The Need for Fine Hole Finishes and High Productivity Rates

The three keys to hole quality are diametral accuracy, form and position, and surface finish. Boring tools are the undisputed king in all of these areas, but they’re also one of the slowest methods of hole finishing, and in most cases are limited to 10:1 depth to diameter ratios or less. Conventional carbide-tipped reamers produce good hole quality, are substantially faster than boring and able to reach much deeper, but they also have an Achilles heel. The steel shank to which the carbide flutes are brazed has a thermal coefficient three times that of carbide, and is subject to growth during machining operations. Worse, sharpening of these tools often leads to less than desirable results. The mixture of carbide and steel wreaks havoc on grinding wheels, providing a reground edge that is rarely as good as the original tool. Also, PVD and especially CVD coating of reground tools is problematic, because the temperature inside most coating vessels reaches upwards of 530 deg C (986 deg F), leading to micro-movement of the brazed carbide flutes.

The Top Ream carbide reaming system from WIDIA Products Group (Latrobe, PA) addresses these problems and more. Instead of four to eight (or more) individually brazed carbide tips, Top Ream uses a single carbide disc and brazed joint, providing a strong connection that is virtually immune to thermal effects during machining operations. “Steel-bodied reamers tend to get banged up on the ends,” notes Tom Bobos, a manufacturing engineer at WIDIA. “The center can get nicked or distorted, preventing an accurate regrind. With carbide, you always have a good center to locate on.” The result is a minimum of four “like new” regrinds vs. an average of three questionable ones. However, there’s more to this system than its ability to hold an accurate edge: “Overall it’s just a better design,” says Bobos. “A single piece of carbide is inherently more stable and resistant to vibration. The through-hole style has an 18 deg left hand spiral that does a great job of pushing the chip forward. It’s really best in class.”

The Top Ream platform offers best in class carbide as well. The WU05PR advanced reaming grade was developed specifically for the demanding tool wear and surface finish requirements encountered in most hole reaming operations. For example, tests performed over a total cut distance 100 ft (30 m) long showed an ability to consistently maintain surface finishes of 32 µin Ra (0.8 µm) in 4140 steel alloy and 64 µin Ra (1.6 µm) in gray cast iron, three times that of TiAlN-coated tools. Top Ream covers hole diameters up to 42 mm (1.65 in), with the TRF shank-style starting at 14 mm (0.551 in), and the TRM modular tool from 20 mm (0.787 in) and up. “This size range covers the lion’s share of requests from our users,” states Jerry Hanna, the director of sales operations at WIDIA. “We also offer a wide variety of custom geometries, diameters, and edge preps, all available in three weeks or less.”

“With reaming, 98 percent of the tools are custom,” explains Bobos. “We encourage users to try standard sizes, but they should also ask for advice on optimizing systems specifically for any application . . . there are specific geometries and coatings for machining titanium. Same with 316 stainless or Inconel. A slight tweak to the hone or modifying the leading edge a little bit can make a huge difference in productivity and hole quality.” A big feature of Top Ream is the mounting mechanism that makes simultaneous contact on the cutting head’s face and taper. Twist the locking screw and the reamer head pops out, with no need for head to body orientation. This provides a strong, vibration-free and, most importantly, extremely precise reamer interface. “There’s virtually zero run out with the modular design,” adds Bobos. “Once you have everything dialed in, you just put the head on and tighten it down. There’s never a need to re-indicate after a tool change.”

Hanna agrees, “This unique design is geared towards any shop that needs fine hole finishes and high productivity rates, whether it’s a Tier 1 automotive supplier or a small job shop down the street. And as the use of additive manufacturing and other near net-shape processes continue to grow, so too will the need for accurate, cost effective hole finishing. That makes Top Ream an ideal reaming system for applications today and tomorrow.”

WIDIA Products Group, 1600 Technology Way, Latrobe, PA 15650, 724-539-5000, www.widia.com.