Honing is an abrasive finishing process used for the precision machining of bores and other functional surfaces. A fine-grained honing tool performs a combined rotary and reciprocating motion. This produces the characteristic cross-hatch pattern, which provides favourable sliding and lubrication conditions.
Honing enables bore diameters to be produced very precisely and existing form deviations to be corrected in a controlled manner. The process combines high dimensional and geometrical accuracy with excellent surface quality and is suitable for series production as well as individual components and repair work.
During honing, the honing stones make area contact with the bore wall. The superimposed rotary and axial reciprocating motions create intersecting machining marks. The resulting cross-hatch supports lubricant distribution and retention and contributes to favourable friction and wear properties of the functional surface.
The honing stones are expanded in a controlled manner during machining. This allows the diameter to be brought progressively towards its target size. Deviations left by the preceding operation can be reduced at the same time, provided that tool design, allowance, overtravel and process parameters are matched to the workpiece.
Honing does more than improve surface roughness. A suitably designed honing process can also significantly improve the dimensional and geometrical quality of a bore. Depending on the workpiece, material, bore dimensions, initial condition and the tool and gauging technology used, tolerances and form deviations in the range of a few micrometres can be achieved.
| Quality characteristic | Effect of the honing process |
|---|---|
| Bore diameter | Precise approach to the target size and repeatable machining within narrow tolerances |
| Roundness | Reduction of ovality and local roundness deviations to the range of a few micrometres |
| Cylindrical form | Correction of taper, barrel shape and hourglass shape along the machining length |
| Surface | Production of a defined roughness and a functional cross-hatch pattern |
The quality that can actually be achieved must always be assessed for the specific application. Particularly important factors include uniform pre-machining, a suitable honing allowance, stable workpiece clamping, sufficient tool overtravel and a gauging strategy matched to the process.
The process is used wherever bores must meet demanding dimensional, geometrical and surface requirements. Typical applications include cylinder liners, hydraulic and pneumatic cylinders, valve bores, bearing seats, connecting rods, transmission components and precision guide bores.
Honing is suitable for different materials and component sizes. In addition to high-volume production, the process can also be used economically for small batches, individual components and repair work.
Honing can be performed on dedicated honing machines. These machines are specifically designed for the motion sequences, expansion, process monitoring and gauging required for honing and provide particularly favourable conditions for high accuracy and productive series processes.
With suitable tooling, clamping and process technology, honing can also be performed on general-purpose machine tools and machining centres. Expandable Xstep® honing tools or hydraulically actuated coolEX® tool systems allow bore finishing to be integrated into existing manufacturing sequences. Pre-machining, honing and additional operations can therefore often be combined in a single setup.
Influencing factors and process design: The interaction of workpiece, tool and machine determines the result.
For a stable honing result, the honing stone specification, tool geometry, expansion strategy, cutting speed, stroke speed and coolant are matched to the particular application. The position and length of the bore, interruptions in the surface and the available tool overtravel also influence process design.
Appropriate pre-machining provides a honing allowance that is as uniform as possible. In addition, a suitable gauging strategy can measure the diameter during or after machining and support any necessary corrections. Measurements at several axial positions are useful for assessing cylindrical form.
What is the main difference between honing and drilling or reaming? Drilling and reaming produce or size a bore mainly with geometrically defined cutting edges. Honing is an abrasive finishing process with bonded abrasive grains and is used in particular to improve size, form and surface in a controlled manner.
Which form errors can be corrected by honing? Depending on the initial condition and process design, ovality, taper, barrel shape and hourglass shape can be reduced.
What levels of accuracy can be achieved? Under suitable process conditions, diameter, roundness and cylindrical form tolerances in the range of a few micrometres can be achieved. The specific capability must be demonstrated for the individual component and process.
Is honing only possible on dedicated honing machines? No. In addition to honing machines, general-purpose machine tools and machining centres can be used if they are equipped with suitable tooling, expansion, clamping and process technology.
Honing produces precise bore diameters, improves roundness and cylindrical form, and creates a functional surface with a characteristic cross-hatch. The process is used in many industries and is suitable for both individual components and series production.
Depending on the manufacturing task, machining can be performed on a dedicated honing machine or on a general-purpose machine tool equipped with suitable tooling technology. Honing can therefore be used flexibly as a separate process or as an integrated step in complete machining.