Forging method and forging apparatus

Abstract

A forging method is set in a shaping hole of a die body, and the forging material is pressed with a punch to perform plastic shaping of the forging material. Ultrasonic vibration having a vibration frequency is applied to the die body with a vibration applying apparatus during the plastic shaping of the forging material. The vibration frequency is converged to a resonance frequency of the die body when the vibration frequency is within a tracking range of the vibration applying apparatus during the plastic shaping of the forging material. When the tracking range is shifted in accordance with a discontinuous change of the resonance frequency during the plastic shaping of the forging material to deviate from the vibration frequency, the reference frequency is changed so as to fall within a shifted tracking range.

Claims

1. A forging method comprising: setting a forging material in a shaping hole of a die body; pressing the forging material with a punch to perform plastic shaping of the forging material; applying ultrasonic vibration having a reference frequency as an initial value of a vibration frequency to the die body with a vibration applying apparatus during the plastic shaping of the forging material; and converging the vibration frequency to a resonance frequency of the die body during the plastic shaping of the forging material when the vibration frequency is within a tracking range of the vibration applying apparatus, wherein when the tracking range is shifted in accordance with a discontinuous change of the resonance frequency during the plastic shaping of the forging material to deviate from the vibration frequency, the reference frequency is changed so as to fall within a shifted tracking range, wherein the forging material is extruded rearward so as to be filled into a punch outer peripheral gap between a punch outer peripheral side surface and a shaping hole inner peripheral surface of the die body during the plastic shaping of the forging material, wherein a contact state of the forging material with respect to the punch outer peripheral side surface changes during a process that the forging material is being filled in the punch outer peripheral gap from an insufficient contact state to a sufficient contact state, and wherein the reference frequency is changed after shifting of the contact state of the forging material with respect to the punch outer peripheral side surface from the insufficient contact state to the sufficient contact state.

2. The forging method as recited in claim 1, wherein a contact state of the forging material with respect to a shaping hole inner peripheral surface of the die body changes during the plastic shaping of the forging material from an insufficient contact state to a sufficient contact state, and wherein the reference frequency is changed after shifting of the contact state of the forging material with respect to a shaping hole inner peripheral surface of the die body from the insufficient contact state to the sufficient contact state.

3. The forging method as recited in claim 1, further comprising: obtaining a punch load at a time of shifting of a contact state of the forging material with respect to a shaping hole inner peripheral surface of the die body from an insufficient contact state to a sufficient contact state; and determining a time of changing the reference frequency based on the obtained punch load.

4. The forging method as recited in claim 1, further comprising: obtaining a time of shifting of the contact state from the insufficient contact state to the sufficient contact state based on an elapsed time from a start time of the plastic shaping of the forging material by the punch; and determining a time of changing the reference frequency based on the obtained time.

5. The forging method as recited in claim 1, further comprising: obtaining a punch load at a time of shifting of the contact state from the insufficient contact state to the sufficient contact state; and determining a time of changing the reference frequency based on the obtained punch load.

6. A forging method comprising: setting a forging material in a shaping hole of a die body; pressing the forging material with a punch to perform plastic shaping of the forging material; applying ultrasonic vibration having a reference frequency as an initial value of a vibration frequency to the die body with a vibration applying apparatus during the plastic shaping of the forging material; converging the vibration frequency to a resonance frequency of the die body during the plastic shaping of the forging material when the vibration frequency is within a tracking range of the vibration applying apparatus, wherein when the tracking range is shifted in accordance with a discontinuous change of the resonance frequency during the plastic shaping of the forging material to deviate from the vibration frequency, the reference frequency is changed so as to fall within a shifted tracking range; obtaining a time of shifting a contact state of the forging material with respect to a shaping hole inner peripheral surface of the die body from an insufficient contact state to a sufficient contact state based on an elapsed time from a start time of the plastic shaping of the forging material by the punch; and determining a time of changing the reference frequency based on the obtained time.

7. A forging method comprising: setting a forging material in a shaping hole of a die body; pressing the forging material with a punch to perform plastic shaping of the forging material; applying ultrasonic vibration having a reference frequency as an initial value of a vibration frequency to the die body with a vibration applying apparatus during the plastic shaping of the forging material; and converging the vibration frequency to a resonance frequency of the die body during the plastic shaping of the forging material when the vibration frequency is within a tracking range of the vibration applying apparatus, wherein when the tracking range is shifted in accordance with a discontinuous change of the resonance frequency during the plastic shaping of the forging material to deviate from the vibration frequency, the reference frequency is changed so as to fall within a shifted tracking range, and wherein application of vibration by the vibration applying apparatus is stopped immediately before changing the reference frequency, and the application of vibration by the vibration applying apparatus is restarted when the reference frequency is changed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Some embodiments of the present invention are shown by way of example, and not limitation, in the accompanying figures.

(2) FIG. 1 is a block diagram showing a forging apparatus capable of executing a forging method according to a first embodiment of the present invention.

(3) FIG. 2A is a block diagram showing a state immediately after introducing a forging material in a forging apparatus according to the first embodiment.

(4) FIG. 2B is a block diagram showing a state immediately after start of shaping in the forging apparatus according to the first embodiment.

(5) FIG. 2C is a block diagram showing a state immediately after shifting of a contact state to a sufficient contact state in which the forging material is in sufficient contact with an inner peripheral surface of the shaping hole in the forging apparatus according to the first embodiment.

(6) FIG. 2D is a block diagram showing a state immediately after start of filling of the forging material into a punch outer peripheral gap in the forging apparatus according to the first embodiment.

(7) FIG. 2E is a block diagram showing a state immediately after start of filling of the forging material into the punch outer peripheral gap in the forging apparatus according to the first embodiment.

(8) FIG. 2F is a block diagram showing a state immediately after completion of plastic shaping of the forging material in the forging apparatus according to the first embodiment.

(9) FIG. 3A is a block diagram showing a relation between a resonance frequency and a shaping process time in the forging apparatus according to the first embodiment.

(10) FIG. 3B is a block diagram showing a relation between a reference frequency and a shaping process time in the forging apparatus according to the first embodiment.

(11) FIG. 4A is a graph showing an impedance curve line immediately after shaping in the forging apparatus according to the first embodiment, and FIG. 4B is a graph showing an impedance curve line immediately after shifting of a contact state to a sufficient contact state in which the forging material is in sufficient contact with a shaping hole inner peripheral surface.

(12) FIG. 5 is a graph showing an impedance curve line for explaining a tracking range of a resonance frequency.

(13) FIG. 6 is a graph showing an impedance curve line to which an overload set value is added immediately after start of shaping in a forging apparatus according to the first embodiment.

(14) FIGS. 7A to 7E each are a plan view for explaining a contact state of the forging material with respect to a die shaping hole inner peripheral surface.

(15) FIG. 8A is a block diagram for explaining a relation between a surface pressure and a vibration stress in a forging die.

(16) FIG. 8B is a block diagram for explaining a relation between a surface pressure and a vibration stress in the forging die.

(17) FIG. 8C is a block diagram for explaining a relation between a surface pressure and a vibration stress in the forging die.

(18) FIG. 9 is a block diagram showing a forging apparatus capable of executing a forging method according to a second embodiment of the present invention.

(19) FIG. 10A is a graph showing a relation between a contact state of a forging material with respect to a shaping hole inner peripheral surface and a process elapsed time.

(20) FIG. 10B is a graph showing a relation between a center angle maximum value max between contact points and a process elapsed time.

(21) FIG. 10C is a graph showing a relation between a resonance frequency and a process elapsed time.

(22) FIG. 11 is a block diagram showing a forging apparatus capable of executing a forging method according to a third embodiment of the present invention.

(23) FIG. 12A is a graph showing a relation between a contact state of a forging material with respect to a shaping hole inner peripheral surface and a process elapsed time.

(24) FIG. 12B is a graph showing a relation between a center angle maximum value max between contact points and a punch load.

(25) FIG. 12C is a graph showing a relation between a resonance frequency and a process elapsed time.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

(26) In the following paragraphs, some embodiments in this disclosure will be described by way of example and not limitation. It should be understood based on this disclosure that various other modifications can be made by those in the art based on these illustrated embodiments. In the drawings, the size and position of each member may be exaggerated or simplified for clarity.

(1) First Embodiment

(27) FIG. 1 is a schematic block diagram showing a forging apparatus capable of executing a forging method according to a first embodiment of the present invention. As shown in FIG. 1, this forging apparatus is provided with, as fundamental structural elements, a die 1 as a lower die, a punch 2 as an upper die, a raising-and-lowering driving mechanism 3 for raising and lowering the punch 2, a vibrator 4 for generating ultrasonic vibration, and an ultrasonic vibration device 5 for driving the vibrator 4.

(28) The die 1 is provided with a cylindrically-shaped or doughnut-shaped die body 11 having a columnar shaping hole 12 at its center, and a shaping pin 15 arranged at a lower end portion in the shaping hole 12 of the die body 11. The inner peripheral surface of the shaping hole 12 shapes an outer peripheral surface of a forged article W2, and the upper end surface of the shaping pin 15 shapes a lower surface of the forged article W2.

(29) The shaping pin 15 may be configured to be movable in the up-down direction to concurrently use as a knock-out pin for pushing out the forged article W2 from the shaping hole 12 after forging. Alternatively, instead of concurrently using the shaping pin 15 as a knock-out pin, a separate knock-out mechanism may be provided.

(30) The punch 2 is coaxially arranged in the shaping hole 12, and is movable up and down by the raising-and-lowering driving mechanism 3. As shown in FIG. 2A, in a state in which a forging material W1 is placed in the shaping hole 12 of the die body 11, the punch 2 is driven into the shaping hole 12 by lowering the punch 2. This applies a predetermined shaping load to the forging material W1, so that a cup-shaped forged article W2 corresponding to the inner shape of the die 1 as shown in FIG. 2F is formed.

(31) In this embodiment, using a disk-shaped material as a forging material W1, a cup-shaped forged article W2 is obtained. Needless to say, however, in the present invention, the shape of the forging material W1 is not limited to a disk-shape, but may be of any shape, such as, e.g., a polygonal columnar shape, a spherical shape, and a polygonal shape. Further, the forged article W2 is not limited to a cup-shaped article, but may be of any shape.

(32) As shown in FIG. 1, a vibrator 4 is coupled or attached to an outer peripheral surface of the die body 11. The vibrator 4 is configured to generate ultrasonic vibration depending on the output value of the ultrasonic vibration device 5. The ultrasonic vibration wave generated by the vibrator 4 is transmitted to the die body 11 via the contact surface contacting the die body 11.

(33) In the present invention, it may be configured such that a horn is provided between the vibrator 4 and the die body 11 to transmit the ultrasonic vibration generated by the vibrator 4 to the die body 11 via the horn.

(34) In this embodiment, the vibrator 4 and the ultrasonic vibration device 5 constitute a vibration applying apparatus. In cases where a horn is provided, the horn, the vibrator 4, and the ultrasonic vibration device 5 constitute a vibration applying apparatus.

(35) In this embodiment, as a material of the forging material W1, a material produced by a method of, e.g., cutting an aluminum (including its aluminum alloy) continuously cast material into a predetermined length, a material produced by a method of, e.g., compressively shaping aluminum powder into a billet shape, then shaping it into a round bar-shape by hot extrusion, and cutting the extruded material into a predetermined length, a drawn material, or a pressed material, etc., may also be used.

(36) In this embodiment, the ultrasonic vibration device 5 is configured such that at the time of vibrating the vibrator 4, the reference frequency as an initial value of a vibration frequency can be changed arbitrarily and that the reference frequency can be changed arbitrarily during the shaping operation. Further, the ultrasonic vibration device 5 of this embodiment is provided with a tracking function as will be detailed later, and when the vibrator 4 is driven in a state in which the reference frequency is set near the resonance frequency of the die body 11, the vibration frequency of the vibrator 4 is converged from the initial reference frequency to the resonance frequency, and becomes equal to the resonance frequency.

(37) <Explanation of Change of Resonance Frequency>

(38) In the forging apparatus of this embodiment, as will be described below, during the process of plastic shaping of the forging material W1, the resonance frequency of the die body 11 changes.

(39) That is, FIG. 3 is a graph showing a relation between a resonance frequency of the die body 11 and a shaping process time according to the ultrasonic forging of this embodiment. The vertical axis indicates a resonance frequency, and the horizontal axis indicates a shaping process time.

(40) In this graph, the time 0 of the shaping process time corresponds to the time when the forging material W1 is loaded in the shaping hole 12 of the die 1. In this state, as shown in FIG. 2A, the forging material W1 and the shaping hole inner peripheral surface are substantially not in contact with each other, and there exists a certain clearance between them.

(41) The time t0 corresponds to, as shown in FIG. 2B, the time when the forging material W1 is pressed with the descending punch 2 and the forging material W1 starts contacting with the shaping hole inner peripheral surface. This time t0 corresponds to the time when shaping of the forging material W1 by the punch 2 starts.

(42) In the forging, after the time t0, contact points of the forging material W1 to the shaping hole inner peripheral surface start to appear, and thereafter as the shaping process progresses, contact points are generated probabilistic phenomenally, and increase.

(43) The time t1 corresponds to, as shown in FIG. 2C, the time when the forging material W1 is sufficiently and plastically deformed outward (in the radially outward direction) and the forging material W1 starts sufficiently contacting with the shaping hole inner peripheral surface. Thus, between the time t0 and immediately before the time t1, a state in which the forging material W1 is not sufficiently in contact with the shaping hole inner peripheral surface, i.e., an insufficient contact state, is maintained, and shifted to a sufficient contact state at the time t1. Here, at the time t0, the resonance frequency of the die body 11 is fr0. On the other hand, at the time t1, the resonance frequency increases instantaneously to fr1 discontinuously (significantly).

(44) Between the time t1 and the time t2, the contact state of the forging material W1 with respect to the shaping hole inner peripheral surface shifts from a sufficient contact state to a substantially perfectly contact state (complete contact state).

(45) The latter time t2 corresponds to, as shown in FIG. 2D, the time when filling of the forging material W1 in a gap between the punch 2 and the shaping hole 12 (punch outer peripheral gap) starts, i.e., the time when the rearward extrusion starts. Here, from the time t1 to the time t2, the resonance frequency gradually increases from fr1 to fr2 in a continuous manner.

(46) The time t3 corresponds to, as shown in FIG. 2E, the time when the forging material W1 is in the middle of being filled in the punch outer peripheral gap by the rearward extrusion and the forging material W1 starts sufficiently contacting with the shaping hole inner peripheral surface. Thus, between the time t2 and immediately before the time t3, a complete contact state in which the forging material W1 is in complete contact with the shaping hole inner peripheral surface (die inner peripheral side surface) is maintained, and at the time t3, it becomes a state in which the forging material W1 is in sufficient contact with the punch outer peripheral side surface. Here, at the time t2, the resonance frequency of the die body 11 is fr2. On the other hand, at the time t3, the resonance frequency increases instantaneously to fr3 discontinuously (significantly).

(47) The time t4 corresponds to, as shown in FIG. 2F, the time when the forging material W1 is completely filled in the punch outer peripheral gap and the shaping is completed. Thus, between the time t3 and immediately before the time t4, a state in which the forging material W1 is sufficiently in contact with the punch outer peripheral side surface is maintained. Here, between the time t3 and the time t4, the resonance frequency gradually increases from fr3 to fr4 continuously.

(48) In this embodiment, in a contact state in which the forging material W1 is in contact with the shaping hole inner peripheral surface, an insufficient contact state means a state in which contact points of the forging material W1 to the shaping hole inner peripheral surface are eccentrically arranged to a part of the shaping hole inner peripheral surface in the peripheral direction. A sufficient contact state means a state in which contact points of the forging material W1 to the shaping hole inner peripheral surface are arranged dispersedly over a long range in the circumferential direction. A complete contact state means a state in which the forging material W1 is in contact with the shaping hole inner peripheral surface over the entire area in the circumferential direction of the shaping hole inner peripheral surface.

(49) Further, in a contact state in which the forging material W1 is in contact with the punch outer peripheral side surface, an insufficient contact state means a state in which the forging material W1 is not sufficiently filled in the punch outer peripheral gap. A sufficient contact state means a state in which the forging material W1 is sufficiently filled in the punch outer peripheral gap.

(50) The insufficient contact state and the sufficient contact state with respect to the shaping hole inner peripheral surface and the punch outer peripheral side surface will be explained.

(51) <Explanation of Tracking Range>

(52) FIG. 4A is a graph showing an impedance curve line at the time t0 in this embodiment, and the vertical axis indicates an impedance proportional to a vibrator load, and the horizontal axis indicates a frequency.

(53) As shown in this graph, in the state at time t0 in which the forging material W1 is not sufficiently in contact with the shaping inner peripheral surface, the fr0 is a resonance frequency of the die body 11, which is a frequency at which the die body 11 vibrates in the radial direction and the impedance of the vibrator 4 is a minimum value as well. This means that a vibration force (vibrator load) required for the vibrator 4 becomes minimum at the time when the vibration frequency becomes equal to the resonance frequency by changing the vibration frequency of the vibrator 4 while controlling so that the amplitude of vibration by the vibrator 4 is maintained constant. This state can be said as the most efficiently vibrating state. Further, there exist sub-resonance frequencies fa0 and fb0 around the resonance frequency fr0, and these sub-resonance frequencies fa0 and fb0 each are a valley bottom of the impedance curve line in the same manner as the resonance frequency fr0. However, the vibration manner at the sub-resonance frequencies fa0 and fb0 are different from the vibration manner at the resonance frequency fr0, and includes, for example, torsional vibration and bending vibration, and the amplitudes at the shaping hole inner peripheral surface are unequal. Further, at the sub-resonance frequencies fa0 and fb0, as compared with the case at the resonance frequency fr0, the impedance is higher, and the load of the vibrator 4 increases, which makes it difficult to effectively vibrate the die body 11.

(54) On the other hand, as a tracking method which is generally used in the ultrasonic vibration device 5, a PLL (Phase Locked Loop) method is known. In this method, the vibration frequency of the ultrasonic vibration device 5 is tracked so as to conform to the resonance frequency by converging the driving frequency (vibration frequency) of the vibrator 4 by the ultrasonic vibration device 5 to the valley bottom of the impedance curve line. For example, as shown in FIG. 5, when the vibration frequency of the ultrasonic vibration device 5 is within a range of the tracking range fl of the resonance frequency, the vibration frequency converges to the resonance frequency fr, and when not within the tracking range fl, the vibration frequency converges to the sub-resonance frequency fa or fb in another frequency range. Therefore, the tracking range means a range in which the vibration frequency of the ultrasonic vibration device 5 can be converged to a resonance frequency, and is a specific range including a resonance frequency fr0.

(55) In an ultrasonic shaping using a normal PLL method, it is configured such that the reference frequency as an initial vibration frequency of the ultrasonic vibration device 5 is set to fs0 as shown by in FIG. 4A in the tracking range, and driving of the vibrator 4 is initiated at this frequency fs0 and the vibration frequency is made to be converged to the resonance frequency fr0 to thereby vibrate the die body 11 at the resonant condition.

(56) In the PLL method, the impedance is not directly measured, and as disclosed in the aforementioned Patent Document 2, etc., it is common that the vibration frequency is made to be converged to the valley bottom of the impedance curve line by converging the phase difference between the current and the voltage of the vibrator to zero.

(57) The resonance frequency fr changes during the forging process as explained above with reference to FIG. 3A. In accordance with the change, the tracking range fl also changes. For example, as shown in FIG. 3B, a predetermined frequency range including a resonance frequency fr becomes a tracking range fl, and the tracking range fl continuously rises so as to follow the continuous rise of the resonance frequency fr.

(58) Here, as shown in FIGS. 3A and 3B, the resonance frequency fr increases instantaneously in a discontinuous manner when shifting from the time t0 to the time t1, and in accordance with the instantaneous increase, the tracking range fl is also changed instantaneously in a discontinuous manner. For example, at the time t0, the impedance curve line is in a state shown in FIG. 4A. On the other hand, at the time t1, the impedance curve line changes instantaneously to the state shown in FIG. 4B. For this reason, even if the vibration frequency of the ultrasonic vibration device 5 matches the resonance frequency fr0 immediately before the time t1, the resonance frequency changes instantaneously to fr1 at the time of t1, and in accordance with that, the tracking range fl also shifts instantaneously. As a result, as shown by in FIG. 4B, the vibration frequency of the ultrasonic vibration device 5 moves away from the shifted tracking range. As a result, the vibration frequency of the vibrator 4 does not converge to the shifted resonance frequency fr1, but converges to, for example, the shifted sub-resonance frequency fa1. For the reasons described above, the die body 11 cannot be vibrated in a resonant condition, and therefore desired effects cannot be obtained.

(59) Under the circumstance, in this embodiment, when the resonance frequency shifts in a discontinuous manner, specifically when the time shifts from the time t0 to the time t1, as shown by .circle-solid. in FIG. 4B, the resonance frequency is shifted to fs1 within the tracking range of the shifted resonance frequency fr1. With this, the vibration frequency of the ultrasonic vibration device 5 converges to the resonance frequency fr1, which enables effective vibration of the die body 11 in a resonant condition. Thus, desired effects can be obtained.

(60) In the same manner, when the time has reached from the time t2 to the time t3 and the resonance frequency discontinuously shifts to fr3, as shown in FIGS. 3A and 3B, the reference frequency is changed to fs3 which is within the tracking range fl of the shifted resonance frequency fr3. With this, the vibration frequency of the vibrator 4 converges to the resonance frequency fr3, which enables effective vibration of the die body 11 in a resonant condition. Thus, desired effects can be obtained.

(61) In an ultrasonic forging, normally, an overload set value is set to avoid excessive current flow in the ultrasonic vibration device 5, and the substantial tracking range changes also by the overload set value. That is, when a voltage equal to or higher than a predetermined value is applied to the ultrasonic vibration device 5, the ultrasonic vibration device 5 is deactivated to stop generation of vibration, generating an overload error. At that time, when current is made constant to attain a constant amplitude, a voltage rises as the impedance increases, and therefore the impedance exceeding a predetermined value causes an overload error, resulting in stopping of vibration. For example, as shown in FIG. 6, in a case in which the impedance exceeds the overload set value Ls at a location other than the vicinity of the resonance frequency fr0, the tracking range fl is essentially limited to a narrow range equal to or below the overload set value Ls, and therefore it is required to set the reference frequency fs0 within this narrow range.

(62) Further, in cases where an overload error occurs at a location other than the vicinity of the resonance frequency by the overload set value Ls, in order to prevent occurrence of an overload error when changing the reference frequency to fs1 after the time t0 to t1 at which the resonance frequency changes in a discontinuous manner, it is preferable that vibration be stopped immediately before reaching the time t0 and the reference frequency is changed to fs1 approximated to the resonance frequency fr1 after reaching the time t1, and then vibration is restarted.

(63) In the same manner, in order to prevent occurrence of an overload error when changing the reference frequency to fs3 at the time of t2 to t3, it is preferable that vibration be stopped immediately before reaching the time t2 and the reference frequency is changed to fs3 approximated to the resonance frequency fr3 after reaching the time t3, and then vibration is restarted.

(64) <Explanation of Contact State of Forging Material to Shaping Hole Inner Peripheral Surface>

(65) Next, in this embodiment, a contact state of the forging material W1 with respect to the shaping hole inner peripheral surface will be explained in detail with specific examples.

(66) FIGS. 7A to 7E each are a plan view for explaining a contact state of the forging material W1 with respect to a shaping hole inner peripheral surface (inner peripheral side surface) of a die. As shown in these figures, in a plan view state or a horizontal cross-sectional view, the contact point of the forging material W1 with respect to the shaping hole inner peripheral surface of the die 1 is defined as A. In a case in which there are two or more (plural) contact points A, an angle between the line segment AO connecting one of contact points between adjacent two contact points A and the center O of the shaping hole 12 and the line segment AO connecting the other contact point A and the center O of the shaping hole 12 is defined as . When the maximum value max among the center angles of the adjacent contact points exceeds 180 degrees (max>180 degrees), the contact state is defined as an insufficient contact state. When the maximum value max is equal to or less than 180 degrees (max180 degrees), the contact state is defined as an sufficient contact state.

(67) For example, in the case of FIGS. 7A and 7B, since max exceeds 180 degrees, the contact state is defined as an insufficient contact state. Further, in the case of FIG. 7C, since max is equal to or less than 180 degrees, the contact state is defined as a sufficient contact state.

(68) Further, even in cases where the forging material W1 is in line contact with the shaping hole inner peripheral surface in a plan view (horizontal cross-sectional view) state, contact states can be classified based on the center angle maximum value max. For example, in the case of FIG. 7D, since max exceeds 180 degrees, the contact state is defined as an insufficient contact state. Further, in the case of FIG. 7E, since max is less than 180 degrees, the contact state is defined as a sufficient contact state.

(69) For reference, in cases where the number of contact points A is 2 and the center angle is 180 degrees, the contact state is defined as a sufficient contact state. Further, in cases where the number of contact points A is 1, the contact state is defined as an insufficient contact state.

(70) In this embodiment, the center of the shaping hole 12 is a least-square circle applied to the shaping hole contour line (inner peripheral surface). This least-square circle is obtained by a least-square method.

(71) Here, in this embodiment, the distance along the shaping hole inner peripheral surface between adjacent two contact points (circumferential directional length) is defined as a distance between adjacent contact points. A case in which the maximum value between adjacent contact points exceeds the half of the shaping hole entire peripheral length is defined as a state in which a plurality of contact points A are arranged disproportionately in a range less than half of the shaping hole inner peripheral surface. This state corresponds to the state in which max exceeds 180 degrees (the state of [max>180 degrees]), and is defined as an insufficient contact state. Further, the case in which the maximum value between adjacent contact points is less than half of the shaping hole entire peripheral length is defined as a state in which a plurality of contact points A are arranged in a range more than half of the shaping hole inner peripheral surface. This state corresponds to the state in which max exceeds 180 is equal to or less than 180 degrees (the state of [max180 degrees]), and is defined as a sufficient contact state.

(72) In this embodiment, the cross-sectional shape (planar shape) of the shaping hole 12 of the die body 11 is formed into a circular shape, but not limited to it. In the present invention, the cross-sectional shape of the shaping hole 12 may be a non-circular shape, such as, e.g., a polygonal shape, an elliptical shape, an oval shape, and an irregular shape. In this case, with reference to the center angle between adjacent contact points, the contact states may be classified into an insufficient contact state and a sufficient contact state. Alternatively, with reference to the distance between adjacent contact points (circumferential directional length), the contact states may be classified into an insufficient contact state and a sufficient contact state.

(73) In this embodiment, the state from the time when the forging material W1 starts contacting with the shaping hole inner peripheral surface (shaping start time) until the time when the contact state becomes a sufficient contact state is defined as an insufficient contact state, but not limited to it. In the present invention, the state from the time when the forging material W1 is loaded in the shaping hole 12 until the time when the shaping starts (i.e., non-contact state) may be included in an insufficient contact state. In other words, a case in which the forging material W1 has no contact point to the shaping inner peripheral surface (i.e., a case in which the number of contact points is 0), the state of the case may be defined as an insufficient contact state.

(74) <Explanation of Resonance Frequency Changes Due to Changes of Vibration Manner>

(75) In this embodiment, when the contact state of the forging material W1 to the shaping hole inner peripheral surface shifts from an insufficient contact state to a sufficient contact state, the resonance frequency changes in a discontinuous manner. However, the detail analysis revealed that the vibration manner changes instantaneously and immediately before being shifted to the sufficient contact state, and the resonance frequency shifts in a discontinuous manner at the time of shifting.

(76) That is, as shown in FIGS. 8A to 8C, the vibration manner changes instantaneously at the time when the relation between the surface pressure P of the forging material W1 and the vibration stress V by ultrasonic vibration reverses during the forging in this embodiment, and in accordance with it, the resonance frequency also changes instantaneously.

(77) The vibration stress V means a vibration stress on the shaping hole inner peripheral surface of the die body 11 vibrated by vibration given by the vibrator 4. This vibration stress V is a stress generated when the die body 11 is expanded and contracted by vibration, and corresponds to a vibration stress generated in a radial direction at the interface between the shaping hole inner peripheral surface and the forging material W1. This vibration stress V is caused by vibration of the vibrator 4, and therefore regardless of the process time, the vibration stress V is basically maintained constant.

(78) Under the circumstance, when the surface pressure P of the forging material W1 is lower than the vibration stress V, as shown in FIG. 8A, at the moment when the die body 11 is being contracted by vibration, the shaping hole inner peripheral surface and the forging material W1 are in contact with each other, and as shown in FIG. 8B, at the moment when the die body 11 is being expanded by vibration, the shaping hole inner peripheral surface and the forging material W1 are separated. In other words, when the surface pressure P is lower than the vibration stress V, the contact and the separation are repeated. In cases where the contact and the separation are repeated, the vibration state of the die body 11 is not affected by the vibration from the forging material W1.

(79) On the other hand, when the surface pressure P of the forging material W1 is larger than the vibration stress V, even at the moment when the die body 1 is contracted as shown in FIG. 8A, or even at the moment when the die body 1 is expanded as shown in FIG. 8C, the close contact state of the shaping hole inner peripheral surface and the forging material W1 is always maintained. That is, at the contact portion of the shaping hole inner peripheral surface and the forging material W1, the forging material W1 is not separated from the shaping hole inner hole peripheral surface and integral therewith in a sense. For this reason, at the contact portion, the vibration of the die body 11 is transmitted to the forging material W1, and the vibration of the forging material W1 is transmitted to the die body 11. In this state, the stiffness of the vibration system increases, and the frequency increases suddenly. At the time when the surface pressure P becomes larger than the vibration stress V, the frequency changes instantaneously, but when the contact state has not been shifted to a sufficient contact state (when the contact portion is arranged disproportionally), the vibration manner is unstable. When ultrasonic vibration is applied to the die body 11 from the vibrator 4 in a state in which the vibration manner is unstable, an overload occurs in the ultrasonic vibration device 5. Therefore, in this embodiment, when the contact state to the shaping hole inner peripheral surface is insufficient, it is preferable that application of ultrasonic vibration be suspended and initiated after being shifted to sufficient contact state.

(80) <Explanation of Contact State of Forging Material to Punch Outer Peripheral Side Surface>

(81) In the shaping process of this embodiment, the forging material W1 is expanded in the radial direction as shown in FIGS. 2A to 2C, and thereafter extruded rearward to be filled in the punch outer peripheral gap as shown in FIGS. 2D to 2F. The case in which the maximum surface pressure generated at the punch outer peripheral side surface at the time when the rearward extrusion is initiated (corresponding to FIG. 2D) is less than the vibration stress is regarded as a contact state in which the contact state of the forging material to the punch outer peripheral side surface is insufficient. The case in which the maximum surface pressure generated at the punch outer peripheral side surface is larger than the vibration stress (corresponding to FIG. 2E, etc.) is regarded as a sufficient contact state.

(82) <Structure and Effects>

(83) As explained above, in the ultrasonic forging, the vibration manner changes from the time t0 immediately before changing of the contact state of the forging material W1 with respect to the shaping hole inner peripheral surface from an insufficient contact state to a sufficient contact state to the time t1 when the contact state has changed to the sufficient contact state. At this time, the resonance frequency of the die body 11 suddenly changes, and in accordance with the sudden change, the tracking range also changes suddenly. For this reason, the vibration frequency of the ultrasonic vibration device 5 deviates from the shifted tracking range, which sometime prevents the vibration frequency from being converged to the changed resonance frequency. As a result, it becomes unable to vibrate the die body 11 in a resonant condition, which may cause a difficulty in obtaining sufficient effects by applying vibration.

(84) Under the circumstance, in this embodiment, when the tracking range is shifted due to the change of resonance frequency, the reference frequency is changed within the shifted tracking range. Specifically, immediately after shifting from an insufficient contact state to a sufficient contact state, the reference frequency is changed so as to fall within a tracking range corresponding to a shifted resonance frequency. As a result, the vibration frequency can be assuredly converged to the changed resonance frequency. Accordingly, it becomes possible to vibrate the die body 11 with a sufficient amplitude in a resonant condition, which in turn can attain effects by vibration application, such as, e.g., decrease of shaping load and improvement of shape transfer property.

(85) Further, in this embodiment, the resonance frequency changes in a discontinuous manner and the tracking range also shifts instantaneously when the contact state of the forging material W1 with respect to the punch outer peripheral side surface changes (t2 to t3), and at that time, the vibration frequency is changed so as to fall within a shifted tracking range. With this, in the same manner as explained above, the vibration frequency can be converged to the shifted resonance frequency, which enables effective vibration of the die body 11 in a resonant condition. Specifically, immediately after shifting from an insufficient contact state of the forging immaterial W1 with respect to the punch outer peripheral side surface to a sufficient contact state, the reference frequency is changed so as to fall within the tracking range corresponding to a shifted resonance frequency. Therefore, the vibration frequency can be assuredly converged to the changed resonance frequency.

(86) In this embodiment, the fr1 and fr3 as reference frequencies are values obtained based on experimental data or data of previous forging.

(87) Further, in this embodiment, the vibration is once stopped immediately before changing of the tracking range in a discontinuous manner due to the discontinuous change of the resonance frequency, the reference frequency is changed so as to fall within a shifted tracking range after shifting of the tracking range, and then vibration is restarted. For this reason, troubles which occur due to continuous application of vibration, e.g., vibration manner becomes unstable before changing of the reference frequency, changing of the vibration frequency in a region exceeding an overload set value, which in turn causes overload errors, can be effectively prevented.

(2) Second Embodiment

(88) In a forging process of ultrasonic forging, as described above, the contact state of the forging material W1 with respect to the shaping hole inner peripheral surface changes as time passes. Therefore, based on the process elapsed time, the time when the forging material W1 shifts from an insufficient contact state with respect to the shaping hole inner peripheral surface to a sufficient contact state, i.e., the time when the resonance frequency changes in a discontinuous manner, can be predicted. Further, the contact state of the forging material W1 with respect to the punch outer peripheral side surface changes as time passes. Therefore, based on the process elapsed time, the time when the forging material W1 shifts from an insufficient contact state with respect to the punch outer peripheral side surface to a sufficient contact state, i.e., the time when the resonance frequency changes in a discontinuous manner, can be predicted.

(89) In this second embodiment, at the predicted time, the reference frequency (vibration frequency) of the ultrasonic vibration device 5 is changed so as to fall within a tracking range corresponding to the changed resonance frequency to effectively vibrate the die body 11.

(90) FIG. 9 is a block diagram showing a forging apparatus (forging die) capable of executing a forging method according to the second embodiment of the present invention. As shown in this figure, this forging apparatus is equipped with a raising-and-lowering control device 6 and a reference frequency changing means 7. In the reference frequency changing means 7, a resonance frequency and a frequency changing time which are obtained by the following method, etc., are set in advance.

(91) The raising-and-lowering control device 6 detects the time when the punch 2 is lowered to press the forging material W1 to initiate shaping of the forging material W1 based on the information from the raising-and-lowering driving mechanism 3. For example, in the case of a mechanical type raising-and-lowering driving mechanism (press) 3, based on the output information from a sensor which detects a rotation angle of a crankshaft of the press 3, the raising-and-lowering control device 6 detects a time when the punch 2 has reached the shaping initiation height as a shaping start time, or based on the output information from a sensor which detects a slide position of the punch 2, the raising-and-lowering control device 6 detects a time when the punch 2 has reached the shaping initiation height as a shaping start time (corresponding to the time t0 in FIG. 3A). The raising-and-lowering control device 6 that detected the shaping start time t0 as described above outputs a signal for the shaping start time to the reference frequency changing means 7.

(92) The reference frequency changing means 7 that received the signal, based on the built-in timer 71, measures a time from the shaping start time t0 (process elapsed time) and transmits a vibration start signal to the ultrasonic vibration device 5. The ultrasonic vibration device 5 that received the vibration start signal drives the vibrator 4 at a vibration frequency as an initial reference frequency (corresponding to fs0 in FIG. 3B) to start the vibration of the die body 11. Subsequently, the reference frequency changing means 7 transmits a first reference frequency changing signal to the ultrasonic vibration device 5 immediately after the measured time has reached a first frequency changing time (corresponding to the time t1 in FIG. 3A).

(93) The ultrasonic vibration device 5 that received the first reference frequency changing signal changes the vibration frequency to a first reference frequency (corresponding to fs1 in FIG. 3B) and drives the vibrator 4 to vibrate the die body 11. Subsequently, the reference frequency changing means 7 transmits a second reference frequency changing signal to the ultrasonic vibration device 5 immediately after the measured time has reached the second frequency changing time (corresponding to the time t3 in FIG. 3A). The ultrasonic vibration device 5 that received the second reference frequency changing signal changes the vibration frequency to the second reference frequency (corresponding to fs3 in FIG. 3B) and drives the vibrator 4 to vibrate the die body 11.

(94) On the other hand, when the forging is completed, application of the ultrasonic vibration is stopped. That is, the raising-and-lowering control device 6 detects the time when the shaping is completed (corresponding to the time t4 in FIG. 3A) based on the information from the raising-and-lowering driving mechanism 3. For example, based on the output information from a sensor that detects a rotational angle of a crankshaft of the press or the output information from a sensor that detects a slide position of the press, the raising-and-lowering control device 6 detects a time when the press has reached the stroke bottom dead point as a shaping completion time. The raising-and-lowering control device 6 that detected the shaping completion time transmits the signal on the shaping completion to the ultrasonic vibration device 5. The ultrasonic vibration device 5 that received the shaping completion signal stops outputting to the vibrator 4. With this, the ultrasonic vibration of the die body 11 by the vibrator 4 is stopped.

(95) Such forging is repeated, so that a forged article is produced sequentially.

(96) In this embodiment, the raising-and-lowering control device 6 and the reference frequency changing means 7 are constituted by, for example, a microcomputer. In this embodiment, the reference frequency changing means 7 functions as a reference frequency changing device.

(97) In this forging apparatus according to the second embodiment, in order to more assuredly prevent occurrence of overload errors, as described above, the vibration may be stopped once immediately before changing to the first reference frequency or immediately before changing to the second reference frequency.

(98) <How to Obtain Resonance Frequency Switching Time>

(99) Next, a method for obtaining the reference frequency changing time will be described specifically.

(100) FIG. 10A is a graph showing a relation between a contact state of the forging material with respect to the shaping hole inner peripheral surface and a process elapsed time. FIG. 10B is a graph showing a relation between a center angle maximum value max between the contact points and the process elapsed time. FIG. 10C is a graph showing a relation between a resonance frequency and a process elapsed time.

(101) In these graphs, in the same manner as in the graph of FIGS. 3A and 3B, t0 denotes a time showing a time when the punch 2 is lowered to start shaping, t1 denotes a time showing a time when the forging material W1 shifts from the insufficient contact state with respect to the shaping hole inner peripheral surface (max>180 degrees) to the sufficient contact state (max180 degrees), and the time t1.5 denotes a time showing a time when the forging material W1 shifts from the sufficient contact state to the insufficient contact state (max=180 degrees). As will be understood from these graphs, since the resonance frequency changes in a discontinuously immediately before reaching t1 and the tracking range also shifts instantaneously, when a time reached t1 with the frequency at the time when a time has not reached t1 (range shown by X in the graph), the vibration frequency of the ultrasonic vibration device 5 deviates from the shifted tracking range, which prevents the vibration frequency from being converged to the resonance frequency. On the other hand, when the reference frequency is changed so as to fall within the shifted tracking range at the time after t1 (in the range shown by in the graph), the vibration frequency can be converged to the resonance frequency, which enables vibration in the resonant condition.

(102) Considering these circumstances, it is understood that in the forging apparatus shown in FIG. 9, the time corresponding to t1 is set as a reference frequency changing time tc1.

(103) Initially, in this embodiment, in the forging apparatus shown in FIG. 9, the reference frequency changing time tc1 is provisionally set as t0 to start forging.

(104) In this forging, the time to change the reference frequency is too early, resulting in deviation of the vibration frequency from the tracking range, which prevents the vibration frequency from being converged to the resonance frequency. As a result, the vibration state becomes disordered to cause an overload error, which can be confirmed. Next, the reference frequency changing time tc1 is set as a time slightly delayed from the aforementioned provisionally set time t0, and forging is performed in the same manner to confirm that an overload error occurs. By repeating these operations, the reference frequency changing time tc1 to be provisionally set is gradually and sequentially set to a delayed time, to experimentally find out the earliest time among times at which vibration state is not disturbed and no overload error occurs. The time is considered as a qualified reference frequency changing time tc1, and the time tc1 is set to the forging apparatus shown in FIG. 9.

(105) On the other hand, in the same manner as described, based on the time when the contact state of the forging material W1 with respect to the die outer peripheral side surface shifts from an insufficient contact state to a sufficient contact state, a reference frequency changing time tc3 corresponding to t3 of FIG. 3A can be decided. That is, any time between t1 and t2 shown in FIG. 3A is set as a second reference frequency changing time tc3, and forging is performed.

(106) In this forging, the time to change the reference frequency is too early, resulting in large deviation of the vibration frequency from the tracking range, which prevents the vibration frequency from being converged to the resonance frequency. Next, a second reference frequency changing time tc3 is set to a time slightly delayed from the aforementioned provisionally set time, and forging is performed in the same manner to confirm that an overload error occurs. By repeating these operations, the reference frequency changing time tc3 to be provisionally set is gradually and sequentially set to a delayed time, to experimentally find out the earliest time among times at which vibration state is not disturbed and no overload error occurs. The time is considered as a qualified second reference frequency changing time tc3, and the time tc3 is set to the forging apparatus shown in FIG. 9.

(107) By performing forging as described above using the forging apparatus to which the first and second reference frequency changing times tc1 and tc2 are set, the forging material can be vibrated assuredly in a resonant condition, which can assuredly attain effects by ultrasonic vibration, such as, e.g., decrease of the shaping load and improvement of the shape transfer property.

(108) In this embodiment, the reference frequency changing time tc1 and tc3 is set as the earliest time causing no overload error, but not limited to it. In the present invention, as long as no overload error occurs, any time can be set as the qualified reference frequency changing time tc1 and tc3.

(109) According to the forging method of this second embodiment, since the time to change the reference frequency is decided based on the elapsed time, the forging can be performed easily.

(110) In the case of predicting the time (reference frequency changing time) for shifting to a sufficient contact state based on the process elapsed time, the predicted value is stochastic and fractional. In addition, the shaping speed of the forging material W1 changes due to various factors. Accordingly, the predicted value of the time of shifting to a sufficient contact state is preferably set with allowance. For example, a predicted value having a certain allowance (range) is obtained, and considering surrounding environments, shaping conditions, etc., an appropriate time within the range is set as a reference frequency changing time tc1 and tc3.

(3) Third Embodiment

(111) Experiments by the present inventors revealed that there is a relation between a load change of the punch and a contact state of the forging material. So, in this third embodiment, a punch load that causes the forging material W1 to shift the contact state with respect to the shaping hole inner peripheral surface and the punch outer peripheral side surface from an insufficient contact state to a sufficient contact state, i.e., a punch load at which the resonance frequency changes in a discontinuous manner, is obtained. And, based on the punch load (reference frequency changing load value), the reference frequency (vibration frequency) of the ultrasonic vibration device is changed so as to fall within a tracking range corresponding to the changed resonance frequency to effectively vibrate the die body 11.

(112) FIG. 11 is a block diagram showing a forging apparatus (forging die) capable of executing a forging method according to a third embodiment of the present invention. As shown in this figure, the forging apparatus is provided with a load detector 81 that detects a load of the punch 2 applied to the forging material W1, and a reference frequency changing means 8 that acquires a signal on the punch load from the load detector 81.

(113) In the reference frequency changing means 8, a reference frequency changing load value obtained by the following method, etc., is set in advance. The reference frequency changing means 8 detects the load (punch load) of the punch 2 applied to the forging material W1 when the punch 2 is lowered based on the information from the load detector 81, and transmits a reference frequency changing signal to the ultrasonic vibration device 5 at the time when the punch load has reached the reference frequency changing load value.

(114) The ultrasonic vibration device 5 that received the reference frequency changing signal changes the vibration frequency of the vibrator 4 by adjusting the vibrator driving electric power to change the vibration frequency to be applied to the die body 11. Thus, the reference frequency is changed and forging is performed.

(115) On the other hand, when the forging is completed, application of the ultrasonic vibration is stopped. That is, the raising-and-lowering control device 6 detects the time when the shaping is completed based on the information from the raising-and-lowering driving mechanism 3. The ultrasonic vibration device 5 that received the shaping completion signal stops outputting to the vibrator 4. With this, the ultrasonic vibration of the die body 11 by the vibrator 4 is stopped.

(116) Such forging is repeated, so that a forged article is produced sequentially.

(117) In this embodiment, the reference frequency changing means 8 is constituted by a microcomputer, etc., and functions as a reference frequency changing device. Further, the load detector 81 functions as a load detecting apparatus.

(118) In the forging apparatus according to the third embodiment, in the same manner as described above, the vibration may be stopped once immediately before changing the reference frequency.

(119) <How to Obtain Reference Frequency Switching Load Value>

(120) Next, a method for obtaining a reference frequency changing time will be described specifically.

(121) FIG. 12A is a graph showing a relation between a contact state of a forging material and a punch load. FIG. 12B is a graph showing a relation between a contact point center angle maximum value max and a punch load. FIG. 12C is a graph showing a relation between a resonance frequency and a punch load.

(122) In these graphs, L0 denotes a load value at the time when the punch 2 is lowered to start shaping, L1 denotes a load value at the time when the forging material W1 shifts from the insufficient contact state with respect to the shaping hole inner peripheral surface (max>180 degrees) to the sufficient contact state (max180 degrees), and L1.5 denotes a load value at the time when the forging material W1 shifts from the sufficient contact state with respect to the shaping hole inner peripheral surface to the insufficient contact state (max=180 degrees).

(123) As will be understood from these graphs, since the resonance frequency changes in a discontinuously and immediately before reaching L1 and the tracking range also shifts instantaneously, when it reaches L1 with the frequency at the time when it has not reached L1 (range shown by X in the graph), the vibration frequency of the ultrasonic vibration device 5 deviates from the shifted tracking range, which prevents the vibration frequency from being converged to the resonance frequency. On the other hand, when the reference frequency is changed so as to fall within the shifted tracking range at the time after L1 (in the range shown by in the graph), the vibration frequency can be converged to the resonance frequency, which enables vibration in the resonant condition.

(124) Considering these circumstances, it is understood that in the forging apparatus shown in FIG. 8, the reference frequency changing load value Lc1 is set to L1.

(125) Initially, in this embodiment, in the forging apparatus shown in FIG. 11, the reference frequency changing load value Lc1 is provisionally set to no load (0 kN) to start forging. In this forging, the time to change the reference frequency is too early, resulting in deviation of the vibration frequency from the tracking range, which prevents the vibration frequency from being converged to the resonance frequency. As a result, the vibration state becomes disordered to cause an overload error, which can be confirmed. Next, the provisionally set reference frequency changing load value Lc1 is set to a value slightly higher than 0 kN, and forging is performed in the same manner to confirm that an overload error occurs. By repeating these operations, the provisionally set reference frequency changing load value Lc1 is set to a gradually increased value, to experimentally find out the minimum load among loads that vibration state is not disturbed and no overload error occurs. The load value is considered as a qualified reference frequency changing load value Lc1, and the load value Lc1 is set to the forging apparatus shown in FIG. 8.

(126) On the other hand, in the same manner as described, based on the time when the contact state of the forging material W1 with respect to the punch outer peripheral side surface shifts from an insufficient contact state to a sufficient contact state, a reference frequency changing time Lc3 corresponding to t3 of FIG. 3A can be decided. That is, the load value corresponding to a load value between t1 and t2 shown in FIG. 3A is provisionally set as the second reference frequency changing load value Lc3, and forging is performed.

(127) In this forging, the time to change the reference frequency is too early, resulting in large deviation of the vibration frequency from the tracking range, which prevents the vibration frequency from being converged to the resonance frequency. Next, the secondary set reference frequency changing load value Lc3 is set to a value larger than the aforementioned provisionally set load value, and forging is performed in the same manner to confirm that an overload error occurs. By repeating these operations, the reference frequency changing load value Lc3 to be previously set is set to a gradually increased value, to experimentally find out the minimum load among loads that vibration state is not disturbed and no overload error occurs. The load value is considered as a qualified second reference frequency changing load value Lc3, and the load value Lc3 is set to the forging apparatus shown in FIG. 11.

(128) By performing forging as described above using the forging apparatus to which the first and second reference frequency changing load values Lc1 and Lc3 are set, the forging material can be vibrated assuredly in a resonant condition, which can assuredly attain the effects by ultrasonic vibration, such as, e.g., decrease of the shaping load and improvement of the shape transfer property.

(129) In this embodiment, as the reference load values Lc1 and Lc3, the smallest loads causing no overload error are set, but not limited to it. In the present invention, as long as no overload error occurs, any load can be set to the reference load values Lc1 and Lc3.

(130) In the forging method according to the third embodiment, since the time (time of changing the reference frequency) for shifting the contact state to a sufficient contact state based on the punch load is predicted, no influence is given by the change of the shaping speed of the forging material W1. For this reason, the forging method according to the third embodiment can predict the time for changing the reference frequency with a high degree of accuracy as compared with a forging method according to the second embodiment in which the changing time is predicted from the process elapsed time. As a result, an occurrence of an overload error can be prevented more assuredly, and decreasing of the shaping load and improvement of the shape transfer property can be attained more assuredly.

(131) In the ultrasonic forging, it is preferable to perform the frequency change at as an early stage as possible. Therefore, in the forging method according to the third embodiment capable of accurately grasping the time for shifting to a sufficient contact state, the reference frequency can be accurately changed at as an earlier stage as possible. From this point of view, the aforementioned effects can be obtained more assuredly

(132) The forging method according to the present invention can be applied to a forging apparatus, etc., that performs forging using ultrasonic vibration.

(133) It should be understood that the terms and expressions used herein are used for explanation and have no intention to be used to construe in a limited manner, do not eliminate any equivalents of features shown and mentioned herein, and allow various modifications falling within the claimed scope of the present invention.

(134) While the present invention may be embodied in many different forms, a number of illustrative embodiments are described herein with the understanding that the present disclosure is to be considered as providing examples of the principles of the invention and such examples are not intended to limit the invention to preferred embodiments described herein and/or illustrated herein.

(135) While illustrative embodiments of the invention have been described herein, the present invention is not limited to the various preferred embodiments described herein, but includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.

DESCRIPTION OF REFERENCE SYMBOLS

(136) 1: die 11: die body 12: shaping hole 2: punch 4: vibrator (vibration application apparatus) 5: ultrasonic vibrator (vibration application apparatus) 7, 8: reference frequency changing means (reference frequency changing device) 81: load detector (load detecting apparatus) f1: tracking range fr, fr0 to fr4: resonance frequency fs0, fs1, fs3: reference frequency Lc1: resonance frequency changing load value Lt1: reference frequency changing time t0: shaping start time W1: forging material