WO2017012184A1 - 一种变光斑多层交错激光冲击均匀强化叶片的方法 - Google Patents

一种变光斑多层交错激光冲击均匀强化叶片的方法 Download PDF

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WO2017012184A1
WO2017012184A1 PCT/CN2015/089214 CN2015089214W WO2017012184A1 WO 2017012184 A1 WO2017012184 A1 WO 2017012184A1 CN 2015089214 W CN2015089214 W CN 2015089214W WO 2017012184 A1 WO2017012184 A1 WO 2017012184A1
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laser
layer
spot
axis
impact
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PCT/CN2015/089214
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English (en)
French (fr)
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鲁金忠
刘月
罗开玉
王志龙
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江苏大学
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Priority to US15/308,596 priority Critical patent/US10640844B2/en
Publication of WO2017012184A1 publication Critical patent/WO2017012184A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D10/00—Modifying the physical properties by methods other than heat treatment or deformation
    • C21D10/005—Modifying the physical properties by methods other than heat treatment or deformation by laser shock processing
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
    • F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
    • F01D5/12—Blades
    • F01D5/28—Selecting particular materials; Particular measures relating thereto; Measures against erosion or corrosion
    • F01D5/286—Particular treatment of blades, e.g. to increase durability or resistance against corrosion or erosion
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/06—Surface hardening
    • C21D1/09—Surface hardening by direct application of electrical or wave energy; by particle radiation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D10/00—Modifying the physical properties by methods other than heat treatment or deformation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2221/00—Treating localised areas of an article
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2230/00—Manufacture
    • F05D2230/90—Coating; Surface treatment
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
    • F05D2300/00—Materials; Properties thereof
    • F05D2300/50—Intrinsic material properties or characteristics
    • F05D2300/516—Surface roughness

Definitions

  • the invention relates to a laser surface impact strengthening technology, in particular to a laser beam impact uniform strengthening process method, which is suitable for uniform strengthening treatment of blade edge parts of a turbine low-pressure transition zone blade, a gas turbine blade, an aircraft turbine and the like.
  • Laser shock peening is a new type of surface strengthening technology.
  • the strong shock wave formed by the strong laser on the metal surface causes the plastic surface to undergo severe plastic deformation, induces deep residual compressive stress and refines the grain, and significantly improves the surface properties of the metal parts.
  • it has four distinct characteristics: high pressure (the shock wave pressure reaches the GGa-TPa level), high energy (peak power reaches the GW order), ultra-fast (tens of nanoseconds) and ultra-high strain rate (reach);
  • the residual compressive stress layer formed by the invention can effectively eliminate the stress concentration inside the material and inhibit the initiation and expansion of the crack, and can significantly improve the fatigue life and corrosion resistance and wear resistance of the metal parts.
  • the shape of the spot is also an important factor affecting the impact effect.
  • the square spot with uniform distribution of single pulse energy produces a plane shock wave of equal intensity, and the uniformity of residual compressive stress induced by the "face strengthening" effect is good, the roughness is small, and the strengthening effect is good;
  • the research proves that the laser shock peening technology is an effective means to prolong the crack initiation time and reduce the crack propagation speed to improve the life of the material. It is also one of the advanced manufacturing methods under extreme conditions, and has the unparalleled advantages and remarkable technical advantages of conventional processing methods.
  • microstructure and residual stress of the workpiece surface and the grain refinement depth have a significant influence on the quality and performance of the workpiece surface, directly affecting the contact strength, corrosion resistance, wear resistance, sealing property and fatigue resistance of the workpiece surface;
  • the present invention proposes a method for uniformly strengthening a blade by a variable-spot multi-layer interlaced laser impact; that is, a multi-layer interlaced laser impact method using a plurality of spot sizes of a square spot to effectively reduce surface roughness and generate Thicker residual stress and grain refining layer enhance corrosion resistance and improve workpiece life; it should be noted that the laser energy density should be prevented from exceeding the threshold that the material can withstand, causing damage to the surface of the material. Different, need specific analysis.
  • the spot size variation of the present invention is only considered in the destruction threshold range.
  • FIG. 2 is a front view of the grid-like absorbing layer, and the side length of a single grid is a.
  • the output power and spot parameters of the laser are set by the laser control device so that the spot shape is square, the side length is also a, and the adjacent square spots are not overlapped.
  • the laser is turned on, and the first layer laser shock strengthening of the workpiece to be processed surface is realized by the numerical control system controlling the movement and rotation of the five-axis table by the progressive processing method.
  • the laser spot size parameter is changed by the laser control device so that the spot shape is square, the side length is a/2, the adjacent square spot is not overlapped, and other process parameters are unchanged.
  • the laser is turned on, and the second layer laser shock strengthening is performed on the surface to be processed of the workpiece by controlling the movement and rotation of the five-axis table by the numerical control system.
  • the pulsed laser beam for laser shock enhancement used in the present invention is a square spot having a side length a of 2-8 mm, a frequency of 1-5 Hz, a pulse width of 8-30 ns, and a pulse energy of 3-15 J.
  • the back of the absorbent layer is tacky and can be attracted to the smooth surface of the workpiece.
  • the invention has the beneficial effects that the method uses multiple adjacent light spots to overlap the layers, and performs interlayer interlacing impacts of different spot sizes, which can effectively eliminate the spot boundary effect, reduce the roughness of the processed surface, and refine the stress layer.
  • the grain has the effect of uniformly strengthening the surface residual stress layer; and under the same laser energy density condition, the larger size spot makes the residual stress and the grain refinement area deeper, and a larger uniform strengthening layer is obtained. It can more effectively eliminate stress concentration inside the material and inhibit the initiation and expansion of cracks, and significantly improve the fatigue life and corrosion resistance and wear resistance of metal parts.
  • Fig. 1 is a schematic view of a device for obtaining a uniform strengthening and corrosion-resistant surface by a square spot laser shock.
  • FIG. 2 is a front view of a grid-like absorbing layer; (a) a first layer of absorbing layer, (b) a second, three layer of absorbing layer; a, a/2 is a single grid size.
  • A is the first laser shock start point
  • B is the second laser strike start point
  • C is the third laser strike start point.
  • Figure 4 is a schematic diagram of the residual stress layer when the a, a/2 spot size impacts the target, respectively, and is the residual stress layer depth.
  • Figure 5 is a comparison of the metallographic structure, a, b are the multi-spot interlaced laser impact of the variable spot and the ordinary single-shot metallographic diagram.
  • the invention provides a method for uniformly strengthening a blade by a variable-spot multi-layer interlaced laser impact, that is, an inter-layer interlaced impact of different spot sizes is performed by using adjacent spots without overlapping, so as to eliminate the spot boundary effect.
  • the surface roughness of the machined surface is reduced, and the surface grain is refined to form a large-area uniform strengthening effect on the surface of the workpiece and a large depth.
  • the surface to be processed of the workpiece 6 is covered with the grid-like absorbing layer 5, and the workpiece 6 is mounted on the five-axis table 7.
  • the output power and spot parameters of the laser 1 are set by the laser control device 2 so that the spot shape is square, the square spot size is a, and the adjacent square spots are not overlapped.
  • the laser 1 is turned on, and the first layer laser shock strengthening of the surface to be processed of the workpiece 6 is realized by the numerical control system 8 controlling the movement and rotation of the five-axis table 7 by the progressive processing method.
  • the spot size parameter of the laser 1 is adjusted by the laser control device 2 so that the spot shape is square, the square spot size is a/2, the adjacent square spots are not overlapped, and other parameters are unchanged.
  • the laser 1 is turned on, and the movement and rotation of the five-axis table 7 are controlled by the numerical control system 8 by the progressive processing method to realize the second layer laser shock strengthening of the surface to be processed of the workpiece 6.
  • the pulsed laser beam for laser shock enhancement used in the present invention is a square spot having a side length of 2-8 mm, a frequency of 1-5 Hz, a pulse width of 8-30 ns, and a pulse energy of 3-15 J; the mesh absorption layer The design is adjacent to the square.
  • the spot is not overlapped; the multi-layer interlaced laser impact enhancement of different sizes is adopted.
  • the size of the first layer of laser shock treatment is different from that of the second, third, second and third layers, and the other processes of the three-layer laser shock treatment.
  • the parameters are the same; and the starting point position of each layer of laser shock tensification processing is different from the starting point of the previous layer of laser shock tensification processing by a/3 in the X direction, and the difference in the Y direction is a/3.
  • the preparation method of the invention adopts the absorption layer: mixing GN-521 silicone gel, cyanoacrylate and methyl tert-butyl ether in a ratio of mass ratio of 5:3:2, and reacting at 70-90 ° C for 10 min to 30 min.
  • the front side is pressed according to the side length of the square spot and the lap joint, and the back surface is a flat surface. After cooling, a mesh absorbing layer having a thickness of 0.8-1 mm is formed.
  • the laser impact enhancement of the center of 24 mm ⁇ 18 mm of 65 mm ⁇ 32 mm ⁇ 2 mm LY2 aluminum alloy is carried out; the process parameters of the laser are: pulse width 10 ns, frequency 5 Hz, pulse energy 6 J, spot shape is square, spot size a is 6mm, the adjacent square spots are not overlapped.
  • the specific steps are as follows:
  • the laser spot size parameter is adjusted by the laser control device to be 3 mm, and other parameters are unchanged.
  • the implementation of this example enables the material surface to be effectively eliminated with respect to a single layer point-by-point laser shock mode under the same parameters.
  • the spot boundary effect, surface roughness has good consistency, the surface roughness Rz is about 2.6, the grain is further refined as shown in Fig. 5, and the grain size after refinement is about 3-5 um; thus forming on the surface of the workpiece and at a large depth.

Abstract

一种采用不同光斑尺寸的激光对叶片进行多层交错冲击强化的方法。该方法的特点包括：以相邻光斑紧挨不搭接的方式进行三层冲击，在第一层采用大光斑的激光进行冲击以产生较深残余应力层，第二和第三层采用小光斑的激光进行交错冲击以消除光斑边界效应并降低加工表面的粗糙度。

Description

一种变光斑多层交错激光冲击均匀强化叶片的方法 技术领域
本发明涉及到激光表面冲击强化技术，特指一种变光斑激光冲击均匀强化工艺方法，适合于汽轮机低压过渡区叶片、燃气轮机叶片、飞机涡轮等叶片类零件边缘均匀强化处理。
背景技术
激光冲击强化是一种新型的表面强化技术，强激光作用于金属表面形成的超强冲击波使金属表层产生剧烈塑性变形，诱导较深残余压应力和细化晶粒，显著提高了金属零件表面性能，与其他技术相比具有高压(冲击波压力达到GPa-TPa量级)、高能(峰值功率达到GW量级)、超快(几十纳秒)和超高应变率(达到)四个鲜明特点；其形成的残余压应力层能有效地消除材料内部的应力集中和抑制裂纹的萌生和扩展，能够显著提高金属零件的疲劳寿命以及抗腐蚀和抗磨损能力。而光斑形状也是影响冲击效果的重要因素，单脉冲能量均匀分布的方形光斑产生等强度的平面冲击波，形成“面强化”效应诱导的残余压应力均匀性好，粗糙度小，强化效果佳；大量的研究证明激光冲击强化技术是延长裂纹萌生时间降低裂纹扩展速度提高材料寿命的有效手段，也是极端条件下的先进制造方法之一，具有常规加工方法无可比拟的优点和显著的技术优势。
1994年12月，在美国国防部制造技术(ManTech)研究计划下，美国通用电气(GE)公司和激光冲击强化技术(LSPT)公司合作开发激光冲击强化技术，以提高整体叶盘和风扇叶片的耐久性和降低其对外来物损伤的敏感性。
2002年开始，美国金属改性公司(MIC)将激光冲击强化技术商业化推广，对波音、空客、湾流等公司飞机叶片进行强化处理，并拓展到汽轮机叶片的强化处理上，取得了显著的强化效果和经济效益。
本世纪初期，法国科学家Peyre就尝试将激光冲击强化技术应用到奥氏体不锈钢抗点蚀性能的研究上，结果表明AISI 316不锈钢经激光冲击强化后在0.5MNaCl溶液中的抗点蚀性能明显提高。
工件表面的微观形貌和残余应力及晶粒细化深度对其质量和性能有显著影响，直接影响到工件表面的接触强度、抗腐蚀性、耐磨性、密封性、抗疲劳性等；
由于激光冲击强化在大面积搭接连续冲击时，特别是冲击曲面时，由于在超短时间内产生超强等离子体汽化爆炸，多次冲击时非常容易使吸收层翘曲、剥落，从而导致材料表 面烧蚀和破损；因此采用激光冲击强化提高抗腐蚀性能必须解决以下几个共性基础问题：(1)冲击导致的残余压应力场和表面微形貌均匀性问题；(2)材料变截面沿展向长度相对厚度不同的强化效果一致性问题；(3)材料变曲率扭曲表面的激光冲击强化工艺准则；(4)大面积搭接冲击时搭接区域吸收层易翘曲、易剥落的难题。
发明内容
为了解决上述问题，本发明提出了一种变光斑多层交错激光冲击均匀强化叶片的方法；即采用方形光斑多次不同光斑尺寸的多层交错激光冲击的方法，有效的降低表面粗糙度，产生更厚的残余应力和晶粒细化层，增强抗腐蚀性能，提高工件寿命；需要说明的是要防止激光能量密度超过材料能承受的阈值，造成材料表面的损伤，这一阈值不同材料有所不同，需要具体分析。本发明的光斑尺寸变化只考虑在破坏阈值范围。
具体操作步骤为：
(1)在工件待加工表面覆盖网格状吸收层，并将工件安装五轴工作台上；图2为网格状吸收层正面示意图，单个网格的边长为a。
(2)通过激光器控制装置设定激光器的输出功率和光斑参数，使其光斑形状为方形，边长尺寸为同样为a，相邻方形光斑紧挨不搭接。
(3)通过数控系统调节五轴工作台使激光束位置与网格状吸收层角点的单个网格重合，作为第一层的激光冲击强化处理起始点位置，即图3-a中的A点，并使网格约束层的X轴和Y轴与工作台的X轴和Y轴一致。
(4)采用流水作为约束层，打开激光器，采用逐行加工的方法通过数控系统控制五轴工作台的移动和转动实现对工件待加工表面进行第一层激光冲击强化。
(5)通过激光器控制装置改变激光器光斑尺寸参数，使其光斑形状为方形，边长尺寸为a/2，相邻方形光斑紧挨不搭接，其他工艺参数不变。
(6)通过数控系统调节五轴工作台使激光束位置与偏移点位置重合，偏移点从步骤(3)中的冲击区域起始点在X方向向冲击区域外偏移a/3，Y方向向冲击区域外偏移a/3，作为第2层的激光冲击强化处理起始点位置，即图3-b中的B点，并使网格约束层的X轴和Y轴与工作台的X轴和Y轴一致。
(7)采用流水作为约束层，打开激光器，采用逐行加工的方法通过数控系统控制五轴工作台的移动和转动实现对工件待加工表面进行第2层激光冲击强化。
(8)通过数控系统调节五轴工作台使激光束位置与偏移点重合位置，偏移点从步骤(6)中的冲击区域起始点位置在X方向向冲击区域外偏移a/3，Y方向向冲击区域外偏 移a/3，作为第3层的激光冲击强化处理起始点位置，即图3-b中的C点，并使网格约束层的X轴和Y轴与工作台的X轴和Y轴一致；激光器的工艺参数同步骤5。
(9)采用流水作为约束层，打开激光器，采用逐行加工的方法通过数控系统控制五轴工作台的移动和转动实现对工件待加工表面进行第三层激光冲击强化。
本发明所采用的激光冲击强化用的脉冲激光束为正方形光斑，边长a为2-8mm，频率为1-5Hz，脉宽为8-30ns，脉冲能量3-15J。
激光光斑尺寸减少的设计可以用公式来说明，激光功率密度计算公式：；式中E为脉冲能量(J)，为脉宽(ns)，D为光斑直径(cm),＝0.8；如图4在相同的激光能量密度的条件下，光斑尺寸较大会使得塑性变形深度变大，产生更厚的残余应力和晶粒细化层；而较小尺寸的光斑产生的残余应力层较小，网格吸收层背面具有粘性，能够吸附在光滑工件表面。
本发明的有益效果：本方法使用相邻光斑紧挨不搭接的方式，进行多次不同光斑尺寸的层间交错冲击，能够有效消除光斑边界效应，减少加工表面的粗糙度，细化应力层晶粒，获得均匀强化表面残余应力层的效果；并且相同激光能量密度的条件下，较大尺寸的光斑，使得残余应力和晶粒细化区域变得更深，获得了较大的均匀强化层，能更加有效地消除材料内部的应力集中和抑制裂纹的萌生和扩展，显著提高金属零件的疲劳寿命以及抗腐蚀和抗磨损能力。
附图说明
图1为一种方形光斑激光冲击获得均匀强化及抗腐蚀表面的装置示意图。
图2为网格状吸收层正面示意图；(a)第一层网格吸收层,(b)第二，三层网格吸收层；a,a/2为单个网格尺寸。
图3为工件表面激光冲击区域光斑示意图；A为第一层激光冲击起始点，B为第二层激光冲击起始点，C是第三点的激光冲击起点。
图4中分别为a，a/2光斑尺寸对靶材冲击时的残余应力层示意图；，分别为其残余应力层深度。
图5金相组织对比图，a，b分别为变光斑多层交错激光冲击和普通单次冲击金相图。
图中：1.激光器，2.激光器控制装置，3.方形激光束，4.流水约束层，5.网格状吸收层，6.工件，7.五轴工作台，8.数控系统，9.矩形激光冲击区域。
具体实施方式
下面结合附图对本发作明详细说明。
本发明提供了一种变光斑多层交错激光冲击均匀强化叶片的方法，即使用相邻光斑紧挨不搭接的方式，进行多次不同光斑尺寸的层间交错冲击，以达到消除光斑边界效应，减少加工表面的粗糙度，细化表层晶粒，从而在工件表面及较大深度形成大面积均匀强化的效果，具体步骤为：
(1)将工件6待加工表面覆盖网格状吸收层5，并把工件6安装到五轴工作台7上。
(2)通过激光器控制装置2设定激光器1的输出功率和光斑参数，使其光斑形状方形，方形光斑尺寸为a，相邻方形光斑紧挨不搭接。
(3)通过数控系统8调节五轴工作台7使方形激光束3角点位置与网格状吸收层5角点的单个网格重合在A点，并使网格约束层的X轴和Y轴与工作台的X轴和Y轴一致。
(4)采用流水约束层4，打开激光器1，采用逐行加工的方法通过数控系统8控制五轴工作台7的移动和转动实现对工件6待加工表面进行第一层激光冲击强化。
(5)通过激光器控制装置2调节激光器1的光斑尺寸参数，使其光斑形状方形，方形光斑尺寸为a/2，相邻方形光斑紧挨不搭接，其他参数不变。
(6)通过数控系统8调节五轴工作台7使方形激光束3角点位置与网格状吸收层5的单个网格偏移点位置B点重合，并使网格约束层的X轴和Y轴与工作台的X轴和Y轴一致。
(7)采用流水约束层4，打开激光器1，采用逐行加工的方法通过数控系统8控制五轴工作台7的移动和转动实现对工件6待加工表面进行第二层激光冲击强化。
(8)通过数控系统8调节五轴工作台7使方形激光束3的角点位置由步骤(6)中B点偏移到C点重合，并使网格约束层的X轴和Y轴与工作台的X轴和Y轴一致。
(9)采用流水约束层4，打开激光器1，采用逐行加工的方法通过数控系统8控制五轴工作台7的移动和转动实现对工件6待加工表面进行第三层激光冲击强化。
本发明所采用的激光冲击强化用的脉冲激光束为正方形光斑，边长为2-8mm，频率为1-5Hz，脉宽为8-30ns，脉冲能量3-15J；所述的网格吸收层的设计为相邻方形。
光斑紧挨不搭接；采用不同尺寸多层交错激光冲击强化，第一层激光冲击处理光斑尺寸不同于第二，三层，第二，三层光斑尺寸相同，三层激光冲击处理的其他工艺参数相同；并且每一层激光冲击强化处理起始点位置与前一层激光冲击强化处理起始点位置在X方向上向外相差a/3，Y方向上向外相差a/3。
本发明采用吸收层制备方法为：将GN-521有机硅凝胶、氰基丙烯酸酯、甲基叔丁基醚按照质量比5：3：2的比例混合后在70-90℃反应10min～30min，正面根据方形光斑边长和搭接率制凸模压制，背面为平面，冷却以后形成0.8-1mm厚度的网格吸收层。
实施实例
如图3对65mm×32mm×2mm的LY2铝合金的中心24mm×18mm区域进行激光冲击强化；激光器的工艺参数为：脉宽10ns，频率5Hz，脉冲能量6J，光斑形状为方形，光斑尺寸a为6mm，相邻方形光斑的紧挨不搭接，具体操作步骤如下：
(1)以图3-a，3-b方式制备24mm×18mm(网格数4×3)网格状吸收层，单个吸收层网格边长为6mm,以及24mm×18mm(网格数8×6)网格状吸收层,单个吸收层网格边长为3mm。
(2)将工件清洗抛光处理并把待加工表面覆盖上网格状吸收层，再将工件安装于五轴工作台，以流水作为约束层。
(3)使激光束起始位置与网格状吸收层拐角的单个网格角点重合在A点，并沿网格约束层的X轴和Y轴精确定位，采用逐行加工的方法对工件待加工表面进行第一层激光冲击强化。
(4)通过激光器控制装置调节激光器光斑尺寸参数为3mm，其他参数不变。
(5)将冲击过的网格吸收层去除，在工件表面覆盖新的24mm×18mm(网格数8×6)网格状吸收层，其中激光冲击光斑角点位置B点从网格吸收层中A点位置向在X方向上向外偏移a/3，Y方向上向外偏移a/3，并沿网格约束层的X轴和Y轴精确定位，采用逐行加工的方法对工件待加工表面进行第二层激光冲击强化直到整个加工区域加工完成，形成如图3-b所示的27mm×21mm(光斑数9×7)的第二层激光冲击区域，单个激光光斑边长为3mm。
(6)将冲击过的网格吸收层去除，在工件表面覆盖新的24mm×18mm(网格数8×6)网格状吸收层，其中冲击光斑角点起始位置位于C点，即从B点位置向在X方向上向外偏移a/3，在Y方向上向外偏移a/3，并沿网格约束层的X轴和Y轴精确定位，采用逐行加工的方法对工件待加工表面进行第三层激光冲击强化直到整个加工区域加工完成。形成如图3-b所示的30mm×24mm(光斑数10×8)第三层激光冲击区域，单个激光光斑边长为3mm。
本例的实施使的材料表面相对与相同参数下单层逐点的激光冲击模式有效的消除 光斑边界效应，表面粗糙度拥有良好的一致性，表面粗糙度Rz约为2.6，晶粒进一步细化如图5，细化后晶粒尺寸大约3-5um；从而在工件表面及较大深度形成大面积均匀强化的效果。

Claims (5)

  1. 一种变光斑多层交错激光冲击均匀强化叶片的方法，其特征在于：使用相邻光斑紧挨不搭接的方式，进行多次不同光斑尺寸的层间交错冲击，冲击层数为三层，第一层激光光斑尺寸为a，第二层和第三层激光光斑尺寸为a/2，并且每一层激光冲击强化处理起始点位置在X方向相差a/3，Y方向相差a/3；其他激光冲击强化参数不变。
  2. 如权利要求1所述的一种变光斑多层交错激光冲击均匀强化叶片的方法，其特征在于具体步骤如下：
    (1)在工件待加工表面覆盖网格状吸收层，并将工件安装五轴工作台上，单个网格的边长为a；
    (2)通过激光器控制装置设定激光器的输出功率和光斑参数，使其光斑形状为方形，边长尺寸同样为a，相邻方形光斑紧挨不搭接；
    (3)通过数控系统调节五轴工作台使激光束位置与网格状吸收层角点的单个网格重合，作为第一层的激光冲击强化处理起始点位置，并使网格约束层的X轴和Y轴与工作台的X轴和Y轴一致；
    (4)采用流水作为约束层，打开激光器，采用逐行加工的方法通过数控系统控制五轴工作台的移动和转动实现对工件待加工表面进行第一层激光冲击强化；
    (5)通过激光器控制装置改变激光器光斑尺寸参数，使其光斑形状为方形，边长尺寸为a/2，相邻方形光斑紧挨不搭接，其他工艺参数不变；
    (6)通过数控系统调节五轴工作台使激光束位置与偏移位置重合，偏移点从步骤(3)中的冲击区域起始点在X方向向冲击区域外偏移a/3，Y方向向冲击区域外偏移a/3，作为第2层的激光冲击强化处理起始点位置，并使网格约束层的X轴和Y轴与工作台的X轴和Y轴一致；
    (7)采用流水作为约束层，打开激光器，采用逐行加工的方法通过数控系统控制五轴工作台的移动和转动实现对工件待加工表面进行第2层激光冲击强化；
    (8)通过数控系统调节五轴工作台使激光束位置与偏移位置重合，偏移点从步骤(6)中的冲击区域起始点位置在X方向向冲击区域外偏移a/3，Y方向向冲击区域外偏移a/3，作为第3层的激光冲击强化处理起始点位置，并使网格约束层的X轴和Y轴与工作台的X轴和Y轴一致；激光器的工艺参数同步骤(5)；
    (9)采用流水作为约束层，打开激光器，采用逐行加工的方法通过数控系统控制五轴工作台的移动和转动实现对工件待加工表面进行第三层激光冲击强化。
  3. 如权利要求1或2所述的一种变光斑多层交错激光冲击均匀强化叶片的方法，其特征在于：所采用的激光冲击强化用的脉冲激光束为正方形光斑，边长a为2-8mm，频率为1-5Hz，脉宽为8-30ns，脉冲能量3-15J。
  4. 如权利要求2所述的一种变光斑多层交错激光冲击均匀强化叶片的方法，其特征在于所述的网格状吸收层的设计为：网格吸收层单位网格的设计与每一次激光冲击光斑尺寸大小相同；网格吸收层背面具有粘性，能够吸附在光滑工件表面。
  5. 如权利要求2或4所述的一种变光斑多层交错激光冲击均匀强化叶片的方法，其特征在于所述网格状吸收层的制备方法为：将GN-521有机硅凝胶、氰基丙烯酸酯、甲基叔丁基醚按照质量比5：3：2的比例混合后在70-90℃反应10min～30min，正面根据方形光斑边长和搭接率制凸模压制，背面为平面，冷却以后形成0.8-1mm厚度的网格吸收层。
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