JP2004344907A - Method for producing semi-product for piston - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a semi-product for piston by which the semi-product for piston can be produced with a good formability in high yield of material and a production control is facilitated. <P>SOLUTION: In a first process, an intermediate formed part 3 formed as a working body part and a projecting part from the working body part, is formed by extrusion-forming a working material with pin type pressing from the one side of one shaft direction. In a second process, the working body part is formed into a cup part 4 by coming into the outer peripheral space part 13 of a punch 12 by pushing in the punch 12 from the one side. In a third process, a prescribed shape of the arm part, is formed by pushing the intermediate formed arm part 3 from the other side. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a semi-finished product for a piston having a bottomed cylindrical cup portion and an arm portion.
[0002]
[Prior art]
A piston member used in a compressor or the like slides and reciprocates a cylinder bore in the compressor. The piston member is connected (connected) to a head that slides in the cylinder bore and a driving device that reciprocates the head. ). The head portion has a hollow structure to reduce the weight. The head portion is manufactured by press-fitting (friction) a bottomed cylindrical cup portion and a lid-shaped cap member separate therefrom. It is made hollow by welding or the like.
[0003]
Conventionally, as a method of producing a semi-finished product for a piston having a bottomed cylindrical cup portion constituting the hollow head portion, a forging method performed by moving a die in two axial directions is conventionally known ( For example, see Patent Document 1).
In this method, as shown in FIGS. 14A, 14B and 14C, the workpiece 53 is moved by a mold (not shown) moving in the direction of the first shaft 51 (the direction of the paper surface of FIG. 14). A burr forming process by hot forging is performed (via a preforming process shown in FIG. 14B) to form a first processed product 54 having portions 57, 57 corresponding to arm portions. Thereafter, the first processed product 54 is once taken out of the mold and subjected to a deburring process (trim process) as shown in FIG. As shown in FIG. 14 (e), a portion (both sides) to be a cup portion of the first processed product 54 is hot (or cold) forged and formed by a mold (punch) (not shown). It is a processed product 55. Thereafter, cap members 56 manufactured in a separate process are pressed (friction welded) on both end sides of the second processed product 55 to form a third processed product 58 having a hollow head portion as shown in FIG. I have. Then, the third processed product 58 is cut into two parts at the center (arrow portion in FIG. 14 (f)) and subjected to cutting, surface treatment, and the like to obtain a piston product.
[0004]
[Patent Document 1]
JP 2001-259781 A
[Problems to be solved by the invention]
In the conventional manufacturing method, as shown in FIG. 14C, the first processed product 54 has a problem that many burrs are formed and the material yield is low. In addition, many steps are required until a piston product (semi-finished product) is obtained. In particular, a trimming step of deburring is required during molding by forging, which complicates the manufacturing process. Also, forging with a die from a biaxial direction makes the apparatus huge, requires a plurality of presses, or complicates the apparatus.
[0006]
Further, in the product molded by the conventional method, as shown in FIG. 14 (f), the joint 59 (press-welded portion) with the cap member 56 is a portion close to the arm portion 57 '. In the operating state of the compressor, since it is a part that goes in and out of the cylinder bore and is susceptible to thermal distortion, cracks and distortions are likely to occur at the joint 59 after operation, which may be a weak point.
[0007]
Therefore, an object of the present invention is to provide a method for producing a semi-finished product for a piston which has good material yield, easy production control, and good moldability.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a method of manufacturing a semi-finished product for a piston according to the present invention comprises extruding a workpiece by pressing a pin from one side in an axial direction to form the workpiece body and the workpiece. A first step of molding an intermediate molding arm portion projecting from the material body portion, and pressing the punch from one side to cause the workpiece body portion to enter the outer peripheral space of the punch, thereby forming the workpiece material. A second step of molding the main body into a cup; and a third step of pressing the intermediate molding arm from the other side to mold the arm into a predetermined shape.
[0009]
In the first step, a connecting portion is formed between the workpiece body and the intermediate molding arm, and in the second step, the workpiece body is connected to the outer peripheral space of the punch. When entering, the joint portion is crushed to plastically flow the joint portion toward the workpiece body portion side, and the intermediate molding arm portion is drawn into the workpiece body portion side and deformed. To prevent.
In the first step, the intermediate molding arm is extruded so that the axis of the arm is eccentric to the axis of the workpiece body, and the connecting part is provided with the intermediate molding arm. It is molded in an inclined manner so that the volume increases toward the side.
Further, in the first step, the intermediate molding arm portion to be extruded from the direction opposite to the pressing direction by the pin mold is molded while controlling the pressure.
Further, in the second step, molding is performed while controlling the pressing of the entering workpiece main body portion in opposition to the entry of the workpiece main body portion into the outer peripheral space portion.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail based on the illustrated embodiments.
[0011]
The semi-finished product for a piston manufactured by the manufacturing method of the present invention constitutes a piston member for a compressor used for, for example, an air conditioner. The piston member reciprocates in a cylinder bore of the compressor. As shown in FIG. 13, the piston member is connected to a head 30 that actually slides in the cylinder bore, and a driving device that reciprocates the head 30 ( And an arm (wing) 6 to be connected). The head section 30 has a hollow structure to reduce the weight.
The piston semi-finished product 29 manufactured by the present invention is a portion shown by a solid line in FIG. 13, and the piston semi-finished product 29 has a hollow head 30 (70% to 80% of the entire hollow head 30). The cup portion 4 has a bottomed cylindrical shape, and the arm portion 6 is continuous with the cup portion 4. Then, the cap member 28 produced in another step is joined (pressed) to the opening end of the cup portion 4 to form the hollow head portion 30. The cap member 28 is indicated by a two-dot chain line in FIG.
[0012]
1 to 8 are cross-sectional side views of a manufacturing apparatus (die) for explaining a manufacturing method according to the present invention. FIGS. 10 to 13 show that a workpiece 1 is molded and a piston semi-finished product 29 is formed. FIG.
The production method of the present invention is performed hot (or warm or cold), and has a first step, a second step, and a third step. The workpiece 1 is extruded by pressing the pin mold 11 to form the workpiece body 2 and the intermediate molding arm 3 projecting from the workpiece body 2 (FIGS. 1 and 2). In the second step, the workpiece body 2 enters the outer peripheral space 13 of the punch 12 by pushing the punch 12 from one side in the uniaxial direction, and the workpiece body 2 is molded into the cup 4. (FIGS. 3-4). Then, in the third step, the intermediate molding arm 3 is pressed from the other side to form the arm 6 having a predetermined shape (FIGS. 5 to 8). 1 to 4 are cross-sectional side views of the product viewed from the same one direction, while FIGS. 5 to 8 are cross-sectional side views of the product viewed from the orthogonal direction. is there. The “one side” is the side that becomes the cup part 4 in the product, and “from the other side” is the side that becomes the arm part 6.
[0013]
That is, in the first step, the short intermediate workpiece 1 is extruded to form the first intermediate product 7 having the workpiece main body 2 and the intermediate molding arm 3 (FIGS. 10 to 11). In the second step, the workpiece body 2 of the first intermediate product 7 is molded into the cup portion 4 to form the second intermediate product 8 (FIG. 12). In the third step, the intermediate molding of the second intermediate product 8 is performed. The arm 3 is formed into an arm 6 having an uneven portion in a radial direction which is a direction orthogonal to the axial direction of the product, thereby forming a semi-finished product 29 for a piston (FIG. 13).
[0014]
Next, each step will be described. First, in the first step, as shown in FIG. 1, the workpiece 1 is mounted in the first large-diameter space 15 of the first space 14 of the first lower die 9. The outer peripheral shape of the workpiece 1 is substantially the same as (slightly smaller than) the inner peripheral shape of the large-diameter space 15. The first space 14 has a linear first large-diameter space 15 corresponding to the outer shape of the workpiece body 2 obtained in the first step, and the outer periphery of the intermediate molding arm 3 obtained in the first step. And a linear first small-diameter space 16 corresponding to the shape, and the space 14 penetrates the first lower die 9 (up and down).
A first upper die 10 is disposed above the first lower die 9, and the lower die 9 and the upper die 10 are installed on a press (not shown) or the like so that they can approach and separate from each other. The upper die 10 is provided with a pin die 11 having an outer peripheral shape corresponding to the inner peripheral shape of the large-diameter space portion 15 of the lower die 9.
[0015]
In FIG. 2, the first upper mold 10 is lowered to approach the first lower mold 9, the tip of the pin mold 11 is brought into contact with the upper end surface of the workpiece 1, and is further pushed in. The workpiece 1 mounted in the space 14 is extruded forward, and the lower part of the workpiece 1 is formed as an intermediate molding arm 3 corresponding to the shape of the small-diameter space 16 of the space 14. Is molded into the workpiece body 2 corresponding to the shape of the large-diameter space 15.
[0016]
In the first step, a connecting portion 5 is formed between the workpiece body 2 and the intermediate molding arm 3. As will be described later, in the second step shown in FIG. 4, when the workpiece body 2 enters the outer peripheral space 13 of the punch 12, the connecting portion 5 is crushed and connected. The portion 5 is to be plastically flowed toward the workpiece body 2 side to prevent the intermediate molding arm portion 3 from being drawn into the workpiece body portion 2 and deformed. It becomes a volume part for flow.
[0017]
When specifically describing the shape of the connecting portion 5, as shown in FIG. 11, in a first step of molding a first intermediate product 7, the intermediate molded arm 3, the arm axis C ₁ is workpiece body with the axis C ₂ of part 2 (is parallel) to the eccentric, are extruded, the connecting portion 5, formed into inclined such that the volume is increased toward the arrangement side of the intermediate molded arm 3 Is done. That is, molded towards from the axis C ₂ of the workpiece main body 2 to the arm axis C ₁ direction, the connecting portion 5 which the thickness of the axial direction is increased. The thickness of the connecting portion 5 increases linearly. That is, the surface of the connecting portion 5 on the side of the intermediate molding arm 3 becomes a linear inclined surface.
[0018]
It is preferable that the thickness gradient θ of the connecting portion 5 (the angle formed between the linear inclined surface of the connecting portion 5 and the plane orthogonal to the axis) θ be set in a range of 10 ° to 25 °. If there is, the volume to be applied (plastic flow) at the time of molding of the cup portion 4 in the second step is insufficient, and if it exceeds the upper limit, a large load is locally generated at the time of molding in the second step to cause molding failure. There is a risk.
That is, in the first space portion 14 of the first lower mold 9, the first large-diameter space portion 15 and the first small-diameter space portion 16 are continuous via the first stepped surface portion 31, and the first stepped surface portion is provided. The angle of inclination of 31 may be set to 10 ° to 25 °. 1 and 2, the angle θ is set to 20 °.
[0019]
Further, as shown in FIG. 1 and FIG. 2, in the first step, the intermediate molding arm portion 3 which is extruded forward by the pin mold 11 from the direction opposite to the downward pressing direction by the pin mold 11 is press-controlled. while (while applying a back pressure P ₁₎ has been molded (die cushion). More specifically, in the penetrating space 14, an opposing pin 17 having an outer peripheral shape corresponding to the inner peripheral shape of the small-diameter space 16 is provided on the opposite side to the insertion side of the pin mold 11. It is in an inserted state at 16 predetermined standby positions. Then, the opposing pin 17 is retreated (in the direction of arrow a) with resistance while the front end surface of the opposing pin 17 is in contact with the front end surface of the intermediate molding arm portion 3 formed by extrusion molding using the pin mold 11. The first intermediate product 7 is obtained by applying a load (flow resistance) to the intermediate molding arm 3 to be molded. In other words, to act in the opposite direction back pressure P ₁ and a retracted to go the direction (arrow a) of the counter-pin 17.
[0020]
When the opposing pin 17 is retracted while pressing the tip surface of the intermediate molding arm 3 being molded, the material flow of each part of the intermediate molding arm 3 to be extruded is not uneven in speed, and the molding is made uniform. Can be achieved.
Although not shown, the pin mold 11 is retracted from the state shown in FIG. 2 to the upper separated position, and further, the retreated counter pin 17 is raised and the first intermediate product 7 is pushed up, so that the first lower mold 9 is raised. From the first intermediate product 7 can be easily taken out.
[0021]
Next, the second step will be described. As shown in FIG. 3, the first intermediate product 7 molded in the first step is mounted on the second lower mold 18. The second space portion 20 of the second lower die 18 includes a linear second large-diameter space portion 21 corresponding to the outer peripheral shape of the cup portion 4 obtained in the second step, and an intermediate molding arm obtained in the first step. And a second small-diameter space portion 22 having the same shape as the first small-diameter space portion 16 of the first lower die 9 and a linear second small-diameter space portion 22 corresponding to the outer peripheral shape of the portion 3. The lower die 18 is penetrated (up and down).
In the space 20, the large-diameter space 21 and the small-diameter space 22 are continuous via the second stepped surface 32, and the space 20 is attached to the second stepped surface 32 and the second lower die 18. A small gap portion 23 is formed between the first intermediate product 7 and the inclined surface of the connecting portion 5 of the first intermediate product 7. That is, the second stepped surface portion 32 of the second lower mold 18 is formed as a plane having an angle of 0 ° to 5 ° with respect to the plane orthogonal to the axis. In FIGS. 3 and 4, this angle is 5 °.
[0022]
In the second step, the punch 12 attached to the second upper die (not shown) and the second lower die 18 are placed on a press machine or the like, and are brought close to each other (the second upper die is lowered), and the punch 12 The tip end face of the workpiece 12 is brought into contact with the end face of the workpiece body 2 of the first intermediate product 7 and further pressed to mold the workpiece body 2 into the cup part 4 (reverse extrusion molding). When the workpiece body 2 enters the outer peripheral space 13 of the punch 12, the connecting part 5 is crushed to cause the connecting part 5 to plastically flow toward the workpiece body 2, and the intermediate molding arm part 3 is prevented from being pulled into the workpiece body 2 side (under tension) and deformed. That is, the punch 12 and the second stepped surface portion 32 are crushed (for example, crushed from 20 ° to 5 °) so as to reduce the inclination angle of the connecting portion 5 and are crushed and compressed (plastic flow). The portion of the connecting portion 5 is applied to the outer peripheral space 13 side of the punch 12.
[0023]
In the second step shown in FIG. 4, the workpiece body 2 entering the workpiece body 2 is evenly distributed over the entire circumference so as to face (oppose) entry of the workpiece body 2 into the outer peripheral space 13. in, (while applying a back pressure P ₂₎ pressing control while being molded (die cushion). More specifically, in the space portion 20, the outer peripheral shape corresponding to the inner peripheral shape of the large-diameter space portion 21 is formed, and the outer peripheral shape is slidable on the punch 12 so as to be slidable. The attached annular counter mold 25 advances with the approach (down) of the punch 12 to the second lower mold 18 until it comes into contact with the workpiece body 2. And it is made into the insertion state in the 2nd large diameter space part 21.
Then, while the tip surface of the annular counter mold 25 is brought into contact with the annular tip surface of the cup portion 4 which is gradually formed by press-molding with the punch 12, the annular counter mold 25 is given resistance (in the direction of arrow b). 2) The second intermediate product 8 is obtained by retreating and performing molding while applying a load (flow resistance) to the cup portion 4 being molded. That is, while the punch 12 is advanced in the pushing direction (arrow c), which is the forward direction, the annular counter mold 25 is retracted in the opposite direction. Moreover, the action of back pressure P ₂ in the direction opposite to the direction (arrow b) the receding of the annular counter type 25.
Since the annular counter mold 25 retreats while pressing the material, the speed of the material flow in each part of the molded cup portion 4 in the circumferential direction does not become uneven over the entire circumference, and uniform molding can be achieved.
[0024]
As shown in FIGS. 3 and 4, a pin member 26 is inserted below the second small-diameter space portion 22 of the second lower mold 18, and the intermediate molding of the first intermediate product 7 is performed. The distal end surface of the arm portion 3 and the distal end surface of the pin member 26 maintain the contact state in the second step. Therefore, even if the molding by the punch 12 is performed, the shape of the intermediate molding arm 3 is maintained without deformation (plastic flow).
[0025]
Further, the punch 12 and the annular counter mold 25 are retracted from the state shown in FIG. 4 to the upper separated position, and the pin member 26 inserted into the second small-diameter space portion 22 is further raised. By pushing up, the second intermediate product 8 can be easily taken out from the second lower mold 18.
[0026]
Next, the third step will be described. As shown in FIG. 5, the second intermediate product 8 molded in the second step is mounted on the third lower mold 33. The second intermediate product 8 has a direction opposite to the posture in the first and second steps (the posture in which the cup portion 4 is located below the intermediate molding arm portion 3).
The third lower mold 33 includes a main body 35 having a hole 34 that is fitted into the cup 4 and a lower punch 36 that is closely inserted into the cup 4, and an opening end surface of the cup 4. A second intermediate member including an annular mold 37 received over the circumference and split molds 38a and 38b disposed on the upper surface of the main body 35 and forming substantially half of the outer shape of the semi-finished product 29 for the piston on the side of the arm 6; The article 8 is held as shown in FIG.
[0027]
The third upper die 39 located above the third lower die 33 has an inner tapered surface 41 that comes into contact with a tapered surface 40 formed on the outer peripheral portion of the split dies 38a and 38b, and is closed. An upper punch that presses the intermediate molding arm 3 in a space 43 composed of a holding mold 42 for clamping and fixing the molds 38a and 38b and a divided mold 38a and 38b in a closed state to form the arm 6. 44. The split die 38a, which can be split into right and left, by the pressing force of the pressing die 42 of the third upper die 39 in the vertical direction (by a press machine not shown) and the action of the tapered surface 40 and the inner tapered surface 41. 38b is tightened from the side (horizontal direction) with a force exceeding the molding load to prevent the formation of a gap.
[0028]
Then, as shown in FIGS. 6 and 7, the upper punch 44 is lowered, the upper punch 44 presses the intermediate molding arm 3 of the second intermediate product 8, and the shape of the cup 4 is changed by the third lower die 33. While being maintained, the intermediate molding arm portion 3 is compressed so as to reduce its axial length and swells in the direction orthogonal to the axial direction, and is molded into an arm portion 6 having a predetermined shape. Then, as shown in FIG. 8, the third upper die 39 is raised, the split dies 38a and 38b are opened, and the annular die 37 is raised. 33 can be easily taken out from the main body 35.
[0029]
Further, as shown in FIG. 5, when the second intermediate product 8 produced in the second molding step is mounted on the main body 35 of the third lower die 33 in the third step, the second intermediate product 8 is formed by the phase determining means. The second intermediate product 8 can be mounted on the third lower mold 33 in a predetermined phase (direction). That is, in the semi-finished product 29 for the piston, since the arm 6 and the cup 4 are in an eccentric state, the second intermediate product 8 determines the phase with respect to the third upper mold 39 and the third lower mold 33. It is necessary to mount and attach.
[0030]
As shown in FIGS. 9A and 9B, the phase determining means includes a part of the outer peripheral surface of the cup portion 4 of the second intermediate product 8 formed in the second step and the second step in the third step. A part of the inner peripheral surface of the space part of the third lower mold 33 to which the intermediate product 8 is attached is constituted by a convex part 46 (having a semi-cylindrical cross section) formed on one side and a concave groove 47 formed on the other side. 9 (a) and 9 (b), the convex portion 46 (for example, having a circular cross section with a radius of about 1 mm) is formed simultaneously on the second intermediate product 8 in the second step, and the convex portion 46 is formed on the third lower mold 33. A concave groove 47 to be fitted into 46 is formed in advance. The protrusion 46 may be a linear protrusion or a protrusion formed in the axial direction, and the groove 47 may have a shape corresponding thereto. According to this, the second intermediate product 8 cannot be mounted on the third lower die 33 only when the convex portion 46 and the concave groove 47 are fitted, and the phase of the second intermediate product 8 with respect to the third lower die 33 is not increased. Decisions can be made easily.
[0031]
Further, as another embodiment of the phase determining means, as shown in FIGS. 9C and 9D, one of the inner peripheral surfaces of the cup portion 4 of the second intermediate product 8 molded in the second step. And a convex portion 46 formed on one side and a concave groove formed on the other of a part of the outer peripheral surface of the lower punch 36 for externally mounting the cup portion 4 of the second intermediate product 8 in the third step. 9C and 9D, the convex portion 46 is formed on the cup portion 4 of the second intermediate product 8 at the same time in the second step, and the convex portion 46 is formed on the lower punch 36. A concave groove 47 for fitting is formed in advance, and the phase is matched by mounting the second intermediate product 8 on the lower punch 36.
[0032]
【The invention's effect】
The present invention has the following effects by the above configuration.
[0033]
(According to claim 1) In order to carry out plastic working step by step in each step, molding can be performed with an optimum mold shape, burrs do not occur, the material yield is good, and the mold load is extremely small. And the mold life can be extended. That is, the load for molding can be small, and as a result, an unreasonable load is not applied to the molded product. Further, the initial cost can be reduced by simplifying the mold, and the running cost can also be reduced, thereby improving the productivity.
Furthermore, since different portions are molded in order in each process, the operation of the mold is simple, and work management is easy to perform. Therefore, it is possible to improve product accuracy and eliminate occurrence of defective products.
In each process, the supply and discharge of the lubricating oil can be performed by a method suitable for the shape of the mold (product shape).
[0034]
According to the second aspect, the material of the connecting portion 5 is drawn in at the time of molding the cup portion 4, so that the intermediate molded arm portion 3 is not deformed. By applying the material of the connecting portion 5 to the side of the cup portion 4 being molded, the molding of the cup portion 4 is facilitated.
(According to claim 3) Molding can be performed stably on a piston semi-finished product having a complicated shape, and a desired product shape can be plastically processed without difficulty.
According to the fourth aspect, the speed of the material flow of the extruded intermediate molding arm 3 can be made uniform, and a product with good dimensional accuracy can be obtained.
(According to claim 5) In particular, if the arm axis C ₁ and the axis C ₂ of the workpiece body portion 2 is such that eccentricity, the speed of the circumferential direction of the material flow in the peripheral wall of the cup portion 4 ( (Push-up height) tends to be unequal, but this can be prevented, the shape of the cup portion 4 can be made uniform, and the product accuracy can be improved.
[Brief description of the drawings]
FIG. 1 is a sectional view of a manufacturing apparatus illustrating a first step of a manufacturing method of the present invention.
FIG. 2 is a cross-sectional view of the manufacturing apparatus showing a state after molding in a first step.
FIG. 3 is a cross-sectional view of the manufacturing apparatus showing a state before molding in a second step.
FIG. 4 is a sectional view of the manufacturing apparatus showing a state after molding in a second step.
FIG. 5 is a sectional view of the manufacturing apparatus showing a preparation state in a third step.
FIG. 6 is a sectional view of the manufacturing apparatus showing a state at the start of molding in a third step.
FIG. 7 is a cross-sectional view of the manufacturing apparatus showing a state after molding in a third step.
FIG. 8 is a cross-sectional view of the manufacturing apparatus for explaining a product removal operation in a third step.
FIG. 9 is a cross-sectional view illustrating a phase determining unit.
FIG. 10 is a side view of a workpiece.
FIG. 11 is a side view and a front view of the first intermediate product.
FIG. 12 is a side view and a front view of a second intermediate product.
FIG. 13 is a plan view, a side view, and a front view of a semi-finished product for a piston.
FIG. 14 is a side view of a product for explaining a conventional manufacturing method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS ₁ Workpiece ₂ Workpiece main body part 3 Intermediate molding arm part 4 Cup part 5 Connecting part 6 Arm part 11 Pin type 12 Punch 13 Outer space part C ₁ Arm axis C C ₂ axis

Claims (5)

The workpiece (1) is extruded by pressing the pin mold (11) from one side in the uniaxial direction, and the workpiece main body (2) and the intermediate molding that projects from the workpiece main body (2). A first step of molding the arm portion (3), and by pushing the punch (12) from the one side, the workpiece body (2) enters the outer peripheral space (13) of the punch (12). A second step of molding the workpiece body portion (2) into a cup portion (4), and pressing the intermediate molding arm portion (3) from the other side to form an arm portion (6) having a predetermined shape. A process for producing a semi-finished product for a piston, comprising: In the first step, a connecting portion (5) is formed between the workpiece body (2) and the intermediate molding arm (3), and in the second step, the workpiece body ( When the 2) enters the outer peripheral space portion (13) of the punch (12), the connecting portion (5) is crushed to move the connecting portion (5) toward the workpiece body (2). 2. The method for producing a semi-finished product for a piston according to claim 1, wherein the semi-finished product for a piston is prevented from being deformed by being plastically flown to draw the intermediate molding arm (3) toward the workpiece body (2). In the first step, the intermediate molding arm (3) is extrusion-molded such that its arm axis (C ₁ ) is eccentric with the axis (C ₂ ) of the workpiece body (2). The method for producing a semi-finished product for a piston according to claim 2, wherein the connecting portion (5) is formed so as to be inclined so that the volume increases toward the side where the intermediate forming arm portion (3) is provided. The piston according to claim 1, 2 or 3, wherein in the first step, the intermediate molding arm (3) being extruded from the direction opposite to the direction of pressing by the pin mold (11) is molded while controlling the pressure. Production method for semi-finished products. In the second step, the workpiece body (2) faces the entry of the workpiece space (13) into the outer peripheral space (13), and is formed while controlling the pressure of the workpiece body (2) to enter. Item 5. A method for producing a semi-finished product for a piston according to Item 1, 2, 3, or 4.

Images