Concave curve titanium alloy angle material forming method

Abstract

The present invention proposes a method for forming a concave curve titanium alloy angle material, which belongs to the technical field of titanium alloy sheet metal manufacturing. In view of the fact that when the concave curve is bent, the web surface is subjected to pressure along the bending line, the material has a tendency to accumulate, and is prone to wrinkling. The present invention adjusts the structure of the hot forming die to increase the web surface forming pressure to increase the flow resistance of the web surface material, and adjusts the shape and size of the rough material to reduce the bending forming resistance, thereby weakening the tendency of material accumulation to cause thickening during the part forming process, thereby avoiding wrinkling during the part forming process; and then through means such as hot correction, the shape characteristics such as the bending angle of the angle material are trimmed. The surface of the part using this method is smooth and flat, without wrinkles; at the same time, the curvature of the part is directly drawn, not bent by traditional hot pressing, and there is no obvious rebound on the curved surface of the part after forming, and the gap for tire inspection is small; the difficulty of part processing is significantly reduced, the part processing cycle is shortened, and production efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium alloy sheet metal manufacturing, and relates to a concave curve titanium alloy angle material forming method, which is used for hot forming processing of concave curve titanium alloy angle materials and similar parts, and can effectively avoid the generation of surface wrinkles during the part processing process, and is particularly suitable for titanium alloy structural parts with high requirements for appearance accuracy. Background Art

[0002] Titanium alloys have been increasingly widely used in aviation, navigation and other industries due to their excellent high temperature resistance and corrosion resistance. With the improvement of the performance of the new generation of aircraft, the proportion of titanium alloy parts in aircraft structures is increasing, and titanium alloy parts are showing a trend of large-scale and complex development, and the processing precision requirements are also constantly increasing. For titanium alloy angle materials, there are a large number of applications in various types of aircraft structures, and the allowable assembly clearance is getting smaller and smaller, the minimum fit clearance is within 0.3mm, and wrinkles are not allowed on the connecting surfaces of the parts. For titanium alloy angle materials, the general hot forming scheme is hot drawing or die hot pressing. During the hot drawing process, the forming temperature of the parts is difficult to monitor, and the stable fluctuation is large, which can no longer meet the current aircraft parts processing process control requirements. For the direct hot pressing of the die, for angle material parts with large curvature, the surface of the parts is very easy to wrinkle when the parts are collected and discharged due to the direction of the forming pressure, resulting in excessive fit clearance when assembled with other parts. In addition, the processing springback of titanium alloy parts is large, and the wrinkles on the surface are extremely difficult to repair, and it is almost impossible to completely eliminate them. At the same time, it will also lead to a significant increase in the processing cycle and cost of the parts. How to avoid wrinkling of parts during the forming stage has become a major difficulty in the forming of titanium alloy angle parts. Summary of the invention

[0003] In order to solve the above technical difficulties and avoid wrinkling during hot forming of titanium alloy angle parts, the present invention provides a method for forming concave curve titanium alloy angles. In view of the fact that during the bending of the concave curve, the web surface is subjected to pressure along the bending line, the material tends to accumulate, and is prone to wrinkling. By adjusting the structure of the hot forming mold, increasing the forming pressure of the web surface to increase the flow resistance of the web surface material, and appropriately adjusting the shape and size of the rough material to reduce the bending forming resistance, the tendency of material accumulation and thickening during the part forming process is weakened, thereby avoiding wrinkling during the part forming process. Then, through auxiliary forming or hot correction and other means, the bending angle of the angle material, the depression on the forming surface and other external features are adjusted.

[0004] The technical solution of the present invention is:

[0005] A concave curve titanium alloy angle forming method is realized by a special structure of hot forming die (similar to hot drawing die). Figure 1) is illustrated by a forming case. The material of this part is Ti-6Al-4V, and the material thickness is 0.8 mm; the part is a concave curve angle bar, the web surface is approximately flat, and the bending angle of the flange is from left to right (see Figure 1 ) is 73° to 81°; there is a depression on the flange of the part, and the depression depth is 0.8 mm; both the flange and the web of the part are connecting surfaces, the assembly relationship is complex, and wrinkles are not allowed on the overall surface of the part. The specific forming method includes the following steps:

[0006] 1. Process design

[0007] First, confirm the main features of the part's outer shape. The part structure should be of the concave curve angle bar type, and the web surface of the angle bar should be flat or approximately flat. Then measure other features such as the bending angle of the flange and the surface depression of the part. If the bending angle of the part's flange is greater than or equal to 90°, and there is no depression or the depression is only located on the web surface, the part is directly formed to the final state. If the bending angle of the part's flange is less than 90°, or the depression is located on the flange, it is necessary to first form it to an intermediate state, and then through a hot straightening process to obtain the final bending angle and depression.

[0008] The deep drawing forming process of the part is as Figure 2 shown. After the blank is formed, the cross-section is in the shape of "儿" (not connected in the middle). Removing the machining allowance 2 can obtain the part or the transitional blank 1 for subsequent processing. When designing the part forming process, symmetrical parts or parts with similar arcs (or forming two parts at a time) should be selected, and they should be placed symmetrically front and back for forming to balance the forming pressure on both sides.

[0009] 2. Design the hot forming die

[0010] Refer to the hot deep drawing die to design the hot forming die. The purpose is to form the flange arc surface and the flange, and obtain the part or the transitional blank 1. This process is the key step in part forming and directly determines the outer shape quality of the part. The hot forming die mainly includes the upper die 3, the blank holder 4 and the lower die 5; the specific structure is as Figure 3 shown.

[0011] 1) Upper die

[0012] The upper die 3 is a concave die, and its length and width are determined according to the size of the edge ring 4, and the height can meet the strength requirements; the concave mold surface of the upper die 3 is designed according to the inner surface of the part or transition blank 1. Because the part is formed by the punch 10, a certain gap is reserved between the upper surface of the concave mold surface of the upper die 3 and the part surface to avoid insufficient drawing height caused by surface interference. The upper die 3 is cast with medium silicon molybdenum ductile iron, and a weight-reducing opening is set on the top; ears 8 are set at both ends for mold opening inspection and mold handling. The mold base is set with a processing reference, and the surface is processed by CNC, and the surface accuracy is required to be ±0.1mm; both sides of the upper die 3 in the length direction are provided with pressure plate grooves 7 for fixing the mold on the hot forming machine; the size of the pressure plate groove 7 depends on the size of the mold fixing device on the hot forming machine. Guide slide grooves are opened at both ends of the upper die 3, which cooperate with the guide slide plate 11 on the lower die 5 for mold positioning and forming guidance.

[0013] 2)Blanket holding ring

[0014] The upper surface of the blank holder 4 is a blank holder plane, and its length and width should be larger than the minimum rough material size, and finally determined in combination with the position of the equipment push rod; the middle part of the blank holder 4 is opened according to the shape of the punch 10 on the lower die 5, and the thickness can meet the strength requirements. The lower surface should be designed according to the structure of the hot forming machine, and the mechanism connected to the equipment push rod should be designed. The push rod 6 is connected to the blank holder 4 by bolts, and a connecting mechanism may not be provided, but the upper surface of the blank holder 4 should be kept horizontal during use to ensure that the blank holder force is evenly distributed. The material of the blank holder 4 is medium silicon molybdenum ductile iron, and the mold surface is CNC machined. The machining datum is set at the machining allowance position, and the mold surface accuracy requirement is ±0.1mm. Lifting ears 8 are provided at both ends of the blank holder. Two locating pins 9 are provided on the upper surface of the blank holder 4 at the position of the symmetry axis of the two parts, which are used to position the rough material during hot forming. The calculation method of the minimum rough material size is as follows (only used for mold design and material preparation, not the actual blanking size):

[0015] L 毛料 =L 零件 +2h+2k

[0016] W 毛料 =W+2h+2k

[0017] L 零件 = Maximum chord length of the part

[0018] W (drawing width) = maximum spacing between parts;

[0019] h (drawing height) = maximum bending height of the part + (5-10) mm;

[0020] k (raw material edge pressing width) = part web width + (100~150) mm.

[0021] 3) Lower die

[0022] The lower die 5 is a punch. The profile of the punch 10 is designed according to the outer profile of the part or transition blank 1. The height of the punch 10 is determined according to the bending height of the part and the thickness of the blank holder 4. The length and width of the lower die 5 are determined according to the blank holder 4. The thickness can meet the strength requirements. The lower die 5 is cast as a whole with medium silicon molybdenum ductile iron. A weight-reducing opening is set at the bottom, and a push rod hole is opened at the position of the push rod 6 at the bottom of the blank holder 4. Lifting ears 8 are set at both ends for mold transportation. The base surface of the mold is set with a processing reference, and the profile is processed by CNC. The profile accuracy of the punch 10 is required to be ±0.1mm. A pressure plate groove 7 is opened throughout the bottom, and the size is determined according to the clamping device of the hot forming machine. Guide slides 11 are set at both ends of the lower die 5 to guide the upper die 3 and the blank holder 4 to move up and down. After the guide slide 11 is processed separately, it is connected to the lower die 5 by bolts, or the guide slide 11 is directly cast and processed with the lower die 5.

[0023] 3. Raw material shape and forming process

[0024] When forming a concave curved angle part, tensile stress parallel to the bending line is generated inside the bent edge, the material tends to thin and is not easy to wrinkle. However, in order to maintain the integrity of the material, compressive stress parallel to the bending line is generated inside the web surface material, the material tends to thicken and wrinkles easily. Because the wrinkling resistance is less than the thinning resistance during material forming, according to the law of least resistance, the web is prone to wrinkling during material forming. In order to avoid wrinkling of parts, the method adopted by the present invention is to increase the wrinkling resistance during part forming through the special structure of the hot forming mold, and at the same time reduce the part bending forming resistance (reduce the degree of thinning).

[0025] In order to increase the wrinkling resistance of the part, the present invention sets a blank holder 4 between the upper and lower dies of the hot forming die. When the part is formed, the blank holder 4 can provide an upward blanking force, and the combined force of the blank holder 4 and the downward forming pressure of the upper die 3 tightly clamps the raw material. At this time, if the part is to form wrinkles, in addition to overcoming its own material strength, it also needs to overcome the blank holder force applied by the equipment, and the wrinkling resistance is greatly improved. At the same time, when processing the part, the use of forming lubricants in the blank holder area is appropriately reduced to further increase the wrinkling resistance of the web.

[0026] On the other hand, in the selection of the shape of the forming blank, the present invention does not adopt the traditional drawing process to draw the entire blank, but the two parts are cut and formed separately ( Figure 2 The machining allowance 2 is not connected in the middle), which avoids the pulling effect of the connected material in the middle on the parts on both sides during forming, greatly reduces the tension inside the material along the bending direction during bending, thereby reducing the thinning of the parts. Using sheet metal simulation software for simulation calculation, the thinning of the bending position is less than 4% when split raw material is formed (if the whole raw material is deep drawn, the thinning rate of the bending is more than 20%). In addition, when processing parts, the bending area and the machining allowance area surrounded by the bending should be fully lubricated to further reduce the resistance to bending forming.

[0027] 4. Thermal calibration

[0028] For parts with a bending angle less than 90° or a bent edge with a sag, after the aforementioned deep drawing, it is necessary to perform heat correction to obtain the final bending angle and sag of the part. Figure 4 ) is implemented, and a typical heat correction mold of a part is now used as an example to explain in detail. The typical heat correction mold includes a male mold 15 and a female mold 16, and the specific structure is as follows Figure 4 shown.

[0029] 1) Punch 15

[0030] The size of the punch 15 is designed according to the actual size of the part, and an appropriate processing allowance is added, and the height meets the strength requirements. The convex model surface 12 is designed according to the inner surface of the part 13, and the surface area should be slightly larger than the edge of the part (5-10mm). The punch 15 is cast as a whole with medium silicon-molybdenum ductile iron, a weight-reducing opening is set on the top, and a lifting lug 8 is set on the side for transporting the mold and opening the mold to check the surface. The processing reference is set on the base surface of the mold, and the surface is processed by CNC. The accuracy of the convex model surface 12 is required to be ±0.1mm, and there are pressure plate grooves 7 on both sides (for fixing the mold on the thermoforming machine). The size of the pressure plate groove 7 depends on the mold fixing device on the thermoforming machine.

[0031] 2) Die 16

[0032] The size of the die 16 is designed according to the punch 15, and the die surface 14 is designed according to the outer profile of the part 13. The die 16 is cast as a whole with medium silicon molybdenum ductile iron, with a weight-reducing opening at the bottom and a lifting lug 8 on the side for opening and transporting the mold. The base surface of the mold is set with a processing reference, and the profile is processed by CNC. The accuracy of the die surface 14 is required to be ±0.1mm. There are platen grooves 7 on both sides (for fixing the mold on the hot forming machine), and the size of the platen grooves 7 depends on the mold fixing device on the hot forming machine. A guide column 17 is installed on the die 16, and a guide column hole is opened at the corresponding position of the punch 15 for guiding the male and female molds.

[0033] Beneficial effects of the present invention:

[0034] 1) High forming quality

[0035] Angle parts are generally used for connecting aircraft body structures, and high assembly precision is required. The concave curve angle parts processed according to the present invention have smooth and flat surface without wrinkles. At the same time, the curvature of the parts is formed by direct deep drawing, not bending by traditional hot pressing. After forming, the curved surface of the parts has no obvious springback, and the clearance is less than 0.4mm when checking the tire.

[0036] 2) High forming efficiency

[0037] Because the parts have good adhesion to the tire after forming and no wrinkles on the surface, the repeated rest work after the forming of general edge strip parts is eliminated, which greatly reduces the difficulty of part processing, shortens the part processing cycle, and improves production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of a typical parts structure.

[0039] Figure 2 This is a schematic diagram of a typical tooling cross section.

[0040] Figure 3 Schematic diagram of the hot forming mold structure.

[0041] Figure 4 Schematic diagram of the thermal correction mold structure.

[0042] In the figure: 1 transition blank; 2 machining allowance; 3 upper die; 4 pressure ring; 5 lower die; 6 ejector pin; 7 pressure plate groove; 8 lifting ear; 9 positioning pin; 10 punch; 11 guide plate; 12 convex model surface; 13 part; 14 concave model surface; 15 punch; 16 concave die; 17 guide column. DETAILED DESCRIPTION

[0043] The specific implementation of the present invention is further explained below in conjunction with the examples and drawings, but is not intended to limit the present invention.

[0044] A concave curve titanium alloy angle material forming method comprises the following steps:

[0045] 1. Parts raw material preparation

[0046] The two parts are cut separately, and the surface of the parts is cleaned to remove surface dirt and writing.

[0047] 2. Hot drawing preparation

[0048] Place the hot forming die in the hot forming machine for clamping, then test whether the blank holder 4 can move up and down normally, and check whether the molding surface is level during the movement of the blank holder 4. After checking that there is no problem, spray high-temperature lubricant on the upper die 3, the punch 10 and the blank holder 4 (no lubricant is sprayed on the upper die 3 and the blank holder 4), and heat to the forming temperature (the typical part forming temperature in this embodiment is about 680°C).

[0049] 3. Spray lubricant

[0050] Spray high temperature resistant forming lubricant on the upper and lower surfaces of the rough material.

[0051] 4. Hot drawing (forming parameters are only used to describe the forming process, not actual processing parameters)

[0052] 1) Raise the blank holder 4 to the level with the top of the punch 10, place the rough materials on the blank holder 4, and position them according to the positioning pin 9; after keeping warm for 10 minutes, start hot pressing, the forming pressure is about 70 tons, and the pressure of the blank holder 4 is 40 tons.

[0053] 2) The upper die 3 first moves downward to close the mold with the blank holder 4 to clamp the part; then, under the joint action of the upper and lower pressures, the upper die 3 and the blank holder 4 clamp the rough material and move downward together to form the part or bend the transition blank 1 with the punch 10.

[0054] 3) After the upper and lower molds of the thermoforming mold are closed, keep the temperature and pressure for 20 minutes, and then take out the parts.

[0055] 5. Rough cutting shape (on demand)

[0056] After the transition blank 1 is taken out, the shape of the part is roughed out according to the heat-correcting mold. The shape size of the transition blank 1 should be roughly equivalent to the surface of the heat-correcting model.

[0057] 6. Hot calibration preparation (on demand)

[0058] The hot shaping mold is clamped in a hot forming machine and heated to the shaping temperature (the shaping temperature of a typical part in this embodiment is about 680° C.).

[0059] 7. Spray lubricant (as needed)

[0060] The high temperature resistant forming lubricant is sprayed on the inner and outer surfaces of the transition blank 1 .

[0061] 8. Thermal calibration (on demand, calibration parameters are only used to describe the forming process, not actual processing parameters)

[0062] Put the transition blank 1 into the hot shaping mold, keep it warm for 10 minutes, and then start hot pressing shaping. The shaping pressure is about 50 tons. After the upper and lower molds of the hot shaping mold are closed, keep warm and pressurized for 20 minutes, and then take out the part.

[0063] 9. Marking shape

[0064] The part is marked with edge lines according to the template or inspection mold, and the shape of the part 13 is produced.

[0065] 10. Check the parts

[0066] The finished parts 13 are checked for shape and contour according to the sample or inspection mold.

[0067] 11. Surface treatment

[0068] After the parts are inspected and qualified, they are sent to the surface treatment workshop to remove the hot forming oxide layer, and then they can be delivered with coding.

Claims

1. A concave curve titanium alloy angle material forming method, characterized in that: The method comprises the following steps: (1) Process design First, confirm the main features of the concave curve angle material, and then measure the bending angle and profile depression of the concave curve angle material; if the bending angle is greater than or equal to 90°, and there is no depression or the depression is only on the web surface, the part is directly formed to the final state; if the bending angle of the part is less than 90°, or the depression is on the bending edge, it needs to be formed to the intermediate state first, and then go through the hot correction process to obtain the final bending angle and depression; (2) Design of thermoforming mold for thermoforming A thermoforming die is used to form the edge strip arc surface and the bent edge to obtain a part or a transition blank; the thermoforming die comprises an upper die (3), a blank holder (4) and a lower die (5); The upper die (3) is a concave die, and the concave die surface of the upper die (3) is designed according to the inner die surface of the part or the transition blank; the upper die (3) is cast as a whole with medium silicon molybdenum ductile iron; both sides of the upper die (3) in the length direction are provided with pressure plate grooves (7) for fixing the die on the hot forming machine; guide slide grooves are provided at both ends of the upper die (3), which cooperate with the guide slide plate (11) on the lower die (5) for die positioning and forming guidance; The upper surface of the blank holder (4) is a blank holder plane, the length and width of which are greater than the minimum rough material size and are ultimately determined in combination with the position of the equipment push rod; the middle of the blank holder (4) is opened according to the shape of the upper punch (10) of the lower die (5); a push rod (6) is provided on the lower surface of the blank holder (4); two positioning pins (9) are provided on the upper surface of the blank holder (4) at the position of the symmetry axis of the two parts, which are used to position the rough material during hot forming; The lower die (5) is a punch, and the profile of the punch (10) is designed according to the profile of the outer side of the part or the transition blank, and the height of the punch (10) is determined according to the bending height of the part and the thickness of the pressure ring (4); the lower die (5) is cast as a whole with medium silicon molybdenum ductile iron, and a push rod hole is opened according to the position of the push rod (6) at the bottom of the pressure ring (4); a pressure plate groove (7) is opened on the side of the lower die (5); guide slide plates (11) are arranged at both ends of the lower die (5) to guide the upper die and the pressure ring to move up and down; During thermoforming: 1) The hot forming die is placed in a hot forming machine for clamping, and then the blank holder (4) is tested to see whether it moves up and down normally, and whether the molding surface is level during the movement of the blank holder (4); after checking that there is no problem, a high-temperature lubricant is sprayed on the upper die (3), the punch (10) and the blank holder (4), wherein the upper die (3) and the blank holder (4) are not sprayed with lubricant at the blank holder position, and are heated to the forming temperature; 2) Raise the blank holder (4) to the level with the top of the punch (10), place the rough materials on the blank holder (4), and position them according to the positioning pins (9); after keeping warm, start hot pressing; 3) The upper die (3) first moves downward to close the die with the blank holder (4) to clamp the part; then, under the combined action of the upper and lower pressures, the upper die (3) and the blank holder (4) hold the rough material and move downward together to form the part or the transition blank with the punch (10); 4) After the upper and lower molds of the thermoforming mold are closed, the parts are taken out after heat preservation and pressure maintenance; (3) Thermal calibration For parts with a bending angle less than 90° or a bent edge with a sag, after hot forming, hot shaping is required to obtain the final bending angle and sag of the parts; the hot shaping of the parts is achieved by a hot shaping die, and the hot shaping die comprises a male die (15) and a female die (16); The size of the punch (15) is designed according to the actual size of the part, and the processing allowance is increased, and the height meets the strength requirement; the convex mold surface (12) is designed according to the inner surface of the part, and the surface area is 5 to 10 mm larger than the edge of the part; the punch (15) is cast from medium silicon molybdenum ductile iron, with a weight-reducing opening on the top and lifting ears (8) on the sides; and pressure plate grooves (7) are provided on both sides of the punch (15) for fixing the mold on a hot forming machine; The size of the concave die (16) is designed according to the convex die (15), and the concave die surface (14) is designed according to the outer surface of the part; the concave die (16) is integrally cast from medium silicon-molybdenum ductile iron, a weight-reducing opening is arranged at the bottom, and a lifting lug (8) is arranged on the side; pressure plate grooves (7) are arranged on both sides of the concave die (16) for fixing the mold on a hot forming machine; guide posts (17) are installed on the concave die (16), and guide post holes are opened at corresponding positions of the convex die (15) for guiding the male and female dies when they are combined; During heat calibration, the transition blank is placed in a heat calibration mold for heat pressing calibration. After the heat calibration mold is closed, the part is taken out after heat and pressure are maintained. (4) Stroke-lined shape The parts are marked with edge lines according to the template or inspection mold, and the part shape is produced; (5) Check parts Check the shape and contour of the machined parts according to the sample or inspection mold; (6) Surface treatment After the parts are inspected and qualified, they are sent to the surface treatment workshop to remove the hot forming oxide layer, and then delivered with coding.

2. The concave curve titanium alloy angle material forming method according to claim 1, characterized in that: The minimum rough material size is calculated as follows: <h2 style=";text-align:left;direction:ltr">L<h2 style=";text-align:left;direction:ltr"> 毛料 <h2 style=";text-align:left;direction:ltr"> =L<h2 style=";text-align:left;direction:ltr"> 零件 <h2 style=";text-align:left;direction:ltr"> +2h+2k <h2 style=";text-align:left;direction:ltr">W<h2 style=";text-align:left;direction:ltr"> 毛料 <h2 style=";text-align:left;direction:ltr"> =W+2h+2k L 零件 = Maximum chord length of the part Drawing width W = maximum spacing between parts; Drawing height h = maximum bending height of the part + (5-10) mm; The blank edge pressing width k = part web width + (100~150) mm.

3. A concave curve titanium alloy angle material forming method according to claim 1 or 2, characterized in that: Both ends of the upper die (3), the pressure ring (4) and the lower die (5) are provided with lifting ears (8); a weight-reducing opening is provided at the top of the upper die (3) and a weight-reducing opening is provided at the bottom of the lower die (5).

4. A concave curve titanium alloy angle material forming method according to claim 1 or 2, characterized in that: The length and width of the upper die (3) and the lower die (5) are determined according to the size of the edge ring (4), and the height only needs to meet the strength requirements.

5. The concave curve titanium alloy angle material forming method according to claim 3, characterized in that: The length and width of the upper die (3) and the lower die (5) are determined according to the size of the edge ring (4), and the height only needs to meet the strength requirements.

Images