Continuous and high-repetition-frequency nanosecond pulse laser hole forming method

Abstract

The invention discloses a continuous and high-repetition-frequency nanosecond pulse laser pore-forming method, which comprises the following steps of: focusing laser on the surface of a metal material in a low-pressure environment, and continuously adding high-repetition-frequency nanosecond pulse laser in a continuous laser irradiation process so as to increase the removal rate of the material. Compared with an existing continuous laser drilling technology, the continuous laser drilling method has higher machining efficiency, the area of a recast layer can be reduced by 50% or above, and the continuous laser drilling method can be used for machining thicker metal plates.

Description

Technical Field

[0001] The invention belongs to a special processing technology for drilling holes in metal materials, in particular to a method for forming holes by continuous and high-repetition-rate nanosecond pulse laser. Background Art

[0002] Drilling holes in metal parts is a common process with various purposes. For example, the document "Diver, C., et al." Micro-EDM drilling of tapered holes for industrial applications." Journal of Materials Processing Technology 149.1-3 (2004): 296-303" introduces a method of using EDM technology to produce reverse tapered micro holes to improve diesel engine emissions. The document "Nedialkov, N.; Sawczak, M.; Jendrzejewski, R.; Atanasov, P.; Martin, M.; G. Analysis of surface and material modifications caused by laser drilling of AlNceramics. Appl. Surf. Sci. 2007, 254, 893–897. “Laser drilling technology was used to successfully avoid the problem of mechanical drilling tool breakage, and more precise and higher quality small holes were obtained, thereby increasing the service life of the small holes. Common metal drilling methods include mechanical drilling, electric spark drilling, ultra-high pressure water jet drilling and laser drilling. Mechanical drilling and punching drilling cannot process high-strength alloys, the size accuracy of the holes is not high, and the wear of the drilling tools needs to be considered; the cost of electric spark drilling is high, the processing time is long, and it is at a disadvantage in terms of production efficiency; the cost of high-pressure water jet drilling equipment is high, and regular maintenance of high-pressure equipment is required, and it is not suitable for processing high-hardness and thick plate materials; laser drilling can be used for the processing of almost all metal materials, whether it is low-hardness aluminum, copper, or high-hardness alloy steel, and the processed holes have good surface quality and high precision. However, for thick metal materials, the speed of laser drilling will be significantly slower and the drilling efficiency will be reduced.

[0003] In order to improve the efficiency of laser drilling of thick metal materials, the surface of the material to be processed is usually pretreated before laser drilling, such as removing oil and oxide layer on the surface of the material, and coating the surface of the material with high absorption rate substances. The pretreatment of the surface of the material can speed up the drilling efficiency. Alternatively, during the laser drilling process, a high-pressure airflow device is used to blow air into the drilling area to promote the discharge of the melt, thereby improving the laser drilling efficiency. However, pretreatment of the material surface will increase additional costs and time. The high-pressure gas-assisted method requires a small-aperture high-pressure air nozzle, which limits the positioning method of the drilling. It can be seen that these operations will directly or indirectly affect the efficiency of laser drilling of metals.

[0004] Compared with the existing continuous laser drilling technology, the present invention has higher processing efficiency, can reduce the area of ​​the recast layer by more than 50%, and can be used to process thicker metal plates, solving the problem of low laser material removal rate during continuous laser drilling. Summary of the invention

[0005] The purpose of the present invention is to provide a method for continuous and high repetition rate nanosecond pulse laser drilling to improve the material removal rate of the laser during the continuous laser drilling process.

[0006] The technical solution to realize the present invention is: a method for continuous and high repetition rate nanosecond pulse laser hole forming, comprising:

[0007] Place the metal material in a vacuum chamber and reduce the chamber pressure to a set pressure range;

[0008] The continuous laser and pulse laser are controlled to emit light according to the set timing and are focused on the front surface of the metal material through a converging lens.

[0009] Preferably, the metal material is one of titanium alloy, stainless steel or aluminum alloy.

[0010] Preferably, the laser wavelength is between 532 nm and 10.6 μm.

[0011] Preferably, the repetition rate of the pulsed laser is between 40 kHz and 80 kHz, and the pulse width is less than 150 ns.

[0012] Preferably, the pressure in the vacuum chamber is between 10Pa and 60Pa.

[0013] Preferably, the distance between the continuous laser and the pulsed laser and the center of the target spot does not exceed 10 μm.

[0014] Preferably, the continuous laser spot radius is between 1.5 and 2.5 times the pulse laser spot radius.

[0015] Preferably, the continuous laser emits light first, and the pulsed laser emits light after a delay of 20ms-80ms, and the simultaneous action ends after 100ms-500ms.

[0016] Preferably, the power density of the continuous laser and the pulsed laser are both greater than the melting threshold of the metal material.

[0017] Preferably, a DG535 digital signal delay generator is used to send a 24V high-level signal to enable the continuous laser and the pulse laser to emit light in a set time sequence, thereby ensuring that the continuous laser and the pulse laser emit light in sequence according to the set time sequence.

[0018] Compared with the prior art, the present invention has the following significant advantages: 1) the present invention can drill holes on high-hardness and high-brittle metal parts by a non-contact processing method; 2) the present invention can improve the material removal rate in continuous laser drilling; 3) the present invention can effectively avoid the loss and oxidation of the workpiece surface;

[0019] The present invention is described in further detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the composite laser drilling experiment on a metal plate.

[0021] Figure 2 Schematic diagram of continuous pulse timing light output.

[0022] Figure 3 The continuous laser power density in Example 1 is 23.1 kW / cm 2 Ablation of the front surface of titanium alloy by continuous laser and composite laser. (a) Continuous laser; (b) Composite laser.

[0023] Figure 4 The continuous laser power density in Example 2 is 50.5 kW / cm 2 Ablation of the front surface of titanium alloy by continuous laser and composite laser. (a) Continuous laser; (b) Composite laser.

[0024] Figure 5 The continuous laser power density in Example 2 is 50.5 kW / cm 2 The amount of material removed after continuous laser and compound laser irradiation. (a) The amount of material removed by evaporation after 200ms of continuous laser irradiation. (b) The amount of material removed by evaporation within 5 pulse cycles of compound laser after 150ms of continuous laser irradiation. (c) Comparison of the amount of material removed by compound laser and continuous laser within 5 pulse cycles after 150ms of continuous laser irradiation.

[0025] Figure 6These are the optical microscope images of the drilling effects of continuous laser alone (a) and compound laser (b) on 1 mm thick titanium alloy in Example 3. DETAILED DESCRIPTION

[0026] like Figure 1 As shown in the figure, a method of continuous and high repetition rate nanosecond pulse laser hole forming is used. In a low pressure environment, a continuous laser and a high repetition rate nanosecond pulse laser with a wavelength of 1064nm are used, and appropriate laser parameters are selected to drill submicron-sized holes on a metal plate. For metal plates of the same thickness, the size of the holes drilled by the composite laser is smaller than that of the single continuous laser. The specific steps are:

[0027] The metal material is placed in a vacuum chamber, and the pressure of the chamber is reduced to below 60Pa. Two laser beams are focused on the front surface of the material through a focusing device, and the center positions of the two target light spots are highly overlapped by fine-tuning one of the optical paths. Then, the time sequence of the two laser beams is controlled by a delay device to drill a submicron-sized hole on the material. The power density of the laser is greater than the ablation threshold of the metal material.

[0028] For a 1 mm thick titanium alloy plate, the laser is a 1064 nm point light source with Gaussian distribution. The spot radius of the continuous laser and pulsed laser to the material surface is 400 μm and 200 μm respectively. The power density of the continuous laser is 23.1 kW / cm 2 Up to 150.2kW / cm 2 , the pulse laser power density is 3.97×10 10 W / m 2 The continuous laser irradiation time is 400ms, the pulse laser light is delayed by 50ms, and both are turned off at the same time.

[0029] In a further embodiment, the air pressure in the cavity is between 17Pa and 35Pa.

[0030] Example 1

[0031] A titanium alloy plate with a side length of 2 cm and a thickness of 1 mm was used.

[0032] The front surface of the titanium alloy was polished with 600-grit sandpaper, cleaned with alcohol, and fixed in a vacuum chamber.

[0033] The wavelength of continuous and pulsed lasers are both 1064nm, and the repetition rate and pulse width of the pulsed laser are 50kHz and 120ns respectively. The laser is emitted into the cavity through the vacuum cavity window and focused on the front surface of the material.

[0034] A 250mm focal length lens is selected to focus the action beam so that the spot radius of the continuous laser and pulse laser reaching the sample surface are 400μm and 200μm respectively.

[0035] Reduce the air pressure in the cavity to 17Pa.

[0036] For a 1 mm thick TC4 plate, set the CW laser power density to 23.1 kW / cm 2 , the pulse laser power density is 3.97×10 10 W / m 2 The signal delay generator is used to make the continuous laser emit light for 50ms and then the pulse laser emit light. After 200ms, the two lasers stop emitting light at the same time.

[0037] like Figure 3 As shown in (a), after the continuous laser alone irradiates the sample, a crater-like surface morphology will be left on the front surface of the sample. In the composite laser ablation sample experiment, the action of the pulsed laser will cause the molten pool to splash violently, resulting in a large amount of material removal and increasing the material removal rate. The effect is shown in Figure 3 (b) as shown.

[0038] Example 2

[0039] A titanium alloy plate with a side length of 2 cm and a thickness of 1 mm was used.

[0040] The front surface of the titanium alloy was polished with 600-grit sandpaper, cleaned with alcohol, and fixed in a vacuum chamber.

[0041] The wavelength of continuous and pulsed lasers are both 1064nm, and the repetition rate and pulse width of the pulsed laser are 50kHz and 120ns respectively. The laser is emitted into the cavity through the vacuum cavity window and focused on the front surface of the material.

[0042] A 250mm focal length lens is selected to focus the action beam so that the spot radius of the continuous laser and pulse laser reaching the sample surface are 400μm and 200μm respectively.

[0043] Reduce the air pressure in the cavity to 17Pa.

[0044] For a 1 mm thick TC4 plate, set the CW laser power density to 50.5 kW / cm 2 , the pulse laser power density is 3.97×10 10 W / m 2 The signal delay generator is used to make the continuous laser emit light for 50ms and then the pulse laser emit light. After 200ms, the two lasers stop emitting light at the same time.

[0045] Figure 4 In (a), after continuous laser ablation of the material alone, the radius and depth of the ablation pit are 287 μm and 56 μm, respectively. Figure 4(b) After composite laser ablation, the radius and depth of the ablation pit are 348 μm and 98 μm. From the experimental results, after composite laser irradiation, the molten pool size is larger and the amount of material removed is greater.

[0046] Figure 5 This is the result of simulating the material evaporation removal process. From the simulation results, it can be found that the addition of pulsed laser can significantly increase the evaporation removal quality of the sample.

[0047] Example 3

[0048] A titanium alloy plate with a side length of 2 cm and a thickness of 1 mm was used.

[0049] The front surface of the titanium alloy was polished with 600-grit sandpaper, cleaned with alcohol, and fixed in a vacuum chamber.

[0050] The wavelength of continuous and pulsed lasers are both 1064nm, and the repetition rate and pulse width of the pulsed laser are 50kHz and 120ns respectively. The laser is emitted into the cavity through the vacuum cavity window and focused on the front surface of the material.

[0051] A 250mm focal length lens is selected to focus the action beam so that the spot radius of the continuous laser and pulse laser reaching the sample surface are 400μm and 200μm respectively.

[0052] Reduce the air pressure in the cavity to 17Pa.

[0053] For a 1 mm thick TC4 plate, set the CW laser power density to 150.2 kW / cm 2 , the pulse laser power density is 3.97×10 10 W / m 2 The signal delay generator is used to make the continuous laser emit light for 50ms and then the pulse laser emit light. After 400ms, the two lasers stop emitting light at the same time.

[0054] Figure 6 In (a), after continuous laser irradiation, the radius of the through hole and the radius of the recast layer on the titanium alloy plate are 205μm and 846μm respectively. Figure 6 In (b), the composite laser drilled a through hole with a radius of 154 μm on the titanium alloy plate and the radius of the recast layer was only 447 μm. Figure 6 (a) Using the same parameters of continuous laser through-hole, the through-hole radius and recast layer area of ​​the composite laser are reduced by 24.8% and 70.4%, respectively.

[0055] This embodiment is applicable to drilling a through hole with a diameter less than 1 mm in a 1 mm thick titanium alloy plate.

Claims

1. A method for continuous and high repetition rate nanosecond pulse laser hole forming, characterized in that: include: Place the metal material in a vacuum chamber and reduce the chamber pressure to a set pressure range; The continuous laser and pulse laser are controlled to emit light according to the set timing and are focused on the front surface of the metal material through a converging lens.

2. The method for continuous and high repetition rate nanosecond pulse laser hole forming according to claim 1, characterized in that: The metal material is one of titanium alloy, stainless steel or aluminum alloy.

3. The method for continuous and high repetition rate nanosecond pulse laser hole forming according to claim 1, characterized in that: The laser wavelength is between 532 nm and 10.6 μm.

4. The method for continuous and high repetition rate nanosecond pulse laser hole forming according to claim 1, characterized in that: The repetition rate of the pulsed laser is between 40kHz and 80kHz, and the pulse width is less than 150ns.

5. The method for continuous and high repetition rate nanosecond pulse laser hole forming according to claim 1, characterized in that: The pressure inside the vacuum chamber is between 10Pa and 60Pa.

6. The method for continuous and high repetition rate nanosecond pulse laser hole forming according to claim 1, characterized in that: The distance between the continuous laser and pulse laser and the center of the target spot does not exceed 10μm.

7. The method for continuous and high repetition rate nanosecond pulse laser hole forming according to claim 1, characterized in that: The continuous laser spot radius is between 1.5 and 2.5 times that of the pulsed laser spot radius.

8. The method for continuous and high repetition rate nanosecond pulse laser hole forming according to claim 1, characterized in that: The continuous laser emits light first, and then the pulsed laser emits light after a delay of 20ms-80ms, and the simultaneous action ends after 100ms-500ms.

9. The method for continuous and high repetition rate nanosecond pulse laser hole forming according to claim 1, characterized in that: The power density of continuous laser and pulsed laser is greater than the melting threshold of metal materials.

10. The method for continuous and high repetition rate nanosecond pulse laser hole forming according to claim 1, characterized in that: Use the DG535 digital signal delay generator to send a 24V high-level signal to the continuous laser and pulse laser to enable light emission in the set time sequence, ensuring that the continuous laser and pulse laser emit light in sequence according to the set timing.

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