Faster Trials Speed Resolutions to Design Problems

Netafim, Israel, a global leader in irrigation-based systems and water technologies, owns a
number of molds that are crucial to the production of its complex micro sprinkler systems. The problem the engineering team experienced was that the quality of the small parts produced with these molds deteriorated and the mold set-up time was too long. Specifically, one of the components of the sprinkler system contained an air trap on a section that had to be absolutely flawless to meet the high sealing quality standards.

The company is committed to uncompromising quality. Given the nature of its products, and methods to preserve water — one of the world’s most precious resources — this commitment is a way of life.

The company’s engineers used trail and error to alter the process parameters in order to move the air trap to an acceptable location. Of course this tedious approach resulted in a lengthy set up time. The company’s management considered this situation unacceptable. They challenged a team under the leadership of G.S. Design LTD, Israel, to improve the current part and mold design. The team’s goals were to ensure a decrease in set-up time and that the parts met Netafim’s stringent quality requirements.

G.S. Design engineers chose the 3D module of Moldflow Plastics Insight® (MPI), from Moldflow Corp., for this project because it can accurately predict complex filling patterns and help resolve tough quality problems. The challenge the team had was the air trap formation in the middle of the part, the critical section that ensured the water-tight seal. Further, the part itself was small with lots of variation in the wall thickness. This unique design required a three-dimensional approach to analyze the situation.

Traditionally, plastic parts have thin, uniform walls which make the prediction of how the plastic will flow straightforward. However, with thick parts, molten plastic can flow in all directions, making an accurate prediction challenging. Not with MPI/3D, though. In fact, MPI/3D lets you perform true, three-dimensional simulations on parts that tend to be very thick and solid in nature, as well as those that have extreme changes in wall thicknesses. The accurate results are achieved by using a proven technology based on a solid tetrahedral, finite-element volume mesh created directly from a solid CAD model.

The production of complex micro sprinkler systems required small molds. When plastic flowed into one specific mold pattern, an air trap formation formed near the part’s critical middle section that would compromise a water-tight seal.

The team ran a number of scenarios changing the wall thicknesses and, therefore, shifted the flow pattern so that it “pushed” the air trap away from the critical spot and towards a major parting line, which could easily be vented. The MPI/3D software module accurately predicted the air trap formation, showing the root cause of the quality problems. The team then communicated the part and mold design changes to the tool shop that created new production-quality hot runner molds.

Engineers changed the wall thickness in the design using Moldflow Plastics Insight®, which “moved” the air trap towards the main parting line, a less critical section of the part.

According to Gal Sherbelis, President and CEO of G.S. Design, MPI’s 3D module was an obvious choice for this project because of the module’s analysis accuracy: “Predicting how the plastic material flows in this small, complex part with many surfaces and thickness changes requires true 3D simulation capabilities. With MPI/3D, we knew exactly where weld lines formed and air traps occurred. This was absolutely critical for us in the part and mold design.”

Concurred Shomar Yair, Netafim, “We were very happy with the team’s work and especially pleased with the analysis accuracy. We molded parts and verified that the predicted fill pattern closely matched the actual fill pattern. This gave us confidence in the simulation results and enabled us to make the required part and mold design changes to quickly improve our quality.”

Further, with MPI/3D, all velocities, pressures, temperatures, flow front positions and heat transfer effects are computed in three dimensions for maximum accuracy.

The CAD files of the new part and mold designs along with a Moldflow Communicator file were sent to the mold maker. “In addition, we used Moldflow Communicator to communicate not only the analysis results, but also the assumptions we made,” said Sherbelis. “Communicator helped both Netafim and the mold maker visualize, quantify and compare the result files we created in MPI/3D.” Consequently, the mold maker could clearly visualize tool requirements, reducing costly mold rework and minimize mold trials.

The new design saves Netafim an estimated $10,000 per year.

MoldFlow Corp.
http://www.moldflow.com/ 

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