Unimerco When performing interrupted rough drilling or reaming through ductile iron valve body spool bores, a tool enters a void at the end of each land and the last piece of workpiece material—in the shape of a ring—can get pushed into the void or slip off the reamer as it retracts (bottom). Unimerco offers ring-free core drills that shred ductile iron into chips that are easily evacuated. lamellae in pearlite, they are easily sheared and are in their most machinable form. “Severe undercooling can create primary carbides,” Wood said, “and that’s what you don’t want when it comes to machining.” He added that primary carbides are caused by highalloy carbide formers, such as chrome in scrap steel. Drilling Challenges End users also don’t want to create rings, or “wedding bands,” when performing interrupted rough drilling or reaming through ductile iron valve body spool bores, according to Jim Stead, director of technical applications for Unimerco Inc., Saline, Mich. In these applications, a tool enters a void at the end of each land and the last piece of workpiece material—in the shape of a ring—can get pushed into the void or slip off the reamer as it retracts. The probability of this happening increases as the tool dulls. Many valve body manufacturers manually inspect parts to find any debris, according to Stead. “Sometimes they perform 100 percent inspection with a flashlight and bore gage to make sure there are no chips or wedding bands hung up in the voids,” he said. If one is found, tweezers are used to remove it. Unimerco’s approach to preventings these rings from forming and eliminating the time and expense associated with final inspection is to employ multistepped tools. Unimerco offers ring-free core drills that shred ductile iron into chips that are easily evacuated from the bores through voids. Additionally, compared with applying conventional drills, the tools allow a manufacturer to increase drilling speed from 250 mm/min. to 600 to 700 mm/min. and typically decrease the overall cycle time by 50 to 75 percent when machining spool bores, Stead said. “As a general rule, we can take a five-pass operation down to three in ductile iron,” he said, which includes passes with a pilot drill, a core drill and a finish reamer. Core Shifting In addition, the ring-free core drills can effectively remove more stock from one side of the bore than the other when
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