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Some users may need to overcome preconceptions about multifunction grooving tools, according to Matt Schmitz, turning product manager, U.S. north central, Iscar Metals Inc., Arlington, Texas. While a traditional grooving tool usually has a dead-sharp front edge, a grooving/turning insert includes a chipformer and edge preparations on the front, left and right sides of the insert to enhance tool life, productivity and chip control, he said. Edge preparations include T-lands for machining cast iron, ground periphery and diamond polish for aluminum and more positive geometries for high-temperature work materials.
Yet despite the added geometry, many shops presume that moving a grooving insert in the Z-axis to turn or profile will magnify chip control problems. “You would think that would be one of your biggest challenges, but it’s not,” Schmitz said. “It can be difficult to break a chip in a simple plunge-grooving cut, especially in a gummy material.
“But in a side-turning operation with a properly designed groove/turn insert, if you are taking a deep enough DOC, the chip wants to curl back toward the insert and the part and typically will break easily,” he said. “Programming can optimize each of the three cutting edges, but the programmer must ensure that only one cutting edge is engaged in the cut at a time, and be aware that, when generating radii during a plunging move, that the side edge may engage any material that has not been cleared away.”
Schmitz said some shops are skeptical about side turning with a grooving tool because “they look at a grooving tool, get nervous and say, ‘I’m not supposed to turn with this thing!’ ” Some of the concern regards tool deflection caused by side forces that are not present in simple plunge grooving. Actually, a controlled degree of deflection is desirable. “When it comes to groove/turning, if you don’t get deflection, the tool edge sits flat on the part and is going to chatter to beat the band because there is a lot of surface contact,” he said.
Conversely, when side-cutting pressures deflect the tool in a groove/turn operation, the insert tilts slightly and tool edge contact with the workpiece is reduced. Schmitz said the deflection must be carefully controlled by managing several variables, including feed rate, cutting speed, DOC, tool overhang, insert width support and the workpiece’s cutting characteristics. When those factors are balanced and kept constant, tolerances as tight as ±0.0004 " can be achieved. Schmitz said the results are similar to that of wiper-geometry turning inserts for imparting fine surface finishes.
Although programming rough grooving/turning operations is typically straightforward, peak accuracy, especially in finishing, usually requires in-process adjustment, according to Schmitz. “For finish cuts, it’s not going to be ‘program it, hit the green button and go,’ ” he said. “You have to tweak it.” He said changing the feed rate is typically the best starting point for adjustments.
A tool operating in a deflected orientation will not produce a square shoulder, he added. “The key is to program the tool to leave the cut at a 45º angle before reaching the side of the shoulder, and then plunge the shoulder separately,” Schmitz said. “When you are plunging, you don’t have deflection.” Similarly, if a groove needs to be machined at the end of a turned section of the part, the tool should be moved in the direction opposite the feed for about 0.1mm, releasing the deflection, before the plunge grooving begins.
According to Schmitz, Iscar’s HELI-GRIP tools are capable of external, internal and face groove/turn operations. The inserts have a double-ended, twisted body that avoids backside contact with the machined groove surface, and the tool’s geometry manages chip formation in both axial and radial directions.
Not all grooving inserts can deflect, Schmitz noted. For example, inserts in Iscar’s PENTA tooling line have a rigid, deflection-resist