CA2923915C

CA2923915C - Crankshaft production method

Info

Publication number: CA2923915C
Application number: CA2923915A
Authority: CA
Inventors: Takeshi Tatsumi; Tomoya Tanaka
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 2015-03-24
Filing date: 2016-03-16
Publication date: 2018-05-22
Anticipated expiration: 2036-03-16
Also published as: CN106001380B; JP2016179480A; CA2923915A1; JP5992064B1; CN106001380A

Abstract

As a lower die (210) of a rough forging die (200), a lower die (210) is used having a bottom face of a groove (221) positioned in a direction orthogonal to an axial direction of a second pin shaping portion (214) has a sloped face (S) for suppressing the growth of burrs (931). A production method of crankshafts for inline 3-cylinder engines is characterized by, in the rough forging step, each burr formed in the material (910) in the upset forging step is made to engage with the grooves (221) in the lower die (210) of the upset forging die (200) in the rough forging step, respectively, and the material (920) shaped in the upset forging step is position relative to the lower die (210) of the rough forging die (200).

Description

CRANKSHAFT PRODUCTION METHOD
This application is based on and claims the benefit of priority from Japanese Patent Application No. 2015-060613, filed on 24 March 2015.
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to a production method of crankshafts.
Related Art Conventionally, a production method of crankshafts for inline 3-cylinder engines has been known (e.g., Patent Document 1). The first pin, second pin and third pin of the crankshaft of an inline 3-cylinder engine are arranged at 120-degree intervals in the circumferential direction of journal axial center, due to the explosion interval. In this way, the crankshafts used in inline 3-cylinder engines have a complicated shape, and in the case of shaping a crankshaft by hot forging, it is difficult to die cut a crankshaft in its completed shape from the die as is. For this reason, after forging using a shaping die to mold a material into a shape for which die cutting is easy, twist machining is conducted that twists every predetermined angle, e.g., 60 , in a

2 clockwise direction and counter-clockwise direction with the shaft center of the journal axis as a center.
In forge casting, in the case of shaping the crankshaft of an inline 3-cylinder engine without performing twist machining, elevation differences arise at the separation positions of the die due to the phases of the first pin, second pin and third pin (e.g., Patent Document 2). In addition, as a technology for lessening and suppressing the variation arising in forge casting, forming a sloped step face in the die has been known (e.g., Patent Document 3).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2012 - 86265 Patent Document 2: Japanese Unexamined Patent Application, Publication No. S58 - 132342 Patent Document 3: Japanese Examined Patent Application Publication No. S62 - 45009 SUMMARY OF THE INVENTION
In the case of shaping a crankshaft for an inline 3-cylinder engine by forge casting without performing twist machining, elevation differences occur at the separating position of the die as mentioned above. For this reason, upon performing an upset forging process, a preforming process and a finish shaping process in forge casting, positioning of the material relative to the die is required upon the material being conveyed from the respective steps to a subsequent step.

3 For this positioning, measures such as providing an elevation difference are necessary for the burrs arising in the respective processes of forging. However, in this case, since it is necessary to actively generate burrs, drawbacks arise such as the yield rate declining.
The present invention has an object of providing a production method of crankshafts that can position material easily in each process, and can suppress a decline in yield rate.
The present invention provides a production method of crankshafts for performing hot forging, comprising an upset forging step, a rough forging step, and a finish forging step, in which the upset forging step, with a columnar billet (e.g., the billet (material )910 described later) as a starting material, shapes a billet as the material into a shape resembling a final product shape of a crankshaft, according to respective shapes of a crankshaft using an upset forging die (e.g., the upsetforging die 100 described later) having a lower die (e.g., the lower die 110 described later) and an upper die; the rough forging step performs shaping of the material (e.g., the material 920 described later) shaped in the upset forging step into a shape further resembling the final product shape of the crankshaft, using a rough forging die (e.g., the rough forging die 200 described later) having a lower die (e.g., the lower die 210 described later) and an upper die; the finish forging step performs shaping of the material shaped in the rough

4 forging step into the final product shape of the crankshaft having a machining allowance, using a finish forging die (e.g., the finish forging die 300 described later) having a lower die (e.g., the lower die 310 described later) and an upper die; a lower die is used as the lower die of the upset forging die, the lower die of the rough forging die, and the lower die of the finish forging die, in which a second pin shaping portion (e.g., the second pin shaping portion 114, 214 described later) that shapes a second pin of the crankshaft is aligned below in a vertical direction a journal shaft shaping portion (e.g., the journal shaft shaping portion 112, 212 described later) that shapes a journal shaft of the crankshaft, in which a groove (e.g., the trapezoidal groove 121, 221) is formed in the lower die that recesses vertically downwards, as well as extending along a separation face (e.g., the separation face 111, 211 described later) of each of the upset forging die, the rough forging die and the finish forging die and in communication with the second pin shaping portion, and in which at least a pair of the grooves is formed to produce a burr (e.g., the burr 931 described later) of the groove that is connected to the second pin of the crankshaft;
a lower die is used as the lower die of the rough forging die, = wherein a bottom face of the groove positioned in a direction orthogonal to an axial direction of the second pin shaping portion has a sloped face (e.g., the sloped face S described later) for suppressing the growth of a burr constituted by material flowing out from the groove along the separation face of the rough forging die; and the rough forging step causes each of the burrs formed in the material at the groove of the lower die of the upset forging die in the upset forging step to engage with the groove of the lower die of the rough forging die in the rough forging step, and aligns the material shaped in the upset forging step relative to the lower die of the rough forging die.
According to the present invention, by the burrs being supported by the at least one pair of grooves, it is possible to position the material relative to the lower die of the rough forging die, and possible to stably support on the lower die of the rough forging die. In addition, by way of the sloped face, it is possible to suppress the growth of the burr constituted by the material flowing out from the groove. For this reason, it is possible to curb a decline in yield rate.
In addition, in the case of forming the sloped face only in the pair of grooves and not forming in other portions, it is possible to curb the load from rising during forging. In addition, in the case of forming the sloped face in the groove that is in communication with the second pin shaping portion, it is possible to suppress the growth of the burr from increasing, in the case of a counterweight not being provided to the arm part adjacent to the second pin. For this reason, since it is possible to curb the jutting out of the burr from the rough forging die, it becomes possible to arrange the dies used in other steps adjacently, and it is possible to curb the burr from becoming a hindrance during conveyance, etc. of the forged article. In addition, it is possible to fill the material into the cavity of the die effectively and easily by the amount for which it is possible to curb the growth of the burr.
Further, as the lower die of the upset forging die in the upset forging step, a lower die (e.g., the lower die 110 described later) is used having a first upset die flat face (e.g., the first upset die flat face 124) in a region enclosed by a first pin shaping portion (e.g., the first pin shaping portion 113 described later) that shapes a first pin of the crankshaft and an arm part shaping portion (e.g., the arm part shaping portion 116 described later) that shapes an arm part adjacent to the first pin of the crankshaft, and having a third upset die flat face (e.g., the third upset die flat face 125) in a region enclosed by a third pin shaping portion (e.g., the third pin shaping portion 115) that shapes a third pin of the crankshaft and an arm part shaping portion (e.g., the arm part shaping portion 118) that shapes an arm part adjacent to the third pin of the crankshaft; as the lower die of the rough forging die in the rough forging step, a lower die (e.g., the lower die 210 described later) is used having a first rough die flat face (e.g., the first rough die flat face 224 described later) in a region enclosed by a first pin shaping portion (e.g., the first pin shaping portion 213 described later) that shapes a first pin of the crankshaft and an arm part shaping portion (e.g., the arm part shaping portion 216 described later) that shapes an arm part adjacent to the first pin of the crankshaft, and having a third rough die flat face (e.g., the third rough die flat face 225 described later) in a region enclosed by a third pin shaping portion (e.g., the third pin shaping portion 215 described later) that shapes a third pin of the crankshaft and an arm part shaping portion (e.g., the arm part shaping portion 218 described later) that shapes an arm part adjacent to the third pin of the crankshaft; a depth from a separation face until the first upset die flat face of the lower die of the upset forging die is the same as a depth from a separation face until the first rough die flat face of the lower die of the rough forging die; and a depth from a separation face until the third upset die flat face of the lower die of the upset forging die is the same as a depth from a separation face until the third rough die flat face of the lower die of the rough forging die.
In the upset forging step, since it is thereby possible to place the billet serving as the material on the first upset die flat face and third upset die flat face in the upset forging step, it is possible to arrange the columnar billet on the upset forging die in a positional relationship substantially matching the axial center of the journal shaft shaping portion. For this reason, it is possible to curb a decline in yield rate from becoming the positional relationship in which the axial center of the columnar billet slopes relative to the axial center of the journal shaft shaping portion.

In addition, in the rough forging step, the burrs of the material are supported by the pair of grooves in the lower die of the rough forging die, respectively, and along with this, the first rough die flat face abutting face and third rough die flat face abutting face of the material are supported by the first rough die flat face and third rough die flat face, respectively. In other words, the material can be supported by a total of four portions of the rough forging die. For this reason, the material can be positioned relative to the lower die of the rough forging die without rattling occurring, and thus it is possible to stably support on the lower die of the rough forging die.
Furthermore, as the lower die of the finish forging die in the finishing step, a lower die (e.g., the lower die 310 described later) is used having a first material support portion (e.g., the first material support portion 324 described later) in a region enclosed by a first pin shaping portion (e.g., the first pin shaping portion 313 described later) that shapes a first pin of the crankshaft and arm part shaping portion (e.g., the arm part shaping portion 316 described later) that shapes an arm part adjacent to the first pin of the crankshaft, and having a third material support portion in a region enclosed by a third pin shaping portion (e.g., the third pin shaping portion described later) that shapes a third pin of the crankshaft and an arm part shaping portion that shapes an arm part adjacent to the third pin of the crankshaft; a depth from a separation face until the first material support portion of the lower die of the finish forging die is the same as a depth from a separation face until the first rough die flat face of the lower die of the rough forging die; and a depth from a separation face until the third material support portion of the lower die of the finish forging die is the same as a depth from a separation face until the third rough die flat face of the lower die of the rough forging die.
The burrs of the material are thereby supported on the at least one pair of grooves in the lower die of the finish forging die, respectively, in the finish forging step, and along with this, the first material support portion abutting face and third material support portion abutting face of the material are respectively supported by the projecting end face of the first material support portion and the projecting end face of the third material support portion. In other words, the material can be supported by a total of four portions of the finish forging die. For this reason, it is possible to position the material relative to the lower die of the finish forging die without rattling occurring, and thus possible to stably support on the lower die of the finish forging die.
According to the present invention, it is possible to provide a production method of crankshafts that can easily position a material in each process, and can curb a decline in yield rate.
BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a lower die 110 of an upset forging die 100 used in a production method of crankshafts for inline 3-cylinder engines according to an embodiment of the present invention;
FIG. 2 is an enlarged cross-sectional view showing an aspect of a billet 910 being placed on a first upset die flat face 124 of the lower die 110 of the upset forging die 100, in an upset forging step of the production method of crankshafts for inline 3-cylinder engines according to the embodiment of the present invention;
FIG. 3 is a plan view showing a lower die 210 of a rough forging die 200 used in the production method of crankshafts for inline 3-cylinder engines according to the embodiment of the present invention;
FIG. 4 is an enlarged cross-sectional view showing an aspect of a material 920 being placed on a first flat face 224 of the lower die 210 of the rough forging die 200, in the rough forging step of the production method of crankshafts for inline 3-cylinder engines according to the embodiment of the present invention;
FIG. 5 is an enlarged cross-sectional view showing a sloped face S of the rough forging die 200 used in the production method of crankshafts for inline 3-cylinder engines according to the embodiment of the present invention;
FIG. 6 is a plan view showing a material and the lower die 210 of the rough forging die 200 used in the production method of crankshafts for inline 3-cylinder engines according to the II
embodiment of the present invention;
FIG. 7 is a cross-sectional view along the line B-B in FIG. 6;
FIG. 8 is a cross-sectional view along the line A-A in FIG. 6;
FIG. 9 is a cross-sectional view along the line C-C in FIG. 6; and FIG. 10 is an enlarged cross-sectional view showing an aspect of a material 930 being placed on a first material support portion 324 of a lower die 310 of a finish forging die 300, in a finish shaping step of the production method of crankshafts for inline 3-cylinder engines according to the embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be explained in detail while referencing the drawings.
FIG. 1 is a plan view showing a lower die 110 of an upset forging die 100 used in the production method of crankshafts for inline 3-cylinder engines according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing an aspect of a billet 910 being placed on a first upset die flat face 124 of the lower die 110 of the upset forging die 100, in an upset forging step of the production method of crankshafts for inline 3-cylinder engines according to the embodiment of the present invention. FIG. 3 is a plan view showing a lower die 210 of a rough forging die 200 used in the production method of crankshafts for inline 3-cylinder engines according to the embodiment of the present invention.
FIG. 4 is an enlarged cross-sectional view showing an aspect of a material 920 being placed on a first flat face 224 of the lower die 210 of the rough forging die 200, in the rough forging step of the production method of crankshafts for inline 3-cylinder engines according to the embodiment of the present invention; FIG. 5 is an enlarged cross-sectional view showing a sloped face S of the rough forging die 200 used in the production method of crankshafts for inline 3-cylinder engines according to the embodiment of the present invention.
FIG. 6 is a plan view showing a material and the lower die 210 of the rough forging die 200 used in the production method of crankshafts for inline 3-cylinder engines according to the embodiment of the present invention. FIG. 7 is a cross-sectional view along the line B-B in FIG. 6. FIG. 8 is a cross-sectional view along the line A-A in FIG. 6. FIG. 9 is a cross-sectional view along the line C-C in FIG. 6. FIG. 10 is an enlarged cross-sectional view showing an aspect of a material 930 being placed on a first material support portion 324 of a lower die 310 of a finish forging die 300, in a finish shaping step of the production method of crankshafts for inline 3-cylinder engines according to the embodiment of the present invention.
The crankshaft forged by the production method of crankshafts for inline 3-cylinder engines according to the present invention converts the reciprocal motion of pistons into rotational motion with the cooperation of connecting rods, in an internal combustion engine (engine). The crankshaft is configured for use in an inline 3-cylinder engine.
The crankshaft is shaped by hot forging that is performed in the production method of crankshafts for inline 3-cylinder engines according to the present embodiment. Hot forging includes an upset forging set, rough forging step and finish shaping step. The upset forging step, an upset forging die 100 having a lower die 110 and upper die (not illustrated) is used. In the rough forging step, a rough forging die 200 having a lower die 210 and upper die 250 is used. In the finish shaping step, a finish forging die 300 having a lower die 310 and an upper die (not illustrated) is used.
First, the upset forging die 100 used in the upset forging step will be explained. The upset forging die 100 shapes a billet 910 serving as a material having a columnar shape (refer to FIG. 2, which is an enlarged cross-sectional view along the line D-D in FIG. 1) in a shape resembling the finished prodnnt shape of a crankshaft, according to the respective shapes of the crankshaft.
As shown in FIG. 1, the lower die 110 of the upset forging die 100 includes a lower-die separation face 111, journal shaft shaping portion 112, first pin shaping portion 113, second pin shaping portion 114, third pin shaping portion 115, arm shaping portions 116, 117, 118, weight shaping portions 119, trapezoidal groove 121, convex parts 122, 123, first upset die flat face 124, and third upset die flat face 125.
A part of the separation face 111 abuts an upper die separation face of the upper die (not illustrated) upon forging by sandwiching the billet 910 serving as the raw material between the lower die 110 and the upper die of the upset forging die 100 in the upset forging step. The journal shaft shaping portion 112 shapes a journal shaft (not illustrated) that is a portion of the crankshaft that is rotatably supported in the cylinder block of the engine. So that a plurality of the journal shafts having a positional relationship arranged with intervals between each other on the same axis line, the journal shaft shaping portions 112 are formed having a positional relationship arranged with intervals between each other on the same axis line in the lower die 110. So that a substantially columnar shape is formed by the respective journal shaft shaping portions 112 of the lower die 110 and the respective journal shaft shaping portions of the upper die (not illustrated), the respective journal shaft shaping portions 112 of the lower die 110 have a shape such that cuts the substantially columnar shape in a cross-section including the axial center thereof.
The first pin shaping portion 113, second pin shaping portion 114 and third pin shaping portion 115 are arranged so as to be respectively positioned between the plurality of journal shaft shaping portions 112, at positions separated from the axial center position of the journal shaft shaping portion 112, in the axial center direction (left-right direction in FIG. 1) of each of the journal shaft shaping portions 112. In the first pin shaping portion 113, a first pin of the crankshaft to be connected to the connecting rod of the piston is shaped. Similarly, in the second pin shaping portion 114, the second pin of the crankshaft to be connected to the connecting rod of the piston is shaped, and in the third pin shaping portion 115, the third pin of the crankshaft to be connected to the connecting rod of the piston is shaped.
In the vertical direction, the second pin shaping portion 114 is arranged below the journal shaft shaping portion 112 shaping the journal shaft of the crankshaft. More specifically, between the journal shaft shaping portion 112 and the journal shaft shaping portion 112, the second pin shaping portion 114 is formed to be depressed in the vertical direction from the axial center position of the journal shaft shaping portion 112 having a positional relationship matching the separation face 111.
In contrast, the first pin shaping portion 113 is formed having a positional relationship having a phase 1200 shift in the circumferential direction with the axial center of the journal shaft shaping portion 112 in the counter-clockwise direction relative to the second pin shaping portion 114 about the axial center of the journal shaft shaping portion 112, when viewed from a direction viewing by the first pin shaping portion 113 being positioned nearer than the second pin shaping pin 114, which is a direction in which the axial center of the journal shaft shaping portion 112 extends (when viewing in a direction from the left to right in FIG. 1).
Therefore, in the first pin shaping portion 113 of the lower die 110, only merely one part of the first pin is shaped, and the majority of the first pin is shaped in the first pin shaping portion of the upper die (not illustrated).
Similarly, the third pin shaping portion 115 is formed having a positional relationship having a phase 1200 shift in the circumferential direction with the axial center of the journal shaft shaping portion 112 in the clockwise direction relative to the second pin shaping portion 114 about the axial center of the journal shaft shaping portion 112, when viewed from a direction viewing by the first pin shaping portion 113 being positioned nearer than the second pin shaping pin 114, which is a direction in which the axial center of the journal shaft shaping portion 112 extends (when viewing in a direction from the left to right in FIG. 1). Therefore, in the third pin shaping portion 115 of the lower die 110, only merely one part of the third pin is shaped, and the majority of the third pin is shaped in the first pin shaping portion of the upper die (not illustrated).
The arm part shaping portions 116, 117 and 118 mold the arm parts, which are integrally shaped in the first pin, second pin and third pin of the crankshaft, respectively. So that the arm parts are integrally shaped in the journal shaft extending as pairs from each of the first pin, second pin and third pin to the respective journal shafts, in a direction substantially orthogonal to the axial direction of the journal shaft, the arm part shaping portions 116, 117 and 118 are in communication with the respective end parts of the first pin shaping portion 113, second pin shaping portion 114 and third pin shaping portion 115 in the axial center direction of the journal shaft shaping portions 112 (left-right direction in FIG. 1), and the journal shaft shaping portions 112.
The weight part shaping portion 119 shapes the weight part extending in a plate shape from the journal shaft in a direction substantially orthogonal to the journal shaft and a direction in which each separate from the first pin, second pin and third pin. So that the weight part is shaped integrally with the arm part and shaped in a plate shape wider in width than the arm part, the weight part shaping portion 119 is formed in communication with each of the arm part shaping portions 116, 118 and with a wider width than the arm part shaping portions 116, 118. The arm part shaping portions 116, 118 are formed to make a pair; however, so that the weight parts shaped integrally with each arm part, respectively, are also formed, the arm part shaping portions 116, 118 are formed to make a pair. It should be noted that the weight parts are not integrally shaped in the arms, which are integrally shaped to the second pin. For this reason, a weight part shaping portion that is in communication with the arm part shaping portion 117 is not formed.
The trapezoidal groove 121 has a trapezoidal shape in which a cross section orthogonal to the longitudinal direction of the trapezoidal groove 121 tapers as approaching the bottom of the groove (refer to the tapered groove 221 shown in FIG. 9 of the lower die 210 of the rough forging die 200 of substantially the same shape as the trapezoidal groove 121).
The trapezoidal groove 121 extends making a pair along the separation face 111 of the upset forging die 100 along with depressing in the vertical direction, which is the shaping direction, so as to space out in a direction orthogonal to the axial center direction of the journal shaft shaping portion 112, i.e. up-down direction in FIG. 1. The base end of the trapezoidal groove 121 is in communication with the second pin shaping portion 114. An extending end of the trapezoidal groove 121 in a direction along the separation face 111 is positioned at the edge part of the lower die 110. Upon the billet 910 serving as the starting material being shaped by the upset forging die 100, a part of the starting material is worked into the trapezoidal groove 121. A burr connected to the second pin of the crankshaft is thereby made to form. In other words, the part of the starting material entering into the trapezoidal groove 121 becomes part of a burr.
Convex parts 122, 123 extend making a pair in directions orthogonal to the axial center direction of the journal shaft shaping portion 112, i.e. in the down direction and up direction in FIG. 1, along the separation face 111 of the upset forging die 100, as well as projecting vertically upwards. The base end of the convex part 122 extending in the down direction in FIG. 1 is in communication with the first pin shaping portion 113, and the extending end of the convex part 122 in a direction following the separation face 111 is positioned at an edge part on the lower side in FIG. 1 of the lower die 110. The base end of the convex part 123 extending in the up direction in FIG. 1 is in communication with the third pin shaping portion 115, and the extending end of the convex part 123 in a direction following the separation face 111 is positioned at an edge part on the upper side in FIG. 1 of the lower die 110. Therefore, as shown in FIG. 2, a downwards slope from the convex part 122 to the first pin shaping portion 113 is formed in a cross section of the lower die 110 orthogonal to the axial center of the journal shaft shaping portion 112, as shown in FIG. 2.
Then, in the plan view shown in FIG. 1, a region of the lower die 110 enclosed by the first pin shaping portion 113 that is above the region, the pair of arm part shaping portions 116 shaping the pair of arm parts adjacent to the first pin of the crankshaft, and the pair of weight part shaping portions 119 in communication with the pair of arm part shaping portions 116 and shaping the pair of weight parts, i.e. the portion on the left side from the portion at which the slope ends downwards shown in FIG. 2, has a first upset die flat face 124. The first upset die flat face 124 forms a first rough die flat face abutting face 921 (refer to FIG. 4) configured from a flat face, in a portion of the starting material serving as a portion from the first pin to the weight part, in the upset forging step.
For the convex part 123 joining with the third pin shaping portion 115, similarly, a portion of a region of the lower die 110 enclosed by the third pin shaping portion 115, pair of arm part shaping portions 118 shaping the pair of arm parts adjacent to the third pin of the crankshaft, and the pair of weight part shaping portions 119 in communication with the pair of arm part shaping portions 118 and shaping the pair of weight parts has a third upset die flat face 125, as shown in FIG. 1. The third upset die flat face 125 forms a third rough die flat face abutting face (not illustrated) configured from a flat face at a portion of the starting material corresponding to a portion from the third pin to the weight part, in the upset forging step.
The journal shaft shaping portion 112, first pin shaping portion 113, second pin shaping portion 114, third pin shaping portion 115, arm part shaping portions 116, 117, 118, weight part shaping portions 119, first upset die flat face 124 and third upset die flat face 125 constitute a part of a cavity shaping a portion that becomes the crankshaft from the billet 910 serving as the starting material, in the upset forging step.
It should be noted that a portion of the upper die (not illustrated) of the upset forging die 100, which is positioned at the upper die of a cavity shaping a portion that becomes the crankshaft from the starting material, is configured so as to mold a portion other than a part of the crankshaft that is shaped in the lower die 110. In other words, the upper die (not illustrated) has a journal shaft shaping portion similarly to the journal shaft shaping portion 112 of the lower die 110. In addition, the upper die (not illustrated) has an upper die separation face that opposes and abuts the lower die separation face 111. In addition, the upper die has a first pin shaping portion, third pin shaping portion, arm part shaping portion and weight part shaping portion (not illustrated), which mold a portion of the first pin, a portion of the third pin, a portion of the arm part and a portion of the weight part that are not shaped by the lower die 110.
In addition, the upper die has formed therein a trapezoidal convex part having a shape slightly smaller than the trapezoidal groove 121 and engaging with the trapezoidal groove 121 is formed in the lower die 110, and a concaved groove that is slightly larger than the convex part 122 and engaged by the convex part 122 formed in the lower die 110.
Next, the rough forging die 200 used in the rough forging step will be explained. The rough forging die 200 shapes the material 920 shaped in the upset forging step into a shape further resembling the shape of a crankshaft as the final product. For this reason, the lower die 210 of the rough forging die 200, similarly to the lower die 110 of the upset forging die 100, has a lower die separation face 211, journal shaft shaping portion 212, first pin shaping portion 213, second pin shaping portion 214, third pin shaping portion 215, arm part shaping portions 216, 217, 218, and weight part shaping portion 219. These enable shaping the material in a shape further resembling the shapes of each part of the crankshaft as a final product. For these portions which are substantially the same as the configurations of the upset forging die 100, explanations will be omitted, and the characteristic configurations of the rough forging die 200 other than these which differ from the configuration of the upset forging die 100 will be explained hereinafter.
As shown in FIG. 5 as a cross-sectional view along the line F-F in FIG. 3, the bottom face of the trapezoidal groove 221 of the lower die 210 of the rough forging die 200 has a sloped face S. The sloped face S is the bottom surface of the trapezoidal groove 221, and exists at the bottom face of the trapezoidal groove 221 positioned in a direction orthogonal to the axial direction of the second pin shaping portion 214 (up direction, down direction in FIG. 3). The sloped face S exists so as to have a positional relationship orthogonal to the extending direction of the trapezoidal groove 221 (up direction or down direction in FIG. 3), and transverse the trapezoidal groove 221. For this reason, with the sloped face S as a border, the bottom face of the trapezoidal groove 221 on a side distanced from the second pin shaping portion has a positional relationship one step raised above in the vertical direction relative to the bottom face of the trapezoidal groove 221 on a side close to the second pin shaping portion, as shown in FIG. 5. In other words, when comparing between the burr 931 in the trapezoidal groove 221 in the cross section along the line A-A shown in FIG. 6 (refer to FIG. 8) and the burr 931 in the trapezoidal groove 221 in the cross section along the line B-B shown in FIG. 6 (refer to FIG. 7), they are configured so that the positions of the height of the burr 931 formed in the bottom part of the trapezoidal groove 221 differ.
The slope angle relative to the vertical direction (up/down direction in FIG. 8) of the portion 220 (refer to FIGS. 8, etc.) corresponding to a pair of sloped sides of the trapezoid of the trapezoidal groove 221 in the lower die 210 of the rough forging die 200 is the same as the slope angle relative to the vertical direction of the portion (not illustrated) corresponding to the two sloped sides of the trapezoid of the trapezoidal groove 121 in the lower die 110 of the upset forging die 100 corresponding to this.
In addition, the lower end of the trapezoidal convex part of the upper die (not illustrated) of the rough forging die 200, which engages with the trapezoidal groove 221 in the lower die 210 of the rough forging die 200 has a shape following the trapezoidal groove 221 and sloped face S of the lower die 210. A burr is produced in the rough forging step, and the sloped face S curbs the spreading out of the burr by running out from the trapezoidal groove 221 along the separation face 211 and spreading, and thus suppresses the growth of burrs.
As shown in FIG. 3, the convex parts 222, 223 of the lower die 210 of the rough forging die 200, similarly to the convex parts 122, 123 of the lower die 110 of the upset forging die 100, project vertically upwards, as well as extending in directions orthogonal to the axial center direction of the journal shaft shaping portion, i.e. down direction, up direction in FIG. 3, respectively, along the separation face 211 of the rough forging die 200. The base end of the convex part 222 extending in the down direction in FIG. 1 is in communication with the first pin shaping portion 213, and the extending end of the convex part 222 along the separation face 211 is positioned at an edge part on the lower side in FIG. 3 of the lower die 210. The base end of the convex part 223 extending in the up direction in FIG. 3 is in communication with the third pin shaping portion 215, and the extending end of the convex part 223 along the separation face 211 is positioned at an edge part on the upper side in FIG. 3 of the lower die 210. Therefore, as shown in FIG. 4, which is an enlarged cross sectional view along the line E-E in FIG. 6 established in a state placing the material 920 on the lower die 210 of the rough forging die 200, a downward slope from the convex part 222 towards the first pin shaping portion 213 is formed in the cross section of the lower die 210 orthogonal to the axial center of the journal shaft shaping portion 212.
Then, in a plan view shown in FIG. 3, a portion in a region of the lower die 210 enclosed by the first pin shaping portion 213 that is above the slope, and the pair of arm part shaping portions 216 that mold the pair of arm parts adjacent to the first pin of the crankshaft, i.e. portion of the lower die 210 on the left side from the portion at which the slope ends downwards, shown in FIG. 4, has a first rough die flat face 224. In the vertical direction, which is the shaping direction, the depth from the separation face 111 of the lower die 110 of the aforementioned upset forging die 100 until the first upset die flat face 124 is the same as the depth from the separation face 211 of the lower die 210 of the rough forging die 200 until the first rough die flat face 224.
In addition, the positional relationship in the vertical direction between the trapezoidal groove 221 of the rough forging die 200 and the first rough die flat face 224 is the same as the positional relationship between the trapezoidal groove 121 of the upset forging die 100 and the first upset die flat face 124. In the rough forging step, the first rough die flat face abutting face 921 configured by the flat face formed in the starting material in the upset forging step abuts at the face with the first rough die flat face 224.
Then, the first rough die flat face 224 forms a first material support portion abutting face 932 (refer to FIG. 10) configured by a flat face in a portion of the material corresponding to a portion from the first pin reaching the arm part, in the rough forging step.
Then, a portion closer to the weight part shaping portion 219 than the first rough die flat face 224, i.e. portion on the left side from the first rough die flat face 224 shown in FIG. 4, has a downward slope from the first rough die flat face 224 further formed therein, and in a downwards ending portion that is enclosed by the weight part in the plan view shown in FIG. 3, a flat face 226 for shaping a part of the weight part is further formed.
For the convex part 223 in which the portion at which the slope ends downwards is in communication with the third pint shaping portion 215, similarly, a portion of the region of the lower die 210 enclosed by the third pin shaping portion 215, and the pair of arm part shaping portions 218 shaping the pair of arm parts adjacent to the third pin of the crankshaft has a third rough die flat face 225 (refer to FIG. 3). In the vertical direction, which is the shaping direction, the depth from the separation face 111 until the third upset forging flat face 125 of the lower die 110 of the aforementioned upset forging die 100 is the same as the depth from the separation face 211 until the third rough die flat face 225 of the lower die 210 of the rough forging die 200.
In addition, in the vertical direction, the positional relationship between the trapezoidal groove of the rough forging die 200 and the third rough die flat face 225 is the same as the positional relationship between the trapezoidal groove 121 of the upset forging die 100 and the third upset die flat face 125. In the rough forging step, the third rough die flat face abutting face (not illustrated) configured by a flat face formed in the material in the upset forging step surface abuts the third rough die flat face 225. Then, the third rough die flat face 225 forms the third material support portion abutting face (not illustrated) configured by a flat face in a portion of the material from the third pin reaching the arm part, in the rough forging step.

Then, a portion closer to the weight part shaping portion 219 than the third rough die flat face 225 (down direction in FIG. 1) has a downward slope from the third rough die flat face 225 further formed therein, and in the downwards ending portion that is enclosed by the weight part shaping portions 219 in the plan view shown in FIG. 3, a flat face 227 for shaping a part of the weight part is further formed.
Next, the finish forging die 300 used in the finish forging step will be explained. The finish forging die 300 (refer to FIG. 10) shapes the material shaped in the rough forging step into the final product shape of the crankshaft having machining allowance. For this reason, a lower die 310 of the finish forging die 300, similarly to the lower die 210 of the rough forging die 200, has a lower die separation face (not illustrated), journal shaft shaping portion (not illustrated), first pin shaping portion 313, second pin shaping portion (not illustrated), third pin shaping portion (not illustrated), arm part shaping portion 316, and weight part shaping portions 319; however, these mold each part of the nran1c5haft having machining allowance. Therefore, explanations for these portions that are substantially the same as the configurations of the rough forging die 200 will be omitted, and characteristic configurations other than these of the finish forging die 300 that differ from the configuration of the rough forging die 200 will be explained hereinafter.
As shown in FIG. 10, the convex parts 322 of the lower die 310 of the finish forging die 300, similarly to the convex part 222 of the lower die 210 of the rough forging die 200, each project vertically upwards, and extend in a direction orthogonal to the axial center direction of the journal shaft shaping portion (not illustrated), along the separation face of the finish forging die 300. Therefore, as shown in FIG. 10, in the cross section of the lower die 310 orthogonal to the axial center of the journal shaft, a downward slope spanning from the convex part 322 to the first pin shaping portion 313 is formed.
Then, a portion in a region of the lower die 310 enclosed by the first pin shaping portion 313 that is above the slope, and the pair of arm part shaping portions 316 shaping the pair of arm parts adjacent to the first pin of the crankshaft (region corresponding to a region of the lower die 210 enclosed by the first pin shaping portion 213, and pair of arm part shaping portions 216 adjacent to the first pin of the crankshaft shown in FIG. 3 of the rough processing), i.e.
portion of the lower die 310 on the left side from the portion at which the slope ends downwards shown in FIG. 10, has a flat face. A first material support portion 324 is formed at an end close to the weight part of this flat face. The first material support portion 324 has a substantially trapezoidal shape in a cross section orthogonal to the journal shaft shaping portion, and projects vertically upwards, as shown in FIG. 10. The depth from the separation face (not illustrated) until the projecting end face of the first material support portion 324 in the lower die 310 of the finish forging die 300 is the same as the depth from the separation face 211 until the first rough die flat face 224 in the lower die 210 of the rough forging die 200.
In addition, in the vertical direction which is the shaping direction, the positional relationship between the trapezoidal groove (not illustrated) of the finish forging die 300 and the projecting end face of the first material support portion 324 is the same as the positional relationship between the trapezoidal groove 221 of the rough forging die 200 and the first rough die flat face 224. A first material support portion abutting face 932 configured by a flat face formed in the material in the rough forging step abuts the projecting end face of the first material support portion 324.
The slope angle relative to the vertical direction (up/down direction in FIG. 8) of the portion 220 (refer to FIGS. 8, etc.) corresponding to the two sloped sides of the trapezoid of the trapezoidal groove 221 in the lower die 210 of the rough forging die 200 is the same as the slope angle relative to the vertical direction of the portion corresponding to the two sloped sides of the trapezoid of the trapezoidal groove in the lower die 310 of the finish forging die 300 corresponding to this.
In addition, in a portion closer to the weight part shaping portion 319 than the first material support portion 324, i.e. portion on the left side from the first material support portion 324 shown in FIG. 10, a flat face 325 for shaping a part of the weight part is further formed.
Next, a production method of crankshafts for inline 3-cylinder engines using the upset forging die 100, rough forging die 200 and finish forging die 300 of the above-mentioned configurations will be explained.
In the production method of crankshafts for inline 3-cylinder engines performs hot forging as mentioned earlier, the hot forging including an upset forging step, rough forging step and finish forging step, and the hot forging being performed in this order.
In the upset forging step, as shown in FIG. 2, with the columnar billet 910 as the starting material, the billet 910 as the material is shaped into a shape resembling the final product shape of the crankshaft, according to the respective shapes of the crankshaft, using the upset forging die 100 (refer to FIG. 1). More specifically, in a portion of the lower die 110 constituting a part of the cavity, the columnar billet 910 serving as the material is arranged in a positional relationship in which the axial center of the billet 910 substantially matches the axial center of the journal shaft shaping portion 112. At this time, the billet 910 is placed in the first upset die flat face 124, as shown in FIG. 2, in the vicinity of the first pin shaping portion 113. Similarly, the billet 910 is places on the third upset forging flat face 125, in the vicinity of the third pin shaping portion 115.
In this way, since the billet 910 is placed on the first upset die flat face 124 and third upset die flat face 125, the columnar billet 910 as the material is stably arranged in a positional relationship in which the axial center of the billet 910 substantially matches the axial center of the journal shaft shaping portion 112. In this state, die clamping is performed by bringing the separation face 111 of the lower die 110 and the separation face of the upper die (not illustrated) towards each other and causing to abut, whereby the columnar billet 910 is shaped into a shape resembling the final product shape of the crankshaft in the cavity formed by the lower die 110 and upper die (not illustrated). At this time, the portion of the material placed on the first upset die flat face 124 and third upset die flat face 125 is pressed by the first upset die flat face 124 and third upset die flat face 125. As shown in FIG. 4, the first rough die flat face abutting face 921 and third rough die flat face abutting face (not illustrated) each configured by flat faces are thereby formed in these portions of the material 920. In addition, a trapezoidal burr (similar burr to the trapezoidal burr in the rough forging step shown in FIG. 8) is formed in the trapezoidal groove 121.
Next, in the rough forging step, the material 920 that was shaped in the upset forging step is shaped into a shape further resembling the final product shape of the crankshaft using the rough forging die 200. More specifically, first, the material 920 shaped in the upset forging step is arranged at a portion of the lower die 210 of the rough forging die 200 constituting a part of the cavity.

At this time, a pair of trapezoidal burrs 931 formed in the material of the trapezoidal groove 121 in the lower die 110 of the upset forging die 100 in the upset forging step is engaged with the trapezoidal grooves 221 in the lower die 210 of the rough forging die 200, respectively, as shown in FIG. 9 showing an aspect of placing the material 920 on the lower die 210 of the rough forging die 200 in a cross-sectional view along the line C-C in FIG. 6. At the same time as this, the first rough die flat face abutting face 921 and third rough die flat face abutting face (not illustrated) shaped by the first upset die flat face 124 and third upset die flat face 125 of the lower die 110 of the upset forging die 100 in the upset forging step are made to abut the first rough die flat face 224 and third rough die flat face 225, respectively.
In other words, in the trapezoidal groove 221 in the lower die 210 of the rough forging die 200, as shown in FIG. 9, a portion abutting the two sloped sides of the trapezoid of the trapezoidal groove 221; and a portion of the two sloped sides of the trapezoidal burr 931 formed in the material of the trapezoidal groove 121 in the lower die 110 of the upset forging die 100 in the upset forging step abut at the surfaces; therefore, the trapezoidal burr 931 reliably engages the trapezoidal groove 221, and the material 920 is stably supported by the lower die 210 of the rough forging die 200.
In addition, the first rough die flat face abutting face 921 and the third rough die flat face abutting face (not illustrated) abut by surfaces at the first rough die flat face 224 and third rough die flat face 225, respectively. The material is thereby supported by the four portions of the pair of trapezoidal grooves 221, the first rough die flat face 224 and the third rough die flat face 225, being aligned relative to the lower die 210 of the rough forging die 200 without rattling occurring, and being supported stably on the lower die 210 of the rough forging die 200.
In this state, the separation face 211 of the lower die 210 and the separation face (not illustrated) of the upper die 250 are brought towards each other, made to abut and die clamping is performed, and the material 920 is shaped into a shape further resembling the final product shape of the crankshaft in the cavity formed by the lower die 210 and upper die 250. At this time, the portions of the material placed on the first rough die flat face 224 and third rough die flat face 225 are pressed by the first rough die flat face 224 and third rough die flat face 225, and the first material support portion abutting face 932 and third material support portion abutting face (not illustrated) configured by the respective flat faces are formed in these portions. In addition, the trapezoidal burrs like those shown in FIGS. 7 and 8 are formed in the trapezoidal grooves 221 of the rough forging die 200.
At this time, the burr 931 spreading and flowing out from the trapezoidal groove 221 receives resistance from the sloped face S of the trapezoidal groove 221 in the lower die 210 of the rough forging die 200 (refer to FIG. 5), whereby spreading out more than this is curbed, and the growth of the burr 931 is suppressed. A sloped face portion is formed in the middle of the trapezoidal burr 931 by the sloped face S of the trapezoidal groove 221 of the rough forging die 200.
Next, in the finish forging step, the material shaped in the rough forging step is shaped into the final product shape of the crankshaft having machining allowance, using the finish forging die 300. More specifically, as shown in FIG. 10, first, the material 920 shaped in the rough forging step is arranged at a portion constituting a part of the cavity in the lower die 310 of the finish forging die 300.
At this time, a pair of trapezoidal burrs formed in the material at the trapezoidal grooves 221 in the lower die 210 of the rough forging die 200 in the rough forging step are made to engage with the pair of trapezoidal grooves (not illustrated) in the lower die 310 of the finish forging die 300. At the same time as this, the first material support portion abutting face 932 and third material support portion abutting face (not illustrated) shaped by the first rough die flat face 224 and third rough die flat face 225 of the lower die 210 of the rough forging die 200 in the rough forging step are made to abut a projecting end face of the first material support portion 324 and third material support portion (not illustrated), respectively.
In other words, similarly to the rough forging step, in the trapezoidal grooves in the lower die 310 of the finish forging die 300, a portion corresponding to the two sloped sides of the trapezoidal of the trapezoidal groove (not illustrated) of the lower die 310 and a portion of the two sloped sides of the trapezoidal burr 931 formed in the material at the trapezoidal groove 221 in the lower die 210 of the rough forging die 200 in the rough forging step respectively abut at surfaces; therefore, the trapezoidal burr reliably engages with the trapezoidal groove 221, and the material 930 is stably supported by the lower die 310 of the finish forging die 300. In addition, the first material support portion abutting face 932 and third material support portion abutting face (not illustrated) are abutting by surfaces at the projecting end faces of the first material support portion 324 and third material support portion (not illustrated), respectively. The material 930, similarly to the case of the rough forging step, is thereby supported by the four portions of the pair of trapezoidal grooves (not illustrated), the projecting end face of the first material support portion 324 and the projecting end face of the third material support portion (not illustrated), being positioned relative to the lower die 310 of the finish forging die 300 without rattling occurring, and being stably supported on the lower die 310 of the finish forging die 300.
In this state, the divided (not illustrated) of the lower die 310 and the separation face of the upper die (not illustrated) are brought towards each other, made to abut and die clamping is performed, and the material 930 is shaped into the final product shape of the crankshaft having machining allowance in the cavity formed by the lower die 310 and upper die. At this time, since the sloped face is formed also in the trapezoidal groove (not illustrated) in the lower die 310 of the finish forging die 300, it curbs the burr from spreading out, and thus the growth of burrs is suppressed.
The following effects are exerted according to the present embodiment.
In the present embodiment, in a production method of inline 3-cylinder engine crankshafts for performing hot forging, including an upset forging step, a rough forging step, and a finish forging step, the upset forging step, with a columnar billet 910 as a starting material, shapes a billet 910 as the material into a shape resembling a final product shape of a crankshaft, according to respective shapes of a crankshaft using an upset forging die 100 having a lower die 110 and an upper die (not illustrated); the rough forging step performs shaping of the material shaped 920 in the upset forging step into a shape further resembling the final product shape of the crankshaft, using a rough forging die 200 having a lower die 210 and an upper die; and the finish shaping step performs shaping of the material 930 shaped in the rough forging step into the final product shape of the crankshaft having a machining allowance, using a finish forging die 300 having a lower die 310 and an upper die.
As the lower die 110 of the upset forging die 100, the lower die 210 of the rough forging die 200, and the lower die 310 of the finish forging die 300, a lower die is used in which a second pin mold part that shapes a second pin of the crankshaft is aligned below in a vertical direction a journal shaft shaping portion that shapes a journal shaft of the crankshaft, in which a trapezoidal groove is formed in the lower die that recesses vertically downwards, as well as extending along a separation face of each of the upset forging die 100, the rough forging die 200 and the finish forging die 300 and in communication with the second pin shaping portion, and in which a pair of the trapezoidal grooves is formed to produce a burr that is connected to the second pin of the crankshaft in the trapezoidal groove.
As the lower die 210 of the rough forging die 200, a lower die 210 is used in which a bottom face of the trapezoidal groove 221 positioned in a direction orthogonal to an axial direction of the second pin shaping portion 214 has a sloped face S for suppressing the growth of a burr constituted by material 920 flowing out from the trapezoidal groove 221 along the separation face 211 of the rough forging die 200.
The rough forging step causes each of the burrs 931 formed in the material at the trapezoidal groove 121 of the lower die 110 of the upset forging die 100 in the upset forging step to engage with the trapezoidal groove 221 of the lower die 210 of the rough forging die 200 in the rough forging step, respectively, and aligns the material 920 shaped in the upset forging step relative to the lower die 210 of the rough forging die 200.
By the trapezoidal burrs 931 being supported by the pair of trapezoidal grooves 221, it is thereby possible to position the material 920 relative to the lower die 210 of the rough forging die 200, and possible to stably support on the lower die 210 of the rough forging die 200. In addition, by way of the sloped face S, it is possible to suppress the growth of the burr 931 constituted by the material flowing out from the trapezoidal groove 221. For this reason, it is possible to curb a decline in yield rate. In addition, since the sloped face S is formed only in the pair of trapezoidal grooves 221 and not formed in other portions, it is possible to curb the load from rising during forging. In addition, since the sloped face S is formed in the trapezoidal groove 221 that is in communication with the second pin shaping portion 214, it is possible to suppress the growth of the burr 931 from increasing, in the case of a counterweight not being provided to the arm part adjacent to the second pin, as in the present embodiment. For this reason, since it is possible to curb the jutting out of the burr 931 from the rough forging die 200, it becomes possible to arrange the dies used in other steps adjacently, and it is possible to curb the burr 931 from becoming a hindrance during conveyance, etc. of the forged article. In addition, it is possible to fill the material into the cavity of the die effectively and easily by the amount for which it is possible to curb the growth of the burr 931.
Then, as the lower die 110 of the upset forging die 100 in the upset forging step, a lower die 110 is used having a first upset die flat face 124 in a region enclosed by a first pin shaping portion 113 that shapes a first pin of the crankshaft and a pair of arm part shaping portions 116 that mold a pair of arm parts adjacent to the first pin of the crankshaft, and having a third upset die flat face 125 in a region enclosed by a third pin shaping portion 115 that shapes a third pin of the crankshaft and a pair of arm part shaping portions 118 that mold arm parts adjacent to the third pin of the crankshaft.
As the lower die 210 of the rough forging die 200 in the rough forging step, a lower die 210 is used having a first rough die flat face 224 in a region enclosed by a first pin shaping portion 213 that shapes a first pin of the crankshaft and a pair of arm part shaping portions 216 that mold a pair of arm parts adjacent to the first pin of the crankshaft, and having a third rough die flat face 225 in a region enclosed by a third pin shaping portion 215 that shapes a third pin of the crankshaft and a pair of arm part shaping portions 218 that mold arm parts adjacent to the third pin of the crankshaft.
A depth from the separation face 111 until the first upset die flat face 124 of the lower die 110 of the upset forging die 100 is the same as a depth from a separation face until the first rough die flat face 224 of the lower die 210 of the rough forging die 200, and a depth from the separation face 111 until the third upset die flat face 125 of the lower die 110 of the upset forging die 100 is the same as a depth from the separation face until the third rough die flat face 225 of the lower die 210 of the rough forging die 200.
In the upset forging step, since it is thereby possible to place the billet 910 serving as the material on the first upset die flat face 124 and third upset die flat face 125 in the upset forging step, it is possible to arrange the columnar billet 910 on the upset forging die 100 in a positional relationship substantially matching the axial center of the journal shaft shaping portion 212. For this reason, it is possible to curb a decline in yield rate from becoming the positional relationship in which the axial center of the columnar billet 910 slopes relative to the axial center of the journal shaft shaping portion 212.
In addition, the trapezoidal burrs 931 of the material 920 are supported by the pair of trapezoidal grooves 221 in the lower die 210 of the rough forging die 200, respectively, and along with this, the first rough die flat face abutting face 921 and third rough die flat face abutting face (not illustrated) of the material 920 are supported by the first rough die flat face 224 and third rough die flat face 225, respectively, whereby the material 920 is supported by a total of four portions of the rough forging die 200. For this reason, the material 920 is positioned relative to the lower die 210 of the rough forging die 200 without rattling occurring, and thus is stably supported on the lower die 210 of the rough forging die 200.
Then, as the lower die 310 of the finish forging die 300 in the finishing step, a lower die 310 is used having a first material support portion 324 in a region enclosed by a first pin shaping portion 313 that shapes a first pin of the crankshaft and a pair of arm part shaping portions 316 that mold a pair of arm parts adjacent to the first pin of the crankshaft, and having a third material support portion (not illustrated) in a region enclosed by the third pin shaping portion that shapes a third pin of the crankshaft and the pair of arm part shaping portions that mold the arm part adjacent to the third pin of the crankshaft.
A depth from the separation face until the first material support portion 324 of the lower die 310 of the finish forging die 300 is the same as a depth from the separation face 211 until the first rough die flat face 224 of the lower die 210 of the rough forging die 200, and a depth from a separation face until the third material support portion of the lower die 310 of the finish forging die 300 is the same as a depth from the separation face 211 until the third rough die flat face 225 of the lower die 210 of the rough forging die 200.
The trapezoidal burrs 931 of the material 930 are thereby supported on the pair of trapezoidal grooves (not illustrated) in the lower die 310 of the finish forging die 300, respectively, in the finish forging step, and along with this, the first material support portion abutting face 932 and third material support portion abutting face (not illustrated) of the material 930 are respectively supported by the projecting end face of the first material support portion 324 and the projecting end face of the third material support portion, whereby the material 930 is supported by a total of four portions of the finish forging die 300. For this reason, the material 930 is positioned relative to the lower die 310 of the finish forging die 300 without rattling occurring, and thus is stably supported on the lower die 310 of the finish forging die 300.
The present invention is not to be limited to the above-mentioned embodiments, and modifications, improvements, etc.
within a scope that can achieve the objects of the present invention are also included in the present invention.
For example, although one pair of the trapezoidal grooves is formed in the lower die 110 of the upset forging die 100, the lower die 210 of the rough forging die 200, and the lower die 310 of the finish forging die 300 in the present embodiment, it is not limited to this configuration. It is satisfactory so long as at least one pair of trapezoidal grooves is formed. In addition, the configurations of the dies used in the production method of crankshafts for inline 3-cylinder engines is not limited to the configurations of the upset forging die 100, rough forging die 200 and finish forging die 300 of the present embodiment.
EXPLANATION OF REFERENCE NUMERALS
100 upset forging die 110 lower die 111, 211 separation face 112, 212 journal shaft shaping portion 113 first pin shaping portion 114, 214 second pin shaping portion 115 third pin shaping portion 116 arm part shaping portion 118 arm part shaping portion 121, 221 trapezoidal groove (groove) 125 third upset die flat face 200 rough forging die 210 lower die 213 first pin shaping portion 215 third pin shaping portion 216 arm part shaping portion 218 arm part shaping portion 223 sloped face 224 first rough die flat face 225 third rough die flat face 300 finish forging die 310 lower die 313 first pin shaping portion 316 arm part shaping portion 324 first material support portion 910 billet (material) 920 material 931 burr

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A production method of crankshafts for performing hot forging, comprising an upset forging step, a rough forging step, and a finish forging step, wherein the upset forging step, with a columnar billet as a starting material, shapes a billet as the material into a shape resembling a final product shape of a crankshaft, according to respective shapes of a crankshaft using an upset forging die having a lower die and an upper die;
wherein the rough forging step performs shaping of the material shaped in the upset forging step into a shape further resembling the final product shape of the crankshaft, using a rough forging die having a lower die and an upper die;
wherein the finish forging step performs shaping of the material shaped in the rough forging step into the final product shape of the crankshaft having a machining allowance, using a finish forging die having a lower die and an upper die;
wherein a lower die is used as the lower die of the upset forging die, the lower die of the rough forging die, and the lower die of the finish forging die, wherein a second pin shaping portion that shapes a second pin of the crankshaft is aligned below in a vertical direction a journal shaft shaping portion that shapes a journal shaft of the crankshaft, wherein a groove is formed in the lower die that recesses vertically downwards, as well as extending along a separation face of each of the upset forging die, the rough forging die and the finish forging die and in communication with the second pin shaping portion, and wherein at least a pair of the grooves is formed to produce a burr that is connected to the second pin of the crankshaft in the groove;
wherein the lower die is used as the lower die of the rough forging die, wherein a bottom face of the groove positioned in a direction orthogonal to an axial direction of the second pin shaping portion has a sloped face for suppressing the growth of a burr constituted by material flowing out from the groove along the separation face of the rough forging die; and wherein the rough forging step causes each of the burrs formed in the material at the groove of the lower die of the upset forging die in the upset forging step to engage with the groove of the lower die of the rough forging die in the rough forging step, and aligns the material shaped in the upset forging step relative to the lower die of the rough forging die.

2. The production method of crankshafts according to claim 1, wherein the lower die is used as the lower die of the upset forging die in the upset forging step, and has a first upset die flat face in a region enclosed by a first pin shaping portion that shapes a first pin of the crankshaft and an arm part shaping portion that shapes an arm part adjacent to the first pin of the crankshaft, and having a third upset die flat face in a region enclosed by a third pin shaping portion that shapes a third pin of the crankshaft and an arm part shaping portion that shapes an arm part adjacent to the third pin of the crankshaft;
wherein the lower die is used as the lower die of the rough forging die in the rough forging step, and has a first rough die flat face in a region enclosed by a first pin shaping portion that shapes a first pin of the crankshaft and arm part shaping portion that shapes an arm part adjacent to the first pin of the crankshaft, and having a third rough die flat face in a region enclosed by a third pin shaping portion that shapes a third pin of the crankshaft and an arm part shaping portion that shapes an arm part adjacent to the third pin of the crankshaft;
wherein a depth from a separation face until the first upset die flat face of the lower die of the upset forging die is the same as a depth from a separation face until the first rough die flat face of the lower die of the rough forging die; and wherein a depth from a separation face until the third upset die flat face of the lower die of the upset forging die is the same as a depth from a separation face until the third rough die flat face of the lower die of the rough forging die.

3. The production method of crankshafts according to claim 2, wherein the lower die is used as the lower die of the finish forging die in the finishing step, and has a first material support portion in a region enclosed by a first pin shaping portion that shapes a first pin of the crankshaft and arm part shaping portion that shapes an arm part adjacent to the first pin of the crankshaft, and having a third material support portion in a region enclosed by a third pin shaping portion that shapes a third pin of the crankshaft and an arm part shaping portion that shapes an arm part adjacent to the third pin of the crankshaft;
wherein a depth from a separation face until the first material support portion of the lower die of the finish forging die is the same as a depth from a separation face until the first rough die flat face of the lower die of the rough forging die; and wherein a depth from a separation face until the third material support portion of the lower die of the finish forging die is the same as a depth from a separation face until the third rough die flat face of the lower die of the rough forging die.