Method for turning thin-walled cylinder of TC18 titanium alloy

Abstract

A kind of method for turning TC18 titanium alloy thin-walled cylinder, adopt the process route of semi-finishing turning inner type→natural aging→finishing turning inner type→natural aging→finishing turning outer type→trimming, and directly machining in place from one end.The invention adopts lengthened damping tool bar to avoid the part from vibrating during turning, self-made rubber winding tooling is used to fill the part to enhance the rigidity of the part, and the cutting parameters during finishing turning the outer type of thin-walled cylinder are refined.During finishing turning the outer surface, the wall thickness of the part needs to be turned from 3.25mm to 1.25mm, in order to reduce the tool setting condition of part deformation during machining, the rubber winding tooling is used to fill the part to enhance the rigidity of the part and reduce the deformation.Due to the technical measures taken, the processing time of the part is greatly shortened, the time node of scientific research and production is guaranteed, the processing precision and good product rate of the part are improved, the processing cost is reduced, and the defects such as cylinder cracking and spinning marks caused by unsuitable spinning parameters in the prior art are overcome.

Description

Technical Field

[0001] This invention relates to the field of machining, specifically a method for machining a thin-walled cylindrical body made of TC18 titanium alloy. Background Technology

[0002] TC18 titanium alloy possesses advantages such as high strength, high plasticity, light weight, good fatigue resistance, and good corrosion resistance. In the aerospace field, TC18 titanium alloy is widely used in load-bearing structural components. However, TC18 titanium alloy has poor thermal conductivity and a lower elastic modulus than steel. During cutting, the machined surface exhibits significant springback, resulting in intense friction and severe wear on the tool rake face. Therefore, thin-walled parts machined from TC18 titanium alloy have poor rigidity and are prone to deformation.

[0003] This part is a thin-walled cylindrical body with an outer diameter of φ180-0.05-0.30mm, a wall thickness of 1.25+0.12-0.03mm, and a length of 673.5mm. The part mainly consists of a cylindrical section, four lugs, and one slider. A simplified structural diagram of the part is attached. Figure 1 Currently, the conventional process flow for this type of titanium alloy thin-walled cylindrical parts is as follows: 1. First, the thin-walled cylindrical section of the part is machined by spinning or expansion; 2. Then, external components such as lugs and sliders are welded to the corresponding positions on the outer circle of the cylindrical section.

[0004] Currently, spinning and thermal expansion forming methods for thin-walled titanium alloy cylinders are relatively mature. Shenyang Aircraft Industry Co., Ltd., in its invention publication CN114985526A, proposed a precise forming method for titanium alloy cylinders based on a thermal expansion mold. This method involves designing a thermal expansion mold and improving upon existing heat treatment and shaping fixtures, building upon the existing internal mandrel and external jig. For closed-structure cylindrical parts like titanium alloy cylinders, the method utilizes the principle of thermal expansion to correct their roundness. Based on a specially designed thermal expansion mold, the method leverages the difference in thermal expansion coefficients of different materials at high temperatures to process cylindrical parts using the thermal expansion forming principle. Based on these steps, the titanium alloy cylindrical parts are precisely formed. However, this method is suitable for determining the correction parameters for TC2 titanium alloy cylindrical parts and is not applicable to the forming of thin-walled cylinders made of other titanium alloy materials. Further experimentation to determine the expansion parameters for other types of titanium alloys is still needed.

[0005] Beijing Hangxing Machinery Manufacturing Co., Ltd., in its invention publication CN114029358A, proposed a method for manufacturing a titanium alloy thin-walled cylinder. The method involves preparing an integrated bulging mold based on the dimensions of the titanium alloy thin-walled cylinder to be manufactured. A titanium alloy blank is cut and rounded to obtain a first intermediate part. This first intermediate part is then welded into a cylindrical component. After applying an anti-oxidant to the cylindrical component, it is fitted onto the mold body of the integrated bulging mold. The cylindrical component fitted onto the integrated bulging mold is then bulged, and finally detached from the mold to obtain a second intermediate part. The remaining material in the second intermediate part is then removed to obtain the titanium alloy thin-walled cylinder. However, this method results in axial weld seams after the plate is rolled and welded, affecting the appearance. Furthermore, the production process is overly complex, and the strength of the weld seams after bulging does not meet the performance requirements of aerospace solid rocket motor parts.

[0006] The Northwest Nonferrous Metals Research Institute proposed a method for manufacturing large-diameter, thin-walled, seamless titanium alloy cylinders in its invention publication CN112427893A. This method uses arc additive manufacturing to prepare titanium alloy cylinder blanks, followed by stress-relief annealing and air cooling. The blanks are then machined to obtain spun titanium alloy cylinder blanks, which are then subjected to multi-pass high-intensity hot spinning. Finally, heat treatment yields the large-diameter, thin-walled, seamless titanium alloy cylinder. This method achieves the deformation of difficult-to-deform titanium alloys, improving the spinnability and ultimate thinning rate of large-diameter, thin-walled titanium alloy cylinders. However, this method, through hot spinning, machining, multi-pass hot spinning, and heat treatment, ensures the surface quality and forming accuracy of the thin-walled titanium alloy tubes. The production process is complex, the preparation cycle is long, and the mold cost is high.

[0007] Currently, the manufacturing characteristics of this type of thin-walled parts, such as spinning and expanding, are that the processing time for spinning and expanding molds is long, requiring at least one month for tooling preparation, and the mold cost is hundreds of thousands, which greatly increases the manufacturing cycle and processing cost of the parts. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, such as long tooling preparation cycles and high tooling costs, this invention introduces a method for machining TC18 titanium alloy thin-walled cylindrical parts.

[0009] The specific process of this invention is as follows:

[0010] Step 1, delineate the area to be processed on the outer circumference of the part: Divide the area to be processed on the outer circumference of the part into region A, region B, and region C according to the position of the external component to be welded. When dividing region A, region B, and region C, start from the end face near the position of the external component and extend axially towards the other end of the external component.

[0011] Region A, starting from the aforementioned starting point, extends from 0 to 95 mm on the welded outer component, with a length of 95 mm. Region B extends from 185 to 349 mm on the welded outer component, with a length of 164 mm. Region C extends from 448 to 718.5 mm, with a length of 270.5 mm.

[0012] Step 2, Prepare the tooling:

[0013] The tooling includes a plug, a cutter box, and a rubber roll. The plug, cutter box, and rubber roll are processed according to the tooling design.

[0014] The plug is disc-shaped, with two symmetrically distributed tooling disassembly threaded through holes. At the center of the plug is a center hole for positioning and tightening the machine tool tailstock.

[0015] The tool holder has a U-shaped cross-section. One end of the tool holder is a connecting end; connecting holes are distributed on the two sides of the connecting end, which are used for connecting the machine tool and the tool holder, and for connecting the tool holder and the tool holder, respectively.

[0016] The rubber roll is cylindrical, with an outer diameter of φ154mm, the same as the inner diameter of the part blank, and a length of 645mm, the same as the length of the cylinder.

[0017] Step 3, clamping:

[0018] Insert the tool holder into the tool box. Following the machining sequence determined by the process, mount the cutting head and insert for machining the internal hole onto the tool holder. Mount the tool box containing the tool holder onto the CNC lathe tool post.

[0019] The blank part is clamped on the machine tool and aligned.

[0020] Two machining strips are machined on the outer circumference surface of the part blank, each 70mm from both end faces. These two machining strips are located on the outer circumference of region A and region C, respectively. Specifically, the machining strip on the outer circumference of region A is located 628.5mm to 648.5mm from the end face of the cantilever, and the machining strip on the outer circumference of region C is located 70mm to 90mm from the end face of the cantilever.

[0021] The specific location for adding the machine tape on the outer circumference of region A is 628.5mm to 648.5mm from the end face of the cantilever, and the specific location for adding the machine tape on the outer circumference of region C is 70mm to 90mm from the end face of the cantilever.

[0022] Step 4, Semi-finish turning of the inner hole of the part blank:

[0023] Place the lathe's center rest on the machining belt of the outer cylindrical surface of region C of the part blank, and adjust the center rest rollers to ensure the runout is less than 0.03 mm. Perform semi-finish turning on the inner hole of the part. Obtain the part blank after semi-finish turning.

[0024] Cutting parameters for machining the inner hole of the workpiece blank: machine tool spindle speed is 40 rad / min, cutting depth is 0.1 mm, and machine tool feed rate is 1 mm / rad.

[0025] Step 5, Natural aging of the part blank:

[0026] The partially finished part blanks are left to stand for 24 hours to release stress.

[0027] Step 6, finish turning of the inner hole of the part:

[0028] Place the lathe center rest on the machining belt on the outer circumferential surface of the workpiece blank in area A, and support the outer circumferential surface of the machining belt with rollers on the center rest. Adjust the spindle jaws so that the circumferential runout of the machining belt at the two locations is <0.03mm.

[0029] The inner hole of the part blank is precision machined to obtain a semi-finished part.

[0030] Cutting parameters for precision turning of the inner hole of the part blank: machine tool spindle speed is 40 rad / min, cutting depth is 0.05 mm, and lathe feed rate is 0.4 mm / rad.

[0031] Step 7, Natural aging of semi-finished parts:

[0032] The semi-finished parts were left to stand for 24 hours to release stress.

[0033] Step 8, Preparation for precision machining of the semi-finished part's shape:

[0034] The preparation for the precision machining of the semi-finished part's shape is the installation tooling.

[0035] Insert the rubber roll into the inner cavity of the semi-finished part, ensuring the rubber roll fills the entire inner cavity. Install a plug on the non-clamping end of the part, ensuring the end face of the plug is flush with the end face of the part. After installing the rubber roll and plug required for the machining of the semi-finished part, prepare for the precision turning of the semi-finished part's shape.

[0036] Step 9, Preparing the semi-finished shape of the precision-machined part:

[0037] Re-clamp the parts; adjust the spindle jaws until the runout at the two machining points is less than 0.03mm.

[0038] The finishing process of a semi-finished part involves turning the outer circumference of the semi-finished part into three cutting zones: I, J, and K.

[0039] Step 10: Determine the machining parameters for the semi-finished part's shape:

[0040] Using test specimens, conventional testing methods were employed to determine the machining parameters of the external shape.

[0041] The determined machining parameters for the finishing turning of the outer shape are as follows: machine tool spindle speed 40 rad / min, lathe feed rate 0.4 mm / rad; the optimal depth of cut for the first pass of finishing turning is 0.1 mm; the optimal depth of cut for the second pass of finishing turning is 0.05 mm; and the optimal depth of cut for the third pass of finishing turning is 0.02 mm.

[0042] Step 11, precision turning the semi-finished part's shape:

[0043] According to the determined process path, multi-pass layer-by-layer turning is used for each cutting area to ensure that the cutting amount of the same layer in each cutting area is the same.

[0044] The precision machining process for the semi-finished part is as follows:

[0045] Ⅰ First turning pass:

[0046] Turning zone I; the cutting zone starts from the starting point 0mm and extends axially towards the other end of the part, with a length of 275.5mm. Set the cutting depth to 0.1mm. After two passes in zone I, until the cutting depth is 0.2mm, the first pass of turning in zone I is complete. Proceed to zone J for turning.

[0047] Turn region J; keeping the depth of cut constant at 0.1mm, the cutting area starts at 369.5mm and ends at 533.5mm, with a length of 164mm. After two passes in region J, with a cutting depth of 0.2mm, the first pass of turning in region J is complete. Proceed to region K for turning.

[0048] Turn region K; keep the depth of cut constant at 0.1mm, the cutting area starts at 623.5mm and ends at 673.5mm, with a length of 50mm. After turning region K twice until the turning amount is 0.2mm, the first pass of turning region K is completed.

[0049] Repeat the turning process of region I, region J and region K in the first turning pass three times in sequence until the total amount of turning is 0.6 mm, thus completing the first turning pass and proceeding to the second turning pass.

[0050] The parameters for the first turning pass are: machine spindle speed of 40 rad / min, depth of cut of 0.1 mm, and lathe feed rate of 0.4 mm / rad.

[0051] II. Second turning pass:

[0052] Turning zone I; the cutting zone starts from the starting point 0mm and extends axially towards the other end of the part, with a length of 275.5mm. Set the cutting depth to 0.05mm and perform one pass in zone I to complete the second pass of turning in zone I. Proceed to zone J for turning.

[0053] Turn region J; maintain a constant depth of cut of 0.05 mm, with the cutting area starting at 369.5 mm and ending at 533.5 mm, for a length of 164 mm. Perform one pass in region J to complete the second pass of turning in region J. Proceed to region K for turning.

[0054] Turn region K; keep the depth of cut constant at 0.05mm, the cutting area starts at 623.5mm and ends at 673.5mm, with a length of 50mm. Turn one cut in region K to complete the second pass of turning in region K.

[0055] Repeat the turning process of region I, region J and region K in the second turning pass eight times in sequence until the total amount of turning is 0.4 mm, then complete the second turning pass and proceed to the third turning pass.

[0056] The parameters for the second turning pass are: machine spindle speed of 40 rad / min, depth of cut of 0.05 mm, and lathe feed rate of 0.4 mm / rad.

[0057] III. Third turning pass:

[0058] Turning zone I; the cutting zone starts from the starting point 0mm and extends axially towards the other end of the part, with a length of 275.5mm. Set the cutting depth to 0.02mm and perform one pass in zone I to complete the third pass of turning in zone I. Proceed to zone J for turning.

[0059] Turn region J; maintain a constant depth of cut of 0.02 mm, with the cutting area starting at 369.5 mm and ending at 533.5 mm, for a length of 164 mm. Perform one pass in region J to complete the third pass of turning in region J. Proceed to region K for turning.

[0060] Turn region K; keep the depth of cut constant at 0.02mm, the cutting area starts at 623.5mm and ends at 673.5mm, with a length of 50mm. Turn one cut in region K to complete the third pass of turning in region K.

[0061] Repeat the above steps until the semi-finished part meets the design requirements, and complete the precision machining of the semi-finished part.

[0062] The parameters for the third turning pass are: machine spindle speed of 40 rad / min, depth of cut of 0.02 mm, and lathe feed rate of 0.4 mm / rad.

[0063] Step 12, cutting and machining of the part:

[0064] According to the drawings, the parts that have completed the precision turning of the outer shape are cut off to obtain the finished parts, thus completing the entire processing.

[0065] This completes the machining of the TC18 titanium alloy thin-walled cylinder.

[0066] The technical solution proposed in this invention is: a machining method for thin-walled cylindrical parts made of TC18 titanium alloy. The machining method is completed on a horizontal CNC lathe CK6185. The process route is: semi-finish turning of the inner shape → natural aging → finish turning of the inner shape → natural aging → finish turning of the outer shape → trimming.

[0067] Because the part is a thin-walled cylindrical structure made of titanium alloy, the internal surface quality requirements are high. Traditional machining methods using tools from both ends cannot guarantee dimensional accuracy and internal surface quality. Furthermore, the part is over 700mm long, with a finished wall thickness of only 1.25 ± 0.12 - 0.03mm, making it prone to vibration during machining, leading to dimensional inconsistencies and scrapping. Moreover, due to the titanium alloy material, ordinary cutting tools are insufficient for machining requirements. To address these issues, this invention utilizes a series of measures, including improved machining methods, customized cutting tools, self-made tooling, and experimental selection of machining parameters, to successfully machine the part.

[0068] Since the two-end tooling method cannot meet the requirements of the internal surface of the part, this invention adopts a method of machining directly from one end. When machining the deep hole of a thin-walled cylindrical part directly from one end, an extended damping tool holder is usually used in conjunction with a corresponding tool to turn the internal surface to avoid vibration during the turning process. However, since the length of this part is over 700mm, a regular φ80mm extended tool holder can only extend 3-4 times its own diameter, that is, a maximum extension of 320mm. A φ80mm hydraulic damping tool holder can usually only extend 5-8 times its own diameter, that is, a maximum extension of 640mm, neither of which can meet the size requirements of the part. If the tool holder is extended even longer, the possibility of vibration during cutting will greatly increase, which leads to a higher requirement for the damping function of the tool holder. In this case, this invention uses a customized φ80mm hydraulic damping tool holder from the Sandvik brand, model 570-3C 80 1400CR, with a length-to-diameter ratio of 13. Furthermore, to prevent vibration during turning, a self-made tool holder was designed to clamp the hydraulically damped tool holder, thereby enhancing the rigidity of the clamping area. This effectively reduces tool deflection caused by insufficient tool rigidity, preventing vibration during turning and playing a crucial role in ensuring machining accuracy. The specific structure of the self-made tool holder is shown in the appendix. Figure 3 Meanwhile, for machining titanium alloy materials, due to their high strength, high hardness, and high-temperature oxidation resistance, the tool material needs to possess high hardness, strength, and heat resistance. Simultaneously, the tool structure must consider cutting forces and heat dissipation conditions, and should possess high rigidity and stability to reduce vibration and improve cutting accuracy. Considering the above issues and based on the different machining requirements of internal and external surfaces, this invention selects a Chloe insert with a carbide coating for machining the internal surface (model VCGT160404-AK) and a Seco insert for machining the external surface (model DNMG150604-MF1800). Finally, during the finishing of the external surface, since the part wall thickness needs to be turned from 3.25mm to 1.25mm, to reduce deformation and tool deflection during machining, a self-made rubber roll fixture was used to fill the part to enhance its rigidity and reduce deformation.

[0069] Compared to the traditional method of first spinning and then machining thin-walled cylindrical titanium alloy parts, the direct turning method proposed in this invention achieves the turning of TC18 titanium alloy thin-walled parts with an outer diameter of φ180-0.05-0.30mm, a wall thickness of 1.25+0.12-0.03mm, and a length of 673.5mm by planning the turning route, optimizing the clamping method, adjusting appropriate cutting parameters, and selecting custom tools. This method is of great significance for ensuring the dimensional accuracy of solid rocket motor parts, controlling costs, and shortening the machining cycle.

[0070] Compared with the prior art, the innovation of this invention mainly lies in the following aspects:

[0071] 1. Innovations were made in the processing flow;

[0072] This invention changes the traditional approach of spinning titanium alloy cylindrical parts before machining, and proposes a method that directly machines them without spinning. It innovates and optimizes the processing flow, eliminates the need for spinning technology, uses more common CNC lathes, has wider applicability, lower cost, and is easy to promote and use.

[0073] Changing the method from spinning before machining to direct machining increases the workload of the machining process and also raises the corresponding machining difficulty to some extent. First, since the part is made of titanium alloy, it cannot be machined with ordinary cutting tools, and given that the part is about 700mm long, an extended anti-vibration tool holder is required. Second, titanium alloy has a low elastic modulus, so it is prone to deformation and bending under radial force during turning, which will ultimately cause the turning parameters to fail to meet the accuracy requirements of the part's dimensions. Therefore, appropriate cutting parameters must be determined based on the machining tools, part size, and structure. Finally, since the part wall thickness needs to be machined from 7.3mm to 1.25mm, the vibration during machining must be pre-treated to avoid affecting the part's dimensions and surface quality.

[0074] 2. This solves the problem of excessive tool holder overhang affecting surface quality and dimensional accuracy.

[0075] When selecting machining tools, this invention customizes the tool holder and inserts based on the part material and structural dimensions. Titanium alloy material has characteristics such as high strength, high toughness, high hardness, and low thermal conductivity. Therefore, when selecting tools, the strength and hardness of the insert material must be considered, while also ensuring good rigidity and thermal stability. Large cutting forces are required during machining, thus demanding specific insert angles. Ultimately, after comparative analysis, a 55° rhomboid insert with a carbide coating was selected. Carbide inserts possess excellent hardness, maintaining rigidity and stability during machining. Furthermore, the surface of the carbide insert is covered with a hard carbide coating, effectively resisting wear and thermal corrosion. The 55° rhomboid insert has a moderate cutting angle, providing greater cutting force compared to a 35° insert, while avoiding the short lifespan and poor cutting surface quality of 70° or 90° inserts. This results in better cutting performance, reduced tool vibration and burrs on the part surface, and improved tool life. Additionally, due to the chemical properties of titanium alloy material, it is prone to bonding with other metals under high temperatures during machining, affecting machining quality and causing significant tool wear. Taking all factors into account and considering the different requirements for machining external and internal surfaces, coated carbide rhomboid inserts from Chloe and Seco were customized respectively, with specific parameters shown in Table 1. This type of insert has good red hardness, good thermal conductivity, and low affinity with titanium alloys, resulting in higher precision parts and a 1.5-fold increase in part qualification rate. At the same time, the tool life is more than 3 times longer than that of ordinary inserts.

[0076] Meanwhile, for the selection of the tool holder to match the cutting insert, this invention uses a Sandvik brand hydraulically damped extended tool holder. Since the part length is over 700mm, ordinary extended tool holders can only extend up to 320mm, and φ80mm hydraulically damped tool holders can typically only extend to 640mm, neither of which can meet the part size requirements. In this case, this invention customized a Sandvik 570-3C 80 1400CR hydraulically damped tool holder with a length-to-diameter ratio of 13. After trial machining, it was found that the excessive overhang of the tool holder caused intermittent chattering during cutting, affecting surface quality and dimensional accuracy. To prevent chattering during turning, this invention proposes using a self-made tool holder to clamp the hydraulically damped tool holder; its specific structure is shown in the appendix. Figure 3 The material is 45 steel that has undergone quenching and tempering. The self-made tool holder enhances the rigidity of the clamping area and improves the overall rigidity of the tool, effectively reducing tool deflection caused by insufficient tool rigidity and preventing vibration during turning. This plays a crucial role in ensuring machining accuracy.

[0077] 3. The cutting parameters for finishing thin-walled cylindrical shapes have been refined.

[0078] Since the minimum thickness of the cylinder is 3.25mm after the internal machining is completed, and the wall thickness gradually decreases to 1.25mm as the turning progresses, the cutting depth not only affects the deformation of the thin-walled cylinder, but also affects the final finished product size. Therefore, the cutting parameters for machining the external shape of the part need to be refined.

[0079] The cutting parameters for finishing the thin-walled cylindrical body were determined through experiments. A titanium alloy thin-walled cylindrical part of the same dimensions as the workpiece was selected as the test piece. The shape of the test piece was identical to that of the final workpiece, with three cutting zones: region I, region J, and region K. Turning experiments were conducted using conventional methods, and the refined turning parameters were obtained from these experiments. During the experiments...

[0080] Set the machine tool spindle speed to 40 rad / min; set the machine tool feed rate to 0.4 mm / rad.

[0081] The cutting depths of the three cutting regions, I, J, and K, are set respectively:

[0082] The cutting depth in region I of the test piece was set to 0.1 mm per pass;

[0083] The cutting depth in region J of the test piece was set to 0.05 mm per pass;

[0084] The cutting depth of region K of the test piece was set to 0.02 mm per pass.

[0085] After obtaining the refined turning parameters through machining experiments, multi-pass layer-by-layer turning was adopted for each cutting area, and the determined process path is as follows:

[0086] In area I, turn 1 cut (1 pass), then in area J, turn 2 cuts (2 passes), then in area K, turn 5 cuts (5 passes).

[0087] Repeat the single-cycle machining process 10 times. Observe the product vibration, machining dimensions, machining deformation, and tool wear during the machining process.

[0088] When machining each cylindrical section, the change in wall thickness of each section from 3.25mm to 1.25mm is recorded. The circumferential runout of the outer circle of each section is recorded when the wall thickness is 3.25mm, 2.75mm, 2.25mm, 1.75mm, and 1.25mm. Combined with the machining time required, the cutting parameters for finishing the outer shape are determined.

[0089] Table 1. Variation of circular runout of the test piece during turning with depth of cut and wall thickness.

[0090]

[0091] The final experimental results and their causes are analyzed as follows:

[0092] Higher cutting forces may place additional loads on the tool and workpiece, requiring careful consideration of their load-bearing capacity. Higher cutting temperatures may affect tool life and workpiece surface quality, necessitating cooling and lubrication control. When machining to a wall thickness of 1.75mm, noticeable chatter and deformation occurred in region I of the cylinder with a depth of cut of 0.1mm, with circular runout ranging from 0.25 to 0.32mm, and the cutting tool exhibited sticking, affecting machining. When machining region J of the cylinder with a depth of cut of 0.05mm to a wall thickness of 1.25mm, the circular runout ranged from 0.16 to 0.26mm, exceeding the outer diameter tolerance range. In selecting machining parameters, the primary considerations are: firstly, ensuring that the machining dimensions are within tolerance and that the circumferential runout is minimal; secondly, preventing visible chatter during machining to guarantee machining stability and tool life; and finally, considering both of these requirements, the final specific machining parameters are as follows:

[0093] The optimal parameters for finishing are: machine tool spindle speed 40 rad / min, lathe feed rate 0.4 mm / rad; the optimal depth of cut for the first pass of finishing is 0.1 mm; the optimal depth of cut for the second pass is 0.05 mm; and the optimal depth of cut for the third pass is 0.02 mm.

[0094] Using these cutting parameters effectively improves machining efficiency while ensuring machining quality.

[0095] 4. Solved the problem of vibration during machining caused by rigidity of parts. This invention enhances the rigidity of the tool and the part by making its own tooling, thereby eliminating machining vibration. First, a tool box and tool holder are made and installed together, as described in question (1); then, a rubber roll is made and paired with the part to increase the rigidity of the part. During the machining of the inner surface, the wall thickness changes from 7.3mm to 3.25mm. At this time, the vibration of the part can be effectively avoided by strengthening the anti-vibration tool holder and cooperating with the corresponding cutting parameters. When machining the outer surface, the wall thickness changes from 3.25mm to 1.25mm. As the wall thickness of the part decreases, the rigidity of the part decreases, and the cutting force and heat during the cutting process are more likely to cause vibration and deformation of the part. During the trial machining process, when machining the outer surface, the frequency of vibration is low in the first half of the machining range. Later, with the wear of the tool, the decrease in the rigidity of the part and the accumulation of cutting heat, the frequency of vibration of the part increases significantly. To avoid such problems, a self-made cylindrical rubber roll fixture is used to fill the inner hole of the part during the machining of the outer surface, thereby increasing the overall rigidity of the part. Rubber has high elasticity and can quickly return to its original shape after being subjected to force. It also has good vibration absorption properties, absorbing external vibrations and impacts and reducing damage to other components. Therefore, the rubber roll is selected as a buffer against part vibration. This rubber roll fixture has a cylindrical structure, with its diameter and length dimensions matching the inner hole size of the part's interface and the length of the part, respectively. It is inserted into the inner hole of the part during machining. Experimental analysis shows that after adding the rubber roll, vibration is virtually non-existent during the machining of the outer surface, with a frequency essentially zero. Furthermore, measurements after machining show that the change in outer diameter after inserting the rubber roll is between 0.02-0.05 mm, while the change in diameter without the rubber roll is between 0.04-0.12 mm. This demonstrates that inserting the rubber roll effectively improves the rigidity of the part and also contributes to improved machining accuracy, making it an effective method for eliminating vibration during part machining.

[0096] Based on the analysis of the above problems, the processing method proposed in this invention is an effective and innovative measure.

[0097] 5. This invention effectively reduces processing costs. Existing spinning technology for thin-walled titanium alloy parts requires at least three spinning passes on the titanium alloy blank, with vacuum stress relief in a heat treatment furnace between each spinning pass. Processing the parts requires matching spinning machines and heat treatment furnaces to complete the forming process. The method proposed in this invention can be completed entirely on a CNC lathe, reducing dependence on spinning equipment and heat treatment. Furthermore, traditional spinning technology requires the fabrication of a spinning mandrel with a corresponding inner diameter for each spinning pass. Based on market mandrel manufacturing costs, each mandrel costs between 80,000 and 120,000 yuan. This invention eliminates the need for mandrels, requiring only a cap, with a processing cost of 800 yuan, directly reducing tooling costs by hundreds of thousands of yuan. The cost reduction and efficiency improvement results in significant economic benefits.

[0098] 6. This invention greatly shortens the processing time of parts and effectively ensures the completion of scientific research tasks.

[0099] Using traditional spinning technology, the design time and mandrel tooling preparation time for existing bulging spinning technology for thin-walled titanium alloy parts is about 30 days. During this period, the parts cannot be processed. However, the method proposed in this invention can directly process the parts, and the actual part processing time is also shortened compared to the past, which greatly advances the production delivery node and improves production efficiency by about 5 times.

[0100] 7. Improved part machining accuracy and yield. The machining method proposed in this invention eliminates the need for heat treatment during part processing. Compared to traditional spinning forming methods, it reduces part deformation caused by stress-relief annealing between spinning processes. Furthermore, the use of customized cutting tools and the control of appropriate cutting parameters through variable manipulation results in better part dimensional accuracy. Compared to the spinning parameters of TC18 titanium alloy, this invention allows for better control of the TC18 titanium alloy turning tools and parameters, thus better ensuring the quality of machined parts. This method also eliminates defects such as cylinder cracking and spinning marks caused by bulging or unsuitable spinning parameters. According to actual machining data, the yield of parts machined using this method is more than 50% higher than that of traditional spinning techniques. Attached Figure Description

[0101] Figure 1 This is a schematic diagram of the finished structure of a titanium alloy cylindrical part.

[0102] Figure 2 This is a schematic diagram of the blank structure of a titanium alloy cylindrical part.

[0103] Figure 3 This is a schematic diagram of a homemade knife box; in which, Figure 3 'a' is the main view. Figure 3 b is the left view.

[0104] Figure 4 This is a schematic diagram of the part clamping method.

[0105] Figure 5 This is a schematic diagram of the plug structure; in which, Figure 5 'a' is the main view. Figure 5 b is Figure 5 Sectional view of section AA in section a.

[0106] Figure 6 This is a flowchart of the present invention.

[0107] In the figure: 1. Welded external component; 2. Plug; 3. Machine tool center; 4. Center hole; The specific meanings of the markings at A, B, C, D, E, I, J, and K are described in the implementation method. Detailed Implementation

[0108] This embodiment describes a control method for machining TC18 titanium alloy thin-walled cylindrical parts using a horizontal CNC lathe CK6185. The blank of the part to be machined is a thin-walled cylinder with external components welded on, such as... Figure 2 As shown, the end face, inner circumferential surface, and outer circumferential surface of this thin-walled cylindrical part all have machining allowances. The outer circumference of the area where the welded outer components are located does not require machining; only the inner cavity dimensions are machined.

[0109] Based on the location of the welded outer component, the outer circumference area to be machined is divided into regions A, B, and C. When dividing these regions, the starting point is the end face closest to the welded outer component, extending axially along the other end of the welded outer component. Specifically: Region A, starting from this point, has a segment on the welded outer component ranging from 0 to 95 mm, with a length of 95 mm; Region B has a segment ranging from 185 to 349 mm, with a length of 164 mm; and Region C has a segment ranging from 448 to 718.5 mm, with a length of 270.5 mm.

[0110] The inner and outer circumferential surfaces of areas A, B, and C all require machining. The final finished product has an outer diameter of 180-0.05-0.30 mm, a wall thickness of 1.25+0.12-0.03 mm, and an inner hole size of φ177.5-0.24-0.29 mm. The finished part after machining is shown in the image. Figure 1 As shown.

[0111] The process route in this embodiment is as follows: spare parts → semi-finished internal machining → natural aging → finish internal machining → natural aging → finish external machining → trimming.

[0112] Throughout the machining process, coated carbide rhomboid inserts are selected. This type of insert has good red hardness, good thermal conductivity, and low affinity with titanium alloy. Specific models are shown in Table 1.

[0113] Table 2 Tool List

[0114]

[0115]

[0116] The specific process of this embodiment is as follows:

[0117] Step 1: Define the area to be machined on the outer circumference of the part:

[0118] Based on the position of the welded outer component, the outer circumference area to be processed is divided into area A, area B, and area C; when dividing area A, area B, and area C, the end face closest to the position of the welded outer component is used as the starting point and extended axially to the other end of the welded outer component.

[0119] Step 2, Prepare the tooling:

[0120] The tooling includes a plug, a knife box, and a rubber roll.

[0121] A machined plug is prepared; the plug is disc-shaped and has two symmetrically distributed tooling removal threaded through holes 7. A center hole 8 is located at the center of the plug for positioning and tightening the machine tool tailstock. The plug facilitates clamping of the part during machining and enhances the rigidity of the part, preventing significant deformation.

[0122] In this embodiment, the diameter of the plug is φ177.5-0.28-0.30mm.

[0123] Machining the tool box; the tool box is strip-shaped with a U-shaped cross-section, such as... Figure 3 As shown. One end of the tool box is a connecting end; four threaded connecting holes are distributed on the two sides of the connecting end, of which: the two threaded connecting holes at the bottom are fitted with screws for connecting the machine tool and the tool box, and serve to fix the tool box; the two threaded connecting holes at the top are a set of tool shank connecting holes. At the same time, there are two other tool shank connecting holes on the side wall of the other end of the tool box. The tool box and the tool shank are connected through the two sets of tool shank connecting holes, and serve to fix the tool shank.

[0124] The width of the U-shaped groove in the tool holder is greater than the width of the tool shank. In this embodiment, the tool shank width is 18mm, and the groove width of the tool holder is 20mm, to ensure a tight fit between the tool holder and the tool shank, resulting in better stability of the tool shank during machining. The tool holder increases the rigidity of the tool shank, preventing it from vibrating during machining and ensuring the machining accuracy of the parts.

[0125] Processing a rubber roll; the rubber roll is cylindrical, with an outer diameter of φ154mm, the same as the inner diameter of the part blank, and a length of 645mm, the same as the length of the cylinder. In use, the rubber roll is placed inside the part's cavity to enhance its rigidity and reduce vibration during machining.

[0126] Step 3, clamping the part blank:

[0127] The custom-made Sandvik tool holder is installed into the tool holder. The Sandvik brand hydraulically damped tool holder is a 570-3C 80 1400CR with a length-to-diameter ratio of 13, providing excellent vibration damping and anti-chatter effects during machining. The tool holder extends 800mm beyond its original length, and the tool holder and tool holder are secured with bolts.

[0128] Following the machining sequence determined by the process, install the cutting head and insert for machining the internal hole onto the tool holder. Then, install the tool box with the tool holder onto the CNC lathe tool post.

[0129] Clamp the workpiece blank on the four-jaw chuck of the machine tool spindle. Use a dial indicator to measure the circumferential runout of the outer circle at a distance of 50mm from the end face of the workpiece clamping fixed end. Select four symmetrical points with smaller circumferential runout and adjust the machine tool spindle chuck until the distance difference between these four points and the center of the machine tool spindle is 0.

[0130] A machining strip is machined on the outer circumference surface at 70mm from each end face of the part blank. The two machining strips are located on the outer circumference of area A and area C, respectively. The specific location of the machining strip on the outer circumference of area A is 628.5mm to 648.5mm from the end face of the cantilever, and the specific location of the machining strip on the outer circumference of area C is 70mm to 90mm from the end face of the cantilever.

[0131] In this embodiment, the outer diameter of the machined belt is 184 mm and the axial length is 20 mm.

[0132] Step 4, Semi-finish turning of the inner hole of the part blank:

[0133] Place the lathe's center rest on the machining zone of the outer diameter of area C of the workpiece blank, and use a dial indicator to measure the two machined areas of the workpiece blank. Adjust the center rest rollers so that the dial indicator shows a runout of less than 0.03 mm. Perform semi-finish turning on the inner hole of the workpiece. Obtain the workpiece blank after semi-finish turning.

[0134] Cutting parameters for machining the inner hole of the workpiece blank: machine tool spindle speed is 40 rad / min, cutting depth is 0.1 mm, and machine tool feed rate is 1 mm / rad.

[0135] Step 5, Natural aging of the part blank:

[0136] The partially finished part blanks are left to stand for 24 hours to release stress.

[0137] Step 6, finish turning of the inner hole of the part:

[0138] Place the lathe center rest on the machining belt on the outer circumferential surface of the workpiece blank in area A, and support the outer circumferential surface of the machining belt with rollers on the center rest. Use a dial indicator to measure the machining belt at two locations on the workpiece blank, and adjust the spindle jaws to ensure that the circumferential runout of the machining belt at both locations is <0.03mm.

[0139] The inner hole of the part blank is precision machined to obtain a semi-finished part.

[0140] Cutting parameters: machine tool spindle speed is 40 rad / min, cutting depth is 0.05 mm, and lathe feed rate is 0.4 mm / rad.

[0141] Step 7, Natural aging of semi-finished parts:

[0142] After finishing the inner bore, disassemble the parts and let them stand for 24 hours to release stress.

[0143] Step 8, Preparation for precision machining of the semi-finished part's shape:

[0144] First, insert a rubber roll into the inner cavity of the semi-finished part. Insert the rubber roll into the opening of the cavity and use a copper rod to push the rubber roll into the cavity until it fills the entire cavity. Then, install a plug on the non-clamping end of the part, such as... Figure 4 As shown. Ensure the end face of the plug is flush with the end face of the part, and install it in place. Install the rubber roll and plug required for the semi-finished part processing, and prepare for the precision machining of the semi-finished part.

[0145] Step 9, Preparing the semi-finished shape of the precision-machined part:

[0146] according to Figure 4 The part is re-clamped, with the CNC lathe's four-jaw chuck directly clamping the outer diameter of the part at point D, ensuring the end face of the semi-finished part is flush against the chuck. The tailstock of the CNC lathe rests against the center hole of the plug. A dial indicator is used to measure the runout at two machining points on the outer circumference of the part. The spindle jaws are adjusted using standard methods until the runout at the two machining points is less than 0.03 mm.

[0147] When precision machining the semi-finished shape of a part, the presence of welded external components divides the part's shape into three cutting areas: area I, area J, and area K.

[0148] When dividing the I, J, and K regions, the starting point is the end face of the machine tool clamping end, extending axially towards the other end of the semi-finished part. Specifically: Region I, starting from this point, extends from 0 to 275.5 mm on the semi-finished part, with a length of 275.5 mm; Region J extends from 369.5 to 533.5 mm, with a length of 164 mm; Region K extends from 623.5 to 673.5 mm, with a length of 50 mm.

[0149] Step 10: Determine the machining parameters for the semi-finished part's shape:

[0150] Using test specimens, conventional testing methods were employed to determine the machining parameters of the external shape.

[0151] The determined machining parameters for the finishing turning of the outer shape are as follows: machine tool spindle speed 40 rad / min, lathe feed rate 0.4 mm / rad; the optimal depth of cut for the first pass of finishing turning is 0.1 mm; the optimal depth of cut for the second pass of finishing turning is 0.05 mm; and the optimal depth of cut for the third pass of finishing turning is 0.02 mm.

[0152] Step 11, precision turning the semi-finished part's shape:

[0153] According to the determined process path, multi-pass layer-by-layer turning is used for each cutting area to ensure that the cutting amount of the same layer in each cutting area is the same.

[0154] In this embodiment, the turning process consists of three passes, and the specific process is as follows:

[0155] Ⅰ First turning pass:

[0156] Turning zone I; the cutting zone starts from the starting point 0mm and extends axially towards the other end of the part, with a length of 275.5mm. Set the cutting depth to 0.1mm. After two passes in zone I, until the cutting depth is 0.2mm, the first pass of turning in zone I is complete. Proceed to zone J for turning.

[0157] Turn region J; keeping the depth of cut constant at 0.1mm, the cutting area starts at 369.5mm and ends at 533.5mm, with a length of 164mm. After two passes in region J, with a cutting depth of 0.2mm, the first pass of turning in region J is complete. Proceed to region K for turning.

[0158] Turn region K; keep the depth of cut constant at 0.1mm, the cutting area starts at 623.5mm and ends at 673.5mm, with a length of 50mm. After turning region K twice until the turning amount is 0.2mm, the first pass of turning region K is completed.

[0159] Repeat the turning process of region I, region J and region K in the first turning pass three times in sequence until the total amount of turning is 0.6 mm, thus completing the first turning pass and proceeding to the second turning pass.

[0160] The parameters for the first turning pass are: machine spindle speed of 40 rad / min, depth of cut of 0.1 mm, and lathe feed rate of 0.4 mm / rad.

[0161] After the first turning pass is completed, use an outside micrometer to measure the external dimensions of the machined position and record them.

[0162] II. Second turning pass:

[0163] Turning zone I; the cutting zone starts from the starting point 0mm and extends axially towards the other end of the part, with a length of 275.5mm. Set the cutting depth to 0.05mm and perform one pass in zone I to complete the second pass of turning in zone I. Proceed to zone J for turning.

[0164] Turn region J; maintain a constant depth of cut of 0.05 mm, with the cutting area starting at 369.5 mm and ending at 533.5 mm, for a length of 164 mm. Perform one pass in region J to complete the second pass of turning in region J. Proceed to region K for turning.

[0165] Turn region K; keep the depth of cut constant at 0.05mm, the cutting area starts at 623.5mm and ends at 673.5mm, with a length of 50mm. Turn one cut in region K to complete the second pass of turning in region K.

[0166] Repeat the turning process of region I, region J and region K in the second turning pass eight times in sequence until the total amount of turning is 0.4 mm, then complete the second turning pass and proceed to the third turning pass.

[0167] The parameters for the second turning pass are: machine spindle speed of 40 rad / min, depth of cut of 0.05 mm, and lathe feed rate of 0.4 mm / rad.

[0168] After the second turning operation is completed, use an outside micrometer to measure the external dimensions of the machined position and record them.

[0169] III. Third turning pass:

[0170] Turning zone I; the cutting zone starts from the starting point 0mm and extends axially towards the other end of the part, with a length of 275.5mm. Set the cutting depth to 0.02mm and perform one pass in zone I to complete the third pass of turning in zone I. Proceed to zone J for turning.

[0171] Turn region J; maintain a constant depth of cut of 0.02 mm, with the cutting area starting at 369.5 mm and ending at 533.5 mm, for a length of 164 mm. Perform one pass in region J to complete the third pass of turning in region J. Proceed to region K for turning.

[0172] Turn region K; keep the depth of cut constant at 0.02mm, the cutting area starts at 623.5mm and ends at 673.5mm, with a length of 50mm. Turn one cut in region K to complete the third pass of turning in region K.

[0173] Repeat the above steps until the semi-finished part meets the design requirements, and complete the precision machining of the semi-finished part.

[0174] The parameters for the third turning pass are: machine spindle speed of 40 rad / min, depth of cut of 0.02 mm, and lathe feed rate of 0.4 mm / rad.

[0175] During the third turning process, after each turning pass, the external dimensions of the machining position are measured with an outside micrometer to avoid dimensional deviations during machining.

[0176] Step 12, cutting and machining of the part:

[0177] According to the drawings, the parts that have completed the precision turning of the outer shape are cut off, the reserved 45mm machining allowance is removed, and the total length of the part after cutting is ensured to be 675mm, so as to obtain the finished part.

[0178] This completes the machining of the TC18 titanium alloy thin-walled cylinder.

Claims

1. A method for machining a thin-walled cylindrical body of TC18 titanium alloy, characterized in that, The specific process is as follows: Step 1: Define the area to be machined on the outer circumference of the part: The outer circumference area to be processed is divided into region A, region B and region C according to the position of the welding outer component of the part; when dividing region A, region B and region C, the end face near the position of the welding outer component is used as the starting point and extended axially to the other end of the welding outer component. Step 2, Prepare the tooling: The tooling includes a plug, a knife box, and a rubber roll; Complete the processing of the plug, knife box, and rubber roll according to the tooling design; Step 3, clamping the part blank: Insert the tool holder into the tool box; According to the machining sequence determined by the process, install the cutting head and insert for machining the inner hole on the tool holder; install the tool box with the tool holder on the CNC lathe tool post; Clamp the part blank on the machine tool and align it; Two machining strips are machined on the outer circumference surface at 70mm from each end face of the part blank, forming two machining strips; the two machining strips are located on the outer circumference of region A and region C, respectively; wherein The specific location for adding the tape on the outer circumference of area A is 628.5mm to 648.5mm from the end face of the cantilever, and the specific location for adding the tape on the outer circumference of area C is 70mm to 90mm from the end face of the cantilever. Step 4, Semi-finish turning of the inner hole of the part blank: Place the lathe's center rest on the machining belt on the outer cylindrical surface of the workpiece blank in area C, and adjust the center rest rollers to make the runout less than 0.03mm; perform semi-finish turning on the inner hole of the workpiece; and obtain the workpiece blank after semi-finish turning. Cutting parameters for machining the inner hole of the workpiece blank: machine tool spindle speed is 40 rad / min, cutting depth is 0.1 mm, and machine tool feed rate is 1 mm / rad; Step 5, Natural aging of the part blank: The partially finished part blanks were left to stand for 24 hours to release stress. Step 6, finish turning of the inner hole of the part: Place the lathe center rest on the machining belt on the outer circular surface of the workpiece blank area A, and support the outer circumferential surface of the machining belt with rollers on the center rest; adjust the spindle jaws so that the circumferential runout of the machining belt at the two locations is <0.03mm; The inner hole of the part blank is precision machined; Obtain a semi-finished product of the parts; Cutting parameters for precision turning of the inner hole of the part blank: machine tool spindle speed is 400 rad / min, depth of cut is 0.05 mm, and lathe feed rate is 0.4 mm / rad; Step 7, Natural aging of semi-finished parts: The semi-finished parts were left to stand for 24 hours to release stress. Step 8, Preparation for precision machining of the semi-finished part's shape: The preparation for the precision machining of the semi-finished part's shape is the installation tooling; Insert the rubber roll into the inner cavity of the semi-finished part and make the rubber roll fill the entire inner cavity of the semi-finished part; install a plug on the non-clamping end of the part; and make the end face of the plug's stop end fit tightly against the end face of the part; install the rubber roll and plug required for the processing of the semi-finished part and prepare for the precision turning of the semi-finished part's shape. Step 9, Preparing the semi-finished shape of the precision-machined part: Re-clamp the parts; Adjust the spindle jaws until the runout at the two machining points is less than 0.03mm; The precision turning of a semi-finished part involves turning the outer circumference of the semi-finished part into three cutting zones: I zone, J zone, and K zone. Step 10: Determine the machining parameters for the semi-finished part's shape: The turning parameters of the shape are determined by experimental methods using test pieces; The determined turning parameters for the external precision turning are: machine tool spindle speed 40 rad / min, lathe feed rate 0.4 mm / rad; The optimal depth of cut for the first pass of finish turning is 0.1 mm; the optimal depth of cut for the second pass of finish turning is 0.05 mm. The optimal depth of cut for the third pass of precision machining is 0.02 mm; Step 11, precision turning the semi-finished part's shape: According to the determined process path, multi-pass layer-by-layer turning is used for each cutting area to make the cutting amount of the same layer in each cutting area the same; Step 12, cutting and machining of the part: This completes the machining of the TC18 titanium alloy thin-walled cylinder.

2. The method for machining a TC18 titanium alloy thin-walled cylindrical body as described in claim 1, characterized in that, Region A, starting from the aforementioned starting point, extends from 0 to 95 mm on the welded outer component, with a length of 95 mm. Region B extends from 185 to 349 mm on the welded outer component, with a length of 164 mm. The range of region C is 448–718.5 mm, and the length of region C is 270.5 mm.

3. The method for machining a TC18 titanium alloy thin-walled cylindrical body as described in claim 1, characterized in that, The plug is disc-shaped, with two tooling disassembly threaded through holes symmetrically distributed on it; and a center hole for positioning and tightening the machine tool tailstock center is located in the center of the plug. The cross-section of the tool box is U-shaped; one end of the tool box is a connecting end; there are connecting holes distributed on the two sides of the connecting end, which are used for the connection between the machine tool and the tool box and the connection between the tool box and the tool holder, respectively. The outer diameter of the rubber roll is the same as the inner diameter of the part blank, and the length is the same as the length of the cylinder.

4. The method for machining a TC18 titanium alloy thin-walled cylindrical body as described in claim 1, characterized in that, The specific location for adding the machine tape on the outer circumference of region A is 628.5mm to 648.5mm from the end face of the cantilever, and the specific location for adding the machine tape on the outer circumference of region C is 70mm to 90mm from the end face of the cantilever.

5. The method for machining a TC18 titanium alloy thin-walled cylindrical body as described in claim 1, characterized in that, The precision machining process for the semi-finished part is as follows: Ⅰ First turning pass: Turning area I; the cutting area starts from the starting point 0mm and extends axially to the other end of the part, with a length of 275.5mm; set the cutting depth to 0.1mm, and after turning two times in area I until the turning amount is 0.2mm, the first pass of turning in area I is completed; proceed to turning area J. Turn region J; keep the depth of cut constant at 0.1mm, the cutting area starts at 369.5mm and ends at 533.5mm, with a length of 164mm; after turning region J twice until the turning amount is 0.2mm, the first pass of turning region J is completed; proceed to turn region K. Turn the K region; keep the cutting depth constant at 0.1mm, the cutting area starts at 623.5mm and ends at 673.5mm, with a length of 50mm; after turning the K region twice until the turning amount is 0.2mm, the first pass of turning the K region is completed; Repeat the turning process of region I, region J and region K in the first turning pass three times in sequence until the total amount of turning is 0.6 mm, then complete the first turning pass and proceed to the second turning pass. II. Second turning pass: Turning area I; the cutting area starts from the starting point 0mm and extends axially to the other end of the part, with a length of 275.5mm; set the cutting depth to 0.05mm, turn once in area I to complete the second pass of turning in area I; then proceed to turning area J. Turn region J; maintain a cutting depth of 0.05mm, the cutting area starts at 369.5mm and ends at 533.5mm, with a length of 164mm; make one pass in region J to complete the second pass of turning in region J; then proceed to region K for turning; Turn the K region; keep the depth of cut constant at 0.05mm, the cutting area starts at 623.5mm and ends at 673.5mm, with a length of 50mm; turn one cut in the K region to complete the second pass of turning the K region; Repeat the turning process of region I, region J and region K in the second turning pass eight times in sequence until the total amount of turning is 0.4 mm, then complete the second turning pass and proceed to the third turning pass. III. Third turning pass: Turning area I; the cutting area starts from the starting point 0mm and extends axially to the other end of the part, with a length of 275.5mm; set the cutting depth to 0.02mm, turn once in area I to complete the third pass of turning in area I; then proceed to turning area J. Turn region J; maintain a cutting depth of 0.02mm, the cutting area starts at 369.5mm and ends at 533.5mm, with a length of 164mm; make one pass in region J to complete the third pass of turning in region J; then proceed to region K for turning; Turn the K region; keep the depth of cut constant at 0.02mm, the cutting area starts at 623.5mm and ends at 673.5mm, with a length of 50mm; turn one cut in the K region to complete the third pass of turning in the K region; Repeat the above steps until the semi-finished part meets the design requirements, and complete the precision machining of the semi-finished part. Step 10, cutting and machining of the part: According to the drawings, the parts that have completed the precision turning of the outer shape are cut off to obtain the finished parts, thus completing the entire processing.

6. The method for machining a TC18 titanium alloy thin-walled cylindrical body as described in claim 5, characterized in that, The parameters for the first turning pass are: machine spindle speed of 40 rad / min, depth of cut of 0.1 mm, and lathe feed rate of 0.4 mm / rad.

7. The method for machining a TC18 titanium alloy thin-walled cylindrical body as described in claim 5, characterized in that, The parameters for the second turning pass are: machine spindle speed of 40 rad / min, depth of cut of 0.05 mm, and lathe feed rate of 0.4 mm / rad.

8. The method for machining a TC18 titanium alloy thin-walled cylindrical body as described in claim 5, characterized in that, The parameters for the third turning pass are: machine spindle speed of 40 rad / min, depth of cut of 0.02 mm, and lathe feed rate of 0.4 mm / rad.

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