A method for precision machining of a nickel-titanium-iron shape memory alloy pipe joint with an annular inner rib

Abstract

A kind of precision machining method of nickel-titanium-iron shape memory alloy pipe joint with annular inner rib, the present application belongs to the technical field of mechanical processing of shape memory alloy.The present application solves the problems that existing nickel-titanium-iron shape memory alloy cutting is difficult, there is poor chip fracture, burr formation and serious tool wear in the process of chip formation, and precision machining of pipe joint cannot be realized.Method:one, cutting;Two, through-hole processing;Three, end face turning;Four, outer circle diameter turning processing;Five, turning processing of inner rib and inner hole.The present application is used for precision machining of nickel-titanium-iron shape memory alloy pipe joint with annular inner rib.

Description

Technical Field

[0001] This invention belongs to the field of machining technology of shape memory alloys. Background Technology

[0002] Nickel-titanium iron (NiTiFe) shape memory alloys are widely used in electronics, machinery, and medical fields due to their shape memory effect and superelasticity. NiTiFe shape memory alloy pipe fittings are commonly used in aerospace and aviation for sealing various gas and oil circuits, offering advantages such as high pressure resistance, simple connection methods, reliable fastening, and reduced structural weight. The austenitic transformation temperature of NiTiFe is very low, typically below zero degrees Celsius. The basic principle of these shape memory alloy pipe fittings is as follows: In the low-temperature martensitic phase state below zero degrees Celsius, the pipe fitting undergoes a certain amount of diameter expansion deformation and is then stored in an environment below the martensitic transformation end temperature. When needed, it is removed and fitted onto the joint of the two pipes to be connected. Under the thermal effect of room temperature, the shape memory alloy pipe fitting transforms into the austenitic phase and ultimately shrinks and deforms due to the shape memory effect, completing the pipe connection.

[0003] The high elasticity and high work hardening rate of nickel-titanium-iron shape memory alloys lead to difficult machining and poor workpiece quality. The machining process of these alloys is also affected by their unconventional strain-stress behavior, resulting in poor chip breakage, burr formation, and severe tool wear, such as dulling or breakage of lathe tools. Therefore, ordinary cutting tools cannot machine these alloys. Furthermore, the presence of multiple annular internal ribs on the inner wall of the pipe joint further complicates precision machining. Existing cutting parameters offer very little reference value, and tool wear observed when using these parameters remains extremely severe.

[0004] Nickel-titanium iron (NiTiFe) shape memory alloys exhibit a B2 structure in the austenitic state, possessing the symmetry of a cubic structure, resulting in extremely high hardness and stiffness. However, in the martensitic state, they exhibit a B19′ monoclinic structure, which is asymmetrical and possesses good ductility and flexibility. This leads to a very narrow machining window for this type of material. Furthermore, because the martensitic transformation end temperature of NiTiFe is below zero degrees Celsius, it remains in the austenitic state at room temperature, making machining extremely difficult. Therefore, a reasonable precision machining method for NiTiFe pipe fittings with annular internal ribs is needed. Summary of the Invention

[0005] This invention aims to solve the problems of high machining difficulty of nickel-titanium-iron shape memory alloys, poor chip breakage, burr formation, and severe tool wear during the cutting process, which makes it impossible to achieve precision machining of pipe joints. Instead, it provides a method for precision machining of nickel-titanium-iron shape memory alloy pipe joints with annular internal ribs.

[0006] A method for precision machining of a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs, comprising the following steps:

[0007] I. Cutting:

[0008] The original nickel-titanium-iron shape memory alloy rod was cut to obtain the cut rod.

[0009] II. Through-hole machining:

[0010] The cut bar is placed in liquid nitrogen for cryogenic treatment for 1 to 2 hours to obtain cryogenically treated bar. The cryogenically treated bar is then mounted on a drilling machine. Under the conditions of drilling speed of 18 to 22 m / min, feed rate of 0.02 mm / r to 0.04 mm / r and liquid nitrogen spraying on the surface of the bar, a twist drill made of cobalt high-speed steel is used to perform through hole machining along the axial direction of the cryogenically treated bar. After machining, the bar is stored in liquid nitrogen to obtain a tube blank.

[0011] III. Vehicle end face:

[0012] The tube blank is mounted on a lathe fixture. Under the conditions of turning speed of 18m / min to 22m / min, feed rate of 0.05mm / r to 0.07mm / r and liquid nitrogen spraying on the surface of the tube blank, the two ends of the tube blank are machined using a cutting tool made of cemented carbide containing tungsten carbide until the length of the tube blank after machining reaches the length L of the pipe joint with annular inner rib, and the tube blank with both ends machined is obtained.

[0013] IV. Turning of outer diameter:

[0014] Under the conditions of turning speed of 18m / min~22m / min, feed rate of 0.05mm / r~0.07mm / r and liquid nitrogen spraying on the surface of the tube blank, the tube blank is further machined on the lathe fixture using an external turning tool made of cemented carbide containing tungsten carbide until the outer diameter of the machined tube blank reaches the outer diameter D1 of the pipe joint with annular inner rib, thus obtaining the tube blank after external turning;

[0015] V. Turning of internal ribs and internal holes:

[0016] ① Replace the external turning tool made of tungsten carbide cemented carbide with an internal grooving tool made of integral tungsten steel with a nano-coating;

[0017] ② Under the conditions of turning speed of 30m / min~35m / min, feed speed of 0.005mm / r~0.02mm / r and liquid nitrogen spraying on the surface of the tube blank, the tube blank rotates with the lathe spindle, the inner hole grooving tool feeds along the axial direction of the tube blank, and then feeds radially outward until the inner diameter D2 of the pipe joint with annular inner rib is reached. The inner hole grooving tool returns to its original position, and the axial and radial feeds are repeated.

[0018] ③ Under the conditions of turning speed of 30m / min~35m / min, feed speed of 0.005mm / r~0.02mm / r and liquid nitrogen spraying on the surface of the tube blank, the inner hole is machined along the axial direction of the tube blank until the diameter d and length of the inner rib of the pipe joint with annular inner rib are reached, and the annular inner rib is obtained.

[0019] ④ Repeat steps 5.2 and 5.3 to process the inner hole and the annular inner rib in the pipe joint with the annular inner rib in sequence.

[0020] ⑤ After turning, a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs is obtained.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention utilizes the relatively good machinability of martensitic materials to propose a low-temperature machining method that keeps nickel-titanium iron shape memory alloys in a martensitic state throughout the entire machining process. By employing a suitable combination of cutting tools, cutting speed, and feed rate, the machining of nickel-titanium iron shape memory alloy pipe joints with annular internal ribs is completed in the martensitic state, avoiding tool sticking problems, significantly reducing tool wear, and improving tool life.

[0023] 2. In the entire processing, the present invention uses a spray gun to spray liquid nitrogen onto the workpiece. The liquid nitrogen cooling process is adjusted according to the turning speed and workpiece size. The nickel-titanium-iron alloy is always in the martensitic state, which makes the cutting performance better and avoids the influence of temperature-induced phase transformation on its dimensional accuracy.

[0024] 3. During the cutting process of this invention, a twist drill made of M35 cobalt-containing (5% cobalt content) high-speed steel, a turning tool containing tungsten carbide, and a full tungsten carbide internal grooving tool with a nano-coating are used. With specific cutting speed and feed rate, the machined nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs is burr-free, with a machining accuracy of IT9 and a surface roughness of Ra1.6.

[0025] This invention relates to a precision machining method for a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs. Attached Figure Description

[0026] Figure 1This is a schematic diagram of the nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs prepared in Example 1;

[0027] Figure 2 This is a schematic diagram of the inner hole with an inner diameter of D2 and a length of N1 processed in step 5② of Example 1;

[0028] Figure 3 This is a schematic diagram of the first inner rib with an inner diameter of d and a length of T1, and the inner hole with an inner diameter of D2 and a length of N2, processed in steps 5, ③ and ④ of Example 1.

[0029] Figure 4 This is a schematic diagram of the second inner rib with an inner diameter of d and a length of T2, and an inner hole with an inner diameter of D2 and a length of M, processed in step five ④ of Example 1.

[0030] Figure 5 This is a schematic diagram of the third inner rib with an inner diameter of d and a length of T3, and an inner hole with an inner diameter of D2 and a length of N3, processed in step five ④ of Example 1.

[0031] Figure 6 This is a schematic diagram of the fourth inner rib with an inner diameter of d and a length of T4, and an inner hole with an inner diameter of D2 and a length of N4, processed in step five ④ of Example 1.

[0032] Figure 7 This is an external photograph of the nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs prepared in Example 1;

[0033] Figure 8 This is an internal photograph of the nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs prepared in Example 1;

[0034] Figure 9 This is a comparison image of the external appearance of a pipe fitting when a portion of its outer diameter is machined. Detailed Implementation

[0035] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0036] Specific Implementation Method 1: This implementation method provides a precision machining method for a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs, which is carried out according to the following steps:

[0037] I. Cutting:

[0038] The original nickel-titanium-iron shape memory alloy rod was cut to obtain the cut rod.

[0039] II. Through-hole machining:

[0040] The cut bar is placed in liquid nitrogen for cryogenic treatment for 1 to 2 hours to obtain cryogenically treated bar. The cryogenically treated bar is then mounted on a drilling machine. Under the conditions of drilling speed of 18 to 22 m / min, feed rate of 0.02 mm / r to 0.04 mm / r and liquid nitrogen spraying on the surface of the bar, a twist drill made of cobalt high-speed steel is used to perform through hole machining along the axial direction of the cryogenically treated bar. After machining, the bar is stored in liquid nitrogen to obtain a tube blank.

[0041] III. Vehicle end face:

[0042] The tube blank is mounted on a lathe fixture. Under the conditions of turning speed of 18m / min to 22m / min, feed rate of 0.05mm / r to 0.07mm / r and liquid nitrogen spraying on the surface of the tube blank, the two ends of the tube blank are machined using a cutting tool made of cemented carbide containing tungsten carbide until the length of the tube blank after machining reaches the length L of the pipe joint with annular inner rib, and the tube blank with both ends machined is obtained.

[0043] IV. Turning of outer diameter:

[0044] Under the conditions of turning speed of 18m / min~22m / min, feed rate of 0.05mm / r~0.07mm / r and liquid nitrogen spraying on the surface of the tube blank, the tube blank is further machined on the lathe fixture using an external turning tool made of cemented carbide containing tungsten carbide until the outer diameter of the machined tube blank reaches the outer diameter D1 of the pipe joint with annular inner rib, thus obtaining the tube blank after external turning;

[0045] V. Turning of internal ribs and internal holes:

[0046] ① Replace the external turning tool made of tungsten carbide cemented carbide with an internal grooving tool made of integral tungsten steel with a nano-coating;

[0047] ② Under the conditions of turning speed of 30m / min~35m / min, feed speed of 0.005mm / r~0.02mm / r and liquid nitrogen spraying on the surface of the tube blank, the tube blank rotates with the lathe spindle, the inner hole grooving tool feeds along the axial direction of the tube blank, and then feeds radially outward until the inner diameter D2 of the pipe joint with annular inner rib is reached. The inner hole grooving tool returns to its original position, and the axial and radial feeds are repeated.

[0048] ③ Under the conditions of turning speed of 30m / min~35m / min, feed speed of 0.005mm / r~0.02mm / r and liquid nitrogen spraying on the surface of the tube blank, the inner hole is machined along the axial direction of the tube blank until the diameter d and length of the inner rib of the pipe joint with annular inner rib are reached, and the annular inner rib is obtained.

[0049] ④ Repeat steps 5.2 and 5.3 to process the inner hole and the annular inner rib in the pipe joint with the annular inner rib in sequence.

[0050] ⑤ After turning, a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs is obtained.

[0051] In step one of this specific implementation method, electrical discharge machining (EDM) technology is used for cutting.

[0052] In this specific embodiment, liquid nitrogen is sprayed during the drilling process to prevent the material from undergoing an austenitic phase transformation due to temperature rise.

[0053] The beneficial effects of this embodiment are:

[0054] 1. This embodiment utilizes the relatively good machinability of martensitic materials to propose a low-temperature machining method that keeps the nickel-titanium iron shape memory alloy in a martensitic state throughout the entire machining process. By employing a suitable combination of cutting tools, cutting speed, and feed rate, the machining of the nickel-titanium iron shape memory alloy pipe joint with annular internal ribs is completed in the martensitic state, avoiding the problem of tool sticking, significantly reducing tool wear, and improving tool life.

[0055] 2. In this embodiment, liquid nitrogen is sprayed onto the workpiece using a spray gun throughout the entire processing. The liquid nitrogen cooling process is adjusted according to the turning speed and workpiece size. The nickel-titanium-iron alloy remains in the martensitic state, resulting in better machinability and avoiding the impact of temperature-induced phase transformation on its dimensional accuracy.

[0056] 3. In this embodiment, during the cutting process, a twist drill made of M35 cobalt-containing (5% cobalt content) high-speed steel, a turning tool containing tungsten carbide, and a full tungsten carbide internal grooving tool with a nano-coating are used. With specific cutting speed and feed rate, the machined nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs is burr-free, and the machining accuracy can reach IT9, and the surface roughness can reach Ra1.6.

[0057] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the diameter of the original nickel-titanium-iron shape memory alloy rod mentioned in step one is 1mm to 3mm larger than the outer diameter D1 of the pipe joint with annular inner ribs. Everything else is the same as in Specific Implementation Method One.

[0058] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the length of the cut rod described in step one is 3mm to 5mm longer than the length L of the pipe joint with the annular inner rib. Everything else is the same as in Specific Implementation Method One or Two.

[0059] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the diameter of the through hole in the tube blank described in step two is 2mm to 3mm smaller than the diameter d of the inner rib of the pipe joint with annular inner ribs. Everything else is the same as in Specific Implementation Methods One to Three.

[0060] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that, in steps Two to Five, liquid nitrogen is sprayed onto the surface at a spraying speed of not less than 40 mL / min. Everything else is the same as in Specific Implementation Methods One to Four.

[0061] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the cobalt-containing high-speed steel mentioned in step two is M35 cobalt-containing high-speed steel. Everything else is the same as in Specific Implementation Methods One to Five.

[0062] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the tungsten carbide-containing cemented carbide mentioned in steps three and four is EF05 tungsten carbide-containing cemented carbide. Everything else is the same as in Specific Implementation Methods One to Six.

[0063] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the nano-coating in the integral tungsten steel with nano-coating described in step five① is TiSiN. Everything else is the same as in Specific Implementation Methods One to Seven.

[0064] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: in step five ②, the feed distance of the inner hole grooving cutter along the tube blank axis is less than or equal to one grooving cutter width. Everything else is the same as in Specific Implementation Methods One to Eight.

[0065] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: the nickel-titanium-iron shape memory alloy pipe joint with annular inner ribs described in step five (⑤) has multiple annular inner ribs inside. Everything else is the same as in Specific Implementation Methods One to Nine.

[0066] The beneficial effects of the present invention are verified using the following embodiments:

[0067] Example 1, combined with Figures 1 to 6 Specifically, in this embodiment, the pipe joint with annular inner ribs has an outer diameter D1 = 13mm, an inner diameter D2 = 11mm, and a length L = 40mm. Two sets of inner ribs are symmetrically arranged in the pipe joint with annular inner ribs, with a spacing M = 12mm between the two sets of inner ribs. Each set of inner ribs consists of two annular inner ribs with an inner diameter of 7mm and a length of 2mm, and the spacing between the two annular inner ribs is 5mm.

[0068] Specifically, the pipe joint with annular inner ribs consists of, from one side, an inner hole with an inner diameter of D2 = 11 mm and a length of N1 = 5 mm, a first inner rib with an inner diameter of d = 7 mm and a length of T1 = 2 mm, an inner hole with an inner diameter of D2 = 11 mm and a length of N2 = 5 mm, a second inner rib with an inner diameter of d = 7 mm and a length of T2 = 2 mm, an inner hole with an inner diameter of D2 = 11 mm and a length of M = 12 mm, a third inner rib with an inner diameter of d = 7 mm and a length of T3 = 2 mm, an inner hole with an inner diameter of D2 = 11 mm and a length of N3 = 5 mm, a fourth inner rib with an inner diameter of d = 7 mm and a length of T4 = 2 mm, and an inner hole with an inner diameter of D2 = 11 mm and a length of N4 = 5 mm.

[0069] A method for precision machining of a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs, comprising the following steps:

[0070] I. Cutting:

[0071] The original nickel-titanium-iron shape memory alloy rod was cut to obtain the cut rod.

[0072] The nickel-titanium-iron shape memory alloy is Ni 47 Ti 50 Fe3 (atomic percentage); the original diameter of the nickel-titanium-iron shape memory alloy rod is 14mm; the length of the cut rod is 43mm;

[0073] II. Through-hole machining:

[0074] The cut bar was cryogenically treated in liquid nitrogen for 1 hour to obtain cryogenically treated bar. The cryogenically treated bar was then mounted on a drilling machine. Under the conditions of drilling speed of 20 m / min, feed rate of 0.03 mm / r and liquid nitrogen spraying on the surface of the bar, a twist drill made of cobalt high-speed steel was used to perform through hole machining along the axial direction of the cryogenically treated bar. After machining, the bar was stored in liquid nitrogen to obtain a tube blank.

[0075] The spraying rate of liquid nitrogen on the surface of the rod is 40 mL / min;

[0076] The diameter of the through hole in the tube blank is 5mm;

[0077] III. Vehicle end face:

[0078] The tube blank is mounted on a lathe fixture. Under the conditions of turning speed of 20m / min, feed rate of 0.06mm / r and liquid nitrogen spraying on the surface of the tube blank, the two ends of the tube blank are machined using a cutting tool made of cemented carbide containing tungsten carbide until the length of the tube blank after machining reaches the length of the pipe joint with annular inner rib L=40mm, and the tube blank with both ends machined is obtained.

[0079] The spraying rate of liquid nitrogen on the surface of the tube blank is 40 mL / min;

[0080] IV. Turning of outer diameter:

[0081] Under the conditions of turning speed of 20m / min, feed rate of 0.06mm / r and liquid nitrogen spraying on the surface of the tube blank, the tube blank is further machined on the lathe fixture using an external turning tool made of tungsten carbide until the outer diameter of the turned outer diameter reaches the outer diameter D1 of the pipe joint with annular inner ribs, which is 13mm, and the tube blank after external turning is obtained.

[0082] The spraying rate of liquid nitrogen on the surface of the tube blank is 40 mL / min;

[0083] V. Turning of internal ribs and internal holes:

[0084] ① Replace the external turning tool made of tungsten carbide cemented carbide with an internal grooving tool made of integral tungsten steel with a nano-coating;

[0085] ② Under the conditions of turning speed of 32m / min, feed speed of 0.01mm / r and liquid nitrogen spraying on the surface of the tube blank, the tube blank rotates with the lathe spindle, the inner hole grooving tool is fed along the axial direction of the tube blank, and then fed radially outward by dimension δ, where δ=3mm, until the inner diameter D2 of the pipe joint with annular inner rib is reached. The inner hole grooving tool is returned to its original position, and the axial and radial feeds are repeated to obtain an inner hole with an inner diameter D2=11mm and a length N1=5mm.

[0086] The spraying rate of liquid nitrogen on the tube blank surface is 20 mL / min;

[0087] ③ Under the conditions of turning speed of 32m / min, feed speed of 0.01mm / r and liquid nitrogen spraying on the surface of the tube blank, the inner hole is machined along the axial direction of the tube blank until the diameter d and length T1 of the first inner rib of the pipe joint with annular inner rib are reached, and the inner hole diameter d = 7mm and the length T1 = 2mm of the first inner rib are obtained.

[0088] The spraying rate of liquid nitrogen on the tube blank surface is 20 mL / min;

[0089] ④ Repeat steps 5.2 and 3 to sequentially process the following inner ribs in the pipe joint with annular inner ribs: inner hole with diameter D2 = 11mm and length N2 = 5mm, second inner rib with diameter d = 7mm and length T2 = 2mm, inner hole with diameter D2 = 11mm and length M = 12mm, third inner rib with diameter d = 7mm and length T3 = 2mm, inner hole with diameter D2 = 11mm and length N3 = 5mm, fourth inner rib with diameter d = 7mm and length T4 = 2mm, and inner hole with diameter D2 = 11mm and length N4 = 5mm.

[0090] ⑤ After turning, a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs is obtained.

[0091] The cobalt-containing high-speed steel mentioned in step two is specifically M35 cobalt-containing high-speed steel.

[0092] The tungsten carbide-containing cemented carbide mentioned in steps three and four is specifically EF05 tungsten carbide-containing cemented carbide.

[0093] In step 5①, the nano-coating of the integral tungsten steel with nano-coating is TiSiN, and the integral tungsten steel is YL10.2 integral tungsten steel.

[0094] In step 5②, the axial feed distance of the internal grooving tool is equal to the width of one grooving tool.

[0095] Figure 7 This is an external photograph of the nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs prepared in Example 1; Figure 8 The image shows the internal structure of the nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs prepared in Example 1. As can be seen from the image, the outer surface and inner hole dimensions of the pipe joint after machining are relatively smooth, and there are no burrs visible to the naked eye.

[0096] The pipe fitting prepared in Example 1 was tested and found to have a dimensional accuracy of IT9 and a surface roughness of Ra1.6. No significant wear was observed on the cutting tool after machining.

[0097] Comparative Experiment: This comparative experiment differs from Example 1 in that the external turning speed in step four is 3 m / min and the feed rate is 0.24 mm / r. Everything else is the same as in Example 1.

[0098] Figure 9 The image shows the external surface of the pipe fitting after a portion of its outer diameter has been machined for comparison. As can be seen from the image, the machined outer surface is very rough, with obvious tool marks. Testing showed that the pipe fitting prepared in the comparative experiment achieved an IT12 dimensional accuracy and a Ra25 surface roughness, with no significant tool wear observed after machining.

Claims

1. A method for precision machining of a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs, characterized in that... It is done in the following steps: I. Cutting: The original nickel-titanium-iron shape memory alloy rod was cut to obtain the cut rod. II. Through-hole machining: The cut bar is placed in liquid nitrogen for cryogenic treatment for 1 to 2 hours to obtain cryogenically treated bar. The cryogenically treated bar is then mounted on a drilling machine. Under the conditions of drilling speed of 18 to 22 m / min, feed rate of 0.02 mm / r to 0.04 mm / r and liquid nitrogen spraying on the surface of the bar, a twist drill made of cobalt high-speed steel is used to perform through hole machining along the axial direction of the cryogenically treated bar. After machining, the bar is stored in liquid nitrogen to obtain a tube blank. III. Vehicle end face: The tube blank is mounted on a lathe fixture. Under the conditions of turning speed of 18m / min to 22m / min, feed rate of 0.05mm / r to 0.07mm / r and liquid nitrogen spraying on the surface of the tube blank, the two ends of the tube blank are machined using a cutting tool made of cemented carbide containing tungsten carbide until the length of the tube blank after machining reaches the length L of the pipe joint with annular inner rib, thus obtaining the tube blank with machined ends. IV. Turning of outer diameter: Under the conditions of turning speed of 18m / min~22m / min, feed rate of 0.05mm / r~0.07mm / r and liquid nitrogen spraying on the surface of the tube blank, the tube blank is further machined on the lathe fixture using an external turning tool made of cemented carbide containing tungsten carbide until the outer diameter of the machined tube blank reaches the outer diameter D1 of the pipe joint with annular inner rib, thus obtaining the tube blank after external turning; V. Turning of internal ribs and internal holes: ① Replace the external turning tool made of tungsten carbide cemented carbide with an internal grooving tool made of integral tungsten steel with a nano-coating; ② Under the conditions of turning speed of 30m / min~35m / min, feed speed of 0.005mm / r~0.02mm / r and liquid nitrogen spraying on the surface of the tube blank, the tube blank rotates with the lathe spindle, the inner hole grooving tool feeds along the axial direction of the tube blank, and then feeds radially outward until the inner diameter D2 of the pipe joint with annular inner rib is reached. The inner hole grooving tool returns to its original position, and the axial and radial feeds are repeated. ③ Under the conditions of turning speed of 30m / min~35m / min, feed speed of 0.005mm / r~0.02mm / r and liquid nitrogen spraying on the surface of the tube blank, the inner hole is machined along the axial direction of the tube blank until the diameter d and length of the inner rib of the pipe joint with annular inner rib are reached, and the annular inner rib is obtained. ④ Repeat steps 5.2 and 5.3 to process the inner hole and the annular inner rib in the pipe joint with the annular inner rib in sequence. ⑤ After turning, a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs is obtained.

2. The precision machining method for a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs according to claim 1, characterized in that... The diameter of the original nickel-titanium-iron shape memory alloy rod mentioned in step one is 1mm to 3mm larger than the outer diameter D1 of the pipe joint with annular inner ribs.

3. The precision machining method for a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs according to claim 1, characterized in that... The length of the cut bar described in step one is 3mm to 5mm longer than the length L of the pipe joint with the annular inner rib.

4. A method for precision machining of a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs according to claim 1, characterized in that... In step two, the diameter of the through hole in the tube blank is 2mm to 3mm smaller than the diameter d of the inner rib of the pipe joint with annular inner rib.

5. A method for precision machining of a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs according to claim 1, characterized in that... In steps two through five, liquid nitrogen is sprayed onto the surface at a spraying speed of not less than 40 mL / min.

6. A method for precision machining of a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs according to claim 1, characterized in that... The cobalt-containing high-speed steel mentioned in step two is M35 cobalt-containing high-speed steel.

7. A method for precision machining of a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs according to claim 1, characterized in that... The tungsten carbide cemented carbide mentioned in steps three and four is EF05 tungsten carbide cemented carbide.

8. A method for precision machining of a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs according to claim 1, characterized in that... The nano-coating in the integral tungsten steel with nano-coating mentioned in step 5① is TiSiN.

9. A method for precision machining of a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs according to claim 1, characterized in that... In step 5②, the feed distance of the inner hole grooving tool along the tube blank axis is less than or equal to one grooving tool width.

10. A method for precision machining of a nickel-titanium-iron shape memory alloy pipe joint with annular internal ribs according to claim 1, characterized in that... The nickel-titanium-iron shape memory alloy pipe joint with annular inner ribs described in step 5.⑤ has multiple annular inner ribs inside.

Images