The processing method of forming Cylindrical Dies produces plastic deformation of the workpiece to obtain threads. Thread rolling is generally carried out on a thread rolling machine or an automatic lathe equipped with an automatic opening and closing thread rolling head. It is suitable for mass-producing external threads of standard fasteners and other threaded connections. The outer diameter of the rolled thread generally does not exceed 25mm, and the length does not exceed 100mm. The thread accuracy can reach level 2 (GB197-63), and the diameter of the blank used is roughly equal to the pitch diameter of the processed thread. Rolling generally cannot process internal threads, but for workpieces with softer materials, slotless extrusion taps can be used to cold extrude internal threads (with a maximum diameter of about 30 millimeters), and the working principle is similar to tapping. The torque required for cold extrusion of internal threads is approximately twice that of tapping, and the machining accuracy and surface quality are slightly higher than tapping.
The advantages of Cylindrical Dies are:
- The surface roughness is less than that of turning, milling, and grinding;
- The surface of the thread after rolling can improve strength and hardness due to cold work hardening;
- High material utilization rate;
- Productivity increases exponentially compared to cutting and is easy to achieve automation;
- The service life of rolling molds is very long. However, rolling threads require that the hardness of the workpiece material should not exceed HRC40; High requirements for the accuracy of blank dimensions; The precision and hardness requirements for rolling molds are also high, making it difficult to manufacture molds; they are not suitable for rolling threads with asymmetric tooth shape.
According to different rolling molds, thread rolling can be divided into two types:
There are three types of thread rolling: radial thread rolling, tangential thread rolling, and rolling head thread rolling Radial thread rolling: Two (or three) thread-shaped thread rolling wheels are installed on parallel shafts, and the workpiece is placed on a support between the two wheels. The two wheels rotate at the same speed in the same direction, and one wheel also performs radial feed motion. The workpiece rotates under the drive of the thread rolling wheel, and the surface is radially squeezed to form a thread. For certain screws with low precision requirements, similar methods can also be used for rolling forming.