Processing method of an elongated double-layer pipe body for a wind tunnel

Abstract

The application relates to a processing method of an elongated double-layer pipe body for a wind tunnel, which is sleeved with an outer pipe body made of stainless steel or a high-temperature alloy and an inner pipe body made of a high-nickel alloy steel. The outer pipe body is semi-finished, and the inner hole of the outer pipe body is finished to the required inner hole size of the sleeving, and the outer circle is reserved with a machining allowance of 8 mm. The inner pipe body is semi-finished again, and the inner hole of the inner pipe body is reserved with a machining allowance of 8 mm. The outer circle is finished to be 0.2-0.4 mm larger than the inner hole of the semi-finished outer pipe body, that is, the interference amount of the sleeving is 0.2-0.4 mm. Then, the semi-finished inner pipe body is sleeved into the outer pipe body by means of hot sleeving. The sleeved double-layer pipe body is finished to the required size. When each pipe body is finished, the frame is first machined, and then the inner hole is machined by using the frame as the reference. The spindle speed, the axial feed and the cutting depth are controlled during the machining of the inner hole. The wood guide key is used for supporting and guiding during each machining, so that the straightness of the inner hole can be effectively controlled. After the inner hole is machined, the centering end cover is assembled. After the centering, the outer circle is machined. The spindle speed, the axial feed and the cutting depth are controlled during the machining process, so that the coaxiality of the inner hole and the outer circle of the inner pipe body can be effectively controlled.

Description

Technical Field

[0001] This invention belongs to the field of mechanical manufacturing technology, specifically relating to a method for processing a slender double-layer tube for wind tunnels, which is made of stainless steel or high-temperature alloy and high-nickel alloy steel in a double-layer slender tube body, using CNC lathes, deep hole drilling and boring machines and pit-type heat treatment furnaces. Background Technology

[0002] my country is currently vigorously developing its aerospace industry, and the foundation for this development is the establishment of various types of wind tunnel testing equipment. The main component of a wind tunnel is the high-pressure gas generating device: the high-pressure tube system. This system typically consists of 6 to 15 tubes. Because the gas inside the tubes contains hydrogen, the tubes are often designed with two layers. The inner layer is made of stainless steel or a high-temperature alloy, while the outer layer is made of pressure-bearing high-nickel alloy structural steel 35CrNi3MoV or 36CrNi3MoV. The inner tube needs to be interference-fitted into the outer tube. The characteristics of this type of tube are: total length 3000–7000 mm, outer diameter 300–1200 mm. The inner and outer tubes are interference-fitted together, and after fitting, the straightness of the inner hole of the inner tube is no greater than 0.1 mm, and the coaxiality between the outer diameter of the outer tube and the inner hole is no greater than 0.2 mm. Because thickness gauges cannot detect the wall thickness of the inner tube in a double-layered tube system, the processing of this type of tube is difficult, necessitating the design of a reasonable manufacturing process. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for processing a slender double-layer tube for wind tunnels, which is made of stainless steel or high-temperature alloy and high-nickel alloy structural steel. The inner tube is made of stainless steel or high-temperature alloy, and the outer tube is made of pressure-bearing high-nickel alloy structural steel 35CrNi3MoV or 36CrNi3MoV. The inner tube needs to be interference-fitted into the outer tube. After assembly, the finished tube is required to have an inner hole straightness of no more than 0.1 mm and an outer diameter coaxiality of no more than 0.2 mm with the inner hole.

[0004] The objective of this invention is achieved as follows: a method for manufacturing a slender double-layered tube for wind tunnels, with the specific manufacturing steps as follows:

[0005] Step 1) Before assembly, perform semi-finishing on the outer tube body: Use a CNC lathe to machine the carriage position at both ends of the outer tube body blank, 200-300mm from the end face. The carriage position should be at least 100mm long, and the outer diameter should be rounded with a runout of less than 0.05mm. After machining the carriage position, transfer the blank to a deep hole drilling and boring machine. Using this carriage position as a reference, align the outer diameter at the carriage position on the deep hole drilling and boring machine until the runout is no more than 0.1mm before performing deep hole machining. During machining, control the spindle speed at 40-65r / min and the axial feed at 25-30mm / min. Simultaneously, control the boring depth of cut to 2-3mm per pass, with the final cut between 0.4-0.6mm. Each machining operation uses wooden guide keys for support and guidance, effectively controlling the straightness of the inner hole. After boring, the blank is transferred to a CNC lathe for machining. Centering end caps are used at both ends for direct centering. The outer diameter is precision turned to the set size. During machining, the speed is controlled at 50-60 r / min, the feed is controlled at 0.4-0.6 mm / r, the depth of cut is between 2-4 mm, and the depth of cut of the last cut is no more than 0.5 mm. Afterwards, the lathe is turned again at 200-300 mm from the end face at both ends. The length of the lathe position is required to be no less than 100 mm, and the runout of the outer diameter is less than 0.05 mm. This effectively controls the coaxiality of the inner hole and outer diameter of the outer tube. The lathe is then turned again at both ends to facilitate the subsequent precision machining of the double-layer tube after assembly.

[0006] Step 2) Semi-finishing of the inner tube before assembly: Using a CNC lathe, position the carriage at 200-300mm from the end face on both ends of the inner tube blank. The carriage length should be no less than 100mm, and the outer diameter runout should be less than 0.05mm. After setting the carriage, transfer the blank to a deep hole drilling and boring machine. Using this carriage as a reference, align the outer diameter runout at the carriage position on the deep hole drilling and boring machine to ensure it is no more than 0.1mm before performing deep hole machining. During machining, control the spindle speed at 40-65r / min and the axial feed at 4-6mm / min. Simultaneously, control the boring depth of cut to 2-3mm per pass, with the final cut being 0.4-0.6mm. During each machining operation, wooden guide keys are used for support and guidance to effectively control the straightness of the inner hole. After boring, the blank is transferred to a CNC lathe for machining. Centering end caps are used at both ends for direct centering. The outer diameter is precision machined to the set size. The machining process controls the speed at 40-50 r / min, the feed at 0.2-0.4 mm / r, and the depth of cut at 0.5-2 mm for each pass, with the final pass reaching a depth of cut of 0.2-0.4 mm. The inner tube body is then semi-finished again, requiring an 8 mm machining allowance to be left in the inner hole of the inner tube. The outer diameter is finished to be 0.2-0.4 mm larger than the inner hole of the semi-finished outer tube body, ensuring an interference fit of 0.2-0.4 mm.

[0007] Ensure the interference fit of the assembly to effectively control the coaxiality of the inner tube's inner bore and outer diameter, facilitating heat fitting.

[0008] Step 3) Assemble the inner and outer tubes: Heat-fit the semi-finished inner tube into the semi-finished outer tube. During heat fitting, use a pit furnace to heat the semi-finished outer tube at 350℃~400℃ and hold for at least 8 hours. At this time, the inner hole of the outer tube expands, and the inner hole size is larger than the outer diameter of the inner tube. Then, install the semi-finished inner tube into the semi-finished outer tube. After lifting the whole tube out, air cool it to room temperature.

[0009] Step 4) Finishing the double-layer tube after assembly: Transfer the assembled double-layer tube blank to a deep hole drilling and boring machine. Using the outer diameter runout at the position of the semi-finish machining turner for the outer layer tube as a reference (no more than 0.1mm), directly bore the tube. During boring, control the spindle speed at 40-65 r / min, the axial feed at 4-6 mm / min, and the depth of cut for each pass between 1-3 mm. The final cut should be between 0.4-0.6 mm. Use wooden guide keys for support and guidance during each pass. Effective control of the straightness of the inner hole; after boring, the blank is transferred to a CNC lathe for machining, with centering end caps at both ends for direct centering, and the outer diameter is precision turned to the set size. During the machining process, the speed is controlled at 50-60 r / min, the feed is controlled at 0.4-0.6 mm / r, the depth of cut is between 1-3 mm, and the depth of cut of the last cut is no more than 0.5 mm, ensuring that the coaxiality between the outer diameter of the outer tube and the inner diameter of the inner tube is no more than 0.2 mm, and finally machining into a double-layer tube.

[0010] In step 1), the outer tube is semi-finished first. At this time, the inner hole of the outer tube is required to be finished to the required inner hole size for the set, and an 8mm machining allowance is reserved on the outer circle.

[0011] In the above steps, when centering end caps are fitted at both ends, the outer circle of the centering end cap assembly step is 0.03mm smaller than the inner diameter of the double-layer tube, and the outer circle of the limiting step is 10mm smaller than the final outer circle size of the double-layer tube.

[0012] The beneficial effects of this invention are as follows: First, the outer tube is semi-finished, requiring the inner hole of the outer tube to be finished to the required inner hole size for assembly, with an 8mm machining allowance on the outer diameter. Then, the inner tube is semi-finished again, requiring an 8mm machining allowance on the inner hole, and the outer diameter is finished to be 0.2-0.4mm larger than the semi-finished outer tube's inner hole, ensuring an interference fit of 0.2-0.4mm. Then, the semi-finished inner tube is fitted into the outer tube using a heat-fitting method. Finally, the assembled double-layer tube is finished to the required dimensions. For each type of tube, the frame position is first turned, then the inner hole is machined using the frame position for alignment. When machining the inner hole, the spindle speed, axial feed, and depth of cut must be controlled. Wooden guide keys are used for support and guidance during each machining operation, effectively controlling the straightness of the inner hole. After machining the inner hole, a centering end cap is installed, and the outer diameter is machined after centering. Controlling the spindle speed, axial feed, and depth of cut during the machining process effectively controls the coaxiality of the inner tube's inner hole and outer diameter.

[0013] This invention utilizes a CNC lathe and a deep hole drilling and boring machine. A centering end cap is designed to effectively control the precision machining of the inner and outer tubes of a double-layered tube, ensuring good coaxiality and straightness of the inner hole before assembly. The inner tube is fitted into the outer tube using a heat-fitting method. Due to a certain interference fit, the inner and outer tubes will not move relative to each other under subsequent machining forces, ensuring effective precision machining of the double-layered tube. Finally, a CNC lathe and a deep hole drilling and boring machine are used again, with a centering end cap to further precision machine the double-layered tube, effectively controlling the straightness of the inner hole to no more than 0.1 mm and the coaxiality between the outer diameter and the inner hole to no more than 0.2 mm. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a double-layered tube.

[0015] Figure 2 This is a schematic diagram of the centering end cap.

[0016] Figure 3 A schematic diagram of centering end caps installed at both ends of a semi-finished outer tube.

[0017] Figure 4 A schematic diagram of centering end caps installed at both ends of a semi-finished inner tube.

[0018] Figure 5 A schematic diagram showing the centering end caps installed at both ends of a double-layered tube.

[0019] 1 is the outer tube of the double-layer tube, 2 is the inner tube of the double-layer tube, 3 is the centering end cap, 4 is the inner tube in the semi-finished state, and 5 is the outer tube in the semi-finished state. Detailed Implementation

[0020] This invention uses a CNC lathe and a deep hole drilling and boring machine to perform semi-finish machining of the inner tube's inner bore and finish machining of its outer diameter; and to perform semi-finish machining of the outer diameter and finish machining of the inner bore of the outer tube, while controlling the interference fit to be 0.2–0.4 mm. A pit-type heat treatment furnace is used to assemble the inner and outer tubes. Finally, a CNC lathe and a deep hole drilling and boring machine are used to perform finish machining of the inner bore and outer diameter of the assembled double-layer tubes.

[0021] The centering end cap has a built-in center hole. When using it, the outer diameter Φd2 of the assembly step should be matched according to the size of the hole inside the tube (see details). Figure 2 Ensure that Φd2 is 0.03mm smaller than the inner diameter of the tube body. This ensures that the centering end cap can be inserted into the tube body without rotating during machining. It also ensures that the axial deviation between the self-contained center hole and the inner diameter of the tube body is no greater than 0.03mm. This effectively guarantees that the coaxiality between the outer diameter and the inner diameter will not exceed 0.2mm when machining the outer diameter. A limiting step is made for the outer diameter ΦD2 (see details). Figure 2Ensure that ΦD2 is 10mm smaller than the outer diameter of the inserted tube to avoid affecting the machining of the outer diameter of the inserted tube. The specific machining steps are as follows:

[0022] Step 1) Before assembly, the outer tube body is semi-finished: A CNC lathe is used to position the outer tube body blank at both ends. Using this position as a reference, a deep hole drilling and boring machine is used for deep hole machining. During machining, the spindle speed, axial feed, and depth of cut are controlled. Wooden guide keys are used for each machining operation to effectively control the straightness of the inner hole. After machining the inner hole, the machine is transferred to the CNC lathe for further machining. Centering end caps are used at both ends for direct centering. The outer diameter is semi-finished, and the spindle speed, feed, and depth of cut are controlled during the machining process to effectively control the coaxiality of the inner hole and outer diameter of the outer tube body. The two ends are then positioned again to facilitate subsequent precision machining of the double-layer tube body after assembly.

[0023] Step 2) Semi-finishing of the inner tube before assembly: Using a CNC lathe, position the inner tube blank at both ends. Using this position as a reference, align the blank on a deep hole drilling and boring machine before deep hole machining. During machining, control the spindle speed, axial feed, and depth of cut per pass. Use wooden guide keys for support and guidance during each pass to effectively control the straightness of the inner hole. After machining the inner hole, transfer the blank to the CNC lathe for further machining. Use centering end caps at both ends for direct centering and finish turning the outer diameter. At this point, control the outer diameter to be 0.2–0.4 mm larger than the inner diameter of the outer tube before assembly to ensure sufficient interference fit. Controlling the spindle speed, feed, and depth of cut per pass during machining effectively controls the coaxiality of the inner tube's inner diameter and outer diameter, facilitating hot assembly.

[0024] Step 3) Assemble the inner and outer tubes: heat-fit the semi-finished inner tube into the semi-finished outer tube. During heat fitting, use a pit furnace heat treatment furnace to heat the semi-finished outer tube at a temperature of 350℃~400℃ and hold for no less than 8 hours. At this time, the inner hole of the outer tube expands, and the inner hole size is larger than the outer diameter of the inner tube. Then, install the semi-finished inner tube into the semi-finished outer tube.

[0025] Step 4) After assembly, perform finishing on the double-layer tube: Using the lathe's frame position as a reference during the semi-finish machining of the outer tube, perform deep hole machining. During machining, control the spindle speed, axial feed, and depth of cut per pass. Use wooden guide keys for support and guidance during each pass, effectively controlling the straightness of the inner hole. After machining the inner hole, transfer to a CNC lathe for further machining. Use centering end caps at both ends for direct centering and finish turning the outer diameter. Control the spindle speed, feed, and depth of cut per pass during machining to ensure that the coaxiality between the outer diameter of the outer tube and the inner hole of the inner tube is no greater than 0.2mm.

[0026] In the above steps, when centering end caps are fitted at both ends, the outer circle of the centering end cap assembly step is 0.03mm smaller than the inner diameter of the double-layer tube, and the outer circle of the limiting step is 10mm smaller than the final outer circle size of the double-layer tube.

[0027] Example 1:

[0028] Step 1) Semi-finishing of the outer tube before assembly: ① Using a CNC lathe, machine the carriage position at both ends of the inner tube blank, 200-300mm from the end face. The carriage position length should be no less than 100mm, and the outer diameter runout should be less than 0.05mm. ② After machining the carriage position, transfer the blank to a deep hole drilling and boring machine. Align the carriage position so that the outer diameter runout is no more than 0.1mm before deep hole machining. For solid blanks, drill first and then bore; for hollow parts, bore directly. Ultimately, control the inner hole size to ΦD (see details). Figure 3 Because the material is 35CrNi3MoV or 36CrNi3MoV, the spindle speed should be controlled at 40-65 r / min and the axial feed at 25-30 mm / min during drilling and boring. Simultaneously, the boring depth should be controlled between 2-3 mm per pass, with the final pass between 0.4-0.6 mm. Wooden guide keys should be used for each pass to ensure the straightness of the inner hole is no greater than 0.1 mm. ③ After boring, the blank is transferred to a CNC lathe for machining, with centering end caps fitted at both ends (at this time, the centering end caps are fitted with the stepped outer diameter Φd2 (see details)). Figure 2 The inner diameter of the outer tube is 0.03mm smaller than that of the semi-finished outer tube, and the outer diameter of the limiting step is ΦD2 (see attached). Figure 2 (10mm smaller than the final outer diameter of the semi-finished outer tube body), directly center and precision machine the outer diameter, controlling the outer diameter to be 8mm larger than the finished outer diameter of the double-layer tube body, i.e., ΦD1+8m (see details). Figure 3 The machining process involves controlling the rotational speed at 50–60 r / min, the feed rate at 0.4–0.6 mm / r, and the depth of cut for each pass at 2–4 mm, with the final pass having a depth of cut no greater than 0.5 mm. Afterward, the machine is positioned 200–300 mm from the end face at both ends, requiring a minimum length of 100 mm and an outer diameter runout of less than 0.05 mm. This effectively controls the coaxiality of the inner bore and outer diameter of the outer tube, while also facilitating subsequent precision machining.

[0029] Step 2) Semi-finishing of the inner tube before assembly: ① Using a CNC lathe, machine the carriage position at 200-300mm from the end face at both ends of the inner tube blank. The carriage position length should be no less than 100mm, and the outer diameter runout should be less than 0.05mm. ② After machining the carriage position, transfer the blank to a deep hole drilling and boring machine. After aligning the carriage position and ensuring the outer diameter runout is no more than 0.1mm, proceed with deep hole machining. For solid blanks, drill first and then bore. For hollow parts, bore directly. Ultimately, control the inner hole size to be 8mm smaller than the finished inner hole size of the double-layer tube, i.e., Φd1-8mm (see appendix for details). Figure 4Because the material is stainless steel or high-temperature alloy, the spindle speed should be controlled at 40-65 r / min and the axial feed at 4-6 mm / min during drilling and boring. Simultaneously, the boring depth should be controlled between 2-3 mm per pass, and the final pass should be between 0.4-0.6 mm. Wooden guide keys should be used for support and guidance during each pass to ensure the straightness of the inner hole is no greater than 0.1 mm. ③ After boring, the blank is transferred to a CNC lathe for machining, with centering end caps fitted at both ends (at this time, the centering end caps are fitted with the stepped outer diameter Φd2 (see details)). Figure 2 The inner bore of the semi-finished inner tube is 0.03mm smaller than that of the inner tube, and the outer diameter of the limiting step is ΦD2 (see details). Figure 2 (10mm smaller than the final outer diameter of the semi-finished inner tube body), directly center and finish machine the outer diameter, controlling the outer diameter to be smaller than the inner diameter ΦD of the semi-finished outer tube body (see details). Figure 3 The difference is 0.2–0.4 mm larger, i.e., ΦD + 0.2–0.4 mm (see details). Figure 4 The machining process controls the rotation speed at 40-50 r / min, the feed rate at 0.2-0.4 mm / r, the depth of cut for each pass at 0.5-2 mm, and the depth of cut for the last pass at 0.2-0.4 mm. This effectively controls the coaxiality of the inner tube's inner bore and outer diameter, facilitating heat fitting.

[0030] Step 3) Assemble the inner and outer tubes: heat-fit the semi-finished inner tube into the semi-finished outer tube. During heat fitting, use a pit furnace to heat the semi-finished outer tube at a temperature of 350℃~400℃ and hold for at least 8 hours. At this time, the inner hole of the outer tube will expand and the inner hole size will be larger than the outer diameter of the inner tube. Then, install the semi-finished inner tube into the semi-finished outer tube, lift it out as a whole, and air-cool it to room temperature.

[0031] Step 4) Finishing the double-layer tube after assembly: ① After assembly, the double-layer tube blank is transferred to a deep hole drilling and boring machine. The outer diameter runout at the position of the semi-finish machining turner for the outer tube is aligned to be no more than 0.1mm before deep hole machining. Direct boring is performed, ultimately controlling the inner hole size to Φd1 (see details). Figure 1 Because the inner tube is made of stainless steel or high-temperature alloy, the spindle speed should be controlled at 40-65 r / min and the axial feed at 4-6 mm / min during boring. The depth of cut should be controlled between 1-3 mm, and the last cut should be between 0.4-0.6 mm. Wooden guide keys should be used for support and guidance during each machining operation to ensure that the straightness of the inner hole is no more than 0.1 mm. ③ After boring, the blank is transferred to a CNC lathe for machining, and centering end caps are fitted at both ends (at this time, the centering end caps are fitted with the stepped outer diameter Φd2 (see details)). Figure 2 The inner diameter of the double-layer tube is 0.03mm smaller than that of the inner diameter of the tube, and the outer diameter of the limiting step is ΦD2 (see details). Figure 2(10mm smaller than the final outer diameter of the double-layer tube), directly center, precision machine the outer diameter, and control the outer diameter to ΦD1 (see details). Figure 1 The machining process controls the rotation speed at 50-60 r / min, the feed rate at 0.4-0.6 mm / r, the depth of cut for each pass at 1-3 mm, and the depth of cut for the last pass at no more than 0.5 mm. This effectively controls the coaxiality between the outer diameter of the outer tube and the inner diameter of the inner tube to be no more than 0.2 mm.

[0032] Example 2: A 6000mm double-layer tube with an inner layer of S22053 material and an outer layer of 35CrNi3MoV. The outer diameter of the tube is Φ550mm, the inner diameter is Φ300mm, and the mating diameter between the two layers is Φ380mm. The straightness of the inner hole is required to be no greater than 0.1mm, and the coaxiality between the outer diameter and the inner hole is required to be no greater than 0.2mm. Both the inner and outer tube blanks are solid parts. The specific processing procedure is as follows:

[0033] Step 1) Semi-finishing of the outer tube before assembly: ① Using a CNC lathe, position the carriage at 200-300mm from the end face at both ends of the inner tube blank. The carriage length should be no less than 100mm, and the outer diameter runout should be less than 0.05mm. ② After positioning the carriage, transfer the blank to a deep hole drilling and boring machine. After aligning the carriage position and ensuring the outer diameter runout is no more than 0.1mm, proceed with deep hole machining. Drill first, then bore, ultimately controlling the inner hole size to Φ380mm. Because the material is 35CrNi3MoV or 36CrNi3MoV, control the spindle speed at 50r / min and the axial feed at 28mm / r during drilling and boring. Simultaneously, control the boring depth of cut to 2-3mm per pass, with the final cut at 0.5mm. Use wooden guide keys for support and guidance during each machining operation, ultimately achieving an inner hole straightness of 0.05mm. ③ After boring, the blank is transferred to a CNC lathe for machining. Centering end caps are fitted at both ends (at this point, the outer diameter of the centering end cap assembly step is Φ379.97mm, and the outer diameter of the limiting step is Φ548mm). Direct centering and finish turning of the outer diameter are performed, controlling the outer diameter dimension to Φ558mm. During machining, the speed is controlled at 55r / min, the feed rate at 0.4mm / r, and the depth of cut is between 2 and 4mm for each pass, with the final pass reaching a depth of 0.4mm. Afterward, the lathe is repositioned 200-300mm from the end face at both ends, requiring a repositioning length of at least 100mm and an outer diameter runout of less than 0.05mm. This effectively controls the coaxiality of the inner hole and outer diameter of the outer tube, while the repositioning facilitates subsequent finish machining.

[0034] Step 2) Semi-finishing of the inner tube before assembly: ① Using a CNC lathe, position the carriage at 200-300mm from the end face on both ends of the inner tube blank. The carriage length should be no less than 100mm, and the outer diameter runout should be less than 0.05mm. ② After positioning the carriage, transfer the blank to a deep hole drilling and boring machine. After aligning the carriage position and ensuring the outer diameter runout is no more than 0.1mm, proceed with deep hole machining. Drill first, then bore, ultimately controlling the inner hole size to Φ292mm. During drilling and boring, control the spindle speed at 55r / min and the axial feed at 4mm / min. Simultaneously, during boring, control the depth of cut of the boring bar at 2-3mm per pass, with the final cut at 0.6mm. Use wooden guide keys for support and guidance during each machining operation. The final inner hole straightness is 0.07mm. ③ After boring, the blank is transferred to a CNC lathe for machining. Centering end caps are fitted at both ends for direct centering (at this point, the outer diameter of the centering end cap assembly step is Φ291.97mm, and the outer diameter of the limiting step is Φ370mm). The outer diameter is then finished to Φ380.3mm. During machining, the rotational speed is controlled at 45r / min, the feed rate is controlled at 0.3mm / r, the depth of cut is between 1 and 2mm for each pass, and the final cut depth is 0.3mm. The final coaxiality of the inner and outer diameters is 0.1mm.

[0035] Step 3) Assembly of inner and outer tubes: The semi-finished inner tube is hot-loaded into the semi-finished outer tube. During hot loading, a pit furnace is used to heat the semi-finished outer tube, controlling the heating temperature at 350℃~400℃ and holding it at that temperature for 9 hours. At this time, the inner hole of the outer tube expands, and the inner hole size is larger than the outer diameter of the inner tube. The semi-finished inner tube is then installed into the semi-finished outer tube, and the whole assembly is lifted out and air-cooled to room temperature.

[0036] Step 4) Finishing the double-layer tube after assembly: ① After assembly, the double-layer tube blank is transferred to a deep hole drilling and boring machine. After aligning the outer tube at the position of the semi-finish machining lathe, the runout of the outer diameter should not exceed 0.1mm before deep hole machining. Direct boring is performed, ultimately controlling the inner hole size to Φ300mm. Because the inner tube material is stainless steel or high-temperature alloy, the spindle speed is controlled at 55r / min and the axial feed at 4mm / min during boring. The depth of cut is controlled at 2, 1.4, and 0.6mm each time, with wooden guide keys used for support and guidance each time, thus controlling the straightness of the inner hole to 0.06mm. ③ After boring, the blank is transferred to a CNC lathe for machining. Centering end caps are fitted at both ends (at this time, the outer diameter of the centering end cap assembly step is Φ299.97mm, and the outer diameter of the limiting step is Φ540mm). Direct centering and finish machining of the outer diameter are performed, controlling the outer diameter size to Φ550mm. The machining process controls the rotation speed at 55 r / min, the feed rate at 0.4 mm / r, and the depth of cut for each pass at 2, 1.7, and 0.3 mm. Ultimately, the coaxiality between the outer diameter of the outer tube and the inner diameter of the inner tube is controlled to 0.12 mm.

[0037] Following the above requirements, a double-layered tube, 6000mm long, with an outer diameter of Φ550mm and an inner diameter of Φ300mm, was successfully manufactured. The inner layer is made of S22053 material, and the outer layer is made of 35CrNi3MoV material. The tube has an outer diameter of Φ300mm and an inner diameter of Φ52053 material. The straightness of the inner diameter was 0.06mm, and the coaxiality between the outer diameter and the inner diameter was 0.12mm. The requirements are met.

Claims

1. A method of processing an elongated double-wall tube body for a wind tunnel, characterized by: The specific processing steps are as follows: Step 1), before sleeving, the outer layer pipe body is semi-finished: use a numerical control lathe to turn a frame at both ends of the outer layer pipe body blank, 200-300 mm away from the end face, the frame length is required to be not less than 100 mm, and the outer circle is turned with a runout of less than 0.05 mm; after turning the frame, the blank is transferred to a deep hole drilling and boring machine, and the outer circle runout at the frame position is found on the deep hole drilling and boring machine, and the deep hole is processed after the runout is not greater than 0.1 mm, the spindle speed is controlled at 40-65 r / min during processing, the axial feed is controlled at 25-30 mm / min, the boring hole should control the boring cutter to eat the depth of each time between 2-3 mm, the last cutter should be between 0.4-0.6 mm, wood guide key is used to support and guide each time, and the straightness of the inner hole is effectively controlled; after boring the hole, the blank is transferred to the numerical control lathe for processing, the two ends are directly centered with the centering end cover, the outer circle is finished to the set size, the speed is controlled at 50-60 r / min during processing, the feed is controlled at 0.4-0.6 mm / r, the depth of each cutter is between 2-4 mm, the last cutter depth is not greater than 0.5 mm, then the frame is turned at both ends, 200-300 mm away from the end face, the frame length is required to be not less than 100 mm, and the outer circle is turned with a runout of less than 0.05 mm; the coaxialities of the inner hole and the outer circle of the outer layer pipe body are effectively controlled, then the frame is turned at both ends again, which is convenient for subsequent double-layer pipe body finishing; Step 2), before sleeving, the inner layer pipe body is semi-finished: use a numerical control lathe to turn a frame at both ends of the inner layer pipe body blank, 200-300 mm away from the end face, the frame length is required to be not less than 100 mm, and the outer circle is turned with a runout of less than 0.05 mm; after turning the frame, the blank is transferred to a deep hole drilling and boring machine, and the outer circle runout at the frame position is found on the deep hole drilling and boring machine, and the deep hole is processed after the runout is not greater than 0.1 mm, the spindle speed is controlled at 40-65 r / min during processing, the axial feed is controlled at 4-6 mm / min, the boring hole should control the boring cutter to eat the depth of each time between 2-3 mm, the last cutter should be between 0.4-0.6 mm, wood guide key is used to support and guide each time, and the straightness of the inner hole is effectively controlled; after boring the hole, the blank is transferred to the numerical control lathe for processing, the two ends are directly centered with the centering end cover, the outer circle size is finished to the set size, the speed is controlled at 40-50 r / min during processing, the feed is controlled at 0.2-0.4 mm / r, the depth of each cutter is between 0.5-2 mm, the last cutter depth is 0.2-0.4 mm; the inner layer pipe body is semi-finished again, at this time, the inner layer pipe body inner hole is reserved with a processing allowance of 8 mm, the outer circle is finished to be 0.2-0.4 mm larger than the inner hole of the semi-finished outer layer pipe body, that is, the sleeving interference is 0.2-0.4 mm, which ensures the sleeving interference, effectively controls the coaxialities of the inner hole and the outer circle of the inner layer pipe body, and is convenient for hot sleeving; Step 3), the inner and outer layer pipe body is sleeved: the semi-precision plus inner layer pipe body is hot-mounted into the semi-precision plus outer layer pipe body, the semi-precision plus outer layer cylinder is heated by using a pit furnace heat treatment furnace when hot-mounting, the heating temperature is 350-400 DEG C, and the heat preservation is not less than 8 hours, at this time, the inner hole of the outer layer pipe body expands, the inner hole size is larger than the outer circle size of the inner layer pipe body, the semi-precision plus inner layer pipe body is mounted into the semi-precision plus outer layer pipe body; after being directly hoisted out, air cooling is carried out to room temperature; Step 4), the double-layer pipe body is finished after sleeving: the sleeved double-layer pipe body blank is transferred to a deep hole drilling and boring machine, the outer layer pipe body is directly bored after alignment based on the outer circle runout of the semi-precision plus outer layer pipe body, the spindle speed is controlled at 40-65 r / min during boring, the axial feed is controlled at 4-6 mm / min, the boring cutter is controlled to have a cutting depth of 1-3 mm each time, the last cut should be between 0.4-0.6 mm, the wood guide key is used for supporting and guiding each time, and the inner hole straightness is effectively controlled; after boring, the blank is transferred to a numerical control lathe for machining, the two ends are directly centered with the centering end cover, the outer circle is precisely machined to the set size, the speed is controlled at 50-60 r / min during machining, the feed is controlled at 0.4-0.6 mm / r, the cutting depth is controlled at 1-3 mm each time, the last cutting depth is not greater than 0.5 mm, the coaxiality between the outer circle of the outer layer pipe body and the inner hole of the inner layer pipe body is not greater than 0.2 mm, and finally the double-layer pipe body is machined.

2. The method of claim 1, wherein: In step 1), the outer layer pipe body is semi-precision machined, and the inner hole of the outer layer pipe body is precisely machined to the sleeving required inner hole size, and the outer circle is reserved with a machining allowance of 8 mm.

3. The method of claim 1, wherein: In the above steps, when the two ends are provided with the centering end cover, the centering end cover assembly step outer circle is 0.03 mm smaller than the double-layer pipe body inner hole, and the limiting step outer circle is 10 mm smaller than the final double-layer pipe body outer circle size.

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