Corrugated pipe forming springback control method and mold based on stress regulation and control

Abstract

The invention provides a corrugated pipe forming springback control method and die based on stress regulation and control, and relates to the technical field of metal processing. The method comprises the following steps: obtaining a circumferential strain increment expression according to a material bending deformation principle; a plastic strain increment expression, a plastic stress differential equation and a circumferential strain increment expression are combined to obtain a circumferential stress and axial stress relational expression, and according to the circumferential stress and axial stress relational expression, a relation curve with the circumferential compression dependent variable as an independent variable and the ratio of the axial stress to the pre-compression as a dependent variable is obtained; after the pipe blank is bent and deformed, the wave troughs can move towards the axis of the pipe blank in the radial direction of the pipe blank to achieve radial shrinkage of the wave troughs, so that the circumferential stress of the wave troughs is increased, the axial stress difference of the inner surface and the outer surface is reduced, then the axial stress of the corrugated pipe is reduced, and the axial springback of the corrugated pipe is effectively controlled.

Description

Technical Field

[0001] The present invention relates to the technical field of metal processing, and in particular to a bellows forming springback control method and a die based on stress regulation. Background Art

[0002] Due to its excellent flexibility, energy absorption and motion compensation characteristics, bellows are often used to make pipeline connection structures and engine shock absorption structures. They are widely used in the aerospace industry, automobile industry, chemical industry, and oil and gas industry. Usually, bellows are made of stainless steel, aluminum alloy, high-temperature alloy and other materials. Titanium alloy is an ideal material for bellows under extreme service conditions due to its high specific strength, corrosion resistance, high service temperature, fatigue resistance and excellent low-temperature toughness.

[0003] The hydraulic forming of bellows is the most mainstream bellows forming method, and its advantages are low economic and time costs. The general process is: the two ends of the linear tube blank in the axial direction are fixed by the moving die and the fixed die of the forming equipment respectively, and at the same time, a plurality of intermediate dies are arranged between the moving die and the fixed die, and the plurality of intermediate dies are provided with trough forming protrusions and peak forming cambers symmetrical about the trough forming protrusions. The moving die and the fixed die are respectively provided with the same peak forming cambers at one end facing the intermediate die. During preparation, the trough forming protrusion on the intermediate die is pressed against the outer wall of the tube blank, and then the tube blank is pressurized from the inside of the tube blank, and the movement of the moving die toward the fixed die is relied on so that the peaks of the corrugated tube are formed at the adjacent peak forming cambers, and the troughs of the corrugated tube are formed at the trough forming protrusions.

[0004] However, during the process of forming the troughs and peaks, the outer wall of the tube blank undergoes elastic bending deformation. After the bellows is prepared, the troughs and peaks will elastically rebound along the axial direction of the tube blank, resulting in a relatively large forming error of the bellows, affecting the forming quality of the bellows. Summary of the invention

[0005] The problem solved by the invention is how to reduce the springback amount of the corrugated pipe forming so as to improve the forming quality of the corrugated pipe.

[0006] In order to solve the above problems, on the one hand, the present invention provides a bellows forming springback control method based on stress regulation, comprising:

[0007] According to the bending deformation process of the tube blank, a mold profile is constructed, and the curvature of the mold profile is set to be constant, so that the trough of the mold profile moves radially toward the axis of the tube blank;

[0008] According to the material bending deformation principle, the difference between the axial strain of the inner surface of the trough of the mold surface and the axial strain of the neutral layer, and the difference between the circumferential strain of the inner surface and the circumferential strain of the neutral layer during radial movement are analyzed to obtain the plastic strain increment expression;

[0009] According to the material plastic deformation yield condition expression, the plastic stress differential equation is obtained;

[0010] According to the material bending deformation principle, the expression of the hoop strain increment is obtained;

[0011] The expression of plastic strain increment, plastic stress differential equation and hoop strain increment is combined to obtain the expression of the relationship between hoop stress and axial stress. Based on the expression of the relationship between hoop stress and axial stress, a relationship curve is obtained with the hoop compression strain as the independent variable and the ratio of the axial stress to the value before compression as the dependent variable.

[0012] Optionally, the step of causing the trough of the mold profile to move radially toward the axis of the tube blank comprises:

[0013] The peak diameter of the required bellows is used as the peak diameter of the intermediate mold; and the difference between the peak diameter of the bellows and the inner diameter of the trough of the bellows is used as the first difference;

[0014] Taking the difference between the diameter of the wave crest forming structure of the intermediate mold and the diameter of the wave trough forming structure of the intermediate mold as a second difference, so that the second difference is smaller than the first difference;

[0015] Fix one end of the tube blank in the axial direction by a fixed die; fix the other end of the tube blank in the axial direction by a movable die; and cover the intermediate die on the portion of the tube blank located between the fixed die and the movable die;

[0016] The tube blank is subjected to bulging and drum wave operations, and the tube blank is separated from the trough forming structure of the intermediate die by the push wave movement of the movable die toward the fixed die.

[0017] Optionally, it is characterized in that the bellows forming springback control method based on stress regulation further includes:

[0018] The formed tube blank is subjected to pressure relief and unloading operations.

[0019] Optionally, the fixed mold is fixed on a frame of the forming equipment, and the movable mold moves toward the fixed mold through a hydraulic drive system.

[0020] Optionally, the bellows forming springback control method based on stress regulation further includes:

[0021] The axial springback amount of the tube blank after forming is checked. If the axial springback amount of the tube blank after forming is greater than the actual required springback error range, the second difference is reduced.

[0022] Compared with the prior art, the bellows forming springback control method based on stress regulation of the present invention constructs a mold profile according to the bending deformation process of the tube blank, sets the curvature of the mold profile constant, and makes the trough of the mold profile move radially toward the axis of the tube blank; according to the material bending deformation principle, analyzes the difference between the axial strain of the inner surface of the trough of the mold profile and the axial strain of the neutral layer, and the difference between the circumferential strain of the inner surface and the circumferential strain of the neutral layer during the radial movement to obtain the plastic strain increment expression; according to the material plastic deformation yield condition expression, obtains the plastic stress differential equation; according to the material bending deformation principle , obtain the expression of the circumferential strain increment; combine the expression of the plastic strain increment, the plastic stress differential equation and the circumferential strain increment expression to obtain the expression of the relationship between the circumferential stress and the axial stress, and according to the expression of the relationship between the circumferential stress and the axial stress, obtain a relationship curve with the circumferential compression strain as the independent variable and the ratio of the axial stress to the stress before compression as the dependent variable. After the tube billet is bent and deformed, the trough can be moved along the radial direction of the tube billet toward the axis of the tube billet to achieve radial contraction of the trough, thereby increasing the circumferential stress of the trough, reducing the axial stress difference between the inner and outer surfaces, and then reducing the axial stress of the bellows, thereby effectively controlling the axial rebound of the bellows.

[0023] On the other hand, the present invention also provides a mold, based on the corrugated tube forming rebound control method based on stress regulation as described above, including a movable mold, an intermediate mold and a fixed mold, all of which are arranged in a ring shape, the intermediate mold is located between the movable mold and the fixed mold, the movable mold and the fixed mold are respectively used to be fixedly connected to the two ends of the tube blank in the axial direction, the movable mold is used to be moved toward the fixed mold, and the movable mold and the fixed mold are both provided with a first arc surface structure at one end facing the intermediate mold, the intermediate mold is provided with an arc-shaped protrusion and a second arc surface structure located on both sides of the arc-shaped protrusion, the first arc surface structure and the second arc surface structure cooperate to form a wave peak forming groove, or, two adjacent second arc surface structures on different intermediate molds cooperate to form a wave peak forming groove; the arc-shaped protrusion is used to form a wave valley of the corrugated tube; the inner diameter of the intermediate mold is larger than the inner diameter of the movable mold and the fixed mold.

[0024] Optionally, the intermediate mold is used to be movable along the radial direction of the tube blank.

[0025] Optionally, there are multiple intermediate molds, and the multiple intermediate molds are used to move synchronously along the radial direction of the tube blank.

[0026] Optionally, the number of the intermediate molds is N-1, wherein N is the number of waves of the bellows actually required.

[0027] Optionally, the movable mold is used to move toward the fixed mold through a hydraulic drive structure.

[0028] Compared with the prior art, the mold of the present invention utilizes the setting that the diameter of the trough on the intermediate mold is larger than the diameter of the hole surrounded by the movable mold. After the wave peak is formed, the material in the trough area can shrink and deform, so that the material enters the plastic deformation state again. In this way, after the bellows is prepared, the axial rebound of the trough can be reduced, and the axial rebound of the bellows can be effectively controlled to improve the forming quality of the bellows. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flowchart of a titanium alloy bellows forming method in an embodiment of the present invention;

[0030] Figure 2 It is a schematic diagram of the structure when the movable die and the fixed die in the embodiment of the present invention are respectively connected to the two ends of the tube blank in the axial direction;

[0031] Figure 3 It is a schematic diagram of the structure of a tube blank during the bulging process in an embodiment of the present invention;

[0032] Figure 4 It is a schematic diagram of the structure of a tube blank during the drum wave process in an embodiment of the present invention;

[0033] Figure 5 It is a schematic diagram of the structure of the tube blank during the wave pushing process in an embodiment of the present invention;

[0034] Figure 6 It is a schematic structural diagram of a tube blank during the diameter reduction process in an embodiment of the present invention;

[0035] Figure 7 It is a structural schematic diagram of a tube blank during pressure relief and unloading operations in an embodiment of the present invention;

[0036] Figure 8 is a schematic diagram of displacement of a movable mold in an embodiment of the present invention;

[0037] Fig. 9 is a line graph of the change in internal pressure of the tube blank in the embodiment of the present invention;

[0038] Fig.10 is a line graph of the springback change of the tube blank in the embodiment of the present invention;

[0039] Fig.11 It is a principle diagram of the stress of the tube blank after processing in an embodiment of the present invention;

[0040] Fig.12 A schematic diagram of the spacing between adjacent floating molds in an embodiment of the present invention;

[0041] Fig.13 is a structural schematic diagram of a floating mold in an embodiment of the present invention;

[0042] Fig.14 It is a curve diagram of the change of the annular shrinkage strain and the ratio of the axial stress to the stress before compression in the embodiment of the present invention.

[0043] Description of reference numerals:

[0044] 1-movable mold; 2-floating mold; 21-arc-shaped protrusion; 3-fixed mold; 4-tube blank. DETAILED DESCRIPTION

[0045] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0046] In the accompanying drawings, the Z axis represents the vertical position, and the positive direction of the Z axis (that is, the direction in which the arrow of the Z axis points) represents the upper side, and the negative direction of the Z axis (that is, the direction opposite to the positive direction of the Z axis) represents the lower side; in the accompanying drawings, the X axis represents the horizontal position, and the positive direction of the X axis (that is, the direction in which the arrow of the X axis points) represents the right side, and the negative direction of the X axis (that is, the direction opposite to the positive direction of the X axis) represents the left side. It should also be noted that the aforementioned Z axis and X axis are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0047] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein.

[0048] Due to its excellent flexibility, energy absorption and motion compensation characteristics, bellows are often used to make pipeline connection structures and engine shock absorption structures. They are widely used in the aerospace industry, automobile industry, chemical industry, and oil and gas industry. Usually, bellows are made of stainless steel, aluminum alloy, high-temperature alloy and other materials. Titanium alloy is an ideal material for bellows under extreme service conditions due to its high specific strength, corrosion resistance, high service temperature, fatigue resistance and excellent low-temperature toughness.

[0049] The hydraulic forming of bellows is the most mainstream bellows forming method, and its advantages are low economic and time costs. The general process is: the two ends of the linear tube blank in the axial direction are fixed by the moving die and the fixed die of the forming equipment respectively, and at the same time, multiple intermediate dies are arranged between the moving die and the fixed die, and the multiple intermediate dies are provided with trough forming protrusions and peak forming cambers symmetrical about the trough forming protrusions. The moving die and the fixed die are respectively provided with the same peak forming cambers at one end facing the intermediate die. During preparation, the trough forming protrusion on the intermediate die is pressed against the outer wall of the tube blank, and then the tube blank is pressurized from the inside of the tube blank, and the adjacent peak forming cambers form the peaks of the corrugated tube by relying on the movement of the moving die toward the fixed die, and the trough forming protrusions form the troughs of the corrugated tube.

[0050] However, during the process of forming the troughs and crests, the outer wall of the tube blank undergoes elastic bending deformation. After the bellows is manufactured, the troughs and crests will elastically rebound along the axial direction of the tube blank, resulting in a relatively large forming error of the bellows, which affects the forming quality of the bellows. To solve the above problems, the present invention provides a bellows forming method.

[0051] Combination Figure 1 and Fig.14 As shown, the present invention provides a bellows forming springback control method based on stress regulation, comprising the following steps:

[0052] Step S100: constructing a mold profile according to the bending deformation process of the tube blank 4, setting the curvature of the mold profile constant, and making the trough of the mold profile move radially toward the axis of the tube blank 4;

[0053] Step S200: According to the material bending deformation principle, the difference between the axial strain of the inner surface of the trough of the mold surface and the axial strain of the neutral layer, and the difference between the hoop strain of the inner surface and the hoop strain of the neutral layer during the radial movement are analyzed to obtain a plastic strain increment expression;

[0054] Step S300: Obtaining a plastic stress differential equation according to a material plastic deformation yield condition expression;

[0055] Step S400: obtaining an expression for the hoop strain increment according to the material bending deformation principle;

[0056] Step S500: Combine the plastic strain increment expression, the plastic stress differential equation and the hoop strain increment expression to obtain the relationship expression between the hoop stress and the axial stress, and based on the relationship expression between the hoop stress and the axial stress, obtain a relationship curve with the hoop compression strain as the independent variable and the ratio of the axial stress to the value before compression as the dependent variable.

[0057] Specifically, the inner surface of the trough refers to the surface of the trough facing the bending direction, the outer surface of the trough refers to the surface of the trough away from the bending direction, and the neutral layer refers to the position between the inner surface of the trough and the outer surface of the trough. Figure 2 To Attachment Figure 6 The radial movement of the trough of the bellows model toward the axis of the tube blank is referred to as the trough shrinkage. During the trough shrinkage process, since the bending curvature remains unchanged, the increment of the difference in axial strain between the inner surface and the neutral layer during the compression process remains unchanged, that is,

[0058] dε l -dε l,mid =0#(1)

[0059] During the compression process, the deformation in the compression direction is uniform, and the increment of the difference between the hoop strain of the inner surface and the neutral layer remains unchanged, that is,

[0060] dε θ -dε θ,mid =0#(2)

[0061] Expanding the above formula for elastic and plastic deformation, we can get

[0062]

[0063] After combining and sorting,

[0064]

[0065] During the plastic deformation of the material, the stress meets the yield condition.

[0066]

[0067] Ignoring material work hardening, differentiating the above equation yields

[0068] 2σ θ dσ θ +2σ l dσ l -σ θ dσ l -σ l dσ θ =0#(7)

[0069] The hoop strain increment dε b Perform elastic and plastic expansion to

[0070]

[0071] Combining equations (9), (11) and (12), we get

[0072]

[0073] Solving the above differential equation we can get Fig.14 The results show that when the circumferential shrinkage is more than 4%, the axial stress is reduced to 1.5%; when it is more than 5%, the axial stress can be controlled within 5‰. At this time, the stress on the outer surface and the inner surface of the trough area are basically the same. Therefore, when the bellows is circumferentially compressed, the stress on the inner and outer surfaces of the tube blank is reduced, and the rebound of the bellows is effectively suppressed.

[0074] Therefore, in this embodiment, according to the bending deformation process of the tube blank 4, the mold profile is constructed, and the curvature of the mold profile is set constant, so that the trough of the mold profile moves radially toward the axis of the tube blank 4; according to the bending deformation principle of the material, the difference between the axial strain of the inner surface of the trough of the mold profile and the axial strain of the neutral layer, and the difference between the circumferential strain of the inner surface and the circumferential strain of the neutral layer in the radial movement process are analyzed to obtain the plastic strain increment expression; according to the plastic deformation yield condition expression of the material, the plastic stress differential equation is obtained; according to the bending deformation principle of the material, the circumferential strain increment expression is obtained; the plastic strain increment expression is combined with the plastic strain increment expression. The expression of the relationship between the hoop stress and the axial stress is obtained by using the expression of the relationship between the hoop stress and the axial stress. According to the expression of the relationship between the hoop stress and the axial stress, a relationship curve with the hoop compression strain as the independent variable and the ratio of the axial stress to the stress before compression as the dependent variable is obtained. After the tube blank 4 is bent and deformed, the radial contraction of the trough can be achieved by moving the trough along the radial direction of the tube blank 4 toward the axis of the tube blank 4, so as to increase the hoop stress of the trough, reduce the axial stress difference between the inner and outer surfaces, and then reduce the axial stress of the bellows, thereby effectively controlling the axial rebound of the bellows.

[0075] Optionally, combined Figures 2 to 6 , Fig.13 As shown, the trough model is radially moved toward the axis of the tube blank 4, including:

[0076] The required peak diameter of the bellows is used as the peak diameter of the intermediate mold 2; and the difference between the peak diameter of the bellows and the inner diameter of the trough of the bellows is used as the first difference;

[0077] The difference between the diameter of the wave crest forming structure of the middle mold 2 and the diameter of the wave trough forming structure of the middle mold 2 is set as a second difference, so that the second difference is smaller than the first difference;

[0078] One end of the tube blank 4 in the axial direction is fixed by the fixed die 3; the other end of the tube blank 4 in the axial direction is fixed by the movable die 1; and the intermediate die 2 is placed on the portion of the tube blank 4 between the fixed die 3 and the movable die 1;

[0079] The tube blank 4 is subjected to bulging and drum wave operations, and the tube blank 4 is separated from the trough forming structure of the intermediate die 2 by the push wave movement of the movable die 1 toward the fixed die 3 .

[0080] Specifically, bulging means that the outer wall of the tube blank 4 is pressed against the lower end of the intermediate mold 2 by internal pressure, and bulging means that after bulging, the tube blank 4 is kept pressurized so that the outer wall of the tube blank 4 further bulges outward to form a corrugated shape. During the bulging process, the trough is gradually formed by the obstruction of the lower end of the intermediate mold 2. During forming, the tube blank 4 is extended into the intermediate mold 2; and the two ends of the tube blank 4 in the axial direction are respectively connected to the movable mold 1 and the fixed mold 3, and a gap is set between the intermediate mold 2 and the outer wall of the tube blank 4. The tube blank 4 is pressurized to expand and deform, and the outer wall of the tube blank 4 abuts against the lower end of the intermediate mold 2. The current pressure on the tube blank 4 is maintained, so that the outer wall of the tube blank 4 bulges toward the gap between the intermediate mold 2 and the movable mold 1 and the fixed mold 3 to form a preliminary waveform, and the portion where the outer wall of the tube blank 4 contacts the intermediate mold 2 forms a trough, and the movable mold 1 is driven to move, so that the movable mold 1 moves toward the fixed mold 3 to eliminate the gap to form a wave crest of the corrugated tube. As the wave crest is formed, the trough is gradually moved away from the lower end of the intermediate mold 2 by the obstruction of the intermediate mold 2. Fig.10 According to the Mises yield criterion, the part between the crest and the trough is stretched to generate hoop stress to achieve plastic deformation, thereby reducing the inner diameter of the corrugated section of the tube blank 4.

[0081] In this way, by taking the peak diameter of the required corrugated tube as the peak diameter of the intermediate die 2; taking the difference between the peak diameter of the corrugated tube and the inner diameter of the trough of the corrugated tube as the first difference; taking the difference between the diameter of the peak forming structure of the intermediate die 2 and the diameter of the trough forming structure of the intermediate die 2 as the second difference, making the second difference smaller than the first difference, which is equivalent to enlarging the trough diameter of the intermediate die 2, a certain gap can be created between the tube blank 4 and the intermediate die 2 before forming, and fixing one end of the tube blank 4 in the axial direction by the fixed die 3; fixing the other end of the tube blank 4 in the axial direction by the movable die 1; and fixing the intermediate die 2 in the axial direction by the movable die 1. The intermediate die 2 is sleeved on the part where the tube blank 4 is located between the fixed die 3 and the movable die 1; the tube blank 4 is subjected to bulging and waving operations, and the movable die 1 is moved toward the fixed die 3 by pushing waves to separate the tube blank 4 from the trough forming structure of the intermediate die 2. Therefore, combined with the above-mentioned expression of the relationship between the annular stress and the axial stress, after the trough diameter of the intermediate die 2 is enlarged, a certain gap can be created between the tube blank 4 and the intermediate die 2 before forming, so that radial shrinkage can occur in the final stage of bellows forming, so as to effectively control the axial rebound of the bellows.

[0082] Optionally, the bellows forming springback control method based on stress regulation also includes:

[0083] The formed tube blank is subjected to pressure relief and unloading operations.

[0084] Specifically, pressure relief refers to the release of pressure inside the tube blank, and unloading refers to the removal of the formed bellows from the mold.

[0085] In this way, the pressure inside the formed bellows is prevented from affecting the disassembly of the bellows by performing pressure relief and unloading operations on the formed tube blank.

[0086] Optionally, the fixed die is fixed on a frame of the forming device, and the movable die moves toward the fixed die through a hydraulic drive system. In this way, not only the use stability of the fixed die can be improved, but also the moving accuracy of the movable die can be improved, thereby ensuring the forming quality of the corrugated pipe.

[0087] Optionally, the bellows forming springback control method based on stress regulation also includes:

[0088] Check the axial springback of the tube blank after forming. If the axial springback of the tube blank after forming is greater than the actual required springback error range, reduce the second difference.

[0089] In this way, in the process of controlling the springback, there is no need for any additional equipment or additional processing steps. It is only necessary to reduce the difference between the diameter of the peak forming structure of the intermediate mold 2 and the diameter of the trough forming structure of the intermediate mold 2, that is, to increase the size of the gap between the intermediate mold 2 and the outer wall of the tube blank 4, thereby improving the applicability of corrugated tube forming.

[0090] Based on the above-mentioned bellows forming method, the embodiments of the present invention provide several different bellows forming cases.

[0091] Example 1

[0092] In this example, the forming method of a TA34 corrugated pipe component with a wave number N of 10, a thickness t of 1mm, a wave pitch L0 of 15mm, a peak width D0 of 10mm, a trough diameter D1 of 100mm, a peak diameter D2 of 120mm, and a maximum axial dimensional accuracy error ΔL of 10mm with a yield strength σs of 500MPa is designed as an example. The dimension R1 on the intermediate die 2 is 1mm, and the die surface adjustment dimension ΔD is 5mm. The initial billet length L1 is 28.5mm, and the distance L1-L0 between the intermediate dies 2 is 13.5mm. The internal pressure P1 at the end of bulging is 12MPa, the internal pressure P2 at the end of drum wave is 15MPa, the displacement d1 of the movable die 1 at the end of push wave is 85mm, and the punch displacement d2 at the end of compression is 135mm.

[0093] Example 2

[0094] In this example, the forming method of a TA34 corrugated pipe component with a wave number N of 10, a thickness t of 1mm, a wave pitch L0 of 15mm, a peak width D0 of 10mm, a trough diameter D1 of 100mm, a peak diameter D2 of 120mm, and a maximum axial dimensional accuracy error ΔL of 10mm with a yield strength σs of 500MPa is designed as an example. The dimension R1 on the intermediate die 2 is 1mm, and the die surface adjustment dimension ΔD is 5mm. The initial billet length L1 is 28.5mm, and the distance L1-L0 between the intermediate dies 2 is 13.5mm. The internal pressure P1 at the end of bulging is 24MPa, the internal pressure P2 at the end of drum wave is 30MPa, the displacement d1 of the movable die 1 at the end of push wave is 85mm, and the punch displacement d2 at the end of compression is 135mm.

[0095] Example 3

[0096] In this example, the forming method of a TA34 corrugated pipe component with a wave number N of 10, a thickness t of 1mm, a wave pitch L0 of 15mm, a peak width D0 of 10mm, a trough diameter D1 of 100mm, a peak diameter D2 of 120mm, and a maximum axial dimensional accuracy error ΔL of 10mm with a yield strength σs of 500MPa is designed as an example. The dimension R1 on the intermediate die 2 is 1mm, and the die surface adjustment dimension ΔD is 5mm. The initial billet length L1 is 28.5mm, and the distance L1-L0 between the intermediate dies 2 is 13.5mm. The internal pressure P1 at the end of bulging is 3MPa, the internal pressure P2 at the end of drum wave is 30MPa, the displacement d1 of the movable die 1 at the end of push wave is 85mm, and the punch displacement d2 at the end of compression is 135mm.

[0097] Example 4

[0098] In this example, the forming method of a TA34 corrugated pipe component with a wave number N of 10, a thickness t of 1mm, a wave pitch L0 of 15mm, a peak width D0 of 10mm, a trough diameter D1 of 100mm, a peak diameter D2 of 120mm, and a maximum axial dimensional accuracy error ΔL of 10mm with a yield strength σs of 500MPa is designed as an example. The dimension R1 on the middle die 2 is 1mm, and the die surface adjustment dimension ΔD is 10mm. The initial billet length L1 is 28.5mm, and the distance L1-L0 between the middle dies 2 is 13.5mm. The internal pressure P1 at the end of bulging is 12MPa, the internal pressure P2 at the end of drum wave is 15MPa, the displacement d1 of the moving die 1 at the end of push wave is 85mm, and the displacement d2 of the moving die 1 at the end of compression is 135mm.

[0099] Example 5

[0100] In this example, the forming method of 2219-O aluminum alloy bellows components with a wave number N of 10, a thickness t of 1mm, a wave distance L0 of 15mm, a peak width D0 of 10mm, a trough diameter D1 of 100mm, a peak diameter D2 of 120mm, and a maximum axial dimensional accuracy error ΔL of 10mm with a yield strength σs of 500MPa is designed as an example. The dimension R1 on the middle die 2 is 1mm, and the die surface adjustment dimension ΔD is 5mm. The initial billet length L1 is 28.5mm, and the distance L1-L0 between the middle dies 2 is 13.5mm. The internal pressure P1 at the end of bulging is 1.8MPa, the internal pressure P2 at the end of drum wave is 2.25MPa, the displacement d1 of the moving die 1 at the end of push wave is 85mm, and the displacement d2 of the moving die 1 at the end of compression is 135mm.

[0101] Combination Figures 2 to 11 As shown, another embodiment of the present invention further provides a mold, based on the bellows forming rebound control method based on stress regulation as described above, including a movable mold 1, an intermediate mold 2 and a fixed mold 3, all of which are arranged in a ring shape, the intermediate mold 2 is located between the movable mold 1 and the fixed mold 3, the movable mold 1 and the fixed mold 3 are respectively used to be fixedly connected to the two ends of the tube blank 4 in the axial direction, the movable mold 1 is used to be moved toward the fixed mold 3, and the movable mold 1 and the fixed mold 3 are both provided with a first arc surface structure at one end facing the intermediate mold 2, the intermediate mold 2 is provided with an arc-shaped protrusion 21 and a second arc surface structure located on both sides of the arc-shaped protrusion 21, the first arc surface structure and the second arc surface structure cooperate to form a peak forming groove, or two adjacent second arc surface structures on different intermediate molds 2 cooperate to form a peak forming groove; the arc-shaped protrusion 21 is used to form a trough of the corrugated tube; the inner diameter of the intermediate mold 2 is larger than the inner diameters of the movable mold 1 and the fixed mold 2.

[0102] It can be understood that the movable die 1, the intermediate die 2 and the fixed die 3 are all annular structures for being sleeved on the tube blank 4. Since the two ends of the tube blank 4 in the axial direction can be fixed by the movable die 1 and the fixed die 3 respectively, the apertures of the movable die 1 and the fixed die 3 are the same and are consistent with the outer diameter of the tube blank 4, while the inner diameter of the intermediate die 2 (that is, the diameter of the hole surrounded by the arc-shaped protrusion 21) is larger than the inner diameters of the movable die 1 and the fixed die 3 (the diameter of the hole surrounded by the movable die 1 and the fixed die 3), that is, the inner diameter of the intermediate die 2 is larger than the outer diameter of the tube blank 4, or, before the tube blank 4 is formed, the arc-shaped protrusion 21 of the intermediate die 2 has a certain distance from the outer wall of the tube blank 4.

[0103] Specifically, when preparing the bellows, Figure 2As shown, the two ends of the straight tube blank 4 in the axial direction are fixed by the movable die 1 and the fixed die 3 respectively, and because the aperture surrounded by the arc-shaped protrusion 21 on the intermediate die 2 is larger than the aperture surrounded by the movable die 1, a certain initial distance ΔD is spaced between the arc-shaped protrusion 21 on the intermediate die 2 and the outer wall of the tube blank 4. After the tube blank 4 is fixed, the tube blank 4 is pressurized from the inside. Figure 3 As shown, after the tube blank 4 is pressurized, the outer wall (corrugated section) of the tube blank 4 between the movable die 1 and the fixed die 3 will expand outwards until it abuts against the arc-shaped protrusion 21 on the middle die 2. Keep pressurizing the tube blank 4, as shown in FIG. Figure 4 As shown, the outer wall of the tube blank 4 will continue to expand and bulge outward between two adjacent second curved surface structures to form a preliminary corrugated shape due to the obstruction of the arc-shaped protrusion 21 (i.e., the trough-forming structure described above). Figure 5 As shown, the movable die 1 moves toward the fixed die 3, reducing the linear distance between the two adjacent second curved surface structures (i.e., the wave crest forming structure described above), so that the outer wall of the tube blank 4 between the two adjacent second curved surface structures undergoes a larger bending deformation, and at the same time, the arc-shaped protrusion 21 completes the formation of the wave trough of the corrugated tube. Keep pressurizing the tube blank 4, and as the movable die 1 continues to move, as shown in FIG. Figure 6 As shown, the movement of the movable mold 1 makes the two adjacent second curved surface structures spliced ​​together, so that the outer wall of the tube blank 4 forms a wave peak under the approach of the two adjacent second curved surface structures, and in the process of wave peak forming, the two arc segments forming the wave peak approach each other under the two adjacent second curved surface structures, and the outer wall of the tube blank 4 is attached to the second curved surface structure. Therefore, due to the obstruction of the second curved surface structure, in the process of the two arc segments forming the wave peak gradually approaching, the wave trough will gradually move away from the arc-shaped protrusion 21, that is, the wave trough moves toward the central axis of the tube blank 4, so that the distance between the wave trough and the wave peak is increased, and the outer wall between the wave trough and the wave peak is stretched to produce plastic deformation, and in the process of stretching, since the wave trough is separated from the support of the arc-shaped protrusion 21, the two arc segments of the wave trough will be closer. In this way, when the pressure is released, Figure 7 As shown, the overall rebound amount of the bellows is very small, and the rebound amount of the bellows can be effectively controlled.

[0104] Corresponding to the above, if Fig.11As shown in the figure, from the perspective of stress, the forming process of the wave crest and trough of the corrugated pipe is the process of overcoming the yield strength of the material. The elliptical curve is the elliptical curve corresponding to the Mises yield criterion, σ11 is the axial stress, σ22 is the hoop stress, and X is the thickness direction of the tube blank 4. The elliptical curve on the left is the stress analysis coordinate diagram before stress regulation (traditional corrugated pipe forming). During the forming process, taking the forming at the trough as an example, the outer wall at the trough is compressed and the inner wall at the trough is stretched. The stresses of the two are equal in magnitude and opposite in direction. The two stresses are located in the first quadrant and the third quadrant respectively. In the late forming stage, the stress causes the material to undergo micro-plastic deformation, that is, the material maintains the formed shape and cannot rebound to the initial shape. The corresponding elliptical curve change process is that the stress gradually increases during bending, and it folds back after reaching the elliptical curve. The lateral distance between the folding back and the coordinate origin is the elastic rebound amount. After stress regulation (the corrugated tube formed by the present invention), the trough separates from the arc-shaped protrusion 21 in the later stage, as shown in the elliptical curve coordinate system on the right, the stress gradually increases, and turns back after reaching the elliptical curve. After turning back, the downward annular stress is increased to reach the elliptical curve, and moves toward the coordinate origin along the elliptical curve. The lateral distance between the stress on the elliptical curve and the coordinate origin is the rebound amount after stress regulation. It can be seen that the rebound amount after stress regulation is smaller than the rebound amount before stress regulation. The deformation process corresponding to the annular stress is that as the wave crest is formed, the trough and the wave crest gradually move away, the aperture surrounded by the trough gradually decreases, and the aperture surrounded by the wave crest remains unchanged. The material between the trough and the wave crest is further stretched under the action of the annular stress to undergo plastic deformation. Therefore, after the bellows is formed, the rebound amount at the trough is smaller, so as to reduce the overall axial rebound amount of the bellows, thereby effectively controlling the axial rebound of the bellows.

[0105] Therefore, in this embodiment, the diameter of the aperture surrounded by the arc-shaped protrusion 21 on the middle mold 2 is larger than the diameter of the aperture surrounded by the movable mold 1 and the fixed mold 3. After the wave peak is formed, the material in the trough area can shrink and deform, so that the material enters the plastic deformation state again. In this way, after the preparation of the corrugated pipe is completed, the axial rebound of the trough can be reduced, thereby achieving effective control of the axial rebound of the bellows to improve the forming quality of the bellows.

[0106] In some embodiments, if the aperture surrounded by the arc-shaped protrusion 21 is 50 mm and the aperture surrounded by the movable mold 1 is 40 mm, and it is found after preparation that the axial rebound of the corrugated tube is greater than the actual requirement, the aperture surrounded by the arc-shaped protrusion 21 is adjusted to 55 mm, so that the distance between the arc-shaped protrusion 21 and the outer wall of the tube blank 4 is further increased.

[0107] Based on the above embodiments, combined with Figures 8 to 10, 12 and 13, the embodiment of the present invention provides a forming process of a corrugated tube. For the forming of a corrugated tube with wave number N, thickness t, wave pitch L0, wave peak width D0, wave valley diameter D1, wave peak diameter D2, and maximum axial dimensional accuracy error ΔL, the size of the intermediate mold 2 is combined with Fig.12 As shown, R1 is the fillet at the crest of the mold, which is generally 1 mm; ΔD is the mold surface adjustment size, which is the main influencing factor for the final springback of the formed part. It is determined according to the actual springback of the formed part and is generally 0.05D1. Before forming, multiple intermediate molds 2 can be fixed equidistantly between the moving mold 1 and the fixed mold 3, where the distance between the intermediate molds 2 is L1-L0, L1 is the initial billet length, which is expressed as km[D2-D1+(π / 2-1)L0], and km is the material influence coefficient, which is usually in the range of 1 to 1.1. During the forming process, Fig. 9 As shown, the punch is fed with displacement dPunch, and at the same time, the pressure P inside the tube is used to form the tube. Figure 8 As shown in Figure 2. The internal pressure P during the forming process is as follows: Fig.10 As shown. Among them, P1 is the internal pressure at the end of bulging, expressed as kP1σst / D1; P2 is the internal pressure at the end of drum wave, expressed as kP2σst / D1, kP1 and kP2 are the internal pressure influence coefficients, ranging from 2.3 to 2.5 and 2.8 to 3.0 respectively. The punch feed displacement dPunch during the forming process is as follows Fig.10 As shown. Among them, d1 is the displacement of the moving die 1 at the end of the push wave, expressed as kdN (L1-L0-ΔD), kd is the displacement influence coefficient, usually in the range of 0.8 to 1.2; d2 is the punch displacement at the end of compression, expressed as N (L1-L0). After the forming is completed, the component will produce an axial rebound of Δd. If the axial rebound Δd of the formed component is greater than the maximum error of the axial dimensional accuracy ΔL, it is necessary to increase the die surface adjustment size ΔD to further reduce the rebound.

[0108] For example, for the forming of TA34 corrugated pipe with a wave number N of 10, a thickness t of 1mm, a wave pitch L0 of 15mm, a wave peak width D0 of 10mm, a wave valley diameter D1 of 100mm, a wave peak diameter D2 of 120mm, and a maximum axial dimension accuracy error ΔL of 10mm, and a yield strength σs of 500MPa. The size R1 of the intermediate die 2 is 1mm, the die surface adjustment size ΔD is 5mm, and the other sizes are based on Fig.13 The initial blank length L1 is 28.5 mm, and the distance between the floating dies L1-L0 is 13.5 mm. During the forming process, the matching relationship between the displacement dPunch of the moving die 1 and the internal pressure P of the tube blank is given by Fig. 9 , Fig.10It is determined that the internal pressure P1 at the end of bulging is 12MPa, the internal pressure P2 at the end of drum wave is 15MPa, the punch displacement d1 at the end of push wave is 85mm, and the punch displacement d2 at the end of compression is 135mm. After the punch is unloaded at the end of forming, the component will produce an axial rebound of Δd. If the axial rebound Δd of the formed component is greater than the maximum error of the axial dimensional accuracy of 10mm, it is necessary to increase the mold surface adjustment size ΔD to further reduce the rebound.

[0109] In some embodiments, for the forming of high-precision corrugated tubes with a maximum axial dimension accuracy error of 1 mm, ΔD is 10 mm. The purpose is to generate a larger strain in the diameter reduction stage of the tube blank 4 to further control the springback.

[0110] In some embodiments, for the formation of a corrugated tube with a trough diameter D1 of 1000 mm and a peak diameter D2 of 1100 mm, the die surface adjustment dimension ΔD is 20 mm. The purpose is to use a relatively smaller compression amount to avoid wrinkling of the tube blank 4 for a structure with a large diameter-to-thickness ratio.

[0111] In some embodiments, for the forming of a multi-layer corrugated tube with a total thickness of 1 mm, the mold surface adjustment dimension ΔD is 10 mm. The purpose is to generate a larger strain in the compression stage of component forming to further control the springback.

[0112] In some embodiments, for forming a thicker corrugated tube with a thickness of 3 mm, the upper dimension R1 of the floating die is 3 mm, which is intended to increase the contact area between the intermediate die 2 and the tube blank 4 during the wave pushing process to reduce wear.

[0113] Optionally, the middle mold 2 is arranged to be movable along the radial direction of the tube blank 4 .

[0114] Specifically, the intermediate mold 2 can be hydraulically driven to move along the radial direction of the tube blank 4, that is, the distance between the intermediate mold 2 and the outer wall of the tube blank 4 is adjustable. In this way, by moving the intermediate mold 2 along the radial direction of the tube blank 4, the distance between the intermediate mold 2 and the outer wall of the tube blank 4 can be adjusted, thereby improving the use flexibility of the intermediate mold 2.

[0115] Optionally, there are multiple intermediate molds 2, and the multiple intermediate molds 2 are used to move synchronously along the radial direction of the tube blank 4.

[0116] Specifically, the plurality of intermediate dies 2 are all located between the movable die 1 and the fixed die 3. Among the plurality of intermediate dies 2, the leftmost intermediate die 2 is spaced a certain distance from the movable die 1, the leftmost intermediate die 2 is spaced a certain distance from the fixed die 3, and the adjacent intermediate dies 2 are arranged at equal intervals, and the plurality of intermediate dies 2 can be synchronously moved along the radial direction of the tube blank 4. In this way, by synchronously moving the plurality of intermediate dies 2 along the radial direction of the tube blank 4, while realizing the forming of a plurality of troughs, the moving accuracy of the plurality of intermediate dies 2 is improved, so as to improve the forming quality of the corrugated tube.

[0117] Optionally, the number of the intermediate molds 2 is N-1, where N is the number of waves of the corrugated pipe actually required. Specifically, when the number of waves N of the corrugated pipe is 5, the number of the intermediate molds 2 is 5-1=4. In this way, the intermediate mold 2 can form multiple troughs at one time, thereby improving the forming efficiency.

[0118] Optionally, the movable mold 1 is used to move toward the fixed mold 3 through a hydraulic drive structure. Specifically, the hydraulic drive structure is a hydraulic cylinder, and the output end of the hydraulic cylinder is drivingly connected to the movable mold 1 to control the movement of the movable mold 1 through the telescopic movement of the cylinder rod. In this way, through the driving connection between the hydraulic drive structure and the movable mold 1, the movement accuracy of the movable mold 1 can be effectively controlled to improve the movement stability of the movable mold 1 during the wave pushing process.

[0119] Optionally, the fixed die 3 is used to be fixed on a frame of a forming device, so that the stability of the fixed die 3 during the tube blank 4 forming process can be improved.

[0120] Although the disclosure is disclosed as above, the protection scope of the disclosure is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. A bellows forming springback control method based on stress regulation, characterized in that: include: According to the bending deformation process of the tube blank, a mold profile is constructed, and the curvature of the mold profile is set to be constant, so that the trough of the mold profile moves radially toward the axis of the tube blank; According to the material bending deformation principle, the difference between the axial strain of the inner surface of the trough of the mold surface and the axial strain of the neutral layer, and the difference between the circumferential strain of the inner surface and the circumferential strain of the neutral layer during radial movement are analyzed to obtain the plastic strain increment expression; According to the material plastic deformation yield condition expression, the plastic stress differential equation is obtained; According to the material bending deformation principle, the expression of the hoop strain increment is obtained; The expression of plastic strain increment, plastic stress differential equation and hoop strain increment is combined to obtain the expression of the relationship between hoop stress and axial stress. Based on the expression of the relationship between hoop stress and axial stress, a relationship curve is obtained with the hoop compression strain as the independent variable and the ratio of the axial stress to the value before compression as the dependent variable.

2. The bellows forming springback control method based on stress regulation according to claim 1, characterized in that: The step of causing the trough of the mold profile to move radially toward the axis of the tube blank comprises: The peak diameter of the required bellows is used as the peak diameter of the intermediate mold; and the difference between the peak diameter of the bellows and the inner diameter of the trough of the bellows is used as the first difference; Taking the difference between the diameter of the wave crest forming structure of the intermediate mold and the diameter of the wave trough forming structure of the intermediate mold as a second difference, so that the second difference is smaller than the first difference; Fix one end of the tube blank in the axial direction by a fixed die; fix the other end of the tube blank in the axial direction by a movable die; and cover the intermediate die on the portion of the tube blank located between the fixed die and the movable die; The tube blank is subjected to bulging and drum wave operations, and the tube blank is separated from the trough forming structure of the intermediate die by the push wave movement of the movable die toward the fixed die.

3. The bellows forming springback control method based on stress regulation according to claim 2, characterized in that: Also includes: The formed tube blank is subjected to pressure relief and unloading operations.

4. The bellows forming springback control method based on stress regulation according to claim 2, characterized in that: The fixed mold is fixed on a frame of a forming device, and the movable mold moves toward the fixed mold through a hydraulic drive system.

5. The bellows forming method according to claim 2, characterized in that: Also includes: The axial springback amount of the tube blank after forming is checked. If the axial springback amount of the tube blank after forming is greater than the actual required springback error range, the second difference is reduced.

6. A mold, based on the bellows forming springback control method based on stress regulation as described in any one of claims 1 to 5, characterized in that: It comprises a movable die, an intermediate die and a fixed die, all of which are arranged in a ring shape. The intermediate die is located between the movable die and the fixed die. The movable die and the fixed die are respectively used to be fixedly connected to the two ends of the tube blank in the axial direction. The movable die is used to be moved toward the fixed die. The movable die and the fixed die are both provided with a first arc surface structure at one end facing the intermediate die. The intermediate die is provided with an arc-shaped protrusion and a second arc surface structure located on both sides of the arc-shaped protrusion. The first arc surface structure cooperates with the second arc surface structure to form a peak forming groove, or two adjacent second arc surface structures on different intermediate dies cooperate to form a peak forming groove; the arc-shaped protrusion is used to form a trough of the corrugated tube; it is characterized in that the inner diameter of the intermediate die is larger than the inner diameters of the movable die and the fixed die.

7. The mold according to claim 6, characterized in that The intermediate mold is used to be movably arranged along the radial direction of the tube blank.

8. The mold according to claim 6, characterized in that There are multiple intermediate molds, and the multiple intermediate molds are used to move synchronously along the radial direction of the tube blank.

9. The mold according to claim 8, characterized in that The number of the intermediate molds is N-1, wherein N is the number of waves of the bellows actually required.

10. The mold according to claim 6, characterized in that The movable mold is used to move toward the fixed mold through a hydraulic driving structure.

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