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At PEI, we develop bends by machining a relief on the underside of the material and applying heat along the bend line to allow the plastic to be formable. Once the proper angle is achieved, the joint is cooled and the bend is set in place. For 90 degree bends, the outside radius will be approximately the same as the thickness of the material. As an example, a 90 degree bend using 0.125" thick material will have a 1/8" outside radius. It should be noted here that the shrinkage of the material during the cooling stage is minimized using this process because the amount of BTUs (heat) absorbed by the plastic and the square surface area targeted are minimized as much as possible. Therefore, the less heat going into the plastic, the less heat that must be dissipated which is the root cause of shrinkage and distortion. For bends less than 90 degrees, the actual outside radius will still be equal to the thickness of the material, however, visually, the radius will appear to be greater. This is because an arc of less than 90 degrees appears to follow a curve rather than pivoting at a point. For true curves (not bends), we can form the material to follow an arc of up to 180 degrees of rotation. We achieve this using a proprietary cold bending method that eliminates the typical distortion of the plastic caused by shrinkage during the cooling phase. In order to accomplish this, there is special machining and structural support involved that may affect other features of the enclosure. Finally, it should be understood that developing bends and curves for a particular enclosure design is done within the constraints of our process and the configuration of that design. As such, there may be times when a particular bend or curve is not achievable due to adjacent components, cutouts, or similar details. During the design stage, such constraints would be addressed and if a design conflict arises alternatives would always be presented to the customer for their approval. |
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When properly designed, the mechanical strength of enclosures produced with our process can be as tough as any other plastic. From drop testing to moisture proofing, over the years we have successfully supplied enclosures that have met customers' functional specifications in just about every type of environment imaginable. One of the keys to the strength of our enclosures is our 'Tab Lock' welding process that ensures both sheer and tensile integrity are maintained. By interlocking all permanent joints, we are able to transfer sheer and tensile loads directly to the substrate material, thereby reducing the reliance on a separate bonding medium or filler material. Additionally, we have developed our own specialized chemical welding method for all joints and seams, which greatly increases the mechanical integrity of every enclosure we build. This process involves welding of similar materials by chemically melting adjoining surfaces and then applying pressure to enhance the fusion. The end result is joints that are stronger than what could be achieved with standard gluing or heat staking. As a final
note on this subject, our experience has been that our joints are so
strong that the substrate material is as likely to fail as the seam.
For that reason, we are confident that if plastic is the right material
for a customer's application, then the PEI process can be a very attractive
alternative to injection molding or thermoforming. |
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As an example, with sheet metal enclosures, standoffs, such as PCB mounts, might be pressed in or spot welded through the panel wall. With the PEI process, we cut a pocket and either sonic weld or solvent bond a molded insert in place. Two of the advantages of this method are that we do not have to break through an outside panel surface and the height of the standoff can be set to a greater variety of dimensions simply by varying the depth of the pocket. As with all such processes, there are limitations to the amount of height variation achievable due to the material thickness and the beginning heights of the standoffs. However, even with such limitations, the variety of height dimensions is much greater than what can be achieved with the sheet metal fabrication. Additionally, with our 'no tooling' process we can place standoffs and other molded-in type of components on any surface without incurring additional upfront costs. With injection molding or thermoforming, placing holes, standoffs, or similar feature can be difficult or unfeasible depending on location and/or mold configuration. |
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Copyright 2000-2006 Plastronic Enclosures, Inc.- | All Rights Reserved A Plastic Enclosure Company |
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