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 the table below.

 Table 1: Aluminum v. Steel properties

Based on this table, 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: 5 sided box with 0.118" nominal wall

• Hot drop on top center of part
• Cooling lines with 115F inlet temperatures targeting a 140F average mold temperature.
• Cooling lines are 0.500" in diameter along with four baffles in the core circuits.
• Mold block size is 10" x 15" x 15"

 Below is an image of 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. Below are just a few of many results which can support the benefits of using flow analysis to support the use of aluminum tooling.

Mold Core Temperature Comparison

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

Time For Part To Reach Ejection Temperature Comparison

The 'Time for the part to reach ejection temperature' plot is probably the most compelling plot as it can be related directly to cycle time savings.

The TIME TO REACH EJECTION temperature plot for the P-20 steel 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 is very high so it would not be likely to cut back on the cycle time due to part deformation from the ejector pins.

The TIME TO REACH EJECTION temperature plot for the aluminum A1 tool 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. 

Note: Both tools will use an additional 7 seconds for mold open and close time

The table above makes it quite clear how an aluminum tool can translate into increased revenue.

In summary, 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.