JPH11754A - Manufacturing method of cylinder block - Google Patents

Abstract

(57) [Problem] To provide a method of manufacturing a cylinder block in which a molded body is supported outside of a bore insert via a projection, between a bore insert and the molded body divided into a plurality of portions by the projection. Make sure that the molten metal flows all over the gap. SOLUTION: A hot water path 1 is provided at a longitudinal end of a projection 11.
3. A method of manufacturing a cylinder block in which a molten metal is poured with 3 provided. There are the following three methods for forming the hot water path 13.
The tip of the projection 11 is retracted from the tip face 1b of the bore insert 1. The shoulder of the facing mold 3a of the bore insert 1 is cut out over the entire circumference in the circumferential direction while keeping the length of the projection 11 as it is. With the length of the projection 11 kept as it is, the bore insert 1 is shortened to form a space between the distal end surface 1b of the bore insert 1 and the facing mold 3a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a cylinder block, and more particularly to a method of manufacturing a cylinder block in which the inner surface of a cylinder bore is formed of a metal matrix composite material (MMC).

[0002]

2. Description of the Related Art Conventionally, a method of manufacturing a cylinder block in which the inner surface of a cylinder bore is made of a metal matrix composite material is shown in FIG.
As shown in FIG. 1, a bore insert 1 having a tapered outer periphery
01, a pre-heated preform, a molded body 102 having a tapered inner periphery and a straight shape having an outer periphery parallel to the axis is disposed, and a bore insert in which the molded body is disposed is disposed in a cavity 104 in a mold 103. Then, the molten metal 105 is poured into the cavity 104 by the injection cylinder 106, and is injected and pressed by the plunger tip 107 to form the compact 10.
The molten metal is impregnated into the molded body 102 only from the outer peripheral surface side of 2 to make the molded body part a metal-based composite material. After cooling, the cylinder block product is removed from the mold 103 and the bore insert 101 and taken out. The process comprises machining the inner surface of the cylinder bore made of the material to form a cylinder bore having a right cylindrical surface of a predetermined dimension. However, the conventional method of manufacturing a cylinder block has the following problems.
In the conventional manufacturing method, a slight clearance 108 is provided between the bore insert 101 and the molded body 102 as shown in FIG.
Always occurs. The clearance 108 is, for example, a tolerance between a taper angle of the bore insert 101 and a taper angle of the molded body 102, a bore insert temperature (for example, 100 to 200 ° C.).
And a temperature variation of the compact temperature (for example, 500 to 900 ° C.). This clearance 10
When pressure is applied to the molten aluminum and the molded body 102 is impregnated with the molten aluminum in a state where the molten metal 8 exists, the molded body 102 generates a compression shear crack 109 as shown in FIG.
That is, when the circumferential compressive stress generated in the molded body 102 by the pressure from the outer periphery exceeds the allowable shear stress, shear fracture occurs along a plane 45 ° to the direction of the compressive force, and buckling occurs along the fracture plane. Is caused, and a portion where the density of the reinforcing fibers of the molded body is high is locally generated. If this part slides with the piston ring in actual use, the wear of the piston ring increases. Further, the molded body 102 is generally formed by immersing a gas-permeable mold in a slurry mixed with reinforcing fibers, sucking the inside of the gas-permeable mold, laminating and forming the reinforcing fibers on the surface of the gas-permeable mold, and then drying. Since it is manufactured by a method of removing the air-permeable mold from the body, the reinforcing fibers are oriented in the circumferential direction and are laminated in the thickness direction (Baumkuchen shape) in the molded body 102, and the interlayer strength is increased. Is relatively weak. for that reason,
When the cracks 109 caused by the compressive shear propagate in the circumferential direction in the middle of the thickness direction to form circumferential cracks 110 (FIG. 14), the molten metal penetrates and solidifies, and this portion is exposed during processing. As shown in FIG.
11 results. If such a portion 111 exists, abnormal wear or seizure of the piston ring occurs during actual use. Further, since the molded body 102 is in surface contact with the bore insert 101, the temperature of the molded body 102 is rapidly reduced, and the molten metal is not easily impregnated into the molded body at the time of pouring, and is impregnated over the entire thickness of the molded body. Before the pressure of the molten metal increases, the unimpregnated portion is compressed and easily crushed over the entire circumference. Since the inner diameter of the molded body is tapered (1 ° or more) due to mold release during the production of the molded body, as shown in FIG. 16, the collapse of the molded body is larger at the portion corresponding to the lower portion of the bore. When machining is performed on the inner surface of the cylinder bore of the cylinder block manufactured in this state, a portion without reinforcing fibers may be exposed,
If this portion slides with the piston ring during actual use, abnormal wear or seizure of the piston ring occurs. In order to solve the problems caused by the application of the molten metal pressure only to the outer peripheral surface of the molded body (that is, at least one of generation of compression shear cracking of the molded body, propagation of the crack in the circumferential direction, and collapse of the molded body) The applicant of the present application has previously filed
143996 (filed on June 2, 1997)
As shown in FIGS. 17 and 18, the molded body 2 having the inner peripheral surface 2 a is divided into the outer peripheral surface 1 a of the bore insert 1 having the plurality of projections 11 extending in the axial direction on the outer peripheral surface 1 a and the inner periphery of the molded body 2. Face 2a
So that a gap 8 through which the molten metal 5 is guided is formed between
A first step of disposing the molten metal 5 into the cavity 4 and impregnating the molten metal 5 into the molded body 2 from the inner peripheral surface 2a and the outer peripheral surface 2b of the molded body 2 to form the composite 2 A method for manufacturing a cylinder block comprising the second step and the second step is proposed. In this method, the molten metal pressure is applied to the molded body from both the outer peripheral surface and the inner peripheral surface, so that the molten metal pressure is balanced, and no compression shear cracks are generated in the molded body. The propagation of the crack in the circumferential direction from the crack is also eliminated, and the inner circumferential side is not crushed. Further, since the molten metal is impregnated from both the outer peripheral surface and the inner peripheral surface, the impregnation speed is high and the molten metal is impregnated into the entire thickness of the molded body before the molten metal pressure becomes high, so that the molded body does not collapse in the thickness direction.

[0003]

However, in the above-mentioned prior application, the molded body 2 must be set in the cavity in the first step so that the molten metal flows around the gap 9 when the molten metal is poured in the second step. Must. That is, as shown in FIGS. 17 and 18, the molten metal flowing from the portion 4a corresponding to the crank journal portion of the cavity 4 communicates with the portion 4a corresponding to the crank journal portion in the gap 8 divided by the protrusion 11. Into the part 8a
Part 4a of gap 8 corresponding to crank journal part
The hot water does not sufficiently enter the portion 8b that is not communicated with the water. As a result, the portion of the molded body 2 that is in contact with the gap portion 8b is
The pressure balance between the inside and outside may be lost, and the molded body 2 may be damaged by an external pressure as shown in FIG. An object of the present invention is to form a gap divided into a plurality of portions by a projection between a bore insert outer peripheral surface and a molded body inner peripheral surface by supporting the molded body on a bore insert having a protrusion protruding from the outer peripheral surface. In the method of manufacturing a cylinder block, in which molten metal flows into the gap at the time of pouring so that molten metal pressure is applied to the molded body from inside and outside, the gap between the bore inner peripheral surface and the molded body inner peripheral surface during molten metal pouring Is to allow the molten metal to flow around all parts.

[0004]

The present invention to achieve the above object is as follows. (1) A gap through which the molten metal is introduced is formed between the outer peripheral surface of the bore insert having a plurality of projections extending in the axial direction on the outer peripheral surface and the inner peripheral surface of the molded body. A first step of disposing the molten metal in the cavity so as to be formed, and impregnating the molten metal with the molten metal from the inner peripheral surface and the outer peripheral surface of the molded body to form a composite of the molded body A method of manufacturing a cylinder block, comprising: forming a plurality of melts to be poured in the second step on the longitudinal ends of the projections in the first step by the projections. A method for manufacturing a cylinder block, in which a hot water path is provided for turning over the entire portion of the gap divided into portions. (2) The cylinder block according to (1), wherein the molten metal path is formed by retreating at least a part of the axial end of each projection in the projection height direction from the axial end surface of the bore insert. Manufacturing method. (3) A portion which faces the projection of the type which faces the bore insert axially while the axial direction end of each protrusion is aligned with the axial end face of the bore insert. Is formed by notching over the entire circumference. (4) The molten metal circulating path is formed between the bore inserter axial end face and the mold facing the bore insert axially by retreating the axial end face of the bore insert from the axial end of each projection. The method for manufacturing a cylinder block according to (1), wherein the molten metal path is formed so as to include a space to be formed.

In the method of manufacturing a cylinder block described in (1), the molten metal path is provided, so that the molten metal may go around the entire circumference through the molten metal path and flow into all portions of the gap divided by the projections. it can. In the method of manufacturing the cylinder block of (2), the length of the projection in the axial direction is shorter than that of the bore insert to form the molten metal path. In the method of manufacturing a cylinder block described in (3) above, the length of the protrusion in the axial direction is kept as it is, and the shoulder of the mold facing the bore insert is cut out to form the molten metal path. In the method of manufacturing a cylinder block described in (4) above, while keeping the axial length of the projection as it is, the bore insert is shortened to form a molten metal path at the tip of the bore insert.

[0006]

1 to 6 show a method for forming a runner of a cylinder block according to a first embodiment of the present invention. FIGS. 7 and 8 show a cylinder block according to a second embodiment of the present invention. 9 and 10 show a method for forming a runner of a cylinder block according to a third embodiment of the present invention. Components common or similar throughout all embodiments of the present invention are denoted by the same reference numerals throughout all embodiments of the present invention.

First, a part of the method for manufacturing a cylinder block according to the present invention which is common to all embodiments of the present invention is as follows.
This will be described with reference to FIGS. The method for manufacturing a cylinder block according to the present invention includes a pre-heated inner and outer peripheral surface 2a,
The molten metal 5 is placed between the outer peripheral surface 1a of the bore insert 1 having a plurality of projections 11 extending in the axial direction on the outer peripheral surface 1a and the inner peripheral surface 1a of the molded body 2. The gap 8 to be guided (preferably a gap having a thickness of about 0.5 mm or more to allow hot water to flow) extends over the entire inner peripheral surface of the molded body 2 (however, when the protrusion 11 contacts the molded body 2). A first step of disposing the molten metal 5 in the cavity 4 so as to be formed, and pouring the molten metal 5 into the cavity 4 so as to form the molded body 2 from both the inner peripheral surface 2a and the outer peripheral surface 2b. And a second step of impregnating the molded body 2 with the molten metal 5 to composite the molded body 2. The molten metal 5 to be poured in the second step is fed around the entire circumference of the bore insert 1 at the longitudinal end of the projection 11 in the first step, that is, the entire part of the gap 8 divided into a plurality of parts by the projection. A hot water path 13 for turning the molten metal 5 is provided.

The method for manufacturing a cylinder block according to the present invention comprises:
A third step of removing the cylinder block product from the mold 3 and the bore insert 1 after cooling and solidifying the molten metal;
Then, the inner surface of the cylinder bore formed of the metal-based composite material is machined to obtain a cylinder bore having a straight cylindrical surface having a predetermined dimension.
May be included.

In FIG. 2, reference numeral 6 denotes an injection cylinder for injecting and pressurizing the molten metal into the cavity 4, and reference numeral 7 denotes a plunger tip of the injection cylinder. In the illustrated apparatus, the bore insert 1 and the molded body 2 are arranged so as to be in the vertical direction, but may be a horizontal mold. The molten metal 5 is, for example, an aluminum molten metal (however, it is not limited to the aluminum molten metal).

The preheating temperature of the molded body 2 may be lower than in the prior art, and the temperature at the time of taking out the preheating furnace was conventionally required to be about 700 ° C. or more.
C or higher. Although the bore insert temperature is lower than that, for example, about 100 to 200 ° C., the temperature drop of the molded body 2 is slowed down by the gap 8 between the molded body 2 and the bore insert 1. Can be lowered.

The relationship between the change in molten metal pressure and the start and completion of impregnation in the second step is as follows. During a predetermined period from the start of the pouring of the molten metal, the pressure of the molten metal hardly increases while the cavity is being filled with the molten metal. When the molten metal fills the cavity, the molten metal pressure starts to rise suddenly, and when the pressing is completed, it is approximately 750 to 850 kg / cm ² (73.5 to 83.3).
MPa). And about 3 to 30 kg / cm at the initial stage where the pressure rises from the pressure sudden increase start point
^{At a} pressure of ² (0.294 to 2.94 MPa), the impregnation of the molten metal into the molded body is performed and completed. When the molten metal pressure is applied only to the outer peripheral surface of the molded body as in the related art, about 3 kg / cm ² (0.2
Although compression shear occurs in the molded body at 94 MPa), in the present invention, since the pressure on the inner and outer peripheral surfaces is balanced or almost balanced, no compression shear is generated until the pressurization is completed.

Next, the operation of the parts common to the above embodiments will be described. Since the molten metal is poured in a state where the gap 8 is formed over the entire circumference except for the projection 11 between the molded body 2 and the bore insert 1, the molded body 2 is poured at the time of pouring and pressurizing in the second step.
Pressure is applied from both the inner peripheral surface 2a and the outer peripheral surface 2b. As a result, the inner and outer pressures of the molded body 2 are balanced, and a surface having a 45 ° inclination in the circumferential direction and a circumferential compressive force of the molded body generated when only the outer peripheral surface is pressed as in the related art. Along with the shear cracks (cracks 109 in FIG. 13), the generation of a dense portion of the reinforcing fibers in the vicinity does not occur. Further, a circumferential crack generated from the tip of the shear crack (crack 11 in FIG. 14)
0) also shows that no shear cracking itself occurs, and
Is pressed in the thickness direction from the inner and outer peripheries, so that there is no force for separating the member in the thickness direction, and therefore, this does not occur.

In addition, it is unlikely that the conventional molding is impregnated only from the outer peripheral surface and the entire periphery of the portion near the bore insert in the thickness direction of the molding is crushed. The reason is as follows. In general, it can be said that if the compressive strength of the molded body is equal to or higher than the pressure at the time when the infiltration of the molten metal into the molded body is completed, the collapse of the molded body will not occur. Pressure is considered high. The reason is that the temperature of the tip portion of the molten metal that penetrates into the compact decreases, so that the solid fraction increases and the viscosity increases. And, as the temperature of the pre-heated molded body is lowered by being cooled by the bore nest as it is closer to the bore nest, the temperature drop at the tip of the molten metal also increases, and Pressure becomes very large. Since the molded body is a porous body, there is a limit in increasing the compressive strength, and it is difficult to prevent the collapse of the molded body by the conventional technology.

On the other hand, in the method of the present invention, the bore nest 1
By providing a gap 8 between the molded body 2 and the inner surface of the molded body 2, the contact between the molded body 2 and the bore insert 1 is minimized, so that the temperature of the preheated molded body 2 is hardly reduced. Since the molten metal is impregnated into the molded body 2 from the inner and outer peripheral surfaces, the distance at which the molded body starts to be crushed can be reduced to half of the conventional distance, and the molten metal can be impregnated also from the inner peripheral surface of the molded body 2. In addition, the total surface area of the surface on which the molten material can be impregnated into the molded body 2 is increased, and even when the molded body has a low compressive strength, the distance at which the molded body starts to collapse (distance from the surface) can be increased. Since the crushing of the molded body 2 is less likely to occur than, the crushing of the molded body as in the related art can be prevented.

Next, a description will be given of a method of forming the molten metal path 13 and its operation in the method of each embodiment of the present invention. In the first embodiment of the present invention, as shown in FIGS. 1 to 6, at least a part of the runner path 13 in the axial direction of the axial end of each projection 11 is formed in the axial direction of the bore insert 1. It is formed by retracting from the end face 1b. The example of FIG. 2 and FIG.
By retreating the entire length of each projection 11 in the projection height direction from the axial end face 1b of the bore insert 1, the projection 1
1 and shorten the length of the projection 11 in the axial direction with the bore insert 1.
3 shows a case where the hot water path 13 is formed by retreating from the axial end face 1b. As shown in FIG. 3, there is no protrusion 11 at the position of
Is continuous over the entire circumference. In this case, as shown in FIG. 4, if the length of the protrusion 11 is too short, the pressure of the molten metal applied to the molded body 2 from the inside of the molded body becomes larger than the pressure of the molten metal applied to the molded body 2 from the outside of the molded body. If the length of the protrusion 11 is too long, the pressure of the molten metal applied to the molded body 2 from the outside of the molded body is larger than the pressure of the molten metal applied to the molded body 2 from the inside of the molded body. May crack. Therefore, it is necessary to select the length of the protrusion 11 in a non-defective area where cracks do not occur. 2 and 3, since the length of the protrusion 11 (the length of the protrusion in the axial direction of the bore insert) is shortened, the distal end of the protrusion 11 in the longitudinal direction (the distal end of the bore insert distal end) is located ahead of the protrusion 11. The hot water path 13
And the molten metal 5 can be supplied to all of the plurality of portions of the gap 8 divided by the projections 11 (not only the portion 18a in FIG. 17 but also the portion 18b).

In the examples shown in FIGS. 2 and 3, when a load due to the difference between the inner and outer melt pressures is applied to the molded body ahead of the tip end surface of the projection, depending on the thickness of the molded body 2 and the speed of the molten metal 5, the tip end surface of the projection and the molded body may be removed. A crack may occur in the molded body 2 at a corner where the surface intersects. In such a case, as shown in FIGS. 5 and 6, a part of the axial end of each projection 11 in the projection height direction (the other part 11a is left as it is) is the axial end face of the bore insert 1. 1b
What is necessary is just to make it retreat more. The molded body 2 is supported to the tip by the remaining portion 11a of the projection 11. 5 and 6, the length of the projection 11 (the length of the projection in the bore insertion axis direction) is partially shortened in the height direction. The molten metal path 13 is secured, and the molten metal 5 can be supplied to all of the plurality of portions divided by the projections 11 in the gap 8.

In the second embodiment of the present invention, FIGS.
As shown in the figure, while the axial end of each projection 11 is aligned with the axial end face 1b of the bore insert, the mold (fixed type) 3a axially facing the bore insert is axially By cutting the opposing part over the entire circumference, the hot water path 1
3 is formed. In this example, the length of the projection 11 is not shortened, and the type is opposed to the bore insert in the axial direction (fixed type).
The hot water path 13 is formed over the entire circumference toward 3a. A part of the hot water path 13 may be a groove as shown in FIG. Regarding the operation of the second embodiment of the present invention, since the runner path 13 is formed in the mold 3a that faces the bore insert 1 in the axial direction, the runner path 13 is secured ahead of the longitudinal end of the projection 11; The molten metal 5 can be supplied to all of the plurality of portions of the gap 8 divided by the protrusions 11 (not only the portion 18a in FIG. 17 but also the portion 18b).

In the third embodiment of the present invention, FIGS.
As shown in FIG. 0, the molten metal path 13 is fixed to the axial end face 1b of the bore insert by shortening the axial length of the bore insert 1 without shortening the axial length of each projection 11. Side 3
A space having a thickness and a circular shape is formed between the space and the space a. Regarding the operation of the third embodiment of the present invention, since the molten metal path 13 is formed between the bore insert 1 and the mold 3a axially opposed to the bore insert 1, the molten metal 5 is divided by the projections 11 in the gap 8. Among the plurality of portions, the gas flows through a portion 8a (corresponding to the portion 8a in FIG. 17) which directly communicates with the journal portion 4a of the cavity 4, and from the portion 8a enters the hot water path 13 and further flows into the hot water path 13
Flows from the gap 8 to a portion 8b (corresponding to the portion 8b in FIG. 17) of the gap 8 which does not directly communicate with the journal portion 4a, so that the entire portion of the gap 8 (the portion 18a in FIG.
The molten metal 5 can also be supplied to b). After the molten metal is solidified, the part solidified in the molten metal path 13 is removed during the cylinder bore inner diameter processing, but can be removed in the same processing step as the bore processing, so that the processing is easy.

[0019]

According to the method of manufacturing a cylinder block according to the first aspect of the present invention, since the molten metal path is provided, the molten metal flows around the entire circumference through the molten metal path and flows into all portions of the gap divided by the projections. can do. According to the method of manufacturing the cylinder block of the second aspect, the runner path can be formed by making the axial length of the protrusion shorter than the bore insert. According to the method for manufacturing a cylinder block of claim 3,
The runner path can be formed by notching the shoulder of the mold facing the bore insert while keeping the axial length of the projection. According to the method of manufacturing the cylinder block of the fourth aspect, the length of the bore in the axial direction is kept as it is, and the length of the bore insert is shortened to form a molten metal path at the tip of the bore insert.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating a state in which a method of manufacturing a cylinder block according to a first embodiment of the present invention is performed. FIG. 1 is applicable to the second and third embodiments of the present invention.

FIG. 2 is a sectional view of one cylinder bore taken along line AA of FIG. 1;

FIG. 3 is a sectional view taken along line BB of FIG. 2;

FIG. 4 is a graph showing the relationship between the occurrence of cracks and the projection length in the method of manufacturing the cylinder block according to the first embodiment of the present invention.

FIG. 5 is a cross-sectional view of the same portion as FIG. 2 when only a part of the protrusion in the height direction in FIG. 2 is retracted from the bore insert tip.

FIG. 6 is a sectional view taken along line BB of FIG. 5;

FIG. 7 shows an apparatus for performing the method according to the second embodiment of the present invention;
FIG. 2 is a cross-sectional view of one cylinder bore along the line AA in FIG. 1.

FIG. 8 shows an apparatus for performing the method according to the second embodiment of the present invention;
FIG. 2 is a sectional view taken along the line CC of FIG. 1.

FIG. 9 shows an apparatus for performing the method according to the third embodiment of the present invention;
FIG. 2 is a cross-sectional view of one cylinder bore along the line AA in FIG. 1.

FIG. 10 is a sectional view of an apparatus for performing the method according to the third embodiment of the present invention, taken along line CC of FIG. 1;

FIG. 11 is a sectional view of an apparatus for performing a conventional method of manufacturing a cylinder block.

FIG. 12 is a sectional view of a bore insert and a formed body in a conventional method.

FIG. 13 is a cross-sectional view of a part of a molded body showing compression shearing of the molded body in a conventional method.

FIG. 14 is a cross-sectional view of a part of a formed body showing a circumferential crack of the formed body in a conventional method.

FIG. 15 is a perspective view of a part of the molded body showing a state where a circumferential crack portion of the molded body is exposed at the time of processing in the conventional method.

FIG. 16 is a cross-sectional view of a part of a cylinder block showing collapse of a formed body in a conventional method.

FIG. 17 is a plan view of an apparatus for carrying out a method of manufacturing a cylinder block, for explaining a problem that would occur if countermeasures against hot water are not taken in the prior application (Japanese Patent Application No. 9-143996).

18 is a sectional view of one cylinder bore taken along line AA of FIG. 17;

19 is a plan view of one cylinder bore of FIG. 17 (when the molded body is damaged).

[Explanation of symbols]

 Reference Signs List 1 bore insert 1a bore insert outer peripheral surface 1b bore insert distal end surface 2 molded body 2a molded inner peripheral surface 3 mold 3a fixed mold 3b movable mold 4 cavity 4a journal part 5 molten metal 8 gap 8a part directly communicating with journal part 8b Portion not directly communicating with journal 11 Projection 13 Hot water path

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Manabu Fujine 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Hiroto Yamazaki 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Masuo Shimizu 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (4)

[Claims] 1. A molten metal is guided from a molded body having an inner peripheral surface to a space between the outer peripheral surface of a bore insert having a plurality of protrusions extending in an axial direction on an outer peripheral surface and the inner peripheral surface of the molded body. A first step of disposing the molten metal in the cavity so as to form a gap, and impregnating the molded body with the molten metal from the inner peripheral surface and the outer peripheral surface of the molded body, A method of manufacturing a cylinder block, comprising: a second step of forming a composite, wherein in the first step, the second end is provided at a longitudinal end of the projection.
A method for producing a cylinder block, in which a molten metal path is provided in which the molten metal poured in the step is routed through all the gaps divided into a plurality of portions by the projections. 2. The molten metal circulating path is formed by retreating at least a part of the axial end of each projection in the projection height direction from the axial end surface of the bore insert.
A method for manufacturing the cylinder block described in the above. 3. The protrusion of a type that is axially opposed to the bore insert while the axial direction end of each protrusion is aligned with the axial end surface of the bore insert. 2. The method for manufacturing a cylinder block according to claim 1, wherein the portion to be formed is formed by notching over the entire circumference. 4. The molten metal circulating path is formed between an axial end face of the bore insert and a mold axially opposed to the bore insert by retreating an axial end face of the bore insert from an axial end of each projection. 2. The method for manufacturing a cylinder block according to claim 1, wherein the molten metal path is formed so as to include a space formed in the cylinder block.