Shuifu Hanyang Machinery Technology Co., Ltd. takes you to understand the main advantages of cold heading technology
Cold heading is carried out under normal temperature conditions. Cold heading can improve the mechanical properties of metal parts.
2. Cold heading technology can improve material utilization efficiency. Taking cold heading bolts as an example, the new process of "concave hole" hexagonal head bolts can achieve a material utilization rate of over 99%. Except for the loss of material heads and tails, it has achieved complete zero cutting processing. If cutting is used, the material utilization rate is only 40%. The material utilization rate of cold heading nuts can also reach about 80%, while the material utilization rate of cutting nuts is only 54%.
3. Cold heading technology can greatly improve productivity. Compared with the original cutting process, the productivity of cold heading nuts is increased by about 25-30 times.
4. Due to the use of multi station cold heading machines, each process can be processed simultaneously on one machine tool, thereby reducing equipment investment, minimizing the production space occupied by equipment, reducing the transportation of semi-finished products between processes, especially reducing the labor intensity of workers and improving working conditions.
5. Cold heading technology can improve the surface smoothness of products and ensure product accuracy. The general smoothness can reach V5, and special requirements can reach V6. For mass production of bolts, nuts, etc., their accuracy can be fully guaranteed.
Cold heading technology is increasingly widely used in mechanical manufacturing, especially in the production of standard fasteners, due to its high productivity, good product quality, greatly reduced material consumption, lowered production costs, and improved working conditions. Among them, the most representative products produced by multi station cold heading machines are bolts, screws, and nuts.
Requirements for raw materials for cold heading
1. Require high plasticity and low hardness
Due to the presence of tangential tensile stress on the side surface of the blank during cold heading, longitudinal surface cracks are prone to occur. Therefore, the cold heading process should use specialized materials with high plasticity and low hardness. For steel, a surface hardness of 75-85HRB is generally required.
2. High surface quality requirements
Due to the fact that cold heading technology is mainly used for the production of standard parts, these products generally do not undergo cutting processing, especially for standard parts such as screws and bolts. The deformation of the rod during cold heading is minimal, and the original surface of the blank is still maintained. Therefore, it is necessary to require that the raw materials used for cold heading have a low surface roughness, and no surface defects such as scratches, pitting, rust, etc. are allowed.
3. High dimensional accuracy requirements
Method for expressing the degree of cold heading deformation and allowable degree of deformation
During cold heading processing, due to the work hardening effect of the metal, the greater the degree of cold heading deformation, the greater the deformation resistance. When the degree of cold heading deformation exceeds the maximum allowable deformation of the metal material itself, cracks will form on the side surface of the part; When the unit pressure of cold heading exceeds the allowable pressure of the mold, it will cause damage to the mold. Therefore, for various sizes, shapes, and cold heading materials, a reasonable degree of deformation should be selected.
Determination of cold heading frequency
When the degree of cold heading deformation exceeds the above data, in order to prevent cracking, intermediate annealing should be carried out to eliminate the hardening phenomenon caused by cold heading deformation, and then continue the forging. In addition to considering the maximum allowable deformation degree, intermediate annealing must also be considered for cold heading products with excessively complex geometric shapes. If intermediate annealing process is used, cold heading can only be carried out in sequence.
In addition to being affected by the degree of deformation mentioned above, the cold heading process must also consider the bending of the material during forging. The general practice is to determine the number of upsetting times based on the ratio of the free height h of the wire without clamping to its diameter dm.
Calculation of billet length during cold heading
The length of the billet during cold heading can be determined based on the principle of constant volume, that is, the volume of the billet before plastic deformation is equal to the volume of the part after cold heading. If edge cutting or cutting is required after cold heading, the volume of the billet should also be added with the corresponding cutting amount.