![]() Unfortunately this type of analysis data is not available for many plastic parts, so molders need a method to establish an ideal fill time that they can employ on the shop floor. Ideally, every part would be evaluated for fill time using mold-filling simulation performed by a skilled analyst with plastics processing experience. Evaluating the fill time used on similar parts and molds.Molders use several methods to establish a fill time, some of which begin with one of the following methods: The key question is: How does one go about identifying an ideal fill time for a given mold? Therefore once the ideal fill time is established for a given mold, that fill time should live with the mold forever and should be allowed to vary only slightly (☐.04 sec, as per John Bozzelli’s recommendation). Any change in fill time may adversely affect the final molded part. Fill time affects how much shear heating and shear thinning the plastic experiences, which in turn affect the material’s viscosity, the pressure and temperature of the plastic inside the cavities, and the overall part quality (dimensions, aesthetics, strength, etc.). Fill time is an indication of how fast the plastic is injected into the mold. One of the important process parameters to establish and record for any injection molded part is its injection or fill time. For example, if you are documenting the melt temperature you would document the temperature of the plastic coming out of the machine nozzle-not the barrel temperature settings on the machine controller. This requires that the process is recorded by referencing plastic variables, not machine variables, and is done using a “universal setup sheet” (a term used by John Bozzelli, ). These approaches also teach that the process must be documented in a manner that allows it to be transferred to other molding machines with the intent of achieving relatively consistent part quality. relative shear rate” curves), as well as methods for establishing an ideal transfer position, ensuring the proper melt temperature, finding the ideal hold pressure, identifying pressure losses within the mold, and finding the time when gate seal (gate freeze) occurs. Among the procedures taught are a method for determining a fill time or fill speed using in-mold rheology curves (a.k.a “relative viscosity vs. These approaches involve similar specific procedures that help establish a foundation on which to build a process. A number of schools, companies, and individuals provide a valuable service to the industry by teaching these structured methods, which have been labeled with terms such as Scientific Molding, Decoupled Molding, and 2-Stage and 3-Stage processes. Injection molding process methodologies have evolved over the decades from a seat-of-the-pants black art to a more structured approach.
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