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Plastics Today, September 2015

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InjectIon Molds PlastIcstoday.coM Global PlastIcs RePoRt 2015 49 No need to compromise tool life Now that conformal cooled inserts can be built from fully heat-treatable H13 tool steel, there is no need to compro- mise tool life to experience the benefits. This steel option also allows conformal cooling to be applied to pressure die cast tooling. Zinc die casting would be an ideal application, as the amount of cooling in the tool is often the limiting factor in the achievable production rate. Blowmolding is another process that could be improved by the application of conformal cooling. While laser sintering has been used for decades, there is still a learning curve to its best use in conformal cooling applications. Guidance is needed for where and how to use the technique to ensure a positive cost/benefit ratio. One area where a company with expertise in the design and manufacture of conformal cooled mold tools can help is in mixing the metal-building process (laser sintering) and the metal-removal process (machining) to achieve the best results. Metal building can be applied to a pre-machined blank, so that the total volume of laser sintering is minimized to areas where it is needed, while the tool part is kept in one piece and cost is kept in check. The completed laser-sintered part then must be machined to achieve the desired cavity surface finish; thus, the correct machining allowance must be added to the sintering process, where appropriate. As a policy, New Zealand-based tool- maker RPM International Tool & Die computer models all tools in 3D CAD, currently Creo2 (formerly known as Pro Engineer). This means that all thermal and flow simulations and water channel designs can be accurately modeled and analyzed, no matter how complex the geometry. With 5-axis machining and laser sintering, these 3D CAD models are accurately reproduced in metal with no geometrical compromises. Game-changing technology for complex tool design Using laser sintering to produce tool parts is now a proven technology. It should be a serious consideration for all jobs that pose challenges in the tool split- ting, filling, ejecting and cooling balance. Indeed, conformal cooling is a game- changing technology for complex tool design, making the previously impos- sible not only possible but practical and affordable, as well. The following example of an insert for an injection molding tool, which was made with conventional cooling chan- nels and re-made with conformal cooling channels, provides a direct comparison in costs and benefits. In this case, the conventional insert cost $1200, whereas the conformal cooled insert cost $1250. The small cost difference was a result of the higher cost of laser sintering, which was mitigated by a reduction in machining time for the cavity surfaces. In production, the conformal cooled insert reduced cycle time from 24 to 18 seconds and mini- mized warpage. In this example, the need for conformal cooling is not obvious, but the benefits are clear and very cost effective. It shows how this technology should be considered for use in any tool, not just very difficult ones. Another example of a tool with con- formal cooling, made at RPM, is shown above. The upper left image shows a conventionally cooled moving half insert with 16-mm-diameter blind holes and baffles. Note that the white holes are for ejector pins. In the upper right is the insert with a complex arrangement of conformal cooling channels with feed lines from the back of the part. The con- ventional and conformal inserts on the fixed half of the tool are shown in the bottom left and right, respectively. The difference in cooling channels between the two sets of inserts is strik- ing, with the conformal design not even considered necessary, let alone deemed possible, in the first empirically designed set. However, component warpage was eliminated and the cycle time of the tool was reduced by 30% in this instance. The cost of the conformal inserts was quickly recovered, and similar results could be achieved with other injection mold tools. This article was authored by Mike Godber, who works as a tool designer at New Zealand's largest toolmaker, RPM International Tool & Die. The company has particular expertise in the design and manufacture of conformal cooled mold tools. By integrating this technology into the whole tool design, RPM is able to provide customers with cost-effective, high- quality products. For more information on conformal cooling and direct metal laser sintering, go to the company website at www.rpmtoolanddie.com. A conventionally cooled moving half insert with 16-mm-diameter blind holes and baffles is pictured in the top left image. On the upper right is the insert with a complex arrangement of conformal cooling channels with feed lines from the back of the part. Conventional and conformal inserts on the fixed half of the tool are shown in the bottom left and right, respectively.

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