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Aluminum tooling has come a long way. With different aluminum alloys, it is now possible to create production tools using aluminum. In this discussion, we will show how moldfilling analysis can provide data revealing the advantages of using aluminum for injection molding.

Chris Czeczuga

February 8, 2010

4 Min Read
Moldfilling analysis can show the benefits of aluminum tooling

Aluminum tooling has come a long way. With different aluminum alloys, it is now possible to create production tools using aluminum. In this discussion, we will show how moldfilling analysis can provide data revealing the advantages of using aluminum for injection molding.

To begin, we must understand the benefits of using aluminum, as compared to that of steel, for injection molds. The benefit is mainly from aluminum having a higher thermal conductivity, which translates into a faster cycle time. Because aluminum can extract heat from the cavity faster, the time to cool the part decreases and the cycle time is reduced. Let's look at the properties of the two materials in Table 1.

Table 1: Aluminum v. steel properties
Material          Density (lb/in3)      Thermal           Elastic          Poissons ratio
                                               conductivity     modulus (psi)     (v) 0-0.5
                                               (Btu/ft*h*F)
Aluminum (A1)    0.101156         109.784         10,290,000          0.33
P-20 Steel           0.281791         16.7565         29,733,200          0.29


We can see that aluminum has a higher conductivity than steel. As a matter of fact, aluminum is 6.55 times more conductive than steel. This will translate into much more effective cooling and much shorter cycle times.

We have utilized Autodesk Moldflow Insight to analyze the cooling of two molds. One mold is P-20 steel and the other is aluminum A1. The process conditions for both analyses are identical. The analysis provides the data that supports the benefits of aluminum tooling.

Part geometry: Five-sided box with 0.118-inch nominal wall.
• Hot drop on top center of part.

Bozilla-table2.jpg

Table 2


Bozilla1.jpg

Figure 1


Bozilla2.jpg

Figure 2


Bozilla3.jpg

Figure 3


Bozilla4.jpg

Figure 4


Bozilla5.jpg

Figure 5


• Cooling lines with 115°F inlet temperatures targeting a 140°F average mold temperature.
• Cooling lines are 0.500 inch in diameter along with four baffles in the core circuits.
• Mold block size is 10 by 15 by 15 inches.

Figure 1 shows the tool design utilized in the analysis. After running a cooling analysis on this tool comparing P-20 and aluminum, we will now discuss the differences each mold material has on the process. Following are just a few of many results that show the benefits of using flow analysis to support the use of aluminum tooling.

Comparison: Mold core temperature
If we look at the core temperature of the mold when using P-20 (Figure 2), we see that there is a tremendous amount of heat trapped in the corners. The overall temperature distribution on the core is between 134.3°F and 237.4°F. A large temperature distribution represents non-uniform cooling, which lends itself to poor part quality.

Looking at the core temperature of the mold when using aluminum (Figure 3), we see that the temperature range is much narrower—121.5°F to 147.5°F. The difference in maximum core temperature between the P-20 steel and the aluminum is 90 deg F. The overall temperature of the core is very uniform, and uniform temperatures translate into uniform properties in the part.

Comparison: Time for part to reach ejection temperature
This plot is probably the most compelling as it can be related directly to cycle time savings. The plot for the P-20 steel (Figure 4) reaches 29.5 seconds in a large portion of the part (corners of the part). Unfortunately, the odds of having ejector pins in these regions are very high so it would not be likely to cut back on the cycle time due to part deformation from the ejector pins.

The plot for the aluminum A1 tool (Figure 5) reaches a maximum of 20.1 seconds in those same regions, signifying a 9.4-second cycle time savings. The time to eject is very uniform at about 20.1 seconds, so our ejector pins should not deform the part if the cycle is not reduced beyond 21 seconds.

A 9.4-second cycle time savings under “ideal” conditions is tremendous. If we were to compare the calculated monthly (30-day) savings on these two tools running 24/7, we'd be looking at the results in Table 2. (Note: Both tools will use an additional 7 seconds for mold open and close time.) The table makes it quite clear how an aluminum tool can translate into increased revenue.
The decision to use aluminum for injection molding is becoming more and more popular. It is best to become as knowledgeable as possible about aluminum before making that decision. One of the best ways to understand the potential benefits is to have an analysis performed on the proposed mold. The analysis can provide in-depth data as well as hard numbers that can directly translate into cost savings.

This article originally appeared in the Feb. 4, 2010 “FEA Focus” newsletter published by plastics molding consultant Bozilla Corp. and is reproduced with permission.

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