Aluminum is one of the most valuable metals in industry. It’s lightweight which means that structures and assemblies that are made from aluminum have less of an energy penalty for movement than equivalents made of materials like steel. This lower energy penalty does offer a substantial operational cost reduction. It also reduces wear and tear on equipment as less weight translates to less strain. It is also very strong for being so light weight although not quite as strong as denser material on a one to one basis.

In spite of all these advantages, aluminum—and its various alloys—is not a metal that is intuitively understood. It can be harder to differentiate between cast aluminum tooling plate vs. 6061 or other more common aluminum alloys.

Cast Aluminum Tooling Plate vs. Aluminum Castings

In order to understand the difference between a jig plate or cast aluminum tooling plate vs. 6061 rolled plate, it’s important to understand how metals are made. A cast metal is one that has been heated until it is fully molten and then poured into a mold where it’s allowed to solidify. The reason that cast iron is so easily differentiated from steel is that the casting process leaves a rough surface both from the mold the molten iron was poured into and from the chemical reactions the molten metal had with the atmosphere as it cooled.

There is a type of cast aluminum that is the result of a similar process. It too has a rough, extremely porous surface and a very porous structure all the way through the material. This is not the same material as cast aluminum tooling plate. This type of cast aluminum product is usually called a casting. Aluminum castings are rare in industry and manufacturing because structurally they tend to not have a great deal of strength and as a result have a very narrow use profile. For example, aluminum vacuum forming molds where the porous nature of the material helps with pulling air from the mold and the thermal conductivity of the aluminum helps transfer heat away swiftly. Other than that, aluminum castings are chiefly used in cookware and lightweight decorative elements.

Cast aluminum plate vs. rolled aluminum, on the other hand, is a precision engineered product. It is carefully formulated, cast ground within approximate tolerances, heat treated to relieve internal stresses, and then fine ground to its final dimensions. It is an expensive product beyond that of the already somewhat pricey 6061 aluminum stock. In spite of that, it is so useful in industry that it is much more common in manufacturing than much less expensive aluminum castings.

Cast Aluminum Tooling Plate vs. 6061 Plate

There is a reason that aluminum tooling plates go through a relatively complicated process, and it has to do with how 6061 aluminum, specifically plate aluminum 6061 is made. The initial forming process presses aluminum 6061 through sets of rollers that flatten the 6061 into the needed dimensions. This process creates internal tensile stresses in the plates. Material towards the interior core of the plate tends to pull inwards towards the center while the exterior tends to pull outward. While 6061 T6 does undergo heat treatment this is a long term, high temperature baking of the metal that is designed to improve the structural strength of the metal. The internal stresses are retained through the process.

In the intact plate these internal stresses are balanced against each other. However, when the plate is machined parts of the plate are removed. This alters the balance of forces within the plate and can cause it to curve or distort as material is removed. This is not typical when machining 6061 aluminum, and it tends to be minor. However, it does happen often enough and is significant enough that it can keep the final piece from meeting high specifications.

The other key difference to consider when it comes to aluminum tooling plate vs. 6061 is that 6061 is subject to thermal distortion. In truth, almost all aluminum alloys are extremely prone to thermal distortion compared to other metals. Thermal distortion is the tendency of a metal to expand under heat and contract as it cools. Obviously this can be an issue in manufacturing where heat input through machining and welding is part of working with aluminum, and aluminum that is used as a mold material.

Cast aluminum tooling plates are a notable exception to this general rule of aluminum distorting under temperatures, and this stability combined with precision, and the ability to quickly dissipate heat has made aluminum tooling plates a very desirable material for molds. These advantages are the result of how cast aluminum alloys are formulated, and this formulation can cause some challenges regarding the workability of cast aluminum.

Disadvantages of Aluminum Tooling Plate

In all things the good comes with some drawbacks. Cast aluminum tooling plate is no different, or at least it has been in the past. MIC-6 has long been the aluminum tooling plate of choice. Essentially it has been the only choice. The formulation of the MIC-6 alloy contains a lot of zinc and silicon as alloying elements. These elements tend to give MIC-6 aluminum some undesirable properties including:

Poor Weldability	Although it isn’t impossible to weld the weldability of cast aluminum has tended to be poor. While silicon in MIC-6 helps molten metal flow more smoothly and is a benefit in the casting process it does tend to create brittleness in the heat affected zones. Creating welds that will hold tends to require a high level of expertise and this can pose a problem with working with and maintaining cast aluminum materials.
Poor Anodization Response	The zinc and silicon in the mix react poorly in the acid baths that are part of the anodization process. The silicon can dissolve, and the zinc can change colors. This means that anodized surfaces on MIC-6 tend to be of poor quality if they can be generated at all.
Surface Granularity	MIC-6 tends to have a rough grain structure at the surface compared to other aluminums. This tends to rule out its use in things like vacuum deposition chambers (VDCs) where otherwise its dimensional stability and machinability would make it ideal. Alternative aluminum tooling plate like Alimex do not share this same disadvantage.

Traditionally these issues have meant poor workability for aluminum tooling plate vs. 6061. However, MIC-6 alternatives have a different formulation, and don’t share the same issues. In many ways they offer the best of both aluminum tooling plate and 6061 being both dimensionally consistent, easily worked, and anodizing well. New formulations like Alca 5 have a surface grain structure that is suitable for use in vacuum deposition chambers offering new options for semiconductor manufacturing.

Industrial Metal Service is at the forefront of supplying aluminum to hardworking machinists and fabricators. This includes new aluminum tooling plate formulations like Alca 5 and ACP 5080. These aluminum tooling plates are available in standard sizes, and in custom cut to order sizes that are process ready.