Joining Bimetallics with Low Force Friction Welding

Low force friction welding, a
hybrid technology developed by EWI and MTI, uses an external energy source to
raise the interface temperature of the parts being welded, reducing process
forces required to make a solid-state weld compared to traditional friction

Low Force Friction Welding of
Bimetallics: Aluminum 6061 to 1020 Steel Tubes
, written by EWI Senior Technology Leader
Jerry Gould with Zach Roelofs, explores the capabilities of using this
technology tubular geometries with dissimilar metals.

You are invited to download
this paper, for free, by submitting the form on this page.

To learn more about low force
friction welding or to discuss using this process for your manufacturing
application, contact Jerry Gould at [email protected].

Complete the 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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Prediction Capability for Laser-welded Blank Formability

Laser welded blanks (LWBs) are produced by laser welding two sheet materials together, typically prior to a forming process. The sheet materials can be identical or dissimilar depending on the application. The LWB process allows the designer to ‘tailor’ the location of the desired material properties in the blank for crashworthiness and light-weighting. LWB technology was introduced in the US automotive industry in the early 1990s and it has been widely used in automotive body structures such as door inner panels, fenders, roof stiffeners, and pillar stiffeners (Figure 1). The application can also be used for hot-stamping of multi-strength sheet materials.

The behaviors of a laser welded blank during forming are significantly influenced by blank conditions such as thickness variation and the strength ratio of the two materials, as well as the weld quality. These conditions can cause variation in the local formability of the weld area, making the numerical simulation of forming LWBs more complicated than simulation of monolithic sheets. Unfortunately, the local formability of the LWB weld area is often over-simplified in forming simulations. The base material properties are simulated in the weld area, which completely neglects the heat affected zone (HAZ) and weld properties. Using this method on certain steels has been reasonably effective due to the weld and HAZ being stronger than the base metal, forcing necking failures to occur in the thinner or softer base metal away from the weld area (Figure 1).

Third generation advanced
high strength steels (GEN3 AHHS) have not shown a trend similar to previous
generations. Instead, fractures in the weld and HAZ are observed more often
with GEN3 steels than the conventional steels. When the over-simplified
simulation method is used on these materials, the physical results do not
correlate well with simulation. This can cause costly design changes and production

If designers can better predict the formability and unique behaviors of GEN3 AHHS (and other material) LWBs during forming, many costly design changes and production issues could be avoided. To address this emerging challenge in predicting local failure in welds and HAZs during the forming of LWBs, the EWI Forming Center is working with industry partners to develop a LWB forming prediction model with an emphasis on GEN3 steels.

To learn more about this work, contact Hyunok Kim, EWI Forming Center Director, at [email protected].

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EWI Awarded Multiple Research Grants from the NSRP

EWI is pleased to announce the receipt of three research
awards from the
National Shipbuilding Research Program
(NSRP) as part of its continuing
mission to reduce costs associated with U.S. shipbuilding and ship repair. The
funded EWI projects include:

  • Portable
    Single-Pass Buried Arc Welding of Steel Plate During Ship Erection
  • High
    Productivity Reduced Emissions Arc Gouging Process
  • Next
    Generation Double Electrode GMAW Processes for Precision Fillet Welding

EWI is also a partner on a fourth grant-awarded project, Optimized
Weld Records
, led by software developer TruQC.

For more information about the EWI-led projects and others
in the NSRP R&D project portfolio (valued at $2.64M), read
the full press release here

To learn more about EWI, visit

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EWI to Offer Webinars on Additive Manufacturing in December

EWI is pleased to present two additive manufacturing (AM) events this coming month. These free webinars are open to all interested participants:

  • Working Towards a Full Additive Manufacturing Data Ecosystem
    Wednesday, December 9, 2020
    1:00-1:30 pm EST

    As a founding partner of the ASTM Additive Manufacturing Center of Excellence (AM CoE), EWI has played an active role in the effort to advance the Center’s three primary goals: 1) Develop a Common Data Dictionary (CDD) to set consistent terms and relationships for AM data, 2) develop a Common Data Exchange Format (CDEF) to enable robust data sharing, and 3) automate data acquisition for affordable, fast, and accurate data capture. Presented by EWI Applications Engineer Luke Mohr, this session will cover the latest standards research in the AM community and the the progress being made to implement AM standards.  
  • High Deposition Gas Metal Arc Welding Technology for Large-Scale AM
    Tuesday, December 15, 2020
    10:00-11:00 am EST
    Robotic directed energy deposition (DED) is a versatile, rapidly developing technology for digital welding, AM, and parts repair. EWI is currently leading a range of large-scale DED AM initiatives to mature this technology for aerospace, energy & chemical, defense, heavy manufacturing, and shipbuilding structures. The technology offers many benefits and is compatible with robotic computer-aided manufacturing software. Senior Technology Leader Dennis Harwig and Applications Engineer Mike Carney will discuss recent work investigating the suitability of tandem/twin gas-metal arc welding for directed energy deposition as well as other aspects of EWI’s new research program for advancing arc DED technology.

There is no charge to attend either of these programs, but advanced registration is required.

To reserve your spot for Working Towards a Full Additive Manufacturing Data Ecosystem on December 9th, click here.

To hold your place for High Deposition Gas Metal Arc Welding Technology for Large-Scale AM on December 16th, click here.

For more information about EWI webinars and events, visit

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Qualifying 3D-printed replacement parts for use in critical medical products

In response to urgent need during the COVID pandemic, EWI
conducted a study to validate the use of polymer additive manufacturing to make
replacement parts for medical ventilators. The results of this research
demonstrate that high-quality, leak-tight parts can be made quickly and
efficiently using the 3D printing technology.

To read the details of this work, you are invited view a
paper by EWI associates Jeff Ellis and Dan Kowalik, Evaluating the
Feasibility of 3D-printed Parts for Medical Ventilators with Quantitative Leak
The paper can be downloaded for free by submitting the form on
this page.

For more information about using additive manufacturing
processes to produce polymer parts, 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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Rotational Low Force Friction Welding

Solid-state welding processes
are a group of technologies in which joining is accomplished without melting
the individual substrates. In these processes, bonding is accomplished by a
combination of heating and forging. Heating is used to both lower the flow
stresses enabling forging, as well as promote diffusion between the individual
substrates. Common variations of these processes include flash-butt, upset,
projection, and mash-seam welding, as well as friction-based welding processes
such as direct-drive, inertia, and linear friction welding.

A key aspect of producing high-quality,
solid-state welds is the creation of interfacial strain between the substrates.
This strain is introduced in various forms depending on the joining process. For
resistance welding processes, strain is achieved by utilizing heat and a
compression force. A typical representation of a resistance butt weld is shown
in Figure 1.  Strains are largely tensile
(along the faying surface), requiring considerable forging to achieve joint
properties. For friction-based processes, heating is generated through relative
motion. Here, resulting strains are both parallel and perpendicular to the
faying surface. The former strains are related to rotational motion, the latter,
axial motion. A typical representation of an inertia weld is shown in Figure 2.

A new addition to solid-state joining technologies is low force friction welding, a hybrid welding process jointly developed by EWI and MTI (of South Bend, IN) which combines resistance and friction welding. The resistance welding component contributes bulk heating to the interface coupled with an axial forging force. The friction welding component provides transverse oscillations to the bond line resulting in lateral surface strains. The coupling of these two processes improves the resulting strain field and ensures high-quality weld joints at lower welding forces than used by the individual processes. Hence, the hybrid approach has the benefit of simplifying compressive applied pressure requirements and reducing the total amount of forged material. To date, low force friction welding has been performed on machines that only have translational, linear motion (like linear friction welding). However, numerous industry applications consist of round cross-sections (e.g. shafts, struts, and cylinders, which would be better suited to rotational oscillations at the joint line.

An example of a rectangular cross-sectioned
weld using this low force friction welding is shown in Figure 3; note the
reduction in upset material. Initial applications have estimated equipment cost
reductions up to 50% compared to conventional friction welding approaches. However,
work on rounded cross sections has shown that the translational linear systems do
not work as well for circular joints.

To support this application, EWI and MTI are undertaking the build of a prototype for a rotational motion-based modular system. The system will allow transference of both axial force and welding current from the resistance welding frame and augment these with rotational motion. The initial concept for the prototype is shown in Figure 4. The system is intended to address near-term applications in the automotive, aerospace, oil and gas, light manufacturing, and defense markets. Planned launch of this welder is the spring of 2021.

For more information about this project contact Tim Stotler at [email protected], Greg Firestone at [email protected], or Jerry Gould at [email protected].

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EWI to Present Free Webinar on Manufacturing Automation

There are many benefits to automation in manufacturing, from increasing productivity to improving quality to enhancing worker safety on the factory floor. If your manufacturing operation is small or medium sized, however, you may feel that you are behind in developing effective automation processes for your production line. Your questions might include:

  • What types of automation should we consider?
  • How can we use automation to support and enhance
    our workforce?
  • How do we know that an automation solution we design
    will work?
  • How will we train our teams to use and maintain
    automated systems?
  • Where can we find expertise to guide us in implementation?
  • How do we get started?

If you’re looking for a solid foundation on which to base your automation efforts, EWI invites you attend a free lunch-and-learn event, A Customer’s Journey Through Automation, on November 19, 2020, from noon to 1:00pm. This information session, presented by EWI’s automation team, will cover common stumbling blocks in starting with automation, resources for finding the right systems, using automation to address workforce gaps, and steps to take to put your automation plan into action.

Automating your process may seem like a stressful endeavor,
but it does not have to be. Join EWI on Thursday, November 19th, to
learn how your company can succeed with advanced automation.

This event is free, but advanced registration is required. To sign up for the session by November 18th, click the button below.

A Customer’s Journey Through Automation
November 19, 2020 | 12:00-1:00pm EST
Questions? Contact Michelle Bulan at 716.710.5513 or [email protected].

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New Tool to Assess Torque During Inertia Welding

Inertia welding is a well-established, friction-based,
solid-state joining process. Many different applications use this welding
process, ranging from aircraft engine parts to air bag inflators to hand tools.
Process parameters associated with inertia welding (spindle speed, welding
force, inertia, and displacement) have been widely studied since the process
gained traction in the late 1960s. One characteristic that has received less
scrutiny is the torque generated during the process. Torque is known to vary
widely during a given welding event. Resulting torques occurring during welding
are a key factor in tooling designs and may offer further insight into the
quality of the joint.

Most of the previous work performed to understand torque
variations during inertia and direct-drive friction welding was done with strain
gauges attached to the part or the tooling. Attaching strain gauges presents
two drawbacks. First, the data can only be collected once, as the strain gauge
is a consumable attached to the workpiece. Second, the gauges are often
destroyed during the welding process, which limits usable data. Attaching strain
gauges to the tooling does not totally reflect the torque generated.

Recently, EWI developed a monitoring capability for assessing dynamic torque during welding. Here, the tailstock of a Model 120B inertia welder was modified to allow for free rotation during welding. A torque arm was then mounted on that tailstock and coupled to a load cell. The combination enabled direct and calibratable measurement of reaction torques during welding. For comparison, measured torques from the developed system were compared to that from strain gauges placed on a bar that holds the stationary test sample.

The EWI system offers opportunity to directly assess the
physical requirements for joining new candidate applications. This information
has the potential to improve sizing of equipment and reduce risk in specific
tooling designs. In addition, the described monitoring system can provide
additional information allowing understanding inertia and friction weldability
of specific materials and dissimilar metal combinations.

To learn more about this system, contact Tim Stotler, Principal Engineer, at [email protected].

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Plastic or Elastic: Polymer Dynamics in MedTech Devices

by Jeff Ellis

A polymer can act rubbery or glassy depending on its
temperature or rate of deformation, such as from an impact. This is important
for medtech devices that are stored at low temperature, vibrate, or are
required to pass drop testing. In general, the quicker the polymer is impacted,
the more brittle it acts and the greater the chance it will crack. Let’s examine
why this phenomenon occurs, ways to measure it, and how to use material
selection to avoid failures.

Some real-world examples are:

  • An autoinjector drug-delivery device cracks
    after a larger drive spring is implemented. The larger drive spring releases
    faster which decreases impact time, thus causing the polymer to act more
  • An ultrasound probe used to visualize a fetus in
    utero operates at 5 MHz and cracks a durable polymer housing with its high
    frequency signal.

The rubbery to glassy transition occurs at the polymer’s
glass transition temperature (Tg). At temperatures lower than the Tg,
the polymer acts glassy, whereas above it, the polymer acts rubbery. The
transition is based on the amount of thermal movement that the polymer chains
possess. Like a cold-blooded animal, at low temperatures the chains have
slower, more limited mobility than at higher temperatures. Along the same
lines, when impacted at low temperature the chains do not have time to
rearrange and accept the stress, so the polymer responds plastically by cracking
(glassy). At higher temperatures, the stress can be absorbed by fast chain
movement and the polymer will respond elastically by absorbing the energy (rubbery).

This phenomenon also applies to the polymer’s behavior when
impacted at different frequencies, such as spring size in an autoinjector. Frequency
and impact time are inversely proportional (frequency = 1 / impact time), so a
larger spring contacts the polymer with lower impact time, inducing higher
frequency.  Consider a polymer like
polypropylene (PP) or silicone that is rubbery at room temperature. If the
spring impacts the polymer faster than the chains can rearrange, then it will
act glassy even though the temperature is above the Tg. The high
frequency shifts the Tg to a higher temperature than its stationary
Tg, making the polymer more susceptible to cracking.

The frequency induced shift in Tg can be
experimentally determined using a dynamic mechanical analyzer (DMA). For
frequencies less than 100 Hz this test is simple to run as temperature sweeps
at multiple frequencies. The DMA oscillates a polymer, with small amplitude,
and measures the in-phase component (storage modulus) and out-of-phase component
(loss modulus). Tan Delta, the damping behavior, is the ratio of the loss to
the storage moduli. A maximum in Tan Delta is a good indicator of the polymer’s
Tg. As displayed in the figure, the Tg of polyethylene
terephthalate (PET) shifts 10°C when the frequency is increased from 0.1 to 10

Figure 1. Polyethylene terephthalate (PET) frequency induced Tg shift (plot reproduced from TA Instruments Thermal Analysis-2010 data)

Higher frequencies are common in medical applications and can cause large Tg shifts to occur. Consider the ultrasound probe that operates at 5 MHz; it can increase the Tg of a polymer by tens of degrees. This is enough to shift the Tg of PP from -10°C to ambient temperature. This shift can be estimated using the DMA by running frequency sweeps at multiple temperatures. Then, using time-temperature superposition (TTS) techniques, the data can be shifted out to higher frequencies to create a master curve in order to find Tg values at high frequencies. (For more background on TTS, see my earlier post on Long-term Polymer Properties). In essence, the lowest temperature data gets shifted to the highest frequency. This technique has been used to shift data orders of magnitude into the megahertz range and can explain how a silicone damping material can shatter when in use with a 5 MHz oscillating sensor.

When performing material selection to reduce the risk of
product failure, there are many factors that must be considered. A polymer like
PP might be chosen because it is inexpensive, easy to mold, and the data sheet
indicates it has a high enough impact strength to pass a drop test at room
temperature. However, when it is put into use in a high frequency device, it
ultimately fails by brittle fracture. The Tg, how it will shift at
use frequencies, and the product’s use temperature range should be considered
in this scenario. The Tg is not always listed on the polymer’s
technical data sheet, but a range for a class of polymers can be found in various
technical resources. A rule of thumb is to choose a polymer that has a Tg
at least 10°C away from the expected temperature range the product will
encounter. For products that vibrate at high frequency or experience impacts
like released springs or drops, a larger difference from the Tg
should be implemented to avoid product cracking.

Unexpected failures can occur during prototyping if the dynamic polymer properties are not considered early in the design cycle. Once the injection molding tools have been machined, a material change can be costly and time consuming. Material choice and proper characterization of expected behavior across the product’s frequency and temperature use ranges will mitigate risk of failure.

If you would like to learn more about how to avoid these issues, contact Jeff Ellis at [email protected] or 614.688.5114.

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

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