Cold extrusion process of thin-wall internal spline tube

Abstract

The invention discloses a cold extrusion forming process of a thin-walled internal spline tube, comprising: blanking; performing phosphorus saponification treatment on the tube blank after blanking; placing the tube blank after phosphorus saponification treatment into a prefabricated extrusion die for cold extrusion, wherein the extrusion die comprises an upper die core and a concave die, wherein the upper die core is vertically arranged, a step is provided in the middle, and an upper hole expansion part and a lower spline forming part are provided under the step; a forming hole is vertically arranged in the middle of the concave die and corresponds to the upper die core, comprising an upper forming hole and a lower forming hole, wherein the diameter of the upper forming hole is greater than the diameter of the upper hole expansion part, the diameter of the upper forming hole is greater than the diameter of the lower forming hole, and a tapered surface transition is provided between the upper forming hole and the lower forming hole; during cold extrusion, the tube blank is firstly placed into the forming hole of the concave die, and then the upper die core is controlled to descend by a press, the upper die core is inserted into the hollow part of the tube blank, and as the upper die core continues to descend, the tube blank is expanded, roughened, reduced in diameter and spline extruded.

Description

Technical Field

[0001] The invention relates to the field of tube forming and manufacturing, and in particular to a cold extrusion forming process of a thin-wall internal spline tube. Background Art

[0002] At present, when manufacturing pipes with internal splines, the splines are generally formed by broaching with a broach, and the length-to-diameter ratio limit of the broached splines is generally no more than 6 times. For internal spline pipes with a relatively large length-to-diameter ratio, it is obviously difficult or even impossible to use a broaching method with a broach. For example, the rotary forging technology can also be used to produce spline pipes with a relatively large length-to-diameter ratio, but the rotary forging technology has high investment costs, high risks, low productivity, and is not practical enough. In order to solve the above problems, a Chinese patent with application number 2011102390817 discloses a method for forming a precision slender internal spline pipe, which includes the following steps: selecting seamless steel pipe sawing materials of suitable specifications, spheroidizing annealing, turning outer circle correction, shot blasting, phosphorus saponification treatment, through-extrusion of the blank, low-temperature annealing, shot blasting, phosphorus saponification treatment, and extruding the internal spline. When the blank is subjected to through-extrusion, the blank is placed in the positive extrusion die, and then the upper slider drives the barrel upper die core and the core upper die core to extrude downward together. During extrusion, the blank material flows downward along the die edge and the core upper die core to deform. After deformation, the outer diameter and inner diameter of the semi-finished product are reduced. When extruded to the bottom dead center, the upper die returns, and the semi-finished product remains in the die. Then the second product is placed in the die for extrusion, and the product pushes the product, and then the first product is extruded from the die. When extruding the internal spline, the semi-finished product is first placed in the die of the hydraulic press worktable, and then the spline upper die core is placed in the semi-finished product, and then the upper slider moves downward, and the pressure rod presses the spline upper die core and moves downward together. At the end of extrusion, the spline upper die core is separated from the product and no longer returns from the extruded product. When ejecting, the product, the annular ejector and the spline upper die core are ejected from the die together.

[0003] As can be seen from the above, when making an internal spline tube by extrusion, two sets of dies are required, one for positive extrusion of the blank to make the tube longer by extrusion, and finally for spline extrusion of the semi-finished product through the spline upper die core. In the above method, positive extrusion and spline forming are formed by a set of dies respectively, which has high mold cost and complicated manufacturing process. At the same time, only conventional straight tubes can be splined, which cannot meet the production of internal spline tubes with different diameters at the upper and lower ends. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a mold which can produce tubes with different diameters at the upper and lower ends through one-time extrusion and has high molding accuracy.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A cold extrusion forming process for a thin-walled internal spline tube, characterized in that it includes the following steps: S1, blanking, selecting a seamless drawn annealed steel tube with a cross-sectional shrinkage rate of 30%-50% for blanking; S2, phosphating and saponifying the tube blank after blanking; S3, placing the tube blank after phosphating and saponifying into a prefabricated extrusion die for cold extrusion, wherein the extrusion die includes an upper die core and a concave die, wherein the upper die core is vertically arranged, a step is provided in the middle, and an upper reaming portion and a lower spline forming portion are provided under the step; a forming hole is vertically arranged in the middle of the concave die and corresponds to the upper die core, including an upper forming hole and a lower forming hole, wherein the diameter of the upper forming hole is larger than the diameter of the upper reaming portion, the diameter of the upper forming hole is larger than the diameter of the lower forming hole, and a conical surface transition is passed between the upper forming hole and the lower forming hole; during cold extrusion, the tube is firstly The material blank is placed in the forming hole of the concave die, and then the upper die core is controlled to move downward by the press, and the upper die core is inserted into the hollow part of the tube blank, and as the upper die core continues to move downward, the upper hole expansion part of the upper die core circumferentially squeezes the upper end of the tube blank, so that the aperture of the tube blank is expanded, until the step on the upper die core abuts against the upper end of the blank, and the hole expansion of the blank tube is completed; after the hole expansion is completed, the step surface on the upper die core pushes the expanded tube blank to move downward together, and in the process of moving downward, the lower end of the tube blank flows, the length becomes longer, and the tube produces a certain cross-sectional shrinkage, specifically, the cross-sectional shrinkage rate is 30%-50%; at the same time, the tube is roughened under the joint action of the step, the tapered surface and the lower spline forming part, and the internal spline extrusion is completed; S4, the extruded tube is taken out and the internal spline tube is turned according to the product size. In this way, when cutting, a seamless drawn annealed steel pipe with a large cross-sectional shrinkage rate is used, which can effectively ensure that the pipe blank can form a certain extrusion resistance after being extruded, ensure that the hole expansion and upsetting can proceed smoothly, and finally ensure the size of the finished product. Using an extrusion die, the hole expansion, upsetting and spline extrusion molding can be completed at one time, which effectively reduces the extrusion process. The conical surface set in the middle of the die can ensure that the pipe blank is positioned when it is initially placed and will not move down. At the same time, it can also form an upward resistance when the upper die core is extruded, and together with the step on the upper die core, the upper end of the pipe blank is upset to form a thick wall at the upper end of the thin-walled internal spline tube. In addition, during the continuous downward extrusion of the upper die core, the conical surface can well introduce the pipe material into the lower forming hole, and together with the lower spline forming part of the upper die core, the material flowing into the lower forming hole is formed lateral extrusion to achieve diameter reduction and internal spline molding.

[0007] Furthermore, the upper die core is composed of an upper connecting section and a lower forming section, the lower forming section is composed of the upper reaming portion and the lower spline forming portion, and the step is located between the upper connecting section and the lower forming section; the axial height of the upper forming hole is greater than the axial height of the tube blank, the axial height of the lower forming hole is greater than the axial height of the tube blank, and the axial height of the lower forming hole is greater than the axial height of the upper die core. In this way, the step set in the middle of the upper die core can form a downward push on the tube blank, ensuring that the tube blank can enter the lower forming hole under the push of the upper die core. The upper end of the upper connecting section is connected to the press to ensure that the press can directly act on the upper die core. The set lower forming section can effectively ensure that after the tube blank is extruded, the forming diameter of the lower end corresponds to the diameter of the lower end of the product to be formed, and the inner wall and the upper die core together form a two-way extrusion of the tube.

[0008] Furthermore, the outer diameter of the tube blank is smaller than the diameter of the upper forming hole and larger than the diameter of the lower forming hole, and the inner diameter of the tube blank is larger than the major diameter of the lower spline forming part and smaller than the diameter of the upper expansion part. In this way, the tube blank can be placed in the die and is located in the upper forming hole when initially placed. After continuous extrusion, the tube blank is pushed downward to perform roughening and internal spline extrusion on the tube blank.

[0009] Furthermore, the outer diameter of the tube blank is smaller than the outer diameter of the upper end of the finished internal spline tube, and larger than the outer diameter of the lower end of the finished internal spline tube. In this way, the arrangement can effectively ensure that the selected tube blank is effectively roughened and internally splined after being extruded.

[0010] Furthermore, the axial lengths of the upper and lower forming holes of the die are greater than the axial lengths of the corresponding forming sections of the internal spline tube after forming. In this way, the tube has enough space to extend during extrusion deformation, ensuring that the length of the initially formed product is greater than the preset length of the product.

[0011] Furthermore, a lifting rod corresponding to the forming hole is provided under the die, and the lifting rod can move up and down in the axial direction under the drive of a hydraulic cylinder; when the tube blank is extruded, the lifting rod rises under the drive of the hydraulic cylinder and pushes the cold extruded tube out of the die. In this way, after the tube blank is extruded and formed, the lifting rod can push the extruded profile out of the die after the lifting rod lifts it upward.

[0012] Furthermore, an elastic pad is also provided at the upper end of the jacking rod. In this way, during the jacking process, the jacking rod will not come into hard contact with the extrusion molding, thus providing a better protective effect on the molded product.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] After the blank is directly subjected to one-time cold pressing, the processes of hole expansion, upsetting, diameter reduction and spline extrusion molding can be realized. The extrusion molding quality is good and the molding process is simple.

[0015] The extrusion die used is mainly composed of an upper die core and a concave die, and has a simple structure and low manufacturing cost.

[0016] During extrusion, the conical surface set in the middle of the die can ensure that the tube blank is positioned when initially placed and will not move downward. At the same time, it can also form upward resistance when the upper die core is extruded, and together with the step on the upper die core, the upper end of the tube blank is roughened to form a thick wall at the upper end of the thin-walled internal spline tube. In addition, during the continuous downward extrusion of the upper die core, the conical surface can well introduce the tube material into the lower forming hole, and together with the lower spline forming part of the upper die core, it forms lateral extrusion on the material flowing into the lower forming hole to achieve diameter reduction and internal spline forming. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the cross-sectional structure of the thin-walled internal spline tube after molding in the embodiment;

[0018] Figure 2 It is an extrusion process diagram of the tube blank expansion, upsetting, diameter reduction and external spline extrusion molding in the embodiment;

[0019] Figure 3 Schematic diagram of the structure of the extrusion die in the embodiment. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0021] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invention product is usually placed when used, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", etc. do not mean that the components are absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] The present application will be further described below in conjunction with the accompanying drawings. Figure 1 This is a cross-sectional view of the internal spline tube to be produced. The upper end tube wall thickness of the product is 3.5mm, the wall thickness of the lower end spline part is 2.81mm, and the upper end tube diameter is larger than the lower end. The lower end inner wall is provided with a long spline. The axial length of the spline is large, and the thinnest part of the spline wall is only 1.62mm.

[0023] like Figure 2As shown, the cold extrusion forming process of the thin-walled internal spline tube in this embodiment is as follows: S1, blanking, selecting a seamless drawn annealed steel tube for blanking; S2, phosphating and saponifying the tube blank after blanking; S3, placing the tube blank after phosphating and saponifying into a prefabricated extrusion die for cold extrusion, the extrusion die comprising an upper die core 1 and a die 2, the upper die core 1 is vertically arranged, a step 13 is provided in the middle, and an upper reaming portion 121 and a lower spline forming portion 122 are provided under the step 13 (specifically, the lower spline forming portion 122 is composed of a plurality of circumferentially arranged portions); a forming hole is vertically arranged in the middle of the die 2 and corresponds to the upper die core 1, comprising an upper forming hole 21 and a lower forming hole 23, the diameter of the upper forming hole 21 is greater than the diameter of the upper reaming portion 121, the diameter of the upper forming hole 21 is greater than the diameter of the lower forming hole 23, and a tapered surface 22 is provided between the upper forming hole 21 and the lower forming hole 23 for transition. During cold extrusion, the tube blank is first placed in the forming hole of the die 2, and then the upper die core 1 is controlled to move downward by the press, and the upper die core 1 is inserted into the hollow part of the tube blank. As the upper die core 1 continues to move downward, the upper reaming portion 121 of the upper die core 1 circumferentially extrude the upper end of the tube blank, so that the aperture of the tube blank is enlarged until the step 13 on the upper die core abuts against the upper end of the blank, completing the reaming of the blank tube. After the reaming is completed, the step 13 on the upper die core 1 pushes the expanded tube blank to move downward together, and in the process of moving downward, the lower end of the tube blank flows, the length becomes longer, and the tube produces a certain cross-sectional shrinkage. Specifically, the cross-sectional shrinkage rate is 30%-50%; at the same time, the tube is roughened under the joint action of the step 13, the tapered surface 22 and the lower spline forming portion 122, and the internal spline extrusion is completed; S4, the extruded tube is taken out and the internal spline tube is turned according to the product size. In this way, a seamless drawn annealed steel pipe with a certain specification and a large cross-sectional shrinkage rate is used when cutting, and the hardness is 130-150HB, ensuring that the cross-sectional shrinkage rate is 30-50% during cold extrusion, which can effectively ensure that the pipe blank can form a certain extrusion resistance after being extruded, ensure that the hole expansion and upsetting can be carried out smoothly, and finally ensure the size of the finished product. Using an extrusion die, the hole expansion, upsetting and spline extrusion molding can be completed at one time, which effectively reduces the extrusion process. The conical surface set in the middle of the die can ensure that the pipe blank is positioned when it is initially placed and will not move down. At the same time, it can also form an upward resistance when the upper die core is extruded, and together with the step on the upper die core and the lower spline forming part 122, the upper end of the pipe blank is upset to form a thick wall at the upper end of the thin-walled inner spline tube. In addition, during the continuous downward extrusion of the upper die core, the tapered surface can effectively introduce the pipe material into the lower forming hole, and together with the lower spline forming part of the upper die core, it forms lateral extrusion on the material flowing into the lower forming hole, thereby achieving diameter reduction and internal spline forming.

[0024] Furthermore, the upper die core 1 is composed of an upper connecting section 11 and a lower forming section 12, the lower forming section 12 is composed of an upper reaming portion 121 and a lower spline forming portion 122, and the step 13 is located between the upper connecting section 11 and the lower forming section 12; the axial height of the upper forming hole 21 is greater than the axial height of the tube blank, and the axial height of the lower forming hole 23 is greater than the axial height of the tube blank. In this way, the step set in the middle of the upper die core can form a downward push on the tube blank, ensuring that the tube blank can enter the lower forming hole under the push of the upper die core. The upper end of the upper connecting section is connected to the press to ensure that the press can directly act on the upper die core. The set lower forming section can effectively ensure that after the tube blank is extruded, the forming diameter of the lower end corresponds to the diameter of the lower end of the product to be formed, and the inner wall and the upper die core together form a two-way extrusion of the tube.

[0025] Furthermore, the outer diameter of the tube blank is smaller than the diameter of the upper forming hole 21 and larger than the diameter of the lower forming hole 23. The inner diameter of the tube blank is larger than the major diameter of the lower spline forming part and smaller than the diameter of the upper expansion part. The outer diameter of the tube blank is smaller than the outer diameter of the upper end of the finished inner spline tube and larger than the outer diameter of the lower end of the finished inner spline tube. In this way, the tube blank can be placed in the die and, when initially placed, is located in the upper forming hole. After continuous extrusion, the tube blank is pushed downward to perform roughening and internal spline extrusion on the tube blank. This can effectively ensure that the selected tube blank is effectively roughened and internally splined after being extruded.

[0026] After the cut tube is extruded, the tube flows under pressure and becomes longer, and some burrs will appear at the end due to extrusion. Therefore, it is necessary to turn the upper and lower ends of the inner spline tube after extrusion to ensure the flatness of the end surface and the length requirements, so as to ensure that the length of the spline tube after extrusion is greater than the length of the molded product. To meet the above requirements, the axial lengths of the upper molding hole 21 and the lower molding hole 23 of the die 2 are greater than the axial length of the corresponding molding section of the inner spline tube after molding. In this way, when the tube is extruded and deformed, there is enough space to extend, ensuring that the length of the initially molded product is greater than the preset length of the product.

[0027] After the product is extruded, in order to facilitate the removal of the formed spline tube, a lifting rod 3 corresponding to the forming hole is provided under the die 2. The lifting rod 3 can move up and down in the axial direction driven by a hydraulic cylinder. By controlling the hydraulic cylinder to lift upward, the formed spline tube can be ejected from the forming hole of the die. In order to avoid damage to the product after the lifting rod and the formed internal spline tube are in hard contact, an elastic gasket is provided at the upper end of the lifting rod 3. The elastic gasket can form a certain buffering force when lifting the formed internal spline tube to avoid hard contact between the lifting rod and the lower end of the formed internal spline tube.

[0028] In order to facilitate the upper die core to quickly correspond to the through hole in the middle of the pipe blank and be inserted into the pipe blank, an annular chamfer is provided at the bottom of the lower forming section.

[0029] In addition, in order to ensure that the forming holes of the upper mold core 1 and the die 2 are coaxial, a base is provided under the die 2, and four guide pillars are distributed in a rectangular shape on the base. Four guide sleeves corresponding to the guide pillars are provided at the lower end of the pressure plate at the upper end of the upper mold core 1. The guide sleeves can be sleeved on the guide pillars when moving downward to guide the upper mold core.

[0030] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A cold extrusion forming process for a thin-walled internal spline tube, characterized in that: The method comprises the following steps: S1, blanking, selecting a seamless drawn annealed steel pipe for blanking; S2, phosphating and saponifying the blank pipe after blanking; S3, placing the blank pipe after phosphating and saponifying into a prefabricated extrusion die for cold extrusion, wherein the extrusion die comprises an upper die core and a concave die, wherein the upper die core is vertically arranged, a step is arranged in the middle, and an upper reaming portion and a lower spline forming portion are arranged under the step; a forming hole is vertically arranged in the middle of the concave die and corresponds to the upper die core, comprising an upper forming hole and a lower forming hole, wherein the diameter of the upper forming hole is greater than the diameter of the upper reaming portion, the diameter of the upper forming hole is greater than the diameter of the lower forming hole, and a conical surface transition is provided between the upper forming hole and the lower forming hole; the upper die core is composed of an upper connecting section and a lower forming section, wherein the lower forming section is composed of the upper reaming portion and the lower spline forming portion, and the step is located between the upper connecting section and the lower forming section; the axial height of the upper forming hole is greater than the axial height of the blank pipe height, the axial height of the lower forming hole is greater than the axial height of the tube blank; during cold extrusion, the tube blank is first placed in the forming hole of the die, and then the upper die core is controlled to move downward by the press, and the upper die core is inserted into the hollow part of the tube blank, and as the upper die core continues to move downward, the upper hole expansion part of the upper die core circumferentially extrude the upper end of the tube blank, so that the aperture of the tube blank is expanded, until the step on the upper die core abuts against the upper end of the blank, and the hole expansion of the blank tube is completed; after the hole expansion is completed, the step surface on the upper die core pushes the expanded tube blank to move downward together, and in the process of moving downward, the lower end of the tube blank flows, the length becomes longer, and the tube produces a certain cross-sectional shrinkage, specifically, the cross-sectional shrinkage rate is 30%-50%; at the same time, the tube is roughened under the joint action of the step, the tapered surface and the lower spline forming part, and the internal spline extrusion is completed; S4, the extruded tube is taken out and the internal spline tube is turned according to the product size.

2. The cold extrusion forming process of the thin-wall internal spline tube according to claim 1 is characterized in that: The outer diameter of the tube blank is smaller than the diameter of the upper forming hole and larger than the diameter of the lower forming hole. The inner hole diameter of the tube blank is larger than the major diameter of the lower spline forming part and smaller than the diameter of the upper expansion hole part.

3. The cold extrusion forming process of the thin-wall internal spline tube according to claim 1 or 2, characterized in that: The outer diameter of the tube blank is smaller than the outer diameter of the upper end of the finished internal spline tube, and larger than the outer diameter of the lower end of the finished internal spline tube.

4. The cold extrusion forming process of the thin-wall internal spline tube according to claim 3 is characterized in that: The axial lengths of the upper forming hole and the lower forming hole of the die are both greater than the axial length of the corresponding forming section of the internal spline tube after forming.

5. The cold extrusion forming process of the thin-wall internal spline tube according to claim 4, characterized in that: A lifting rod corresponding to the forming hole is also provided under the die, and the lifting rod can move up and down in the axial direction driven by a hydraulic cylinder; when the tube blank is extruded, the lifting rod rises under the drive of the hydraulic cylinder and ejects the cold-extruded tube from the die.

6. The cold extrusion forming process of the thin-wall internal spline tube according to claim 5, characterized in that: An elastic gasket is also arranged on the upper end of the jacking rod.

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