Elements for successful endmilling

When an endmill efficiently makes chips, everybody is happy: the end user, the parts buyer, and the cutting tool manufacturer and distributor. Achieving that by having the tool follow the correct toolpaths and run at productivity-boosting parameters, however, requires an endmill with optimized geometry, substrate and coating.

“It’s all about optimizing,” said Sherry DePerno, president and CEO of Advanced Tool Inc., Marcy, N.Y., which exclusively produces solid-carbide endmills. And once the pieces of the endmill puzzle are optimized for an application, she emphasized the need for consistency when making the tools. “Operators should be able to put a new tool in and get the same number of parts every time. Inconsistency is not acceptable”

This 2-flute ballnose endmill from Advanced Tool is made with the proper web thickness and gash, which refers to the center of the endmill. A slight “S” curve to the gash, known as a helical gash, runs from the top to the bottom. A helical gash on a ball endmill is an advanced geometry design, enabling less of the cutting edge to contact the part at one time and reducing pressure to the cutting edge.

Gary Schmidt, application engineer for M.A. Ford Manufacturing Co. Inc., Davenport, Iowa, agreed it’s essential to examine all aspects of a customer’s application when providing an ideal solid-carbide endmill rather than merely an acceptable one. “By envisioning the end result, you can apply the right tool.”

One key aspect is the workpiece material. Schmidt recalled an aerospace company that struggled to machine an uncommon, difficult-to-cut material. M.A. Ford did a side-by-side comparison of the customer’s material with a similar material that was able to be effectively cut with a known tool geometry. “We ended up recommending a standard high-performance endmill with a slight modification,” he said. “Side-by-side comparison of work materials is a powerful tool.”

When developing a solution, Advanced Tool incorporates its trademarked Wear Analysis process, which includes microscopic inspection to examine how an endmill is wearing and finite element analysis to help determine which avenues to follow. Based on the analysis, the toolmaker will determine whether to target the substrate, geometry or coating first. “We try to only change one or two elements at a time and build upon that,” DePerno said. “Then we put that tool out in the field, do another Wear Analysis and ask ‘Are we getting further or closer to where we’re trying to be?’ “

For example, when poor tool life occurs, Advanced Tool looks at geometry as a possible culprit, DePerno noted. The endmill may require an adjustment to the core thickness, clearance angles, rake angle or helix angle to improve performance. Poor tool manufacturing can also cause issues. A web that is too thick, for instance, creates a dead area on top of the tool that requires more pressure for it to cut, causing premature wear.

However, end users may not understand a tool’s nuances, which can lead to inefficient cutting and, ultimately, poor tool life. “They want to put an endmill in a holder and cut,” DePerno said. “At the end of the day, it’s all about results.”

The web shown at the center of this “brand X” 2-flute ballnose endmill is paper thin. It is far too thin for the tool to perform properly, because the section is too weak and will ultimately break during use. This endmill also has a poor surface finish, indicated by the highly visible small lines running horizontally on the cutting edge.

To achieve the desired results, the substrate must suit the workpiece material. “One thing that has not been widely publicized is that aluminum has a tendency to stick to the cobalt in carbide,” said M.A. Ford’s Schmidt. “Carbide substrates that have 6 percent cobalt or less are ideal for aluminum applications.”