Thread processing technology of titanium alloy pipe joints!

Release time：2022-09-26 17:08:46 丨 Number of visits：

Unlike other metals, titanium alloys have their own characteristics that make the threading of titanium alloy pipe joints the most difficult part of the titanium alloy processing process. In this paper, the metal characteristics and processing characteristics of titanium alloys are analyzed, and it is proposed that the selection of titanium alloy processing tools and the improvement of processing technology can achieve high-precision processing of titanium alloy pipe joint threads.

Titanium alloy pipe joint is a part of the hydraulic system that connects the pipeline or installs the pipeline on the hydraulic component. A pipe joint is a connecting tool between pipes and pipes, and a detachable connection point between components and pipes. It plays an indispensable role in pipe fittings, and it is one of the two main components of hydraulic pipelines. Titanium alloy is an alloy composed of titanium metal element and other metal elements. As a special material, titanium alloy is widely used in the aviation industry due to its light weight, high strength, high heat resistance and high corrosion resistance. Especially in the manufacture of aircraft and rocket spacecraft, titanium alloys are used as important materials to give full play to their characteristics. However, for the mechanical processing of titanium alloys, its poor processing performance directly affects the processing quality and processing efficiency of titanium alloy parts, especially in the processing technology of threads, there are considerable difficulties. This paper conducts in-depth research on the material processing characteristics of titanium alloys, discusses the process suitable for titanium alloy thread processing, and solves the difficult problems in the titanium alloy tapping process.

1. Processing characteristics and characteristics of titanium alloys

The low thermal conductivity of titanium alloy directly leads to its poor heat dissipation. During thread processing operations, the temperature dispersion and cooling performance are very poor, resulting in deformation due to large springback after processing. Moreover, the cutting edge of the processing tool is severely worn, which reduces the service life of the tool. In addition, the small deformation coefficient of titanium alloy directly leads to the increase of tool loss. Its chemical activity is large, and it is easy to chemically react with other metal materials under the condition of high temperature during processing, resulting in the bonding of the tool and the tap, resulting in the phenomenon of "biting the knife". In order to increase the strength of titanium metal elements, alloying elements are added to pure titanium to form titanium alloys. There are three types of titanium alloys: one is titanium alloy, which is represented by TA; one is titanium alloy, which is represented by TB; and the other is + titanium alloy, which is represented by TC. +Titanium alloy is a dual-phase alloy, which is the most widely used and an important titanium alloy raw material in the aviation industry. Titanium alloy has good metal performance characteristics, which are embodied in: its high strength and low density, but its strength is much greater than that of many alloy steels; its heat resistance is good, and its heat resistance strength is several hundred times higher than that of aluminum alloys. Good thermal stability; its low temperature performance is good, and it still has good performance under ultra-low temperature conditions; its corrosion resistance is good, and its resistance to acid, alkali, humidity, chloride, etc. is very strong; Reacts with various chemical elements such as oxygen, nitrogen and carbon in the air; its thermal conductivity is low, and its thermal conductivity is much lower than that of iron, aluminum and other metals.

2. Selection of thread machining tools for titanium alloys

Titanium alloy thread processing mostly uses staggered taps for tapping operations, that is, the teeth of the tap are removed one at a time, and they are arranged in a staggered arrangement, so that the workpiece and the tap are only in contact with one side to reduce mutual friction and reduce friction. generated torque. This can effectively prevent the tap from being stuck or damaged, thereby improving the quality of thread processing. The use of this staggered-tooth tap can double the cutting thickness and the depth is greater than the cold work hardened layer. The increase in cutting thickness directly leads to an increase in the cutting force of the tap teeth, but it is easier for cutting chip removal. Reduced, tap and chip sticking is reduced, thereby improving tap durability and thread accuracy. In the design of staggered taps, it should be noted that the final number of tooth slots is odd to reduce the force on the tooth edge. In the thread processing of titanium alloy materials, the use of staggered taps can effectively maintain the stability of tapping and improve thread accuracy. For threading of titanium alloys, high-speed taps are recommended. The taps made of this material have high toughness and deformation resistance, and also have good wear resistance. For the tapping of titanium alloy materials, a high-speed steel tap can be used for preliminary tapping, and then a cemented carbide tap can be used to correct the screw hole. With the in-depth research on tool materials, there will be more suitable materials to make taps for better processing of titanium alloy threads.

3. Processing technology of titanium alloy pipe joint thread

The increase of the thread bottom hole can effectively reduce the cutting force and heat generated during machining. The strength of the titanium alloy pipe is relatively large, and the precondition for increasing the specific amount of the diameter of the bottom hole of the thread is the requirement for the contact rate of the thread and the specific number of thread heads. From the point of view of processing technology, the inner diameter of the thread can be appropriately increased, so that the thread height can be reduced. Appropriately increase the diameter of the thread, which is especially suitable for tapping of special materials such as titanium alloys. Although the thread contact rate is reduced, the connection of the thread is still stable and reliable due to the increase in its length. In order to prevent the tap from breaking due to excessive pressure during processing, the processing technology of machine tool tapping can be selected.

3.1 Cutting speed and tool control

Because of the metal properties of titanium alloy materials, the cutting speed during processing is controlled to keep it at a lower speed, which is more conducive to the threading work. But pay attention to the speed can not be too small, generally keep the speed per minute at 200mm ~ 300mm is appropriate. When threading titanium alloys, the geometry of the tool should be considered. The selection of a suitable rake angle can increase the strength of the cutting edge and improve the durability of the tool; the selection of a suitable large clearance angle is conducive to chip removal during processing. In the deep hole tapping of titanium alloy pipes, the method of reducing the number of chip flutes can be used to increase the chip space and enhance the chip removal capacity of the tap.

3.2 Tap chuck and coolant control

When using the machine tool for tapping, you need to use a special tap chuck, combined with a wrench for tapping. For threading of titanium alloys, the thread tail is usually longer than the standard length. It is best to design the undercut so that even when the tap taps to the bottom, no chipping occurs. A highly active coolant with good lubricating function can be selected to directly cool the tap. The excessive temperature generated during the processing of the tap will cause the tap and the chip to stick together, which will affect the processing speed and processing accuracy of the tap. It is recommended to use a mixture of oleic acid, sulfurized oil and kerosene in an appropriate proportion to cool the tap. You can also choose to use F43 cutting oil, which can also achieve the ideal cooling effect. When threading titanium alloy materials, a cooling groove can be opened on the back of the tap to ensure that the cooling can also reach the cutting edge smoothly.

  4 Conclusion

In summary, for the thread processing of titanium alloy pipe joints, we must first fully understand the metal characteristics and processing characteristics of titanium alloy materials, so as to adopt appropriate tap design and selection of tap materials according to their characteristics. Secondly, appropriate and effective processing technology must be adopted to effectively avoid the weaknesses of titanium alloy materials during processing. Through the cooperation of both the tool and the machining process, the thread machining accuracy and machining speed of the titanium alloy are improved. With the in-depth research of metal materials and the development of processing technology, there will be better titanium alloy processing technology.