Threading is a process that uses tools to make threads and uses cutting, turning, milling, grinding and other processes to process workpieces. It generally refers to the 

method of processing threads on workpieces with forming tools or grinding tools. The main ones include turning and milling. , tapping, threading, grinding, grinding and 

whirlwind cutting, etc.

1. Thread cutting

Generally refers to the method of processing threads on the workpiece using forming tools or abrasive tools, mainly including turning, milling, tapping, threading, grinding, 

grinding and whirlwind cutting. When turning, milling and grinding threads, every time the workpiece rotates, the transmission chain of the machine tool ensures that the 

turning tool, milling cutter or grinding wheel moves one lead accurately and evenly along the axial direction of the workpiece. When tapping or threading, the tool (tap or die)

and the workpiece perform relative rotational motion, and the previously formed thread groove guides the tool (or workpiece) to move axially.

For turning threads on a lathe, you can use a forming turning tool or a thread comb (see thread processing tools). Turning threads with a forming turning tool is a common 

method for single-piece and small-batch production of threaded workpieces due to its simple tool structure; turning threads with a thread comb tool has high production efficiency, but the tool structure is complex and is only suitable for medium and large batch production. Turning fine threaded workpieces with short threads. The pitch accuracy of trapezoidal thread turning with ordinary lathes can generally only reach level 8 to 9 (JB2886-81, the same below); when threads are processed on a specialized thread lathe, productivity or accuracy can be significantly improved.

2. Thread milling

Milling is performed on a thread milling machine with a disc or comb cutter. Disc milling cutters are mainly used for milling trapezoidal external threads on screw rods, 

worms and other workpieces. Comb-shaped milling cutters are used for milling internal and external ordinary threads and tapered threads. Multi-edged milling cutters are 

used for milling. The length of the working part is greater than the length of the thread being processed, so the workpiece only needs to be rotated 1.25~1.5 turns to 

process. Done, very productive. The pitch accuracy of thread milling can generally reach level 8~9, and the surface roughness is R5~0.63 microns. This method is suitable for 

batch production of thread work with general accuracy or for rough machining before grinding.

3. Thread grinding

Mainly used for processing precision threads of hardened workpieces on thread grinders.

Thread grinding is divided into two types: single-line grinding wheel and multi-line grinding wheel grinding according to the different cross-sectional shapes of the grinding 

wheel. The pitch accuracy that can be achieved by single-line grinding wheel grinding is 5~6, the surface roughness is R1.25~0.08 micron, and the grinding wheel dressing is 

more convenient.

This method is suitable for grinding precision screws, thread gauges, worms, small batches of threaded workpieces and relief grinding of precision hobs. Multi-line grinding 

wheel grinding is divided into two types: longitudinal grinding and plunge grinding. The width of the grinding wheel in the longitudinal grinding method is smaller than the 

length of the thread being ground. The grinding wheel can be moved longitudinally once or several times to grind the thread back to the final size. The width of the grinding 

wheel in the plunge grinding method is greater than the length of the thread to be ground. The grinding wheel cuts into the surface of the workpiece radially. The workpiece 

can be ground in about 1.25 turns. The productivity is high, but the accuracy is slightly lower, and the grinding wheel dressing is more complicated. The plunge grinding 

method is suitable for relieving large batches of taps and grinding certain fastening threads.

4. Thread grinding

Nut-type or screw-type thread grinding tools are made of soft materials such as cast iron. The parts of the processed threads on the workpiece that have pitch errors are 

ground in forward and reverse rotation to improve the pitch accuracy. Hardened internal threads are also usually ground to eliminate variations and improve accuracy.

5. Tapping and thread threading

Tapping is to use a certain torque to screw a tap into a pre-drilled bottom hole on the workpiece to process internal threads.

Threading is to use a die to cut external threads on the bar (or pipe) workpiece. The processing accuracy of tapping or threading depends on the accuracy of the tap or die. 

Although there are many methods for processing internal and external threads, small-diameter internal threads can only be processed with taps. Tapping and threading can 

be performed manually, or lathes, drill presses, tapping machines and threading machines can be used.

6. Thread rolling

A processing method that uses a forming rolling die to plastically deform the workpiece to obtain threads. Thread rolling is usually performed on a thread rolling machine. 

Thread rolling machine or automatic lathe equipped with automatic opening and closing thread rolling head, suitable for mass production of external threads of standard 

fasteners and other threaded connections.

The outer diameter of rolled threads generally does not exceed 25 mm, and the length does not exceed 100 mm. The thread accuracy can reach level 2 (GB197-63). The 

diameter of all blanks is roughly equal to the medium diameter of the thread being processed. Rolling generally cannot process internal threads, but for softer workpieces, 

grooveless extrusion taps can be used to cold-extrude internal threads (the maximum diameter can reach about 30 mm). The working principle is similar to tapping. The 

torque required for cold extrusion of internal threads is approximately twice that of tapping, and the processing accuracy and surface quality are slightly higher than those of 

tapping.

The advantages of thread rolling are:

1. Surface roughness is smaller than that of turning, milling and grinding;

2. The strength and hardness of the thread surface after rolling can be improved due to cold work hardening;

3. The material utilization rate is high; the productivity is doubled compared with cutting processing, and it is easy to realize automation;

4. The rolling die has a long life. However, rolling threads requires that the hardness of the workpiece material does not exceed HRC40;

5. The requirements for blank size accuracy are relatively high;

6. The precision and hardness requirements of rolling molds are also high, and it is difficult to manufacture molds;

7. It is not suitable for rolling threads with asymmetrical tooth shapes.

According to different rolling dies, thread rolling can be divided into two types: thread rolling and thread rolling.

Rubbing:

Two thread-shaped thread plates are arranged relative to each other with a staggered pitch of 1/2, the static plate is fixed, and the moving plate makes a reciprocating linear 

motion parallel to the static plate. When the workpiece is fed between the two plates, the moving plate advances and rubs the workpiece, causing its surface to plastically 

deform to form threads.

Thread rolling:

There are three types of radial thread rolling, tangential thread rolling and rolling head thread rolling. Radial thread rolling: 2 (or 3) thread rolling wheels are installed on 

parallel axes. The workpiece is placed on the support between the two wheels, and the two wheels rotate in the same direction and at a constant speed.

One of the rounds also performs radial feed motion. The workpiece rotates driven by the rolling wheel, and the surface is radially extruded to form threads. For some screws 

that do not require high precision, similar methods can also be used to roll forming. Tangential thread rolling: Also known as planetary thread rolling, the rolling tool consists 

of a rotating central rolling wheel and three fixed arc-shaped wire plates.

During thread rolling, the workpiece can be fed continuously, so the productivity is higher than that of thread rolling and radial thread rolling. Thread rolling head: It is 

performed on an automatic lathe and is generally used to process short threads on the workpiece. The rolling head has 3 to 4 rolling wheels evenly distributed around the 

periphery of the workpiece.

During thread rolling, the workpiece rotates and the rolling head feeds axially to roll the workpiece out of the thread.