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A comprehensive collection of news and information about composites.

Posted by: Ginger Gardiner

28. January 2015
 

After significant testing using CFRP plates (laminates representative of those in the BMW i3 shown here), Nedschroef has developed fastener solutions which include coatings for an aluminum bolt (center fastener, top photo) and for steel bolts (left and right pairs in bottom two photos) which survived more than 1,000 hours of corrosive salt spray testing.
SOURCE: Nedschroef.

This is my summary of research findings sent to me by material engineer Max Wagner, for global automotive fastener supplier Nedschroef (Helmond, The Netherlands), based on a large development program conducted at its Techno Centre, also in Helmond.

Why research fasteners for CFRP
Because only serious weight reductions will result in extended driving range for electric vehicles, the future of e-mobility depends on progress in lightweight solutions. Though carbon fiber reinforced plastic (CFRP) plays a major role in the next generation of these lightweight solutions, until recently, it was only used in exclusive, high-end models. BMW is the first OEM to use CFRP for larger volume production, with both i3 and i8 models using CFRP for most internal structure and body components to compensate for the added weight of electric engine,  battery and control systems.

One issue for continued expansion of lightweight CFRP in automobiles is attachment. To provide easy exchangeability of single components like seats or doors, fasteners must be used, regardless of whether the vehicle is made from steel, aluminum or CFRP. As a leading supplier of automotive fasteners in Europe for over 100 years, Nedschroef  realized a need for development of mass produced fasteners for CFRP automotive parts. This led to a project at its Techno Centre R&D facility.

CFRP test plates
To gain more experience with CFRP, tests on the laminates — including structural analysis and tensile testing — were performed. These showed that despite vast differences in the test plates from OEM and supplier sources, the product properties were comparable.  The CFRP products were quite disparate, including:

  • A wide variety of layups;
  • Thermosets as well as thermoplastics;
  • Unidirectional, multi-axial, and woven fabric laminates.

Fastener-related investigations on the CFRP plates were also performed.

Fastener testing
A surface pressure test was developed to investigate the CFRP plates’ resistance to this type of loading. During the test a cylinder made from ultra-high strength NT16 steel is pushed with a defined force into the CFRP plate until indentation is visible. Results showed that the higher the fastener grade, the more geometrical adjustments are required. This means that as stronger fasteners are used, they must be designed with larger bearing surfaces in order to avoid indentations in CFRP counter plates.

Because friction is a critical parameter for proper fastener function, friction tests were also performed. For initial tests, bolts were tightened until yield and the average friction coefficient was determined at 75% of this value, according to European and international standard test method EN ISO 16047. Next, an average torque was calculated by using the determined friction coefficient and the average value from the surface pressure test. Another friction test using this calculated torque was performed. Results for the above CFRP plates showed an average friction coefficient of 0.07 with very small deviation. According to Wagner, this means that friction of automotive fasteners on CFRP plates is roughly 40% to 50% lower than on metal plates.

Wagner explains that with this value it is possible to calculate the preliminary tightening parameters for joints in CFRP assemblies and to ensure their proper function — e.g., prevent loosening of bolted joints. However, for calculations with final products it will be necessary to perform friction tests according to specific customer demands. For example, some specific applications require several tightening and untightening operations before final measurement to define a friction value.

Wagner concludes these test results should allow Nedschroef to modify its current portfolio of products to provide faster and more cost-efficient solutions for upcoming CFRP applications. In addition to these adjusted products, Nedschroef will also introduce completely new fasteners for CFRP components to the market.

Corrosion testing
An additional challenge for fastening to CFRP is galvanic corrosion, which results from the large difference in electrochemical potentials between carbon fiber and the standard metals used in fasteners, for example, boron and chromium steels. Stainless steel grades 304 and 316 are also used in small amounts as well as aluminum alloys EN AW 5xxx, EN AW 6xxx and EN AW 7xxx series. The material used has a significant economic impact on the fastening solution: raw material costs alone are approx. $1,000/ton for steel, $2,000/ton for stainless steel and more than $5,000/ton for aluminum.

In addition to exploring more complex materials for fasteners — including titanium, copper and different grades of stainless steel and aluminum — the Techno Centre dove deep into coatings. As the interface between the fastener material and the CFRP, coatings should allow standard materials to provide a better price performance ratio than expensive solutions like titanium. To explore this ratio, coatings commonly used in the automotive industry were tested first. Metallic and non-metallic coatings — with and without organic or inorganic topcoats — were investigated and can be divided into electrolytic, mechanical or thermic applied and lacquer systems.

Due to the failing of all tested coatings in corrosion testing, non-automotive coatings like ceramic, insulation and nanocoatings were also investigated. Some of these coatings were new developments, supplied by local partners, which has expanded Nedschroef’s coating technology knowledge. For example, the best coatings solutions were identified as well as optimized coating thickness.

To investigate galvanic corrosion behavior between different CFRP plates, several insulation coatings were chosen for a salt spray test with test plates from OEMs and suppliers. The salt spray test is required by the automotive industry to accelerate corrosion, and results allow predicting coating behavior in an environment with aggressive media. No difference in galvanic corrosion behavior was observed. Coatings which resisted galvanic corrosion did so for all CFRP plates. Observed corrosion damage on failed parts had comparable quantity.

CFRP fastener solutions
Solutions resulting from this extensive research include:

  • A new insulation coating for EN AW 6056 aluminum fasteners;
  • Two new coatings for steel fasteners;
  • A special heat treatment for stainless steel grade 316 fasteners.

Tested samples achieved promising results after more than 1,000 hours inside the salt spray chamber. The stainless steel and coated aluminum test samples showed no sign of corrosion. The steel test samples showed very little sign of corrosion, which can’t be avoided due to the sacrificial characteristics of these coatings.

At the end of this challenging project, Nedschroef now offers different solutions for fastening to CFRP components. These bolts and screws, which are directly connected with CFRP, reportedly allow transfer of higher forces than other fastening solutions and the best possibility for success in exploiting the benefits of lightweight CFRP for automotive components.

Posted by: Ginger Gardiner

21. January 2015

 

1/10th scale petal (ogive and upper barrel) tool for NASA SLS payload fairing made using No Oven, No Autoclave (NONA) materials. SOURCE: NONA Composites.

 

Last year, I wrote a blog on the No-oven, No-autoclave (NONA) composites technology aimed at more cost-effective processing by eliminating the need for an oven or autoclave. Now I’m giving an update on where that technology stands with regard to composite tooling. A 177°C capable composite tool was fabricated for NASA and subsequently used to cure an infused epoxy part. This work was presented at CAMX 2014 and will be featured on the new NONA Composites web-site, slated to go live at the beginning of February.

NONA Composites (Dayton, OH, US) was spun off from Cornerstone Research Group (CRG, Dayton, OH) to commercialize two-part epoxy resin technology that enables room-temperature infused composites within hours using no additional heat source beyond the resin’s exotherm during cure. NASA is interested in this technology as one of a variety of materials and manufacturing methods for potential use in manufacturing large composite tools and structures for the Space Launch System (SLS) and other programs. NASA wants to take advantage of the weight and cost benefits of single-piece composite structures, but must remove the size restrictions and cost penalties of current processing to make these structures affordable.

Through Phase I and Phase II Small Business Innovative Research (SBIR) programs, Cornerstone Research Group and NONA Composites have been able to mature No Oven, No Autoclave composite processing to a Technology and Manufacturing Readiness Level (TRL/MRL) of 9. The latest demonstration reviewed at CAMX was a tool for fabricating a 1/10th scale petal (ogive and upper barrel) for a NASA SLS payload fairing. (Note: CW reported on a 1/6th scale tool made out of autoclave by Janicki in the Sep 2013 issue of HPC). The scaled fairing part made using NONA composites is approximately 192 cm long, 81 cm wide, and 41 cm high.

A master model for the tool was made by General Plastics (Tacoma, WA, US) using its FR-4718 high temperature polyurethane foam due to its low thermal conductivity and high temperature resistance. The machined foam was coated with Duratec vinyl ester primer and finished by hand. Airtech International (Huntington Beach, CA, US) Tooltec CS5 adhesive backed Teflon film was applied during the second tool facesheet fabrication described below.

The tool was built from the master model using NONA RT-177 two-part infusion resin. The resin was mixed by hand, degassed in a Laco Technologies (Salt Lake City, UT, US) degassing unit to an absolute pressure of 13.3 Pa (0.1 torr) over 10 minutes, and kept below 30 °C throughout the infusion. Simply stirring the resin maintains adequate temperature control for batches less than 1 kg. However, the larger batch size used for this tool fabrication required use of a static cold water bath and occasional stirring. Absolute pressure less than 133 Pa (1 torr) was maintained within the vacuum bag during infusion to increase fiber compaction and decrease laminate porosity.

Fabrics used for the tool included 2x2 twills made from 3k and 12k standard modulus carbon fiber. Two separate tooling facesheet trials were completed for development purposes. The first used a 28-ply, quasi-isotropic layup with the 3k 2x2 twill fabric and the second used fifteen 0° plies of the 12k 2x2 twill fabric. Flow media, resin feed tubing and valves, and vacuum bagging were all rated for 177 °C + because the NONA cure process generated heat during cure. Very low-cost bag-side insulation was used to maintain the heat of exotherm within the laminate during cure, which is critical to NONA processing.

The first tooling facesheet used 25 kg of resin and infused in 30 minutes while the second consumed 35 kg of resin and infused in 48 minutes. For both, the facesheet layups were debulked prior to infusion. Temperature in the NONA tool and master was logged with 32 thermocouples. For the second fabrication, the average temperature on the tool facesheet was 162.5 ±3.8°C. The first thermocouple peaked 165 minutes after the infusion, reaching 165 °C, and the last thermocouples on the part peaked 177 minutes after infusion, reaching 161 °C and 160 °C.

After reaching peak temperature, the system began to cool back down. Insulation was removed when the facesheet temps were between 40°C and 50 °C. A leak check to evaluate the vacuum integrity of the facesheet showed a rate of 0.46 torr/min over 24 minutes, measured with a digital vacuum gauge. This leak rate was determined more than sufficient for most prepreg and infusion applications.

Dimensional measurement of the second tool facesheet was performed using a ROMER Absolute Arm SI 3D laser scanner coordinate measurement system (Hexagon Metrology, North Kingstown, RI, US). Over 2.9 million points were collected. The assembled tool was heat-cycled with holds at 120°C and 177°C and allowed to cool down slowly to room temperature. CMM was performed again and the dimensions were shown to be very similar, ranging from -0.132 mm to 0.155 mm across the part area (average absolute deviation of 0.075 mm) , illustrating the thermal stability of the NONA resin and the resulting dimensional stability of the tool.

Infused carbon/epoxy part made using NONA Ogive tool for NASA.
SOURCE: NONA Composites.

This NONA tool was then used to fabricate a resin-infused composite fairing part. The tool was polished, sealed and coated with mold release. A 4-ply layup of 12K carbon 2x2 twill fabric was infused with Momentive Epon 862 epoxy resin using Epikure W curing agent. The part was cured during a 6.5 hr heating and cooling cycle, with a 1.5 hr hold at 177 °C. The cured part showed a smooth surface with little visible porosity and was sent to NASA Marshall Space Flight Center (Huntsville, AL, US), where multiple 177°C, 80 psi autoclave cure trials have been run without any issues.

“We’ve demonstrated that NONA can indeed be used to produce high-quality tooling without an autoclave or oven,” says NONA Composites president, Ben Dietsch. “Our goal now is to get NONA materials into more manufacturers so they can see the benefits of making tools with this technology.”

The company is also working to prove out machining parameters on large-scale NONA tools. CTO Michael Rauscher explains, “We’ve designed our materials so that you can get really good net-shaped tools without machining, even to tolerances of 0.127 mm. We believe if you can remove the machining step, it’s one less point for thermal degradation. However, there are manufacturers who do want to machine tools. Instead of developing a new NONA system, we are cycling current NONA tools that have been machined and showing the quality of part surface we can produce. We want the industry to see how well NONA compares to other tooling materials and that it is truly a robust tooling system.”

Dietsch adds, “We have a definite path for this technology. There continues to be a lot of interest and we’re talking to a lot of different primes. We’re also continuing our own capabilities to build increasingly larger tools.”

Follow this link for more information regarding NONA Composites tooling capabilities or contact Ben Dietsch at dietschb@nonacomposites.com.

20. January 2015

CFM International's LEAP 1 at the 2012 Farnborough International Air Show (Farnborough, UK).

The January issue of CompositesWorld features a Market Outlook by Chris Red that assesses current and future use of composite materials in large aircraft engines. His report is full of data that characterizes where and how composites are used, and how this important market is expected grow (rapidly) over the next decade. 

CW started looking at the engines in the market, and coming into the market, and wondered what the total composites value is for each major engine platform. Red helped us pull the data together and the below data are the result. 

There are three important variables to consider: Composites fraction per engine, engine size (as defined by thrust) and production volume. The engine with the largest composites fraction is Pratt & Whitney's PurePower, at 35%. The engine with the largest composites value is the GE Aviation's GE9X, at $972,000. However, the engine with the largest total composites value 2005-2023 is the CFM Inernational LEAP1, at $5.7 billion. 

In any case, it's clear that composites are enjoying significant application in large aircraft engines manufactured by each of the big four OEMs. 

 

Engine OEM Composites value (est.) Composites fraction (est.) Thrust (000, lbf) '05-'23 production volume (units) '05-'23 total composites value
LEAP 1 CFM $458,635 33% 20-32.9 12,390 $5.7B
LEAP 56 CFM $258,592 17% 19.5-34 14,173 $3.7B
GEnx GE $810,053 19% 53-75 4,504 $3.7B
Trent 1000 R-R $413,086 11% 53-75 2,893 $1.2B
PurePower P&W $773,126 35% 15-33 1,465 $1.1B
GE90 GE $468,550 8% 76-115 1,975 $925.4M
GE9X GE $972,000 18% 90-100 952 $925.3M
PW 4000 P&W $323,052 11% 52-99 2,019 $652.2M
Trent 900 R-R $288,854 8% 70-80 1,178 $340.3M
Trent 700 R-R $258,380 9% 67.5-71 665 $171.8M

 

 

 

 

 

 

 

 

 

 

 

CFM: CFM International
GE: GE Aviation
P&W: Pratt & Whitney
R-R: Rolls-Royce

 

Posted by: Sara Black

8. January 2015

Tension control plays a vital role in composites manufacturing in order to achieve automated processing, continuous processing, reduced scrap, increased product quality, and more, says a new white paper released by The Montalvo Corp. (Gorham, ME, US). Montalvo's global marketing manager Bryon Williams says “In the evolving process of composites manufacturing, more and more emphasis will be placed on  tension control systems to allow manufacturers to achieve faster, automated, and continuous processing. Tension control systems can often be integrated into existing manufacturing equipment, making it easier to add in these new capabilities without investing in new machines or large, stand-alone equipment. This article dives deeper into the existing and new tension control technology that makes this possible.”

Montalvo has been manufacturing and providing industry leading tension control products, services and support for over 67 years. They serve various industries such as composites, pulp and paper, flexible packaging, corrugated, tag and label, and more, for both end users and original equipment manufacturers. The following is taken from their white paper about tension control:

So what is tension control?

This paper often uses the word "web". A web is a generic catchall term used to refer to any type of material you are processing, so a web could be carbon fiber, fiberglass, you name it. Just as we find tension control is a new concept to composite manufacturers, so too is the idea of referring to their material as a web.

Web tension is defined as the amount of stress or strain put on a web of material as it is moves through processing. Different materials have different properties and thus have different tension requirements to ensure they maintain their quality from start to finish. 

Too little or too much tension can create a variety of problems and process defects. Defect such as stretching, wrinkling, breaking, wandering, delamination and more can exist if a web’s tension is not properly controlled.

For example, polyester may run best at 0.5 to 1.0 pounds per linear inch of width, while polypropylene may run best at 0.25 to 0.3 pounds per linear inch of width. The reason is that polypropylene is a much more extensible material. If you pull it too tight, it will neck down and distort your end product. If you don’t pull the polyester tight enough, it may wrinkle, and again distort your end product.

Fiberglass may require a different tension than carbon fiber. Some carbon fibers may be more brittle than other carbon fibers, and require less tension. Even a paper carrier sheet used to transport a series of composite mats in a hand lay application will require the correct tension during unwind, as well as rewind. If the web is pulled too tight, the paper may rip causing the material to be scrapped. With some carbon fiber costing around $900 a pound, ensuring you don’t end up with scrap is highly important.

Tension control is the process of maintaining a predetermined or set amount of stress or strain on a given material between two points to maintain its desired properties (such as form, appearance, etc.) and quality. This process often takes place in specific control zones: unwind/payout, process (nip), and rewind/take up, with each having unique tension control requirements.

So tension control is the process of ensuring your material gets from point A to point B in a uniform and consistent manner without any loss to material quality. Under this basic definition most applications can already get their material processed from point A to B, but perhaps it is very manual, or is slower than it could be. In your current application could you double your speed without sacrificing end product quality?

Automating the process, creating a continuous process and increasing productivity are all going to rely heavily on proper tension control to ensure consistent and high quality results.

So how do we control tension?

With a fixed torque in an unwind application, as the roll diameter decreases, the tension applied to the web will increase, and will increase more rapidly as the roll diameter gets closer to core. In rewind applications, it’s just the opposite. As the roll diameter builds, with a fixed torque, tension will decrease as the roll diameter increases, as shown in the diagram below.

Mathematically, tension equals torque divided by radius. This means that as a roll diameter increases or decreases, torque must be adjusted to maintain tension at the optimal value, or setpoint. So in a basic sense, by controlling the torque in a uniform manner in relation to the roll, we control tension.

There are three primary types of tension control: manual control, closed loop control and open loop control. Just as it implies, manual control is the process of visually or physically determining if tension is correct, and then making manual adjustments to maintain the desired tension level. With manual tension control a web is subject to constant up and down spikes as an operator is always correcting the tension. Maintaining proper tension gets increasingly difficult as roll diameters decrease and changes happen more frequently. This method is also exposed to the subjectivity of different operators, typically resulting in non-uniform results (image below).

Open loop systems utilize products such as ultrasonic sensors or proximity sensors to measure, or calculate, roll diameter. Based on inputs into the controller, the controller uses any detected changes in roll diameter to regulate torque and maintain tension, as opposed to closed loop systems which receive tension feedback directly from the web of material.

Although not as precise as closed loop systems, open loop systems still provide automated, consistent tension control and outperform manual control. Open loop systems are generally less expensive than closed loop systems because you are not utilizing additional products, like load cells.

Finally, closed loop tension control refers to a continuous flow of communication from a web tension measurement device, to a torque controller, to a torque device. Web tension measurement devices include load cells or a dancer position feedback sensor, that are constantly relaying tension changes directly from the web of material to the tension controller that regulates the output of the torque device, which may be a brake, clutch, or drive to maintain the desired tension level. If any changes in tension are detected the controller can instantly alter the torque device to maintain set tension.

This ensures that throughout your entire process your tension is consistent, uniform and precise. And all of this happens automatically. We like to use the term "set it and forget it" to describe how a high-quality tension control system should operate.

A type of closed loop control system that most people are familiar with is the cruise control system of your vehicle. In your vehicle you set your speed, like you would set your tension, and then as the vehicle gets feedback on the constantly changing elevations of the road it controls the speed to maintain what you set, just as a tension controller would regulate torque to maintain your set tension.

In both closed loop and open loop, tension is managed by the torque applied to the center of the roll from a brake, clutch, or drive. Tension controllers automatically regulate this torque, making any necessary correction or adjustments, throughout the process, allowing for continuous production. Operators simply input the parameters of the production run (such as speed, tension, etc), press start/run and allow the controller to automatically manage production.

As mentioned, one of the key elements to improved productivity and profitability can be traced to the lack of effective tension control. Often we find that due to their manufacturing process or poor tension control, manufacturers are not able to run their material rolls all the way down to the core affecting both productivity and profitability.

This means leaving money on the core, only to end up as scrap. Other sources of scrap and lost productivity come from web breaks, and inconsistent end product. Quality tension control helps to eliminate these scrap producers by creating a uniform and consistent process.

Currently the composites industry relies primarily on new equipment to provide tension control systems, but the purchase of new equipment is not always feasible for manufacturers. Montalvo specializes in incorporating the latest tension control technology and innovations into existing applications, which often require minimal adjustment to account for the new tension control equipment being added to the machine.

In the composites industry, many early control systems were designed for very large, heavy applications in other industries, while the requirements for the composites industry have been, and are quite often, small and inexpensive. For example, it would be very expensive to purchase a closed loop system for each tow in a process containing hundreds of tows.

By miniaturizing, or adapting new technology, it is now possible to automatically control the tension of all your webs cost-effectively. Montalvo is constantly developing new technologies that are not only composites industry specific, but application-specific.

Multi Tow Tension Control

As shown in the image, some applications may have several tension zones, and require several types of tension control. Starting at the beginning of the process (right side of image) several tows are being pulled from their creels into the machine process. The creels can be manually set to create a small amount of tension on each tow by adjusting small, low torque brake assemblies. This may include spring applied manual brakes, or other manually applied brakes that will require some attention from the machine operator, or the tension on the tows may reach a point where they break.

Some machines may now include a load cell roller that will measure the total tension of all of the tows in a process as they travel across the idler roll. This gets you a little closer to closed loop control, but the operator still needs to make coarse adjustments to the tow brakes to try and equalize the tension of all of the tows.

To solve the two aforementioned problems of manual and inconsistent control, the tows of material canbe  pulled into a NIP tensioning device. Since the pressure across the NIP is loaded with equal pressure from front to back, and the length of all of the tows is equal from the exit of the tensioning NIP to the entrance of the process NIP, the tows will all exit the tensioning NIP at equal tension. Using load cell feedback to control the total tension of all of the tows, measured at a load cell idler roll downstream from the NIP stand, the amount of tension can be trimmed using a brake to develop a small amount of torque at the NIP. The tension on each tow will remain constant no matter what the diameter of the tow material on each of the creels. If some of the creels are new complete rolls, and some are partial, it won’t matter in this case because there are no changing diameters at the NIP. The diameter change takes place at the creels, in a different tension zone.

By selecting a desired tension to be applied to each tow, let’s say 0.25pli, you can determine the tension setpoint required to best run the tows exiting the NIP control by multiplying the 0.25pli times the width of all of the tows together. So let’s say there are a total of 240 tows coming from this bank of creels, and let’s say the width of 240 tows is 60 inches, you simply multiply 0.25(pli) times the 60 inches of width, or 15 pounds.

So in this example the tension setpoint would be 15 pounds. If the individual tows need to be 0.50pli, then the tension setpoint would be 30 pounds, and so on. Now when you run the tows through the NIP, the control system will monitor the tension and make minor adjustments to the torque device (the brake) to maintain tension at the selected setpoint.

The next tension zones, upper and lower unwind tension, in this instance, are load cell based unwind tension control zones. These webs in this case are upper and lower paper carrier sheets. The tension on these webs is created by the brake mounted at the center of the unwind rolls. As the paper unwinds, it wraps around load cell rollers. The tension signal from the load cells is sent to a closed loop tension controller where the actual tension is compared to the setpoint selected by the machine operator. If the actual tension varies away from setpoint, the controller makes the appropriate changes to the torque at the brake to bring the tension back to setpoint. Since this is a closed loop system, paper, setpoint, torque, the tension will remain at, or close to setpoint from full roll to core, and this will remain true roll after roll. In this case each tow is fed into an extruder where product is extruded between the two sheets.

From here we go to the next tension zone, the top paper carrier rewind. Since this material isn’t that important, and is basically waste, the control doesn’t need to be that precise. You only need to be able to wind it without breaking the web. An open loop control system might be used in this application. An ultrasonic diameter sensor, or proximity sensors, can be used to monitor the diameter of the roll as it builds, and increase the torque slightly as the roll builds.

The next tension zone is just downstream from where the top carrier sheet is pulled from the extruded product. A poly unwind is used to control the tension on a poly web to cover the extruded product. It’s important to note that the tension applied to the poly web will be substantially less than the bottom carrier paper (remember, the bottom carrier is still under closed loop tension control). The paper carrier is a fairly strong material, and is not extensible at all. The poly layer is very extensible, so the tension applied to this layer needs to be precisely controlled at a tension that is a fraction of the tension required for the paper. If the poly is pulled too tight, the web necks down. When the roll is rewound, the roll may look fine, but during storage, or curing, the poly will try and get back to its relaxed state. This can cause wrinkles, or starring of rolls. If the poly is not tight enough, again, you may find wrinkles in the web after curing.

The last tension zone is the rewind zone. In this application it’s an open loop control that again controls tension based on the increase in diameter as the roll is built. In many applications it would be a load cell based, or closed loop control. Either choice will improve roll quality. Some control systems include a "Taper Tension" option. The Taper function will give the operator the ability to make the first few wraps of the rewind roll tightly wound, and will gradually reduce the tension setpoint as the roll diameter increases. This will help to eliminate starred, or telescoping rolls. Different materials will require different amounts of Taper. In some cases, rolls look good as they are removed from the machine, but will develop issues as they cure.

 

Laminator Tension Control

    

 

When laminating two or more materials together it is very important to control the tension applied to each web.

The image above depicts three very different materials in a process that will laminate into one web. The bottom layer is a 60 pound basis weight paper that will probably run best at about 1.5pli. By running best I mean that it is tight enough that it will nor wrinkle, or bag, but not so tight that it will break. If the web width in this application is 50 inches we again multiply the width in inches times the assumed pli, or 75 pounds of total tension.

Now we move on to a fiberglass layer that for this example runs best at 1.0pli. Since the web is still 50 inches wide, the tension setpoint for this web should be about 50 pounds of total tension.

The third and final layer in this application is a 2 mil poly film. The expected tension on this layer would be about 0.50pli. Again, the web is 50 inches wide multiplied times the 0.50 pli, or 25 pounds of total tension.

If closed loop tension control is not used on these three very different materials, you run the risk of damaging one, or all layers of the laminated end product. If the film layer is run too tight it will neck down, and will not completely cover the other layers. There is also a possibility that the film will try to relax after being wound into the finished product, creating wrinkles, or delamination. If the fiberglass layer isn’t run using closed loop tension control you run the risk of running the web too tight causing discoloration, or delamination.

Controlling Tension in Rovings Applications

As with tow control, where the tows are pulled from creels, a NIP station can be used to control the tension of each tow being pulled from the center of the roll of material in a roving. A NIP station is the best option in this case because no torque can be developed as the tow is pulled from the center of the rovings. Just as described previously, it doesn’t matter if there is any tension applied to the tow as it enters the NIP, the tension on each tow will be equal, and under control by trimming the torque developed at the hold back brake. The operator will select a total tension setpoint based on the width, and type of material running through the NIP. If the tows are 0.25 inches in width, and the best tension is determined to be 1pli, the operator simply multiplies the width, times the required tension, in this case 0.25 pounds. If for example there are 100 tows, each at a tension of 0.25 pounds, the total tension setpoint should be 25 pounds. If there are 200 tows, the total tension should be set for 50 pounds.

Hand Layup

Open, or closed loop tension control, or a combination of both can be very useful in hand layup applications. By using a brake on the paper carrier unwind roll, and adding a drive motor to the rewind, it becomes possible to automate a hand lay application. Currently, where a carrier web is pulled over a table, and carbon fiber, or fiberglass pieces are laid out in a pattern, the web is hand wound onto a roll where the finished roll of material is built. By adding a drive motor to the wind up, and a brake at the unwind roll, you can run slowly (1 to 2fpm) along the table, slow enough for the pieces to be properly positioned, and is constantly wound up.

By adding tension control to the rewind, it becomes possible to build the rolls with a consistent web tension. If a poly web layer is required, a closed loop control system can be added, and the insulating layer of poly can be added without wrinkles, and will not neck down as the rolls cure.

Even if the web is not constantly moving, you can automatically run the carrier sheet the length of the table, stop the web, and lay out the pattern, and then wind up the web until the carrier is clear the length of the table, stop the web, place the pattern again, and wind up that portion. Since everything is under control, the tension throughout the roll will be consistent. By controlling the rewind tension, either open loop, or closed loop, it becomes possible to build consistent rolls.

Products

This article has referred to variety of products used for precisely controlling tension, such as load cells, controllers, brakes and nips.

Load cells directly measure the tension of the material you are running. Load cells come in a variety of styles to best meet the exact needs of your application but all operate under the same principle. As your web moves over the load cells itself, or the roller they are attached to the tension of your materials creates deflection or bend, which the load cell interprets into an electrical signal which the controllers utilizes to control the torque device. Any changes in electrical signal represent a change in tension which the controller corrects. The greater the sensitivity of the load cell you use the more precise it is at detecting even the slightest changes in the tension of your material.

 

  

Tension controllers are the brains of the operation. Process parameters are entered into the controller and then depending on your type of controller, it will utilize load cells, dancer position feedback, or diameter calculations to control the torque of a brake, clutch or drive to maintain set tension. High quality tension controllers also come with a variety of additional functions such as soft start, anti coast, web break detection, splice, taper and more. Depending on your process these functions increase your processes capabilities to ensure maximum productivity.

 

 

     

Brakes are often either pneumatic or electrical and apply torque to your roll of material to properly apply tension to your web. In pneumatic brakes, friction pads engage with the brake disc in what we refer to as continuous slip to control the amount of torque being applied to the brake. In electrical brakes, or magnetic particle brakes, electrical current is used to produce the amount of torque output of the brake.

One of the latest innovations for composites manufacturing has been the modification of our nip technology to create what we refer to as modular automated tensioners. Modular automated tensioners easily integrate into existing machines to create a single location for producing precise tension control for multiple creel applications. These devices are fully customizable and so can be longer or shorter, or multiple units stacked on top of each other, you name it. For example, in one application we are controlling over 250 individual tows of material. Modular Automated Tensioners ensure material is at precise and consistent tension as it enters processing, or before material gets its resin bath to ensure uniform coating.

Contact The Montalvo Corporation (www.montalvo.com) for more information.

Posted by: Sara Black

7. January 2015

Stiles Education offers courses to anyone desiring knowledge of CNC machine control and maintenance. An instructor is shown here teaching a recent class.

 

 

 

 

 

Brett Chouinard of Altair Engineering Inc. speaks at the recent CW Carbon Fiber 2014 conference about composite design and getting the message out to design engineers about optimized design.

 

 

It seems that just as composites finally earn their way into a wide array of applications and industrial sectors, and growth seems certain, there’s a risk of a shortage of skilled workers. The U.S. economy, at least, seems to be on the road to recovery, and the composites industry in particular is growing, but can companies keep hiring and retaining enough talent to keep the boom going, particularly to replace retiring baby boomers with extensive skill sets?

CW has reported on many company initiatives, consortia, partnerships among colleges and universities, military veteran training programs, outreach to high schools, and more, that are aimed at providing the skills for manufacturing jobs. In one example, Airbus is working with local companies in the Mobile, AL, US area, and has built a training center adjacent to its fabrication plant there, to ensure a competent workforce. In Washington State in the US, several educational groups and consortia are working to increase worker training at local colleges that feed Boeing’s aircraft fabrication. Check out these published articles, among others, at compositesworld.com: http://www.compositesworld.com/articles/training-surge-too-little-too-late; http://www.compositesworld.com/columns/composites-education-improvement-through-collaboration). Recently I learned about two more interesting and focused solutions for workforce training.

“The manufacturing supplier base has evolved,” asserts Stephan Waltman, vice president of marketing and communications at Stiles Machinery Inc., Grand Rapids, MI, US. “To maintain viability, you now have to supply more than just materials and technology — you have to supply solutions to get the job done, and that includes education and training of people.” Stiles has certainly walked the walk. They established, in 1990, an in-house school to provide education to anyone who wants to learn about advanced CNC machines, not just Stiles customers.

Waltman says the idea came during a strategic planning meeting: “We realized that a deterrent to selling complex CNC machining centers over time would be a shortage of qualified maintenance people and operators. We felt we had to do something ourselves, and not sit back and hope that high schools around the country would add courses on machine logic.” With no qualified educators or instructors within the company, Stiles hired a well-known educator in the industry to head the school, called Stiles Education.  This unique program has since been recognized by Michigan State University (MSU) as an educational provider, and has been accredited as an Authorized Provider by the International Association for Continuing Education and Training (IACET, McLean, VA, US) and complies with the ANSI/IACET standard of good practice.

More than 30,000 students have passed through the school, which includes courses on programming and machine language, maintenance of electrical and digital CNC controls, cutting processes, fixturing and advanced materials including composites. While primarily offering a fixed schedule of classes, Waltman says that customized courses can be created for any company, to teach a specific syllabus on, for instance, composite materials machining or drilling.  He emphasizes that the courses are not related to selling Stiles equipment, but geared toward understanding the technologies employed in digital manufacturing.

“This is a long-term planning challenge,” adds Waltman. “We can all do a better job at solving this problem, by being more proactive today and working with our communities and trade associations, creating apprenticeships, and mobilizing resources to create the skills we need.”

Another Michigan company, Altair Engineering Inc. (Troy, MI, US), is taking the proactive approach to ensure its product is understood by engineers, which benefits both its business model and composites design. Brett Chouinard, chief operations officer, spoke recently at CompositesWorld’s Carbon Fiber 2014 conference in La Jolla, CA, US about recent projects, and Altair’s concept of Optimization Centers for clients.

“Our whole industry is filled with engineers who don’t know how to design,” declared Chouinard during his La Jolla presentation. Altair’s HyperWorks OptiStruct design software allows engineers to take existing structures and, based on physics and mathematical discipline, optimize the structures by taking out weight and unneeded material. He cited a project for Airbus, in which wing leading edge ribs were redesigned in 13 weeks by a team of Altair and Airbus engineers, resulting in a weight savings of 500 kg. Another project involved a wheel manufacturer who called in Altair in response to a competitor’s new product. With optimization, the Altair/customer team came up with an entirely new concept that ultimately put the competitor out of business, according to Chouinard.

He is passionate about educating customers in a “pervasive” design environment, and believes in interacting with design engineers through Optimization Centers, which are “skill centers of excellence” where optimization methods are practiced. “It’s a different way of thinking about design,” adds Chouinard, “and takes into account weight, cost, manufacturability and performance.” So far, Altair has set up 20 Centers at customer sites, including The Boeing Co. (Chicago, IL, US), to help train designers in optimization methods.

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