New Tech Powers Productivity Gains in Indexable Milling

Many of the recent advances in the brutally competitive world of indexable tooling may seem incremental. The details of others are shrouded in secrecy. But since cutting tool choices can have outsized impacts on productivity, it’s always worth asking the experts what’s new.

Let’s start with the age-old question of deciding between indexable and solid-carbide milling cutters. The first considerations, as Luke Pollock, product manager at Walter USA, Waukesha, Wis., put it, are “how much material needs to be removed and how much working space do you have?… When you have the room and a large amount of material to remove, I definitely think indexable tooling is the much better way to go. We even see use of indexable tools on small components for the first few operations, just to increase the material removal rate due to the tool’s size and number of teeth.”

Dan Tucker, manager for the product management group and milling specialist for the western U.S. at Sandvik Coromant, Fair Lawn, N.J., quantified the trade off by saying solid-carbide surpasses indexable milling tools for diameters of 5/8" (15.88 mm) and below and “you could even make the argument that ¾" [19.05 mm] diameter solid carbide might surpass indexable as far as productivity. It is often hard to get enough indexable inserts into a smaller tool to compete, not only in terms of how many are put in the cutter, but also the length of the inserts to match up to a solid carbide.” Tucker’s colleague, Joe DeRoss, milling specialist for the eastern U.S., said there are rare cases in which it’s more cost-effective to rough with a small-diameter indexable tool, even though it would have fewer teeth than a solid tool of the same size. That’s because it’s less expensive (at least from a tooling standpoint) to chunk out material with a two-flute indexable mill and then switch out inserts when they wear.

From an applications standpoint, Edwin Tonne, training and technical specialist at Horn USA Inc., Franklin, Tenn., said slot milling or disk milling (face milling) are the best examples in which indexables beat solid tools. “Another example would be face milling in smaller closed pockets. With the Horn 304 mini mill, the bottom of a deeper pocket can be machined without the expense of a longer solid carbide tool,” he said.

Surface Finish, Tolerance Trade-Offs

For Sandvik Coromant’s DeRoss, the driving factor in picking a solid-carbide tool over an indexable is the need to achieve a superior surface finish. Wiper inserts can be added to an indexable tool to improve the surface finish, but DeRoss said the only way to compete with the solid tool’s higher flute count is to slow the process. Pollock explained that by its nature, an indexable tool will never present a continuous cutting edge as perfectly as a solid tool. “Even though a long-edged indexable tool might line up well, maybe even to the point where you don’t feel a witness line, there is almost always a witness line. … There will always be a little bit of mismatch due to an indexable tool being an assembly. It is [comprised of] inserts put into a steel body. It is never going to have a pocket in the perfect location, and you’re never going to be able to grind the insert to an exact size. There’s always going to be a little bit of a stack up. That is not true with solid tools.”