Although the barrel cutter has much potential and has been available for at least 20 decades, its use is confined for the most part to specialty work, such as cutting the blades of a blisk or finishing the sides of a deep spiral groove. This is because CAM development has been lacking in this area. With so few software companies supporting it, most machine shops were unable to take advantage of the barrel cutter. And because barrel cutters were custom-grounded at every purchase, which in turn, leads to longer delivery times, it is not viable commercially.
But recent developments in CAM software have enabled and eased new applications for barrel cutters to enter the market. In response, some tool manufacturers are producing these tools and offering them as catalog items.
To benefit from these developments, machine shops must first have a basic knowledge of barrel cutters and then calculate if money can be saved by adopting this technology.
A barrel cutter is a solid carbide milling tool, and its overall dimensions are similar to the commonly available ballnose cutters (or ball end mills.) So, a cutting tool manufacturer could ground one from their existing stock of ballnose cutters. When seen from the side, it is visibly different as it has a large swept radius over its flute length. So the cutting edge resembles that of a very large ballnose cutter at the workpiece-cutter interaction zone.
Since it costs more to make a barrel cutter than a standard ballnose cutter, you may wonder how the increased cost can improve your process. A barrel cutter reduces machining time and has a longer tool life. This lowers the total cost of production.
But it is more tricky to program CAM software to use barrel cutters. Unlike a ballnose cutter, the barrel cutter does not have a hemispherical shape at the tip of its flutes. So the contact point of the cutting edge and the machined surface is along the arc segment. Besides, the programmer must find a workaround to create a toolpath by deriving the center from the barrel surface. This calculation is more complex than for a ballnose cutter. If the CAM software does not handle it, the computation would be a tiring exercise in geometry.
Roughing to Finishing
A common problem with conventional pocket milling is the increased load on the tool when machining corners. Recent developments in CAM software have introduced advanced roughing techniques to maximize the material removal rate. These methods use complex algorithms to eliminate sharp directional changes in the toolpath, reducing roughing times by 40 to 75 percent. So the time required to finish the surface now constitute a larger portion of the machine cycle time, and focusing on finishing operations is now more crucial than ever.
Take a plastic mold for example. Ballnose cutters are often used to contour gentle slopes. What about the parting surfaces where the molds mate? These demand high precision, and are usually finished with ballnose cutters. Using barrel cutters on these surfaces will reduce machining times dramatically.
It was often not possible to machine narrow planar faces with a barrel cutter because toolholders or spindles often gets in the way. Extra-long cutters were traditionally used to handle these long, deep, open slots. But developments in programming software have resolved this problem and allowed the use of barrel cutters, reducing machining times on these faces by as much as 90 percent.
The conical barrel cutter is designed with a tapering tip ranging from 20 to 40 degrees. This facilitates a shorter shank, and consequently, greater rigidity. Because its effective cutting surface is not perpendicular to the cutter axis, the cutter has to be tilted by 10 or 20 degrees when machining the side wall, and by 70 degrees when machining the bottom. This inclination keeps the tool, the holder, and the spindle away from the surface being machined. The extremely large stepover distances of a barrel cutter can now be used in areas never before possible.
The advantages of conical barrel cutters:
They are less expensive and more rigid.
They make single-point contact. Deflection and double-cutting is likely to happen when milling with the side of a cylindrical end mill. It is also easier to blend between successive passes with a conical barrel cutter.
They are less affected by thermal expansion or spindle growth or both. Since the cutter lengths of face mills deviates more, conical barrel cutters are more suited for machining mold lock surfaces.
Barrel cutters, however, is unable to reach certain areas such as corners and adjacent surfaces. Under these circumstances, the ballnose at the tip of a barrel cutter ought to be used for the remaining material. A simultaneous five-axis machine makes it possible to provide a complete solution .
To be practical for moldmakers, CAM software ought to create toolpaths for barrel cutters with minimum user interaction. For example, the operator need to enter tool descriptions only. Other parameters including center points of the tip and the corner radii should be calculated automatically. Using a calculator to obtain the required parameters may not be popular.
In conclusion, CAM software innovation will certainly make the use of barrel cutters realistic, and fostering its adoption across all industries.
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