TechFront New Developments in Manufacturing and Technology Hard Turning Finishes Strong with PCBN R
ecent advances in PCBN cutting tool technology have increased the acceptance of hard turning as a finishing operation of critical surfaces, according to Seco Tools
Inc. (Troy, MI). PCBN tool inserts, combined with the latest plunge turning technique, are said to produce as good or better tolerances than conventional grind- ing for finishing steel parts hardened to Rc
45–64.
The economics of hard turning are fairly well known. CNC lathes are less capital-intensive than grinders (one-third to one-half the cost) and extremely flexible in terms of machine capabilities and tool change time. Lathes take up less space, avoid messy government-regulated chip disposal and reclamation issues, and involve simpler tool maintenance. PCBN tool inserts can be quickly indexed to a new edge or removed and replaced with new inserts and don’t require truing or dress- ing to maintain the cutting profile. According to Seco, the turning process consists of small depths of cut, yet estimates of reduced machining time are as high as 60% for conventional hard turning, and 90% for the latest plunge-turning techniques. For increased productivity in conventional side turning and profiling, cutting tool manufacturers have engi- neered PCBN inserts with a wiper geometry that permits increased feed rates without sacrificing surface integrity.
the solid PCBN inserts to various tipped inserts, cost per edge savings ranged from 25 to 208%.
An added advantage is found in the fact that CBN060K and CBN100 make plunge turning possible because of the
Seco studies have shown that by using the right combination of insert nose radii, feed rate, or the new wiper insert technology, hard turning can produce a better surface finish than grinding. Performing multiple hard turning operations in a single chucking as opposed to multiple grinding setups also contributes to a high degree of accuracy. Seco’s solid insert grades, CBN060K, CBN100, and CBN300, provide use of all edges similar to conventional carbide inserts, and have long edges, not common to PCBN inserts. Due to their solid construction, the PCBN inserts offer higher wear resistance and lower cost per edge. Comparing
In conventional turning, surface finish is largely determined by insert nose radius and feed rates, and to some extent also cutting speed and depth of cut. The surface quality of plunge-turned components is mainly dependent on the quality of the cutting edge.
properties of the grades and the long usable cutting edges. Plunge turning is a highly productive form of finish hard turn- ing that uses the entire cutting edge or a portion of the cutting edge to create an orthogonal cut.
The most critical properties of ground or hard-turned components are dimension (diameter), roundness, straight- ness, bearing area, surface roughness and residual stresses. For the first four properties, plunging can achieve the fol- lowing tolerances for a gear wheel or bearing ring: diameter