Key elements of hard turning

Hard turning is a substitute for shops that need to streamline their throughput. It is an alternative to grinding. But hard turning does take some attention to process detail. It's a finishing process with emphasis on dimensional accuracy and surface finish quality that has been heat treated and then turn to final size and surface finish specifications. Applications that were automatically given to a grinding machine are being rerouted to the turning centre. The motivation for hard turning instead of grinding comes from reduced setup, better throughput, reduced machining rates and cycle time reductions, especially on complex ID and OD contours. It generally costs less to run a lathe than a grinder. Not as hard as you think The clear attraction to hard turning is the possibility of eliminating grinding operations. For some shops, the process of repeatedly turning parts that are harder than 45 Rc to grinding-level accuracies is still a bit cloudy. A properly dialled-in hard turning process can deliver surface finish of 0.00011-inch, roundness of 0.000009-inch and diameter tolerance of ±0.0002-inch. Such performance can be achieved on the same machine that "soft" turns the part prior to hardening, maximising equipment utilisation. However, some shops misstep by initially using the wrong or less expensive tool insert for the application. Others may not be sure if their machine possesses the rigidity to handle cutting pressures that can be twice that of a typical turning operation. " A properly dialled-in hard turning process can deliver surface finish of 0.00011-inch, roundness of 0.000009-inch and diameter tolerance of ±0.0002-inch." Process elements to keep in mind Though 45-Rc part material is hard turning's starting point, hard turning is regularly performed on parts that are 60 Rc and higher. Commonly hard-turned materials include tool, bearing and case-hardened steels, as well as inconel, hastelloy, stellite and other exotic materials. From a metallurgical standpoint, materials with a small hardness deviation, less than two Rc points, throughout the cutting depth allow the best process predictability. In some cases, a part's size or geometry simply does not lend itself to hard turning. Parts that are best suited for hard turning have a small length-to-diameter (L/D) ratio. In general, an L/D ratio for unsupported workpieces should be no more than 4:1, and it should be no more than 8:1 for supported workpieces. Despite tailstock support for long, thin parts, high cutting pressures would likely induce chatter. The degree of machine rigidity dictates the degree of hard turning accuracy. Most machines made in the last 15 to 20 years have sufficient rigidity to handle some hard turning applications. In many cases, a machine's overall condition is more of a factor than its age. Even an old, well-maintained manual lathe can be a candidate for hard turning. However, as required part tolerances get tighter and surface finishes get finer, machine rigidity becomes more of an issue. Maximising system rigidity means minimising all overhangs, tool extensions and part extensions, as well as eliminating shims and spacers. The goal is to keep everything as close to the turret as possible. Some shops are initially put-off by the high cost of cubic boron nitride (CBN) inserts, despite the fact that these inserts are the best all-around grade for hard turning. CBN inserts hold up well during interrupted cutting and offer good tool wear for continuous cutting. With a properly tuned hard turning process, these inserts are second only to grinding in terms of holding diameter tolerances. Ceramic is not as tough as CBN, and it normally is not used when tolerances are tighter than ?.001-inch. It is also not appropriate for interrupted cuts, and it should not be used with coolant because of the risk of damage resulting from thermal shock.Adidas Yeezy Boost