LU502231B1 - Method for thinning and forming inner wall of elongated hollow tube - Google Patents

Abstract

The present invention discloses a method for thinning and forming an inner wall of en elongated hollow tube, including the following steps performed by a spinning machine and a three-roll skew rolling mill: first, locally thinning the inner wall of the elongated hollow tube on the spinning machine by using an internal spinning process, such that an end of the elongated hollow tube has a wall thickness greater than that of a middle section of the elongated hollow tube; and then machining an outer wall of the machined elongated hollow tube on the three-roll skew rolling mill by using a skew rolling process, so as to reduce a positioning outer diameter of the end of the elongated hollow tube to form a necking. Due to the fact that the elongated hollow tube is first locally thinned, and a necking process is then performed on the end, the present invention has the following advantages: a necked portion of a part can meet a requirement for a thickening amount, the whole part can be cold-formed without the need for cutting a blank, and the material utilization rate is high.

Description

Description LU502231 Title: METHOD FOR THINNING AND FORMING INNER WALL OF ELONGATED HOLLOW

TUBE Technical Field The present invention relates to the technical field of plastic forming, and in particular to a method for thinning and forming an inner wall of en elongated hollow tube. Background Art A process for reducing in diameter, thickening and necking an end of a traditional hollow tube part (such as a pull rod of an aircraft) is performed with a hot necking process. In this process, the end of the part is locally hot-formed, which destroys the consistency of the microstructure of the part. Therefore, the formed part needs to be heat-treated, so that the process is complicated and costly. The necking is performed with a cold forging process. Four forging dies are provided. A high-speed rotating part is forged with one of the dies at a time to realize the necking. However, this process has a low rate of finished products, an unstable forming process, and very high consistency requirements for a rotational speed, a feed speed of parts and a feed speed of dies, and can easily cause defects such as indentation and substandard roundness on the surface of the parts. Therefore, it is necessary to seek a new process for reducing in diameter, thickening and necking an end of en elongated hollow tube, for example, Chinese Patent Publication No. CN 102581016 B with the date of authorized announcement of 05 March 2014, entitled “MACHINING METHOD FOR THICKENING LOCAL PORTION OF STEEL TUBE”, discloses a forming method, including the following steps: 1) concentrically mounting a die (1), which is provided with a hydraulic ejector rod, on a guide rail at one end of a rotary rolling mill 4; 2) heating a portion of a steel tube that needs to be thickened in an induction heating furnace at a heating temperature of 900°C - 1200°C; 3) transferring the steel tube into the rotary rolling mill and positioning and clamping the steel tube; 4) starting the rotary rolling mill to drive the steel tube to rotate, with a rotating speed n of the steel tube being 175-200 r/min; 5) controlling the die to advance and operate, and thickening the portion to be thickened of the steel tube; and 6) after the heated portion of the steel tube reaches a required thickening amount and the die returns to an initial position, stopping the rotary rolling mill, removing the steel tube, and ending the thickening process of the steel tube. However, the forming method mentioned above still has some problems. For example, for the production of some parts with high size requirements, a thickening amount of a skew rolling mill is limited by the die, and it is difficult to meet the requirements. In addition, this is a hot processing process, which still destroys the consistency of the microstructure of the parts.

Therefore, the formed part needs to be heat-treated, so that the process is complicated and costl{U502231 Summary of the Invention An objective of the present invention is to provide a method for thinning and forming an inner wall of en elongated hollow tube in order to overcome the deficiencies in the prior art. A new combined forming process is proposed, in which the elongated hollow tube is first locally thinned, and a necking process is then performed on an end thereof, so that a necked portion of a part can meet a requirement for a thickening amount, the whole part can be cold-formed without the need for cutting a blank, and the material utilization rate is high. In order to achieve the objective, the present invention uses the following technical solution: a method for thinning and forming an inner wall of en elongated hollow tube includes the following steps performed by a spinning machine and a three-roll skew rolling mill: (1) locally thinning the inner wall of the elongated hollow tube on the spinning machine by using an internal spinning process, such that an end of the elongated hollow tube has a wall thickness greater than that of a middle section of the elongated hollow tube; and (2) machining an outer wall of the elongated hollow tube machined in Step (1) on the three- roll skew rolling mill by using a skew rolling process, so as to reduce a positioning outer diameter of the end of the elongated hollow tube to form a necking.

Preferably, in Step (1), the middle section of the elongated hollow tube is in a machining region of the spinning machine, so as to reduce the wall thickness of the middle section of the elongated hollow tube. The thickness of the end of the elongated hollow tube remains unchanged. The spinning machine directly reduces the wall thickness of the middle section of the elongated hollow tube. Conversely, the end of the elongated hollow tube has a thickening effect.

Preferably, after the elongated hollow tube is machined by the spinning machine, a ratio of the wall thickness of the middle section of the elongated hollow tube to the wall thickness of the end of the elongated hollow tube is 0.2-0.8. The wall thickness of the middle section of the elongated hollow tube needs to be thinned within a rational range to ensure final forming quality. The middle section that is too thin is likely to affect surface forming quality, and is easy to be twisted and deformed, the middle section that is too thick cannot meet an ideal relative thickening requirement, and is not conducive to deformation during a next step of skew rolling.

Preferably, in Step (1), an inner wall of the middle section of the elongated hollow tube is connected to an inner wall of the end of the elongated hollow tube via an inner conical surface, and the inner conical surface is used for transition of a spinning roller. The inner conical surface is mainly used for feed transition of the spinning roller, and is also used for smooth transition between the inner wall of the middle section of the elongated hollow tube and the inner wall of the end of the elongated hollow tube.

Preferably, in Step (2), the end of the elongated hollow tube is in a machining region of theU502231 three-roll skew rolling mill. The three-roll skew rolling mill directly performs a necking process of reducing in diameter and thickening the outer wall, and has a main machining region in which the end of the elongated hollow tube is located, so that better effects of reducing in diameter and thickening the outer wall can be achieved.

Preferably, the elongated hollow tube is cold-formed during the machining in both Step (1) and Step (2). Due to two times of deformation machining, a deformation amount in the single machining is small, which provides a basis for cold forming. In this way, a series of problems in hot forming, such as an uneven microstructure and the need for subsequent heat treatment can be solved.

The beneficial effects of the present invention are as follows. In the present invention, an internal spinning process and a skew rolling process are combined, the inner wall of the elongated hollow tube is first locally thinned in the internal spinning process, and an end of the outer wall of the elongated hollow tube is then necked in the skew rolling process, so that a necked portion of a part can meet a requirement for a thickening amount, and the whole part can be cold-formed, without the problems associated with the microstructure in hot forming and the need for heat treatment. The internal spinning process and the skew rolling process are both plastic forming without the need for cutting a blank, and the material utilization rate is high.

Brief Description of the Drawings FIG. 1 is a schematic structural diagram of en elongated hollow tube of the present invention; FIG. 2 is a schematic structural diagram of the elongated hollow tube of the present invention after being machined by a spinning machine; and FIG. 3 shows a schematic structural diagram of the elongated hollow tube of the present invention after being machined by a three-roll skew rolling mill.

Detailed Description of Embodiments The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

As shown in the figures, a method for thinning and forming an inner wall of en elongated hollow tube is used for machining an elongated hollow tube 1, and includes the following steps performed by a spinning machine 2 and a three-roll skew rolling mill 3: (1) locally thinning the inner wall of the elongated hollow tube 1 on the spinning machine 2 by using an internal spinning process, such that an end 11 of the elongated hollow tube has a wall thickness greater than that of a middle section 12 of the elongated hollow tube; and (2) machining an outer wall of the elongated hollow tube 1 machined in Step (1) on the three-

roll skew rolling mill 3 by using a skew rolling process, so as to reduce a positioning outer diametesU502231 of the end of the elongated hollow tube 1 to form a necking.

In Step (1), the middle section 12 of the elongated hollow tube is in a machining region of the spinning machine 2, so as to reduce the wall thickness of the middle section 12 of the elongated hollow tube.

The thickness of the end 11 of the elongated hollow tube remains unchanged.

The spinning machine 2 directly reduces the wall thickness of the middle section 12 of the elongated hollow tube.

Conversely, the end 11 of the elongated hollow tube has a thickening effect.

After the elongated hollow tube is machined by the spinning machine, a ratio of the wall thickness of the middle section of the elongated hollow tube to the wall thickness of the end of the elongated hollow tube is 0.2-0.8, The wall thickness of the middle section of the elongated hollow tube needs to be thinned within a rational range to ensure final forming quality.

The middle section that is too thin is likely to affect surface forming quality, and is easy to be twisted and deformed, the middle section that is too thick cannot meet an ideal relative thickening requirement, and is not conducive to deformation during a next step of skew rolling.

In Step (1), an inner wall of the middle section 12 of the elongated hollow tube is connected to an inner wall of the end 11 of the elongated hollow tube via an inner conical surface.

The inner conical surface is mainly used for feed transition of a spinning roller, and is also used for smooth transition between the inner wall of the middle section 12 of the elongated hollow tube and the inner wall 11 of the end of the elongated hollow tube.

In Step (2), the end of the elongated hollow tube 1 is in a machining region of the three-roll skew rolling mill 3. The three-roll skew rolling mill 3 directly performs a necking process of reducing in diameter and thickening the outer wall, and has a main machining region in which the end of the elongated hollow tube 1 is located, so that better effects of reducing in diameter and thickening the outer wall can be achieved.

The forgoing is only a preferred embodiment of the present invention, but is not intended to limit the patent scope of the present invention.

Under the inventive concept of the present invention, any equivalent structures and variations made using the description and accompanying drawings of the present invention, which are directly/indirectly applied in other relevant technical fields, should fall within the scope of patent protection of the present invention.

Claims (6)

1. À method for thinning and forming an inner wall of en elongated hollow tube, characterized by 5 comprising the following steps performed by a spinning machine and a three-roll skew rolling mill: (1) locally thinning the inner wall of the elongated hollow tube on the spinning machine by using an internal spinning process, such that an end of the elongated hollow tube has a wall thickness greater than that of a middle section of the elongated hollow tube; and (2) machining an outer wall of the elongated hollow tube machined in Step (1) on the three-roll skew rolling mill by using a skew rolling process, so as to reduce a positioning outer diameter of the end of the elongated hollow tube to form a necking.

2. The method for thinning and forming an inner wall of an elongated hollow tube according to claim 1, characterized in that in Step (1), the middle section of the elongated hollow tube is in a machining region of the spinning machine, so as to reduce the wall thickness of the middle section of the elongated hollow tube.

3. The method for thinning and forming an inner wall of an elongated hollow tube according to claim 1, characterized in that after the elongated hollow tube is machined by the spinning machine, a ratio of the wall thickness of the middle section of the elongated hollow tube to the wall thickness of the end of the elongated hollow tube is 0.2-0.8.

4. The method for thinning and forming an inner wall of an elongated hollow tube according to claim 1, characterized in that in Step (1), an inner wall of the middle section of the elongated hollow tube is connected to an inner wall of the end of the elongated hollow tube via an inner conical surface, and the inner conical surface is used for transition of a spinning roller.

5. The method for thinning and forming an inner wall of an elongated hollow tube according toV502231 claim 1, characterized in that in Step (2), the end of the elongated hollow tube is in a machining region of the three-roll skew rolling mill.

6. The method for thinning and forming an inner wall of an elongated hollow tube according to any one of claims 1 to 5, characterized in that the elongated hollow tube is cold-formed during the machining in both Step (1) and Step (2).