Transparent material / metal heterogeneous material ultrafast laser welding method based on burst mode

Abstract

The invention discloses a transparent material / metal dissimilar material ultrafast laser welding method based on a burst mode, and belongs to the technical field of laser micro-nano machining, and the transparent material / metal dissimilar material ultrafast laser welding method comprises the steps that the surface roughness and flatness of a pre-welded piece are treated through a mirror grinding and polishing technology, so that a sample piece reaches the optical contact condition, the pre-welded piece is in lap joint with a tool platform through a specially-made clamp, and the pre-welded piece is welded to the tool platform; when a visual Newton ring appears on a contact surface and an ultrafast laser focus is located at a material interface, using a burst mode under an ultrafast laser processing platform to increase the number of sub-pulses, welding a micro-area, equally dividing the energy of a single pulse into a plurality of pulses, and then emitting light in a pulse sequence mode, by using the burst mode containing multiple pulses, the heat accumulation effect can be achieved more easily, the ablation efficiency and the connection strength and stability of the transparent material and the metal heterogeneous material are improved while the machining rate is increased, and the method has wide application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of laser micro-nano processing, and in particular relates to an ultrafast laser welding method of transparent material / metal heterogeneous material based on burst mode. Background Art

[0002] The focused ultrashort pulse laser has an ultra-high peak power density, which can selectively induce nonlinear absorption of materials in space and form high-density plasma, thereby generating a series of stimulated response processes such as local high temperature and high pressure, surface ablation, melting, vaporization, and condensation. When the focused laser acts on the interface of closely contacted materials, local fusion of materials can be established in the series of stress response processes, achieving selective welding between materials. Therefore, the essence of ultrashort pulse laser micro welding is the process of laser-matter interaction to induce local modification of the material interface, thereby establishing a strong bond.

[0003] Traditional bonding / welding technologies include gluing, solid-phase bonding, anodic bonding, and fusion welding. Among them, gluing generally refers to the technology of using the curing reaction process of organic or inorganic adhesives to achieve the bonding between objects. The operation process is simple and applicable to a wide range of materials, but it has disadvantages such as easy bleaching, easy aging, and release of harmful gases, making it difficult to use in the aviation field, high temperature and high load conditions. Solid-phase bonding can achieve large-area welding between objects, but it has high requirements for the surface preparation of the objects to be welded and the welding process takes a long time. In addition, when welding dissimilar materials, it is often necessary to embed a transition layer to alleviate the mismatch of material physical property parameters and stress concentration. Anodic bonding is a bonding process that can quickly achieve strong bonding at a relatively low temperature. However, this technology requires that the thermal expansion coefficients of the two materials to be bonded are highly matched, otherwise it will greatly affect the fatigue resistance of the welded object. Fusion welding is different from the above three technologies. It uses a local heat source to cause the material at the interface of the object to melt and solidify, thereby establishing a strong bonding effect.

[0004] At present, traditional fusion welding is widely used in the welding of metal materials. Due to the restriction of heating source, the heat affected zone induced by traditional hot melt welding is large and the residual stress is strong. Therefore, how to regulate the interface residual stress and mutual melting behavior during ultrafast laser transmission welding of transparent materials with different thermal expansion coefficients and metal heterogeneous materials has become a new problem and challenge. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a transparent material / metal heterogeneous material ultrafast laser welding method based on burst mode. By changing the light emission mode of the ultrafast laser, the single pulse laser is converted into a Burst pulse sequence cluster. Since each light emission does not emit only one high-energy pulse, but emits a pulse sequence cluster composed of multiple high-frequency pulses, on the one hand, it can improve the laser absorption efficiency while reducing the high residual stress problem caused by the large difference in thermal expansion coefficient of the heterogeneous material, and finally form a better joint area, so as to realize high-quality, high-efficiency and low-cost welding of most transparent hard and brittle materials and metal heterogeneous materials.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The present invention provides a method for ultrafast laser welding of transparent materials / metal heterogeneous materials based on burst mode, comprising the following steps:

[0008] (1) Use mirror polishing process to process the surface roughness and flatness of metal materials, and perform ultrasonic cleaning in an ultrasonic cleaning machine with anhydrous ethanol for 8-10 minutes to improve its surface finish;

[0009] (2) Processing is performed by passing the laser beam through the top transparent material, and the transparent material and the metal material are fixed with a fixture for overlapping and stacking, so that the interface gap is less than one-quarter of the wavelength of light (nominal optical contact). At this time, if you look directly above the clamping plane, you can observe more obvious Newton rings, that is, the pre-treatment of the pre-welded parts has reached the weldability;

[0010] (3) Adjusting the ultrafast laser in the processing platform, changing the normal light emission mode to the burst mode, and emitting multiple high-frequency pulse sequence clusters to control the heat accumulation effect between pulses, reduce residual stress, and achieve efficient fusion or combination of two heterogeneous materials;

[0011] (4) Ultrafast laser welding is performed along the scanning path to achieve the connection between transparent materials and metal heterogeneous materials.

[0012] Wherein, the metal material is a mirror-treated metal material, and the transparent material is a transparent hard and brittle material with a flatness less than λ / 4;

[0013] The burst mode is a pulsed light Burst mode, in which the incident laser is split by a beam splitter to form two beams of light, namely, a transmitted light and a reflected light. The transmitted light and the reflected light return along the original path after a certain optical path, and are combined again at the beam splitter to generate a double pulse sequence processing mode, that is, each light emission emits a pulse sequence cluster consisting of multiple high-frequency pulses.

[0014] Preferably, the transparent material is selected from sapphire, fused quartz, and glass ceramics.

[0015] Preferably, the metal material is selected from Invar alloy, Kovar alloy, stainless steel and titanium alloy.

[0016] Preferably, in step (1), the surface roughness of the treated metal material is controlled to be between 0.15-0.3 μm, and the flatness difference is not higher than 40 μm, so as to ensure that the surface ablation phenomenon caused by the subsequent ultrashort pulse laser acting on the surface of the transparent material is effectively suppressed, thereby improving the welding quality.

[0017] Preferably, in step (3), the focus of the ultrafast laser is located at the interface of the heterogeneous materials.

[0018] Preferably, in step (3), the ultrafast laser includes a laser, a beam expander, a reflector and a focusing mirror, and also includes a laser optical path component for adjusting the laser emission, a fixture for fixing the transparent material and the metal material, and a three-dimensional xyz motion platform for driving the fixture to move, and the fixture is used to adjust the gap between the heterogeneous materials. In addition, by adjusting the pulsed light Burst mode, the thermal accumulation effect of the material can be reduced while improving the fusion degree, which has a very obvious advantage for material systems with large differences in thermal expansion coefficients.

[0019] Preferably, in step (4), the ultrafast laser is a femtosecond pulse laser or a picosecond laser, the wavelength of the ultrafast laser is 1030 nm, the maximum laser power is 52 W, the repetition frequency is 0.025-5 MHz, and the pulse width is 0.3-8 ps.

[0020] The present invention provides a transparent material / metal heterogeneous material ultrafast laser welding device based on burst mode, comprising: an ultrafast laser 1, a beam expander 2, a reflector 3, a beam splitter 4, a pulse delay control device 7, a camera 8, a control platform 9 and a galvanometer 10; the use method thereof comprises: the laser reaches the beam splitter 4 after being adjusted in direction by the reflector 3, the beam splitter 4 is placed at an angle of 45 degrees to ensure that the energy of the transmission arm and the reflection arm are equal and the directions are vertical, the split light 5 is reflected by the reflectors A and B and reaches the beam splitter C for beam combination, and reaches the reflector D to emit a double pulse light beam 6 in the form of double pulses with equal sub-pulse energy; when the control computer draws the welding area, the signal is transmitted to the laser 1 and the control platform 9, the laser 1 emits light and is processed by the galvanometer 10.

[0021] Compared with the prior art, the present invention aims at the problems that it is difficult to obtain high-strength and high-quality joints and it is difficult to reduce the high residual stress generated during the welding process in the prior art. A method and device for ultrafast laser welding of transparent materials / metal heterogeneous materials based on burst mode is proposed, which has the following beneficial effects:

[0022] 1. Different heterogeneous materials of transparent hard and brittle materials / metals have high residual stress problems during welding due to the difference in thermal expansion coefficients. For example, during welding, the difference in expansion coefficients leads to uneven melt flow, cracks and crack propagation at the edge of the connection area. The present invention adjusts the pulse laser light emission mode to emit a pulse sequence cluster (Burst mode) composed of multiple high-frequency pulses. The number of sub-pulses is increased, the laser absorption efficiency is improved, and the heat accumulation effect between pulses is effectively regulated, the residual stress is reduced, the welding strength is improved, and the efficient fusion of heterogeneous materials is achieved.

[0023] 2. The transparent material / metal heterogeneous material ultrafast laser welding platform based on the burst mode in the present invention realizes the change of the optical path difference between the transmitted light and the reflected light by changing the position of the end reflector of the transmitted light or the reflected light, that is, changing the delay time or number of sub-pulses, which can reduce the high residual stress problem caused by the large difference in thermal expansion coefficients of heterogeneous materials. On the other hand, by reducing the size of the interface gap, the sputtered plasma is confined to the inside of the welding micro-area, adhered to the lower surface of the transparent material to melt and solidify, thereby forming a better joint area, realizing efficient fusion and connection of transparent hard and brittle materials and metals in the optical contact area, which helps to improve the welding strength.

[0024] 3. Use ultrafast laser to achieve effective welding of transparent / metallic heterogeneous materials to be welded according to the designated area, and in the application of heterogeneous material welding, the main focus is on the shear strength and air tightness of the weld. The present invention uses a burst pulse sequence cluster, which, on the one hand, significantly reduces the high residual stress problem caused by expansion coefficient mismatch and improves the continuity and shear strength of the weld; on the other hand, since the escape range of the plasma in the optical contact area is controlled within a very small range, the thickness of the mixed layer is ensured to be greater than the gap width, which can further improve the welding stability and improve the welding air tightness.

[0025] In summary, the present invention processes the surface roughness and flatness of the pre-welded parts through mirror polishing technology, so that the sample reaches the optical contact condition, and the pre-welded parts are overlapped on the tooling platform through a special fixture. When a visual Newton ring appears on the contact surface, the ultrafast laser focus is located at the material interface, and finally the burst mode is used in the ultrafast laser processing platform to increase the number of sub-pulses (Burst) to weld the micro-area. This mode divides the energy of a single pulse into multiple pulses and then emits light in a pulse sequence. The use of a burst mode containing multiple pulses can make it easier to achieve the thermal accumulation effect, improve the processing rate while improving the ablation efficiency, and improve the connection strength and stability of transparent materials such as glass, ceramics, etc. and metal heterogeneous materials. That is, while solving the effective welding of transparent / metal heterogeneous materials, the strength, stability and air tightness of the welding can be further significantly improved. It has significant technical advantages and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the ultrafast laser welding device for transparent materials / metal heterogeneous materials based on burst mode in the embodiment; the figure numbers are as follows: 1 ultrafast laser; 2 beam expander; 3 reflector; 4 beam splitter; 5 split beam; 6 double pulse beam; 7 pulse delay control device; 8 camera; 9 control platform; 10 scanning galvanometer; 11 processing sample. DETAILED DESCRIPTION

[0027] In order to make the technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] like Figure 1 As shown, an ultrafast laser welding device for transparent materials / metal heterogeneous materials based on burst mode is exemplarily proposed, which is composed of an ultrafast laser 1, a beam expander 2, a reflector 3, a beam splitter 4, a pulse delay control device 7, a camera 8, a control platform 9, and a galvanometer 10; wherein the laser reaches the beam splitter 4 after being adjusted in direction by the reflector 3. To ensure that the energy of the transmission arm and the reflection arm are equal and the directions are vertical, the beam splitter 4 is placed at an angle of 45 degrees. After the split beam 5 is reflected by the reflectors A and B, it reaches the beam splitter C for beam combination, and reaches the reflector D to emit a double pulse beam 6 in the form of double pulses with equal sub-pulse energy. When the control computer draws the welding area, it transmits the signal to the laser 1 and the control platform 9, and the laser emits light and is processed by the scanning galvanometer 10.

[0029] The following embodiment proposes a method for ultrafast laser welding of transparent materials / metal heterogeneous materials based on burst mode, including:

[0030] Step 1: Process the surface roughness and flatness of the metal material by mirror polishing technology, and clean it in an ultrasonic cleaner with anhydrous ethanol for 8-10 minutes to improve its surface smoothness. The materials used are mirror-treated metal materials and transparent hard and brittle materials with a flatness less than λ / 4.

[0031] Step 2: overlap the transparent material and the metal material, so that the laser beam can be processed through the top transparent material. Then, fix the material with a special fixture so that the interface gap is less than one-quarter of the wavelength of light (nominal optical contact). At this time, look directly above the clamping plane. If obvious Newton rings are observed, it proves that the pre-treatment of the pre-welded part has reached the weldability.

[0032] Step 3: By adjusting the ultrafast laser in the processing platform, the normal light mode is changed to the burst mode. It is a pulse sequence cluster. Each time the light is emitted, it does not emit only one high-energy pulse, but a pulse sequence cluster composed of multiple high-frequency pulses. The increase in the number of sub-pulses improves the laser absorption efficiency while effectively regulating the heat accumulation effect between pulses, reducing residual stress, improving welding strength, and realizing efficient fusion or bonding of heterogeneous materials.

[0033] Step 4: Ultrafast laser welding is performed according to the specified scanning path to finally connect the samples.

[0034] In some embodiments, in step one, the surface roughness of the mirror-treated material is controlled between 0.15-0.3 μm, and the flatness difference is no more than 40 μm, thereby ensuring optical contact. The surface ablation phenomenon caused by the ultrashort pulse laser acting on the surface of the transparent material can be effectively suppressed, thereby improving the welding quality.

[0035] In some embodiments, in step three, the ultrafast laser femtosecond pulse laser has a wavelength of 1030nm; the burst mode refers to splitting the incident laser through a beam splitter to form two beams of transmitted light and reflected light. The transmitted light and the reflected light return to the original path after a period of optical path and are combined again at the beam splitter to produce a double pulse sequence processing mode.

[0036] In some embodiments, in step three, the focus of the ultrafast laser is located at the interface of the heterogeneous materials.

[0037] In some embodiments, in step 1 and step 2, the transparent material is sapphire, fused quartz, or glass ceramic.

[0038] In some embodiments, in step 1 and step 2, the metal material is Invar alloy, Kovar alloy, stainless steel, or titanium alloy.

[0039] In some embodiments, in step 3, the ultrafast laser includes a laser, a beam expander, a reflector, and a focusing mirror, and also includes a laser optical path component for adjusting the laser emission, a fixture for fixing transparent materials and metal materials, and a three-dimensional xyz motion platform for driving the fixture to move, and the fixture is used to adjust the gap between the heterogeneous materials. In addition, by adjusting the pulsed light Burst mode, the thermal accumulation effect of the material can be reduced while improving the degree of fusion, which has a very obvious advantage for material systems with large differences in thermal expansion coefficients.

[0040] In some embodiments, in step 4, the ultrafast laser uses a femtosecond pulse laser or a picosecond laser, the wavelength of the ultrafast laser is 1030nm, the maximum laser power is 52W, the repetition frequency is 0.025-5MHz, and the pulse width is 0.3-8ps. During operation, the wavelength output by the ultrafast laser 1 is 1030nm, the laser beam is expanded by the beam expander 2, and then the beam is reflected by the reflector 3; the double-pulse laser beam is focused between the transparent material and the metal material interface through the scanning galvanometer 10. The control computer adjusts the light output mode, controls the number of Burst pulse clusters, and transmits the processing signal to the workbench and the laser 1 to implement the welding process, completing the transparent material / metal welding based on the Burst mode.

[0041] Example 1

[0042] This embodiment takes sapphire as the transparent material and Invar alloy as the metal material as an example. The size of the selected single crystal sapphire (Al2O3) is 10mm×10mm×3mm and the size of the Invar alloy (0.639Fe-0.361Ni, mass fraction, %) is 15mm×40mm×3mm. The roughness of the mirror-polished metal material Sa=0.14μm, and the roughness of sapphire is less than 170nm, both of which are smaller than the interface gap value between the transparent material and the metal. Figure 1 The transparent material / metal heterogeneous material ultrafast laser welding device based on burst mode shown in the figure performs the above heterogeneous material ultrafast laser welding, and the specific steps are as follows:

[0043] (1) Use mirror polishing to improve the surface roughness and flatness of metal materials, and use ultrasonic cleaning to improve its surface finish;

[0044] (2) Processing is performed by passing the laser beam through the top transparent material, and the transparent material and the metal material are fixed with a fixture for overlapping and stacking, so that the interface reaches nominal optical contact, thereby improving the weldability of the pre-welded part;

[0045] (3) Adjusting the ultrafast laser from the normal light mode to the pulsed light mode, and emitting multiple high-frequency pulse clusters to control the heat accumulation effect between pulses, reduce residual stress, and achieve efficient fusion or combination of two heterogeneous materials;

[0046] (4) Ultrafast laser welding is performed along the scanning path to achieve sample connection.

[0047] In the process of transparent / metal material welding, the pulsed light beam amplified by the beam expander 2 is reflected multiple times into the pinhole aperture to eliminate the stray light outside the spot. Finally, the light beam is focused through the microscope objective lens. The laser focus is located at the interface of sapphire / Invar alloy. The light beam emitted by the ultrafast laser 1 is focused at the interface of heterogeneous materials through the focusing mirror in the scanning galvanometer 10 through the control system. The parameters of the ultrafast laser are set as follows: the output wavelength is 1030nm, the pulse width is 800fs, the repetition frequency is 200kHz, the number of burst pulse sequence clusters is 2, the sub-pulse interval time is 30ps, the scanning speed is 25mm / s, the line spacing is 40μm, and the output power is 5.85W.

[0048] The processing method is: first horizontal and then vertical grid welding is performed through the xy scanning galvanometer 10. By changing the interval time and number of the Burst pulse sequence cluster, the high residual stress problem caused by the large difference in thermal expansion coefficient of heterogeneous materials can be reduced. The sputtered plasma is confined inside the welding micro-area, adheres to the lower surface of the transparent material, melts and solidifies to form a better joint area, thereby realizing efficient fusion and connection of transparent hard and brittle materials and metals in the optical contact area.

[0049] The above is a preferred embodiment of the present invention, but the present invention should not be limited to the contents disclosed in the embodiment. Therefore, any equivalent or modification completed without departing from the spirit disclosed in the present invention shall fall within the scope of protection of the present invention.

Claims

1. A method for ultrafast laser welding of transparent materials / metallic heterogeneous materials based on burst mode, characterized in that: The following steps are involved: (1) Use mirror polishing process to process the surface roughness and flatness of metal materials, and perform ultrasonic cleaning in an ultrasonic cleaning machine with anhydrous ethanol for 8-10 minutes to improve its surface finish; (2) Processing by passing the laser beam through the top transparent material, fixing the transparent material and the metal material with a fixture to overlap and stack them, so that the interface gap is less than one-quarter of the wavelength of light. At this time, look directly above the clamping plane and wait for visual Newton rings to appear on the contact surface, which means that the pre-weld pretreatment has reached the weldability; (3) Adjusting the ultrafast laser in the ultrafast laser processing platform, adjusting the normal light emission mode to the burst mode, and emitting multiple high-frequency pulse sequence clusters to control the heat accumulation effect between pulses, reduce residual stress, and achieve efficient mutual fusion or combination of transparent materials and metals; (4) Ultrafast laser welding is performed along a specified scanning path to achieve the connection of two heterogeneous materials, transparent material and metal; Wherein, the transparent material is a transparent hard and brittle material with a flatness less than λ / 4; The burst mode is a pulsed light Burst mode, in which the incident laser is split by a beam splitter to form two beams of light, namely, a transmitted light and a reflected light. The transmitted light and the reflected light return along the original path after a certain optical path, and are combined again at the beam splitter to generate a double pulse sequence processing mode, that is, each light emission emits a pulse sequence cluster consisting of multiple high-frequency pulses.

2. The method for transparent material / metal heterogeneous material ultrafast laser welding based on burst mode according to claim 1, characterized in that: The transparent material is selected from sapphire, fused quartz and glass ceramics.

3. The method for transparent material / metal heterogeneous material ultrafast laser welding based on burst mode according to claim 1, characterized in that: The metal material is selected from Invar alloy, Kovar alloy, stainless steel and titanium alloy.

4. The method for transparent material / metal heterogeneous material ultrafast laser welding based on burst mode according to claim 1, characterized in that: In step (1), the surface roughness of the treated metal material is controlled between 0.15-0.3 μm, and the flatness height difference is not higher than 40 μm.

5. The method for transparent material / metal heterogeneous material ultrafast laser welding based on burst mode according to claim 1, characterized in that: In step (3), the focus of the ultrafast laser is located at the interface between the transparent material and the metal.

6. The method for transparent material / metal heterogeneous material ultrafast laser welding based on burst mode according to claim 1, characterized in that: In step (3), the ultrafast laser includes a laser, a beam expander, a reflector and a focusing mirror; It also includes a laser optical path component for adjusting laser emission, a fixture for fixing transparent materials and metals and adjusting the gap between two heterogeneous materials, and a three-dimensional xyz motion platform for driving the fixture to move.

7. The method for transparent material / metal heterogeneous material ultrafast laser welding based on burst mode according to claim 1, characterized in that: In step (4), the ultrafast laser is a femtosecond pulse laser or a picosecond laser, the wavelength of the ultrafast laser is 1030nm, the maximum laser power is 52W, the repetition frequency is 0.025-5MHz, and the pulse width is 0.3-8ps.

8. A burst-mode transparent material / metal heterogeneous material ultrafast laser welding device, comprising: Ultrafast lasers, beam expanders, reflectors, beam splitters, pulse delay control devices, cameras, control platforms, and scanning galvanometers; The method of using the method includes: the ultrafast laser reaches the beam splitter after being adjusted in direction by a reflector. To ensure that the transmission arm and the reflection arm have equal energy and are in vertical directions, the beam splitter is placed at an angle of 45 degrees. After the split light is reflected by reflectors A and B, it reaches the beam splitter C for beam combination, and reaches the reflector D to emit a double pulse light beam in the form of a double pulse with equal sub-pulse energy 6; when the control computer draws the welding area, the signal is transmitted to the ultrafast laser and the control platform, and the ultrafast laser emits light and is processed by the scanning galvanometer.

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