The plastic processing method of producing bolts or screws with thread roll die (screw die) is called thread roll rolling (screw die). The general production mode is as follows: the screw pitch of the screw die cavity of the screw die is the same as that of the product, the two rub make the blank die be arranged relative to each other, through the relative movement of the screw die or the roller push to squeeze the blank in the forming area, the surface metal deforms plastic in the process of rotation, gradually fill the screw die cavity, and the shape is male thread. There are three types of rolling die: rectangular (rolling sheet), cylindrical and combined
The blank is processed at room temperature, and the wire rolling is the traditional way, which is suitable for the thread with small diameter. The movable wire drawing board moves in a reciprocating straight line relative to the fixed wire drawing board, and the thread is formed when the mould chamber is placed on the side and rubbed for 5-6 times. The advantages of this method are that it is more convenient to feed and die, with low efficiency (the output of small diameter thread is about 150 pieces /min, the direct disadvantage is that the return trip of movable die is empty, and the output of larger bolts with diameter no more than 25mm is 30~40 pieces /min). The combined screwing die shown in the table below is used to make threads between the rotary cylindrical die and the fixed combined die, which can avoid the empty travel and improve the production efficiency. When producing threads with a diameter of 36mm, the output is up to 400~600 pieces /min.