Difficult Materials Challenge Micro-Endmill Users

Difficult Materials Challenge Micro-Endmill Users
June 1, 2011

By Bill Kennedy, Contributing Editor for Micro Manufacturing Magazine

Toolmakers mix, match and refine features to maximize workpiece surface quality. For example, Harvey Tool Co. LLC, Rowley, Mass., introduced multiflute, high-helix finishing endmills. The tools combine flute helix angles that vary from 39° to 42°, a coating and edge prep, and as many flutes as the tool diameter allows. Tools with diameters less than 0.031" have four flutes, tools from 0.031" to 0.047" in diameter have six flutes, and diameters of 0.062" and larger have seven flutes.

The finishing endmills are designed to be preceded in an operation by a mill that hogs out main contours of a part, leaving 0.002" or less for a finishing pass.

In finishing operations, Harvey Tool recommends a full axial DOC, but a light radial DOC. Compared to hogging, which may engage half of the tool’s circumference, finishing may engage 20 percent or less of the tool.

According to Jeff Davis, vice president of engineering for Harvey, maximizing the number of flutes on a tool allows the flutes to share the burden of cutting tough, abrasive materials. “Even in an ideal scenario, the life of a 4-flute tool is going to be approximately half what you might see with a 7-flute tool,” he said.

Increasing the number of flutes increases the tool’s core diameter and reduces the size of the chip gullets between the flutes. Because it’s more rigid, a larger core diameter enhances tool performance at higher feed rates. In a roughing tool, Davis noted that the smaller gullets may restrict chip flow, but pairing the light DOC characteristic of finishing endmills with sufficient coolant flow should permit chips to exit easily.

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