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VW Explores Thermoplastic RTM

By: Matthew H. Naitove 5. September 2014

I recently posted news that BMW in Germany had installed a large vertical press from Engel to mold composite parts with liquid reactive thermoset resins. Now, it appears that Volkswagen in Germany is also pursuing liquid reactive molding of composites, but in this case with thermoplastics.

KraussMaffei (U.S. office in Florence, Ky.) is developing equipment systems for thermoplastic RTM, involving conversion of liquid caprolactam monomer into nylon 6. Because of the low-viscosity of molten caprolactam, it can impregnate dry fabric reinforcements in a mold, which would be impossible with viscous nylon in its polymerized state. KM has pursued what it has dubbed “T-RTM” using one of its own PUR metering machines paired with a vertical-clamp, tilting mold carrier (introduced at K 2013). This equipment comes from the Composites/Surfaces Business Unit of the Reaction Process Machinery Div. at KM.

The first products made with KM’s T-RTM process are B-pillar reinforcement prototypes made at the FRP TechCenter of the Volkswagen Group Research Center in Wolfsburg, Germany. The project utilized caprolactam supplied by BASF SE (U.S. office in Wyandotte, Mich.). A special RimStar series metering machine was adapted specifically to the extremely low viscosity of caprolactam and was fitted with a special mixhead, high-performance axial pumps, and a fully electric temperature-control system.

FEA Software Predicts Material Response to Repeated Snap Fits

By: Matthew H. Naitove 22. August 2014

Designing parts with snap fits present a particular challenge because of the repeated cyclic loading and unloading. During such cycles, the viscoelastic nature of thermoplastic materials determines how the bouncing back to “normal” occurs—and how it varies with time over multiple stress-strain cycles.

 

That’s part of the challenge that faced Novo Nordisk of Copenhagen, Denmark, a world leader in insulin self-injection pens. These pens are small, but they are precision instruments with a number of complex parts that must work in perfect coordination. Some pens are durable, containing a replaceable drug cartridge, while disposable ones come pre-filled with a drug. Injection typically involves twisting a short needle onto the pen, turning a dial to the required dose, and pushing a button to deliver the medication under the skin. After a given number of doses is injected, either the cartridge is replaced (for a durable device) or the pen is discarded (if a disposable version). In either case, audible clicks occur at key stages of the procedure, reassuring patients that they are engaging the device correctly at each step. But every one of those reassuring clicks represents a challenge to the design engineers. So do the clicks the patient never hears—those that occur during assembly of the pens in production.

 

To integrity of their designs, Novo Nordisk’s Device Simulation department rely on computer simulation with Abaqus finite-element analysis (FEA) software from Simulia, an application of Dassault Systèmes of France (U.S. headquarters in Providence, R.I.). “Over a decade ago, I and my colleagues explored a number of commercial software codes,” says Torben Strøm Hansen, principal scientist in the Device R&D division of Novo Nordisk. “We chose Abaqus because it was a well-integrated solution that could model the nonlinear behavior of the fine details our designs correctly, including the high number of interfaces in contact.”

CAD model of insulin pen components. Gray and red parts snap fit onto the green part.

 

Besides modeling viscoelastic response to repeated snap fits over time, the designers had to predict the behavior of the materials in different environments, including elevated temperatures, even though the pens are assembled from different materials. And, some materials may contain carbon or glass fibers that show anisotropic behavior, which can be hard to predict. Even just sitting on a pharmacy shelf or in a consumer’s medicine cabinet, the materials are prone to creep and relaxation over time at rates that can vary with temperature.

Injection molded ratchet component from a medical device used by Novo Nordisk for a snap-fit benchmark study.

 

Hansen’s team at Novo Nordisk is now using the “parallel rheological framework” methodology available in Abaqus to model polymers’ nonlinear viscoelasticity with greater accuracy than before. The framework makes use of an arbitrary number of viscoelastic networks and an elastic equilibrium network to create a nonlinear model to predict and track changes in the internal structural networks of a polymer as it responds to repeated cyclic snap-fit loads. “Having material models incorporating time-dependent viscous behavior is very important for our work,” says Hansen. “We’re now able to simulate both creep and relaxation with Abaqus.” Since every type of polymer shows a different response to temperature, load, etc., the team continues to explore ways to identify the characteristics of different polymer networks.

 

Not only are such advanced models useful to designers in fine-tuning the latest insulin pen configuration, the data can help in manufacturing processes at the factory. “We have a process-simulating capability, through Autodesk Moldflow, for which Abaqus has an interface. This allows us to input the stress fields that result from the injection molding process right into our models. As a result, we have greater insight into our manufacturing process and are more able to design parts that have very low levels of residual stress in critical regions.”

BMW Ups Its Stake in Composites

By: Matthew H. Naitove 20. August 2014

BMW continues its exploration of large composite parts for lightweight automotive structures. It just installed a 3600-metric-ton model of the new v-duo vertical v-duo two-platen injection press from Engel Austria (U.S. office in York, Pa.), a smaller version of which was shown at K 2013 in Dusseldorf (see our January show report). The machine was delivered to BMW’s plant in Landshut, Germany, where it will be used to mold large structural elements from fiber composites using the HP-RTM (high-pressure RTM) process. This process injects liquid reactive components for thermosets (epoxy or polyurethane) or thermoplastics (caprolactam for in-situ polymerization into nylon 6) over a layup of dry reinforcing mats or fabrics. BMW plans to use the Engel press for thermoset composites, but would not specify the resin system.

 

The press has two slide tables to remove finished parts and insert fiber reinforcements. Engel notes that the machine has a much smaller weight, footprint, and height than typical vertical compression presses. The clamp unit is accessible from all four sides instead of just two. The press uses ecodrive servo-driven hydraulic pumps for energy efficiency, without any hydraulic accumulators.

Machine-Hour Rates Report Awaits Your Participation

By: Matthew H. Naitove 20. August 2014

We’re getting close, but still not there yet. Maybe it’s due to summer vacations, but more custom injection molders still need to provide data (anonymously) on their midyear machine-hour rates before our next survey can be published. I know from your emails that you find our survey report—broken down by machine size and region of the country—valuable and unique (it’s available nowhere else). But you have to give something to get something. So go online now and take five minutes to fill out the survey here. If we hear from enough of you in the next week or so, we’ll be able to get the report out on time in October.

 

Thanks!

Single-Serve Wine Spritzer in Plasma-Coated PET

By: Matthew H. Naitove 19. August 2014

When it comes to barrier containers, the smaller the package volume, the greater the relative surface area and the more challenging it is to achieve barrier protection. A case in point is a new 330-ml PET screw-top bottle for wine spritzers, which must retain carbonation to preserve the “spritz” as well as prevent oxygen ingress that would spoil the wine.

 

That was the challenge facing Amcor Rigid Plastics, Ann Arbor, Mich., in designing the bottle for Andrew Peller Ltd., Grimsby, Ont., a Canadian wine producer and marketer. Its wines are made from grapes grown in Ontario, British Columbia, and around the world. Its new skinnygrape line of ready-to-drink wine coolers are low-calorie drinks aimed largely at women. That factor determined the slender, comfortable shape of the custom PET bottles. Barrier properties are afforded by an ultrathin <100 nm) silicon oxide (SiOx) plasma coating applied to the inside of the bottle, which is clear, resistant to cracking and delamination, and does not degrade over time. This glass coating is applied using technology from KHS Plasmax GmbH in Germany (U.S. office in Waukesha, Wis.).




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