JP4550516B2 - Connecting rod manufacturing method and connecting rod - Google Patents

Description

  The present invention relates to a connecting rod manufacturing method and a connecting rod which are used by dividing a large end portion by breaking and rejoining.

  Conventionally, connecting rods that require high strength, such as connecting rods for automobile engines, have been formed by forging. In this type of connecting rod, when the connecting rod base material having a connecting rod large end and a connecting rod small end is formed by forging, and the crank pin hole is formed in the connecting rod large end, the connecting rod large end is the connecting rod main body. And the cap. The cap is fastened to the connecting rod body with two cap fixing bolts with a crank pin sandwiched between the cap and the connecting rod body.

When the connecting rod large end is divided as described above, it is performed by breaking in order to improve the positioning accuracy of the cap when the cap is assembled to the connecting rod body after the dividing and to improve the roundness of the crankpin hole. (See, for example, Patent Document 1).
This breakage is performed by fitting a pair of sliders that can move between the small end of the connecting rod and the opposite side into the large end of the connecting rod, and driving a wedge between the sliders.

  In the connecting rod shown in Patent Document 1, a dividing groove serving as a dividing starting point is formed on the hole wall surface of the crankpin hole so that the connecting rod main body and the cap are divided at a desired position at the time of dividing by fracture. This dividing groove has crankpins at two locations (two locations that serve as connecting portions between the connecting rod body and the cap) that intersect a virtual line extending in a direction perpendicular to the longitudinal direction of the connecting rod base material on the hole wall surface of the crankpin hole. It is formed so as to extend along the axial direction of the hole. The conventional connecting rod dividing groove is formed by subjecting the crank pin hole to machining such as drilling.

  As described above, the connecting rod main body and the cap formed by dividing the connecting rod base material are assembled to the crankpin in a state where the bearing metal formed in a semicircular cross section is attached to the crankpin hole. The bearing metal is formed to have a larger radius of curvature than the crankpin hole, and is press-fitted into the crankpin hole in an elastically deformed state. When attaching this bearing metal to the connecting rod body and the cap, one end of the bearing metal in the circumferential direction is brought into contact with the end of the crank pin hole on the fracture surface side, and the bearing metal is turned around this one end. The other end is pushed into the crankpin hole.

  Since the edge on the fracture surface side of the crankpin hole is formed by fracture, minute irregularities having sharp corners are formed. For this reason, when the bearing metal is press-fitted into the crankpin hole as described above, the outer peripheral surface of the bearing metal may be damaged by the sharp corner formed at the end edge. If the outer peripheral surface of the bearing metal is damaged as described above, the plating layer formed so that the lubricating oil easily adheres to the outer peripheral surface may be peeled off.

Conventionally, in order to solve such a problem, the edge portion is chamfered so that the outer peripheral surface of the bearing metal is in sliding contact with the inclined surface of the chamfered portion when the bearing metal is press-fitted into the crankpin hole. Yes. This chamfering is performed by grinding the connecting rod body and the end portion of the cap after division. After this chamfering is performed, the connecting rod body and the cap are cleaned to remove grinding powder adhering to the fracture surface.
In addition, the applicant could not find any prior art documents closely related to the present invention by the time of filing other than the prior art documents specified by the prior art document information described in the present specification. .
JP 2004-52775 A (page 5, FIG. 1)

In dividing the connecting rod base material into the connecting rod body and the cap by breaking, it is important to form the dividing groove as narrow as possible. This is because by narrowing the groove width of the dividing groove, the stress concentration at the time of division is promoted, the load applied at the time of division can be reduced, the deformation of the connecting rod base material at the time of division is suppressed, and the crank pin This is because the roundness of the hole can be kept high.
However, since the conventional connecting rod manufacturing method configured as described above forms the dividing groove on the hole wall surface of the crankpin hole by machining, the groove width of the dividing groove can be reduced. There was a limit.

  Further, according to the conventional connecting rod manufacturing method described above, fine grinding powder may remain on the fracture surface even if the fracture surface is cleaned after chamfering the edge of the crank pin hole on the fracture surface side. It was. If the foreign matter remains on the fracture surface in this way, when the cap is assembled to the connecting rod body, the foreign matter is caught between the fracture surfaces of the two, and the fracture surfaces cannot be completely matched. For this reason, in such a case, the roundness of the crankpin hole is lowered. Such problems can be solved to some extent by extending the cleaning time and reducing the amount of residue. However, even if the cleaning time is increased, the residue cannot be completely removed, and the cycle time in the manufacturing process is increased by the increase in the cleaning time, resulting in an increase in manufacturing cost. .

  The present invention has been made to solve such a problem, and can maintain a high roundness of the crankpin hole and prevent the cycle time from becoming long, while preventing a long cycle time of the crankpin hole. It is an object of the present invention to make it possible to form an inclined surface at the edge of the plate.

In order to achieve this object, the manufacturing method of the connecting rod according to the present invention forms a dividing groove extending in the axial direction of the crankpin hole on the hole wall surface of the crankpin hole formed in the connecting rod base material by wire electric discharge machining . A method of manufacturing a connecting rod in which the connecting rod base material is divided into a connecting rod body and a cap by breaking the connecting rod base material so that these grooves become the starting points, and an electric discharge wire is drawn with an arrow pointing in the radial direction of the crankpin hole The dividing groove corresponding to the two sides located on the radially outer side of the crankpin hole in the arrow by cutting the hole wall surface of the crankpin hole, A cutting process for exposing the inclined wall, and a bearing metal having a semicircular cross section in each crank pin hole of the connecting rod main body and the cap after the division. It is a manufacturing method of a connecting rod and a step of fitting by sliding contact.

According to a second aspect of the present invention, there is provided a connecting rod in which the connecting rod base material is divided into a connecting rod body and a cap by a fracture surface extending from a groove formed in a hole wall surface of the crankpin hole. A semi-finished connecting rod in which the groove is formed in the shape of an arrow pointing in the radial direction of the crankpin hole as viewed from the side.

  According to the present invention, a dividing groove having a narrower groove width than that of a dividing groove formed by a drill can be formed by wire electric discharge machining. For this reason, the load at the time of a division | segmentation can be reduced and the roundness of a crankpin hole can be improved further.

Further , according to the present invention , the inclined surface with which the outer peripheral surface of the bearing metal is slidably contacted when the bearing metal is assembled to the crankpin hole can be formed in advance on the connecting rod base material by wire electric discharge machining prior to the dividing step. . For this reason, compared with the conventional manufacturing method which forms the said inclined surface by chamfering after a division | segmentation, a grinding powder does not adhere to a torn surface.

Therefore, when the cap is assembled to the connecting rod body, the fracture surfaces at the time of division can be combined, so that the roundness of the crankpin hole can be further improved. Moreover, since the time for the cleaning process can be shortened, the cycle time in the manufacturing process can be shortened and the manufacturing cost can be reduced.
In addition, according to this connecting rod manufacturing method, the dividing groove is formed in the shape of an arrow by wire electric discharge machining, and unnecessary portions other than the inclined surface of the arrow are removed by the subsequent cutting process. The machining time can be shortened compared with the case where the portion is removed by wire electric discharge machining. Also from this point, since the cycle time in the manufacturing process can be shortened, the manufacturing cost can be reduced.

According to the second aspect of the present invention, the connecting rod base material is divided into the connecting rod main body and the cap by breaking, whereby an inclined surface is formed at the edge of the crankpin hole on the fracture surface side. This inclined surface is one in which the outer peripheral surface of the bearing metal comes into sliding contact when the bearing metal is assembled to the crankpin hole.
For this reason, the connecting rod according to the present invention has no grinding powder adhering to the fracture surface as compared with the conventional connecting rod in which the inclined surface is formed by chamfering after dividing. As with division, the fracture surfaces can be combined properly.
Therefore, this connecting rod can further improve the roundness of the crankpin hole. In addition, the connecting rod can be provided at low cost because the cleaning process time can be shortened, the cycle time required for the production can be shortened, and the production cost can be kept low.

Hereinafter, a manufacturing method of a connecting rod according to the present invention and an embodiment of a connecting rod formed by the manufacturing method will be described in detail with reference to FIGS.
1A and 1B are diagrams showing a connecting rod base material in which a dividing groove is formed by the connecting rod manufacturing method according to the present invention. FIG. 1A is a front view, and FIG. It is line sectional drawing. FIG. 2 is a front view showing a state where the connecting rod base material is divided into a connecting rod body and a cap. 3 is an enlarged front view showing the first dividing groove, and FIG. 4 is an enlarged front view showing the second dividing groove. FIG. 5 is a diagram for explaining the moving direction of the wire during wire electric discharge machining. FIG. 5 (a) shows the process of moving the wire in the radial direction of the crankpin hole, and FIG. 5 (b) shows the crankpin hole. The process of moving the wire in the circumferential direction is shown. FIG. 6 is a view for explaining the procedure for assembling the bearing metal to the connecting rod body. FIG. 6 (a) shows the state in which the pawl piece of the bearing metal is inserted into the positioning recess of the crank pin hole. Fig. (B) shows a state in which the other end of the bearing metal is in contact with the inclined surface, Fig. (C) shows a state in which the bearing metal is in sliding contact with the inclined surface during press-fitting, and Fig. (D) shows The state where the bearing metal is assembled to the connecting rod body is shown. 7 and 8 are views showing examples of wire electric discharge machining.

  In these drawings, the reference numeral 1 indicates a connecting rod base material used for manufacturing the connecting rod 2 (see FIG. 2) according to this embodiment. The connecting rod base material 1 is formed into a predetermined shape by forging. In this state, a connecting rod large end portion 4 having a crankpin hole 3 and a connecting rod small end portion 6 having a piston pin hole 5 are integrally formed. Yes. The connecting rod base material 1 is divided into a connecting rod body 7 having a connecting rod small end portion 6 and a cap 8 by dividing the connecting rod large end portion 4 by breaking, as shown in FIG.

The connecting rod body 7 and the cap 8 are attached to each other by a cap fixing bolt (not shown) with a bearing metal 11 (see FIG. 6) attached to the crankpin hole 3 and sandwiching a crankpin (not shown). The As shown in FIG. 6, the bearing metal 11 is formed in a semicircular cross section such that a cylinder is divided into two in the radial direction, and a positioning protrusion 12 protrudes to the outer peripheral side at one end in the circumferential direction. It is formed to do. The bearing metal 11 is formed to have a larger radius of curvature than the crankpin hole 3 and is press-fitted into the crankpin hole 3 in the same manner as that attached to the conventional connecting rod. The bearing metal 11 according to this embodiment is formed in only one type for one connecting rod 2 and is attached to the connecting rod body 7 and the cap 8 in different directions. The surface of the bearing metal 11 is plated in the same manner as the conventional bearing metal 11.
The cap fixing bolt is screwed into the bolt insertion hole 13 formed on both sides of the crankpin hole 3 from the cap 8 side.

  Before the connecting rod large end portion 4 is divided into the connecting rod body 7 and the cap 8, as shown in FIG. 1, the crank pin hole 3, the bolt insertion hole 13, and the dividing starting point when dividing. First and second dividing grooves 14 and 15 and two concave grooves 16 and 17 for inserting the positioning protrusions 12 of the bearing metal 11 are formed. These concave grooves 16 and 17 are at substantially the same position in the circumferential direction of the crankpin hole 3 and are formed by machining such as grinding at one end and the other end in the axial direction of the crankpin hole 3. .

  The first and second dividing grooves 14, 15 are formed in the hole wall surface 3 a of the crankpin hole 3 by wire electric discharge machining, and the connecting rod large end portion 4 extends from one end along the axial direction of the crankpin hole 3. It extends so as to penetrate to the end. In the wire electric discharge machining, a thin wire 18 (see FIG. 5) is brought close to the hole wall surface 3a of the crankpin hole 3, and a part of the connecting rod base material 1 is melted by discharging between the wire 18 and the hole wall surface 3a. Is done by letting

  The wire electric discharge machine used to form the first and second dividing grooves 14 and 15 is a general one formed to manufacture a mold, and the connecting rod base material 1 is used instead of the mold. It is comprised so that can be hold | maintained as a workpiece | work. Although not shown, this wire electric discharge machine has a connecting rod water tank for holding the connecting rod base material 1 so that the axial direction of the crankpin hole 3 is parallel to the vertical direction, and an electric discharge machining wire 18 from above. And a wire supply head that translates in the left-right direction and the front-rear direction while feeding downward.

  The said water tank is formed in the box shape opened upwards, and the structure which hold | maintains the connecting rod base material 1 in the state by which the axial direction of the crankpin hole 3 becomes parallel to an up-down direction at the inner bottom part is taken. A slit-like hole through which the electric discharge machining wire 18 is inserted is formed at the bottom of the water tank. Further, the water tank is configured so that water is supplied and drained from the wire insertion hole formed at the bottom and the drainage port, and discharged from the upper end opening by overflow. The connecting rod base material 1 is formed with the first and second dividing grooves 14 and 15 by wire electric discharge machining while being immersed in the water tank.

  The electric discharge machining wire 18 is fed from above to below through a crank pin hole 3 of a connecting rod base material fixed to the bottom of the water tank and a wire insertion hole formed in the bottom. The wire supply head is configured to feed the wire 18 downward as described above while energizing the wire 18, and moves in a predetermined moving direction in this energized state during processing. The connecting rod base material 1 is melted.

As shown in FIG. 3, the cross-sectional shape of the first dividing groove 14 is an arrow shape that points in the radial direction of the crankpin hole 3 (leftward in the figure) when viewed from the axial direction of the crankpin hole 3. Is formed. As shown in FIG. 4, the sectional shape of the second dividing groove 15 is formed in a straight line extending from the hole wall surface 3a of the crankpin hole 3 in the radial direction (rightward in the figure).
The depths of the first and second dividing grooves 14 and 15 (the length in the radial direction) are determined in a state where the hole wall surface 3a of the crankpin hole 3 is cut in a later process. It is set so that the bottom of the left part remains. This cutting is performed in order to expand the crankpin hole 3 to a hole diameter close to the final diameter. The position of the hole wall surface 3a after this cutting step is shown by a two-dot chain line in FIGS.

  In the first dividing groove 14, two inclined walls 21 and 22 corresponding to two sides located on the radially outer side of the crankpin hole 3 in the arrow are exposed in the crankpin hole 3 by the cutting process. It is formed as follows. The cutting process may be performed before or after the connecting rod base material 1 is divided into the connecting rod body 7 and the cap 8. In this embodiment, however, a minute distortion at the time of the dividing is obtained by cutting. It is carried out after division so that it can be removed.

  Here, the procedure for forming the first dividing groove 14 in the shape of the arrow by wire electric discharge machining will be described in detail with reference to FIGS. In FIG. 5, the range melted by the electric discharge machining wire 18 is indicated by a circle. The first dividing groove 14 according to this embodiment is formed by moving the wire 18 so as to draw an arrow pointing in the radial direction of the crankpin hole 3. In order to form the first dividing groove 14 as described above, first, as shown in FIG. 5 (a), the electric discharge machining wire 18 is moved closer to the hole wall surface 3a from the crank pin hole 3, and the hole wall surface is formed. 3a is melted. Then, as shown by an arrow A in FIG. 5A, the wire 18 is moved in the radial direction of the crankpin hole 3 so that the melted portion becomes deep.

  After the electric discharge machining wire 18 is moved by a predetermined distance in the radial direction, as shown by an arrow B in FIG. 5A, the wire 18 is moved in the direction opposite to the above and returned slightly. Next, as shown by an arrow C in FIG. 5B, the wire 18 is moved obliquely in one direction in the circumferential direction of the crankpin hole 3 and closer to the hole wall surface 3a to become one side of the arrow. An inclined wall 21 is formed, and the wire 18 is moved to the other side along the circumferential direction as indicated by an arrow D in FIG. Thereafter, as indicated by an arrow E in the figure, the inclined wall 22 is formed by moving the wire 18 obliquely in one of the circumferential directions and away from the hole wall surface 3a. After the wire 18 is moved so as to draw an arrow in this way to form the first dividing groove 14, the wire 18 is returned to the hole wall surface 3 a side, and the inside of the crankpin hole 3 is crossed as it is to make the second division. A working groove 15 is formed. The second dividing groove 15 is formed by moving the wire 18 from the hole wall surface 3a to a predetermined depth in the radial direction and then returning it to the hole wall surface 3a side.

Next, the manufacturing method of the connecting rod which concerns on this invention is demonstrated.
The connecting rod 2 according to this embodiment has concave grooves 16 and 17 into which a crank pin hole 3 and a piston pin hole 5, a bolt insertion hole 13, and a projecting piece 12 of a bearing metal 11 are inserted into the connecting rod base material 1 shown in FIG. Are formed, the first dividing groove 14 and the second dividing groove 15 are formed.
The first dividing groove 14 is formed by moving the electric discharge machining wire 18 so as to draw an arrow pointing in the radial direction of the crankpin hole 3, and the second dividing groove 15 is formed by the electric discharge machining wire. 18 is formed by reciprocating in the radial direction of the crankpin hole 3. After forming the first and second dividing grooves 14 and 15 in this way, carburizing is performed on the entire surface of the connecting rod base material 1, and a female screw is formed in the bolt insertion hole 13.

Thereafter, the connecting rod base material 1 is immersed in liquid nitrogen and cooled. The reason why the connecting rod base material 1 is cooled in this way is to reduce the load applied to the connecting rod base material 1 in the next dividing step.
After the connecting rod base material 1 is cooled to a predetermined temperature, this low temperature connecting rod base material 1 is loaded into a dividing device (not shown) and divided into a connecting rod body 7 and a cap 8 by breaking. For example, as disclosed in Patent Document 1, this splitting device is configured to fit a pair of sliders having a semicircular cross section into the crankpin hole 3 so as to be aligned along the longitudinal direction of the connecting rod. A configuration in which a wedge is driven in between can be used. In this dividing step, tensile stress concentrates on the first and second dividing grooves 14 and 15 formed in the hole wall surface 3a of the crankpin hole 3, and cracks are generated starting from these grooves. The connecting rod large end 4 is divided into two parts.

  Thus, the connecting rod main body 7 and the cap 8 formed by dividing the connecting rod base material 1 are immersed in the cleaning water, and the fracture surface is cleaned. In this cleaning process, the temperature of the connecting rod body 7 and the cap 8 that has been cooled in the dividing process is raised to a temperature at which the operator can hold the hand. After washing the fracture surface in this way, the cap 8 is fixed to the connecting rod body 7 with two cap fixing bolts. Then, the hole wall surface 3a of the crankpin hole 3 is cut in this temporarily assembled state, and the crankpin hole 3 is expanded to a hole diameter close to the final diameter. By this cutting, the position of the hole wall surface 3a is moved from the position indicated by the solid line in FIGS. 3 and 4 to the position indicated by the two-dot chain line, and the two inclined walls 21 and 22 of the first dividing groove 14 are cranked. It is exposed in the pin hole 3. Thereafter, the hole wall surface 3a is finished by grinding or the like.

Thereafter, as shown in FIG. 6, the connecting rod 2 is attached to the crank pin hole 3 of the connecting rod main body 7 and the cap 8, and the halved bearing metal 11 is attached to a crankshaft (not shown).
In order to attach the bearing metal 11 to the crankpin hole 3, first, as shown in FIG. 6A, the positioning protrusion 12 of the bearing metal 11 is inserted into the concave grooves 16 and 17 of the crankpin hole 3. One end of the bearing metal 11 in the circumferential direction is brought into contact with the end of the crankpin hole 3 on the fracture surface side. Then, as shown in FIG. 4B, the bearing metal 11 is turned around the one end and the other end is pushed into the crankpin hole 3. At this time, the outer peripheral surface of the bearing metal 11 is in sliding contact with the inclined walls 21 and 22 located on the other end side of the crankpin hole 3. By pushing the bearing metal 11 further into the crank pin hole 3 in this state, the bearing metal 11 is assembled in the crank pin hole 3 in a state of being elastically deformed as shown in FIG.

  Therefore, according to the connecting rod manufacturing method described above, since the first and second dividing grooves 14 and 15 are formed by wire electric discharge machining, the grooves 14 and 15 are formed by machining such as drilling. The groove width can be made narrower than in the case of doing so. In this embodiment, by using an electric discharge machining wire 18 having a thickness of about 0.2 mm, the groove widths of the first and second dividing grooves 14 and 15 can be made larger than when a drill is used. It was possible to form extremely narrowly. For this reason, when manufacturing the connecting rod 2 by this embodiment, the load at the time of a division | segmentation was able to be reduced compared with the past.

  In the connecting rod manufacturing method according to this embodiment, the inclined surfaces (inclined walls 21 and 22) with which the outer peripheral surface of the bearing metal 11 is slidably contacted when the bearing metal 11 is assembled are divided before the connecting rod base material 1 is divided. Since it can be formed in advance, it is possible to prevent the grinding powder from adhering to the fracture surface as compared with the conventional manufacturing method in which the inclined surface is formed by chamfering after the division.

Furthermore, according to this connecting rod manufacturing method, the first dividing groove 14 is formed in an arrow shape by wire electric discharge machining, and the inclined surfaces (inclined walls 21 and 22) of the arrow are removed by cutting performed thereafter. since unnecessary portions Ru is removed, it is possible to shorten the processing time as compared with the case of removing the unnecessary portion by wire electric discharge machining. In order to remove the unnecessary portion by wire electric discharge machining, it is conceivable to adopt a machining method as shown in FIG.

  The processing method shown in FIG. 7 is a method of forming the inclined walls 21 and 22 by moving the wire 18 so as to draw a V shape in the hole wall surface 3 a of the crankpin hole 3. In this method, the triangular prism-shaped unnecessary portion 23 to be removed (shown by the left-downward hatching in the figure) contacts the electric discharge machining wire 18 when it is cut off from the connecting rod base material 1 at the end of the machining process. In such a case, the wire 18 is disconnected. In this type of wire electric discharge machine, when the wire 18 is broken in the middle of machining, the electric discharge machining must be interrupted to correct the cut end of the wire 18. For this reason, if the electric discharge machining wire 18 is broken in the middle as described above, the cycle time in the manufacturing process for manufacturing the connecting rod will be long.

  The problem that the electric discharge machining wire 18 is disconnected in the machining method shown in FIG. 7 is eliminated by moving the wire 18 so that the grooves are gradually formed deeper as shown in FIGS. can do. That is, as shown in FIGS. 8A to 8C, the groove depth is gradually increased in the groove machining in which the electric discharge machining wire 18 is moved in the circumferential direction of the crank pin hole 3 so as to draw a V shape. The first dividing groove 14 is formed by repeating a plurality of times. The feed amount of the wire 18 in the radial direction of the crankpin hole 3 when grooving is set to be smaller than the outer diameter of the meltable range indicated by a circle in FIG.

By performing grooving in this way, it is possible to prevent small pieces, which are so-called processing scraps, from coming into contact with the wire 18 for electric discharge machining, and thus it is possible to prevent the wire 18 from being disconnected. However, in this machining method, since the feed amount in the radial direction of the crankpin hole 3 is very small, it is necessary for machining to form the first dividing groove 14 having a desired depth by this machining method. Time is significantly increased.
Therefore, as compared with the case where the machining method shown in FIGS. 7 and 8 is adopted, as shown in FIG. 5, the electric discharge machining wire is moved by moving the electric discharge machining wire 18 so as to draw an arrow. The inclined surface can be formed quickly while preventing the 18 from being cut.

  In the above-described embodiment, an example in which the electric discharge machining wire 18 is moved with respect to the connecting rod base material 1 in forming the first dividing groove 14 and the second dividing groove 15 has been shown. The invention is not limited to such a limitation, and it is possible to form both the grooves 14 and 15 by fixing the position of the electric discharge machining wire 18 and moving the connecting rod base material 1 relative to the wire 18. it can.

It is a figure which shows the connecting rod base material in which the groove | channel for division | segmentation was formed by the manufacturing method of the connecting rod which concerns on this invention. It is a front view which shows the state which divided | segmented the connecting rod base material into the connecting rod main body and the cap. It is a front view which expands and shows the 1st groove | channel for a division | segmentation. It is a front view which expands and shows the 2nd groove | channel for a division | segmentation. It is a figure for demonstrating the moving direction of the wire at the time of wire electric discharge machining. It is a figure for demonstrating the procedure when attaching a bearing metal to the connecting rod main body. It is a figure which shows the process example of wire electric discharge machining. It is a figure which shows the process example of wire electric discharge machining.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Connecting rod base material, 2 ... Connecting rod, 3 ... Crank pin hole, 3a ... Hole wall surface, 7 ... Connecting rod main body, 8 ... Cap, 11 ... Bearing metal, 14 ... 1st division | segmentation groove | channel, 15 ... 2nd division | segmentation Grooves, 21, 22, ... inclined walls.

Claims (2)

Splitting grooves extending in the axial direction of the crankpin hole are formed in the hole wall surface of the crankpin hole formed in the connecting rod base material by wire electric discharge machining, and the connecting rod base material is broken by breaking so that these grooves become the starting points of the splitting. A method of manufacturing a connecting rod that is divided into a connecting rod body and a cap ,
The step of forming the dividing groove by moving the electric discharge machining wire so as to draw an arrow pointing in the radial direction of the crankpin hole, and cutting the hole wall surface of the crankpin hole, A cutting process for exposing the inclined walls of the dividing grooves corresponding to the two sides located on the outer side in the radial direction, and a semicircular bearing metal having a semicircular cross section in the crank pin holes of the connecting rod body and the cap after the dividing. A method of manufacturing a connecting rod, comprising: a step of sliding and fitting on a wall . In a connecting rod in which a connecting rod base material is divided into a connecting rod main body and a cap by a fracture surface extending from a groove formed in a hole wall surface of the crankpin hole, the radial direction of the crankpin hole is oriented as viewed from the axial direction of the crankpin hole. A semi-finished connecting rod formed by forming the groove in the shape of an arrow.

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