Additive Fabrication Facilitates Successful Injection Mold Design and Build
The appropriate use of RP additive models in conjunction with injection mold toolmaking has a positive impact on communication and verification, styling and ergonomics, and fit and functional issues.
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While the value of additive prototyping as a concept modeling tool is very well known—as per The Wohlers Report 2005—additive prototyping also has considerable value as an adjunct to the production toolmaking processes in order to avoid costly, time-consuming and potentially disastrous missteps in injection mold design and fabrication.
Communication and Verification
The same attributes that make additive prototyping very desirable as a communication tool for concept modeling tool (i.e., communication, verification, ergonomics, and fit and functionality) also serve to make it a very useful partner in the development of injection mold tooling, and in ancillary production processes.
Understand, additive prototyping is not—nor ever will be—a stand-alone replacement for current and future CAD/CAM software related to moldmaking. Rather it is an outstanding supplemental tool to facilitate understanding of mold-making issues especially when working in partnership with an audience of limited technical background.
Communicating with a non-technical customer in regard to toolmaking issues is always difficult. Current CAD/CAM software is remarkable in its ability to identify and highlight areas of concern in injection mold design. Undercuts and similar parting line issues are made highly visible two dimensionally on our computer monitors—allowing us to avoid costly and time-consuming errors. Similarly, necessary mold actions, considerations in regard to melt flow, cooling issues and ejection problems are made visible “virtually” to the skilled technologist through the use of these powerful tools.
However, communicating these same molding issues as they appear on the two-
dimensional screen to someone not conver-sant with the process can be somewhere between difficult and impossible. Visual aids as provided by “real parts,” made through an additive process can be an invaluable tool in the communication process. This handy translation from the two-dimensional screen to an actual three-dimensional representation of the item of interest can make explanations of moldmaking considerations clear—even for relative novices—and verifies that the client will be getting the results that he desires prior to the cutting of metal.
Additive models help tool builders commit to timelines and costs and thereby avoid unpleasant surprises and client conflicts. In essence, the three-dimensional additive part can allow for consensus and partnership between the moldmaker and the client in regard to potentially expensive and time-consuming complex mold features and actions. A typical rule of thumb in this area is: the more complex the part, the higher the value of the three-dimensional additive model in client interaction.
Styling and Ergonomics
While mold features and actions are certainly very important items about which to have clarity with our customers, given their impact on economics and timing, perhaps nothing is more important than ensuring that the parts made, really reflect the ergonomic design intent.
While it is very easy to wrap your hand around the grip or handle of a physical part, it is profoundly difficult to do so virtually. RP additive models provide enormous value in allowing designers, moldmakers and potential customers to touch, feel and manipulate the envisioned parts prior to the creation of production tools. Doing so replaces the complexity of trying to mentally/virtually manipulate an item, with the absolutely simple, visceral, intuitive physical process of actual touch.
As an individual who has been involved in the development of hundreds of different blow molded bottles with flowing organic shapes, I can say without fear of contradiction that unless you have a physical model of your intended design, the risk of producing an article that is aesthetically appealing, but almost unusable is very real. I have seen many, many proposed products that were beautiful on the computer monitor, and in two-dimensional renderings, sent back to the virtual drawing board for major design revisions early in the development process because of basic ergonomic issues revealed through the use of RP additive models. Yet another rule of thumb might be: the more that your end user will need to physically manipulate your injection or blow molded product, the higher the value of an additive model in the early stages of product development.
Fit and Function
In addition to styling and ergonomics, and communication and verification, RP additive models are enormously valuable for fit and functional testing prior to beginning injection mold toolmaking. Almost never, is a single injection molded part a “stand-alone item;” nearly all injection molded or blow molded articles will be part of a larger assembly, perhaps requiring threaded closures, drain-back caps, snap fits, living hinges, sonic welds and other features.
Current automated assembly methods make an in-depth understanding of fit and function issues absolutely essential. Problems that can be examined with RP additive parts can be as basic as ensuring that molded parts will not “nest” into one another making them difficult to separate online. Adding “de-nest” lugs to a part design prior to beginning the toolmaking process is a cheap and simple way to save thousands of hours of effort for a mass-produced item down the road.
CAD programs are excellent at virtually assembling complex arrays of injection molded parts together, whether the forces required are problematic or not. Changing a snap fit prior to cutting a tool is a simple matter, changing it after cutting the tool, is not. In lieu of a wealth of CAE and FEA data, having RP additive parts in hand that can supply the necessary information in an approximate fashion will ensure that automated assembly issues will be understood and successfully addressed prior to molding is an enormously valuable tool.
Still other automated post-molding considerations include decorative operations such as labeling, hot stamping, painting, and others—and these too can be better understood though the of RP additives models. A final rule of thumb might then be: the more complex the assembly and decoration process, the more value that there is to be gained through the use of RP additive models in combination with injection mold design.
To conclude, the appropriate use of RP additive models in conjunction with injection mold toolmaking has a positive impact on three major areas: (1) communication and verification, (2) styling and ergonomics, and (3) fit and functional issues.
Additive models facilitate consensus building and understanding in regard to molding issues with naïve clients. RP additive models are essential to an understanding of ergonomics prior to committing to the toolmaking process. And these same models can facilitate post molding assembly and decorative processes—in short, allowing us to produce injection molded products with fewer missteps, cheaper, faster and better.
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