Machinability of Aluminum Bar Stock

“Machinability,” simply stated, refers to how easily a metal responds to bending, cutting, drilling, milling and punching, among other fabrication processes. Machinable construction materials are characterized as being easily cut and yielding an acceptable finish without wearing out the tool too quickly. Aluminum, although soft when compared to other substrates, is considered relatively machinable, with three main factors influencing the machining results.

Factor #1—The Machining Process
It may appear simplistic to indicate that the type of equipment and cutting tools affect the machinability of aluminum bar stock, but they do. Well maintained, high quality equipment and sharp cutting edges are of utmost importance. Additionally, it is not advisable to utilize ceramic or synthetic cutting materials with aluminum. Instead, tool or high speed steel, diamond and cemented carbides are recommended.

A knowledgeable and experienced technician is also essential, as feed rates, rake angles, cutting speeds and pressures, and application of lubricants—among other critical process details—will influence the observed machinability.

Factor #2—The Alloy’s Characteristics
The second factor is directly related to the chipping characteristics of the aluminum alloy being machined. Generally, the harder alloys produce the shortest, tightest chips during machining. Small chips are preferable to long and/or continuous chips that may interfere with the tooling elements and damage the end product. Since aluminum is a soft metal, improving its strength and machinability is accomplished by alloying with other metals like copper and magnesium.

Alloys are engineered with specific applications in mind, and different alloys lend themselves more readily to different machining processes. Selecting a high quality alloy whose characteristics most closely align with the desired product is key to maximizing machinability.

Factor #3—The Material’s Processing
The third factor in determining machinability involves the processing of the aluminum bar as it was being extruded. Since the development of the indirect press method, extruded products like aluminum bar materials are more consistent in size and metallurgical properties than those produced using direct presses. The lower heat of friction achieved with indirect presses, coupled with less variance in temperature and pressure, optimizes consistency in grain structure, which positively impacts machinability.

For a specialist who can provide the highest quality material and specialized cutting, consult Howard Precision Metals, Inc. at The professionals at HPM make it their business to know your business.

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