阅读说明：本技术 一种利用激光辅助改性提升软质金属表面加工质量的方法 (Method for improving surface processing quality of soft metal by laser-assisted modification ) 是由 赖敏 薛志富 房丰洲 游开元 于 2021-10-18 设计创作，主要内容包括：本发明涉及一种利用激光辅助改性提升软质金属表面加工质量的方法,利用激光产生的热效应使软质金属表面亚表面材料快速熔化,再冷却后形成晶粒细化改性层,该晶粒细化改性层改变了材料晶界状态,提升了材料的可加工性。本发明所提出的方法,不但可以应用于平面加工,也可以应用于曲面加工、微结构加工。(The invention relates to a method for improving the processing quality of a soft metal surface by using laser-assisted modification, which utilizes the thermal effect generated by laser to rapidly melt the sub-surface material of the soft metal surface and form a grain refinement modified layer after cooling, wherein the grain refinement modified layer changes the grain boundary state of the material and improves the machinability of the material. The method provided by the invention can be applied to plane processing, curved surface processing and microstructure processing.)

1. A method for improving the processing quality of a soft metal surface by using laser-assisted modification is characterized by comprising the following steps:

the thermal effect generated by laser is utilized to rapidly melt the sub-surface material on the surface of the soft metal, and a grain refinement modified layer is formed after the sub-surface material is cooled, so that the grain boundary state of the material is changed by the grain refinement modified layer, and the machinability of the material is improved.

2. The method of claim 1, wherein: the soft metal comprises lead, tin, zinc, magnesium, silver, gold, aluminum or copper.

3. The method of claim 1, wherein: the laser processing technological parameters are as follows: laser power density 10⁴～10⁷W/mm²The scanning speed is 1-100 mm/s, and the repetition rate is 1-200 μm.

4. The method of claim 1, wherein: the cooling comprises one or the combination of more than two modes of air cooling, ethanol spraying, liquid nitrogen cooling or water cooling, and the cooling is carried out until the temperature required by processing is reached.

5. The method of claim 1, wherein: the surface processing is various processing methods, including one or a combination of more than two processing modes of ultra-precision turning, ultra-precision fly-cutting, ultra-precision milling, ultra-precision grinding, ultra-precision planing and ultra-precision polishing.

6. The method of claim 1, wherein: and (3) before the laser modification treatment, pretreating the soft metal to remove a surface oxide layer.

7. The method of claim 1, wherein: the laser modification treatment modulation with different powers and different processing times can be carried out on the sample piece for many times, and different cooling modes are matched.

Technical Field

The invention belongs to the field of metal material processing, relates to a laser technology, and particularly relates to a method for improving the processability of a material by modifying the surface of a soft metal by using the laser technology.

Background

The processing of part of key functional elements of an advanced scientific experimental device needs to be realized by adopting an ultra-precision processing method, and the processing surface integrity (comprising the aspects of surface roughness, defects, microstructures, residual stress and the like) is provided with higher and higher homogenization controllable manufacturing requirements. The integrity of the ultra-precision machined surface, particularly the surface roughness, defect controllability and machining limit, are problems which are urgently needed to be solved at present.

Soft low-melting point materials (such as red copper, tin, lead and alloys thereof) play a very important role in the high-tech field, but the micro-nano scale processing process of the soft metal materials is easy to generate plastic deformation, and defects such as surface scratches, pits and the like and lateral flow are easy to form in the micro-structure processing process, so that high surface shape precision and low surface roughness are difficult to realize. Therefore, the surface modification based processability control technology plays an important role in improving the anti-deformation capability and the processing precision of the soft material.

Surface modification can generally be achieved by elemental doping, surface heat treatment or mechanical methods, but the following problems exist: (1) surface modification techniques are mostly applied to traditional machining, not the field of ultra-precision machining; (2) the traditional surface modification process aims at improving the surface strength and the wear resistance of a part, and is after a mechanical processing link, but the invention aims at improving the processability of soft metal by the technology and is a pretreatment means, so that a higher homogenization requirement is put forward on the modified material structure. As a new method for ultra-precision machining of soft metals, no relevant literature reports exist at present.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for modifying a soft metal by laser assistance, wherein a grain refinement layer is formed on the surface of the soft metal by using a laser technology, and the hardness of the material is improved. The modified material is processed ultraprecisely, and a processed surface with higher quality can be obtained.

The technical scheme adopted by the invention for solving the technical problem is as follows:

a method for improving the processing quality of a soft metal surface by using laser-assisted modification is characterized in that a sub-surface material on the soft metal surface is rapidly melted by using a thermal effect generated by laser and then cooled to form a grain refinement modified layer, and the grain refinement modified layer changes the grain boundary state of a material and improves the machinability of the material.

The soft metal is metal and alloy with Mohs hardness less than or equal to 3 and melting point less than or equal to 1200 ℃, and further, the soft metal is lead, tin, zinc, magnesium, silver, gold, aluminum or copper and alloy thereof.

Moreover, the laser processing technological parameters are as follows: laser powerRate density 10⁴～10⁷W/mm²The scanning speed is 1-100 mm/s, and the repetition rate is 1-200 μm.

And the cooling comprises one or more of air cooling, ethanol spraying, liquid nitrogen cooling and water cooling, and is carried out to the temperature required by processing.

The surface processing is a combination of one or more of ultra-precision turning, ultra-precision fly-cutting, ultra-precision milling, ultra-precision grinding, ultra-precision planing, and ultra-precision polishing.

And, before the laser modification treatment, the soft metal is pretreated to remove the surface oxide layer.

Moreover, the laser modification treatment modulation with different powers and different processing times can be carried out on the sample piece for many times.

The invention has the advantages and beneficial effects that:

1. the invention provides a novel method for processing the ultra-smooth surface of a soft metal and alloy element with high efficiency and high precision. The method improves the processability of soft metal and alloy materials.

2. The invention adopts a method of laser surface modification assisted ultra-precision machining, and can effectively realize high-quality machining of soft metal and alloy elements.

3. The method provided by the invention can be applied to plane processing, curved surface processing and microstructure processing.

Drawings

FIG. 1 is a schematic diagram of laser-assisted modification of soft metals and their alloys;

FIG. 2 is a flow chart of a laser-assisted modification process for soft metals and alloys thereof;

FIG. 3a is an EBSD representation image of the grain distribution on the surface of the unmodified material;

FIG. 3b is an EBSD representation image of the grain distribution on the surface layer of the modified material;

FIG. 4a is a hardness nanoindentation test of the surface layer of an unmodified material;

FIG. 4b is a nano indentation test of the hardness of the surface layer of the modified material;

FIG. 5a is a white light interferometry image of an ultra-precision machined surface of an unmodified material;

FIG. 5b is a white light interferometry image of the ultra-precision machined surface of the modified material.

Detailed Description

The present invention is further illustrated by the following specific examples, which are intended to be illustrative, not limiting and are not intended to limit the scope of the invention.

FIG. 1 is a schematic diagram of laser-assisted modification of soft metals and their alloys. Firstly, modifying the surface of a sample by adopting a laser scanning mode on the surface to obtain a modified layer with a certain depth. Then, the sample is subjected to ultra-precision machining within the modified layer to achieve a high-quality machined surface.

FIG. 2 is a flow chart of the laser-assisted modification process of soft metals and their alloys. The technical scheme adopted by the invention is as follows: fixing a laser on a mechanical support, clamping a metal blank on a displacement table, adjusting the initial position of a laser spot on the blank, controlling the movement of the displacement table by a program to enable the laser to perform scanning movement on the surface of the metal blank, selecting proper laser power density, and controlling the temperature to reach the phase change point or the melting point of metal so as to perform modification. The method specifically comprises the following steps:

(1) cutting, grinding and other operations are carried out on the metal blank to obtain a sample;

(2) mounting the sample on a motorized displacement table through a clamp;

(3) adjusting the position and distance of the laser emergent light path relative to the surface of the sample, and selecting a proper light spot size;

(4) setting laser power density, scanning speed, repetition rate and a modification area;

(5) depending on the characteristics of the metal being processed, an inert gas protection device may be selected: if the metal to be modified reacts with components in the air under the action of laser to influence the modification quality, starting an inert gas protection device to prevent the metal from reacting with the air under the action of high temperature;

(6) carrying out laser modification and applying a proper cooling mode to obtain the modified sample surface;

(7) selecting a proper ultra-precision processing means for the modified surface according to the specific processing requirements of the soft metal and alloy device, wherein the proper ultra-precision processing means comprises but is not limited to ultra-precision turning, ultra-precision fly-cutting, ultra-precision milling, ultra-precision grinding, ultra-precision planing and other means;

(8) and (5) characterizing and evaluating the processing result by adopting measuring equipment.

The main technical problem of the invention is that the technical means of laser-assisted modification process, ultra-precision machining and the like of soft metals and alloy elements thereof are mature. To verify the feasibility of this method, polycrystalline tin (Sn, a typical soft metal) laser-assisted modification and ultra-precision machining experiments were performed. The laser modification parameters of the polycrystalline tin are as follows: laser power density 5.8 x 10⁴W/mm²Scanning speed 10mm/s, repetition rate 10 μm. The ultra-precision machining parameters are as follows: the main shaft rotating speed is 1200r/min, the back cutting amount is 2 mu m, and the feeding amount is 2 mu m.

The following effects are obtained:

(1) the invention refines the grains on the surface layer of the material and improves the surface hardness.

The EBSD technical means is adopted to characterize the grain distribution of the material, the average grain diameter of the unmodified surface layer material is 100 μm as shown in figure 3a, the average grain diameter of the modified surface layer material is 15 μm as shown in figure 3b, and the grain size is obviously refined. The surface hardness of the material is tested by adopting a nano indentation technical means, under the same indentation depth, the nano indentation hardness of the unmodified material is 0.20GPa as shown in figure 4a, and the hardness of the modified material is 0.32GPa as shown in figure 4b, so that the hardness of the material is obviously improved. (2) The surface quality of the modified material obtained by ultraprecise processing is obviously improved.

The surface roughness after ultraprecise machining is measured by adopting a white light interference technology, under the same cutting parameter, the roughness of the machined surface of the unmodified material is 11.71nm as shown in figure 5a, and the roughness of the machined surface of the modified material can reach 2.16nm as shown in figure 5b, so that the surface roughness is obviously improved.

Soft low melting point metals suitable for use in the present invention include, but are not limited to, the metals listed in Table 1 and alloys thereof.

TABLE 1 Soft Low melting Point metals that can be modified with laser assistance

As a means for preprocessing the surface of the metal processing, the surface processing performance of the soft metal is improved, so that the metal processing surface with high surface shape precision, low surface roughness and low subsurface damage is obtained.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the inventive concept, and these changes and modifications are all within the scope of the present invention.