Method for evaluating friction in forming and damage after forming of multi-layer composite board
By making standard samples and using bending molds to simulate the forming strain state of the composite plate, combined with quick change structure adjustment probe, non-destructive detection of friction and damage of multi-layer composite plates is achieved, and friction evaluation and damage detection problems in the actual forming strain state cannot be simulated in the prior art.
Patent Information
- Application Number
- CN202510294854.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-13
- Publication Date
- 2025-07-25
AI Technical Summary
The prior art is difficult to simulate the actual strain state for friction evaluation during the forming process of multi-layer composite panels, and it is difficult to detect coating damage after forming non-destructively.
By making standard samples, the strain state of composite plate multi-station forming is simulated by using a bending mold, combined with the quick-change structure adjustment probe, friction coefficient testing and damage characterization are performed to avoid direct use of formed components for destructive experiments.
It realizes the acquisition of data of multiple strain areas simultaneously on the same set of devices, realizes the joint characterization of friction and damage, and solves the problem of friction evaluation and non-destructive detection of coating damage in the actual forming strain state in the prior art.
Smart Images
Figure CN120369600A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a technology in the field of sheet metal forming, specifically a method for evaluating friction and post-forming damage in the forming of multi-layer composite sheets. Background Art
[0002] The forming quality of multi-layer composite sheets (especially coated composite sheets) directly affects the service performance of their composite sheet components. The friction conditions between the sheet material and the die during the forming process and the damage condition of the surface coating of the sheet material after forming affect the forming quality of the composite sheet. Therefore, it is urgent to develop efficient evaluation technologies. For the forming of composite sheets, especially for the friction conditions during multi-step forming processes, the existing publicly available testing technologies lack testing means and mostly perform characterization tests on the original sheet material. Even if the deformed sheet material is used for substitutional characterization, it is difficult to simulate the strain state during sheet metal forming. For the damage condition of the surface coating of the sheet material after forming, the visual method cannot observe invisible damage, such as the weakening of the bonding between the coating or surface layer material and other layer materials; while the conventional bonding force testing method, which belongs to post-detection, requires damaging the formed component and is generally not suitable for use. Summary of the Invention
[0003] In view of the above deficiencies in the prior art, the present invention proposes a method for evaluating friction and post-forming damage in the forming of multi-layer composite sheets. By fabricating standard specimens and using different degrees of bending of the composite sheet to simulate the strain states of different parts of the intermediate workpiece at different stations during the multi-station forming of the composite sheet, the friction coefficient is tested under the determined strain state, overcoming the deficiency of using the original sheet material for characterization testing; on the same set of devices, the probe is adjusted using a quick-change structure, and the damage condition is characterized by the moving resistance of the probe. This method avoids directly using the formed composite sheet component for destructive experiments, can obtain data of multiple strain regions simultaneously on the same set of devices, and realizes the joint characterization of friction and damage, effectively solving the technical problems in the prior art of being unable to simulate the friction evaluation under the actual forming strain state and the difficulty of non-destructively detecting coating damage.
[0004] The present invention is realized through the following technical solutions:
[0005] The present invention provides a method for evaluating friction and post-forming damage during the forming of the surface material of a composite sheet, including:
[0006] Step 1) Preparation of the composite sheet to be tested: Cut the composite sheet to be tested into rectangular thin plates, and evenly distribute and paste strain gauges on the front surface of the test workpiece along the axis on the opposite side of the long side to form a test workpiece;
[0007] Step 2) Real-time adjustment of the strain state of the composite sheet: Use a bending forming die to deform the test workpiece, place the front surface of the test workpiece facing the concave die, and make the pressure head contact the back surface of the test workpiece and press down until the workpiece protrudes into an arc surface.
[0008] The strain gauge measures the strain magnitude at each monitoring point on the protruding arc surface of the workpiece in real time during the pressing process of the indenter until the deformation reaches the corresponding representative strain and then stops. The indenter stops without being withdrawn to provide support for the friction test of the workpiece.
[0009] The bending forming die described above includes: an indenter, a female die arranged oppositely, and a blank holder arranged around the indenter. Among them: the contact surface between the lower end of the indenter and the reverse side of the test workpiece is an arc surface, and the cross-sectional shape dimensions at various positions along the arc length direction are the same. After the indenter presses the test workpiece downward for bending deformation, on the protruding curved surface of the test workpiece, at the same monitoring point on the curved surface, the equivalent strain in the length direction is the same; the press applies pressure downward and transmits it to the blank holder through a spring to achieve blank holding of the test workpiece, control the flow of the material on the outer side of the test workpiece, and make the bending deformation occur only at the central curved surface.
[0010] The intermediate forming dimension of the female die is matched with the forming dimension of the indenter.
[0011] The fitting clearance between the forming dimension of the female die and the forming dimension is the thickness of the test workpiece.
[0012] The lower end opening of the female die is used to place the friction test mechanism.
[0013] Step 3) Friction condition test: Using the friction test mechanism, according to the strain distribution on the curved surface of the test workpiece after stamping deformation, set the position of the probe, the hydraulic load, and the movement speed of the probe, and conduct a linear friction test on the test workpiece to measure the shear force F τ and the vertical stress F, combined with the surface slope k, according to the formula Calculate the normal stress F received by the test workpiece at the corresponding monitoring point N , combined with the shear force F τ The friction coefficient can be calculated where: L is the radius of the monitoring point.
[0014] The friction test mechanism described above includes: a probe arranged in the friction position adjusting device, and a driving device horizontally connected and a hydraulic device vertically connected to the friction position adjusting device respectively. The top of the probe contacts the corresponding strain monitoring point on the reverse side of the test workpiece.
[0015] The friction position adjusting device includes: a grooved semi-circular seat, a fixing bolt horizontally and vertically arranged in it respectively, and a probe. The probe is arranged at the head of the bolt, and the nut is screwed at the bolt outside the groove of the semi-circular seat. By adjusting the tightening position, the position of the bolt head is moved, so as to adjust the monitoring point where the probe is located. This monitoring point is determined according to the distribution of the stamping strain degree of the test workpiece.
[0016] The described driving device includes: a push rod motor, a number of strain gauges arranged on the bottom surface of the workpiece, a force measuring sensor, a sliding table and a guide rail. The bottom of the guide rail is connected to a hydraulic device. The sliding table is movably arranged on the guide rail and connected to the push rod motor. The force measuring sensor is respectively connected to the strain gauges and the push rod motor. The force measuring sensor measures the shear force during the friction test through the strain gauges.
[0017] Step 4) Forming damage test: Using a friction test mechanism, after the friction test, replace the probe in the friction position adjusting device, increase the hydraulic load, perform linear progressive friction on the test workpiece, measure the shear force Fτ, and judge the damage degree by comparing the change range of the shear force during the linear sliding process. Description of the Drawings
[0001] Figure 1 It is a schematic diagram of the main forming part device for bending deformation and the preparation of the test workpiece;
[0002] Figure 2 It is a schematic diagram of the overall friction test device and a schematic diagram for calculating the surface slope of the test workpiece;
[0003] Figure 3 It is a schematic diagram of the friction position adjusting device;
[0004] Figure 4 It is a schematic diagram of the friction driving device. Detailed Embodiment
[0005] A method for evaluating friction during the forming process and damage after forming of the surface material of a composite board according to this embodiment includes:
[0006] Step 1) Preparation of the composite board to be tested: Select an aluminum plate with surface phosphating treatment as the implementation part, cut it into a rectangular thin plate with a length / width / thickness of 100 mm / 100 mm / 2 mm respectively to form a test workpiece 109. On its front surface, evenly distributed strain gauges 112 are pasted along the axis on the opposite side of the long side, as shown on the right side; Figure 1 as shown on the right side;
[0007] Step 2) Adjust the strain state of the composite board (in real time): Use the bending forming die shown on the left side to deform the test workpiece. The front surface of the test workpiece 109 is placed facing the concave die 107, and the pressing head 111 contacts the back surface of the test workpiece 109 and presses it down to the protruding arc surface of the workpiece 109. Figure 1 as shown on the left side;
[0008] The strain gauge 112 measures the strain at each radius of the protruding arc surface of the workpiece 109 in real time during the downward pressing process of the indenter 111 until it is pressed down by 7 mm. At this time, at the radius monitoring points 1 / L2 / L3 of 9 mm / 11 mm / 13 mm respectively, the deformation strains are 4% / 6% / 8%. The indenter 111 stops without being withdrawn to provide support for the friction test of the workpiece 109.
[0009] The bending forming die described above includes: an indenter 111, a female die 107 arranged oppositely, and a blank holder 105 arranged around the indenter. Among them: the contact surface at the lower end of the indenter 111 and the reverse side of the test workpiece 109 is an arc surface, and the circular arc radius R is 25 mm. After the indenter 111 presses the test workpiece 109 downward to cause bending deformation, on the convex curved surface of the test workpiece 109, at the monitoring point radii L1 / L2 / L3 of 9 mm / 11 mm / 13 mm, the equivalent strains in the length direction are the same, which are 4% / 6% / 8% respectively; the press applies downward pressure to the blank holder 105 to realize the blank holding of the test workpiece 109 and control the flow of the material on the outside of the test workpiece 109, so that the bending deformation only occurs at the central curved surface.
[0010] The intermediate forming size of the female die 107 is matched with the forming size of the indenter 111. Specifically: the fitting clearance is the thickness of the test workpiece 109.
[0011] The lower end of the female die 107 is open for placing the friction test mechanism.
[0012] Step 3) Friction condition test: Using the friction test mechanism, according to the strain distribution on the curved surface of the test workpiece 109 after bending deformation, set the radii L1 / L2 / L3 of the probe monitoring points to 9 mm / 11 mm / 13 mm respectively, the hydraulic load to 5 N, and the probe speed to 1 mm / s, and conduct a linear friction test on the test workpiece 109 to measure the combined shear force F τ and the vertical stress F. According to Figure 2 The right-side schematic diagram and the calculation formula Calculate that the surface slopes k1 / k2 / k3 are 0.386 / 0.490 / 0.609 respectively, so as to calculate the normal stress and the friction coefficient where: L is the radius of the monitoring point.
[0013] As shown in Table 1, it can be seen that there are obvious differences in the friction coefficients corresponding to the phosphatized coated aluminum sheet at different strains.
[0014] Table 1 Strain (%) μ Bonding force (N) 4 0.122 5.1 6 0.131 12.3 8 0.146 19.5
[0015] As Figure 2As shown on the left side, the friction test mechanism includes: a indenter 111 for maintaining the stress state of the test workpiece, a probe 210 arranged in the friction position adjusting device, a friction position adjusting device 220, a friction test driving device 240, and a vertically connected hydraulic device 230, where: the top of the probe 210 contacts the corresponding strain radius on the opposite side of the test workpiece 109, and the probe 210 is arranged at the head of the friction position adjusting device 220.
[0016] As Figure 3 shown, the friction position adjusting device 220 includes: a grooved semi-circular seat 221, a fixing bolt 222 and a probe 210 respectively arranged horizontally and vertically therein. The probe 210 is arranged at the head of the bolt 222, and a nut 223 is screwed at the bolt 222 outside the semi-circular seat groove 221. By adjusting the tightening position, the position of the head of the bolt 222 is moved, thereby adjusting the position of the probe 210. This position is determined according to the distribution of the stamping strain degree of the test workpiece 109.
[0017] The hydraulic device 230 is provided with a force measuring sensor, which can measure the vertical stress F during the friction process in real time.
[0018] As Figure 4 shown, the driving device includes: a push rod motor 244, a force measuring sensor 243, a sliding table 241 and a guide rail 242, where: the bottom of the guide rail 242 is connected to the hydraulic device 230, the sliding table 241 is arranged on the guide rail 242, and is connected to the push rod motor 244 through the force measuring sensor 243. The force measuring sensor 243 measures and calculates the shear force F during the friction test process through strain measuring chips τ .
[0019] Step 4) Forming damage test: Using the friction test mechanism, after the friction test, replace the probe 210 in the friction position adjusting device 220, increase the hydraulic load to 30N, perform linear progressive friction on the test workpiece, and measure the combined shear force F τ , and compare the change range of the combined force during the linear sliding process to judge the damage degree.
[0020] As shown in Table 1, it can be seen that there are obvious differences in the damage conditions of the aluminum plates with phosphating coatings under different strains.
[0021] Compared with the prior art, this method realizes non-destructive detection of the surface damage of the composite plate by simulating with standard specimens instead of directly damaging the formed components. At the same time, by using a press-bending forming die to simulate the actual strain state, it solves the problem that the prior art cannot evaluate the friction performance under real stress conditions. Through the friction position adjusting device, data of multiple strain regions can be obtained on the same specimen, and the friction test and damage assessment are integrated in the same test process, providing a more comprehensive evaluation of material properties.
[0022] The above specific embodiments can be locally adjusted in different ways by those skilled in the art without departing from the principles and purposes of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above specific embodiments. All implementation solutions within its scope are subject to the present invention.
Claims
1. A method for evaluating friction during the forming of the surface material of a composite board and damage after forming, characterized in that, Including: Step 1) Preparation of the composite sheet to be measured: Cut the composite sheet to be measured into rectangular thin sheets, and paste strain gauges evenly distributed along the front surface of the long-side opposite axis on the front surface of the test workpiece to form a test workpiece. Step 2) Real-time adjustment of the strain state of the composite sheet: Use a bending and forming die to deform the test workpiece. Place the front surface of the test workpiece facing the concave die, and the punch contacts the back surface of the test workpiece and presses down until the workpiece protrudes into an arc surface. Step 3) Friction condition test: Using a friction test mechanism, according to the surface strain distribution of the test workpiece after stamping deformation, set the probe position, hydraulic load, and probe movement speed, and conduct a linear friction test on the test workpiece to measure the shear force F τ and the vertical stress F. Combining with the surface slope k, according to the formula calculate the normal stress F received by the test workpiece at the corresponding monitoring point N , combining with the shear force F τ to calculate the friction coefficient where: L is the radius of the monitoring point; Step 4) Forming damage test: Use a friction test mechanism. After the friction test, replace the probe in the friction position adjustment device, increase the hydraulic load, perform linear progressive friction on the test workpiece, measure the shear force Fτ, and judge the damage degree by comparing the change range of the shear force during the linear sliding process. The strain gauges measure the strain magnitudes at each monitoring point on the protruding arc surface of the workpiece in real time during the downward pressing of the punch until the deformation reaches the corresponding representative strain and then stops. The punch stops without being withdrawn to provide support for the friction test of the test workpiece.
2. The method for evaluating friction during the forming of the surface material of the composite board and damage after forming according to claim 1, characterized in that, The bending and forming die includes: a punch, a concave die arranged oppositely, and a blank holder arranged around the punch. Among them: the contact surface between the lower end of the punch and the back surface of the test workpiece is an arc surface, and the cross-sectional shape and size are the same at each point along the arc length direction. After the punch presses down to bend the test workpiece, on the protruding curved surface of the test workpiece, along the same monitoring point on the curved surface, the equivalent strain in the length direction is the same; the press applies pressure downward and transfers it to the blank holder through a spring to achieve blank holding of the test workpiece and control the flow of the material on the outer side of the test workpiece, so that the bending deformation only occurs at the central curved surface.
3. The method for evaluating friction during the forming of the surface material of the composite board and damage after forming according to claim 2, characterized in that The intermediate forming size of the concave die is matched with the forming size of the punch. Specifically: the fitting clearance is the thickness of the test workpiece.
4. The method for evaluating friction during the forming of the surface material of the composite board and damage after forming according to claim 2 or 3, characterized in that, The lower end of the concave die is open for placing the friction test mechanism.
5. The method for evaluating friction during the forming of the surface material of the composite board and damage after forming according to claim 1, characterized in that, The friction test mechanism includes: a punch for maintaining the stress state of the test workpiece, a probe arranged in the friction position adjustment device, a friction position adjustment device, a friction test driving device, and a vertically connected hydraulic device. Among them: the top of the probe contacts the back surface of the test workpiece at the corresponding strain radius, and the probe is arranged at the head of the friction position adjustment device.
6. The method for evaluating friction during the forming of the surface material of the composite board and damage after forming according to claim 5, characterized in that, The friction position adjustment device includes: a grooved semi-circular seat, a fixing bolt and a probe respectively arranged horizontally and vertically therein. The probe is arranged at the head of the bolt, and the nut is screwed on the bolt outside the groove of the semi-circular seat. By adjusting the tightening position, the position of the bolt head is moved, so as to adjust the monitoring point where the probe is located, and this monitoring point is determined according to the distribution of the stamping strain degree of the test workpiece.
7. The method for evaluating friction during the forming of the surface material of the composite board and damage after forming according to claim 5, characterized in that The friction test driving device includes: a push rod motor, several strain measurement pieces arranged on the bottom surface of the workpiece, a force measuring sensor, a sliding table and a guide rail. The bottom of the guide rail is connected to the hydraulic device, the sliding table is movably arranged on the guide rail and is connected to the push rod motor, and the force measuring sensor is respectively connected to the strain measurement pieces and the push rod motor. The force measuring sensor measures the shear force during the friction test through the strain measurement pieces.
8. The method for evaluating friction during the forming of the surface material of the composite board and damage after forming according to claim 5, characterized in that, A force measuring sensor is arranged inside the hydraulic device, which can measure the vertical stress F during the friction process in real time.