JP2016016794A - Manufacturing method of flange part of fuel tank for automobile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a tank flange part of a fuel tank for an automobile capable of easily forming a flange attachment hole on a tank flange part of the fuel tank.SOLUTION: A manufacturing method of a flange part of a fuel tank for an automobile which is formed by a blow molding includes a process of forming a flange attachment hole on a tank flange part 2. In the process of forming the flange attachment hole, ring-shaped protrusion parts 52, 62 which form an inner circumference of the flange attachment hole are provided on a part for forming the tank flange part 2 of a blow molding mold, and the protrusion parts are pushed against the tank flange part 2 to form a flange attachment hole cutting part 23 and a flange attachment hole thin wall part 24. After taking out a fuel tank main body 7 from the blow molding mold, the flange attachment hole thin wall part 24 is cut and the flange attachment hole cutting part 23 is taken out to form the flange attachment hole.SELECTED DRAWING: Figure 6

Description

The present invention relates to a method of manufacturing a flange portion of a fuel tank for an automobile that is attached under a floor panel of the automobile.

Conventionally, the structure of fuel tanks for automobiles and the like has been made of metal, but in recent years, thermoplasticity has been achieved by reducing the weight of the vehicle, eliminating rust, and easily forming into a desired shape. Those made of synthetic resin have come to be used.
In the production of an automotive fuel tank made of a thermoplastic synthetic resin, a blow molding method has been often used because of the ease of molding a hollow body. In the blow molding method, a parison of a molten thermoplastic synthetic resin member is formed into a cylindrical shape and extruded from above, and the parison is sandwiched between molds and air is blown into the parison to manufacture an automobile fuel tank.

As shown in FIG. 1, a fuel tank 101 manufactured by blow molding has a tank flange portion 102 formed around the fuel tank 101, and the fuel tank 101 is attached to the vehicle body at a corner portion of the tank flange portion 102. A flange mounting hole 103 is formed. Bolts and nuts or clamps are inserted into the flange mounting holes 103 to fix the fuel tank 101 to the vehicle body (see, for example, Patent Document 1).

Conventionally, as shown in FIGS. 8 and 9, the flange mounting hole 103 is manufactured by taking out a fuel tank 101 formed by blow molding from a blow molding die and forming a tank flange formed around the fuel tank 101. A flange mounting hole 103 is formed in the part 102 by a punching machine 170.

As shown in FIG. 8, the tank flange portion 102 of the fuel tank 101 is formed by combining the fuel tank upper side wall 120 and the fuel tank lower side wall 130, and the upper surface and the lower surface of the tank flange portion 102 are the skin layers of the parison. 111 or an outer body layer 112 is formed, and an inner body layer 116 is formed inside. Barrier layers 114 are formed on the upper and lower sides between the outer body layer 112 and the inner body layer 116.

In order to form the flange mounting hole 103, as shown in FIG. 9, before the parison is completely solidified, the tank flange portion 102 is placed on the holding base 172 of the boring machine 170 and positioned by the fixing plate 174. A punch hole 173 corresponding to the flange mounting hole 103 is formed in the holding base 172, and when the drive punch 171 corresponding to the flange mounting hole 103 is moved up and down in the direction of the arrow in FIG. The flange mounting hole 103 from which the portion 123 is removed can be opened.

As shown in FIG. 10, when the flange mounting hole 103 is opened in the tank flange portion 102, the flange mounting hole scrap 123 is generated. However, since the tank flange portion 102 is not completely solidified, Deburring is likely to occur in the surroundings, which takes time for deburring work. Furthermore, the flange mounting hole scrap 123 may stick to the holding base 172 and the punch hole 173, and there is a problem that it takes time and effort to remove it.

In addition, since the outer body layer 112, the barrier layer 114, and the inner body layer 116 are present in the cross section of the flange mounting hole 103, there is a risk that fuel will penetrate into the fuel tank 101 via the inner body layer 116. was there.

JP 2009-132297 A

An object of the present invention is to provide a method for manufacturing a tank flange portion of a fuel tank for an automobile, in which a flange mounting hole can be easily formed in a tank flange portion of a fuel tank formed by blow molding.

The present invention of claim 1 for solving the above-mentioned problems is a method of manufacturing a flange portion of a fuel tank for automobiles formed by blow molding.
Holding the parison between the blow molds formed in a divided manner, forming a fuel tank body, and forming a tank flange around the fuel tank body,
The step of forming the tank flange portion includes the step of forming a flange mounting hole in the tank flange portion,
In the step of forming the flange mounting hole, a ring-shaped protrusion that forms the inner periphery of the flange mounting hole is formed on one or both of the portions that form the tank flange portion of the blow-molded mold formed in a divided manner. When the tank flange is formed, the protrusion is pressed against the tank flange, and the flange mounting hole cut off from the flange mounting hole of the parison, and the tank flange on the outer periphery of the flange mounting hole cutting After forming the flange mounting hole thin part to connect the flange mounting hole cut part and taking out the fuel tank body from the blow molding die, cut the flange mounting hole thin part and remove the flange mounting hole cut part from the flange mounting hole. It is a manufacturing method of the flange part of a fuel tank characterized by taking out and forming a flange attachment hole.

According to the first aspect of the present invention, in a method of manufacturing a flange portion of an automobile fuel tank formed by blow molding, a fuel tank main body is formed by sandwiching a parison between divided blow molding dies. In addition, there is a step of forming a tank flange portion around the fuel tank body. For this reason, the fuel tank main body and the tank flange portion can be integrally formed at the same time, the manufacturing process of the fuel tank can be simplified, and the rigidity of the fuel tank can be improved.

The step of forming the tank flange portion includes a step of forming a flange mounting hole in the tank flange portion. For this reason, in the blow molding process for forming the tank flange portion, the flange mounting hole can be formed at the same time, and the flange mounting hole is not formed in a separate process, and the productivity is good.

In the step of forming the flange mounting hole, a ring-shaped protrusion that forms the inner periphery of the flange mounting hole is formed on one or both of the portions that form the tank flange portion of the blow-molded mold formed in a divided manner. Provided. Therefore, the flange mounting hole can be formed by simultaneously moving the protrusion when closing the blow-molded mold formed separately or by sliding the protrusion when forming the tank flange.

When forming the tank flange part, press the protrusion against the tank flange part to cut the flange mounting hole cut out from the parison flange mounting hole and the flange mounting hole cut part, and the flange on the tank flange part. A flange mounting hole thin portion connecting the mounting hole cut portions is formed. For this reason, the flange mounting hole can be formed with the flange mounting hole cutout portion remaining in the flange mounting hole, and the flange mounting hole cutout portion does not remain in the blow molding die, and the flange mounting hole has no burr. Since it does not remain, manufacturing is easy.

After removing the fuel tank body from the blow molding die, the flange mounting hole thin portion is cut and the flange mounting hole cut out portion is taken out from the flange mounting hole to form a flange mounting hole. For this reason, the flange mounting hole thin portion can be easily cut by hand and the flange mounting hole cut-out portion can be taken out, and the flange mounting hole can be easily manufactured.

According to the present invention of claim 2, the fuel tank is manufactured from a multi-layer parison having a multilayer structure having at least an outer body layer, an outer adhesive layer, a barrier layer, an inner adhesive layer, and an inner body layer. Is the method.

In the present invention of claim 2, the fuel tank has a multilayer structure having at least an outer body layer, an outer adhesive layer, a barrier layer, an inner adhesive layer, and an inner body layer. For this reason, the synthetic resin which has the rigidity of an outer side body layer and an inner side body layer, and has fuel oil resistance can be used. A material having low fuel permeability can be used for the barrier layer. The strength and durability of the upper side wall and the lower side wall can be improved by firmly bonding the barrier layer, the outer main body layer, and the inner main body layer with the outer adhesive layer and the inner adhesive layer.

The present invention of claim 3 is the method for manufacturing the flange portion of the fuel tank in which the inner surface of the flange mounting hole is mostly covered with the skin layer or the outer body layer of the multilayer parison.

In the third aspect of the present invention, the inner surface of the flange mounting hole covers most of the skin layer or the outer main body layer of the multilayer parison. Therefore, the barrier layer covers the inner main body layer at the cut portion of the flange mounting hole. Is covered with the skin layer or the outer body layer of the multi-layer parison, so that the fuel in the fuel tank does not penetrate from the cross section of the flange mounting hole, and the strength of the flange mounting hole portion can be ensured.

When forming the tank flange part, press the protrusion against the tank flange part to form the flange mounting hole cutout part and the flange mounting hole thin part, so that the flange mounting hole cutout part remains in the flange mounting hole, Since the flange mounting hole can be formed, the flange mounting hole cut-out portion does not remain in the blow molding die, and burrs do not remain in the flange mounting hole, so that manufacturing is easy.

After removing the fuel tank body from the blow mold, cut the flange mounting hole thin part and take out the flange mounting hole cut out part from the flange mounting hole to form the flange mounting hole. The flange mounting hole cut-out portion can be taken out by cutting with ease, and the manufacture of the flange mounting hole is easy.

It is a perspective view of the fuel tank manufactured by this invention. It is an expanded sectional view of the outer wall of the fuel tank main body manufactured by this invention. It is an expanded sectional view of the tank flange part and flange attachment hole of the fuel tank manufactured by this invention. It is an expanded sectional view of a tank flange part of a blow molding die just before clamping a tank flange part, showing a process of forming a flange attachment hole in a tank flange part of a fuel tank of the present invention. It is an expanded sectional view of the flange attachment hole of the tank flange part of the blow mold after showing the process of forming a flange attachment hole in the tank flange part of the fuel tank of the present invention, and pinching the tank flange part. The process of forming a flange attachment hole in the tank flange part of the fuel tank of the present invention is shown. After the flange attachment hole is formed in the tank flange part, the tank flange part of the blow molding die in a state separated from the blow molding die is shown. It is an expanded sectional view of a flange attachment hole. It is an expanded sectional view of a tank flange part in the state where a process of forming a flange attachment hole in a tank flange part of a fuel tank of the present invention was shown and a flange attachment hole scrap was removed from a flange attachment hole of a tank flange part. It is an expanded sectional view of the flange attachment hole of the tank flange part of the conventional fuel tank. It is sectional drawing which shows the process of forming a flange attachment hole in the conventional tank flange part, and has made the flange attachment hole in the tank flange part with the drilling machine. It is an expanded sectional view of the flange attachment hole of the tank flange part of the conventional fuel tank.

In the embodiment of the present invention, first, the structure of the tank flange portion 2 of the fuel tank 1 manufactured by the manufacturing method of the present invention will be described with reference to FIGS. The process of forming the flange mounting hole 3 in the tank flange portion 2 of the tank 1 will be described with reference to FIGS.

The fuel tank 1 manufactured in the embodiment of the present invention is formed by blow molding, and the fuel tank outer wall 10 which is the outer wall of the fuel tank main body 7 is formed from one parison with the fuel tank upper side wall 20 and the fuel tank lower side wall 30. Are integrally formed. And the fuel tank upper side wall 20 and the fuel tank lower side wall 30 protrude in the outer peripheral direction at the connecting portion to be connected, and the tank flange portion 2 is formed.

As shown in FIG. 1, a flange attachment hole 3 for attaching the fuel tank 1 to the vehicle body is formed at a corner portion of the tank flange portion 2. The flange mounting hole 3 is appropriately formed not only at the corner portion but also at a portion necessary for fixing the fuel tank 1 to the vehicle body. Bolts and nuts (not shown), clamps or the like can be inserted into the flange mounting holes 3 and fixed to the vehicle body.

As shown in FIG. 3, the flange mounting hole 3 is formed in the tank flange portion 2. The tank flange portion 2 is formed to protrude from the fuel tank outer wall 10 of the fuel tank 1, and the tank flange portion 2 The tank upper side wall 20 and the fuel tank lower side wall 30 are formed in a united portion. The tank flange portion 2 can improve the strength of the fuel tank body 7.
The fuel tank outer wall 10 is formed of one parison, and both the fuel tank upper side wall 20 and the fuel tank lower side wall 30 have the configuration shown in FIG.

In the present embodiment, the fuel tank body 7 is formed by multi-layer blow molding, and the fuel tank upper side wall 20 and the fuel tank lower side wall 30 of the fuel tank outer wall 10 have an integral synthetic resin multi-layer structure, as shown in FIG. As shown, the outer skin layer 11, the outer body layer 12, the outer adhesive layer 13, the barrier layer 14, the inner adhesive layer 15, and the inner body layer 16 are formed in order from the outside. The composition of each layer will be described later.

In the embodiment of the present invention, the parison composed of the above six layers is used in blow molding. However, it is possible to use a single layer or a parison having a layer configuration other than six layers. Further, as will be described later, the skin layer 11 is used when a reproducing member, a filler, or the like is mixed into the outer body layer 12, but the skin layer 11 may be omitted.

As shown in FIG. 3, the tank flange portion 2 in which the flange mounting hole 3 is formed has an upper surface made of the material of the fuel tank upper side wall 20 and a lower surface made of the material of the fuel tank lower side wall 30. In the present embodiment, the outermost layers of the upper surface and the lower surface of the tank flange portion 2 are formed by the skin layer 11, and the outer body layer 12, the outer adhesive layer 13, the barrier layer 14, and the inner adhesive are formed inside the skin layer 11. It is formed continuously with the layer 15. The inner main body layer 16 of the fuel tank upper side wall 20 and the fuel tank lower side wall 30 is united with the inner center of the barrier layer 14.

In the flange mounting hole 3, the inner surface of the flange mounting hole 3 is covered with the outer body layer 12 from the skin layer 11 of the multilayer parison. Inside the outer body layer 12, the inner body layer 16 is covered by the barrier layer 14, so that the fuel in the fuel tank does not permeate from the flange mounting hole 3, and the strength of the flange mounting hole 3 can be ensured. it can.

As shown in FIG. 1, a pump unit mounting hole 4 is formed in a fuel tank upper wall 20 of the fuel tank main body 7 for taking in and out a fuel pump (not shown) and the like. After the fuel pump (not shown) is mounted in the fuel tank 1 from the pump unit mounting hole 4, the pump unit mounting hole 4 can be closed by a pump unit mounting lid (not shown).

Further, an inlet pipe connecting portion 5 for connecting to an inlet pipe (not shown) for injecting fuel into the fuel tank 1 from a fuel filler port (not shown) provided in the vehicle body is attached to the upper side wall 20 of the fuel tank. ing. An attachment portion 6 such as a fuel pipe attachment portion for sending fuel from the fuel pump to the engine is also attached. Furthermore, an electric cord for driving the fuel pump and various pipes for adjusting the evaporated fuel in the fuel tank 1 are attached.

The composition of the fuel tank outer wall 10 is that the outer skin layer 11 and the outer body layer 12 are made of a thermoplastic synthetic resin that has high impact resistance and maintains rigidity against fuel oil, and is made of high-density polyethylene (HDPE). Preferably it is formed. When the outer main body layer 12 contains an inorganic filler, the outer skin layer 11 is used to cover the surface of the outer main body layer 12, so that the inorganic filler does not appear on the surface and the surface can be smoothed. .

The outer body layer 12 may be formed using a recycled material mainly containing high-density polyethylene (HDPE) as a main material. Recycled materials mainly containing high-density polyethylene (HDPE) are used, for example, when the fuel tank 1 collected after use is crushed and recycled and used during the manufacturing process of the fuel tank 1 In some cases, scraps and defective products generated in the above are crushed and recycled. Since the fuel tank 1 is mainly composed of high density polyethylene (HDPE), the recycled material obtained by pulverizing the fuel tank 1 mainly has high density polyethylene (HDPE).
There are cases where 100% of these recycled materials are used and cases where new high density polyethylene (HDPE) is mixed with the recycled materials.

The barrier layer 14 is made of a thermoplastic synthetic resin that has very little permeation of fuel oil. The thermoplastic synthetic resin constituting the barrier layer 14 is, for example, ethylene vinyl alcohol copolymer (EVOH), polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide (PPS), liquid crystal polymer (LCP), semi-aromatic nylon (PPA). Can be used, but ethylene vinyl alcohol copolymer (EVOH) is preferred.
Since the barrier layer 14 is provided, fuel oil such as gasoline that has permeated the inner body layer 16 described later can be prevented from permeating through the barrier layer 14, and the fuel oil can be prevented from evaporating into the atmosphere.

When an ethylene vinyl alcohol copolymer (EVOH) is used as the barrier layer 14, the barrier layer 14 is excellent in gasoline permeation prevention and can be melt-molded and processed. Moreover, it is excellent in gasoline permeation prevention even under high humidity. Furthermore, it can have excellent permeation resistance for gasoline containing alcohol.

The outer adhesive layer 13 is provided between the outer body layer 12 and the barrier layer 14 to bond the two layers, and the inner adhesive layer 15 is provided between the inner body layer 16 and the barrier layer 14. Adhere these two layers. The outer adhesive layer 13 and the inner adhesive layer 15 are formed of the same material, and are formed of a synthetic resin having adhesiveness to both the high density polyethylene (HDPE) and the barrier layer 14. Therefore, the outer adhesive layer 13 and the inner adhesive layer 15 are firmly bonded to the barrier layer 14, the outer body layer 12 and the inner body layer 16, respectively, and the respective layers are in close contact with each other, The fuel permeation preventing property and strength of the fuel tank outer wall 10 can be ensured.

As an adhesive thermoplastic synthetic resin used for the outer adhesive layer 13 and the inner adhesive layer 15, for example, a modified polyolefin resin can be used, and an unsaturated carboxylic acid modified polyolefin resin, particularly an unsaturated carboxylic acid. A modified polyethylene resin is preferred. This can be produced by copolymerizing or graft-polymerizing an unsaturated carboxylic acid to a polyolefin resin.
As described in the skin layer 11, the inner main body layer 16 uses high-density polyethylene (HDPE), which is the same material as that used by the skin layer 11.

Next, the process of forming the flange mounting hole 3 in the tank flange portion 2 of the fuel tank 1 for an automobile will be described with reference to FIGS.
The fuel tank 1 is molded by sandwiching the parison between the blow upper mold 50 and the blow lower mold 60 of the blow molding die 40 divided into two parts, blowing the parison, and fueling with the blow upper mold 50. The tank upper side wall 20 is formed, and the fuel tank lower side wall 30 is formed by the blow lower mold 60. At this time, as shown in FIG. 1, the fuel tank upper side wall 20 and the fuel tank lower side wall 30 around the fuel tank 1 are sandwiched by a blow upper mold 50 and a blow lower mold 60, and are connected to a tank flange. Part 2 is formed.

As described above, a plurality of flange attachment holes 3 for attaching the fuel tank 1 to the vehicle body are formed in the corner portion of the tank flange portion 2. The flange mounting hole 3 has one reference hole as a round hole, and the other hole is formed to be slightly larger than the long hole or the reference hole so as to absorb expansion and contraction of the fuel tank 1 or dimensional variation. Can do.
As shown in FIG. 4, an upper mold nesting part 51 and a lower mold nesting part 61 are attached to the blow upper mold 50 and the blow lower mold 60, which are portions that form the flange mounting holes 3, respectively.

The upper mold nest 51 is formed with a ring-shaped upper mold first protrusion 52 for forming the flange mounting hole 3, and the flange mounting hole cutout 23 is formed inside the upper mold first protrusion 52. A stowable upper die cutout recess 53 is formed. On the outer peripheral side of the upper mold first protrusion 52, an upper mold flange concave portion 54 in which the tank flange portion 2 can be formed is formed. An upper mold second protrusion 56 is formed on the outer periphery of the upper mold flange recess 54 in order to separate the tank flange part 2 and the tank flange part cutting part 25. An upper mold cutout recess 55 that can accommodate the tank flange cutout portion 25 is formed.

Similarly to the upper mold insert 51, the lower mold insert 61 is formed with a ring-shaped lower mold first protrusion 62 for forming the flange mounting hole 3. Is formed with a lower die cutout recess 63 in which the flange mounting hole cutout portion 23 can be accommodated. A lower mold flange recess 64 in which the tank flange portion 2 can be formed is formed on the outer peripheral side of the lower mold first protrusion 62. A lower mold second projection 66 is formed on the outer periphery of the lower mold flange recess 64 in order to separate the tank flange portion 2 and the tank flange portion cutting portion 25. A lower mold cutting recess 65 that can accommodate the tank flange cutting section 25 is formed.

When the upper tank side wall 20, the fuel tank lower wall 30 and the tank flange portion 2 are formed, and the upper blow mold 50 and the lower blow mold 60 are closed as shown in FIG. The mold insert 61 is also closed to form the flange mounting hole 3. Note that, after the tank flange portion 2 is formed, the upper mold insert 51 and the lower mold insert 61 can be slid and brought into contact with each other as a slide core.

At this time, the tips of the upper mold first protrusion 52 and the lower mold first protrusion 62 are in contact with each other, and a thin flange mounting hole thin portion 24 is formed in the contact portion. A flange mounting hole cutout portion 23 is formed in the upper die cutout recess 53 and the lower die cutout recess 63, and the flange mounting hole cutout portion 23 is held on the inner peripheral surface of the flange mounting hole 3 by the flange mounting hole thin portion 24. Has been.

The tips of the upper mold second protrusion 56 and the lower mold second protrusion 66 are in contact with each other, and a thin tank flange portion thin portion 26 is formed in the contact portion. A tank flange portion cutout portion 25 is formed in the upper mold cutout recess portion 55 and the lower mold cutout recess portion 65, and the tank flange portion cutout portion 25 is held on the outer peripheral side of the flange mounting hole 3 by the tank flange portion thin portion 26. Has been.

In the present embodiment, the upper mold first protrusion 52 and the lower mold first protrusion 62 and the upper mold second protrusion 56 and the lower mold second are formed on both the upper mold nest 51 and the lower mold nest 61. The protrusion 66 is formed, but the first protrusion and the second protrusion are formed on one of the upper mold nest 51 and the lower mold nest 61, and the other is formed in a planar shape. The flange mounting hole cutout portion 23 and the flange mounting hole thin portion 24, and the tank flange portion cutting portion 25 and the tank flange portion thin portion 26 are formed by bringing the protrusion and the second protrusion into contact with the flat portion. You can also

When the blow molding is completed and the blow upper mold 50 and the blow lower mold 60 are opened as shown in FIG. 6, the upper mold insert 51 and the lower mold insert 61 are also opened, and the flange mounting hole 3 has a flange. The mounting hole cutout portion 23 is held by the flange mounting hole thin portion 24, and the tank flange portion cutout portion 25 is also held by the tank flange portion thin portion 26 and can be taken out from the blow molding die 40 together with the fuel tank body 7. .

For this reason, the flange mounting hole 3 is formed while the flange mounting hole cutout portion 23 is held in the flange mounting hole 3 and the tank flange portion cutting portion 25 is held in the tank flange portion 2, and is taken out from the blow molding die 40. Therefore, the flange mounting hole cutout portion 23 and the tank flange portion cutout portion 25 do not remain in the blow molding die 40, and no burrs remain in the flange mounting hole 3, so that manufacture is easy. .

After the fuel tank body 7 is taken out from the blow molding die 40, as shown in FIG. 7, the flange mounting hole thin portion 24 is cut and the flange mounting hole cut-out portion 23 is taken out from the flange mounting hole 3, and the flange mounting hole is removed. 3 is formed. At this time, since the flange mounting hole thin portion 24 is formed thin, it can be easily cut by hand and the flange mounting hole cutout portion 23 can be taken out, and the flange mounting hole 3 can be easily formed. . The tank flange portion cutout portion 25 can also be easily cut from the tank flange portion 2 by hand or the like.

DESCRIPTION OF SYMBOLS 1 Fuel tank 2 Tank flange part 3 Flange mounting hole 7 Fuel tank main body 10 Fuel tank outer wall 20 Fuel tank upper side wall 23 Flange mounting hole cutout part 24 Flange mounting hole thin part 30 Fuel tank lower side wall 40 Blow molding die 50 Blow upper mold 60 Blow lower mold

Claims (3)

In the manufacturing method of the flange part of the fuel tank for automobiles formed by blow molding,
Holding the parison between the blow molds formed in a divided manner, forming a fuel tank body, and forming a tank flange portion around the fuel tank body,
The step of forming the tank flange portion includes the step of forming a flange mounting hole in the tank flange portion,
The step of forming the flange mounting hole is a ring-shaped structure in which the inner periphery of the flange mounting hole is formed in one or both of the parts forming the tank flange portion of the blow-molding die formed separately. When the tank flange portion is formed, the flange mounting hole cut-out portion cut from the flange mounting hole of the parison by pressing the protrusion against the tank flange portion and the flange mounting A flange mounting hole thin portion for connecting the flange mounting hole cutting portion to the tank flange portion is formed on the outer periphery of the hole cutting portion, and after removing the fuel tank body from the blow molding die, the flange mounting hole thin portion And the flange mounting hole cut out portion is taken out from the flange mounting hole to form the flange mounting hole. Manufacturing method of the flange portion. 2. The method of manufacturing a flange portion of a fuel tank according to claim 1, wherein the fuel tank is formed of a multilayer parison having a multilayer structure having at least an outer body layer, an outer adhesive layer, a barrier layer, an inner adhesive layer, and an inner body layer. . The method for manufacturing a flange portion of a fuel tank according to claim 2, wherein the inner surface of the flange mounting hole covers most of the skin layer or the outer body layer of the multilayer parison.