Thread machining is a tool that uses thread making tools to process workpieces using cutting, turning, milling, grinding, etc. It generally refers to the method of forming threads on workpieces with forming tools or grinding tools, mainly turning, milling , tapping, threading, grinding, grinding and cyclone cutting. When turning, milling, and grinding threads, the machine’s drive train ensures that the turning, milling, or grinding wheel moves exactly and evenly along the axis of the work piece, one revolution per revolution of the workpiece. During tapping or threading, the tool (taper or die) rotates relative to the workpiece, and the previously formed thread groove guides the tool (or workpiece) to move axially. CNC Milling Service | Leading Recycling Equipment
The application of the thread principle can be traced back to the spiral water lifting tool created by Greek scholar Archimedes in 220 BC. In the 4th century AD, the Mediterranean coastal countries started to apply the principle of bolts and nuts on presses for winemaking. At that time, the external thread was wound around a cylindrical bar with a string and then marked with this mark while the internal thread was often hammered with a softer material wrapped around the external thread. Around 1500, sketches of thread-processing devices drawn by the Italian Leonardo da Vinci have been used to envisage the use of a master screw and an exchange gear for machining different pitch threads. Since then, the method of mechanical thread cutting has developed in the European watchmaking industry. In 1760, the British brothers J. Wyatt and W. Wyatt obtained patents for cutting wood screws with specialized devices. In 1778, the British J. Ramsden had made a thread cutting device driven by a worm gear pair, which could produce long threads with high precision. In 1797, the Englishman H. Mozley laid the basic method of turning threads on his modified lathe, using the female lead screw and the exchange gear to turn out different pitch metal threads. In the 1820s, Mosley manufactured the first taps and dies for threading. At the beginning of the 20th century, the development of the automobile industry further promoted the standardization of threading and the development of various precision and high-efficiency thread processing methods. Various automatic spreading dies and automatic shrinking taps were successively invented, and thread milling began to be applied. In the early 1930s, thread grinding occurred. Although the thread rolling technology was patented at the beginning of the 19th century, it was slow to develop due to mold manufacturing. Until World War II (1942 to 1945), the need for arms production and the development of thread grinding technology were solved. The accuracy of mold manufacturing has only been rapidly developed. CNC Milling Service | Leading Recycling Equipment
Turning threads on a lathe can use a turning tool or a comb (see threading tools). Turning the thread with a turning tool is a common method for producing single-piece and small-batch threaded workpieces due to the simple structure of the tool; turning the thread with a comb comb cutter has high production efficiency, but the tool structure is complex and is only suitable for medium and large batch production. Short-threaded workpiece turning fine teeth. The pitch accuracy of trapezoidal threads on general turning lathes can only reach 8 to 9 grades (JB2886-81); the production of threads on specialized threaded lathes can significantly increase productivity or accuracy.
Milling with a disk or comb cutter on a thread milling machine. Disc cutters are mainly used for milling trapezoidal threads on workpieces such as screws and worms. Comb milling cutters are used to mill internal and external common threads and taper threads. Because they are milled with a multi-edged cutter, the length of the working part is longer than the length of the thread being machined, so the workpiece can be processed only by rotating 1.25 to 1.5 revolutions. 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 threaded workpieces or roughing before grinding. CNC Milling Service | Leading Recycling Equipment
It is mainly used for precision threading of hardened workpieces on a thread grinder. It can be divided into two types according to the shape of the grinding wheel: single-line grinding wheel and multi-line grinding wheel. The precision of pitch that can be achieved by single-line grinding wheel is 5-6, and the surface roughness is R1.25-0.08 micron. The dressing of grinding wheel is more convenient. This method is suitable for grinding precision screw, thread gauges, worms, small batches of threaded workpieces and sharpening hobs. Multi-line grinding wheel grinding vertical grinding method and cut into two kinds. The grindstone width of the longitudinal grind method is less than the length of the grinded thread. The grindstone can move the grindstone longitudinally once or several times to grind the thread to the final size. The width of the grindstone that is cut into the grindstone is greater than the length of the grinded thread. The grindstone cuts into the surface of the workpiece in a radial direction. The workpiece can be grinded after about 1.25 rotations. The productivity is high, but the accuracy is slightly lower and the dressing of the grindstone is more complicated. The plunge cut method is suitable for grinding large batches of taps and grinding certain fastening threads. CNC Milling Service | Leading Recycling Equipment
Using a softer material such as cast iron, a nut or screw-type thread lap is used to carry out forward and reverse rotation grinding on the part of the thread that has been processed on the workpiece to increase the pitch accuracy. Hardened internal threads are usually also ground to remove distortion and improve accuracy.
Tapping and threading
Tapping is the use of a certain torque to screw the tap into the pre-drilled bottom hole of the workpiece to produce the internal thread.
The thread is made by cutting a male thread on a bar (or pipe) workpiece. The accuracy of tapping or threading depends on the accuracy of the tap or die. Although there are many methods for machining internal and external threads, the internal threads of small diameter can only be processed by taps. Tapping and threading can be done manually. Lathes, drilling machines, tapping machines and threading machines can also be used. CNC Milling Service | Leading Recycling Equipment
Forming rolling molds to plastically deform workpieces to obtain threading methods Thread rolling is usually performed on a rolling machine reeling machine or on an automatic lathe attached with an automatic opening and closing thread rolling head, suitable for mass production standards External threads of fasteners and other threaded couplings. The outside diameter of the rolling thread is generally not more than 25mm, the length is not more than 100mm, and the thread precision can reach Grade 2 (GB197-63). The diameter of the blank to be used is approximately equal to the diameter of the thread to be machined. Rolling generally cannot process internal threads, but it can be used for non-grooved extrusion taps of cold-worked workpieces (maximum diameter up to 30 mm). The working principle is similar to tapping. The required torque when cold-extruding the internal thread is approximately 1 times larger than the tapping, and the machining accuracy and surface quality are slightly higher than the tapping. CNC Milling Service | Leading Recycling Equipment
Advantages of thread rolling: 1 The surface roughness is less than turning, milling and grinding; 2 After rolling, the thread surface can be improved in strength and hardness due to cold hardening; 3 The material utilization rate is high; 4 The productivity is doubled than the cutting process. , And easy to achieve automation; 5 rolling die life is very long. However, the rolling thread requires that the hardness of the workpiece material does not exceed HRC40; the dimensional accuracy of the blank is required to be high; the precision and hardness of the rolling die are also required to be high, and the manufacture of the die is difficult; and it is not suitable for asymmetric thread rolling.
According to different rolling molds, thread rolling can be divided into two types of wire rolling and rolling.
Filament: The two reeds with a thread profile are staggered with a 1/2-pitch offset, the stationary plate is stationary, and the moving plate makes a reciprocating linear motion parallel to the stationary plate. When the workpiece is fed between the two plates, the moving plate advances and presses the workpiece to plastically deform the surface into threads. CNC Milling Service | Leading Recycling Equipment
Rolling thread: There are three kinds of radial thread rolling, tangential thread rolling and rolling head rolling. 1 Radial thread rolling: 2 (or 3) thread rolling wheels with thread profile are mounted on parallel axes, the workpiece is placed on the support between the two wheels, and the two wheels rotate in the same direction at the same speed. The wheel also performs radial feed movements. The workpiece rotates with the thread rolling wheel, and the surface is pressed into the thread by radial extrusion. For some screw rods with low precision requirements, similar methods can be used for roll forming. 2 tangential rolling: Also known as planetary rolling thread, the rolling tool consists of a rotating central rolling wheel and 3 fixed curved wire plates. During thread rolling, the workpiece can be continuously fed, so the productivity is higher than that of the niobium yarn and the radial one. 3 thread rolling thread: It is carried out on an automatic lathe and is generally used for machining short threads on workpieces. Rolling heads have 3 to 4 rolling wheels that are evenly distributed around the workpiece. During thread rolling, the workpiece rotates and the rolling head feeds axially, rolling the workpiece out of the thread.CNC Milling Service | Leading Recycling Equipment