Moldflow Analysis Is a Must—Especially for Tight-Tolerance, Plastic Parts

Posted by Al Elger on Aug 23, 2012 4:00:00 PM

blank.pngMoldflow analysis is a frequently used term in the injection molding industry but is often poorly misunderstood. The process utilizes a sophisticated computer program to predict the flow of plastic during all phases of the injection molding process, including flow, pack, and cooling. There are different levels of analytical software that are available; selecting the right one for your project (and interpreting it correctly) is critical for success.

The most basic level of moldflow analysis includes a simulation for the fill and packing phases. This helps optimize gate location, gate sizes, balance runners, and process conditions. More advanced simulations compare runner systems, mold temperatures, and can even predict fiber orientation. Undertaking moldflow simulation during the design phase ensures higher-quality parts and optimizes cycle times and tooling trials.

More advanced moldflow applications provide critical information for predictions regarding more complex parts and processes, such as mold cooling, shrinkage, and warpage. Shrink is unavoidable in plastic and is typically a result of material structure (for example, semi-crystalline or amorphous), packing pressure, and wall thickness. Engineers must be able to accurately estimate shrinkage to properly size the mold. Warp is a result of shrink and can come from three sources: unbalanced mold cooling, fiber orientation, and non-uniform shrinkage. Warpage analysis can identify the causes of warpage and where warpage will occur before the mold is built, allowing engineers the opportunity to optimize design, material selection, and processing parameters to minimize deformation, before production starts.

Other key parameters that can be predicted through moldflow analysis are processing conditions, flow-induced shear stress, weld line location, air trap prediction, bore diameter sizing, sequential valve gauging, cavity/part temperature differential, coolant temperature, and coolant flow rate.

Because it identifies and mitigates potential problems before the mold is constructed, moldflow analysis reduces risk, improves quality, and lowers overall production costs. In some cases, such as extremely simple parts made from common materials, moldflow analysis may not be required or even be very beneficial. However, for most projects, especially those with complex, high-tolerance parts that require precise dimensional stability, not doing moldflow analysis is a big mistake. When suppliers or customers state they have moldflow capability, be sure to determine what they can accurately achieve. Top-level moldflow analyses are expensive and require highly skilled personnel to run them. Above all, don’t make a moldflow decision based simply on cost—work with an experienced injection molder like Kaysun to discuss the details and determine the best moldflow option for your project.

Topics: Plastic Part Design