Honing is a finishing process. The oil stone of the honing tool generally needs to be trimmed before formal processing of the workpiece. There are many ways to trim the oil stone.

In mechanical processing, honing of holes belongs to finishing and finishing processing, which has the characteristics of high processing precision, good surface quality, long service life of the processed surface, high cutting efficiency and wide processing range. Generally, single oilstone honing tools are used for workpieces with a hole diameter of 4 to 10 mm. In the production of automobile parts, single oilstone honing tools are widely used for parts with small diameter through holes and hardness of about 60HRC.

Limited by the manufacturing accuracy, there are certain errors in the slope angle and size of the oil stone base and the push piece. There is an axial parallelism error between the guide shoe groove of the honing rod and the guide arc surface. In addition, there is an error in the flatness of the oil stone cutting surface. This makes the cutting surface of the honing stone and the guide arc surface of the honing rod axially non-parallel after the four parts of the honing tool are assembled, which is commonly known as the uneven oil stone. This causes the cutting surface of the oil stone to be axially aligned with the inner hole of the workpiece during initial processing. There are places that are out of reach, causing taper errors in the inner hole of the workpiece. Therefore, the oil stone needs to be trimmed.

Due to the manufacturing errors of honing stone, honing stone base and honing head, it is impossible for honing stone of honing head to form a uniform and discontinuous cylinder after assembly to ensure good contact between honing stone and machined surface. Although in the honing process, the honing stone can be dressed with the workpiece, but the workpiece is small, so it is impossible to get adequate dressing in the initial honing process. 

If the contact between the cutting surface of the oil stone and the inner hole of the workpiece is continuous and uninterrupted in the length direction (after trial machining the workpiece, observe the cutting surface of the oil stone against the light, and the place where it contacts the workpiece hole is shiny), the workpiece can be processed. .

The decisive factor for the surface quality of honing is the honing stone.

The choice of oil stone mainly depends on the following factors: workpiece material, product drawing requirements and margin allocation, etc.

The performance of oil stone is mainly determined by factors such as abrasive, abrasive particle size, sand bar hardness and binder.

Currently, two commonly used abrasives are diamond and CBN (cubic boron nitride).

Diamond oil stone is mainly used in the processing of cast iron and other low-hardness metals, and CBN oil stone is mainly used in the processing of hard steel. In the practical application of these two high-hardness grinding materials, diamond accounts for 55% and boron nitride accounts for 45%.

The particle size of the abrasive indicates the particle size of the abrasive particles. The unit of particle size is microns. The smaller the particle size number, the finer the abrasive particles. The larger the particle size number, the coarser the abrasive particles. The choice of particle size mainly depends on the requirements for processing accuracy and production efficiency of the workpiece surface. Coarse and medium grits have better cutting performance and are suitable for rough honing and semi-finish honing; fine grits are used for fine honing. The physical and mechanical properties of the parts being processed are also one of the factors that determine the grain size. Materials with low hardness, ductility and toughness should be processed with coarse-grained tools, while materials with high hardness and brittleness should be processed with fine-grained tools.

Oil stone hardness and abrasive grain hardness are two concepts, which refer to the strength of the binding agent to the abrasive grains. The hardness of the honing abrasive strip is too low, the binding ability of the binder to the abrasive grains is weak, the abrasive grains fall off quickly, the size easily exceeds the specified value, and the oil stone is consumed quickly; the hardness of the honing oil stone is too high, and the worn abrasive grains are not easy to fall off, and the honing The self-sharpening properties of the strips are poor, and the surface is easily clogged, resulting in low or even disappearance of cutting performance, and the size often does not reach the specified value.

The self-sharpening property of the oil stone is related to the adjustment of machine tool parameters. Under certain pressure conditions, the self-sharpening properties of sand strips are better. During work, the gradually dulled sand grains must be able to fall off and be gradually renewed. If the dull abrasive grains do not fall off, the groove cannot be pulled; if the dull abrasive grains fall off, it will cause waste and fail to achieve the principle of making the best use of materials.

The hardness of oil stone is related to the selection and proportion of binder. Common bonding agents include bronze bonding agents, ceramic bonding agents, resin bonding agents and electroplated metal bonding agents.

In particular, the honing stone of diamond and CBN abrasives cannot be fully dressing because of its abrasion resistance. Therefore, it is impossible to get the ideal machining surface in the processing, and the accuracy cannot be guaranteed. Therefore, when using a new honing stone, the honing stone must be repaired (also known as rounding) before processing. 

The dressing of oil stone such as silicon carbide and white corundum is to install the oil stone directly on the grinding head used and round it on the external grinder. The dressing of diamond and CBN honing stone can be done with silicon carbide grinding wheel on the external grinder. The grinding wheel speed is 18-25m/s, the grinding head speed is 1-3m/min, the feed depth is generally 0.02-0.04mm/stroke, and the finishing is 0.01mm/ stroke. And it requires a lot of coolant.

---EDITOR: Doris Hu, Sarah Shi

---POST： Doris Hu