A two-step hot stamping forming method for the leading edge skin of a TB8 titanium alloy blade

Abstract

The present invention discloses a two-step hot stamping forming method for the leading edge skin of a TB8 titanium alloy blade. According to the part model of the leading edge skin of the TB8 titanium alloy blade, the blank design of the part before forming is carried out. The stamping direction design and die design are respectively carried out for the two-step hot stamping forming process. The blank cutting and die manufacturing are carried out according to the blank design and die design. The two-step hot stamping forming of the leading edge skin is implemented, which is applicable to the hot stamping forming of the leading edge skin parts of blades with similar torsion characteristics and can ensure the precise assembly of the leading edge skin of the blade and the blade after forming.

Description

Technical Field

[0001] The present invention belongs to the field of precision plastic forming of titanium alloys, and relates to a metal sheet stamping forming, specifically a two-step hot stamping forming method for forming a TB8 titanium alloy blade leading edge skin part with a certain torsional angle at both the head and the tail ends. Background Art

[0002] To achieve the purpose of weight reduction, the fan blades of turbofan engines, the rotor blades of helicopters, and the fan blades of hovercrafts, etc. have gradually changed from traditional metal materials to composite materials with reinforcing materials such as fiberglass, carbon fiber, and Kevlar fiber. However, in complex geographical environments and harsh climate conditions, due to the poor impact resistance of composite blades, they are extremely vulnerable to being impacted by flying sand, gravel, and other foreign objects during rotation, resulting in damage. Generally, one or several metal skins are arranged at the leading edge of the blade to protect the blade and prevent delamination and damage of the blade during impact. To prevent the skin from falling off, the shape accuracy of the skin is required to be extremely high, and it needs to be accurately assembled on the leading edge of the blade and then connected to the blade by means of bonding or riveting, etc. At present, there are mainly two forms for forming the blade skin: mechanical stamping forming and electroforming. Among them, mechanical stamping forming is suitable for thin-walled products with relatively simple and regular shapes such as the skins of main and tail rotor blades; electroforming is suitable for forming skins with complex shapes, but has high requirements for the electrolyte ratio, and the subsequent processing technology of electroforming is cumbersome. Summary of the Invention

[0003] To achieve the purpose of weight reduction, the blade leading edge skin part of the present invention is made of titanium alloy thin plate. Titanium alloy has low plasticity and serious springback at room temperature, and its forming performance is greatly improved at high temperature, and the springback can be effectively suppressed under the high temperature stress relaxation effect. Therefore, titanium alloy thin plate parts usually adopt the hot stamping forming method. The shape of the TB8 titanium alloy blade leading edge skin part of the present invention is complex, the cross-sectional shapes of each section along the length direction are different, and there is a certain torsional angle at both the head and the tail ends, and there is a stamping negative angle. Therefore, it cannot be formed by one-step hot stamping.

[0004] The present invention realizes the precise forming of a TB8 titanium alloy blade leading edge skin part with a certain torsional angle at both the head and the tail ends through a designed two-step hot stamping forming method. According to the model of the TB8 titanium alloy blade leading edge skin part, the blank of the part before forming is designed. The stamping direction design and die design are respectively carried out for the two-step hot stamping forming process. According to the blank design and die design, blank cutting and die manufacturing are carried out, and the two-step hot stamping forming of the leading edge skin is implemented. The specific steps include:

[0005] 1. Blank design:

[0006] 1-1) The leading-edge skin part of the TB8 titanium alloy blade is made of thin plates. The cross-sections of the part along the length direction are V-shaped and gradually twist and transition from one end to the other. Taking the head and tail ends as boundaries, multiple equidistant planes are made, and the intersection curves of these planes and the part are obtained. The angular bisectors of the intermediate transition arc segments of the head-end intersection curve and the tail-end intersection curve are respectively taken, and further the angular bisector of the two angular bisectors is taken as the blank design projection direction.

[0007] 1-2) Select the plane perpendicular to the angular bisector as the blank development projection plane, and respectively take the midpoints of each intersection curve and project them onto this vertical plane. Based on each midpoint, each intersection curve is developed into a corresponding straight-line segment according to the length on the vertical plane, and the endpoints of the straight-line segments on both sides are respectively connected to obtain the edge curves on both sides of the blank. The combination of the edge curves on both sides and the projection line segments at the head and tail ends forms the contour of the blank without allowance. To prevent local material shortage caused by the offset of the part during the forming process, the final blank contour needs to be offset 5 mm outward.

[0008] 2. Stamping direction design: In the planes where the head-end intersection curve and the tail-end intersection curve are located, the same reference coordinate system is adopted, and the left limit and right limit of the one-step stamping forming direction at the tail end, and the left limit and right limit of the one-step stamping forming direction at the head end are respectively obtained. The first-step stamping forming direction is taken between the left limit and right limit of the one-step stamping forming direction at the tail end, and the second-step stamping forming direction is taken between the left limit and right limit of the one-step stamping forming direction at the head end. Find the two end planes of the part-forming interval along the first-step stamping forming direction, and find the two end planes of the part-forming interval along the second-step stamping forming direction. The two-step stamping forming directions need to satisfy that there is an overlapping section in the two-step forming intervals, and the head-end side limit plane of the first-step stamping forming section is located outside the head-end dividing plane, and the tail-end side limit plane of the second-step stamping forming section is located outside the tail-end dividing plane.

[0009] 3. Die design:

[0010] 3-1) After the part model is freely extended 20 mm outward at both the head and tail ends respectively, the first-step hot stamping forming die is designed according to the first-step stamping forming direction. The two side limit planes of the stamping negative angle section of the first-step hot stamping forming die are found, and the die forming surface is trimmed to have no stamping negative angle. The gap between the punch and the die is taken as 1.1 times the sheet thickness. The die material is selected as 2520 stainless steel, and the die adopts a scaling factor of 0.994 to complete the design of the punch and die of the first-step hot stamping forming die;

[0011] 3-2) After the part model is freely extended 20 mm outward at both the head and the tail ends respectively, the second-step hot stamping forming die is designed according to the stamping forming direction in the second step. Find the limit planes on both sides of the stamping negative angle section of the second-step hot stamping forming die. The punch-die clearance is taken as 1.1 times the sheet thickness. The die material is selected as 2520 stainless steel. The die uses a scaling factor of 0.994. Trim the female die of the second-step hot stamping forming die so that there is no stamping negative angle on the forming surface of the die, and complete the design of the punch and the female die of the second-step hot stamping forming die;

[0012] 3-3) Finally, positioning, guiding and other structures need to be added to the two forming dies.

[0013] 4. Forming process:

[0014] 4-1) Manufacture the blank and the die respectively according to the blank design and the die design; Install the two-step hot stamping forming die in the hot stamping machine tool. Among them, the female die of the first-step hot stamping forming die is at the bottom and the punch is at the top. The punch of the second-step hot stamping forming die is at the bottom and the female die is at the top. The two dies are heated in the furnace to 650 °C and kept warm, and the holding time is not less than 1 hour; Spray boron nitride or graphite water agent on the surface of the blank, and after natural air drying or drying, move it onto the female die of the first-step hot stamping forming die and keep warm for 10 minutes; Carry out the first-step hot stamping, and keep the die closed for 12 minutes after the die is closed; Raise the punch of the first-step hot stamping forming die, take out the part, place it on the punch of the second-step hot stamping forming die, keep warm for 10 minutes, carry out the second-step hot stamping, and keep the die closed for 12 minutes after the die is closed; Raise the female die of the second-step hot stamping forming die, take out the part, and cool it naturally to complete the two-step hot stamping forming of the leading edge skin of the TB8 titanium alloy blade.

[0015] 4-2) Obtain the leading edge skin part of the TB8 titanium alloy blade that meets the final design requirements through subsequent surplus removal and surface cleaning.

[0016] Beneficial effects

[0017] The present invention can achieve the precise forming of the leading edge skin of the TB8 titanium alloy blade with a certain torsion angle at both the head and the tail ends, is applicable to the hot stamping forming of the leading edge skin parts of blades with similar torsion characteristics, and can ensure the precise assembly of the leading edge skin of the blade and the blade after forming. Description of the drawings

[0018] Figure 1 It is a part drawing of the leading edge skin of the TB8 titanium alloy blade;

[0019] Figure 2 It is a schematic diagram of the multi-section division of the part;

[0020] Figure 3 It is a schematic diagram of the selection of the projection direction of the part blank unfolding;

[0021] Figure 4 It is a schematic diagram of the blank development of the part.

[0022] Figure 5 It is a schematic diagram for selecting the stamping direction of two-step hot stamping forming.

[0023] Figure 6 It is a schematic diagram of the range of two-step hot stamping forming.

[0024] Figure 7 It is a schematic diagram of the die design for the first-step hot stamping forming.

[0025] Figure 8 It is a schematic diagram of the die design for the first-step hot stamping forming.

[0026] In the figure, 1. The leading-edge skin part of the TB8 titanium alloy blade, 2 - 12 are the multi-section division planes of the part, 2 is the leading-end division plane, 12 is the trailing-end division plane, 3 - 11 are the intermediate-section division planes, 13 - 23 are the intersection curves between sections 2 - 12 and the outer surface of the leading-edge skin part 1 of the TB8 titanium alloy blade, 13 is the leading-end intersection curve, 23 is the trailing-end intersection curve, 14 - 22 are the intermediate-section intersection curves, 24. The angular bisector of the intermediate transition arc section of the leading-end intersection curve 13, 25. The angular bisector of the intermediate transition arc section of the trailing-end intersection curve 23, 26. The angular bisector of 24 and 25, 27. The blank development projection plane, 28. The contour of the blank without allowance, 29. The left limit of the one-step stamping forming direction at the trailing end, 30. The right limit of the one-step stamping forming direction at the trailing end, 31. The first-step stamping forming direction, 32. The left limit of the one-step stamping forming direction at the leading end, 33. The right limit of the one-step stamping forming direction at the leading end, 34. The second-step stamping forming direction, 35. The trailing-end side limit plane of the first-step stamping forming section, 36. The leading-end limit plane of the second-step stamping forming section, 37. The leading-end side limit plane of the first-step stamping forming section, 38. The trailing-end limit plane of the second-step stamping forming section, 39. The leading-end limit plane of the stamping negative angle trimming section of the first-step hot stamping forming die, 40. The trailing-end limit plane of the stamping negative angle trimming section of the first-step hot stamping forming die, 41. The punch of the first-step hot stamping forming die, 42. The die of the first-step hot stamping forming die, 43. The trailing-end limit plane of the stamping negative angle trimming section of the second-step hot stamping forming die, 44. The leading-end limit plane of the stamping negative angle trimming section of the second-step hot stamping forming die, 45. The punch of the second-step hot stamping forming die, 46. The die of the second-step hot stamping forming die. x, y, and z respectively represent the spatial axial coordinates in three directions in sequence. Specific implementation mode

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings. A two-step hot stamping forming method for the leading-edge skin of a TB8 titanium alloy blade is as follows:

[0028] 1. Blank Design: The leading edge skin part of the TB8 titanium alloy blade is made of thin plate, and its shape is as shown in Figure 1 . The cross-sections of the part along the length direction are similar to V-shape and gradually twist and transition from one end to the other end. As shown in Figure 2 , taking the head and tail ends as boundaries, make 11 equally spaced planes 2 - 12, and take the intersection curves 13 - 23 of these 11 planes and the part. Respectively take the angular bisectors 24 and 25 of the intermediate transition arc segments of the leading intersection curve 13 and the trailing intersection curve 23, and further take the angular bisector 26 of 24 and 25 as the blank design projection direction. As shown in Figure 4 , select the plane 27 perpendicular to the angular bisector 26 as the blank development projection plane. Respectively take the midpoints of the intersection curves 13 - 23 and project them onto the plane 27. Based on each midpoint, expand the intersection curves 13 - 23 into corresponding straight line segments in length on the plane 27. Connect the endpoints of the straight line segments on both sides respectively to obtain the edge curves on both sides of the blank. The combination of the edge curves on both sides and the projection line segments at the head and tail ends forms the contour of the blank without allowance 28. To prevent local material shortage caused by part offset during the forming process, the final blank shape needs to be offset 5 mm outward.

[0029] 2. Stamping Direction Design: Adopt the same reference coordinate system in the planes where the leading intersection curve 13 and the trailing intersection curve 23 are located, and respectively obtain the left limit 29 and right limit 30 of the one-step stamping forming direction at the trailing end, and the left limit 32 and right limit 33 of the one-step stamping forming direction at the leading end; take the first-step stamping forming direction 31 between the left limit 29 and right limit 30 of the one-step stamping forming direction at the trailing end, and take the second-step stamping forming direction 34 between the left limit 32 and right limit 33 of the one-step stamping forming direction at the leading end; the part forming interval along the first-step stamping forming direction 31 is between the planes 35 and 37, and the part forming interval along the second-step stamping forming direction 34 is between the planes 36 and 38; the stamping forming directions 31 and 34 need to satisfy that there is an overlapping section in the two-step forming intervals, and the trailing side limit plane 35 of the first-step stamping forming section is located outside the leading division plane 2, and the leading limit plane 36 of the second-step stamping forming section is located outside the trailing division plane 12.

[0030] 3. Die Design: As shown in Figure 7 , after freely extending the part model 20 mm outward at both the head and tail ends respectively, carry out the design of the first-step hot stamping die according to the first-step stamping forming direction 31. Among them, the interval between the planes 39 and 40 is the stamping negative angle section of the first-step hot stamping die. Trim the model to make the die forming surface without stamping negative angle. The gap between the punch and die is taken as 1.1 times the sheet thickness. The die material is selected as 2520 stainless steel, and the die adopts a scaling factor of 0.994 to complete the design of the punch 41 and die 42 of the first-step hot stamping die; as shown in Figure 8As shown, after the part model is freely extended by 20 mm outward at both the head and the tail ends respectively, the second-step hot stamping die is designed according to the stamping forming direction 34 in the second step. Among them, the section between the planes 43 and 44 is the stamping negative angle section of the second-step hot stamping die, and the punch-die clearance is taken as 1.1 times the sheet thickness. The female die of the second-step hot stamping die is trimmed so that there is no stamping negative angle on the die forming surface. The die material is selected as 2520 stainless steel, and the die adopts a scaling factor of 0.994. The design of the punch 45 and the female die 46 of the second-step hot stamping die is completed; finally, positioning, guiding and other structures need to be added to the two forming dies.

[0031] 4. Forming process: The blank and the die are manufactured respectively according to the blank design and the die design; the two-step hot stamping dies are installed in the hot stamping machine tool. Among them, the female die of the first-step hot stamping die is at the bottom and the punch is at the top, and the punch of the second-step hot stamping die is at the bottom and the female die is at the top. The two dies are heated in the furnace to 650 °C and kept warm for at least 1 hour; the surface of the blank is sprayed with boron nitride or graphite water agent, and after natural air drying or drying, it is moved onto the female die of the first-step hot stamping die and kept warm for 10 minutes; the first-step hot stamping is carried out and the die is closed and kept for 12 minutes; the punch of the first-step hot stamping die is lifted, the part is taken out and placed on the punch of the second-step hot stamping die, kept warm for 10 minutes, and the second-step hot stamping is carried out. After the die is closed, it is kept for 12 minutes; the female die of the second-step hot stamping die is lifted, the part is taken out and cooled naturally to complete the two-step hot stamping forming of the leading edge skin of the TB8 titanium alloy blade. The final TB8 titanium alloy blade leading edge skin part that meets the design requirements is obtained through subsequent surplus removal and surface cleaning.

Claims

1. A two-step hot stamping forming method for the leading edge skin of a TB8 titanium alloy blade, characterized in that, it includes the following steps: 1). Blank design: 1-1) A TB8 titanium alloy blade leading edge skin part is made from a thin plate. The cross-sections of the part along the length direction are V-shaped and gradually twist and transition from one end to the other. Taking the head and tail ends as boundaries, multiple equidistant planes are made, and the intersection curves of these multiple planes with the part are obtained. The angular bisectors of the intermediate transition arc segments of the head end intersection curve and the tail end intersection curve are respectively taken, and further the angular bisector of the two angular bisectors is taken as the blank design projection direction; 1-2) Select the plane perpendicular to the angular bisector as the blank unfolding projection plane, and respectively take the midpoints of each intersection curve and project them onto this perpendicular plane. Based on each midpoint, each intersection curve is unfolded into a corresponding straight line segment according to the length on the perpendicular plane, and the endpoints of the straight line segments on both sides are respectively connected to obtain the edge curves on both sides of the blank. The combination of the edge curves on both sides and the projection line segments at the head and tail ends forms the contour of the blank without allowance; 2). Stamping direction design: In the planes where the head end intersection curve and the tail end intersection curve are located, the same reference coordinate system is adopted, and the left limit and right limit of the first-step stamping forming direction at the tail end, and the left limit and right limit of the first-step stamping forming direction at the head end are respectively obtained. The first-step stamping forming direction is taken between the left limit and right limit of the first-step stamping forming direction at the tail end, and the second-step stamping forming direction is taken between the left limit and right limit of the first-step stamping forming direction at the head end. Find the two end planes of the part that can be formed along the first-step stamping forming direction, and find the two end planes of the part that can be formed along the second-step stamping forming direction. The two-step stamping forming directions need to satisfy that there is an overlapping section in the two-step forming intervals, and the head end side limit plane of the first-step stamping forming section is located outside the head end dividing plane, and the tail end side limit plane of the second-step stamping forming section is located outside the tail end dividing plane; 3). Die design: 3-1) After the part model is freely extended 20 mm outside the head and tail ends respectively, the first-step hot stamping forming die is designed according to the first-step stamping forming direction. The two limit planes on both sides of the stamping negative angle section of the first-step hot stamping forming die are found, and the die forming surface is trimmed to have no stamping negative angle, and the convex die and concave die of the first-step hot stamping forming die are completed; 3-2) After the part model is freely extended 20 mm outside the head and tail ends respectively, the second-step hot stamping forming die is designed according to the second-step stamping forming direction. The two limit planes on both sides of the stamping negative angle section of the second-step hot stamping forming die are found, and the concave die of the second-step hot stamping forming die is trimmed to have no stamping negative angle, and the convex die and concave die of the second-step hot stamping forming die are completed; 3-3) Finally, positioning and guiding structures need to be added to the two forming dies; 4). Forming process: 4-1) Manufacture the blank and the die according to the blank design and the die design respectively; Install the two-step hot stamping forming die in the hot stamping machine tool. For the first-step hot stamping forming die, the female die is at the bottom and the male die is at the top. For the second-step hot stamping forming die, the male die is at the bottom and the female die is at the top. Heat it in the furnace and keep it warm. Spray boron nitride or graphite water agent on the surface of the blank. After natural air drying or drying, move it onto the female die of the first-step hot stamping forming die and keep it warm for 10 minutes; Conduct the first-step hot stamping. After closing the die, keep it for 12 minutes; Raise the male die of the first-step hot stamping forming die, take out the part, place it on the male die of the second-step hot stamping forming die, keep it warm for 10 minutes, conduct the second-step hot stamping, and keep it for 12 minutes after closing the die; Raise the female die of the second-step hot stamping forming die, take out the part, and cool it naturally to complete the two-step hot stamping forming of the leading edge skin of the TB8 titanium alloy blade. 4-2) Obtain the leading edge skin part of the TB8 titanium alloy blade that meets the final design requirements through subsequent surplus removal and surface cleaning.

2. The forming method according to claim 1, characterized in that, In the stamping direction design in 2), in order to prevent local material shortage caused by part offset during the forming process, the outer contour of the blank without surplus needs to be increased by 5 mm outward.

3. The forming method according to claim 1, characterized in that, In 3) die design 3-1) and 3-2), the clearance between the male die and the female die is taken as 1.1 times the sheet thickness. The die material is selected as 2520 stainless steel, and the die uses a scaling factor of 0.

994.

4. The forming method according to claim 1, characterized in that, In the 4) forming process 4-1), in the second-step hot stamping forming, the male die and the female die are heated to 650 °C, and the holding time is not less than 1 hour.

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