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On Thread That Point, Do You Really Understand? ! (c)

Thread machining elements


1. Thread rolling forming process

(1) Forming principle of the rolling thread

Thread rolling is a process of plastic deformation, which is to squeeze the top of a thread rolling wheel or thread rolling plate into the blank material of parts at room temperature so that all materials at the bottom of the thread are squeezed to the top of thread tooth to form the thread on the part.

The rolling thread is processed according to the principle of invariable volume, so the accuracy of the thread is related to the size of the screw blank.

(2) Processing method

                             Thread cutting                                                                 Rolled thread


(3) Features:

•The thread formed by rolling does not chip and cut off the original metal fiber;

•High thread precision;

•The hardness and surface roughness of the threaded bottom is improved by cold extrusion hardening;

•At the same time, there is residual stress of compression, so the shear strength and tensile fatigue strength are increased by 30% - 100% compared with the cutting thread. However, after heat treatment, the hardening and compression residual stress of the cold working will disappear;

•Suitable for mass production;

•Thread rolling can be divided into rolling before heat treatment and heat treatment before rolling;

(it should be noted that when the hardness of the material is higher than hrc36, the raw material should be annealed (42CrMo). Some industries require heat treatment before thread rolling.)

  1. Thread rubbing process

(1) Rolling of thread rolling plate

Thread rolling is to fix one screw plate, and another movable screw plate moves back and forth to drive the product to move. The screw blank is plastically deformed by extrusion to form the required thread.

• Suitable for M1 ~ M30

• The precision is lower than that of the thread rolling wheel and the efficiency is high.


(2) Rolling with wire roller

Thread rolling is to use two corresponding screw rollers, relative positive rotation, using extrusion to produce plastic deformation of the product to form the required thread.

• Suitable for large size and long thread, suitable for a full thread of rod.

• The accuracy is higher.

• Production efficiency is relatively low.


(3) Planetary thread rolling dies

The arc thread plate does not move, screw roller rotates at high speed, extruding the screw blank

• Suitable for small sizes (machine screw type)

• High production efficiency


  1. Cutting method of internal thread tap

• The internal thread processing uses the tap to tap into the nut to cut the thread. Proper lubrication is required during tapping to improve cutting conditions.

• The accuracy of the nut's internal thread depends on screw tapping accuracy, material, speed, and lubrication.

• The enlarged thread of hot galvanizing refers to the increase in pitch diameter of the screw tap.


Post time: Dec-04-2020