Seco's Square T4-08 insert has true 90º so the helix stays true to form throughout the length.Click image to enlargeby Tim Wilson

Tangential milling brings direct results to roughing applications

Tangential milling refers to when a tool’s inserts are mounted around a cutter’s outer diameter, as compared to traditional mounting along the radius of the tool body. Essentially, the inserts lie flat in the cutter instead of standing up, which, according to industry suppliers, increases edge life in rough milling applications.

“Tangentially mounted inserts offer two advantages over conventional mounted inserts,” says Tim Aydt, product manager for indexable milling at Seco Tools. “First, there is a larger depth of cut capability in smaller diameter tools. Second, the tangential mount offers more core diameter versus conventional mounting, which makes the tool stronger.”

Tangential milling also allows the cutter body to have a thicker cross section. This results in increased rigidity, and improved machining stability.

“The cutting forces are directed to the thickest part of the insert, which absorbs these forces much better,” says Jeff Shope, an application and sales engineer at Horn USA. “There are also increased metal removal rates.”

Iscar's multi-functional Multi-Master system: a modular system to fit manufacturers' varied needs.Click image to enlargeHorn’s 406 tangential milling system now includes side milling cutters and screw-in milling cutters. For these systems and others, having a bigger core means more than added support behind the insert: there is also the opportunity to add more inserts on the cutter body. In most diameters you can have finer pitch cutters than a regular helical mill. And, with tangential milling, an integrated trailing chamfer can help produce cleaner surfaces.

“This is because of the positive insert geometry and axial angle,” says Shope. “It helps ensure minimal tool pressure, which in turn creates a much better surface finish.”

Tangential mounts are now becoming more common. Iscar’s multi-functional Multi-Master system, for example, allows for the tangentially-clamped Helitang T490 4 edge inserts. These provide extra value for those who already have a T490 or Multi-Master in their shop.

“If the customer gets a particular job that requires a longer reach than current T490 end mills, he can use the same insert but
on a Multi-Master shank,” says Tom Hagan product manager for milling tools at Iscar. “This is completely modular to fit requirements.”

Iscar also has its new Tang slot cutter line, which has four insert edges and 8 mm as well as 12 mm inserts. The advantage with dovetail clamping is that the insert is secure in the pocket, which provides stability and reliability. It also generates lower cutting forces, with the cutter able to perform at higher feed rates.

“The double-sided tangential insert has four right-hand cutting edges, whereas a regular helical mill has only two edges,” says
Hagan. “The thickness and clamping of the insert increases the feed rates, with high metal removal.”

For its part, Seco Tools has its Square T4-08 product, which achieves “true 90°”: the insert has a helix, but the helix stays true to form throughout the length.

“In my opinion,” says Aydt, “the contact area between the insert and the pocket is more critical at the area where the insert is mounted 90 degrees to where the screw mount is located.”

THorn's 406 tangential milling system now includes side and screw-in milling cutters.Click image to enlargehis is a reasonable argument, given that this area is within the cutting force direction, with the interface between the insert and the pocket being extremely important to ensure insert security. The interlock design between the insert and the pocket also affects the rigidity and the balance of the tool, as well as tool life.

“This tool, because it utilizes an insert with multi-edges, is best suited for low chipping materials such as medium to harder steels, and grey and ductile irons,” says Aydt. “But it will work with many other materials as well. We also now have a larger version called SQT4-12, with higher depth of cut capability. This provides two ranges in a tangential mount.”

Finally, because tangentially arranged inserts provide more carbide behind the cutting edge, the process allows for higher feed per tooth. But getting the right coating can be an issue when adressing wear resistance and higher cutting speeds. This can be a trade-off, with the best combination resulting in shorter cycle times and improved performance, particularly with difficult-to-cut materials such as high strength steel alloys like 300M, some stainless steels, and heat resistant alloys containing nickel and cobalt, like Inconel 718 and Inconel 909. SMT

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