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Honing is employed to improve surface finish, size, and surface geometry. In most GMPTD applications, the tool makes a light cut with a fine grained abrasive (240-600 grain size) and conforms to the workpiece geometry. The most common application is on internal cylindrical surfaces, but it also may be used elsewhere such as on flat surfaces. The abrasive grains are bonded to form stones which are typically both rotated and reciprocated in contact with the work surface. In face honing both the part and tool rotate about parallel but not coaxial centerlines.
Each abrasive grain in contact with the workpiece removes a small chip and the grains are continuously broken down by the process to expose new, sharp grains. In this manner, honing stones are self-sharpening. Great care should be exercised in selecting rotary speed, stone pressure, bond hardness, and coolant to assure correct stone breakdown, avoiding glazing and produce the desired surface finish.
Single stroke honing resembles reaming, but with an abrasive rather than fluted tool. The tool has a diamond abrasive coated sleeve that can be expanded to adjust size. Like a reamer, the tool is rotated and fed axially through the hole, cutting on its lead taper. Because of the lead taper, the hole must have at least 15 mm axially of clearance beyond the sized portion. Unlike a reamer, the tools cannot control the position of the hole. Therefore either the part or tool must float. Stock removal is limited to 0.02-0.03 mm on diameter. Multiple passes with progressively larger tools are used.
Superfinishing and polishing (Figure 2.62) are analogous to honing for improvement of surface finish. Whereas honing is common for inside diameters, these processes are used for outside diameters. In general, polishing is done with a soft backing for an abrasive tape and does very little to improve part geometry. Superfinishing is done with firm or rigid abrasives either in stone form or as abrasive paper with a rigid backup, and does improve surface geometry. Grit size of 320-6000 is common with surface finishes as fine as 0.1 mm (4) at GMPTD, shaft bearing journals are commonly polished or superfinished after being ground to alter the aggressive surface left by production grinding. |
Figure 2.62A Diamond Tools & Arbors for Single Pass Honing (Courtesy ACCU-CUT Diamond) 
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