JP6253488B2 - Front extrusion method, hollow member manufacturing method, and front extrusion processing apparatus - Google Patents

Description

  The present invention relates to a forward extrusion method, a method for producing a hollow member, and a forward extrusion apparatus.

  Various hollow cold forgings have been manufactured in response to demands for weight reduction and cost reduction of machine parts such as automobile parts. For example, a solid member is hollowed out by backward extrusion and subsequent punching, and further upsetting and forward extrusion are performed from there to form a predetermined shape. However, just as internal cracks called chevron cracks may occur during forward extrusion of solid members, cracks may occur in the inner diameter portion (inner diameter surface) depending on conditions in forward extrusion of hollow members. .

  In Patent Document 1, a work material having a work hardening index n value of 0.2 or more is used, or heat treatment is performed so that a work hardening index n value of the work material becomes 0.2 or more. There has been proposed a method capable of suppressing internal cracks in forward extrusion. Patent Document 2 proposes a method of suppressing internal cracking by applying back pressure in forward extrusion of a solid sintered body containing iron as a main component.

Japanese Patent Laid-Open No. 2000-312947 JP 2002-137039 A

  However, the method disclosed in Patent Document 1 is limited to a workpiece having a work hardening index n value of 0.2 or more, and requires a heat treatment step for making the n value 0.2 or more. The manufacturing cost was forced to increase. In addition, the method disclosed in Patent Document 2 has a demerit that a die and a forging device become large and complicated in order to apply a back pressure, and as a result, a manufacturing cost increases.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to suppress cracks on the inner surface of various hollow members without a significant increase in manufacturing cost. It is an object of the present invention to provide a new and improved forward extrusion method, a method for manufacturing a hollow member, and a forward extrusion apparatus.

  In order to solve the above-described problems, according to a certain aspect of the present invention, in a forward extrusion method in which a hollow member is forwardly extruded using a die and a mandrel, a hollow is formed by an outer diameter drawn portion provided on an inner diameter surface of the die. The step of narrowing the outer diameter surface of the member, and the step of expanding the inner diameter surface of the hollow member by an inner diameter enlarged portion provided at a position facing the outer diameter throttle portion of the outer diameter surface of the mandrel. A forward extrusion method is provided.

  Here, the outer diameter throttle part may be provided in a plurality of stages along the traveling direction of the hollow member. In this case, the inner diameter enlarged portion may not be provided at the opposing position of all the outer diameter restricting portions, but at least one stage is provided with the inner diameter enlarged portion at a position facing the outer diameter restricting portion. Need to be.

  Further, the angle formed by the surface intersecting the traveling direction of the hollow member in the inner diameter enlarged portion and the traveling direction of the hollow member may be 60 ° or more.

  Moreover, 2% or less of the outer diameter of a hollow member may be sufficient as the amount of diameter changes of the internal diameter surface of the hollow member by an internal diameter expansion part.

  Further, the hollow member may be a hollow member that is hollowed out by backward extrusion and subsequent punching before performing forward extrusion.

  The hollow member may be a metal member.

  The metal member may be a steel material.

  According to another aspect of the present invention, in the method of manufacturing a hollow member in which a hollow member is forwardly extruded using a die and a mandrel, the forward extrusion is performed by an outer diameter drawing portion provided on an inner diameter surface of the die. Squeezing the outer diameter surface of the mandrel, and expanding the inner diameter surface of the hollow member by an inner diameter enlarged portion provided at a position facing the outer diameter throttle portion, of the outer diameter surface of the mandrel. A method for manufacturing a hollow member is provided.

  According to another aspect of the present invention, in a forward extrusion apparatus that forwardly extrudes a hollow member using a die and a mandrel, an outer diameter restricting portion that is provided on the inner diameter surface of the die and restricts the outer diameter surface of the hollow member; A forward extrusion processing apparatus is provided, comprising: an outer diameter surface of the mandrel, the inner diameter expansion portion provided at a position facing the outer diameter throttle portion and expanding the inner diameter surface of the hollow member. Is done.

  According to the present invention described above, the inner diameter enlarged portion becomes resistance to the progress of the hollow member, and the generation of tensile stress on the inner diameter surface is suppressed, so that the possibility of occurrence of inner surface cracks is reduced. Further, the inner surface crack can be suppressed regardless of the work hardening index n value of the hollow member. Moreover, since the inner surface crack can be suppressed only by providing the inner diameter enlarged portion on the mandrel, the manufacturing cost is not significantly increased. The present invention is applicable not only to cold forging but also to hot forging and tube extrusion (and drawing).

It is a longitudinal cross-sectional view which shows schematic structure of the front extrusion processing apparatus which concerns on embodiment of this invention. It is a longitudinal cross-sectional view which shows the detailed structure of the outer diameter aperture | diaphragm | squeeze part which concerns on the embodiment. It is a longitudinal cross-sectional view which shows the detailed structure of the internal diameter enlarged diameter part which concerns on the same embodiment. It is a longitudinal cross-sectional view which shows the example of the conventional front extrusion processing apparatus. It is a longitudinal cross-sectional view which shows the other example of the conventional front extrusion processing apparatus. It is a longitudinal cross-sectional view which shows the example of the front extrusion processing apparatus which concerns on embodiment of this invention which provided the internal diameter enlarged diameter part in the example shown in FIG. It is a graph which shows the correspondence of the ductile fracture index | exponent of each small area | region of a hollow member, and the position of each small area | region (outer diameter surface 1 step | paragraph). It is a graph which shows the correspondence of the ductile fracture index | exponent of each small area | region of a hollow member, and the position of each small area | region (outer diameter surface 2 step | paragraph drawing). It is a figure explaining the process of hollowing a solid member by back extrusion and subsequent punching. It is a longitudinal cross-sectional view which shows the example of the front extrusion apparatus which concerns on embodiment of this invention which provided two internal diameter enlarged parts in the example shown in FIG.

Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol. Moreover, in the following description, the direction in which the hollow member travels (flows) in the front extrusion processing apparatus is the downstream direction, and the reverse direction of the downstream direction is the upstream direction.

<1. Study conducted by the present inventor>
The inventor examined the cause of the occurrence of inner surface cracks in the hollow member and a method for suppressing the inner surface cracks, and as a result, the inventors have conceived the forward extrusion apparatus and the forward extrusion method according to the present embodiment. Therefore, first, the study conducted by the present inventor will be described.

  The present inventor estimated the ductile fracture index generated in the hollow member during forward extrusion by finite element analysis in order to find out the cause of the occurrence of the inner surface crack in the hollow member. The process will be described with reference to FIGS.

  First, the present inventor estimated the ductile fracture index when the outer diameter surface of the hollow member was reduced by one step. FIG. 4 is a longitudinal sectional view showing an outline of the forward extrusion processing apparatus 100 that narrows the outer diameter surface of the hollow member by one step. The front extrusion processing apparatus 100 includes a die 101 and a mandrel 102. The die 101 is a substantially cylindrical member. An outer diameter restricting portion 130 is formed on the inner diameter surface 101 b of the die 101.

The outer diameter throttle portion 130 includes a land portion 131, an inclined surface 132, and a relief portion 133.
The land portion 131 is a portion protruding to the mandrel 102 side. The inclined surface 132 is a surface that intersects the traveling direction (arrow A1 direction) of the hollow member W, and connects the land portion 131 and the inner diameter surface 101b on the upstream side of the land portion 131. The escape portion 133 is formed on the downstream side of the land portion 131. The inner diameter surface (surface) of the escape portion 133 is disposed on the outer side (outer diameter surface side of the die 101) than the inner diameter surface (surface) of the land portion 131. That is, a gap is formed between the escape portion 133 and the hollow member W.

  The mandrel 102 is a substantially cylindrical member, and is provided coaxially with the die 101 inside the die 101. A straight line 102a indicates the central axis of the mandrel 102 (and the die 101). A gap is formed between the outer diameter surface 102 b of the mandrel 102 and the inner diameter surface 101 b of the die 101.

  The forward extrusion method using this forward extrusion apparatus 100 is as follows. That is, the hollow member W is passed between the die 101 and the mandrel 102, and the hollow member W is extruded forward. Thereby, the hollow member W advances in the arrow A1 direction. The outer diameter surface of the hollow member W is squeezed (ie, reduced in diameter) by the outer squeezed portion 130. Thereby, the hollow member W is shape | molded.

  The inventor estimated the ductile fracture index generated in the hollow member W during forward extrusion by finite element analysis. That is, the hollow member W was divided into a plurality of small regions, and the ductile fracture index generated in each small region was estimated. The ductile fracture index is expressed by the following formula (1).

Here, I is the ductile fracture index, σ _max is the maximum principal stress, σ _eq is the equivalent stress, and ε _eq is the equivalent plastic strain. The integral expression written in the numerator on the right side of Equation (1) is a ductile fracture condition equation called Cockcroft &Latham's equation. To do. That is, when the ductile fracture index reaches 1, it is determined that cracking occurs.

  The analysis conditions are as follows. A hollow member W having an outer diameter of φ20 mm and an inner diameter of φ10 mm was formed by forward extrusion so as to have an outer diameter of φ19.5 mm and an inner diameter of φ10 mm. The angle between the traveling direction of the hollow member W and the inclined surface 132 is 45 °, the radius of curvature of the corner portion of the inclined surface 132 is 0.5 mm, the length of the land portion 131 is 2.0 mm, and the escape amount is 0.1 mm. . The shear friction coefficient m = 0.1, the axisymmetric model, the die and mandrel were rigid bodies, the workpiece was a rigid plastic body (square element), and the deformation resistance curve of the S55C spheroidized annealed material was used.

The analysis results are shown in FIG. 7 (L20 and L21). In FIG. 7, the vertical axis represents the ductile fracture index of the small area, and the horizontal axis represents the position of the small area. The position of the small region is a length r of a perpendicular line drawn from the small region to the inner diameter surface of the hollow member W, and a distance r ₀ from the inner diameter surface to the outer diameter surface of the hollow member W on the cross section passing through the small region. represented by the ratio _r / r _0. That is, r / r ₀ = 0 represents the inner diameter surface, and r / r ₀ = 1 represents the outer diameter surface.

  A graph L20 shows a correspondence relationship between the ductile fracture index of the small region on the transverse cross section (planar cross section) C in FIG. 4 and the position of the small region. The graph L21 shows the correspondence between the ductile fracture index of the small region on the cross section D and the position of the small region. As can be seen from the graphs L20 and L21, by reducing the outer diameter surface of the hollow member W, the ductile fracture index of the inner diameter surface of the hollow member W is greatly increased.

  Next, the present inventor estimated the ductile fracture index when the outer diameter surface of the hollow member was narrowed by two steps. FIG. 5 is a longitudinal cross-sectional view showing an outline of a front extrusion processing apparatus 200 for reducing the outer diameter surface of the hollow member by two steps. The front extrusion processing apparatus 200 is obtained by changing the die 101 of the front extrusion processing apparatus 100 to a die 201.

  The die 201 is a substantially cylindrical member. On the inner diameter surface 201 b of the die 201, two stages of outer diameter restricting portions 230 are formed. The outer diameter restricting portion 230 includes a land portion 231, an inclined surface 232, and a relief portion 233. The function of each part of the outer diameter restrictor 230 is the same as that of the outer diameter restrictor 130. The forward extrusion method using the forward extrusion apparatus 200 is the same as the forward extrusion method using the forward extrusion apparatus 100.

  The inventor estimated the ductile fracture index generated in the hollow member W during forward extrusion by finite element analysis. That is, the hollow member W was divided into a plurality of small regions, and the ductile fracture index generated in each small region was estimated. The analysis conditions are as follows. A hollow member W having an outer diameter of φ20 mm and an inner diameter of φ10 mm was first set to an outer diameter of φ19.5 mm and an inner diameter of φ10 mm, and then further forward extrusion was performed in two stages so as to obtain an outer diameter of φ19.0 mm and an inner diameter of φ10 mm. The angle formed by the traveling direction of the hollow member W and the inclined surface 232 is 45 °, the radius of curvature of the corner of the inclined surface 232 is 0.5 mm, the length of the land portion 231 is 2.0 mm, and the escape amount is 0.1 mm. . The shear friction coefficient m = 0.1, the axisymmetric model, the die and mandrel were rigid bodies, the workpiece was a rigid plastic body (square element), and the deformation resistance curve of the S55C spheroidized annealed material was used.

  The analysis results are shown in FIG. 8 (L23 and L24). The meanings of the vertical axis and the vertical axis in FIG. 8 are the same as those in FIG. A graph L23 shows a correspondence relationship between the ductile fracture index of the small region on the cross section (planar cross section) E in FIG. 5 and the position of the small region. A graph L24 shows the correspondence between the ductile fracture index of the small area on the cross section F and the position of the small area. As can be seen from the graphs L23 and L24 and the graphs L20 and L21 shown in FIG. 7, the ductile fracture index of the inner diameter surface of the hollow member W is accumulated each time the number of steps where the outer diameter surface of the hollow member W is reduced. Therefore, the possibility of occurrence of inner surface cracks increases as the number of outer diameter stops increases. In the example shown in FIG. 8, since the ductile fracture index of the inner surface exceeds 1, the possibility of occurrence of inner surface cracks is very high.

  As described above, depending on the processing conditions, the outer diameter surface of the hollow member W may be narrowed, so that the ductile fracture index of the inner diameter surface may be greatly increased. This is because a large tensile stress is generated on the inner diameter surface of the hollow member W at a position facing the outer diameter throttle portion, and the inner diameter surface is subjected to plastic deformation under the tensile stress.

As a method for preventing such cracks on the inner surface, the surface area of the forward extrusion process is increased, the angle of the inclined surface (reduced diameter angle θ ₁ described later) is decreased, and the curvature radius of the inclined surface corner portion (described later). Measures such as increasing the curvature radius R ₁ ) have been proposed. These are all methods for relieving the tensile stress generated on the inner diameter surface, but due to restrictions on the shape of the final product, none of the inner surface cracks could be sufficiently suppressed. Therefore, the present inventor studied to relieve the tensile stress generated on the inner diameter surface by another method, and as a result, considered expanding the inner diameter surface of the hollow member W.

  Specifically, first, the present inventor considered expanding the inner diameter surface of the hollow member W in the forward extrusion processing apparatus 100 shown in FIG. An implementation example is shown in FIG. A forward extrusion apparatus 300 shown in FIG. 6 is obtained by changing the mandrel 102 of the forward extrusion apparatus 100 shown in FIG.

  The mandrel 302 is a substantially cylindrical member, and is provided coaxially with the die 101 inside the die 101. A straight line 302a indicates the central axis of the mandrel 302 (and the die 101). A gap is formed between the outer diameter surface 302 b of the mandrel 302 and the inner diameter surface 101 b of the die 101.

  In addition, an inner diameter enlarged portion 340 is provided at a position facing the outer diameter throttle portion 130 on the outer diameter surface 302 b of the mandrel 302. The inner diameter enlarged portion 340 includes a land portion 341, an inclined surface 342, and a relief portion 343. The land portion 341 is a portion protruding toward the die 101 side. The inclined surface 342 is a surface that intersects the traveling direction of the hollow member W, and connects the land portion 341 and the outer diameter surface 302b on the upstream side of the land portion 341. The escape portion 343 is formed on the downstream side of the land portion 341. The outer diameter surface (surface) of the escape portion 343 is disposed on the inner side (center axis (= straight line 302a) side of the mandrel 302) than the outer diameter surface (surface) of the land portion 341. That is, a gap is formed between the escape portion 343 and the hollow member W.

  The forward extrusion method using this forward extrusion apparatus 300 is as follows. That is, the hollow member W is passed between the die 101 and the mandrel 302, and the hollow member W is extruded forward. Thereby, the hollow member W advances in the arrow A1 direction. The outer diameter surface of the hollow member W is squeezed (ie, reduced in diameter) by the outer squeezed portion 130. Further, the inner diameter surface of the hollow member W is expanded by the inner diameter expanded portion 340. At this time, the tensile stress generated on the inner diameter surface of the hollow member W due to the narrowing of the outer diameter surface is offset by the compressive stress generated when the inner diameter enlarged portion 340 becomes resistance to the progress of the hollow member W. However, by expanding the inner diameter surface of the hollow member W, the tensile stress generation position shifts from the inner diameter surface of the hollow member W to the inside, and the ductile fracture index increases inside the hollow member W as will be described later. To do.

  The inventor estimated the ductile fracture index generated in the hollow member W during forward extrusion by finite element analysis. That is, the hollow member W was divided into a plurality of small regions, and the ductile fracture index generated in each small region was estimated. The analysis conditions are as follows. A hollow member W having an outer diameter of φ20 mm and an inner diameter of φ10 mm was formed by forward extrusion so as to have an outer diameter of φ19.5 mm and φ10.5 mm. The angle between the traveling direction of the hollow member W and the inclined surface 132 and the inclined surface 342 is 45 °, the curvature radius of the corner of the inclined surface 132 and the inclined surface 342 is 0.5 mm, and the length of the land portion 131 and the land portion 341 is The escape amount was set to 2.0 mm and 0.1 mm. The shear friction coefficient m = 0.1, the axisymmetric model, the die and mandrel were rigid bodies, the workpiece was a rigid plastic body (square element), and the deformation resistance curve of the S55C spheroidized annealed material was used.

  A graph L22 in FIG. 7 shows a correspondence relationship between the ductile fracture index of the small region on the cross section H and the position of the small region. The correspondence relationship between the ductile fracture index of the small region on the cross section G and the position of the small region is as shown in the graph L20. When the graphs L21 and L22 are compared, it can be seen that the peak position of the ductile fracture index generated in the hollow member W shifts from the inner diameter surface of the hollow member W to the inside by expanding the inner diameter surface of the hollow member W. . Therefore, since the ductile fracture index of the inner diameter surface of the hollow member W is reduced, the possibility of occurrence of inner diameter surface cracks is reduced. Moreover, the reduction in area ratio is increased and the peak height of the ductile fracture index itself is reduced by expanding the inner diameter.

  The inventor further studied to enlarge the inner diameter surface of the hollow member W, and came up with the forward extrusion apparatus 10 and the forward extrusion method according to the present embodiment. Hereinafter, the front extrusion apparatus 10 and the front extrusion method according to the present embodiment will be described.

<2. Configuration of forward extrusion processing equipment>
Next, based on FIGS. 1-3, the structure of the front extrusion apparatus 10 is demonstrated. The front extrusion processing apparatus 10 includes a die 11 and a mandrel 12. The die 11 is a substantially cylindrical member. On the inner diameter surface 11 b of the die 11, a plurality of outer diameter throttle portions 30 are formed. In the present embodiment, the order of the outer diameter throttle parts 30 is counted as the first stage and the second stage in order from the outermost diameter throttle part 30 on the most upstream side.

As shown in FIGS. 1 and 2, the outer diameter restricting portion 30 includes a land portion 31, an inclined surface 32, and a relief portion 33. The land portion 31 is a portion protruding to the mandrel 12 side. The distance 0.5 × d ₁ from the inner diameter surface (surface) of the land portion 31 to the inner diameter surface 11b on the upstream side of the land portion 31 is not particularly limited as long as it is a value that the conventional outer diameter throttle portion 30 can take. It is applicable to. Here, the distance d _1, the amount of the outer-diameter throttle portion 30 the outer diameter surface of the hollow member W is squeezed, i.e. corresponding to diameter reduction of the outer diameter. Further, the inner diameter surface 11b on the upstream side of the land portion 31 corresponds to the first-stage escape portion 33 when the land portion 31 is in the second stage.

The inclined surface 32 is a portion that connects the land portion 31 and the inner diameter surface 11 b on the upstream side of the land portion 31. For example, the inclined surface 32 of the second stage outer diameter throttle part 30 connects the relief part 33 of the first stage outer diameter throttle part 30 and the land part 31 of the second stage outer diameter throttle part 30. The angle (reduction angle) θ ₁ formed between the inclined surface 32 and the traveling direction of the hollow member W is not particularly limited, and any value that can be taken by the conventional outer diameter restricting portion 30 is applicable.

Moreover, the radius of curvature R ₁ of the upper portion 32a and lower portion 32b of the inclined surface 32 is not particularly limited, it can be arbitrarily applied to any conventional values outside diameter throttle portions 30 can take.

The escape portion 33 is formed on the downstream side of the land portion 31. The inner diameter surface (surface) of the escape portion 33 is disposed on the outer side (outer diameter surface side of the die 11) than the inner diameter surface (surface) of the land portion 31. That is, a gap is formed between the escape portion 33 and the hollow member W. The distance 0.5 × d ₂ between the inner diameter surface of the escape portion 33 and the inner diameter surface of the land portion 31 is not particularly limited, and any value that can be taken by the conventional outer diameter throttle portion 30 can be applied. Here, the distance d ₂ corresponds to the size, i.e. clearance amount of provided a gap between the hollow member W and a flank portion 33.

  The mandrel 12 is a substantially cylindrical member, and is provided coaxially with the die 11 inside the die 11. A straight line 12a indicates the central axis of the mandrel 12 (and the die 11). A gap is formed between the outer diameter surface 12 b of the mandrel 12 and the inner diameter surface 11 b of the die 11.

  Further, an inner diameter enlarged portion 40 is provided at a position of the outer diameter surface 12 b of the mandrel 12 that faces the second stage outer diameter throttle portion 30. As shown in FIGS. 1 and 3, the inner diameter enlarged portion 40 includes a land portion 41, an inclined surface 42, and a relief portion 43.

The land portion 41 is a portion protruding toward the die 11 side. The distance 0.5 × d ₃ from the outer diameter surface (surface) of the land portion 41 to the outer diameter surface 12b on the upstream side of the land portion 41 is not particularly limited. Here, the distance d ₃ is diameter change of the inner diameter surface of the hollow member W by the inner diameter expanded portion 40, i.e. corresponding to the enlarged diameter of the inner diameter. The distance d ₃ is preferably not more than 2% of the outer diameter of the hollow member W. The lower limit of the distance d ₃ is not particularly limited, is greater than 0 (i.e., if the protruding even slightly land portion 41) Good. When the diameter change amount d ₃ is within this range, ductile fracture index inner surface of the hollow member W is reduced more.

The inclined surface 42 is a surface that intersects the traveling direction of the hollow member W, and connects the land portion 41 and the outer diameter surface 12 b on the upstream side of the land portion 41. The angle (expansion angle) θ ₂ formed by the inclined surface 42 and the traveling direction of the hollow member W is not particularly limited, but is preferably 60 ° or more. If the diameter angle theta ₂ is in such a range, ductile fracture index inner surface of the hollow member W is reduced more. The upper limit of the diameter expansion angle theta ₂ is not particularly limited, and may be less than 90 °.

Although the radius of curvature R ₂ of the upper portion 42a and lower portion 42b of the inclined surface 42 is not particularly limited, it greater are preferred. Further, the lower end portion 42 b of the inclined surface 42 is disposed on substantially the same cross section as the lower end portion 32 b of the inclined surface 32 of the second-stage outer diameter throttle portion 30. Here, “substantially the same” means not only that both are arranged on the same cross section, but also that at least part of the tensile stress generated on the inner diameter surface of the hollow member W due to the outer diameter surface being reduced, If the inner diameter enlarged portion 40 is offset by the compressive stress generated by the resistance to the progress of the hollow member W, it means that the positions of both may be shifted. Both are preferably disposed on the same cross section, and more preferably, the lower end portion 42b is disposed somewhat downstream from the lower end portion 32b. However, at least a part of the land portion 41 faces the land portion 31 of the second stage outer diameter restricting portion 30.

The escape portion 43 is formed on the downstream side of the land portion 41. The outer diameter surface (surface) of the escape portion 43 is disposed on the inner side (the central axis (= straight line 12a) side of the mandrel 12) than the outer diameter surface (surface) of the land portion 41. That is, a gap is formed between the escape portion 43 and the hollow member W. The distance 0.5 × d ₄ between the outer diameter surface of the escape portion 43 and the outer diameter surface of the land portion 41 is not particularly limited. Here, the distance d ₄ corresponds to the width of the gap provided between the hollow member W and the escape portion 33, that is, the escape amount.

  In the present embodiment, the die 11 is provided with two stages of the outer diameter throttle part 30, but more stages of the outer diameter throttle part 30 may be provided. In this case, for all the outer diameter throttle parts 30, the inner diameter enlarged part 40 does not have to be provided at the facing position, but at least one stage has an inner diameter enlarged diameter at a position facing the outer diameter throttle part 30. The part 40 needs to be provided.

  Further, the outer diameter throttle part 30 may be one stage. In this case, the inner diameter enlarged portion 40 is provided at a position facing the outer diameter throttle portion 30. That is, this embodiment also includes the configuration shown in FIG.

  FIG. 10 shows a forward extrusion apparatus 400 that is another example of the forward extrusion apparatus according to the present embodiment. The front extrusion apparatus 400 is obtained by changing the mandrel 102 of the front extrusion apparatus 200 shown in FIG.

  The mandrel 401 is a substantially cylindrical member, and is provided coaxially with the die 201 inside the die 201. A straight line 400a indicates the central axis of the mandrel 401 (and the die 201). A gap is formed between the outer diameter surface 400 b of the mandrel 401 and the inner diameter surface 201 b of the die 201.

  Further, an inner diameter enlarged portion 440 is provided at a position facing the outer diameter restricting portion 230 at the first stage and the second stage on the outer diameter surface 12 b of the mandrel 12. The inner diameter enlarged portion 440 includes a land portion 441, an inclined surface 442, and a relief portion 443. The land portion 441, the inclined surface 442, and the escape portion 443 have the same configuration as the land portion 41, the inclined surface 42, and the escape portion 43 shown in FIG.

<3. Forward extrusion method>
Next, a front extrusion method using the front extrusion apparatus 10 will be described. The hollow member W is passed between the die 11 and the mandrel 12, and the hollow member W is extruded forward. Thereby, the hollow member W advances in the arrow A1 direction. The outer diameter surface of the hollow member W is first squeezed (that is, reduced in diameter) by the first-stage outer diameter squeezing portion 30. The hollow member W further proceeds in the direction of arrow A1. Thereafter, the outer diameter surface of the hollow member W is squeezed by the second-stage outer diameter restricting portion 30, and at the same time, the inner diameter surface of the hollow member W is expanded by the inner diameter expanding portion 40. That is, in the example shown in FIG. 5, the ductile fracture index is accumulated on the inner diameter surface of the hollow member W every time the hollow member W passes through the outer diameter throttle portion 230. In contrast, in this embodiment, first, when the outer diameter surface is narrowed by the first-stage outer diameter throttling portion 30, the ductile fracture index increases on the inner diameter surface of the hollow member W. Next, when the outer diameter surface is squeezed by the second-stage outer diameter restricting portion 30, the inner diameter surface of the hollow member W is enlarged by the inner diameter enlarged portion 40, so that the ductile fracture index is inside the hollow member W. Rises. Thus, the ductile fracture index generated in the hollow member W is dispersed between the inner diameter surface and the inside of the hollow member W, and the possibility of occurrence of inner diameter surface cracks is reduced.

  In addition, the kind in particular of hollow member W is not restrict | limited, A metal member may be sufficient. The metal member may be a steel material.

  The inventor estimated the ductile fracture index generated in the hollow member W during forward extrusion by finite element analysis. That is, the hollow member W was divided into a plurality of small regions, and the ductile fracture index generated in each small region was estimated. The analysis conditions are as follows. The hollow member W having an outer diameter of φ20 mm and an inner diameter of φ10 mm was first made to have an outer diameter of φ19.5 mm and an inner diameter of φ10 mm, and further subjected to two-stage forward extrusion so as to have an outer diameter of φ19.0 mm and an inner diameter of φ10.5 mm. The angle between the traveling direction of the hollow member W and the inclined surface 32 and the inclined surface 42 is 45 °, the curvature radius of the corners of the inclined surface 32 and the inclined surface 42 is 0.5 mm, and the lengths of the land portion 31 and the land portion 41 are The escape amount was set to 2.0 mm and 0.1 mm. The shear friction coefficient m = 0.1, the axisymmetric model, the die and mandrel were rigid bodies, the workpiece was a rigid plastic body (square element), and the deformation resistance curve of the S55C spheroidized annealed material was used.

  A graph L25 in FIG. 8 shows the correspondence between the ductile fracture index of the small region on the cross section C and the position of the small region. The correspondence relationship between the ductile fracture index of the small area on the cross section A and the position of the small area is as shown in the graph L23. As can be seen from the graphs L23 to L25, when the outer diameter surface is squeezed by the second-stage outer diameter throttle portion 30, if the inner diameter surface of the hollow member W is enlarged by the inner diameter enlarged portion 40, the ductile fracture index increases. Since the position shifts from the inner diameter surface of the hollow member W to the inside, the ductile fracture index is dispersed between the inner diameter surface and the inside of the hollow member W. Therefore, since the ductile fracture index of the inner diameter surface of the hollow member W is reduced, the possibility of occurrence of inner diameter surface cracks is reduced.

<4. Hollowing out a solid member by backward extrusion and subsequent punching>
As shown in FIG. 9, the hollow member may be formed by hollowing the solid member by backward extrusion and subsequent punching before the forward extrusion process. Further, heat treatment may be performed. However, in consideration of productivity, it is preferable to perform forward extrusion and punching sequentially, and then forward extrusion as it is. In this case, the hollow member is given a large strain on the inner diameter surface in the backward extrusion process, and the ductility is remarkably lowered by work hardening. Therefore, when the outer diameter is reduced by forward extrusion, the inner surface crack is likely to occur. However, according to the present invention in which the inner diameter surface of the hollow member is expanded, the occurrence of the inner surface crack can be prevented.

Example 1
Next, in order to confirm the ranges of preferable diameter change amount d ₃ , diameter expansion angle θ ₂ , and radius of curvature R ₂ , the following examples were performed.

Also in the present example, as described above, the ductile fracture index generated in the hollow member W was estimated by the finite element method analysis. The analysis conditions are as follows. A hollow member having an outer diameter of φ20 mm and an inner diameter of φ10 mm was subjected to forward extrusion so as to have an outer diameter of φ19.5 mm and an inner diameter of φ (10 + d ₃ ) mm. As for the outer diameter narrowed portion, the angle formed by the traveling direction of the hollow member and the inclined surface (that is, the reduced diameter angle θ ₁ ) is 45 °, the radius of curvature of the corner portion of the inclined surface is 0.1 mm, and the length of the land portion is 2. 0.0 mm and the escape amount was 0.1 mm. For the inner diameter enlarged portion, the diameter change amount is d ₃ , the angle between the traveling direction of the hollow member and the inclined surface (that is, the enlarged diameter angle) is θ ₂ , the curvature radius of the corner portion of the inclined surface is 0.05 mm, and the land portion The length was 2.0 mm, and the escape amount was 0.1 mm. The shear friction coefficient m = 0.1, the axisymmetric model, the die and mandrel were rigid bodies, the workpiece was a rigid plastic body (square element), and the deformation resistance curve of the S55C spheroidized annealed material was used.

(Confirmation of combination of preferred diameter change and diameter expansion angle)
Among the above analysis conditions, a preferable diameter change is obtained by changing the combination of the diameter change amount d ₃ and the diameter expansion angle θ _{2 in} a range of 0.2 mm <d ₃ <4.0 mm, 5 ° <θ ₂ <85 °. It confirmed the combination of the amount d ₃ and enlarged angle theta _2. The results are shown in Table 1.

  According to Table 1, the larger the expansion angle, the lower the ductile fracture index of the inner surface, and it is preferably 60 ° or more. Further, it was found that the smaller the amount of change in diameter, the lower the ductile fracture index of the inner diameter surface, and it is preferably 0.4 mm or less (= 2% or less of the outer diameter of the hollow member).

(Confirmation of preferred curvature radius)
Of the above analysis condition, enlarged angle 45 °, as 0.4mm and diameter change amount, by changing the radius of curvature _{R 2} in the range of _{0 mm} <R 2 <3 mm, confirm the preferred range of the curvature radius _{R 2} did. The results are shown in Table 2.

According to Table 2, the radius of curvature R ₂ was found to be better greater are preferred.

(Example 2)
Next, in order to confirm that the present invention is suitable when the hollow member W is obtained by hollowing the solid member by backward extrusion and subsequent punching before performing the forward extrusion process, An example was conducted.

  First, a solid member of S43C subjected to spheroidizing annealing (outer diameter φ45 mm, spheroidization rate is about 70%, components are mass%, C: 0.43%, Si: 0.22%, Mn: 0 .80%, P: 0.011%, S: 0.016%, the balance being Fe) was cut to an outer diameter of φ19.9 mm and subjected to a phosphate soap film treatment for lubrication. And as shown in FIG. 9, after shape | molding in the cup shape by cold back extrusion, the cup bottom was pierced and it was set as the hollow member of outer diameter (phi) 20mm and internal diameter (phi) 10mm. This is the hollow member Wf.

  Next, the hollow member Wf was formed to have an outer diameter of φ19.5 mm and an inner diameter of φ10 mm using the forward extrusion apparatus 100 shown in FIG. The angle between the traveling direction of the hollow member Wf and the inclined surface 132 is 45 °, the radius of curvature of the corner portion of the inclined surface 132 is 0.5 mm, the length of the land portion 131 is 2.0 mm, and the escape amount is 0.1 mm. ([Conventional method] Forward extrusion apparatus 100).

  In addition, the hollow member Wf is first made to have an outer diameter φ19.5 mm and an inner diameter φ10 mm by using the front extrusion processing apparatus 200 shown in FIG. 5, and then further arranged in two stages so as to have an outer diameter φ19.0 mm and an inner diameter φ10 mm. Forward extrusion was performed. The angle between the traveling direction of the hollow member Wf and the inclined surface 232 is 45 °, the radius of curvature of the corner of the inclined surface 232 is 0.5 mm, the length of the land portion 231 is 2.0 mm, and the escape amount is 0.1 mm. ([Conventional method] Forward extrusion apparatus 200).

  Further, the hollow member Wf was molded to have an outer diameter of 19.5 mm and an inner diameter of 10.5 mm using the forward extrusion apparatus 300 shown in FIG. The angle between the traveling direction of the hollow member Wf and the inclined surface 132 and the inclined surface 342 is 45 °, the curvature radius of the corner of the inclined surface 132 and the inclined surface 342 is 0.5 mm, and the length of the land portion 131 and the land portion 341 is The escape amount was 2.0 mm and 0.1 mm ([present invention] forward extrusion apparatus 300).

  Further, the hollow member Wf is first made to have an outer diameter φ19.5 mm and an inner diameter φ10.25 mm by using the forward extrusion processing apparatus 400 shown in FIG. 10, and then further becomes an outer diameter φ19.0 mm and an inner diameter φ10.5 mm. Two-stage forward extrusion was performed. The angle between the traveling direction of the hollow member Wf and the inclined surface 232 and the inclined surface 442 is 45 °, the radius of curvature of the corners of the inclined surface 232 and the inclined surface 442 is 0.5 mm, and the length of the land portions 231 and 441 is 2. The clearance was 0 mm and the clearance was 0.1 mm ([present invention] forward extrusion apparatus 400).

Each of the above moldings was performed using a press machine having a maximum load capacity of 6000 kN and a stroke of 300 mm at a speed of 20 spm and room temperature. After forward extrusion, the hollow member was divided in half, and the inner diameter surface was visually observed to confirm the occurrence of inner surface cracks.
The results are shown in Table 3.

  According to Table 3, inner surface cracks occurred when the forward extrusion of the hollow member Wf was performed using the front extrusion apparatuses 100, 200, but inner diameter surface cracks occurred when the front extrusion apparatuses 300, 400 were used. Did not occur.

  Before the hollow member Wf is subjected to forward extrusion processing, a strain of about 300% to 400% is imparted to the inner diameter surface by backward extrusion, and the ductility of the inner diameter surface is significantly reduced by work hardening. For this reason, when the forward extrusion is performed using the forward extrusion apparatuses 100 and 200 (both of which are conventional methods) in which a large tensile stress is generated on the inner diameter surface and the inner diameter surface undergoes plastic deformation under the tensile stress, the inner diameter surface crack is generated. Occurred.

  On the other hand, in the case of using the forward extrusion processing apparatuses 300 and 400 of the present invention in which the inner diameter enlarged portion is provided in the mandrel, the generation of tensile stress on the inner diameter surface is suppressed by the inner diameter enlarged portion of the mandrel. Occurrence did not occur. The mandrel is provided with an inner diameter enlarged portion, so that tensile stress is generated inside the inner surface instead of the inner surface. However, unlike the inner surface, the inner part has a relatively small decrease in ductility in the backward extrusion process, and cracks are generated. This was confirmed by observing the cross section of the hollow member Wf after forward extrusion.

  As described above, the hollow member Wf in which the solid member is hollowed by the backward extrusion and the subsequent punching is cracked in the inner diameter surface even in the single-stage forward extrusion (front extrusion processing apparatus 100) in the conventional method in which tensile stress is generated on the inner diameter surface. Has occurred. On the other hand, if the present invention is applied, even if it is a hollow member W in which the ductility of the inner diameter surface is remarkably reduced by moving the position where the tensile stress is generated to the inside, two steps without causing the inner surface cracks. It is possible to perform forward extrusion (front extrusion processing apparatus 400).

  As described above, according to the present embodiment, first, when the outer diameter surface of the hollow member W is narrowed by the first-stage outer diameter restricting portion 30, the ductile fracture index increases on the inner diameter surface of the hollow member W. Next, when the outer diameter surface of the hollow member W is squeezed by the second-stage outer diameter restricting portion 30, the inner diameter surface of the hollow member W is expanded by the inner diameter expanding portion 40. Increases the ductile fracture index. Thus, the ductile fracture index generated in the hollow member W is dispersed between the inner diameter surface and the inside of the hollow member W, and the possibility of occurrence of inner diameter surface cracks is reduced.

  Further, the type of the hollow member W is not particularly limited. For example, the hollow member W to which the present embodiment is applicable is not limited to a metal member having a specific work hardening index n value. That is, this embodiment is applicable to all metal members. This embodiment may be a steel material among these metal members. Moreover, in this embodiment, since it is only necessary to provide the inner diameter enlarged portion 40 in the mandrel 12, the possibility of occurrence of inner surface cracks can be reduced without significantly increasing the manufacturing cost.

Further, by setting the diameter expansion angle θ ₂ to 60 ° or more, the possibility of occurrence of inner surface cracks is further reduced.

Further, diameter change amount d ₃ is, by less than 2% of the outer diameter of the hollow member, possibly inner surface cracking occurs is further reduced.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Front extrusion apparatus 11 Die 12 Mandrel 30 Outer diameter reducing part 31 Land part 32 Inclined surface 33 Escape part 40 Inner diameter enlarged part 41 Land part 42 Inclined surface 43 Escape part

Claims (18)

In a forward extrusion method of forward extrusion of a hollow member using a die and a mandrel,
Squeezing the outer diameter surface of the hollow member by an outer diameter throttle portion provided on the inner diameter surface of the die;
Expanding the inner diameter surface of the hollow member by an inner diameter enlarged portion provided at a position facing the outer diameter throttle portion of the outer diameter surface of the mandrel. Processing method. The outer diameter throttle portion is provided in a plurality of stages along the traveling direction of the hollow member,
The forward extrusion method according to claim 1, wherein the inner diameter enlarged portion is provided at a position facing the outer diameter throttle portion.   The angle formed by the surface intersecting the traveling direction of the hollow member and the traveling direction of the hollow member in the inner diameter enlarged portion is 60 ° or more. Forward extrusion method.   4. The forward extrusion according to claim 1, wherein a diameter change amount of an inner diameter surface of the hollow member by the inner diameter enlarged portion is 2% or less of an outer diameter of the hollow member. Processing method.   5. The hollow member according to claim 1, wherein the hollow member is formed by hollowing out a solid member by backward extrusion and subsequent punching before performing the forward extrusion process. 6. Forward extrusion method.   The forward extrusion method according to claim 1, wherein the hollow member is a metal member.   The forward extrusion method according to claim 6, wherein the metal member is a steel material. In the method of manufacturing a hollow member that forwardly extrudes the hollow member using a die and a mandrel,
The forward extrusion process includes a step of squeezing the outer diameter surface of the hollow member by an outer diameter squeezing portion provided on the inner diameter surface of the die;
Expanding the inner diameter surface of the hollow member with an inner diameter enlarged portion provided at a position facing the outer diameter throttle portion, of the outer diameter surface of the mandrel. Manufacturing method. The outer diameter throttle portion is provided in a plurality of stages along the traveling direction of the hollow member,
The method for manufacturing a hollow member according to claim 8, wherein the inner diameter enlarged portion is provided at a position facing the outer diameter restricting portion.   The angle formed by the surface intersecting the traveling direction of the hollow member in the inner diameter enlarged portion and the traveling direction of the hollow member is 60 ° or more, 10 or 9, A method for producing a hollow member.   The hollow member according to any one of claims 8 to 10, wherein a diameter change amount of the inner diameter surface of the hollow member by the inner diameter enlarged portion is 2% or less of an outer diameter of the hollow member. Manufacturing method.   12. The hollow member according to claim 8, wherein the hollow member is formed by hollowing out a solid member by backward extrusion and subsequent punching before performing the forward extrusion process. 12. A method for producing a hollow member.   The said hollow member is a metal member, The manufacturing method of the hollow member of any one of Claims 8-12 characterized by the above-mentioned.   The method for manufacturing a hollow member according to claim 13, wherein the metal member is a steel material. In a front extrusion processing apparatus that forward-extrudes a hollow member using a die and a mandrel,
An outer diameter restricting portion that is provided on the inner diameter surface of the die and restricts the outer diameter surface of the hollow member;
A forward extrusion processing apparatus comprising: an outer diameter surface of the mandrel, the inner diameter expansion portion provided at a position facing the outer diameter throttle portion and expanding the inner diameter surface of the hollow member. . The outer diameter throttle portion is provided in a plurality of stages along the traveling direction of the hollow member,
The forward extrusion processing apparatus according to claim 15, wherein the inner diameter enlarged portion is provided at a position facing the outer diameter throttle portion.   The angle formed by the surface intersecting the traveling direction of the hollow member in the inner diameter enlarged portion and the traveling direction of the hollow member is 60 ° or more, 17 or 16, Forward extrusion processing equipment. The forward extrusion process according to any one of claims 15 to 17, wherein a diameter change amount of the inner diameter enlarged portion with respect to an outer diameter surface of the mandrel is 2% or less of an inner diameter of the die. apparatus.

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