JP7723973B2 - Drawing and ironing method for magnesium alloys - Google Patents

Description

This disclosure relates to a method for drawing and ironing magnesium alloys.

BACKGROUND ART Various processing 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, cylinders, 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, magnesium, etc.

For example, Patent Document 1 describes a pressed magnesium alloy material containing calcium, which has a bent portion formed by bending the magnesium alloy using a press die, and is characterized in that the ratio _R1 / _R2 of the inner diameter _R1 to the outer diameter _R2 is 0< _R1 / _R2 <6, the ratio _R2 /t of the outer diameter _R2 to the plate thickness t is 0.2≦ _R2 /t≦12.0, and the plate thickness t is 1 mm≦t≦6 mm.

Japanese Patent Application Laid-Open No. 2018-176266

Conventionally, there has been a method of heating metal materials to high temperatures (e.g., 700°C to 870°C) to impart ductility to the material before processing. 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 metal material but also the device to high temperatures is thought to shorten the device's lifespan.
Furthermore, some metallic materials should not be heated to high temperatures, and it is preferable to process such metallic materials at relatively low temperatures (for example, 400° C. or lower).
However, for example, it has been very difficult to process metal materials (such as magnesium alloys (also simply referred to as "Mg alloys" in the present disclosure)) that have low ductility in the low temperature range at low temperatures.
On the other hand, Mg alloys are very light and highly useful as metal materials to be processed, and there has been a demand for a method for processing Mg alloys at relatively low temperatures.
Furthermore, the processing method for the Mg alloy is preferably a processing method with a relatively high degree of freedom. For example, it is preferable that the obtained Mg alloy processed product can have a curved shape, and it is also preferable that the obtained Mg alloy processed product can be processed into a cylindrical shape.
The method disclosed in Patent Document 1 has room for improvement in terms of the processing method for Mg alloys.
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 one embodiment of the present disclosure aims to solve is to provide a method for drawing and ironing an Mg alloy that can process the Mg alloy into a cylindrical shape at low temperatures.

Means for solving the above problems include the following aspects.
<1> A method for drawing and ironing an Mg alloy blank material into a cylinder, the method comprising: a pressing step in which the Mg alloy, having a temperature of 0°C to 300°C, is placed between a blank holder and a die, and the peripheral portion of the Mg alloy is pressed using the blank holder without being pressed with a punch; and a drawing step in which the Mg alloy, having a temperature of 0°C to 300°C, is placed between the blank holder and the die, and the peripheral portion of the Mg alloy is pressed with the blank holder at a force of 2 kN or less, or with no pressing, and the Mg alloy is drawn into a cylindrical shape using the punch, 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 Mg alloy before processing, is 0.70 or more and 1.0 or less.
<2> The method for drawing and ironing an Mg alloy according to <1>, which includes alternating the pressing step and the drawing step multiple times, and changes the pressure applied by the blank holder to the peripheral portion of the Mg alloy at least once during the multiple pressing steps.
<3> The method for drawing and ironing an Mg alloy according to <2>, wherein the pressure applied by the blank holder to the peripheral portion of the Mg alloy is changed in the second or subsequent pressing steps among the multiple pressing steps.
<4> The method for drawing and ironing an Mg alloy according to <2> or <3>, wherein the pressure applied to the peripheral portion of the Mg alloy by the blank holder after the change is higher than the pressure applied to the peripheral portion of the Mg alloy by the blank holder before the change.
<5> The method for drawing and ironing an Mg alloy according to any one of <1> to <4>, wherein in the pressing step, the pressure applied by the blank holder to the peripheral portion of the Mg alloy satisfies the following formula 1:

In Equation 1, BHF is the pressure that the blank holder applies to the peripheral portion of the Mg alloy, P ₀ is expressed by the following Equation 2, and A is the area [mm ² ] over which the blank holder applies pressure to the peripheral portion of the Mg alloy.

In Equation 2, D ₀ is the diameter [mm] of the Mg alloy before processing, d ₁ is the diameter [mm] of the punch, t is the thickness [mm] of the Mg alloy before processing, and s is the tensile strength [N/mm ² ] of the Mg alloy before processing.
<6> The method for drawing and ironing a Mg alloy according to any one of <1> to <5>, wherein the thickness t [mm] is 0.50 mm or more, and the clearance ratio c/t is 0.75 to 0.90.

Embodiments of the present disclosure provide a method for drawing and ironing an Mg alloy, which can process the Mg alloy into a cylindrical shape at low temperatures.

FIG. 1 is a cross-sectional view illustrating a case where an Mg alloy is drawn into a cylindrical shape with a clearance ratio of 1.0 or more. FIG. 10 is a cross-sectional view illustrating a case where an Mg alloy is drawn into a cylindrical shape with a clearance ratio of less than 1.0. 1 is a cross-sectional view of a die, an Mg alloy, 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, an Mg alloy, a punch, and a blank holder for explaining the 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 showing an example of an Mg alloy workpiece according to the present disclosure. FIG. 1 is a graph showing the relationship between time, BHF, and punch stroke when a magnesium alloy is processed using the drawing and ironing method of the present disclosure.

Hereinafter, an embodiment of the drawing method of the present disclosure will be described in detail with reference to Figures 1 to 9. However, the present disclosure is not limited to the embodiment described below.

<Squeezing and ironing method>
The method for drawing and ironing an Mg alloy according to the present disclosure (also referred to simply as the "drawing and ironing method of the present disclosure" in the present disclosure) is a method for drawing and ironing an Mg alloy, in which an Mg alloy blank is formed into a cylinder, and
a pressing step in which, in a state in which an Mg alloy having a temperature of 0°C to 300°C is placed between a blank holder and a die, the Mg alloy is not squeezed by a punch, and the peripheral portion of the Mg alloy is pressed using the blank holder;
a drawing process in which, in a state in which an Mg alloy having a temperature of 0°C to 300°C is placed between a blank holder and a die, the peripheral portion of the Mg alloy is pressed with a force of 2 kN or less using the blank holder, or is not pressed, and the Mg alloy is drawn into a cylindrical shape using a punch;
Including,
In the drawing process, 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 Mg alloy before processing, is 0.70 or more and 1.0 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, conventionally, Mg alloys have low ductility in the low temperature range, and it has been very difficult to process them at low temperatures.
However, even if a high temperature (for example, 500°C or higher) is applied to the Mg alloy, separate equipment and processes for heating the Mg alloy, 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 thus can process an Mg alloy that has low ductility in the low temperature range without heating it to a high temperature.
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 Mg alloy can be drawn into a cylindrical shape so as to reduce the thickness 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, part of the Mg alloy does not reach the gap between the die and the punch during drawing, and remains in the bent portion. By controlling the inflow of the Mg alloy within a certain range as the drawing and ironing process progresses, the thickness of the bent portion, at which fracture is likely to occur, can be kept within a certain range.
By incorporating the above-mentioned features and other configurations, the drawing and ironing method of the present disclosure can proceed with processing even at low temperatures and suppress damage such as breakage.

The drawing and ironing method of the present disclosure preferably includes a pressing step and a drawing step alternately repeated multiple times. That is, the drawing and ironing method of the present disclosure preferably processes the Mg alloy into a cylinder by alternately repeating the pressing step and the 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 an Mg alloy workpiece with highly uniform wall thickness while suppressing the occurrence of wrinkles in the resulting Mg alloy workpiece.

The drawing and ironing method of the present disclosure allows for drawing and ironing of Mg alloys at low temperatures (e.g., below 300°C), eliminating the need to heat the Mg alloy to high temperatures. This makes it possible to draw and iron Mg alloys using simple, commonly used equipment. This reduces manufacturing costs and improves operational simplification.
Furthermore, the drawing and ironing method of the present disclosure can prevent the wall thickness of the resulting Mg alloy workpiece from being partially reduced, thereby enabling the production of Mg alloy workpieces with excellent wall thickness uniformity.

<Pressing process>
The pressing process in the present disclosure is a process in which an Mg alloy having a temperature of 0°C to 300°C is placed between a blank holder and a die, and the Mg alloy is not squeezed by a punch, but the peripheral portion of the Mg alloy is pressed using the blank holder.
This can prevent wrinkles from occurring in the resulting Mg alloy workpiece.

~One embodiment of the pressing step~
An embodiment of the pressing step in the present disclosure will be described with reference to FIG.
FIG. 3 is a cross-sectional view of a die, an Mg alloy, a punch, and a blank holder for explaining the pressing process in the present disclosure.
In one embodiment of the pressing process of the present disclosure, as shown in Fig. 3, the Mg alloy 11 is placed between the blank holder 7 and the die 5, and the blank holder 7 is used to press, for example, a scrap portion 13 of the Mg alloy 11 in a direction from the blank holder 7 toward the die 5. At this time, the punch 9 does not push the Mg alloy 11 up into the hole 5C of the die 5 and squeeze it into the hole 5C.

The drawing and ironing method of the present disclosure includes a pressing step and a drawing step alternately repeated multiple times, and it is preferable to change the pressure (BHF: Blank Holding Force) applied by the blank holder to the peripheral portion of the Mg alloy at least once during the multiple pressing steps.
This allows the thickness of the Mg alloy sheet to be controlled before the Mg alloy material flows into the die during the drawing and ironing process. As a result, in addition to the drawing and ironing process in die 5, forming including two types of operations can be performed using a single die.

In the drawing and ironing method disclosed herein, it is preferable to change the BHF in the second or subsequent pressing steps among multiple pressing steps, in order to actively control the thickness of the flange portion of the Mg alloy.

In the drawing and ironing method of the present disclosure, it is preferable that the pressure (BHF) applied to the peripheral portion of the Mg alloy by the blank holder after the change is higher than the pressure (BHF) applied to the peripheral portion of the Mg alloy by the blank holder before the change.
In the drawing and ironing method of the present disclosure, it is preferable to increase the BHF during multiple pressing steps, that is, it is preferable to increase the BHF at least once during multiple pressing steps.

It is preferable that BHF satisfy the following formula 1.

In Equation 1, BHF is the pressure applied by the blank holder to the periphery of the Mg alloy, P ₀ is expressed by the following Equation 2, and A is the area [mm ² ] over which the blank holder applies pressure to the periphery of the Mg alloy.

In Equation 2, D ₀ is the diameter [mm] of the Mg alloy before processing, d ₁ is the diameter [mm] of the punch, t is the thickness [mm] of the Mg alloy before processing, and s is the tensile strength [N/mm ² ] of the Mg alloy before processing.

Equation 1 represents the lower limit of BHF.
Whether the BHF is changed or not during multiple pressing steps, it is preferable that the BHF satisfies Equation 1.
For example, when the BHF is increased during multiple pressing steps, it is preferable to increase the BHF within a range that satisfies Equation 1.

P ₀ ×A in Equation 1 is also referred to as the minimum BHF.
Equation 1 means that the BHF is 15 times or more the minimum BHF.

(Mg alloy)
The Mg alloy in the present disclosure is the material of the Mg alloy 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 an Mg alloy that has low ductility in the low temperature range, the Mg alloy can be processed without heating the Mg alloy to a high temperature.

Among the above, the Mg alloy in the present disclosure is preferably titanium or a titanium alloy, which is an Mg alloy with low ductility in the low temperature range.
When an Mg alloy having low ductility in the low temperature range is processed in the low temperature range, defects such as fracture and wrinkles tend to occur, making it difficult to process it satisfactorily. However, the drawing and ironing method of the present disclosure makes it possible to process an Mg alloy having low ductility in the low temperature range into a desired shape.

Examples of metals or non-metals other than magnesium (also referred to as Mg in this disclosure) contained in the Mg alloy include Al, Zn, and Ca.
As the Mg alloy in the present disclosure, an AZ alloy containing Al and Zn is preferred, and an AZ31 alloy is more preferred.

From the viewpoint of the strength of the workpiece obtained after processing, the thickness t of the Mg alloy 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 Mg alloy 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 Mg alloy in this disclosure is not particularly limited. For example, the Mg alloy may be in the shape of a disk.

When the Mg alloy is in the shape of a disk, the diameter of the Mg alloy is preferably 50 mm to 80 mm.
When the diameter of the circumscribed circle is 50 mm or more, the amount of inflow of the Mg alloy can be well controlled during the drawing and ironing process.
From the above viewpoint, the diameter of the circumscribed circle is more preferably 55 mm or more, and even more preferably 60 mm or more.
Furthermore, by setting the diameter of the circumscribed circle to 80 mm or less, the Mg alloy can be allowed to flow smoothly onto the ironing surface without being fractured.
From the above viewpoint, the diameter of the circumscribed circle is more preferably equal to or less than 75 mm, further preferably equal to or less than 70 mm, and particularly preferably equal to or less than 65 mm.

(lubricant)
The Mg alloy preferably contains a lubricant on the surface.
This reduces friction between the die and the punch, thereby protecting the Mg alloy and suppressing adhesion of the Mg alloy to the die and the punch.
Specifically, by including a lubricant on the surface of the Mg alloy, when the Mg alloy is drawn using a die and a punch in the drawing process, sliding between the Mg alloy and at least one of the die and the punch can be suppressed. Therefore, it is preferable that the Mg alloy includes 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 Mg alloy may have an oxide film on the surface, which can protect the Mg alloy and prevent it from adhering to the die.
The oxide film can be formed on the Mg alloy 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)
The die of the present disclosure will be described with reference to FIG.
FIG. 5 is a cross-sectional view illustrating an example of a die according to the present disclosure.
5, the die 5 has a generally cylindrical hole 5C and a side wall 5E in the center, and may have a bent portion 5D at the open end of the hole 5C on the side (lower surface 5B side) where the Mg alloy 11 is placed so as to be in contact with the die 5. The Mg alloy 11 placed so as to be in contact with the die 5 can be squeezed along the hole 5C using a punch 9 in the direction from the lower surface 5B toward the upper surface 5A, thereby processing the Mg alloy workpiece into a desired cylindrical shape.
The drawing and ironing method of the present disclosure is a method of drawing and ironing an Mg alloy in which an Mg alloy blank is formed into a cylinder, and therefore the shape of the hole 5C of the die 5 in the present disclosure is preferably cylindrical.

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 desired Mg alloy 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 that the blank holder 7 applies to the periphery of the Mg alloy 11 can be adjusted appropriately depending on the type of Mg alloy 11 .
The BHF in this step may be, for example, 2 kN to 50 kN, preferably 3 kN to 10 kN, and more preferably 4 kN to 7 kN.

The blank holder of the present disclosure will be described with reference to FIG.
FIG. 6 is a cross-sectional view showing an example of a blank holder according to the present disclosure.
As shown in Fig. 6, the blank holder 7 has a hole 7A, which is, for example, circular, and supports the Mg alloy 11 when it is placed between the blank holder 7 and the die 5, as shown in Fig. 3. In addition, pressure is applied to the peripheral portion (flange portion) of the surface of the Mg alloy 11 opposite to the surface that contacts the die 5. This makes it possible to suppress the occurrence of wrinkles in the Mg alloy workpiece.
As shown in Figure 6, the blank holder 7 has a circular 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 Mg alloy 11, thereby drawing it into a cylindrical shape.

The blank holder 7 may be disk-shaped with a circular 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 an Mg alloy having a temperature of 0°C to 300°C is placed between a blank holder and a die, and the peripheral portion of the Mg alloy is pressed with or without being pressed with a force of 2 kN or less using the blank holder, and the Mg alloy is drawn into a cylindrical shape using a punch.
This step makes it possible to suppress shear deformation caused by tensile stress, which is the cause of fracture, and to deform the Mg alloy into a desired cylindrical shape.

If the peripheral portion of the Mg alloy is not pressed using the blank holder during the drawing process, the peripheral edge side of the Mg alloy blank material may be sandwiched between the blank holder and the die, or the peripheral edge side of the Mg alloy blank material 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.
FIG. 4 is a cross-sectional view of a die, an Mg alloy, a punch, and a blank holder for explaining the drawing process in the present disclosure.
In one embodiment of the drawing process of the present disclosure, as shown in Figure 4, the punch 9 is operated while the Mg alloy 11 is placed between the blank holder 7 and the die 5, so that the punch 9 passes through the hole 7A of the blank holder 7 and presses, for example, the inner bottom surface 11D (see Figure 8) of the Mg alloy 11, pushing the titanium alloy up into the hole 5C of the die 5 to draw the Mg alloy 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 the Mg alloy 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 Mg alloy placed between the blank holder and the die.

This process is carried out by pressing the Mg alloy with a blank holder at a pressure of 2 kN or less, or without pressing. This allows the wall thickness of the resulting Mg alloy workpiece to be uniform. Among the above, the wall thickness of the side and shoulder parts of the Mg alloy workpiece can be uniformed well.
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 Mg alloy at a pressure of 2 kN or less, or not press it at all, and it is more preferable not to press it at all.

(punch)
The punch in this disclosure will be described with reference to FIG.
FIG. 7 is a cross-sectional view showing an example of a punch according to the present disclosure.
7, punch 9 can be, for example, substantially cylindrical, have a body portion 9B, and can be provided with a circular pressing surface 9A on body portion 9B for pressing Mg alloy 11. As shown in FIG. 4, punch 9 is used to press a portion of the surface of Mg alloy 11 opposite to the surface that contacts die 5, thereby squeezing Mg alloy 11 into hole 5C of die 5.

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

The Mg alloy drawing and ironing method disclosed herein is a method for drawing and ironing an Mg alloy blank into a cylinder. Therefore, it is preferable that the shape of the punch 9 be cylindrical.

The load (punch load) applied by the punch 9 when pressing the Mg alloy 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 the Mg alloy 11 can be adjusted appropriately depending on the type of Mg alloy 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 Mg alloy 11 (punch speed) can be adjusted appropriately depending on the type of Mg alloy 11. For example, the punch speed can be set to 5 mm/min to 500 mm/min.
In this disclosure, the punch speed refers to the speed at which the Mg alloy is forced into the hole in the die by the punch.

The method for drawing and ironing an Mg alloy according to the present disclosure preferably includes alternating multiple cycles of the pressing step and the drawing step.
This will be explained with reference to FIG.
FIG. 9 is a graph showing the relationship between time, BHF, and punch stroke when a magnesium alloy is processed using the drawing and ironing method of the present disclosure.

As shown in Figure 9, the punch stroke increases by alternately repeating the pressing process and the drawing process. In this case, the punch stroke near the maximum punch load may be, for example, around 9 mm. In the pressing process, 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 Mg alloy from the point where the punch comes into contact with the Mg alloy 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 Mg alloy into a cylindrical 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 during the above adjustment.

In the drawing and ironing method disclosed herein, it is preferable to change the BHF during multiple pressing processes. As shown in Figure 9, the BHF at the time when the BHF is changed is larger than the BHF before that time. Then, from that time onwards, the pressing processes are carried out using the changed BHF.

<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 die to the thickness t [mm] of the Mg alloy before processing, is 0.70 or more and 1.0 or less.
This allows the drawing and ironing process to be carried out as described above, and when the Mg alloy is drawn, a portion of the Mg alloy does not reach the gap between the die and the punch, but 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 Mg alloy flowing into the Mg alloy flow portion consisting of the blank holder and die, which results in an increased thickness of the bent portion, which is prone to fracture, in the resulting Mg alloy workpiece.

The above will be described in detail with reference to FIGS.
FIG. 1 is a cross-sectional view illustrating the case where an Mg alloy is drawn into a cylindrical shape with a clearance ratio of 1.0 or more.
FIG. 2 is a cross-sectional view illustrating the case where an Mg alloy is drawn into a cylindrical shape with a clearance ratio of less than 1.0.
First, as shown in Figure 1, when the clearance ratio exceeds 1.0, the length of the clearance 10 exceeds the pre-processing thickness t of the Mg alloy 11. When drawing and ironing is performed with the clearance ratio exceeding 1.0, when the Mg alloy 11 is drawn using the die 5, the Mg alloy 11 can pass between the die 5 and the punch 9 without decreasing in thickness, and therefore, a portion of the Mg alloy 11 is unlikely to remain in the bent portion 8 during processing.
On the other hand, as shown in Figure 2, when the clearance ratio is 1.0 or less, the length of the clearance 10 is less than the thickness t of the Mg alloy 11 before processing. When drawing and ironing is performed with a clearance ratio of 1.0 or less, it is possible to prevent all of the drawn and ironed portion of the Mg alloy 11 from reaching between the die 5 and the punch 9 when drawing the Mg alloy 11 using the die 5. The portion of the drawn and ironed portion of the Mg alloy 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 Mg alloy flowing into the Mg alloy flow portion consisting of the blank holder and the die. As a result, the thickness of the bent portion, where fracture is likely to occur, can be increased in the resulting Mg alloy workpiece.
As described above, by increasing the thickness of the bent portion, it is possible to suppress the occurrence of fracture in the resulting Mg alloy workpiece.

The clearance ratio is 1.0 or less, and preferably 0.90 or less, from the viewpoint of processing the Mg alloy without problems such as breakage by controlling the thickness of the bent portion.
Moreover, from the viewpoint of effectively suppressing fracture and obtaining sufficient strength in the resulting Mg alloy processed product, the clearance ratio is more preferably 0.75 or more, and even more preferably 0.80 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 0.75 to 0.90.

(Draw ratio)
When the Mg alloy 11 is disk-shaped and the punch 9 is cylindrical, the ratio of the diameter ( _D0 ) of the Mg alloy 11 to the diameter ( _d1 ) of the punch 9 (drawing ratio: _D0 / _d1 ) 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 _D0 , i.e., the larger the drawing ratio, the more likely the Mg alloy workpiece is to fracture 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 5 kN to 100 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 Mg alloys over a wide temperature range, and may further include a temperature adjustment step of adjusting the temperature of the Mg alloy to 0°C to 300°C before the pressing step and the drawing step.
When performing work in which the temperature of the Mg alloy is set to less than 0°C, it is thought that costs will increase. However, by adjusting the temperature of the Mg alloy to 0°C or higher, the increase in costs can be suppressed.
From the above viewpoint, the temperature of the Mg alloy is preferably 15° C. or higher.
Furthermore, by adjusting the temperature of the Mg alloy 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 Mg alloy and the die. It is also possible to prevent damage to the Mg alloy, 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 Mg alloy 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, there is no need to adjust the temperature if the temperature is room temperature (e.g., 25°C), and even if temperature adjustment is not performed, the drawing and ironing method disclosed herein makes it possible to process Mg alloys without 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.

The Mg alloy was subjected to drawing and ironing by the drawing and ironing method described below.
In this example, the die, punch, Mg alloy, 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 38.0 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 40.0 mm.

The punch used had a cylindrical outer shape with a circular pressing surface having a diameter (d ₁ ) of 33.0 mm and a body length of 130 mm.

The Mg alloy used was an AZ31 alloy in the shape of a disk. The diameter (D ₀ ) of the circular surface of the disk and the thickness t before processing are as shown in Table 1.
The ratio of the diameter (D ₀ ) of the circle of the Mg alloy to the diameter (d ₁ ) of the circle of the punch (drawing ratio: D ₀ /d ₁ ) is as shown in Table 1.
The diameter _D0 of the Mg alloy before processing is 60.0 mm.
The tensile strength s of the Mg alloy before processing is 250×10 ⁶ N/mm.

The clearance c obtained by the above punch and die was 0.4 mm. The clearance ratio c/t for each example or comparative example is shown in Table 1.

In this example, the area A over which the blank holder applies pressure to the periphery of the Mg alloy is 1972 mm ² .

Example 1
- Arrangement of Mg alloy -
The Mg alloy was placed on a blank holder, and the blank holder was driven by a servo motor to move it toward the die, so that the Mg alloy was sandwiched between the die and the blank holder. The temperature of the Mg alloy is shown in Table 1.

- Pressing process -
As shown in Figure 3, the Mg alloy placed between the blank holder and the die was pressed using the blank holder in a direction from the blank holder to the die, with a BHF force shown in Table 1. At this time, the Mg alloy was not squeezed into the hole in the die by the punch.

- Drawing process -
As shown in Figure 4, the Mg 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 Mg alloy, forcing the Mg alloy up into the hole in the die and drawing it into the hole. At this time, the flange portion of the Mg alloy was not pressed using the blank holder. The punch speed in the drawing process was 90 mm/min.

The punch stroke, BHF, and punch load were adjusted appropriately, and the pressing and drawing processes were repeated alternately multiple times. The processing of the Mg alloy 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 15 mm when the flange portion of the resulting Mg alloy workpiece was placed in contact with a horizontal surface, and a cylindrical Mg alloy workpiece was produced.

The obtained Mg alloy workpiece will be described with reference to FIG.
FIG. 8 is a cross-sectional view showing an example of an Mg alloy workpiece according to the present disclosure.
The obtained Mg alloy workpiece had a bottom diameter (11R in Figure 8) of 34.0 mm, and when the Mg alloy workpiece was placed on a horizontal surface as shown in Figure 8, the vertical height 11h from the horizontal surface to the bottom was 16 mm.

Example 2
A cylindrical Mg alloy workpiece was produced in the same manner as in Example 1, except that the BHF was changed as shown in Table 1 at the time points (number of pressing steps) shown in Table 1 during the multiple pressing steps, and the changed BHF was maintained in the pressing steps after the time points shown in Table 1.

(Comparative Example 1)
The pressing and drawing steps were not repeated alternately multiple times, but were each performed simultaneously once. That is, with the Mg alloy placed between the blank holder and the die, the peripheral portion of the Mg alloy was pressed with a pressure of more than 4 kN using the blank holder, and the Mg alloy was drawn into a cylindrical shape using the punch.
The BHF in the pressing process was changed to 5 kN, and the punch stroke in the drawing process was increased at a constant rate.
An attempt was made to manufacture a cylindrical Mg alloy workpiece in the same manner as in Example 1, except for the above points.
That is, an attempt was made to manufacture a cylindrical Mg alloy workpiece by a conventional deep drawing method.

~Evaluation~
(Evaluation of processability)
The Mg alloy workpieces produced in each Example or Comparative Example 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 Mg alloy processed product.
B: No cracks were observed in the Mg alloy workpiece, but wrinkles were observed.
C: Cracks were observed in the Mg alloy 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 Mg alloy 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 Mg alloy workpieces were measured using a microscope (DMI5000, manufactured by Leica Microsystems). The results are shown in Table 1.

(Evaluation of wall thickness uniformity of Mg alloy workpiece)
The Mg alloy 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 Mg alloy workpieces were measured using a microscope (DMI5000, 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 Mg 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 Mg alloy before processing, and dividing the absolute value by the thickness of the Mg alloy before processing.
-Evaluation criteria-
A: The distortion of the wall thickness at the shoulder was less than 27%.
B: The strain in the wall thickness of the shoulder portion was 27% or more and less than 35%.
C: The strain in the wall thickness of the shoulder portion was 35% or more, or fracture occurred in the obtained Mg alloy workpiece.

As shown in Table 1, this is a drawing and ironing method for forming a blank Mg alloy into a cylinder, and includes: a pressing step in which the Mg alloy, which is at a temperature of 0°C to 300°C, is placed between a blank holder and a die, and the peripheral portion of the Mg alloy is pressed using the blank holder without being pressed with a punch; and a drawing step in which the Mg alloy, which is at a temperature of 0°C to 300°C, is placed between the blank holder and the die, and the peripheral portion of the Mg alloy is pressed with the blank holder at a force of 2 kN or less, or not pressed, and the Mg alloy is drawn into a cylindrical shape using the punch. In the drawing step, 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 Mg alloy before processing, was 0.70 or more and 1.0 or less. Examples using this drawing and ironing method for forming a blank Mg alloy showed excellent workability and uniformity in wall thickness. Therefore, the Mg alloy could be processed into a cylindrical shape at low temperatures.
On the other hand, in Comparative Example 1, in which the pressing step and the drawing step were performed simultaneously once each, instead of repeating the pressing step and the drawing step alternately multiple times, cracks were observed, and the workability was poor, so the Mg alloy could not be worked into a cylindrical shape at low temperatures.

5... Die 5A... Upper surface 5B... Lower surface 5C... Hole 5D... Bent 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... Bent portion 9... Punch 9A... Pressing surface 9B... Body portion 10... Clearance 11... Mg alloy 11D... Inner bottom surface 11h... Height 11R... Diameter 13... Scrap portion 110... Mg alloy workpiece 111... Bottom 112... Side 113... Shoulder portion 114... Flange portion

Claims (5)

A method for drawing and ironing an Mg alloy, in which a blank Mg alloy is processed into a cylinder, comprising the steps of:
a pressing step in which the Mg alloy, whose temperature is 0°C to 300°C, is placed between a blank holder and a die, and the Mg alloy is not squeezed by a punch, but the peripheral portion of the Mg alloy is pressed using the blank holder;
a drawing process in which the Mg alloy having a temperature of 0°C to 300°C is placed between a blank holder and the die, and the peripheral portion of the Mg alloy is pressed with the blank holder at a pressure of 2 kN or less, or not pressed, and the Mg alloy is drawn into a cylindrical shape by the punch;
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 Mg alloy before processing, is 0.70 or more and 1.0 or less;
The pressing step and the squeezing step are alternately repeated multiple times,
a pressure applied by the blank holder to the peripheral portion of the Mg alloy is changed at least once during the multiple pressing steps . 2. The method for drawing and ironing an Mg alloy according to claim 1 , wherein the pressure applied by the blank holder to the peripheral portion of the Mg alloy is changed in the second or subsequent pressing steps among the multiple pressing steps. 3. A method for drawing and ironing an Mg alloy according to claim 1 , wherein the pressure applied to the peripheral portion of the Mg alloy by the blank holder after the change is higher than the pressure applied to the peripheral portion of the Mg alloy by the blank holder before the change . The method for drawing and ironing an Mg alloy according to any one of claims 1 to 3 , wherein the pressure applied by the blank holder to the peripheral portion of the Mg alloy in the pressing step satisfies the following formula 1:


In Equation 1, BHF is the pressure [N/mm ² ] that the blank holder applies to the peripheral portion of the Mg alloy, P ₀ is expressed by the following Equation 2, and A is the area [mm ² ] over which the blank holder applies pressure to the peripheral portion of the Mg alloy.


In Equation 2, D ₀ is the diameter [mm] of the Mg alloy before processing, d ₁ is the diameter [mm] of the punch, t is the thickness [mm] of the Mg alloy before processing, and s is the tensile strength [N/mm ² ] of the Mg alloy before processing. The method for drawing and ironing an Mg alloy according to any one of claims 1 to 4 , wherein the thickness t [mm] is 0.50 mm or more, and the clearance ratio c/t is 0.75 to 0.90.