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SIGMASOFT® Virtual Molding Improves Shrinkage and Warpage Prediction in Injection Molded Parts

Thermally induced stresses are based on more realistic boundary conditions

SIGMASOFT® Virtual Molding Technology reproduces exactly the process conditions in injection molding, working as a “virtual injection molding machine”. The analysis includes all mold components with their actual physical properties. The software accurately reproduces the transient thermal boundary conditions responsible for thermally induced stresses. This example illustrates how the software can be used to improve the reliability of shrinkage and warpage prediction.

SIGMASOFT® Virtual Molding improves the predictability of shrinkage and warpage results. It reproduces the true mold behavior over several molding cycles, capturing the temperature behavior of the mold surrounding the part increasing the accuracy of the stress calculation.

SIGMASOFT® Virtual Molding was first presented at the K-Show in Düsseldorf, in October 2013. It has been conceived as a virtual injection-molding machine, able to reliably reproduce the injection molding process, with all mold components, over several cycles. Because of this approach, it is used to find out whether a given process set-up, mold layout, part design and runner concept will work as expected, and if not, why?

"The response to our Virtual Molding technology SIGMASOFT® has been very positive", states Dr. Marco Thornagel, executive director at SIGMA. "Users have welcomed the ability to know upfront how an injection molded part will behave. Shifting this workload from the molding machine out in the plant and into the computer has improved the process greatly".

SIGMASOFT® Virtual Molding is a completely new technology, which reproduces the complex thermal and rheological interactions that happen in the injection mold over several molding cycles. The result is that the molder can visualize, at any point and any time in the molding process, what happens to the mold and to the molded part. In this way, molding defects can be detected early, or process inefficiencies can be identified and corrected, even before the mold is built. The first industrial users of our technology have reported that they now get first-shot success in their molds: the designs previously optimized through SIGMASOFT® Virtual Molding can produce successful parts from the first run, without the need for additional trials.

In addition to the obvious economic advantages due to the cost reduction associated to reducing mold trials; machine occupation and scrap production during the setup process, by using virtual molding, the molder will gain more insight and understanding of the entire process. "Our customers have told us they can more confidently develop product quotations, as they now have a deeper understanding of how the part and mold will behave and what the real cycle and energy consumption will be", states Dr. Thornagel. "On the other side, they are more confident to become involved in innovation processes, because now they will know upfront whether a given concept will work or not".

As a further advantage, Virtual Molding development makes it easier for a company to communicate with their customers as they now have documentation to support their expertise.

An industrial example illustrates the advantages of SIGMASOFT® Virtual Molding. In this case, when considering all components within the mold, the results delivered a realistic outcome, compared to a conventional injection molding simulation approach.

A cylindrical area of a thermoplastic part needed to have a specific amount of interference with a mating part for a snap-fit. The molder used a conventional simulation analysis to predict the part warpage. In this analysis, the hot runner and the part were simulated but the melt surroundings (the mold temperature) were assumed to be constant. With this isothermal approach the warpage predicted was too low, and the parts had assembly problems.

The company asked SIGMA to analyze the problem in SIGMASOFT® Virtual Molding. In this case, the complete mold was considered in the simulation, with all its components, and the molding cycle was reproduced over several cycles in the machine. It was found that the hot runner manifold had a large influence over the mold temperature, and that this temperature substantially deviated from the one predicted by the molder.

The melt temperature was expected to be 300°C. However, due to the thermal effect of the hot runner and the shear heating experienced by the material in the runner channel, the temperature in the melt as it reached the cavity was actually 350°C. This increase in the mold temperature and the thermal history of the melt over several cycles generated a temperature delta of around 30°C with respect to the original simulation results.

Because of the larger temperature of the melt present in the cavity, the thermally induced stresses were also higher, producing an increase of about 40% in the part deformation predicted under isothermal boundary conditions.

This is a typical example of the value behind the more comprehensive approach taken by the SIGMASOFT® team. This powerful Virtual Molding tool, with its comprehensive approach, can be used to find the root causes of real problems and provide an explanation for the related phenomena. Injection molding is a complex process, only when the big picture is considered will reliable results be achieved.

Figure 1 – Left: an isothermal analysis predicted lower molding temperatures in the part, and therefore lower thermally induced stresses. Right: SIGMASOFT® Virtual Molding analysis captures the real behavior of the melt, influenced by non-isothermal surroundings.

Figure 2 – SIGMASOFT® Virtual Molding analysis improves the predictability of shrinkage and warpage results. As it reproduces the real mold temperature over several cycles, it calculates the temperature behavior of the part surroundings and better predicts thermally induced stresses.

For further information on this story, please contact:

Matt Proske
SIGMA Plastic Services, Inc.
11 N. Martingale Road, Suite 425
Schaumburg, IL 60173
Phone 847-558-5600


Marketing Contact:
Wendy Pilcher
SIGMA Plastic Services, Inc.

7701 Las Colinas Ridge, Ste. 800, Irving, TX 75063