CN112082679A - Residual stress measuring method based on femtosecond laser processing - Google Patents
Residual stress measuring method based on femtosecond laser processing Download PDFInfo
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- CN112082679A CN112082679A CN202010797567.1A CN202010797567A CN112082679A CN 112082679 A CN112082679 A CN 112082679A CN 202010797567 A CN202010797567 A CN 202010797567A CN 112082679 A CN112082679 A CN 112082679A
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- strain gauge
- femtosecond laser
- residual stress
- processing
- sample piece
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/0047—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes measuring forces due to residual stresses
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/36—Removing material
- B23K26/362—Laser etching
Abstract
A femtosecond laser processing-based residual stress measurement method comprises the steps of firstly arranging a femtosecond laser processing measurement system, and then polishing a sample piece to-be-measured part; coating an adhesive on the bottom surface of the strain gauge, leveling, aligning to a part to be measured of the sample, and horizontally placing the bottom surface of the strain gauge on the sample downwards; aligning a round hole in the middle of the wiring terminal with the bonded strain gauge, flatly placing the round hole on the sample piece, and respectively connecting a lead of the strain gauge and a test lead to the corresponding wiring terminal; respectively connecting the strain gauge and the compensation gauge to the ports of the strain gauge; checking the insulation degree and resistance value change conditions of the strain gauge and the sample piece, setting corresponding parameters of a laser, and then focusing femtosecond laser pulses on the surface to be measured of the sample piece for processing to obtain a line; and measuring the data of the strain released by the corresponding processing area and calculating the residual stress. The invention innovatively applies the femtosecond laser with ultrashort pulse to process the material, realizes the reduction of the heat affected zone from hundreds of microns to several microns, and has extremely high processing precision.
Description
Technical Field
The invention relates to the technical field of optical design, in particular to a residual stress measuring method based on femtosecond laser processing.
Background
Residual stress, which is a major factor in material failure, exists in almost all materials and causes problems such as cracking and deformation of the materials in actual production processes. Therefore, it is important to effectively measure the residual stress in the material.
The traditional mechanical processing measurement method generates additional mechanical stress due to the direct contact of the equipment and the sample piece, and the additional stress has great uncertainty and influences the measurement precision of the residual stress. Meanwhile, the conventional machining process also generates a heat effect, which affects the performance of the material on one hand and generates additional thermal stress on the other hand. The femtosecond laser is used as a pulse with the pulse width of femtosecond magnitude (10 to 10)-15s) has the characteristics of ultrashort pulses and superstrong peak power, and can eliminate the thermal effect and additional mechanical stress generated in the traditional machining measurement process through the interaction of a focusing optical system and a substance. Meanwhile, the femtosecond processing also has the advantages of non-contact, no pollution, wide adaptability, high precision, high efficiency and the like, so that the femtosecond processing can be widely applied to the field of material processing.
Disclosure of Invention
The invention provides a method for measuring residual stress based on femtosecond laser processing, which can solve the defects in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for measuring residual stress based on femtosecond laser processing comprises the following steps:
the method comprises the following steps: and polishing the part to be measured of the sample piece to ensure smooth surface. And cleaning and drying the surface of the sample piece by using acetone and ethanol.
Step two: and coating a layer of adhesive on the bottom surface of the strain gauge, leveling, immediately aligning to the part to be measured of the sample, horizontally placing the bottom surface of the strain gauge on the sample, lightly pressing the strain gauge to be tightly combined with the surface of the sample, and drying the strain gauge in the shade after a period of time.
Step three: and aligning the round hole in the middle of the wiring terminal with the bonded strain gauge, flatly placing the strain gauge on the sample piece, and respectively connecting the lead of the strain gauge and the test lead to the corresponding wiring terminal.
Step four: and connecting a strain gauge, and respectively connecting the strain gauge and the compensation plate to the port of the strain gauge.
Step five: and (4) zero setting of the strain gauge, checking the insulation degree and resistance value change condition of the strain gauge and the sample piece, and simultaneously checking whether the direction of the patch is correct, whether bubbles exist or not, warping and the like.
Step six: setting corresponding parameters of a laser, and then focusing femtosecond laser pulses on the surface to be measured of the sample piece for processing to obtain a line;
step seven: and when the indication of the strain gauge is stable for 3-5 min, the measured strain value data corresponding to the release of the processing area calculates the residual stress according to the principle of elastic mechanics.
Further, polishing the part to be measured of the sample by using sand paper until the surface is smooth, wiping off abrasive dust, and then respectively soaking acetone and alcohol in the sample by using a cotton ball for cleaning to remove impurities on the surface of the sample;
further, after a layer of adhesive is coated on the bottom surface of the strain gauge in the second step, a small piece of plastic film is covered on the strain gauge, excessive adhesive and air bubbles are squeezed out by hands, and then the strain gauge is slightly torn off.
Furthermore, in the third step, the lead of the strain gauge and the test lead can be connected to the wiring terminal in a soldering tin connection mode, the welding spot is smooth and full, and the welding requirement is accurate and rapid.
Furthermore, the femtosecond laser parameters are that the center pulse width of the femtosecond laser is 50-400fs, the wavelength is 400-1064nm, the single-pulse energy is 10-1000 muj, and the repetition frequency is 1-100 kHz.
Further, the processing line width d of the femtosecond laser on the measurement sample piece is 1-3mm, the line width d is small compared with the size of the test piece, and the thickness of the test piece is not less than 4 d.
The method for measuring the residual stress based on the femtosecond laser processing measures the residual stress in the material through the femtosecond laser processing technology, solves the problems of thermal effect and additional mechanical stress generated in the mechanical processing measuring process, and simultaneously eliminates the defect that the hard and brittle material is not easy to process by machinery.
According to the invention, the femtosecond laser technology is utilized to wire on the workpiece, the obtained hole has high precision and no residue, the measurement range is expanded, the released residual strain is measured by the strain gauge, and then the residual stress is calculated. The femtosecond laser processing-based residual stress measuring method is different from the traditional mechanical processing measuring method, and the ultrashort pulse femtosecond laser is innovatively applied to process materials, so that the heat affected zone is reduced from hundreds of micrometers to several micrometers, and the processing precision is extremely high.
Compared with the prior art, the invention has the beneficial effects that:
1. the femtosecond laser is adopted, the pulse duration is very short, the peak power is high, the generated thermal effect influence is very small, the micro-nano-level fine processing on the surface of a workpiece can be realized, and the processing precision is high;
2. the micro-nano composite structure is directly processed on the surface of the workpiece by femtosecond laser, the mechanical structure is simple and convenient, the operation is convenient, the technology is mature, and the processing efficiency is high;
3. the processing device is prevented from being directly contacted with the sample piece, and the generation of additional mechanical stress is avoided;
4. the method can be used for measuring the residual stress of the metal material and the non-metal material, and particularly can solve the problem that the hard and brittle material is difficult to process in the traditional machining measurement method;
5. the measuring range can be extended by a method of processing a wire.
Drawings
FIG. 1 is a flow chart of the method for measuring residual stress based on femtosecond laser processing according to the invention;
fig. 2 is a schematic structural diagram of a measuring system for measuring residual stress based on femtosecond laser processing.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention.
As shown in fig. 1, the method for measuring residual stress based on femtosecond laser processing according to the embodiment arranges a measuring system of femtosecond laser processing, and comprises the following steps:
s100, polishing the part to be measured of the sample piece to ensure that the surface is smooth;
s200, coating a layer of adhesive on the bottom surface of the strain gauge, leveling, immediately aligning to a part to be measured of the sample, horizontally placing the bottom surface of the strain gauge on the sample, lightly pressing the strain gauge to be tightly combined with the surface of the sample, and drying the strain gauge in the shade after a set time;
s300, aligning a round hole in the middle of the wiring terminal with the bonded strain gauge, flatly placing the round hole on the sample piece, and respectively connecting a lead of the strain gauge and a test lead to the corresponding wiring terminal;
s400, connecting a strain gauge, and respectively connecting a strain gauge and a compensation plate to the port of the strain gauge;
s500, zero setting of the strain gauge, checking the insulation degree and resistance value change conditions of the strain gauge and the sample piece, and simultaneously checking whether the direction of the patch is correct;
s600, setting corresponding parameters of a laser, and focusing femtosecond laser pulses on the surface to be measured of the sample piece for processing to obtain a line;
and S700, when the strain gauge indicates stability, measuring strain value data released by the corresponding processing area, and calculating the residual stress according to the principle of elastic mechanics.
Wherein the content of the first and second substances,
as shown in fig. 2, the measurement system for femtosecond laser processing is arranged as follows:
adjusting the height of the femtosecond laser 1 to enable laser energy emitted by the femtosecond laser to horizontally enter the reflector group 2, properly adjusting the angle of the reflector and the height of the beam expander 3 to enable the laser energy reflected from the reflector group 2 to horizontally enter the beam expander 3, horizontally enter the scanning galvanometer 5 after beam expansion, place a measuring sample 6 on a moving platform 7, and swing the position to be processed under the processing objective 4; the strain gauge 10 is connected with a strain gauge on the measurement sample piece through a connecting wire 8 and then connected with a PC (personal computer) 9, so that a measurement result can be obtained.
The test method is described in detail below:
the method comprises the following steps: and (3) polishing the part to be detected of the sample piece by using sand paper until the surface is smooth, wiping off abrasive dust by using paper, then respectively soaking the sample piece in acetone and alcohol for cleaning, removing impurities on the surface of the sample piece, and drying in the shade under natural conditions.
Step two: after a layer of adhesive is coated on the bottom surface of the strain gauge, a small piece of plastic film is covered on the strain gauge, redundant adhesive and bubbles are extruded out by hands, then the adhesive is removed slightly, the plastic sheet is used for scraping the adhesive, the adhesive is aligned with the part to be measured of the sample, the bottom surface of the strain gauge is horizontally placed on the sample, the strain gauge is tightly combined with the surface of the sample by slight pressure, and the strain gauge is dried in the shade after a period of time.
Step three: the round hole in the middle of the wiring terminal is aligned to the bonded strain gauge, the strain gauge is flatly placed on the sample piece, the lead of the strain gauge and the test lead are respectively connected to the corresponding wiring terminal, the lead of the strain gauge and the test lead can be connected to the wiring terminal in a soldering tin connection mode, the welding spot is smooth and full, and the welding requirement is accurate and rapid. A bead of adhesive may then be dropped across the terminal and sample gap.
Step four: and connecting a strain gauge, and respectively connecting the strain gauge and the compensation plate to the port of the strain gauge.
Step five: and (4) zero setting of the strain gauge, checking the insulation degree and resistance value change conditions of the strain gauge and the sample piece, and checking whether the open circuit condition exists or not, and checking whether the position of the patch is correct or not, whether bubbles exist or not, warping and the like to prevent the transmission of the shadow response force from causing test errors.
Step six: setting corresponding parameters of a laser, wherein the parameters of the femtosecond laser are that the central pulse width of the femtosecond laser is 50-400fs, the wavelength is 400-1064nm, the single pulse energy is 10-1000 muj, the repetition frequency is 1-100kHz, the processing line width d of the femtosecond laser on a measurement sample piece is 1-3mm, and the thickness of the test piece is more than or equal to 4 d.
Specifically, the parameter range of the femtosecond laser is comprehensively selected in relevant experiments and the range mentioned by other references. Different parameters are selected according to different processing material properties in the processing experiment. Meanwhile, the parameter setting can process the sample piece with higher precision, and excessive laser energy cannot be consumed.
The line width d is selected according to the stress measured by the conventional drilling method, so that the method has the advantages that the stress balance of the sample piece is broken, the variable of the stress can be measured, and the normal function of the sample piece is not influenced. The thickness of the test piece is not less than 4d to prevent the test piece from being too thin and broken after machining, and to reduce errors.
Wherein the laser after intensity adjustment that femto second laser instrument 1 sent is through the 2 reflection backs of speculum group, expand the beam through beam expander 3 again, scanning shakes mirror 5 and has included the rotary type speculum of X axle direction and Y axle direction, according to the law of reflection, can be with the reflection of certain angle behind the laser incidence speculum, the angle that changes the speculum can make laser propagate towards different directions, laser shakes and jets out from processing objective 4 behind the mirror 5 through the scanning, and focus on the measurement sample 6 on moving platform 7. The moving platform 7 can drive the measuring sample piece 6 to move, and the laser irradiation direction is changed by matching with the scanning galvanometer 5, so that the femtosecond laser pulse can be focused on the surface of the part to be measured of the sample piece for routing.
Step seven: and when the indication of the strain gauge is stable for 3-5 min, the measured strain value data corresponding to the release of the processing area calculates the residual stress according to the principle of elastic mechanics.
As can be seen from the above, the principle of measuring the residual stress by the method of this embodiment is to drill a line in the stress field, and the balance of the stress is broken, so that the stress around the line is readjusted, and the elastic strain increment near the line is measured by using the strain gauge, so as to calculate the residual stress by using the principle of elasticity mechanics.
The invention eliminates the influence of thermal effect and additional mechanical stress brought by the traditional mechanical processing measurement, has simple and convenient mechanical structure, convenient operation and easy realization, simultaneously improves the processing measurement precision, has low requirement on the finished measurement environment and avoids the direct contact of a processing device and a sample piece. The method for measuring the residual stress based on femtosecond laser processing can be used for measuring the residual stress of metal materials and non-metal materials, and particularly solves the problem of processing hard and brittle materials which is difficult to solve by the traditional mechanical processing measuring method. Meanwhile, the method can measure the residual stress of the sample piece in a wider range by a processing line method.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (8)
1. A femtosecond laser processing-based residual stress measurement method comprises the steps of arranging a femtosecond laser processing measurement system, and is characterized in that:
further comprising the steps of:
s100, polishing the part to be measured of the sample piece to ensure that the surface is smooth;
s200, coating a layer of adhesive on the bottom surface of the strain gauge, leveling, immediately aligning to a part to be measured of the sample, horizontally placing the bottom surface of the strain gauge on the sample, lightly pressing the strain gauge to be tightly combined with the surface of the sample, and drying the strain gauge in the shade after a set time;
s300, aligning a round hole in the middle of the wiring terminal with the bonded strain gauge, flatly placing the round hole on the sample piece, and respectively connecting a lead of the strain gauge and a test lead to the corresponding wiring terminal;
s400, connecting a strain gauge, and respectively connecting a strain gauge and a compensation plate to the port of the strain gauge;
s500, zero setting of the strain gauge, checking the insulation degree and resistance value change conditions of the strain gauge and the sample piece, and simultaneously checking whether the direction of the patch is correct;
s600, setting corresponding parameters of a laser, and focusing femtosecond laser pulses on the surface to be measured of the sample piece for processing to obtain a line;
and S700, when the strain gauge indicates stability, measuring strain value data released by the corresponding processing area, and calculating the residual stress according to the principle of elastic mechanics.
2. The femtosecond laser processing-based residual stress measurement method according to claim 1, wherein:
and after the polishing in the S100, cleaning and drying the surface of the sample by using acetone and ethanol.
3. The femtosecond laser processing-based residual stress measurement method according to claim 2, wherein:
the S100 specifically includes:
and (3) polishing the part to be detected of the sample piece by using sand paper until the surface is smooth, wiping off abrasive dust, and then respectively soaking an absorbent cotton ball in acetone and alcohol for cleaning to remove impurities on the surface of the sample piece.
4. The femtosecond laser processing-based residual stress measurement method according to claim 1, wherein:
in the step S200, coating and leveling a layer of adhesive on the bottom surface of the strain gauge, specifically including:
after a layer of adhesive is coated on the bottom surface of the strain gauge, a small piece of plastic film is covered on the strain gauge, and redundant adhesive and bubbles are extruded by hands and then are slightly removed.
5. The femtosecond laser processing-based residual stress measurement method according to claim 1, wherein:
in S300, the strain gauge lead and the test lead are connected to the connection terminal by soldering.
6. The femtosecond laser processing-based residual stress measurement method according to claim 1, wherein:
a measurement system for placement of femtosecond laser machining comprising the steps of:
adjusting the height of a femtosecond laser (1), enabling laser energy emitted by the femtosecond laser to horizontally enter a reflector set (2), adjusting the angle of a reflector and the height of a beam expander (3), enabling the laser energy reflected from the reflector set to horizontally enter the beam expander (3), horizontally entering a scanning galvanometer (5) after beam expansion, placing a measuring sample piece (6) on a moving platform (7), and placing a position to be processed under a processing objective lens (4); the strain gauge (10) is connected with a strain gauge on the measuring sample piece (6) through a connecting wire (8) and then connected with a PC (9).
7. The femtosecond laser processing-based residual stress measurement method according to claim 6, wherein:
the femtosecond laser parameters of the femtosecond laser (1) are that the center pulse width of the femtosecond laser is 50-400fs, the wavelength is 400-1064nm, the single-pulse energy is 10-1000 muj, and the repetition frequency is 1-100 kHz.
8. The femtosecond laser processing-based residual stress measurement method according to claim 1, wherein:
the processing line width d of the femtosecond laser on the measurement sample piece is 1-3mm, and the thickness of the test piece is more than or equal to 4 d.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114812891A (en) * | 2022-05-06 | 2022-07-29 | 山东鼎泰昇交通科技有限公司 | Automatic measuring device for depth distribution of residual stress of workpiece based on laser material reduction |
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| DE102015006697A1 (en) * | 2015-05-21 | 2016-11-24 | Universität Stuttgart | Optical method and arrangement for measuring residual stress, in particular on coated objects |
| CN106695125A (en) * | 2017-02-20 | 2017-05-24 | 上海海事大学 | System and method for improving laser processing surface integrity of workpiece on line |
| CN109954966A (en) * | 2019-03-28 | 2019-07-02 | 大族激光科技产业集团股份有限公司 | The method for carrying out Treatment of Metal Surface by femtosecond laser |
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2020
- 2020-08-10 CN CN202010797567.1A patent/CN112082679A/en active Pending
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6553275B1 (en) * | 1999-03-11 | 2003-04-22 | Jyoti Mazumder | In-situ stress monitoring during direct material deposition process |
| CN101722361A (en) * | 2009-11-05 | 2010-06-09 | 江苏大学 | Device and method for controlling residual stress on surface of metal microstructure |
| CN103411711A (en) * | 2013-07-11 | 2013-11-27 | 南京航空航天大学 | Measuring device of tubular part inner wall processing stress and measuring method thereof |
| DE102015006697A1 (en) * | 2015-05-21 | 2016-11-24 | Universität Stuttgart | Optical method and arrangement for measuring residual stress, in particular on coated objects |
| CN106695125A (en) * | 2017-02-20 | 2017-05-24 | 上海海事大学 | System and method for improving laser processing surface integrity of workpiece on line |
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| CN114812891A (en) * | 2022-05-06 | 2022-07-29 | 山东鼎泰昇交通科技有限公司 | Automatic measuring device for depth distribution of residual stress of workpiece based on laser material reduction |
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Application publication date: 20201215 |