A device for strengthening a straight pipe, including a first positioning mold, a second positioning mold, a split mold, a rounding mold, a first cavity and a second cavity. A method for strengthening a straight pipe is further provided. The split mold is adjusted to position the pipe. The pipe is inserted into the first and second positioning molds. First and second sealing rings are arranged in an inner cavity of the pipe. Hydraulic oil is injected into the first cavity to expand the pipe to perform an expanding deformation. When the hydraulic oil is unloaded, the split mold moves towards an axis of the first positioning mold to perform a reducing deformation. After the expanding and reducing deformations, the pipe is transported into the rounding mold, and hydraulic oil is injected into the second cavity to expand the pipe to perform the rounding.

A bellows having tweezers-shaped corrugated portions for increasing resistance and restoring force against torsion includes: a first flat part having a flat cylindrical shape; a second flat part having a flat cylindrical shape and disposed opposite to the first flat part; and a plurality of corrugated portions, each having a tweezers shape and disposed between the first flat part and the second flat part, wherein each of the plurality of corrugated portions is sequentially connected to each other, so as to increase resistance and restoring force against torsion.

A bellows having tweezers-shaped corrugated portions for increasing resistance and restoring force against torsion includes: a first flat part having a flat cylindrical shape; a second flat part having a flat cylindrical shape and disposed opposite to the first flat part; and a plurality of corrugated portions, each having a tweezers shape and disposed between the first flat part and the second flat part, wherein each of the plurality of corrugated portions is sequentially connected to each other, so as to increase resistance and restoring force against torsion.

Disclosed is a method for forming a tube with high internal pressure and low external pressure. The method comprises: putting a tube to be formed into a cavity, such that a bulging area (15) is formed between the tube to be formed and an inner wall of the cavity; continuously injecting a low-pressure fluid into the bulging area, and then injecting a high-pressure fluid into the interior of the tube to be formed, the high-pressure fluid creating a pressure on an outer wall of the tube to be formed such that the tube to be formed starts to expand to the bulging area; stopping the supply of the low-pressure fluid when the tube is bulged to conform to the inner wall of the cavity; and taking the formed tube out to complete a working cycle. Further disclosed is a forming machine for forming a tube according to the above method. According to the machine for forming a tube with high internal pressure and low external pressure, a mold body (1) is provided with a first through hole (13) and a second through hole (14) for circulating a low-pressure fluid into and out of a bulging area, so as to create a certain pressure P1 on the tube and ensure uniform bulging of the entire tube, thereby achieving a better forming effect.

A method and device for manufacturing a large-sized thin-walled tubular part by gas-liquid internal high pressure forming (IHPF). A gas and a liquid are filled at a certain volume ratio into a thin-walled blank. The pressure of the gas-liquid mixed fluid is mainly determined by the gas pressure. During the deformation of the thin-walled blank, due to a large compression ratio of the gas, the gas-liquid pressure will not basically change with the change of the volume of a blank cavity. A support pressure on the cavity of the thin-walled blank is stable in the entire forming process. In addition, even if there is a slight leakage of the liquid or gas during the forming process, the medium pressure inside the blank will not fluctuate largely. In this way, embodiments lower the requirements for the sealing effect during the tubular part forming process.

An expansion forming apparatus that shapes a metal material with a die includes an electrode that comes into contact with the metal material and performs energization heating, and an electrode mounting unit having an electrode movement actuator that moves the electrode along an extension direction of the metal material during heating.

A forming device includes a blow-forming die and a shielding member. The blow-forming die includes a first die that protrudes from a first die holder towards a second die holder and a second die that protrudes from the second die holder towards the first die holder. The shielding member is configured to extend from the first die holder to the second die holder before the blow-forming die commences forming a flange part of a pipe in a sub-cavity part. The sub-cavity part is between a main cavity part and the shielding member. The shielding member is separated from the first die and the second die.

A forming device includes a blow-forming die and a shielding member. The blow-forming die includes a first die that protrudes from a first die holder towards a second die holder and a second die that protrudes from the second die holder towards the first die holder. The shielding member is configured to extend from the first die holder to the second die holder before the blow-forming die commences forming a flange part of a pipe in a sub-cavity part. The sub-cavity part is between a main cavity part and the shielding member. The shielding member is separated from the first die and the second die.

A forming device that forms a metal pipe by heating and expanding a metal pipe material includes: a pair of an upper die and a lower die between which the metal pipe material is heated and expanded; upper electrodes and lower electrodes that sandwich both end parts of the metal pipe material therebetween from upper and lower sides to heat the metal pipe material; and a busbar that is connected only to either the upper electrodes or the lower electrodes to supply electric power from a power supply.

A forming device that forms a metal pipe by heating and expanding a metal pipe material includes: a pair of an upper die and a lower die between which the metal pipe material is heated and expanded; upper electrodes and lower electrodes that sandwich both end parts of the metal pipe material therebetween from upper and lower sides to heat the metal pipe material; and a busbar that is connected only to either the upper electrodes or the lower electrodes to supply electric power from a power supply.