Advantages of Aluminum Extrusions
Representing about 20% of total aluminum consumption in the United States, extruded aluminum enables the end-product designer an element of flexibility over other metalforming methods. Specifically, a variety of standard and custom enclosures are made from one-piece extrusions. Modular keypad enclosures, rack frames and circuit board front panels are also made by this process. The advantages over plastic or multipiece sheet metal are ruggedness, fewer assembly steps, lower cost, excellent heat dissipation and RFI/EMI shielding.
Presses rated to 2400 tons with a maximum 8" are used to produce two major types of aluminum extrusions. They are solid shapes (simple channels) or complex configurations (gears). The largest consumer of these extrusions is the building and construction segment of industry, but other markets such as machinery, electrical components, appliances and transportation units are also served.
The properties of aluminum in these applications yield attractive appearance, close tolerances, easy fabrication and recycling. The ability to meet machining-type tolerances is limited to small shapes, but can they be achieved with secondary milling operations.
In addition, milling, drilling, tapping, countersinking and punching are applied to increase the use of extruded aluminum. Cutting tolerances of +0.005" are reportedly common.
A design rule of thumb is to attempt to keep wall thickness similar across the profile. Although not mandatory, a ratio up to 10:1 is possible. Running characteristics of aluminum will improve with an even flow. Another guideline to consider is the depth of channel. It should not be more than three times the width.
The limiting size of the profile is determined by the extruders press opening or "circle" size. Beyond 8", dies are expensive and wall thickness increases geometrically. Generally, an inch in width then can run close to 0.005". Estimate about 0.010" additional tolerance/inch as the shape gets larger. Extruders can improve on tolerances, but as profiles widen dimensional challenges increase.
The alloy used most for extrusion is 6063-T5. Alloys 6061-T6 and 6005-T5 have twice the strength characteristics, but carry a slight cost premium and do not finish well if anodized.
To improve the attractive qualities of extrusions they are anodized or painted (powder or wet). An example of cost efficiency from this process are collections (families) of standard dies and products used to manufacture electronic enclosures and rack systems, thereby eliminating die expense. Focus should be on reduced setups and small lots that allow shipment from stock. "Pull systems" that support ongoing customer requirements enable automatic restocking as needed. Note that process flexibility and special relationships with vendors allow an aluminum extrusion supplier to be responsive to prototype and production start-up situations.
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