American Machinist

Cutting tools for the 90s. (Cover Story)

Cutting tools for the 90s

HAVE YOU EVER SEEN a new multi-million-dollar manufacturing system with many machining centers, pallet and tool transport systems, automation features--Yet the system is equipped with cutting tools that are 20 years old in design, except for a few coated-carbide insert grade? Are there too few tool or manufacturing engineers at some of our major manufacturers to adequately support to effort of machining modernization? Million for systems but no investment in cutting-tool modernization?

In the interests of productivity and competitiveness it is as important to keep up with cutting-tool technology as it is with overall machining systems. Here are assembled eleven different cutting-tool applications, arranged in three groups: drilling> milling> and turning, boring, and facing. It is likely that one or move can help you chip making operations.


when it's 80% of your work

When your average part requires over 2000 holes, evaluating the latest in drills is an ongoing process. Aqua-Chem Inc (Knoxville, Tenn) tests nearly every new drill that comes on the market. A typical part at Aqua-Chem can require thousands of holes, with a depth of 2-3 times diameter, in materials like copper-nickel, Inconel, and titanium. Aqua-Chem Manufacturing, Engineer Jerry Hardwick says, "about 80% of our work is drilling, so evaluating new drills is very important to us--we look at both tool cost and machine cost per hole." The company makes large water-desalination units used to produce fresh water from salt water. They also produce other types of water-purification equipment as well as heat exchangers for ships.

One of the most challenging parts that go into these units are "tube sheets," which are used as support members for copper-nickel tubing. An average tube sheet might be 30 in. x 40 in., 5/8-in. to 1 3/4-in. thick, and filled with anywhere from a few hundred to a few thousand holes. Copper-nickel tubes are inserted into the finished holes and are fixed in place by a rolling operation. If the holes are not straight, round, and consistent in size, the rolling operation cannot create proper fastening of the tubes.

Further complicating the machining of many of these parts is the multiple layers the drill must penetrate. Often, two or three 5/8-in. sheets are stacked or, in some cases, the drill must penetrate two sheets of material separated by a 3/4-in. void. And as a final challenge, many of the parts are drilled from an "as cast" surface which can make the drill's entry into the workpiece difficult.

Aqua-Chem recently tested an SE drill from Hertel Cutting Technologies Inc (Oak Ridge, Tenn). The SE (Sculptured Edge) is Hertel's high-performance solid-carbide drill. The "sculptured edge" design features a smooth transition from the major cutting edge to the drill point, which removes any stress peaks, and allows free chip flow over the entire cutting edge. The SE point also allows the drill to actively cut metal from the center to the outer diameter, enabling it to handle much higher loads. This also improves chip breaking, and contributes to the self-certaring capabilities of the drill.

Aqua-Chem ran a test on a 1 3/4-in. thick, 90/10 copper-nickel tube sheet that requires 2202 holes. They had been using conventional HSS twist drills, running at 800 rpm and 8.008-0.010 ipr for the job. The test ran on an older Giddings & Lewis machine having a top spindle speed of 1500 rpm.

Aqua-Chem tested a 0.630-in.-dia SE drill with internal coolant holes running on the same machine at 1500 rpm and 0.008 ipr. At these speeds the 2202 holes were completed in 24 hours compared with 60 hours previously. The new drill also eliminated two additional operations that were required with the HSS drills: pilot-drilling and final reaming. The SE drill produced a 32-[mu]in. finish and holes that were within final specs. With the elimination of these two operations and a eight-ten fold increase in tool life, total tool cost per hole went from 3.4[ to 2.0[ and machine-operating cost went from $1.10 to 0.44[ per hole.

Hertel Technical Director Kurt Schnettler says, "the SE drill was designed to take full advantage of the inherent physical properties of carbide in terms of stiffness and hot hardness." It is designed with a 30-35% thicker web and narrower flutes than conventional designs, giving it significantly greater stiffness than other carbide drills (carbide already has a three-to-one advantage in stiffness over HSS). Because it is more resistant to bending and torsional load, the SE drill is capable of penetration rates seven-and-a-half times greater than HSS and five times greater than conventional two-flute carbide drills. Even though the flutes are narrower, they are designed with optimum flute and helix-angle geometries that provide excellent chip evacuation without sacrificing cross-sectional strength. …

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