Classification and characteristics of thread rolling

Thread rolling is mainly divided into two categories based on the dies used: thread rolling and thread turning. Depending on the feeding method, thread turning can be further subdivided into several forms. In axial thread rolling, the rollers move along the workpiece axis to form the thread. Tangential thread rolling, also known as planetary thread rolling, involves the rollers cutting into the workpiece from the side. Radial thread rolling uses two or three rollers to form the thread in a single rotation. There is also head rolling, commonly found on automatic lathes, which uses multiple evenly distributed rolling wheels.

Thread rolling has several advantages. Its surface roughness is superior to turning, milling, and grinding. The work hardening produced by rolling increases the strength and hardness of the thread. This process has high material utilization, high production efficiency, and is easily automated. Furthermore, the rolling dies have a long lifespan.

Thread rolling also has certain limitations or specific requirements. The hardness of the workpiece material should generally not exceed HRC40, and high dimensional accuracy of the blank is required. High precision and hardness requirements are placed on the rolling dies, making manufacturing difficult, and it is generally unsuitable for rolling threads with asymmetrical tooth profiles. Machining parameters must be strictly controlled. Too many rolling revolutions can lead to low efficiency, thread separation, or cross-threading, while too few revolutions can result in out-of-round threads or shortened die life. Common machining defects include surface cracks, scratches, cross-threading, and partial out-of-roundness of the threads.