A method of electric field assisted forming of complex thin-walled components of a difficult-to-deform alloy

Abstract

The application discloses a kind of complex thin-walled components of difficult deformation alloy electric energy field auxiliary forming method, the sheet of difficult deformation alloy is clamped with lower die;First type tool head is locally applied to the suspended area of sheet material close to lower die by a predetermined distance Partial pressure, make sheet material occur elastic deformation, form the elastic deformation zone of concave surface, and the elastic deformation zone is partially attached to lower die;Second type tool head is carried out electric auxiliary stress relaxation to the part of elastic deformation zone of sheet material attached to lower die, make sheet material rapidly heat up and convert elastic deformation into plastic deformation;First type tool head and second type tool head are moved according to preset machining trajectory, and sheet material is gradually machined and formed into complex thin-walled component. By the progressive electric auxiliary stress relaxation machining method, the area that occurs elastic deformation and is elastically attached to lower die is carried out electric auxiliary stress relaxation, and the elastic deformation is converted into plastic deformation, the tool head acting pressure is very small in the process of processing, and the influence on sheet material thickness is smaller, and the wall thickness reduction rate can be greatly reduced.

Description

Technical Field

[0001] This invention relates to the forming and processing of difficult-to-deform alloys, specifically to an electric field-assisted forming method for complex thin-walled components made of difficult-to-deform alloys. Background Technology

[0002] Incremental forming has attracted widespread attention due to its short development cycle, low cost, and advantages such as process flexibility and strong adaptability. Existing technologies, such as the "Incremental Forming Method for Complex Sheet Metal Parts," propose using an incremental forming method to form complex sheet metal parts. This method can save time and costs in producing small batches of complex parts, and experiments have successfully produced high-quality human faces.

[0003] However, during incremental forming, the material in the forming area undergoes axial shear flow under the forming force of the tool head, resulting in severe thinning of the sheet metal and uneven thickness distribution. Existing technologies have addressed this issue of uneven sheet metal thickness distribution. For example, the "Numerical Simulation and Experimental Study of Multi-Pass Two-Point Incremental Forming" proposes using multiple forming passes and variable interval angles for two-point incremental forming, which can improve the uniformity of wall thickness distribution in incrementally formed parts, with the effect becoming more pronounced as the number of forming passes increases. However, the problem of excessive wall thinning still exists. Another example is the "Multi-Pass Incremental Forming of TB8 Titanium Alloy Straight-Wall Square Box," which proposes using an alternating up-and-down reciprocating forming trajectory to overcome the severe thickness thinning problem in traditional incremental forming paths. Experimental studies show that traditional incremental forming methods result in a maximum wall thickness thinning rate of 65.6%, while the improved processing method reduces the maximum wall thickness thinning rate to 42.6%. Excessive thinning of the formed part has a significant impact on strength. Although the above methods and studies have improved the thickness distribution of incremental forming to some extent, they have not yet effectively solved the problem of excessive wall thinning. Summary of the Invention

[0004] Purpose of the invention: In view of the above-mentioned shortcomings, the present invention provides an electric field-assisted forming method for complex thin-walled components of difficult-to-deform alloys that solves the problems of severe wall thinning and uneven thickness distribution in formed parts.

[0005] Technical solution: To solve the above problems, the present invention employs an electric field-assisted forming method for complex thin-walled components made of difficult-to-deform alloys, comprising the following steps:

[0006] Step 1: Clamp the sheet of the difficult-to-deform alloy to the lower die;

[0007] Step 2: The first type of tool head applies pressure locally to the suspended area of ​​the sheet metal near the lower die at a preset distance, causing the sheet metal to undergo elastic deformation, forming an elastic deformation zone with a concave curved surface, and the elastic deformation zone partially fits the lower die.

[0008] Step 3: The second type of tool head applies electrical-assisted stress relaxation to the part of the sheet metal that is in contact with the lower die in the elastic deformation zone, so that the sheet metal heats up rapidly and converts the elastic deformation into plastic deformation;

[0009] Step 4: The first type of tool head and the second type of tool head move according to the preset processing trajectory to complete the first preliminary forming of the sheet metal;

[0010] Step 5: Change the feed rate of the first type of tool head and the second type of tool head, and repeat steps 2 to 4 on the unformed part of the sheet metal to perform progressive processing and form a complex thin-walled component.

[0011] Furthermore, in step 2, several first-type tool heads simultaneously apply pressure to the sheet metal locally, so that the concave curved surface forming the elastic deformation zone has different shapes to adapt to the lower model surface.

[0012] Furthermore, if the sheet material is not easily deformed or the amount of elastic deformation is too small, in step 2, the sheet material can be softened by passing electricity through the first type of tool head, and local low-temperature heating and pressure can be applied to the sheet material.

[0013] Furthermore, the first type of tool head locally heats the sheet metal at a low temperature, ensuring that the highest local temperature reached by the sheet metal does not exceed 0.25T. m T m This is the melting point temperature of the sheet material.

[0014] Furthermore, the maximum temperature range achievable by the sheet material is 0.4–0.5T. m .

[0015] Furthermore, the first type of tool head, sheet metal, mold, temperature control unit, and first power supply form a first circuit loop, and the second type of tool head, sheet metal, mold, temperature control unit, and second power supply form a second circuit loop.

[0016] Furthermore, in steps 2 and 3, the temperature of the sheet metal is obtained by an infrared thermal imager, and the output current density of the first power supply and the second power supply is controlled based on the obtained temperature, thereby controlling the temperature of the deformation area on the sheet metal.

[0017] Furthermore, the pressure applied to the sheet metal by the first type of tool head is calculated by the stress-strain curve at the processing temperature or obtained by finite element simulation; the position where the first type of tool head applies pressure to the sheet metal is determined by simulation calculation, and the fit between the deformation area and the mold is selected to achieve the optimal balance; the heating temperature and pressure of the second type of tool head on the sheet metal are selected by the sheet metal stress relaxation curve to make the stress relaxation rate and the pressure of the second type of tool head the optimal solution.

[0018] Furthermore, the processing position of the second type of tool head is 2-3mm away from the edge of the elastic deformation zone. The second type of tool head is electrically heated in the elastic deformation zone of the sheet metal and at the point where it fits with the mold, causing high-temperature stress relaxation in this area and accelerating the transformation of elastic deformation into permanent plastic deformation. The current density and magnitude of the second type of tool head are optimally determined by the temperature corresponding to the selected stress relaxation curve. By controlling the current density and magnitude of the second type of tool head, the processing temperature of the deformation zone can be controlled. The moving speed of both types of tool heads should be relatively slow to ensure sufficient time for plastic deformation.

[0019] Beneficial Effects: Compared to existing technologies, the significant advantage of this invention is that it utilizes a progressive electro-assisted thermoforming method. This method involves high-temperature stress relaxation of the material in areas of elastic deformation, transforming elastic deformation into plastic deformation. The radial force is small, unlike traditional progressive forming methods where the tool head directly plastically shapes the sheet metal. During elastic deformation, the material wall thickness remains almost unchanged. The almost unthinned elastic deformation zone is transformed into plastic deformation through electro-assisted stress relaxation. Since the stress relaxation process only converts elastic deformation into plastic deformation, it generally does not produce additional thinning, thus effectively improving the problem of excessive wall thickness reduction. Applying pressure only induces elastic deformation in the sheet metal, significantly reducing the probability of scratching. Using a full-shape or partial support mold allows for higher forming limits and forming accuracy than single-point progressive forming. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the sheet metal and the mold clamping state in this invention.

[0021] Figure 2 This is a schematic diagram of the structure of the first type of tool head in this invention, which applies pressure to the sheet metal and then springs back after unloading.

[0022] Figure 3 This is an isometric view of the elastic deformation of the sheet metal under pressure in this invention.

[0023] Figure 4 This is a schematic diagram of the cone-shaped mold of the present invention.

[0024] Figure 5 This is a schematic diagram illustrating the operation of multiple first-type tool heads in this invention.

[0025] Figure 6 This is a schematic diagram of the system structure for forming sheet metal using the first / second type of tool head in this invention.

[0026] Figure 7 This is a schematic diagram of the temperature distribution in the deformation region of the sheet metal in this invention.

[0027] Figure 8 This is a schematic diagram of the progressive processing and forming process in this invention.

[0028] Figure 9 This is a schematic diagram of the structure of the sheet metal after shaping in this invention.

[0029] Figure 10 This is a schematic diagram of the structure of the sheet metal and the mold clamping state in the second embodiment of the present invention.

[0030] Figure 11 This is a schematic diagram of the structure of the first type of tool head applying pressure to the sheet metal of the second embodiment in this invention and the springback after unloading.

[0031] Figure 12 This is a schematic diagram of the system structure for sheet metal forming processing using the first / second type of tool head in the second embodiment of the present invention.

[0032] Figure 13 This is a schematic diagram of the structure after a certain step in the progressive processing of the second embodiment of the present invention.

[0033] Figure 14 This is a partially enlarged schematic diagram of the sheet metal after shaping in the second embodiment of the present invention.

[0034] Figure 15 This is a schematic diagram of the overall structure of the sheet metal after shaping in the second embodiment of the present invention.

[0035] Figure 16 The stress relaxation curves of TC4 titanium alloy at different temperatures in this invention are shown.

[0036] Figure 17 The stress-strain curves of the TC4 titanium alloy in this invention at different temperatures are shown. Detailed Implementation

[0037] Example 1

[0038] This embodiment describes an electric field-assisted forming method for complex thin-walled components made of difficult-to-deform alloys. Taking TC4 titanium alloy as an example, with a thickness of 1.5 mm, the sheet metal 4 is processed into a shaped part through multiple processes using a tool head. During the forming process, electric assistance is used to locally heat the sheet metal. The specific steps are as follows:

[0039] Step 1: As Figure 1 As shown, the flat sheet 4 is suspended and clamped, and is kept pressed against the mold 3 below by the clamping device 5.

[0040] Step 2: As Figures 2 to 5 As shown, the first type of tool head 1 (pressure tool head) applies pressure locally to the sheet metal 4, causing the sheet metal 4 to undergo elastic deformation. For some high-strength alloy sheets that are difficult to deform, in order to reduce the load of elastic deformation caused by the downward pressure of the first type of tool head, electric heating at a lower temperature can also be used, according to... Figure 17The stress-strain curves of TC4 titanium alloy at different temperatures are shown. The pressure magnitude and pressure point location of the first type of tool head 1 are set. In this embodiment, the pressure magnitude is 300N. The sheet metal 4 undergoes elastic deformation to form an elastic deformation zone, which partially adheres to the mold 3. The distance between the pressure applied by the first type of tool head 1 and the point where the mold 3 and sheet metal 4 adhere is 22mm. Figure 5 As shown, by simultaneously applying pressure to the sheet metal 4 using multiple first-type tool heads 1, elastic deformation areas of different shapes will appear to adapt to the lower model surface, thereby accelerating the forming speed and improving the forming accuracy.

[0041] Step 3: As Figure 6 and Figure 7 As shown, the second type of tool head 2 (electric tool head) discharges electricity onto the portion of the sheet metal 4 that is in contact with the mold during elastic deformation, providing electrically assisted heating, according to... Figure 16 The stress relaxation curves of TC4 titanium alloy at different temperatures are shown. The moving speed and pressure of the second type of tool head 2 are set. In this embodiment, the stress relaxation curve at 720℃ is selected. The feed speeds along the X, Y, and Z axes are set to 200–3000 mm / min, moving along a circular trajectory along the X and Y axes with a radius range of 0–20 mm. The first type of tool head 1 is positioned 20 mm outside the second type of tool head 2, and maintains a horizontal distance of 22 mm from the edge of the mold. The temperature is controlled to rise to 720℃ (approximately 0.43T) in a very short time. m This forms a high-temperature zone; in the high-temperature zone, the sheet material 4 undergoes high-temperature stress relaxation, and the elastic deformation is converted into plastic deformation, changing from recoverable deformation to permanent deformation.

[0042] Step 4: As Figures 6 to 8 As shown, the temperature control device 6 includes a host computer, a temperature control unit, and an infrared thermal imager. The initial temperature is set in the host computer. The first type of tool head 1 and the second type of tool head 2 move along the preset trajectory. During the movement, in order to maintain a high stress relaxation temperature at the contact surface between the sheet material 4 and the mold 3, the infrared thermal imager needs to be set to monitor in real time. The temperature control unit controls the output current density of the power supply 7, thereby controlling the sheet material temperature. At the same time, the first type of tool head 1 and the second type of tool head 2 should move synchronously to complete the first preliminary forming of the sheet material.

[0043] Step 5: Change the feed rate of the first type of tool head 1 and the second type of tool head 2. Repeat steps 2 to 4 for the unformed parts of the sheet metal. Through multiple passes, the sheet metal is shaped to obtain complex thin-walled components, such as... Figure 9 As shown, after the sheet metal 4 is formed, the first type of tool head 1 and the second type of tool head 2 stop moving and the power supply stops. The sheet metal is formed into a frustum with a taper of 30°, a height of 20mm, and a top diameter of 30mm.

[0044] Example 2

[0045] This embodiment describes an electric field-assisted forming method for complex thin-walled components made of difficult-to-deform alloys. Taking TC4 titanium alloy as an example, with a thickness of 1.5 mm, a tapered plate 11 is machined into a formed part through multiple processes using a tool head. During the forming process, electric assistance is used to locally heat the plate. The specific steps are as follows:

[0046] Step 1: As Figure 10 As shown, the conical plate 11 is suspended and clamped, and is kept pressed against the second mold 10 by the second clamping device 12.

[0047] Step 2: As Figure 11 and Figure 12 As shown, the first type of tool head 1 (pressure tool head) applies pressure locally to the tapered sheet 11, causing the tapered sheet 11 to undergo elastic deformation, according to... Figure 17 The stress-strain curves of TC4 titanium alloy at different temperatures are shown. The pressure magnitude and pressure point position of the first type of tool head 1 are set. In this embodiment, the pressure magnitude is 300N. The tapered plate 11 elastically deforms to form an elastic deformation zone. The elastic deformation zone partially fits into the second mold 10. The position where the first type of tool head 1 applies pressure is 14mm away from the point where the second mold 10 fits into the plate 4.

[0048] Step 3: As Figure 13 As shown, the second type of tool head 2 (electric tool head) discharges electricity onto the portion of the tapered sheet 11 that is in contact with the mold in the elastic deformation zone, providing electrically assisted heating, according to... Figure 16 The stress relaxation curves of TC4 titanium alloy at different temperatures are shown. The moving speed and pressure of the second type of tool head 2 are set. In this embodiment, the stress relaxation curve at 720℃ is selected. The feed speeds along the X, Y, and Z axes are set to 200–3000 mm / min, moving along a circular trajectory along the X and Y axes. The first type of tool head 1 is positioned 14 mm horizontally from the edge of the mold. The temperature is controlled to rise to 720℃ (approximately 0.43T) in a very short time. m This forms a high-temperature zone; within the high-temperature zone, the conical plate 11 undergoes high-temperature stress relaxation, and the elastic deformation is converted into plastic deformation, changing from recoverable deformation to permanent deformation.

[0049] Step 4: As Figures 14 to 16As shown, the initial temperature is set in the host computer. The first type of tool head 1 and the second type of tool head 2 move along the preset trajectory. During the movement, in order to control the temperature of the contact surface between the conical sheet 11 and the second mold 10 to maintain a high stress relaxation temperature, an infrared thermal imager needs to be set up for real-time monitoring. The power supply output current density is controlled through the temperature control unit to control the sheet temperature. At the same time, the first type of tool head 1 and the second type of tool head 2 should move synchronously to complete the first preliminary forming of the conical sheet 11.

[0050] Step 5: Change the feed rate of the first type of tool head 1 and the second type of tool head 2. Repeat steps 2 to 4 for the unprocessed portion of the tapered sheet 11. Through multiple passes, the sheet is processed and shaped to obtain a complex thin-walled component, such as... Figure 17 As shown, the conical sheet 11 is formed, the first type of tool head 1 and the second type of tool head 2 stop moving and the power is stopped. The sheet is formed into a cone with a taper of 30° and a corrugated disc with a height of 15mm and a top diameter of 200mm.

Claims

1. An electric field-assisted forming method for complex thin-walled components made of difficult-to-deform alloys, characterized in that, Includes the following steps: Step 1: Clamp the sheet of the difficult-to-deform alloy to the lower die; Step 2: The first type of tool head applies pressure locally to the suspended area of ​​the sheet metal near the lower die at a preset distance, causing the sheet metal to undergo elastic deformation, forming an elastic deformation zone with a concave curved surface, and the elastic deformation zone partially fits the lower die. Step 3: The second type of tool head applies electrical-assisted stress relaxation to the part of the sheet metal that is in contact with the lower die in the elastic deformation zone, so that the sheet metal heats up rapidly and converts the elastic deformation into plastic deformation; Step 4: The first type of tool head and the second type of tool head move according to the preset processing trajectory to complete the first preliminary forming of the sheet metal; Step 5: Change the feed rate of the first type of tool head and the second type of tool head, and repeat steps 2 to 4 on the unformed part of the sheet metal to perform progressive processing and form a complex thin-walled component.

2. The electric field-assisted forming method according to claim 1, characterized in that, In step 2, several first-type tool heads simultaneously apply pressure to the local area of ​​the sheet metal, so that the concave curved surface forming the elastic deformation zone has different shapes to adapt to the lower model surface.

3. The electric field-assisted forming method according to claim 2, characterized in that, In step 2, the sheet material is locally heated at low temperature and pressure is applied using a first type of tool head.

4. The electric field-assisted forming method according to claim 3, characterized in that, The first type of tool head provides localized low-temperature heating to the sheet metal, ensuring that the highest local temperature reached by the sheet metal does not exceed 0.25T. m T m This is the melting point temperature of the sheet material.

5. The electric field-assisted forming method according to claim 4, characterized in that, The maximum temperature range that the sheet metal can reach is 0.4–0.5T. m .

6. The electric field-assisted forming method according to claim 5, characterized in that, The first type of tool head, sheet metal, mold, temperature control unit, and first power supply form the first circuit loop, and the second type of tool head, sheet metal, mold, temperature control unit, and second power supply form the second circuit loop.

7. The electric field-assisted forming method according to claim 6, characterized in that, In steps 2 and 3, the temperature of the sheet metal is obtained by an infrared thermal imager, and the output current density of the first power supply and the second power supply is controlled according to the obtained temperature, thereby controlling the temperature of the deformation area on the sheet metal.

8. The electric field-assisted forming method according to claim 7, characterized in that, The pressure applied to the sheet metal by the first type of tool head is calculated by the stress-strain curve at the processing temperature or obtained by finite element simulation; the position where the first type of tool head applies pressure to the sheet metal is determined by simulation calculation.

9. The electric field-assisted forming method according to claim 7, characterized in that, The heating temperature and pressure of the second type of tool head on the sheet are selected based on the sheet stress relaxation curve.

10. The electric field-assisted forming method according to claim 9, characterized in that, The processing position of the second type of tool head is 2-3mm away from the edge of the elastic deformation zone.

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