Machine Design

Software optimizes unique Moldmaking Process

Tightly integrated CAD, CAM, and analysis software permits more efficient molds.

Direct-metal deposition uses lasers, sensors, and powder metallurgy to build molds from molten metal, layer by layer.

The unique manufacturing process requires software that supports and provides seamless integration between CAD, CAM, and analysis software such as FEA and mold flow.

The process makes possible features in molds such as conformal cooling channels and embedded copper heat sinks which are not possible using traditional machining methods.

Direct-metal deposition (DMD) is a manufacturing process that combines lasers, CAD, CAM, sensors, and powder metallurgy to build molds from molten metal, layer by layer. This process makes it possible to include features in molds, such as conformal cooling channels and embedded copper heat sinks, which are not possible using traditional machining methods that carve out molds from solid metal blocks. The use of DMD results in molds with faster cooling cycles and faster overall cycle times.

The DMD process was developed by POM Group Inc., a service bureau based in Plymouth, Mich., that grew out of the University of Michigan's Center for LaserAided Intelligent Manufacturing. The company combines a unique manufacturing process with state-of-theart CAD, CAM, and mold-flow analysis to increase the productivity of plastic injection molds and dies.

The process requires software that supports the unique manufacturing process and provides seamless integration between CAD, CAM, and analysis software. This enables POM to design and produce thermodynamically optimized molds faster than possible through conventional manufacturing techniques.

For instance, mold-flow analysis enables the designer to optimize the mold's thermal characteristics prior to manufacturing. Well-integrated design and analysis programs mean CAD geometry can be used as the basis for the analysis mesh. Tightly integrated CAD and CAM software means toolpaths for the laser can be generated directly from CAD geometry, further speeding production.

The company also required CAM software with the flexibility to define toolpaths as needed for the metaldeposition process that runs counter to traditional mold manufacturing which involves metal removal. The CAM software must be able to create toolpaths from the part geometry itself, rather than starting from a solid piece of material and subtracting from it.

POM selected I-DEAS software from SDRC, Milford, Ohio, as the foundation for the mold optimization and manufacturing process. I-DEAS is a mechanical-design, automation software package that supports digital master models. The ability to develop digital master product models with CAE/CAD/CAM software technology has made it possible to more fully understand products from a manufacturability standpoint during the early design stage. The depth of product information contained in a digital master model makes it easier to communicate data to everyone involved in the product development process, including design, manufacturing, management, and outside suppliers.

POM went with I-DEAS because it provides the necessary integration between CAD and CAM, and between CAD and POM's mold-flow analysis software. It also provided the needed support for nontraditional mold manufacturing.

In use, a client supplies POM with an IGES file of a mold, which company engineers import into I-DEAS Master Modeler. There, they modify surfaces as necessary to make them more suitable for analysis. I-DEAS Finite Element Modeling generates the analysis mesh.

Using MPI/Flow and MPI/Cool from Moldflow Corp., Lexington, Mass., an analysis of the original mold serves as the baseline from which to evaluate modifications. Engineers make changes to the model of the original mold, adding features such as conformal cooling channels and embedded heat sinks to better cool the part. They repeat the flow and cooling analyses to evaluate the effectiveness of the modifications on parameters such as cooling time and heat distribution throughout the mold.

After the thermodynamics have been optimized, POM builds the optimized mold using the DMD process. Engineers slice the CAD models into thin layers from top to bottom. Then they use I-DEAS Generative Machining to create a toolpath for each layer. The toolpaths are run through a proprietary program that reverses the paths created by CAM

software so that rather than starting at the top and cutting material away, they start at the bottom and build material up.

The beauty of moldmaking with the DMD process is that conformal cooling channels can be built right into the part, instead of later drilling in straight lines. Also, the mold can include an embedded copper heat sink. Not only does this make it possible to position heat sinks more effectively, it also prevents the copper from quickly eroding in the typical production environment.

Results are impressive. By combining the DMD manufacturing process with advanced design, manufacturing, and mold-flow-analysis software packages, POM can make changes to molds that improve their performance dramatically. In molds with hot spots, for example, POM's modifications have reduced cooling cycle time by 80% and overall molding-cycle time by 50%.

The POM process can even improve molds that are working well in production. For instance, the productivity of a mold for a plastic relay cover improved 30% after engineers added conformal cooling channels and an embedded copper heat sink. These changes decreased cooling time from 6.5 to 3.9 sec, and greatly reduced the temperature difference between the two sides of the mold, reducing the number of rejected parts. The client received the optimized mold just two and a half weeks after supplying a CAD file of the original mold.

In addition to offering DMD as a service, POM intends to eventually offer fully configured DMD systems.

Information for this story was provided by SDRC, Milford, Ohio.

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