Honing (metalworking)

Honing is a finishing process -machined for almost all materials and is in production the last production process and aims to improve the dimensional and shape accuracy, mainly to be a positive influence on the tribological properties. The most popular applications are the piston bearing surfaces of cylinders of internal combustion engines and hydraulic components.

Word origin

The term comes from the English verb honing to hone, which originally meant the removal or sharpening of an object on a stone. The first use in mass production took place in 1923 at the automobile company Ford in the U.S. Detroit.

The tool honing tool

The removal of the material is performed with geometrically undefined cutting through the in honing stones (also called honing stones ) summarized abrasives ( bonded grain ). Depending on the material to be processed and the desired result, the honing stones of the same materials with the same or similar compounds may be made as in grinding wheels. They are (also shoe) each used in a force-or form-fitting tracked carrier.

The tool, also known as a honing tool is moved in both the longitudinal axis and rotationally; Therefore, a honed surface usually on the cross cut (cross line ) is apparent. This cross-cut is characteristic of the machining process " honing " = honing, it improves the sliding and emergency running properties, as can collect oil into the minor grooves. In addition, the roundness of the machined workpiece is significantly improved. The cylindricity of the workpiece can be influenced by appropriate control of the tool turning points: If the return point about 1/3 extended tool length selected results at the ends of the workpiece removal of larger and vice versa. Also, it is possible for almost all honing machines to turn the tool at any point in the workpiece, which opens up great possibilities for influencing the cylindricity.

Thus, the honing stones not equated with the abrasive slurry (usually with special honing oil ) flushed during operation plentiful.

Method

In DIN 8589 honing is divided according to different criteria. When ordering criteria the shape and the position of the generated surface can be used. The procedures are Innenrundhonen (positive or non-positive ), Außenrundhonen ( between centers or centerless ), flat honing and Profilhonen.

Together the method is composed of two directions cyclic cutting movement, of which one is usually oscillatingly. Depending on the frequency of the oscillating motion of the honing in the so-called Long-stroke as well as the short-stroke (also fine honing ) can be divided.

Long-stroke

The long-stroke honing a bore of, for example, the tool rotates around its own axis and is in this case over the entire length of the bore back and forth, that is oscillating, is moved. By repeatedly passing over the same area opposite the feed direction, the typical for honing straight or elliptical cross furrows arise on the surface, which, at best, have an angle of about 45 degrees for a low cutting force. The required tribological properties but often stand in the way, so that the optimal tool life can not be achieved. An important application of Langhubhonens is that known as plateau honing, which plays a role, especially for the machining of cylinder liners.

Short-stroke

In contrast, short-stroke produces a sine touches in the form of intersecting machining marks, as the turning point of the tool is within the workpiece. This process is also known as Super Micro Finish or Finish. Another peculiarity is that in this process the workpiece can perform the rotation and the tool, the oscillating motion. When both long-stroke motions by the tool are always realized.

Flat Honing

Laser honing

An entirely new method which is based not on the machining process but ablation (thermal ablation ), laser - honing (eg with cylinder liners ). The use of this technique is found mainly in diesel engines. In this laser honing, a laser beam melts the metal surface, it is evaporated in part and thus produces the desired fine oil -retaining wells. Advantage of this method is the additional training generated by the melting process hard enamel edges, which are very resistant to wear. A wear reduction and life extension by about 75 % can be reached this way.

Honing Machines

Honing are possible on ordinary lathes and vertical boring machines, in mass production, however, special honing machines with vertical or horizontal spindle are common. Furthermore, there are also plane-parallel flat honing for workpieces.

Is on a honing machine - similar to a milling machine - a tool inserted into the bore to be machined and is rotating and rocking motion (longitudinal to and fro). Crucial for optimal results is the variability of the speed and especially the lift control, since the latter can be influenced by the cylindricity of the bore within wide limits. The actual cutting strips of silicon carbide, corundum or diamond are pressed through a form or force closure adjustable in the tool pressure at the hole.

Result, the surface of the inner cylinder receives a characteristic appearance with it (usually at an acute angle ) intersecting at an angle in the cylinder extending grooves and gets defined Rauhigkeitseigenschaften, often with a residual adhesion of fluids ( hydraulic oils, motor oils).

This processing is done regularly in a strong flow of liquid to quickly remove the chips from the machining process and to cool the workpiece so that the required tolerances are respected. Therefore, the volume of the auxiliary fuel tank and the quality of the excipient filtering decisive role in the suitability of a machine for manufacturing each desired result.