It is a direct machining method to use rolling tools to improve the finish of metal surface. The coarseness and shortness of metal workpieces has always been an important process for many metal workpieces, such as hydraulic cylinder, Jack, automobile hub, etc. due to long-term work collision, high finish can greatly improve the collision strength of products and improve the direct service life of products. It has also been stated in mechanics that the smoother the product, the faster the mechanical collision and rotation, and the more labor-saving. Therefore, how to improve the surface roughness has always been our careful research topic.

Rolling tools are widely used in machining. If turning tools, boring tools, milling tools, etc., they are also suitable for a variety of different machine tools, such as lathes, drilling machines, boring machines, etc. The cutting tool itself is mostly machined by cutting, so as to meet the size and process requirements of the product workpiece. Today, we will introduce a special machining tool, which breaks the original cutting mode and uses the principle of extrusion to achieve the plastic deformation of metal products. The purpose of use is mostly to improve the surface finish and the surface hardness of metal workpieces. Related reading: use and structure of inner hole extrusion knife

The hydraulic cylinder is one of the most important components of the hydraulic knife support, The traditional processing methods are: blanking → quenching and tempering → turning datum plane → rough boring → turning (repairing datum plane) → fine boring → fine turning → (finishing datum plane) → honing (divided into rough honing and fine honing). The process has the following disadvantages: ⑴ the process route is long and takes a long time; ⑵ because the honing head is seriously worn in honing, the honing head needs to be replaced continuously, which increases the honing cost; ⑶ honing pollution is serious. Because aviation kerosene needs to be used for cooling and lubrication during honing, it causes air pollution and seriously affects the health of workers Good health. The route of boring rolling composite process widely used by the factory is: blanking → quenching and tempering → turning (datum) → rough boring → turning (datum plane) → boring and rolling. After the boring and rolling composite process replaces the push boring and honing, the working efficiency is greatly improved, the process route is greatly shortened and the cost is reduced. After the boring and rolling composite process is adopted, the hardness and strength of the inner hole surface of the cylinder block are improved, the surface roughness is reduced and the service life of the cylinder block is prolonged. This process can not only ensure the quality, but also significantly improve the machining efficiency The utility model has the advantages of high efficiency and low processing cost.

1. Machining principle of rolling cutter for hydraulic cylinder

Rolling cutter machining is a common surface strengthening method of metal materials. It applies a certain pressure to the workpiece surface through the rolling head. The rolling head rolls the inner hole wall of the hydraulic cylinder radially with a roller, the workpiece rotates, and the rolling head feeds along the axial direction of the workpiece. When the compressive stress on the surface of the inner hole exceeds the elastic limit, dislocation slip and fracture occur between metal grains, and the metal specific volume increases, resulting in plastic deformation. It not only flattens the micro unevenness of the inner hole surface, but also produces cold work hardening on the surface after rolling, which improves the surface hardness and surface quality. The rolling head is installed on the boring bar, and the boring bar is installed on the tool carrier. The rolling processing of the inner hole of the hydraulic cylinder is realized by moving the tool carrier along the axis direction.

2. Changes of physical and mechanical properties of machined surface

Through the inner hole surface of the hydraulic cylinder of the rolling head, the machined surface layer will produce cold work hardening due to plastic deformation; The change of metallographic structure will produce residual compressive stress on the surface. The cold work hardening of the machined surface layer of the workpiece reduces the elastic and plastic deformation of the contact part of the friction pair, so as to improve the wear resistance.

(1) cold work hardening of surface layer

In rolling tool engineering, if the plastic deformation produced by machining the surface layer causes shear slip between crystals, the lattice will be seriously distorted, and the grains will be elongated, broken and fibrotic, resulting in the uniform improvement of the strength and hardness of the surface layer, which is the phenomenon of cold work hardening. The cold work hardening index of the machined surface is mainly expressed by the depth h of the hardened layer, the microhardness h of the surface layer and the hardening degree H / H0. Generally, the greater the degree of hardening, the greater the depth of the hardened layer.

The degree of hardening of the surface layer depends on the rolling pressure and rolling speed that produce plastic deformation. The greater the rolling pressure, the greater the plastic deformation and the greater the degree of hardening. The greater the rolling speed, the less sufficient the plastic deformation. The degree of hardening produced is reduced accordingly. The greater the wear of the rolling head, the greater the hardness and depth of the cold work hardening layer. When the rolling speed increases, the hardness and depth of the surface cold work hardening layer decrease. This is because: on the one hand, the increase of rolling speed will increase the temperature, which is conducive to the recovery of cold work hardening; On the other hand, the increase of rolling speed and the short contact time between the rolling head and the workpiece will also reduce the plastic deformation. When the feed rate increases, the rolling pressure increases and the degree of plastic deformation increases, so the cold work hardening phenomenon of the surface layer also increases. The lower the hardness and the greater the plasticity of the processed material, the more serious the cold work hardening of the surface layer after rolling.

⑵ metallographic structure of surface layer

With the rolling process, the metal shape will change continuously, but its volume remains unchanged. Because the metal constituting the oil cylinder is of polycrystalline structure, its plastic deformation is the result of comprehensive plastic deformation of many single grains. When polycrystals are subjected to external force, the deformation is first carried out in those grains with the most favorable orientation. In these grains, dislocations will move along the most favorable slip surface, stop when they move to the grain boundary, and generally can not directly pass through the grain boundary. Whether dislocations can cross grain boundaries mainly depends on the properties of grain boundary layers and the orientation of adjacent grains. The finer the grain size of the metal, the larger the grain boundary area, and the more grains with different orientations around each grain, so the deformation resistance is large and the plasticity is good. From the point of view of general use, fine grain materials have high strength and good plasticity. Therefore, fine grain structure should be obtained as much as possible in production. The structure of the rolled layer becomes compact, the grain becomes finer, and the grain shape extends along the direction of the maximum deformation. Through rolling, the internal microstructure and grain of the metal are refined, and the strength of the rolled metal surface is improved.

(3) residual stress of surface layer

The surface layer of parts obtained by various machining methods will have large or small tensile or compressive residual stresses. In the process of cold plastic deformation, the residual stress of the machined surface layer will be generated if the metallographic structure of the surface layer changes during the machining process, and the metal specific gravity decreases and the specific volume increases after the cold plastic deformation of the surface layer, resulting in the change of the stress state of the surface layer. After cold plastic deformation, some atoms are always moved from their stable and balanced lattice position. It turns out that the atoms in the crystal lattice are arranged very closely and plastic deformation occurs in cold state