Generally refers to the use of forming tools or grinding tools in the workpiece thread processing methods, mainly including turning, milling, tapping, thread sleeve, grinding and whirlwind cutting.
When turning, milling and grinding threads, the drive chain of the machine tool ensures that the tool, milling cutter or grinding wheel move a guide path accurately and uniformly along the workpiece axis at each turn of the workpiece. In tapping or threading, the tool (tap or die) rotates relative to the workpiece, and the tool (or workpiece) is guided axial by a threaded groove formed first.
The forming tool or thread comb tool can be used to cut the thread on the lathe. Because of the simple structure of the tool, it is a common method to produce single and small batch of threaded workpieces. Using the thread carding tool to cut the thread, the production efficiency is high, but the tool structure is complex, only suitable for the short thread workpiece of turning fine teeth in medium and large quantity production.
The pitch precision of turning trapezoid thread can only reach 8~9 grades (JB2886-81).
The productivity or precision of machining threads on a specialized threaded lathe can be improved significantly.
Use disk or comb milling cutter for milling on thread milling machine. Disc milling cutter is mainly used for milling outside trapezoid thread on workpiece such as screw rod and worm. The comb milling cutter is used for milling the internal and external common threads and taper threads. Because the length of working part is greater than the length of the thread being processed, the workpiece can be processed with only 1.25~1.5 revolutions of rotation, and the efficiency is high.
The pitch precision of thread milling can 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 rough machining before grinding.
It is mainly used to process precision thread of hardened workpiece on thread grinding machine.
The thread grinding is divided into two types: single line grinding wheel and multi-line grinding wheel according to the shape of the grinding wheel cross section. The grinding precision of single line grinding wheel is 5~6 grades, the surface roughness is R1.25~0.08 microns, and the grinding wheel dressing is convenient. This method is suitable for grinding precision screw, thread gauge, worm, small batch threaded workpiece and grinding 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 the longitudinal grinding method is less than the length of the thread. The width of the grinding wheel is larger than the length of the thread being grinding, the productivity is higher, but the precision is lower, and the dressing of the grinding wheel is more complicated. The cutting – in grinding method is suitable for shoveling large quantity taps and grinding some fastening threads.
Tapping and thread
The processing precision of tapping or thread sleeve depends on the precision of tap or die. There are many ways to process internal and external threads. But the small diameter of the inner thread can only rely on the tap processing. Tapping and threading can be operated by hand, as well as by lathes, drilling machines, tapping machines and threading machines.
Thread rolling is a method to obtain thread by forming a rolling die to produce plastic deformation of the workpiece. Thread rolling is usually carried out on a wire rolling machine, a wire rolling machine, or an automatic lathe with an automatic opening and closing thread rolling head. Thread rolling is suitable for mass production of standard fasteners and other threaded couplings for external threads.