JP7731131B2 - Drawing and ironing method for metal materials - Google Patents

Description

This disclosure relates to a method for drawing and ironing metal materials.

2. Description of the Related Art Various methods have been proposed for processing metal materials.
For example, press working is a processing method in which a material such as metal is placed between a pair of tools including a die and pressure is applied to the material to form it into a shape that corresponds to the die.
Drawing is a type of press working known as a type of metal forming. Drawing is a metal sheet forming method that is used to form containers with bottoms of various shapes, such as cylinders, square tubes, and cones, from a single metal sheet. By using drawing, it is possible to form metal into a seamless container shape.

Metal materials used in drawing include, for example, titanium, titanium alloys, aluminum, iron, stainless steel, copper, and magnesium. Titanium and titanium alloys, in particular, are expected to be used in a wide range of fields due to their high corrosion resistance, high strength, and low specific gravity, and various methods for processing titanium and titanium alloys are being investigated.

For example, Patent Document 1 describes a method for forming a titanium alloy material by spinning using a tool, characterized in that it comprises a heating step in which the point of application of the tool to the titanium alloy material is locally heated by high-frequency induction heating, and a deformation step in which the tool is moved from the outer periphery of the titanium alloy material to the inner periphery, thereby drawing and deforming the titanium alloy material.

For example, Patent Document 2 describes a method for forging a metallic material workpiece, which includes repeating free press forging of the workpiece and rotating the workpiece to a desired degree of rotation until the total amount of imparted strain is sufficient to initiate microstructural refinement.

JP 2012-192414 A Special Publication No. 2016-512173

Although there is a method of heating a metal material at a high temperature (e.g., 700°C to 870°C) to impart ductility to the material before processing, it has been extremely difficult to process metal materials at low temperatures, such as titanium alloys, which have low ductility at low temperatures (e.g., 400°C or lower), because ductility cannot be obtained at low temperatures.
As a method for imparting ductility to metal materials (e.g., titanium alloys) that have low ductility at low temperatures by heating them to high temperatures and then processing them, one method involves heating the titanium alloy Ti-6Al-4V alloy to approximately 800°C using a heating means such as a burner and then forming it. However, this method requires the use of a large-scale heating device to heat the entire die to a high temperature, which increases costs and tends to worsen workability. Furthermore, the exposure of not only the Ti-6Al-4V alloy but also the device to high temperatures is thought to shorten the life of the device.
The method described in Patent Document 1 simply heats only the portion of the material to be deformed, while Patent Document 2 describes a method in which the surface of the material is forged little by little in the temperature range of 600°C to the β transus transformation point in order to refine the crystal grains.
The methods described in Patent Documents 1 and 2 are both processing methods in which a titanium alloy is heated to a high temperature range, and it is considered that processing methods in which a titanium alloy is heated to a high temperature range usually require the use of special dies, special heating devices, etc., and therefore cannot be expected to be advantageous in terms of manufacturing cost, ease of operation, etc.
For these reasons, there is a demand for a technology that can process metal materials (especially metal materials that have low ductility in the low temperature range) at low temperatures (for example, below 400°C).

The problem that the embodiments of the present disclosure aim to solve is to provide a method for drawing and ironing metal materials that can process metal materials into rectangular tubes at low temperatures.

The means for solving the above problems include the following aspects.
<1> A method for drawing and ironing a metal material blank into a rectangular tube, the method comprising the steps of: placing the metal material, which has a temperature of 0°C to 300°C, between a blank holder and a die; using the die to press the peripheral portion of the metal material against the die without drawing the metal material with a punch; and using the blank holder to press the peripheral portion of the metal material against the die while the metal material, which has a temperature of 0°C to 300°C, is placed between the blank holder and the die. a drawing step in which the edge portion is pressed or not pressed against a die with a force of 2 kN or less, and the metal material is squeezed into a rectangular tube shape by the punch using the die, wherein in the drawing step, a clearance ratio c/t, which is the ratio of the clearance c [mm] between the punch and the die to the thickness t [mm] of the metal material before processing, is 0.7 or more and 1.0 or less, and in the pressing step, a pressing time s [seconds] for pressing the metal material is 4.0 t or more and 8.0 t or less.
<2> The drawing and ironing method according to <1>, wherein the metal material is a titanium alloy.
<3> The drawing and ironing method according to <1> or <2>, wherein the thickness t [mm] is 0.50 mm or more and the clearance ratio c/t is 1.0.
<4> The method for drawing and ironing a metal material according to any one of <1> to <3>, wherein the metal material has a circumscribed circle with a diameter of 20 mm to 50 mm and an octagonal flat plate shape.
<5> The method for drawing and ironing a metal material according to any one of <1> to <4>, wherein the pressing step and the drawing step are alternately repeated to form the metal material into a rectangular tube.

According to an embodiment of the present disclosure, a method for drawing and ironing metal materials can be provided that can process metal materials into rectangular tubes at low temperatures.

10 is a cross-sectional view illustrating a case where a metal material is drawn into a rectangular cylindrical shape with a clearance ratio of 1.0 or more. FIG. 10 is a cross-sectional view illustrating a case where a metal material is drawn into a rectangular tube shape with a clearance ratio of less than 1.0. FIG. 1 is a cross-sectional view of a die, a metal material, a punch, and a blank holder for explaining a pressing process in the present disclosure. FIG. 1 is a cross-sectional view of a die, a metal material, a punch, and a blank holder for explaining a drawing process in the present disclosure. FIG. FIG. 2 is a cross-sectional view illustrating an example of a die according to the present disclosure. FIG. 1 is a cross-sectional view showing an example of a blank holder in the present disclosure. FIG. 1 is a cross-sectional view illustrating an example of a punch according to the present disclosure. 1 is a cross-sectional view illustrating an example of a metal workpiece according to the present disclosure. 1 is a graph showing the relationship between time, BHF, and punch stroke when a metal material is processed using the drawing and ironing method of the present disclosure. 1 is a graph showing a punch load-punch stroke curve and a BHF-punch stroke curve in Example 1. 1 is a photograph of a metal processed product obtained in Example 1. 1 is a graph showing a punch load-punch stroke curve and a BHF-punch stroke curve in Example 2. 1 is a photograph of a metal processed product obtained in Example 2.

Hereinafter, an embodiment of the drawing method of the present disclosure will be described in detail with reference to Figures 1 to 10. However, the present disclosure is not limited to the embodiment shown below.

<Squeezing and ironing method>
The drawing and ironing method for metal material of the present disclosure (also simply referred to as the drawing and ironing method of the present disclosure in the present disclosure) is a drawing and ironing method for metal material, which is a blank material, to be processed into a rectangular tube, and includes: a pressing step in which, with a metal material having a temperature of 0°C to 300°C placed between a blank holder and a die, the die is used to press the peripheral portion of the metal material against the die without pressing the metal material with a punch, and the blank holder is used to press the peripheral portion of the metal material against the die with a force of 2 kN or less, with or without pressing the peripheral portion of the metal material against the die with a punch, and the die is used to draw the metal material into a rectangular tube shape;
In the drawing step, a clearance ratio c/t, which is a ratio of a clearance c [mm] between the punch and the die to a thickness t [mm] of the metal material before processing, is 0.7 or more and 1.0 or less,
In the pressing step, the pressing time s (seconds) for pressing the metal material is 4.0t (seconds) or more and 8.0t (seconds) or less.

In this disclosure, clearance refers to the shortest distance between the surface of the die and the surface of the punch during the drawing process.

As described above, metal materials that have low ductility in the low temperature range must be heated to a high temperature in order to be formed, and forming at low temperatures has been difficult.
However, in order to apply a high temperature (for example, 500° C. or higher), separate equipment and processes for heating the metal material, die, etc. are required, which raises concerns about increased manufacturing costs.

The drawing and ironing method of the present disclosure includes the above-described configuration, and therefore can process metal materials without heating them to high temperatures, even when processing metal materials that have low ductility in the low temperature range.
The reason why the above effects are obtained is believed to be as follows.
By performing the drawing process with the clearance ratio being 1.0 or less, the metal material can be squeezed into a rectangular tube shape so that the thickness becomes small between the die and the punch in the drawing process, which is known as drawing and ironing.
When the drawing and ironing process is performed with a clearance ratio of 1.0 or less, when the metal material is drawn using the die, some of the metal material does not reach the gap between the die and the punch and remains in the bent portion. By controlling the inflow of the metal material within a certain range as the drawing and ironing process progresses, the thickness of the bent portion, which is prone to fracture, can be kept within a certain range. As a result, fracture can be suppressed.

In the drawing and ironing method of the present disclosure, it is preferable to process the metal material into a square tube by alternately repeating a pressing step and a drawing step.
This allows the drawing and ironing method of the present disclosure to proceed slowly so as to prevent wrinkles from occurring and the wall thickness from decreasing, resulting in a metal workpiece with highly uniform wall thickness while suppressing the occurrence of wrinkles in the resulting metal workpiece.

The drawing and ironing method of the present disclosure allows for drawing and ironing of metal materials at low temperatures (e.g., below 300°C), eliminating the need to heat the metal materials to high temperatures, and thus enabling metal materials to be drawn using simple, commonly used equipment, thereby reducing manufacturing costs and improving ease of operation.
Furthermore, the drawing and ironing method of the present disclosure can prevent the wall thickness of the resulting metal workpiece from being partially reduced, making it possible to produce a metal workpiece with excellent wall thickness uniformity.

The drawing and ironing method of the present disclosure is a drawing and ironing method for metal material, in which a metal material serving as a blank is processed into a square tube.
When metal material is formed into a square tube by drawing and ironing, the amount of metal material flowing into the four corners and the four sides is different, making it very difficult to make the thickness of the square tube uniform.
The drawing and ironing method of the present disclosure includes the above-described configuration, and can process a metal material into a square tube at a low temperature.

<Clearance ratio>
In the drawing and ironing method of the present disclosure, the clearance ratio c/t, which is the ratio of the clearance c [mm] between the punch and the die to the thickness t [mm] of the metal material before processing, is 0.7 or more and 1.0 or less.
This allows the drawing and ironing process to be performed as described above, and when the metal material is drawn using the die, part of the metal material does not reach the space between the die and the punch and remains in the bent portion.
The thickness of the bent portion can be controlled by controlling the amount of drawing and ironing in the drawn and ironed portion and the amount of metal material flowing into the portion consisting of the blank holder and die, which allows the thickness of the bent portion, which is prone to fracture, to be increased in the resulting metal workpiece.

The above will be described in detail with reference to FIGS.
1 , when the clearance ratio exceeds 1.0, the length of the clearance 10 exceeds the pre-processing thickness t of the metal material 11. When drawing and ironing is performed with the clearance ratio exceeding 1.0, when the metal material 11 is drawn using the die 5, the metal material 11 can pass between the die 5 and the punch 9 without decreasing in thickness, and therefore, a portion of the metal material 11 is less likely to remain in the bent portion 8 during processing.
On the other hand, as shown in FIG. 2 , when the clearance ratio is 1.0 or less, the length of the clearance 10 is less than the thickness t of the metal material 11 before processing. When drawing and ironing is performed with a clearance ratio of 1.0 or less, when the metal material 11 is drawn using the die 5, it is possible to prevent all of the drawn and ironed portion of the metal material 11 from reaching between the die 5 and the punch 9. The portion of the drawn and ironed portion of the metal material 11 that does not reach between the die 5 and the punch 9 remains in the bent portion. The thickness of the bent portion can be controlled by controlling the amount of drawing and ironing in the drawn and ironed portion and the amount of metal material flowing into the metal material flow section consisting of the blank holder and the die. As a result, the thickness of the bent portion, which is prone to fracture, can be increased in the resulting metal workpiece.
As described above, by increasing the thickness of the bent portion, it is possible to suppress the occurrence of fractures in the resulting metal processed product.

The clearance ratio is preferably 1.00 or less from the viewpoint of processing the metal material without problems such as breakage by controlling the thickness of the bent portion.
Moreover, from the viewpoint of effectively suppressing breakage and obtaining sufficient strength in the metal processed product, the clearance ratio is more preferably 0.75 or more, and even more preferably 0.90 or more.

The clearance ratio may be adjusted by the value of the thickness t.
For example, in the drawing and ironing method of the present disclosure, the thickness t may be 0.50 mm or more and the clearance ratio may be 1.0.

<Pressing process>
The pressing process in the present disclosure is a process in which a metal material having a temperature of 0°C to 300°C is placed between a blank holder and a die, and the metal material is not squeezed by a punch using the die, and the peripheral portion of the metal material is pressed against the die using the blank holder, and the pressing time s for pressing the metal material is 4.0t [seconds] or more and 8.0t [seconds] or less.
This can prevent wrinkles from occurring in the resulting metal workpiece.

The pressing time s for pressing the metal material is 4.0t seconds or more and 8.0t seconds or less.
The above t is the thickness (mm) of the metal material before processing.
By setting the pressing time s for pressing the metal material to 4.0 t or more, wrinkles in the resulting rectangular tubular compact can be suppressed. Furthermore, when squeezing the metal material using a die, the amount of metal material flowing between the die and the punch can be increased to an extent that a rectangular tubular compact can be formed.
From the above viewpoint, the pressing time s for pressing the metal material is preferably 4.0 t or more, and more preferably 5.0 t or more.

By setting the pressing time s for pressing the metal material to 8.0 t or less, the thickness of the scrap portion can be maintained, and the square cylindrical molded body can be prevented from breaking.
From the above viewpoint, the pressing time s for pressing the metal material is preferably 8.0 t or less, and more preferably 7.5 t or less.

~One embodiment of the pressing step~
An embodiment of the pressing step in the present disclosure will be described with reference to FIG.
3, in a state in which the metal material 11 is placed between the blank holder 7 and the die 5, the blank holder 7 is used to press, for example, the scrap portion 13 of the metal material 11 in the direction from the blank holder 7 toward the die 5 for 4.0t seconds to 8.0t seconds. At this time, the punch 9 does not push the metal material 11 up into the hole 5C of the die 5 and squeeze it into the hole 5C.

(metallic material)
The metal material in the present disclosure is the material of the metal workpiece obtained by the drawing and ironing method of the present disclosure.
According to the drawing and ironing method of the present disclosure, even when processing a metal material that has low ductility in the low temperature range, the metal material can be processed without heating the metal material to a high temperature.

Metal materials referred to in this disclosure include, for example, titanium, titanium alloys, aluminum, iron, stainless steel, copper, magnesium, nickel, etc.

Among the above, the metallic material in the present disclosure is preferably titanium or a titanium alloy, which is a metallic material with low ductility in the low temperature range.
When metal materials with low ductility in the low temperature range are processed in the low temperature range, defects such as breakage and wrinkles are likely to occur, making good processing difficult. However, with the drawing and ironing method of the present disclosure, titanium and titanium alloys, which are metal materials with low ductility in the low temperature range, can be well processed into the desired shape.
From the above viewpoint, the metal material in the present disclosure is more preferably a titanium alloy.

Examples of metals or non-metals other than titanium that may be contained in titanium alloys include Al, V, Mo, Fe, Pd, Ru, Pt, Ni, Cr, and Sn.
Examples of titanium alloys in the present disclosure include Ti-6Al-4V and Ti-15V-3Cr-3Sn-3Al, and Ti-6Al-4V is more preferred from the viewpoint of better achieving the effects of the present disclosure.

From the viewpoint of the strength of the workpiece obtained after processing, the thickness t of the metal material before processing is preferably 0.30 mm or more, more preferably 0.35 mm or more, and even more preferably 0.50 mm or more.
Furthermore, the thickness t of the metal material before processing is preferably 1.5 mm or less, more preferably 1.2 mm or less, and even more preferably 1.0 mm or less, from the viewpoint of suppressing wrinkles in the workpiece obtained after processing.

The shape of the metal material in this disclosure is not particularly limited. For example, the shape of the metal material may be an octagonal flat plate.

The diameter of the circumscribing circle of the metal material is preferably 20 mm to 50 mm.
When the diameter of the circumscribed circle is 20 mm or more, the inflow amount of the metal material can be well controlled during the drawing and ironing process.
From the above viewpoint, the diameter of the circumscribing circle is more preferably 25 mm or more, and even more preferably 30 mm or more.
Furthermore, by making the diameter of the circumscribed circle 50 mm or less, the metal material can be smoothly flowed onto the ironing surface without being broken.
From the above viewpoint, the diameter of the circumscribed circle is more preferably 45 mm or less, further preferably 40 mm or less, and particularly preferably 35 mm or less.

The metal material preferably has a circumscribed circle with a diameter of 20 mm to 50 mm and is in the shape of an octagonal flat plate.

(lubricant)
The metal material preferably contains a lubricant on the surface.
This reduces friction between the die and the punch, thereby protecting the metal material and suppressing adhesion of the metal material to the die and the punch.
Specifically, by including a lubricant on the surface of the metal material, when the metal material is drawn using a die and a punch in the drawing process, sliding between the metal material and at least one of the die and the punch can be suppressed. Therefore, it is preferable that the metal material include a lubricant in the portion that comes into contact with at least one of the die and the punch when the drawing process is performed.

Known lubricants can be used, such as PTFE (polytetrafluoroethylene) and PE (polyethylene).
Among the above, from the viewpoint of reducing friction and suppressing adhesion, the lubricant is preferably a solid lubricant, more preferably PTFE having a thickness of 10 μm to 200 μm, and even more preferably PTFE having a thickness of 50 μm to 100 μm.

The metal material may have an oxide coating on the surface, which can protect the metal material and prevent it from adhering to the die.
The oxide film can be formed on the metal material by any known method, such as atmospheric oxidation or anodic oxidation.
Atmospheric oxidation is a method of forming an oxide film by using oxygen in the air to form an anatase-type oxide film on the surface of a metal.
Anodization is a method of forming an oxide film in which a metal is used as an anode and an electric current is passed through it to form a rutile-type oxide film on the metal surface.

(Thailand)
5, the die 5 has a square hole 5C in the center and a side wall 5E, and may have a bent portion 5D at the open end of the hole 5C on the side (lower surface 5B side) where the metal material 11 is placed so as to be in contact with the die 5. The metal material 11 placed so as to be in contact with the die 5 is squeezed along the hole 5C using a punch 9 in a direction from the lower surface 5B toward the upper surface 5A, thereby processing the metal workpiece into a desired rectangular cylindrical shape.
The drawing and ironing method for a metal material according to the present disclosure is a method for drawing and ironing a metal material blank into a rectangular tube, and therefore, the shape of the hole 5C of the die 5 according to the present disclosure is preferably a rectangular tube shape.

The shape of the die 5 may be, for example, a cylindrical shape with an approximately rectangular cylindrical hole 5C inside, and the height 5h of the die 5 and the inner diameter 5r and outer diameter 5R of the hole 5C on the upper surface side can be adjusted appropriately depending on the shape of the target metal workpiece, etc.
The material of the die 5 is not particularly limited, but examples thereof include SKD61, SKD11, and the like.

(Blank holder)
In this process, the pressure (BHF: Blank Holding Force) that the blank holder 7 applies to the metal material 11 can be adjusted appropriately depending on the type of the metal material 11 .
The BHF in this step may be, for example, 5 kN to 100 kN, preferably 7 kN to 50 kN, and more preferably 10 kN to 30 kN.

As shown in Fig. 6, the blank holder 7 has a hole 7A, which is, for example, rectangular, and supports the metal material 11 when it is placed between the blank holder 7 and the die 5, as shown in Fig. 3. The blank holder 7 also applies pressure to the peripheral portion (flange portion) of the surface of the metal material 11 opposite to the surface that contacts the die 5. This makes it possible to suppress the occurrence of wrinkles in the metal workpiece.
As shown in FIG. 6 , the blank holder 7 has a square hole 7A through which a punch passes. Therefore, when performing the drawing process described below, a punch 9 passes through the hole 7A and presses the metal material 11, thereby drawing the metal material 11 into a square tube shape.

The blank holder 7 may be disk-shaped with a square hole 7A in the center, as shown in FIG.
The outer diameter 7R of the blank holder 7 is preferably the same as the outer diameter 5R of the die 5.
The inner diameter 7r of the blank holder 7 is preferably an inner diameter that does not hinder the passage of the punch 9 through the hole 7A.
The thickness 7h of the blank holder 7 is not particularly limited, but may be, for example, 1 cm to 2 cm.
The material of the blank holder 7 is not particularly limited, but examples thereof include SKD61, SKD11, and the like.

<Drawing process>
The drawing process in the present disclosure is a process in which a metal material having a temperature of 0°C to 300°C is placed between a blank holder and a die, and the blank holder is used to press the peripheral portion of the metal material against the die with a force of 2 kN or less, or not, and the die is used to draw the metal material into a rectangular tube shape with a punch.
This process suppresses shear deformation caused by tensile stress, which is the cause of fracture, and also enables the metal material to be deformed into the desired rectangular tube shape.

If the blank holder is not used to press the peripheral portion of the metal material against the die during the drawing process, the peripheral edge side of the metal material that is the blank may be sandwiched between the blank holder and the die, or the peripheral edge side of the metal material that is the blank may be positioned between the blank holder and the die without contacting at least one of the blank holder and the die.

~One embodiment of the drawing process~
An embodiment of the drawing process in the present disclosure will be described with reference to FIG.
In one embodiment of the drawing process of the present disclosure, as shown in Figure 4, a punch 9 is operated while a metal material 11 is placed between a blank holder 7 and a die 5, so that the punch 9 passes through a hole 7A of the blank holder 7 and presses, for example, an inner bottom surface 11D (see Figure 8) of the metal material 11, pushing the titanium alloy up into a hole 5C of the die 5 and drawing the metal material 11. At this time, the titanium alloy 11 is pressed with a force of 2 kN or less using the blank holder 7, or is not pressed at all.

One method of pressing metal material using a blank holder is to provide a servo motor to move the blank holder, and use the servo motor to move the blank holder toward the die, pressing the metal material placed between the blank holder and the die.

This process is carried out with or without pressing the metal material with a blank holder at a pressure of 2 kN or less, thereby achieving a uniform wall thickness of the resulting metal workpiece, particularly in the side and shoulder portions of the metal workpiece.
In particular, the shoulder portion is the portion that comes into contact with the end of the pressing surface of the punch during drawing (shoulder portion 113 in Figure 8), and therefore the reduction in wall thickness is significant.However, the drawing method disclosed herein can effectively suppress the reduction in wall thickness (especially the shoulder portion).
From the viewpoint of effectively suppressing a reduction in wall thickness, it is preferable to press the metal material with a pressure of 2 kN or less, or not press it at all, and it is more preferable to not press it at all.

(punch)
7, the punch 9 can be, for example, a substantially rectangular cylindrical shape, has a body 9B, and can be provided with a rectangular pressing surface 9A on the body 9B for pressing the metal material 11. As shown in FIG. 4, the punch 9 presses a portion of the surface of the metal material 11 opposite to the surface that contacts the die 5, thereby squeezing the metal material 11 into the hole 5C of the die 5.

There are no particular restrictions on the material of the punch 9, but examples include SKD61, SKD11, etc.

The metal drawing and ironing method disclosed herein is a method for drawing and ironing a metal blank into a rectangular tube. Therefore, it is preferable that the shape of the punch 9 be a rectangular tube.

The load (punch load) applied by the punch 9 when pressing the metal material 11 can be adjusted appropriately by adjusting the length of the stroke (punch stroke) of the punch 9, as shown in Figure 9, for example. As the forming of the titanium alloy 11 progresses and the punch stroke becomes longer, the punch load can be increased. This allows the titanium alloy 11 to be formed into the desired shape.

The maximum load (maximum punch load) when the punch 9 presses against the metal material 11 can be adjusted appropriately depending on the type of metal material 11. For example, the maximum punch load can be set to 2 kN to 200 kN.

The speed at which the punch 9 presses the metal material 11 (punch speed) can be adjusted appropriately depending on the type of metal material 11. For example, the punch speed can be set to 5 mm/min to 500 mm/min.
In this disclosure, punch speed refers to the speed at which the punch pushes the metal material into the hole in the die.

It is preferable that the pressing step and the drawing step are performed alternately.
This will be explained with reference to FIG.
FIG. 9 is a graph showing the relationship between time, BHF, and punch stroke when a metal material is processed using the drawing and ironing method of the present disclosure.

FIG. 9 shows the cases where the pressing time s in the pressing step is x and 2x.
As shown in FIG. 9, when the pressing time s is 2x, the increasing speed of the punch stroke is smaller than when the pressing time s is x.
In both cases where the pressing time s is x and 2x, the punch stroke is increased by alternately repeating the pressing step and the drawing step. In this case, the punch stroke near the maximum punch load may be, for example, around 9 mm. In the pressing step, the BHF is set to around 20 kN, which is a substantially constant value regardless of the value of the punch stroke.
The punch stroke refers to the distance traveled by the punch when pressing the metal material from the point where the punch comes into contact with the metal material and no BHF is added until the material breaks or the drawing process ends.
After the punch stroke has increased to near the maximum punch load, it is preferable to adjust the punch load in order to process the metal material into a rectangular tube shape. At this time, the punch load may be gradually decreased or maintained. Even after the punch stroke has increased to near the maximum punch load, the punch stroke may increase while making the above adjustment.

(Draw ratio)
When the metal material 11 has a rectangular flat plate shape and the punch 9 has a rectangular cylindrical shape, the ratio of the diameter (D) of the circumscribed circle of the metal material 11 to the diameter (d) of the punch 9 (drawing ratio: D/d) is preferably 1.5 or more. A drawing ratio of 1.5 or more is likely to be practical in general industry. The larger the value of D, i.e., the larger the drawing ratio, the more likely the metal workpiece is to break after one drawing, and the drawing ratio can be an indicator of the drawability of the material.
From the same viewpoint as above, the drawing ratio is more preferably 1.7 or more, and even more preferably 1.8 or more.

The punch load in this process can be adjusted appropriately by changing the length of the punch stroke. For example, the punch load can be set to 500 kN to 1000 kN.

The BHF used in this process can be adjusted appropriately depending on the type of titanium alloy, but can be set to, for example, 10 kN to 50 kN.

The punch speed in this step can be adjusted appropriately depending on the type of titanium alloy, but can be set to, for example, 10 mm/min to 900 mm/min.
From the viewpoint of processability, the speed is preferably 20 mm/min to 700 mm/min, and more preferably 30 mm/min to 300 mm/min.

(Temperature adjustment process)
The drawing and ironing method of the present disclosure is capable of processing metal materials over a wide temperature range, and may further include a temperature adjustment step of adjusting the temperature of the metal material to 0°C to 300°C before the pressing step and the drawing step.
When performing work in which the temperature of the metal material is set to less than 0°C, it is thought that costs will increase, but by adjusting the temperature of the metal material to 0°C or higher, the increase in costs can be suppressed.
From the above viewpoint, the temperature of the metal material is preferably 15° C. or higher.
Furthermore, by adjusting the temperature of the metal material to 300°C or less before the pressing and drawing processes, it is possible to prevent deterioration of the sliding properties due to seizure between the metal material and the die. Also, it is possible to prevent damage to the metal material, the die, etc. due to heat. Furthermore, when a solid lubricant such as PTFE is used, it is possible to prevent damage to the solid lubricant due to heat.
From the above viewpoint, the temperature of the metal material is preferably 250°C or less, more preferably 200°C or less, and even more preferably 150°C or less.

The method for adjusting the temperature in the temperature adjustment step is not particularly limited, and examples thereof include methods using a heater, heating in a furnace, etc.
Furthermore, if the temperature is room temperature (e.g., 25°C), there is no need to adjust the temperature, and even if temperature adjustment is not performed, the drawing and ironing method disclosed herein can process metal materials without any problems such as breakage.

The present disclosure will be explained in more detail below using examples, but the present disclosure is not limited to the following examples as long as it does not deviate from the gist of the disclosure. Unless otherwise specified, "parts" are by mass.

A titanium alloy (Ti-6Al-4V) as a metal material was subjected to drawing and ironing by the drawing and ironing method described below.
In this example, the die, punch, metal material, drawing ratio, clearance c, and clearance ratio are as follows:

The die used had an outer shape of a cylinder with an outer diameter of 140 mm and a height of 18 mm when placed on a horizontal surface, and the inner diameter of the hole was 16.0 mm.
The blank holder used had a cylindrical shape with an outer diameter of 140 mm and a height of 18 mm, and the inner diameter of the hole was 16.0 mm.

The punch used had a rectangular column shape with a pressing surface diameter (d) of 15.0 mm and a body length of 130 mm.

The metal material used was a titanium alloy (Ti-6Al-4V) in the shape of an octagonal flat plate. The diameter (D) of the circumscribed circle on the octagonal surface of the square cylindrical shape is as shown in Table 1.
The ratio of the diameter (D) of the circumscribing circle of the metal material to the diameter (d) of the circumscribing circle of the punch (drawing ratio: D/d) was 1.71 in Examples 1 and 2, and 1.49 in Example 3.

The clearance c obtained by the punch and die was 0.5 mm. The clearance ratios in each example and comparative example are shown in Table 1.
The clearance ratio c/t in each of the examples and comparative examples is shown in Table 1.

Example 1
- Arrangement of metal materials -
The titanium alloy (thickness t before processing: 0.50 mm) was placed on a blank holder, and the blank holder was driven by a servo motor to move closer to the die, so that the titanium alloy was sandwiched between the die 5 and the blank holder. The temperature of the titanium alloy was 24°C, which was the same as room temperature.

- Pressing process -
As shown in Figure 3, the titanium alloy placed between the blank holder and the die was pressed with a BHF force of 15 kN in the direction from the blank holder to the die by using the blank holder to press the scrap portion of the titanium alloy. At this time, the punch was not used to squeeze the titanium alloy into the hole in the die.
The pressing time s (seconds) for pressing the metal material is shown in Table 1.

- Drawing process -
As shown in Figure 4, the titanium alloy after the pressing process was placed between the blank holder and the die, and the punch was operated so that the punch passed through the hole in the blank holder and pressed against the inner bottom surface of the metal material, forcing the titanium alloy up into the hole in the die and drawing it into the hole. At this time, the flange portion of the titanium alloy was not pressed using the blank holder. The punch speed in the drawing process was 30 mm/min.

The punch stroke, BHF, and punch load were adjusted as needed, and the pressing and drawing processes were repeated alternately. The processing of the metal material 11 was completed when the inner bottom surface 11D was pressed to a position where the length from the horizontal plane to the bottom surface (11h in Figure 8) was 9 mm when the flange portion of the resulting metal workpiece was placed in contact with a horizontal surface, and the metal workpiece was manufactured.

The obtained metal workpiece had a bottom diameter (11R in Figure 8) of 16 mm, and when the metal workpiece was placed on a horizontal surface as shown in Figure 8, the vertical height 11h from the horizontal surface to the bottom was 9.5 mm.
A graph showing the punch load-punch stroke curve and the BHF-punch stroke curve in Example 1 is shown in FIG.
A photograph of the metal workpiece obtained in Example 1 is shown in FIG.

Example 2
A metal workpiece was produced in the same manner as in Example 1, except that the following temperature adjustment step was further carried out before the pressing step and the drawing step.
-Temperature adjustment process-
First, the same titanium alloy as in Example 1 was heated to 300°C using a heating device (warm die, manufactured by Erichsen Co., Ltd.).
Next, the heated titanium alloy was placed on a blank holder, and the blank holder was driven by a servo motor to move it closer to the die, so that the titanium alloy was sandwiched between the die and the blank holder.

Example 3
A metal workpiece was manufactured in the same manner as in Example 1, except that the diameter of the circumscribing circle of the blank before machining was set as shown in Table 1 and the stop position of the punch stroke was set to 11 mm according to the diameter of the inscribing circle of the blank. When the obtained metal workpiece was placed on a horizontal surface, the vertical height from the horizontal surface to the bottom (11h in Figure 8) was 11.5 mm.
FIG. 12 shows graphs illustrating the punch load-punch stroke curve and the BHF-punch stroke curve in Example 3.
A photograph of the metal workpiece obtained in Example 3 is shown in FIG.

(Comparative Example 1)
Metal workpieces were manufactured in the same manner as in Example 3, except that the clearance ratio was set as shown in Table 1 by changing the plate thickness of the metal material, and PTFE (polytetrafluoroethylene) was applied to the surface of the titanium alloy as a lubricant.

~Evaluation~
(Evaluation of processability)
The metal processed products produced in each of the Examples and Comparative Examples were visually inspected for the presence or absence of wrinkles and their state, and were evaluated based on the following evaluation criteria. The evaluation results are shown in Table 1.
-Evaluation criteria-
A: No defects such as wrinkles or cracks were observed in the metal processed product.
B: No cracks were observed in the metal processed product, but wrinkles were observed.
C: Cracks were observed in the metal processed product.

(Measurement of the ratio of the thickness of the side to the maximum thickness of the bent part (side thickness/maximum thickness of the bent part))
The metal workpieces produced in each Example or Comparative Example were linearly cut so that the area of the bottom was halved. The thicknesses of the shoulder and side walls (also referred to as wall thickness) of the cross sections of the cut metal workpieces were measured using a microscope (DMI5000, manufactured by Leica Microsystems). The results are shown in Table 1.

(Assessing the uniformity of wall thickness of metal workpieces)
The metal workpieces produced in each Example or Comparative Example were linearly cut so that the area of the bottom was halved. The thicknesses of the shoulder and side walls (also referred to as wall thickness) of the cross sections of the cut metal workpieces were measured using a microscope (DMI 5000, manufactured by Leica Microsystems) and evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1.
In the following evaluation criteria, the distortion of wall thickness refers to the percentage of the wall thickness that has decreased or increased, based on the thickness of the titanium alloy before processing.
The distortion of the wall thickness is expressed as a percentage obtained by subtracting the wall thickness after processing measured with a microscope from the thickness of the titanium alloy before processing, and dividing the absolute value by the thickness of the titanium alloy before processing.
-Evaluation criteria-
A: The shoulder wall thickness strain was less than 27% and the side wall thickness strain was less than 27%.
B: The distortion in the wall thickness of the shoulder portion was 27% or more and less than 35%, or the distortion in the wall thickness of the side portion was 27% or more and less than 35%.
C: The strain in the wall thickness of the shoulder and side was 35% or more, or the resulting metal workpiece broke.

As shown in Table 1, Examples 1 to 3 were excellent in processability and uniformity of wall thickness.
On the other hand, Comparative Example 1, in which the clearance ratio was greater than 1.0, was inferior in processability and uniformity of wall thickness.

5... Die 5A... Upper surface 5B... Lower surface 5C... Hole 5D... Bending portion 5E... Side wall 5h... Height 5R... Outer diameter 5r... Inner diameter 7... Blank holder 7A... Hole 7R... Outer diameter 7r... Inner diameter 7h... Height 8... Bending portion 9... Punch 9A... Pressing surface 9B... Body portion 10... Clearance 11... Metal material 11D... Inner bottom surface 11h... Height 11R... Diameter 13... Scrap portion 110... Metal workpiece 111... Bottom 112... Side portion 113... Shoulder portion 114... Flange portion

Claims (5)

A drawing and ironing method for a metal material in which a metal material blank is processed into a square tube,
a pressing step in which the metal material, whose temperature is 0°C to 300°C, is placed between a blank holder and a die, and the metal material is pressed against the die using the blank holder without being squeezed by a punch using the die;
a drawing process in which, in a state in which the metal material having a temperature of 0°C to 300°C is placed between a blank holder and the die, the peripheral portion of the metal material is pressed against the die with a force of 2 kN or less using the blank holder, or is not pressed, and the metal material is drawn into a rectangular tube shape by the punch using the die;
Including,
In the drawing step, a clearance ratio c/t, which is a ratio of a clearance c [mm] between the punch and the die to a thickness t [mm] of the metal material before processing, is 0.7 or more and 1.0 or less;
In the pressing step, the pressing time s [seconds] for pressing the metal material is 4.0 t or more and 8.0 t or less,
The method for drawing and ironing a metal material, wherein in the pressing step, the pressure applied by the blank holder to the metal material is 5 kN to 100 kN . The drawing and ironing method according to claim 1, wherein the metal material is a titanium alloy. The drawing and ironing method described in claim 1 or claim 2, wherein the thickness t [mm] is 0.50 mm or more and the clearance ratio c/t is 1.0. A method for drawing and ironing a metal material according to any one of claims 1 to 3, wherein the metal material has a circumscribed circle with a diameter of 20 mm to 50 mm and an octagonal flat plate shape. The method for drawing and ironing a metal material according to any one of claims 1 to 4, in which the pressing step and the drawing step are alternately repeated to form the metal material into a rectangular tube.