Method for predicting multi-degree-of-freedom envelope forming concave drawing defect of ribbed cylinder part
By dividing the plastic deformation zone of the ribbed cylinder and establishing the mechanical conditions of the dent defect, the problem of predicting the dent defect in the multi-degree-of-freedom envelope forming process is solved, fast and accurate prediction and control are achieved, and the forming quality and manufacturing efficiency of the ribbed cylinder are improved.
Patent Information
- Application Number
- CN202510832304.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-20
- Publication Date
- 2025-10-17
AI Technical Summary
In the existing technology, during the multi-degree-of-freedom envelope forming process of ribbed cylindrical parts, the transition zone between the web and the annular ribs is prone to dent defects, resulting in low surface quality or even direct scrapping, and there is a lack of effective prediction methods.
A method for predicting dent defects in multi-degree-of-freedom envelope forming of ribbed cylindrical parts is constructed. By dividing the plastic deformation zone into web deformation zone, transition zone deformation zone and rib deformation zone, the mechanical conditions for the formation of dent defects are established. The size and force balance of the transition zone deformation zone are calculated, and it is determined whether the deformation dead zone can be moved, thereby predicting the occurrence of dent defects.
It can quickly and accurately predict the concave defects, scientifically control the defects, shorten the process design cycle, optimize the manufacturing process, and improve the forming quality of ribbed tubes.
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Figure CN120805409A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of forming manufacturing of stiffened cylinder, more particularly, to a kind of stiffened cylinder multi-degree-of-freedom envelope forming draw concave defect prediction method. BACKGROUND
[0002] Stiffened cylinder has the advantages of light weight, strength and rigidity, etc., and is widely used in manufacturing aircraft, carrier rocket, missile, ship and other core load-bearing components of carrying equipment. Stiffened cylinder is composed of cylindrical web and ring rib distributed in the middle of the inner side of the web, and is mainly manufactured by cutting process, which has problems of weak mechanical properties, long processing cycle, low material utilization rate and high manufacturing cost. Stiffened cylinder multi-degree-of-freedom envelope forming is a new material processing technology, which can not only accurately form the complex profile of stiffened cylinder, but also significantly refine the grain size of stiffened cylinder, so as to realize the high-performance, high-efficiency and low-cost manufacturing of stiffened cylinder. However, the geometry of stiffened cylinder changes constantly during multi-degree-of-freedom envelope forming process, resulting in extremely complex stress state and metal flow pattern, and the transition zone between web and ring rib is prone to draw concave defects, resulting in low surface quality of stiffened cylinder or even direct scrap. At present, there is no literature report on the draw concave defect prediction method of stiffened cylinder multi-degree-of-freedom envelope forming. SUMMARY
[0003] The technical problem to be solved by the present application is to provide a kind of stiffened cylinder multi-degree-of-freedom envelope forming draw concave defect prediction method, which can quickly and accurately predict whether the transition zone of stiffened cylinder multi-degree-of-freedom envelope forming process produces draw concave defect.
[0004] The technical scheme adopted by the present application to solve its technical problem is: a kind of stiffened cylinder multi-degree-of-freedom envelope forming draw concave defect prediction method is constructed, including the following steps:
[0005] S1, the plastic deformation zone of stiffened cylinder is divided into web deformation zone, transition zone deformation zone and rib deformation zone, the mechanical conditions for forming draw concave defect in stiffened cylinder multi-degree-of-freedom envelope forming process are established, and the transition zone deformation zone is divided into rigid deformation zone and deformation dead zone based on the upper limit method;
[0006] S2, the size of rigid deformation zone and deformation dead zone in transition zone deformation zone is calculated;
[0007] S3, the external force of each rigid deformation zone is calculated in turn, and the force balance equation of deformation dead zone along the normal direction of web is established accordingly, if the force of deformation dead zone along the normal direction of web is unbalanced, the whole deformation dead zone moves to rib and draw concave defect is formed, if the force of deformation dead zone along the normal direction of web is balanced, the whole deformation dead zone cannot move to rib and draw concave defect cannot be formed;
[0008] S4, the depth of draw concave defect in middle transition zone is calculated.
[0009] According to the above scheme, in the step S1, the multi-degree-of-freedom envelope forming process of the ribbed cylinder part is averagely divided into m passes, and the feeding amount of the cylindrical concave die is the same in each pass; meanwhile, the following assumptions are made: (1) the shear deformation occurs at the interface between adjacent rigid deformation zones, the shear deformation occurs at the interface between the rigid deformation zone and the deformation dead zone, and no deformation occurs inside the rigid deformation zone and the deformation dead zone, the rigid deformation produces displacement, and the deformation dead zone does not produce displacement; (2) the shapes of the rigid deformation zone and the deformation dead zone are both approximately triangular prisms, the axial section of the deformation dead zone is a triangle denoted as △IKM, the axial sections of the five rigid deformation zones are denoted as △GHI, △HIK, △MNO, △KMO, △HKO and △HOP respectively, △GHI and △HIK are located on the upper side of the deformation dead zone, △MNO and △KMO are located on the lower side of the deformation dead zone, △HKO and △HOP are located on the right side of the deformation dead zone, HK, HI, IK, KM, KO, NO and HO are shear surfaces, KJ is the perpendicular line of △IKM, KL is the perpendicular line of △HKO, GH is perpendicular to GI, MN is perpendicular to NO, and HP is perpendicular to OP, the length of IJ is denoted as y1, the length of JM is denoted as y2, and the length of JK is denoted as x; (3) the plastic instability does not occur in the multi-degree-of-freedom envelope forming process of the ribbed cylinder part, and the material flow stress remains unchanged; (4) the deformation stress state and the geometric appearance are unchanged in each pass, and only change between adjacent passes.
[0010] According to the above scheme, in the step S2, the lengths y1, y2 and x of IJ, JM and JK are calculated according to the upper bound method, and the calculation formula is as follows:
[0011]
[0012] wherein, is the maximum internal force work power of the transition zone deformation zone;
[0013] In the formula (1), The calculation equation is as follows:
[0014]
[0015] wherein, Q mf is the work power of the transition zone deformation zone to overcome the friction force, Q ms is the work power of the transition zone deformation zone to produce shear deformation, and Q mp is the work power of the transition zone deformation zone to overcome the back pressure;
[0016] Based on the upper bound analysis method, the maximum external force work power of the transition zone deformation zone is denoted as:
[0017]
[0018] where N GHu is the maximum normal stress on the GH prism, W NOu is the maximum normal stress on the NO prism, v m is the average width of the transition zone deformation zone in the tangential direction, v
[0019] W m in equation (3) is equal to the equivalent contact length between the middle end of the envelope roll and the web, and its calculation equation is as follows:
[0020]
[0021] where R m is the radius of the inner circumferential surface of the web at the lower end surface of the ring rib, r m is the radius of the middle end of the envelope roll;
[0022] Q mf in equation (2) is expressed as:
[0023]
[0024] where, is the length of the line segment GI, v is the length of the line segment MN, is the length of the line segment OP, and K is the shear strength of the ribbed cylinder material;
[0025] Q ms in equation (2) is expressed as:
[0026]
[0027] where v IH is the slip velocity on the shear surface IH, is the length of the line segment IH, v IK is the slip velocity on the shear surface IK, is the length of the line segment IK, v HK is the slip velocity on the shear surface HK, is the length of the line segment HK, v KO is the slip velocity on the shear surface KO, is the length of the line segment KO, v MK is the slip velocity on the shear surface MK, is the length of the line segment MK, v MO is the slip velocity on the shear surface MO, is the length of the line segment MO, v HO is the slip velocity on the shear surface HO, is the length of the line segment HO, and SΔGHI is the area of triangle GHI, S ΔHIK is the area of triangle HIK, S ΔHKO is the area of triangle HKO, S ΔKMO is the area of triangle KMO, S ΔMNO is the area of triangle MNO, S ΔHOP is the area of triangle HOP;
[0028] In formula (2), Q mp Expressed as:
[0029] Q mp =P m v5W m w m (7)
[0030] Among them, P m w is the back pressure exerted by the middle rib deformation zone on the middle transition zone, m is the width of the middle rib;
[0031] Assuming that the deformation zone of the middle end reinforcement only produces shear deformation along its radial direction, the P in formula (7) is obtained by analyzing the stress of the deformation zone of the middle end reinforcement. m The calculation formula is:
[0032]
[0033] Among them, h m is the radial height of the middle rib;
[0034] According to the volume conservation principle, the relationship between v3, v4 and v5 in formula (5) is expressed as:
[0035]
[0036] Where, ΔL b is the length of the lower loading area along the busbar direction, ΔL s is the length of the upper loading zone along the generatrix direction;
[0037] Assume that line segment JL is the metal confluence surface in the middle transition zone, and line segment JL and line segment IM are perpendicular to each other; ΔL in formula (9) b and ΔL s Expressed as:
[0038]
[0039] in, is the length of line segment GJ, is the length of line segment JN, β is the angle between the web and the axis of the reinforced cylinder;
[0040] Combining the geometric characteristics of the middle-end transition zone, the geometric relationship between each line segment in formula (5) and formula (6) and x, y1 and y2 in S2 is represented as follows:
[0041]
[0042] Combining the geometric characteristics of the middle-end transition zone, the area of the specific triangle in formula (6) is calculated by the following equation:
[0043]
[0044] Combining the fast-end diagram, the quantitative relationship between the specific slip velocity in formula (6) and v3 is as follows:
[0045]
[0046] wherein, α2 is the included angle of line segment GI and line segment HI, θ2 is the included angle of line segment HI and line segment HK, γ2 is the included angle of line segment IM and line segment IK, α3 is the included angle of line segment MN and line segment MP, θ3 is the included angle of line segment MO and line segment KO, and γ3 is the included angle of line segment IM and line segment KM;
[0047] Combining the geometric characteristics of the middle-end transition zone, the calculation equation of the specific angle in formula (13) is represented as follows:
[0048]
[0049] According to the above scheme, in the step S3, when x or y1+y2 obtained by formula (1)-(14) is 0, the middle-end transition zone does not have a deformation dead zone, and the middle-end transition zone is entirely in a plastic deformation state; when x, y1 and y2 obtained are all not 0, the middle-end transition zone has a deformation dead zone. When the deformation dead zone is separated from the inner conical surface of the cylindrical female die, a draw concave defect is formed at the bottom of the middle-end transition zone.
[0050] According to the above scheme, in the step S3, by force analysis on the deformation dead zone of the middle-end transition zone, the critical mechanical condition for the draw concave defect is obtained:
[0051]
[0052] wherein, S ΔIKM is the area of the axial section of the middle-end deformation dead zone, N IK is the normal stress on the interface IK, N KM is the normal stress on the interface KM; by force analysis on each rigid deformation zone and combining formula (3), N IK and N KM can be obtained.
[0053] By simplifying formula (15), the criterion for the draw concave defect of the middle-end transition zone is obtained:
[0054]
[0055] According to the above scheme, in the step S4, first, the geometric model of the deformation dead zone before and after the occurrence of the draw recess is established, ΔIKM represents the deformation dead zone profile when the draw recess just occurs, the quadrilateral I'K'K''I'', the quadrilateral K'M'M''K'' represent the deformation dead zone profile after the occurrence of the draw recess, ΔI''K''M'' represents the profile of the draw recess defect, represents the depth of the draw recess defect, ΔI'K'M' represents the profile of the deformation dead zone ΔI'K'M' when the draw recess just occurs, the quadrilateral IKK'I', the quadrilateral KMM'K' represent the area converted from the deformation dead zone to the deformation zone; after the draw recess occurs in the middle end transition zone, the metal in the deformation zone flows to the middle end rib, so that the middle end rib is elongated and raised; according to the metal volume conservation law, the area of the draw recess area ΔI''K''M'' is equal to the area of the quadrilateral IKK'I' and the quadrilateral KMM'K', and the calculation formula is as follows:
[0056]
[0057] wherein, represents the length of the line segment I''J, represents the length of the line segment JM'', x' represents the length of the line segment JK', y1' represents the length of the line segment I'J, and y2' represents the length of the line segment JM';
[0058] The draw recess defect depth and width satisfy the following relationship:
[0059]
[0060] Combined with formula (17) and formula (18), the calculation equation of the middle end draw recess defect depth is obtained:
[0061]
[0062] Formula (19) is only applicable to the calculation of the draw recess defect depth when x' is less than x'; when x' is more than x', the draw recess defect depth is equal to x'.
[0063] According to the above scheme, it further includes the step S5, if the draw recess defect is found in the transition zone of the multi-degree-of-freedom envelope forming process of the ribbed cylinder part, the blank wall thickness and the rib back pressure should be increased, so as to hinder the draw recess defect in the transition zone.
[0064] The implementation of the draw recess defect prediction method of the multi-degree-of-freedom envelope forming of the ribbed cylinder part has the following beneficial effects:
[0065] 1. The present application can quickly predict whether the transition zone of the multi-degree-of-freedom envelope forming process of the ribbed cylinder produces a draw-in defect, and can also scientifically control the draw-in defect.
[0066] 2. The present application can greatly shorten the process design cycle and the manufacturing cycle of the ribbed cylinder.
[0067] 3. The present application can provide theoretical guidance for the multi-degree-of-freedom envelope forming process optimization design of the ribbed cylinder. BRIEF DESCRIPTION OF DRAWINGS
[0068] The present application will be further described below in conjunction with the drawings and examples, in which:
[0069] Figure 1 (a) and (b) in the drawings are respectively the axial cross-sectional schematic diagram of the ribbed cylinder without draw-in defect and the ribbed cylinder with draw-in defect;
[0070] Figure 2 is the schematic diagram of the multi-degree-of-freedom envelope forming principle of the ribbed cylinder;
[0071] Figure 3 is the schematic diagram of the position relationship between the deformation zone and the non-deformation zone in the multi-degree-of-freedom envelope forming process of the ribbed cylinder;
[0072] Figure 4 is the division schematic diagram of the rigid deformation zone in the transition zone of the multi-degree-of-freedom envelope forming process of the ribbed cylinder;
[0073] Figure 5 is the velocity-end diagram of each rigid deformation zone in the transition zone of the ribbed cylinder;
[0074] Figure 6 is the force analysis schematic diagram of the deformation dead zone and the rigid deformation zone in the transition zone of the ribbed cylinder;
[0075] Figure 7 is the axial cross-sectional schematic diagram of the deformation dead zone in the transition zone of the ribbed cylinder before and after the draw-in defect is produced;
[0076] Figure 8 is the draw-in defect and its depth prediction process in the transition zone of the multi-degree-of-freedom envelope forming process of the ribbed cylinder;
[0077] Figure 9 is the comparison of the analytical results and the finite element simulation results of the draw-in defect formation condition in the transition zone of the multi-degree-of-freedom envelope forming process of the ribbed cylinder;
[0078] Figure 10 is the finite element simulation result of the multi-degree-of-freedom envelope forming process of the ribbed cylinder without draw-in defect. DETAILED DESCRIPTION
[0079] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.
[0080] like Figure 1 As shown in (a), the ribbed tube 4 is composed of a cylindrical web and annular ribs located at the middle end of the web. Its multi-degree-of-freedom enveloping forming principle is as follows: the cylindrical die 1 completely constrains the outer circumference and end face of the ring blank 3, the enveloping roller 2 contacts the inner circumference of the ring blank 3, the cylindrical die 1 drives the ring blank 3 to rotate around its own axis, and the enveloping roller 2 performs multi-degree-of-freedom motion, which can be decomposed into rotation around its own axis and radial feed motion. Under the extrusion action of the enveloping roller 2, the metal in the deformation zone of the ring blank 3 gradually flows into the cavity of the enveloping roller 2, thereby realizing continuous local enveloping forming of web thinning and annular rib growth, and finally realizing the overall plastic forming of the ribbed tube 4. During the multi-degree-of-freedom enveloping forming process of the ribbed tube 4, the transition zone between the web and the ribs is very prone to pull-concave defects, such as Figure 1 As shown in (b), the surface precision of the ribbed cylinder 4 is low, and the ribbed cylinder 4 may even be scrapped.
[0081] The method for predicting and controlling the concave defects of the ribbed cylindrical component with 4 multi-degree-of-freedom envelope forming of the present invention comprises the following steps:
[0082] S1, the plastic deformation zone of the ribbed cylinder 4 is divided into the web deformation zone, the transition zone deformation zone and the rib deformation zone, as shown in Figure 3 、 Figure 4 As shown, the stress state of each deformation zone will change with the time of the geometric structure of the ribbed tube 4. In order to establish the mechanical conditions for the formation of the concave defect in the multi-freedom envelope forming process of the ribbed tube 4, the transition zone deformation zone is divided into 6 rigid deformation zones and 1 deformation dead zone based on the upper limit method, and the multi-freedom envelope forming process of the ribbed tube 4 is evenly divided into m passes, that is, the feed amount of the cylindrical die 1 in each pass is the same. At the same time, the following assumptions are made: (1) Shear deformation occurs at the interface between adjacent rigid deformation zones, and shear deformation occurs at the interface between the rigid deformation zone and the deformation dead zone. No deformation occurs inside the rigid deformation zone and the deformation dead zone. Displacement occurs in the rigid deformation zone, and no displacement occurs in the deformation dead zone; (2) The shapes of the rigid deformation zone and the deformation dead zone are approximately triangular prisms, and the axial sections of the rigid deformation zone and the deformation dead zone are both triangular. The axial section of the deformation dead zone is represented by △IKM, and the axial sections of the five rigid deformation zones are represented by △GHI, △HIK, and △MN respectively. O, △KMO, △HKO, △HOP, △GHI and △HIK are located on the upper side of the deformation dead zone, △MNO and △KMO are located on the lower side of the deformation dead zone, △HKO and △HOP are located on the right side of the deformation dead zone, HK, HI, IK, KM, KO, NO, HO are shear planes, KJ is the perpendicular line of △IKM, KL is the perpendicular line of △HKO, GH is perpendicular to GI, MN is perpendicular to NO, HP is perpendicular to OP, the length of IJ is expressed as y1, the length of JM is expressed as y2, and the length of JK is expressed as x, as shown inFigure 7 (3) the plastic instability does not occur in the multi-degree-of-freedom envelope forming process of the ribbed cylinder 4 and the material flow stress remains unchanged; (4) the deformation stress state and the geometric appearance are unchanged in each pass, and they only change between adjacent passes.
[0083] S2, the size of the rigid deformation zone and the deformation dead zone in the transition zone deformation zone is calculated. First, y1, y2 and x are calculated according to the upper bound method, and the calculation formula is as follows:
[0084]
[0085] wherein, is the maximum internal force power of the transition zone deformation zone.
[0086] In formula (1), N The calculation equation is as follows:
[0087]
[0088] wherein, Q mf is the power of the transition zone deformation zone to overcome the friction force, Q ms is the power of the transition zone deformation zone to overcome the back pressure force. mp
[0089] Based on the upper bound analysis method, the maximum external force power of the transition zone deformation zone can be expressed as:
[0090]
[0091] wherein, N GHu is the maximum normal stress on the GH prism surface, as shown in Figure 6 N NOu is the maximum normal stress on the NO prism surface, W m is the average width of the transition zone deformation zone along the tangential direction, and v3 is the inflow velocity of the upper metal in the transition zone deformation zone, and v4 is the inflow velocity of the lower metal in the transition zone deformation zone.
[0092] In formula (3), W m is equal to the equivalent contact length between the middle end of the envelope roll 2 and the web, and the calculation equation is as follows:
[0093]
[0094] wherein, R m is the radius of the inner circumferential surface of the web at the lower end surface of the ring rib, and r m is the radius of the middle end of the envelope roll 2.
[0095] In formula (2), Q mf may be expressed as:
[0096]
[0097] wherein, is the length of the line segment GI, v5 is the outflow velocity of the transition zone deformed zone metal, is the length of the line segment MN, is the length of the line segment OP, K is the shear strength of the material of the ribbed cylinder 4.
[0098] Q in equation (2) can be expressed as: ms may be expressed as:
[0099]
[0100] wherein, v IH is the slip velocity on the shear plane IH, is the length of the line segment IH, v IK is the slip velocity on the shear plane IK, is the length of the line segment IK, v HK is the slip velocity on the shear plane HK, is the length of the line segment HK, v KO is the slip velocity on the shear plane KO, is the length of the line segment KO, v MK is the slip velocity on the shear plane MK, is the length of the line segment MK, v MO is the slip velocity on the shear plane MO, is the length of the line segment MO, v HO is the slip velocity on the shear plane HO, is the length of the line segment HO, S ΔGHI is the area of the triangle GHI, S ΔHIK is the area of the triangle HIK, S ΔHKO is the area of the triangle HKO, S ΔKMO is the area of the triangle KMO, S ΔMNO is the area of the triangle MNO, S ΔHOP is the area of the triangle HOP.
[0101] Q in equation (2) can be expressed as: mp may be expressed as:
[0102] Q mp = P m v5W m w m (7)
[0103] wherein, P m is the back pressure applied by the middle end rib deformed zone to the middle end transition zone, w mwidth of the middle end rib.
[0104] Assuming that the deformation zone of the middle end rib only generates shear deformation along its radial direction, by force analysis of the deformation zone of the middle end rib, the calculation formula of P in equation (7) is obtained as follows: m
[0105]
[0106] wherein, h m is the radial height of the middle end rib.
[0107] According to the volume conservation criterion, the relationship among v3, v4 and v5 in equation (5) can be expressed as:
[0108]
[0109] wherein, ΔL b is the length of the lower loading zone along the generatrix direction, and ΔL s is the length of the upper loading zone along the generatrix direction.
[0110] Assuming that the line segment JL is the metal convergence surface in the middle end transition zone, and the line segment JL is perpendicular to the line segment IM. Therefore, ΔL b and ΔL s in equation (9) can be expressed as:
[0111]
[0112] wherein, is the length of the line segment GJ, is the length of the line segment JN, and β is the included angle between the web and the axis of the ribbed cylinder 4.
[0113] Combined with the geometric characteristics of the middle end transition zone, the geometric relationship between each line segment in equations (5) and (6) and x, y1 and y2 in S2 can be expressed as:
[0114]
[0115] Combined with the geometric characteristics of the middle end transition zone, the area of the specific triangle in equation (6) can be calculated by the following equation:
[0116]
[0117] Combined with the velocity end view in Figure 5 , the quantitative relationship between the specific slip velocity and v3 in equation (6) is:
[0118]
[0119] wherein a2 is the angle between line segment GI and line segment HI, θ2 is the angle between line segment HI and line segment HK, γ2 is the angle between line segment IM and line segment IK, a3 is the angle between line segment MN and line segment MP, θ3 is the angle between line segment MO and line segment KO, and γ3 is the angle between line segment IM and line segment KM.
[0120] In combination with the geometric characteristics of the middle transition zone, the calculation equation of the specific angle in equation (13) can be expressed as:
[0121]
[0122] S3, establishing the criterion for the generation of the draw-recess defect in the middle transition zone. When x or y1+y2 obtained by equations (1)-(14) is 0, the middle transition zone does not have a deformation dead zone, and the middle transition zone is entirely in a plastic deformation state; when x, y1 and y2 obtained are not all 0, the middle transition zone has a deformation dead zone. When the deformation dead zone is separated from the inner conical surface of the cylindrical concave die 1, the draw-recess defect is formed at the bottom of the middle transition zone. Through force analysis of the deformation dead zone of the middle transition zone, the critical mechanical condition for the generation of the draw-recess defect is obtained:
[0123]
[0124] wherein S ΔIKM is the area of the axial section of the middle deformation dead zone, N IK is the normal stress on the interface IK, N KM is the normal stress on the interface KM. Through force analysis of each rigid deformation zone and in combination with equation (3), N IK and N KM can be obtained.
[0125] Through simplification of equation (15), the criterion for the generation of the draw-recess defect in the middle transition zone is obtained:
[0126]
[0127] S4, calculating the depth of the draw-recess defect in the middle transition zone. First, the geometric model of the deformation dead zone before and after the occurrence of the draw-recess is established. ΔIKM represents the contour of the deformation dead zone when the draw-recess is just generated, quadrilateral I'K'K”I” and quadrilateral K'M'M”K” represent the contours of the deformation dead zone after the occurrence of the draw-recess, and ΔI”K”M” represents the contour of the draw-recess defect, represents the depth of the draw-recess defect, ΔI'K'M'represents the profile of the draw-recess when the deformation dead zone ΔI'K'M'just occurs, the quadrilateral IKK'I'and the quadrilateral KMM'K'represent the areas where the deformation dead zone is converted into the deformation zone. After the draw-recess occurs in the middle-end transition zone, the metal in the deformation zone flows to the middle-end rib entirely, so that the middle-end rib is elongated. According to the metal volume conservation law, the area of the draw-recess area (ΔI”K”M”) is equal to the area of the deformation zone (the quadrilateral IKK'I'and the quadrilateral KMM'K'), and the calculation formula is as follows:
[0128]
[0129] wherein, represents the length of the line segment I”J, represents the length of the line segment JM”, x'represents the length of the line segment JK', y1'represents the length of the line segment I'J, and y2'represents the length of the line segment JM'. The values of x', y1'and y2'can be obtained through the formulae (1)-(14).
[0130] In addition, the draw-recess defect satisfies the following relationship between the depth and the width:
[0131]
[0132] In combination with the formula (17) and the formula (18), the calculation equation of the middle-end draw-recess defect depth is obtained:
[0133]
[0134] It is pointed out here that the formula (19) is only applicable to the calculation of the draw-recess defect depth when x' is less than x'; when x' is more than x', the draw-recess defect depth is equal to x'.
[0135] S5, draw-recess defect control of the multi-degree-of-freedom envelope forming of the ribbed cylinder 4. According to the transition zone draw-recess defect prediction model established in steps S1-S3, it is found that the transition zone of the multi-degree-of-freedom envelope forming process of the ribbed cylinder 4 will produce a draw-recess defect based on the wall thickness of 7 mm of the ring blank. According to the above prediction model, it is found that increasing the wall thickness of the ring blank 3 by 2 mm can effectively prevent the transition zone from producing a draw-recess defect.
[0136] To verify the feasibility of the method for predicting and controlling the draw-in defects of the multi-degree-of-freedom envelope forming of the ribbed cylinder 4, a plurality of finite element simulations were performed on the multi-degree-of-freedom envelope forming of the ribbed cylinder 4, and the matching forms of the ring rib width and the wall thickness of the ring blank 3 were different between each simulation. In this example, the key dimensions of the ring blank 3 and the ribbed cylinder 4 are shown in Table 1, and the process parameters are shown in Table 2. The material of the ring blank 3 is 6061 aluminum alloy, the forming temperature is constant at 480℃, and the material shear strength K is 70MPa. Based on the draw-in defect prediction model of the multi-degree-of-freedom envelope forming of the ribbed cylinder 4 according to the present application, the draw-in defects of the transition zone of the ribbed cylinder 4 were predicted, and the calculation process is shown in Figure 8 . Finally, the evolution law of the draw-in defect depth of the transition zone in the multi-degree-of-freedom envelope forming process of the ribbed cylinder 4 was obtained, as shown in Figure 9 . By comparing the finite element simulation results in Figure 9 with the theoretical analysis results, it is found that the theoretical analysis results are basically consistent with the finite element simulation results (the error is less than 8%). In order to suppress the draw-in defects in the transition zone, according to the draw-in defect prediction and control method of the present application, when the wall thickness of the ring blank 3 increases to 9mm, the draw-in defects will not occur in the multi-degree-of-freedom envelope forming process of the ribbed cylinder 4. Based on the above conditions, the finite element simulation of the multi-degree-of-freedom envelope forming of the ribbed cylinder was performed, and the results are shown in Figure 10 . As shown in Figure 10 , the draw-in defects do not occur in the transition zone in the multi-degree-of-freedom envelope forming process of the ribbed cylinder 4. The above analysis can show that the method for predicting and controlling the draw-in defects of the multi-degree-of-freedom envelope forming of the ribbed cylinder according to the present application is reliable.
[0137] Table 1. Key dimensions of the ring blank 3 and the ribbed cylinder 4 in this example
[0138]
[0139] Table 2. Process parameters for implementing this example
[0140]
[0141] The embodiments of the present application are described above in combination with the drawings, but the present application is not limited to the above specific embodiments, and the above specific embodiments are only illustrative, not limiting, and those skilled in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims.
Claims
1. A method for predicting concave defects in multi-degree-of-freedom envelope forming of ribbed cylindrical parts, characterized in that: The following steps are involved: S1. The plastic deformation zone of the ribbed tube is divided into the web deformation zone, the transition zone deformation zone, and the rib deformation zone. The mechanical conditions for the formation of the dent defect during the multi-degree-of-freedom envelope forming process of the ribbed tube are established. The transition zone deformation zone is divided into the rigid deformation zone and the deformation dead zone based on the upper limit method. S2. Calculate the size of the rigid deformation zone and the deformation dead zone in the transition zone deformation zone; S3. Calculate the external forces acting on each rigid deformation zone in sequence, and establish a force balance equation for the deformation dead zone along the web normal direction based on the force balance equation. If the deformation dead zone is subjected to unbalanced force along the web normal direction, the deformation dead zone will move toward the rib as a whole, thereby forming a dent defect. If the deformation dead zone is subjected to balanced force along the web normal direction, the deformation dead zone will not move toward the rib as a whole, thereby preventing the formation of a dent defect. S4. Calculate the depth of the concave defect in the mid-transition zone.
2. The method for predicting concave defects in multi-degree-of-freedom envelope forming of ribbed cylindrical parts according to claim 1 is characterized in that: In step S1, the multi-degree-of-freedom envelope forming process of the ribbed cylindrical part is divided into m passes on average, and the feed amount of the cylindrical die in each pass is the same; at the same time, the following assumptions are made: (1) shear deformation occurs at the interface between adjacent rigid deformation zones, shear deformation occurs at the interface between the rigid deformation zone and the deformation dead zone, no deformation occurs inside the rigid deformation zone and the deformation dead zone, rigid deformation produces displacement, and the deformation dead zone does not produce displacement; (2) the shapes of the rigid deformation zone and the deformation dead zone are approximately triangular prisms, and the axial sections of the rigid deformation zone and the deformation dead zone are both triangular. The axial section of the deformation dead zone is represented by △IKM, and the axial sections of the five rigid deformation zones are represented by △GHI, △HIK, △MNO, △KMO, △HKO, △HOP, △GHI and △HIK are located on the upper side of the deformation dead zone, △MNO and △KMO are located on the lower side of the deformation dead zone, △HKO and △HOP are located on the right side of the deformation dead zone, HK, HI, IK, KM, KO, NO, HO are shear planes, KJ is the perpendicular line of △IKM, KL is the perpendicular line of △HKO, GH is perpendicular to GI, MN is perpendicular to NO, HP is perpendicular to OP, IJ length is represented by y1, JM length is represented by y2, and JK length is represented by x; (3) No plastic instability occurs in the multi-degree-of-freedom envelope forming process of the ribbed tube and the material flow stress remains unchanged; (4) The stress state and geometric morphology of each deformation remain unchanged in each pass and only change between adjacent passes.
3. The method for predicting concave defects in multi-degree-of-freedom envelope forming of ribbed cylindrical parts according to claim 2, characterized in that: In step S2, the IJ length y1, JM length y2, and JK length x are calculated according to the upper limit method, and the calculation formula is as follows: in, is the maximum internal force work power in the transition zone and deformation zone; In formula (1) The calculation equation is as follows: Among them, Q mf Q is the power to overcome friction in the transition zone and deformation zone. ms Q is the power of shear deformation work in the transition zone and deformation zone, mp It is the power to overcome the back pressure in the transition zone and deformation zone; Based on the upper limit analysis method, the maximum external force work power in the transition zone and deformation zone Expressed as: Among them, N GHu is the maximum normal stress on the GH prism surface, N NOu is the maximum normal stress on the NO prism surface, W m is the average width of the transition zone deformation zone along the tangential direction, v3 is the inflow velocity of the metal on the upper side of the transition zone deformation zone, and v4 is the inflow velocity of the metal on the lower side of the transition zone deformation zone; In formula (3), W m It is equal to the equivalent contact length between the middle end of the envelope roller and the web, and its calculation equation is as follows: Among them, R m is the radius of the inner surface of the web at the lower end of the ring reinforcement, r m is the radius of the middle end of the enveloping roller; In formula (2), Q mf Expressed as: in, is the length of the line segment GI, v5 is the outflow velocity of the metal in the transition zone and deformation zone, is the length of line segment MN, is the length of line segment OP, K is the shear strength of the reinforced cylinder material; In formula (2), Q ms Expressed as: Among them, v IH is the slip velocity on the shear plane IH, is the length of line segment IH, v IK is the sliding velocity on the shear surface IK, is the length of line segment IK, v HK is the slip velocity on the shear surface HK, is the length of line segment HK, v KO is the slip velocity on the shear plane KO, is the length of line segment KO, v MK is the slip velocity on the shear surface MK, is the length of line segment MK, v MO is the slip velocity on the shear plane MO, is the length of line segment MO, v HO is the slip velocity on the shear plane HO, is the length of line segment HO, S ΔGHI is the area of triangle GHI, S ΔHIK is the area of triangle HIK, S ΔHKO is the area of triangle HKO, S ΔKMO is the area of triangle KMO, S ΔMNO is the area of triangle MNO, S ΔHOP is the area of triangle HOP; In formula (2), Q mp Expressed as: Q mp =P m v5W m w m (7) Among them, P m w is the back pressure applied by the middle rib deformation zone to the middle transition zone, m is the width of the middle rib; Assuming that the deformation zone of the middle end reinforcement only produces shear deformation along its radial direction, the P in formula (7) is obtained by analyzing the stress of the deformation zone of the middle end reinforcement. m The calculation formula is: Among them, h m is the radial height of the middle rib; According to the volume conservation principle, the relationship between v3, v4 and v5 in formula (5) is expressed as: Where, ΔL b is the length of the lower loading area along the busbar direction, ΔL s is the length of the upper loading zone along the generatrix direction; Assume that line segment JL is the metal confluence surface in the middle transition zone, and line segment JL and line segment IM are perpendicular to each other; ΔL in formula (9) b and ΔL s Expressed as: in, is the length of line segment GJ, is the length of line segment JN, β is the angle between the web and the axis of the reinforced cylinder; Combined with the geometric characteristics of the mid-end transition zone, the geometric relationship between each line segment in Equation (5) and Equation (6) and x, y1 and y2 in S2 is expressed as follows: Combined with the geometric characteristics of the mid-end transition zone, the area of the specific triangle in formula (6) is calculated by the following equation: Combined with the speed-end diagram, the quantitative relationship between the specific slip velocity and v3 in equation (6) is: Among them, α2 is the angle between line segment GI and line segment HI, θ2 is the angle between line segment HI and line segment HK, γ2 is the angle between line segment IM and line segment IK, α3 is the angle between line segment MN and line segment MP, θ3 is the angle between line segment MO and line segment KO, and γ3 is the angle between line segment IM and line segment KM; Combined with the geometric characteristics of the mid-end transition zone, the calculation equation for the specific angle in formula (13) is expressed as:
4. The method for predicting concave defects in multi-degree-of-freedom envelope forming of ribbed cylindrical parts according to claim 3, characterized in that: In step S3, when x or y1+y2 obtained by equations (1)-(14) is 0, there is no deformation dead zone in the middle transition zone, and the middle transition zone enters the entire plastic deformation state. When x, y1, and y2 are all non-zero, there is a deformation dead zone in the middle transition zone. When the deformation dead zone deviates from the inner conical surface of the cylindrical die, a concave defect is formed at the bottom of the middle transition zone.
5. The method for predicting concave defects in multi-degree-of-freedom envelope forming of ribbed cylindrical parts according to claim 4, characterized in that: In step S3, by analyzing the stress on the deformation dead zone in the middle transition zone, the critical mechanical condition for the generation of the dent defect is obtained: Among them, S ΔIKM is the area of the shaft section in the middle deformation dead zone, N IK is the normal stress on the interface IK, N KM is the normal stress on the interface KM; by analyzing the stress of each rigid deformation zone and combining formula (3), we can get N IK 、N KM ; By simplifying formula (15), the criterion for the occurrence of dent defects in the mid-transition zone is obtained:
6. The method for predicting concave defects in multi-degree-of-freedom envelope forming of ribbed cylindrical parts according to claim 5, characterized in that: In step S4, first, a geometric model of the deformation dead zone before and after the occurrence of the dent is established. ΔIKM represents the deformation dead zone contour when the dent just occurs. The quadrilateral I'K'K"I" and quadrilateral K'M'M"K" represent the deformation dead zone contour after the dent occurs. ΔI"K"M" represents the contour of the dent defect. represents the depth of the dent defect, ΔI'K'M' represents the outline of the deformation dead zone ΔI'K'M' when the dent just occurs, and quadrilaterals IKK'I' and KMM'K' represent the area from the deformation dead zone to the deformation zone. After the dent occurs in the middle transition zone, all the metal in the deformation zone flows to the middle rib, thereby achieving the height of the middle rib. According to the law of conservation of metal volume, the area of the dent region ΔI”K”M” is equal to the area of quadrilaterals IKK'I' and KMM'K' in the deformation zone, and its calculation formula is as follows: in, represents the length of line segment I”J, represents the length of line segment JM", x' represents the length of line segment JK', y1' represents the length of line segment I'J, and y2' represents the length of line segment JM'; The depth and width of the dent defect satisfy the following relationship: Combining equations (17) and (18), the calculation equation for the depth of the mid-end concave defect is obtained: Formula (19) is only applicable to Calculation of the depth of the concave defect when it is less than x'; When it exceeds x', the depth of the concave defect is equal to x'.
7. The method for predicting concave defects in multi-degree-of-freedom envelope forming of ribbed cylindrical parts according to claim 6, characterized in that: The method further includes step S5: if it is found that a dent defect occurs in the transition zone of the multi-degree-of-freedom envelope forming process of the ribbed cylinder, the wall thickness of the blank and the back pressure of the rib should be increased to prevent the dent defect from occurring in the transition zone.