Profile die extrusion is a process widely used to manufacture products with fairly complicated cross-sectional shapes for the packaging, construction (insulation, structural foams), automotive, and food industries, to mention just a few. These products often have a complex foamed structure and exhibit unique properties of stiffness or strength for a given weight of material, flexibility, or even taste!

Since material cost can be up to 70% of the product cost, foaming is an important way to reduce weight, material consumption, product cost, and waste. Die design, however, is still more an art than a science. In the foamed product industry, the process of setting up an extrusion line remains mostly empirical and follows a long and costly trial-and-error procedure. Numerical modeling using POLYFLOW can now improve this design process.

Replacing the "Trial and Error" Design Method

POLYFLOW has acquired a world-wide leadership position in the numerical simulation of extrusion and in the design of extrusion dies. Techniques to calculate the flow, temperature, and pressure distribution in a die, as well as the required die shape, are advanced and used widely. Today, new models in POLYFLOW allow this die design methodology to be applied to foamed as well as dense product shapes. Prediction of die shape for foamed products reduces the number of trial dies that must be examined during the design process, reducing the time to market for new products.

Simulating foamed products in extrusion necessitates the tracking of additional variables such as the foam density and the kinetics of the physical foaming, in addition to the free surface position and the velocity and pressure. Chemical/physical reactions coupled with the flow calculation predict variations in density and extrusion shape produced by chemical or physical blowing agents. The new foaming model yields very significant improvements in the predicted die shapes for foamed products.

The new foaming model extends POLYFLOW's die design capability to foamed products. Here, the extrusion of a part with a rectangular cross section of 10-to-1 aspect ratio is modeled. The solution, which shows a more pronounced swelling of the thinner dimension and larger bubble sizes near the external surface, compares favorably with experimental results.

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