Precision casting and processing of large ultra-long titanium alloy special-shaped thin shells and manufacturing method for controlling welding deformation

Abstract

The present invention belongs to the field of non-ferrous metal plastic forming and precision machining technology, and discloses a large, ultra-long titanium alloy special-shaped thin shell precision casting and processing and welding deformation control technology. The large, ultra-long titanium alloy special-shaped thin shell comprises: a cylindrical thin shell composed of a first cylindrical section, a first conical cylindrical section, a second cylindrical section, a second conical cylindrical section, and a third cylindrical section connected in sequence along a first direction, and the cylindrical thin shell is provided with a radially protruding convex semicircular bulge along the shell generatrix, and the thickness of the cylindrical thin shell ranges from 2.5 mm to 0.5 mm. The manufacturing method comprises: dividing the cylindrical thin shell into two parts, an inner cylinder small section and an inner cylinder large section, at the second cylindrical section, and casting them separately; performing lathe-milling composite rough machining and semi-finishing on the inner cylinder small section and the inner cylinder large section; assembling the inner cylinder small section and the inner cylinder large section and performing laser welding, and then performing cylinder body finishing. The large, ultra-long titanium alloy special-shaped thin shell precision casting and processing and welding deformation control technology provided by the present invention can improve manufacturing efficiency and product quality.

Description

Technical Field

[0001] The present invention relates to the technical field of nonferrous metal plastic forming and precision machining, and in particular to a method for precision casting and machining a large ultra-long titanium alloy special-shaped thin shell and controlling welding deformation. Background Art

[0002] Titanium and its alloys have become indispensable materials in the fields of aviation, aerospace, energy, shipbuilding, chemical engineering, and medicine. However, titanium's high chemical activity makes casting difficult, and existing casting technologies struggle to meet the current demand for thin-walled, special-shaped, and structurally and functionally unified titanium alloy precision castings in aerospace and other fields. Consequently, the manufacturing of large, complex structural parts, such as large, ultra-long titanium alloy thin shells, is inefficient, challenging, and of uncertain quality. Summary of the Invention

[0003] The present invention provides a method for precision casting and machining of large ultra-long titanium alloy special-shaped thin shells and controlling welding deformation, which solves the technical problems in the prior art of low manufacturing efficiency, great difficulty and unreliable quality of large ultra-long titanium alloy special-shaped thin shell parts.

[0004] In order to solve the above technical problems, the present invention provides a method for precision casting, processing and welding deformation control of a large-scale ultra-long titanium alloy special-shaped thin shell, wherein the large-scale ultra-long titanium alloy special-shaped thin shell comprises: a cylindrical thin shell composed of a first cylindrical section, a first conical cylindrical section, a second cylindrical section, a second conical cylindrical section and a third cylindrical section connected in sequence along a first direction, and a radially protruding convex semicircular bulge along the shell busbar is provided on the cylindrical thin shell, a reinforcing rib plate is provided in the convex semicircular bulge, an annular reinforcing rib is provided on the outer side of the first cylindrical section, a plurality of partitions are provided on the inner side of the cylindrical thin shell, a first flange and a second flange are provided at both ends of the cylindrical thin shell respectively, the diameter of the first cylindrical section is smaller than the diameter of the second cylindrical section, the diameter of the second cylindrical section is smaller than the diameter of the third cylindrical section, and the thickness range of the cylindrical thin shell is 2.5 mm ± 0.5 mm;

[0005] The manufacturing method comprises:

[0006] Dividing the cylindrical thin shell into two parts, a small inner cylinder section and a large inner cylinder section, at the second cylindrical section and casting them separately;

[0007] performing turning-milling composite rough machining and semi-finishing machining on the small section of the inner cylinder and the large section of the inner cylinder respectively;

[0008] The inner cylinder small section and the inner cylinder large section are assembled and laser welded, and then the cylinder body is finely processed.

[0009] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0010] The large-scale ultra-long titanium alloy special-shaped thin shell precision casting and processing and welding deformation control manufacturing method provided in the embodiment of the present application adopts split casting, precision machining and laser welding schemes to effectively improve the casting quality of castings, control the deformation of castings and effectively perform hot isostatic pressing of castings to eliminate defects of castings, thereby improving product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0012] Figure 1 A schematic structural diagram of a large, ultra-long titanium alloy special-shaped thin shell provided in an embodiment of the present invention;

[0013] Figure 2 A schematic structural diagram of an inner cylinder segment provided in an embodiment of the present invention;

[0014] Figure 3 A schematic structural diagram of the inner barrel section provided in an embodiment of the present invention;

[0015] Figure 4 The overall process design and manufacturing process flow provided for the embodiments of the present invention;

[0016] Figure 5 A schematic diagram of the cross-sectional structure of an inner cylinder provided in an embodiment of the present invention;

[0017] Figure 6 A schematic diagram of disassembling a through-groove partition provided in an embodiment of the present invention;

[0018] Figure 7 A casting process flow chart provided in an embodiment of the present invention;

[0019] Figure 8 A diagram of the front section casting of the inner cylinder provided in an embodiment of the present invention;

[0020] Figure 9 A drawing of the rear section casting of the inner barrel provided in an embodiment of the present invention;

[0021] Figure 10 A schematic diagram of the front section casting system of the inner barrel provided in an embodiment of the present invention;

[0022] Figure 11 A schematic diagram of the rear section casting system of the inner barrel provided in an embodiment of the present invention;

[0023] Figure 12Schematic diagram of the front and rear section pouring system provided by the embodiment of the present invention

[0024] Figure 13 A schematic diagram of the installation and welding of a baffle (or partition) built into the inner cylinder provided by an embodiment of the present invention;

[0025] Figure 14 A diagram of a casting of the front section of the inner cylinder provided in an embodiment of the present invention;

[0026] Figure 15 A drawing of the rear section of the inner barrel provided in an embodiment of the present invention;

[0027] Figure 16 A schematic diagram of a three-dimensional model of a product casting after hot isostatic pressing provided in an embodiment of the present invention;

[0028] Figure 17 A schematic diagram before machining provided by an embodiment of the present invention;

[0029] Figure 18 Schematic diagrams of welding of I-shaped and rectangular partitions provided in embodiments of the present invention;

[0030] Figure 19 A schematic diagram of two-section butt welding provided in an embodiment of the present invention;

[0031] Figure 20 A schematic diagram of a three-dimensional model 1 of a casting system for a casting provided in an embodiment of the present invention;

[0032] Figure 21 A schematic diagram of the structure of a large-section graphite casting mold for an inner cylinder provided in an embodiment of the present invention;

[0033] Figure 22 A schematic diagram of the structure of a graphite casting mold for a small section of an inner cylinder provided in an embodiment of the present invention;

[0034] Figure 23 A schematic diagram of a second three-dimensional model of a casting system for a casting provided in an embodiment of the present invention;

[0035] Figure 24 A schematic diagram of a three-dimensional model of a casting system for a casting provided in an embodiment of the present invention;

[0036] Figure 25 A schematic diagram of a three-dimensional model 5 of a casting system for a casting provided in an embodiment of the present invention;

[0037] Figure 26 A cross-sectional view of a three-dimensional model 1 of a casting system for a casting provided in an embodiment of the present invention;

[0038] Figure 27 A cross-sectional view of a second three-dimensional model of a casting system for a casting provided by an embodiment of the present invention;

[0039] Figure 28 A schematic diagram of a three-dimensional model six of a casting system for a casting provided in an embodiment of the present invention;

[0040] Figure 29 A schematic diagram of a three-dimensional model seven of a casting system for a casting provided in an embodiment of the present invention;

[0041] Figure 30 A schematic diagram of a three-dimensional model 8 of a casting system for a casting provided in an embodiment of the present invention;

[0042] Figure 31 A schematic diagram of a nine-dimensional model of a casting system for a casting provided in an embodiment of the present invention;

[0043] Figure 32 A schematic diagram of a three-dimensional model 10 of a casting system for a casting provided in an embodiment of the present invention;

[0044] Figure 33 A schematic diagram of a three-dimensional model 11 of a casting system for a casting provided in an embodiment of the present invention;

[0045] Figure 34 A cross-sectional view from a first perspective of a three-dimensional model of a casting system of a casting provided by an embodiment of the present invention;

[0046] Figure 35 A sectional view from a second perspective of a three-dimensional model of a casting system of a casting provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0047] The present application is described below with reference to specific embodiments in conjunction with the accompanying drawings.

[0048] The embodiments of the present application solve the technical problems of low manufacturing efficiency, great difficulty and unreliable quality of large and extra-long titanium alloy special-shaped thin shell parts in the prior art by providing a large and extra-long titanium alloy special-shaped thin shell precision casting and processing and welding deformation control technology.

[0049] See also Figure 1 、 Figure 2 and Figure 3, this embodiment provides a method for precision casting, processing and welding deformation control of a large ultra-long titanium alloy special-shaped thin shell, wherein the large ultra-long titanium alloy special-shaped thin shell comprises: a cylindrical thin shell composed of a first cylindrical section 11, a first conical cylindrical section 12, a second cylindrical section 13, a second conical cylindrical section 14 and a third cylindrical section 15 connected in sequence along a first direction, and a radially protruding convex semicircular bulge 16 along the shell busbar is provided on the cylindrical thin shell, a reinforcing rib plate is provided in the convex semicircular bulge 16, an annular reinforcing rib is provided on the outer side of the first cylindrical section 11, a plurality of partitions are provided on the inner side of the cylindrical thin shell, a first flange 17 and a second flange 18 are provided at both ends of the cylindrical thin shell respectively, the diameter of the first cylindrical section 11 is smaller than the diameter of the second cylindrical section 13, the diameter of the second cylindrical section 13 is smaller than the diameter of the third cylindrical section 15, and the thickness range of the cylindrical thin shell is 2.5 mm ± 0.5 mm.

[0050] Specifically, this embodiment is described in detail using a specific example. The large ultra-long titanium alloy special-shaped thin shell product is a long cylindrical structure. The product part has an external dimension of 2220.0×580.0×550.0mm, a main wall thickness of 2.5mm, and a theoretical weight of 43.2Kg. The schematic diagram and structural dimensions of the part are as follows: Figure 1 and Figure 2 As shown in the figure, the main structure of the intermediate section of this thin-walled, irregularly shaped shell has a skin thickness of 2.5mm, and the total length of the thin-walled skin area is 2180mm. The outer diameter of the small section ranges from ￠240mm to ￠309mm, while the diameter of the large section ranges from ￠309mm to ￠392mm. The transition zone from the small section to the large section is a conical section that gradually transitions from ￠240mm to ￠309mm. The total length of the thin-walled shell is 2220mm.

[0051] The manufacturing method comprises:

[0052] The cylindrical thin shell is divided into two parts, a small inner cylinder section and a large inner cylinder section, at the second cylindrical section 13 and casted separately;

[0053] performing turning-milling composite rough machining and semi-finishing machining on the small section of the inner cylinder and the large section of the inner cylinder respectively;

[0054] The inner cylinder small section and the inner cylinder large section are assembled and laser welded, and then the cylinder body is finely processed.

[0055] Furthermore, the reinforcing ribs are arranged as multiple ribs arranged at intervals. Twelve reinforcing ribs are distributed axially on the inner semicircular bulge to install the circuit and strengthen the rigidity of the shell. Theoretical calculation and analysis show that after the 12 ribs are reinforced, the overall rigidity of the shell can be increased by about 25%. It should be noted that the original design used continuous and uninterrupted integral ribs, but due to the consideration of the casting process, sand could not be removed. At the same time, there were unpredictable risks in process factors such as quality defects and inspection during the casting filling process, so it was divided into 12 discontinuous reinforcing ribs.

[0056] Among the multiple partitions arranged in the inner cylinder small section and the inner cylinder large section, the partitions close to the cylinder openings at both ends are cast as a whole, and the other partitions are fixed by welding and the inner surfaces are finely processed to reduce the difficulty of casting and processing.

[0057] Furthermore, during the semi-finishing process, process flanges are respectively provided on the edges to be welded of the small inner barrel section and the large inner barrel section as machining coordination benchmarks for the large and small sections.

[0058] At the same time, the process flanges are all configured as open flange structures rather than closed circular structures. The use of an open structure is beneficial for effectively achieving the function of clamping and aligning the process benchmark, while avoiding large deformation of the barrel caused by the sharp attenuation of stiffness when the closed circular flange is finally removed.

[0059] Furthermore, after the small inner barrel section and the large inner barrel section are cast, hot isostatic pressing heat treatment is performed to eliminate defects of the castings.

[0060] Furthermore, before performing the turning-milling composite rough machining, the small inner cylinder section and the large inner cylinder section are subjected to fluorescence detection and three-dimensional scanning detection;

[0061] After completing the turning-milling composite rough machining, the three-dimensional scanning reference conversion coordination is carried out and then semi-finishing is carried out.

[0062] Before laser welding the small inner tube section and the large inner tube section, the partition welding is completed respectively, and then the small inner tube section and the large inner tube section are docked, and then the flanges at both ends are finely processed and tested for coaxiality.

[0063] Furthermore, the small inner tube section and the large inner tube section are butt-welded with a stop, and the effective welding thickness is 4.5 mm; the welding power range is 3.4-3.8 KW, and the speed is 1.7-1.9 m / min.

[0064] Furthermore, a 5mm margin is left on the front end face of the first flange, a 3mm margin is left on the inner end face of the first flange, a 3mm margin is left on one side of the end face groove of the first flange, a 3mm margin is left on the bottom face of the first flange, a 16mm margin is left on the outer diameter of the bottom face of the first flange, and a 5mm margin is left on one side of the inner shape surface of the bottom face of the first flange;

[0065] A 5mm margin is left on the rear end face of the second flange, a 3mm margin is left on the inner end face of the second flange, a 3mm margin is left on one side of the end face groove of the second flange, a 3mm margin is left on the bottom face of the second flange, a 16mm margin is left on the outer diameter of the bottom face of the second flange, and a 5mm margin is left on one side of the inner shape surface of the bottom face of the second flange.

[0066] The manufacturing method and its advantages will be described in detail below for the above-mentioned specific workpiece.

[0067] The manufacturing method involved in this embodiment mainly includes the following parts:

[0068] 1) Precision casting process and mold design and casting of large ultra-long titanium alloy special-shaped thin shells;

[0069] 2) Calculation of precision turning and milling composite machining of large, ultra-long titanium alloy special-shaped thin shells;

[0070] 3) Laser welding technology and airtightness testing of large, ultra-long titanium alloy special-shaped thin shells;

[0071] 4) 3D digital scanning and inspection of large thin-walled titanium alloy special-shaped shells.

[0072] This embodiment includes a series of key methods in the precision forming, manufacturing and testing process of titanium alloy thin-walled special-shaped shells, involving the structural design and process characteristic control of large-scale ultra-long thin-walled titanium alloy special-shaped shell products, the design of precision casting forming process schemes for large-scale ultra-long titanium alloy special-shaped shells, simulation and optimization of various casting systems and three-dimensional digital camera scanning and detection technology for castings, CNC turning and milling composite rough and fine processing and benchmark conversion coordination technology for large-scale ultra-long titanium alloy special-shaped shells, high-power laser welding technology for large-scale ultra-long titanium alloy special-shaped shells, and comprehensive external pressure and airtightness testing and detection technology for large-scale thin-walled titanium alloy special-shaped shells.

[0073] The precision casting, deformation control and processing of large-scale ultra-long titanium alloy special-shaped thin shells and the manufacturing method of welding deformation control explored in the embodiments of the present invention provide an effective new and reliable solution for the precision forming and processing of similar large-scale thin-walled special-shaped shell structure products.

[0074] Titanium alloy casting involves pouring and pressing molten metal into a mold cavity, where it solidifies into a casting with a defined shape and properties. Casting is characterized by its ability to form the metal in a single step, offering great process flexibility and adaptability to castings of virtually any composition, shape, and weight, all at a low cost. Casting methods include sand casting and specialty casting, selected based on the alloy type, size, batch size, and quality requirements of the casting. Mechanized and automated equipment can be used for large-scale production. Due to the physical and chemical properties of titanium, the titanium alloy casting process has unique requirements and characteristics, both in terms of the molding material ratio and the process method.

[0075] First, it requires the molding material to have very high fire resistance. Second, pouring must be carried out under high vacuum or inert gas protection, sometimes accompanied by centrifugal force. Using mold shells of different materials, there are three different mold casting systems according to the mold material.

[0076] (1) Pure graphite shell system. Graphite powder of varying particle sizes is used as refractory filler and sanding material, and resin is used as a binder. The shell features high strength, light weight, low cost, and a wide variety of raw material sources. Suitable for centrifugal or gravity casting.

[0077] (2) Refractory metal surface shell system. As a composite system, except for the surface layer requiring special processing due to the different molding materials (refractory metals such as tungsten powder), the back layer, from molding materials to shell making process, is the same as the investment casting of cast steel.

[0078] (3) Oxide ceramic shell system. The surface and back layers of the shell are made of oxide as the molding material, so the shell has high strength and the thermal conductivity is the smallest among the three shells. It is suitable for casting thin-walled castings with complex shapes.

[0079] The chemical composition and mechanical properties of titanium castings cast by the above three shell systems are not much different; however, there are obvious differences in surface quality. The shrinkage rate of the latter two shells is significantly lower than that of the graphite shell, so the dimensional accuracy of the castings is higher.

[0080] Technical problems to be solved

[0081] ①Uniformity of very thin wall thickness: There are four options for designing machining allowances: leaving no allowance for the inner and outer shapes, leaving allowance for both the inner and outer shapes, leaving allowance for the inner shape but no allowance for the outer shape, or leaving allowance for the outer shape but no allowance for the inner shape;

[0082] ② The defects of castings are Class I castings: integral casting and split casting, split casting scheme design, and casting system design;

[0083] ③ The casting is very long and is prone to deformation: control measures for casting deformation;

[0084] ④ Welding sealing and compatibility: preparation before welding, control of welding process and welding parameter design

[0085] ⑤ Rationality of processing technology design: benchmark control, coaxiality control, and processing deformation control

[0086] ⑥ External pressure stability and airtightness testing methods: As well as instability control methods, reasonable pressurization control should be carried out after external pressure stability calculation, including pressure test detection and control. Gradual pressurization measures and pressure holding time should be taken; including internal inflation for airtightness testing measures.

[0087] The three-stage division control and implementation requirements are as follows:

[0088] In this embodiment, the advantages of titanium alloy and its application in aerospace are utilized to overcome the difficulties in precision casting and processing of thin-walled titanium alloy, and the comprehensive advantages of laser welding, precision casting and mechanical processing are fully utilized.

[0089] The following three stages are described:

[0090] Phase I: Overall design of shell segmentation and precision casting, including product features, overall process design, casting process design, casting system design and simulation, mold design and manufacturing, processing and assembly, graphite mold precision casting, hot isostatic pressing and post-processing;

[0091] The second stage: precision machining and expansion heat treatment of the front and rear sections, precision machining, expansion heat treatment, and 3D scanning airtightness test;

[0092] The third stage: laser welding and precision machining of the front and rear sections of the shell, laser welding, precision machining, and airtightness testing.

[0093] See also Figure 4 , overall process design and manufacturing process flow chart.

[0094] 1) Product structural features and process design innovation: The structural features of the titanium alloy thin shell are as follows:

[0095] 2) Precision casting technology for large, ultra-long titanium alloy special-shaped thin shells, with three casting process options;

[0096] 3) Turn-milling composite machining of large, ultra-long titanium alloy special-shaped thin shells, design of datums and control of opening deformation;

[0097] 4) Laser welding technology for large, ultra-long titanium alloy special-shaped thin shells, laser welding technology and parameter control, and welding process flow;

[0098] 5) Comprehensive testing technology for large thin-walled titanium alloy special-shaped shells, including external pressure testing and internal pressure airtightness testing.

[0099] The characteristics of a large ultra-long special-shaped thin shell structure disclosed in this patent are as follows: The large ultra-long titanium alloy special-shaped thin shell product is a long cylindrical structure. The outer dimensions of the product part are 2220.0×580.0×550.0mm, the main wall thickness is 2.5mm, and the theoretical weight of the part is 43.2Kg. The schematic diagram and structural dimensions of the part are as follows: Figure 1 and Figure 2 As shown. The main structure of the thin-walled, irregularly shaped shell has a 2.5mm thick skin, and the total length of the thin-walled skin area is 2180mm. The outer diameter of the small section ranges from ￠240mm to ￠309mm, while the diameter of the large section ranges from ￠309mm to ￠392mm. The transition zone from the small section to the large section is a conical section that gradually transitions from ￠240mm to ￠309mm. The total length of the thin-walled shell is 2220mm. According to process requirements, it is divided into two parts (details will be described in subsequent examples): a small section with a length of 1119.6mm and a large section with a length of 110.4mm. The small section consists of three parts: a large flange with a diameter of ￠580mm and a thickness of 20mm at the front end, a cylindrical section with a diameter of ￠240mm and a length of 899.6.mm, and a conical section with a diameter of ￠240mm to ￠309mm and a length of 200mm; the large section is composed of three parts at the rear end: a cylindrical section with a diameter of ￠309mm and a length of 740mm, a conical section with a diameter of ￠309mm to ￠392mm and a length of 200mm, a cylindrical section with a diameter of ￠392mm and a length of 140mm, and a small flange with a diameter of ￠550mm and a thickness of 20mm at the rear end.

[0100] The external structure of the thin-walled titanium alloy shell required to be disclosed in the embodiment: As can be seen from the figure, the flanges at both ends of the shell are thin-walled structures, and are distributed with many processing features including lightening grooves, two sealing grooves on the outside and the end face, and stepped holes for mounting nozzles on the inside of the shell flange; the central barrel area is relatively complex, including a convex semicircular bulge along the shell busbar that passes through the front and rear end faces of the shell, and the small section of the shell has six annular reinforcement ribs; the wall thickness of the shell skin is 2.5mm±0.5mm, which is a large and extra-long thin-walled shell.

[0101] The internal structure of the thin-walled titanium alloy cylinder shell: From the internal cross-sectional view of the shell, it can be seen that there are 12 reinforcing ribs distributed along the axial direction of the internal semi-circular bulge. The ribs are mainly used to install the circuit and strengthen the rigidity of the shell. After the 12 ribs are strengthened according to theoretical calculation and analysis, the overall rigidity of the shell can be increased by about 25%. It should be noted that the original design uses continuous and uninterrupted integral ribs, but due to the consideration of casting process, sand cannot be removed. At the same time, there are unpredictable risks in process factors such as quality defects and inspection during the casting filling process. Therefore, it is divided into 12 discontinuous reinforcing ribs. The front and rear baffles of the large and small sections of the inner cylinder are cast as a whole. The 4 baffles in the middle of the small section and the 4 baffles in the middle of the large section are connected by welding and then the inner surface is finely machined to reduce the difficulty of casting and processing. The integration of this design and process is not easy to imagine. In addition, during the machining process, two new process flanges are added to the welding edges of the large and small sections as the processing coordination benchmarks of the large and small sections. The newly added process flanges are designed as open structures rather than closed circular structures. The use of open structures is beneficial for effectively achieving the function of clamping and aligning the process benchmark, and at the same time, it can avoid large deformation of the cylinder body caused by the sharp attenuation of stiffness when the closed circular flange is finally removed.

[0102] Considering the difficulty of sand removal due to casting process and to increase rigidity by controlling deformation during processing, the front and rear baffles of the large and small sections of the inner tube are cast as a whole. The four baffles in the middle of the small section and the four baffles in the middle of the large section are connected by welding, and then the inner surface is fine-machined. Both flanges are designed as open structures rather than closed ring structures. The purpose is to facilitate clamping and release processing stress during processing. This structure can effectively avoid the deformation of the inner tube with a special cross-section due to structural damage and rapid loss of rigidity when the ring is removed after fine processing. If the weld seam does not fit properly after fine processing, hot calibration can be adopted. Vacuum heat treatment at a temperature of 550-750° is used for expansion. The expansion tooling is made of 45# steel or 20Cr martensitic stainless steel, and the tooling interference is controlled between ￠0.2-￠0.5mm.

[0103] The process design for the segmented inner barrel is based on the following considerations: Due to the large size of the product, the casting and machining are particularly challenging. The casting process also requires comprehensive consideration of the special areas and large, spatially shaped curved surfaces; the control of internal quality and mechanical properties; the control of defects such as porosity, sand holes, cracks, and pinholes; the uniformity of the large casting wall thickness; the control of deformation during heat treatment and hot isostatic pressing; the control of deformation during rough and fine machining; the product's geometric tolerances, such as parallelism, flatness, and coaxiality; and the product assembly dimensional tolerances, including overall length, external diameter dimensions, seal groove depth and width, and oil nozzle machining control. The casting of this large, ultra-long titanium alloy, special-shaped thin shell can generally be carried out using both integral and split casting methods. Among them, the use of integral casting has advantages such as relatively simple production management, small number of tooling and low cost, but it has disadvantages such as high technical risk, difficulty in one-time investment, low and uncontrollable product qualification rate, etc. In particular, in terms of the technical quality of the integral casting process, there are almost insurmountable problems such as large casting molds and high assembly precision requirements, complex casting systems with high failure rates, short casting filling time, uncontrollable casting defects, and difficulty in controlling casting deformation. The main reason is that the product size is large and titanium alloy is particularly active at high temperatures and reacts with almost all elements in the air, so vacuum casting is required to achieve it. Moreover, since the product is an ultra-long thin-walled part, whether horizontal casting or vertical centrifugal casting is used, the existing casting furnace equipment has a large gap in capacity. In addition, the size of the existing related hot isostatic pressing furnaces in China does not meet the requirements, and there are problems such as large deformation of the ultra-long thin-walled parts during the hot isostatic pressing process.

[0104] Therefore, in the embodiments of the present invention, the preferred method of split casting + precision machining + laser welding can effectively improve the casting quality of the casting, control the deformation of the casting, and effectively perform hot isostatic pressing (HIP) on the casting to eliminate casting defects. The specific split method is described in the requirements of the aforementioned embodiments. This method is beneficial for titanium alloy precision casting mold filling, as well as for graphite sand removal after casting, hot isostatic pressing and heat treatment after casting, clamping alignment and wall thickness measurement during machining, argon arc welding of the partition and laser welding of two sections for butt welding, and 3D imaging and digital scanning of the internal and external surfaces after casting and during machining, among other advantages. If an integrated method is used, the casting filling cannot be ensured to be completed smoothly, which will inevitably lead to numerous defects and hot isostatic pressing and heat treatment cannot be achieved. During machining, the internal surface processing requires a large horizontal lathe with a center frame of more than 5 meters or a horizontal milling and turning complex machining center / large gantry five-axis machining center. The internal partition casting cannot be effectively cleaned and normal welding operations cannot be achieved. The 3D digital camera scanning cannot achieve 3D inspection of the entire area due to the size specifications of the scanning head and the equipment travel limit. Therefore, this embodiment stipulates that the two sections are cast and then distributed for hot isostatic pressing heat treatment process, and then fluorescence detection and three-dimensional scanning detection are carried out; then the two sections are subjected to turning and milling composite rough processing and semi-finishing after three-dimensional scanning reference conversion and coordination; then the two sections are welded to the partition and then the two sections are laser welded and connected, and finally the flanges at both ends are finished and the coaxiality and other tests are carried out; the final process arranges external pressure stability and internal pressure airtightness testing.

[0105] Overall analysis of difficulties:

[0106] ① Uniformity of very thin wall thickness: Since the product is a thin-walled, large, ultra-long, weakly rigid titanium alloy part, and due to limitations in domestic equipment capabilities, it is currently impossible to implement the integral casting and hot isostatic pressing heat treatment process, so a solution of split casting followed by welding is adopted. The grade requirement for the casting is GJB2896A-2007 Class I B casting, which places very high demands on the various properties and defect control of the casting. The split-casting design alleviated the pressure caused by insufficient domestic equipment capabilities to a certain extent. However, due to the special requirements of the product structure, the front and rear sections of the split body still faced great difficulties and technical risks. Because the shell wall thickness is very thin, only 2.5mm, the length is very long, reaching 1200mm, and the diameter is very large, reaching nearly ￠400mm, the length-to-thickness ratio of the integral casting is 480:1, the width-to-thickness ratio is 600:1, and the area-to-thickness ratio is close to 300,000:1. Due to the special casting process of titanium alloy materials, even if the thickness is doubled to 5mm, the casting difficulty is very great. Therefore, it is very important to first reasonably decompose the split-body solution, considering the cleaning of the casting mold graphite sand and the convenience of subsequent processing and welding operations (the split surface in the figure is based on a solution that allows for easy processing, efficient welding and sand cleaning). However, the design of the casting system is the most core link. The quality of the entire casting process and the successful casting are completely dependent on the design of the casting system. The design of the casting system must take into account the thin-walled nature of the casting. First, mold filling reliability must be considered. Second, given the large diameter and long length of the casting shell, the mold's high-temperature rigidity and heat absorption and heat dissipation during casting and solidification must be carefully considered to ensure the mold's heat resistance and controllable shrinkage and deformation during cooling. Third, due to the thin-walled, irregularly shaped structure and relatively complex internal features of the casting, the mold casting system must be refined to ensure that all parts fully meet the performance requirements of Class I, Class B castings while avoiding related quality defects such as shrinkage, shrinkage cavities, and absolutely unacceptable cracks. Fourth, consideration must be given to whether the high-temperature and high-pressure heat treatment during hot isostatic pressing (HIP) will cause significant deformation of the casting. Finally, in conjunction with subsequent machining and welding processes, appropriate process bosses or ribs, casting datums, and casting processing and inspection benchmarks must be set to facilitate smooth machining, reasonable machining allowances, and controllable processing costs and cycles. This also facilitates controllable deformation and ease of operation during subsequent welding.

[0107] ② Rationality of machining process design: Since castings require precision machining, comprehensive consideration should be given to the casting blank design, blank machining datum design and alignment, product machining process guarantee measures for geometric and dimensional tolerances, deformation control measures during machining, pre- and post-machining datum coordination and inspection control, product fixture design and manufacture, machining process division and machine tool selection, and the rational formulation of titanium alloy machining tools and cutting parameters, etc. Among them, coordination with the casting blank state is the first to be fully considered, including the setting of casting machining datums, the design of machining allowances, the formulation of inspection methods, the division of machining processes, the clamping and alignment of machining machines and fixtures, and the compilation of CNC machining plans. There are 4 schemes for the design of machining allowance, including Scheme I that leaves no allowance for the inner and outer forms of the shell, Scheme II that leaves allowance for both the inner and outer forms, Scheme III that leaves allowance for the inner form but no allowance for the outer form, and Scheme IV that leaves allowance for the outer form but no allowance for the inner form. Among the four schemes, Scheme I that leaves no allowance for the inner and outer forms is the optimal goal, but the casting process cannot be achieved and cannot be carried out. Scheme II that leaves allowance for both the inner and outer forms brings many disadvantages such as high processing cost, long cycle, and poor quality and reliability; Scheme III that leaves allowance for the inner form but no allowance for the outer form and Scheme IV that leaves allowance for the outer form but no allowance for the inner form each have their own advantages and disadvantages. The advantage of Scheme III that leaves allowance for the inner form but no allowance for the outer form is that it is sufficient The bulge is convex on the outside and the inner shape is a standard cylindrical and conical surface of a rotating body, which can be efficiently cut by CNC turning. If the solution IV is adopted, where an allowance is left for the outer shape but not for the inner shape, the outer shape surface needs to be completed by milling due to the bulge being convex, which has many disadvantages such as long processing cycle, cost and poor quality. Therefore, the allowance design of this solution adopts the solution III where an allowance is left for the inner shape but not for the outer shape (it is worth noting that if the bulge is concave towards the inner shape, the solution IV method where an allowance is left for the outer shape but not for the inner shape is adopted. The principle is the same, and efficient turning of the outer shape is used to achieve efficient processing of the product. This embodiment also includes this method). The added processing technology datum adopts the end face circular ring flange structure, which has been described in detail above.

[0108] ③ Sealing and coordination of welding: Welding needs to coordinate the interface status with mechanical processing, including the realization of the welding interface form and the welding clamping and assembly accuracy requirements. This embodiment stipulates that laser welding requires the gap of the butt joint to be no more than 0.15mm, and the internal control is required to be no more than 0.10mm. The flatness of the mechanically processed butt end face is controlled at 0.05mm, and the tensile strength of the welding performance is required to be no less than 85% of the low-pressure base material. Due to the butt welding method, when the welding gap is greater than 0.25mm, the weld connection strength decreases by about 20%. When the butt welding gap exceeds 0.3mm, the performance drops sharply by more than 30%. When the welding gap reaches 0.2mm, the weld tensile strength performance reaches 90% of the parent material. When the gap is less than 0.15mm, the weld tensile strength reaches 95%, which is basically close to the performance of the parent material. Therefore, the weld butt gap is required to be no more than 0.15mm, and the process internal control requirement is less than 0.10mm, so that the flatness of the two ends of the machining needs to be less than 0.05mm, so as to ensure the tensile strength mechanical properties and airtightness of the laser welding weld caused by internal stress during actual use of the product. Secondly, this embodiment stipulates that the total depth of the stop at the welding point is 5mm, of which laser welding butt welding must be used for depths above 4mm to ensure the mechanical properties of the welding. The groove between 4.5mm and 5mm is required to be chamfered between 0.5-1mm and 0.75mm, and then 1mm laser welding and filler wire welding are used. The purpose is to prevent the airtightness precautions taken after the welding gap is uneven due to machining flatness, that is, after assembly. The final sealing is performed by 1mm laser filler wire welding for secondary reinforcement; this embodiment stipulates that the material used for laser filler wire welding can preferably be recommended to use TC4 / TA15 brand titanium alloy laser welding wire. When this type of titanium alloy laser welding wire is not available, 0Cr18Ni9Ti (316) welding wire can be used as an alternative implementation scheme of the process. After actual verification, it can also achieve the target requirement of welding airtightness.Due to the low thermal conductivity of titanium alloy, the high temperature generated during welding is dissipated slowly. At the same time, due to the limitation of the size of the vacuum annealing furnace equipment of this shell, this embodiment stipulates that annealing treatment is not required after laser welding. However, corresponding heat dissipation measures and anti-oxidation measures need to be taken during the welding process. Specifically, a copper plate with a thickness of 60mm-100mm and a diameter of ￠304±0.05mm and a guide device is provided on the inner surface and clamped and supported inside the welding stop in the form of an overfit for the purpose of heat dissipation. At the same time, the diameter of the middle opening of the copper plate is ￠1 The 00mm through-hole is used to store argon between the two sections of the shell; before welding, sealing measures are taken at both ends of the shell, and argon is filled with sufficient concentration according to the volume of the inner cavity. Before filling with argon, vacuum measures are taken first, and the vacuum degree must reach below 0.01Mpa. In addition, during the welding process, argon is used for external protection to prevent the titanium alloy from reacting with nitrogen in the air during welding; the welding process parameters are as follows: when the effective welding thickness is 4.5mm, the laser welding process parameters are: P=3.4-3.8KW; V=1.7-1.9m / min; ΔF=+3~+4mm.

[0109] ④ Deformation control and data detection at each stage: In addition to the three-dimensional scanning detection data required in the embodiment manual for the five stages, fluorescent flaw detection is also indispensable. At the same time, the room temperature mechanical properties and high temperature mechanical properties of titanium alloys must be carried out in accordance with relevant standards. At the same time, the metallographic structure of titanium alloys at room temperature and corresponding high temperature states must be detected, so as to establish a mapping relationship between the macroscopic mechanical properties of titanium alloys at room temperature and high temperature states and the microscopic structure metallographic structure under the corresponding temperature conditions.

[0110] ⑤ Application of simulation methods: This patent discloses four casting system schemes for the same type of products, including three horizontal static casting systems and one vertical centrifugal casting system, four of each, for a total of eight casting system schemes. The horizontal static casting and vertical centrifugal casting systems were simulated respectively, providing better optimization guidance for the macro optimization and micro refinement of the casting system of this type of products.

[0111] ⑥ External pressure stability and airtightness testing methods: As for instability control methods, reasonable pressurization control should be carried out after external pressure stability calculation, including pressure test detection and control. Gradual pressurization measures and pressure holding time control measures are adopted. Each inflation is 10% of the pressure, and after stabilization for 5 minutes, inflation is carried out in ten times and two air replenishment measures. After each air replenishment, the pressure is stabilized for 30 minutes and then the air replenishment is continued. If there is no pressure drop after the first air replenishment, the second air replenishment is not carried out. A maximum of three air replenishments shall not be carried out. It should be noted that because the gas compression temperature will increase during the gas inflation process, there will be a certain pressure drop as the gas temperature gradually drops after the pressure is stabilized. Therefore, it is normal to take necessary gas replenishment measures. It should be further explained that due to the difference in seasonal temperature and day and night temperature, the pressure of gas molecules will fluctuate and change at different speeds with temperature. Therefore, the ambient temperature during inflation and the time and temperature after pressure maintenance need to be recorded and calculated in detail. Finally, in areas with different altitudes, inflation and pressure maintenance need to be appropriately adjusted according to the local altitude and temperature differences. The most critical thing is that if inflation is carried out in winter and the pressure is maintained until the temperature rises in summer, it is necessary to pay special attention to the temperature difference. The pressure of the internal gas will change greatly and the pressure needs to be carefully tested to avoid safety accidents.

[0112] The casting of large, ultra-long titanium alloy special-shaped thin shell products can generally be carried out using both integral and split casting methods. However, integral casting has disadvantages such as difficulty, high cost, and long cycle times. In terms of process quality, integral casting suffers from short mold filling time, uncontrollable casting defects, and difficulty controlling casting deformation. The existing hot isostatic pressing furnaces in China do not meet the requirements and suffer from large deformation during the hot isostatic pressing process. Using split casting plus laser welding can effectively improve casting quality, control casting deformation, and effectively eliminate casting defects through hot isostatic pressing.

[0113] The split casting scheme adopts the method of casting in two sections along the length direction, such as Figure 3 As shown; then it is machined and welded, leaving a small bulge on the top. After the two sections are welded, the remaining small bulge is welded. The front and rear sections can be directly butt-welded using laser welding. Allowances are left at both ends, and after welding, they are machined and matched to the length of the thin shell assembly position. The maximum flange diameter of the front section of the inner cylinder casting is φ560, the length is 1080mm, and the wall thickness is 2.5mm. It is a long cylindrical thin-walled casting. The product structure is as follows Figure 3 The maximum flange diameter of the rear section of the cabin tube casting is φ590, the length is 1180mm, the wall thickness is 2.5mm, and it is a long cylindrical thin-walled casting. The product structure is as follows Figure 4 The front and rear sections of the inner barrel are difficult to cast.

[0114] Based on the requirements for the part's use, the following process was adopted: only the inner surface (excluding the through-slot), flange mounting surface, and holes were machined for the front and rear sections of the inner barrel, leaving the outer shape and flange back unmachined. After the casting passed the test, the inner cavity and butt joints were machined, and the holes and mounting surfaces were left open for welding and then finished to ensure dimensional accuracy. Analysis of the part's structure revealed that the top through-slot structure was not conducive to mold cleaning, X-ray inspection, or penetrant testing, and therefore could not guarantee the quality of the through-slot casting. To address this issue, the organization developed three through-slot molding solutions:

[0115] 1. Inner partition welding

[0116] See also Figure 6 , remove the 2.5mm partition in the through groove, and after the inner cavity is processed, spot weld the partition 19 to the inner wall of the inner cylinder by manual argon arc welding. The partition is 100mm wide and is placed at intervals of 100mm.

[0117] After the partitions are removed, the interior of the casting is completely exposed, facilitating mold cleaning, X-ray inspection, and penetrant testing, ensuring the overall quality of the casting. Disadvantages: The 2.5mm wall thickness at the top of the through-channel cannot be molded and needs to be thickened to 4.0mm. The narrow space in the inner cylinder only allows for manual argon arc welding, which can only be spot welded locally, not continuously. The welding precision and quality are low, and the through-channel partitions can only be used to isolate cables, but cannot meet the requirements of supporting the structure and bearing force.

[0118] 3.1 Casting process of thin-walled inner tube

[0119] See also Figure 7 , casting process flow of the front and rear sections of thin-walled special-shaped inner cylinder.

[0120] 3.2 Thin-walled inner tube casting process design

[0121] 1) Process design

[0122] ① Casting design: According to the results of part structure analysis, the casting structure design is carried out, the allowance is placed in the processing part, the casting process ring is cast, etc. The casting structure diagram is as follows Figure 13 and Figure 14 As shown, the green surface is the machined surface, and a 5-8mm margin is used to facilitate subsequent adjustment of the center reference. Based on the structural characteristics, quantity, and development schedule of the casting, the CNC machine plus graphite casting process was selected.

[0123] ② Casting system design 1

[0124] See also Figure 8 and Figure 9Whether the casting is formed or not is closely related to the design of the casting gating system. The design of the gating system should follow the following principles: first, the casting should be completely filled; second, the runner should be opened in the thick and large parts of the casting; third, an open gating system should be adopted to ensure the rapid filling of the casting. Based on the above principles and the structural characteristics of the casting, when pouring the castings in the front and rear sections of the inner tube, ring casting is adopted, and 6 φ30 gates are evenly distributed on each ring. Figure 15 and Figure 16 The ingate is opened in the thick part of the casting, which can be used for filling the mold and also for shrinkage-feeding the thick part of the casting.

[0125] ③ Casting system design 2

[0126] See also Figure 10 and Figure 11 According to the structural characteristics of the casting and the requirements of the product drawings and technical agreements, a horizontal centrifugal pouring process is adopted, with one front section and one rear section cast in each furnace. A relatively thick main runner is set, and six cross runners are connected to the casting to feed the shrinkage of the casting under the action of centrifugal force.

[0127] ④ Determination of shrinkage: Based on past experience and product characteristics, a shrinkage of 0.8% was selected for the casting. To maintain the critical dimensions and shape of the casting, a margin was added to the non-machined surface of the casting, which was removed before delivery.

[0128] ⑤Analysis of process difficulties: The outer surface is not processed, there are non-processed surfaces inside, the wall thickness of the final product is 2.5mm, the cylinder length is long, and the internal quality and surface quality requirements are high.

[0129] 2) Graphite mold design: Based on the casting system plan and the structural characteristics of the casting, the graphite model is designed according to the following principles: ① Reduce the block size of the graphite mold; ② Use screws to string the long graphite core to fix it; ③ Use positioning stoppers between graphite molds to prevent group deviation; ④ Use gaskets between the outer shape and the core to ensure uniform wall thickness of the casting;

[0130] The inner cylinder is made of titanium alloy casting TC4, and its structure is a long thin-walled part with a total length of 2240mm. The forming plan of the inner cylinder is to cast and process it in two sections in the length direction and then weld it. The length of the front section of the inner cylinder is 1070mm, and the length of the rear section of the inner cylinder is 1173mm. The front and rear sections of the inner cylinder do not include partitions. The front and rear sections are laser welded with stoppers, leaving allowances on both end faces, and are guaranteed by machining after welding.

[0131] The main machining content of the front and rear sections of the inner tube is the inner hole, the outer circle of the flange, the groove and hole, and the welding groove. Based on their processing characteristics, the main processing process is: material datum alignment --- machining the top groove --- top welding --- rough turning and rough milling of the inner cavity and flange surface --- stress relief annealing --- finish turning the inner cavity and finish milling the butt joint --- front and rear tube butt welding --- finish turning the flange sealing surface.

[0132] After segmented casting and machining, baffles (or partitions) are intermittently welded between the bulge and the baffle body within each segment before being assembled into a complete inner tube. The weld groove is laser welded using a fork-shaped butt joint. Circumferential welding during segmented assembly (including the bulge arc and the barrel arc) can be achieved through segmented robot teaching programming to achieve closed welding. The product is divided into two sections, making it difficult to machine the matching dimensions during assembly. During laser welding, the matching gap and the fitting gap (both required to be less than 0.1mm, with a local allowance of 0.15mm) are difficult to guarantee. Measures are planned to optimize welding process specifications and groove types to expand the adaptability of the laser welding process. Prior to assembly welding, the relevant dimensional tolerances of each component will be strictly controlled to reduce welding quality risks.

[0133] 3.4 Solutions to process difficulties

[0134] The inner cylinder casting is a special-shaped structure with a through-slot within a long cylinder. The front section of the inner cylinder is 1080mm long, with a flange diameter of φ560mm and a minimum outer diameter of φ309±0.5mm. The outer surface is unmachined, the inner surface of the through-slot is also unmachined, and the wall thickness at the through-slot is 2.5mm. The rear section of the inner cylinder is 1180mm long, with a flange diameter of φ590mm and a minimum outer diameter of φ240±0.5mm. The outer surface contains annular ribs and is unmachined, the inner surface of the through-slot is also unmachined, and the wall thickness at the through-slot is 2.5mm. The large, thin-walled, special-shaped structure of the inner cylinder makes it prone to deformation during casting. Furthermore, the outer surface is not machined, and the inner surface is turned to ensure uniform wall thickness. Therefore, sufficient allowances are required on the outer diameter and end faces of the flanges at both ends to facilitate adjustment of the coaxiality of the outer diameters of the front and rear sections of the inner cylinder during machining and after welding. Laser welding requires high precision for butt joints. At the same time, it is a special-shaped structure butt joint, so it is necessary to improve the overall contour of the butt weld to ensure the normal progress of laser welding and the airtightness requirements after welding.

[0135] 1. Analysis of casting process difficulties and solutions

[0136] 1) Mold Filling: The SFC inner barrel's front and rear sections are manufactured using a graphite casting process. Due to graphite's rapid cooling and thermal conductivity, the 5.5mm wall thickness of the casting presents some challenges in casting. Solutions: ① Increase the casting's process allowance to appropriately thicken the wall and improve mold filling; ② Increase the pouring height and pressure; ③ Preheat the mold before pouring.

[0137] 2) Deformation: The front and rear sections of the SFC inner barrel castings were not machined, resulting in a finished product thickness of only 2.5mm. This deformation made the casting unmachinable, and the thin walls resulted in poor overall rigidity. Solution: Reduce mold segmentation during parting to minimize assembly errors. Secure the casting with a fastening fixture before pouring. Extend the mold cooling time after pouring, and remove the mold fastening fixture once the mold has completely cooled. Anneal the deformed areas with a tooling annealing tool.

[0138] 2 Difficulties and solutions of machining process

[0139] 1) High dimensional accuracy requirements: The coaxiality of the front and rear flange sealing surfaces is 0.05, and the total length of the part is 2240, which is difficult to ensure. The dimensional accuracy of the countersunk hole on the back of the flange is ±0.05, which is difficult to directly machine and ensure. Solution: After welding the front and rear flanges, the entire body is fine-machined to ensure dimensional accuracy requirements; the welding process is adjusted to reduce welding deformation; a special reverse-bore tool is customized for the flange countersunk hole, and local dimensional discharge machining is performed;

[0140] 2) Part deformation during machining: The wall thickness of the finished part is 2.5mm, which is easy to deform during machining; Solution: Develop a reasonable machining process and make special tooling;

[0141] 3) High dimensional accuracy requirements for welding interfaces: The front and rear sections are connected, and the welding assembly gap accuracy requirements are high; Solution: The front and rear sections are matched and processed, and multiple measurements and trial matching are performed;

[0142] 3 Difficulties in laser welding of front and rear sections and partitions

[0143] Welding deformation and solutions: Develop specialized tooling to improve positioning accuracy; develop a reasonable welding process to reduce welding deformation. During product development, strictly follow special process validation procedures to monitor internal and external weld quality, as well as process factors including equipment, materials, personnel, environment, and process parameters. Pre-weld test pieces are used to confirm welding parameters, butt-weld the front and rear sections, check the gap before welding, perform tack welding, laser welding, post-weld inspection, and perform airtightness testing.

[0144] Deformation control measures:

[0145] Casting deformation control measures, machining deformation control measures, welding deformation control measures, casting and machining accuracy assurance measures.

[0146] Expansion deformation control measures: Through the expansion process measures, the front and rear sections of the inner tube are heat treated and expanded. The specific principle is to take advantage of the small linear expansion coefficient and elastic modulus of titanium alloy, and the small thermal stress during the heating expansion process, so that the purpose of plastic deformation can be achieved before the complete vacuum annealing temperature. The tooling is made of 20Cr martensitic stainless steel or 45# steel or 0Cr18Ni9Ti (316) austenitic stainless steel for expansion. Considering the high temperature strength and temperature resistance of the tooling itself and the influence on the surface finish of titanium alloy during the expansion process, 0Cr18Ni9Ti (316) austenitic stainless steel or 20Cr martensitic stainless steel is commonly used as the tooling. This patent method uses two kinds of stainless steel as expansion tooling for expansion to improve the contour accuracy of the butt joint assembly before welding of special-shaped sections. The single-side expansion allowance is obtained by calculation and analysis of the incomplete annealing temperature of 500℃-750℃. The inner diameter of the shell at the joint is ￠304mm / the outer diameter is ￠309mm. Incomplete annealing is performed at a temperature of 550℃ for expansion. Since TC4 titanium alloy faces the risk of a sharp decline in performance above 550℃, incomplete isothermal annealing is performed at a temperature not exceeding 550℃.

[0147] The expansion of the titanium alloy shell and the corresponding tooling in the diameter direction and the high temperature thermal stress under constraint conditions are calculated respectively. The linear expansion coefficient of titanium alloy is a=8.6X10-6mm / m.℃, and the elastic modulus E is 110GPa (corresponding to the elastic modulus of 80GPa at 550℃). The linear expansion coefficient of the corresponding 20Cr13 martensitic stainless steel is a=12.5X10-6mm / m.℃, and the elastic modulus E is 220GPa (corresponding to the elastic modulus of 160GPa at 550℃). The diameter expansion of TC4 titanium alloy is ΔD=a*D*ΔT=8.6*10 -6*304*500mm=1.3072mm, that is, the expansion of the TC4 titanium alloy shell in the diameter direction is 1.3072mm, and in the radius direction is 0.6536mm; the corresponding diameter expansion of 20Cr13 martensitic stainless steel is ΔD=a*D*ΔT=12.5*10-6*304*500=1.9mm, and in the radius direction is 0.95mm; therefore, the diameter interference under this temperature environment is 0.5928mm, and the radius interference is 0.2964mm, which meets the original process design requirement of 0.2-0.5mm single-side interference. During the expansion process, the thermal stress of the titanium alloy and the thermal stress of the tooling are calculated to determine whether its safety is reliable. The ultimate thermal stress of the TC4 titanium alloy itself is calculated to be σ= a*E*ΔT=8.6*10-6*80Gpa*500=8.6*40Mpa=344Mpa when the TC4 titanium alloy is fully constrained so that it does not expand. Even so, it is less than the tensile strength of the titanium alloy under the temperature environment conditions. The required constraint strength of 20Cr13 martensitic stainless steel if its thermal expansion under a temperature environment of 500°C is calculated to be σ= a*E*ΔT=12.5*10-6*160Gpa*500=12.5*80Mpa=1000Mpa. Comparing the two groups, it can be seen that under the environmental conditions of 500°C, when 20Cr martensitic stainless steel is used for expansion, the titanium alloy shell cannot constrain the high-temperature expansion of the tooling, thereby achieving the goal of effectively supporting the expansion circle and improving the contour of the weld joint.

[0148] Under the limiting conditions of the above formula, both parties are fully constrained. Actual stress is balanced based on the true interference fit. During expansion, the 20Cr13 martensitic stainless steel tooling is constrained by the titanium alloy and prevents free expansion. The titanium alloy's own expansion is also constrained by its own material strength and the support of the tooling, thus achieving the goal of rounding and correcting the shape. By inversely calculating the interference fit, the high-temperature linear expansion coordination coefficients for the two materials, TC4 and 20Cr13, are calculated to be 3.9*10-6, respectively. Based on these linear expansion coordination coefficients, the thermal stress of the TC4 titanium alloy shell after heating and tooling support is calculated to be σ = a*E*ΔT = 3.9*10-6*80Gpa*500 = 156Mpa, while the compressive thermal stress of the 20Cr13 tooling is σ = 3.9*10-6*160Gpa*500 = 312Mpa. Further comparison of the high-temperature performance of the two materials shows that the expansion method is scientific, reasonable, and effective. Since the ratio of the tensile strength to the yield strength of titanium alloy, that is, the yield strength ratio coefficient, is very close, basically reaching 760 / 840=0.905, it is very difficult to plastically shape titanium alloy at room temperature, and it often needs to be achieved through large deformation. However, this method is too risky. If the applied load is too small to reach the critical deformation strain requirement, the shaping will fail. If the applied load is too large and exceeds the critical strain, it may cause damage and cannot be recovered. Therefore, it is reasonable to call titanium alloy a shape memory alloy. It is just that the shape memory alloy at room temperature has a good effect of thermal expansion and shaping at high temperature, and it has a high safety factor and is safe and reliable.

[0149] This embodiment stipulates the following requirements for the process design of the size allowance of the casting blank: the design criteria for the blank allowance need to comprehensively consider the effective wall thickness of the titanium alloy casting vacuum casting filling, the angular error of the casting after cooling and deformation, the coaxiality error of the large and small ends, and other comprehensive metallurgical tolerance distribution and calculation analysis. This embodiment is based on the product deformation angle error along the axis not exceeding 0.5°, and the minimum casting thickness of the wall thickness is calculated and arranged according to the large area of titanium alloy to achieve 5mm smooth filling, and finally the casting processing allowance of the two sections of the shell is determined. The specific embodiment requirements are as follows: 1) Considering the processability and processing processability of the casting, this embodiment stipulates that the outer surface of the shell is used as the reference, and the outer surface of the shell barrel section has no allowance and is guaranteed by graphite precision casting; since the inner surface of the bulge is very difficult to process by traditional machining and basically cannot be processed, the outer surface of the bulge area is also relatively complex, and the wall thickness of the bulge area is 5mm, so there is no allowance on the outer surface in the bulge area, which is guaranteed by the casting system. 2) A 5mm margin is left on the front end face of the flange of the small section of the inner cylinder, a 3mm margin is left on the inner end face of the flange, a 3mm margin is left on one side of the flange end face groove, a 3mm margin is left on the bottom face, and a 16mm margin is left on the outer diameter; the embodiment stipulates that a 5mm margin is left on one side of the inner surface of the cylinder shell, and no margin is left on the outer surface; a 100mm long partition is cast near the outlet position at each end of the internal groove, and an open process flange with a diameter of Φ440 and a width of 20 is cast at the position where it connects with the large section of the inner cylinder. The rest is cast in place according to the drawing. 3) A 5mm margin is left on the rear end face of the flange of the large inner tube section, a 3mm margin on the inner end face of the flange, a 3mm margin on one side of the flange end face groove, a 3mm margin on the bottom face, a 16mm margin on the outer diameter, and a 5mm margin on one side of the inner surface; 4) A connecting baffle with a length of 100mm and a thickness of 5mm is cast near the outlet of each end of the internal groove of the large and small front and rear sections of the shell, as required by the design. The remaining six baffles are located in the central area of the front and rear sections, three each, and are secured by welding after machining the baffles. They include three rectangular baffles and three I-shaped baffles; 5) To facilitate the coordinated adjustment of the machining base, a process flange with a diameter of Φ430mm and a thickness of 18mm and a petal-shaped opening groove is cast at each of the front and rear section connections. The rest are cast in place according to the drawing.

[0150] See also Figure 14 and Figure 15 , the specific castings specified in this embodiment, this embodiment stipulates that the casting dimensions shall be manufactured and all dimensions shall be inspected in accordance with the casting drawings, the casting blank tolerance shall not be greater than CT8 level as specified in GB / T6414-1999 "Casting Dimension Tolerances", and no fillet R3 shall be added; the shell casting weight tolerance shall comply with the MT7 level requirements in GB / T11351-89 (upper and lower deviations are the same) ±4%; after processing is completed, an air tightness test shall be carried out, and an air source inflation test shall be adopted. No air leakage shall be maintained for 60±1min at 0.35MPa±0.002Mpa, and there shall be no pressure drop on the pressure gauge.

[0151] The repair and correction technical requirements specified in this embodiment are as follows: 1) Any defects may be removed by machining or manual methods, but the tolerance and surface quality of the tank must meet the requirements. 2) Except for areas within 40 mm of the tank end frame joints (such as joint bolt holes and joint grooves), all brackets, instrument mounting bosses, ribs at the junction of the skin and the port frame, and other areas where repair welding is not permitted, repair welding is permitted in other areas that are convenient for repair welding, polishing, and inspection. 3) Repair welding of castings shall be performed using tungsten inert gas welding or other methods agreed upon by both parties. 4) The area and number of repair welds at a single tank section shall comply with the requirements of Table 5. The margins of the repair weld area (including the reverse repair weld area) shall not be less than the sum of the two adjacent repair weld areas. 5) The number of repair welds at the same tank section shall not exceed two before heat treatment and one after heat treatment. All tank sections that have been repair welded must be heat treated according to the original heat treatment specifications after repair welding. Repair welding is not permitted after the tank section has been mechanically processed. 6) The repair weld area must be free of defects such as cracks, incomplete weld penetration, and delamination. Two pores or slag inclusions with a diameter no greater than 2mm and a depth no greater than one-third of the wall thickness are permitted within the same repair weld area, with a margin of at least 10mm. 7) Hot shaping of the tank section is permitted. Fluorescence inspection must be performed on the shaping area, and cracks are not permitted.

[0152] Table 5 Requirements for the area and number of repair welding at a single location in a compartment

[0153]

[0154] The requirements for the CNC machining process flow of the front section and the back section are as follows (due to the similarities between the two shells, the machining principles and process solutions are basically the same):

[0155] 1) Perform 3D scanning of castings, measure wall thickness, and specify the best clamping and alignment solution;

[0156] 2) Clamping and alignment: Using the outer surface as a reference, align the centers of the two cross-section circles of the outer contour. During the alignment process, adjust the four points of the large end surface by adjusting the shims to ensure that the outer surface reaches the best state according to the best fitting outer circle; make quadrant marks for reference in subsequent reference adjustments.

[0157] 3) CNC vertical lathe rough machining of the small end flange end face and outer circle to see the light, the end face and outer circle single side allowance is required to be more than 3mm:

[0158] 4) CNC vertical lathe rough machining of the large end flange end face and outer circle to see the light: turn around, use the small end flange after rough machining as the clamping positioning reference, align the outer circle center, rough machine the large end flange end face and outer circle to see the light, and require the end face and outer circle single-sided allowance to be greater than 3mm.

[0159] 5) Turning rough machining of the inner surface of the shell: CNC horizontal lathe (this process can also be done with a CNC vertical lathe, which requires a vertical lathe with a Z-stroke of more than 2 meters. Currently, there are not many companies with this type of vertical lathe, so it is more convenient to use a CNC horizontal lathe. For example, the commonly used CK6180x3000 or CK61125x3000 / 5000 can be used.) Using the large end flange as the reference, use a three-jaw chuck or a four-jaw chuck to clamp and align the outer circle of the large end flange, while the center stand supports the outer circle of the small end flange; rough turning and semi-finishing turning of the inner hole, rough turning to remove the allowance to see the light; semi-finishing turning of the inner hole surface, leaving an allowance of no more than 2mm;

[0160] 6) 3D scanning, wall thickness measurement and fluorescence detection, airtightness detection: After rough processing, perform 3D scanning and wall thickness measurement on the shell to find out whether the allowance distribution is reasonable and whether the deformation is within the controllable range of the process; at this time, fluorescence ray detection can be effectively used to check whether the shell is loose or cracked, and defective parts can be analyzed and airtightness treated. Comprehensively judge whether there are pores, shrinkage holes and cracks that need to be repaired by welding, and industrial CT should be used to detect whether the depth of the crack meets the design index requirements, such as Figure 16 shown.

[0161] 7) Clamping and alignment: Using the outer surface as a reference, align the centers of the two cross-section circles of the outer contour. During the alignment process, adjust the four points of the large end surface by adjusting the gasket to ensure that the outer surface is in the best state according to the best fitting outer circle; refer to the quadrant mark of process 2, the 3D scanning data and the wall thickness distribution, and make slight adjustments to achieve the best uniform wall thickness distribution.

[0162] 8) Semi-precision turning of the small end flange end face and outer circle by CNC vertical lathe or CNC horizontal lathe requires the end face allowance to be 2±0.2mm and the outer circle single side allowance to be 1mm±0.2mm;

[0163] 9) Semi-precision turning of the large end flange by CNC vertical lathe to see the light on the end face and outer circle: Turn around, use the small end flange after semi-precision turning as the clamping positioning reference, align the outer circle center, and semi-precision turn the large end flange end face and outer circle to see the light, requiring the end face allowance to be 2±0.2mm and the outer circle single side allowance to be 1mm±0.2mm;

[0164] 10) Finish turning of the inner surface of the housing: CNC horizontal lathe (CK6180x3000 or CK61125x3000 / 5000 can be used) uses the large end flange as the reference, adopts a three-jaw chuck or a four-jaw chuck to clamp and align the outer circle of the large end flange, and at the same time, the upper center frame supports the outer circle of the small end flange; precision turning of the inner surface to the designed theoretical size;

[0165] 11) 3D scanning, wall thickness measurement and coaxiality detection and analysis: Perform 3D scanning and wall thickness measurement on the shell after precision machining, summarize the effectiveness of allowance allocation and deformation control measures and improvement measures; at the same time, perform coaxiality detection on the outer circle of the flanges of the large and small end faces to meet the form and position tolerances after subsequent butt welding, such as the parallelism of the large and small end face flanges, the coaxiality of the outer circle, the roundness and contour of the internal welding stop, and whether they are within the controllable range of the process.

[0166] 12) Weigh before welding and calculate in combination with the subsequent allowance removal. If the weight exceeds the standard: according to the data of the three-dimensional scanning, appropriate allowance removal will be carried out in the next process according to the parts where the wall thickness slightly exceeds the standard; if the weight index meets the requirements, the weight removal process will not be carried out.

[0167] 13) Horizontal machining center or horizontal turning compound machining center, large vertical gantry machining center: Horizontal machining center is preferred because it can complete the precision milling of most features of the two end faces in one clamping; it should be noted that the outer circle and end face of the large end flange are not machined, and all other features are machined in place, including the outer shape process ring of the welding butt stop and the welding stop and groove.

[0168] 14) Laser welding and wire welding: spot welding, wire welding, expansion measures as auxiliary tooling; preparation and welding of partitions, partitions are carried out using handheld laser welding

[0169] 15) Large CNC horizontal turning center: Finish-machine the welded inner cylinder shell, put on the center stand, align the center of the shell inner surface with the horizontal lathe spindle to within 0.1mm, and in principle not more than 0.2mm, precision-turn the outer circle and end faces of both end faces, and precision-turn two sealing grooves on the end face and two sealing grooves on the outer circle, with a width of 5mm and a depth of 2.65mm, and a sealing ring with a diameter of ￠3.5mm.

[0170] 16) Air tightness test: Use four sealing rings with a diameter of ￠3.5mm and install special tooling to conduct air tightness pressure test. Maintain no leakage for 60±1min at 0.35MPa±0.002Mpa, and there should be no pressure drop on the pressure gauge. The pressure drop shall not exceed 5% after 24 hours.

[0171] See also Figure 16 、 Figure 17 、 Figure 18 and Figure 19 The control measures for machining deformation and welding deformation are summarized as follows:

[0172] Machining: 1) 3D scanning; 2) Datum conversion and deformation control; 3) Special process control: using turning and milling composite machining; 4) Using Songhua paraffin oil to coat titanium alloy tapping; 5) Using point cloud-based machining trajectory design and programming to reasonably ensure wall thickness while achieving the weight requirements of the design indicators.

[0173] Welding

[0174] 1) The design of the welding seam enables butt welding to achieve high-performance welding of titanium alloys through laser welding.

[0175] 2) Control the butt joint and fit before welding, and use the linear expansion coefficient to perform deformation expansion and micro plastic deformation fit.

[0176] 3) Spot welding positioning before welding, and positioner welding coordination robot visual teaching control, welding distance and welding parameter design optimization control.

[0177] 4) Air tightness detection and fluorescence detection after welding, thermal expansion control deformation of the middle support ring, laser welding power parameters, and partition welding process parameters.

[0178] Butt welding of the middle reinforcement frame (laser welding + argon arc welding cover / laser welding groove blunt edge size is 6mm)

[0179] P=4.9-5.4KW; V=1.8-2.1m / min; ΔF=+3~+4mm;

[0180] The front and rear sections of the inner tube are welded (butt welding of the seams, effective welding thickness is 4.5mm)

[0181] P=3.4-3.8KW; V=1.7-1.9m / min; ΔF=+3~+4mm;

[0182] Casting: 1) Product design innovation and detailed casting system design; 2) Simulation optimization of three casting methods; 3) Wire EDM for runner removal, which also facilitates sand removal; 4) Optimized hot isostatic pressing and heat treatment, with optimal timing for runner removal: hot isostatic pressing after runner removal, with heat treatment scheduled after rough machining. Appropriate partial annealing was used to eliminate residual stress during machining.

[0183] See also Figures 20 to 35The front and rear molds are designed using the same principles. Each mold is also integrated into a block-based design, butted together through contours. Machining is performed on CNC machines to ensure high-precision docking. Because the mold is based on the exterior surface, to ensure the reliability of the exterior mold, both the upper and lower exterior mold plates are inlaid with high-density graphite material to ensure shrinkage and surface finish during casting. The remaining parts are made of the same graphite material commonly used for titanium alloy graphite casting. The high-density, high-carbon graphite material has a density of 2.0g / cm³ and uses high-carbon graphite with a carbon content of LG200-90 or higher, requiring a high-carbon graphite particle size of ￠200um and a fixed carbon C content greater than 90%. The remaining parts are made of medium- and low-carbon graphite materials with a fixed carbon content of approximately 75% and a graphite particle size of ￠80um-￠150um. Insertion and embedding are used for positioning and assembly between the main bodies to ensure sufficient positioning accuracy. The upper and lower templates, left and right side panels, and center core mold are all connected by plug-in embedded positioning. The center core mold is divided into three sections, each of which is connected by plug-in using a high-precision fit of standard cylindrical holes and cylindrical shafts. The insertion guide depth is greater than 20mm. The core mold is assembled and locked using two titanium alloy straight shafts with a diameter of ￠30mm to ensure the assembly rigidity of the mold in the axial direction and the linear expansion coefficient of the mold is consistent with that of the casting during the heating and cooling process of the casting. The upper and lower templates are precisely positioned and connected using 5mm deep bosses and grooves, and the left and right side panels are precisely assembled and positioned using four triangles. To facilitate the cooling rate of the mold and increase the elongation of the casting, the wall thickness of the upper and lower templates on the outer surface is designed to be greater than 150mm to ensure that the casting can quickly dissipate heat through the mold during rapid cooling. The two bulge areas are arranged at the bottom of the casting system. The graphite core support of the mold at the bottom of the front bulge adopts 6 auxiliary fulcrums to support the graphite insert plug-in at the center of the bulge, while the graphite core support of the mold at the bottom of the rear bulge adopts 5 auxiliary fulcrums to support the graphite insert plug-in at the center of the bulge. This innovative design of the titanium alloy graphite mold casting mold with a sandwich structure has two very prominent advantages. First, since the bulge area requires near-net shape both inside and outside, arranging it at the bottom allows the titanium alloy casting liquid to fully utilize the advantage of gravity during the filling process to ensure that the bulge area can be completely filled. Second, since the mold has a hollow structure in the bulge area and needs to be supported, arranging it at the bottom can just use the bulge shape facing downward to connect with the shape by designing several support points to support this weight (if it is arranged at the top, it cannot fully utilize the advantage of gravity. Secondly, the support cannot be effectively designed with a hanging point structure and is prone to collapse. Arranging it at the bottom is also not easy to think of. If it is arranged on both sides, it is also not as advantageous as arranging it at the bottom).At the same time, before filling, the mold is preheated to above 80° to about 200°. The purpose is to ensure the smoothness of the titanium alloy filling process, avoid the room temperature mold absorbing a lot of heat during the filling process, which is not conducive to timely filling and cooling and solidification. The total heat deposition of the mold is insufficient, which affects the subsequent performance caused by untimely heat dissipation.

[0184] 2) The middle main runner of the two-section mold casting system is divided into three layers. The longitudinal main runner is a cylindrical core casting channel with a diameter of ￠80mm. The diameter of the gate is ￠120mm. It is distributed in the central part of the shell mold in the axial direction as the III section. There are four circular transverse runners with a diameter of ￠30mm on both sides of the main runner of the III section; the diameter of the core longitudinal main runner is ￠60mm, which runs through the front and rear ends of the shell mold in the axial direction of the shell. It is the second main casting key channel after the main runner. The transverse annular distribution of five sections is set along the longitudinal direction. The transverse main runner is the third most important key casting channel; among them, the I section is the small end of the small section (the rear end of the small section) and the small end of the large section (the front end of the large section) with 6 annular distributions. The V section is a rectangular 30mmX30mm transverse main runner, of which 8 annular rectangular 30mmX30mm transverse main runners are distributed at the flanges of the large end of the small section (front end of the small section) and the large end of the large section (rear end of the large section); the transverse main runners of sections II and IV are distributed at the front and rear ends of the transverse main runner of section III along the axial direction, the transverse main runner of section II is located between the transverse main runners of sections I and III, and the transverse main runner of section IV is located between the transverse main runners of sections III and V. Along the longitudinal main runner diameter of ￠60mm, 6 circular transverse runners with a diameter of ￠30mm are distributed in an axial ring, which together with the transverse runners of other sections constitute the third important key casting channel of the shell casting system mold. The center of the small end flange of the two sections, that is, the center of the end face cylinder for subsequent laser welding, adopts 6 cross runners with a 60° circular distribution angle symmetrically distributed along the center of the outer circle of the shell, which is conducive to filling the mold while avoiding negative impact on the bulging area of the shell; and the center of the large end flange of the two sections, that is, the center of the front and rear flange end faces of the shell, adopts 8 cross runners with a 45° circular distribution angle symmetrically distributed along the center of the outer circle of the shell, to ensure that the outer circle of the two sections of the large end flange and the surrounding area are fully filled, and at the same time avoid deformation of the two sections of shell during casting cooling and solidification.

[0185] 3) According to this embodiment, there are five partitions in each section of the front and rear bulge area, a total of ten. Among them, the partitions close to the flange end faces of the front and rear sections are ensured by casting, and the partitions in the central part are connected by subsequent welding. Because there is no margin on the outer surface in the bulge area and the wall thickness is relatively thin, in order to ensure stable filling of the casting mold and no deformation during the subsequent hot isostatic pressing heat treatment, it is necessary to fully consider the bulge area. For this reason, reinforcing ribs are set on both sides of the surface in the bulge area to achieve a bridge. As shown in the figure, in the front section, that is, in the small section The profile is provided with 11 cylindrical reinforcement ribs with a diameter of ￠12mm and relatively evenly distributed to realize the bridge structure. In the rear section, i.e., the large section, the profile is provided with 7 cylindrical reinforcement ribs with a diameter of ￠12mm and relatively evenly distributed to realize the bridge structure. A total of 18 cylindrical reinforcement ribs with a diameter of ￠12mm are provided in the two sections to realize the bridge structure. The bridge structure on both sides of the bulge is realized by 18 cylindrical reinforcement ribs, which has three advantages. One is that the casting system is further refined and optimized, and the conventional three-stage runner is upgraded to a four-stage runner. The first is to achieve effective filling of long and thin-walled key fine structures while avoiding various defects of the casting system without this level; the second is to effectively improve the shell rigidity during the high-temperature casting and subsequent cooling process of the thin-walled shell, thereby reducing the shell deformation after casting and hot isostatic pressing (after calculation, the 18 cylindrical reinforcement ribs with a diameter of ￠12mm and rectangular / I-shaped partitions can effectively improve the shell rigidity by more than 30%. The 18 cylindrical reinforcement ribs with a diameter of ￠12mm are not removed before hot isostatic pressing but are arranged in the hot isostatic pressing hot place). Thirdly, the 18 cylindrical ribs (Ø12 mm in diameter) can be used as specimens after hot isostatic pressing (HIP) to replace the casting itself for testing and verifying its room- and high-temperature mechanical properties and metallographic and microstructural structures. This allows for mapping the microstructural and metallographic structures of titanium alloy castings at different temperatures to their mechanical properties and elongation, ultimately establishing a mapping between microstructure and macroscopic properties. This advantage is often not readily apparent.

[0186] 4) This embodiment requires the inclusion of auxiliary casting supports and performance sampling arrangements, including sample sampling locations, flanges at both ends of the petal structure that serve as a reference for casting and subsequent processing, and shrinkage feeding arrangements at the top riser of the casting system. Specifically, these include the aforementioned 18 cylindrical reinforcing ribs with a diameter of ￠12mm and 24 cylindrical furnace specimens with a diameter of ￠16mm. The 24 cylindrical furnace specimens with a diameter of ￠16mm are arranged along eight circumferentially distributed third-level transverse main runners at the small end of the front section (the rear end of the small section) and the large end of the rear section (the rear end of the large section). Three cylindrical furnace specimens with a diameter of ￠16mm and a length of 150mm are placed on each of the eight cross runners. The most important purpose of this arrangement is to compensate for insufficient mold filling and storage buffer during the casting process and to provide shrinkage feeding for the casting, which is not easy to imagine. Secondly, it ensures that a sufficient number of titanium alloy high-temperature mechanical property specimens are tested under the different temperature conditions required by the design process. The embodiment provides for the front and rear section welding butt end faces designed for the casting system mold filling and support and subsequent processing reference of the petal structure flange, the flange outer diameter is ￠430mmX18mm thick, it adopts a circular flange structure and at the same time, 7 U-shaped through grooves are opened on the flange (including the bulge through groove, a total of 8 open grooves), and the U-shaped groove size is 100mmX45mm; the advantages of this design are manifested in three aspects, one is that the use of the end face flange can better ensure the smooth filling of the casting system; the second is to strengthen the overall rigidity of the small end face of the large and small segments. While improving the overall rigidity of the thin-walled barrel, it is also conducive to the convenience of hot isostatic pressing and clamping of the casting, which further helps to reduce the large deformation caused by structural asymmetry and imbalance during the solidification and subsequent hot isostatic pressing heat treatment of the casting; thirdly, the eight U-shaped grooves set in the middle help the end face of the casting absorb heat during solidification and improve the performance of the area close to the welding end face; fourthly, and also very important, the circular flange is convenient for the reference coordination and reference conversion of rough and precision machining in the subsequent mechanical processing and turning process; finally, it is very conducive to the establishment of three-dimensional digital camera scanning detection references at various stages of castings.

[0187] The shrinkage feeding of the casting system is set on the two sealing plates on the top of the mold, and the advantages of structure and gravity can be used to effectively realize the casting and solidification shrinkage feeding.

[0188] 5) The embodiment requires five stages of 3D camera scanning inspection: the first stage is a 3D scan after mold processing and assembly; the second stage is a 3D scan after casting, after the main runner and three-level auxiliary runners are removed, and before hot isostatic pressing; the third stage is a 3D scan after hot isostatic pressing, before the final four-level auxiliary runners are added and before delivery to the machine for machining; the fourth stage is a 3D scan after the first rough machining and fluorescence inspection; and the fifth stage is a 3D scan after all required finishing operations are completed, before laser butt welding. The purpose of the first stage of 3D scanning of the mold is to detect discrepancies between the overall surface contour and assembly accuracy of the mold after assembly and the theoretical design 3D model of the mold. Necessary repairs and adjustments are made based on the detection accuracy to avoid subsequent casting contour accuracy, positional errors, and allowance allocation errors caused by mold processing or assembly accuracy, which would make it difficult to coordinate positioning, clamping, and alignment during machining. The second stage involves a 3D scan of the casting after removing the main runner and important auxiliary runners. The purpose is to detect the difference between the overall contour of the casting and the target accuracy, so as to effectively calculate whether the shrinkage rate settings in various directions are reasonable, thereby providing data support for the high-precision design of the shrinkage rate of mass-produced castings. The purpose of the third stage of 3D scanning of the hot isostatically pressed casting is to compare the changes in the casting's overall contour before and after hot isostatic pressing, thereby providing effective process support for tooling design, clamping, and runner removal during the hot isostatic pressing process. More importantly, it provides an accurate 3D digital physical model of the casting for subsequent machining to use as a reference for alignment of the outer contour and the flanges at both ends, and for allowance coordination. In other words, it provides the 3D model state of the casting's blank machining as a theoretical and physical basis for clamping and alignment. The 3D scanning in the fourth stage is used to compare the changes before and after rough machining of the casting, explore the casting's deformation before and after rough machining, and provide theoretical data support for the rationalization of cutting processing parameters and clamping and alignment optimization. But more importantly, it is used to provide the most accurate theoretical data for the reference conversion coordination before the second semi-precision machining. By comparing the physical point cloud data with the theoretical model through a computer, the correct coordination direction and the most accurate coordination amount are determined for the actual reference adjustment operation.The purpose of the 5th stage of three-dimensional scanning of the two-section casting after fine machining is to detect whether the two-section casting fully meets the process design quality requirements and whether it reaches the correctness and rationality of the state before the final welding, so as to provide necessary process data support for the welding deformation control measures; and through the two-section point cloud assembly and physical assembly, the measures required to be taken during the welding process are verified, so as to provide the final coordination reference direction for the key assembly processing features such as the precision machining allowance of the outer circle of the two end flanges and the end face and sealing groove, the overall length dimensional accuracy, and the coaxiality of the outer circle at both ends after the final welding, and take necessary control and rescue measures according to the actual situation; the embodiment stipulates that the fitting accuracy of the small flange assembly and plug-in connection of the two sections' respective welding end faces can be improved by using expansion tooling and auxiliary clamping tooling to improve the plug-in and docking assembly dimensional accuracy required before the two sections are welded (including necessary repair measures for the plug-in structure, and secondary fine machining of the fitting features of the small flange plug-in parts of the two sections can be adopted to achieve the reference accuracy required for the fine machining of the product after welding).

[0189] Early products had the following issues: ① The front and rear sections of the inner barrel were large castings with relatively thin walls, which easily deformed during the casting process due to the uneven solidification shrinkage of the titanium alloy. ② Because the final wall thickness of the product was only 2.5mm, the wall thickness tolerance was (0, +0.5) and the profile was 0.5. Therefore, high requirements were placed on the dimensional accuracy of the casting's external surface. Early products had large areas of increased wall thickness by 1.5-2.0mm, with some areas even thickening as much as 3.2mm. ③ High surface quality requirements for the casting, requiring it to meet Grade A standards, were not met in early castings. ④ High internal quality requirements for the casting, requiring it to meet Grade A standards, were not met in early castings. ⑤ High weight tolerance requirements for the casting, resulting in early products exceeding the weight tolerance by 17 kg.

[0190] Table 11 Problems with the front section of the inner tube

[0191]

[0192] Cause analysis: The casting problem is that the part shape has not been processed, and it is a casting surface, resulting in large wall thickness deviation and length dimension deviation; the welding groove size 1 deviation is caused by part processing deformation and unreasonable process design; the step on the bottom surface of the φ45 countersunk hole is the connection mark between the lathe surface and the milling surface.

[0193] Table 12 Problems with the rear section of the inner tube

[0194]

[0195] Cause analysis: The casting problem is that the part shape has not been processed, and it is a casting surface, resulting in thickness deviation; the pin hole size deviation is due to the operator's hand swing when manually reaming, resulting in hole diameter deviation; the three basic dimensions of the hole position are due to the fact that the accuracy of these dimensions is guaranteed by the processing accuracy of the machine tool itself, and the accuracy of the machine tool itself has the greatest impact. Secondly, the parts may be deformed after processing, which together cause these dimensional deviations; the welding groove size deviation is due to part processing deformation and unreasonable process design.

[0196] In response to the above problems, corresponding improvement measures need to be taken in the machining process. The product processing improvement measures are shown in Table 16.

[0197] Table 16 Product processing improvement measures

[0198]

[0199] 6.3 Optimization design of inner barrel casting process

[0200] Based on the cause analysis and solution of the inner tube casting product quality problems, the following five important improvement measures were formulated to optimize the design of the inner tube front and rear section casting process:

[0201] 1. The inner cylinder casting is a long cylinder with a through-slot structure, with thinner walls in some areas and large structural dimensions. It is a large, thin-walled titanium alloy casting. Based on the previous product dimensions, the shrinkage ratio of the inner cylinder casting after optimization was determined: inner surface reduction: 0.3%, outer surface reduction: 1.2%, height reduction: 1%, inner surface grinding allowance: 0.5mm, and outer surface grinding and correction allowance: 1mm.

[0202] 2. In the graphite mold design for the inner barrel casting, while ensuring machining accuracy and ease of processing, the design minimizes parting surfaces to reduce dimensional disqualifications caused by accumulated mold errors. The mold is generally divided into five layers, and a square stop is used between the core and the outer shell to prevent core movement.

[0203] 3. The selection of the gating system and the design of the pouring method are crucial for producing qualified castings with crack-free surfaces, dense interiors, and no bending or deformation. After analyzing previous product developments and taking into account the equipment characteristics and casting structural properties, a top-injection pouring system was selected for this casting, using a vertical static pouring process.

[0204] 4. The main runner in the front section of the inner barrel is placed at the center of the cylinder. The runners are designed in four layers, with four runners evenly spaced on each layer. The runners measure 40x40mm. In the rear section of the inner barrel, due to its smaller diameter, the built-in runner is difficult to remove. Therefore, the main runner is located on the outside of the barrel. The runners are designed in four layers, with runners evenly spaced on the outside of each layer. The bottom runner measures 60x35mm, while the other three layers of runners are annular runners located on the outer sides. These two gating system designs ensure that the molten metal quickly and evenly fills the mold cavity during casting, resulting in sequential solidification, reducing shrinkage cavities and porosity in the casting, and producing high-quality castings.

[0205] 5. To ensure the surface and internal quality of the casting, the gating system was optimized and computer simulated several times. The results of the computer simulation showed that there were subtle shrinkage defects in the casting and runner locations, which could be completely eliminated through hot isostatic pressing.

[0206] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0207] The large-scale ultra-long titanium alloy special-shaped thin shell precision casting and processing and welding deformation control technology provided in the embodiments of the present application adopts split casting, precision machining and laser welding solutions to effectively improve the casting quality of castings, control the deformation of castings and effectively perform hot isostatic pressing of castings to eliminate defects of castings, thereby improving product quality.

[0208] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A method for precision casting and processing of large ultra-long titanium alloy special-shaped thin shells and controlling welding deformation, characterized in that: The large ultra-long titanium alloy special-shaped thin shell includes: a cylindrical thin shell composed of a first cylindrical section, a first conical cylindrical section, a second cylindrical section, a second conical cylindrical section and a third cylindrical section connected in sequence along a first direction, and a radially protruding convex semicircular bulge along the shell generatrix is provided on the cylindrical thin shell, a reinforcing rib plate is provided inside the convex semicircular bulge, an annular reinforcing rib is provided on the outer side of the first cylindrical section, a plurality of partitions are provided on the inner side of the cylindrical thin shell, a first flange and a second flange are provided at both ends of the cylindrical thin shell respectively, the diameter of the first cylindrical section is smaller than the diameter of the second cylindrical section, the diameter of the second cylindrical section is smaller than the diameter of the third cylindrical section, and the thickness range of the cylindrical thin shell is 2.5 mm ± 0.5 mm; The manufacturing method comprises: The cylindrical thin shell is divided into two parts at the second cylindrical section: a small inner cylinder section and a large inner cylinder section, and the two parts are cast separately, wherein the small inner cylinder section includes the first cylindrical section and the first conical cylinder section, and the large inner cylinder section includes the second cylindrical section, the second conical cylinder section, and the third cylindrical section; performing turning-milling composite rough machining and semi-finishing machining on the small section of the inner cylinder and the large section of the inner cylinder respectively; Assembling the inner cylinder small section and the inner cylinder large section and performing laser welding, and then performing cylinder body fine processing; Among the multiple partitions arranged in the inner cylinder small section and the inner cylinder large section, the partitions close to the cylinder openings at both ends are cast as a whole, and the other partitions are fixed by welding and the inner surfaces are finely processed.

2. The method for precision casting and processing of large ultra-long titanium alloy special-shaped thin shells and controlling welding deformation according to claim 1 is characterized in that: The reinforcing ribs are configured as a plurality of ribs arranged at intervals.

3. The method for precision casting and processing of large ultra-long titanium alloy special-shaped thin shells and controlling welding deformation according to claim 1 is characterized in that: During the semi-finishing process, process flanges are respectively provided on the edges to be welded of the small inner cylinder section and the large inner cylinder section as machining coordination benchmarks for the large and small sections.

4. The method for precision casting and processing of large ultra-long titanium alloy special-shaped thin shells and controlling welding deformation as claimed in claim 3 is characterized in that: The process flanges are all configured as open flange structures.

5. The method for precision casting and processing of large ultra-long titanium alloy special-shaped thin shells and controlling welding deformation according to claim 1 is characterized in that: After the inner cylinder small section and the inner cylinder large section are cast and formed, hot isostatic pressing heat treatment is performed.

6. The method for precision casting and processing of large ultra-long titanium alloy special-shaped thin shells and controlling welding deformation as claimed in claim 5, characterized in that: Before performing the turning-milling composite rough machining, the small section of the inner cylinder and the large section of the inner cylinder are subjected to fluorescence detection and three-dimensional scanning detection; After completing the turning-milling composite rough machining, the three-dimensional scanning reference conversion coordination is carried out and then semi-finishing is carried out.

7. The method for precision casting and processing of large ultra-long titanium alloy special-shaped thin shells and controlling welding deformation according to claim 6 is characterized in that: Before laser welding the small inner tube section and the large inner tube section, the partition welding is completed respectively, and then the small inner tube section and the large inner tube section are docked, and then the flanges at both ends are finely processed and tested for coaxiality.

8. The method for precision casting and processing of large ultra-long titanium alloy special-shaped thin shells and controlling welding deformation as claimed in claim 1, characterized in that: The small section of the inner tube and the large section of the inner tube are butt-welded with the seams, and the effective welding thickness is 4.5 mm; the welding power range is 3.4-3.8 KW, and the speed is 1.7-1.9 m / min.

9. The method for precision casting and processing of large ultra-long titanium alloy special-shaped thin shells and controlling welding deformation according to claim 1, characterized in that: A 5mm margin is left on the front end face of the first flange, a 3mm margin is left on the inner end face of the first flange, a 3mm margin is left on one side of the end face groove of the first flange, a 3mm margin is left on the bottom face of the first flange, a 16mm margin is left on the outer diameter of the bottom face of the first flange, and a 5mm margin is left on one side of the inner shape surface of the bottom face of the first flange; A 5mm margin is left on the rear end face of the second flange, a 3mm margin is left on the inner end face of the second flange, a 3mm margin is left on one side of the end face groove of the second flange, a 3mm margin is left on the bottom face of the second flange, a 16mm margin is left on the outer diameter of the bottom face of the second flange, and a 5mm margin is left on one side of the inner shape surface of the bottom face of the second flange.

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