Thread processing method

Mon Jul 04 14:03:15 CST 2022

A wide variety of thread machining methods and tools, suitable for different parts, thread shape and pitch. Each threading method and tool has its own advantages under certain conditions, so let's take a look at the various threading methods and advantages

1. Thread cutting

Generally refers to the method of processing thread on the workpiece with forming tool or abrasive tool, mainly including turning, milling, tapping sleeve wire grinding, grinding and cyclone cutting. When turning, milling, and grinding threads, the transmission chain of the machine tool ensures that the turning tool, milling cutter, or grinding wheel moves accurately and evenly along the axial direction of the workpiece with each turn of the workpiece. When tapping or threading, the tool (tap or die) rotates relative to the workpiece, and the thread groove formed first guides the tool (or workpiece) to move in the axial direction.

2. Thread turning

Turning thread on the lathe can be used to form turning tool or thread comb insert with forming turning tool turning thread, because the tool structure is simple, is a common method of single and small batch production thread workpiece; With thread comb cutter turning thread, the production efficiency is high, but the tool structure is complex, only suitable for turning fine teeth in mass production of short thread workpiece. The pitch precision of ordinary lathe turning trapezoidal thread can only reach 8 ~ 9 level generally, and the productivity or precision can be significantly improved when machining thread on specialized thread lathe.

3.Thread milling

Milling is done with disc or comb milling cutter on thread milling machine. Disk milling cutter is mainly used for milling screw, worm and other workpiece trapezoidal external thread. Comb type milling cutter is used for milling internal and external common thread and conical thread, because it is milling with multi-edge milling cutter, the length of its working part is greater than the length of the thread being processed, so the workpiece only needs to rotate 1.25 ~ 1.5 turn can be processed, the productivity is very high. The pitch accuracy of thread milling is generally 8 ~ 9, and the surface roughness is R5 ~ 0.63 micron. This method is suitable for batch production of thread workpiece with average accuracy or rough machining before grinding.

4.Thread grinding

It is mainly used for machining precision thread of hardened workpiece on thread grinder. It can be divided into single grinding wheel and multi-grinding wheel according to different shape of grinding wheel section.

The pitch accuracy of single grinding wheel is 5 ~ 6, the surface roughness is R1.25 ~ 0.08 micron, and the grinding wheel dressing is convenient. This method is suitable for grinding precision screw, thread gauge, worm, small batch thread workpiece and precision hob.

Multi - line grinding wheel grinding is divided into longitudinal grinding method and cut - in grinding method. The width of the grinding wheel in longitudinal grinding method is less than the length of the thread to be ground, and the thread can be ground to the final size by moving the grinding wheel longitudinal once or several times. The width of the grinding wheel is larger than the length of the grinding thread. The grinding wheel cuts into the surface of the workpiece in a radial way, and the workpiece can be ground after about 1.25 revolution. The productivity is higher, but the accuracy is slightly lower, and the dressing of grinding wheel is more complicated. Plunge grinding is suitable for grinding taps with large batch and some fastening threads.

5. Thread grinding

Using soft materials such as cast iron to make nut type or screw type thread grinding tools, on the workpiece has been processed thread pitch error parts for positive and negative rotation grinding, in order to improve pitch accuracy. Hardened internal threads are also usually ground to eliminate deformation and improve accuracy.

6. Tapping and covering

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

Set wire is to use die in bar material (or pipe material) on the workpiece to cut out the external thread. The precision of tapping or threading depends on the precision of tap or die. Although there are many ways to process internal and external threads, small diameter internal threads can only rely on tap processing. Tapping and threading can be done by hand, as well as lathes, drilling machines, tapping and threading machines.

7. Screw rolling

Thread rolling is generally carried out on the thread rolling machine or on the automatic lathe attached with the automatic opening and closing thread rolling head. It is suitable for mass production of standard fasteners and external threads of other thread joints. The outer diameter of the rolling thread is generally not more than 25 mm, the length is not more than 100 mm, the thread accuracy can reach 2 (GB197-63), the diameter of the blank is roughly equal to the middle diameter of the thread being processed. Rolling generally can not process the internal thread, but on the material of the soft workpiece can be used no groove extrusion tap cold extrusion internal thread (maximum diameter up to 30 mm or so), the working principle is similar to tapping. Cold extrusion internal thread required torsion is about 1 times larger than tapping, the processing accuracy and surface quality is slightly higher than tapping

The advantages of thread rolling are:
(1)The surface roughness is less than turning tool, milling and grinding;
(2)After rolling, the thread surface can improve strength and hardness due to cold hardening;
(3) High material utilization rate;
(4) productivity doubled than cutting, and easy to achieve automation;
(5)The rolling die has a long life.