WO2019154000A1 - Method and apparatus for predicting metal sheet residual stress based on measurement of warpage amount caused by residual stress release - Google Patents

Abstract

A method for predicting the metal sheet residual stress based on measurement of the warpage amount caused by residual stress release, comprising: using one of the X-ray method, the blind hole method, the ultrasonic method, the crack compliance method or the finite element analysis method to perform residual stress measurement on sheets of different thicknesses; cutting a sample by machining, the residual stress release causing the sheets to warp, measuring the warpage amounts using a displacement sensor, so as to obtain the relationship, for the sheets of different thicknesses, between the residual stress and the warpage amount; obtaining a quadratic equation by means of curve fitting: y = ax2 + bx + c, where x - residual stress, y - warpage amount, and a, b and c represent the fitting coefficient; and on the basis of the established functional relationship between the residual stress and the warpage amount, measuring the warpage amount y at a specific linear cutting percentage, and calculating the residual stress according to formula (I). Also provided is an apparatus for measuring the metal slab deformation amount caused by residual stress release. The present invention can quickly evaluate the magnitude of the overall residual stress of the material, and the fluctuation of the residual stress between batches, facilitating to establish sheet residual stress control criteria.

Description

Method and device for predicting residual stress of sheet metal based on measurement of residual stress release warpage

This application is based on a Chinese patent application with the application number of 2011018139760.9, the application date is February 11, 2018, and the Chinese patent application with the application number of 201810132387.4 and the application date of February 09, 2018, and the Chinese patent application is required. Priority of the patent application, the entire contents of which is hereby incorporated by reference.

Technical field

The present invention relates to a method for predicting residual stress of a sheet metal based on measurement of residual stress release warpage and a device for measuring warpage of residual stress of sheet metal.

Background technique

Aluminum alloy thick plates are widely used in large equipment such as aerospace. In the production process of aerospace aluminum alloy thick plates, in order to improve the mechanical properties of the plates, solid solution, quenching and aging treatment processes are usually employed. During the quenching process, since the core is slower than the surface cooling, the surface of the aluminum alloy thick plate is subjected to compressive stress after quenching, and the core is tensile stress. The existence of residual stress causes the aluminum alloy thick plate to be deformed during machining into aerospace parts. Although the pre-stretching treatment after quenching can reduce the residual stress, the dimensional accuracy of the aerospace components is high, and the aluminum alloy thick plate is required. Residual stress control requirements are very demanding, and large residual stresses can easily lead to incomplete dimensional accuracy of components. Only by controlling the residual stress within a certain range of values can the deformation caused during the processing of the aluminum alloy thick plate be reduced to obtain qualified parts. The detection of residual stress in aluminum alloy slabs is a prerequisite for ensuring that the machining of aerospace components meets the deformation requirements.

Aluminum alloy thick plates such as 7050, 7075, and 7085 are widely used in aerospace and other large equipment due to their high specific strength and excellent mechanical properties. In the production process of aluminum alloy slabs, in order to improve the mechanical properties of the slabs, solid solution quenching and aging treatment are usually used. However, during the solution quenching process, the surface of the slabs and the core are not uniformly cooled, which makes the aluminum alloy slabs very high. The residual stress, because the core is slower than the surface cooling, the surface is compressive after the final quenching, the tensile stress of the core, and the existence of residual stress, so that the aluminum alloy thick plate is deformed during machining into aeronautical components, resulting in Component deformation is invalid. In order to reduce the residual stress of the aluminum alloy thick plate, after the solution hardening, the pre-stretching treatment is carried out, and the plastic tensile force generated by the pre-stretching process releases the residual stress portion, and the residual stress is controlled within a certain numerical range. In order to reduce the deformation caused by the processing of aluminum alloy thick plate, qualified parts can be produced.

However, the existing residual stress testing equipment is expensive, and the testing environment is demanding. It is not suitable for industrial aluminum alloy thick plates, especially 7050, 7075, 7085 and other aluminum alloy thick plates in quenched, pre-stretched and aged states. Under the residual stress detection, therefore, there is a need for a low-cost, high-precision test method and special equipment that can be applied to the industrial process of aluminum alloy thick plate production.

Summary of the invention

In order to solve the above technical problem: the present invention provides a method and apparatus for predicting residual stress of a metal sheet based on measurement of residual stress release warpage, and the present invention is suitable for effective characterization of residual stress in industrial production of aerospace aluminum alloy thick plates. The device for measuring the residual stress release deformation of the metal thick plate is used for detecting special equipment for measuring the wire cutting deformation in the quenched state, the pre-stretched state and the aging state of the aluminum alloy thick plate such as 7050, 7075, 7085, thereby obtaining aluminum Residual stress level of alloy sheet.

The invention is achieved by the following technical solutions:

A method for predicting residual stress of a sheet metal based on a residual stress release warpage amount, the method comprising:

(1) Residual stress test of plates of different thicknesses by using one of X-ray method, blind hole method, ultrasonic method, crack compliance method or finite element analysis method;

(2) Using the machining method to cut the specimen along the thickness direction, the residual stress is released to cause the warpage of the sheet, and the warping amount is tested by the displacement sensor, and the relationship between the residual stress and the warpage of the sheet with different thickness is obtained; Sub-equation: y=ax ² +bx+c, where x-residual stress, y-warpage amount, a, b, c- are fitting coefficients;

(3) Based on the established residual stress as a function of the amount of warpage, the metal sheet is cut to test the warpage amount y at a specific line cutting percentage, according to the formula

Calculate the residual stress.

According to the above method, in the step (2), the machining method preferentially employs the wire cutting method.

According to the above method, in the step (2), the cutting of the sample is to fix one end of the metal plate, the length of the fixed portion is less than 1/2 of the length of the sample, and the wire cutting position is preferably selected at a length of 1/2 of the sample. And cut along the thickness of the board.

According to the above method, in the step (2), the measurement of the amount of warpage is performed at one end away from the chucking portion.

According to the above method, the percentage of the specific line cut in the step (3) is the percentage of the line cut controlled at a position where the amount of warpage tends to be gentle.

According to the above method, the cutting depth in the step (3) is 62.5% to 75% of the plate thickness, and the recommended cutting depth is 75% to 95% of the plate thickness, and the recommended cutting depth is 50% to 62.5%. Finally, the recommended cutting depth is 30% to 50% of the thickness;

According to the above method, the predicted residual stress is the residual stress of the metal sheet.

A device for measuring residual stress release deformation of a metal slab, the device comprising a clamping device, the clamping device comprising a base, a fixing rod, a displacement testing seat, and a displacement testing device; the base comprises a first bottom plate, two a vertical baffle, a connecting plate and a pressure plate, wherein the two ends of the first bottom plate are respectively fixedly connected with a vertical baffle, and the two vertical baffles are respectively provided with bolt holes, and the first bottom plate is The side edges are fixedly connected to one end of the connecting plate to form a "T" shape, the pressing plate is located above the two vertical baffles, and the pressing plate is provided with a through hole corresponding to the position of the bolt holes of the two vertical baffles. The pressure plate is connected to the two vertical baffles by bolts; the lower end of the fixing rod is fixedly connected with the other end of the connecting plate; one end of the displacement test seat is sleeved outside the fixing rod, and the other end of the displacement test seat is The lower end of the dial gauge is connected.

According to the above apparatus, the apparatus further includes a deformation testing platform, the deformation testing platform includes a second bottom plate, a fixing plate, a first clamping block and a second clamping block; the lower end of the fixing plate is fixed to one end of the second bottom plate Connecting, a fixing hole is formed on a surface of the fixing plate; one end of the first clamping block is fixedly connected to one end of the fixing plate surface, and a lower end of the first clamping block is fixedly connected with the second bottom plate; The second clamping block is opposite to the first clamping block, and one end of the second clamping block is provided with a bolt hole corresponding to the position of the fixing plate connecting hole, and the second clamping block is provided with one end of the bolt hole and the fixing plate surface. Connected by bolts, and the lower end of the second clamping block is fixedly connected with the second bottom plate; the clamping device is located above the second bottom plate, and one end of the clamping device base is located at the first clamping block and the second clamping frame Between blocks.

According to the above apparatus, the displacement test socket includes a support plate, both ends of the support plate are provided with through holes, and a lower end of the displacement test device is inserted into a through hole at one end of the support plate; the fixing rod is inserted into the support plate In the through hole at the other end.

According to the above device, the through holes at the two ends of the support plate are bolt holes, the lower end of the displacement test device is threaded, and the lower end of the displacement test device is screwed into the bolt hole at one end of the support plate to be connected with the support plate;

The fixing rod is threaded, and the fixing rod is screwed into the bolt hole at the other end of the supporting plate to be connected with the supporting plate.

According to the above apparatus, the displacement test socket includes a first chuck and a second chuck that are connected to each other, the first chuck is clamped to a lower portion of the displacement testing device, and the second chuck is clamped to the fixed rod on.

According to the above apparatus, the displacement test device employs a dial gauge.

According to the above device, the vertical baffle is provided with two bolt holes.

According to the above device, the connecting plate is an elongated plate, and the upper plate surface of the elongated plate is stepped.

The beneficial technical effect of the invention is that the method establishes the relationship between the residual stress and the amount of warpage by accumulating a large amount of experimental data, and the residual stress level can be evaluated only by measuring the amount of warpage of the sample. The method is simple, intuitive and has high measurement efficiency and is suitable for the detection of industrial production processes. The invention provides a device for measuring residual stress release deformation of a metal thick plate, by which the residual stress inside the material and the fluctuation of residual stress between different batches of plates can be quickly evaluated, thereby realizing the residual stress of the plate. Effective monitoring helps to establish the residual stress control standard of the sheet and improve the uniformity of the residual stress of the sheet. The method and equipment are not only suitable for the residual stress test of the sheet metal, but also can be applied to the testing of the structure of the profile, the pipe, the bar and the like.

DRAWINGS

1 is a schematic view showing a wire cutting process of an aluminum alloy thick plate according to an embodiment of the present invention;

2 is a schematic view showing a thickness distribution of residual stress of an aluminum alloy thick plate according to an embodiment of the present invention;

3 is a schematic view showing a warpage displacement of a percentage of different wire cutting depths of an aluminum alloy thick plate according to an embodiment of the present invention;

4 is a schematic view showing prediction of residual stress of aluminum alloy thick plates under different thicknesses and warpages according to an embodiment of the present invention;

5 is a schematic structural view of an apparatus for measuring a residual stress release warpage of a metal thick plate according to an embodiment of the present invention;

6 is a side view of an apparatus for measuring a residual stress release warpage of a metal plate according to an embodiment of the present invention;

FIG. 7 is a schematic structural view of a device for measuring a residual stress release warpage of a metal thick plate according to an embodiment of the present invention;

FIG. 8 is another schematic structural view of an apparatus for measuring a residual stress release warpage of a metal plate according to an embodiment of the present invention.

Wherein, the base-1; the fixed rod-2; the displacement test seat-3; the displacement test device-4; the first bottom plate-5; the two vertical baffles-6, 6'; the connecting plate-7; the pressing plate-8; First collet-9; second collet-10; second bottom plate-11; fixed plate-12; first clamping block-13; second clamping block-14; sample to be tested-15; linear cutting machine- 16; bolt -17; bolt -18.

Detailed ways

The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

Embodiments of the present invention provide a method for measuring residual stress of a metal sheet based on a residual stress release warpage amount, including the following steps:

(1) Residual stress measurement of aluminum alloy plates of different thicknesses is carried out by one of X-ray method, blind hole method, ultrasonic method, crack compliance method or finite element analysis method. The residual stress distribution of aluminum alloy thick plates is shown in Fig. 2 is shown.

(2) Fix one end of the aluminum alloy thick plate, as shown in the section line of Figure 1, the length of the fixed part is less than 1/2 of the length of the sample, and then place a displacement sensor such as a dial gauge or laser sensor on the sample to be tested. At the point a of the center of one end edge, the initial value is recorded, and at the length of the sample 1/2, the wire cutter is used to perform line cutting along the plate thickness. According to the bending depth displacement of the aluminum alloy thick plate according to the percentage of the line cutting depth percentage, as shown in Fig. 3, the percentage depth when the warpage amount tends to be gentle is taken as the percentage of the wire cutting; the cutting depth is preferably 62.5% to 75% of the plate thickness. ; Record the value of point a after cutting; the amount of change in the value of point a is the amount of warpage of the sheet.

(3) Measuring the amount of warpage of plates of different thicknesses, and obtaining the relationship between residual stress and warpage; obtaining a quadratic equation by fitting the curve: y=ax ² +bx+c, where x-residual stress, y-warping The quantities, a, b, c- are the fitting coefficients.

(4) Based on the established residual stress as a function of the amount of warpage, the sheet metal is cut by measuring the amount of warpage y at a specific line cutting percentage, according to the formula

The residual stress is calculated, as shown in Fig. 4, and the distribution of residual stress under different plate thickness and warpage can be obtained.

As shown in FIG. 5-8, a device for measuring residual stress release deformation of a metal thick plate includes a clamping device including a base 1, a fixing rod 2, a displacement test seat 3, a displacement testing device 4, and a base The first bottom plate 5, the two vertical baffles 6, 6', the connecting plate 7, the pressing plate 8, the first bottom plate is a horizontally arranged rectangular plate, the two vertical baffles are vertical rectangular plates, and one end of the first bottom plate The first baffle is fixedly connected to the vertical baffle 6 , and the other end of the first bottom plate is fixedly connected with the vertical baffle 6 ′, and the two vertical baffles are respectively provided with bolt holes, one side of the first bottom plate and one end of the connecting plate The first bottom plate and the connecting plate form a "T"-shaped structure, the connecting plate is a long strip-shaped plate, the upper plate surface of the long-shaped plate is stepped, and the other end of the connecting plate has a connecting hole, and the pressing plate is a rectangular plate The pressure plate is located on the upper surface of the two vertical baffles, and the pressure plate is provided with a through hole corresponding to the position of the bolt holes of the two vertical baffles. The pressure plate and the two vertical baffles are connected by bolts 17. The bolts are preferably hexagonal screws, connecting plates It is also possible to use a spacer to pad the sample to be tested, etc., to avoid the pressing force of the pressing plate. Resulting in additional deformation of the sample to be tested; the fixing rod is preferably a cylindrical rod, and the lower end of the fixing rod is inserted into the connecting hole of the connecting plate and fixedly connected with the other end of the connecting plate; one end of the displacement test seat is sleeved outside the fixing rod, and the displacement test seat is The other end is connected to the lower end of the displacement test device. Specifically, the displacement test seat has a structure: the displacement test seat includes a support plate, and both ends of the support plate are provided with through holes, and the lower end of the displacement test device is inserted into one end of the support plate. In the hole, the fixing rod is inserted into the through hole at the other end of the supporting plate; preferably, the through hole at both ends of the supporting plate is a bolt hole, the lower end of the displacement testing device is threaded, and the lower end of the displacement testing device is screwed into the bolt hole at one end of the supporting plate. Connected to the support plate; the fixing rod is threaded, and the fixing rod is screwed into the bolt hole at the other end of the support plate to be connected with the support plate.

Another structure of the displacement test socket: the displacement test socket comprises a first collet 9 and a second collet 10 connected to each other, the grip ends of the two collets are facing outward, and the first collet is clamped in the displacement test device In the lower part, the second chuck is clamped on the fixing rod, and the ends of the two chucks are fastened by fastening bolts 18. The displacement test device can be used with any other contact type, non-contact displacement test device, preferably a dial gauge.

The device further includes a deformation test platform including a second bottom plate 11, a fixed plate 12, a first clamping block 13 and a second clamping block 14; the second bottom plate is a horizontal rectangular plate, and the fixing plate is a vertical rectangular plate. The lower end of the fixing plate is fixedly connected with one end of the upper surface of the second bottom plate, and a plurality of connecting holes are formed on the surface of the fixing plate; the first clamping block and the second clamping block are vertical plates, and one end of the first clamping block Fixedly connected to one end of the fixed plate surface, and the lower end of the first clamping block is fixedly connected with the upper surface of the second bottom plate; the second clamping block is opposite to the first clamping block, and one end of the second clamping block is provided with the fixing plate a bolt hole corresponding to the position of the connecting hole, one end of the second clamping block provided with the bolt hole is bolted to the fixing plate surface, and the lower end of the second clamping block is fixedly connected with the upper plate surface of the second bottom plate; the clamping device is located at the The upper surface of the second bottom plate, and one end of the base of the clamping device is located between the first clamping block and the second clamping block.

In use, the sample to be tested 15 is placed in the base of the clamping device, and the connecting bolts of the pressing plate and the two vertical baffles are tightened, and the sample to be tested is fixed in the base of the clamping device, and the displacement test seat is adjusted. The position of the dial gauge is adjusted so that the measuring head of the dial gauge contacts the surface of the sample to be tested, and the measuring head is slightly pressed down by 1-3 mm, and then the clamping device is placed flat on the second bottom plate of the deformation testing platform. Upper end of the clamping device base is located between the first clamping block and the second clamping block, and the position of the second clamping block is adjusted to clamp the device. Then, the test sample is cut by the linear cutting machine 16. Since the residual stress of the sample to be tested (quenched state, pre-stretched state, aging state) is the surface compressive stress and the state of the tensile stress state of the core, the sample to be tested is first One side of the cutting is bent, and the bending deformation touches the dial gauge. By calculating the difference between the dial gauge readings before and after the wire cutting, the deformation amount of the sample to be tested at a certain cutting depth is obtained, and the deformation amount according to the cutting depth of the same line is obtained. Difference, judge the overall level of residual stress inside the aluminum alloy thick plate.

The materials that can be tested in this device are all kinds of plates, belts, extruded materials, and pipe-like structures, and are not limited to specific sizes. The test material is any material that can be removed with low external force and is not limited to specific metal materials and non-metal materials. Residual stress release method, using low external force to remove materials, including wire cutting, electric spark.

The above description is only one of the embodiments of the present invention, and is not limited to the invention. It should be noted that those skilled in the art can make other equivalent improvements under the technical suggestion provided by the present invention, or can be directly applied to other occasions without improvement, and can achieve the object of the present invention. It should be considered as the scope of protection of the present invention.

Claims (18)

1. A method for predicting residual stress of a sheet metal based on residual stress release warpage, characterized in that the method comprises:

   (1) Residual stress test of plates of different thicknesses by using one of X-ray method, blind hole method, ultrasonic method, crack compliance method or finite element analysis method;

   (2) Using the machining method to cut the specimen along the thickness direction, the residual stress is released to cause the warpage of the sheet, and the warping amount is tested by the displacement sensor, and the relationship between the residual stress and the warpage of the sheet with different thickness is obtained; Sub-equation: y=ax ² +bx+c, where x-residual stress, y-warpage amount, a, b, c- are fitting coefficients;

   (3) Based on the established residual stress as a function of the amount of warpage, the metal sheet is cut to test the warpage amount y at a specific line cutting percentage, according to the formula

   

   Calculate the residual stress.
2. The method according to claim 1, characterized in that in the step (2), the machining method preferentially employs a wire cutting method.
3. The method according to claim 1, wherein in the step (2), the cutting of the sample is to fix one end of the metal plate, and the length of the fixing portion is less than 1/2 of the length of the sample, and the cutting position is preferentially selected. The length of the sample is 1/2 and cut along the thickness direction.
4. The method according to claim 1, wherein in said step (2), the measurement of the amount of warpage is performed at one end away from the chucking portion.
5. The method according to claim 1, wherein said specific line cutting percentage in said step (3) is controlled at a position where the amount of warpage tends to be gentle.
6. The method according to claim 1, wherein the sample is cut to a depth of 62.5% to 75% of the sheet thickness in the step (2).
7. The method according to claim 1, wherein the sample is cut to a depth of from 75% to 95% of the thickness of the sheet in the step (2).
8. The method according to claim 1, wherein in the step (2), the sample is cut to a depth of 50% to 62.5% of the sheet thickness.
9. The method according to claim 1, wherein the sample is cut to a depth of 30% to 50% of the sheet thickness in the step (2).
10. The method of claim 1 wherein the predicted residual stress is a residual stress of the sheet metal.
11. A device for measuring a residual stress release deformation of a metal slab, wherein the device comprises a clamping device, the clamping device comprising a base, a fixing rod, a displacement testing seat, and a displacement testing device; a bottom plate, two vertical baffles, a connecting plate, and a pressure plate, wherein two ends of the first bottom plate are respectively fixedly connected with a vertical baffle, and the two vertical baffles are respectively provided with bolt holes, One side of one bottom plate is fixedly connected with one end of the connecting plate to form a "T" shape, the pressing plate is located above the two vertical baffles, and the pressing plate is provided with the position of the bolt holes of the two vertical baffles The through hole is connected to the two vertical baffles by bolts; the lower end of the fixing rod is fixedly connected with the other end of the connecting plate; one end of the displacement test seat is sleeved outside the fixing rod, and the displacement test seat The other end is connected to the lower end of the dial gauge.
12. The device according to the above, characterized in that the device further comprises a deformation test platform, the deformation test platform comprising a second bottom plate, a fixed plate, a first clamping block and a second clamping block; the lower end of the fixing plate and the second One end of the bottom plate is fixedly connected, and a fixing hole is formed on the surface of the fixing plate; one end of the first clamping block is fixedly connected to one end of the fixing plate surface, and the lower end of the first clamping block and the second bottom plate The second clamping block is opposite to the first clamping block, and one end of the second clamping block is provided with a bolt hole corresponding to the position of the fixing plate connecting hole, and the second clamping block is provided with one end of the bolt hole The fixing plate surface is connected by bolts, and the lower end of the second clamping block is fixedly connected with the second bottom plate; the clamping device is located above the second bottom plate, and one end of the clamping device base is located at the first clamping block Between the second clamp and the second clamp.
13. The device according to claim 11, wherein the displacement test seat comprises a support plate, both ends of the support plate are provided with through holes, and a lower end of the displacement test device is inserted into a through hole at one end of the support plate. The fixing rod is inserted into the through hole at the other end of the support plate.
14. The device according to claim 13, wherein the through hole at both ends of the support plate is a bolt hole, the lower end of the displacement test device is threaded, and the lower end of the displacement test device is screwed into the end of the support plate. The hole is connected to the support plate; the fixing rod is threaded, and the fixing rod is screwed into the bolt hole at the other end of the support plate to be connected with the support plate.
15. The apparatus according to claim 11, wherein said displacement test socket comprises a first collet and a second collet connected to each other, said first collet being clamped at a lower portion of said displacement testing device, said The second chuck is clamped on the fixed rod.
16. The apparatus according to claim 11, wherein said displacement testing means employs a dial gauge.
17. The apparatus according to claim 11 wherein said vertical baffle has two bolt holes therein.
18. The device according to claim 11, wherein the connecting plate is an elongated plate, and the upper plate surface of the elongated plate is stepped.

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