CN112122419A

CN112122419A - Bending die with small bending radius and bending method of bent pipe

Info

Publication number: CN112122419A
Application number: CN202010948895.7A
Authority: CN
Inventors: 李恒; 杨恒; 金凤臻; 王雨菲; 边天军
Original assignee: Northwestern Polytechnical University
Current assignee: Northwestern Polytechnical University
Priority date: 2020-09-10
Filing date: 2020-09-10
Publication date: 2020-12-25

Abstract

The invention provides a small-bending-radius pipe bending die and a bending method of a bent pipe, wherein the small-bending-radius pipe bending die comprises a die, the die is clamped by a clamp of a pipe bending machine, and an insulating pad is isolated between the die and the clamp; a cavity is arranged in the die, a pipe is arranged in the cavity, electrodes are respectively arranged at two ends of the pipe, and the electrodes are electrically connected with the pulse circuit to form a loop; the invention introduces pulse current in the original numerical control bending forming process and reasonably divides the forming process into a plurality of sub-bending processes, wherein each sub-bending process comprises a force loading step and a pulse current loading step. The invention avoids the problems of low heating efficiency, long time consumption, uneven temperature distribution, oxidation of the surface of the pipe and the like caused by resistance heating bending, has small deformation resistance and high plasticity of the titanium alloy due to the electro-plastic effect in the processing process, does not present strong anisotropy during deformation, and improves the bending forming limit and the forming quality of the titanium alloy pipe difficult to deform.

Description

Bending die with small bending radius and bending method of bent pipe

Technical Field

The invention relates to the field of numerical control machining and current-assisted machining forming of pipes, in particular to a bending die and a bending method for a bent pipe which are used for assisting in the asynchronous loading of pulse current and difficult to deform.

Background

The numerical control pipe bending process is an advanced pipe bending forming technology generated by combining the traditional pipe bending process with the numerical control technology, can meet the requirements of the pipe bending process on high precision, high efficiency and digital processing, and plays an important role in the high-tech fields of aviation, aerospace, navigation, medical treatment and the like and shows wide application prospects. The titanium alloy elbow fitting is light in weight, can bear higher working pressure, is applied to pipeline systems of airplane hydraulic pressure, fuel oil, air conditioners and the like, and can meet the urgent requirements of advanced airplane development on high performance, light weight, high efficiency and the like. The titanium alloy materials such as pure titanium and TC4 have good biological ease, and have wide application prospect in the fields of artificial bones, artificial blood vessels and the like.

However, due to poor fluidity of the titanium alloy material, plastic deformation often shows strong anisotropy and tension-compression asymmetry, so that the problems of cracking, wrinkling, excessive wall thickness reduction, excessive flattening of the cross section and the like are easily caused in the room-temperature numerical control bending process of the pipe, the yield of the bent pipe is low, bending forming with large bending radius (the bending radius R/the pipe diameter D is more than 2) can only be carried out, and the urgent requirements of the titanium alloy bent pipe with small bending radius in the high-tech fields of aviation, aerospace, navigation, medical treatment and the like cannot be met. In the patent with the publication number of CN 201127971Y, CN 102527848B, CN 105537342B, a heating hole is added in a bending die, the resistance is used to heat the die, and the temperature of the pipe is raised through heat conduction, so as to realize numerical control hot bending to improve the forming limit of the pipe; the resistance heating mould has large energy consumption, and the heat conduction between the mould and the machine tool easily influences the service performance of the machine tool, so that the service life of the machine tool is reduced; meanwhile, the temperature distribution of the pipe bending area and the reasonable temperature distribution of the hot bending are different due to uneven heat transfer, so that the bending forming quality/forming limit of the pipe is not improved; moreover, the resistance heating consumes long time, the surface of the pipe is easy to be oxidized, and the forming quality of the bent pipe fitting is reduced; the reasons are not favorable for the precise bending forming of the titanium alloy pipe with small bending radius, and the improvement of the bending forming quality/forming limit of the titanium pipe is seriously restricted.

Disclosure of Invention

A small bending radius pipe bending die comprises a die, wherein the die is clamped by a clamp of a pipe bending machine, and an insulating pad is isolated between the die and the clamp; a cavity is arranged in the die, a pipe is arranged in the cavity, electrodes are respectively arranged at two ends of the pipe, and the electrodes are electrically connected with the pulse circuit to form a loop;

optionally, the die comprises a pressure die, a crease-resist die, a clamping die and a bending die; the pressure die and the crease-resist die are combined, and a first cavity is formed between the pressure die and the crease-resist die; a clamping die is arranged on one side of the pressure die, a bending die is arranged at one end of the crease-resist die, the clamping die is involuted with the bending die, and a second cavity is formed between the clamping die and the bending die; the first cavity and the second cavity are located on the same horizontal line, and the pipe is arranged in the first cavity and the second cavity.

Optionally, a mandrel is arranged in the pipe, two ends of the mandrel are respectively provided with a socket, and an insulating rod is inserted into the socket in the direction corresponding to the pressure die; and a connecting rod is inserted into the insertion opening close to the insertion opening in the direction of the clamping die, a core ball is inserted into the connecting rod, and the core ball is positioned at the transition part of the bent pipe.

Optionally, the anti-wrinkling die and the mandrel are respectively and uniformly sprayed with a lubricant.

Optionally, the lubricant is a high temperature resistant solid lubricating paste or a graphite lubricant.

Optionally, the material of the pipe is titanium alloy.

The invention also comprises a bending method of the bent pipe, which comprises a small bending radius bent pipe die, and the bending steps of the pipe are as follows:

(1) insulating the die and the pipe bender; an insulating pad is arranged between the assembling surface of the die and the connecting surface of the pipe bender;

(2) assembling and debugging the die, and uniformly spraying a lubricant on the crease-resist die, the mandrel and the core ball;

(3) setting the bending speed of a pipe bender and the boosting speed of a pressure die, wherein the boosting speed of the pressure die is the same as the axial speed of the pipe when the pipe is bent; closing the pipe bender after parameter design is finished;

(4) setting a bending angle; dividing the numerical control bending process into N sub-bending processes according to the total bending angle alpha, and ensuring that the maximum strain of the outer ridge line of the pipe in each sub-bending process is within 8 percent, wherein the bending angle of each sub-bending process is alpha/N;

(5) setting parameters of a pulse circuit; setting the current density, pulse width, frequency, electric loading time, electric loading times and electric loading interval time of pulse current;

(6) bending the pipe fitting, wherein each bending angle is alpha/N; opening the pipe bender, and bending the pipe fitting according to the set bending speed and angle;

(7) pulse current processing; after the pipe is bent to the first alpha/N angle, the electrode and the pipe fitting are connected to form a loop, a power switch of a pulse circuit is turned on, current is loaded to the pipe fitting according to set parameters, the power switch is turned off after the pulse current loading is finished, and the electrode and the pipe fitting are disconnected;

(8) after the step 7, the pipe fitting is air-cooled to room temperature, then the second time of distortion of the alpha/N angle is carried out, after the bending is finished, a power switch of the pulse circuit is opened again, current is loaded to the pipe fitting according to set parameters, and the power switch is closed after the pulse current loading is finished; finally, cooling the pipe fitting to room temperature until the Nth angle bending is finished, and obtaining the pipe fitting subjected to final bending forming;

(9) unloading; and disassembling the electrode, operating the pipe bender to loosen the dies, and taking down the formed pipe fitting.

Optionally, the bending speed of the bending machine is 0.05-5 DEG/s.

The bending angle alpha is 10-180 degrees, and the bending times N are 1-18 times.

The invention avoids the problems of low heating efficiency, long time consumption, uneven temperature distribution, oxidation of the surface of the pipe and the like caused by resistance heating bending, has small deformation resistance and high plasticity of the titanium alloy due to the electro-plastic effect in the processing process, does not present strong anisotropy when deformed, improves the bending forming limit and the forming quality of the titanium alloy pipe difficult to deform, and can bend titanium alloy bent pipes with different angles according to requirements.

Drawings

FIG. 1 is a schematic view of a tube of the present invention when unbent;

FIG. 2 is a schematic view of a blank holder and a bending die;

FIG. 3 is a schematic view of a mandrel;

FIG. 4 is a schematic view of the tube after it has been bent;

FIG. 5 is a schematic view of the tubing of the present invention after bending;

description of the figures: the device comprises a die 1, a pressure die 11, a crease-resist die 12, a clamping die 13, a bending die 14, a cylindrical die 141, an insert 142, a rotating shaft 143, an insulating pad 2, a pipe 3, a positive electrode 4, a negative electrode 5, a mandrel 6, an insulating rod 7, a connecting rod 8, a core ball 9, a head 91, a tail 92 and a ball connecting rod 10;

Detailed Description

The invention is described in detail below with reference to the attached drawing figures:

in fig. 1-4, the small bending radius pipe bending mold comprises a mold 1, the mold 1 is clamped and fixed by a clamp of the pipe bending machine, and an insulating pad 2 is isolated between the mold 1 and the clamp (i.e. the insulating pad 2 is arranged between an assembling surface of the mold and a connecting surface of the pipe bending machine); a cavity is arranged in the die 1, a pipe 3 is accommodated in the cavity in a matching manner, electrodes are respectively arranged at two ends of the pipe 3, the electrodes are respectively a positive electrode 4 and a negative electrode 5, the electrodes are electrically connected with a pulse circuit of pulse equipment to form a loop, the loop connection between the pulse circuit and the electrodes can be realized by adopting the prior art, and detailed description is omitted;

the insulating pad 2 insulates the pulse current output end and the pipe bending machine so as to ensure normal work of the pipe bending machine, and as an optimal mode, the pipe 3 is made of a titanium alloy material, and the pipe bending machine is a numerical control pipe bending machine and can be used for designing parameters such as angle bending and mold pushing speed on the pipe bending machine.

More preferably, the die 1 and the insulating pad 2 are made of high-temperature-resistant metal materials, the high-temperature-resistant metal materials used as the insulating pad 2 are subjected to surface insulation treatment, and the insulating pad 2 and the die 1 can be fixed through connecting pieces such as bolts and studs; connecting pieces such as bolts and studs connected with the insulating pad 2 need to be subjected to surface insulation treatment, so that the pipe bender and operators are prevented from being injured in the electric loading process.

As an option, the die 1 comprises a pressure die 11, a crease-resist die 12, a clamping die 13 and a bending die 14; the pressure die 11 and the crease-resist die 12 are combined, and a first cavity is formed between the pressure die 1 and the crease-resist die 12; a clamping die 13 is arranged on one side of the pressure die 11, a bending die 14 is arranged at one end of the crease-resist die 12, the clamping die 13 is matched with the bending die 14, and a second cavity is formed between the clamping die 13 and the bending die 14; the first cavity and the second cavity are located on a horizontal line to form a cavity of the complete mold.

The pressure die 11 is connected with a slide block of a clamp of the pipe bender, and the slide block can drive the pressure die 11 to horizontally move back and forth, so that the pipe 3 is driven to advance.

As a preferred option, the bending die 14 comprises a cylindrical die 141, an insert 142; the upper surfaces of the cylindrical die 141 and the insert 142 are a plane, one side of the crease-resistant die 12 is provided with an arc-shaped groove, the cylindrical die 141 and the arc-shaped groove are arranged in a tangent manner, the center of the cylindrical die 141 is provided with a rotating shaft 143, and the rotating shaft 143 is connected with a main shaft of the pipe bender; when the bending die 14 is in operation, the bending die 14 can rotate by taking the rotating shaft 143 as a rotating point;

in fig. 3, as an option, because the tube 3 is a hollow structure, the tube 3 is easy to deform during the bending process, and in order to prevent the tube 3 from deforming and flattening, a mandrel 6 is disposed in the tube 3, as shown in fig. 3, the diameter of the mandrel 6 is adapted to the inner diameter of the tube, two ends of the mandrel 6 are respectively provided with a socket, an insulating rod 7 is inserted into the socket on one side of the mandrel 6 to ensure that the mandrel 6 is not conductive, a connecting rod 8 is inserted into the socket close to the direction of the clamping die 13, and a core ball 9 is disposed in the connecting rod 8.

The bending die 14 has a set bending radius, the clamping die 13 presses the pipe 3 on the bending die 14, and the pipe 3 is pulled to generate bending deformation along with the rotation of the bending die 14; the anti-wrinkling die 12 is used for inhibiting wrinkling on the inner side of the thin-walled pipe of the pipe 3; the pressure die 11 provides bending and plays roles of compressing and boosting the pipe 3 at the rear end of the bending, and the crease-resist die 12 is matched to prevent the inner side of the pipe 3 from wrinkling and promote the stable forming of the bent pipe; the core ball and the core shaft play a supporting role on the pipe wall in the inner cavity of the pipe, and prevent the inner cavity of the pipe 3 from wrinkling and the cross section from being excessively flattened.

As an option, the core ball 9 comprises a head part 91, a tail part 92, and a curved connector, the head part 91 and the tail part 92 are connected together through the curved connector, the tail part 92 can move along the curved connector, the curved connector can be a steel ball, or a connector as disclosed in 102161059B, the tail part of the core ball 9 is provided with a ball connecting rod 10, the surface of the ball connecting rod 10 is in an arc structure, and the core ball 9 is placed at the transition of the bent pipe of the pipe 3; the core ball 9 plays a supporting role in the bending process of the pipe 3, and the pipe 3 is prevented from being excessively flattened.

Alternatively, the head 91 is a spherical structure.

As an option, a lubricant is uniformly sprayed on the anti-creasing die 12, the mandrel 6 and the core ball 9 respectively, and the lubricant is a high-temperature-resistant solid lubricating paste or a graphite lubricant, so that the friction force between the anti-creasing die 12, the mandrel 6, the core ball 9 and the pipe 3 is reduced.

Alternatively, one or more grooves are formed on the surfaces of the press die 11, the blank-holding die 12, the holding die 13 and the bending die 14, and protrusions adapted to the grooves are formed on the insulating pad 2, so that the insulating pad 2 can be more closely combined with the corresponding die parts.

In the invention, the bending angle of the pipe 3 is 10-180 degrees, and the selection range of the bending times N is 1-18 times.

The bending method of the bent pipe comprises the following steps:

(1) insulating the die and the pipe bender; an insulating pad 2 is arranged between the assembling surface of the die and the connecting surface of the pipe bender;

(2) assembling and debugging the die, and uniformly spraying a lubricant on the crease-resist die 12, the mandrel 6 and the core ball 9;

(3) setting the bending speed of the pipe bender and the boosting speed of the pressure die 11, wherein the boosting speed of the pressure die is the same as the axial speed of the pipe when the pipe 3 is bent; the bending speed of the pipe bender is adjusted between 0.05-5 degrees/s, and the pipe bender is closed after parameter design is completed;

(4) setting a bending angle; dividing the numerical control bending process into N sub-bending processes (namely bending times) according to the total bending angle alpha, and ensuring that the maximum strain of the outer ridge line of the pipe in each sub-bending process is within 8 percent, wherein the bending angle of each sub-bending process is alpha/N;

The invention avoids the problems of low heating efficiency, long time consumption, uneven temperature distribution, oxidation of the surface of the pipe and the like caused by resistance heating bending, has small deformation resistance and high plasticity of the titanium alloy due to the electro-plastic effect in the processing process, does not present strong anisotropy during deformation, and improves the bending forming limit and the forming quality of the titanium alloy pipe difficult to deform.

The following is a description taking specific parameters as examples:

the tube used in this example was a TC4 titanium tube having a diameter of Φ 13.7 × t0.5mm, i.e., a tube diameter D of 13.7mm, a wall thickness t of 0.5mm, a bending radius R of 16.85mm to 1.22D, a bending angle of 90 degrees, a bending speed of 1 °/s, and a pressure die assist speed of 0.3 mm/s.

The tube 3 of this embodiment needs to be bent to an angle of 90 degrees, and is divided into 6 bending angles to complete the 90-degree bending, and each bending angle is 90/6-15 degrees.

Setting parameters of a pulse circuit; setting the current density, pulse width, frequency, electric loading time, electric loading times and electric loading interval time of pulse current; the pulse current parameters are related to the diameter and the wall thickness of the pipe, the mechanical property of the pipe and the bending angle, and need to be determined by combining finite element simulation; the current density of the pulse current of this example was 28.9A/mm²Pulse width 1ms, frequency 100Hz, electric loading time 10s, electric loading times 3 times and electric loading interval time 30 s.

The pipe bending machine clamps the clamping die 13, opens the pipe bending machine, and bends the pipe 3 according to the set bending speed and angle;

pulse current processing; after the pipe 3 is bent to 15 degrees for the first time, a power switch of the pulse circuit is turned on, current is loaded on the pipe 3 according to set parameters, and the power switch is turned off after the pulse current loading is finished; after the titanium alloy material with a certain deformation is subjected to pulse current treatment under proper electrical parameters, the number of crystal defects is reduced, and the plasticity is recovered; and the titanium alloy of the tubular product 3 has small deformation resistance and high plasticity in the bending process, and does not have strong anisotropy in deformation, so the processed tubular product has high forming quality.

After the first angular bending is finished, the pipe fitting 3 is cooled to room temperature in air, so that various performances of the pipe fitting 3 are recovered to be normal, then the second 15-degree bending is carried out, a power switch of a pulse circuit is turned on again after the bending is finished, current is loaded to the pipe fitting 3 according to set parameters, so that the plasticity of the pipe fitting 3 is recovered again, and the power switch is turned off after the pulse current loading is finished; finally, cooling the pipe fitting 3 to room temperature until the 6 th angular bending is completed, so as to obtain a pipe fitting subjected to final bending forming, as shown in fig. 5;

unloading; and disassembling the electrode, operating the pipe bender to loosen the dies, and taking down the formed pipe fitting.

As an alternative, the order of releasing the molds is: the mandrel 6, the pressure die 11 and the clamping die 13; after the formed pipe 3 is removed, the press die 11, the clamp die 13, and the mandrel 6 are returned to the positions before bending, and the pipe bender is closed.

The invention introduces pulse current in the original numerical control bending forming process and reasonably divides the forming process into a plurality of sub-bending processes, wherein each sub-bending process comprises a force loading step and a pulse current loading step, and because of the electro-plastic effect in the bending forming process, the titanium alloy has small deformation resistance, high plasticity and does not present strong anisotropy during deformation, thereby avoiding the problems of low heating efficiency, long consumed time, uneven temperature distribution, oxidation of the surface of the pipe and the like caused by resistance heating bending, inhibiting the defects of thickening and even wrinkling of the inner side wall of the pipe, thinning and even cracking of the outer side wall, flattening of the cross section and the like, and improving the bending forming limit and the forming quality of the titanium alloy pipe difficult to deform. The invention is used for bending and forming the TC4 titanium alloy pipe with the small bending radius (R is 16.85mm is 1.22D) with the pipe diameter D of 13.7mm and the wall thickness t of 0.5mm, the inner side of the pipe does not wrinkle after the pipe is bent within the forming limit, the surface of the pipe does not have scratch, the thickness reduction rate of the outer side wall is less than 20 percent, the section flattening rate is less than 5 percent, and the invention can meet the requirements of the fields of aviation, aerospace, medical treatment and the like on the TC4 titanium alloy pipe with the small bending radius.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention shall be included in the scope of the present invention.

Claims

1. The utility model provides a small bend radius bending die which characterized in that: the pipe bending machine comprises a die, wherein the die is clamped by a clamp of the pipe bending machine, and an insulating pad is isolated between the die and the clamp; a cavity is arranged in the die, a pipe is arranged in the cavity, electrodes are respectively arranged at two ends of the pipe, and the electrodes are electrically connected with the pulse circuit to form a loop.

2. The small bend radius bend mold of claim 1, wherein: the die comprises a pressure die, a crease-resist die, a clamping die and a bending die; the pressure die and the crease-resist die are combined, and a first cavity is formed between the pressure die and the crease-resist die; a clamping die is arranged on one side of the pressure die, a bending die is arranged at one end of the crease-resist die, the clamping die is involuted with the bending die, and a second cavity is formed between the clamping die and the bending die; the first cavity and the second cavity are located on the same horizontal line, and the pipe is arranged in the first cavity and the second cavity.

3. The small bend radius bend mold of claim 1, wherein: a core shaft is arranged in the pipe, two ends of the core shaft are respectively provided with a socket, and an insulating rod is inserted into the socket in the direction corresponding to the pressure die; a connecting rod is inserted into the insertion opening close to the direction of the clamping die, a core ball is inserted into the connecting rod, and the core ball is positioned at the transition part of the bent pipe.

4. The small bend radius bend mold of claim 3, wherein: and the anti-wrinkling die and the mandrel are respectively and uniformly sprayed with a lubricant.

5. The small bend radius bend mold of claim 4, wherein: the lubricant is high-temperature resistant solid lubricating paste or graphite lubricant.

6. The small bend radius bend mold of claim 1, wherein: the pipe is made of titanium alloy.

7. A method for bending a bent pipe, characterized in that: comprising the small bend radius bend mold of any of claims 1-6, further comprising the steps of:

8. The bending method of an elbow pipe according to claim 7, wherein: the bending speed of the pipe bender is 0.05-5 DEG/s.

9. The bending method of an elbow pipe according to claim 7, wherein: the bending angle alpha is 10-180 degrees, and the bending times N are 1-18 times.