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Aluminum vs. steel: Study tackles the two tooling materialsAluminum vs. steel: Study tackles the two tooling materials

A study comparing the cooling properties, cooling time, and warpage of parts produced with aluminum and P20 steel inserts found that on average there was a 10 °C disparity in mold temperature between the metals, which resulted in an average of 1mm less warpage in parts ran in the aluminum inserts when compared to steel.

PlasticsToday Staff

June 10, 2011

2 Min Read
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A study comparing the cooling properties, cooling time, and warpage of parts produced with aluminum and P20 steel inserts found that on average there was a 10 °C disparity in mold temperature between the metals, which resulted in an average of 1mm less warpage in parts ran in the aluminum inserts when compared to steel. Conducted by Penn State Erie Behrend College students Laird Raybuck and Chad Shumaker and presented at the Society of Plastics Engineers (SPE) ANTEC 2011, the study utilized polyethylene (PE), polyamide (PA), acrylonitrile butadiene styrene (ABS), and polycarbonate (PC), with consistent cooling water temperatures applied when switching between the inserts.

The researchers found that aluminum, which is approximately four times more thermally conductive than steel, did cool parts more quickly than steel. However, although aluminum tooling will decrease cooling time due to its higher thermal conductivity, the researchers posited that it can ultimately cost more over time due to wear and having to replace the mold. "Aluminum tooling will cost less but over time could prove more costly when examining mold expenses," the study stated, noting an (OFAT), One Factor At a Time, type of experiment was utilized.

Raybuck and Shumaker said that the increased cooling rate possible with aluminum inhibits crystal growth and therefore decreases the density and the overall warpage of a semi-crystalline material. A less dense amorphous material helps the polymer chain to orient under high pressures like that which occurs during fill velocity.

The authors concluded that the three processing variables that appear to cause warpage by themselves are cooling time, cooling temperature, and cooling distribution in the mold.

In the warpage study, the parts made in the aluminum insert warped between 0.2 to 2 mm less than that of the parts made in the steel thanks to the greater thermal conductivity of the aluminum. This conductivity allowed more heat to be removed from the part and cool it more quickly. Because of that, part warpage decreases since the polymer orientation is essentially frozen into place and not allowed to relax.

The researchers found that the aluminum inserts had between a 5 to 15 °C decrease in temperature when compared to steel, which ultimately not only lowered warpage but resulted in a faster cooling time. It took the steel inserts 15 seconds longer to reach the same water temperature of the aluminum at the same cooling water temperature.

In the future, Raybuck and Shumaker would like to measure the aluminum vs. steel tooling wear in a production type run.

ANTEC 2011 - Penn State Behrend College View more presentations from rsmierciak

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