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Mold Material Photo courtesy of MSI Mold Builders. By Roger Klouda The Hybrid Mold Hybrid cars, hybrid flowers, hybrid corn, so why not hybrid molds? F or years we have been hearing about the virtues of aluminum molds for injection parts, and MSI Mold Builders has built its fair share���mostly for specialpurpose applications that did not require many actions. For smaller molds using specialty aluminum has its benefits; and, if cycle times are critical, you can justify the high cost. However, our experience has led us to a different set of solutions: hybrid molds���P-20 cavities and inexpensive aluminum cores. Here are six facts about hybrids: (1) they are not a cure for all programs; (2) have a limited market, but larger ���Experience has led than all-aluminum molds; us to a different set (3) are good transition molds before plunging into of solutions: hybrid an all-aluminum mold; molds���P-20 cavities and (4) solve many issues that all-aluminum molds caninexpensive aluminum not; (5) offer many benefits cores.��� of aluminum molds with less risk; and, (6) fill a gap for programs that don���t have high-volume, but require high cosmetics on the cavities. There are basically two different types of hybrid molds: 1. P-20 with full aluminum core. The core block is aluminum with a steel ejector box. Some say you need steel from the parting line through the aluminum core block to the riser, but we have not found that to be the case unless special circumstances exist. This option also limits potential water locations and can increase costs. 2. P-20 cavity with aluminum core inserted into P-20 support plate. Unless you are making a core insert because of part requirements, this improves mold life and gives you a steel parting line on both sides as well as thermal conductivity and ease of machining. Cost savings are less than P-20 with full aluminum core, but better than an all-P-20 mold. If you are inserting just to have an aluminum core, review the part configuration to justify. Oftentimes, the act of inserting drives the cost up, but you will still see cycle time improvement. Aluminum���s thermal conductivity rate is five times that of P-20���basically the same as beryllium copper. You insert beryl- 36 MoldMaking Technology March 2013 A large container mold built by MSI Mold Builders. lium copper to enhance heat removal from areas of a P-20 mold. You also get a rise in surface temperature at injection, which in many cases will improve the flow characteristics and still cool the part faster than P-20. Also you can obtain and maintain the same finish as a P-20 mold since the cavity is P-20. We���ve had success in certain materials with texturing or applying a high finish to an aluminum mold, but the likelihood of it washing out or fading is increased. However, if you are only going for a few pieces (fewer than 5,000), you may be successful with an all-aluminum mold. The material itself is significantly less expensive than P-20. We generally use a cast material, and in 15 years we have not seen pits, inclusions, etc. Keep in mind that this is also the core side; it machines and polishes in about a third of the time it takes P-20���if we go slowly. Generally, the core has the most time associated with it. EDMing ribs and features in a core is very expensive and we are limited in P-20 to approximately five to 10 times the diameter of the cutter when cutting ribs. In aluminum, we are routinely limited by the available cutters with enough flute length. Polishing ribs/features in P-20 is expensive and time consuming. We estimate an 80% savings over P-20 from our experience with aluminum. On most cores today we are only polishing for pull, so only the ribs/features are getting polished. We can apply fillet radii when polishing rather than valuable machine time. We can also drop off one electrode for each burn location. High-speed machining makes short work of aluminum. Currently, thick section P-20 materials are difficult to come by, increasing material costs���making aluminum a better value. As noted, thermal conductivity is similar to beryllium copper and with a complete core side in aluminum, the expectation is significantly reduced cycle times. Our customers have not been willing to make a set of duplicate molds for a side by side test, but simulations projected a significant cycle reduction, and the actual cycle time reductions were greater. Typically, the core side of the mold has the most detail, so if you can decrease the hours associated with building the core, leadtime can decrease. Since we decrease polishing, EDM, etc., we will decrease the total leadtime of the mold.