1, thread cutting
Generally refers to the method of machining threads on a workpiece by using a forming tool or an abrasive tool, mainly including turning, milling, tapping, threading, Grinding, grinding, and cyclone cutting. When turning, milling and grinding threads, the machine's drive chain ensures that the turning tool, milling cutter or Grinding Wheel can accurately and evenly move a lead along the workpiece axis. During tapping or threading, the tool (taper or die) rotates relative to the workpiece and guides the tool (or workpiece) for axial movement by the previously formed threaded groove.
For turning threads on a lathe, a forming turning tool or a threaded comb can be used (see threading tool). Turning the thread with a forming turning tool, because of the simple structure of the tool, it is a common method for producing threaded workpieces in single and small batches; threading with a threaded comb has high production efficiency, but the tool structure is complex and suitable only for medium and large batch production. Short threaded workpiece for turning fine teeth. The precision of the pitch of the trapezoidal thread for general lathe turning can only reach 8~9 grades (JB2886-81, the same below); the threading on the special threading lathe can significantly improve the productivity or precision.
2, thread milling
Milling with a disc cutter or comb cutter on a thread milling machine. Disc cutters are mainly used for milling trapezoidal external threads on workpieces such as screw and worm. Comb milling cutter is used for milling. Because it uses ordinary thread and taper thread, multi-blade milling cutter, the length of its working part is larger than the length of the thread to be machined, so the workpiece can be processed only by rotating 1.25~1.5 turns. Completed, high productivity. The pitch precision of thread milling can generally reach 8~9 grades, and the surface roughness is R5~0.63 microns. This method is suitable for batch production of general precision thread work or roughing before grinding.
3, thread grinding
Mainly used for machining precision threads of hardened workpieces on thread grinders.
Thread grinding is divided into two types: single-line grinding wheel and multi-line grinding wheel according to the shape of the grinding wheel. The pitch precision of single-line grinding wheel can reach 5~6 grades, the surface roughness is R1.25~0.08 micron, and the grinding wheel is more convenient to trim.
This method is suitable for grinding precision screws, thread gauges, worms, small batches of threaded workpieces and shovel precision hobs. Multi-line grinding wheel grinding is divided into two types: longitudinal grinding method and cutting grinding method. The grinding wheel width of the longitudinal grinding method is smaller than the length of the thread to be ground, and the grinding wheel can be reversely threaded to the final size by moving one or several times in the longitudinal direction. The width of the grinding wheel is larger than the length of the thread to be ground. The grinding wheel cuts radially into the surface of the workpiece. The workpiece can be ground by about 1.25 turns. The productivity is high, but the precision is slightly lower, and the grinding wheel is more complicated. The plunge grinding method is suitable for shoveling larger batches of taps and grinding certain fastening threads.
4, thread grinding
A nut-type or screw-type threaded lap is made of a soft material such as cast iron, and the portion where the thread has a pitch error on the workpiece is subjected to forward and reverse rotation grinding to improve the pitch precision. Hardened internal threads are also usually ground to eliminate variations and improve accuracy.
5, tapping and threading
Tapping is to machine the internal thread by screwing the tap into the pre-drilled bottom hole of the workpiece with a certain torque.
The thread is used to cut the external thread on the bar (or pipe) workpiece. The precision of tapping or threading depends on the precision of the tap or die. Although there are many methods for machining internal and external threads, small diameter internal threads can only be processed by taps. Tapping and threading can be done manually, as well as lathes, drills, tapping machines and threaders.
6, thread rolling
A method of processing a workpiece by plastically deforming a workpiece by a forming rolling die. Thread rolling is generally in a thread rolling machine. The wire reeling machine or on an automatic lathe with automatic threading and rolling heads is suitable for mass production of standard external fasteners and other threaded couplings.
The outer diameter of the rolling thread is generally not more than 25 mm, the length is not more than 100 mm, the thread precision is up to 2 (GB197-63), and the diameter of all the blanks is approximately equal to the median diameter of the thread to be machined. Rolling generally cannot be machined, but for workpieces with softer material, the grooveless extrusion tap can be used to cold-squee the internal thread (up to a diameter of up to 30 mm). The working principle is similar to tapping. The torque required for cold extrusion of the internal thread is about 1 times larger than the tapping, and the machining accuracy and surface quality are slightly higher than the tapping.
The advantages of thread rolling are:
1. Surface roughness is less than turning, milling and grinding;
2. The surface of the thread after rolling can improve the strength and hardness due to cold work hardening;
3, high material utilization rate; productivity is multiplied than cutting, and easy to automate;
4. Rolling die has a long life. However, the rolling thread requires that the hardness of the workpiece material does not exceed HRC40;
5. High requirements on the dimensional accuracy of the blank;
6. The precision and hardness requirements of the rolling die are also high, and it is difficult to manufacture the die;
7, not suitable for rolling the tooth profile asymmetrical thread.Depending on the rolling die, the thread rolling can be divided into two types: twisting and rolling.
Silk
Two threaded teeth are arranged in a staggered 1/2 pitch, the static plate is fixed, and the moving plate is parallel to the reciprocating linear motion of the static plate. When the workpiece is fed between the two plates, the moving plate advances to press the workpiece, and the surface thereof is plastically deformed into a thread.
Rolling
There are three types of radial rolling, tangential rolling and rolling head rolling. Radial rolling: Two (or three) threaded rolling wheels are mounted on mutually parallel shafts, the workpiece is placed on the support between the two wheels, and the two wheels rotate in the same direction at the same speed.
One of the rounds also performs a radial feed motion. The workpiece is rotated by the rolling wheel and the surface is radially extruded to form a thread. For some precision-adjusted lead screws, a similar method can be used for roll forming. Tangential rolling: Also known as planetary rolling, the rolling tool consists of a rotating central rolling wheel and three fixed curved wire plates.
When the wire is rolled, the workpiece can be fed continuously, so the productivity is higher than that of the wire and the radial wire. Rolling head rolling: On automatic lathes, it is generally used to machine short threads on workpieces. The rolling head has 3 to 4 rolling wheels that are evenly distributed around the periphery of the workpiece.
When the wire is rolled, the workpiece is rotated, the rolling head is axially fed, and the workpiece is rolled out of the thread.
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