The Automotive industry frequently uses a process known as “backmolding” where a laminate containing a design or texture is molded into the part on the class A surface side. The part geometry near the parting line must be modified slightly to create the seal and is critical to the process. The gas must be sealed at the parting line and any ejector pin areas to prevent escape. Gas pressure is then either fully vented by the same manner as introduced, or may be reduced with some remaining gas pressure retained for use in encouraging ejection. Gas pressure is held constant until the plastic has cooled and is self-supporting. The gas is introduced via a porous metal insert, gas pin, or poppet. Gas is not injected into the plastic material, but onto the plastic creating a layer or “blanket” of gas across the entire sealed surface area or selected sealed areas of the molded article. Gas is then injected at low pressure (typically less than 1000 psi) through the core side of the mold. The molding machine applies no pack pressure or additional material. This is accomplished using the normal filling phase of the injected molding machine. In 1999 Incoe obtained licensed rights to use and sell this patented technology in North America.Ī quantity of plastic is injected into the mold. Recently Asahi purchased the entire ICP worldwide patent portfolio. The process, however, was not brought to commercial status.Īt the same time, Asahi Chemical of Japan was independently working on a similar process and also achieved promising results. The “Injection Compression Process”, as it was called, was the first patented use of gas as a packing or compression technique in injection molding. The work on this process began in the 80’s and was invented in the U.S.A. It is our belief these problems can significantly be improved or eliminated with the use of a new process developed - External Gas Molding. The results are surface imperfections such as indentations or weld lines.Ĭonventional gas molding also requires an entry and exit hole that is retained as a blemish on the part. Naturally, the pressure dissipates the further the distance is from the gas channel. When gas is used to pressurize multiple channels the gas pressure applied is obviously greater at or near the gas channel. Although state-of-the-art gas control devices may eliminate some of these occurrences, there will continue to be part geometries that still produce this problem. “Fingering” is another undesirable condition caused when the gas is not retained in the thick section of the part and spreads to the nominal wall section. If the plastic flow hesitates or stops, marks or flow lines will be evident on the surface and, therefore, unacceptable on the Class A surface finish. Shadow marks can be caused during the injection of gas. There are still, however, molding challenges. As an example, nearly all TV cabinets produced today use this Gas Assisted Molded method. The benefits of these techniques have made significant improvements in many molded products. Properly located gas channels can also reduce the tendency for warpage in the molded part that is otherwise caused by the induced stress during the packing phase of the standard injection molding cycle. Gas channels can be added along the length of these ribs, and by injecting gas in the center of the channels will pressurize the immediate area and eliminate sink marks. In the last several years, the Gas Assisted Molding process has also been used to improve the surface quality of molded parts that have ribs, bosses or pillars that are required geometry in injection molded parts. Initially, the process was used to core out thick sections of injection-molded articles and has been the subject of many papers presented at earlier conferences. The process known as Gas Assisted Molding is a proven and beneficial molding method of improving a variety of injection molding conditions.
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