Following the thread
- January 22, 2003
New technology keeps operations productive
by Jim Barnes
Threading, one of the oldest metal cutting technologies, has never faced bigger challenges than it is facing today. The demand for higher feeds and speeds, coupled with growing use of tougher, heat-resistant materials and soaring demand from new energy infrastructure projects, is pushing the technology to the limit.
“We’re seeing very large increases in Canada in threading insert consumption. We’re seeing double-digit growth every year,” says Steve Geisel, senior product manager at Iscar Tools Inc. Oakville, ON.
“Threading is really an abusive operation; it’s high feed turning,” says David Andrews, product and application specialist–Turning Products, Sandvik Coromant Canada, Mississauga, ON. The situation becomes even more acute with materials like titanium and Inconel. While they were once most commonly used in aerospace, “more of them are coming up in oil and gas work, particularly offshore,” he says.
Industry’s needs drive innovation, and the tooling manufacturers have developed new technology in response.
For example, Top Notch thread tooling from Kennametal Inc. of Latrobe, PA, spans a wide range of grades and offers a rigid clamping system. As well, it incorporates Beyond insert technology, according to the firm. The Beyond grades are designed for tough alloys and feature new PVD (physical vapour deposition) coatings.
Sandvik has introduced a new threading program, CoroThread 266. Besides offering better rigidity through its iLock interface, it includes the new 1135 grade for materials like stainless steels and heat-resistant superalloys. “It’s a very fine-grained, PVD-coated grade. It has very good toughness. It also incorporates a very sharp, cutting edge, so it’s very free-cutting,” says Andrews.
The threading program at Iscar, too, is growing quickly. “We’re expanding our standard product line to include a lot of oil industry threads. The business is getting so big we can justify making a lot of those strip profiles. That makes it easy for the customer,” says Geisel.
Improvements in insert rigidity are important in applications involving these difficult materials and high feeds
“Traditionally, you would have trapped a laydown-style insert in a V-pocket–a 60°, triangular pocket. Because of the high feed rate needed to generate the pitch, the pocket would open up over time,” explains Andrews.
The CoroThread 266 inserts have slots for each of their three indexable cutting edges. The iLock design has a raised rail on the shim. When that raised rail locks into a groove on the other side of the insert, there is no way the insert can twist in the pocket. “The rigidity that results lets you run higher cutting data. Fewer passes are required to make the thread,” notes Andrews. “Users can expect at least a 20 per cent improvement in their cutting data, either in the form of higher speeds or fewer passes.”
Chip control is another focus. “Typically in turning, a significant amount of the insert is engaged in the work piece. You’re getting a wider chip that is more difficult to break,” says Andrews. Sandvik decided to use technology from the turning product line–a C-geometry–on the insert for chip breaking.
The infeed method is also a factor. “In the past, when you were creating say a 60° thread, you would feed directly in with the insert, so you’d do a straight, radial move,” says Andrews. With the C-geometry, the company recommends that customers program a modified flank in-feed.
“It is actually feeding down along one flank of the thread, so you’re feeding at a 30° angle, or a 29° angle. You are directing the chip on the leading edge of the insert against that chip breaking bump. You cut the width of the chip in half, because you’re only using the leading edge of the insert,” says Andrews. That enables the user to better control where it lands on the chip-breaker.
“We use an insert-and-shim combination to set the insert up with the correct inclination angle for threading. We try to make sure that the customer is using the correct inclination angle, based on the diameter and pitch of the thread, to get the insert setting correctly in the helix of the thread to give us proper clearance,” adds Andrews.
Even if you’re not using the C-geometry, Andrews says it’s the best way to form a thread. “You reduce the cutting force dramatically on the insert, because you are only engaging one flank at a time. But we find a lot of people are still doing a straight, radial infeed.” SMT