Processing of Bolt Head and Thread

How is the bolt head and thread processed? The head of bolt is formed by cold upsetting plastic processing. Compared with the cutting process, the metal fiber (metal wire) is continuous along the product shape without cutting off in the middle. Therefore, the strength of the product is improved, especially the mechanical properties are excellent. The cold heading forming process includes cutting and forming, single position single click, double-click cold heading and multi station automatic cold heading. Instead, an automatic cold heading machine is used to cut and upset (if necessary) the blank from the bar and wire rod. The blank must be reshaped before the cavity is extruded. The blank can be obtained by shaping. The blank does not need to be reshaped before upsetting, necking and forward extrusion. After the blank is cut, it is sent to the upsetting and shaping station. This station can improve the quality of the blank, reduce the forming force of the next station by 15-17%, and prolong the life of the die. Multiple necking can be used for manufacturing bolts.

The screw thread is usually processed by cold working. The thread blank within a certain diameter range is formed by the screw plate (rolling die) pressure through the screw plate (rolling die). The plastic streamline of the thread part can be obtained without cutting off, the strength is increased, the precision is high and the quality is uniform, so it is widely used. In order to make the outer diameter of the thread of the final product, the diameter of the thread blank needed is different, because it is limited by the factors such as thread accuracy, whether the material has coating or not. Rolling (rubbing) thread is a processing method that uses plastic deformation to form thread teeth. It uses a rolling die with the same pitch and profile as the processed thread, extrudes the cylindrical screw blank and makes the screw blank rotate at the same time, and finally transfers the tooth shape on the rolling die to the screw blank to form the thread. The common point of rolling (rubbing) thread processing is that the rolling speed is not too much, if too much, the efficiency is low, and the thread surface is easy to produce separation phenomenon or random thread phenomenon. On the contrary, if the number of revolutions is too small, the thread diameter is easy to be out of roundness, and the pressure in the initial rolling stage will increase abnormally, which will shorten the die life. Common defects of rolling thread: surface crack or scratch of thread part; random thread; out of roundness of thread part. If these defects occur in large numbers, they will be found in the processing stage. If the quantity is small and the production process does not notice these defects, it will flow to users and cause trouble. Therefore, the key problems of processing conditions should be summarized and should be controlled in the production process.

Bolt Head and Thread