JP2016078275A - Method for forming opening of blow molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming an opening of a blow molding that allows efficient mounting of an insert member and removal of a cut-off piece from the opening.SOLUTION: In a method for forming an opening of a blow molding having an insert member embedded in the opening, an insert mounting device 70 is arranged so as to be close to a blow molding die 60, and the insert mounting device 70 is formed with insert holding parts 71 and cut-off piece locking parts 72. The blow molding die 60 holds a cut-off piece 14 cut off from the opening on a cut-off piece holding part 62. After the insert member 30 is mounted to the blow molding die 60 with the insert member 30 being held by the insert holding parts 71, the insert mounting device 70 is slid and the cut-off piece 14 is sandwiched by the cut-off piece locking parts 72 to remove the cut-off piece 14 from the cut-off piece holding part 62, and mounting of the insert member 30 and removal of the cut-off piece 14 are performed in one step.SELECTED DRAWING: Figure 9

Description

The present invention relates to a method for forming an opening of a blow molded product made of a thermoplastic synthetic resin, and relates to a method for forming an opening of a blow molded product having an insert member in the opening.

Conventionally, as a blow-molded product, for example, a fuel tank structure for automobiles or the like has been made of metal. However, in recent years, the weight of the vehicle is reduced, rust is not generated, and the desired shape is molded. For example, those made of a thermoplastic synthetic resin have come to be used.
For the production of automobile fuel tanks made of synthetic resin, blow molding methods have been often used because of the ease of molding hollow bodies. 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.

A blow molded product fuel tank, which is a hollow body, has an opening for taking in and out components to be mounted inside the tank. The opening is formed by forming the fuel tank body by blow molding and simultaneously forming the opening.
For example, as shown in FIG. 13, an opening 110 and a lid 140 that closes the opening are attached (see, for example, Patent Document 1).

In the configuration of FIG. 13, an insert member 130 that locks the lid 140 around the opening 110 is embedded, the lid 140 is sandwiched between the ring-shaped fixing member 120 and the opening 110, and the fixing member 120 is sandwiched between the insert members 130. Is pressed to fix the lid 140. At this time, in order to seal between the lid 140 and the opening 110, a seal ring 150 is attached therebetween.

When the opening 110 is formed, it is necessary to attach the insert member 130 to the blow molding die 160 in order to embed the insert member 130 in the opening 110. As shown in FIG. 14, the insert member 130 is attached to the blow molding die 160 by attaching the insert member 130 to the insert holding portion 171 at the tip of the insert attachment device 170 attached to a robot arm (not shown).

Then, after the blow molding die 160 is opened and the molded blow molded product is taken out and before the next blow molded product is molded, the insert mounting portion 161 of the portion for molding the opening 110 of the blow molding die 160 is formed. Then, the robot arm is moved, and the insert member 130 is attached by the insert attachment device 170.

At this time, in order to form the opening 110 of the blow-molded product taken out, the excision piece 114 excised from the parison (not shown) is held by the excision-piece holding portion 162 of the blow molding die 160 and blow-molded. It remains in the mold 160 and needs to be removed from the blow mold 160.

In order to remove this excision piece 114, as shown in FIG. 15, the excision piece removing device 180 is provided separately from the insert attachment device 170, and the excision piece removal device 180 is attached either before or after the insertion of the insert member 130. The cut piece 114 was sandwiched and taken out by the cut piece holding portion 181 of the cut piece taking out device 180 after being put in the blow molding die 160.

However, newly providing the cut piece removing device 180 also increases the cost of the device itself, and requires two steps of an insert member 130 attaching step and a cut piece 114 taking out step. As a result, the molding cost increases.
JP 2002-187162 A

  Therefore, this invention provides the formation method of the opening part of the blow molded product with which an insert member is embed | buried under the opening part which can remove the excision piece excised from the opening part while attaching an insert member efficiently. This is the issue.

The present invention of claim 1 for solving the above-mentioned problems is a method for forming an opening of a blow molded product, which is formed of a thermoplastic synthetic resin using a blow molding die, and an insert member is embedded in the opening. ,
An insert mounting device for attaching the insert member to the blow molding die is disposed so as to be close to the blow molding die, an insert holding portion for holding the insert member in the insert mounting device, and an extension extending from the insert holding portion and excising from the opening. Forming a cut piece locking portion for holding the cut piece,
The blow molding die holds the insert member in the portion where the opening of the blow molding die is formed, forms an opening in which the insert member is embedded in the blow molded product at the time of blow molding, and the cut piece is blow molded Hold it on the excision holding part of the mold,
After taking out the blow molded product from the blow mold,
After holding the insert member on the insert holding part of the insert mounting device and mounting the insert member on the blow mold, slide the insert mounting device to hold the cut piece at the cut piece locking part and hold the cut piece Forming an opening of a blow-molded product characterized in that the cut piece is removed from the part and the insert mounting device is moved from the blow mold to perform the attachment of the insert member and the removal of the cut piece in one step. Is the method.

In this invention of Claim 1, the insert attachment apparatus which attaches an insert member to a blow molding die is arrange | positioned so that proximity to a blow molding die, The insert holding part which hold | maintains an insert member in an insert attachment apparatus, From an insert holding part A cut piece locking portion that extends to hold the cut piece is formed. For this reason, while being able to make an insert attachment apparatus and a cutting piece extraction apparatus into one apparatus, an insert member, attachment, and removal of a cutting piece are performed in one process by making an insert attachment apparatus adjoin to a blow molding die. Can do.

In the blow molding die, the insert member is held in the portion where the opening of the blow molding die is formed, so when forming the opening of the blow molding product simultaneously with the molding of the blow molding product with the blow molding die, An insert member can be embedded and formed in the opening, and the opening can be reinforced and a member for attaching the lid member to the opening can be easily attached.

At the time of blow molding, blow molding is performed with a blow molding die to form an opening in which an insert member is embedded in the blow molded product, and to hold the cut piece cut out from the opening in the cut piece holding portion of the blow molding die. At the same time as the molding of the product, the excised piece excised when forming the opening of the blow molded product is held in the excised piece holding part of the blow molding die, and the inside of the blow molding die in which the excised piece is held The position can be clarified.

After taking out the blow molded product from the blow molding die, the insert member is held in the insert holding portion of the insert mounting device, and the insert member is attached to the blow molding die. For this reason, the insert member used for the next molding can be attached to the blow molding die that has molded the blow molded product, and the insert member can be attached to the opening of the next blow molded product simultaneously with the blow molding.

The insert mounting device is slid, the cut piece is clamped at the cut piece locking portion, the cut piece is removed from the cut piece holding portion, and the insert mounting device is moved from the blow molding die to insert the insert member. Removal of the excised piece is performed in one step. For this reason, it is possible to immediately remove the cut piece from the blow mold by using the insert mounting device to which the insert member is mounted, and it is possible to shorten the molding time and improve the efficiency.

The present invention of claim 2 is a method for forming an opening of a blow molded product in which the cut piece holding portion of the blow molding die has an inclined surface.

According to the second aspect of the present invention, since the excised piece holding portion of the blow molding die has an inclined surface, the excised piece can be held in the excised piece holding portion after the opening is formed, and the excised piece is excised. When removing from the piece holder, it can be easily removed because of the inclined surface.

The present invention of claim 3 is a method for forming an opening of a blow-molded product in which the inclined surface of the cut piece holding part has an inclination angle of 10 to 20 degrees.

In the third aspect of the present invention, since the inclined surface of the excision holding part has an inclination angle of 10 to 20 degrees, the excision can be reliably held in the excision holding part, and the excision can be removed from the excision. When removing from the holding part, it can be easily removed due to the inclination angle. When the inclination angle is less than 10 degrees, the inclination angle is small, the resistance when removing the excision piece from the excision piece holding part is large, and when the inclination angle exceeds 20 degrees, the excision piece within the blow mold When it is held on the excision holding part, it becomes easy to come off.

According to a fourth aspect of the present invention, the cut piece holding portion is formed in a truncated cone shape, and the portion with which the cut piece locking portion abuts is a method for forming an opening of a blow molded product having a portion cut out in a planar shape. is there.

In the present invention of claim 4, the excised piece holding part is formed in a truncated cone shape, and the part with which the excised piece locking part abuts has a part that is cut out in a flat shape, so that the excised piece is removed from the excised piece holding part. When removing it, it can be easily removed due to the tilt angle of the truncated cone, and the excised piece held in the flat part of the part where the excised piece locking part abuts becomes flat, and the excised piece is locked. The portion can securely hold the excised piece.

The present invention according to claim 5 is a method for forming an opening of a blow molded product in which a concavo-convex shape is formed on a surface of the cut piece locking portion that comes into contact with the cut piece.

In the fifth aspect of the present invention, since the concavo-convex shape is formed on the surface of the cut piece locking portion that comes into contact with the cut piece, the cut piece locking portion of the insert mounting device securely holds the cut piece, It can be removed from the blow mold.

The present invention of claim 6 is a method of forming an opening of a blow molded product in which the insert holding portion and the cut piece locking portion are respectively attached to a plurality of attachment arms.

In this invention of Claim 6, since the insert holding | maintenance part and the cutting piece latching | locking part were each attached to the some attachment arm, an insert member is reliably hold | maintained with a some insert holding part, and a cutting piece is made into several cutting pieces. The locking portion can be securely held.

The present invention of claim 7 is a method for forming an opening of a blow molded product, which is a fuel tank of an automobile.

In the present invention of claim 7, since the blow molded product is an automobile fuel tank, it is possible to efficiently mold an automobile fuel tank having an opening in which an insert member is embedded. The cut pieces of the fuel tank can be surely removed, and the cut pieces in the fuel tank do not enter.

The insert member is attached to the blow molding die by the insert mounting device, and the insert mounting device is slid, the cut piece is locked by the cut piece locking portion, and the cut piece is removed from the cut piece holding portion. Since the attachment of the member and the removal of the cut piece are performed in one step, the cut piece can be immediately removed from the blow mold by using the insert mounting device with the insert member attached, thereby shortening the molding time. Efficiency can be improved.

It is sectional drawing of the opening part of the fuel tank main body shape | molded by embodiment of this invention. It is a partial expanded sectional view which shows the structure of the part which latches the cover body of the opening part of FIG. It is a perspective view of the lid locking member used for an embodiment of the invention. It is a perspective view of an insert member used for an embodiment of the invention. It is a perspective view before attaching the insert member which is embodiment of this invention to an insert attachment apparatus, and attaching to the shaping | molding part of the opening part of a blow molding die. It is a perspective view of the state where the insert member which is an embodiment of the invention was attached to the insert attachment device and attached to the molding part of the opening of the blow molding die. It is a perspective view of the state where the insert holding part of the insert attaching device which is an embodiment of the invention leaves the insert member, and the excision piece locking part pinches the excision piece. It is the perspective view of the state which the cut piece latching | locking part of the insert attachment apparatus which is embodiment of this invention clamped the cut piece, and took out the cut piece from the blow molding die. It is an expanded sectional view of the state where the insert member which is an embodiment of the invention was attached to the insert attachment device, and was attached to the molding part of the opening of a blow molding die. It is an expanded sectional view of the state where the insert holding part of the insert attaching device which is an embodiment of the invention leaves the insert member, and the excision piece locking part has pinched the excision piece. It is an expanded sectional view of the state where the excision piece latching | locking part of the insert attachment apparatus which is embodiment of this invention clamped the excision piece, and took out the excision piece from the blow molding die. It is a perspective view of the excision piece excised by embodiment of this invention. It is sectional drawing of the opening part of the conventional fuel tank main body. It is an expanded sectional view of the state where the conventional insert member was attached to the insert attachment device and attached to the molding portion of the opening of the blow molding die. It is an expanded sectional view of the state in which the cutting piece latching | locking part of the conventional cutting piece extraction apparatus clamped the cutting piece.

In the embodiment of the present invention, a method for forming an opening of a blow-molded product will be described by taking an example of a method for forming an opening of a fuel tank for an automobile which is a blow-molded product. The present invention can be used not only for the method of forming the opening of the fuel tank, but also for the method of forming the opening in which the insert member of the blow molded product is embedded.

First, the shape of the opening 10 of the automobile fuel tank 1 formed according to the present invention will be described, and then the method of forming the opening 10 of the automobile fuel tank 1 will be described.
FIG. 1 is a cross-sectional view of an opening 10 of a fuel tank 1 according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a portion for locking the lid 40 of FIG. FIG. 3 is a perspective view of the lid attachment member 20 for attaching the lid body 40 in the embodiment of the present invention. FIG. 4 is a perspective view of the insert member 30 embedded in the opening 10 in the embodiment of the present invention.

In the first embodiment of the present invention, as shown in FIGS. 1 and 2, the fuel tank 1 has an opening portion for taking in and out a main body of the fuel tank 1 and a fuel pump (not shown) in the main body. 10 is formed.
The main body of the fuel tank 1 is formed by blow molding, and its outer wall is composed of three layers: an outer layer 2, an inner layer 3, and an intermediate layer 4 formed between the outer layer 2 and the inner layer 3. In blow molding, a parison composed of the above three layers is used.

As the blow molded product, a single layer or a multi-layer parison other than three layers can also be used.
The outer layer 2 and the inner layer 3 are made of a thermoplastic synthetic resin that has high strength and maintains strength against fuel oil, and the intermediate layer 4 is made of a thermoplastic synthetic resin that has very little permeation of fuel oil. .

As shown in FIG. 1, the opening 10 is formed on the upper surface of the fuel tank 1, and a lid 40 is attached to the opening 10 and locked.
As shown in FIG. 2, the locking structure of the lid body 40 in the opening 10 sandwiches the lid 40 between the insert member 30 and the lid mounting member 20 embedded in the opening 10.
The lid body 40 is formed in a substantially disk shape, and a flange portion 41 protruding along the inner periphery of the opening 10 is formed on the lower surface to prevent the lid body 40 from shifting.

As shown in FIG. 3, the lid mounting member 20 that sandwiches the lid 40 has a ring shape and an engaging claw portion 24 extending from an upper flat plate portion 22 having a flat cross-sectional shape. As shown in FIG. 4, the insert member 30 embedded in the opening 10 is formed with a locking hole 32 at a portion corresponding to the engaging claw portion 24. As will be described later, the engaging claw portion 24 is inserted into the locking hole 32 and the lid 40 can be locked.

The opening 10 of the fuel tank 1 is formed integrally with the same material from the fuel tank 1 and extends outward. An insert member 30 is embedded in the opening 10.
As shown in FIGS. 2 and 4, the insert member 30 is made of a metal plate and is formed in a bent substantially cylindrical shape.

The lid mounting member 20 presses the periphery of the lid 40 that closes the opening 10 of the fuel tank 1 against the opening 10 to form an annular upper flat plate portion 22 having a plane parallel to the opening surface. When the is attached to the insert member 30, the entire periphery of the lid 40 can be pressed by the upper flat plate portion 22, the lid 40 can be brought into close contact with the opening 10, and a sealing property can be ensured.

As shown in FIG. 2 and FIG. 3, a lower vertical wall portion 23 that is bent downward with a predetermined width is extended from a plurality of positions on the outer end of the upper flat plate portion 22 of the lid mounting member 20. Further, an engaging claw portion 24 bent in an L shape from the tip of the lower vertical wall portion 23 toward the center of the opening 10 is formed.
As shown in FIG. 4, the insert member 30 has an annular locking upper surface portion 31 having a plane parallel to the opening surface. A plurality of locking holes 32 are formed in the locking upper surface portion 31 in the circumferential direction.

A locking step portion 33 is formed in a stepped manner downward from the end face of the hook in the locking upper surface portion 31. Since the end of the bent portion 12 of the opening 10 on the outside of the vehicle can contact and be held by the locking step 33, the strength of the opening 10 can be increased. Further, the locking flat plate portion 34 is lowered from the position of the locking upper surface portion 31 by the locking step portion 33, and the locking flat plate portion 34 of the insert member 30 is positioned on the lower surface of the bent portion 12 of the opening 10. Can do.

The locking vertical wall portion 35 is bent downward from the locking flat plate portion 34 and is formed in a cylindrical shape. When the insert member 30 is embedded in the opening 10, the locking vertical wall 35 is embedded in the outer layer 2 of the tubular portion 11 of the opening 10. Therefore, the entire insert member 30 can be firmly held by the locking vertical wall portion 35, and the locking vertical wall portion 35 can increase the radial strength of the tubular portion 11 of the opening 10.

As shown in FIG. 2, the opening 10 is formed of a cylindrical portion 11 and a bent portion 12.
The cylindrical portion 11 is formed by extending a thermoplastic synthetic resin wall composed of three layers of an outer layer 2, an inner layer 3 and an intermediate layer 4 constituting the outer wall of the fuel tank 1 outwardly from the fuel tank 1 in a cylindrical shape. Is done. An engaging vertical wall portion 35 of the insert member 30 is embedded in the outer layer 2 of the cylindrical portion 11. As described above, the material constituting the thermoplastic synthetic resin wall of the outer layer 2 enters the fixing hole 36 or the cutout portion of the insert member 30. For this reason, the insert member 30 can be firmly fixed to the opening 10.

Next, the manufacturing method of the opening part 10 of the fuel tank 1 is demonstrated based on FIGS.
As described above, when the insert member 30 is embedded in the opening 10 and the fuel tank 1 is formed, the fuel tank 1 is removed from the blow molding die 60. At that time, as shown in FIG. 5 and FIG. 9, the cut piece 14 cut from the parison to form the opening 10 is formed in the blow mold 60, and the cut piece holding part 62 of the blow mold 60. Is held in.

In order to hold the cut piece 14 cut out from the opening 10 at the time of blow molding in the cut piece holding part 62 of the blow molding die 60, the opening of the fuel tank 1 is simultaneously formed with the molding of the fuel tank 1 by the blow molding die 60. The excision piece 14 excised when forming 10 is held in the excise piece holding part 62 of the blow molding die 60 to clarify the position in the blow molding die 60 where the excision piece 14 is held. it can. For this reason, the excision piece 14 can be reliably taken out in the step of taking out the excision piece 14 described later.

Thereafter, the blow molding process of the next fuel tank 1 is started. Before the blow molding, the insert member 30 used in the next blow molding is attached to the blow molding die 60 and the cut piece is removed from the blow molding die 60. 14 is performed.

As shown in FIG. 9, the cut piece 14 is held by the cut piece holding part 62 of the blow molding die 60, but the cut piece holding part 62 is formed in a truncated cone shape in this embodiment. . Due to the inclination angle of the truncated cone-shaped inclined surface 63, as will be described later, when the cut piece 14 is sandwiched by the cut piece engaging portion 72 of the insert mounting device 70 and moved in the axial direction of the truncated cone, the cut piece 14 Can be easily removed.

It is preferable that the inclined surface 63 of the excision holding part 62 has an inclination angle of 10 to 20 degrees. In this case, when the excision piece 14 is excised from the parison by forming the opening 10, the excise piece 14 can be securely held by the excise piece holding part 62, and there is no hindrance to the blow molding process. When the piece 14 is removed from the cut piece holding portion 62, it can be easily removed due to the inclination angle of the inclined surface 63. Further, the cut piece 14 does not fall into the molded fuel tank 1.

When the inclination angle of the inclined surface 63 is less than 10 degrees, the inclination angle is small, and when the excision piece 14 is removed from the excision piece holding part 62, the resistance that the inclined surface 63 and the excision piece 14 come into contact with each other is large. When the inclination angle of the inclined surface 63 exceeds 20 degrees, it becomes easy to come off when the excision piece 14 is held by the excision piece holding part 62.

The inclined surface 63 of the excision retaining part 62 may have a portion that is cut out in a planar shape when the excision retaining member 72 holds the excision fragment 14. preferable. In this case, when the excision piece 14 is removed from the excision piece holding part 62, the part of the excision piece 14 in which the excision piece locking part 72 abuts on the part cut out in a planar shape (the excision piece 14 shown in FIG. The excised piece locking part 72 can securely hold the flat part 14a). A plurality of planar portions 14a can be provided according to the number of the plurality of cut piece locking portions 72.

Next, as shown in FIG. 5, the insert member 30 is held by the insert holding portion 71 of the insert mounting device 70. The insert holding portion 71 is attached to the insert attachment device 70 by an attachment arm 74 together with a cut piece locking portion 72 described later. A plurality of attachment arms 74 are attached to the insert attachment device 70, and each of the attachment arms 74 is provided with one insert holding portion 71 and one cut piece locking portion 72.

As shown in FIGS. 6 and 9, the insert mounting device 70 holding the insert member 30 is brought close to the blow molding die 60 that is taken out of the fuel tank 1 to open the insert member 30 to the blow molding die. Attach to 60 insert mounting portions 61. At this time, as shown in FIG. 9, a gap is provided between the cut piece 14 and the cut piece locking portion 72 of the insert mounting device 70.

In the blow molding die 60, since the insert member 30 is held by the insert mounting portion 61 which is a portion forming the opening 10 of the fuel tank 1, the insert member 30 used for the next molding is attached to the blow molding die 60. Thus, the insert member 30 can be attached to the opening 10 of the next fuel tank 1.
When forming the opening 10 simultaneously with the molding of the fuel tank 1 that is a blow molded product by the blow molding die 60, the insert 10 can be embedded in the opening 10 to reinforce the opening 10. In addition, the opening 10 can be easily formed.

Next, as shown in FIGS. 7 and 10, the attachment arm 74 of the insert attachment device 70 is slid to hold the resection piece 14 by the plurality of resection piece locking portions 72. At this time, an uneven shape can be formed on the contact surface 73 that contacts the cut piece 14 of the cut piece locking portion 72. In this case, the concavo-convex shape of the contact surface 73 of the cut piece locking portion 72 of the insert mounting device 70 securely holds the cut piece 14, and the cut piece 14 is cut into the cut piece holding portion of the blow molding die 60. 62 can be removed.

After the cut piece locking portion 72 holds the cut piece 14, as shown in FIGS. 11 and 8, the insert attachment device 70 is moved away from the cut piece holding portion 62 of the blow molding die 60. At that time, since the plurality of cut piece locking portions 72 securely hold the cut piece 14 and the cut piece holding portion 62 is the inclined surface 63, the insert mounting device 70 is slid in the lateral direction so that the cut piece 14 is cut. Can be removed from the cut piece holder 62.

Thus, in order to attach the insert member 30 to the blow molding die 60 and remove the excised piece 14 from the excised piece holding part 62, the insert member 30 can be attached and the excised piece 14 can be removed in one step. it can. For this reason, the cutting piece 14 can be immediately removed from the blow molding die 60 by using the insert attaching device 70 to which the insert member 30 is attached, and the molding time can be shortened and the efficiency can be improved.
Thereafter, the parison is blow-molded by a blow molding die 60 by a normal blow molding method, and the fuel tank 1 can be molded.

DESCRIPTION OF SYMBOLS 1 Fuel tank main body 10 Opening part 14 Cut piece 30 Insert member 60 Blow molding die 61 Insert mounting part 62 Cut piece holding part 70 Insert mounting apparatus 71 Insert holding part 72 Cut piece locking part 74 Mounting arm

Claims (7)

In the method of forming an opening of a blow molded product, which is formed of a thermoplastic synthetic resin using a blow molding die, and an insert member is embedded in the opening,
An insert mounting device for attaching the insert member to the blow molding die is disposed so as to be close to the blow molding die, and an insert holding portion for holding the insert member in the insert mounting device, and extending from the insert holding portion And forming a cut piece locking portion for holding the cut piece cut from the opening,
The blow molding die is configured to hold the insert member in a portion of the blow molding die that forms the opening, and form the opening in which the insert member is embedded in the blow molded product at the time of blow molding, Holding the excised piece in the excised piece holding part of the blow mold,
After taking out the blow molded product from the blow mold,
After holding the insert member on the insert holding portion of the insert mounting device and mounting the insert member on the blow molding die, the insert mounting device is slid to hold the cut piece at the cut piece locking portion. And removing the cut piece from the cut piece holding part and moving the insert mounting device from the blow molding die to perform the attachment of the insert member and the removal of the cut piece in one step. A method for forming an opening of a blow molded product. The method for forming an opening of a blow molded product according to claim 1, wherein the cut piece holding portion of the blow mold has an inclined surface. The method for forming an opening of a blow-molded product according to claim 2, wherein the inclined surface of the cut piece holding part has an inclination angle of 10 to 20 degrees. The blow piece according to any one of claims 1 to 3, wherein the cut piece holding portion is formed in a truncated cone shape, and a portion with which the cut piece engaging portion abuts has a flat cutout portion. A method for forming an opening of a molded product. The method for forming an opening of a blow-molded product according to any one of claims 1 to 4, wherein a concavo-convex shape is formed on a surface of the cut piece locking portion that comes into contact with the cut piece. The method for forming an opening of a blow molded product according to any one of claims 1 to 5, wherein the insert holding portion and the cut piece locking portion are respectively attached to a plurality of attachment arms. The method for forming an opening of a blow molded article according to any one of claims 1 to 6, wherein the blow molded article is a fuel tank of an automobile.