A method for manufacturing a die for superplastic forming / diffusion bonding of titanium alloys

Abstract

The present application relates to the technical field of die manufacturing, and discloses a manufacturing method of a titanium alloy superplastic forming / diffusion bonding die, which comprises the following steps: firstly, detecting a casting; then, sequentially performing the following steps on the casting: heat surface treatment, reference plane processing, deep hole processing, rough machining of a cavity, welding, air tightness detection, fine machining of the cavity, small hole processing, polishing of the cavity, cavity detection, die assembly and die testing; and finally, completing the forming manufacturing of the whole die; if the air tightness of the casting is found unqualified in the air tightness detection, marking the air leakage points of the casting, determining the weldability of the air leakage points, and determining whether to weld the casting according to the weldability. The method can accurately find the defects affecting the air tightness of the die in the earliest process of the manufacturing process, take measures to remedy or determine the casting blank to be scrapped, and avoid the economic waste and manufacturing cycle delay caused by the repair and scrapping of the unqualified blank after the complete machining of the blank.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mold manufacturing, in particular to the field of superplastic forming / diffusion bonding of titanium alloy parts, and more particularly to a manufacturing method of a superplastic forming / diffusion bonding mold for titanium alloy. BACKGROUND

[0002] Titanium alloy material has excellent elongation and good diffusion performance in the high temperature range. By applying pressure, diffusion bonding can be generated on the bonding surface of two or more layers of sheet material, and superplastic forming can be performed on the non-bonding part, thereby forming a part with complex shape, hollow body, high rigidity and strength structure. Compared with traditional riveting and welding processes, superplastic forming / diffusion bonding technology can effectively improve material utilization, shorten processing cycle and reduce manufacturing cost, and has become one of the key manufacturing technologies for lightweight advanced aircraft in the fields of aviation and aerospace.

[0003] Superplastic forming / diffusion bonding forming technology of titanium alloy material has been researched for many years by foreign aviation and aerospace powers. In the field of aviation and aerospace in China, a large amount of research has also been conducted for the manufacture of advanced aircraft, and great progress has been made, some of which have reached the international advanced level. From the published data, the research on superplastic forming / diffusion bonding forming technology of titanium alloy material is mainly focused on the parameter research of superplastic forming / diffusion bonding forming of a certain type of titanium alloy part, and the size of the titanium alloy part researched is small and the corresponding mold structure is simple. However, there is less research on mold manufacturing technology, especially on large, complex and precise mold manufacturing technology.

[0004] For example, the invention patent with publication number CN111604645A proposes a method for forming an aircraft engine inlet pipe, which features nine steps and related parameters for realizing superplastic forming / diffusion bonding of titanium alloy parts. However, it does not involve the mold structure and mold manufacturing process method corresponding to the product.

[0005] For another example, the invention patent with publication number CN109175917A proposes a manufacturing method for a titanium alloy lightweight reinforced wing surface, which features ten steps and related parameters for realizing superplastic forming / diffusion bonding of titanium alloy parts. This document does not involve the mold structure and mold manufacturing process method corresponding to the product.

[0006] Further, the invention patent with publication number CN106271439A proposes a method for superplastic forming / diffusion bonding forming of titanium alloy parts. Although the document designs mold manufacturing, it provides less information on mold manufacturing, and the manufacturing of large, precise and complex molds cannot meet the requirements. SUMMARY

[0007] In order to solve the problems and deficiencies in the prior art, the present application provides a manufacturing method of a titanium alloy superplastic forming / diffusion bonding die, which can accurately find defects affecting the air tightness of the die in the earliest process of the manufacturing process and take measures to remedy or determine the rejection of the casting blank, thereby avoiding the economic waste and manufacturing cycle delay caused by the repair and rejection of the unqualified blank after the complete processing.

[0008] In order to achieve the above-mentioned application purposes, the technical scheme of the present application is as follows:

[0009] The manufacturing method of the titanium alloy superplastic forming / diffusion bonding die first detects the die casting, then sequentially performs heat surface treatment, reference plane machining, deep hole machining, cavity rough machining, welding, air tightness detection, cavity finishing, small hole machining, cavity polishing, cavity detection, die assembly and die testing, and finally completes the forming manufacturing of the whole die; if the air tightness of the casting is found to be unqualified in the air tightness detection process, the air leakage point of the casting is marked, and the weldability of the air leakage point is determined; if it is determined that the air tightness of the casting can be guaranteed by welding, the die casting is welded and the air tightness is detected again; if it is determined that the air tightness of the casting cannot be guaranteed by welding, the casting is rejected and a new blank is made.

[0010] Preferably, the die casting detection includes: detecting the casting by visual inspection and ordinary measuring tools respectively; if all surfaces of the casting have no visible cracks, porosity and penetrating defects, and the minimum excess of the machining surface is 5 mm and the maximum excess is 10 mm, it indicates that the casting can be used to manufacture the die, otherwise the casting is discarded.

[0011] Preferably, the heat surface treatment includes: placing the casting in an annealing furnace for annealing treatment, the heating speed is 40-80℃ / h, then keeping the temperature at 980±20℃ for 3-4h, and then cooling in the furnace to below 200℃ and discharging, after the die casting is cooled to room temperature, the surface oxide scale and adhered sand are removed by shot blasting process.

[0012] Preferably, the reference plane machining includes: machining the bottom surface of the die, first machining with a minimum excess of 5 mm, if the flatness is ≤0.05mm and the roughness Ra is ≤0.8μ, no further machining is needed; if the flatness and roughness do not meet the requirements, further machining is needed, but the maximum machining excess is not more than 10 mm.

[0013] As preferably, the deep hole machining comprises: drilling a deep hole in the casting by using a deep hole drill, first, finding the cross center line of the mold around the contour to determine the cross center line as the reference of X direction and Y direction, taking the bottom surface after the reference plane processing as the reference of Z direction, and then drilling the mold; after the drilling, the center axis position degree of each deep hole is less than 0.2mm, the straightness is less than 0.5mm / m, the hole diameter deviation is ±0.5mm, and the roughness Ra is not greater than 6.4μm; meanwhile, the temperature measuring hole of the mold is processed to the size required by the numerical mold, and the roughness Ra is not greater than 6.4μm.

[0014] As preferably, the cavity rough machining comprises: in the processing, taking the cross center line of the deep hole machining process as the reference of X direction and Y direction, taking the bottom surface after the reference plane processing as the reference of Z direction, first processing with the minimum allowance of 5mm, if the surface quality and the roughness have not reached the above requirements, then judging the allowance value of the continuous processing according to the depth value of the defect, and the maximum processing allowance cannot exceed 15mm in total; meanwhile, the guide groove, the positioning pin hole and the pickup groove of the mold are processed to the size required by the numerical mold, and the roughness Ra is ≤1.6μm.

[0015] As preferably, the welding comprises welding the deep hole plug of the mold and the gas pipe joint; in the welding, first, removing the iron filings and oil stains in the deep hole, then polishing the surface of the welding area at both ends of the deep hole to expose the body of the mold casting metal matrix, then cleaning the surface of the welding area with a cleaning agent, pressing the deep hole plug at both ends of the mold deep hole and the gas pipe joint at the gas outlet hole of the mold, and finally welding the deep hole plug and the gas pipe joint with the mold firmly by using the welding rod with the temperature resistance not less than 1000℃ and the same thermal expansion coefficient as the matrix, to meet the air tightness requirement.

[0016] As preferably, the air tightness detection comprises: injecting 1-1.5Mpa high pressure gas into the deep hole through the gas pipe, spraying the liquid that can produce bubbles on the bottom plane, all the lightened cavities, the surrounding plane and the cavity of the mold, and visually checking whether bubbles are produced; if no bubbles are found on all surfaces within not less than 5 minutes, it is determined that the air tightness of the mold is qualified, otherwise it is unqualified.

[0017] As preferably, in the cavity finishing, the allowance is removed ≤0.5mm, the roughness is ≤Ra1.6, and the center of each small hole is marked by dotting.

[0018] As preferably, the small hole processing includes: preparing the electrode wire, surrounding the 10mm high liquid storage tank around the small hole center about 10mm with the cement; clamping the electrode and aligning the small hole center mark point, then adding the spark machining liquid in the oil storage tank, starting to process the small hole; when the small hole is found to be processed in place, pressing the pause key of the spark machine tool, keeping the electrode wire position, removing the cement and cleaning the remaining processing liquid; finally starting the power supply, lifting the electrode out of the small hole, and sealing the small hole with clean cement; repeating the above steps until the processing of all small holes is completed.

[0019] As preferably, the cavity polishing includes: using compressed air to remove the residual liquid in the deep hole, then sealing the small hole with cement, and finally polishing the whole profile of the mold, and the roughness Ra of the cavity after polishing is ≤0.4μm.

[0020] As preferably, the cavity detection includes: using the measuring machine to measure the cavities of the upper mold and the lower mold respectively, and meeting the tolerance requirement of ±0.1mm.

[0021] As preferably, the mold assembly includes: removing the burrs, sharp edges and sharp corners of the non-working surface of the mold, assembling the guide plate and the positioning pin, and marking the mold figure number.

[0022] As preferably, the mold test includes: first putting the mold into the heating furnace of the hot press, and connecting the upper mold and the lower mold with the upper and lower working platforms of the machine tool, the carbon dioxide cylinder and the gas source pipeline respectively; lifting the upper working platform together with the upper mold by at least 200mm height; heating the mold, and keeping the temperature at 200±20℃ for 1h; placing a 1mm thick aluminum plate on the lower mold, which has the same size as the titanium alloy part plate blank; lowering the upper mold, and applying a pressure of 50-100 tons to the aluminum alloy plate; opening the carbon dioxide cylinder to charge the upper mold and the lower mold with gas, and if the pressure value of the pressure gauge of the cylinder decreases by ≤0.1Mpa after 60 minutes, it is determined that the mold gas tightness is qualified, otherwise it is unqualified.

[0023] As preferably, the weldability of the air leakage point is determined by drilling a hole with a diameter of 5-10mm and a depth of 5-8mm, visually judging the defect characteristics in the hole and making corresponding treatment; if the hole is a gas hole and there is no loose structure, welding repair is carried out, and the gas tightness detection is carried out again; if the hole is a loose structure, the casting is scrapped.

[0024] The beneficial effects of the present application are:

[0025] (1) The mold manufacturing method of the present application can accurately find defects affecting the air tightness of the mold in the earliest process of the manufacturing process, and take measures to remedy or determine the rejection of the casting blank, thereby avoiding the economic waste and manufacturing cycle delay caused by the repair and rejection of unqualified blanks after the entire processing is completed, and thus is the best method for realizing the high-quality, fast and low-cost goal of large, complex and precise titanium alloy superplastic forming / diffusion bonding mold manufacturing.

[0026] (2) The present application strictly controls the machining allowance of the casting, and processes according to the actual situation of the casting, which can avoid the defects such as casting deformation and surface sand inclusion of the casting, which are not processed due to too small machining allowance, affecting the surface quality; at the same time, it can also avoid the risk of surface quality and air tightness unqualified caused by too large machining allowance which will increase the machining of the relatively dense layer of the casting.

[0027] (3) In the process of hot surface treatment, the annealing temperature is strictly controlled between 980℃±20℃, which reduces the hardness and improves the machining performance, and the drill bit for deep hole machining is not easy to break. BRIEF DESCRIPTION OF DRAWINGS

[0028] The foregoing and subsequent specific description of the present application becomes more apparent when read in conjunction with the following drawings, in which:

[0029] Figure 1 is a method flowchart of the present application;

[0030] Figure 2 is a schematic diagram of the structure of a titanium alloy part;

[0031] Figure 3 is a schematic diagram of the overall structure of the mold;

[0032] Figure 4 is a schematic diagram of the mold surface;

[0033] Figure 5 is a sectional view of the mold;

[0034] Figure 6 is Figure 5 is a local structure enlargement of the middle part. DETAILED DESCRIPTION

[0035] In order for those skilled in the art to better understand the technical solutions in the present application, the following will further illustrate the technical solutions for achieving the purpose of the present application through several specific examples. It should be noted that the technical solutions claimed by the present application include but are not limited to the following examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor shall fall within the scope of protection of the present application.

[0036] Titanium alloy material has excellent elongation and good diffusion performance in high temperature range, diffusion connection can be generated on the bonding surface of two or more than two layers of sheet material by applying pressure, and the non-bonding part can be superplastic formed, thereby forming a part with complex shape, hollow integral and high rigid strength structure. Compared with the traditional riveting and welding process, the superplastic forming / diffusion bonding technology can effectively improve the material utilization, shorten the processing cycle and reduce the manufacturing cost, and has become one of the key manufacturing technologies for lightweight advanced aircraft in aviation and aerospace

[0037] The superplastic forming / diffusion bonding forming technology of titanium alloy material has been studied for many years by foreign aviation and aerospace powers, and a large amount of research has been conducted in the field of domestic aviation and aerospace for manufacturing advanced aircraft. At present, great progress has been made, and some have reached the international advanced level. In view of the research on the superplastic forming / diffusion bonding forming technology of titanium alloy material, according to the public data, the research on the parameters of the superplastic forming / diffusion bonding forming of a certain type of titanium alloy part is more, and the size of the researched titanium alloy part is smaller and the corresponding mold structure is simpler, but the research on the mold manufacturing technology is less, especially the research on the manufacturing technology of large, complex and precise molds is less.

[0038] Therefore, the research on the manufacturing technology of large, complex and precise molds is insufficient, which restricts the precision, performance, cost, cycle and competitiveness of the superplastic forming / diffusion bonding forming of large, complex and high-precision titanium alloy parts, and has become one of the bottlenecks affecting the quality of the superplastic forming / diffusion bonding forming of large, complex and high-precision titanium alloy parts.

[0039] Based on this, the embodiment of the present application proposes a manufacturing method of a titanium alloy superplastic forming / diffusion bonding mold, which can accurately find defects affecting the air tightness of the mold in the earliest process of the manufacturing process and take measures to remedy or determine the rejection of the casting blank, thereby avoiding the economic waste and manufacturing cycle delay caused by the discovery of air tightness unqualified after the unqualified blank is completely processed.

[0040] First of all, it needs to be pointed out that the product to which the mold of the present application is directed is a large, complex and high-precision titanium alloy part (see the product in the drawings attached to the specification Figure 2 ), which has the following characteristics:

[0041] The projection area of the product is greater than or equal to 1 square meter, the height difference of the high and low points of the complex surface is greater than or equal to 50 mm; the number of bulges for superplastic forming is large (tens of them), and the amplitude of the curved surface changes greatly; the area of the diffusion connection region is large and the shape is complex.

[0042] Further, the typical structure of the corresponding mold of the present application is shown in the drawings attached to the specification Figures 3-6 , and such a mold has the following characteristics:

[0043] (1) In order to realize precision superplastic forming / diffusion bonding of each bulge, a small hole with a diameter of about 1 mm is arranged at the lowest part of the bottom of each bulge cavity, and is connected with a grid of longitudinal and transverse intersecting deep holes to form a gas path network, such as Figure 4 , Figure 5 and Figure 6 , for vacuumizing and exhausting air during superplastic forming and for injecting high-pressure gas during diffusion bonding. For this purpose, the mold is required to have a low vacuum degree and a good high-pressure gas tightness under high-temperature working conditions.

[0044] (2) In order to reduce the cost, the mold material is ZG35Cr24Ni7SiN, and the upper mold and the lower mold blanks are both castings. However, the castings have defects such as loose internal structure (not dense), even shrinkage holes, much surface slag inclusion, and possible local cracks. When several deep holes and small holes need to be machined in the castings, the gas tightness of the mold is difficult to be qualified.

[0045] The embodiment discloses a manufacturing method of a titanium alloy superplastic forming / diffusion bonding mold. The mold manufacturing method first detects a mold casting, and then sequentially performs heat surface treatment, reference plane machining, deep hole machining, cavity rough machining, welding, gas tightness detection, cavity finishing, small hole machining, cavity polishing, cavity detection, mold assembly and mold testing on the mold casting, and finally completes the forming manufacturing of the whole mold. If the gas tightness of the casting is found to be unqualified in the gas tightness detection, the gas leakage points of the casting are marked, and the weldability of the gas leakage points is judged. If it is judged that the gas tightness of the casting can be ensured by welding, the mold casting is welded and the gas tightness is detected again. If it is judged that the gas tightness of the casting cannot be ensured by welding, the casting is scrapped and a new blank is made.

[0046] In the embodiment, the casting is a blank for making the mold. After the blank casting is manufactured and processed, the mold can be finally obtained. The mold casting includes an upper mold casting and a lower mold casting, and after being manufactured and processed, the upper mold and the lower mold can be obtained. The processing and manufacturing methods of the upper mold and the lower mold are the same. Referring to the drawings in the description, Figure 1 , the processing and manufacturing method of the mold is as follows.

[0047] Step S1. Casting detection

[0048] First, the surface of the casting is detected by visual inspection, and the surface of the casting is required to be free of visible cracks, loose and penetrating defects. Then, a measuring tool is used to measure the machining allowance of the casting, wherein the minimum allowance of the machining surface of the casting is 5 mm, and the maximum allowance is 10 mm.

[0049] In the embodiment, the measuring tool can be a measuring device such as a tape measure.

[0050] In the embodiment, the upper mold and the lower mold are both detected by the above-mentioned method.

[0051] Step S2. Hot surface treatment

[0052] The castings are put into an annealing furnace for annealing to improve the processability, which requires that the heating rate is 40-80°C / h, then the temperature is kept at 980±20°C for 3-4h, and then the furnace is cooled to below 200°C and the castings are taken out; after the castings are cooled to room temperature, the shot blasting process is used to remove all the surface oxides, sand sticking and the like.

[0053] In this embodiment, if the residual oxide and sand sticking on the surface of the castings cannot be removed by the shot blasting process, manual knocking or grinding and the like are used to remove them completely.

[0054] In this embodiment, the upper die and the lower die are both subjected to the hot surface treatment in the above manner.

[0055] Step S3. Reference plane processing

[0056] The reference plane processing refers to the processing of the bottom surface of the die, which requires that the processing is first performed according to the minimum allowance of 5mm, if the requirements of the flatness ≤0.05mm and the roughness Ra≤0.8μm are reached, the processing is not performed again; if the flatness and the roughness are not reached, the processing needs to be continued, but the maximum processing allowance cannot exceed 10mm.

[0057] In this embodiment, after the bottom surface of the die is processed, the die pressing plate groove and the step surface thereof are also processed to the size required by the numerical die, and the roughness Ra≤1.6μm.

[0058] In this embodiment, the upper die and the lower die are both subjected to the reference plane processing in the above manner.

[0059] Step S4. Deep hole processing

[0060] The deep hole drilling is performed on the castings by using the deep hole drill, in which the cross center line is determined by aligning the upper die and the lower die around the outer shape, the cross center line is used as the reference of the X direction and the Y direction, and the bottom surface in the reference plane processing procedure is used as the reference of the Z direction, the center axis position degree of each deep hole is ≤0.2mm, the straightness is ≤0.5mm / m, the hole diameter deviation is between ±0.5mm, and the roughness Ra≤6.4μm.

[0061] In this embodiment, the temperature measuring holes of the upper die and the lower die are also processed to the size required by the numerical die, and the roughness Ra≤6.4μm.

[0062] In this embodiment, the upper die and the lower die are both subjected to the deep hole processing in the above manner.

[0063] Step S5. Rough cavity processing

[0064] The rough machining of the cavity refers to machining the upper and lower cavity of the mold and the reference hole. The specific steps are as follows: during machining, the cross center line of step S4 is taken as the X direction and Y direction reference, and the bottom surface is taken as the Z direction reference. First, machining is performed with a minimum allowance of 5 mm. If the profile has reached the requirement of no visual defects (such as slag inclusion, porosity, and loose defects) and the roughness has reached Ra≤3.2 μm, no further machining is performed. If the surface quality and roughness do not meet the above requirements, the depth value of the defect is determined to determine the machining allowance, but the total maximum machining allowance cannot exceed 15 mm.

[0065] In this embodiment, the defect is generally a concave defect, so the depth value refers to the depth of the concave.

[0066] In this embodiment, the upper mold and the lower mold are both machined in the above manner.

[0067] Step S6. Mold welding

[0068] In this machining process, welding mainly includes welding the deep hole plug of the mold casting and the gas pipe joint. The specific process is as follows: first, the iron filings and oil stains in the deep hole are removed by compressed air, the surface of the welding area at both ends of the deep hole is polished to expose the body of the metal matrix of the mold casting, and no oxide skin and burrs are ensured. Then, the deep hole plug is pressed into both ends of the deep hole, and the gas pipe joint is pressed into the gas outlet hole of the mold. Next, the surface of the deep hole plug and the gas pipe joint and the mold welding area is cleaned with a cleaning agent such as acetone. Finally, a welding rod with a temperature resistance of not less than 1000°C and a thermal expansion coefficient same as the matrix (such as H1Cr19Ni9Ti) is used to firmly weld the deep hole plug and the gas pipe joint to the mold, meeting the air tightness requirement.

[0069] In this embodiment, the upper mold and the lower mold are both welded in the above manner.

[0070] Step S7. Air tightness detection

[0071] High pressure gas (such as air, carbon dioxide gas, etc.) with a pressure of 1-1.5 MPa is injected into the deep hole of the upper mold and the lower mold through the gas pipe. The liquid (such as water with a concentration of not less than 1‰ of detergent, washing powder, etc.) that can produce bubbles is sprayed on the surface of the bottom of the upper mold and the lower mold, all the lightening cavities, the surrounding planes (including the plug weld), and the cavity, etc. Visual inspection is performed to check whether bubbles are generated. If no bubbles are generated on all surfaces within a time of not less than 5 minutes, it is determined that the air tightness of the upper mold and the lower mold is qualified.

[0072] Step S7.1. Leak point marking

[0073] If bubbles are generated during the air tightness detection, the bubble generation position (i.e. the air leakage defect point) is marked with a marker.

[0074] Step S7.2. Weldability determination

[0075] According to the above marking, the weldability of the gas leakage defect is determined by drilling a hole at the gas leakage point, the hole diameter is 5-10 mm, the hole depth is 5-8 mm, the defect characteristics in the hole are visually judged and corresponding treatment is made; if the hole is a gas hole without loose structure, the gas leakage point is repaired by the welding method of step S6, and the gas tightness test is performed again; if the hole is a loose structure, the casting is directly scrapped.

[0076] Step S7.3. Casting scrapping and remaking

[0077] Before the casting is scrapped and remaked, the cause of the loose structure is analyzed, and a new method for improving the performance of the casting structure is developed, such as reducing the wall thickness of the loose part of the casting, adjusting the position and number of the pouring and runner.

[0078] In this embodiment, the upper mold and the lower mold are subjected to gas tightness test in the above manner, and whether the gas tightness is qualified and whether the casting needs to be scrapped are determined.

[0079] Step S8. Cavity finishing

[0080] The reference hole is located on the mold, and the cavity is finished, which requires that the excess amount is removed ≤0.5 mm, the roughness Ra is ≤1.6 mm, and at the same time, a dot is marked at the center of each small hole.

[0081] In this embodiment, the upper mold and the lower mold are subjected to cavity finishing in the above manner.

[0082] Step S9. Small hole processing

[0083] The small holes are processed one by one by using electric spark, and the specific step flow is as follows: the gas pipe hole is blocked with cement, etc., to ensure that the gas pressure in the deep hole of the mold is not less than 1 atmosphere, the purpose is to prevent the electric spark processing liquid from quickly penetrating into the deep hole; prepare the electrode wire (its diameter is small hole diameter d-0.4 mm); surround the small hole center with about 10 mm high liquid storage tank with cement; after clamping the electrode and locating the small hole center mark point, add electric spark processing liquid in the oil tank, start processing the small hole; when it is found that the small hole is processed in place, immediately press the pause key of the electric spark machine tool, keep the electrode position unchanged, remove the cement as soon as possible, clean up the remaining processing liquid; finally, start the power supply, lift the electrode out of the small hole, and block the small hole with clean cement (the purpose is also to ensure that the gas pressure in the deep hole of the mold is not less than 1 atmosphere, to prevent the electric spark processing liquid from quickly penetrating into the deep hole), that is, the processing of one small hole is completed; in this way, the processing of all small holes is completed.

[0084] In this embodiment, the small hole is processed in place means that the small hole is processed through.

[0085] In the present embodiment, both the upper die and the lower die are subjected to the small hole processing in the above-described manner.

[0086] Step S10. Cavity polishing

[0087] Residual liquid in the deep hole is removed by compressed air or the like, and the small hole is blocked by mastic; then, the entire profile is polished, and the roughness of the cavity after polishing is required to be ≤0.4 μm.

[0088] In the present embodiment, both the upper die and the lower die are subjected to the cavity polishing processing in the above-described manner.

[0089] Step S11. Cavity detection

[0090] The cavities of the upper die and the lower die are measured by a measuring machine, respectively, to meet the requirement of a tolerance of ±0.1 mm.

[0091] In the present embodiment, both the upper die and the lower die are subjected to the cavity detection in the above-described manner.

[0092] Step S12. Die assembly

[0093] The non-working surface burrs, sharp edges, and sharp corners of each part are removed, and then the guide plates and the positioning pins are assembled, and finally the die figure number is marked, and the like.

[0094] In the present embodiment, both the upper die and the lower die are subjected to the die assembly in the above-described manner.

[0095] Step S13. Die trial

[0096] A low-cost and rapid method is adopted to remove the cutting fluid residues on the surface of the die cavity and in the deep hole, and to verify the air tightness of the die, the machine tool, and the gas source pipeline connection, and the like. The specific process is as follows: the machined die is placed into a heating furnace of a hot press, wherein the upper die is arranged on an upper working platform of the machine tool, and the lower die is arranged on a lower working platform of the machine tool, and both the upper die and the lower die need to be fixedly connected with a carbon dioxide cylinder (the pressure in the cylinder is ≥0.5 Mpa) and a gas source pipeline; the upper working platform is lifted together with the upper die by at least 200 mm in height; the die is heated, and is kept at an environment of 200±20℃ for 1 h to let the residual cutting fluid completely volatilize; a 1-layer aluminum plate with the same outer dimensions as the titanium alloy part plate blank and a thickness of 1 mm is placed on the lower die; the upper die is lowered to apply a pressure of 50-100 tons to the aluminum alloy plate; the cylinder is opened to charge the upper die and the lower die with air, and if the pressure value of the pressure gauge of the cylinder decreases by ≤0.1 Mpa after 60 minutes, it is determined that the die air tightness is qualified.

[0097] Step S14. Qualified delivery

[0098] After all the above processes are completed and are qualified, it is proved that the die is qualified, and can be used for production.

[0099] The above is only the preferred embodiment of the present application, and does not hinder the present application in any form, and any simple modification or equivalent change of the above embodiment according to the technical essence of the present application falls within the protection scope of the present application.

Claims

1. A method for manufacturing a titanium alloy superplastic forming / diffusion bonding die, characterized in that: The mold manufacturing method first performs mold casting inspection, and then sequentially performs thermal surface treatment, reference plane machining, deep hole machining, cavity rough machining, mold welding, airtightness inspection, cavity finishing, small hole machining, cavity polishing, cavity inspection, mold assembly and mold trialing on the mold casting, and finally completes the molding and manufacturing of the entire mold; If the air tightness of the casting is found to be unqualified during the air tightness test, the leakage point of the casting will be marked and the weldability of the leakage point will be determined. If it is determined that the air tightness of the casting can be guaranteed by welding, the mold casting will be welded and the air tightness test will be carried out again. If it is determined that the air tightness of the casting cannot be guaranteed by welding, the casting will be scrapped and a new blank will be made.

2. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The mold casting inspection includes: visually inspecting the casting and inspecting it with common measuring tools. During the inspection process, if there are no visible cracks, looseness or penetrating defects on the entire surface of the casting, and the minimum allowance of the machined surface is 5mm and the maximum allowance is 10mm, then the casting is suitable for mold manufacturing. Otherwise, the casting is discarded.

3. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The thermal surface treatment includes: placing the casting in an annealing furnace for annealing at a heating rate of 40 to 80°C / h, then keeping the temperature at 980±20°C for 3 to 4 hours, and then cooling it to below 200°C before taking it out of the furnace. After the mold casting cools to room temperature, a shot blasting process is used to remove all surface oxide scale and sand.

4. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The reference plane processing includes: processing the bottom surface of the mold, first processing according to the minimum allowance of 5mm, if the flatness is ≤0.05mm and the roughness Ra is ≤0.8μ, no further processing is performed; if the flatness and roughness do not meet the requirements, processing needs to be continued, but the maximum processing allowance does not exceed 10mm.

5. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The deep hole processing includes: using a deep hole drill to drill deep holes in the casting. When drilling, first align the outer shape of the mold to determine the cross center line, use this cross center line as the reference in the X and Y directions, and use the bottom surface after the reference plane is processed as the Z direction reference, and then drill the mold; after the drilling is completed, the center axis position accuracy of each deep hole is less than 0.2mm, the straightness is less than 0.5mm / m, the aperture deviation is ±0.5mm, and the roughness Ra is not greater than 6.4μm; at the same time, the temperature measuring hole of the mold is processed to the size required by the digital model, and the roughness Ra is not greater than 6.4μm.

6. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The cavity rough machining includes: during machining, using the cross center line of the deep hole machining process as the reference in the X and Y directions, and using the bottom surface after machining the reference plane as the reference in the Z direction, first machining according to the minimum allowance of 5mm, if the molding surface has reached the requirement of no visual defects and the roughness Ra has reached ≤3.2μm, no further machining will be performed; if the surface quality and roughness do not meet the above requirements, the allowance value for continued machining will be determined according to the depth value of the defect, and the maximum machining allowance cannot exceed 15mm in total; at the same time, the guide groove, positioning pin hole and removal groove of the mold are machined to the size required by the digital model, with a roughness Ra≤1.6μm.

7. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The welding includes welding the deep hole plug and the air pipe joint of the mold; during welding, first remove the iron filings and oil stains in the deep hole, then grind the surface of the welding area at both ends of the deep hole to expose the main body of the metal substrate of the mold casting, then use a cleaning agent to clean the surface of the welding area, press the deep hole plug at both ends of the deep hole of the mold and press the air pipe joint at the air outlet of the mold, finally use a welding rod with a temperature resistance of not less than 1000°C and a thermal expansion coefficient the same as that of the substrate to firmly weld the deep hole plug and the air pipe joint to the mold to meet the airtightness requirements.

8. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The airtightness test includes: injecting 1-1.5Mpa high-pressure gas into the deep hole through the air pipe, spraying a bubble-generating liquid on the bottom plane of the mold, all lightening cavities, surrounding planes and the cavity, and visually checking whether bubbles are generated; if no bubbles are found on all surfaces within a time of not less than 5 minutes, the airtightness of the mold is judged to be qualified, otherwise it is unqualified.

9. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: When finishing the cavity, the removal allowance is ≤0.5mm, the roughness is ≤Ra1.6, and a dot is made at the center of each small hole for marking.

10. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The small hole processing includes: preparing an electrode wire, and surrounding a 10 mm high liquid storage tank with clay around the center of the small hole at a distance of 10 mm; after clamping the electrode and aligning the center mark point of the small hole, adding electric spark machining fluid into the oil storage tank and starting to process the small hole; when it is found that the small hole is processed in place, pressing the pause button of the electric spark machine tool, keeping the electrode wire in place, removing the clay and cleaning up the remaining machining fluid; finally, starting the power supply, lifting the electrode out of the small hole, and sealing the small hole with clean clay; repeating the above steps until all the small holes are processed.

11. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The cavity polishing includes: using compressed air to clear the residual liquid in the deep hole, then sealing the small hole with clay, and finally polishing the entire surface of the mold. After polishing, the cavity roughness Ra is less than or equal to 0.4 μm.

12. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The cavity detection includes: using a measuring machine to measure the cavities of the upper mold and the lower mold respectively, and meeting the tolerance requirement of ±0.1mm.

13. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The mold assembly includes: removing burrs, sharp edges and corners from the non-working surface of the mold, assembling the guide plate and positioning pins, and marking the mold drawing number.

14. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The mold trial comprises: firstly placing the mold into the heating furnace of the hot press, and connecting the upper mold and the lower mold to the upper and lower working platforms of the machine tool, as well as the carbon dioxide cylinder and the gas source pipeline respectively; raising the upper working platform together with the upper mold to a height of at least 200 mm; heating the mold and keeping it warm at 200±20°C for 1 hour; placing a layer of aluminum plate with the same external dimensions as the titanium alloy part sheet blank and a thickness of 1 mm on the lower mold; lowering the upper mold and applying a pressure of 50-100 tons to the aluminum alloy sheet; opening the carbon dioxide cylinder to inflate the upper mold and the lower mold respectively, and if the pressure value of the cylinder pressure gauge drops by ≤0.1Mpa after 60 minutes, the mold is judged to be qualified for airtightness, otherwise it is unqualified.

15. The method for manufacturing a titanium alloy superplastic forming / diffusion bonding die according to claim 1, characterized in that: The determination of the weldability of the leak point includes: drilling a hole at the leak point with a hole diameter of 5-10 mm and a hole depth of 5-8 mm, visually determining the defect characteristics in the hole and making corresponding treatment; if the hole is a pore and there is no loose structure, welding repair is performed and airtightness testing is performed again; if the hole is a loose structure, the casting is scrapped.

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