November 2, 2012
Interest in incorporating more aluminum parts into final product designs is causing fabricating operations to reconsider how they approach sawing aluminum. Traditionally, the conversation centered around circular saw technology when it came to cutting aluminum, but now new band saw developments have helped to expand the discussion.
With the continued focus on using lighter materials wherever possible, particularly in the transportation industry, metal fabricators are interested in learning about the best ways to process aluminum materials. Of course, this affects every shop floor activity, including sawing.
This interest in lighter-weight material appears to be a long-term trend. In ThomasNet.com’s annual Industry Market Barometer®, a survey of more than 4,000 manufacturing professionals in North America, 20 percent of respondents listed aerospace and defense as the top growth markets in 2012, which trailed only fabricated metal products (21 percent). This comes even as manufacturers stare at dramatically reduced defense budgets all around the globe, particularly in the U.S. In the same survey, 18 percent considered the automotive market to be the top growth market. What do the aerospace and automotive markets have in common? Companies are interested in reducing the weight of their products because less fuel is needed to power these lighter-weight aircraft and vehicles.
A recent report from the Aluminum Association provides an excellent look at how hot this trend is. The association reported that demand for aluminum semifabricated mill products in the U.S. and Canada, which includes domestic producer shipments and imports, was 1.3 million lbs. in July, up 8.1 percent when compared to a year ago. Aluminum sheet and plate demand jumped to 779 million lbs. in July, up 6.1 percent from the same time frame in 2011. Meanwhile, this growth is taking place as export markets in Europe and Asia struggle to regain their economic footing.
Because great opportunities await those fabricators able to process aluminum efficiently, they need to be aware of cutting technologies that can help them do the job. If the focus is on sawing (see Figure 1), the question is, Do band saws or circular cold saws cut aluminum better? Technological advancements have been made in aluminum sawing with both types of saws, and the answer is often a very firm “It depends.”
One of the more traditional methods of sawing large-diameter aluminum has been with very large circular saw blades. This sawing method caught on because of the speed at which the aluminum could be cut compared to band sawing. The circular saw enters the material at a high speed and maintains that same speed throughout the entire cut, even upon exiting the material. Saw manufacturers call it a constant speed and feed rate.
Traditionally, band saws struggled with this because the blade could be damaged quite easily if it entered the metal at a high speed. The “gumminess” of a metal like aluminum would wreck a band saw blade if it entered the material fast. New technological advancements in band saws—which will be discussed later—have changed this somewhat.
Large circular saws require a large upfront capital investment. That should come as no surprise because the equipment’s size plays an important role in its ability to cut aluminum so quickly. For example, a circular saw cutting a 20-in.-diameter aluminum billet would require a blade of at least 40 in. diameter, and more realistically about 50 in. Of course, the equipment has to be large and sturdy enough to turn that large blade at a consistent and high RPM.
When it comes down to issues such as the finish of the final cut, the circular saw stands out as a suitable choice. By generating a very good finish, the fabricator may be in a position to eliminate a secondary finishing operation, which can result in dramatic labor savings. This is especially evident in fast cutting of single-piece, small-diameter material (see Figure 2). For example, in aluminum extrusion cutting, production volumes can be as high as 5,000 parts per shift, and the end finish is expected to be very clean.
The fact is that circular saws cut aluminum so fast and effectively that a fabricator really needs to develop a productive means for moving material in and out of the saw. A material handling method is either an incline or flat-loading magazine on the input side, coupled with a high-speed output conveyor for sorting of the finished parts. This maximizes the aluminum cutting power of a circular saw.
However, it should be pointed out that while a circular saw delivers a much cleaner cut, the blade will remove a nice chunk of the aluminum because of the blade size. For instance, a 40-in.-diameter blade is about 0.33 in. wide.
Band saws were never really considered to be a wise choice for aluminum cutting, but that has changed recently. With the advancements in band saw technology, large aluminum billet now can be cut almost as quickly as with large circular saws.
The best news for a fabricator is that a band saw for this type of aluminum cutting application requires a significantly smaller capital investment than a circular saw. Simply put, it’s a smaller piece of equipment because its blades are smaller in comparison to circular saw blades and do not require a very large operating footprint to be effective.
To achieve efficient aluminum cutting, band saw technology had to overcome the challenge of turning a blade at a much higher speed than is needed for traditional steel sawing—in fact, as much as 10 times the surface feet per minute (SFM) as steel requires. Band saws now feature ramp feed and speed, which means the blade enters the cut slowly, ramps up, and then exits the cut slowly. Entry and exit are two areas where the possibility of blade damage is greatest, but this controlled process eliminates that. In addition, blades have advanced so that they can revolve that fast around the wheels and be flexible enough not to break (see Figure 3).
Further, these newer band saws provide good control of the blade. The equipment’s ball-screw, servo-drive downfeed (see Figure 4) helps to ensure that the beam is pushed firmly through the material at a feed rate up to 22 inches per minute. To generate the high blade speed (up to 4,000 SFM) requires the appropriate combination of horsepower and torque within the gearbox and motor, so that even at high speeds the equipment is not overworked. Current band saw technology hits all of these very important benchmarks.
If a fabricator is cutting aluminum parts and other materials at lower volumes, say, 1,000 parts or fewer per shift, then a band saw can be a solid performer. If the aluminum material is greater than 7 in. diameter, today’s band saws are probably a good choice for the job. Also, if the squareness of the cut has a high tolerance, the band saw will be able to deliver.
Fabricators also should be aware that a band saw blade is thinner than a circular saw blade, typically about 0.042 in. thick. This results in a significantly smaller kerf removal when compared to the circular saw blade, generating material cost savings over time.
How far has band saw cutting of aluminum come? Band saws are now cutting 11-in.-diameter 6061 aluminum bar in 14 seconds. That is 94 sq. in. of material, which is equivalent to a removal rate of 400 sq. IPM. This means that band saws are now able to cut at 3,500 SFM, which compares favorably to previous generations of band saws that could cut only up to 500 SFM.
The best saw for aluminum sawing depends on the application. Circular saws generally are suitable for cutting aluminum between 0.5 and 6 in. diameter, for high-volume jobs (up to 5,000 parts per shift), and for the best possible finish on the cut piece. Band saws generally make sense for aluminum stock of 6 in. diameter and larger and for shops that are interested in high-speed cutting of aluminum but also frequently cut other materials.
Perhaps the most important point is that band saws are now capable of providing a cost-effective alternative for aluminum sawing, which wasn’t the case several years ago. With the growing reliance on aluminum as part of future product designs, fabricators now have one more tool in the toolbox to tackle this challenging sawing job.
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