What Is Honing Machine Process used For Super Surface Finishing
Honing is a finishing process, in which a tool called hone carries out a combined rotary and reciprocating motion while the workpiece does not perform any working motion. Most honing is done on internal cylindrical surface, such as automobile cylindrical walls. The honing stones are held against the workpiece with controlled light pressure. The honing head is not guided externally but, instead, floats in the hole, being guided by the work surface . It is desired that
1. honing stones should not leave the work surface
2. stroke length must cover the entire work length.
In honing rotary and oscillatory motions are combined to produce a cross hatched lay pattern as illustrated in Fig
|Honing tools and Honing Operations|
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.
The honing stones are given a complex motion so as to prevent every single grit from repeating its path over the work surface. The critical process parameters are:
1. rotation speed
2. oscillation speed
3. length and position of the stroke
4. honing stick pressure
With conventional abrasive honing stick, several strokes are necessary to obtain the desired finish on the work piece. However, with introduction of high performance diamond and cBN grits it is now possible to perform the honing operation in just one complete stroke. Advent of precisely engineered microcrystalline cBN grit has enhanced the capability further. Honing stick with microcrystalline cBN grit can maintain sharp cutting condition with consistent results over long duration.
- 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 slow speed compared with grinding or fine boring, which use 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.