CN112676459B - Ultralow-temperature flexible forming method for aluminum-lithium alloy complex thin-wall structural part - Google Patents

Ultralow-temperature flexible forming method for aluminum-lithium alloy complex thin-wall structural part Download PDF

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CN112676459B
CN112676459B CN202011435530.0A CN202011435530A CN112676459B CN 112676459 B CN112676459 B CN 112676459B CN 202011435530 A CN202011435530 A CN 202011435530A CN 112676459 B CN112676459 B CN 112676459B
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low
die
lithium alloy
aluminum
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CN112676459A (en
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许爱军
宁旭东
代国宝
张斌
赖小明
崔超
刘淑芬
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Beijing Satellite Manufacturing Factory Co Ltd
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Abstract

The invention relates to the technical field of special forming and manufacturing processes of an aluminum-lithium alloy complex thin-wall structural member, in particular to an ultralow-temperature flexible forming method of the aluminum-lithium alloy complex structural member, wherein the thin wall means that the wall thickness of the structural member is not more than 5mm, and the complex structural member means that the appearance of the structural member is a space curved surface structure. The invention utilizes the plasticizing and reinforcing characteristics of the aluminum lithium alloy at ultralow temperature, adopts an ultralow temperature flexible forming method to flexibly form the aluminum lithium alloy plate, and can solve the problems that the complex thin-wall structural member of the aluminum lithium alloy is difficult to form a complex-shaped member at room temperature, has poor fracture toughness, is easy to generate microcracks during room temperature forming, has large forming resilience and is difficult to ensure the dimensional precision of the member shape.

Description

Ultralow-temperature flexible forming method for aluminum-lithium alloy complex thin-wall structural member
Technical Field
The invention relates to the technical field of special forming and manufacturing processes of an aluminum-lithium alloy complex thin-wall structural member, in particular to an ultralow-temperature flexible forming method of the aluminum-lithium alloy complex structural member, wherein the thin wall means that the wall thickness of the structural member is not more than 5mm, and the complex structural member means that the appearance of the structural member is a space curved surface structure.
Background
With the further development of science and technology and the continuous progress of society, the structural lightweight plays an increasingly important role in improving the resource utilization rate, reducing energy consumption and improving the service performance of parts, and becomes one of the development trends of the current manufacturing industry, and two approaches of materials and structures are mainly used for realizing the structural lightweight: the material approach is to adopt light materials such as aluminum alloy, magnesium alloy, titanium alloy and the like to replace heavy materials such as steel and the like. Therefore, an aluminum lithium alloy having excellent comprehensive properties and capable of realizing an obvious structural weight reduction effect is a key point of attention, and the aluminum lithium alloy is a novel aluminum alloy using Li as a main alloying element and is characterized by low density and excellent heat resistance and corrosion resistance. Research shows that 1% of lithium is added into the aluminum alloy, so that the density of the alloy can be reduced by 3%, and the rigidity can be improved by 6%. Therefore, the aluminum lithium alloy is considered to be an ideal structural material in the field of aerospace.
Although the application of the aluminum lithium alloy has a plurality of advantages, the manufacturing process of the aluminum lithium alloy thin-wall integral structure mainly has the following problems:
firstly, the aluminum lithium alloy has poor room temperature plasticity and is difficult to form a component with a complex shape;
secondly, the aluminum-lithium alloy has poor fracture toughness, and the defects of microcracks and the like easily occur by adopting the traditional forming methods such as stamping, deep drawing and the like;
thirdly, the resilience is large, and the shape and size precision of the component is difficult to ensure.
In order to solve the above problems, a hot forming method is generally adopted for forming the aluminum lithium alloy complex structural member at home and abroad. The hot forming mainly utilizes the softening and creep properties of the aluminum lithium alloy material in a heating state to improve the plasticity of the aluminum lithium alloy material, thereby reducing the forming force, improving the formability and reducing the resilience of the forming process and parts. Although the plasticity can be increased and the spring back can be reduced by increasing the forming temperature, the strength of the formed part is reduced, and the strength must be further increased by heat treating the formed part. However, when the heat treatment is carried out after the forming, the shape and the size of the part are changed due to uneven heating in the heating or cooling process; therefore, a new forming process must be designed to realize the precise forming of the aluminum-lithium alloy complex structural member, improve the precision and performance of the formed aluminum-lithium alloy complex structural member and meet the working condition requirements of the complex structural member.
The study of scholars at home and abroad shows that the tensile strength and the yield strength of the aluminum-lithium alloy are increased along with the reduction of the temperature, the elongation rate is basically kept unchanged or even increased, the aluminum-lithium alloy has good low-temperature ductility and toughness, the crack propagation rate of the aluminum-lithium alloy is reduced along with the reduction of the temperature, and the fatigue life and the fracture toughness are increased along with the reduction of the temperature.
According to the characteristics of the aluminum-lithium alloy, Chinese patent CN108326159A discloses a freezing forming method for large-size aluminum alloy tailor-welded blank components, wherein a coolant is used for cooling the aluminum alloy tailor-welded blank to an ultralow temperature range, so that the temperature of a welding seam area is lower than that of a parent metal area, and the large-size aluminum alloy integral curved surface component formed by adopting a mold can solve the cracking problem caused by large deformation of the welding seam area of the tailor-welded blank, and is suitable for manufacturing various aluminum alloy large-size integral thin-wall curved surface components in the aerospace field. However, the fluid medium generates a large reaction force to the die in the forming process, the reaction force is increased along with the increase of the liquid pressure and the acting area of the die, the tonnage of equipment is increased rapidly, and in addition, the forming precision of a final part is controlled by the aid of the profile of the punch in the hydro-mechanical drawing, so that the requirement on the machining precision of the punch is high.
The method has the advantages that the height of the basic body is adjustable, the configuration of complex curved surfaces with different shapes can be realized, the processing cost of the die can be reduced, and the method is particularly suitable for forming special-shaped curved surface parts.
Disclosure of Invention
The technical problem solved by the invention is as follows: the ultra-low temperature forming method for the aluminum-lithium alloy thin-wall structural component overcomes the defects of the prior art, and has the problems that the complex-shaped structural component of the aluminum-lithium alloy thin-wall structural component is difficult to form at room temperature, the fracture toughness is poor, microcracks are easy to appear during room temperature forming, the forming resilience is large, and the dimensional precision of the structural component is difficult to ensure. The invention aims to provide a device and a method for forming a plate by using liquid-filled deep drawing by using a multipoint male die by combining the technical advantages of multipoint forming and low-temperature medium forming and utilizing the new phenomena of plasticization and enhancement of an aluminum lithium alloy at ultralow temperature, and provides an ultralow-temperature forming device and a forming manufacturing method of an aluminum lithium alloy thin-wall structural member, so as to solve the problems that the complex-shaped member of the aluminum lithium alloy complex thin-wall structural member is difficult to form at room temperature, the fracture toughness is poor, microcracks are easy to occur in the room-temperature forming, the forming resilience is large, and the dimensional accuracy of the member shape is difficult to ensure.
The technical solution of the invention is as follows:
an ultralow temperature flexible forming device of an aluminum-lithium alloy thin-wall structural part comprises a die holder 1, a die sleeve 2, a double-layer low-temperature-resistant sealing ring 5, a first cold-insulation heat-preservation layer 6, an ultralow-temperature circumferential sealing ring 7, a multipoint die head 8, a die body 10, a first blank holder 11, a second blank holder inner ring 12, a second cold-insulation heat-preservation layer 14, a low-temperature forming die cushion block A16, a die holder cushion block B17, a third cold-insulation heat-preservation layer 18 and a fourth cold-insulation heat-preservation layer 19;
the die holder 1 is of an integral cylindrical structure, and a cylindrical inner cavity is reserved in the middle, namely the die holder 1 is a hollow cylinder with an opening and a bottom;
the female die sleeve 2 is a hollow cylinder with an opening and a bottom, namely the female die sleeve 2 is provided with a cavity;
the outer diameter of the concave die sleeve 2 is matched with the inner diameter of the concave die holder 1, and the concave die sleeve 2 is placed in the inner cavity of the concave die holder 1; a fourth cold insulation layer 19 is arranged between the outer surface of the die sleeve 2 and the inner surface of the die holder 1;
the male die body 10 is a cylinder with a handle at the top end, and a threaded hole is formed at the bottom end of the male die body 10;
the multipoint male die head 8 comprises a plurality of steel columns, wherein one ends of the steel columns are provided with external threads 9, the other ends of the steel columns are of hemispherical structures, and the ends of the steel columns, which are provided with the external threads 9, are in threaded connection with the bottom ends of the male die bodies 10;
the multipoint convex die head 8 is positioned in the cavity of the concave die sleeve 2; a plurality of steel columns are uniformly and tightly arranged;
the multi-point convex die head 8 and the convex die body 10 form a forming convex die 20;
the second blank holder inner ring 12 is of a circular ring structure;
the first cold insulation layer 6 is of a circular ring structure;
the first blank holder 11 is of a circular ring structure;
the second blank holder inner ring 12, the first cold insulation layer 6 and the first blank holder 11 are sequentially sleeved on the forming male die 20 from bottom to top, namely, the second blank holder inner ring 12 is firstly sleeved on the forming male die 20, then the first cold insulation layer 6 is sleeved on the forming male die 20, and finally the first blank holder 11 is sleeved on the forming male die 20;
the die holder cushion block B17 is of a circular ring structure;
the low-temperature forming female die cushion block A16 is of a circular ring structure, the low-temperature forming female die cushion block A16 is fixedly connected to the upper surface of a female die holder cushion block B17, the low-temperature forming female die cushion block A16 and the female die holder cushion block B17 are sealed through a double-layer low-temperature-resistant sealing ring 5, the low-temperature forming female die cushion block A16 and the female die holder cushion block B17 are sleeved on the female die holder 1 together after being fixedly connected, and the female die holder cushion block B17 and the female die holder 1 are insulated from cold and heat through a third cold-insulation layer 18;
the second blank holder inner ring 12 is positioned above the low-temperature forming female die cushion block A16;
the ultralow-temperature circumferential sealing ring 7 is sleeved on the outer surface of the second edge pressing inner ring 12;
the second cold insulation and heat preservation layer 14 is sleeved on the outer surfaces of the low-temperature forming die cushion block A16 and the die holder cushion block B17 and used for cold insulation and heat preservation of the low-temperature forming die cushion block A16 and the die holder cushion block B17;
the outer profile of the multi-point convex die head 8 is consistent with the inner profile shape of the aluminum lithium alloy thin-wall structural part to be formed, the height of the multi-point convex die head 8 is adjusted by the multi-point convex die head 8 through threads 9, so that the multi-point convex die head 8 can realize configurations with different outer profile shapes, and one or more multi-point convex die heads 8 can be independently replaced according to the inner profile shape of the part of the aluminum lithium alloy plate to be formed;
the forming clearance between the forming convex die 20 and the concave die sleeve 2 needs to be set according to the thickness of the aluminum lithium alloy plate, the forming clearance between the forming convex die 20 and the concave die sleeve 2 is preferably 1.1t mm, and t is the thickness of the aluminum lithium alloy plate; the forming male die 20 is provided with a connecting interface connected with a main cylinder of the double-acting hydraulic machine;
a cavity surrounded by the female die sleeve 2 and the multi-point convex die head 8 is used as a high-pressure low-temperature liquid filling chamber 3, and when the forming is carried out, the cavity surrounded by the female die sleeve 2, the multi-point convex die heads 8 in different shapes and the aluminum lithium alloy plate 15 form the high-pressure low-temperature liquid filling chambers 3 in different shapes together;
through holes are arranged on the side wall of the die holder 1 and the side wall of the die sleeve 2, and the through holes are used as channels for communicating the low-temperature liquid medium system source A and the high-pressure low-temperature liquid filling chamber 3;
a liquid filling interface A-2 connected with a low-temperature liquid medium system source A and a liquid inlet channel A-1 of a high-pressure low-temperature liquid medium are formed in the side edge of the female die holder 1, and a high-pressure low-temperature liquid channel A-3 is formed in the side wall of the female die sleeve 2;
the liquid inlet channel A-1 and the liquid channel A-3 are communicated with the high-pressure low-temperature liquid filling chamber 3;
a metal sealing gasket and a conical surface composite seal are adopted between the joint of the low-temperature liquid filling interface A-2 and the low-temperature liquid medium system source A;
a combined sealing mode of sealing a conical surface seal 13 and a sealing ring 7 is adopted between the low-temperature female die forming cushion block A16 and a female die holder cushion block B17;
the size of the female die sleeve 2 is slightly different for adapting to aluminum lithium alloy plates with different thicknesses and different formed parts, and the female die sleeve can be adjusted and replaced according to the aluminum lithium alloy plates with different thicknesses and the formed parts with different shapes;
the side wall of the female die sleeve 2 is fully distributed with a high-pressure low-temperature liquid channel 4, the side wall of the female die sleeve 2 is also provided with a low-temperature liquid channel A-3, the low-temperature liquid channel A-3 is communicated with a liquid inlet channel A-1 of a high-pressure low-temperature liquid medium opened on the female die base 1, and high-pressure low-temperature liquid output by a low-temperature liquid medium system source A enters the low-temperature liquid channel A-3 opened on the side wall of the female die sleeve 2 through a liquid filling interface A-2 and the liquid inlet channel A-1 of the high-pressure low-temperature liquid medium and then enters the high-pressure low-temperature liquid filling chamber 3 and the high-pressure low-temperature liquid channel 4 fully distributed on the side wall of the female die sleeve 2. The high-pressure cryogenic liquid entering the high-pressure cryogenic liquid channel 4 can be used to lower and adjust the temperature of the die case 2, thereby controlling the temperature of the aluminum lithium alloy plate 15.
When the female die sleeve 2 is used, the fourth cold insulation layer 19 is placed in the female die base 1, and then the female die sleeve 2 is placed in the female die base 1; the inner cavity of the female die sleeve 2 arranged in the female die holder 1, the multi-point male die heads 8 with different shapes and the cavity surrounded by the aluminum lithium alloy plate 15 form the high-pressure low-temperature liquid filling chambers 3 with different shapes;
the first cold insulation layer 6, the second cold insulation layer 14, the third cold insulation layer 18 and the fourth cold insulation layer 19 are main structures for keeping the formed plate in a deep cooling state. For the cold insulation design of the first cold insulation layer 6, the second cold insulation layer 14, the third cold insulation layer 18 and the fourth cold insulation layer 19, the heat insulation material cannot bear the pressure of the hydraulic machine and the die, so that the cold insulation material needs to be placed in a device with the requirement on the compressive strength. The device adopts the middle to fill cold insulation and heat preservation material, and both sides and periphery adopt steel plates to make up, make its compressive strength satisfy the shaping needs. The heat insulation material is perlite concrete, the heat conductivity is 0.12-0.25W/(m.K), the use temperature is-273-200 ℃, and the compressive strength is 1.5-8.5 MPa.
The first blank holder 11, the second blank holder inner ring 12, the low-temperature forming female die cushion block A16 and the female die holder cushion block B17 are all in modular design, and the sizes of the first blank holder, the second blank holder inner ring and the female die holder cushion block B17 are adapted according to aluminum lithium alloy plates with different thicknesses and formed parts with different shapes; the die holder cushion block B17 is of a circular structure, the upper surface of the die holder cushion block B17 is in matched contact with the low-temperature forming die cushion block A16, the matched contact surface of the die holder cushion block B and the low-temperature forming die cushion block A is provided with a double-layer sealing groove, and the double-layer sealing groove is used for placing a double-layer low-temperature-resistant sealing ring 5 for sealing and is used for sealing a high-pressure low-temperature liquid medium in the forming process. The double-layer low-temperature-resistant seal ring 5 is an O-ring that can be made of a metal material such as nickel or indium, has a sealing capability at an ultra-low temperature, and is preferably made of an indium soft metal.
The low-temperature forming female die cushion block A16 is of an annular structure, a boss is reserved on the side face of the low-temperature forming female die cushion block A16, a liquid filling interface B-1 connected with an independent low-temperature liquid medium system source B and a liquid inlet channel B-2 of a high-pressure low-temperature liquid medium are arranged on the right side edge of the low-temperature forming female die cushion block A, the liquid inlet channel B-2 is communicated with a low-temperature liquid medium channel B-3, high-pressure low-temperature liquid output by the low-temperature liquid medium system source B enters the opened low-temperature liquid medium channel B-3 of the low-temperature forming female die cushion block A16 through the liquid filling interface B-1 and the liquid inlet channel B-2 of the high-pressure low-temperature liquid medium, and the high-pressure low-temperature liquid entering the low-temperature liquid medium channel B-3 can be used for reducing and adjusting the temperature of the low-temperature forming female die cushion block A16, so that the temperature of the aluminum lithium alloy plate 15 is controlled. And a metal sealing gasket and a conical surface composite seal are adopted between the joint of the low-temperature liquid filling interface B-1 and the source B of the low-temperature liquid medium system.
The second blank holder inner ring 12 is of a circular ring structure, the side face is a sealing face and is provided with a sealing groove, the side face of the second blank holder inner ring 12 is in sealing fit with a boss reserved on the side face of the low-temperature forming female die cushion block A16, the ultralow-temperature circumferential sealing ring 7 used between the sealing grooves is sealed, the ultralow-temperature circumferential sealing ring 7 is an O-shaped sealing ring made of metal materials such as nickel and indium, the ultralow-temperature circumferential sealing ring has sealing capability at ultralow temperature and is preferably made of indium soft metal, and meanwhile the second blank holder inner ring 12 and the low-temperature forming female die cushion block A16 also adopt a matched conical surface seal 13, so that conical surface sealing is realized. The conical surface seal and seal ring type composite seal is jointly used for sealing high-pressure and low-temperature liquid media in the forming process.
The aluminum lithium alloy plate 15 is a two-dimensional plane plate after the aluminum lithium alloy complex thin-wall structural member is unfolded, the first blank holder 11 is an integral blank holder which is of a circular ring-shaped structure and is arranged right above the first cold insulation and heat preservation layer 6, and an interface connected with a blank holder cylinder of the double-acting hydraulic press is arranged on the blank holder; and a cold insulation layer 6 is arranged between the first blank holder 11 and the second blank holder 12 and between the low-temperature forming die cushion blocks A16 and is used for preventing the ultralow temperature from being transmitted to the first blank holder 11.
When the die is used, the third cold insulation and heat preservation layer 18 is placed on the die holder 1, the die holder cushion block B17 is placed on the third cold insulation and heat preservation layer 18, the double-layer low-temperature-resistant sealing ring 5 is placed in a double-layer sealing groove formed in the die holder cushion block B17, the low-temperature forming die cushion block A16 is placed on the die holder cushion block B17, the aluminum lithium alloy plate 15 is placed on the low-temperature forming die cushion block A16, the die holder 1 is placed on a lower working platform of a hydraulic machine after installation is completed, and the die holder 1 is fixed on the lower working platform of the hydraulic machine by a pressing plate;
secondly, mounting the ultralow-temperature circumferential sealing ring 7 on the second blank holder inner ring 12 by using screws to form a combination E, placing the first cold insulation layer 6 on the combination E formed by the ultralow-temperature circumferential sealing ring 7 and the second blank holder inner ring 12, fastening the combination E by using screws, and then mounting the combination E on the first blank holder 11 to form a large combination F, wherein the large combination F is directly mounted on the blank holder cylinder of the double-acting hydraulic machine through an interface connected with the blank holder cylinder of the double-acting hydraulic machine, and the blank holder force of the aluminum-lithium alloy plate 15 in the forming process can be controlled under the driving of the blank holder cylinder;
finally, the multipoint convex die heads 8 with different shapes are directly connected into threaded holes in the convex die body 10 through threads 9 on the multipoint convex die heads 8, then the forming convex dies 20 are combined, the forming convex dies 20 are directly connected onto a main cylinder of the double-acting hydraulic machine through an interface connected with a main cylinder of the double-acting hydraulic machine, and can move up and down along an inner cavity formed by the first blank holder 11 and the concave die sleeve 2 under the driving of the main cylinder;
the invention also provides an ultra-low temperature forming manufacturing method of the aluminum lithium alloy complex thin-wall structural part by utilizing the forming device, which is used for ultra-low temperature forming of the aluminum lithium alloy thin-wall structural part, and the forming process mainly comprises the following steps:
reading a three-dimensional design model of an aluminum-lithium alloy thin-wall structural part, obtaining a sheet material, a curvature of a curved surface and a thickness of the sheet material of the lithium alloy thin-wall structural part according to the three-dimensional design model, and unfolding the three-dimensional design model of the thin-wall complex structural part into a two-dimensional plane model through finite element analysis according to the obtained sheet material, the curvature of the curved surface and the thickness of the sheet material of the lithium alloy thin-wall structural part;
step two, correcting the two-dimensional plane model obtained in the step one, cutting the aluminum lithium alloy thin-wall structural member unfolded material in a laser cutting mode according to the corrected two-dimensional plane model, wherein the correction means that process allowance is reserved for the two-dimensional plane model;
step three, carrying out solid solution treatment on the unfolded material subjected to laser cutting in the step two, namely putting the unfolded material subjected to laser cutting into a box-type resistance furnace for annealing treatment, wherein the heating temperature T is 500-520 ℃, and the heat preservation time is 1-1.5 h, as shown in fig. 4;
fourthly, placing the third cold insulation and heat preservation layer 18 on the die holder 1, placing a die holder cushion block B17 on the third cold insulation and heat preservation layer 18, then placing the double-layer low-temperature-resistant sealing ring 5 in a double-layer sealing groove formed in a die holder cushion block B17, then placing a low-temperature forming die cushion block A16 on a die holder cushion block B17, and then placing the aluminum-lithium alloy plate 15 on a low-temperature forming die cushion block A16; after the installation is finished, the die holder 1 is placed on a lower working platform of the hydraulic machine, and then the die holder 1 is fixed on the lower working platform of the hydraulic machine by a pressing plate;
fifthly, mounting the ultralow-temperature circumferential sealing ring 7 on the second blank holder inner ring 12 through screws to form a combination E, placing the first cold insulation layer 6 on the combination E formed by the ultralow-temperature circumferential sealing ring 7 and the second blank holder inner ring 12, fastening the combination E through screws, mounting the combination E on the first blank holder 11 to form a large combination F, directly mounting the large combination F on a blank holder cylinder of the double-acting hydraulic machine through an interface connected with the blank holder cylinder of the double-acting hydraulic machine, and controlling the size of blank holder force through controlling the hydraulic pressure of the hydraulic cylinder;
step six, connecting the independent low-temperature liquid medium system source A with the die holder 1 by using a high-pressure adapter, and forming a closed loop with the independent low-temperature liquid medium system source A so as to form a high-pressure low-temperature liquid medium liquid filling chamber 3; the independent low-temperature liquid medium system source B and the die holder cushion block B17 are connected by a high-pressure adapter joint to form a closed loop with the independent low-temperature liquid medium system source B;
step seven, placing the aluminum lithium alloy plate 15 manufactured in the step three on a die holder cushion block B17, and adopting a method for fixing a gap during edge pressing, wherein the gap during edge pressing is realized by adding a semicircular cushion ring beside the gap, the thickness of the semicircular cushion ring is (t +0.1t) mm, and the shape of the semicircular cushion ring is shown in fig. 7, so that the gap between a second edge pressing inner ring 12 and a low-temperature forming die cushion block A16 can be kept to be 1.1tmm in the forming process;
step eight, directly connecting the multipoint convex die heads 8 with different shapes into threaded holes in the convex die body 10 through threads 9 on the multipoint convex die heads 8, and then directly connecting the forming convex die 20 to a main cylinder of the double-acting hydraulic machine through an interface connected with the main cylinder of the double-acting hydraulic machine; connecting the multi-point male die body 10 to a main cylinder of a hydraulic machine, wherein the main cylinder of the hydraulic machine controls the multi-point male die body 10 to move downwards;
step nine, controlling a large assembly F formed by the first cold insulation and insulation layer 6, the ultralow-temperature circumferential sealing ring 7, the first blank holder 11 and the second blank holder 12 to move downwards by using a blank holder cylinder, so that the lower surface of the second blank holder 12 is in contact with the aluminum-lithium alloy plate 15 and applies blank holder force, and keeping the blank holder force unchanged until F;
where, F is Ap, A is the projected area of blank under the binder (unit mm2) p is the unit binder force (unit MPa),
Figure BDA0002821328950000091
z is the reciprocal of the drawing coefficient, D is the diameter (in mm) of the developed material, t is the thickness (in mm) of the aluminum-lithium alloy sheet material, σ is b The tensile strength (unit MPa) of the aluminum lithium alloy sheet is shown.
Step ten, filling a high-pressure low-temperature liquid medium into the low-temperature forming female die cushion block A16 by the independent low-temperature liquid medium system source B through a liquid filling interface B-1 according to an initial liquid chamber pressure curve shown in fig. 5, enabling the high-pressure low-temperature liquid medium to enter a low-temperature liquid medium channel B-3 of the low-temperature forming female die cushion block A16 through a liquid inlet channel B-2, gradually filling the low-temperature liquid medium into the low-temperature forming female die cushion block A16, gradually discharging air, and gradually reducing the temperature of the low-temperature forming female die cushion block A16 so as to reduce the temperature of the aluminum-lithium alloy plate 15; the low-temperature liquid medium is an ultralow-temperature cooling medium and can be one of liquid nitrogen or liquid helium.
Step eleven, controlling the multipoint male die body 10 to move downwards by a main cylinder of the hydraulic machine, driving the multipoint male die head 8 to move downwards along with the multipoint male die body, when the distance between the lower surface of the multipoint convex die head 8 and the upper surface of the aluminum lithium alloy plate is (3-5) t mm, the independent low-temperature liquid medium system source A fills high-pressure low-temperature liquid medium into the die holder 1 through the liquid filling interface A-2 according to the initial liquid chamber pressure curve shown in figure 6, the high-pressure low-temperature liquid medium enters the low-temperature liquid medium channel A-3 formed in the die sleeve 2 through the liquid inlet channel A-1, thereby entering the high-pressure low-temperature liquid filling chamber 3, at the moment, the high-pressure low-temperature liquid filling chamber 3 is gradually filled with low-temperature liquid medium, air is gradually discharged, and the liquid chamber pressure of the initial low-temperature medium of (0.03 sigma s-0.06 sigma s) MPa is established in the high-pressure low-temperature liquid filling chamber 3; the low-temperature liquid medium is an ultralow-temperature cooling medium and can be one of liquid nitrogen or liquid helium.
Step twelve, after the initial liquid chamber pressure of (0.03 σ s-0.06 σ s) MPa is established inside the high-pressure low-temperature liquid filling chamber 3, the main cylinder of the hydraulic machine controls the multipoint male die body 10 to continuously move downwards, the multipoint male die head 8 is driven to continuously move downwards, the edge pressure is kept unchanged in the downward moving process, at the moment, the low-temperature liquid medium is continuously filled into the high-pressure low-temperature liquid filling chamber 3 through the liquid filling hole interface A-2 according to the liquid chamber pressure curve shown in the figure 6, and the pressure of the low-temperature liquid medium inside the high-pressure low-temperature liquid filling chamber 3 is increased to (0.3 σ s-0.6 σ s) MPa;
thirteen, when the liquid chamber pressure of (0.3 sigma s-0.6 sigma s) MPa is established in the high-pressure low-temperature liquid filling chamber 3, then the temperature is kept, the temperature of the measuring die is reduced to-100 ℃ to-196 ℃, at the moment, the temperature of the aluminum lithium alloy plate reaches-100 ℃ to-196 ℃, a main cylinder of a hydraulic machine controls a multi-point male die body 10 to continue descending, the aluminum lithium alloy plate 15 gradually flows in until the forming is finished, and the aluminum lithium alloy thin-wall structural part is formed;
and fourteen steps of unloading the pressure in the low-temperature liquid filling chamber 3 and the pressure in the B-3 in the low-temperature forming die cushion block A16 after the multipoint low-temperature liquid filling forming is finished, driving the multipoint male die body 10 to return by a main cylinder of the hydraulic machine, driving a large assembly F formed by the first cold insulation layer 6, the ultralow-temperature circumferential sealing ring 7, the first blank holder 11 and the second blank holder 12 by a blank holder cylinder of the hydraulic machine to move upwards, unloading the blank holder force, enabling the die to be in an open state, and taking out the formed aluminum-lithium alloy thin-wall structural member.
Compared with the prior art, the invention has the advantages that:
the invention utilizes the characteristics of plasticizing and reinforcing of the aluminum-lithium alloy at ultralow temperature, adopts an ultralow-temperature flexible forming method to flexibly form the aluminum-lithium alloy plate, and can solve the problems that the complex thin-wall structural member of the aluminum-lithium alloy is difficult to form a complex-shaped member at room temperature, has poor fracture toughness, is easy to generate microcracks during room-temperature forming, has large forming resilience and is difficult to ensure the dimensional precision of the member shape;
the invention utilizes the advantages that the outline configuration of the multipoint convex die can be changed according to the forming requirement without additionally processing the die, can realize flexible multi-step forming of parts with complex shapes, and greatly reduces the manufacturing cost of the die;
thirdly, the aluminum-lithium alloy tailor-welded blank member manufactured by the method cannot generate internal microstructure damage, the forming at ultralow temperature basically does not change the structure performance, and the original structure state is recovered after the forming;
in the flexible forming process, the friction maintaining effect and the fluid lubricating effect generated by the aluminum lithium alloy plate under the action of liquid can further improve the forming limit of the aluminum lithium alloy plate and realize the precise forming of the thin-wall complex component, and in addition, a frozen lubricating layer is formed on the working surfaces of the aluminum lithium alloy plate and the multipoint die, so that the flowing friction resistance of the aluminum lithium alloy plate can be reduced, the forming force is reduced, and the tonnage and the manufacturing cost of forming equipment are greatly reduced.
According to the invention, a pre-expansion step can be added before the hydro-mechanical drawing step according to the complexity of the formed part, and the shape of the pre-expansion part is designed according to the forming requirement.
Sixthly, the female die sleeve 2 is in modular design, is in a combined type, detachable or replaceable structure, is an open hollow cylinder with a bottom, has slightly different sizes for adapting to aluminum lithium alloy plates with different thicknesses and different formed parts, and can be adjusted and replaced according to the aluminum lithium alloy plates with different thicknesses and the formed parts with different shapes.
Drawings
FIG. 1 is a schematic view of an ultra-low temperature flexible forming manufacturing apparatus for an aluminum-lithium alloy thin-walled structural member according to the present invention;
FIG. 2 is a process flow for preparing the spread of the present invention;
FIG. 3 is a process flow of ultra-low temperature flexible forming of the thin-walled Al-Li alloy structure according to the present invention;
FIG. 4 is a graph of an annealing process of an aluminum lithium alloy according to the present invention;
FIG. 5 is a schematic view of the initial liquid chamber pressure loading curve of the present invention;
fig. 6 is a schematic view of the pressure loading curve of the liquid chamber of the present invention.
FIG. 7 is a schematic view of a semicircular backing ring of the present invention.
Detailed Description
The invention provides an ultralow temperature forming device and a forming manufacturing method of an aluminum-lithium alloy thin-wall structural part, aiming at the defects of the prior art, the aluminum-lithium alloy thin-wall structural part is difficult to form a complex-shaped member at room temperature, has poor fracture toughness, is easy to generate micro cracks and other defects during room temperature forming, has large forming resilience, and is difficult to ensure the dimensional precision of the member shape.
The invention discloses an ultralow temperature forming device and a forming manufacturing method of an aluminum lithium alloy thin-wall structural member, and relates to an ultralow temperature forming device of an aluminum lithium alloy thin-wall structural member.
The whole device adopts a combined type, detachable, quick-replaceable and modularized structure, and different modules can be adjusted and replaced according to aluminum-lithium alloy plates with different thicknesses and different formed parts.
The invention is further illustrated by the following figures and examples.
Examples
As shown in fig. 1-7, the forming device comprises a die holder 1, a die sleeve 2, a double-layer low-temperature-resistant sealing ring 5, a first cold-insulating and heat-insulating layer 6, an ultralow-temperature circumferential sealing ring 7, a multipoint convex die head 8, a convex die connecting column 9, a convex die body 10, a first blank holder 11, a second blank holder inner ring 12, a second cold-insulating and heat-insulating layer 14, an aluminum-lithium alloy plate 15, a low-temperature forming concave die cushion block a16, a die holder cushion block B17, a third cold-insulating and heat-insulating layer 18 and a fourth cold-insulating and heat-insulating layer 19;
the female die sleeve 2 is an open hollow cylinder with a bottom, and the inner cavity of the female die sleeve 2, the multi-point male die heads 8 with different shapes and the cavity surrounded by the aluminum lithium alloy plate 15 form the high-pressure low-temperature liquid filling chambers 3 with different shapes together;
a combined sealing mode of sealing a conical surface seal 13 and a sealing ring 17 is adopted between the low-temperature female die forming cushion block A16 and a female die holder cushion block B17;
the die holder 1 is of an integral cylindrical structure, and a cylindrical inner cavity is reserved in the middle and used for placing die sleeves 2 of different structural forms; the die holder 1 is an open hollow cylinder with a bottom, a liquid filling interface A-2 connected with a low-temperature liquid medium system source A and a liquid inlet channel A-1 of a high-pressure low-temperature liquid medium are arranged on the side edge of the die holder 1, the liquid inlet channel A-1 is communicated with a cavity defined by the die holder 2 and the multipoint convex die head 8 through a high-pressure low-temperature liquid channel A-3 arranged on the side wall of the die holder 2 and serves as a high-pressure low-temperature liquid filling chamber 3, and a metal sealing gasket and a conical surface are adopted for combined sealing between joints connected with the low-temperature liquid filling interface A-2 and the low-temperature liquid medium system source A;
the female die sleeve 2 is in modular design, is of a combined type, detachable or replaceable structure, is an open hollow cylinder with a bottom, has slightly different sizes for adapting to aluminum lithium alloy plates with different thicknesses and different formed parts, and can be adjusted and replaced according to the aluminum lithium alloy plates with different thicknesses and the formed parts with different shapes;
the side wall of the female die sleeve 2 is fully distributed with a high-pressure low-temperature liquid channel 4, the side wall of the female die sleeve 2 is also provided with a low-temperature liquid channel A-3, the low-temperature liquid channel A-3 is communicated with a liquid inlet channel A-1 of a high-pressure low-temperature liquid medium opened on the female die base, and the high-pressure low-temperature liquid output by the low-temperature liquid medium system source A enters the low-temperature liquid channel A-3 opened on the side wall of the female die sleeve 2 through a liquid filling interface A-2 and the liquid inlet channel A-1 of the high-pressure low-temperature liquid medium and then enters the high-pressure low-temperature liquid filling chamber 3 and the high-pressure low-temperature liquid channel 4 fully distributed on the side wall of the female die sleeve 2. The high-pressure cryogenic liquid entering the high-pressure cryogenic liquid channel 4 can be used to reduce and adjust the temperature of the die case 2, thereby controlling the temperature of the aluminum lithium alloy plate 15.
When the female die sleeve 2 is used, the fourth cold insulation layer 19 is placed in the female die base 1, and then the female die sleeve 2 is placed in the female die base 1; the inner cavity of the female die sleeve 2 arranged in the female die holder 1, the multi-point male die heads 8 with different shapes and the cavity surrounded by the aluminum lithium alloy plate 15 form the high-pressure low-temperature liquid filling chambers 3 with different shapes;
the first cold insulation layer 6, the second cold insulation layer 14, the third cold insulation layer 18 and the fourth cold insulation layer 19 are main structures for keeping the formed plate in a deep cooling state. For the cold insulation design of the first cold insulation layer 6, the second cold insulation layer 14, the third cold insulation layer 18 and the fourth cold insulation layer 19, the heat insulation material cannot bear the pressure of the hydraulic machine and the die, and therefore the cold insulation material needs to be placed in a device with the requirement on the compressive strength. The device adopts the middle to fill cold insulation and heat preservation material, and both sides and periphery adopt steel plates to make up, make its compressive strength satisfy the shaping needs. The heat insulation material is perlite concrete, the heat conductivity is 0.12-0.25W/(m.K), the use temperature is-273-200 ℃, and the compressive strength is 1.5-8.5 MPa.
The first blank holder 11, the second blank holder 12, the low-temperature forming female die cushion block A16 and the female die holder cushion block B17 are all in modular design, and the sizes of the first blank holder and the second blank holder are adapted to aluminum lithium alloy plates with different thicknesses and formed parts with different shapes; the die holder cushion block B17 is of a circular structure, the upper surface of the die holder cushion block B17 is in matching contact with the low-temperature forming die cushion block A16, the contact surface of the die holder cushion block B and the low-temperature forming die cushion block A16, which are matched with each other, is provided with a double-layer sealing groove, and the double-layer sealing groove is used for placing a double-layer low-temperature-resistant sealing ring 5 for sealing and is used for sealing a high-pressure low-temperature liquid medium in the forming process. The double-layer low-temperature-resistant seal ring 5 is an O-ring that can be made of a metal material such as nickel or indium, has a sealing capability at an ultra-low temperature, and is preferably made of an indium soft metal.
The low-temperature forming female die cushion block A16 is of an annular structure, a boss is left on the side face, a liquid filling interface B-1 connected with an independent low-temperature liquid medium system source B and a liquid inlet channel B-2 of a high-pressure low-temperature liquid medium are arranged on the right side edge, the liquid inlet channel B-2 is communicated with a low-temperature liquid medium channel B-3, high-pressure low-temperature liquid output by the low-temperature liquid medium system source B enters the opened low-temperature liquid medium channel B-3 of the low-temperature forming female die cushion block A16 through the liquid filling interface B-1 and the liquid inlet channel B-2 of the high-pressure low-temperature liquid medium, and the high-pressure low-temperature liquid entering the low-temperature liquid medium channel B-3 can be used for reducing and adjusting the temperature of the low-temperature forming female die cushion block A16, so that the temperature of the aluminum lithium alloy plate 15 is controlled. And a metal sealing gasket and a conical surface composite seal are adopted between the joint of the low-temperature liquid filling interface B-1 and the low-temperature liquid medium system source B.
The second blank holder inner ring 12 is of a circular ring structure, the side face is a sealing face and is provided with a sealing groove, the side face of the second blank holder inner ring 12 is in sealing fit with a boss reserved on the side face of the low-temperature forming female die cushion block A16, the ultralow-temperature circumferential sealing ring 7 used between the sealing grooves is sealed, the ultralow-temperature circumferential sealing ring 7 is an O-shaped sealing ring made of metal materials such as nickel and indium, the ultralow-temperature circumferential sealing ring has sealing capability at ultralow temperature and is preferably made of indium soft metal, and meanwhile the second blank holder inner ring 12 and the low-temperature forming female die cushion block A16 also adopt a matched conical surface seal 13, so that conical surface sealing is realized. The conical surface seal and seal ring type composite seal is jointly used for sealing high-pressure and low-temperature liquid media in the forming process.
The aluminum-lithium alloy plate 15 is a two-dimensional plane plate after the aluminum-lithium alloy complex thin-wall structural part is unfolded, the first blank holder 11 is an integral blank holder which is of a circular ring-shaped structure and is arranged right above the first cold insulation and heat preservation layer 6, and an interface connected with a blank holder cylinder of a double-acting hydraulic press is arranged on the blank holder; and a cold insulation layer 6 is arranged between the first blank holder 11 and the second blank holder 12 and between the low-temperature forming die cushion blocks A16 and is used for preventing the ultralow temperature from being transmitted to the first blank holder 11.
The forming punch 20 adopts a multi-point punch structural form, the multi-point punch 20 mainly comprises a punch body 10 and a plurality of multi-point punch heads 8 with different heights, and the multi-point punch heads 8 are directly connected to threaded holes in the punch body 10 through threads 9 on the multi-point punch heads 8. The multiple multi-point convex die heads 8 are uniformly and tightly arranged, are vertically and mutually independent and form a convex die forming module, and the upper surfaces of the multiple multi-point convex die heads 8 form the convex die forming module with the same shape as the inner contour of the thin-wall complex structural part to be manufactured.
The male die body 10 is located right above the multiple multi-point male die heads 8, a plurality of threaded holes are formed in the positions, corresponding to the multiple multi-point male die heads 8, of the male die body 10, the number of the threaded holes is consistent with the number of the multi-point male die heads 8, threads corresponding to the threaded holes in the male die bodies 10 are arranged at the upper ends of the multi-point male die heads 8, the threads at the upper ends of the multiple multi-point male die heads 8 correspond to the threaded holes in the male die bodies 10 in a one-to-one mode and penetrate into the corresponding threaded holes respectively, and threaded connection 9 is adopted.
The forming male die 20 is placed at the center of the first blank holder 11, the profile of the multi-point male die is designed according to the shape of the inner cavity of the aluminum-lithium alloy thin-wall structural component to be formed, and the outer profile of the multi-point male die is consistent with the shape of the inner contour of the aluminum-lithium alloy thin-wall structural component to be formed. The heights of the multipoint convex die heads 8 can be adjusted through the threaded connection 9, so that the multipoint forming convex die 8 can realize the configurations of different outer contour shapes, and one or more multipoint convex die heads 8 can be independently replaced according to the inner contour shape of the part of the aluminum-lithium alloy plate to be formed.
A forming gap between the forming convex die 20 and the concave die sleeve 2 needs to be set according to the thickness of the aluminum lithium alloy plate, the forming gap between the forming convex die 20 and the concave die sleeve 2 is preferably 1.1t mm, and t is the thickness of the aluminum lithium alloy plate; the forming male die 20 is provided with a connecting interface connected with a main cylinder of the double-acting hydraulic machine;
when the die is used, the third cold insulation and heat preservation layer 18 is placed on the die holder 1, the die holder cushion block B17 is placed on the third cold insulation and heat preservation layer 18, the double-layer low-temperature-resistant sealing ring 5 is placed in a double-layer sealing groove formed in the die holder cushion block B17, the low-temperature forming die cushion block A16 is placed on the die holder cushion block B17, the aluminum lithium alloy plate 15 is placed on the low-temperature forming die cushion block A16, the die holder 1 is placed on a lower working platform of a hydraulic machine after installation is completed, and the die holder 1 is fixed on the lower working platform of the hydraulic machine by a pressing plate;
secondly, mounting the ultralow-temperature circumferential sealing ring 7 on the second blank holder inner ring 12 by using screws to form a combination E, placing the first cold insulation layer 6 on the combination E formed by the ultralow-temperature circumferential sealing ring 7 and the second blank holder inner ring 12, fastening the combination E by using screws, and then mounting the combination E on the first blank holder 11 to form a large combination F, wherein the large combination F is directly mounted on the blank holder cylinder of the double-acting hydraulic machine through an interface connected with the blank holder cylinder of the double-acting hydraulic machine, and the blank holder force of the aluminum-lithium alloy plate 15 in the forming process can be controlled under the driving of the blank holder cylinder;
finally, the multipoint convex die heads 8 with different shapes are directly connected into threaded holes in the convex die body 10 through threads 9 on the multipoint convex die heads 8, then the multipoint convex die bodies are combined into a forming convex die 20, the forming convex die 20 is directly connected onto a main cylinder of a double-acting hydraulic press through an interface connected with the main cylinder of the double-acting hydraulic press, and can move up and down along an inner cavity formed by the first blank holder 11 and the concave die sleeve 2 under the driving of the main cylinder;
the invention also provides an ultra-low temperature forming manufacturing method of the aluminum lithium alloy complex thin-wall structural part by utilizing the forming device, which is used for ultra-low temperature forming of the aluminum lithium alloy thin-wall structural part, and the forming process mainly comprises the following steps:
reading a three-dimensional design model of an aluminum-lithium alloy thin-wall structural part, obtaining a sheet material, a curvature of a curved surface and a thickness of the sheet material of the lithium alloy thin-wall structural part according to the three-dimensional design model, and unfolding the three-dimensional design model of the thin-wall complex structural part into a two-dimensional plane model through finite element analysis according to the obtained sheet material, the curvature of the curved surface and the thickness of the sheet material of the lithium alloy thin-wall structural part;
step two, correcting the two-dimensional plane model obtained in the step one, cutting the aluminum lithium alloy thin-wall structural member unfolded material in a laser cutting mode according to the corrected two-dimensional plane model, wherein the correction means that process allowance is reserved for the two-dimensional plane model;
step three, carrying out solid solution treatment on the unfolded material subjected to laser cutting in the step two, namely putting the unfolded material subjected to laser cutting into a box-type resistance furnace for solid solution treatment, wherein the heating temperature T is 500-520 ℃, and the heat preservation time is 1-1.5 h;
step four, firstly, placing a third cold insulation and heat preservation layer 18 on the die holder 1, placing a die holder cushion block B17 on the third cold insulation and heat preservation layer 18, then placing a double-layer low-temperature-resistant sealing ring 5 in a double-layer sealing groove formed in a die holder cushion block B17, then placing a low-temperature forming die cushion block A16 on a die holder cushion block B17, and then placing an aluminum-lithium alloy plate 15 on a low-temperature forming die cushion block A16; after the installation is finished, the die holder 1 is placed on a lower working platform of the hydraulic machine, and then the die holder 1 is fixed on the lower working platform of the hydraulic machine by a pressing plate;
fifthly, mounting the ultralow-temperature circumferential sealing ring 7 on the second blank holder inner ring 12 through screws to form a combination E, placing the first cold insulation layer 6 on the combination E formed by the ultralow-temperature circumferential sealing ring 7 and the second blank holder inner ring 12, fastening the combination E through screws, mounting the combination E on the first blank holder 11 to form a large combination F, directly mounting the large combination F on a blank holder cylinder of the double-acting hydraulic machine through an interface connected with the blank holder cylinder of the double-acting hydraulic machine, and controlling the size of blank holder force through controlling the hydraulic pressure of the hydraulic cylinder;
step six, connecting the independent low-temperature liquid medium system source A with the die holder 1 by using a high-pressure adapter, and forming a closed loop with the independent low-temperature liquid medium system source A so as to form a high-pressure low-temperature liquid medium liquid filling chamber 3; the independent low-temperature liquid medium system source B and the die holder cushion block B17 are connected by a high-pressure adapter joint to form a closed loop with the independent low-temperature liquid medium system source B;
step seven, placing the aluminum lithium alloy plate 15 manufactured in the step three on a die holder cushion block B17, and adopting a gap fixing method during edge pressing, wherein the edge pressing gap is realized in a manner of adding a semicircular cushion ring beside the aluminum lithium alloy plate, the thickness of the semicircular cushion ring is (t +0.1t) mm, the shape of the semicircular cushion ring is shown in figure 7, and the gap between a second edge pressing inner ring 12 and a low-temperature forming die cushion block A16 can be kept to be 1.1tmm in the forming process;
step eight, directly connecting the multipoint convex die heads 8 with different shapes into threaded holes in the convex die body 10 through threads 9 on the multipoint convex die heads 8, and then directly connecting the forming convex die 20 to a main cylinder of the double-acting hydraulic machine through an interface connected with the main cylinder of the double-acting hydraulic machine; connecting the multi-point male die body 10 to a main cylinder of a hydraulic machine, wherein the main cylinder of the hydraulic machine controls the multi-point male die body 10 to move downwards;
controlling a large assembly F formed by the first cold insulation and heat preservation layer 6, the ultralow-temperature circumferential sealing ring 7, the first blank holder 11 and the second blank holder 12 to move downwards by using a blank holder cylinder, so that the lower surface of the second blank holder 12 is in contact with the aluminum-lithium alloy plate 15 and applies blank holder force, and keeping the blank holder force unchanged until F;
where, F is Ap, A is the projected area of blank under the binder (unit mm2) p is the unit binder force (unit MPa),
Figure BDA0002821328950000171
z is the reciprocal of the drawing coefficient, D is the diameter (in mm) of the developed material, t is the thickness (in mm) of the aluminum-lithium alloy sheet material, σ is b The tensile strength (unit MPa) of the aluminum lithium alloy sheet is shown.
Step ten, filling a high-pressure low-temperature liquid medium into the low-temperature forming female die cushion block A16 by the independent low-temperature liquid medium system source B through a liquid filling interface B-1 according to an initial liquid chamber pressure curve shown in fig. 5, enabling the high-pressure low-temperature liquid medium to enter an opened low-temperature liquid medium channel B-3 of the low-temperature forming female die cushion block A16 through a liquid inlet channel B-2, gradually filling the low-temperature liquid medium into the low-temperature forming female die cushion block A16, gradually discharging air, and gradually reducing the temperature of the low-temperature forming female die cushion block A16 so as to reduce the temperature of the aluminum-lithium alloy plate 15; the cryogenic liquid medium is an ultralow temperature cooling medium and can be one of liquid nitrogen or liquid helium.
Step eleven, controlling the multipoint male die body 10 to move downwards by a main cylinder of the hydraulic machine, driving the multipoint male die head 8 to move downwards, when the distance between the lower surface of the multipoint male die head 8 and the upper surface of the aluminum-lithium alloy plate is (3-5) t mm, filling a high-pressure low-temperature liquid medium into the female die holder 1 through a liquid filling interface A-2 by an independent low-temperature liquid medium system source A according to an initial liquid chamber pressure curve shown in figure 5, enabling the high-pressure low-temperature liquid medium to enter a low-temperature liquid medium channel A-3 formed in the female die sleeve 2 through a liquid inlet channel A-1 and further enter a high-pressure low-temperature liquid filling chamber 3, and at the moment, gradually filling the low-temperature liquid medium into the high-pressure low-temperature liquid filling chamber 3, gradually discharging air and enabling the air to be gradually discharged and enabling the high-pressure low-temperature liquid filling chamber 3 to be enabled to move downwardsThe liquid chamber pressure of the initial low-temperature medium with the pressure of 0.03 sigma s-0.06 sigma s is established in the high-pressure low-temperature liquid filling chamber 3; the low-temperature liquid medium is an ultralow-temperature cooling medium and can be one of liquid nitrogen or liquid helium. Sigma s The yield strength of the aluminum lithium alloy plate;
step twelve, after the initial liquid chamber pressure of (0.03 sigma s-0.06 sigma s) MPa is established inside the high-pressure low-temperature liquid filling chamber 3, the main cylinder of the hydraulic machine controls the multipoint male die body 10 to continuously move downwards, the multipoint male die head 8 is driven to continuously move downwards, the edge pressure is kept unchanged in the downward moving process, at the moment, the low-temperature liquid medium is continuously filled into the high-pressure low-temperature liquid filling chamber 3 through the liquid filling hole interface A-2 according to the liquid chamber pressure curve shown in the figure 6, and the pressure of the low-temperature liquid medium inside the high-pressure low-temperature liquid filling chamber 3 is increased to (0.3 sigma s-0.6 sigma s) MPa;
thirteen, when the liquid chamber pressure of (0.3 sigma s-0.6 sigma s) MPa is established inside the high-pressure low-temperature liquid filling chamber 3, then the temperature is kept, the temperature of the mould is measured to be reduced to-100 to-196 ℃, at the moment, the temperature of the aluminum lithium alloy plate reaches-100 to-196 ℃, a main cylinder of a hydraulic machine controls a multi-point male mould body 10 to continuously descend, the aluminum lithium alloy plate 15 gradually flows in until the forming is finished, and the aluminum lithium alloy thin-wall structural part is formed;
and step fourteen, after the multipoint low-temperature liquid-filling forming is finished, unloading the pressure in the low-temperature liquid-filling chamber 3 and the pressure in the B-3 in the low-temperature forming female die cushion block A16, driving the multipoint male die body 10 to return by a main cylinder of the hydraulic machine, driving a large assembly F formed by the first cold insulation and heat preservation layer 6, the ultralow-temperature circumferential sealing ring 7, the first blank holder 11 and the second blank holder 12 by a blank holder cylinder of the hydraulic machine to move upwards, unloading the blank holder force, enabling the die to be in an open state, and taking out the formed aluminum-lithium alloy thin-wall structural member by a tool.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.

Claims (9)

1. An ultralow-temperature flexible forming method of an aluminum-lithium alloy thin-wall structural member is characterized by comprising the following steps of:
reading a three-dimensional design model of the aluminum-lithium alloy thin-wall structural part, obtaining a plate material, a curvature of a curved surface and a thickness of the plate material of the lithium alloy thin-wall structural part according to the three-dimensional design model, and unfolding the three-dimensional design model of the complex aluminum-lithium alloy thin-wall structural part into a two-dimensional plane model through finite element analysis according to the obtained plate material, the curvature of the curved surface and the thickness of the plate material of the aluminum-lithium alloy thin-wall structural part;
step two, correcting the two-dimensional plane model obtained in the step one, and cutting the aluminum-lithium alloy thin-wall structural member unfolded material in a laser cutting mode according to the corrected two-dimensional plane model;
step three, carrying out solid solution treatment on the unfolded material cut by the laser in the step two;
placing a third cold insulation and heat preservation layer on the die holder, placing a die holder cushion block B on the third cold insulation and heat preservation layer, then placing a double-layer low-temperature-resistant sealing ring into a double-layer sealing groove formed in the die holder cushion block B, then placing a low-temperature forming die cushion block A on the die holder cushion block B, and then placing an aluminum-lithium alloy plate on the low-temperature forming die cushion block A; after the installation is finished, the die holder is placed on a lower working platform of the hydraulic machine, and then the die holder is fixed on the lower working platform of the hydraulic machine by a pressing plate;
fifthly, mounting the ultralow-temperature circumferential sealing ring on the second blank holder inner ring by using a first screw to form a combination E, placing the first cold insulation layer on the combination E formed by the ultralow-temperature circumferential sealing ring and the second blank holder inner ring, fastening the combination E by using a second screw, mounting the first cold insulation layer and the combination E on the first blank holder to form a large combination F, and directly mounting the large combination F on the blank holder cylinder of the double-acting hydraulic machine through an interface connected with the blank holder cylinder of the double-acting hydraulic machine;
connecting the independent low-temperature liquid medium system source A with the female die holder by using a first high-pressure adapter, and connecting the independent low-temperature liquid medium system source B with the low-temperature forming female die cushion block A by using a second high-pressure adapter;
step seven, placing the aluminum lithium alloy plate manufactured in the step three on a cushion block A of a low-temperature forming female die, and adopting a method for fixing a gap during edge pressing, wherein the gap for edge pressing is realized by adding a semicircular cushion ring beside the gap;
step eight, the forming male die (20) consists of a multi-point male die body (10) and a plurality of multi-point male die heads (8), the multi-point male die heads with different shapes are directly connected into threaded holes in the multi-point male die body through threads on the multi-point male die heads, and then the multi-point male die body of the forming male die is directly connected onto a main cylinder of the double-acting hydraulic machine through an interface connected with the main cylinder of the double-acting hydraulic machine; a main cylinder of the double-acting hydraulic machine controls the multipoint male die body to move downwards;
controlling the large assembly F to move downwards by using the blank pressing cylinder to enable the lower surface of the second blank pressing inner ring to be in contact with the aluminum-lithium alloy plate and apply blank pressing force;
step ten, filling a first high-pressure low-temperature liquid medium into the low-temperature forming female die cushion block A through a first liquid filling interface by the independent low-temperature liquid medium system source B, enabling the first high-pressure low-temperature liquid medium to enter a first low-temperature liquid medium channel formed in the low-temperature forming female die cushion block A through a first liquid inlet channel, and gradually filling the first high-pressure low-temperature liquid medium into the low-temperature forming female die cushion block A;
step eleven, a main cylinder of the double-acting hydraulic press controls the multipoint male die body to move downwards, and then drives the multipoint male die head to move downwards, when the distance between the lower surface of the multipoint male die head and the upper surface of the aluminum-lithium alloy plate is a set value, an independent low-temperature liquid medium system source A fills a second high-pressure low-temperature liquid medium into the high-pressure low-temperature liquid filling chamber through a second liquid filling interface according to an initial liquid chamber pressure curve, and the second high-pressure low-temperature liquid medium enters a second low-temperature liquid medium channel formed in the female die base and the female die sleeve through a second liquid inlet channel so as to enter the high-pressure low-temperature liquid filling chamber;
and a twelfth step of continuously moving the multi-point male die body downwards, driving the multi-point male die head to continuously move downwards, keeping the edge pressure unchanged in the downward moving process, continuously filling a second high-pressure low-temperature liquid medium into the high-pressure low-temperature liquid filling chamber through a second liquid filling interface, and increasing the pressure of the second high-pressure low-temperature liquid medium in the high-pressure low-temperature liquid filling chamber to 0.3-0.6 sigma s MPa and sigma s s Is the yield strength of the aluminum lithium alloy plate in unitsIs MPa;
thirteen, when the liquid chamber pressure of 0.3 sigma s-0.6 sigma s MPa is established in the high-pressure low-temperature liquid filling chamber (3), the temperature of the aluminum lithium alloy plate reaches-100 to-196 ℃, the multipoint male die body continues to descend, the aluminum lithium alloy plate gradually flows into the high-pressure low-temperature liquid filling chamber until the forming is finished, and the aluminum lithium alloy thin-wall structural part is formed;
fourteen, after the multipoint low-temperature liquid filling forming is finished, unloading the pressure in the high-pressure low-temperature liquid filling chamber and the pressure in the low-temperature forming female die cushion block A, returning the multipoint male die body, then driving the large assembly F to move upwards by a double-acting hydraulic press blank holder cylinder, unloading blank holder force, enabling the die to be in an open state, and taking out the formed aluminum-lithium alloy thin-wall structural part;
the forming device used in the method comprises a female die holder, a female die sleeve, a double-layer low-temperature-resistant sealing ring, a first cold-insulating layer, an ultralow-temperature circumferential sealing ring, a multi-point male die head, a male die body, a first blank holder, a second blank holder inner ring, a second cold-insulating layer, a low-temperature forming female die cushion block A, a female die holder cushion block B, a third cold-insulating layer and a fourth cold-insulating layer;
the die holder is of an integral cylindrical structure, and a cylindrical inner cavity is reserved in the middle of the die holder, namely the die holder is an open hollow cylinder with a bottom;
the female die sleeve is a hollow cylinder with an opening and a bottom, namely the female die sleeve is provided with a cavity;
the outer diameter of the concave die sleeve is matched with the inner diameter of the concave die holder, and the concave die sleeve is placed in an inner cavity of the concave die holder; a fourth cold insulation layer is arranged between the outer surface of the female die sleeve and the inner surface of the female die holder;
the multipoint male die body is a cylinder with a handle at the top end, and a threaded hole is formed at the bottom end of the multipoint male die body;
the multipoint male die head comprises a plurality of steel columns, wherein one ends of the steel columns are provided with external threads, the other ends of the steel columns are of hemispherical structures, and the ends of the steel columns with the external threads are connected with the bottom end of the multipoint male die body through threads;
the multi-point convex die head is positioned in the cavity of the concave die sleeve; a plurality of steel columns are uniformly and tightly arranged;
the forming male die consists of a plurality of multi-point male die heads and a multi-point male die body;
the second blank pressing inner ring is of a circular ring structure;
the first cold insulation and heat preservation layer is of a circular ring structure;
the first blank holder is of a circular ring structure;
the second blank holder inner ring, the first cold insulation and heat preservation layer and the first blank holder are sequentially sleeved on the forming male die from bottom to top, namely the second blank holder inner ring is firstly sleeved on the forming male die, then the first cold insulation and heat preservation layer is sleeved on the forming male die, and finally the first blank holder is sleeved on the forming male die;
the cushion block B of the concave die holder is of a circular ring structure;
the low-temperature forming female die cushion block A is of a circular ring structure, the low-temperature forming female die cushion block A is fixedly connected to the upper surface of the female die holder cushion block B, the low-temperature forming female die cushion block A and the female die holder cushion block B are sealed through a double-layer low-temperature-resistant sealing ring, the low-temperature forming female die cushion block A and the female die holder cushion block B are sleeved on the female die sleeve (2) together after being fixedly connected, and cold insulation and heat preservation are carried out between the female die holder cushion block B and the female die holder through a third cold insulation layer;
the second blank holder inner ring is positioned above the low-temperature forming female die cushion block A;
the ultralow-temperature circumferential sealing ring is sleeved on the outer surface of the second edge pressing inner ring;
and the second cold insulation and heat preservation layer is sleeved on the outer surfaces of the low-temperature forming female die cushion block A and the female die holder cushion block B and is used for cold insulation and heat preservation of the low-temperature forming female die cushion block A and the female die holder cushion block B.
2. The ultra-low temperature flexible forming method of the aluminum-lithium alloy thin-wall structural component according to claim 1, characterized in that: in the second step, the correction refers to reserving process allowance for the two-dimensional plane model.
3. The ultra-low temperature flexible forming method of the aluminum-lithium alloy thin-wall structural component according to claim 1, characterized in that: in the third step, the solution treatment refers to annealing the spread material cut by the laser in a box-type resistance furnace, wherein the heating temperature T is 500-520 ℃, and the heat preservation time is 1-1.5 h.
4. The ultra-low temperature flexible forming method of the aluminum-lithium alloy thin-wall structural component according to claim 1, characterized in that: and step five, controlling the blank holder force by controlling the hydraulic pressure of the blank holder cylinder of the double-acting hydraulic press.
5. The ultra-low temperature flexible forming method of the aluminum-lithium alloy thin-wall structural component according to claim 1, characterized in that: and seventhly, the thickness of the semicircular backing ring is 1.1t, the unit is mm, and t is the thickness of the aluminum lithium alloy plate.
6. The ultra-low temperature flexible forming method of the aluminum-lithium alloy thin-wall structural component according to claim 1, characterized in that: in the ninth step, the edge pressing force is kept to be F when the edge pressing force is applied, wherein F is Ap, A is the projection area of the blank under the second edge pressing inner ring, and the unit is mm 2 P is the unit blank holder force, the unit is MPa,
Figure FDA0003759503210000041
z is reciprocal of drawing coefficient, D is diameter of the developed material in mm, t is thickness of the aluminum lithium alloy plate in mm, sigma b The tensile strength of the aluminum lithium alloy plate is expressed in MPa.
7. The ultra-low temperature flexible forming method of the aluminum-lithium alloy thin-wall structural component according to claim 1, characterized in that: in the tenth step, the first high-pressure low-temperature liquid medium is an ultralow-temperature cooling medium, and is one of liquid nitrogen or liquid helium.
8. The ultra-low temperature flexible forming method of the aluminum-lithium alloy thin-wall structural component according to claim 1, characterized in that: in the eleventh step, the second high-pressure low-temperature liquid medium is an ultralow-temperature cooling medium, and is one of liquid nitrogen or liquid helium.
9. The ultra-low temperature flexible forming method of the aluminum-lithium alloy thin-wall structural component according to claim 1, characterized in that: the outer profile formed by the multiple multi-point convex die heads is consistent with the inner profile shape of the aluminum-lithium alloy thin-wall structural part to be formed, and the multi-point convex die heads adjust the height of the multi-point convex die heads through threads, so that the multiple multi-point convex die heads realize configurations with different outer profile shapes.
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