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AgieCharmilles Cut 30 P

Dexmet has brought the capability of Wire EDM (Electrical Discharge Machining) technology in-house to quicken the development process and provide better turnaround time to its customers.  The new capability will allow Dexmet to quickly generate custom expanding dies for application specific expanded products or provide custom cut geometries out of already expanded materials.

The engineers at Dexmet purchased an AgieCharmilles Cut 30 P from Ross Machinery, also located in Wallingford, CT., because of its advanced features of a simple to use graphics user interface to reduce programming time, large work area and travel capabilities and accuracy at high cut rates . The new Wire EDM technology allows the engineers at Dexmet to execute a range of jobs without any external applications handling everything from contour creation to part production.

The AgieCharmilles CUT 30 P Wire-Cutting EDM has a wide range of cutting capabilities from very hard carbide materials over 300mm thick or the ability to cut intricate shapes in thin delicate foils. Wire-Cut EDM utilizes a fine single-strand metal wire, typically brass, as the electrode and through a series of rapidly recurring electric arching discharges between the electrode and the work piece material is removed along the cutting path by melting and vaporization.  The process produces no cutting forces so there is very low residual stress put on the work piece with little to no change in mechanical properties or shape.

Dexmet new capabilities offer the following advantages to its clients:

• Rapid development of new tools to produce an application specific expanded product
• Custom cut shapes from expanded materials for prototyping
• Quick turnaround on parts – no intricate dies involved
• Ability to produce intricate detail that would be difficult to machine with traditional cutting tools
• Very accurate cutting tolerances and excellent surface finishes
• Delicate and weak materials as well as very hard materials can be machined without any distortion.

The images below are courtesy of Dexmet:

Samples from CUT 30 P

Samples from CUT 30 P

Samples from CUT 30 P

Produced by CUT 30 P

To learn more about the current developments at Dexmet contact Eric Toro via e-mail at: e.toro@dexmet.com

In the filtration industry, expanded mesh products are used in applications requiring membrane support, purification, and separation.  For applications requiring high temperatures to filter caustic gases or fluids, such as the semiconductor, chemical processing, and petroleum/gas industries, the filtration media typically being utilized is polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), and ethylene chlorotrifluoroethylene (ECTFE).  “Although PTFE, PFA and ECTFE have good heat and chemical compatibilities, they lack mechanical strength,” explained Burtt. “Strength is essential in a filter design to assure media integrity and pleat spacing under dynamic flow.  The increase in mechanical strength will allow filter designers to utilize thinner support materials to increase the working surface area of the filter,” continued Burtt.  “As filter performance demands increase, with higher pressures, temperatures, and aggressive environments, there is a need for better performing material, such as VICTREX PEEK polymer.”  Additional advantages of the APTIV PEEK Films include low outgassing and extractables as well as low moisture absorption.  All these performance characteristics combine to enhance performance, reduce systems costs, and increase functionality of the end product.

The advantage of an expanded product, especially important in a filter design, is that the material is one homogenous unit. “The strands don’t move relative to the other strands so opening sizes don’t change,” said Burtt. Another advantage is the geometry of the opening the expanded process produces.  “The material has a three dimensional geometry which allows for multiple flow directions, improving cross flow while reducing pressure drop,” explained Burtt.

Dexmet utilizes a precision expansion process which combines a ‘slit and stretch’ function to produce the high performance mesh product. “It’s a process that has been around for over 100 years,” said Burtt. “What makes it unique to Dexmet is our ability to produce a thin film expanded product with very small openings at wide widths.

There are no other expanders in the world that can expand thin materials, especially polymer films under 0.127 mm (0.005 in) with opening sizes down to 25 microns and widths up to 610 mm (24 inches).”  The process has infinite variability which enables Dexmet to tailor a product to exact performance requirements, whether it is opening (pore) size, open area, weight per area, or overall thickness.

As the premier manufacturer of expanded thin metal foils and polymer films and an innovator in Expanding Technology™, Dexmet Corporation can provide the technical expertise to manufacture an expanded product that will meet tough application requirements.  For more information on products, process capabilities, and industries served, please visit Dexmet Corporation.

Victrex Polymer Solutions combines over 30 years of expertise as the world’s leading manufacturer of high performance polyaryletherketones (PAEK) with unmatched product and technical service capability. For more information on VICTREX PEEK polymers and APTIV Films, please visit APTIV films.

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About Dexmet Corporation

For over 60 years Dexmet Corporation has been manufacturing precision expanded metals and is the innovator in expanding thin metal foils and polymer films with exacting mechanical and electrical properties to meet very tight conductivity, weight and dimensional tolerances. The company maintains a continuous commitment to customer service, quality control and process improvement, including SPC implementation and is ISO 9001:20008 certified.  Ongoing innovations include continued development of highly specialized, proprietary expanding and processing equipment for unique open area products. For more information, please visit www.dexmet.com.

Dexmet®, MicroGrid®, and Polygrid® are registered trademarks of Dexmet Corporation. Expanding Technology™ is a trademark of Dexmet Corporation.

About Victrex

Headquartered in the UK, Victrex Polymer Solutions, a division of Victrex plc, is the world’s leading manufacturer of high performance polyaryletherketones such as VICTREX^® PEEK™ polymer, VICOTE^® Coatings, APTIV^® film and VICTREX Pipes™. These materials are used in a variety of markets and offer an exceptional combination of properties to help OEMs, designers and processors reach new levels of cost savings, quality, and performance. All Victrex material production comes under Victrex’s ISO 9001:2008 quality registration.

VICTREX^® is a registered trademark of Victrex Manufacturing Limited. VICTREX Pipes™ is a trademark of Victrex Manufacturing Limited. PEEK™, PEEK-ESD™, HT™, ST™ and WG™ are trademarks of Victrex plc.  VICOTE^® and APTIV^® are registered trademarks of Victrex plc.

Dexmet continues to apply new process variations to their expanding process. This process variation provides a needed configuration of expanded materials to R&D and engineering departments that are currently developing new advanced battery, structural, filtration, fuel cell and renewable energy applications. See images below:

Top view of corrugated expanded metal

Side view of corrugated expanded metal

For more information on Dexmet’s new corrugated process or for samples of corrugated expanded material, contact Eric Toro, Dexmet’s marketing specialist via e-mail at e.toro@dexmet.com. Samples are subject to availability and may take up to two weeks to receive.

During the expanding process, die teeth pierce the incoming metal foil from above creating the distinctive diamond shape pattern.  Depending on the geometric configuration specified by the customer, the foil may also be put under longitudinal tension.  Both of these processes result in residual stress in the mesh, commonly known as “work hardening”.

As anyone familiar with metals manufacturing knows, work hardened material is stiffer, springier and more brittle than stress free metal.  The good news is that work hardening effects can largely be eliminated through the thermal process of annealing.  However, some amount of residual stress can be helpful.  It is usually easier to handle thin meshes without wrinkling or losing grid geometry if some stress is left in the metal.  More to the point, the amount of residual stress can usually be optimized for the customer’s particular application by controlling the time & temperature cycle of the annealing process.  Dexmet engineers are experts at annealing most metals and can help you choose the right specification for your application.
Another result of the expanding process is that the thickness of finished material is increased by up 800% as a result of the twisting of the strands.  This increase in the z-dimension is quite beneficial in some applications (e.g.; pressing battery electrode powder onto mesh current collectors), but not always.  The z-dimension is also not uniform across the width of the mesh role.  Dexmet can control this parameter to tight specifications by passing the expanded mesh through dimensioning rollers in a post processing step.  The mesh can be “flattened” back to the original incoming foil thickness or lightly rolled to ensure consistent edge to edge thickness.

Also, it is important to note that expanded mesh is anisotropic.  That is, its properties are different in different directions.  Most engineers recognize the difference in latitudinal (stronger) and longitudinal (weaker) strength. But other properties, such as electrical resistance, also vary and control of these should be discussed with a Dexmet engineer.  In roll-to-roll processes, it is important to remember that mechanical behavior is dependent on the directionality of reel.  Dexmet can re-roll mesh on new cores to ensure uniform behavior in the customer’s process.

The more upfront information that is shared with Dexmet engineers during the early product development stage, the more likely your future processing issues will be significantly reduced or eliminated.

FULL  ANNEAL

The most commonly requested process is a full anneal. The temperature to accomplish this depends not only on the alloy of the product but may, in certain cases, depend on the degree of cold work that goes into the metal prior to anneal. Copper is a prime example in that after 100% cold work, a full anneal can generally be achieved at less than 300 degrees Fahrenheit (°F). Since we generally require a fully annealed raw material, with some exceptions, the amount of cold work is rather low. Some say it is in the neighborhood of 20-25%. Under this condition, an annealing temperature of in excess of 600°F is required for full anneal. Sometimes, to get the desired softness, the metal must reach near the sintering point to get the required result. This can occur in several metals but most commonly in copper and nickel.

We have a method to numerically determine the level of softness which we call the BART number. BART stands for Bend Angle Recovery Test and is determined by a proprietary measurement device that we can supply if you desire to have your own. The softer the metal, the lower the amount the metal recovers from being bent 90°F at a distance of 1” from the fulcrum. Values therefore range from just above 0 to just below 90°F  but never at the extremes. Values for a particular mesh configuration and alloy can be developed from testing representative samples. We have predictable values for several configurations but we always run into new ones on a regular basis. Once established, the degree of anneal can be easily quantified. As far as I know, no one else has this capability.

Stress Relieve

The ideal stress relieve will result in a mesh that has the same BART number after heat treatment but lays flatter and feels softer. The ultimate tensile of the product is unchanged. Unfortunately the temperature required to reproduce the ideal situation varies with chemistry and in some cases cold work. It is useful when working the expanded metal around a form without losing the strength of the mesh.

Strand Anneal

The strand anneal is useful for metals, like stainless steel where it must be brought to a sufficiently low temperature from the anneal temperature in a short amount of time. If this is not done, inter-granular corrosion could develop and deposit carbon in the grain boundaries. This can be an issue in some applications.

Removing Residual Oil

Sometimes it is useful to insure the metal has no residual lubricants on it. Here, after degreasing the metal we put it in an oven to remove the last vestiges of any trace of lubricants. For this a temperature of 400°F will suffice.

Regardless of your needs, Dexmet can accommodate them with our oven and furnace capabilities.

Sincerely,

Kirt Griffin, Quality Assurance Manager

After doing numerous tests, we have found the aluminum to completely fail corrosion testing (in part due to dissimilar metals of stainless, brass, and aluminum). Since our system relies in part on continuity, our performance may suffer if the aluminum corrodes. Can you give me some options with stainless steel and a copper alloy? I am open to large variations in conductance but would like to see something with tensile strength comparable to our current material. I want to reduce conductance and improve corrosion resistance so stainless seems like the natural choice.

Answer From Dexmet’s Ken Mull:

First the science. When lightning strikes, the electrical energy vaporizes the aluminum taking out the initial energy punch, it then flows along the conductive surface looking for ground. The primary material characteristic then becomes the heat of vaporization. The heat of fusion and the electrical resistivity are not as important since the heat of fusion for all metals is insignificant by comparison and the electrical resistivity does not come into play until after the strike has occurred. A comparison between aluminum and copper yields a 2:1 difference by weight in favor of the aluminum since aluminum has a much higher heat of vaporization by weight than does the copper. So if you wish to switch to copper at the same weight as your current configuration the result would be a reduction in energy potential of ~50%.

You also mention switching to stainless steel for better corrosion potential. I cannot find the heat of vaporization for stainless steel but can for iron. Iron has a similar value of the heat of vaporization as does copper which would make it similar to the copper in terms of protection, however I am not sure how much of an effect the added chrome and nickel will have on the heat of vaporization since at the moment my search for the heat of vaporization for stainless steel has turned up blank.

Finally, after the strike, the electrical energy needs to flow towards ground and the electrical energy moving through stainless steel with it’s higher resistance (3x over aluminum) may heat up the surrounding material, potentially melting the surfacing layers.

I realize this may not completely answer your question and to verify any change you will need to re-test.

One last comment, changing to either copper or stainless steel will impact on the price since both materials are more expensive than aluminum.