7 Thread Processing Methods

1. Thread cutting

Generally, it refers to machining thread on the workpiece with a forming or grinding tool, mainly including turning, milling, tapping and threading grinding, grinding, whirlwind cutting, etc. When turning, milling, and grinding the thread, the transmission chain of the machine tool ensures that the turning tool, milling cutter, or grinding wheel moves a lead accurately and evenly along the axial direction of the workpiece every rotation of the workpiece. When tapping or threading, the tool (tap or die) rotates relative to the workpiece, and the first formed thread groove guides the tool (or workpiece) to move axially.

 

2. Thread turning

Carding tools can be used to turn or thread the thread on the lathe (see thread processing tool). Turning thread with forming turning tool is a standard method for single piece and small batch production of thread workpiece due to its simple structure; turning thread with thread combing tool has high production efficiency, but its structure is complex, so it is only suitable for turning short thread workpiece with fine teeth in medium and large batch production. The pitch accuracy of turning trapezoidal thread with a general lathe can only reach 8-9 levels (jb2886-81, the same below); the productivity or accuracy can be significantly improved when machining thread on a specialized thread lathe. CNC machining part

 

3. Thread milling

The disc milling cutter or comb milling cutter is used for milling on the thread milling machine. The disc milling cutter is used primarily for milling trapezoid external threads of screw rods, worms, and other workpieces.A combo milling cutter mill internal and external common thread and taper thread. Because its working part is longer than the thread length to be processed by a multi-edge milling cutter, the workpiece can be processed only by rotating 1.25-1.5 revolutions, with high productivity. The pitch accuracy of thread milling can reach 8-9 grades, and the surface roughness is r5-0.63 μ M. This method is suitable for mass production of general precision thread workpieces or rough machining before grindingCNCc milling part

 

4. Thread grinding

It is mainly used to process the precision thread of the hardened workpiece on the thread grinder. According to the different cross-section shapes of the grinding wheel, it can be divided into two kinds: single-line grinding wheel and multi-line grinding wheel. The pitch accuracy of the single-line grinding wheel is 5-6 grades, and the surface roughness is r1.25-0.08 μ m, so it is convenient to finish the grinding wheel. This method is suitable for grinding precision screws, thread gauges, worms, small batches of thread workpieces, and precision hobTwotwo kinds of grinding meth existed: longitudinal grinding and cut-in grinding. The width of the grinding wheel with the longitudinal grinding method is less than the length of the thread to be ground, and the thread can be ground to the final size after the grinding wheel moves longitudinally once or several times. The width of the grinding wheel of the cut-in grinding method is larger than the length of the thread to be ground. The grinding wheel cuts into the surface of the workpiece radially, and the workpiece can be ground after turning about 1.25 revolutions. The productivity is higher, but the precision is slightly lower, and the dressing of the grinding wheel is more complex. The cut-in grinding method is suitable for shoveling large quantities of taps and grinding some fastening threads. plastic part

 

5. Thread grinding

The nut-type or screw-type thread-lapping tool is made of soft materials such as cast iron. The parts of the processed thread on the workpiece with pitch error are ground by forward and reverse rotation to improve pitch accuracy. The hardened internal thread is usually eliminated by grinding to improve the accuracy.

 

6. Tapping and threading

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

Threading is to cut the external thread on the bar (or tube) workpiece with a die. The machining accuracy of tapping or threading depends on the accuracy of the tap or die. Although there are many ways to process internal and external threads, small-diameter internal threads can only be processed by taps. Tapping and threading can be done by hand or by lathe, drilling machine, tapping machine, and threading machine.

 

7. Thread rolling

The processing method of forming and rolling a die to produce plastic deformation of the workpiece to obtain thread rolling is generally carried out on the thread rolling machine or the automatic lathe attached with an automatic opening and closing thread rolling head, which is suitable for mass production of external thread pattern of standard fasteners and other threaded joints. Generally, the outer diameter of the rolling thread is not more than 25 mm, the length is not more than 100 mm, and the thread accuracy can reach level 2 (gb197-63). The diameter of the blank used is roughly equal to the pitch diameter of the thread to be processed. Generally, the internal thread can not be processed by rolling. Still, for the soft workpiece, the cold extrusion internal thread can be used without a slot extrusion tap (the maximum diameter can reach about 30mm), and the working principle is similar to tapping. The torque required for cold extrusion of internal thread is about 1 times larger than that for tapping, and the machining accuracy and surface quality are slightly higher than that for tapping.

The advantages of thread rolling are as follows:

① the surface roughness is less than turning, milling, and grinding;

② the surface of thread after rolling can improve the strength and hardness due to cold work hardening;

③ the material utilization rate is high;

④ the productivity is doubled compared with the cutting process, and it is easy to realize automation;

⑤ the service life of the rolling die is very long. However, the hardness of the workpiece material is not more than hrc40, the accuracy of the blank size is required to be high, and the accuracy and hardness of the rolling die are also high, so it is difficult to manufacture the die. It is not suitable for threads with an asymmetric rolling profile.

 

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

 

Thread rolling: two thread rolling plates with thread profiles are staggered and arranged with 1 / 2 pitch. The static plate is fixed, and the moving plate moves in a reciprocating straight line parallel to the static plate. When the workpiece is sent between the two plates, the moving plate moves forward to rub and press the workpiece, making its surface plastic deformation and forming a thread. Mo Mo Q group 373600976

 

There are three kinds of rolling: radial, tangential,g, and head rolling.

 

① Radial thread rolling: two (or three) thread-shaped thread rolling wheels are installed on mutually parallel shafts, the workpiece is placed on the support between the two wheels, and the two wheels rotate at the same speed in the same direction, one of which also performs radial feed motion. The rolling wheel drives the workpiece to rotate, and the surface is extruded radially to form a thread. A similar rolling method can also be used for some screws with low precision requirements.

 

②tangential thread rolling: also known as planetary thread rolling. The rolling tool comprises a rotating central thread rolling wheel and three fixed arc-shaped thread plates. The workpiece can be fed continuously during rolling, so the productivity is higher than that of thread rubbing and radial rolling.

 

③ Thread rolling of thread rolling head: it is carried out on the automatic lathe and is generally used to process the short thread on the workpiece. There are 3-4 rolling rollers distributed uniformly around the workpiece. When rolling, the workpiece rotates, and the rolling head feeds axially to roll the workpiece out of the thread.