Fixed-diameter honing is an abrasive finishing process for precision bores. Before machining, the tool is set to a defined working diameter and the honing stones are fixed to the tool body. The honing stones are not actively expanded during the machining cycle.
The tool performs a combined rotary and axial feed motion and normally machines the bore in one in-and-out movement, or double stroke. This provides economical correction of bore diameter and roundness together with repeatable surface generation. The process is particularly suitable for production components with stable pre-machining and a uniform honing allowance.
In fixed-diameter honing, the effective tool diameter is set to the required working size before the machining cycle. The honing stones distributed around the circumference guide and machine the bore simultaneously. Stock removal is determined by the tool design, honing stone specification, allowance, rotational speed and feed rate.
During the in-and-out movement, the rotary motion is superimposed on the axial feed motion. The machining marks intersect, comparable to a right-hand helix superimposed on a left-hand helix. With suitably coordinated kinematics, this produces a defined cross pattern. Tool concepts that combine reaming cutting edges and honing stones in a single working stroke can produce a different surface texture and must be assessed separately.
The fixed working diameter is adjusted between machining cycles and corrected as honing-stone wear increases. For larger allowances or different machining tasks, several preset tools can be used successively for rough, intermediate and finish honing.
Preset honing tools combine stable circumferential guidance with a defined working diameter. They are therefore particularly suitable for repeatable bore sizing and the correction of roundness deviations. Depending on the workpiece, material, bore geometry, pre-machining, machine and tool design, achievable dimensional and form quality can reach the range of 1 µm and below.
| Quality characteristic | Effect of fixed-diameter honing |
|---|---|
| Bore diameter | precise sizing to the preset working diameter; tolerances of 1 µm and below are possible under optimised process conditions |
| Roundness | very good correction of ovality and local roundness deviations to the range of 1 µm and below, including in interrupted bores |
| Cylindrical form | good straightness and cylindrical form with uniform allowance and suitable tool guidance |
| Surface | repeatable fine-machined texture; a defined cross pattern is possible with a conventional double stroke |
Comparison with reaming, fine boring and honing with active expansion: Achievable quality depends not only on the process but also on pre-machining, clamping and machine kinematics.
| Quality characteristic | Reaming | Fine boring | Fixed-diameter honing | Honing with active expansion |
|---|---|---|---|---|
| Diameter | economical sizing within narrow tolerances | precise adjustment through the tool and machine axis | highly precise and repeatable sizing with stable allowance | very narrow finished sizes; depending on the technology, expansion or gauging can control the process |
| Roundness | good results but limited correction of existing form errors | good roundness with a stable machine and tool guidance | very good roundness correction through circumferential guidance | very good roundness correction with additional adaptation of the tool diameter during machining |
| Cylindrical form | largely follows the pre-machined bore | good straightness and axis guidance, depending on tool overhang and machine kinematics | good results with uniform allowance; correction capability is limited by the fixed working diameter | particularly flexible correction of taper, barrel shape and hourglass shape |
| Surface | fine surface with a process-related longitudinal texture | fine-machined surface with a characteristic turning texture | defined fine-machined texture; with or without a conventional cross-hatch depending on the tool principle | defined roughness and conventional cross-hatch through superimposed stroke and rotary motion |
| Position and bore axis | only minor correction because the tool follows the bore | good potential for position and axis correction through machine guidance | limited position correction; focus on diameter and roundness | limited position correction; focus on size, form and surface |
Fixed-diameter honing is particularly economical when pre-machining provides a small and uniform allowance. Honing with active expansion offers additional flexibility when allowance varies more strongly or when complex cylindrical form deviations must be corrected selectively.
Fixed-diameter honing is used for precision through bores and, with appropriately designed special tools, for other bore geometries. Typical components include control and valve blocks, hydraulic housings, connecting rods, crank bores, turbocharger housings, guide bores and transmission components. Stable circumferential guidance is particularly advantageous for interrupted bores.
Application sectors include automotive engineering, mechanical and plant engineering, hydraulics and pneumatics, aviation, defence technology and motorsport. The process is particularly suitable for repeatable series production, but application-specific tooling also allows it to be used for smaller batches.
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 distinguishes fixed-diameter honing from honing with active expansion? In fixed-diameter honing, the working diameter is preset before the machining cycle. No active expansion takes place during machining. With active expansion honing, the honing stones are expanded hydraulically or mechatronically during the process.
How is honing-stone wear compensated? The working diameter is corrected manually, with assistance or automatically between machining cycles. Depending on the tool concept, a suitable adjustment system can be used for this purpose.
Is fixed-diameter honing suitable for interrupted bores? Yes. The circumferential guidance provided by preset honing tools can be particularly advantageous at control edges and in heavily interrupted bores. The tool design and honing stone specification must nevertheless be matched to the interruptions.
Can fixed-diameter honing be performed on a machining centre? Yes. With a suitable toolholder, precise axis alignment and coordinated process parameters, fixed-diameter honing can be integrated into milling, turning and general-purpose machining centres. Depending on the application, FDhone® can also be used with hand-held drills or column-type boring machines.
Does every preset tool produce a cross-hatch? No. Conventional double-stroke fixed-diameter honing can produce a cross pattern through the superimposed rotary and axial motions. FDream® combines reaming and honing in one working stroke and does not produce a conventional cross-hatch.
Fixed-diameter honing with preset tools is a precise and economical process for bores with a stable, uniform allowance. It provides repeatable diameter sizing, effective roundness correction and a surface matched to the functional requirement. Circumferential tool guidance offers particular advantages in interrupted bores.
With FDhone®, FDream® and application-specific fixed-diameter honing tools, DIAHON provides different tooling concepts for honing machines and general-purpose machine tools. The selection depends on whether a conventional double-stroke honing process or a compact combination of reaming and honing in one working stroke is required.