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The Differences Between Extruded Aluminum Bar and Cold Finished Aluminum Bar

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The Differences Between Extruded Aluminum Bar and Cold Finished Aluminum Bar

Although they are often produced as the same grade of material, there are many differences between extruded aluminum bar and cold finished aluminum bar.  Both share the major benefits of aluminum: it’s corrosion resistance, thermal conductivity and high strength to weight ratio; but each product has its own set of value and benefits.  It’s important for manufacturers to understand these differences and know what is required of a particular application.

One of the best ways to ensure that you have the right metal for your next job is to work with an experienced material supplier. Even for experts, it’s hard to stay on top of the latest advancements, so it’s important to have a resource to turn to when there is a question about how an alloy will respond in a specific application.

Today’s post will examine extruded and cold finished aluminum bar and focus on pertinent information when considering these products.

What is extruded aluminum?

An extrusion, whether aluminum or otherwise, is when material is transformed into a cross-sectional bar by forcing it through a die.  While there are several steps to the process, it really is quite a simple endeavor.  First, a manufacturer or designer must create a die to produce the final outer dimension of the extruded bar.

The finished die is placed into an extrusion press and an aluminum billet of the desired alloy is heated to the required temperature so that the aluminum becomes malleable.  The aluminum is then forced by the press through the die, resulting in a consistently shaped lineal length of aluminum that comes out of the other side.

The extruded piece is then cooled, stress relieved and cut to the desired length.  At this point, the aluminum can be heat treated and undergo other post production operations.

Because the process takes place at a high temperature, as much as 75 percent of the melting point of aluminum, less pressure is required to force the metal through the die. This means it is faster than cold forming processes.

What is cold finished aluminum?

Whereas an extrusion is typically performed at a high temperature when the aluminum is easier to form, cold finishing takes place at room temperature.  When cold finishing occurs, it leads to extremely close outer diameter tolerances.  The most common form of cold finishing is known as drawing.

Drawing also uses a die to reduce material diameter in aluminum bar production.  The bar’s end has a smaller diameter and is placed through the draw die, then grippers are applied to pull the bar through.  While it is possible to perform drawing at elevated temperatures, it is normally done at room temperature.

The cold finishing depends upon the flow and stretch of the aluminum.  The material reduction process work hardens the material, altering it’s physical and mechanical properties.  This also improves the surface finish of the bar stock.

What are the differences between extruded and cold finished aluminum?

The primary advantage of standard aluminum extrusions is that it is much easier working with the aluminum at higher temperatures.  This equates to faster production speeds and why extruded bar is typically less expensive than cold finished product.  Faster production also makes for shorter lead times to market.

The reduction process involved in cold finished production produces tighter dimensional tolerances, a benefit when using the close-fitting collets in today’s high-speed precision CNC machining centers.  It also elevates the mechanical and physical properties of the material; this increases the machinability and produces smaller chips during machining that break away from the cutting tool’s work area faster.

There is a long list of benefits for aluminum bar that are shared by both products.

What applications use extruded and cold finished aluminum?

While extruded aluminum is extremely common in a wide range of applications, it is not suitable for everything.  Any requirement for elevated properties may turn toward cold finished product as raw material.  Aerospace and defense products requiring high strength often specify cold finished bar, as well as a host of automotive applications.

Some examples of alloys popular in cold finished applications include 2011, 2024, 6061 and 7075.

Alloys commonly used in aluminum extrusions include 1100, 3003, 6061, 6063 and 6101. The most common of these is most likely 6061, which is prized for its beneficial properties and adaptable nature.

To learn more about the differences between extruded and cold finished aluminum bar stock, contact one of the friendly and knowledgeable technical professionals at Clinton Aluminum today.

 

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