Advanced workpiece manufacturing technologies—such as metal injection moulding, 3D printing, investment casting and close-tolerance forging—innovative machine tools, and a quantum leap in digitizing of manufacturing will increase the needs for finishing complex surfaces with minimum machining stock. Article by Andrei Petrilin, ISCAR.
Endmills featuring a cutting edge that is actually the segment of a large-diameter arc were introduced approximately 25 years ago. As the cutting-edge shape of these endmills is reminiscent of a barrel profile, terms such as ‘barrel milling cutters’, ‘barrel endmills’ or, in shop talk, often simply ‘barrels’ soon became common when referring to these types of endmills.
At first, the use of these barrel-shape mills was limited more or less to a few specific applications, such as machining 3D surfaces of complex dies and turbomachinery components. However, advances in 5-axis machining and in CAM systems have significantly expanded the boundaries of barrel endmill applications.
At the same time, the design principle of a cutting edge as the segment of a large-diameter arc has been realized successfully in other types of milling cutter—the tools for high feed milling (HFM), also referred to as ‘fast feed’ (FF) milling. The concept provides a toroidal cutting geometry that ensures productive rough machining at extremely high feed rates due to a chip thinning effect. Unlike high feed milling tools, barrel endmills are intended not for roughing but for finish and semi-finish machining of 3D surfaces with low stock removal.
Traditionally, ball-nose and toroidal cutters perform these machining operations. However, the large-diameter arc of the endmill cutting edge results in a substantial reduction of the cusp height generated between passes machined by a ball-nose or toroidal cutter. Another advantage of this type of cutting edge versus ball-nose and toroidal cutters is a significant increase in the distance between passes (a stepover or a stepdown, depending on the direction of a cutter displacement after every pass)—at least five times more without degradation of the surface finish parameters! (Figure 1) This means that the number of passes and, subsequently, machining time can be noticeably reduced. Increasing the distance between passes also improves tool life and, therefore, diminishes tool cost per part.
The classical barrel shape in endmills has undergone some changes to make these cutters more versatile. Combining a ball-nose tip with peripheral large-arc cutting edges creates a multi-purpose ‘cutting oval,’ which facilitates the use of a barrel endmill as a ball-nose milling tool.
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