A precision machining and deformation control process method for titanium alloy slender shaft before plating

Abstract

The application provides a titanium alloy slender shaft precision machining and deformation control process method before plating, and belongs to the technical field of titanium and titanium alloy part manufacturing, and steps include: preparing a die forging blank, making a tailstock hole, rough turning, semi-finish turning, heat treatment, hot correction, repairing the tailstock hole, finish turning, grinding, secondary heat treatment, size detection and fluorescence inspection. After semi-finish turning, the application eliminates uneven removal of the die forging allowance, or stress sensitivity of the material itself, and residual stress existing in the material itself through a heat treatment process, so that the influence of residual stress on deformation of weak stiffness parts is reduced or eliminated. After rough turning, the application increases heat treatment annealing, effectively releases residual stress, reduces deformation amount during finish machining, and greatly improves the first-time pass rate. Meanwhile, when the deformation is large during the slender shaft machining process, the application also corrects through a newly designed hot correction tooling, and further improves the pass rate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium and titanium alloy part manufacturing, and relates to a titanium alloy slender shaft precision machining and deformation control process method before plating. BACKGROUND

[0002] Titanium alloy has the characteristics of high specific strength, high strength, good corrosion resistance, large chemical activity, poor thermal conductivity and small elastic modulus, and is widely used in many industries such as aviation, aerospace, petroleum, chemical industry, medical treatment and shipbuilding, and is especially suitable for harsh climate environments such as high temperature and high pressure. In the processing of titanium alloy, the fiber structure of the titanium alloy die forging part is consistent with the die forging shape, and the metal flow line is complete, so the titanium alloy die forging part has higher comprehensive mechanical properties. However, the processability of titanium alloy is poor, the tensile strength at room temperature is high, the stamping property and the cutting machinability are poor, and it is difficult to process. When cutting, because the elastic modulus ratio is about one half of that of stainless steel, the toughness is high, and in the cutting process, phenomena such as severe friction and adhesion are easily generated, the cutting process is high in heat, and the thermal stress generated is large, so higher requirements are put forward for the size and shape control of the part.

[0003] In addition, when the titanium alloy die forging part is processed, because the die forging part has the problems of large deformation in the forging process and large clamping error of the die forging part, the processing characteristics of the die forging part are different from those of the bar material. When turning, the metal allowance of the die forging part is removed in a very uneven radial direction, which will cause the stress to rebalance due to the uneven removal of the metal inside after cutting, so that the part is deformed. Especially when processing titanium alloy slender shaft products, such as TC18 titanium alloy die forging material, the material is very sensitive to high strain, and the residual stress generated causes the deformation of the part to be unable to be effectively controlled, resulting in the processing of the finished product being scrapped, which seriously affects the delivery schedule of the product. In view of this, a titanium alloy slender shaft precision machining and deformation control process method before plating is needed to solve the deformation problem in the processing of titanium alloy. SUMMARY

[0004] The purpose of the present application is to provide a titanium alloy slender shaft precision machining and deformation control process method before plating. Through the method adopted in the present application, the problems of precision machining deformation and heat treatment deformation of titanium alloy die forging slender shafts and other weak stiffness materials can be solved.

[0005] A titanium alloy slender shaft precision machining and deformation control process method before plating, the part is a slender stepped shaft part, which is composed of four sections, in turn a1 section, a2 section, a4 section and a3 section, wherein the outer diameter of a1 section and a3 section is the same and the smallest, the outer diameter of a4 section is the largest, the outer diameter of a2 section is between a1 section and a4 section, a2 section is grooved and chamfered, the end of a1 section and a3 section is threaded, a4 section is ear piece, a1 section and a2 section are connected, and the workpiece before plating is provided with column m and column n with a center hole at both ends; the process method comprises the following steps:

[0006] Step 1, preparing the die forging blank: because the die forging has dense structure and excellent mechanical properties, in order to ensure the mechanical properties such as structural strength of the slender shaft part, the die forging blank is used for cutting processing, the die forging blank is a four-section stepped shaft corresponding to a1 section, a2 section, a4 section and a3 section, wherein the outer diameter of the die forging blank a4 section is the same as that of the part a4 section, and the single side allowance of other sections is not less than 3mm.

[0007] Step 2, making the center hole: clamping the die forging blank a2 section, making column m and column n at the ends of a1 section and a3 section, and then making the center hole at the end of column m and column n.

[0008] Step 3, rough turning: rough turning the outer circle of a1 section and a2 section, leaving a margin of 1mm; then rough turning the outer circle of a3 section, leaving a margin of 1mm.

[0009] Step 4, semi-finish turning: clamping the die forging blank with one clamp and one top, turning the outer circle of a1 section, a2 section and a3 section, leaving a margin of 0.5mm, at the same time, milling the groove, chamfer, thread, ear piece and relief groove to the final size to obtain the semi-finish turning blank; the one clamp and one top mode is that when turning a1 section and a2 section, clamping a3 section and topping the center hole at the end of column m, when turning a3 section, clamping a2 section and topping the center hole at the end of column n.

[0010] Step 5, heat treatment: vertically placing the semi-finish turning blank on the heat treatment tooling, performing incomplete annealing to eliminate the residual stress generated during processing, so that the stress and strain are released, and the subsequent precision machining deformation is not controlled; the heat treatment is divided into two stages of heating, the first stage is 450±10℃, the holding time is 25-35min, the second stage is 600-680℃, the holding time is 60-120min, after holding, the blank is taken out after furnace cooling to obtain the heat treated blank, the pressure during heat treatment is P≤6.66MPa.

[0011] The heat treatment tooling includes a hole positioning plate 1, a column 2, a base 3 and a fastening nut 4; the hole positioning plate 1 and the base 3 are supported by the column 2 to form an overall frame of the heat treatment tooling, wherein the column 2 is fixedly connected to the hole positioning plate 1 by the fastening nut 4, and the hole positioning plate 1 and the base 3 are uniformly provided with a plurality of through holes, and the hole spacing is not less than the rotary radius of the semi-finish machining blank, in order to ensure that the semi-finish machining blank maintains a vertical state during the heat treatment process, the hole diameter of the hole in the hole positioning plate 1 is in clearance fit with the outer diameter of the a3 section of the semi-finish machining blank, and the hole diameter of the hole in the base 3 is in clearance fit with the outer diameter of the final size of the a3 section of the elongated shaft part, so as to ensure the positioning accuracy; in use, the a3 section of the semi-finish machining blank is inserted into the hole of the hole positioning plate 1 downwards until the stepped surface of the a3 section and the a4 section is in contact with the upper surface of the hole positioning plate 1.

[0012] Step 6, heat correction: for the heat treatment blank whose deformation exceeds the grinding allowance, a shape correction tooling is used to perform heat correction under the same conditions as step 5, to obtain a corrected blank.

[0013] The shape correction tooling includes a U-shaped groove support plate 5, a U-shaped groove pressing plate 6, an arc-shaped pad 7, a pressing column 8 and a screw 9; the U-shaped groove support plate 5 and the U-shaped groove pressing plate 6 are basically the same in structure, and both have a through groove along the length direction, and left and right protrusions are arranged at both ends of the through groove, a left U-shaped groove 61 is arranged at the top of each left protrusion, and a right U-shaped groove 62 is arranged at the top of each right protrusion, the U-shaped groove pressing plate 6 is arranged above the U-shaped groove support plate 5, the heat treatment blank to be corrected is arranged between the two, the two left U-shaped grooves 61 and the two right U-shaped grooves 62 are matched respectively to clamp the a1 section and the a3 section of the heat treatment blank to be corrected, the U-shaped groove support plate 5 and the U-shaped groove pressing plate 6 are pressed by the screw 9 to clamp the heat treatment blank to be corrected; a deep cavity 63 is arranged in the middle of the U-shaped groove pressing plate 6, which is a rectangular groove, used to avoid the a4 section of the heat treatment blank to be corrected, the deep cavity 63 is hollowed in the groove, and the corresponding position of the U-shaped groove support plate 5 is also hollowed to avoid the ear, a threaded hole is arranged at the bottom of the deep cavity 63 of the U-shaped groove pressing plate 6, the pressing column 8 is screwed into the threaded hole and applies a pressing force to the a4 section of the heat treatment blank to be corrected to correct the deformation, and the arc-shaped pad 7 is arranged between the pressing column 8 and the heat treatment blank to be corrected to prevent damage to the surface of the workpiece.

[0014] Before correction, the highest deflection point of the heat-treated workpiece to be corrected is marked by an optical measuring device, and the correction size is calculated; the heat-treated workpiece to be corrected is placed on the U-shaped groove support plate 5, the a1 section and the a3 section are respectively placed into the left U-shaped groove 61 and the right U-shaped groove 62, the U-shaped groove pressing plate 6 is covered, the highest deflection point is directed to one side of the downward pressing column 8, the screw 9 is tightened to clamp the heat-treated workpiece to be corrected, the downward pressing column 8 is twisted to apply a pressing force, and during the downward pressing process, the downward pressing amount of the top surface of the downward pressing column 8 is calibrated by using a micrometer, and when the downward pressing amount reaches the correction size, the heat correction preparation work is completed, and the heat correction is performed on the heat-treated workpiece to be corrected together with the correction tool.

[0015] Step 7, repair the center hole: the heat-treated workpiece after step 5 or the corrected workpiece after step 6 is placed on the lathe according to the clamping method for manufacturing the center hole, and the center hole at both ends is repaired again to avoid the coaxial error caused by the deformation of the center hole during grinding.

[0016] Step 8, finish machining: the part after step 7 is subjected to finish machining by using the double-end center hole double-top method, leaving a 0.3mm grinding allowance to ensure the coaxiality.

[0017] Step 9, grinding: the double-end center hole double-top method is used to sequentially perform rough grinding and fine grinding on the grinder to the pre-plating size, and the pre-plating workpiece is obtained.

[0018] Step 10, secondary heat treatment: the pre-plating workpiece a3 section is vertically inserted into the hole in the heat treatment tool base 3, and the pre-plating workpiece is subjected to stress relief annealing according to the heat treatment method of step 5 to eliminate the stress generated during grinding and prevent cracks after plating.

[0019] Step 11, size detection and fluorescent inspection: the geometric size of the pre-plating workpiece after heat treatment in step 10 is detected, and the surface is subjected to fluorescent inspection after cleaning to determine whether micro cracks are generated, and if cracks or out-of-tolerance occur, the workpiece is scrapped.

[0020] Further, in step 2, the depth of the center hole is not less than 2mm, and the surface roughness is not less than Ra3.2.

[0021] Further, in step 5, the heat treatment process uses a vacuum pressure furnace.

[0022] Further, in step 5, to prevent oxidation of the titanium alloy surface during heat treatment, the semi-finish machining workpiece is completely buried with titanium chips.

[0023] Further, in step 5, the temperature of the second stage of heat treatment is 640℃, and the holding time is 90min.

[0024] Further, in step 7, if the length allowance of the part raw material is sufficient, the original top hole is cut off and a new top hole is made to ensure the coaxiality during clamping during grinding.

[0025] Further, in step 8, the rotation speed and cutting depth should not be too high, and the optimal rotation speed is 640 r / min, the cutting depth is 0.05, the feed rate is 0.1-0.15 mm / min, and the clamping force is 120-180 N, so as to ensure that the deformation amount is controllable.

[0026] Further, in step 8, the tool tip roundness R used is not greater than 0.2 mm.

[0027] Further, the process method is used for machining of the titanium alloy slender shaft of TC18.

[0028] Further, for the slender shaft made of titanium alloy material which is not sensitive to residual stress, steps 5 and 6 are omitted.

[0029] The beneficial effects of the present application are as follows:

[0030] 1. The qualified rate of the workpiece is improved. The present application selects a reasonable machining scheme of the TC18 titanium alloy slender shaft, and increases the heat treatment annealing after rough turning, effectively releases the residual stress, reduces the deformation amount during finishing, and can greatly improve the one-time machining qualified rate of the slender shaft. At the same time, when the deformation of the slender shaft is large during machining, the heat correction tooling can be used for correction, and the qualified rate of the finished product is further improved.

[0031] 2. The heat treatment tooling and the orthopedic tooling used in the present application have simple structure, are easy to manufacture, and are easy to operate, and have low cost, and are suitable for mass production. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 Flow chart of the precision machining and deformation control process method for the titanium alloy die forging slender shaft before plating

[0033] Figure 2 The figure is a structural schematic diagram of the titanium alloy slender shaft part, wherein a1, a2, a4 and a3 are four sections of the titanium alloy slender shaft part, m and n are columns arranged at two ends of the titanium alloy slender shaft part, H is the total length of the part, L1 is the length of the a1 section, L2 is the length of the a2 section, and L3 is the length of the a3 section.

[0034] Figure 3 It is a clamping and tooling schematic diagram during heat treatment, wherein (a) is an elevation view, and (b) is a plan view.

[0035] Figure 4 It is a heat treatment correction method and tooling schematic diagram, wherein (a) is an A-A sectional view, and (b) is a plan view.

[0036] Figure 5 Fig. 1 is a schematic view of a raw material structure of a die forging.

[0037] Figure 6 Fig. 1 is a schematic view of a raw material structure of a die forging.

[0038] Fig. 1 is a schematic view of a raw material structure of a die forging. DETAILED DESCRIPTION

[0039] The technical solutions of the present application will be described below clearly and completely. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all other embodiments improved or adjusted by those skilled in the art belong to the protection scope of the present application.

[0040] The precision machining of the elongated stepped shaft will be described below as an example:

[0041] Referring to Figure 2 The material of the elongated shaft part involved in the embodiment is aviation titanium alloy TC18, and the main structure is as follows: the whole is a four-segment stepped shaft, sequentially being a1 segment, a2 segment, a4 segment and a3 segment, the length L1 of the a1 segment is 60 mm, the length L2 of the a2 segment is 50 mm, the length L3 of the a3 segment is 76 mm, the total length H is 200 mm, the middle part has four-segment stepped shaft, the outer diameters of the a1 segment and the a3 segment are the same and the smallest, the outer diameter of the a4 segment is the largest, the outer diameter of the a2 segment is between that of the a1 segment and that of the a4 segment, the a2 segment is provided with a groove and a chamfer, the end of the a1 segment and the a3 segment is provided with a thread, the a4 segment is provided with an ear, and the a1 segment and the a2 segment are provided with a tool withdrawal groove, the workpiece before plating is also provided with a column m and a column n with a center hole at both ends, and the total length is 210 mm. The size precision of the elongated shaft part before plating is high, and the size precision of the a1 segment, the a2 segment and the a3 segment before plating is respectively the runout is ≤0.05 mm, and the roughness is ≤0.4. Since the size precision and the surface roughness are high, and the structure is an elongated shaft, the bending deformation resistance is weak, and the machining is easy to deform.

[0042] In order to ensure the size and surface roughness, when machining the titanium alloy slender shaft, the turning process is used to remove large excess, and the grinding process is used to improve the size accuracy and surface smoothness of the slender shaft through precise grinding. At the same time, since the material is TC18 material of a die forging, in order to ensure that the bending amount of the part is within an acceptable range during the machining process and after the grinding is completed, i.e. to meet the runout of 0.05mm, after semi-precision turning, the heat treatment process is used to eliminate the uneven removal of the excess of the die forging, or the stress sensitivity of the material itself, and the residual stress of the material itself, so as to reduce or eliminate the influence of the residual stress on the deformation of the weak stiffness part.

[0043] The titanium alloy slender shaft precision machining and deformation control process method before plating has a flow chart as shown in Figure 1 The method comprises the following steps:

[0044] Step 1, preparing a die forging blank: in order to ensure the mechanical properties such as structural strength of the slender shaft part, the die forging blank is used for cutting, as shown in Figure 6 The die forging blank is a four-section stepped shaft, which corresponds to the a1 section, the a2 section, the a4 section and the a3 section of the part respectively. The outer diameter of the a4 section of the die forging blank is the same as that of the a4 section of the part, and the single-sided excess of the other sections is not less than 3mm. Since the material is a die forging blank, in order to ensure that there is machining allowance under the die forging deformation, the single-sided excess of the slender shaft is not less than 3mm.

[0045] Step 2, making a center hole: the die forging blank a2 section is clamped by three jaws on the lathe, columns m and n are made at the ends of the a1 section and the a3 section respectively, and a center hole is made at the ends of the columns m and n. When the center hole is machined, it must be deep enough and have good smoothness. The depth of the center hole is not less than 2mm, and the roughness is better than Ra3.2.

[0046] Step 3, rough turning: in order to ensure the turning accuracy, the rough turning and the finish turning are separated to remove the excess. In the rough turning stage, the die forging is removed by a large excess, the outer circles of the a1 section and the a2 section are turned to 9mm and 13mm respectively, and the excess is about 1mm; the outer circle of the a3 section is turned to 9mm, and the excess is about 1mm.

[0047] Step 4, semi-finish turning: a one-clamp-one-center method is used to finish turning the outer circles of the a1 section, the a2 section and the a3 section to and respectively, with an excess of more than 0.5mm. The one-clamp-one-center method is that when turning the a1 section and the a2 section, the a3 section is clamped and the center hole at the end of the column m is centered, and when turning the a3 section, the a2 section is clamped and the center hole at the end of the column n is centered. The milling grooves, chamfers, threads, lugs and relief grooves and other features on the slender shaft part are all machined during the semi-finish turning process, so that the residual stress is fully released, and the semi-finish turning blank is obtained.

[0048] Step 5, heat treatment: after semi-finishing machining, most of the excess of the semi-finishing blank is removed, the residual stress value reaches the maximum, and the residual stress existing during machining or in the part itself is eliminated by incomplete annealing, so that the stress is released, the slender shaft is fully deformed, and deformation is prevented during subsequent precision machining; the semi-finishing blank is vertically placed on the heat treatment tooling, and is placed in a vacuum pressure furnace for incomplete annealing; the heat treatment is divided into two stages of heating; the first stage is 450±10℃, and the holding time is 30min; the second stage is 640℃, and the holding time is 90min; after holding, the furnace is cooled and taken out, to obtain a heat treated blank; the furnace pressure during heat treatment is P≤6.66MPa; in order to prevent the degree of oxidation of the titanium alloy surface from being reduced during heat treatment, the semi-finishing blank is completely buried with titanium chips.

[0049] The heat treatment tooling as shown in Figure 3 , including a hole positioning plate 1, a column 2, a base 3 and a fastening nut 4; the hole positioning plate 1 and the base 3 are supported by the column 2 to form an overall frame of the heat treatment tooling, wherein the column 2 is fixedly connected to the hole positioning plate 1 by the fastening nut 4, and the hole positioning plate 1 and the base 3 are respectively and uniformly provided with a plurality of through holes, and the hole spacing is not less than the rotation radius of the semi-finishing blank; in order to ensure that the semi-finishing blank maintains a vertical state during heat treatment, the hole diameter of the hole in the hole positioning plate 1 is in clearance fit with the outer diameter of the a3 section of the semi-finishing blank, and the hole diameter of the hole in the base 3 is in clearance fit with the outer diameter of the final size of the a3 section of the slender shaft part, so as to ensure positioning accuracy; in use, the a3 section of the semi-finishing blank is inserted into the hole of the hole positioning plate 1 downward until the stepped surface of the a3 section and the a4 section contacts the upper surface of the hole positioning plate 1.

[0050] Step 6, after the incomplete annealing is completed, the residual stress is basically eliminated through detection, and the warping deformation of the part changes, generally increases; when the deformation of the heat treated blank is larger than the grinding allowance of 0.5mm, subsequent machining cannot be performed due to the large deformation, and heat correction is required; the heat correction is performed by using the straightening tooling as shown in Figure 4 and Figure 5 , and the same conditions as step 5 are used to obtain a corrected blank.

[0051] The orthopedic tooling includes a U-shaped groove support plate 5, a U-shaped groove pressing plate 6, an arc-shaped pad 7, a pressing column 8 and a screw 9; the U-shaped groove support plate 5 and the U-shaped groove pressing plate 6 are basically the same in structure, both have through grooves along the length direction, both ends of the through grooves are provided with left and right protrusions, the top of the two left protrusions is provided with a left U-shaped groove 61, the top of the two right protrusions is provided with a right U-shaped groove 62, the U-shaped groove pressing plate 6 is arranged above the U-shaped groove support plate 5, the heat treatment workpiece to be corrected is arranged between the two, the two left U-shaped grooves 61 and the two right U-shaped grooves 62 are matched respectively for clamping the heat treatment workpiece to be corrected a1 and a3, the U-shaped groove support plate 5 and the U-shaped groove pressing plate 6 are pressed by the screw 9 to realize the clamping of the heat treatment workpiece to be corrected; the middle part of the U-shaped groove pressing plate 6 is provided with a deep cavity 63 which is a rectangular groove for avoiding the heat treatment workpiece to be corrected a4, the deep cavity 63 is hollowed in the groove, the corresponding position of the U-shaped groove support plate 5 is also hollowed for avoiding the ear, the bottom of the deep cavity 63 of the U-shaped groove pressing plate 6 is provided with a threaded hole, the pressing column 8 is screwed into the threaded hole and applies a pressing force to the heat treatment workpiece to be corrected a4 to realize the deformation correction, the arc-shaped pad 7 is arranged between the pressing column 8 and the heat treatment workpiece to be corrected to prevent damage to the surface of the workpiece.

[0052] Before correction, the highest deflection point of the heat treatment workpiece to be corrected is marked by using an optical measuring device, and the correction size is calculated; the heat treatment workpiece to be corrected is arranged on the U-shaped groove support plate 5, a1 and a3 are arranged in the left U-shaped groove 61 and the right U-shaped groove 62 respectively, the U-shaped groove pressing plate 6 is covered, the highest deflection point is directed to the side of the pressing column 8, the screw 9 is tightened to clamp the heat treatment workpiece to be corrected, the pressing column 8 is twisted to apply a pressing force, during the pressing process, the pressing amount of the top surface of the pressing column 8 is calibrated by using a dial gauge, when the pressing amount reaches the correction size, the heat correction preparation work is completed, and the orthopedic tooling with the heat treatment workpiece to be corrected is subjected to heat correction treatment.

[0053] Step 7, repair the center hole: the heat treatment workpiece after step 5 or the corrected workpiece after step 6 is repaired on the lathe according to the clamping mode of the center hole to repair the center hole of both ends to avoid the coaxiality error caused by the deformation of the center hole during grinding. When the allowance of the die forging part is sufficient, the original center hole is cut off and a new center hole is made. The purpose is that after heat treatment, the left and right center holes are not coaxial, and the coaxiality error will be transmitted to the grinding process. Therefore, the center hole needs to be re-made to ensure the coaxiality of grinding.

[0054] Step 8, finish machining: the part after step 7 is finish machined by using the modified two-end top hole double top method, leaving 0.3mm grinding allowance, the double top clamping force should not be too large, the clamping force is 150N, at the same time, considering that the structure is eccentric structure, the centrifugal force will increase when rotating at high speed, therefore, the rotating speed is selected as 620r / min, the cutting depth is 0.12mm, the feed amount is 0.12mm, the selected tool tip corner is less than R0.2, the a1 section and the a2 section are finish machined to and leaving allowance greater than 0.2mm, the a3 section is finish machined to

[0055] Step 9, grinding: the two-end top hole double top method is used to sequentially perform rough grinding and finish grinding on the grinding machine to the pre-plating size, obtaining the pre-plating workpiece.

[0056] Step 10, secondary heat treatment: in order to avoid cracks caused by residual stress after subsequent plating and in the use process, it is necessary to perform incomplete annealing treatment again to eliminate the residual stress generated by grinding and prevent cracks after plating, the residual stress generated by grinding is much larger than the residual stress generated by turning; the a3 section of the pre-plating workpiece is vertically inserted into the hole on the heat treatment tool base 3, and the pre-plating workpiece is annealed according to the heat treatment method of step 5.

[0057] Step 11, size detection and fluorescent inspection: the geometric size of the pre-plating workpiece after heat treatment in step 10 is detected by precise detection equipment, and fluorescent inspection is performed after cleaning to check whether the surface of the part produces grinding microcracks, if cracks or out-of-tolerance, it is scrapped.

[0058] In addition, the above-mentioned elongated shaft part material is TC18 die forging, when the material of the part is TC2, steps 5 and 6 can be omitted, the reason is that TC18 material is more sensitive to stress than TC2 material.

[0059] The above-mentioned embodiments only express the implementation of the present application, but cannot be interpreted as limiting the scope of the patent of the present application, it should be pointed out that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which all belong to the protection scope of the present application.

Claims

1. A precision machining and deformation control process for a slender titanium alloy shaft before plating, wherein the part is a slender stepped shaft composed of four segments, namely a1, a2, a4, and a3, wherein... Segments a1 and a3 have the same and smallest outer diameter, segment a4 has the largest outer diameter, segment a2 has an outer diameter between segments a1 and a4, segment a2 has a groove and chamfer, segments a1 and a3 have threads at their ends, segment a4 has lugs, and a relief groove is formed at the junction of segments a1 and a2. Before plating, the workpiece also has pillars m and n with center holes at both ends; the process method is characterized by the following steps: Step 1, Prepare the blank for forging: The blank for forging is cut and machined. The blank for forging is a four-segment stepped shaft, corresponding to segments a1, a2, a4 and a3 of the part respectively. The outer diameter of segment a4 of the blank for forging is the same as that of segment a4 of the part. The single-side allowance of the other segments is not less than 3mm. Step 2, make center holes: hold the blank a2 section of the die forging, make column m and column n at the ends of a1 section and a3 section respectively, and then make center holes at the ends of column m and column n. Step 3, rough turning: rough turn the outer diameters of segments a1 and a2, leaving a 1mm allowance; then rough turn the outer diameter of segment a3, leaving a 1mm allowance. Step 4, Semi-finish turning: The forging blank is clamped using a clamping and supporting method. The outer diameters of sections a1, a2, and a3 are turned separately, leaving a allowance of 0.5mm. At the same time, the groove, chamfer, thread, lug, and relief groove are milled to the final dimensions to obtain the semi-finish turned blank. The clamping and supporting method is as follows: when turning sections a1 and a2, section a3 is clamped and supported on the center hole at the end of column m; when turning section a3, section a2 is clamped and supported on the center hole at the end of column n. Step 5, Heat Treatment: Place the semi-finished blank vertically on the heat treatment fixture for incomplete annealing; the heat treatment is divided into two stages of heating. The first stage is held at 450±10℃ for 25-35 minutes, and the second stage is held at 600-680℃ for 60-120 minutes. After holding, the blank is cooled in the furnace and then removed to obtain the heat-treated blank. The pressure during heat treatment is P≤6.66MPa. Step 6, thermal correction: For heat-treated raw materials whose deformation exceeds the grinding allowance, thermal correction is performed using a straightening fixture under the same conditions as in step 5 to obtain corrected raw materials. The straightening fixture includes a U-groove support plate 5, a U-groove pressure plate 6, an arc-shaped pad 7, a lower pressure column 8, and screws 9. The U-groove support plate 5 and the U-groove pressure plate 6 have essentially the same structure; both have through grooves along their length, with left and right protrusions at both ends of each groove. The tops of the two left protrusions each have a left U-groove 61, and the tops of the two right protrusions each have a right U-groove 62. The U-groove pressure plate 6 is placed above the U-groove support plate 5, and the heat-treated blank to be straightened is placed between them. The two left U-grooves 61 and the two right U-grooves 62 respectively cooperate to clamp sections a1 and a3 of the heat-treated blank to be straightened. The U-shaped groove support plate 5 and the U-shaped groove pressure plate 6 are clamped together by screws 9 to clamp the heat-treated blank to be corrected; the U-shaped groove pressure plate 6 has a deep cavity 63 in the middle, which is a rectangular groove to avoid the heat-treated blank a4 segment to be corrected. The deep cavity 63 has a hollowed-out groove, and the U-shaped groove support plate 5 also has a hollowed-out groove at the corresponding position to avoid the lugs. The bottom of the deep cavity 63 of the U-shaped groove pressure plate 6 has a threaded hole. The lower pressure column 8 is screwed into the threaded hole and applies downward pressure to the heat-treated blank a4 segment to be corrected to achieve deformation correction. An arc-shaped pad 7 is installed between the lower pressure column 8 and the heat-treated blank to be corrected to prevent damage to the surface of the workpiece. Before correction, mark the highest point of deflection of the heat-treated material to be corrected and calculate the correction dimension; place the heat-treated material to be corrected on the U-shaped groove support plate 5, and place the a1 section and the a3 section into the left U-shaped groove 61 and the right U-shaped groove 62 respectively. Cover with the U-shaped groove pressure plate 6, and turn the highest point of deflection towards the side of the lower pressure column 8. Tighten the screw 9 to clamp the heat-treated material to be corrected, and turn the lower pressure column 8 to apply the clamping force. Mark the lower pressure amount of the lower pressure column 8. After the lower pressure amount reaches the correction dimension, perform heat correction treatment together with the straightening fixture clamping the heat-treated material to be corrected. Step 7, Repair the center holes: Repair the center holes at both ends of the heat-treated blanks that have completed Step 5 or the straightened blanks that have completed Step 6 to avoid coaxiality errors. Step 8, finish turning: Use a double-center method with center holes at both ends to finish turn the part after step 7, leaving a grinding allowance of 0.3mm to ensure coaxiality; Step 9, Grinding: Use a double-point method with two center holes at both ends to perform rough grinding and fine grinding to the pre-plating size to obtain the pre-plating workpiece; Step 10, Secondary heat treatment: Place the pre-plating workpiece a3 vertically on the heat treatment fixture, and perform stress-relieving annealing on the pre-plating workpiece according to the heat treatment method in Step 5. Step 11, Dimensional Inspection and Fluorescence Inspection: The geometric dimensions of the workpiece before plating after heat treatment in Step 10 are inspected. After cleaning, a fluorescence inspection is performed to check whether micro-cracks are generated on the surface. If cracks or out-of-tolerance are found, the workpiece is scrapped.

2. The method for precision machining and deformation control of a slender titanium alloy shaft before plating according to claim 1, characterized in that, In step 2, the depth of the tip hole is not less than 2 mm and the surface roughness is not less than Ra3.

2.

3. The method for precision machining and deformation control of a slender titanium alloy shaft before plating according to claim 1, characterized in that, In step 5, the heat treatment fixture includes a perforated positioning plate 1, a column 2, and a base 3. The perforated positioning plate 1 and the base 3 are supported by the column 2 to form the overall frame of the heat treatment fixture. The perforated positioning plate 1 and the base 3 are each evenly arranged with several through holes. The spacing between the holes is not less than the turning radius of the semi-finished blank. The diameter of the hole on the perforated positioning plate 1 is clearance-fitted with the outer diameter of the semi-finished blank section a3. The diameter of the hole on the base 3 is clearance-fitted with the final outer diameter of the slender shaft part section a3.

4. The method for precision machining and deformation control of a slender titanium alloy shaft before plating according to claim 1, characterized in that, In step 5, the semi-finished blank is buried with titanium chips to avoid oxidation of the titanium alloy surface during heat treatment.

5. The method for precision machining and deformation control of a slender titanium alloy shaft before plating according to claim 1, characterized in that, In step 5, the temperature of the second stage of heat treatment is 640℃, and the holding time is 90min.

6. The method for precision machining and deformation control of a slender titanium alloy shaft before plating according to claim 1, characterized in that, In step 8, the rotational speed is 640 r / min, the cutting depth is 0.05 mm, the feed rate is 0.1-0.15 mm / min, and the clamping force is 120-180 N.

7. The method for precision machining and deformation control of a slender titanium alloy shaft before plating according to claim 1, characterized in that, In step 8, the fillet radius R of the lathe tool tip is no greater than 0.2mm.

8. A method for precision machining and deformation control of a slender titanium alloy shaft before plating, as described in any one of claims 1 to 7, characterized in that... The aforementioned process is used for machining slender titanium alloy shafts made of TC18 material.

9. A method for precision machining and deformation control of a slender titanium alloy shaft before plating, as described in any one of claims 1 to 7, characterized in that, For slender shafts made of titanium alloys that are insensitive to residual stress, steps 5 and 6 are omitted.

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