A mandrel structure for reducing the friction between the mandrel and the inner wall of a tube during tube bending forming

Abstract

The application discloses a mandrel structure for reducing the friction between a mandrel and the inner wall of a pipe in a pipe bending forming process. The mandrel structure comprises a control shaft, a hollow core shaft and a plurality of inflatable core balls; the hollow core shaft and the plurality of inflatable core balls are arranged outside the control shaft; each inflatable core ball mainly comprises a rolling bearing, a base section, a return spring ring, a sliding pressure disc and an arc piece; the rolling bearing and the base section are sequentially sleeved outside the control shaft from inside to outside, the sliding pressure disc is sleeved outside the control shaft and is threadedly connected with the control shaft, the return spring ring and a plurality of wedge-shaped grooves which are uniformly arranged in a circumferential direction are arranged between the base section and the sliding pressure disc, one arc piece is arranged in each wedge-shaped groove, and all the arc pieces are connected through the return spring ring. The application can be used for pipe bending forming, has a simple structure, is convenient to adjust, can relieve the problems of scratch of the inner wall of the pipe, cross-section distortion defect and core extraction difficulty in pipe forming, and improves the pipe forming quality.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of pipe bending forming, and particularly relates to a mandrel structure for reducing friction between a mandrel and an inner wall of a pipe in a pipe bending forming process. BACKGROUND

[0002] Since a pipe is a hollow structure, cross-section distortion, wrinkling and other defects inevitably occur in the pipe during bending forming. Cross-section distortion and wrinkling of the bent pipe not only affect the appearance quality of the pipe-shaped component, but also affect the structural stability of the pipe-shaped component. When the bent pipe is used as a conveying pipeline, cross-section distortion and wrinkling of the bent pipe will cause pressure loss and flow pulsation of the conveyed fluid. In order to reduce cross-section distortion and wrinkling and other defects of the bent pipe, a mandrel is usually placed in the pipe blank as a support for bending.

[0003] The limitations of the mandrel currently maturely used in production in the pipe bending process mainly include the following aspects:

[0004] (1) Relative sliding between the mandrel and the inner wall of the pipe causes friction and wear of the inner wall of the pipe, affecting the surface quality of the inner wall of the pipe;

[0005] (2) Due to the friction between the inner wall of the pipe and the mandrel, the required bending force increases, which further aggravates the thinning trend of the cross-section of the pipe and even causes the pipe to crack;

[0006] (3) After the pipe bending is completed, it is difficult to extract the mandrel due to the deformation of the cross-section of the pipe;

[0007] (4) The support angle of the mandrel is small, and the mandrel cannot provide support for the pipe during the entire bending process. SUMMARY

[0008] In order to solve the problems in the background art, the present application provides a mandrel structure for reducing friction between a mandrel and an inner wall of a pipe in a pipe bending forming process, which effectively alleviates the friction problem between the existing mandrel and the inner wall of the pipe, improves the forming quality of the pipe, improves the surface roughness of the inner wall of the pipe, and has practical significance and good application prospect.

[0009] The technical solution adopted by the present application is as follows:

[0010] I. A mandrel structure for reducing friction between a mandrel and an inner wall of a pipe in a pipe bending forming process

[0011] The core rod structure comprises a control shaft, a hollow core shaft sleeved outside the control shaft, and a plurality of inflatable core balls; each inflatable core ball mainly comprises a rolling bearing, a base section, a reset spring ring, a sliding pressure plate, and N arc pieces; the rolling bearing and the base section are sequentially sleeved outside the control shaft from inside to outside, the sliding pressure plate is sleeved outside the control shaft and is threadedly connected with the control shaft, the reset spring ring and N wedge-shaped grooves arranged in a uniform circumferential direction are arranged between the base section and the sliding pressure plate, and one arc piece is inserted into each wedge-shaped groove, and all the arc pieces are connected through the reset spring ring.

[0012] The control shaft is divided into a driving part and a driven part, the driving part and the driven part are movably connected, the hollow core shaft is arranged outside the driving part, a plurality of inflatable core balls are arranged on the outer side of the driven part in an axial direction, the first inflatable core ball on the side close to the hollow core shaft is detachably connected with the hollow core shaft, and the adjacent two inflatable core balls are detachably connected.

[0013] The driving part of the control shaft comprises a driving shaft, and the driven part mainly comprises a plurality of driven shafts connected through constant velocity universal joints; the input end of the driving shaft is connected with an external driving mechanism in transmission through the hollow core shaft, and the output end of the driving shaft is connected with the driven shafts through the constant velocity universal joints; the number of the driven shafts is the same as that of the inflatable core balls and is arranged in one-to-one correspondence.

[0014] The base section mainly comprises a first connecting ring, a second connecting ring, and a base disc; the first connecting ring and the second connecting ring are arranged on the axial two sides of the base disc and are connected with the base disc, the base disc is arranged opposite to the sliding pressure plate, a square groove is formed through the sliding pressure plate, the number of the square groove, the first connecting ring, and the second connecting ring is the same, and they are arranged in axial alignment in correspondence; the second connecting ring is hingedly connected with the first connecting ring of the next inflatable core ball through the corresponding square groove.

[0015] N inclined grooves are formed on the opposite surfaces of the base disc and the sliding pressure plate in a uniform circumferential direction, and the inclined grooves on the two opposite surfaces are arranged in axial alignment in correspondence; the inner wall of the groove bottom of each inclined groove is provided as an inclined surface, the corresponding two inclined grooves form a wedge-shaped groove, and the axial width of the wedge-shaped groove increases from inside to outside.

[0016] The arc piece is mainly composed of an arc piece crown and an arc piece stem connected with each other; the arc piece crown adopts an arc-shaped sheet structure, two ends of the arc-shaped sheet structure are respectively provided with an arc-shaped extension and an arc-shaped recessed groove, two adjacent arc pieces are nested and matched through the arc-shaped extension and the arc-shaped recessed groove, and the arc piece crowns of all the arc pieces on the same inflatable core ball form a circular ring; the concave surface of the arc piece crown is arranged with the arc piece stem, the arc piece stem is provided with a reset spring hole, and a reset spring ring passes through the reset spring holes of all the arc pieces; and the end of the arc piece stem is provided with a wedge-shaped structure which is inserted into the wedge-shaped groove.

[0017] The hollow core shaft is provided with a core shaft positioning pin hole.

[0018] Two, a pipe bending forming method using the above core rod structure

[0019] The pipe bending forming method comprises the following steps:

[0020] S1, adjust all the inflatable core balls to the minimum diameter, place the core rod structure into the target position in the pipe to be bent, and drive the driving shaft and the external driving motor in transmission connection.

[0021] S2, use the driving motor to adjust the outer diameter of all the inflatable core balls to the target diameter; the step S2 is specifically as follows: use the driving motor to drive the driving shaft to rotate, the driving shaft drives all the driven shafts 7 to rotate, when each driven shaft rotates, the sliding pressure disc outside the driven shaft moves along the axial direction and approaches the base disc, the axial width of the wedge-shaped groove decreases, the arc piece in each wedge-shaped groove expands radially and further stretches the reset spring ring, the diameter of the circular ring formed by all the arc pieces increases, and the outer diameter of the inflatable core ball increases.

[0022] S3, bend the pipe to be bent.

[0023] S4, after the bending process is completed, use the driving motor to adjust all the inflatable core balls to the minimum diameter; the step S4 is specifically as follows: drive the driving shaft in reverse through the driving motor, drive all the driven shafts 7 in reverse, when each driven shaft reverses, the sliding pressure disc outside the driven shaft moves along the axial direction and moves away from the base disc, the axial width of the wedge-shaped groove increases, the arc piece in each wedge-shaped groove moves along the radial direction and moves inward under the elastic force of the reset spring ring, the diameter of the circular ring formed by all the arc pieces decreases, and the outer diameter of the inflatable core ball decreases.

[0024] S5, take out the core rod structure from the pipe after bending.

[0025] The beneficial effects of the present application are as follows:

[0026] (1) The present application can adjust the diameter of the mandrel after the mandrel structure is placed inside the pipe, and move with the pipe during the pipe bending process, avoiding the relative sliding between the mandrel and the inner wall of the pipe, and improving the surface quality of the inner wall of the pipe.

[0027] (2) The present application reduces the tension required for bending by following the mandrel and the pipe, reduces the cross-sectional thinning trend of the pipe, and reduces the risk of pipe cracking.

[0028] (3) The present application can reduce the diameter of the mandrel after bending by driving the motor, effectively alleviating the problem of core extraction difficulty.

[0029] (4) The present application can increase the number of inflatable core balls to provide support for the entire pipe bending process and improve the forming quality. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The overall structure of the mandrel structure in the present application is shown in the figure;

[0031] Figure 2 The overall structure of the inflatable core ball in the present application is shown in the figure, (a) is a structure diagram at the first angle, and (b) is a structure diagram at the second angle;

[0032] Figure 3 The assembly diagram of the inflatable core ball in the present application is shown in the figure;

[0033] Figure 4 The structure diagram of the base section in the present application is shown in the figure;

[0034] Figure 5 The structure diagram of the arc piece in the present application is shown in the figure;

[0035] Figure 6 The structure diagram of the inflatable core ball in the present application is shown in the figure, (a) is a diagram of the inflatable core ball inflated to the maximum diameter; (b) is a diagram of the inflatable core ball contracted to the minimum diameter;

[0036] Figure 7 The structure diagram of the control shaft in the present application is shown in the figure;

[0037] Figure 8 The overall diagram of the mandrel structure in the bending process of the present application is shown in the figure, (a) is a diagram before the pipe is bent and the inflatable core ball is inflated; (b) is a diagram before the pipe is bent and the inflatable core ball is inflated; (c) is a diagram after the pipe is bent and the core ball is contracted; (d) is a diagram after the pipe is bent and the core ball is contracted;

[0038] Figure 9 The structure and implementation of the present application is shown in the figure, (a) is a diagram before the pipe is bent; (b) is a diagram after the pipe is bent.

[0039] In the diagram: 1. Expandable core ball, 2. Control shaft, 3. Hollow mandrel, 4. Mandrel positioning pin hole, 5. First connecting ring, 6. Second connecting ring, 7. Driven shaft, 8. Rolling bearing, 9. Base section, 10. Arc plate, 11. Return spring ring, 12. Sliding pressure plate, 13. Base plate, 14. Arc plate crown, 15. Return spring hole, 16. Arc plate rod, 17. Drive shaft, 18. Constant velocity universal joint, 19. Spline at the input end of the drive shaft. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] The first aspect of the present invention provides a mandrel structure for reducing friction between the mandrel and the inner wall of the tube during the tube bending and forming process.

[0042] like Figure 1 As shown, the mandrel structure provided by the present invention includes a control shaft 2, a hollow mandrel 3 fitted on the outside of the control shaft 2, and several expandable core balls 1. The hollow mandrel 3 is coaxially arranged with the control shaft 2 and connected to it via bearings. Each expandable core ball 1 is coaxially arranged with the control shaft 2 and connected to it via bearings and threads.

[0043] The first expandable core ball 1 is connected to the hollow mandrel 3 via a hinge, while the remaining expandable core balls 1 are connected sequentially in an open-chain configuration. The control shaft 2 includes a driving shaft 17 and several driven shafts 7, connected by constant velocity universal joints 18. Each driven shaft 7 corresponds to one expandable core ball 1, allowing the number of expandable core balls 1 to be variable. In specific implementations, the number of expandable core balls 1 / driven shafts 7 can be set according to parameters such as the radius of the pipe to be bent and the target bending angle.

[0044] like Figure 2 and Figure 3 As shown, each expandable core ball 1 mainly consists of a rolling bearing 8, a base section 9, a return spring ring 11, a sliding pressure plate 12, and N arc plates 10. Figure 6 As shown, the sliding pressure plate 12 is fitted onto the outer side of the corresponding driven shaft 7 and is threaded into the corresponding driven shaft 7. A return spring coil 11 is arranged in the gap between the base section 9 and the sliding pressure plate 12, and the return spring coil 11 is coaxially arranged with the expandable core ball 1. N arc plates 10 are evenly distributed radially outside the return spring coil 11 along the circumferential spacing of the expandable core ball 1. The rolling bearing 8 and the base section 9 are sequentially fitted onto the outer side of the corresponding driven shaft 7 from the inside to the outside, and the base section 9 is connected to the corresponding driven shaft 7 in the control shaft 2 through the rolling bearing 8.

[0045] Further, the threaded cooperation between the sliding disc 12 and the corresponding driven shaft 7 means that a central hole is formed on the sliding disc 12 in the axial direction, a threaded hole is formed on the hole wall of the central hole, and the threaded hole of the sliding disc 12 is cooperated with the external thread of the corresponding driven shaft 7. When the driven shaft 7 rotates, the sliding disc 12 can be converted from rotation to axial movement through the threaded cooperation, and moves in the axial direction relative to the base section 9, and then approaches or moves away from the base section 9.

[0046] Further, a gap is formed between the base section 9 and the sliding disc 12, and N wedge-shaped grooves are arranged in the circumferential direction of the inflatable core ball 1 and are uniformly arranged, each wedge-shaped groove is arranged in the radial direction, and N arc pieces 10 are respectively inserted into the N wedge-shaped grooves, and the N arc pieces 10 are connected by a reset spring ring 11.

[0047] Further, the adjacent two arc pieces 10 are connected through the matching concave-convex structure.

[0048] Optionally, the connection between the sliding disc 12 and the corresponding driven shaft 7 in the control shaft 2 through the rolling bearing 8 is that the sliding disc 12 is in interference fit with the rolling bearing 8, and the rolling bearing 8 is in interference fit with the control shaft 2.

[0049] Optionally, the connection between the sliding disc 12 and the corresponding driven shaft 7 in the control shaft 2 through the rolling bearing 8 is that an axial positioning component is arranged on the driven shaft 7, the axial positioning component is arranged in cooperation with the rolling bearing 8, and then the axial positioning of the sliding disc 12 is realized.

[0050] Optionally, the rolling bearing 8 is a deep groove ball bearing, and in specific implementation, other bearings can also be selected according to other specific structural needs.

[0051] As shown in Figure 1 , the control shaft 2 is divided into a driving part and a driven part in the axial direction, and the driving part and the driven part are movably connected at one end close to each other. The hollow core shaft 3 is arranged on the radial outer side of the driving part of the control shaft 2, and a plurality of inflatable core balls 1 are arranged on the radial outer side of the driven part of the control shaft 2, each inflatable core ball 1 is sequentially connected in series and is uniformly arranged in the axial direction of the control shaft 2; the driving part of the control shaft 2 is connected with the hollow core shaft 3 through a bearing; and the driven part of the control shaft 2 is connected with the inflatable core ball 1 through a bearing and a thread.

[0052] As shown in Figure 1 and Figure 2 , the first inflatable core ball 1 on the side close to the hollow core shaft 3 (the right side in Figure 1 ) is connected with one end of the hollow core shaft 3 (the left end in Figure 1The first inflatable core ball 1 is detachably connected with the hollow core shaft 3 on one side and detachably connected with the second inflatable core ball 1 on the other side. The last inflatable core ball 1 is detachably connected with the preceding inflatable core ball 1 on one side and left free on the other side. The plurality of inflatable core balls 1 are detachably connected in sequence to form an open chain structure.

[0053] The detachable connection is mainly achieved by the following structure:

[0054] The base section 9 mainly comprises a base disc 13, a plurality of first connecting rings 5 and a plurality of second connecting rings 6. The rolling bearing 8 and the base disc 13 are sequentially sleeved in the control shaft 2 outside the corresponding driven shaft 7 from inside to outside, the base disc 13 is connected with the corresponding driven shaft 7 in the control shaft 2 through the rolling bearing 8, and the base disc 13 is arranged opposite to the sliding pressure disc 12. The first connecting ring 5 and the second connecting ring 6 are arranged on the two axial sides of the base disc 13 respectively and are fixedly connected with the base disc 13, and are used for connecting the adjacent two inflatable core balls 1 or the first inflatable core ball 1 and the hollow core shaft 3.

[0055] The first connecting ring 5 and the second connecting ring 6 are divided into surfaces on the side of the base disc 13 away from and close to the sliding pressure disc 12. A plurality of square grooves are provided through the sliding pressure disc 12, the number of the square grooves, the first connecting ring 5 and the second connecting ring 6 is the same, and they are arranged in alignment along the axial direction respectively. The second connecting ring 6 is connected with the first connecting ring 5 on the rear inflatable core ball 1 through the corresponding square groove (aligned along the axial direction), so that the sliding pressure disc 12 is sleeved on the base disc 13. The sliding pressure disc 12 can move axially relative to the base disc 13, while limiting the relative rotation of the sliding pressure disc 12 and the base section 9.

[0056] Preferably, each square groove / first connecting ring 5 / second connecting ring 6 is arranged in a central symmetry along the circumferential direction. As shown in Figs. Figure 2 and Figure 3 In the embodiment of the present application, the number of the square grooves, the first connecting ring 5 and the second connecting ring 6 is two, and the two square grooves / first connecting ring 5 / second connecting ring 6 are arranged on the same radial straight line in a symmetry.

[0057] The implementation mode of the second connecting ring 6 connected with the corresponding first connecting ring 5 is as follows: a pin hole is provided on each of the first connecting ring 5 and the second connecting ring 6 along the radial direction, the pin holes on each first connecting ring 5 and the corresponding second connecting ring 6 are aligned, a pin is inserted into the pin holes, and the second connecting ring 6 is connected with the corresponding first connecting ring 5 through the cooperation of the pin holes and the pin.

[0058] The hinging of the second connecting ring 6 and the first connecting ring 5 enables the expandable core ball 1 to be detachably hinged with an adjacent expandable core ball 1 or the hollow core shaft 3, thereby enabling the relative rotation between two adjacent expandable core balls 1 or between the first expandable core ball 1 and the hollow core shaft 3 with the pin shaft as the rotation axis.

[0059] The axial width of each wedge-shaped groove can be adjusted by changing the distance between the base disc 13 and the sliding disc 12, and the specific implementation is as follows:

[0060] As shown in Figure 4 , N inclined grooves are arranged on the opposite faces of the base disc 13 and the sliding disc 12 in a uniform circumferential interval, and the inclined grooves on the two opposite faces are arranged in corresponding alignment along the axial direction. Each inclined groove is radially arranged and extends to the outer periphery, and the inner wall of the groove bottom of each inclined groove is arranged as an inclined surface, so that the axial depth of the inclined groove increases from inside to outside. The two inclined grooves on the base disc 13 and the sliding disc 12 in corresponding alignment along the axial direction constitute a wedge-shaped groove, and the axial width of the wedge-shaped groove increases from inside to outside along the radial direction. As shown in Figure 6 , the width of the radial cross section of each wedge-shaped groove increases from inside to outside along the radial direction.

[0061] As shown in Figure 5 , the arc piece 10 includes an arc piece crown 14 and an arc piece rod 16 connected thereto. The arc piece crown 14 adopts an arc-shaped sheet structure, and the two ends of the arc-shaped sheet structure are respectively provided with an arc-shaped extension and an arc-shaped recess groove. The adjacent two arc pieces 10 are nested and fitted through the arc-shaped extension and the arc-shaped recess groove, and the arc piece crowns 14 of all the arc pieces 10 on the same expandable core ball 1 are spliced to constitute a circular ring coaxial with the expandable core ball 1 / control shaft 2. As shown in Figures 1-3 , the nested and fitted of the adjacent two arc pieces 10 through the arc-shaped extension and the arc-shaped recess groove specifically means that the arc-shaped extension of each arc piece 10 is inserted into the arc-shaped recess groove of the previous arc piece 10, and the arc-shaped recess groove of the previous adjacent arc piece 10 is gap fitted, so that the two arc pieces 10 are limited in the axial direction but have the freedom in the radial direction.

[0062] The concave surface of the arc piece crown 14 is arranged with the arc piece rod 16, and the arc piece rod 16 is fixedly connected with the arc piece crown 14. The arc piece rod 16 is provided with a reset spring hole 15, and the reset spring hole 15 is circumferentially arranged and penetrates through the arc piece rod 16. The reset spring ring 11 penetrates through the reset spring holes 15 of all the arc pieces 10, so that all the arc pieces 10 of the same expandable core ball 1 are connected through the reset spring ring 11.

[0063] The end of the arc piece rod part 16 away from the arc piece crown part 14 is provided with a wedge structure, the angle of the wedge structure is matched with the angle of the inclined groove, so that the wedge structure matches the wedge-shaped groove formed by the inclined groove on the base disc 13 and the inclined groove on the sliding pressure plate 12, the wedge structure is inserted into the wedge-shaped groove and tightly matches the wedge-shaped groove under the action of the reset spring ring 11.

[0064] As shown in Figure 7 The driving part of the control shaft 2 includes a driving shaft 17, and the driven part is mainly connected by a plurality of driven shafts 7 through constant velocity universal joints 18. The input end of the driving shaft 17 is in transmission connection with an external driving mechanism after penetrating through the hollow core shaft 3, and the output end of the driving shaft 17 is connected with the driven shaft 7 through the constant velocity universal joint 18. Specifically, the end of the driving shaft 17 close to the driven part is the output end, and the end away from the driven part is the input end. The input end of the driving shaft 17 is provided with a driving shaft input end spline 19, and the input end of the driving shaft 17 is in transmission connection with the external driving mechanism through the driving shaft input end spline 19 after penetrating through the hollow core shaft 3, so that the driving mechanism can drive the driving shaft 17 to rotate. The output end of the driving shaft 17 is provided with a driving shaft ball head, and the hollow core shaft 3 is sleeved outside the input end and the output end of the driving shaft 17. The input end of each driven shaft 7 is provided with a driven shaft ball cage, and the output end is provided with a driven shaft ball head. The output end of the driving shaft 17 is connected with the input end of the first driven shaft 7 through the constant velocity universal joint 18, the output end of each driven shaft 7 is connected with the input end of the next driven shaft 7 through the constant velocity universal joint 18, and the output end of the last driven shaft 7 is empty.

[0065] As shown in Figure 7 The driven shaft 7 is arranged in one-to-one correspondence with the number of the expandable core ball 1. As shown in Figure 6 The one-to-one correspondence between the driven shaft 7 and the expandable core ball 1 specifically means that one expandable core ball 1 is arranged in one-to-one correspondence on the radial outer side of each driven shaft 7. Each driven shaft 7 is provided with external threads on the outer circumferential surface of the rod part, which are matched with the central hole threads of the sliding pressure plate 12. The driven shaft 7 and the sliding pressure plate 12 are connected through the threads, so that when the driven shaft 7 rotates, the sliding pressure plate moves axially, thereby changing the width of the wedge-shaped groove formed by the sliding pressure plate 12 and the base disc 13, and changing the radial position of the arc piece 10.

[0066] Further, the hollow core shaft 3 is provided with a core shaft positioning pin hole 4, which is matched with another positioning pin shaft, and is used to limit the axial rotation of the core rod structure that may occur during bending processing.

[0067] The second aspect of the present application provides a pipe bending forming method using the above-mentioned core rod structure. When the pipe bending processing is performed, the gap between the sliding pressure plate 12 on the expandable core ball and the base disc 13 is changed by driving the motor to drive the control shaft to rotate, so that the core ball is accurately expanded or contracted in the pipe.

[0068] The tube bending forming method provided by the present invention includes the following steps:

[0069] S1, such as Figure 8 As shown in (a), the sliding pressure plate 12 in all expandable core balls 1 is adjusted to the initial position so that all expandable core balls 1 are adjusted to the minimum diameter; at the same time, the axial target position of the mandrel structure in the tube to be bent is determined according to the processing requirements, and the mandrel structure is placed in the target position in the tube to be bent, that is, the expandable core ball 1 is placed between the bending start section and the bending end section, and then the positioning pin is installed using the mandrel positioning pin hole on the hollow mandrel 3. The axial rotation of the mandrel structure that may occur during the bending process is limited by the cooperation between the positioning pin and the mandrel positioning pin hole; then the input end of the drive shaft 17 is connected to the external drive motor through the spline 19 of the drive shaft input end.

[0070] Specifically, when the sliding pressure plate 12 is in the initial position, the axial width of the wedge groove between the sliding pressure plate 12 and the base plate 13 is at its maximum, the reset spring coil 11 is in a stretched state, and the wedge structure of the arc plate rod 16 is tightly fitted with the wedge groove under the elastic force of the reset spring coil 11, allowing the expandable core ball 1 to be adjusted to its minimum diameter.

[0071] Furthermore, step S1 also includes: after determining the number of expandable core balls 1 based on the bending radius and angle of the pipe fitting, installing the target number of driven shafts 7 and expandable core balls 1 at the output end of the drive shaft 17.

[0072] S2, such as Figure 8 As shown in (b), the outer diameter of all expandable core balls 1 is adjusted to the target diameter using a drive motor.

[0073] Step S2 is as follows: The drive motor drives the drive shaft 17 to rotate, and the drive shaft 17 drives all driven shafts 7 to rotate synchronously. When each driven shaft 7 rotates, the sliding pressure plate 12 on the outside of the driven shaft 7 achieves the conversion from rotation to axial movement through the threaded engagement, so that the sliding pressure plate 12 moves axially relative to the base plate 13 and approaches the base plate 13. The axial width of the wedge groove between the sliding pressure plate 12 and the base plate 13 decreases, and the arc plate 10 in each wedge groove expands radially and further stretches the return spring coil 11. The wedge structure of the arc plate rod 16 is tightly engaged with the wedge groove under the elastic force of the return spring coil 11. The diameter of the ring formed by splicing all the arc plates 10 increases, and the outer diameter of the expandable core ball 1 increases accordingly, ensuring the clamping force between each expandable core ball 1 and the inner wall of the pipe to be bent.

[0074] S3, such as Figure 8As shown in (c), the pipe to be bent is bent; during the bending process, the drive shaft 17 does not rotate, and the mandrel structure moves axially with the pipe to ensure that the expandable core ball 1 does not slide relative to the inner wall of the pipe to be bent.

[0075] S4, such as Figure 8 As shown in (d), after the bending process is completed, all expandable core balls 1 are simultaneously adjusted to the minimum diameter using a drive motor.

[0076] Step S4 specifically involves: driving the drive motor to rotate the drive shaft 17 in the reverse direction, which in turn drives all driven shafts 7 to rotate in the reverse direction. When each driven shaft 7 rotates in the reverse direction, the sliding pressure plate 12 on the outer side of the driven shaft 7 achieves a conversion from rotation to axial movement through threaded engagement. This causes the sliding pressure plate 12 to move axially relative to the base plate 13 and move away from the base plate 13. The axial width of the wedge-shaped groove between the sliding pressure plate 12 and the base plate 13 increases. Under the reset force of the reset spring coil 11, the arc plate 10 within each wedge-shaped groove moves radially inward. The ring formed by the splicing of all the arc plates 10 radially contracts, reducing its diameter, and consequently reducing the outer diameter of the expandable core ball 1. When the sliding pressure plate 12 moves to its initial position, all expandable core balls 1 are adjusted to their minimum diameter.

[0077] S5. When all expandable core balls 1 are adjusted to their minimum diameter, the mandrel structure is extracted from the bent tube, and the bending process is completed.

[0078] Comparative Example

[0079] This comparative example provides an existing mandrel structure for bending processes, as shown in the schematic diagram below. Figure 9 As shown in (a), the schematic diagram of the bending embodiment is as follows. Figure 9 As shown in (b).

[0080] When using the mandrel structure in this comparative example for tube bending, the mandrel ball needs to be completely positioned at the front end of the bending initiation section before bending. Figure 9 The right end of (a); during the bending process, there is no relative displacement between the mandrel and the bending center, but there is relative displacement with the inner wall of the pipe, which may scratch the inner wall of the pipe.

[0081] Before bending the pipe, multiple expandable core balls 1 are placed between the bending start section and the bending end section. During the bending process, the core structure moves axially with the pipe, that is, there is a relative displacement between the core structure and the bending center, but no relative displacement with the inner wall of the pipe, thereby reducing the damage to the inner wall of the pipe.

[0082] The above detailed description is intended to explain and describe the application, but not to limit the application. Any modification and change within the spirit and scope of the application will be included in the scope of the application.

Claims

1. A mandrel structure for reducing friction between the mandrel and the inner wall of the tube during tube bending and forming, characterized in that: The mandrel structure includes a control shaft (2), a hollow mandrel (3) fitted on the outside of the control shaft (2), and several expandable core balls (1). The control shaft (2) includes a drive shaft (17) and several driven shafts (7), which are connected by constant velocity universal joints (18); the drive shaft (17) is connected to an external drive mechanism. The number of driven shafts (7) and expandable core balls (1) are the same and they are arranged in a one-to-one correspondence; Each expandable core ball (1) includes a rolling bearing (8), a base section (9), a return spring ring (11), a sliding pressure plate (12), and N arc plates (10); the rolling bearing (8) and the base section (9) are sequentially fitted onto the outer side of the corresponding driven shaft (7) from the inside to the outside, and the sliding pressure plate (12) is fitted onto the outer side of the corresponding driven shaft (7) and threadedly engaged with the driven shaft (7); a return spring ring is arranged between the base section (9) and the sliding pressure plate (12). (11) and N wedge-shaped grooves evenly spaced along the circumference, the axial width of the wedge-shaped grooves increasing from the inside to the outside, each wedge-shaped groove having an arc plate (10) inserted in it, the arc plate (10) including an arc plate crown (14) and an arc plate rod (16) connected to each other; the end of the arc plate rod (16) is provided with a wedge-shaped structure, the wedge-shaped structure being inserted into the wedge-shaped groove; the arc plate rods (16) of all the arc plates (10) are connected by a return spring coil (11); The base section (9) includes a first connecting ring (5), a second connecting ring (6), and a base plate (13); the base plate (13) is connected to the corresponding driven shaft (7) through a rolling bearing (8), the first connecting ring (5) and the second connecting ring (6) are respectively arranged on both sides of the axial direction of the base plate (13) and are both connected to the base plate (13), the base plate (13) is arranged opposite to the sliding pressure plate (12), the sliding pressure plate (12) is provided with a square groove, the square groove, the first connecting ring (5) and the second connecting ring (6) are the same in number and are respectively aligned and arranged in the axial direction; the second connecting ring (6) passes through the corresponding square groove and is hinged to the corresponding first connecting ring (5) on the next expandable core ball (1) by a pin; The drive mechanism can drive the drive shaft (17) to rotate. The drive shaft (17) drives all driven shafts (7) to rotate synchronously. When each driven shaft (7) rotates, the sliding pressure plate (12) moves axially relative to the base plate (13) and approaches the base plate (13), increasing the outer diameter of the expandable core ball (1). When each driven shaft (7) rotates in the opposite direction, the sliding pressure plate (12) moves axially relative to the base plate (13) and moves away from the base plate (13), reducing the outer diameter of the expandable core ball (1).

2. The mandrel structure for reducing friction between the mandrel and the inner wall of the tube during tube bending and forming according to claim 1, characterized in that: The base plate (13) and the sliding pressure plate (12) each have N inclined grooves evenly spaced along the circumference on their opposite surfaces. The inclined grooves on the two opposite surfaces are aligned and arranged in the axial direction. The inner wall of the bottom of each inclined groove is set as an inclined surface, and two corresponding inclined grooves form a wedge-shaped groove.

3. The mandrel structure according to claim 1 for reducing friction between the mandrel and the inner wall of the tube during tube bending and forming, characterized in that: The arc-shaped crown (14) adopts an arc-shaped sheet structure. The two ends of the arc-shaped sheet structure are respectively provided with an arc-shaped extension and an arc-shaped recessed groove. Two adjacent arc plates (10) are nested and matched through the arc-shaped extension and the arc-shaped recessed groove. The arc-shaped crowns (14) of all arc plates (10) on the same expandable core ball (1) form a ring. The arc plate rod (16) is provided with a reset spring hole (15), and the reset spring coil (11) passes through the reset spring holes (15) of all the arc plates (10).

4. The mandrel structure for reducing friction between the mandrel and the inner wall of the tube during tube bending and forming according to claim 1, characterized in that: The hollow mandrel (3) is provided with a mandrel positioning pin hole (4).

5. A tube bending forming method using a mandrel structure as described in any one of claims 1 to 4, characterized in that: The tube bending and forming method includes the following steps: S1. Adjust all expandable core balls (1) to the minimum diameter, place the mandrel structure into the target position inside the tube to be bent, and connect the drive shaft (17) to the external drive motor. S2. Use the drive motor to adjust the outer diameter of all expandable core balls (1) to the target diameter; S3. Perform bending processing on the pipe to be bent; S4. After the bending process is completed, use the drive motor to adjust all expandable core balls (1) to the minimum diameter; S5. Remove the mandrel structure from the bent tube.

6. The tube bending forming method according to claim 5, characterized in that: The specific steps of step S2 are as follows: the drive motor drives the active shaft (17) to rotate, the active shaft (17) drives all driven shafts 7 to rotate, when each driven shaft (7) rotates, the sliding pressure plate (12) on the outside of the driven shaft (7) moves axially and approaches the base plate (13), the axial width of the wedge groove decreases, the arc plate (10) in each wedge groove bulges radially and further stretches the reset spring ring (11), the diameter of the ring formed by all the arc plates (10) increases, and the outer diameter of the expandable core ball (1) increases.

7. The tube bending forming method according to claim 5, characterized in that: The specific steps of step S4 are as follows: the drive motor drives the active shaft (17) to rotate in the opposite direction, the active shaft (17) drives all driven shafts (7) to rotate in the opposite direction, when each driven shaft (7) rotates in the opposite direction, the sliding pressure plate (12) on the outside of the driven shaft (7) moves axially and away from the base plate (13), the axial width of the wedge groove increases, the arc plate (10) in each wedge groove moves radially inward under the elastic force of the reset spring ring (11), the diameter of the ring formed by all the arc plates (10) decreases, and the outer diameter of the expandable core ball (1) decreases.

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