be executed in large build spaces without specific vacuum or heating requirements, this AM method offers a number of advantages – especially where higher production level throughput is needed.

With broad expertise in additive technologies, EWI can provide direction on how best to proceed to maximize your new investments. For more information, contact Mason Roalsvig at [email protected].

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Using corrosion science to improve the quality and longevity of your products and infrastructure

Corrosion is an inescapable, ongoing issue for most manufacturers. There are, however, different science-based options for preventing, detecting, evaluating, and mitigating corrosion.

Josh James, EWI Principal Engineer and Research Leader, provides a concise overview of these approaches in his new paper, Corrosion Science: An Indispensable Tool Kit in All Manufacturing Development Stages. You are invited to download this paper, at no charge, by completing the form on this page.

To learn more about applying corrosion science tools to improve your products, contact [email protected].

Complete this form to download the paper:

To view the paper, please submit the form above.

To speak to an EWI expert about a project, call 614.688.5152 or click here.

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Long-term Polymer Properties – Don’t Be Creepy, Just Relax the Stress Away

by Jeff Ellis

Polymers undergo creep and stress relaxation over long
periods of time, which can be detrimental to the function of medtech products. When
designing medical devices that contain polymers, it is important to understand
the differences, similarities, testing, and mitigation strategies of the two

The major difference between creep and stress relaxation is the way stress and strain act upon them, as shown in this figure.

For creep, a constant force is applied to the material and the material moves (ΔL). For stress relaxation, strain is imparted on the material, and the stress with which the material resists the strain decreases over time. The following include some real-world examples:

  • Creep:
    • A large metal spring applies a nearly constant force on interacting parts as they slowly creep within a polymer auto-injector device.
    • A plastic bandage is applied to a patient to hold an IV line in-place. Over a couple of days, the constant stress on it causes it to stretch and loosen.
  • Stress Relaxation:
    • A polymer spring is used to place a force on a vial to keep it aligned in a diagnostic instrument, but over time the force decreases, and vial is no longer aligned.
    • An all plastic clip is opened and fitted over a group of cables to manage their position. Over time, the clip applies less compression force and the cables can move.

What causes these material property changes? The underlying reasons for creep and stress relaxation are the same. For example, a polymer that has low creep will also have low stress relaxation. Both depend on how much relative motion occurs between polymer chains.

The motion is a function of one or more of these factors:

  • Crystallinity – Some polymer chains pack into a crystalline orientation, the ones that do not are considered amorphous. Crystalline regions pack much more tightly and neatly into organized structures than their amorphous counterparts, which greatly reduces polymer chain mobility. Since the crystalline polymer chains cannot move independently, polymers with a high crystalline percentage have low creep and stress relaxation. An example of a highly crystalline polymer with low creep is polyoxymethylene (POM).
  • Polymer side groups – Polymers with
    larger side groups have less relative mobility than those with small side
    groups. Envision a polymer chain as an extension cord. When you have many short
    extension cords, they easily slide over one another. Now envision that the
    extension cord has lights attached radially in every direction along its
    length. It is difficult to slide these light strands over one another. This is
    the difference between polyethylene (PE), extension cord, and polypropylene
    (PP), light strand. As you can see from this oversimplification, the PP has
    lower creep and stress relaxation than the PE.
  • Molecular weight – A confounding factor
    is that molecular weight (MW) also plays a role. The higher the MW, the longer
    the polymer chain, the lower the melt flow index, and the harder is it to get
    the polymer chains to move independently. Therefore, higher MW also has better
    resistance to creep and stress relaxation.
  • Fillers and glass transition temperature – Fillers
    usually decrease polymer chain mobility and increase the materials modulus;
    both make them more resistant to creep and stress relaxation. Glass fibers are often
    used to reinforce nylon. The is a chemical compatibilizer, called sizing, that
    chemically links the glass to the nylon so that the polymer chains have
    difficulty moving relative to the glass, and vise vera. The glass has a much
    higher modulus than the nylon, so a glass filled composite has a higher modulus
    than the neat polymer. When stress is applied to the filled nylon, less strain
    is imparted due to the higher modulus, meaning that the creep will also be

Long term creep and stress relaxation can be estimated from
short term testing when time-temperature superposition (TTS) techniques are
implemented using a dynamic mechanical analyzer (DMA). Because creep and stress
relaxation can take months or years to appear in normal use, it’s useful to
speed up the process for testing. The DMA can exert controlled stress or stain
on the polymer at a specified temperature. A series of creep or stress
relaxation tests can be performed at the temperature of interest as well as
several elevated temperatures. The elevated temperatures must not come within
10°C of the glass transition temperature because there is a step change in the
polymer’s response that affects prediction accuracy for future polymer
performance at a lower temperature.

Once all the data has been collected, the higher temperature
data points are superpositioned out to longer times, with the highest temperature
being shifted to the longest time. Once shifted, all the data make one master
curve which predicts the long-term creep or stress relaxation. Time-temperature
superposition testing can be completed in about one week and can predict a polymer’s
response several years into the future.

Because most medtech products are designed to last many
years, long-term polymer properties must be considered when designing a product
and choosing a material. Even single-use medical devices, like auto-injectors,
can be assembled years in advance of being used. Design and material come
together to determine the extent of creep or stress relaxation in your product.
The levels of the stress or stain exerted on a polymer can be difficult to
measure, but simple to model using finite element analysis (FEA). A well-understood
design with a creep resistant polymer can last the life of the product, even if
a large spring force is constantly pushing on it.

Are you experiencing failures with your aging plastic products ? EWI can help. Contact Jeff Ellis at [email protected] or 614.688.5114 to learn more.

To read more articles about avoiding material failure in plastic products, click here .

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Development of Sonotrode with Replaceable Knurl Pad for Use in Ultrasonic Welding

According to a report recently published by Fortune Business Insights,1 market demand for vehicle electrification was estimated at 8.6 million units in 2018. This market is projected to exhibit a compound annual growth rate of 21.1% in the forecast period, 2019-2026 and reach 40.6 million units by 2026. A big part of this market is the manufacturing of lithium-ion batteries for electric vehicles which requires a significant amount of welding.

Ultrasonic metal welding (UMW) is a primary welding process for
the manufacture of lithium-ion batteries. This solid-state technology
applies generated ultrasonic vibrations by transducer through
sonotrode to the material and causes shearing of asperities of the materials to
bond them together.

UMW offers a lot of advantages including reduction of welding time and production cost, as well as a higher quality bond than traditional welding methods. One downside, however, is cost. When knurl pads wear down, a complete replacement of the sonotrode is required. A new sonotrode can cost $2k to $5k depending on the design. Typical heat-treated tool steel sonotrodes (Figure 1a) produce approximately 70,000 welds in UMW of copper before needing to be replaced. A single welding machine in a high-volume lithium battery manufacturing facility may run 10,000 welds per day. Considering that a typical facility has eight or more lines, rough estimates show a $0.5M-$2M annual sonotrode cost per battery manufacturing facility.

Therefore, developing sonotrodes with replaceable knurl pad from wear resistant material (Figure 1b) could be very cost-effective and has the potential to cut tooling costs by 50-75%. A bimetal sonotrode not only could improve the life of sonotrode but would also reduce the fabrication cost because the whole sonotrode does not have to be replaced.

EWI’s capabilities in using FEA for the design and
fabrication of ultrasonic tooling for high power ultrasonic systems have
enabled it to invest on this concept. Updates on this project will be available
later this year.

If you are interested in learning more about EWI’s
experience and capabilities in  tool
design for ultrasonic application, please contact Amin Moghaddas, Project
Engineer, at [email protected].


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A Better Way to Test Quality in Plastic Welds

Evaluation of plastic weld quality is a multi-industry
challenge. Typical methods of weld evaluation such as mechanical or leak
testing can determine whether a weld can accommodate a defined application
requirement, but do not indicate whether the weld itself is good. A good weld
is one in which the polymer chains from either side have diffused across the
joint. However, the success of the intermolecular diffusion cannot be
determined via the standard mechanical and leak tests. 

Through previous work at EWI, we have determined that the most effective method for evaluating diffusion is a technique developed internally several decades ago. The process, first published in a paper presented at the Society of Polymer Engineers (SPE) Annual Technical Conference (ANTEC) in 2018, involves heat treating of polished cross sections. While this method has been used at EWI to good effect for years, it has always involved a manual process with a hot air gun. To make the process more consistent, internal research was conducted to apply controlled infrared (IR) lamp heating to perform the heat treating process. Selected cross-sections from previous internal research projects were re-polished and then heat-treated using the IR lamp to establish material-based heat-treating settings. The results and recommendations will be submitted for publication in the proceedings and presented at SPE’s ANTEC conference in 2021.

Before heat treatment
Too much heat treatment
Good heat treatment

To learn more, contact Miranda Marcus at [email protected].

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Better information for predicting fracture toughness in newer and thicker steels

Qualifying very thick steel and new steels for use in construction, shipbuilding, pipes, and heavy equipment is not easy. Charpy tests are usually used, but the resulting data is not always consistent.

Bill Mohr, EWI Principal Engineer for Structural Integrity, has conducted a study of crack specimens with splits. His work shows that Charpy and fracture toughness data can be better understood by noting whether the splits cross into the start notch or appear only on the main crack. This additional information can help product designers avoid fracture risks when using these materials. 

Splitting Behavior Effects on Toughness of Steels discusses these findings. You are invited to download this paper, free of charge, by completing the form on this page.

To learn more about this work, contact [email protected]. For more information about EWI’s work in structural integrity, click here.

Complete this form to download the paper:

To view the paper, please submit the form above.

To speak to an EWI expert about a project, call 614.688.5152 or click here.

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Material Integrity Threats Associated with Conversion to a Hydrogen Economy

The energy economy is experiencing a shift away from oil and
gas sources as European nations and states, such as California, impose
legislation on utilization and sourcing. A primary, would-be displacer of
natural gas in the utility space is hydrogen (or chem + hydrogen hybrid fuels).
In most cases, the preference of industry would be to utilize legacy
infrastructure to transport and store next-generation fuels. However, it is
unclear whether the integrity threats associated with the handling of natural
gas are equivalent in transportation and storage of high hydrogen fuel stocks.

The principal integrity threat from a metallurgical standpoint is a mechanism known as hydrogen embrittlement. Hydrogen gas dissociates into hydrogen protons and infiltrates the microstructure of metallic components. The transported hydrogen collects around defects and degrades mechanical properties. The reduced toughness and load capacity can subsequently lead to brittle fracture and premature failure. The following illustration is a representation of hydrogen infiltration leading to embrittlement:

Schematic depicting the hydrogen infiltration that leads to metal embrittlement.

To ensure safety during conversion to a hydrogen economy,
the industry needs to consider the threats associated with the utilization of
legacy assets. Due to their metallurgical histories and inherent susceptibilities,
many of those materials are potentially vulnerable to embrittlement. Large
scale conversion to hydrogen as an increasingly viable energy source highlights
the need for the development of new materials with implicit resistance to hydrogen-specific
degradation mechanisms. This new frontier will bring new requirements for
joining methodologies, materials characterization, monitoring and NDE
capabilities, and a thorough understanding of the technical trends in the
evolution of the hydrogen economy at large.

To learn more about EWI’s work to address materials and integrity
issues within the U.S. energy infrastructure, contact Josh James at [email protected].

The post Material Integrity Threats Associated with Conversion to a Hydrogen Economy appeared first on EWI.

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Polymer Chemical Resistance – Product Survival Through Harsh Liquid Contact and Sterilization

by Jeff Ellis

Polymer properties can permanently change as they age, which can lead to unexpected failures. These failures can be avoided by considering the polymer’s response to the environment during early product design. Liquids, gases, heat, and irradiation can have irreversible chemical effects on a polymer. Alternatively, in some cases the polymer can affect the liquid’s properties. Both situations can cause unwanted medtech product failures. Some of the most common types of degradation are hydrolysis, oxidation, and chain-scission.

  • Polymer hydrolysis – Cleaning products cause your plexiglass screen to become hazy from induced crazing.
  • Polymer oxidation – Heat and light from devices left in a car can combine with oxygen to make polymer products weak and brittle. An example is an epinephrin auto-injector that may be left in the car. It is under high stress due to containing large springs, so if the polymer embrittles, the device could crack.
  • Polymer chain scission – Too many heat/shear processing cycles cause resins to have reduced molecular weight and decreased strength. This can happen to resins during multiple compounding cycles in which fillers and colorants are added.
  • Polymer sterilization – Gamma irradiation, ethylene oxide gas, and autoclaving all can cause polymer degradation (discoloration, decreased strength, etc.) in medical devices if the polymer is not resistant.
  • Liquid degradation – Drug formation stabilizers can absorb into polymers leaving the drug destabilized with reduced efficacy.

Hydrolysis is initiated through contact with water, acids, or bases. The rate of the degradation increases as a function of increased temperature, increased acidity, or increased basicity. The degradation proceeds through cleavage of the polymer backbone, thus decreasing its molecular weight and reducing its strength. Some sanitizers used in the healthcare industry can initiate high rates of hydrolysis. For example, a 10% bleach solution that is used to wipe down equipment between uses has a very basic pH of 13. After repeated wiping the material can degrade to the point of discoloration, crazing, or even fracturing. Polymers most susceptible to hydrolysis include polycarbonate, polyamides, polyurethanes, polyacetals, and polyesters. Polycarbonates are clear and used as protective barriers but can become hazy after multiple cleanings.

One of the most common tests to assess hydrolysis of a polymer to a liquid is through monitoring of environmental stress cracking (ESC). There are standard methods for performing ESC testing, such as ASTM D1693. Essentially, a bar of the polymer is put under a constant strain and submerged into the challenge liquid. The time and temperature of the submersion are controlled, and the polymer is inspected for signs of degradation (discoloration, crazing, cracking, swelling, etc.) at periodic intervals. This test can be run at accelerated conditions so that long-term polymer performance can be predicted from short-term testing.

Another type of polymer degradation is oxidation of which there are two main forms, photo and thermal. Photo-oxidation occurs from the energy carried by light, most commonly ultraviolet (UV) radiation from the sun. Thermal oxidation occurs more rapidly at elevated temperatures, but also occurs at ambient temperatures over a longer time, as seen in Figure 1. Both types require oxygen from the atmosphere. Oxidation uses free radicals found in the polymer along with oxygen to cleave covalent bonds in the polymer backbone. This type of degradation reduces the polymer molecular weight, reduces strength, and embrittles the polymer. Autoclave sterilization can cause oxidation and has similar effects on polymer properties due to its high temperature. Polymers with low glass transition temperatures, like PVC, are more susceptible to this degradation.

Cracks in the polymer chain direction
induced from years of ambient

Polymer chain scission occurs more often in plastics that experience high temperatures and shear rates for longer times. Most polymer parts for medical devices are injection molded. These polymers are routinely compounded more than once. Fillers are compounded into the polymers to add strength or barrier properties, while colorants enhance aesthetics. The compounding is performed at high temperature and high shear in a mixing extruder. Then, the parts are shaped by injection molding, which is again accomplished at high temperature and shear. The chain scission experienced during each processing cycle causes decreased strength and increased unwanted long-term properties like creep. Similarly, gamma irradiation as a sterilization method also causes chain scission in some polymers, such as PTFE. On the other hand, gamma sterilization causes polymer cross-linking in others, such as polyethylene.  

The most common effects of polymer chemical degradation have been discussed, but there also can be an effect on the contacting fluid. Many drug delivery devices have a wetted fluid path that the drug travels before delivery to the patient. Drug formulations contain stabilizers, such as cresol, and some polymers readily absorb cresol. This decreases the percentage of stabilizer in the formulation, which destabilizes it and can cause denaturization of the drug, rendering it less efficacious. The ultimate consequence of this sequence is that the patient receives a lower active dose than prescribed.

As discussed here, polymers can fail in many ways depending on their chemical make-up and the environments they are exposed to. However, a fundamental understanding of polymers can be used to intelligently select the best material of each product, thus avoiding costly failures.

Do environmental or chemical factors affect the quality and longevity of your plastic products? EWI can help. Contact Jeff Ellis at [email protected] or 614.688.5114 to learn more.

To read more articles about avoiding material failure in plastic products , click here

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High Duty Metal Additive Manufacturing Using Cryogenic Cooling Thermal Control

Robotic arc directed energy
deposition (DED) additive manufacturing (AM) offers maximum build volume for
building structures, adding features to structures, and repairing structures.
The technical requirements for metal DED builds are similar to welding
requirements. For example, the pending NAVSEA Technical Publication – Process
Requirements for Metal Directed Energy Deposition Additive Manufacturing1
will specify maximum interpass temperature for depositing beads on builds.  If above the interpass requirement, the
deposition process is suspended until the build is below the temperature
requirement. Metal fusion DED (wire arc, wire laser, powder laser) processes have
high heat inputs and high deposition rates. Depending on the build thermal conditions,
the build rate and economics will be impacted by interpass temperature requirements.

Thermal spray with LN cryogenic cooling technology used to control interpass temperature and improve duty cycle (© Air Products. Used with permission.)

On recent builds at EWI, up to 80% of build time was spent waiting for the build to cool between deposit passes. Forced air or water spray cooling can be used but both have limitations for DED AM applications. A more efficient approach is the use of cryogenic cooling for either interpass cooling between deposits or in-situ cooling directly behind the torch for maximum duty. Cryogenic cooling technology is commercially available from Air Products, which recently consigned a system to EWI for developing in-situ liquid nitrogen cryogenic cooling (ILNCC) for robotic DED processes. The Air Products’ system can vary LN flow and phase (liquid, liquid-gas, or gas) using infrared sensor feedback to control interpass temperature. 

ILNCC has the potential to address two key challenges in DED AM technology: low productivity due to long wait times for cooling to interpass temperature, and high residual stresses in large deposits.  It also has the potential for developing high temperature cooling rate control and providing builds with uniform isotropic properties.  If interested in exploring this technology for your DED applications, please contact Dennis Harwig, Technology Senior Leader at [email protected]

  1. D.D Harwig, W. Mohr, S. Hovanec, J. Rettaliata, R. Hayleck, E Handler, and J.Farren, “Tech Pub Qualification Scheme Development for Arc Directed Energy Deposition Additive Manufacturing,” In Proceedings of the Ground Vehicle Systems Engineering and Technology Symposium (GVSETS), NDIA, Novi, MI, Aug. 13-15, 2019.

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