Patent Description:
Precision forging, which is cold forging, allows high precision components to be manufactured at low costs and is thus widely used to manufacture small precision components for automobiles and electric/electronic devices (refer to patent document <NUM> and patent document <NUM>). Precision forging combines the basic working processes of upsetting and extrusion to perform shaping. In a final stage of the shaping process, an enormous amount of tool pressure is required to force the workpiece into a non-filled portion of a die.

Non-Patent Document <NUM>: <NPL>], "<NPL>.

Document <CIT> shows a precision forging method and forms the basis for the preamble of claim <NUM>.

Document <CIT> shows a precision forging device and forms the basis for the preamble of claim <NUM>.

With the present technology, there is a need for the tool pressure to be at least three times or greater than the tensile strength of the workpiece even when working conditions, such as the material flow and lubrication of the workpiece, are optimized. Thus, due to the withstanding pressure limits of the tool material, high-strength material and large-dimension components are not subject to precision forging.

<FIG> of Non-Patent Document <NUM> shows the shaping of an outwardly directed flange of a drawn cup. In this example, the outer side of a circumferential wall of the drawn cup is shaved with a punch so that the shaved metal portion becomes the outwardly directed flange. The outwardly directed flange is, however, deformed to extend in the radial direction about the axis of the cup during shaping into free space without any constraint. Thus, the material may crack at the portion of the circumferential wall opposed toward the blade end of the punch. <FIG> shows a cut cross section of a portion connecting the outwardly directed flange and the circumferential wall of the cup when the shaved drawn cup is cut in the axial direction. <FIG> shows the enlarged cross section of the portion inside the square frame in <FIG>. As shown in the two drawings, the material is cracked in the portion connecting the outwardly directed flange and the circumferential wall.

One object of the present disclosure is to provide a precision forging method, a precision forging device, and a precision forging product that avoid cracking and do not require a massive tool pressure during precision forging.

A precision forging method in accordance with appended claim <NUM> includes arranging a metal material including a wall portion, which extends in a moving direction of a punch, and a pre-working projecting wall, which extends from the wall in a direction intersecting the moving direction, in a die cavity of a die, and moving the punch to forge the metal material.

The precision forging method includes a first step of arranging the punch, which includes a working end surface and a cutting blade formed at an edge of the working end surface, in the die cavity so that the punch is opposed toward part of the wall portion thickness-wise and the pre-working projecting wall of the metal material.

Further, the precision forging method includes a second step of moving the punch within a range of a height of the wall portion in a state in which the metal material is held in the moving direction of the punch and a length of the pre-working projecting wall in the intersecting direction is maintained so that the cutting blade cuts the part of the wall portion thickness-wise located in a moving path of the punch and causes shear deformation in the cut part to move the cut part toward the pre-working projecting wall.

The method may further include arranging the metal material, which includes a fit region where at least part of the wall portion comes into plane contact with a wall surface of the die cavity and the pre-working projecting wall located at a side opposite to the fit region, in the die cavity, and arranging the cutting blade of the punch spaced apart from the wall surface of the die cavity by a distance smaller than a thickness of the wall portion. The second step may include cutting the metal material with the cutting blade so that the fit region remains in the wall portion.

Further, the first step may include arranging the metal material in the die cavity so that the wall portion is spaced apart from a wall surface of the die cavity and at least part of the pre-working projecting wall comes into plane contact with the wall surface of the die cavity. The cutting blade is formed inward from a side of the plane contact.

In the precision forging method, the punch is a first punch, and the first step may include arranging a second punch at a side of the pre-working projecting wall opposite to the first punch. Further, the second step may include moving the second punch so as to follow movement of the first punch in the moving direction.

In the precision forming method, when the wall portion is a circumferential wall and an amount of the circumferential wall cut by the punch is expressed by t<NUM>, a length of the punch in the intersecting direction is greater by 2t<NUM> mm than an inner diameter of the circumferential wall. The pre-working projecting wall may have a thickness tc0 that satisfies <NUM> ≤ tc0 ≤ <NUM>. In a joint line between the circumferential wall and the pre-working projecting wall, the joint line located at a side of the pre-working projecting wall opposite to the punch has a radius of curvature expressed by rcp that satisfies rcp/tc0<<NUM>. The metal material may be worked so that t<NUM>/tc0 satisfies inequation (<NUM>), which is as follows:
<MAT>.

In the precision forming method, when the wall portion is a circumferential wall and an amount of the circumferential wall cut by the punch is expressed by t<NUM>, a length of the punch in the intersecting direction is greater by 2t<NUM> mm than an inner diameter of the circumferential wall. The pre-working projecting wall may have a thickness tc0 that satisfies <NUM> ≤ tc0 ≤ <NUM>. In a joint line between the circumferential wall and the pre-working projecting wall, the joint line located at a side of the pre-working projecting wall opposite to the punch has a radius of curvature expressed by rcp that satisfies rcp/tc0≤<NUM>. The metal material may be worked so that t<NUM>/tc0 satisfies inequation (<NUM>), which is as follows:
<MAT>.

In the precision forging method, the second step may include having the stopper come into contact with a distal end surface of the wall portion to hold the metal material in the moving direction of the punch.

A precision forging device in accordance with appended claim <NUM> is for forging a metal material. The precision forging device includes a die, including a die cavity configured to allow for arrangement of the metal material, and a punch configured to move in the die cavity to forge the metal material. The metal material includes a wall portion, which extends in a moving direction of the punch, and a pre-working projecting wall, which extends from the wall portion in a direction intersecting the moving direction. The punch is opposed toward part of the wall portion thickness-wise and the pre-working projecting wall when the metal material is arranged in the die cavity. The punch includes a working end surface and a cutting blade, which is formed on an edge of the working edge surface. When the punch is moved within a range of a height of the wall portion, the cutting blade is configured to cut part of the wall portion thickness-wise in a moving path of the punch and cause shear deformation in the cut part.

Further, the precision forging device includes a stopper configured to come into contact with a distal end surface of the wall portion when the punch moves, thereby holding the metal material in the moving direction of the punch.

A precision forging product in accordance with the present disclosure includes a wall portion extending in a first direction and a post-working projecting wall extending from the wall portion in a second direction that intersects the first direction. The post-working projecting wall includes a first surface, which is at a side where a joint line (A) between the wall portion and the post-working projecting wall is located, and a second surface, which is at a side opposite to the first surface. The precision forging product further includes a metal flow (W) extending from the joint line (A) to a joint line (B) in the second surface.

In the precision forging product, the wall portion may be a circumferential wall extending circumferentially, and the post-working projecting may be an inwardly directed flange or a bottom portion formed on an inner surface of the circumferential wall or an outwardly directed flange formed on an outer surface of the circumferential wall.

In the precision forging product, the wall portion may have the form of a flat plate or be curved or bent as viewed in a transverse cross section that is orthogonal to the first direction.

A precision forging method and a precision forging device in accordance with a first embodiment will now be described with reference to <FIG> and <FIG>. A metal material <NUM> used in the present embodiment will now be described.

Referring to <FIG>, the metal material <NUM> is not limited and may be any material that can be used for plastic working. Examples of thin metal sheets used for plastic working include cold-roll high tensile steel plates (SPFC, SPFCY, SPFH, SPFHY), cold roll steel plates (SPCC, SPCCT, SPCD, SOCE, SPCEN), SPP, and the like. Further, stainless steels used for plastic working include SUS201, SUS304, SUS316, SUS321, SUS440, SUS450, and the like. Aluminum alloy expanded materials used for plating working include A3003, A3004, A5005, A2014, A2017, A2024, and the like. Metal materials used for plastic working also include alloy steel such as SCr (chrome steel), SCM (chrome molybdenum steel), SNCM (nickel chrome molybdenum steel), and the like.

As shown in <FIG>, the metal material <NUM> used in a first step, which will be described later, is shaped to include a circumferential wall <NUM>, which serves as a wall portion and extends circumferentially, and a bottom portion 12A, which is integrally coupled to the circumferential wall <NUM> at one end of the circumferential wall <NUM>. There is no limitation to how to obtain such a shape. For example, drawing or cutting may be performed for shaping. The circumferential wall <NUM> extends in a first direction that is an axial direction. The bottom portion 12A extends from the circumferential wall <NUM> in a direction intersecting (more specifically, direction orthogonal to) the axial direction, that is, in the radial direction and has the form of a flat plate. The bottom portion is denoted by reference character "12A" prior to precision forging, or prior to working, and denoted by reference character "12B" during and subsequent to precision forging. The bottom portion 12A corresponds to a pre-working projecting wall. The bottom portion 12B corresponds to a post-working projecting wall.

The circumferential wall <NUM> surrounds an open space <NUM> and is shaped to have a horizontal cross section in the form of a circle, an ellipsis, a gear, a quadrangle, or the like. However, there is no limitation to the shape.

A precision forging device <NUM> used in the present embodiment will now be described.

As shown in <FIG>, and <FIG>, the precision forging device <NUM> includes a die <NUM>, a punch <NUM>, a stopper <NUM>, and a counter punch <NUM>. For the sake of brevity, <FIG>, <FIG>, and <FIG> show the punch <NUM>, the counter punch <NUM>, the stopper <NUM>, and the die <NUM> reversed so as to be upside down. Thus, the punch <NUM> is moved during forging from the lower side toward the upper side as viewed in the drawings. More specifically, in the actual precision forging device <NUM>, the punch <NUM> is located at the upper side. The counter punch <NUM> is located at the lower side, and is moved during forging to allow the punch <NUM> to move from the upper side toward the lower side. An air cylinder or the like (not shown) applies back pressure to the counter punch <NUM>. In embodiments from a second embodiment that are described below, the punch <NUM>, the counter punch <NUM>, the die <NUM>, and the like are shown in the drawings reversed upside down. Thus, the punch <NUM> is moved during forging from the lower side toward the upper side as viewed in the drawings.

The die <NUM> includes a die cavity <NUM>. The die cavity <NUM> is shaped to have a horizontal cross section in the form of circle in the present embodiment. However, there is no limitation to the shape as long as it conforms to the contour shape of the circumferential wall <NUM>. The stopper <NUM> is fixed horizontally to the wall surface of the die cavity <NUM>. Preferably, the outer circumference of the stopper <NUM> has the same shape as the horizontal cross section of the die cavity <NUM> so that it conforms to the horizontal cross section of the die cavity <NUM>. Accordingly, in the present embodiment, the outer circumference of the stopper <NUM> is shaped as a circular ring in correspondence with the outer shape of the metal material <NUM>.

When the horizontal cross section of the die cavity <NUM> has a shape other than the form of a circle, the stopper <NUM> is shaped as a non-circular ring in conformance with the shape of the horizontal cross section of the die cavity <NUM>. For example, the horizontal cross section of the die cavity <NUM> may have the form of a polygon, such as a triangle, a quadrangle, or a pentagon, or the form of an ellipsis, and the contour of the stopper <NUM> may have a conforming shape.

The stopper <NUM> may have the same thickness in the radial direction as the circumferential wall <NUM> to contact the entire end surface of the circumferential wall <NUM> of the metal material <NUM>. The stopper <NUM> may be an engagement step formed integrally with the die <NUM>.

As shown in <FIG> and <FIG>, the punch <NUM> includes a working end surface <NUM> that is flat. A cutting blade <NUM> that is circular in a plan view is formed along the entire circumference of the working end surface. The cutting blade <NUM> is opposed toward and spaced apart from the wall surface of the die cavity <NUM> in the radial direction. More specifically, the cutting blade <NUM> is arranged so as to be spaced apart by a gap S from the wall surface of the die cavity <NUM>. The cutting blade <NUM> is formed to move continuous chips, which are produced when the bottom portion 12A (12B) of the metal material <NUM> is cut, toward the central portion (axis) of the punch <NUM>.

The punch <NUM> has a diameter that is smaller than the inner diameter of the die cavity <NUM> and is arranged coaxially with the die cavity <NUM>. The punch <NUM> is moved in the die cavity <NUM> so that the circumference of the bottom portion 12A (12B) of the metal material <NUM>, that is, the portion located radially outward from the cutting blade <NUM>, remains in the gap S between the punch <NUM> and the wall surface of the die cavity <NUM>.

The counter punch <NUM>, which is opposed toward the punch <NUM>, is arranged in the open space surrounded by the circumferential wall <NUM> and the bottom portion 12A (12B) of the metal material <NUM> so as to contact the inner bottom surface of the bottom portion 12A (12B). An air cylinder or the like (not shown) applies back pressure to the counter punch <NUM> so that the inner bottom surface of the bottom portion 12A (12B) is constantly pressed. The punch <NUM> corresponds to a first punch, and the counter punch <NUM> corresponds to a second punch. The counter punch <NUM> is not an essential element and may be omitted.

A precision forging method in accordance with the present embodiment will now be described. In the present embodiment, precision forging may also be referred to as cut forging.

The precision forging method will now be described with reference to <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>.

As shown in <FIG>, in a first step, the metal material <NUM>, which includes the bottom portion 12A and the circumferential wall <NUM>, is arranged in the die cavity <NUM> of the die <NUM> of the precision forging device <NUM> so that the distal end surface of the circumferential wall <NUM> comes into contact with the stopper <NUM>. In this state, the circumferential wall <NUM> extends in the direction in which the punch <NUM> is moved in the die cavity <NUM>, and the bottom portion 12A extends in a direction intersecting the moving direction. The moving direction of the punch <NUM> coincides with the axial direction of the circumferential wall <NUM>. Further, the outer circumferential surface of the circumferential wall <NUM> is in a state in plane contact with the wall surface of the die cavity <NUM>. The plane contact region of the outer circumferential surface of the circumferential wall <NUM> corresponds to a fit region. In the present embodiment, the entire outer circumferential surface of the circumferential wall <NUM> is referred to as the fit region that is in plane contact with the wall surface of the die cavity <NUM>. However, the fit region does not have to be the entire outer circumferential surface of the circumferential wall <NUM>. Part of the outer circumferential surface of the circumferential wall <NUM> in the axial direction may be in plane contact with the wall surface of the die cavity <NUM>, and this part may be referred to as the fit region. The bottom portion 12A extends from the circumferential wall <NUM> away from the fit region of the circumferential wall <NUM>. The radial direction of the circumferential wall <NUM> coincides with a thickness-wise direction of the circumferential wall <NUM>. The punch <NUM> is arranged in the die cavity <NUM> and opposed in the axial direction of the circumferential wall <NUM> toward the bottom portion 12A and part of the circumferential wall <NUM> thickness-wise. The part of the circumferential wall <NUM> thickness-wise opposed toward the punch <NUM> is a region of the circumferential wall <NUM> located inward from the outer edge of the cutting blade <NUM>. In the present embodiment, the punch <NUM> is opposed toward part of the circumferential wall <NUM> thickness-wise. However, depending on the position where the cutting blade <NUM> is arranged, the punch <NUM> may be opposed to the entire circumferential wall <NUM> thickness-wise.

In a second step, the punch <NUM> is moved toward and pushed against the bottom portion 12A as the cutting blade <NUM> cuts the bottom portion 12A (refer to <FIG>, and <FIG>). In this state, the metal material <NUM> is held by the stopper <NUM> in the moving direction of the punch <NUM>. The movement amount of the punch <NUM> from where the punch <NUM> initially comes into contact with the bottom portion 12A is in a range that is greater than or equal to the thickness of the bottom portion 12A and less than the height h of the circumferential wall <NUM> (refer to <FIG>).

When the punch <NUM> pushes the bottom portion 12A and cuts part of the circumferential wall <NUM> thickness-wise with the cutting blade <NUM>, a joint line A is formed in the bottom portion 12A (12B) that comes into contact with the cutting blade <NUM>, as shown in <FIG>. As shown in <FIG>, the joint line A is continuously formed at where the remaining part of the circumferential wall <NUM> that was not cut by the cutting blade <NUM> joins the bottom portion 12A (12B). In the present embodiment, the joint line A is formed to extend in the circumferential direction of the circumferential wall <NUM>. The cutting blade <NUM> causes shear deformation between the joint line A and the inner surface edge of the bottom portion 12A (12B). The inner surface edge of the bottom portion 12A (12B) defines a joint line B between the bottom portion 12B and the circumferential wall <NUM>. The joint line B in the present embodiment is formed continuously in the circumferential direction in the corner located at the side of the bottom portion 12A (12B) opposite to the punch <NUM>. The sheared material (chips) cut out by the cutting blade <NUM> enters the bottom portion 12A (12B) between the punch <NUM> and the counter punch <NUM> (i.e., node) and forms a metal flow W between the joint line A and the joint line B, which are shown in <FIG>. Hereinafter, the part of the bottom portion 12B subsequent to cut forging that corresponds to the joint line A is referred to as the edge A.

Further, the inner surface of the bottom portion 12B at the side where the joint line B is located, or the inner bottom surface, corresponds to a second surface, and the surface of the bottom portion 12B at the side opposite to the inner bottom surface, or the outer bottom surface, corresponds to a first surface. The metal flow W extends from the joint line A of the first surface (outer bottom surface) to the second surface (inner bottom surface).

The bottom portion 12A, 12B is constrained by the die <NUM> so that the dimensions do not change in a direction intersecting the moving direction of the punch <NUM>, as shown in <FIG>. Thus, as the working performed by the punch <NUM> progresses, the material (chips) is compressed and moved toward the node to increase the thickness of the node.

The flow of the metal material <NUM> in this state will be described in detail later.

The back pressure Fb applied to the counter punch <NUM> is much smaller than the pushing force F of the punch <NUM>, that is, Fb<<F is satisfied. As the thickness of the node increases as described above, the counter punch <NUM> is moved backward against the urging force (back pressure) applied by the air cylinder or the like (not shown).

Further, as shown in <FIG> and <FIG>, when the punch <NUM> pushes and moves the bottom portion 12A (12B), the portion of the circumferential wall <NUM> located radially outward from the cutting blade <NUM>, namely, the fit region that is in plane contact with the wall surface of the die cavity <NUM> remains in a non-worked state as if to partially fill the gap S between the die <NUM> and the punch <NUM>. The fit region of the circumferential wall <NUM> is tubular. This obtains a precision forging product including a circumferential wall on both sides of the bottom portion 12B, that is, a precision forging product having an H-shaped vertical cross section.

The pushing force p per unit area of the punch <NUM> required for working is estimated from the energy U required for working as shown below. <MAT> (<NUM>: deformation resistance of metal material, tc: node thickness, ϕ: shearing angle, d: diameter of punch <NUM>, µ: friction coefficient).

Here, f(cp) is expressed by the equation shown below.

The derivation of equation (<NUM>) will now be described.

As shown in <FIG>, when the length of the punch <NUM> extending radially outward from the inner surface of the circumferential wall <NUM> is expressed by t<NUM>, the cutting ratio r is as shown below.

Here, t<NUM> is the difference between the radius of the inner surface of the circumferential wall <NUM> and the radius of the punch <NUM>. This is the amount of the circumferential wall <NUM> cut by the punch <NUM> in the radial direction.

Based on conservation of mass of the sheared material, the speed Vc at which chips in the shear region moves in the radial direction of the punch <NUM> is shown below.

Here, V is the speed of the punch <NUM>. The shearing speed Vs when undergoing vector decomposition is Vs=V/cosϕ as shown in <FIG>. The total energy U input by the punch <NUM> during working is U=F V.

Here, F represents the pressing force of the punch <NUM>. The energy Es required during shearing at the shear region can be estimated from the equation shown below.

Here, k represents the shearing resistance (deformation resistance) of the metal material, and d represents the diameter of the punch <NUM>. The energy Ec required for compressing the chips in the radial direction may be calculated as shown below.

The energy Ef dissipated by friction between the chips and the punch <NUM> is calculated from the equation shown below.

Here, µ represents the friction coefficient between the chips and the punch <NUM>. The back pressure (urging force) of the counter punch <NUM> is expressed by Fb, and the energy of the back pressure is expressed by Eb. <MAT><MAT>.

Thus, the pushing force F of the punch <NUM> is expressed by the equation shown below.

Here, Fb<<F is satisfied. Thus, when Fb is a small value that can be ignored, the average pushing force p·of the punch <NUM> (per unit area) is as shown in equation (<NUM>).

In this case, tanϕ is in the range from <NUM> to <NUM> and µ is in the range from <NUM> to <NUM>. This satisfies p/<NUM>=3tc/d to 12tc/d.

Here, tc/d is in the range from <NUM> to <NUM>. Thus, p/<NUM> is less than <NUM> and much smaller than conventional cold forging.

The flow of the metal material <NUM> that occurs during the cut forging of the second step was simulated and checked. The simulation software that was used is commercial finite element code DEFORM2D. The simulation conditions are as shown in table <NUM>.

<FIG> is a cross-sectional view of the metal material <NUM> prior to cut forging. As shown in the drawing, points a1 to a3 are marked on the upper surface (inner surface) of the bottom portion 12A, points a4 to a6 are marked on the inner surface of the circumferential wall <NUM>, points b1 to b4 are marked on the lower surface (outer surface) of the bottom portion 12A, and points c1 to c4 are marked in the moving path of the cutting blade <NUM> of the punch <NUM>.

<FIG> is a cross-sectional view obtained through the simulation of the metal material <NUM> subsequent to completion of the cut forging performed by the punch <NUM>. As shown in the drawing, points a1 to a3 and b1 to b4 on the bottom portion 12B are moved toward the central part of the bottom portion 12B in the radial direction. Further, the points a4 to a6 on the inner surface of the circumferential wall <NUM> are moved to the upper surface of the bottom portion 12B.

Additionally, points c1 to c4 in the moving path of the cutting blade <NUM> shown in <FIG> are all moved to the lower surface of the bottom portion 12B. It is considered that working hardening occurring during cut forging improves the product strength such as pressure resistance at the bottom portion 12B.

<FIG> is a characteristics diagram of p(pressure)/C with respect to the stroke of the punch <NUM> in one example of the simulation.

In <FIG>, points Q1 to Q3 respectively correspond to the stages shown in <FIG> is a cross-sectional view showing the vicinity of a punch corner in an initial stage of cut forging, and <FIG> is an enlarged cross-sectional view of <FIG> is a cross-sectional view showing the vicinity of the punch corner in a stage subsequent to <FIG> is an enlarged cross-sectional view of <FIG> is a cross-sectional view showing the vicinity of the punch corner in a stage subsequent to <FIG> is an enlarged cross-sectional view of <FIG>. In <FIG>, the region between the bottom portion 12A (12B) and the circumferential wall <NUM> connecting the edges A and B in the upper and lower surfaces of the bottom portion 12B is a region where shearing stress concentrates during cut forging. The region where stress concentrates is indicated by hatching lines extending in a direction that differs from the hatching lines of the other part of the bottom portion 12A (12B) and the circumferential wall <NUM>. In the same manner, <FIG>, which will be referred to later, also indicate the region where stress concentrates using hatching lines extending in a direction that differs from the hatching lines of other parts.

As shown in <FIG>, the punch <NUM> comes into contact with the bottom portion 12A and then moves over a distance that is greater than or equal to the thickness of the bottom portion 12A. The movement of the punch <NUM> and the shear deformation between the punch <NUM> and the counter punch <NUM> resulting from the movement moves the bottom portion 12B in the same direction as the punch <NUM>. The bottom portion 12B is kept substantially flat and local bulges do not form under the simulation condition. A recess, slightly recessed and including a gradually recessed surface, is formed in the upper surface (inner surface) of the bottom portion 12B near the corner of the counter punch <NUM>. More specifically, the thickness of the bottom portion 12B slightly decreases near the corner of the counter punch <NUM>. The recess including the gradually recessed surface formed in the upper surface of the bottom portion 12B is enlarged toward the center of the bottom portion 12B in the radial direction as the stroke of the punch <NUM> increases.

As shown in <FIG>, as the stroke (movement amount) of the punch <NUM> increases from point Q1, the pressure of the punch <NUM> suddenly increases. The pressure of the punch <NUM> gradually increases from point Q2 at which the edge (cutting blade <NUM>) of the punch <NUM> reaches the shearing region. The pressure of the punch <NUM> stabilizes in the shearing region that includes point Q3.

Although not shown in the drawings, in simulations in which the back pressure of the counter punch <NUM> was changed a number of times, changes were subtle in the shape of the observed product.

A case where a recess including a gradually recessed surface was formed and a case where a recess having an acute shape (hereafter referred to as sink) was formed were observed in simulations. A recess, which has a gradually recessed surface, and a sink have a relationship with the radius of curvature at the joint line B in the inner surface of the bottom portion 12A opposed toward the corner of the counter punch <NUM>. The radius of curvature at the joint line B in the inner surface of the bottom portion 12A may hereafter be referred to as the shoulder radius. When the shoulder radius is large, in an initial cutting state, the metal material will be insufficient at the joint line B in the inner surface of the bottom portion 12A.

When a recess including a gradually recessed surface is formed, stress is initially concentrated at point a. As shear deformation progresses as shown in <FIG>, the recess including the gradually recessed surface is enlarged.

<FIG> show an example of a simulation in which a sink was formed. <FIG> shows a case in which the shoulder radius rcp of the joint line B in the inner surface of the bottom portion 12A was <NUM>, and the movement amount of the punch <NUM> was <NUM>. In the state prior to cutting shown in <FIG>, there is no stress. <FIG> respectively show cases in which the movement amount of the punch <NUM> from the state of <FIG> were <NUM>, <NUM>, and <NUM>. A sink having an acute shape is formed in the vicinity of the joint line B in the inner surface of the bottom portion 12B, and the size of the sink increases as the movement amount increases. The example of <FIG> shows the sink having grown to a length that is approximately <NUM>% of the thickness of the bottom portion 12B.

The boundary region when the recess including the gradually recessed surface is formed and the boundary region when the sink is formed were searched for in the simulations. In one example of a simulation, the metal material <NUM> was SPCC, and the simulation was conducted under the conditions of t<NUM>=<NUM>, tc(=tc0)=<NUM>, <NUM>, and <NUM>, and d=<NUM>. Combinations of the cutting amount to and the thickness tc0 of the bottom portion 12A were simulated, and simulations results H1 to H5, J1 to J9, and L1 to L5 were obtained (refer to <FIG>).

Further, the flow stress σ satisfied σ=501ε<NUM> MPa, the back pressure Pb/C of the counter punch <NUM> was <NUM>, and the friction coefficient µp between the counter punch <NUM> and the metal material satisfied µp=<NUM>. Here, tc0 is the thickness tc0 of the bottom portion 12A of the metal material <NUM> prior to cut forging.

The simulation results are shown in the characteristics diagram of <FIG>. In <FIG>, the vertical axis is t<NUM>/tc0, and the horizontal axis is rcp/tc0. As shown in the drawing, a regression analysis was conducted on simulation (rcp, t<NUM>/tc0) results H1 to H5, J1 to J9, and L1 to L6 to obtain the line of t<NUM>/tc0 parting cases where a sink was formed from cases where a recess N including a gradually recessed surface was formed. The right-hand side of inequations (<NUM>), (<NUM>), and (<NUM>) to (<NUM>) are inequations representing the line.

Here, H1 to H5 are the simulation results when tc0=<NUM> was satisfied, J1 to J9 are the simulation results when tc0=<NUM> was satisfied, and L1 to L6 are simulation results when tc0=<NUM> was satisfied. The diameter of the punch <NUM> was 2to mm greater than the inner diameter of the circumferential wall <NUM>.

Thus, when the thickness tc0 of the bottom portion 12A is <NUM> and rcp/tc0<<NUM> is satisfied, it is preferred that the condition be set to satisfy inequation (<NUM>) for sink prevention.

Thus, when tc0 is <NUM> and rcp/tc0≥<NUM> is satisfied, it is preferred that the condition be set to satisfy inequation (<NUM>) for sink prevention.

Thus, when tc0 is <NUM> and rcp/tc0<<NUM> is satisfied, it is preferred that the condition be set to satisfy inequation (<NUM>) for sink prevention.

Thus, when tc0 = <NUM> is satisfied and rcp/tc0≥<NUM> is satisfied, it is preferred that the condition be set to satisfy inequation (<NUM>) for sink prevention.

Even when a sink is formed, the sink may not cause no trouble in the forged product. Thus, there is no limitation to the values and the inequations (<NUM>), (<NUM>), and (<NUM>) to (<NUM>).

The simulation results when the thickness of the bottom portion 12A was set to <NUM>, <NUM>, and <NUM> have been described. However, for example, in the case of the commercially available thickness of <NUM>, even when the thickness tc0 of the bottom portion 12A is <NUM> and rcp/tc0<<NUM> is satisfied, as long as the condition is set to satisfy inequation (<NUM>), a recess including a gradually recessed surface will be obtained without a sink.

Further, even when the thickness tc0 of the bottom portion 12A is <NUM> and rcp/tc0≥<NUM> is satisfied, as long as the condition is set to satisfy inequation (<NUM>), a recess including a gradually recessed surface will be obtained without a sink.

In the same manner, in the case of an extremely thick bottom portion, for example, when the thickness tc0 of the bottom portion 12A is <NUM> and rcp/tc0<<NUM> is satisfied, as long as the condition is set to satisfy inequation (<NUM>), a recess including a gradually recessed surface will be obtained without a sink.

The present embodiment has the advantages described below.

In the first step, the punch <NUM> including the working end surface <NUM> and the cutting blade <NUM> formed at the edge of the working end surface <NUM> is arranged in the die cavity <NUM> so that the punch <NUM> is opposed toward the metal material <NUM>, that is, opposed toward part of the wall portion <NUM> thickness-wise and the bottom portion 12A (pre-working projecting wall).

In the second step, in a state in which the metal material <NUM> is held in the moving direction of the punch <NUM> and the length of the bottom portion 12A (pre-working projecting wall) in the intersecting direction is maintained, the punch <NUM> is moved within the range of the height of the wall <NUM> so that its blade cuts the part of the wall portion <NUM> thickness-wise in the moving path of the punch <NUM> and causes shear deformation in the cut part to move the cut part toward the bottom portion 12A (pre-working projecting wall). When the punch <NUM> is opposed toward the entire circumferential wall <NUM> thickness-wise, the punch <NUM> cuts the entire circumferential wall <NUM> thickness-wise in the moving path with the blade and causes shear deformation in the cut part to move the cut part toward the bottom portion 12A (pre-working projecting wall).

Consequently, the present embodiment differs from the prior art in that precision forging can be performed with a low tool pressure. That is, massive tool pressure is not required during precision forging. Further, a chip formation mechanism is implemented during cutting. Thus, chips do not have to be separated from the metal material and can be used as part of the product. Further, since massive tool pressure is not required, the precision forging can be applied to hollow components formed from high-strength material having large dimensions and complicated cross-sectional shapes.

In the second step, the bottom portion 12A (pre-working projecting wall) is held to maintain the dimension in the intersecting direction. Thus, there is no risk of material cracking at the portion of the circumferential wall cut by the punch blade. The precision forging of the present embodiment may be referred to as cut forging that is a novel concept and provides a third basic working process in addition to the two basic working processes of upsetting and extrusion.

(<NUM>) In the first step of the precision forging method in accordance with the present embodiment, the metal material <NUM>, which includes a fit region where at least part of the wall portion <NUM> comes into plane contact with the wall surface of the die cavity <NUM> and the bottom portion 12A (pre-working projecting wall) located at the side opposite to the fit region, is arranged in the die cavity <NUM>, and the cutting blade <NUM> of the punch <NUM> is arranged spaced apart from the wall surface of the die cavity <NUM> by a distance smaller than the thickness of the wall portion <NUM>. Further, in the second step, the metal material <NUM> is cut by the cutting blade <NUM> so that the fit region remains in the wall portion <NUM>. As a result, the remaining fit region allows the part of the remaining circumferential wall <NUM> to be tubular. When a punch that does not include the cutting blade <NUM> and differs from the present embodiment is used to move the entire fit region toward the bottom portion (pre-working projecting wall), the part will be deformed to obtain a non-tubular shape.

(<NUM>) In the precision forging method of the present embodiment, when the punch <NUM> corresponds to the first punch, the counter punch <NUM> that corresponds to the second punch is located at the side of the bottom portion 12A opposite to the punch <NUM>. In the second step, the counter punch <NUM> is moved so as to follow the movement of the punch <NUM> in the moving direction.

As a result, the counter punch, to which a constant back pressure is applied, moves the sheared and discharged chips toward the node (bottom portion) and compresses the chips so that the bottom portion forms a hardened part.

(<NUM>) In the precision forging method in accordance with the present embodiment, when the cutting amount is expressed by t<NUM>, the radial length of the punch <NUM> is greater by 2t<NUM> mm than the inner diameter of the circumferential wall <NUM>. When the shoulder radius rcp and the thickness tc0 of the bottom portion 12A (pre-working projecting wall) satisfy rcp/tc0<<NUM>, the metal material <NUM> is worked so that t<NUM>/tc0 satisfies inequation (<NUM>), which is shown below.

When the shoulder radius rcp and the thickness tc0of the bottom portion 12A (pre-working projecting wall) satisfies rcp/tc0≥<NUM>, the metal material <NUM> is worked so that t<NUM>/tc0 satisfies inequation (<NUM>), which is shown below.

As a result, when inequation (<NUM>) or inequation (<NUM>) are satisfied, a precision forging product that is free from sinks can be obtained.

(<NUM>) In the second step of the precision forging method in accordance with the present embodiment, the stopper <NUM> comes into contact with the circumferential wall <NUM> to hold the metal material <NUM> (specifically, wall, or circumferential wall <NUM>) in the moving direction of the punch <NUM>. As a result, in the second step, cutting is efficiently performed.

(<NUM>) The precision forging device includes the die <NUM> and the punch <NUM>. The metal material <NUM> including the circumferential wall <NUM>, which extends in the moving direction of the punch <NUM>, and the bottom portion 12A, which extends from the circumferential wall <NUM> in a direction intersecting the moving direction, is arranged in the die cavity <NUM>. The movement of the punch <NUM> forges the metal material <NUM>. When the metal material <NUM> is arranged in the die cavity <NUM>, the punch <NUM> is arranged opposed toward part of the circumferential wall <NUM> thickness-wise and the bottom portion 12A. The punch <NUM> includes the working end surface and the cutting blade <NUM>, which is formed on the edge of the working edge surface. When the punch <NUM> is moved within the range of the height of the circumferential wall <NUM>, the cutting blade <NUM> cuts part of the circumferential wall <NUM> thickness-wise in the moving path of the punch <NUM> and causes shear deformation in the cut part.

As a result, forging can be performed with a tool pressure that is less than that of the prior art, that is, a precision forging device that does not require a massive tool pressure during precision forging can be obtained.

The mechanism that forms chips during cutting is applied to precision forging. Thus, in the obtained precision forging device, chips do not have to be separated from the metal material and can be used as part of the product. Further, the present precision forging device does not require a massive tool pressure and can be applied to hollow components formed from high-strength material having large dimensions and complicated cross-sectional shapes.

(<NUM>) The precision forging device of the present embodiment includes the stopper <NUM> that comes into contact with the distal end surface of the circumferential wall <NUM> when the punch <NUM> is moved within the range of the height of the circumferential wall <NUM>, thereby holding the metal material <NUM> in the moving direction of the punch <NUM>. This obtains a precision forging device that performs cutting efficiently.

(<NUM>) The precision forging product not forming part of the claimed invention includes the circumferential wall <NUM>, which extends in the first direction that is the axial direction, and the bottom portion 12B, which extends from the circumferential wall <NUM> in a second direction that is the radial direction intersecting the first direction. The bottom portion 12B includes the first surface, which is at the side where the joint line A between the circumferential wall <NUM> and the bottom portion 12B is located, and the second surface, which is at the side opposite to the first surface. The precision forging product includes the metal flow W extending from the joint line A to the joint line B in the second surface. As a result, the precision forging product can be manufactured with a precision forging device that does not require a massive tool pressure. That is, the precision forging product in accordance with the present embodiment can be obtained with a small tool pressure. More specifically, the precision forging product of the present embodiment does not require a massive tool pressure during precision forging. Further, chips do not have to be separated during cutting and can be used as part of the precision forging product. Since a massive tool pressure is not required, the precision forging product can be a hollow component formed from high-strength material having large dimensions and a complicated cross-sectional shape.

(<NUM>) The precision forging product not forming part of the claimed invention includes the circumferential wall <NUM>, which serves as a wall portion and extends circumferentially, and the bottom portion 12B, which is formed on the inner <NUM> P4P20200175 surface of the circumferential wall <NUM>. As a result, the precision forging product including the circumferential wall and the bottom portion has advantage (<NUM>).

Examples will now be described with reference to <FIG>, <FIG>, <FIG>, and <FIG>. The conditions of the examples are as shown in table <NUM>.

The flow stress σ of the metal material <NUM> is expressed by σ=501ε<NUM>MPa. The initial flow stress of the metal material <NUM> was 193MPa, and the plasticity coefficient of the metal material <NUM> was 501MPa. The metal material <NUM> was obtained by cutting a circular plate having a diameter of <NUM> from a sheet of cold-rolled steel having a thickness of <NUM>. The tool used in the manufacturing process was formed from high-speed tool steel (SKH51(=HRC63)). A coating of TiAIN was applied to the tool for forging work in order to prevent scuffing. The used lubricant was G-<NUM> (manufactured by Nihon Kohsakuyu Co. , Ltd, viscosity at <NUM>°: <NUM>×<NUM>-<NUM>m<NUM>/s). Forging was performed with a <NUM> kN servo press machine. The load on the punch <NUM> during forging was measured with a strain gauge arranged on the back gate of the punch <NUM>. Back pressure was applied to the counter punch <NUM> by an air cylinder.

As shown by the drawing conditions in table <NUM>, drawing was performed on the metal material <NUM> (refer to <FIG>), which is a steel sheet of SPCC (thickness <NUM>), to obtain the cup-shaped metal material <NUM> having the bottom portion <NUM> and the circumferential wall <NUM> formed around the edge of the bottom portion <NUM>, as shown in <FIG>. For the drawing, the diameter of the punch (not shown) was <NUM>, the diameter of the die (not shown) was <NUM>, and the die shoulder radius was <NUM>.

The drawing set the joint line B in the inner surface of the bottom portion <NUM> (refer to <FIG>) to a radius of curvature (punch shoulder radius) of <NUM>.

Then, ironing was further performed to form the forging material cup shown in <FIG>. A punch (not shown) having a diameter of <NUM> and a die (not shown) having a diameter of <NUM> were used for the ironing. The ironing set the radius of curvature (punch shoulder radius) at the joint line B in the inner surface of the bottom portion <NUM> to <NUM>.

Then, the precision forging device <NUM> (refer to <FIG> and the like) was used to perform cut forging by setting the cutting amount to of the forging material cup to <NUM> and <NUM> and the speed V of the punch <NUM> to <NUM>/s. The die <NUM> used for cut forging was the same as the die used for ironing. When the cutting amount to=<NUM> was satisfied, the punch <NUM> that was used had a diameter of <NUM> and the die <NUM> that was used had a diameter of <NUM>. Further, the counter punch <NUM> that was used had a diameter of <NUM>. The back pressure of the counter punch <NUM> was <NUM>. The punch <NUM> had a thickness greater than or equal to that of the bottom portion <NUM> and was moved within a range less than or equal to the height of the circumferential wall <NUM>.

In the shearing work (blanking work) of the prior art, the punch is moved from where it comes into contact with a plate material by an amount greater than or equal to the thickness of the plate material. However, this will break the bottom portion pushed by the punch. The present example differs from the prior art in that the bottom portion is not broken and moved within the range of the height of the circumferential wall together with the punch.

In half-blanking of the prior art, the punch is moved from where it comes into contact with a plate material by a moving amount that does not exceed the thickness of the plate. The present example differs from the prior art in that the bottom portion is moved within the range of the height of the circumferential wall together with the punch.

The cut forging set the radius of curvature of the inner surface and outer surface at the edge of the bottom portion <NUM> to <NUM>. The cut forging allowed the material forming the bottom portion <NUM> to be freely moved without any problem. The load on the punch <NUM> measured with a strain gauge, and the pushing force p/C of the punch <NUM> required for working was approximately <NUM> times the plasticity coefficient of the metal material <NUM>.

<FIG> are photographs showing the cross section of the bottom portion <NUM> and the circumferential wall <NUM> taken by cutting the precision forging product formed as described above in the height-wise direction.

As shown by the broken line in <FIG>, a line indicating the metal flow W appeared in the portion subject to shear deformation because of the cut forging as shown in <FIG>. The metal flow W is unique to the present cut forging. To eliminate the metal flow W, the precision forging product will have to undergo heat treatment, which will greatly increase the cost. When comparing <FIG> of the prior art example with <FIG> of the present example, there is no metal flow W in the prior art example.

<FIG> shows the result of the Vickers hardness in the cross-section of the precision forming product formed as described above measured at multiple locations in the shearing region where shear deformation occurred (region of bottom portion <NUM> leftward from metal flow W in <FIG>) and the region surrounding the shearing region. The values indicate the Vickers hardness. As shown in <FIG>, the Vickers hardness in the shearing region has values that are approximately two times greater than portions near the outer surface of the circumferential wall <NUM> in the precision forging product. Thus, the shearing region is harder than the peripheral region.

A precision forging device in accordance with a second embodiment will now be described with reference to <FIG>, <FIG>. In the embodiments described below including the present embodiment, same reference numerals are given to those components that are the same as the corresponding components of the first embodiment.

As shown in <FIG>, the metal material <NUM> of the present embodiment prior to working includes the circumferential wall <NUM>, which has the form of cylindrical tube in the same manner as the first embodiment, and the bottom portion 12A, which is coupled integrally with the lower part of the circumferential wall <NUM>. The bottom portion <NUM> of the first embodiment is flat and extends in a direction intersecting the axial direction, namely, the radial direction, whereas the bottom portion 12A of the present embodiment includes an outer surface that is a concave surface, which is part of a spherical surface, and an inner surface that is a convex surface, which is part of a spherical surface.

As shown by the double-dashed lines in <FIG>, the bottom portion 12A may include an outer surface that is a convex surface, which is part of a spherical surface, and an inner surface that is a concave surface, which is part of a spherical surface.

Alternatively, although not shown in the drawings, the inner and outer surfaces of the bottom portion 12A may both be a concave surface, which is part of a spherical surface, or a convex surface, which is part of a spherical surface. That is, there is no limit to the plan view shape and cross-sectional shape of the bottom portion 12A.

The precision forging device <NUM> used in the present embodiment will now be described.

As shown in <FIG>, in the same manner as the first embodiment, the precision forging device <NUM> includes the die <NUM>, which has the die cavity <NUM>, the punch <NUM>, the stopper <NUM>, and the counter punch <NUM>.

In the first embodiment, the working end surface <NUM> of the punch <NUM> is flat. In contrast, as shown in <FIG>, in the present embodiment, the working end surface <NUM> of the punch <NUM> has a convex surface conforming to the bottom portion 12A of the metal material <NUM>. That is, as shown in <FIG>, the working end surface <NUM> is a convex surface, which is part of a spherical surface, to conform to the convex outer surface of the bottom portion 12A.

As shown in <FIG>, the cutting blade <NUM> is formed along the entire circumference of the edge of the working end surface <NUM> of the punch <NUM>. In the same manner as the first embodiment, the cutting blade <NUM> is formed to move continuous chips, which are produced when the bottom portion 12A (12B) of the metal material <NUM> is cut, toward the central portion (axis) of the punch <NUM>. Otherwise, the structure is the same as the first embodiment.

The precision forging method according to the second embodiment is the same as the first embodiment and thus will not be described in detail. The first step is shown in <FIG>, and the second step is shown in <FIG>.

<FIG> is a perspective view of the precision forging product subsequent to working, and <FIG> is a vertical, cross-sectional view of the precision forging product subsequent to working. The bottom portion 12B shown by the double-dashed lines In <FIG> is the bottom portion 12B of the precision forging product obtained by working the pre-working metal material <NUM> that includes the bottom portion 12A shown by the double-dashed lines in <FIG>. In this case, although not shown in the drawings, the working end surface <NUM> of the punch <NUM> is concave to conform to the outer surface of the bottom portion 12A of the metal material <NUM>.

The present embodiment has advantages (<NUM>) to (<NUM>) of the first embodiment.

A precision forging device in accordance with a third embodiment will now be described with reference to <FIG>, <FIG>.

As shown in <FIG>, the metal material <NUM> of the present embodiment prior to working includes the circumferential wall <NUM>, which has the form of a cylindrical wall in the same manner as the first embodiment, a top wall <NUM>, which closes the opening at one end of the circumferential wall <NUM>, and an outwardly directed flange 17A, which is coupled integrally with the outer circumferential of the other end of the circumferential wall <NUM> and extended outward in the radial direction. The circumferential wall <NUM> extends in the first direction that is an axial direction. The flange 17A is flat and extends in a direction intersecting the axial direction, that is, in the radial direction.

The top wall <NUM> is flat and extends in a direction intersecting the axial direction, that is, in the radial direction, but does not have to be flat. The top wall <NUM> may include an outer surface that is a concave surface, which is part of a spherical surface, and an inner surface that is a convex surface, which is part of a spherical surface. Conversely, the top wall <NUM> may include an outer surface that is a convex surface, which is part of a spherical surface, and an inner surface that is a concave surface, which is part of a spherical surface. Alternatively, although not shown in the drawings, the inner and outer surfaces of the top wall <NUM> may both be a concave surface, which is part of a spherical surface, or a convex surface, which is part of a spherical surface. That is, there is no limit to the plan view shape and cross-sectional shape of the top wall <NUM>.

As shown in <FIG>, the precision forging device <NUM> includes the die <NUM>, which has the die cavity <NUM>, the punch <NUM>, the stopper <NUM>, a knockout <NUM>, and the counter punch <NUM>. The cross-sectional shape of the die cavity <NUM> is circular but not limited and may have other shapes. The cross-sectional shape of the die cavity <NUM> may be in conformance but does not have to be in conformance with the contour shape of the flange 17A. When the flange 17A does not conform to the wall surface of the die cavity <NUM>, it may be shaped so that at least a part comes into plane contact. In the present embodiment, the flange 17A is shaped in conformance to entirely come into plane contact with the wall surface of the die cavity <NUM>.

As shown in <FIG>, the punch <NUM> has the form of a cylindrical tube. The outer diameter of the punch <NUM> is equal to the inner diameter of the die cavity <NUM>, and the cutting blade <NUM> is formed on the inner circumferential edge of the punch <NUM>. The cutting blade <NUM> is formed to move continuous chips, which are produced when the circumferential wall <NUM> of the metal material <NUM> is cut, toward the radially outer side.

The cutting blade <NUM> of the punch <NUM>, which has an inner diameter that is larger than the inner diameter of the circumferential wall <NUM> and smaller than the outer diameter of the circumferential wall <NUM>, is arranged coaxially with the die cavity <NUM>. That is, the cutting blade <NUM> is formed inward from the side (outer circumferential surface) of the flange 17A that comes into plane contact with the wall surface of the die cavity <NUM>. Thus, the punch <NUM> is arranged opposed toward part of the circumferential wall <NUM> thickness-wise and the flange 17A. Further, the cutting blade <NUM> is arranged so as to allow shear deformation to occur in part of the circumferential wall <NUM> thickness-wise, that is, the outer circumferential region of the circumferential wall <NUM> located radially outward from the inner circumferential edge of the cutting blade <NUM>.

The stopper <NUM>, which is arranged coaxially with the die cavity <NUM>, has a transverse cross section that is circular to conform to the contour shape of the top wall <NUM> of the metal material <NUM>, as shown in <FIG>. The stopper <NUM> is arranged to contact the outer surface of the top wall <NUM> when shear deformation occurs in the outer circumferential region of the circumferential wall <NUM> located radially outward from the cutting blade <NUM>. The stopper <NUM> only has to hold the metal material <NUM> when the metal material <NUM> is cut. Thus, the stopper <NUM> does not have to conform to the other shape of the top wall <NUM> and may be shorter in length in the radial direction than the top wall <NUM> or have a non-circular shape.

The knockout <NUM> includes a main body portion 25a having a circular cross section and a fitting portion 25b having a circular cross section with a smaller diameter than the main body portion 25a. The fitting portion 25b has the same diameter as the diameter of the inner hollow of the circumferential wall <NUM> and can be freely fitted into and removed from the circumferential wall <NUM>. When the circumferential wall <NUM> of the metal material <NUM> does not have the form of a cylindrical tube and has a non-circular cross section, the fitting portion 25b may have a cross-sectional shape conforming to the cross-sectional shape of the inner surface of the circumferential wall <NUM>.

An engagement step 25c is formed between the main body portion 25a and the fitting portion 25b. The engagement step 25c is engaged with the end surface of the circumferential wall <NUM> when the fitting portion 25b is fitted into the circumferential wall <NUM>. The main body portion 25a has an outer diameter set to be proximate to the cutting blade <NUM>. When the punch <NUM> is moved in the die cavity <NUM>, the inner circumferential side of the circumferential wall <NUM>, which is in contact with the engagement step 25c, remains unaffected.

The counter punch <NUM> opposed toward the punch <NUM> has the form of a cylindrical tube and is arranged to contact the flange 17A when entering the open space surrounded by the circumferential wall <NUM> of the metal material <NUM> and the wall surface of the die cavity <NUM>. Further, an air cylinder or the like (not shown) applies back pressure to the counter punch <NUM> so that the counter punch <NUM> constantly presses the flange 17A. The punch <NUM> corresponds to the first punch, and the counter punch <NUM> corresponds to the second punch. The counter punch <NUM> is not an essential element and may be omitted.

A precision forging method in accordance with the present embodiment will now be described.

As shown in <FIG>, in a first step, the metal material <NUM>, which includes the flange 17A and the circumferential wall <NUM>, is arranged in the die cavity <NUM> of the die <NUM> of the precision forging device <NUM> so that the outer surface of the top wall <NUM> comes into contact with the stopper <NUM>. In this state, the circumferential wall <NUM> is arranged in the die cavity <NUM> so as to extend in the punch moving direction, and the flange 17A is arranged so as to extend in a direction intersecting the punch moving direction. The punch moving direction coincides with the axial direction of the circumferential wall <NUM>. Further, the outer circumferential surface of the flange 17A is in plane contact with the wall surface of the die cavity <NUM>.

The punch <NUM> is arranged in the die cavity <NUM> so as to be opposed toward the flange 17A and part of the circumferential wall <NUM> thickness-wise. The part of the circumferential wall <NUM> thickness-wise that is opposed toward the punch <NUM> is an outer circumferential region of the circumferential wall <NUM> located radially outward from the inner circumferential edge of the cutting blade <NUM>.

In a second step, the punch <NUM> is moved toward the flange 17A to press and cut the circumferential wall <NUM> with the cutting blade <NUM>. In this state, the metal material <NUM> remains held by the stopper <NUM> in the moving direction of the punch <NUM>. The moving amount of the punch <NUM> from when the punch <NUM> initially contacts the flange 17A is in a range from greater than or equal to the thickness of the flange 17A and less than the height h of the circumferential wall <NUM> (refer to <FIG>).

As the punch <NUM> presses the flange 17A and cuts part of the circumferential wall <NUM> thickness-wise with the cutting blade <NUM>, shear deformation caused by the cutting blade <NUM> occurs between the joint line A of the flange 17A (17B), which comes into contact with the cutting blade <NUM> formed on the working end surface of the punch <NUM>, and the joint line B, which is located between the flange 17A (17B) and the outer surface of the circumferential wall <NUM>. The reference character "17A" denotes the flange prior to cutting, and the reference character "17B" denotes the flange during and subsequent to cutting. The flange 17A corresponds to a pre-working projecting wall. The flange 17B corresponds to a post-working projecting wall.

The material (chips) cut and sheared by the cutting blade <NUM>, is moved into the flange 17A (node) between the punch <NUM> and the counter punch <NUM> thereby forming the metal flow W between the joint line A and the joint line B, as viewed in <FIG>.

<FIG> is a diagram illustrating a state when cutting has ended where the flange 17B becomes flush with the outer surface of the top wall <NUM>. As shown in <FIG>, the metal flow W extends from the portion denoted by reference character "B" to the portion demoted by reference character "A. " In <FIG>, the portion denoted by reference character "B" is where the joint line B was located until just before the flange 17B became flush with the outer surface of the top wall <NUM>. Even when the flange 17B becomes flush with the outer surface of the top wall <NUM>, the joint line B will be left as a trace. The surface of the flange 17B at the side where the joint line A is located corresponds to a first surface, and the surface of the flange 17B at the side opposite to the first surface corresponds to a second surface.

The flange 17A, 17B is constrained by the die <NUM> so that the dimensions do not change in the direction intersecting the moving direction of the punch <NUM>, as viewed in <FIG>. Thus, as the working performed by the punch <NUM> progresses, the material (chips) is compressed and moved toward the node to increase the thickness of the node.

In the same manner as the first embodiment, the back pressure Fb applied to the counter punch <NUM> is much smaller than the pushing force F of the punch <NUM>, that is, Fb<<F is satisfied. As the thickness of the node increases as described above, the counter punch <NUM> is moved backward against the urging force (back pressure) applied by the air cylinder or the like (not shown).

As shown in <FIG>, as the punch <NUM> presses the flange 17B and moves, the portion of the circumferential wall <NUM> located radially inward from the cutting blade <NUM>, that is, the fit region, which is in plane contact with the outer circumferential surface of the fitting portion 25b of the knockout <NUM>, remains unaffected.

After the cutting performed by the punch <NUM> ends, the stopper <NUM> and the counter punch <NUM> are separated from the die <NUM>. Then, the knockout <NUM> is moved toward the stopper <NUM> to remove the metal material <NUM> from the die <NUM>.

As a result, as shown in <FIG>, in the metal material <NUM> subsequent to cutting, that is, in the precision forging product, the pre-working flange 17A, which is located at one end of the circumferential wall <NUM>, is moved to the other end of the circumferential wall <NUM> and becomes the flange 17B. As shown in <FIG>, the thickness of the post-working flange 17B is greater than the thickness of the pre-working flange 17A, and the circumferential wall <NUM> has a post-working thickness K<NUM> that is less than the pre-working thickness K<NUM>.

The third embodiment has the advantages described below in addition to advantages (<NUM>), (<NUM>), and (<NUM>) to (<NUM>) of the second embodiment.

(<NUM>) The precision forging product not forming part of the claimed invention includes the circumferential wall <NUM>, which extends in the first direction that is the axial direction, and the flange 17B, which extends from the circumferential wall <NUM> in the second direction that is the radial direction. The flange 17B includes the first surface, which is where the joint line A between the circumferential wall <NUM> and the flange 17B is located, and, the second surface, which is the side opposite to the first surface. The precision forging product includes the metal flow W extending from the joint line A to the joint line B in the second surface. As a result, the precision forging product can be manufactured with a precision forging device that does not require a massive tool pressure. That is, the precision forging product in accordance with the present embodiment can be obtained with a small tool pressure. More specifically, the precision forging product of the present embodiment does not require a massive tool pressure during precision forging. Further, chips do not have to be separated during cutting and can be used as part of the precision forging product. Since a massive tool pressure is not required, the precision forging product can be a hollow component formed from high-strength material having large dimensions and a complicated cross-sectional shape.

(<NUM>) The precision forging product not forming part of the claimed invention includes the circumferential wall <NUM>, which serves as a wall portion and extends circumferentially, and the outwardly directed flange 17B, which is formed on the outer surface of the circumferential wall <NUM>. As a result, the precision forging product flange has advantage (<NUM>).

A precision forging device in accordance with a fourth embodiment will now be described with reference to <FIG>, <FIG>. The present embodiment differs in part from the third embodiment. Thus, the description hereafter will focus on the differences.

As shown in <FIG>, the metal material <NUM> of the present embodiment prior to working includes an inner tube <NUM> and an outer tube <NUM> that are arranged coaxially so as to form a duplex tube. One end of the inner tube <NUM> and one end of the outer tube <NUM> are coupled integrally by a bottom portion 64A. A ring-shaped groove <NUM> extends between the inner tube <NUM> and the outer tube <NUM>. The inner tube <NUM>, which corresponds to a circumferential wall and a wall portion, has the form of a cylindrical tube and extends in a first direction that is an axial direction. As shown in <FIG>, the outer tube <NUM>, which has the form of a cylindrical tube, has an outer diameter that is equal to an inner diameter of the die cavity <NUM> of the die <NUM> of the precision forging device.

The bottom portion 64A is flat and extends in a direction intersecting the axial direction, that is, in the radial direction.

The bottom portion 64A is flat and extends in a direction intersecting the axial direction, that is, in the radial direction, but does not have to be flat. The inner tube <NUM> and the outer tube <NUM> have circular cross sections but do not have to be circular and may be shaped differently.

The precision forging device <NUM> used in the present embodiment will now be described.

As shown in <FIG>, the precision forging device <NUM> includes the die <NUM>, which has the die cavity <NUM>, the punch <NUM>, the stopper <NUM>, and the counter punch <NUM>. The die cavity <NUM> has a circular cross section but is not limited to such a shape and only needs to conform to part of the contour shape of the outer tube <NUM>.

The cutting blade <NUM> of the punch <NUM>, which has an inner diameter that is larger than the inner diameter of the inner tube <NUM> and smaller than the outer diameter of the inner tube <NUM>, is arranged coaxially with the die cavity <NUM>. Thus, the punch <NUM> is arranged opposed to part of the inner tube <NUM> thickness-wise and the bottom portion 64A. Further, the cutting blade <NUM> is arranged so as to allow shear deformation to occur in part of the inner tube <NUM> thickness-wise, that is, the outer circumferential region of the inner tube <NUM> located radially outward from the inner circumferential edge of the cutting blade <NUM>. The thickness-wise direction of the inner tube <NUM> coincides with the radial direction.

The stopper <NUM> is arranged coaxially with the die cavity <NUM> and fixed by a fixing member (not shown). As shown in <FIG>, the stopper <NUM> includes a distal end that is fitted to the inner tube <NUM> of the metal material <NUM> and a step 24a that comes into contact with the end surface of the inner tube <NUM>.

The counter punch <NUM>, which is opposed toward the punch <NUM>, has the form of a cylindrical tube. The counter punch <NUM> is fitted in the groove <NUM> between the inner tube <NUM> and the outer tube <NUM> of the metal material <NUM> and arranged to contact the bottom portion 64A. An air cylinder or the like (not shown) applies back pressure to the counter punch <NUM> so that the bottom portion 64A is constantly pressed. The punch <NUM> corresponds to the first punch, and the counter punch <NUM> corresponds to the second punch. The counter punch <NUM> may be omitted.

As shown in <FIG>, in a first step, the metal material <NUM> is arranged in the die cavity <NUM> of the die <NUM> of the precision forging device <NUM>, and the stopper <NUM> is fitted in the inner tube <NUM> so that the step 24a comes into contact with the inner tube <NUM>. In this state, the inner tube <NUM> is arranged in the die cavity <NUM> so as to extend in the punch moving direction, and the bottom portion 64A is arranged so as to extend in a direction intersecting the punch moving direction. The punch moving direction coincides with the axial direction of the inner tube <NUM>. Further, the outer circumferential surface of the bottom portion 64A, that is, the outer circumferential surface of the outer tube <NUM>, is in a state in plane contact with the wall surface of the die cavity <NUM>.

The punch <NUM> is arranged in the die cavity <NUM> so as to be opposed toward the bottom portion 64A and part of the inner tube <NUM> thickness-wise. The part of the inner tube <NUM> thickness-wise that is opposed toward the punch <NUM> is an outer circumferential region of the inner tube <NUM> located radially outward from the inner circumferential edge of the cutting blade <NUM>.

In a second step, the punch <NUM> is moved toward the bottom portion 64A to press and cut the inner tube <NUM> with the cutting blade <NUM>. In this state, the metal material <NUM> remains held by the stopper <NUM> in the moving direction of the punch <NUM>. The movement amount of the punch <NUM> from where the punch <NUM> initially comes into contact with the bottom portion 64A is in a range that is greater than or equal to the thickness of the bottom portion 64A and less than the height of the inner tube <NUM>.

As the punch <NUM> presses the bottom portion 64A and cuts part of the inner tube <NUM> thickness-wise with the cutting blade <NUM>, shear deformation caused by the cutting blade <NUM> occurs between the joint line A of the bottom portion 64A (64B), which comes into contact with the cutting blade <NUM> formed on the working end surface of the punch <NUM>, and the joint line B, which is located between the bottom portion 64A (64B) and the outer circumference of the inner tube <NUM>. The reference character 64A denotes the bottom portion prior to working, and the reference character 64B denotes the bottom portion during and subsequent to working. The bottom portion 64A corresponds to a pre-working projecting wall. The bottom portion 64B corresponds to a post-working projecting wall.

The sheared material (chips) cut out by the cutting blade <NUM> enters the bottom portion 64A between the punch <NUM> and the counter punch <NUM> (i.e., node) and forms a metal flow W between the joint line A and the joint line B, which are shown in <FIG>.

The surface of the bottom portion 64A (64B) where the joint line B is located corresponds to a first surface, and the surface of the bottom portion 64A(64B) at the side opposite to the first surface corresponds to a second surface. <FIG> is a diagram illustrating a state when cutting has ended. As shown in <FIG>, the metal flow W extends from the portion in the first surface denoted by reference character "B" to the portion in the second surface denoted by reference character "A.

The bottom portion 64A, 64B is constrained by the die <NUM> so that the dimensions do not change in a direction intersecting the moving direction of the punch <NUM>, as shown in <FIG>. Thus, as the working performed by the punch <NUM> progresses, the material (chips) is compressed and moved toward the node to increase the thickness of the node.

In the same manner as the first embodiment, the back pressure Fb applied to the counter punch <NUM> is much smaller than the pushing force F of the punch <NUM>, that is, Fb<<F is satisfied. As the thickness of the node increases as described above, the counter punch <NUM> moves backward against the urging force (back pressure) applied by the air cylinder or the like (not shown).

As shown in <FIG>, as the punch <NUM> presses the bottom portion 64B and moves, the portion of the inner tube <NUM> located radially inward from the cutting blade <NUM> remains unaffected.

As a result, as shown in <FIG>, in the metal material <NUM> subsequent to cutting, that is, in the precision forging product, the pre-working bottom portion 64A, which is located at one end of the inner tube <NUM>, is moved toward the other end of the inner tube <NUM> and becomes the bottom portion 64B. As shown in <FIG>, the thickness of the post-working bottom portion 64B is greater than the thickness of the pre-working bottom portion 64A, and the inner tube <NUM> has a post-working thickness K<NUM> that is less than the pre-working thickness K<NUM>.

The fourth embodiment has the same advantages as the third embodiment.

A fifth embodiment will now be described with reference to <FIG>.

As shown in <FIG>, the metal material <NUM> of the present embodiment prior to working includes the circumferential wall <NUM>, which has the form of a cylindrical tube in the same manner as the first embodiment, and the bottom portion 12A, which is coupled integrally with the lower part of the circumferential wall <NUM>.

The precision forging device <NUM> used in the present embodiment differs from the precision forging device <NUM> described in the first embodiment in the shape of the cutting blade <NUM>. In the first embodiment, the working end surface <NUM> of the punch <NUM> is flat, and the cutting blade <NUM>, which is circular, is formed along the entire circumference of the working end surface <NUM> in a plan view of the punch <NUM>. In the present embodiment, the working end surface <NUM> of the punch <NUM> is flat, and the cutting blade <NUM> formed along the entire circumference of the working end surface <NUM> includes recesses and projections that are arranged alternately in the circumferential direction. Except for the cutting blade <NUM> of the punch <NUM> of the precision forging device <NUM>, the structure is the same as the first embodiment. The cutting blade <NUM> does not have to be shaped to include the recesses and projections that are alternately arranged in the circumferential direction and may have any shape.

The precision forging method according to the fifth embodiment is the same as the first embodiment and thus will not be described in detail. The first step is shown in <FIG>, and the second step is shown in <FIG>.

<FIG> is a perspective view of the precision forging product subsequent to working, and <FIG> is a vertical, cross-sectional view of the precision forging product subsequent to working. As shown in <FIG>, the worked side of the inner circumferential surface in the circumferential wall <NUM> of the metal material <NUM> includes projections 14a and recesses 14b that are alternately arranged in the circumferential direction because of the cutting blade <NUM> of the punch <NUM>. As shown in <FIG>, the metal flow W is formed between the joint line A and the joint line B.

As shown in <FIG>, the thickness of the post-working bottom portion 12B is greater than the thickness of the pre-working bottom portion 12A, and the portion of the circumferential wall <NUM> subject to cutting has a post-working thickness K<NUM> that is less than the pre-working thickness K<NUM>.

A sixth embodiment will now be described with reference to <FIG>.

In the first embodiment, the bottom portion 12A is entirely flat. In the present embodiment, the central region of the bottom portion 12A is projected in the direction in which the circumferential wall <NUM> extends and defines a projected portion <NUM> that is a tubular body including a top wall as viewed in <FIG>. The projected portion <NUM> has a circular cross section and is arranged coaxially with the circumferential wall <NUM>. A circular ring-shaped groove 19a extends between the projected portion <NUM> and the circumferential wall <NUM>.

Although not shown in the drawings, the precision forging device <NUM> used in the present embodiment is similar to the precision forging device <NUM> described in the first embodiment and thus will not be described below.

The precision forging method according to the sixth embodiment is the same as the first embodiment and thus will not be described below. <FIG> is a perspective view of the precision forging product subsequent to working, and <FIG> is a vertical, cross-sectional view of the precision forging product subsequent to working.

As shown in <FIG>, as a result of cutting forging performed by the precision forming device, in the metal material <NUM> subsequent to cutting, that is, in the precision forging product, the bottom portion 12A, which is located at one end of the circumferential wall <NUM>, is moved toward the other end of the circumferential wall <NUM> and becomes the bottom portion 12B. As shown in <FIG>, the thickness of the post-working bottom portion 12B is greater than the thickness of the pre-working bottom portion 12A, and the portion of the circumferential wall <NUM> subject to cutting has a post-working thickness K<NUM> that is less than the pre-working thickness K<NUM>.

The sixth embodiment has the same advantages as the first embodiment.

A precision forging device in accordance with a seventh embodiment will now be described with reference to <FIG>.

As shown in <FIG>, the metal material <NUM> has an L-shaped cross section and includes a wall portion <NUM>, which has the form of a quadrangular plate, and a pre-working projecting wall 112A, which has the form of a quadrangular plate and is coupled integrally to the lower part of the wall portion <NUM>. Thus, the pre-working projecting wall 112A extends from the wall portion <NUM> in an orthogonal direction that is a direction intersecting the height-wise direction of the wall portion <NUM>. The wall portion <NUM> corresponds to a flat wall portion. The height-wise direction corresponds to the first direction. The orthogonal direction, which is a direction intersecting the height-wise direction, corresponds to the second direction. In the description hereafter, the reference character "112A" denotes the projecting wall prior to working, and the reference character "112B" denotes the projecting wall during and subsequent to working.

As shown in <FIG>, the precision forging device <NUM> includes the die <NUM>, which has the die cavity <NUM>, the punch <NUM>, the stopper <NUM>, and the counter punch <NUM>.

The die cavity <NUM> has a transverse cross section having rectangular shape, that is, a quadrangular shape, to allow for fitting of the pre-working projecting wall 112A. The die cavity <NUM> includes two wall surfaces 22a and 22b that are opposed toward each other and correspond to the long sides of the rectangular transverse cross section. The first wall surface 22a is in contact with one side of the punch <NUM> and one side of the counter punch <NUM>, and the second wall surface 22b is spaced apart from the other side of the punch <NUM> and the other side of the counter punch <NUM>.

The stopper <NUM> has the form of a polygonal pillar and is fixed to the die <NUM> in contact with the wall portion <NUM>. The stopper <NUM> may be an engagement step formed integrally with the die <NUM>.

As shown in <FIG>, the punch <NUM> has the form of a plate. The working end surface of the punch <NUM> is flat, and the cutting blade <NUM> is formed on the edge of the working end surface opposed toward the second wall surface 22b of the die cavity <NUM>. In <FIG>, the cutting blade <NUM> extends in a direction perpendicular to the plane of the drawing. The cutting blade <NUM> is spaced apart by the gap S from the second wall surface 22b of the die cavity <NUM>. The cutting blade <NUM> is formed to move continuous chips, which are produced when the wall portion <NUM> of the metal material <NUM> is cut, toward the wall surface 22a.

When the punch <NUM> moves in the die cavity <NUM>, the portion of the metal material <NUM> located closer to the wall surface 22b than the cutting blade <NUM> in the gap S between the punch <NUM> and the second wall surface 22b remains unaffected.

The counter punch <NUM>, which is opposed toward the punch <NUM>, is arranged in the open space surrounded by the wall portion <NUM> of the metal material <NUM>, the pre-working projecting wall 112A, the first wall surface 22a, and the like. An air cylinder or the like (not shown) applies back pressure to the counter punch <NUM> so that the counter punch <NUM> constantly presses the projecting wall 112A. The counter punch <NUM> may be omitted.

As shown in <FIG>, in a first step, the metal material <NUM>, which includes the pre-working projecting wall 112A and the wall portion <NUM>, is arranged in the die cavity <NUM> of the die <NUM> so that the wall portion <NUM> comes into contact with the stopper <NUM>. In this state, the wall portion <NUM> is arranged in the die cavity <NUM> so as to extend in the punch moving direction, and the pre-working projecting wall 112A is arranged so as to extend in a direction intersecting the punch moving direction. The punch moving direction coincides with the height-wise direction of the wall portion <NUM>. Further, the end surface of the pre-working projecting wall 112A is in plane contact with the first wall surface 22a of the die cavity <NUM>.

The punch <NUM> is arranged in the die cavity <NUM> so as to be opposed toward the pre-working projecting wall 112A and part of the wall portion <NUM> thickness-wise.

In a second step, the punch <NUM> is moved toward the pre-working projecting wall 112A to press and cut the wall portion <NUM> with the cutting blade <NUM>. In this state, the metal material <NUM> remains held by the stopper <NUM> in the moving direction of the punch <NUM>. The movement amount of the punch <NUM> from where the punch <NUM> initially comes into contact with the pre-working projecting wall 112A is in a range that is less than the height of the wall portion <NUM>.

As the punch <NUM> presses the pre-working projecting wall 112A (112B) and cuts part of the wall portion <NUM> thickness-wise with the cutting blade <NUM>, shear deformation caused by the cutting blade <NUM> occurs between the joint line A of the projecting wall 112A (112B), which comes into contact with the cutting blade <NUM> of the punch <NUM>, and the joint line B, which is located between the projecting wall 112A (112B) and the wall portion <NUM>. In <FIG>, the cutting blade <NUM> extends in a direction perpendicular to the plane of the drawing. Thus, the joint lines A and B of the present embodiment are straight lines.

The sheared material (chips) cut out by the cutting blade <NUM> enters the projecting wall 112A (112B) (i.e., node) between the punch <NUM> and the counter punch <NUM> and forms a metal flow W between the joint line A and the joint line B, as shown in <FIG>. The surface of the projecting wall 112A (112B) where the joint line B is located corresponds to a first surface, and the surface of the projecting wall 112A (112B) at the side opposite to the first surface corresponds to a second surface. As shown in <FIG>, the metal flow W extends from the portion in the first surface denoted by reference character "B" to the portion of second surface denoted by reference character "A.

The pre-working projecting wall 112A (post-working projecting wall 112B) is constrained by the die <NUM> so that the dimensions do not change in a direction intersecting the moving direction of the punch <NUM>, as shown in <FIG>. Thus, as the working performed by the punch <NUM> progresses, the material (chips) is compressed and moved toward the node to increase the thickness of the node.

As a result, as shown in <FIG>, in the metal material <NUM> subsequent to cutting, that is, in the precision forging product, the pre-working projecting wall 112A, which is located at one end of the wall portion <NUM>, is moved toward the other end of the wall portion <NUM>, and becomes the projecting wall 112B.

As shown in <FIG>, the thickness of the post-working projecting wall 112B is less than the thickness of the pre-working projecting wall 112A.

In the seventh embodiment, the wall portion <NUM> has the form of a flat plate but may be bent in a transverse cross section that is orthogonal to the first direction. Preferably, in this case, the cutting blade <NUM> of the punch <NUM> is shaped in conformance with the bend in the wall portion <NUM>.

A precision forging device in accordance with an eighth embodiment will now be described with reference to <FIG>, <FIG>.

As shown in <FIG>, the metal material <NUM> of the present embodiment prior to working includes a semicircular wall portion <NUM> and a semicircular flange 120A extending radially and coupled integrally to the outer circumferential surface of the basal end of the wall portion <NUM>. Thus, the flange 120A extends in the radial direction from the wall portion <NUM> in a direction intersecting the height-wise direction of the wall portion <NUM>. The flange 120A corresponds to an outwardly directed flange. The wall portion <NUM> corresponds to a curved wall portion. The wall portion <NUM> is semicircular in a transverse cross section but does not have to be semicircular and may be shaped to have a different arcuate shape, such as the shape of the alphabet C, or have a shape defined by a radius of curvature varied in the circumferential direction. In the present embodiment, the height-wise direction of the wall portion <NUM> corresponds to the first direction. Further, the radial direction corresponds to the second direction.

The die cavity <NUM> includes the first wall surface 22a, which is a flat surface, and the second wall surface 22b, which is a concave surface, and is shaped to be semicircular in a transverse cross section so as to allow for fitting of the flange 120A. The punch <NUM> and the cutting blade <NUM> are semicircular, have a radius of curvature at the outer side that is the same as that of the second wall surface 22b, and are in plane contact with and slidable on the second wall surface 22b. The working end surface of the punch <NUM> has a length in the radial direction that is greater than the extending amount of the flange 120A from the wall portion <NUM> and less than the total of the extending amount of the flange 120A and the thickness of the wall portion <NUM> in the radial direction. The cutting blade <NUM> is formed along the entire inner edge of the working end surface of the punch <NUM>.

The counter punch <NUM> is semicircular, has a radius of curvature at the outer side that is the same as the second wall surface 22b, and is in plane contact with and slidable on the second wall surface 22b. The inner side of the counter punch <NUM> has the same radius of curvature as the outer surface of the wall portion <NUM> and is in plane contact with and slidable on the outer surface. The end surface of the counter punch <NUM> opposed toward the punch <NUM> is flat and contacts the flange 120A.

The width of the counter punch <NUM> in the radial direction is equal to the extending length of the flange 120A from the wall portion <NUM>.

The punch <NUM> is spaced apart from the first wall surface 22a, and the gap S is formed between the cutting blade <NUM> and the first wall surface 22a. The stopper <NUM> is fixed to the die <NUM>. The stopper <NUM> includes a side surface 24d, which is a flat surface, and a side surface 24e, which is a convex surface, and is shaped to be semicircular in a transverse cross section. The stopper <NUM> includes a main body portion <NUM> and a distal end portion <NUM>. The radius of the side surface 24e in the distal end portion <NUM> is smaller than the radius of the side surface 24e in the main body portion <NUM>, and an engagement step 24f is formed between the main body portion <NUM> and the distal end portion <NUM>.

As shown in <FIG>, the engagement step 24f comes into contact with the wall portion <NUM>. The side surface 24e of the main body portion <NUM> of the stopper <NUM> is in plane contact with and slidable relative to the counter punch <NUM>. Further, the side surface 24e of the distal end portion <NUM> of the stopper <NUM> is in plane contact with the inner surface of the wall portion <NUM>. The side surface 24d of the stopper <NUM> is entirely in plane contact with the first wall surface 22a.

The precision forging method in accordance with the present embodiment and its advantages will not be described since they are similar to the precision forming method in accordance with the seventh embodiment and can be understood by interchanging "the pre-working projecting wall 112A" to "the flange 120A", "the projecting wall 112B subsequent to working" to "the flange 120B", "<FIG>", "<FIG>", "112A" to "120A", and "112B" to "120B". The flange 120A corresponds to the pre-working projecting wall. Further, the cutting blade <NUM> of the punch <NUM> in the present embodiment is semicircular. Thus, the joint lines A and B are semicircular.

In the above description, the post-working flange 120B is located closer to the basal end than the central part of the wall portion <NUM> in the height-wise direction of the wall portion <NUM> but may be located at the upper end with respect to the height-wise direction of the wall portion <NUM>, as shown in <FIG>.

Further, in the eight embodiment that includes the outwardly directed flange, an inwardly directed flange may be used instead of the outwardly directed flange.

Claim 1:
A precision forging method that includes arranging a metal material (<NUM>) including a wall portion (<NUM>, <NUM>, <NUM>), which extends in a moving direction of a punch (<NUM>), and a pre-working projecting wall (12A, 17A, 64A, 112A, 120A), which extends from the wall portion (<NUM>, <NUM>, <NUM>) in a direction intersecting the moving direction, in a die cavity (<NUM>) of a die (<NUM>), and moving the punch (<NUM>) to forge the metal material (<NUM>), the precision forging method being characterized by: a first step of arranging the punch (<NUM>), which includes a working end surface (<NUM>) and a cutting blade (<NUM>) formed at an edge of the working end surface, in the die cavity (<NUM>) so that the punch (<NUM>) is opposed toward part of the wall portion (<NUM>, <NUM>, <NUM>) thickness-wise and the pre-working projecting wall (12A, 17A, 64A, 112A, 120A) of the metal material (<NUM>); and a second step of moving the punch (<NUM>) within a range of a height of the wall portion (<NUM>, <NUM>, <NUM>) in a state in which the metal material (<NUM>) is held in the moving direction of the punch (<NUM>) and a length of the pre-working projecting wall in the intersecting direction is maintained so that the cutting blade (<NUM>) cuts the part of the wall portion (<NUM>, <NUM>, <NUM>) thickness-wise located in a moving path of the punch (<NUM>) and causes shear deformation in the cut part to move the cut part toward the pre-working projecting wall.