CN118371843A - Equipment and method for preparing titanium and titanium alloy titanium pipe based on milling machine stirring friction - Google Patents

Abstract

The invention discloses equipment and a method for preparing titanium and titanium alloy titanium pipes based on stirring friction of a milling machine, wherein the equipment comprises the milling machine, a supporting structure, a clamping device and a stirring head; the support structure is cylindrical and is used for supporting the titanium pipe; the clamping device is used for clamping and fixing the titanium pipe; the diameter of a main shaft of the milling machine is increased, the rotating speed of the speed change gear is improved, and the main shaft has conicity; the main shaft of the milling machine is welded and fixed with the stirring head through an adapter made of high-temperature resistant materials; the axial feeding mechanism of the milling machine provides constant-speed and stable propelling force, and the stroke of the Z axis is expanded; the clamping device and the titanium pipe are fixed on a workbench of the milling machine together; the stirring head comprises a shaft shoulder with the outer diameter of 3-10 mm, and an axially protruding stirring pin is fixed at the center of the bottom of the shaft shoulder. The invention has the advantages of low cost, flexible and convenient use, uniform metallographic structure of the weld zone, no obvious fusion line, strong applicability, high production efficiency and environmental protection.

Description

Equipment and method for preparing titanium and titanium alloy titanium pipe based on milling machine stirring friction

Technical Field

The invention belongs to the technical field of hot working welding, and relates to equipment and a method for preparing titanium and titanium alloy titanium pipes based on stirring friction of a milling machine.

Background

Friction stir welding is a novel solid phase connection technology invented in 1991 by the British welding institute, and the heat generated by friction between metals to be welded by using a stirring head rotating at high speed is utilized to enable the materials to generate plastic deformation, so that the purpose of connection is achieved. Friction stir welding has significant advantages over conventional fusion welding. First, friction stir welding eliminates most of the resolidification-related side effects inherent in conventional fusion welding due to its solid state joining process. Second, the welding method is an all-position welding and can be applied in various environments. Third, friction stir welding also has the characteristics of high efficiency, low cost, and effective connection of low-melting point metals (particularly aluminum alloys). Fourthly, in the welding process of friction stir welding, a stirring needle extends into the joint of the workpiece, and the stirring needle is rubbed with a welding workpiece material through high-speed rotation of a welding head to generate heat, so that connection is realized; this approach is more energy efficient than conventional fusion welding. Fifth, friction stir welding also has the advantages of low welding temperature, small residual stress of the joint, small deformation of the welded workpiece, small influence on the environment, and the like.

Friction stir welding technology has since its advent, and many companies are conducting friction stir welding equipment research and development worldwide. Among them, the green zhibach company (Gerinzerbacher) in germany is an enterprise specially developed for friction stir welding technology. In addition, PTG corporation in the united states also provides a series of friction stir welding devices, such as the Powerstir series of machine tools, which are widely used in the automotive, aerospace, and high speed locomotive industries. Meanwhile, the United kingdom is one of the sources of friction stir welding technology, and gantry friction stir welding equipment is manufactured. In 2002, china introduced this technology from the united kingdom and gradually began the autonomous development of related devices. At present, the research and development level of Chinese friction stir welding equipment is also continuously improved, and various cantilever type and gantry type friction stir welding equipment is successfully researched and developed. But these devices are all characterized by large volume, complex structure, high price, strong speciality, etc. When related friction stir welding technology research is carried out in universities and universities, the use of the large equipment is difficult, so that the research work of the friction stir welding technology is limited to a certain extent.

The titanium and titanium alloy titanium pipe has the advantages of high specific strength, good thermal strength, high corrosion resistance, good creep property and the like, and is widely applied to various fields such as aerospace, offshore oil production, automobile manufacturing and the like. At present, titanium and titanium alloy titanium pipes are mostly formed by traditional arc welding, although the titanium alloy contains less phosphorus, sulfur, carbon and other impurities, the crystallization temperature interval is narrow, the shrinkage amount during welding seam solidification is small, the thermal cracking sensitivity is relatively low, and thermal cracking is easy to occur. Secondly, the titanium alloy reacts with the oxide to easily generate welding pores, thereby reducing the strength and the sealing performance of the welding joint. Finally, titanium alloys are susceptible to reaction with impurities such as oxygen, nitrogen, hydrogen and the like in the atmosphere at high temperatures, resulting in high temperature embrittlement phenomena, which reduce the plasticity and toughness of the welded joint.

Currently, there is little research on performing friction stir welding with non-specialized friction stir welding equipment. Li Hailong et al design a device suitable for friction stir welding of magnesium alloy sheets by adding a hydraulic device on a ZX50CA milling and drilling machine, and select 3mm thick AZ31 magnesium alloy sheets for welding experiments, and find that when the rotating speed of a stirring head is 1400r/min, the welding speed is 15mm/min and the pressing force is 1500N, the surface of a welding joint is well formed. Zhang Hongtao et al modify an XK6336 numerical control rocker milling machine into a back-pumping type friction stir welding machine, reserve the frame and the workbench of the original numerical control milling machine, and redesign the components of a B-axis rotating device, a Z-axis numerical control sliding table, a back-pumping type power head and the like of the welding machine. Subsequently, the function requirement of the welding machine is verified by using a friction stir welding process, and the welding of straight-seam, round and curved welding seams is finished at present. T.Minton et al determined whether a conventional milling machine could be used for friction stir welding, tested by producing 6.3mm and 4.6mm 6082-T6 aluminum plate welds of the same thickness. The results demonstrate that conventional milling machines are capable of performing FSW and joining 6.3mm thick 6082-T6 aluminum material using relatively robustly tools to produce reasonable welds.

While friction stir welding has tended to mature, it is currently mainly directed to the welding of large structural members and thick plates, the modification and lifting of specialized welding equipment, the selection and design of stirring heads, and the like. The welding of titanium pipes by using a common milling machine has at least the following problems:

First, for the panel, there is certain radian on titanium tubular product surface, leads to the shaft shoulder of stirring head and titanium tubular product contact incompletely in the welding process, and titanium tubular product metal flow is insufficient during the welding to produce the defect, reduce the intensity of welded joint. Secondly, friction stir welding of titanium tubing also has the problem of difficult clamping. Thirdly, the titanium pipe is generally thinner, has high processing precision requirement, and is easy to deform and penetrate under the action of stirring and pressure.

Disclosure of Invention

In order to solve the problems, the invention provides equipment for preparing titanium and titanium alloy titanium pipes based on stirring friction of a milling machine, which has the advantages of low cost, flexible and convenient use, uniform metallographic structure of a welding line area, no obvious fusion line, strong applicability, high production efficiency and environmental protection.

The invention also aims to provide a method for preparing titanium and titanium alloy titanium pipes based on stirring friction of a milling machine, which has the characteristics of simplicity, convenience, high efficiency, low cost and high welding quality.

The technical scheme adopted by the invention is that the equipment for preparing the titanium and titanium alloy titanium pipe based on the stirring friction of the milling machine comprises the milling machine, a supporting structure, a clamping device and a stirring head;

the supporting structure is cylindrical and is arranged on the inner wall of the titanium pipe and used for supporting the titanium pipe;

the clamping device is used for clamping and fixing the titanium pipe;

The diameter of a main shaft of the milling machine is increased to 60-150 mm so as to improve the rotation speed of the variable speed gear, and the taper of the main shaft is 3-6 degrees; the main shaft of the milling machine is welded and fixed with the stirring head through an adapter made of high-temperature resistant materials; the axial feeding mechanism of the milling machine provides constant-speed and stable propelling force and expands the stroke of the Z axis; the clamping device and the titanium pipe are fixed on a workbench of the milling machine together;

The stirring head comprises a shaft shoulder with the outer diameter of 3-10 mm, and an axially protruding stirring pin is fixed at the center of the bottom of the shaft shoulder.

Further, the clamping device comprises a movable roller and a fixed roller, and the movable roller and the fixed roller are symmetrically distributed on two sides of the titanium pipe; the lower end of the movable roller is connected with a nut seat of the screw rod, the axis of the screw rod is vertical to the clamping surface of the movable roller, the screw rod is driven manually or electrically to drive the movable roller to move towards or away from the fixed roller, and the distance between the movable roller and the fixed roller is adjusted to clamp titanium pipes with different sizes; the contact position of the movable roller or the fixed roller and the titanium pipe is provided with a pressure sensor.

Further, a plurality of groups of movable rollers and fixed rollers are arranged along the axis direction of the titanium pipe, and the distance between each group of movable rollers and fixed rollers is gradually reduced along the advancing direction of the titanium pipe.

Further, the diameter and the length of the supporting structure are respectively matched with the inner diameter and the length of the titanium pipe, grooves are formed in the surface of the supporting structure along the axial direction, and the grooves are located at welding seams of the titanium pipe.

Further, the width of the groove is 1.5 mm-4 mm, and the depth of the groove is 2 mm-5 mm.

Further, the inner diameter of the shaft shoulder is matched with the diameter of the stirring pin, and the inner diameter of the shaft shoulder is 1.5-6 mm.

Furthermore, the profile shape of the shaft shoulder is conical, inclined plane or special curve.

Further, the ratio of the length to the diameter of the stirring pin is 3:1-5:1, and the stirring area of the stirring pin is in an inverted cone shape or a thread shape.

A method for preparing titanium and titanium alloy titanium pipes based on milling machine friction stir comprises the following steps:

S1, curling and forming a titanium plate to obtain a welding blank of a titanium pipe;

S2, fixing a welding blank of the titanium pipe: placing a cylindrical supporting structure on the inner wall of the titanium pipe for supporting the titanium pipe; clamping and fixing the titanium pipe by a clamping device;

S3, modifying a main shaft system, a stirring head mounting interface and an axial feeding mechanism of the milling machine, connecting the stirring head, and performing friction stir welding on the milling machine; the rotation speed of the stirring head is 1500-1800 r/min, the inclination angle of the stirring head is 2-5 degrees, the pressing amount is 0.1-0.25 mm, and the axial feeding speed is 40-60 mm/min;

And S4, after welding and forming, carrying out hot water cleaning, blow-drying and induction annealing to obtain the alloy.

Further, the step S4 includes the following steps: the alternating current generates an alternating magnetic field with the same frequency as the current around the induction coil, and correspondingly generates induced electromotive force in the tube blank, and induced current is formed on the surface of the tube blank, so that the tube blank is quickly heated to 300-400 ℃ and the induction coil is removed at the speed of 30-50 mm/min, thereby achieving the aim of annealing.

The beneficial effects of the invention are as follows:

1. Compared with the traditional arc welding, the friction stir welding has the advantages that common defects of fusion welding such as cracks, air holes, inclusions and the like can be effectively reduced or even eliminated, so that a welding seam with high strength and high reliability is obtained, and the method has the advantages of high welding speed, no need of a filler wire, small welding heat input, good welding seam quality stability, small residual stress and deformation of a workpiece, no pollution and the like. After the titanium pipe is subjected to friction stir welding, the metallographic structure of a welding zone is uniform and consistent, no obvious weld line exists, the overall performance of the welded joint is improved, and the method is particularly suitable for application scenes with extremely high requirements on material performance in the fields of aerospace, ocean engineering and the like.

2. The invention does not need filling materials and protective gas in the friction stir welding process, does not generate harmful smoke dust and splashes, accords with the green manufacturing concept, and simultaneously reduces the welding cost.

3. The invention can be suitable for welding titanium pipes with different sizes and wall thicknesses, including welding thin-wall titanium pipes. The welding head is flexible in movement, and can be used for welding complex curves, curved surfaces and other three-dimensional space paths by adjusting a workbench of a machine tool or using a multi-axis linkage system, so that the applicability is high.

4. The invention utilizes the special clamping device, can ensure the geometric shape of the cambered surface of the titanium pipe, can apply enough circumferential force, ensures the stability in the welding process of the thin-wall titanium pipe, reduces the deformation and improves the yield.

5. The existing large-scale special friction stir welding equipment has the defects of huge volume, complex structure, high price and the like, and the milling machine can meet the technological parameters required by friction stir welding of titanium pipes and has the characteristics of low cost, flexible and convenient use. The invention takes the milling machine as a basic platform, can better integrate an automatic control system, more precisely control key parameters such as welding speed, axial pressure, rotating speed and the like, reduce a heat affected zone, control grain growth, ensure consistency and repeatability of a welding process, improve welding quality, realize continuous automatic production, greatly shorten welding period, improve production efficiency and reduce dependence on high-skill welders.

In a word, the invention combines friction stir welding with milling machine, is used for welding titanium and titanium alloy pipes with higher precision requirements, can ensure welding quality, can also promote production efficiency, reduces production cost, and is beneficial to realizing the fine, intelligent and green development of high-end manufacturing industry.

Drawings

In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a flow chart of the process for preparing a titanium pipe welding blank in real time.

Fig. 2 is a schematic structural view of a clamping device according to an embodiment of the present invention.

FIG. 3 is a schematic view of a support structure in an embodiment of the invention.

Fig. 4a is a schematic perspective view of a clamping device for clamping a pipe according to an embodiment of the present invention.

Fig. 4b is a three-view of the gripping device gripping a tubular in an embodiment of the invention.

Fig. 5 is a diagram showing the clamping stress effect of the pipe fitting according to the embodiment of the invention.

FIG. 6 is a schematic view of the structure of a stirring head in an embodiment of the invention.

FIG. 7 is a schematic diagram of a milling machine in accordance with an embodiment of the present invention.

Fig. 8 is a schematic diagram of induction heating in an embodiment of the invention.

FIG. 9 is a detail view of a stirring head in an embodiment of the invention.

FIG. 10 is a diagram showing the effect of friction stir welding according to the embodiment of the present invention.

FIG. 11 is a graph of weld hardness distribution for friction stir welded titanium tubes according to an embodiment of the present invention.

FIG. 12a is a metallographic structure of a matrix region of a friction stir weld according to an embodiment of the present invention.

FIG. 12b is a metallographic structure of a heat affected zone of a friction stir weld according to an embodiment of the invention.

FIG. 12c is a weld metallographic structure of a friction stir weld according to an embodiment of the present invention.

FIG. 13a is a metallographic structure of a matrix region of a conventional argon arc weld.

Fig. 13b is a metallographic structure of a heat affected zone of a conventional argon arc welding weld.

Fig. 13c is a weld metallographic structure of a conventional argon arc welding weld.

In the figure, 1, a movable roller, 1-1, a chain, 2, a fixed roller, 3, a screw rod, 4, a supporting structure, 4-1, a groove, 5, a welding line, 6, a shaft shoulder clamping part, 7, a shaft shoulder, 9, a stirring pin, 10, a shaft shoulder stirring area, 11, a connecting part, 12, a connecting part, 13, a stirring pin stirring area, 14, a milling head, 15, a workbench, 16, a transverse sliding plate, 17, a lifting platform, 18, an operating platform, 19, a main shaft speed changing handle, 20, a protection switch, 21, a lathe bed and 22, and a power socket.

Detailed Description

The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

In the case of example 1,

An apparatus for preparing titanium and titanium alloy titanium pipe based on milling machine stirring friction, as shown in figure 7, comprises a milling machine, a stirring head, a supporting structure 4 and a clamping device;

Milling machines are not originally specifically designed for friction stir welding, and so are modified to be FSW (friction stir welding) capable equipment; firstly, the main shaft system needs to be modified, namely the diameter of the main shaft is increased, the speed change gear is increased to improve the rotation speed, and the main shaft has a certain taper so as to prevent the stirring head from falling off due to extrusion under the action of pressure stress; to support high rotational speed, high torque output. Is provided with a special stirring head mounting interface and an axial feeding mechanism. The spindle is capable of providing sufficient torque to drive the stirring head in high speed rotation while also providing sufficient power to support load variations during continuous welding. The modified main shaft can provide stable feeding speed and enough thrust, and is equipped with a precise positioning and control system.

The diameter of the main shaft is 60-150 mm, and the taper range of the main shaft is 3-6 degrees; the excessive diameter makes it difficult to install the spindle in existing milling machine structures; the excessive diameter makes the original transmission device difficult to effectively transmit torque; the oversized diameter causes overweight of the main shaft, influences the overall dynamic performance and stability of the machine tool, and even needs to reinforce the base, the upright post and other basic structures; excessive increase of the diameter of the spindle also leads to significant increase of selected material cost, processing cost, purchasing period and the like, and causes resource waste, which does not conform to the principles of economy and practicality.

Too small taper causes insufficient clamping force between the stirring head and the main shaft, and is easy to loosen or fall off under welding pressure; excessive taper results in assembly difficulties, stress concentrations, and increased risk of wear or damage to the spindle and stirring head.

The milling machine body 21 is provided with a main shaft variable-speed handle 19, a power socket 22 and a milling head 14, and a workbench 15 is arranged right below the milling head 14; the speed of the spindle is regulated by precisely controlling the speed-changing gear through the spindle speed-changing handle 19, so that the convenience of operation, the reliability of speed change and the stability of the milling process are improved.

The protection switch 20 is arranged on the workbench 15, the protection switch 20 is in short-circuit protection, and when a short-circuit fault occurs in a milling machine circuit, the power supply is disconnected through the protection switch 20, so that fire disasters, equipment burning or electric shock accidents caused by short-circuit current are prevented. The protection switch 20 is integrated with a manual emergency stop button which can be directly pressed by an operator to rapidly cut off the power of the equipment once an emergency occurs, so as to ensure the safety of the operator.

In the friction stir welding process, the transverse slide plate 16 is used for bearing and driving the workbench 15, so that the stirring head can accurately and linearly move along the width direction (X axis) of the titanium pipe, and a graduated scale or a digital reading device on the transverse slide plate 16 can help an operator to accurately set and monitor the transverse position of the stirring head relative to the titanium pipe, and perform weld joint starting point positioning, weld joint width adjustment and fine adjustment of a welding path.

The lifting table 17 is used to drive the feeding of the table 15 in the vertical direction (Z-axis), cooperating with the spindle system, by hydraulic or pneumatic means to provide and maintain the constant axial pressure required by the stirring head during welding. The lifting table 17 can also be used for adapting to titanium pipes with different diameters, and the distance between the workbench 15 and the central line of the main shaft is adjusted by moving up and down, so that the titanium pipes are positioned at proper welding positions.

The operation table 18 is connected with the numerical control system through a signal line, so that the three-dimensional movement of the workbench 15 is precisely controlled. The table 15 serves as a base platform for carrying the work pieces and needs to have sufficient carrying capacity and stability to ensure that the work pieces remain stationary during the welding process and to prevent the welding quality from being affected by movement or deformation of the work pieces.

Secondly, the stirring head mounting interface needs to be modified; before transformation: universal interfaces milling machines are typically equipped with standard tool mounting interfaces designed for quick replacement of various milling tools, with a wide range of versatility and standardization. The cutting load is dominant, and the original interface design mainly considers the cutting force in the milling process, including radial and axial components, rather than the continuous pressure required by welding. After transformation: the main shaft of the milling machine is welded and fixed with the shaft shoulder clamping part 6 through the adapter, a standard milling machine interface is converted into a structure suitable for mounting the stirring head, and stable fixing and rotating precision of the stirring head are ensured. The adapter is of a conical structure, one end of the adapter is connected with the main shaft through threads, key grooves and the like, and effective transmission of torque is ensured; the other end of the adapter is welded and fixed with the shaft shoulder of the stirring head to form rigid connection. The modified interface needs to be able to withstand the large and stable axial pressures required during FSW, which is typically much higher than the tool loads during milling. Because a large amount of heat can be generated in the friction stir welding process, the adapter is made of high-temperature resistant materials. The shoulder clamping part 6 is made of quenched and tempered 45 steel, and other parts of the stirring head are made of TZM alloy, so that materials are saved to a great extent, and cost is reduced.

Thirdly, the axial feeding mechanism needs to be modified; before transformation: the axial feeding mechanism of the milling machine is designed to realize high-speed and accurate feeding speed adjustment so as to adapt to the requirements of different cutting processes, including rough machining, finish machining and the like. The milling device has higher dynamic response capability, and can be rapidly accelerated, decelerated or stopped so as to meet the frequently-changed speed requirement in a milling path. The stroke is limited and the Z-axis (axial) stroke of the milling machine is typically set according to its original design task and is typically insufficient to cover the depth or length required for large FSW workpieces. After transformation: during FSW, the axial feed speed is typically low and relatively constant, and the feed mechanism needs to be able to provide the required pressure stably and maintain a constant speed of propulsion, without the need for a quick response capability. Aiming at the requirement of FSW long weld joint, the stroke of the Z axis needs to be increased, and the expansion of the stroke is realized by adding additional sliding rails, ball screws and other parts. The feeding mechanism is additionally provided with an overload protection device, so that equipment damage or welding defects caused by overlarge pressure in the welding process can be avoided.

In some embodiments, the feeding mechanism adopts a high-precision servo motor as a power source for feeding, and the advancing speed and the position of the stirring head can be accurately controlled due to the high response speed, the high control precision and the wide speed regulation range. The motor output converts the high-speed rotation of the motor into low-speed and high-torque linear motion required by the stirring head through a speed reduction device such as a precise planetary gear reducer, a worm gear reducer or a ball screw pair. The linear guide rail and the sliding block are arranged on the milling machine body, so that stable guiding and supporting are provided, and accurate movement of the stirring head along a preset track is ensured. When the pressure exceeds the set value, the pressure source is cut off, and the equipment is protected from damage.

In order to enable the titanium pipe to be well clamped, the clamping device is shown in fig. 2 and comprises a movable roller 1 and a fixed roller 2, the lower end of the movable roller 1 is connected with a nut seat of a screw rod 3, the axis of the screw rod 3 is perpendicular to the clamping surface of the movable roller 1, the screw rod 3 is driven manually or electrically, the movable roller 1 is driven to move towards a direction close to or far away from the fixed roller 2, and the distance between the movable roller 1 and the fixed roller 2 is adjusted to be used for clamping titanium pipes with different sizes.

As shown in fig. 4a-4b, three groups of movable rollers 1 and fixed rollers 2 are arranged along the axial direction of the titanium pipe, the distance between each group of movable rollers 1 and fixed rollers 2 is gradually reduced along the advancing direction of the titanium pipe, and circumferential force is provided during welding, so that the gap of the titanium pipe at the welding seam 5 is as close as possible, and the welding quality is improved.

The pressure sensor is installed at the position of the movable roller 1 or the fixed roller 2, which is contacted with the titanium pipe, when the set pressure is reached, the movement of the movable roller 1 is stopped, so that on one hand, the quick clamping can be realized, and on the other hand, the consistency of clamping force can be ensured.

The tops of the movable roller 1 and the fixed roller 2 are respectively provided with a chain wheel, the chain wheels are coaxially and fixedly connected with the corresponding movable roller 1 or fixed roller 2, the chain 1-1 is in transmission connection with the chain wheels, at least one chain wheel is connected with the output shaft of the motor, the chain 1-1 drives the chain wheels to rotate around the axis to drive the corresponding movable roller 1 or fixed roller 2 to coaxially rotate, and then the titanium pipe is driven to move to the stirring head at a certain speed, and the speed is equal to the moving speed of the stirring needle 9.

In order to ensure that the titanium pipe is deformed little when being stressed and bears larger pressure, the support structure 4 shown in the figure 3 is designed based on the inner diameter of the manufactured titanium pipe, the support structure 4 is cylindrical and is matched with the inner diameter and the length of the titanium pipe, and the surface of the support structure 4 is provided with a groove 4-1 along the axial direction, so that a stirring pin 9 is prevented from directly contacting with the support structure, the resistance is reduced, and the stirring pin 9 is protected; secondly, the titanium tubing to be welded can be avoided from being welded to the support structure 4.

The supporting structure 4 can be adapted according to the inner diameter and the length of the titanium pipe, and the cylindrical supporting structure 4 with the same size is prepared according to the inner diameter and the length of the titanium pipe, so that the precise fitting on the inner wall of the pipe is ensured, and the deformation in the welding process is prevented. Because certain pressure is applied in the welding process of friction stir welding, namely the pressure perpendicular to the welding surface and the pressure in the circumferential direction of the titanium pipe, the pressure is 100-300 MPa, and the material is subjected to plastic deformation when in a molten state by generating heat through rapid stirring; titanium tubing is hollow and must be supported otherwise the titanium tubing is flattened.

The width of the groove 4-1 is 5-20% larger than the diameter of the stirring head, and is generally 1.5-4 mm. The depth is determined by the thickness of the pipe wall and the length of the stirring head, and is generally 2 mm-5 mm. The too wide groove 4-1 can cause local instability of the pipeline in the welding process, increase deformation and insufficient filling of materials at the welding seam, thereby affecting the mechanical property and the sealing property of the welding seam. The excessive depth of the groove 4-1 does not effectively limit radial deformation, but rather may cause additional stress concentration in the welding area due to the blocked material flow, increasing welding risk.

The supporting structure 4 is made of common 45 steel in a supply state, is wide in source and low in price, can be used by directly buying in a supply state (namely, a normalizing or annealing state), has both strength and plasticity and toughness, and can be used for multiple times.

The stirring head is the most critical component in friction stir welding equipment and tools, and its material and shape have a decisive influence on the weld joint performance. Titanium is a high temperature resistant material with a melting point as high as 1678 ℃, so that the material requirement on the stirring head is high when friction stir welding is carried out. TZM alloy (titanium zirconium molybdenum alloy) is selected as the material of the stirring head. The size of the shaft shoulder of the stirring head is 3-5 times of the thickness of the tube blank, and the size of the stirring pin is matched with the gap of the tube blank.

As shown in fig. 6, the stirring head comprises a large-area shaft shoulder 7, the bottom of the shaft shoulder 7 is fixedly connected with a connecting part 12 of a stirring needle 9, the stirring needle 9 axially protrudes out of the bottom of the shaft shoulder 7, a connecting part 11 of the stirring needle 9 and the shaft shoulder 7 is positioned at the center of the bottom of the shaft shoulder 7, and the end head of the stirring needle 9 is a conical stirring needle stirring area 13; the top of the shaft shoulder 7 is provided with a shaft shoulder clamping part 6, and the shaft shoulder clamping part 6 is connected with a main shaft of the welding machine and used for accurately mounting the stirring head on the welding machine, so that the rotation center line of the shaft shoulder clamping part 6 is ensured to be consistent with a welding track, and accurate alignment is realized. The shoulder 7 needs to apply stable axial pressure to the pipe to generate friction heat and plastic flow, and simultaneously applies continuous axial pressure to the welding area to form a closed welding environment, so that the shoulder clamping part 6 is required to bear and transmit high torque transmitted from the main shaft of the welding machine, and the stirring head can work stably under a high-speed rotation state; the stirring pin 9 performs physical stirring and plastic flow on materials in the rotating process, so that mixing and connection among the materials are realized.

The bottom of the shaft shoulder 7 is provided with a shaft shoulder stirring area 10, the shaft shoulder stirring area 10 is directly contacted with the titanium pipe fitting, and the temperature of the titanium pipe fitting is increased and the titanium pipe fitting enters a plastic state through friction heat generated by high-speed rotation; the shoulder 7 applies effective pressure to the plasticized metal, as in forging, forcing the metal to flow into the void formed behind the pin 9, ensuring complete filling of the weld 5, reducing voids and defects, and improving the compactness and strength of the weld 5.

There is a transition zone (i.e. a connection 12) between the shoulder 7 of the stirring head and the stirring pin 9, aimed at ensuring an efficient transfer of heat and mechanical energy, while reducing stress concentrations.

The strong frictional contact between the shoulder 7 and the pipe surface is one of the main ways to generate heat, which can bring the material of the welding zone to a plastic flow state. The shape and size of the shoulder 7 directly affect the path and pattern of the metal plastic flow during welding, and thus the width and depth of the weld. The shaft shoulder 7 plays a role in restraining and guiding surrounding materials, so that plasticized metals cannot overflow from a welding area, and the plasticized metals are guided to be filled and distributed in the whole welding area, and good welding seam forming is ensured; the sealing effect of the shoulder 7 against the workpiece contact surface helps to maintain the high temperature and pressure conditions of the weld area, which is critical to achieving good welding. The concave or side channel shoulder 7 design helps to enhance metal flow and reduce voids. The diameter of the shoulder 7 is matched to the thickness of the welding material and to the welding process parameters to ensure adequate heat input and proper welding pressure while avoiding excessive deformation or cracking of the workpiece. The shoulder 7 is typically made of a high strength, high temperature and wear resistant material with a high surface hardness that can withstand the high temperature friction during long-term welding without wear.

The outer diameter of the shaft shoulder 7 is larger to increase the contact area and thereby increase the friction heat; the inner diameter is smaller, and a similar annular space is formed to wrap and restrain molten or semi-molten metal, so that the molten or semi-molten metal is prevented from overflowing transversely in the welding process, and meanwhile, the metal is guided to flow orderly along the welding direction, so that a continuous and compact welding seam is formed; the height of the shaft shoulder 7 is adjusted, and the installation inclination is adjusted to meet the welding requirements of materials with different thicknesses; the height of the shoulder 7 is adjusted during the design phase and the machining phase, and the installation inclination is adjusted during the installation fixation.

The diameter of the shoulder 7 determines the size of the area in contact with the pipe during welding, and a larger diameter can provide larger welding surface pressure, so that more material is plasticized and flows into the welding seam area, and the width of the welding seam is increased. Meanwhile, the pressure of the shaft shoulder 7 on the pipe fitting is beneficial to enhancing the compactness and mechanical property of the welding seam. The pressing amount of the shaft shoulder 7 refers to the actual contact pressure of the shaft shoulder 7 and the surface of the pipe fitting, and the depth and the width of the welding seam can be increased by properly increasing the pressing amount. The height of the shoulder 7 indirectly affects the amount of heat input and the material flow distance during welding, a high shoulder 7 may widen the weld heat affected zone, while a low shoulder 7 may restrict the metal flow, making the weld relatively shallow.

The outer diameter of the shaft shoulder 7 is larger than the thickness of the welded titanium pipe, so that enough contact area between the shaft shoulder 7 and the base metal is ensured to generate necessary friction heat and apply certain back pressure in the welding process, the material is promoted to flow, and the outer diameter size is 3-10 mm. The diameter of the stirring pin 9 determines the size of the inner diameter of the shaft shoulder 7, the diameter of the stirring pin 9 is a few millimeters, and the inner diameter of the shaft shoulder 7 is slightly larger than the diameter of the stirring pin 9, so that the inner diameter of the shaft shoulder 7 is 1.5-6 mm. The outer diameter of the shaft shoulder 7 is too large, so that the shaft shoulder cannot be smoothly embedded into a preset welding seam position, the welding difficulty is increased, or the deformation is caused by excessive extrusion of the pipe. The too large internal diameter of the shaft shoulder 7 may reduce the stability of the stirring pin 9 or the transmission shaft, increase vibration in the running process, and affect the welding precision and the tool life.

In some embodiments, the shoulder 7 may be designed with a tapered, beveled, or contoured profile that helps optimize metal flow, reduce weld defects, and ensure weld uniformity.

The tapered configuration of the shoulder 7 increases in diameter from the front end to the rear end of the welding tool and this design helps to create a progressive pressure profile from front to rear during the welding process. In the initial contact stage, the smaller diameter part can be easier to insert materials, and the pressure provided by the larger diameter part is gradually increased along with the progress of the welding process, so that the welding seam area is better compacted, the metal overflow in the welding process is prevented, and the compactness and the integrity of the welding seam are ensured.

The surface of the shoulder 7 of the special curve profile is designed with a specific curve or bevel, such as non-circular, hyperbolic, etc., which shapes can optimize the metal flow during welding. The curve profile can guide and disperse material flow, reduce strain concentration in the welding process, and enable molten and plastically deformed metal to be uniformly distributed in the whole welding line area, so that the welding line quality is improved, and internal defects are reduced.

In some embodiments, the length of the pin 9 is generally designed to be slightly less than the thickness of the weld layer of the titanium tube, ensuring that it is able to stir the weld area sufficiently without damage from penetrating the back surface. The length to diameter ratio of the stirring pin 9 is 3:1-5:1. Out of range disadvantages: the welding efficiency is low, and too short stirring pin 9 probably leads to the welding degree of depth not enough, and the required connection thickness can be reached to the welding that needs many times, and efficiency reduces, and welding quality is poor, because the stirring is insufficient, probably leads to welding interface department misce bene, and then influences the mechanical properties and the corrosion resistance of joint. The overlong stirring pin 9 can increase the axial force in the welding process, cause excessive load on equipment, influence the service life and stability of the equipment, and increase welding defects; an improper ratio may result in too high or too low a welding heat input, and may be prone to welding defects such as cracks, pinholes, unfused, etc.

In some embodiments, the pin stir zone 13 is inverted conical or threaded (see fig. 9) to facilitate insertion into the workpiece joint and reduce initial resistance, and the metal material is softened by the frictional heat generated by the high speed rotation and transformed into a plastic state to facilitate subsequent plastic flow and metallurgical bonding. The rotational movement of the pin stir zone 13 promotes microscopic mixing of the metal, helping to eliminate component segregation and improve the metallurgical properties of the weld.

Compared with an embedded stirring head, the fixed stirring head is high in universality and suitable for most conventional FSW applications; the manufacturing cost is relatively low, the structure is relatively simple, a complex embedded mechanism or a special installation interface is not needed, and the manufacturing cost and the maintenance cost are low.

In the case of example 2,

A method for preparing titanium and titanium alloy titanium pipes based on milling machine friction stir comprises the following steps:

s1, curling and forming a titanium plate;

According to the requirements of users on the size and performance of the titanium pipe, a titanium plate with a proper size is selected, and then the titanium plate is sequentially subjected to uncoiling, leveling, cutting, bending, rounding forming, shaping and middle machining treatment to obtain a titanium pipe welding blank, as shown in figure 1.

S2, fixing a welding blank of the titanium pipe;

As shown in fig. 4a, the support structure 4 is arranged in the titanium pipe, the movable roller 1 is regulated by the screw rod 3 to clamp the titanium pipe, the titanium pipe is quickly adapted to titanium pipes with different diameters, and the welding seam 5 of the titanium pipe is positioned right above.

The clamping stress effect diagram is shown in fig. 5, the clamping surfaces of the movable roller 1 and the fixed roller 2 are in close contact with the wall surface of the titanium pipe, so that the clamping force can be uniformly distributed, the pressure concentration on the outer wall of the titanium pipe is reduced, the titanium pipe is ensured to be stable and not to slide in the clamping state, and the straightness and the verticality of the titanium pipe can be maintained especially during welding.

S3, friction stir welding is carried out on a milling machine.

As shown in fig. 7, the whole clamping device is fixed on the workbench 15 through bolts, the stirring head is adjusted to a proper position above the welding line through the operation table 18, then the milling machine is started, and the workbench 15 is controlled to feed along the length position of the tool according to the set welding speed, so that the stirring head is fed along the length direction of the titanium pipe.

Basic parameters of friction stir welding include: stirring head rotation speed n, welding speed v, pressing amount d and stirring head inclination angle a. The basic parameters of friction stir welding of titanium tubing are shown in Table 1.

TABLE 1 ranges of basic parameters for friction stir welding

Titanium pipe welding was accomplished according to the friction stir welding process parameters identified in table 1.

The specific operation is as follows: firstly, sleeving a supporting structure 4 in a tube blank, and aiming at preventing the titanium tube from deforming in the welding process; then the tube blank is placed on a workbench for fixing, and the purpose is to prevent the tube blank from falling off due to the too high rotating speed during friction stir welding. The milling head 14 is adjusted to rotate 2-5 degrees in the opposite direction to the advancing direction of the stirring pin 9. The milling machine is started to preheat a power supply, parameters corresponding to Table 1 are input on an operating table, after the stirring pin 9 reaches the determined rotating speed, the stirring pin is inserted into a gap of a tube blank, a shaft shoulder 7 is tightly pressed on the gap of the tube blank by a pressing amount of 0.1-0.25 mm, and then the operating table 15 drives the titanium tube to advance along the axial direction (welding seam) at a speed of 40-60 mm/min, so that the stirring friction welding of the axial welding seam of the titanium tube is realized.

The rotation speed directly influences the heat generated by friction stir, friction heat can be increased by high-speed rotation, softening and plastic flow of materials are promoted, but too high rotation speed can lead to uneven heat distribution in a welding area, the problems of incomplete welding and poor welding line forming are caused, too low rotation speed can lead a stirring pin to stay in the materials too much, local overheating and expansion of a heat affected zone, grains of the materials become coarse, and the mechanical property of a welded joint is reduced. The welding speed determines the residence time of the material at the weld, thereby affecting the amount of heat input and the degree of mixing of the material; slower welding speeds can provide more heat transfer time, contributing to more uniform material mixing, but too slow may result in overheating or too wide a weld, conversely, too fast welding speeds may result in insufficient heat input, affecting weld formation and joint strength. The pressing amount controls the pressure of the stirring head on the workpiece, and influences the plastic flow and the contact area of the material, thereby influencing the generation of friction heat; an appropriate amount of depression assists in better plastic deformation and mixing of the materials, but excessive pressure may damage the tool or cause deformation of the workpiece. The inclination angle affects the size of the contact surface of the stirring head and the workpiece, and the direction and mode of material flow, and improper inclination angle leads to uneven material mixing or welding defects.

The difficulty in obtaining the rotation speed, welding speed, pressing amount and dip angle of the stirring head in table 1 of the embodiment of the invention is that accurate control is needed and the optimal combination is found, and the method is determined through a large number of experiments and analysis. Experimental researches show that under the condition of fixing other parameters, the welding speed is changed, and the heat input is increased by properly reducing the welding speed, so that the penetration and toughness of the joint are improved, but the microstructure degradation caused by overheating is avoided; by comparing the weld joint properties at different rotational speeds, it was found that moderately increasing the rotational speed effectively increases the tensile strength and plasticity of the joint, as this increases the plastic flow range of the material and the temperature uniformity of the weld zone; test data show that reasonable pressing-down amount can ensure sufficient material contact and friction, and improve the compactness of a welding line, but too high pressing-down amount can cause material extrusion or tool abrasion to be increased; experiments conducted by changing the inclination angle of the stirring head show that the optimized inclination angle can effectively guide the material to flow, reduce welding defects such as air holes and cracks and improve the microstructure uniformity of the welding seam.

S4, induction annealing;

And (3) after welding and forming the welding blank of the titanium pipe, carrying out hot water cleaning and blow-drying, and carrying out induction annealing. An alternating magnetic field with the same current frequency is generated around the induction coil through alternating current (because of the titanium tube, a power frequency power supply of 50Hz is supplied so as to quickly heat the titanium tube), induced electromotive force is correspondingly generated in the tube blank, induced current, namely vortex, is formed on the surface of the tube blank, the vortex rapidly heats the tube blank to 300-400 ℃, and the induction coil is removed at the speed of 30-50 mm/min, so that the annealing purpose is achieved, as shown in figure 8. The induction heating is utilized to rapidly and uniformly heat the tube blank to the annealing temperature, and then the induction coil is slowly removed to control the cooling rate.

In the embodiment 2 of the invention, the physical diagram of the welded seam of the titanium pipe after friction stir welding is shown in fig. 10, and no obvious fusion line exists, so that the integral performance of the welded joint is improved.

In the embodiment 2 of the invention, the hardness distribution curve of the welded seam of the titanium tube after friction stir welding is shown in fig. 11, the hardness of the welded seam is symmetrically distributed along the position of the welded seam, the hardness of a welding heat affected zone after the welding is finished is 179.2HV, the matrix is secondary, and the hardness of the welded seam zone is highest and reaches 268.4HV. The maximum hardness of the welded titanium tube at the weld seam is 198.5HV by arc welding, which is superior to friction stir welding.

The microstructure of the welded seam of the titanium tube after friction stir welding in example 2 of the present invention is shown in FIGS. 12a-12 c; the grains in the matrix area are uniformly distributed, closely distributed and clear in grain boundary, as shown in figure 12a. The heat affected zone is the transition zone between the weld zone and the matrix zone, and compared with the grains in the matrix zone, the grains grow significantly, the sizes of the grains are uneven, and part of the grains deform greatly due to the influence of friction heat generation of the stirring head, as shown in fig. 12b. This is because the heat concentrated around the pin is conducted to a temperature in the vicinity of the heat affected zone which remains high, resulting in grain growth in the heat affected zone. As shown in FIG. 12c, the microstructure of the weld zone is fine and dense, since the original base material grains are crushed into fine grains by the stirring pin during the stirring process. The recrystallization temperature of titanium is between 500 and 600 ℃, and the area passed by the stirring pin is higher than the recrystallization temperature, so that the grains in the stirring area can be recrystallized. The time of the process is relatively short, and the crushed grains and recrystallized grains are not grown so long that the grains in the stirring area are fine. Meanwhile, the phase change of the weld zone is not obvious due to the too short high-temperature time, so that the crystal grains of the weld zone are compact and fine.

With conventional argon arc welding, the microstructure of the weld joint of the titanium tube is shown in fig. 13a-13c, and the weld joint zone mainly comprises coarse beta equiaxed grains, internal needle-like alpha martensite and a small amount of alpha' martensite, because the titanium has poor thermal conductivity, and the high-temperature residence time of the weld joint zone is long, so that coarse beta equiaxed grains are generated. The heat affected zone is affected by the welding heat and is mainly composed of alpha lath grains. The base material is mainly composed of alpha equiaxed grains.

By contrast, the titanium tube welded by friction stir welding in the embodiment of the invention has compact and fine grains at the welding seam, and the fine grains can obviously improve the strength and toughness of the material; the micro defects (such as dislocation, gaps and the like) in the material are distributed more dispersedly, so that the stress concentration phenomenon is reduced, and the wear resistance and fatigue resistance are improved; when the temperature is changed, the internal stress distribution is more uniform, so that the crack formation possibly caused by uneven thermal expansion is reduced, and the thermal stability of the material is improved; the fine grains are helpful for reducing element segregation phenomenon in the casting or solidification process, so that the components of the material are more uniform, and the overall performance is improved; fine grain materials are generally easier to machine in subsequent machining because the fine grain structure can reduce tool wear and reduce cutting resistance.

In the prior art 1 (a friction stir welding method of a thin-walled thin circular tube made of a dissimilar material, CN 103537792A) discloses circumferential welding of the dissimilar material, aiming at low melting point (not exceeding 1700) DEG C, and short welding distance (the diameter of a titanium pipe is not large), and axial force is easy to apply. The embodiment of the invention aims at titanium with high melting point, and is used for longitudinal welding, so that the distance is long, the small plane is easy to appear when radial force is applied, and great technical difficulty exists.

In the embodiment of the invention, the titanium pipe is limited by the geometry of the titanium pipe, and it is very critical to keep stable compression in the axial direction and the radial direction in the welding process, so as to avoid the problem of pipe deformation or weld quality caused by welding stress, and proper clamping devices and supporting structures are required to be designed. The wall thickness of the titanium pipe is small (1.5-2.5 mm), and the heat is quickly conducted, so that the heat input of a welding area is difficult to control, and the quality and mechanical property of a welding line are affected. The welding window of titanium alloy is relatively narrow, and especially in L-FSW (Linear friction stir welding), parameters such as welding speed, rotating speed, axial thrust and the like need to be matched accurately to obtain a high-quality welding seam. According to the embodiment of the invention, the titanium pipe is fixed through the clamping device, the supporting structure is designed in the titanium pipe, the titanium pipe is prevented from deforming during welding, and proper welding parameters are selected through multiple experiments; TZM alloy is selected as a material for the stirring head, and the shapes of a shaft shoulder 7 and a stirring pin 9 are reasonably designed; ensure the uniform heat distribution of the welding area and prevent welding defects such as cracks, air holes and the like caused by overheating or underheating.

The foregoing description is only of the preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims (10)

1. The equipment for preparing the titanium and titanium alloy titanium pipe based on the stirring friction of the milling machine comprises the milling machine and is characterized by further comprising a supporting structure (4), a clamping device and a stirring head;

The supporting structure (4) is cylindrical and is arranged on the inner wall of the titanium pipe and used for supporting the titanium pipe;

the clamping device is used for clamping and fixing the titanium pipe;

The diameter of a main shaft of the milling machine is increased to 60-150 mm so as to improve the rotation speed of the variable speed gear, and the taper of the main shaft is 3-6 degrees; the main shaft of the milling machine is welded and fixed with the stirring head through an adapter made of high-temperature resistant materials; the axial feeding mechanism of the milling machine provides constant-speed and stable propelling force and expands the stroke of the Z axis; the clamping device and the titanium pipe are fixed on a workbench (15) of the milling machine together;

The stirring head comprises a shaft shoulder (7) with the outer diameter of 3-10 mm, and a stirring needle (9) which protrudes axially is fixed at the central position of the bottom of the shaft shoulder (7).

2. The equipment for preparing titanium and titanium alloy titanium pipes based on milling machine stirring friction according to claim 1, wherein the clamping device comprises a movable roller (1) and a fixed roller (2), and the movable roller (1) and the fixed roller (2) are symmetrically distributed on two sides of the titanium pipes; the lower end of the movable roller (1) is connected with a nut seat of the screw rod (3), the axis of the screw rod (3) is vertical to the clamping surface of the movable roller (1), the screw rod (3) is driven manually or electrically to drive the movable roller (1) to move towards a direction close to or far away from the fixed roller (2), and the distance between the movable roller (1) and the fixed roller (2) is adjusted to clamp titanium pipes with different sizes; the position of the movable roller (1) or the fixed roller (2) contacted with the titanium pipe is provided with a pressure sensor.

3. The equipment for preparing titanium and titanium alloy titanium pipes based on stirring friction of a milling machine according to claim 2, wherein a plurality of groups of movable rollers (1) and fixed rollers (2) are arranged along the axis direction of the titanium pipes, and the distance between each group of movable rollers (1) and fixed rollers (2) is gradually reduced along the advancing direction of the titanium pipes.

4. The equipment for preparing titanium and titanium alloy titanium pipes based on milling machine stirring friction according to claim 1, wherein the diameter and the length of the supporting structure (4) are respectively matched with the inner diameter and the length of the titanium pipes, grooves (4-1) are formed in the surface of the supporting structure (4) along the axial direction, and the grooves (4-1) are located at welding seams of the titanium pipes.

5. The equipment for preparing titanium and titanium alloy titanium pipes based on stirring friction of a milling machine according to claim 4, wherein the width of the groove (4-1) is 1.5 mm-4 mm, and the depth of the groove (4-1) is 2 mm-5 mm.

6. The equipment for preparing titanium and titanium alloy titanium pipes based on milling machine stirring friction according to claim 1, wherein the inner diameter of the shaft shoulder (7) is matched with the diameter of the stirring pin (9), and the inner diameter of the shaft shoulder (7) is 1.5-6 mm.

7. The equipment for preparing titanium and titanium alloy titanium pipes based on stirring friction of a milling machine according to claim 1, characterized in that the profile shape of the shaft shoulder (7) is conical, inclined or special curve.

8. The equipment for preparing titanium and titanium alloy titanium pipes based on stirring friction of a milling machine according to claim 1, wherein the length-diameter ratio of the stirring pin (9) is 3:1-5:1, and the stirring area (13) of the stirring pin (9) is in an inverted cone shape or a thread shape.

9. A method for preparing titanium and titanium alloy titanium pipes based on milling machine stirring friction, which is characterized in that the equipment for preparing titanium and titanium alloy titanium pipes based on milling machine stirring friction as claimed in claim 1 is adopted, and comprises the following steps:

S1, curling and forming a titanium plate to obtain a welding blank of a titanium pipe;

s2, fixing a welding blank of the titanium pipe: a cylindrical supporting structure (4) is arranged on the inner wall of the titanium pipe and is used for supporting the titanium pipe; clamping and fixing the titanium pipe by a clamping device;

S3, modifying a main shaft system, a stirring head mounting interface and an axial feeding mechanism of the milling machine, connecting the stirring head, and performing friction stir welding on the milling machine; the rotation speed of the stirring head is 1500-1800 r/min, the inclination angle of the stirring head is 2-5 degrees, the pressing amount is 0.1-0.25 mm, and the axial feeding speed is 40-60 mm/min;

And S4, after welding and forming, carrying out hot water cleaning, blow-drying and induction annealing to obtain the alloy.

10. The method for preparing titanium and titanium alloy titanium pipes based on stirring friction of a milling machine according to claim 9, wherein S4 comprises the following steps: the alternating current generates an alternating magnetic field with the same frequency as the current around the induction coil, and correspondingly generates induced electromotive force in the tube blank, and induced current is formed on the surface of the tube blank, so that the tube blank is quickly heated to 300-400 ℃ and the induction coil is removed at the speed of 30-50 mm/min, thereby achieving the aim of annealing.