JP3057987B2 - Titanium alloy material excellent in stamping workability and stamping method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium alloy material having excellent cold workability and a method for punching the same.

[0002]

2. Description of the Related Art Titanium and titanium alloys are lightweight, high strength,
And it has excellent physical properties such as high corrosion resistance. However, cold workability is a metal belonging to a difficult class.
The punching process of the titanium alloy material is performed by a conventional punching method when a workpiece 2 on a die 1 is punched by a punch 3 as shown in FIG. 5A, and on a die 1 shown in FIG. In the fine blanking method in which the workpiece 2 is pressed by the plate retainer 4 at the periphery thereof and the ejector 5 applies a reverse pressure to punch the workpiece 2, any of the fine blanking methods is equivalent to the punching processing of the steel material. In particular, when punching a high-strength material such as a Ti-6Al-4V alloy, as shown in FIG. 6A, a droop 8 around the die contact surface 7 opposite to the punch contact surface 6. Fine cracks 9 occur in the vicinity. When the crack of the crack 9 propagates to the cut surface 10, the crack 9 is reached. The punched material that has cracked or chipped cannot be applied to the product as it is, but it is necessary to increase the punching dimensions by the finishing allowance that can remove cracks and chips, and to punch out, and finish the entire cut surface with a grinder etc. ing. Cracks and chippings occurring in 8 portions are remarkable in a thick material having a thickness of 1.5 mm or more, and are inevitable in a normal punching method including a fine blanking method. From such a technical situation, when manufacturing a blank from a titanium alloy plate of 1.5 mm or more at present, an electric discharge machining method such as wire cutting is applied. Japanese Patent Application Laid-Open No. 1-177906 discloses a technique for preventing defects generated in a sheared portion. According to the same publication, in a method of cutting a titanium alloy material by shearing, after forming a notch at a cutting position of the material, a shear stress is applied thereto, and a shearing direction is selected from the tip of the notch in a shearing direction during shearing. It is described that since cracks are formed, the inclination of the cut surface can be reduced, and the cutting load decreases, so that the load on the shearing blade can be reduced and the generation of burrs can be suppressed.

[0003]

In the prior art as described above, fine cracks and cracks generated when a high-strength material such as a Ti-6Al-4V alloy is punched are cut to the cut surface. A punched material in which a cut surface is chipped due to propagation cannot be applied as it is, and there is a drawback that the number of steps increases, such as finishing the entire cut surface with a grinder. Also, in punching, including back pressure punches, there is clearance between the punch and the die, so that drooping occurs near the cut surface, and tensile stress due to bending deformation can be avoided at the surface layer of anybody. Absent. When using a back pressure punch,
Although this tends to be suppressed, it is not completely suppressed, and there is a drawback that the number of processes such as grinding the entire cut surface is increased. Further, in the method of forming a notch at a shear position of a material, the number of processing steps is increased, and thus it is a step to be excluded from the viewpoint of productivity.

SUMMARY OF THE INVENTION The present invention has been made to solve the problem related to the defect near the cut surface due to cracking or chipping that occurs when punching a titanium alloy as described above.
It is an object of the present invention to provide a technique that enables a good punching process using a conventional punching method even for a high-strength titanium alloy such as a + β-type titanium alloy.

[0005]

SUMMARY OF THE INVENTION A first invention of a titanium alloy material excellent in stamping workability and a stamping method according to the present invention is an average crystal of an α + β type titanium alloy material stamped in a cold state. It has a crystal structure having a particle size of 7 μm or less. The second invention is characterized in that the punching of a titanium alloy material to be punched in the cold is performed under the condition of the following formula (1). c / t ≦ −4.4 ln d + 23.0 and d ≦ 7.0 (1) where c: clearance (mm) t: thickness of punched material (mm) d: average crystal of punched material Particle size (μm) The third invention is characterized in that the punching process of a titanium alloy material to be punched cold is performed under the condition of the following formula (2). c / t ≦ −4.4 ln d + 25.7 and d ≦ 7.0 (2) where c: clearance (mm) t: thickness of punched material (mm) d: average crystal of punched material Particle size (μm)

[0006]

The titanium alloy material has an α + β type titanium alloy having an α crystal structure and a β crystal structure mixed with each other, and has an equiaxed α + β crystal structure, which has higher ductility than a single β crystal structure. In the case of the α + β type titanium alloy, the average crystal grain size is determined by averaging the grain size of the pro-eutectoid α crystal when the volume fraction of the pro-eutectoid α crystal is usually in the range of 30 to 70%. As it becomes, the ductility gradually improves. Ti-6Al
-4V alloy is usually 10 μm, but can be refined up to 4 μm, and Ti-4.5Al-3V-2Mo-
In the case of a 2Fe alloy, the grain size can be reduced to about 5 μm and 2 μm or less. Regarding the improvement of ductility due to grain refinement, it is conceivable to correspond to the total elongation value in the tensile test, but due to the difference in deformation characteristics of the droop part during the tensile test and punching,
At present, the total elongation value does not correspond one-to-one, and the punching property must be verified in the punching process. In the present invention, among α + β type titanium alloys, the crystal grain size is 7 μm.
By applying a base plate controlled to fine grains of m or less, it is possible to prevent cracks that occur near the drooping part of the punching process, and thereby prevent chipping caused by the propagation of cracks to the cut surface, and punching of titanium alloy This enables processing. In addition, c
It was confirmed that cracking and chipping did not occur by setting / t to the range of the following expression (1) regardless of the plate thickness. c / t ≦ −4.4 ln d + 23.0 and d ≦ 7.0 (1) where c: clearance (mm) t: thickness of punched material (mm) d: average crystal of punched material Particle diameter (μm) In the case of punching with an added reverse thickness, it was confirmed that cracking and chipping did not occur by setting the range of c / t to a range satisfying the following expression (1). Was. c / t ≦ −4.4 ln d + 25.7 and d ≦ 7.0 (2) where c: clearance (mm) t: thickness of the punched material (mm) d: average crystal of the punched material Particle size (μm)

[0007]

Embodiments of the present invention will be described below. The titanium alloy materials A and B having the chemical components shown in Table 1 were melted by vacuum arc, hot-rolled to a thickness of 7 mm, and heat-treated to obtain test materials.

[0008]

[Table 1] The hot rolling was performed twice at a reduction ratio of 3.75 and 2.86, and the material heating temperature during the second hot rolling was changed. Table 2 shows the relationship between the hot rolling temperature conditions (two levels), the heat treatment conditions (three heating levels), the crystal grain size of each test material, and the tensile properties.

[0009]

[Table 2]

The crystal grain size is determined by a cutting method (microscope magnification 800 times,
It is measured with a line segment length of 50 μm and the number of fields of view 5), and is an average of values in a rolling direction and a direction perpendicular to the rolling direction.
The materials of test material numbers A1 to A5 and B1 to B5 have granular α crystals, and the materials of A6 and B6 have acicular α crystals transformed and formed from β grains. I asked. The tensile test was performed using a plate-shaped test piece having a thickness of 3 mm, a width of the parallel portion of 6 mm, a gauge length of 25 mm, and a length of the parallel portion of 32 mm.
In the punching test, these test materials were machined to a thickness of 1.5 mm.
, 3.2 mm and 5.0 mm, and a circle of φ60 mm was punched from a 100 × 100 mm base plate. Tables 3 to 8 show punching conditions and punching results. A part of the test material was punched by applying a reverse pressure. The diameter was the same as that of the back pressure punch, and the back pressure was set to 10% of the punch force. Table 9 shows the punching conditions and the punching results when a back pressure was applied.

[0011]

[Table 3]

[0012]

[Table 4]

[0013]

[Table 5]

[0014]

[Table 6]

[0015]

[Table 7]

[0016]

[Table 8]

[0017]

[Table 9]

The test materials A6 and B6 have a needle-like α + β structure formed by transformation from β grains, and cracks near the cut surface and cracks in the cut surface are largely generated. Obviously not suitable. On the other hand, granular α +
test material A1~A5 and B1~B5 with β tissue, cracking or chipping is minor, it can be seen that are suitable for stamping.

FIGS. 1 to 3 show the relationship between the crystal grain size and c / t (clearance / plate thickness × 100:%) for each plate thickness for specimen numbers A1 to A5 having a granular α + β structure. It is. As is clear from the figure, the crystal grain size is 8 μm.
Above, cracks and chips occur regardless of c / t. When the crystal grain size is 7 μm or less, no cracking or chipping occurs c
/ T range. The range of c / t at which the crystal grain size is 7 μm or less and in which cracking or chipping does not occur is substantially constant regardless of the plate thickness. From this, it has been confirmed that the α + β type titanium alloy material can be punched in a good state without cracking and chipping by setting the punching condition in a range satisfying the following equation (1). Was done. c / t ≦ −4.4 ln d + 23.0 and d ≦ 7.0 (1) where c: clearance (mm) t: thickness of punched material (mm) d: average crystal of punched material FIG. 4 shows specimen numbers A1 to A1 having a granular α + β structure.
This is a case where a reverse pressure is applied to A5 and B1 to B5. As is clear from the figure, the average crystal grain size is 8 μm.
In this case, the occurrence of cracks and chips is not shown in FIGS.
However, the range of c / t that can be punched is greatly expanded, and by setting the punching condition to a range that satisfies the following expression (2) , cracks and chipping do not occur. It was confirmed that punching could be performed in a good condition. c / t ≦ −4.4 ln d + 25.7 and d ≦ 7.0 (2) where c: clearance (mm) t: thickness of punched material (mm) d: average crystal of punched material Particle size (μm)

[0020]

As described above, according to the present invention, in a conventional blanking and a blanking process to which a reverse pressure is applied, an α + β type titanium alloy plate having a crystal grain size suitable for the blanking process is used.
In addition, by applying the optimum clearance according to the thickness of the sheet, there is an excellent effect of enabling the conventional punching of a high-strength titanium alloy material, which has been impossible in the past. In addition, a punch for applying a reverse pressure is arranged on the surface on the opposite side of the punch and the reverse pressure is applied, thereby expanding the range of punching conditions for the titanium alloy material and making the punching process easier. Has an excellent effect.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the average crystal grain size and the state of occurrence of cracks and chips with respect to clearance when an α + β type titanium alloy material is punched by a conventional punching method.

FIG. 2 is a graph showing the relationship between the average crystal grain size and the state of occurrence of cracks and chips with respect to clearance when an α + β type titanium alloy material is punched by a conventional punching method.

FIG. 3 is a graph showing the relationship between the average crystal grain size and the state of occurrence of cracks and chips with respect to clearance when an α + β type titanium alloy material is punched by a conventional punching method.

FIG. 4 is a graph showing the relationship between the average crystal grain size and the state of occurrence of cracks and chips with respect to clearance when an α + β type titanium alloy is punched by applying a reverse pressure.

FIG. 5 is a sectional view showing a punching state.

FIG. 6 is an explanatory diagram showing a state of occurrence of cracks and chips in a punched material.

[Explanation of symbols]

 Reference Signs List 1 die 2 workpiece 3 punch 4 plate holder 5 ejector 9 crack 11 chipping

Claims (3)

(57) [Claims] 1. A titanium alloy material excellent in punching work, characterized in that the α + β type titanium alloy material to be cold-punched has an average crystal grain size of 7 μm or less. 2. The punching of a titanium alloy having excellent punching characteristics, wherein the punching of an α + β type titanium alloy material to be punched in the cold is performed under the condition of the following formula (1). Processing method. c / t ≦ −4.4 ln d + 23.0 and d ≦ 7.0 (1) where c: clearance (mm) t: thickness of punched material (mm) d: average crystal of punched material Particle size (μm) 3. An α + which is subjected to blanking by applying a reverse pressure in a cold state.
A punching method for a titanium alloy material excellent in punching workability, wherein the punching of a β-type titanium alloy material is performed under the following condition (2). c / t ≦ −4.4 ln d + 25.7 and d ≦ 7.0 (2) where c: clearance (mm) t: thickness of punched material (mm) d: average crystal of punched material Particle size (μm)