Cold heading roller is a method of obtaining a roller blank by using a mold to force plastic flow in the metal material section at room temperature, filling the space formed by the concave mold and punch. The mechanical performance of rollers has been improved, and the plastic deformation generated causes the material to undergo cold work hardening. The metal flow line is not cut off, and the original defects of the metal will be compacted.
This production method can save raw materials; High productivity, generally with a high degree of automation for cold heading machines, ranging from 70 to 100 pieces per minute; The size and shape of the roller are accurate, and the surface roughness value is low. The accuracy of the mold and machine tool can ensure the size and shape accuracy of the roller. In cold heading, the metal surface is flattened by the smooth surface of the mold under high pressure, resulting in low surface roughness value.
When cold heading conical rollers, before forming, except for the chamfered area at the small end of the roller and the central part of the column, which are subjected to three-dimensional compressive stress, most of the matrix is subjected to uniaxial compressive stress and two-dimensional tensile stress. The closer the large end of the roller is, the greater the tensile stress, which will cause intergranular deformation of the metal and reduce its plasticity. Therefore, when the shape and size design of the blank or mold is unreasonable, the material is poor, and the process is improper, the cold heading roller often cracks at the large end chamfer.
In addition, the friction between the blank and the mold in the cold heading roller, the uneven internal structure of the material, and the unreasonable size and shape of the mold can also cause additional stress inside the roller, reduce metal plasticity, increase metal deformation resistance, and generate residual stress inside the roller.
This additional stress can cause changes in the size and shape of the rollers and reduce process performance. Especially the additional stress caused by external friction is detrimental to the quality of rollers and processing technology. It mainly occurs in the axial area of the small end chamfer of the rollers, reducing the internal and external quality at the chamfer, increasing mold wear and reducing mold life. The main factors affecting friction include material properties, mold structure shape, surface quality, and lubrication effect.
Due to the fact that cold heading rollers are carried out at room temperature, the deformation resistance is high, especially when the material section is filled with mold space to form the roller blank, the entire roller body is basically subjected to three-dimensional compressive stress. At this time, the deformation resistance is extremely high, and the larger the roller, the greater the deformation resistance. In addition, when the deformation degree of the roller during cold heading exceeds the allowable deformation degree of the material itself, cracks will form on the circumferential surface of the roller.
2023 New Week WBM Product Recommendation:
Steel Ball Cold Heading Tools：
n the steel ball cold heading process, after barstocks are cut into column-shaped blanks, two ends of the column shaped blanks are rubbed and cut into inversed angel or round angle shapes, and then the blanks are transferred to a cold heading mechanism to be headed into steel ball rough cast; a blank rubbing and cutting mechanism is additionally arranged on the corresponding cold heading machine. The quality and eligibility rate of the steel ball rough cast can be enhanced and the manufacturing cost thereof can be reduced. Furthermore, as the shapes of the blanks entering the cold forging mechanism are regular, the stress born by the cold heading mechanism is equal in the punching process, thus the service life of cold heading dies is prolonged.
