Drawing method of titanium base material

Abstract

To provide a drawing method of a titanium base material which can cope with problems such as breakage, cracks and wrinkles generated in each step of a molding process in the case of normal temperature molding.SOLUTION: A drawing method of a titanium base material pressing a titanium base material arranged between a die and a blank holder constituting a drawing mold against a punch, and drawing the titanium base material includes a first step of repeating a gap drawing step S101 of pressing the titanium base material against the punch while maintaining a fixed gap equal to or more than plate thickness of the titanium base material between the die and the blank holder, and a first pressure-drawing step S102 of pressing the titanium base material against the punch while adding a fixed wrinkle suppressing pressure between the die and the blank holder. The drawing method includes: a second step of repeating an arrangement direction rotation step S201 and a second pressure-drawing step S202; a third step including an outer peripheral part removing step S301 and a third pressure-drawing step S302; and a fourth step including a correcting step S401.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for drawing a titanium material. [Background technology]

[0002] Conventionally, when pure titanium and titanium alloys, which are classified as high-strength titanium materials, are plastically processed, they have poor ductility in the cold, with elongation significantly improving in the temperature range of 600°C to 900°C. For this reason, hot stamping, in which the material is heated to the desired processing temperature range, or press forming using an electric heating method have been common.

[0003] When designing molds for hot forming, it is necessary to start with a dimensional design that takes into account the thermal expansion coefficients of the mold and product, and then verify the validity of formability and dimensional quality that arise from various external factors during actual forming. In some cases, there is a risk of increased development costs and extended development times due to the need to re-cut the mold. In addition, when molds are used for many years, an oxide film (scale) that forms on the surface due to bonding with oxygen has a significant impact on product quality, so work is required to remove this. As such, hot forming can increase costs and extend development times in each process of design, manufacturing, and quality assurance.

[0004] In response to this, methods for drawing titanium alloys at low temperatures have been proposed. For example, Patent Document 1 describes an invention relating to a method for drawing titanium alloys in which the titanium alloy is heated to a temperature of 250°C or higher but lower than 400°C and processed, in which the titanium alloy is placed between a blank support material and a die, and a step of pressing the titanium alloy without drawing it and a step of drawing the titanium alloy with or without pressing it are repeated.

[0005] Furthermore, Patent Document 2 describes an invention relating to a method for drawing and ironing metal materials, in which drawing and ironing is performed at a low temperature of less than 400°C. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-059045 [Patent Document 2] Japanese Patent Publication No. 2021-041434 Summary of the Invention [Problem to be solved by the invention]

[0007] If room-temperature forming were possible in the drawing of titanium material, it would be possible to eliminate the increased costs and longer times involved in the design, manufacturing, and quality assurance processes of hot forming.However, in order to draw titanium material, which has poor ductility in cold forming, using room-temperature forming, it is necessary to prevent cracks, cracks, and wrinkles during the forming process, and it is also necessary to address the issues that arise at each stage of the forming process, from the early, middle, late, and final stages.

[0008] For example, when a cylindrical body 100 made of titanium and consisting of an upper surface 101 and vertical walls 102 as shown in Fig. 2 is drawn by room temperature forming, the following problems occur at each stage of the forming process. First, in the early stages of forming, there is a reduction in thickness and cracks in the shoulder rounded portion 103. Then, in the middle to late stages of forming, there are cracks and fractures caused by inflow wrinkles. Finally, in the final stages of forming, there are wrinkles and springback at the bottom end 104 of the vertical walls 102.

[0009] In contrast, the inventions described in Patent Documents 1 and 2 cannot address the issues that arise at each stage of the molding process, such as the early, middle, late, and final stages, and there is room for improvement.

[0010] The present invention solves the above-mentioned conventional problems and provides a method for drawing titanium material that can address issues such as cracks, fissures, and wrinkles that occur at each stage of the forming process when forming at room temperature. [Means for solving the problem]

[0011] In order to solve the above problems, the method for drawing a titanium material of the present invention is a method for drawing a titanium material in which a titanium material placed between a die and a blank holder that constitute a drawing mold is pressed against a punch to perform drawing, and is characterized by having a first process that repeats a gap drawing step in which the titanium material is pressed against the punch while maintaining a constant gap between the die and the blank holder that is equal to or greater than the thickness of the titanium material, and a first pressure drawing step in which the titanium material is pressed against the punch while applying a constant wrinkle suppression pressure between the die and the blank holder.

[0012] Preferably, the method is characterized by having a second process that repeats an arrangement direction rotation step of rotating the arrangement direction of the titanium material in the drawing die, and a second pressure drawing step of pressing the titanium material against the punch while applying a constant anti-wrinkle pressure between the die and the blank holder.

[0013] Preferably, the method further comprises a third process including an outer periphery removal step of removing the outer periphery of the titanium material at the wrinkle-holding surface formed by the die and the blank holder, and a third pressure squeezing step of pressing the titanium material against the punch while applying a constant wrinkle-holding pressure between the die and the blank holder.

[0014] Preferably, the method further comprises a fourth step including a step of correcting the lower end of the vertical wall of the titanium material. [Effects of the Invention]

[0015] The method for drawing a titanium material of the present invention involves pressing a titanium material, positioned between a die and a blank holder that constitute a drawing die, against a punch to perform drawing. The method includes a first step that repeats a gap drawing step and a first pressure drawing step. In the gap drawing step, the titanium material is pressed against the punch while maintaining a constant gap between the die and the blank holder that is equal to or greater than the thickness of the titanium material. This increases the amount of titanium material flowing toward the upper surface of the cylindrical body. In contrast, in the first pressure drawing step, the titanium material is pressed against the punch while applying a constant blank-holding pressure between the die and the blank holder. This reduces the amount of titanium material flowing toward the upper surface of the cylindrical body. In this way, by adjusting the amount of titanium material flowing in during the drawing process, it is possible to address thickness reduction and cracking at the shoulder R portion of the cylindrical body in the early stages of forming.

[0016] It is also preferable to have a second process that repeats a placement direction rotation step in which the placement direction of the titanium material in the drawing die is rotated, and a second pressure drawing step in which the titanium material is pressed against the punch while applying a constant anti-wrinkle pressure between the die and the blank holder. In the middle of forming, anti-wrinkle pressure is applied between the die and the blank holder, but uneven material flow can cause localized inflow wrinkles. Therefore, by performing pressure drawing while changing the placement direction of the titanium material, the material flow can be made uniform, suppressing the occurrence of localized wrinkles and addressing cracks and fractures caused by inflow wrinkles.

[0017] Furthermore, it is preferable to have a third process including an outer periphery removal step in which the outer periphery of the wrinkle-holding surface formed by the die and blank holder is removed from the titanium material, and a third pressure drawing step in which the titanium material is pressed against the punch while applying a constant wrinkle-holding pressure between the die and blank holder. In the later stages of forming, as the area of ​​the wrinkle-holding surface formed by the die and blank holder becomes smaller, variations in the wrinkle-holding pressure occur, resulting in uneven material flow. Therefore, by removing the outer periphery to create a uniform wrinkle-holding surface, the material flow is made uniform, suppressing the occurrence of localized wrinkles and addressing cracks and fractures caused by wrinkles.

[0018] It is also preferable to have a fourth process, which includes a step of straightening the lower end of the vertical wall of the titanium material. Near the drawing limit at the end of forming, inflow wrinkles that could not be suppressed tend to occur at the lower end of the vertical wall, and springback tends to occur after forming. Therefore, by straightening the lower end of the vertical wall of the titanium material, it is possible to deal with the occurrence of wrinkles and springback.

[0019] In this way, the present invention can provide a method for drawing titanium material that can address issues such as cracks, fissures, and wrinkles that occur at each stage of the forming process when forming at room temperature. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a process diagram of a method for drawing a titanium material according to an embodiment of the present invention. [Figure 2] FIG. 2A is a perspective view showing a cylindrical body, and FIG. 2B is a cross-sectional view taken along line AA. [Figure 3] FIG. 1 is an explanatory diagram of a first step. [Figure 4] FIG. 10 is an explanatory diagram of the second step. [Figure 5] FIG. 10 is an explanatory diagram of the third step. [Figure 6] FIG. 10 is an explanatory diagram of the fourth step. [Figure 7] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0021] Next, a method for drawing a titanium material according to an embodiment of the present invention will be described with reference to Figures 1 to 7. The method for drawing a titanium material according to this embodiment involves drawing a titanium material at room temperature to form a cylindrical body. In this embodiment, room temperature forming refers to forming within a temperature range of 5 to 35°C without forced heating or cooling.

[0022] 1 is a process diagram of the method for drawing a titanium material according to this embodiment. This method is composed of steps 1, 2, 3, and 4. Details of each step will be described later.

[0023] (Cylindrical body) 2 shows a cylindrical body 100 formed by this processing method, with (a) a perspective view and (b) a cross-sectional view taken along line AA. The cylindrical body 100 is cylindrical and comprises an upper surface 101 and a vertical wall 102. A shoulder R portion 103 that smoothly connects the outer periphery of the upper surface 101 and the upper end of the vertical wall 102 is formed at the boundary between them. The lower portion of the vertical wall 102 is open, forming a ring-shaped lower end portion 104.

[0024] Examples of titanium materials that can be used include pure titanium JIS types 1 to 4, and titanium alloys such as α-β titanium Ti-6Al-4V and β titanium Ti-15V-3Cr-3Sn-3Al. From the viewpoint of obtaining the effects of the present disclosure, pure titanium JIS type 4, which is classified as the highest strength, and titanium alloys such as Ti-6Al-4V, which are highly versatile, are preferred. The size of the cylinder 100 is preferably a minimum inner diameter of 270 mm, a maximum height of 70 mm, and a plate thickness of 0.5 to 1.0 mm.

[0025] When a cylindrical body 100 made of titanium material is drawn by room temperature forming, the following problems occur at each stage of the forming process. First, in the early stages of forming, there is a reduction in plate thickness and cracks in the shoulder R portion 103. Then, in the middle to late stages of forming, there are cracks and fractures caused by inflow wrinkles. Finally, at the final stage of forming, there are wrinkles and springback at the bottom end 104 of the standing wall 102.

[0026] (1st step) The first step is intended to address issues that arise in the initial stages of forming. As shown in Fig. 1, the first step involves repeating a clearance squeezing step S101 and a first pressure squeezing step S102. Fig. 3 is an explanatory diagram of the first step, including (a) a cross-sectional view showing the squeezing state in the clearance squeezing step S101 and (b) a cross-sectional view showing the squeezing state in the first pressure squeezing step S102.

[0027] As shown in Figure 3, a titanium blank 1 is placed between a die 11 and a blank holder 12 that make up a drawing die 10. A punch 20 is displaced relative to the drawing die 10 to press the titanium blank 1 against the punch 20, gradually forming an upper surface 101 and a vertical wall 102 of a cylindrical body 100. The punch speed is 2 to 7 mm / s, and it is preferable to switch from the first process to the second process once the forming of the shoulder R portion has been completed after the start of forming.

[0028] 3(a), in the gap narrowing step S101, a spacer 30 is arranged between the die 11 and the blank holder 12 so as to maintain a constant gap equal to or greater than the thickness of the titanium material 1. When the titanium material 1 is pressed against the punch 20 in this state, the titanium material 1 is not held by the die 11 and the blank holder 12, so the amount of material flowing toward the upper surface 101 increases, and excess material is generated on the upper surface 101.

[0029] In contrast, in the first pressure drawing step S102, as shown in Figure 3(b), the spacer 30 is not arranged, and a constant blank suppression pressure is applied between the die 11 and the blank holder 12. When the titanium material 1 is pressed against the punch 20 in this state, the titanium material 1 is held by the die 11 and the blank holder 12, so the amount of material flowing toward the upper surface 101 is reduced, and excess material generated on the upper surface 101 is sent toward the shoulder R portion 103. The amount of blank suppression pressure is preferably 490 to 790 kN.

[0030] The first step involves repeating the gap squeezing step S101 and the first pressure squeezing step S102 to perform squeezing while adjusting the amount of flow toward the upper surface 101 of the titanium material 1, thereby addressing the reduction in plate thickness and the occurrence of cracks at the shoulder R portion 103 of the cylindrical body 100 in the early stages of forming.

[0031] (2nd process) The second step is intended to address issues that arise during the middle stage of forming. As shown in Fig. 1, the second step involves repeating an arrangement direction rotation step S201 and a second pressure drawing step S202. Fig. 4 is an explanatory diagram of the second step, including (a) a perspective view showing the rotation state in the arrangement direction rotation step S201 and (b) a cross-sectional view showing the drawing state in the second pressure drawing step S202.

[0032] In the placement direction rotation step S201, the titanium material 1 is rotated horizontally during forming, as shown in Figure 4(a). At this time, the drawing die 10 and punch 20 are removed from the titanium material as needed, and after rotating the titanium material 1, they are reset. The rotation angle is, for example, 45 degrees, and one rotation is achieved by performing the placement direction rotation step S201 eight times. In Figure 4(a), reference numeral 2 indicates the pre-forming flat plate shape, reference numeral 3 indicates the inflow amount, and reference numeral 4 indicates the inflow wrinkles.

[0033] After rotating the titanium material 1 in the arrangement direction rotation step S201, the titanium material 1 is drawn in the second pressure drawing step S202. In the second pressure drawing step S202, as shown in Figure 4(b), a constant blank holder pressure is applied between the die 11 and the blank holder 12. It is preferable that the punch speed is 2 to 7 mm / s, the amount of blank holder pressure is 490 to 790 kN, and the process is switched from the second step to the third step 10 mm or more before the bottom dead center of the forming is reached.

[0034] The second process repeats the placement direction rotation step S201 and the second pressure squeezing step S202 to make the material flow uniform, suppress the occurrence of localized wrinkles, and address cracks and fissures caused by flow wrinkles.

[0035] (3rd step) The third step is intended to address issues that arise in the later stages of forming. As shown in Fig. 1, the third step includes an outer peripheral portion removal step S301 and a third pressure drawing step S202. Fig. 5 is an explanatory diagram of the third step, including (a) a perspective view showing the removal state in the outer peripheral portion removal step S301 and (b) a cross-sectional view showing the drawing state in the third pressure drawing step S302.

[0036] In outer periphery removal step S301, the outer periphery of titanium blank 1 is removed during forming, as shown in Figure 5(a). At this time, drawing die 10 and punch 20 are removed from the titanium blank as needed, and then reset after the outer periphery of the titanium blank has been removed. In Figure 5(a), reference numeral 2 denotes the pre-forming flat plate shape, reference numeral 3 denotes the inflow amount, reference numeral 4 denotes the inflow wrinkles, and reference numeral 5 denotes the outer periphery removal position. The outer periphery removal position 5 is set so that the horizontal distance from the vertical wall surface to the flange end is constant in the radial direction, so that the wrinkle suppression surface is uniform.

[0037] After the outer periphery of the titanium material 1 is removed in the outer periphery removing step S301, the titanium material 1 is drawn in the third pressure drawing step S302. In the third pressure drawing step S302, as shown in Fig. 5(b), a certain amount of blank holder pressure is applied between the die 11 and the blank holder 12. The amount of blank holder pressure is preferably 490 to 790 kN.

[0038] The third process involves removing the outer periphery in the outer periphery removal step S301 and then performing squeezing in the third pressure squeezing step S302, thereby making the material flow uniform and suppressing the occurrence of localized wrinkles, thereby addressing cracks and fractures caused by the flow-in wrinkles.

[0039] (4th step) The fourth step is intended to address issues that arise at the end of forming. As shown in Fig. 1, the fourth step includes a correction processing step S401. Fig. 6 is an explanatory diagram of the fourth step, in which (a) is a perspective view showing the occurrence of vertical wall wrinkles, and (b) is a cross-sectional view showing the drawing processing state in the correction processing step S401.

[0040] Near the drawing limit in the final stage of forming, as shown in FIG. 6(a), inflow wrinkles 6 that have not been completely suppressed tend to occur at the lower end 104 of the standing wall 102, and springback after forming tends to occur. In the correction processing step S401, as shown in FIG. 6(b), the lower end 104 of the standing wall 102 is corrected in the final stage of forming. To achieve this, the shape of the punch 20 is changed to change the gap during drawing near the lower end 104. FIG. 7 is an enlarged cross-sectional view of the drawing die. The punch 20 has a tapered surface 21 that narrows in diameter downward and a tapered surface 22 that widens in diameter, so that the gap during drawing gradually widens and eventually returns to its original size.

[0041] This is because, when drawing is performed from the middle to the latter stages of forming, as the drawing depth increases, the material shrinks from the edge of the blank, and this change gradually causes wrinkles to form downwards on the vertical wall 102, resulting in a tendency for the plate thickness to increase over a wide area; in order to draw smoothly in accordance with this tendency, the vertical wall of the die punch 20 has an inverse tapered structure that narrows in diameter downwards, as shown by reference numeral 21 in Figure 7, and the gap gradually becomes larger than the plate thickness toward the bottom of the vertical wall. On the other hand, when drawing is performed with a high set of wrinkle suppression pressure, the tendency for the plate thickness to increase is alleviated, but the wrinkle suppression pressure acts as a reaction force against the inflow of material, causing springback in the shape of the product vertical wall 102, which tries to return to its original shape, and when the product is removed from the die, the vertical wall 102 deforms into a shape that expands downwards and outwards on the circumference. The die 11 of the mold has a right-angled vertical wall, and the punch 20 has a reverse tapered structure that tapers downward. This allows for deeper and smoother drawing, provided the wrinkles are within the allowable range. The tendency for increased sheet thickness due to wrinkles to occur is absorbed by the punch 20, which has a larger die gap, and springback expansion is also suppressed. However, if forming is continued to the bottom dead center with this die structure, near the drawing limit at the end of forming, unsuppressed inflow wrinkles and springback will cause diameter variation within the die gap below the vertical wall. Since sizing is required to ultimately adjust this unstable diameter to a precise diameter, the die structure at the end of forming expands the diameter of the punch 20, whose gap has widened, as shown by reference numeral 22 in Figure 7, and finally returns the gap to the same size as the punch shoulder R portion, thereby performing correction processing.

[0042] In the fourth step, a straightening step S401 is carried out to straighten the lower end portion 104 of the vertical wall 102 of the titanium material 1, thereby dealing with the occurrence of wrinkles and springback.

[0043] The drawing method for a titanium material according to this embodiment involves pressing a titanium material 1, which is disposed between a die 11 and a blank holder 12 that constitute a drawing die 10, against a punch 20 to perform drawing. The method includes a first step of repeating a gap drawing step S101 and a first pressure drawing step S102. In the gap drawing step S101, the titanium material 1 is pressed against the punch 20 while maintaining a constant gap between the die 11 and the blank holder 12 that is equal to or greater than the thickness of the titanium material 1. This increases the amount of titanium material 1 flowing toward the top surface 101 of the cylindrical body 100. In contrast, in the first pressure drawing step S102, the titanium material 1 is pressed against the punch 20 while applying a constant blank suppression pressure between the die 11 and the blank holder 12. This reduces the amount of titanium material 1 flowing toward the top surface 101 of the cylindrical body 100. In this way, by performing drawing while adjusting the amount of titanium material 1 flowing in, it is possible to address thickness reduction and cracking at the shoulder R portion 103 of the cylindrical body 100 in the early stages of forming.

[0044] The method also includes a second step that repeats an arrangement direction rotation step S201, in which the arrangement direction of the titanium material 1 in the drawing die 10 is rotated, and a second pressure drawing step S202, in which the titanium material 1 is pressed against the punch 20 while applying a constant anti-wrinkle pressure between the die 11 and the blank holder 12. In the middle of forming, anti-wrinkle pressure is applied between the die 11 and the blank holder 12, but uneven material flow can cause localized inflow wrinkles. Therefore, by performing pressure drawing while changing the arrangement direction of the titanium material 1, the material flow can be made uniform, preventing the occurrence of localized wrinkles and addressing cracks and fractures caused by inflow wrinkles.

[0045] The method also includes a third process including an outer periphery removal step S301 in which the outer periphery of the wrinkle-holding surface of the titanium material 1 formed by the die 11 and blank holder 12 is removed, and a third pressure squeezing step S302 in which the titanium material 1 is pressed against the punch 20 while applying a constant wrinkle-holding pressure between the die 11 and blank holder 12. In the later stages of forming, as the area of ​​the wrinkle-holding surface formed by the die 11 and blank holder 12 becomes smaller, variations in the wrinkle-holding pressure occur, causing uneven material flow. Therefore, by removing the outer periphery to create a uniform wrinkle-holding surface, the material flow is made uniform, suppressing the occurrence of localized wrinkles and addressing cracks and fractures caused by wrinkles.

[0046] The method also includes a fourth process step S401 that includes a correction process step for the lower end 104 of the standing wall 102 of the titanium material 1. Near the drawing limit at the end of forming, inflow wrinkles that could not be suppressed tend to occur at the lower end 104 of the standing wall 102, and springback tends to occur after forming. Therefore, by correcting the lower end 104 of the standing wall 102 of the titanium material 1, it is possible to deal with the occurrence of wrinkles and springback.

[0047] In this way, the method for drawing a titanium material according to this embodiment can address issues such as cracks, fissures, and wrinkles that occur at each stage of the forming process when forming at room temperature. [Example]

[0048] The present disclosure will be explained in more detail below with reference to examples, but the drawing method of the present disclosure is not limited to the following examples as long as it does not deviate from the gist of the disclosure. Note that the examples were carried out in a temperature-controlled work area, and the controlled temperature was within the range of 18 to 28°C.

[0049] Example 1 Using the drawing method described below, a titanium alloy (Ti-6Al-4V) with a thickness of 0.93 mm was subjected to cylindrical drawing at room temperature. The resulting compact had a cylindrical inner diameter of Φ270.4 mm. The punch 20 was pressed into the cylinder until the horizontal height from the flange (shown as crease 4 in Figure 6) to the top surface 101 was 80 mm, completing the processing of the titanium alloy and producing the compact. The trim depth of the bottom end 104 of the vertical wall 102 of the cylindrical body 100 required for the final product was 70 mm horizontally from the top surface 101. The excess length, including the flange, required during the drawing process was scrapped after finishing the trimming process.

[0050] -1st process- First, a titanium alloy blank was placed on the blank holder 12, and four 1.2 mm thick spacers 30 were placed around the outside of the blank at equal intervals. The spacers were clamped between the die 11 and the blank holder 12, and the titanium alloy was subjected to S101 clearance drawing in the gap between the clamped die and the blank holder 12 without applying any wrinkle suppression pressure. The gap was controlled by the spacers, which were set to 0.3 mm ± 0.05 mm.

[0051] After performing S101 clearance drawing, the spacer was removed and S102 first process drawing was performed. The wrinkle suppression pressure was 784 kN. The cushion pin arrangement for applying the wrinkle suppression pressure was eight pins, which evenly held the blank holder 12.

[0052] The forming amount of the clearance drawing in S101 was 3 mm, and the forming amount of the first processing drawing in S102 was 2 mm in steps. The cycle of steps S101 and S102 was repeated four times until the forming of the shoulder R portion shown by reference numeral 103 in Figure 2 was completed and the start of forming the vertical wall 102 was confirmed, so that the forming depth between the upper surface of the punch 20 and the wrinkle suppression surface of the die 11 in Figure 3 was 17 mm or more.

[0053] The mold used had a punch 20 with an outer diameter of Φ270.4 at the shoulder and a shoulder R of 5 mm. The blank holder 12 had an outer diameter of Φ500 with a hollow inner diameter of Φ271.1, and the sliding clearance with the punch 20 was set to 0.35 mm. The die 11 had an outer diameter of Φ500 with a vertical wall groove diameter of Φ272.4, and the clearance at the shoulder was set to 7.5% of the plate thickness of the formed body, and the die R was 10 mm.

[0054] The titanium alloy blank plate material used was cut into a circular shape, and the diameter (D) of the circular surface of the plate before starting forming was 450 mm. The ratio (D / d) of the diameter (D) of the blank material to the diameter (d) of the punch 20, which is the pressing member, was 270.4 mm.

[0055] -Second process- As shown in Figure 4, after the first process, the titanium alloy being formed was rotated 45 degrees horizontally and reset using the S201 placement direction rotation. After setting, a wrinkle suppression pressure of 784 kN was applied between the die 11 and the blank holder 12, and the S202 second drawing process was performed.

[0056] The forming amount of the second processing drawing S202 was set to 2 mm steps, and for each step, the workpiece was rotated 45 degrees in the same direction, repeating the S201 placement direction rotation, and the second processing drawing was performed until the bottom dead center was 10 mm up, at which point forming was completed.

[0057] The punch 20 of the die used had a reverse tapered shape toward the bottom end of the vertical wall to improve drawability and prevent springback. The gradient angle of the reverse taper was 0.88 degrees from the diameter of 270.4 mm at the punch shoulder R part toward the bottom end of the vertical wall.

[0058] -3rd process- Using the point in Figure 5 where the inflow volume (3) is greatest and the length of (inflow wrinkles) (4) is smallest as a reference point, the flange edge (5) (outer periphery removal position) where the die 11 and blank holder 12 are clamped was removed from the S301 outer periphery so that it was a constant 30 mm from the vertical wall 102, so that the wrinkle suppression surface would be uniform. During this process, the titanium alloy was removed from the mold, the outer periphery was marked, and then the titanium alloy was removed with a sander, and any burrs or burrs that remained on the edge after removal were completely removed.

[0059] After removing the outer periphery of S301, the titanium alloy was set back in the die and the third drawing process of S302 was carried out. The wrinkle holding pressure was 784 kN.

[0060] -4th process- In the S401 correction process, the diameter of the punch 20 was changed to the same diameter as the punch shoulder R part in the final forming process from the S302 third process drawing to the bottom dead center. By making the punch 20 reverse tapered from the second process drawing, the gap between the punch 20 and the die 11, which was a maximum of 2 mm near the bottom end of the vertical wall of the titanium alloy, was returned to a gap of 1 mm, and the final vertical wall forming was performed using the S401 correction process.

[0061] Example 2 In Example 2, pure titanium (JIS type 4) with a plate thickness of 0.66 mm was subjected to cylindrical drawing at room temperature. The procedure was the same as in Example 1, except that the thickness of the spacer 30 was changed to 1 mm in order to control the gap in the gap drawing in the first step S101 to 0.3 mm ± 0.05 mm.

[0062] (Examples 3-7) Examples 3-7 were carried out using the same material and thickness as Example 1.

[0063] (Examples 3 and 4) In Examples 3 and 4, S101 clearance drawing and S102 first process drawing were repeated, and the first process was carried out continuously without proceeding to the second process. The blank holder pressure was 588 kN. In Example 4, the forming step amount of S101 clearance drawing and S102 first process drawing was changed from that in Example 1.

[0064] (Examples 5, 6, and 7) The first step in Examples 5, 6, and 7 was carried out in the same manner as in Example 1. In the second step in Examples 5 and 6, the S201 arrangement direction rotation was not carried out, and only the S202 second processing drawing was carried out continuously. The wrinkle holder pressure in Example 5 was 588 kN, and the wrinkle holder pressure in Example 6 was 784 kN. The second step in Example 7 was carried out in the same manner as in Example 1, and the third step S301 outer periphery removal was not carried out.

[0065] The above-mentioned conditions and evaluation results are shown in Table 1. The drawing ratio (D / d) shown in Table 1 is for a formed body with a cylindrical diameter of 270.4 mm (d), and the diameter (D) of the flat blank shape is the diameter of a formed body with a vertical wall height of 102 mm, which is usable as a cylindrical product, excluding the portion that will become scrap due to excess length, when developed into a flat blank, and used as the drawing ratio. Note that material elongation during actual forming was not taken into consideration. D=d-2r+rπ+2(hr) (r=5: internal bending radius h=70: product height)

[0066] [Table 1]

[0067] (Evaluation of formability) The molded articles produced in Examples 1 to 7 were visually inspected for cracks, wrinkles, and necks, and their states were evaluated based on the following evaluation criteria. The evaluation results are shown in Table 1. -Evaluation criteria- A: The molded body was molded without cracking up to the bottom dead center, and no defects such as wrinkles, cracks, or necks were observed in the shape of the cylindrical body 100 except for the portion to be removed as scrap. B: A crack occurred in the molded body before it reached the bottom dead point, but the defective part was a scrap part that was not part of the shape of the cylindrical body 100, or some kind of treatment was taken at the time the crack occurred, and it may be possible to mold the body up to the bottom dead point to the extent that the defective part does not affect the shape of the cylindrical body 100. C: Defects such as cracks, wrinkles, and necks were observed within the shape of the cylindrical body 100.

[0068] (Evaluation of thickness reduction) For the cylindrical bodies 100 manufactured in Examples 1 and 2, plate thickness measurements were performed at three locations with different heights: the top surface 101, the shoulder R portion 103, and the vertical wall 102. Evaluation was performed based on the following evaluation criteria, and the evaluation results are shown in Table 1. -Evaluation criteria- A: In the cylindrical body 100, the thickness reduction rate was less than 10% at all measurement points. B: In the cylindrical body 100, the thickness reduction rate was 10% or more and less than 15% at the shoulder R portion 103, and less than 10% at the top surface 101 and the vertical wall 102. C: In the cylindrical body 100, the thickness reduction rate was 15% or more at the shoulder R portion 103, and 10% or more at the upper surface 101 and the vertical wall 102.

[0069] (Springback evaluation) For the cylindrical bodies 100 manufactured in Examples 1 and 2, diameter measurements were taken at four locations at 45 degrees around the circumference at each height of the upper, middle, and lower end portions near the shoulder R portion of the vertical wall 102, and evaluation was performed based on the following evaluation criteria. The evaluation results are shown in Table 1. -Evaluation criteria- A: When the diameter of the vertical wall of the cylindrical body 100 was measured, the amount of springback was within the range of the plate thickness at all points. B: In measuring the diameter of the vertical wall of the cylindrical body 100, there were two or fewer locations where the amount of springback exceeded the plate thickness. C: In measuring the diameter of the vertical wall of the cylindrical body 100, there were three or more locations where the amount of springback exceeded the plate thickness.

[0070] In Example 1, titanium alloy (Ti-6Al-4V) was formed through the first to fourth steps, and the obtained cylindrical body 100 had excellent formability, thickness reduction, and springback suppression.

[0071] In Example 2, pure titanium (JIS Class 4) was subjected to forming from the first step to the fourth step, and the obtained cylindrical body 100 was excellent in formability, thickness reduction, and springback suppression.

[0072] In Examples 3 and 4, titanium alloy (Ti-6Al-4V) was subjected to only the first step (blanket pressure 588 kN) without proceeding to the second step, but defects occurred and final forming was not achieved. However, the product height (h) reached 34 mm and 32 mm, respectively, and at least the shoulder R portion was successfully formed.

[0073] In Example 5, titanium alloy (Ti-6Al-4V) was subjected to the first and second steps (the second step was only S202 second pressure drawing with a wrinkle suppression pressure of 588 kN), but defects occurred and the final forming was not achieved. However, the product height (h) reached 29 mm, and at least the shoulder R portion was successfully formed.

[0074] In Example 6, titanium alloy (Ti-6Al-4V) was subjected to the first and second steps (the second step was only S202 second pressure drawing with a blank holding pressure of 784 kN), but defects occurred and the final forming was not achieved. However, the product height (h) reached 67 mm, and the shoulder R part was successfully formed, and a certain degree of evaluation was also obtained regarding formability.

[0075] In Example 7, titanium alloy (Ti-6Al-4V) was subjected to the first and second steps (784 kN blank holding pressure), but defective parts were generated and final forming was not achieved. However, the product height (h) reached 69 mm, and the shoulder R part was successfully formed, and a certain degree of evaluation was also obtained for formability.

[0076] The method for drawing a titanium material according to an embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and various other modifications are possible. [Explanation of symbols]

[0077] 1. Titanium material 2 Flat plate shape before molding 3 Inflow amount 4 Inflow wrinkles 5 Outer periphery removal position 6 Vertical wall wrinkles 10 Drawing mold 11 Die 12 Blank holder 20 punches 21 Tapered surface 22 Tapered surface 30 spacer 100 Cylinders 101 Top surface 102 Vertical Wall 103 Shoulder R section 104 Lower end

Claims

1. A method for drawing a titanium material, in which a titanium material placed between a die and a blank holder constituting a drawing die is pressed against a punch to perform drawing, a gap squeezing step of pressing the titanium material against the punch while maintaining a constant gap between the die and the blank holder that is equal to or greater than the thickness of the titanium material; a first pressure drawing step of pressing the titanium blank against the punch while applying a constant anti-wrinkle pressure between the die and the blank holder; A method for drawing a titanium material, comprising a first step of repeating the above steps.

2. an arrangement direction rotating step of rotating an arrangement direction of the titanium material in the drawing die; a second pressure drawing step of pressing the titanium blank against the punch while applying a constant anti-wrinkle pressure between the die and the blank holder; 2. The method for drawing a titanium material according to claim 1, further comprising a second step of repeating the steps of:

3. an outer periphery removing step of removing an outer periphery of the titanium material on the wrinkle suppression surface formed by the die and the blank holder; a third pressure drawing step of pressing the titanium blank against the punch while applying a constant anti-wrinkle pressure between the die and the blank holder; 2. The method for drawing a titanium material according to claim 1, further comprising a third step including:

4. 2. The method for drawing a titanium material according to claim 1, further comprising a fourth step including a step of correcting the lower end of the vertical wall of the titanium material.

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