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20 MoldMaking Technology January 2015 Pellet 2 Part (P2P) Plastic Injection Molding Starts with the Pellet Here's what every moldmaker should know about raw materials, including the fundamentals of viscosity curves, Melt Flow Index, Melt Flow Rate, shear and more. 7. What are the part dimension and performance requirements? 8. What is the required cycle time? Flow simulation, commonly known as "mold flow" in our industry (also the trademarked name of a software program), can provide critical information to the part designer, mold builder and injection molder concerning knit line loca- tions, press size, cycle time and other important mold-build details. If a polymer flow simulation is provided, the report will already have taken into account the viscosity curve data (see Graph) used by the simulation provider. If it is not pro- vided, research on the polymer to be used will be required. It is important that only exact data for the specific raw material is used. Substitutions can diminish the accuracy and value of any simulation. Generalizations and assumptions can translate into larger molding machines, longer cycle times, tool rework, part defects, scrap and even part failure. The mold builder's engineering decisions related to the deliv- ery system, gating, cooling and venting will have direct impact Do you want your moldmaking to add more value? Do you want to solve or improve plastic injection molding problems? If you answered yes to either of these questions, then try thinking in plastic first, not steel. This new series will examine the injection molding process by breaking down the path a plastic pellet takes as it is transformed from Pellet 2 Part. 1 2 3 4 5 7 6 8 Image courtesy of KraussMaffei. H 2 O By Rich Oles and Scott E. Powers To begin this 11-part series on plas- tic injection molding, I propose that you keep an open mind and consider modernizing your current approach to mold manufacturing, making the effort to understand other areas of our industry in greater, practical detail. Challenge yourself to ask "Why?" before dismissing something new. As the year and series progress, we will reveal the steps of the injection molding process, begin- ning with the plastic pellet and through its transformation into a part. The series will also review the basics of energy management, including its generation, application, control and removal within the process. We want you, the reader, to learn from the daily processing challenges we present and then be able to provide permanent solutions for your customers. This approach has the potential to transform your business. The Raw Material The selection of raw material will set the direction for the design of the mold. Each plastic injection mold build should start with a design for manufacturing (DFM) meeting that includes the mold builder, injection molder, raw material (poly- mer/resin) provider, flow simulation provider and hot runner manifold supplier (if applicable). Although more questions undoubtedly will arise, the discussion should at least include answers to the following questions: 1. What is the specific grade of raw material? 2. How does that material flow? 3. Are there fillers or additives? 4. What are the estimated shrinkage values? 5. What are the injection molder's standards? 6. What temperature will the mold run at? This article series will review (1) raw material; (2) the melt delivery system: screw, valve and end cap; (3) hot and cold runner systems; (4) hot runner controllers; (5) mold cooling optimized by design; (6) plant water system impact on performance; (7) new and innovative mold cooling technologies; and (8) automated part handling.