MoldMaking Technology

OCT 2017

Advertising in MoldMaking Technology offers

Issue link: https://mmt.epubxp.com/i/877607

Contents of this Issue

Navigation

Page 18 of 59

moldmakingtechnology.com 17 Cooling channel placement also dramatically affects the abil- ity to remove heat from the plastic part. If heat is not removed evenly across the part, then the shrink rate will be drastically different. This yields a product with varying amounts of stress and a high likelihood of warpage. It is possible to manage a small portion of inherent stress through processing. The first step is to ensure that the resin's actual melt temperature is within the recommended range from the material manufacturer. To verify the melt temperature, complete an air shot with normal machine parameters, and insert an immer- sion probe into the center of the melt puddle. If the temperatures are run below the suggested range, then injec- tion pressure will be higher, inducing additional, unwanted stress. Then, ensure that the proper flow rate is set for the injection phase. A shear rate that is set too high at the gate can be higher than the material's limitations, which can cause the melt temperature to increase dramatically and can degrade the polymer or the additives. Here, it is important to understand that the polymer chains are oriented and stretched out dur- ing the filling phase, which means that simply changing the flow rate will vary the amount of stress and cause warpage, sinks, voids, short shots, assembly issues and part performance problems. The amount of pack pressure and time is another relevant factor. After the filling phase, the process transitions into packing, where the molecules are now compressed with pressure applied from the injec- tion unit. Often, these variables are set based on part weight or dimen- sions. Nonetheless, do not ignore the possibility of overpacking, which typically occurs near the gate area in response to overcoming an enormous pressure gradient across the cavity. Lastly, consider mold cooling and its impact on stress. The molder only controls coolant temperature, flow rate and time. When the mold temperatures are set lower than recommended, there could be excessive stress locked into the molded part. Hot material flowing over a colder mold surface Do not ignore the possibility of overpacking, which typically occurs near the gate area in response to overcoming an enormous pressure gradient across the cavity. We've "Got the Muscle" to Complete Your Toughest Job. POCO EDM graphites have the strength to stand up to your most critical requirements – whether it be extreme detailed electrodes, super fine finishes, improved wear resistance, or fast metal removal rates. Need more than just an electrode material? In addition to the highest performing electrode materials, with POCO you also get the added support of knowledgeable applications specialists, a comprehensive EDM technology interactive manual, articles and literature, practical EDM training, and shop floor technical assistance. Everyday you face the competition, let us be there to give you the win. What's your toughest job? sales@poco.com www.poco.com ISO 9001:2008 & AS9100:2009 POCO® is a registered trademark of Poco Graphite, Inc. ©2017 Poco Graphite, Inc., All rights reserved. Direct: +1-940-393-4302 US Toll Free: 1-877-762-6336 x 4302 Follow us on LinkedIn Visit us at South-Tec Booth 420

Articles in this issue

Links on this page

Archives of this issue

view archives of MoldMaking Technology - OCT 2017