阅读说明：本技术 镁合金薄壁管材的双向挤压成型模具及其成型方法 (Bidirectional extrusion forming die for magnesium alloy thin-wall pipe and forming method thereof ) 是由 直妍 梁鹏程 李兴林 胡红军 洪兴 戴庆伟 代俊林 干松林 田野 冉兴 张丁非 于 2019-10-24 设计创作，主要内容包括：本发明公开了一种镁合金薄壁管材的双向挤压成型模具及其成型方法,所述模具包括凹模、挤压杆和挤压针,在凹模内设有相互连通的正向挤压腔、侧向挤压腔和凹模型腔；所述挤压杆包括正向挤压杆和侧向挤压杆,所述正向挤压杆的上端与液压机主缸相接,下端与正向挤压腔相配合,所述侧向挤压杆的一端与液压机的侧缸相接,另一端置于侧向挤压腔内,并与挤压针间隙配合；挤压针靠近凹模型腔的一端外形与凹模型腔相对应,并与凹模型腔之间形成管材成型腔；通过正向挤压杆对坯料正向挤压后,再通过侧向挤压杆将坯料向管材成型腔方向挤压。本发明得到的镁合金薄壁管材的双向挤压成型模具及其成型方法能有效提升镁合金薄壁管材成型后的强度和韧性。(The invention discloses a bidirectional extrusion forming die of a magnesium alloy thin-wall pipe and a forming method thereof, wherein the die comprises a female die, an extrusion rod and an extrusion needle, and a forward extrusion cavity, a lateral extrusion cavity and a female die cavity which are communicated with each other are arranged in the female die; the extrusion rod comprises a forward extrusion rod and a lateral extrusion rod, the upper end of the forward extrusion rod is connected with a main cylinder of the hydraulic machine, the lower end of the forward extrusion rod is matched with the forward extrusion cavity, one end of the lateral extrusion rod is connected with a lateral cylinder of the hydraulic machine, and the other end of the lateral extrusion rod is arranged in the lateral extrusion cavity and is in clearance fit with the extrusion needle; the shape of one end of the extrusion needle close to the cavity of the female die corresponds to that of the cavity of the female die, and a pipe forming cavity is formed between the extrusion needle and the cavity of the female die; after the blank is extruded forwards by the forward extrusion rod, the blank is extruded towards the direction of the pipe forming cavity by the lateral extrusion rod. The bidirectional extrusion forming die and the forming method of the magnesium alloy thin-wall pipe can effectively improve the strength and toughness of the magnesium alloy thin-wall pipe after forming.)

1. A bidirectional extrusion forming die for magnesium alloy thin-wall pipes comprises a female die (3), an extrusion rod and an extrusion needle (4), and is characterized in that a forward extrusion cavity (31), a lateral extrusion cavity (32) and a female die cavity (33) which are communicated with each other are arranged in the female die (3), the forward extrusion cavity (31) is vertically arranged, the lateral extrusion cavity (32) and the female die cavity are transversely arranged, and the lateral extrusion cavity (32) and the female die cavity are coaxial and penetrate through the female die (3); the forward extrusion cavity (31) consists of an upper billet holding area and a lower necking area; the extrusion rod comprises a forward extrusion rod (1) and a lateral extrusion rod (6), the lower end of the forward extrusion rod (1) is matched with an upper blank accommodating area of a forward extrusion cavity (31), the forward extrusion rod can move up and down and be positioned under the driving of a main cylinder of the hydraulic press in the use process, one end, close to a female die, of the lateral extrusion rod (6) is arranged in the lateral extrusion cavity, and the lateral extrusion rod can move left and right and be positioned under the driving of a lateral cylinder of the hydraulic press in the use process; one end of the extrusion needle (4) is sleeved in the lateral extrusion rod (6) and is in clearance fit with the lateral extrusion rod, the appearance of one end, close to the female die cavity (33), of the extrusion needle (4) corresponds to that of the female die cavity, a pipe forming cavity (5) is formed between the extrusion needle and the female die cavity, and the pipe forming cavity (5) is composed of a sizing area, a variable-diameter shearing area and a forming area which are sequentially communicated from inside to outside; when the extrusion die is used, the main cylinder of the hydraulic press is started, so that the forward extrusion rod (1) can be driven to extrude a blank (2) to enter a part of lateral extrusion cavities after passing through the upper blank accommodating area and the lower necking area; the lateral extrusion rod can be driven to move towards the direction of the pipe forming cavity by starting a lateral cylinder of the hydraulic press, the blank is extruded towards the direction of the pipe forming cavity, and a magnesium alloy thin-wall pipe product is obtained after the pipe forming cavity is extruded.

2. The bidirectional extrusion molding die of the magnesium alloy thin-wall pipe according to claim 1, wherein the variable-diameter shearing zone consists of a first shearing zone and a second shearing zone, the inner diameters of the first shearing zone and the second shearing zone are gradually reduced, and the joint of the first shearing zone and the second shearing zone adopts fillet transition.

3. The bidirectional extrusion molding die of a magnesium alloy thin-wall tube according to claim 1 or 2, characterized in that a heating device for heating the female die and the blank is further arranged around the female die (3), and the heating device is electrically connected with an external power supply.

4. The bidirectional extrusion molding die of the magnesium alloy thin-wall tube according to claim 1, wherein the extrusion pin penetrates through the upper end of the lateral extrusion pin through a fixing rod (7) and then is fixedly connected with the female die (3), an assembling hole (61) for clearance fit with the extrusion pin is arranged in the length direction of the lateral extrusion pin (6), a strip-shaped groove is further arranged in the lateral extrusion pin (6) along the length direction of the lateral extrusion pin, and the axial length of the strip-shaped groove is greater than or equal to the extrusion depth of the lateral extrusion pin.

5. The forming method of the magnesium alloy pipe is characterized by comprising the following steps of: s1, homogenizing the blank (2); s2, placing the homogenized blank (2) into a forward extrusion cavity (31) of a die for heating pretreatment, wherein the die is as set forth in claim 3, the blank is in a bar shape and is placed in the forward extrusion cavity of a female die; s3, after the blank temperature reaches the forming temperature, closing the heating device; s4, starting the hydraulic press, operating the main cylinder of the hydraulic press to eject, driving the forward extrusion rod (1) to extrude the blank (2) placed in the forward extrusion cavity (31) in the forward direction until the blank (2) is filled in the lateral extrusion cavity (32), and operating the main cylinder of the hydraulic press to return; and S5, starting the side cylinder of the hydraulic machine to eject towards the cavity direction of the female die, gradually entering a sizing area, a reducing shearing area and a forming area of the pipe forming cavity (5) under the lateral extrusion of a lateral extrusion rod (6) to form a magnesium alloy pipe, and operating the return stroke of the side cylinder of the hydraulic machine after the extrusion is finished.

6. The forming method of the magnesium alloy pipe material according to the claim 5, wherein in S4, when the forward extrusion rod (1) is adopted to extrude the blank (2) in the forward direction, the extrusion speed is 1mm/S to 5mm/S, and the extrusion temperature is 380 ℃ to 420 ℃; when the lateral extrusion rod is adopted to laterally extrude the blank, the extrusion speed is 1-3 mm/s.

7. The forming method of the magnesium alloy pipe according to claim 5, wherein a thermocouple probe for detecting the temperature of the female die is further arranged on the female die (3), and the thermocouple probe is connected with a central control system of the hydraulic machine in a wired or wireless manner to transmit detection data to the central control system of the hydraulic machine.

Technical Field

The invention relates to a pipe forming process, in particular to a bidirectional extrusion forming die of a magnesium alloy thin-wall pipe and a forming method thereof.

Background

the magnesium alloy has a series of characteristics of small density, high specific strength, high specific rigidity and the like. The magnesium alloy has strength similar to that of aluminum alloy, and has low density, so that the magnesium alloy has high specific strength and rigidity similar to that of aluminum alloy. The magnesium alloy shows excellent performance in casting, and the magnesium alloy product has good dimensional stability and is suitable for mass production. The environmental protection property makes magnesium alloy be popular with research and development personnel and be praised as a green engineering material with the most development potential in the 21 st century.

Since magnesium has a hexagonal close-packed structure, it has poor plastic deformability at room temperature. But through extrusion deformation, the sample is subjected to the action of three-dimensional stress, obvious dynamic recrystallization can occur, and the texture is greatly weakened, so that the room-temperature toughness of the magnesium alloy is greatly improved. Therefore, the extrusion deformation is an obvious forming method for preparing the magnesium alloy with excellent and high strength and toughness. The extrusion process has the advantages of simple process flow, high production flexibility, high product size precision, good surface quality and the like, and can be used for producing high-quality products such as bars, pipes, plates, profiles and the like.

The large plastic deformation (SPD) technology is the most effective method for preparing high-performance magnesium alloy pipes in recent years, so far, the SPD technology is not strictly and accurately defined at home and abroad, and the SPD technology generally refers to a process method for realizing high-efficiency strengthening by enabling materials to obtain larger accumulated strain through a specific processing means or path. According to the Hall-Peltier empirical formula, the material strength can be increased due to grain refinement in a certain grain size range, but after the grain size is refined to a certain degree, the single mechanism of fine grain strengthening is not acted, and the coupling action of a plurality of strengthening mechanisms is dominant. The SPD technique is recognized by the materials industry as one of the most promising methods for preparing bulk nano or ultra-fine crystalline materials, and has been widely used in the preparation of high-performance pure metals, alloys, intermetallic compounds, composite materials, and the like. Meanwhile, various novel SPD technologies are proposed and verified on materials such as pure aluminum and copper, and then are gradually expanded to other materials. Magnesium alloy SPD technology represented by equal channel angular extrusion, reciprocating extrusion, high-pressure torsion and the like is gradually becoming one of the research hot spots in the field.

At present, the magnesium industry urgently needs to develop batch high-performance magnesium alloy, advanced low-cost low-energy-consumption original magnesium production technology and complete set technology for producing large-size ultrathin and complex parts, and particularly lacks a manufacturing method of high-performance magnesium alloy thin-wall pipes. The traditional magnesium alloy forming process adopts forward extrusion forming, and in the forward extrusion production process, a strip-shaped structure and a strong basal texture formed along the extrusion direction of the pipe cause anisotropy of the pipe, so that the mechanical property of the formed pipe is reduced, and the like. And the base texture formed after the traditional forward extrusion is easy to cause the defects of shrinkage cavity, looseness and the like in the light alloy casting structure in the secondary processing of the thin pipe, so that the processing precision of the pipe, particularly the thin pipe, is poor. In addition, the transverse section structure of the traditional extruded magnesium alloy part is equiaxial grains, and the longitudinal section structure after extrusion is changed into slender grains, so that the mechanical property of the magnesium alloy part is greatly influenced. For the above reasons, the applicant intends to design a die capable of performing bidirectional extrusion on a magnesium alloy blank, and having a low manufacturing cost and a simple structure. Meanwhile, the die forming process is improved to a certain extent by combining the SPD technology, so that the formed magnesium alloy thin-wall pipe has higher strength and toughness after being formed.

Disclosure of Invention

aiming at the defects of the prior art, the technical problems to be solved by the invention are as follows: how to provide a die which can carry out bidirectional extrusion on a magnesium alloy blank and has low manufacturing cost and simple structure, and a forming method of a magnesium alloy thin-wall pipe which improves the forming process of the traditional magnesium alloy thin-wall pipe and improves the strength and the toughness of the formed magnesium alloy thin-wall pipe.

In order to solve the technical problems, the invention adopts the following technical scheme:

A two-way extrusion forming die for magnesium alloy thin-wall pipes comprises a female die, an extrusion rod and an extrusion needle, and is characterized in that a forward extrusion cavity, a lateral extrusion cavity and a female die cavity which are communicated with each other are arranged in the female die, the forward extrusion cavity is vertically arranged, the lateral extrusion cavity and the female die cavity are transversely arranged, the lateral extrusion cavity and the female die cavity are coaxial and penetrate through the female die, and the connection part of the lateral extrusion cavity and the female die cavity is positioned right below the forward extrusion cavity; the forward extrusion cavity consists of an upper blank accommodating area and a lower necking area; the extrusion rod comprises a forward extrusion rod and a lateral extrusion rod, the lower end of the forward extrusion rod is matched with an upper blank accommodating area of the forward extrusion cavity, the forward extrusion rod can be driven by a main cylinder of the hydraulic machine to move up and down and be positioned in the use process, one end of the lateral extrusion rod, which is close to the female die, is arranged in the lateral extrusion cavity, and the lateral extrusion rod can be driven by a lateral cylinder of the hydraulic machine to move left and right and be positioned in the use process; one end of the extrusion needle is sleeved in the lateral extrusion rod and is in clearance fit with the lateral extrusion rod, the shape of one end, close to the female die cavity, of the extrusion needle corresponds to that of the female die cavity, and a pipe forming cavity is formed between the extrusion needle and the female die cavity and consists of a sizing area, a variable-diameter shearing area and a forming area which are sequentially communicated from inside to outside; by starting a main cylinder of the hydraulic press, the forward extrusion rod can be driven to extrude the blank to enter a part of lateral extrusion cavities after passing through the upper blank accommodating area and the lower necking area; the lateral extrusion rod can be driven to move towards the direction of the pipe forming cavity by starting a lateral cylinder of the hydraulic press, the blank is extruded towards the direction of the pipe forming cavity, and a magnesium alloy thin-wall pipe product is obtained after the pipe forming cavity is extruded. Like this, mould simple structure mainly forms by die and extrusion needle, and the extrusion needle passes through a dead lever fixed connection with the die to form the tubular product shaping chamber together with the die cavity, the forward extrusion of blank and side direction extrusion all form in the die, and the wholeness of mould is good, and intensity is high, can prevent effectively that the mould from being crowded split, has prolonged mould life. Meanwhile, the die is mainly formed by a concave die, so that the use cost of an expensive steel die is saved. The forward extrusion rod and the lateral extrusion rod can drive the blank to be extruded in the forward direction and then extruded in the lateral direction, and the magnesium alloy pipe formed by adopting the bidirectional extrusion can solve a series of problems that in the traditional forward extrusion production process, a banded structure and a strong basal texture are formed along the extrusion direction of the pipe, so that the anisotropy of the pipe is caused, the mechanical property of the formed pipe is reduced, and the like. The pipe forming cavity comprises a reducing shearing area, and after the blank is extruded to the area, the blank forms shearing large plastic deformation, so that the dynamic recrystallization can be effectively promoted, the microstructure (crystal grains) is refined, and the texture of the basal plane is weakened.

Furthermore, the reducing shearing area consists of a first shearing area and a second shearing area, the inner diameter of the first shearing area is gradually reduced, and the joint of the first shearing area and the second shearing area adopts fillet transition. Therefore, the blank passes through the area and undergoes two-side shearing deformation, the internal texture of the blank is regulated and controlled to a great extent, the strain is accumulated, the dynamic recrystallization process is promoted, and the grains are refined.

Furthermore, a heating device for heating the female die and the blank is arranged around the female die, and the heating device is electrically connected with an external power supply. Therefore, the blank is not heated outside the die but directly heated in the die, thereby effectively preventing the loss of the heat of the blank and accurately controlling the forming temperature of the blank.

Further, the extrusion needle passes through a dead lever and is connected with die fixed connection behind the side direction extrusion pole upper end, be equipped with one in side direction extrusion pole length direction be used for with extrusion needle clearance fit's pilot hole, still be equipped with a bar groove that sets up along its length direction on the side direction extrusion pole, the lower extreme of dead lever pass behind the bar groove with extrusion needle fixed connection, the axial length in bar groove is more than or equal to the extrusion depth of side direction extrusion pole. Therefore, the fixing rod cannot block the lateral extrusion rod in the lateral extrusion process of the lateral extrusion rod.

The forming method of the magnesium alloy pipe is characterized by comprising the following steps of: s1, homogenizing the blank; s2, placing the homogenized blank into a forward extrusion cavity of a female die for heating pretreatment, wherein the blank is rod-shaped and is placed into the forward extrusion cavity of the female die as described above; s3, after the blank temperature reaches the forming temperature, closing the heating device; s4, starting the hydraulic press, operating the main cylinder of the hydraulic press to eject, driving the forward extrusion rod to extrude the blank in the forward extrusion cavity in the forward direction, and operating the main cylinder of the hydraulic press to return after the blank is filled in the lateral extrusion cavity; and S5, starting the side cylinder of the hydraulic machine to eject towards the cavity direction of the female die, gradually entering a sizing area, a reducing shearing area and a forming area of a pipe forming cavity under the lateral extrusion of a lateral extrusion rod to form a magnesium alloy pipe, and operating the side cylinder of the hydraulic machine to return after the extrusion is finished. Like this, the extrusion of blank is accomplished through controlling the hydraulic press, and its degree of automation is high, can effectively promote the production efficiency of tubular product, realizes automaticly. After the blank is extruded and formed in a bidirectional extrusion forming mode, the defects of micro holes and the like in the magnesium alloy can be eliminated, the compactness of the material is improved, dendritic crystals are crushed, fine isometric crystals are formed, the texture of a basal plane is weakened, the forming precision and the mechanical property of the pipe are ensured, and the design can also be suitable for forming the alloys such as aluminum, titanium and the like.

Further, in S4, when the blank is extruded forward by the forward extrusion rod, the extrusion speed is 1mm/S to 5mm/S, and the extrusion temperature is 380 ℃ to 420 ℃; when the lateral extrusion rod is adopted to laterally extrude the blank, the extrusion speed is 1-3 mm/s. Therefore, the process parameters can maximize the degree of dynamic recrystallization of the magnesium alloy in the extrusion forming process, further refine grains and improve the performance of the pipe.

Furthermore, a thermocouple probe for detecting the temperature of the female die is arranged on the female die and is connected with a central control system of the hydraulic press in a wired or wireless mode, and detection data are transmitted to the central control system of the hydraulic press. Therefore, after the detection device is arranged, the temperature of the female die and the blank can be known in real time, and the extrusion temperature of the pipe can be accurately controlled.

drawings

FIG. 1 is a half sectional view of a bidirectional extrusion mold in an embodiment;

FIG. 2 is a sectional view of a female mold in the embodiment;

FIG. 3 is a diagram illustrating the entire deformation process of a numerically simulated blank;

FIG. 4 is a polar view of the tube blank during forward extrusion;

Fig. 5 is a polar view of the final formed tubing after lateral extrusion.

In the figure: the device comprises a forward extrusion rod 1, a blank 2, a female die 3, a forward extrusion cavity 31, an extrusion needle 4, a pipe forming cavity, a lateral extrusion rod 6 and a fixing rod 7.

Detailed Description

the invention is further illustrated with reference to the following figures and examples.