- Honing is an operation that is used primarily to improve the surface finish of holes produced by processes such as boring, drilling, and internal grinding.
- The honing tool consists of a set of aluminum oxide or silicon-carbide bonded abrasive sticks, usually called stones (Fig. ). They are mounted on a mandrel that rotates in the hole at surface speeds of 45 to 90 m/min, applying a radial force. The tool has a reciprocating axial motion, which produces a crosshatched pattern on the surface of the hole.
- The stones can be adjusted radially for different hole sizes. Oil- or water-based honing fluids generally are used to help flush away the debris. Honing is also done on external cylindrical or flat surfaces and to manually remove sharp edges on cutting tools and inserts.
- The quality of the surface finish produced by honing can be controlled by the type and size of abrasive used, the pressure applied, and speed. A fluid is used to remove chips and to keep temperatures low. If not performed properly, honing can produce holes that are neither straight nor cylindrical, but rather in shapes that are bell mouthed, wavy, barrel-shaped, or tapered.
Working Of Honing Operations :
Honing Process (micro finishing process) to obtain correct hole geometry:
To correct hole geometry in component, honing is used as a micro finishing process. Honing is an abrading process used mainly for finishing round holes by means of bonded abrasive stones called hones. Honing is primarily used to correct out of roundness, taper, tool marks, and axial distortion. Abrasives used in honing are Silicon carbide, aluminum oxide, diamond or cubic boron nitride. When honing is done manually; the honing tool is rotated and the workpiece is passed back and forth over the tool.
Length of motion is such that the stones extend beyond the workpiece surface at the end of each stroke. For precision honing, the work is usually held in a fixture and the tool is given a slow reciprocating motion as it rotates (shown in Fig.). The stones are thus given a complex motion as rotation is combined with oscillatory axial motion. These two motions combine to give a resulting cross-hatch lay pattern. Honing stones may be held in the honing head by cementing them into metal shells, which are clamped into the holder or they are cemented directly into holders. Coolants are essential to the operation of this process, to flush away small chips and to keep temperatures uniform.
Honing Process Parameters :
- Less complex or low-cost fixtures.
- It is highly accurate.
- It can be used for both long and short bores.
- It maintains the original bore centerline.
- Any material can be finished regardless of its hardness.
- The workpiece need not be rotated by power, there are no chucks, faceplates, or rotating tables needed, so there are no chucking or locating errors.
- The hone is driven from a central shaft, so bending of the shaft cannot cause tapered holes as it does when boring.
The result is a truly round hole, with no taper or high or low spots, provided that the previous operations left enough stock so that the hone can clean up all the irregularities.
- Honing uses a large contact area at a slow speed compared with grinding or fine boring, which uses a small contact area at high speed. Because of the combined rotating and reciprocating motion used, a crosshatched pattern is created which is excellent for holding lubrication. Diameters with 0.001 to 0.0001 inch and closer accuracies can be honed by using diamond stones similar to diamond wheels.
- Honing is though of as a slow process. However, new machines and stones have shortened hone times considerably.
- Horizontal honing may create oval holes unless the work is rotated or supported. If the workpiece is thin, even hand pressure may cause a slightly oval hole.
Application of Honing Process :
- Finishing automobile crankshafts journals
- Finishing round holes
- Finishing hollow cylindrical parts
- Finishing Engine cylinder, bearings, gun barrels, ring gauges, shafts and flange faces, piston pin, automobile crankshaft journals etc.
- Gear Hobbing
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