Rotary extrusion forming method for magnesium alloy thin-wall inner-ring high-rib component under assistance of pulse current

Abstract

The invention discloses a rotating extrusion forming method for a magnesium alloy thin-wall inner-ring high-rib component under the assistance of pulse current, a forming device is applied, the forming device comprises a male die, the male die can extend into the inner wall of a cylindrical magnesium alloy blank, and convex ribs are extruded on the inner wall of the cylindrical magnesium alloy blank. Firstly, pulse current is introduced into a magnesium alloy blank through a male die, the pulse current is made to conduct partial discharge on the magnesium alloy blank at an extrusion point, and the pulse current is continuously introduced in the extrusion process. According to the method, the pulse current is firstly introduced before extrusion, so that the magnesium alloy blank at an extrusion point is softened, the flowability of the magnesium alloy blank is effectively improved, the extrusion resistance is reduced, the pulse current is continuously introduced in the extrusion process, the blank is continuously softened, a mold is protected, and the forming precision is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal plastic forming, in particular to a pulse current assisted magnesium alloy thin-walled inner ring high rib component rotary extrusion forming method. BACKGROUND

[0002] The integrated thin-walled high rib component is a key carrier for breaking through the technical bottleneck of large carrying capacity, low energy consumption and high reliability in aerospace and strategic equipment (such as large carrying capacity rockets, missile shells and underwater vehicles), and its performance directly determines the core competitiveness of the equipment.

[0003] At present, using light and high-strength magnesium alloy components is an ideal choice to achieve extreme lightweight, however, the difficult deformation characteristics of magnesium alloy and the complex geometric characteristics of the extreme coupling of thin-walled and high-rib size make the traditional manufacturing technology face many problems such as insufficient forming precision, high defect rate and substandard performance. When the traditional rotary extrusion technology is used to extrude magnesium alloy blanks, local strain mismatch is easily caused, which in turn induces defects such as folding and incomplete filling, resulting in low forming precision of magnesium alloy thin-walled inner ring high rib components. SUMMARY

[0004] The purpose of the present application is to provide a pulse current assisted magnesium alloy thin-walled inner ring high rib component rotary extrusion forming method, which solves the technical problem of providing an extrusion method for magnesium alloy thin-walled inner ring high rib components with high forming precision.

[0005] To achieve the above purpose, the solution of the present application is: a pulse current assisted magnesium alloy thin-walled inner ring high rib component rotary extrusion forming method, which applies a forming device, the forming device includes a punch, the punch can extend into the inner wall of the cylindrical magnesium alloy blank, and extrude a convex rib on the inner wall, before extrusion, the punch passes pulse current to the magnesium alloy blank, the pulse current locally discharges the magnesium alloy blank at the extrusion point to soften the magnesium alloy blank at the extrusion point, and the pulse current is continuously passed during the extrusion process.

[0006] Further, the side wall of the punch is transversely protruded with a plurality of rib strips, the plurality of rib strips are longitudinally spaced apart, forming grooves between adjacent rib strips, and the end faces of the two adjacent rib strips form flow guide surfaces on both sides of the groove entrance, respectively, the two flow guide surfaces are inclined towards the direction of the groove, respectively, the punch extrudes the inner wall of the magnesium alloy blank through the rib strips, so that the magnesium alloy blank flows into the groove along the flow guide surfaces, the cross-sectional profile of the bottom wall of the groove is in the shape of a circular arc with a radius R0, the middle part of the bottom wall of the groove bulges towards the end part of the rib strip, and the two sides of the bottom wall of the groove extend away from the end part of the rib strip, respectively, the inner wall of the alloy blank is in the shape of a circular ring with a radius R1, R1 is greater than R0, when the magnesium alloy blank abuts against the middle part of the bottom wall of the groove, the side wall of the punch is spaced apart from the inner wall of the magnesium alloy blank, the rib strip continuously extrudes, and the magnesium alloy blank flows along the circumferential direction towards the two sides of the bottom wall of the groove, respectively.

[0007] Furthermore, the inner wall of the magnesium alloy billet is annular with a radius of R1, and the outer contour of the rib end is arc-shaped with a radius of R2. R1 is greater than R2. During the process of the rib extruding the inner wall of the magnesium alloy billet, point contact is formed first, and then the extrusion surface gradually increases.

[0008] Furthermore, the peak current density of the pulse current is 100–250 A / mm², and the pulse frequency is 100–500 Hz.

[0009] Furthermore, the forming device also includes a die, a pulse current device, and an ejection device. The center of the magnesium alloy billet is the billet cavity. The die forms a cavity with a top-side opening and is connected to a rotating device. The punch is located directly above the cavity and can move up and down. The punch is composed of multiple segments, each segment of which can laterally expand outward or laterally converge. The method includes the following steps: Step 1, Pre-forming preparation: The magnesium alloy blank to be formed is inserted downward into the cavity. The multiple segments of the punch are connected to the cathode of the pulse current device through wires, and the die is connected to the anode of the pulse current device through wires. The pulse current device is energized. Step 2, Height Positioning: The punch descends to the predetermined height and is inserted into the inner cavity of the blank; Step 3, extrusion forming: Multiple petals expand radially away from the outside and abut against the inner wall of the blank cavity to form a current loop. The multiple petals continue to expand outward, and the ribs squeeze the inner wall of the blank cavity. The magnesium alloy blank flows into the groove along the guide surface. When the magnesium alloy blank abuts against the middle of the bottom wall of the groove, the multiple petals continue to expand outward. The magnesium alloy blank flows circumferentially towards both sides of the bottom wall of the groove and fills the groove laterally. Step 4, Rotary extrusion forming: The rotating device drives the die to rotate horizontally to different angles and continuously applies pulse current. The ribs extrude different areas to be formed at the same height in the inner cavity of the blank until the inner wall of the blank at the predetermined height is extruded to form a ring-shaped rib. Step 5: Unload the material, turn off the pulse current, multiple petals approach and close laterally, and rise and exit the inner cavity of the blank. The ejector device pushes the formed component upward out of the cavity to complete the demolding.

[0010] Furthermore, after step 4 is completed, steps 2 to 4 are repeated to lower the punch to different heights and extrude ribs of different heights on the inner wall of the blank cavity.

[0011] Furthermore, in step 4, before each rotation of the rotating device, while the ribs remain in contact with the inner cavity of the billet, multiple petals first move laterally closer and exit the inner wall of the billet cavity. After the rotating device rotates, step 3 is repeated.

[0012] After adopting the above solution, the beneficial effects of the present invention are as follows: (1) Before extrusion, pulse current is passed through the magnesium alloy blank first to soften the magnesium alloy blank at the extrusion point, to significantly reduce the flow stress of the magnesium alloy by using the electroplastic effect, to reduce the forming load, to improve the flowability and filling performance of the magnesium alloy blank by using the Joule heating effect to assist in softening the material, to make the blank more easily extruded and filled into the groove, and to improve the forming precision of the component; (2) Secondly, during the extrusion process, the rib end abuts against the inner cavity of the blank first to form point contact, the point contact forms local high extrusion pressure, the force is concentrated, the extrusion resistance is reduced, the initial deformation zone is formed, with the continuous feeding of the extrusion, line contact and surface contact are gradually formed between the two, the contact surface gradually expands, the flow direction of the blank tends to be consistent, the turbulence is reduced, and after the formation of surface contact extrusion, the compressive stress is uniform, and during the extrusion process, the continuous discharge of the pulse current plays a maximum role in the plastic effect of the pulse current on the magnesium alloy blank, at the same time, under the guidance of the flow guide surface, the blank is extruded into the groove, after the blank continues to extrude into the groove, the blank abuts against the back pressure area in the middle of the groove, the back pressure area is extruded by the blank, and at the same time, with the continuous expansion of the petal part, the blank continues to flow into the groove laterally, the blank is filled into the groove on both sides under the action of the back pressure and the lateral extrusion of the blank, which effectively promotes the flow of the blank along the circumference to both sides of the groove, so that the blank is more easily filled into the groove. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is a structure diagram of the male die inserted into the inner cavity of the blank of the present application.

[0014] Figure 2 is a structure diagram of the pulse current device and the male die and the female die of the present application.

[0015] Figure 3 is a structure diagram of the magnesium alloy blank forming demolding of the present application.

[0016] Figure 4 is a structure diagram of the male die rib of the present application.

[0017] Figure 5 is a structure diagram of the male die of the present application.

[0018] Figure 6 is Figure 5 A-A radial cross-sectional view.

[0019] Figure 7 is a radial cross-sectional view of the petal part abutting against the inner cavity of the blank of the present application.

[0020] Figure 8 is a longitudinal cross-sectional view of the magnesium alloy blank abutting against the middle of the bottom wall of the groove of the present application.

[0021] Figure 9is a comparison chart of the extrusion forming effect of the present application and the traditional extrusion forming effect.

[0022] Explanation of reference numerals 1-die, 2-punch, 3-pulse current device, 4-magnesium alloy blank, 5-petal, 6-top die plate, 7-driving member, 8-die sleeve, 9-rotating device, 10-top plate, 11-bottom die plate, 12-ejector pin, 14-wire, 21-rib, 22-groove, 23-flow guide surface, 24-electrode contact, 41-blank inner cavity, 42-protruding rib, 51-second inclined surface, 52-left petal, 53-right petal, 71-first inclined surface, 101-cavity, 221-outer side arc, 222-inner side arc. DETAILED DESCRIPTION

[0023] The application is described in detail below in conjunction with the drawings and specific examples.

[0024] In the claims, specification, and drawings of the present application, terms such as "center", "transverse", "longitudinal", "horizontal", "vertical", "top", "bottom", "inner", "outer", "upper", "lower", "front", "back", "left", "right", "clockwise", "counterclockwise", and the like, merely indicate directions or positions for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation or be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the specific protection scope of the present application.

[0025] As shown in Figures 1-9 The present application provides an extrusion forming method for a magnesium alloy thin-walled inner ring high-rib component, which applies a forming device, the forming device further comprises a die 1, a punch 2, a pulse current device 3, a top die plate 6, a driving member 7, a die sleeve 8, a rotating device 9, an ejector device, and a bottom die plate 11, and further comprises a rotary extruder (not shown in the figure), the punch 2 can extend into the inner wall of the cylindrical magnesium alloy blank 4 to extrude the protruding rib 42 on the inner wall, before extrusion, the pulse current is passed through the punch 2 to the magnesium alloy blank 4 to locally discharge the magnesium alloy blank 4 at the extrusion point, and the pulse current is continuously passed during the extrusion process. Figure 1 As shown in Figure 7As shown in the figure, the number of ribs 21 is preferably 2, and a groove 22 is formed between the two ribs 21. Figure 4 As shown in the figure, the angle α between the two flow guide surfaces 23 on both sides of the entrance of the groove 22 is 135°-145°.

[0026] The key combination Figures 6-7 As shown in the figure, the magnesium alloy blank 4 has a blank inner cavity 41 in the center, the inner contour of the blank inner cavity 41 is a circular ring with a radius R1, the outer contour of the rib 21 is a circular arc with a radius R2, the cross-sectional contour of the bottom wall of the groove 22 is a circular arc with a radius R0, the middle part of the bottom wall of the groove 22 bulges towards the end of the rib 21, and the two sides of the bottom wall of the groove 22 extend away from the end of the rib 21, and R1>R2>R0. When the male die 2 laterally contacts and extrudes the blank inner cavity 41, the extrusion surface between the rib 21 and the blank inner cavity 41 gradually increases. When the magnesium alloy blank 4 flows into the groove 22 and abuts against the middle part of the bottom wall of the groove 22, the side wall of the male die 2 is spaced from the inner wall of the blank inner cavity 41, and the spacing is represented by d (as shown in the figure). Figure 8 As shown in the figure, the male die 2 continues to feed, and the rib 21 is continuously extruded. The magnesium alloy blank 4 in the groove 22 is subjected to back pressure from the bottom wall of the groove 22 and lateral extrusion force from the continuously flowing magnesium alloy blank 4. Under the combined action of the two, the magnesium alloy blank 4 flows freely along the circumference to the two sides of the groove 22, until it gradually fills the groove 22.

[0027] Preferably, the cross section of the groove 22 is a crescent structure, which makes it easier for the magnesium alloy blank 4 to flow to the two sides of the groove 22 after flowing into the groove 22, effectively improving the forming precision of the component. The crescent cross section has an outer arc 221 and an inner arc 222. The inner arc 222 is the bottom wall of the groove 22, the radius of the outer arc 221 is greater than that of the inner arc 222, and the eccentric distance between them is n, the eccentric distance n=Δb, Δb is the total radial feed amount, that is, the feed amount of the radial extrusion after the rib 21 abuts against the blank inner cavity 41. In this specific embodiment, the male die 2 extends longitudinally, and its cross section is a radial cross section.

[0028] In this specific embodiment, the female die 1 forms a top-side-opened cavity 101, and the cavity 101 has a ring structure with an inner contour consistent with the outer contour of the magnesium alloy blank 4. The cavity 101 is for the magnesium alloy blank 4 to embed downward. The male die 2 is located directly above the cavity 101 and can be raised and lowered. After the magnesium alloy blank 4 is embedded in the cavity 101, the male die 2 can be lowered and inserted into the blank inner cavity 41, or raised and withdrawn from the blank inner cavity 41. Specifically, the male die 2 is connected to the lower part of the rotary extruding machine through a sliding assembly (not shown in the figure). The rotary extruding machine drives the male die 2 to raise and lower, and can control the male die 2 to lower to different heights to align with different heights of the blank inner cavity 41. The rotary extruding machine is an existing rotary hydraulic machine.

[0029] Focus on Figure 1 As shown, the punch 2 is composed of a plurality of petal parts 5, each of which is a fan-shaped structure with the same shape, and the plurality of petal parts 5 are arranged in a circumferential array around the longitudinal axis of the punch 2, and can be radially expanded away from each other or radially close to each other. When radially expanded away from each other, each petal part 5 is close to the inner wall of the blank cavity 41 and extrudes the inner wall of the blank cavity 41. When radially close to each other, each petal part 5 is folded into a ring-shaped punch 2. Specifically, the plurality of petal parts 5 include left and right petal parts 52 and 53 arranged symmetrically, and the driving member 7 is arranged between the left and right petal parts 52 and 53. The driving member 7 extends longitudinally and has a columnar structure, the bottom side is inclined and inwardly recessed to form a conical shape, forming a first inclined surface 71. The petal part 5 on the side facing the driving member 7 is provided with a second inclined surface 51 abutting the first inclined surface 71. The top end of the driving member 7 is connected to the ejection cylinder (not shown in the figure) of the rotary extrusion machine. The driving member 7 is driven up and down along the axial direction by the ejection cylinder. During the descending process of the driving member 7, the first inclined surface 71 pushes the second inclined surface 51 downward, so that each petal part 5 radially expands outward. The radial expansion distance of the petal part 5 is controlled by the descending height of the driving member 7. When the driving member 7 rises to reset, the sliding assembly drives the left and right petal parts 52 and 53 to radially close and fold.

[0030] In the specific embodiment, the upper die plate 6 is fixedly installed below the rotary extrusion machine. The sliding assembly includes a pair of slide rails and a pair of connecting keys. The slide rails are respectively distributed on both sides of the upper die plate 6 along the axis of the punch 2. The connecting keys are slidably fitted on the slide rails, and the other ends are respectively fixed to the left and right petal parts 52 and 53. A reset spring (not shown in the figure) is arranged between the connecting keys and the upper die plate 6. The reset spring is used to limit the radial outward movement of the connecting keys along the slide rails by elastic force. This is a prior art and will not be described in detail. The upper die plate 6 has a first through hole longitudinally therethrough. The top end of the driving member 7 passes through the through hole and is connected to the ejection cylinder (not shown in the figure). The rotary extrusion machine drives the upper die plate 6, the punch 2, the driving member 7, and the ejection cylinder to rise or fall as a whole. The ejection cylinder independently drives the driving member 7 to rise and fall relative to the punch 2.

[0031] The rotating device 9 is rotatably arranged on the lower die plate 11 and fixedly connected to the bottom side of the concave die 1. The concave die sleeve 8 is cylindrical. The concave die 1 is embedded in the concave die sleeve 8 and fixedly connected to the concave die sleeve 8, so that the concave die sleeve 8 and the concave die 1 are installed and fixed as a whole on the rotating device 9. The rotating device 9 rotates horizontally, so that the rib 21 can rotate circumferentially to extrude the inner wall of the blank cavity 41 at different positions, so as to form a circular ring-shaped rib 42 radially on the inner wall of the blank cavity 41. Focus on Figure 3As shown, the ejection device includes a top plate 10, a ejector rod 12 and a lifting drive mechanism (not shown in the figure), the top plate 10 is arranged in the cavity 101 and slides up and down, used to eject the magnesium alloy blank 4 upward, the ejector rod 12 is connected to the bottom side of the top plate 10 at one end and connected to the telescopic end of the lifting drive mechanism at the other end, the lower die plate 11 has a second through hole longitudinally through, the top end of the ejector rod 12 passes through the second through hole upward and is fixedly connected to the bottom side of the top plate 10, the lifting drive mechanism can be a lifting cylinder connected to the bottom end of the ejector rod 12 to drive the ejector rod 12 to rise and fall.

[0032] The key is combined Figure 2 As shown, the cathode and anode of the pulse current device 3 are respectively electrically connected to the punch 2 and the die 1, so that the punch 2, the magnesium alloy blank 4, the die 1 and the pulse current device 3 are sequentially conductive to form a current loop, so that the rib 21 can locally discharge the magnesium alloy blank 4 when the rib 21 abuts against the magnesium alloy blank 4. Preferably, the peak current density of the pulse current is 100-250 A / mm², and the pulse frequency is 100-500 Hz.

[0033] The key is combined Figure 2 As shown, in order to ensure that the current effectively flows through the magnesium alloy blank 4, the left lobe 52 and the right lobe 53 are provided with insulating gaskets (not shown in the figure) between the upper die plate 6, the left lobe 52 and the right lobe 53 are provided with insulating gaskets between the driving member 7, the die 1 is provided with insulating gaskets between the die sleeve 8, the die 1 is provided with insulating gaskets between the rotating device 9, the insulating gaskets are used for electrical insulation, these insulating gaskets effectively isolate the conductive path between the punch 2 and the upper die plate 6 and the driving member 7, and the die 1 and the rotating device 9 and the lower die plate 11, so that the current sequentially conducts through the punch 2, the magnesium alloy blank 4, the die 1 and the pulse current device 3 to form a current loop.

[0034] Preferably, the rib 21 is embedded with an electrode contact 24, the electrode contact 24 is strip-shaped and extends circumferentially along the end of the rib 21, the electrode contact 24 protrudes from the end of the rib 21, and the pulse current device 3 is connected to the electrode contact 24 through the wire 14, so that before the punch 2 extrudes the inner cavity 41 of the blank, the pulse current focuses on the to-be-shaped area of the inner wall of the inner cavity 41 of the blank through the electrode contact 24, forms a local high-density current path, locally discharges and softens the blank area covered by the rib 21 on both sides of the groove 22, can reduce the instantaneous resistance generated when the blank directly abuts against the punch 2, and with the continuous feeding of the extrusion of the punch 2, the discharge area changes from point contact discharge to line contact discharge, which can promote the nucleation of recrystallized grains, with the expansion of the discharge area, more uniform joule heat distribution is realized, the abnormal growth of the grains is inhibited, the plasticity of the magnesium alloy is improved, and the electrode contact 24 is made of one of gold, silver, copper and aluminum, which has high conductivity and strong stability.

[0035] In this embodiment, the key is combined Figure 4As shown, the height of the groove 22 is the working height m, and the depth of the groove 22 is the actual rib thickness h. The working height m is dynamically adjusted according to the actual rib thickness h. When h < 30 mm, m = (3.5~3.7) * h; when 30 mm < h < 60 mm, m = (2.4~2.5) * h; and when h > 60 mm, m = (1.8~2.0) * h. The arc-shaped angle r is between 14 mm and 18 mm.

[0036] The present application focuses on Figure 9 As shown, the left side of the drawing shows the cross-sectional results of the rib part formed by rotary extrusion under the conditions of no pulse current and pulse current. When no pulse current is passed, the formed rib height is much lower than the design value, the rib top presents obvious collapse or depression, the rib wall joint part profile is unclear, and there is a filling defect, such as Figure 9 As shown in the left enlarged view, and after the current is passed, as shown in the right enlarged view, the groove 22 is completely and densely filled, the formed rib height accurately reaches the design value, and there is no visible filling defect, folding, etc. Figure 9

[0037] In the specific embodiment, the male die 2 is made of copper-tungsten alloy, and the female die 1 is made of steel material.

[0038] The present application also provides a pulse current assisted magnesium alloy thin-walled inner ring high rib component rotary extrusion forming method, comprising the following steps: Step 1, preparation before forming: embedding the magnesium alloy blank 4 to be formed into the cavity 101, connecting the multiple petal parts 5 of the male die 2 to the cathode of the pulse current device 3 through the wires 14 respectively, connecting the female die 1 to the anode of the pulse current device 3 through the wires 14, and passing the pulse current of the pulse current device 3; Step 2, height positioning: lowering the male die 2 to a predetermined height and inserting it into the inner cavity 41 of the blank; Step 3, extrusion forming: the multiple petal parts 5 expand radially outward to abut against the inner wall of the inner cavity 41 of the blank, forming a current loop, the pulse current locally discharges the magnesium alloy blank 4 at the abutment, the multiple petal parts 5 continue to expand outward, the rib strip 21 extrudes the inner cavity 41 of the blank, the magnesium alloy blank 4 flows into the groove 22 along the flow guide surface 23, when the magnesium alloy blank 4 abuts against the middle part of the bottom wall of the groove 22, the side wall of the male die 2 is spaced from the inner wall of the inner cavity 41 of the blank, the multiple petal parts 5 continue to expand outward, until the side wall of the male die 2 abuts against the inner wall of the inner cavity 41 of the blank, the magnesium alloy blank 4 flows along the circumference to both sides of the bottom wall of the groove 22 respectively, transversely fills the groove 22, and gradually fills the groove 22; Step 4, rotary extrusion forming: rotating the female die 1 horizontally to different angles by the rotating device 9, and continuously passing the pulse current, extruding the same height of different to-be-formed areas of the inner cavity 41 of the blank by the rib strip 21, until the inner wall of the inner cavity 41 of the blank at the predetermined height is extruded to form a circular ring-shaped rib 42; ​Step 5, blanking, closing the pulse current, the plurality of petals 5 are radially close to each other, and are lifted out of the blank inner cavity 41, the ejection device ejects the formed member upward out of the cavity 101, completes demolding, and finally embeds the next magnesium alloy blank 4 to be formed into the cavity 101 to perform extrusion forming of the next formed member.

[0039] Further, after step 4 is completed, steps 2-4 are repeated to lower the male die 2 to different heights to extrude the ribs 42 of different heights on the inner wall of the blank inner cavity 41.

[0040] In step 4, before each rotation of the rotating device 9, the plurality of petals 5 are first radially close to each other, so that the rib 21 only remains in contact with the blank inner cavity 41 to enable the continuous pulse current to be passed through, and after the rotating device 9 is rotated, step 3 is repeated.

[0041] The present application has the following advantages over the conventional integrated magnesium alloy thin-walled high-rib member extrusion method: (1) Improve the flowability of the blank: by passing the pulse current through the magnesium alloy blank 4, local discharge is performed at the extrusion point, the flowability and filling performance of the magnesium alloy blank 4 are improved, and the blank is more easily extruded and filled into the groove 22; (2) Reduce the extrusion resistance of the die: the outer diameter of the male die 2 in the closed state is smaller than the inner diameter of the blank inner cavity 41, and when extruding, point contact is formed, which can form a local high extrusion force, the force is concentrated, the extrusion resistance is reduced, an initial deformation zone is formed, the extrusion resistance is reduced, and at the same time, the continuous effect of the pulse current is maintained, the flowability of the magnesium alloy blank 4 in the extrusion zone is maintained, and the extrusion resistance is further reduced; (3) Improve the filling accuracy: the radial cross section of the groove 22 is in the shape of a crescent, and the bottom wall of the groove 22 is an inner arc 222, when the magnesium alloy blank 4 first abuts against the inner arc 222, a back pressure is formed on the magnesium alloy blank 4, and under the action of the transverse extrusion force generated by the continuous transverse flow of the blank, the magnesium alloy blank 4 flows along the circumference towards the two arc surfaces of the inner arc 222, fills the groove 22, and improves the forming accuracy; (4) Protect the die: after completing one extrusion, under the premise of maintaining abutment with the blank inner cavity 41, the petals 5 are transversely close to each other and away from the blank inner cavity 41, so that when the female die 1 rotates, the petals 5 are not subjected to circumferential extrusion force, wear is reduced, and when the female die 1 rotates to a predetermined angle, the petals 5 are again transversely extruded against the inner wall of the blank inner cavity 41, so that the extrusion effect is ensured and the service life of the die is prolonged.

[0042] The above only describes the preferred embodiments of the present application, and is not a limitation on the design of the present application. Any equivalent changes made based on the key design of the present application fall within the scope of protection of the present application.

Claims

1. A method for rotary extrusion forming of a thin-walled, high-ribbed inner ring component of magnesium alloy assisted by pulsed current, characterized in that: A forming device is used, which includes a punch (2) that can extend into the inner wall of a cylindrical magnesium alloy billet (4) to extrude ribs (4) on its inner wall. Before extrusion, the punch (2) first passes a pulse current to the magnesium alloy billet (4) so ​​that the pulse current partially discharges the magnesium alloy billet (4) at the extrusion point to soften the magnesium alloy billet (4) at the extrusion point, and the pulse current is continuously passed through during the extrusion process.

2. The method for rotary extrusion forming of a thin-walled inner ring high-rib component of magnesium alloy assisted by pulse current as described in claim 1, characterized in that: The punch (2) has multiple ribs (21) protruding laterally on its sidewall. The ribs (21) are arranged longitudinally at intervals, forming a groove (22) between adjacent ribs (21). The end faces of two adjacent ribs (21) form guide surfaces (23) on both sides of the inlet of the groove (22). The two guide surfaces (23) are inclined towards the groove (22). The punch (2) squeezes the inner wall of the magnesium alloy billet (4) through the ribs (21), causing the magnesium alloy billet (4) to flow into the groove (22) along the guide surfaces (23). The bottom wall of the groove (4) The cross-sectional profile is arc-shaped with a radius of R0. The middle of the bottom wall of the groove (4) bulges towards the end of the rib (21). The two sides of the bottom wall of the groove (4) extend away from the end of the rib (21). The inner wall of the alloy billet (4) is annular with a radius of R1, where R1 is greater than R0. When the magnesium alloy billet (4) abuts against the middle of the bottom wall of the groove (22), the side wall of the punch (2) is spaced from the inner wall of the magnesium alloy billet (4), and the rib (21) continues to squeeze. The magnesium alloy billet (4) flows towards the two sides of the bottom wall of the groove (22) along the circumference.

3. The method for rotary extrusion forming of a thin-walled inner ring high-rib component of magnesium alloy assisted by pulse current as described in claim 1, characterized in that: The inner wall of the magnesium alloy billet (4) is annular with a radius of R1. The outer contour of the end of the rib (21) is arc-shaped with a radius of R2. R1 is greater than R2. During the process of the rib (21) extruding the inner wall of the magnesium alloy billet (4), point contact is formed first, and then the extrusion surface gradually becomes larger.

4. The method for rotary extrusion forming of a thin-walled inner ring high-rib component of magnesium alloy assisted by pulse current as described in claim 1, characterized in that: The peak current density of the pulse current is 100-250 A / mm², and the pulse frequency is 100-500 Hz.

5. The method for rotary extrusion forming of a thin-walled inner ring high-rib component of magnesium alloy assisted by pulse current as described in claim 2, characterized in that: The forming device also includes a die (1), a pulse current device (3), and an ejection device. The center of the magnesium alloy blank (4) is the blank cavity (41). The die (1) forms a cavity (101) with a top side opening and is connected to a rotating device (9). The punch (2) is located directly above the cavity (101) and can move up and down. The punch (2) is composed of multiple petals (5). Each petal (5) can expand laterally away from the outside or close laterally. The method includes the following steps: Step 1, Pre-forming preparation: The magnesium alloy blank (4) to be formed is inserted downward into the cavity (101). The multiple segments (5) of the punch (2) are connected to the cathode of the pulse current device (3) through wires (14). The die (1) is connected to the anode of the pulse current device (3) through wires (14). The pulse current device (3) is energized. Step 2, Height positioning: The punch (2) descends to the predetermined height and is inserted into the blank cavity (41). Step 3, extrusion forming: Multiple petals (5) expand radially away from the outside and abut against the inner wall of the blank cavity (41) to form a current loop. Multiple petals (5) continue to expand outward, and the ribs (21) squeeze the inner wall of the blank cavity (41). The magnesium alloy blank (4) flows into the groove (22) along the guide surface (23). When the magnesium alloy blank (4) abuts against the middle of the bottom wall of the groove (22), multiple petals (5) continue to expand outward. The magnesium alloy blank (4) flows circumferentially towards both sides of the bottom wall of the groove (22) and fills the groove (22) laterally. Step 4, Rotary extrusion forming: The rotating device (9) drives the die (1) to rotate horizontally to different angles and continuously applies pulse current. Through the ribs (21), the different areas to be formed at the same height of the blank cavity (41) are extruded until the inner wall of the blank cavity (41) at the predetermined height is extruded to form a ring-shaped rib (4). Step 5: Unload the material, turn off the pulse current, multiple petals (5) move laterally closer together and rise out of the blank cavity (41), and the ejector pushes the forming component upward out of the cavity (101) to complete the demolding.

6. The method for rotary extrusion forming of a thin-walled inner ring high-rib component of magnesium alloy assisted by pulse current as described in claim 5, characterized in that: After step 4 is completed, steps 2 to 4 are repeated to lower the punch (2) to different heights and extrude ribs (4) of different heights on the inner wall of the blank cavity (41).

7. The method for rotary extrusion forming of a thin-walled inner ring high-rib component of magnesium alloy assisted by pulse current as described in claim 5, characterized in that: In step 4, before each rotation of the rotating device (9), under the premise that the ribs (21) are in contact with the inner cavity (41) of the billet, multiple petals (5) first move laterally closer and exit the inner wall of the inner cavity (41) of the billet. After the rotating device (9) rotates, step 3 is repeated.

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