CN111375903A

CN111375903A - Method for processing small hole by laser

Info

Publication number: CN111375903A
Application number: CN202010287674.XA
Authority: CN
Inventors: 张晓兵; 蔡敏; 毛忠; 纪亮; 张伟; 焦佳能
Original assignee: AVIC Beijing Aeronautical Manufacturing Technology Research Institute
Current assignee: AVIC Beijing Aeronautical Manufacturing Technology Research Institute; AVIC Manufacturing Technology Institute
Priority date: 2020-04-13
Filing date: 2020-04-13
Publication date: 2020-07-07

Abstract

The invention relates to a method for processing a small hole by laser. Firstly, processing an initial through hole in a layered scanning filling mode, wherein the initial through hole comprises a round hole and a special-shaped hole; amplifying the outermost outline machining path of each layer of scanning filling machining path to a certain size to be used as a machining path for machining again; and the step one and the step two are continuously finished in the same processing program by adopting the same laser focusing processing equipment under the condition of the same process parameter. The method solves the problem of poor or unstable quality of the processed hole wall of the small hole under the condition of higher power of nanosecond, picosecond and femtosecond short pulse laser in the prior art, realizes no recast layer of the processed hole wall of the small hole by the nanosecond laser, and has very high practical value.

Description

Method for processing small hole by laser

Technical Field

The invention relates to the technical field of laser processing, in particular to a method for processing a small hole by laser.

Background

As shown in the attached figure 1, the current laser processing of small holes mainly comprises a fixed point impact method, a rotary cutting method and a spiral line feeding rotary cutting processing method.

For a long time, millisecond laser drilling has always occupied a mainstream position in small hole processing application of large depth (generally more than 1mm, deepest depth even more than 10mm) and aperture (generally 0.25-1.2mm) of hot end parts and the like of aircraft engines due to the characteristics of high processing efficiency, large penetration depth, high processing technology, high maturity of laser devices and the like. However, due to the long pulse action time and the relatively low power density, the millisecond laser hole making is mainly performed by melting, so that the method cannot avoid generating large heat influence, generating heat-induced defects such as recast layers, even microcracks and the like, has poor hole wall roughness and low dimensional accuracy such as roundness and the like, and cannot meet the technical requirements of quality and accuracy of the processed hole walls of small holes such as high-performance monocrystalline turbine blades of aero-engines and fuel nozzles of automobile engines.

The nanosecond, picosecond and femtosecond pulse laser processing small holes have greatly shortened action time with materials, and the laser power density is at least improved by two orders of magnitude, so that the material removal is mainly based on a gasification mechanism, the heat influence on the periphery of an action area is much smaller, and the small holes processed by a filling method have thinner recast layers and even obtain the small holes almost without the recast layers. The pulse laser small hole processing technology is applied to processing of small holes with large depth and large hole diameters such as aeroengine blades and fuel nozzle oil spray holes, and can also be used for processing special-shaped holes, and is shown in an attached figure 2 (b).

However, nanosecond, picosecond and femtosecond pulse laser has low efficiency in practical application due to low pulse energy and adoption of a filling processing method. Higher average powers were required to improve processing efficiency, but it was found in experiments that processing of small holes at higher powers, such as nanosecond laser processing, had poor wall quality, with a recast layer of less than 5 microns thickness uniformly around the hole wall in the entrance region, as shown in figure 3.

While the higher power picosecond, femtosecond pulse laser drilling still has almost no recast layer, but the hole wall quality is unstable, the consistency is poor, for example, a local ablation area exists, and even irregular ablation craters, shallow grooves and the like with the thickness or the depth of about 2 micrometers exist, as shown in figure 4. In addition, the filling processing of the special-shaped holes has obvious heavy condensate accumulation in the special-shaped hole diffusion sections, which is shown in figure 5.

In view of this, it is an urgent technical problem to be solved by those skilled in the art how to provide a method for processing a small hole by laser, which can further improve the surface quality of the wall of the small hole processed by nanosecond, picosecond, or femtosecond laser.

Disclosure of Invention

(1) Technical problem to be solved

The embodiment of the invention provides a method for processing a small hole by laser. The method comprises the steps of filling and processing an initial through hole, and then sequentially carrying out secondary processing on the existing hole wall in a slightly enlarged size by adopting the same technological parameters, so that the quality problems of an extremely thin recast layer or craters, local ablation and the like on the hole wall during laser hole making are solved, and the processing quality of the hole wall of the small hole is effectively improved.

(2) Technical scheme

The embodiment of the invention provides a method for processing a small hole by laser, which comprises the following steps:

firstly, processing an initial through hole in a layered scanning filling mode, wherein the initial through hole comprises a round hole and a special-shaped hole; amplifying the outermost outline machining path of each layer of scanning filling machining path to a certain size to be used as a machining path for machining again; and the step one and the step two are continuously finished in the same processing program by adopting the same laser focusing processing equipment under the condition of the same process parameter.

Further, the first step and the second step are carried out by a laser focusing processing device provided with a scanning galvanometer and coaxially assist in blowing.

Further, the pulse width of the laser includes the order of nanoseconds, picoseconds, or femtoseconds.

Furthermore, the contour path dimension of the hole wall processed in the second step is circumferentially and uniformly expanded by 0.01-0.03mm compared with the outermost contour dimension of the scanning filling processing path in the first step.

Further, the average power and pulse energy of the laser during the laser processing are kept constant.

(3) Advantageous effects

The method of the invention forms a processing path based on the scanning galvanometer, and can complete processing work by adopting the same laser beam and a process device thereof without secondary processing or adjusting process parameters.

Firstly, processing an initial through hole by a scanning filling processing method; and then, the initial through hole is adopted to scan and fill the outer contour of the processing path and is properly amplified to process the hole wall of the processed through hole again, so that the defects of a recast layer, a local ablation layer, craters, shallow grooves and the like generated by the initial processing of the hole wall are removed, the problem that the quality of the processed hole wall of the small hole is poor or unstable under the condition of higher power of nanosecond, picosecond and femtosecond short pulse lasers in the prior art is solved, the purpose that the hole wall of the small hole is processed by the nanosecond laser without the recast layer is realized, and the practical value is very high.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a schematic diagram of three typical prior art laser via making processes.

FIG. 2 is a schematic view of a circular hole and a special-shaped hole.

FIG. 3 is a metallographic picture of a hole wall of a nanosecond laser filling processing round hole in the prior art.

FIG. 4 is a photomicrograph of a picosecond laser filling process of a circular hole wall with a larger power in the prior art.

FIG. 5 is a photomicrograph of the filling of the entrances of profiled holes in accordance with an embodiment of the present invention.

FIG. 6 is a schematic diagram of filling a machined circular hole according to an embodiment of the present invention.

FIG. 7 is a schematic diagram of a portion of a diffusion section of a filled and machined profile hole according to an embodiment of the present invention.

Fig. 8 is a schematic diagram of an embodiment of the present invention for enlarging the outermost profile of a filling tool path of a circular initial via by a certain dimension as a tool path tool wall profile.

FIG. 9 is a photomicrograph taken using the method of the present invention as shown in the example of the invention applied to a circular aperture.

FIG. 10 is a photomicrograph taken using the method of the present invention as shown in an example of the invention applied to a shaped well.

Fig. 11 is a metallographic micrograph obtained by applying the method of the embodiment of the present invention to nanosecond laser processing of a round hole.

Detailed Description

The embodiments of the present invention will be described in further detail with reference to the drawings and examples. The following detailed description of the embodiments and the accompanying drawings are provided to illustrate the principles of the invention and are not intended to limit the scope of the invention, i.e., the invention is not limited to the described embodiments.

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail with reference to the accompanying examples and figures 5-11.

A method of laser machining a pinhole according to an embodiment of the present invention may include the steps of:

step one, filling and processing small holes: and processing an initial through hole in a layered scanning filling mode, wherein the initial through hole comprises a round hole and a special-shaped hole. For example, a cylindrical through hole is processed at a processing position on a workpiece by a circular reciprocating motion of a plurality of concentric processing paths from inside to outside, the distance between the concentric processing paths ensures that the laser is overlapped without a gap, so as to remove all materials in the hole, namely, the materials are removed in a filling mode, as shown in fig. 6, the concentric processing paths are

concentric circles

1, 2, 3, 4 and 5, the concentric circle 5 is the outermost contour of the processing path, the processing paths of the five concentric circles are processed according to the path 1, and then the processing paths of the 2 path, the 3 path, the 4 path and the 5 path are processed in sequence; the special-shaped hole diffusion section is processed in a similar mode, referring to the attached drawing 7, firstly, the three-dimensional digital model of the special-shaped hole diffusion section is sliced in a layering mode along the hole axis direction to obtain each layer of outline shown in the attached drawing 7(a), then, a scanning filling path of each layer is generated, as shown in the attached drawing 7(b), a plurality of closed outlines from inside to outside similar to the circular hole are processed, and in the example, 6 spiral outlines are selected for a certain layer.

Step two, the hole wall of the processed hole is processed again: amplifying the outermost outline machining path of each layer of scanning filling machining path of the initial through hole machined in the step one by a certain size to be used as a machining path for machining again, and performing scanning filling machining on each layer in a mode of slightly larger than the outermost concentric circle of the filling path, such as a concentric circle 5 in the attached drawing 5; see also fig. 8, that is, the concentric circles 6, or the processing paths with the sizes of the outermost contours (the outermost contours 6 in the drawing) of each layer of the irregular hole diffusion are also slightly enlarged, so that the edge of the initial through hole is processed in a reciprocating manner not less than once.

Compared with other technologies, the method for processing the small hole by using the laser provided by the embodiment of the invention firstly processes the small hole by using a filling processing method, and has the advantage of thin recast layer; meanwhile, considering that the hole wall of the small hole still has an extremely thin recast layer or craters, local ablation and the like, on the basis, the embodiment of the invention adopts the arrangement that the hole wall of the initial through hole is processed again in the second step for the small hole processed in the first step, and the size of the outer contour of the processing path is slightly larger than that of the outermost contour during filling processing in the first step, so that the recast layer, the ablation layer and the like on the hole wall can be further removed, and the quality of the hole wall of the small hole can be further improved. The effect is shown in fig. 9, 10 and 11, wherein fig. 9 is compared with fig. 4, and fig. 10 is compared with fig. 5, and no re-coagulation is accumulated on the pore wall; FIG. 11 is a schematic metallographic picture of a longitudinal section of a nanosecond laser processed round hole, and FIG. 11 is a schematic metallographic picture of a partial metallographic picture of a longitudinal section of a nanosecond laser processed round hole, as compared with FIG. 3, it can be seen that the quality of the hole wall is obviously improved after the round hole is processed by the method of the embodiment of the invention

In summary, in the embodiments of the present invention, a filling processing method is first selected to process a small hole shape; and then, the wall of the small hole is polished by using the same outer contour machining with slightly enlarged size so as to remove the defects of the recast layer of the hole wall, the ablation crater, the accumulation of the re-condensed matters of the diffusion section of the special-shaped hole and the like caused by the machining in the step one, and the quality of the wall of the small hole is obviously improved.

According to yet another embodiment of the present invention, steps one and two may be performed by a scanning galvanometer. Therefore, the same processing equipment and the same laser beam on the same processing equipment can be adopted for processing, and the method has the advantages of one-step processing and forming, does not need secondary processing, and does not need to adjust process parameters; parameters are unchanged and positions of workpieces are unified in the processing processes of the first step and the second step, so that the processing quality can be greatly improved.

According to another embodiment of the present invention, the radius of the concentric circles processed in the second step is equal to the radius of the outermost concentric circle processed in the first step plus 0.02mm ± 0.01mm, i.e. 0.01mm to 0.03 mm. The heterogeneous pore diffuser segment is similar. Further, the average power and the pulse energy of the laser are kept constant during the laser processing of the embodiment of the invention. The average power and the pulse energy of the laser are kept in a constant state, which is beneficial to obtaining the uniform pore wall of the small pore, and meanwhile, one parameter of a processing device can be utilized for one-time processing without adjusting process parameters, and the processing can be automatically finished at one time.

According to a further embodiment of the invention, the pulse width of the laser comprises the order of nanoseconds, picoseconds or femtoseconds. As described above, although the penetration depth of the millisecond laser drilling technology is large, the material removal mechanism is mainly melting, which inevitably generates large thermal influence, easily generates heat-induced defects such as recast layer, even micro-crack and the like on the hole wall of the small hole, and has poor roughness of the hole wall and low dimensional accuracy such as roundness and the like. The action time of processing the small hole by using the pulse laser with nanosecond, picosecond and femtosecond orders of magnitude and the material is greatly shortened, and the laser power density is improved by two or more orders of magnitude compared with that of the millisecond pulse, so that the material removal is mainly based on a gasification mechanism, the heat influence on the periphery of an action area is much smaller, the obtained recast layer of the hole wall of the small hole is very thin, and the quality of the hole wall of the small hole can be greatly improved.

Further, in the processing process of processing the small holes by using the laser, the protective gas is continuously introduced into the small holes. A large amount of heat can be generated in the small hole in the process of processing the small hole by laser, the temperature of a workpiece rises rapidly under the action of the heat, and a high-temperature workpiece is easy to have oxidation reaction with air under the condition of five protective gases to form an oxide layer on the wall of the small hole. Therefore, the protective gas is introduced to avoid the generation of an oxide layer, which is beneficial to improving the quality of the pore wall of the small pore.

Specifically, the protective gas is inert gas. The inert gas is inactive, nontoxic and environment-friendly, and can ensure the separation of the pore wall of the small hole from the air and avoid the formation of an oxide layer to influence the processing quality.

It should be noted that the small holes shown in the embodiments of the present invention are through holes.

The following describes an example of the present invention with another specific comparative test.

Firstly, when the nanosecond laser processing small hole according to the embodiment of the invention is selected and used in the experimental group, the scanning galvanometer is selected and used for processing, the average power of the laser output by the scanning galvanometer is 40W, the pulse energy is 6mJ, the small hole with the depth of 2mm is filled and processed, and finally the small hole with the hole wall basically without a recast layer is obtained, which is shown in figure 11.

The contrast group is implemented by a scanning galvanometer, the scanning galvanometer is operated according to a common mode in the prior art, the average power of laser output by the scanning galvanometer is 40W, the pulse energy is 6mJ, and small holes with the depth of 2mm are filled and processed. After the machining is finished, a recast layer of the small hole is observed to obviously exist, particularly, the recast layer which is about 5m exists in the hole wall area adjacent to the hole inlet, and the recast layer is deposited more and thicker at the edge of the hole inlet, which is shown in the attached figure 3.

The above comparison verification is performed by using the laser with the above parameters, but the protection scope of the present invention is not limited to the above parameters.

It should be clear that the embodiments in this specification are described in a progressive manner, and the same or similar parts in the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. The present invention is not limited to the specific steps and structures described above and shown in the drawings. Also, a detailed description of known process techniques is omitted herein for the sake of brevity.

The above description is only an example of the present application and is not limited to the present application. Various modifications and alterations to this application will become apparent to those skilled in the art without departing from the scope of this invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A method of laser machining an aperture, comprising the steps of:

firstly, processing an initial through hole in a layered scanning filling mode, wherein the initial through hole comprises a round hole and a special-shaped hole;

step two, amplifying the outermost outline machining path of each layer of scanning filling machining path of the initial through hole to a certain size to be used as a machining path for machining again;

and the step one and the step two are continuously finished in the same processing program by adopting the same laser focusing processing equipment under the condition of the same process parameter.

2. A method of laser machining an aperture as claimed in claim 1, wherein the first and second steps are performed by a laser focus machining apparatus equipped with a scanning galvanometer and coaxially assist with air blowing.

3. A method of laser machining an aperture as claimed in claim 1, wherein the pulse width of the laser comprises the order of nanoseconds, picoseconds or femtoseconds.

4. A method of laser machining a small hole as claimed in claim 1, wherein the step two machining a contour path dimension of the hole wall is circumferentially uniformly enlarged by 0.01 to 0.03mm from an outermost contour dimension of the step one scanning and filling machining path.

5. A method of laser machining an aperture as claimed in claim 1, wherein the machining parameters of the laser are maintained constant during the laser machining process.