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Various thread processing methods

1. Thread cutting

Generally refers to the method of machining threads on the workpiece with forming tools or abrasives, mainly turning, milling, tapping, threading, 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 a lead accurately and evenly along the axial direction of the workpiece for each revolution of the workpiece.When tapping or threading, the tool (tap or tooth) rotates relative to the workpiece, and the threaded groove formed first guides the tool (or workpiece) to move axially.

For turning threads on a lathe, forming turning tools or thread combing tools can be used (see thread processing tools).Turning threads with a forming turning tool, due to the simple structure of the tool, is a common method for single-piece and small-batch production of threaded workpieces; 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-scale production of short threaded workpieces with fine teeth.The pitch accuracy of turning trapezoidal threads on ordinary lathes can generally only reach 8~9 levels (JB2886-81, the same below); processing threads on specialized thread lathes, productivity or accuracy can be significantly improved.

2. Thread milling

Use a disc milling cutter or comb milling cutter for milling on a thread milling machine.Disc milling cutters are mainly used for milling trapezoidal external threads on workpieces such as screws and worms.Comb milling cutters are used for milling internal and external ordinary threads and tapered threads, and multi-edged milling cutters are used for milling. The length of the working part is greater than the length of the thread to be processed, so the workpiece only needs to be rotated 1.25~1.5 revolutions to complete the processing, and the productivity is very high.The pitch accuracy of thread milling can generally reach 8~9 levels, and the surface roughness is R5~0.63 microns.This method is suitable for batch production of thread work with general accuracy or roughing before grinding.

3. Thread grinding

It is mainly used for machining precision threads of hardened workpieces on thread grinders.

Thread grinding is divided into two types of single-line grinding wheels and multi-line grinding wheels according to the different cross-section shapes of the grinding wheels.The pitch accuracy that can be achieved by single-line grinding wheel grinding is 5~6 levels, and the surface roughness is R1.25~0.08 microns, which makes grinding wheel dressing more convenient.

This method is suitable for grinding precision screws, thread gauges, worms, small batches of threaded workpieces and shoveling precision hob.Multi-line grinding wheel grinding is divided into two types: longitudinal grinding method and cut-in grinding method.The width of the grinding wheel of the longitudinal grinding method is less than the length of the thread being ground, and the grinding wheel can be moved vertically once or several times to grind the thread to the final size.The width of the grinding wheel of the cut-in grinding method is greater than the length of the thread being ground. The grinding wheel cuts radially into the surface of the workpiece, and the workpiece can be ground at about 1.25 revolutions. The productivity is higher, but the accuracy is slightly lower, and the grinding wheel trimming is more complicated.The cut-in grinding method is suitable for shoveling large batches of taps and grinding certain threads for fastening.

4. Thread grinding

Nut-type or screw-type thread grinding tools are made of softer materials such as cast iron, and the parts of the processed thread with pitch errors on the workpiece are rotated and ground forward and reverse to improve the pitch accuracy.Hardened internal threads are usually ground to eliminate changes and improve accuracy.

5. Tapping and threading

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

Threading is the use of plate teeth to cut out external threads on the bar (or pipe) workpiece.The machining accuracy of tapping or threading depends on the accuracy of the taps or teeth.Although there are many methods for processing internal and external threads, small-diameter internal threads can only be processed by taps.Tapping and threading can be operated manually, as well as lathes, drilling machines, tapping machines and threading machines.

6. Thread rolling

A processing method for plastic deformation of the workpiece by forming and rolling a mold to obtain a thread.Thread rolling is generally in a wire rolling machine.The wire rubbing machine may be carried out on an automatic lathe with an automatic opening and closing thread rolling head, which is suitable for mass production of standard fasteners and other external threads of threaded joints.

The outer diameter of the rolling thread generally does not exceed 25 mm, the length is not greater than 100 mm, and the thread accuracy can reach Level 2 (GB197-63). The diameter of all blanks is roughly equal to the middle diameter of the thread being processed.Rolling generally cannot process internal threads, but for workpieces with softer materials, slotted extrusion taps can be used to cold squeeze 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 about 1 times larger than that of tapping, and the machining accuracy and surface quality are slightly higher than that of tapping.

 

External thread rolling processing!

The advantages of thread rolling are:

1. The surface roughness is less than that of turning, milling and grinding;

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

3. High material utilization rate; productivity is exponentially higher than that of cutting, and it is easy to realize automation.;

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

5. High requirements for the dimensional accuracy of the blank;

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

7. It is not suitable for rolling threads with asymmetric tooth shape.

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

Rub silk

The two threaded toothed wire rubbing plates are staggered and arranged at a pitch of 1/2. The static plate is fixed, and the moving plate moves in 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 plasticize and deform into a thread.

Rolling wire

There are three types of radial wire rolling, tangential wire rolling and rolling head wire rolling.Radial wire rolling: 2 (or 3) threaded toothed wire rolling wheels are mounted on shafts parallel to each other, 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 round also made radial feed movement.The workpiece rotates under the drive of the wire roller, and the surface is radially squeezed to form a thread.For some screws with low precision requirements, a similar method can be used for rolling and forming.Tangential wire rolling: Also known as planetary wire rolling, the rolling tool consists of a rotating central wire rolling wheel and 3 fixed curved wire plates.

When rolling wire, the workpiece can be continuously fed, so the productivity is higher than that of rubbing wire and radial rolling wire.Wire rolling head wire rolling: Carried out on an automatic lathe, generally used to process short threads on workpieces.The rolling head has 3 to 4 wire rolling wheels that are distributed on the periphery of the workpiece.

When rolling the wire, the workpiece rotates, and the rolling head feeds axially, rolling the workpiece out of the thread.

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