Aluminum Alloys

Not All Aluminum Alloys Are Created Equal
Aluminum alloys are differentiated by the manner in which they are produced: when manufactured, they are either a non-heat treated cast material or a heat-treated wrought material.

On one side of the spectrum, non-heat treated material is ideal for low-strength mold applications. Cast products typically display lower strength and provide excellent dimensional stability. Also, cast alloys provide excellent machinability and minimal residual stress. Though not engineered for high strength, cast material is suitable for some low-pressure injection molds and straight injection molds requiring less than a few thousand shots.

On the other side of the spectrum is the high strength, heat-treated wrought Aluminum Alloys. These alloys are technologically advanced alloys with enhancements in heat treating, aging practice or a combination of both. These products exhibit high strength (relative to cast product), excellent machining and polishing characteristics, as well as dimensional through-thickness consistency. These aluminum alloys are suitable to mold nearly 75 percent of all unfilled resins—including PP, HDPE, Nylon, PET, ABS and PE. Molds manufactured using high strength aluminum have been known to successfully run millions of shots. Obviously, proper tool design, setup, running and maintenance of the mold must be adhered to.
Industrial pump cover

This is a picture of the industrial pump cover with molded in threads and brass inserts.

In the middle of the spectrum are what can be referred to as common alloys—such as 2024, 6013, 6061, 7050 and 7075. Common alloys are manufactured at facilities in accordance with the Aluminum Association procedures for manufacturing these materials.

Selecting a High Strength Aluminum Alloy for Production Injection Molds
When designing a production alumi-num mold, several factors need to be taken into consideration for a successful mold.

   1. Is the resin conducive for aluminum?
   2. What is the geometry of the part to be molded?
   3. What is the quantity?
   4. What is the desired cycle time?
   5. How long does the mold need to last?

It is interesting that these factors are very much the same ones designers look at when considering P20 for molds. High-strength aluminum is required for a productionized aluminum mold. As an example, Aluminum Injection Mold Company (Rochester, NY) prefers a high strength, heat-treated wrought aluminum alloy for its production molds using the shop’s “AIM FRAME” because of its high quality, consistent through-thickness hardness as well as its strength and durability. Aluminum Injection Mold developed the “AIM FRAME”—which incorporates steel support pillars and an all steel U-box with guided ejection—to create a mold that has all of the thermal benefits of aluminum matched with the durability of a steel mold. The use of these steel support pillars avoids any possibility of overclamping the mold and crushing the part line.

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