Application of internal grinding

Grinding  using abrasive particles coated or pressed on the grinding tool, the grinding tool and the workpiece move relative to each other under a certain pressure to perform finishing processing (such as cutting processing) on the processing surface.

Grinding can be used to process various metal and non-metal materials. The processed surface shapes include planes, internal and external cylindrical surfaces and conical surfaces, convex and concave spherical surfaces, threads, tooth surfaces and other profiles. The processing accuracy can reach IT5-1, and the surface roughness can reach Ra0.63-0.01 microns.

Internal grinding method is a finishing method for inner holes. Internal grinding can process through holes, blind holes, stepped holes and end faces of parts. Internal grinding can also process hardened workpieces, so it is widely used in mechanical processing. Internal grinding generally achieves high dimensional accuracy.

Application of internal grinding wheel

The diameter of the internal grinding wheel should not be too large or too small.

When grinding the inner hole, if the diameter of the grinding wheel is too large, the contact arc between the grinding wheel and the workpiece will increase, which will increase the grinding heat and make cooling and chip removal difficult. If the diameter of the grinding wheel is too small, it is difficult to achieve the ideal grinding speed (30m/s~50m/s), which will increase the grinding thickness, increase the stress on the abrasive particles, and make it easy to blunt, increase the surface roughness of the inner hole, and reduce production efficiency.

In order to obtain a good grinding effect, the grinding wheel diameter and the inner hole diameter should maintain an appropriate ratio, which is usually between 0.5 and 0.9. When the aperture is small, the problem is that the circumferential speed of the grinding wheel is low, and a large ratio should be taken at this time; when the hole spacing is small, the main problem is that cooling and chip removal are difficult, and a smaller ratio should be used at this time. The selection of the diameter of the internal grinding wheel can refer to the following table:

The width of the internal grinding wheel should not be too wide or too narrow

When grinding the internal circle, if the grinding wheel width is too narrow, the grinding wheel is easy to wear, which is not conducive to improving production efficiency and reducing surface roughness; if the grinding wheel is too wide, the grinding force will increase, which is easy to cause the grinding wheel connecting shaft to bend and deform. Therefore, when grinding the inner hole, a suitable grinding wheel width should be selected. Within the range allowed by the connecting shaft rigidity and machine tool power, the grinding wheel width can be selected according to the workpiece length, see the table below.

Application of honing

Honing is more used to process various cylindrical holes, and the ratio of hole depth to hole diameter can reach 10 or more. Under certain conditions, it can also be used to process planes, outer cylindrical surfaces, spherical surfaces, tooth surfaces, etc.

Honing is mainly used for hole processing. It is an efficient processing method that can achieve high precision, high surface quality and long life of the workpiece surface. It can effectively improve the dimensional accuracy, shape accuracy and reduce the Ra value, but it cannot improve the position accuracy of the hole and other surfaces.

As a kind of finishing process, honing is widely used in the parts processing industry, especially in the automotive industry. It is mainly used for the processing of engine cylinder holes, crankshaft bearing holes, connecting rods, gear inner holes, air compressor cases, control valve bodies, sliding bearings and other step holes.

Characteristics of honing:

(1) Good surface quality. The surface of the workpiece after honing is a cross-net pattern, which is conducive to the storage of workpiece lubricating oil and the maintenance of oil film, and has a higher surface support rate (actual effective contact area ratio)

(2) The honing speed is low. Since the honing bar and the workpiece are in surface contact with the abrasive particles, the average grinding pressure is small, so the heat generated by the workpiece is small, and there is no thermal damage or deterioration layer on the workpiece surface.

(3) There is almost no "sand inclusion" and extruded layer phenomenon on the honing surface. Due to the high cutting pressure of the grinding wheel of the grinding machine, the grinding wheel and the workpiece are in line contact and have a high relative speed, which will generate high temperature in the local area, causing permanent damage (burn) to the surface structure of the workpiece; grinding sand inclusion is due to the relative movement of the workpiece, the grinding tool and the abrasive particles under a certain pressure. Under the action of pressure, the abrasive particles will be embedded in the surface of the workpiece through pressure and movement, thus causing sand inclusion. The abrasive particles embedded in the surface of the workpiece will scratch or wear the surface of the workpiece it matches, affecting the service life of the workpiece and the entire product. Sometimes it will even fall off, causing its components to "seize" and make the entire product unable to work normally.

Main differences between internal grinding and honing

Processing objects

Internal grinding is suitable for a variety of shapes, especially high-precision workpieces.

Honning focuses on high-quality internal hole processing, while taking other simple shapes into consideration.

Heat damage and grit problems

Internal grinding may cause surface damage and grit embedding due to high-speed processing.

Honning effectively avoids these problems through low-speed and gentle processing.

---EDITOR: Doris Hu,Alan Wang

---POST: Doris Hu