WO2018209739A1 - 一种不同厚度小孔构件激光冲击强化方法 - Google Patents

一种不同厚度小孔构件激光冲击强化方法 Download PDF

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WO2018209739A1
WO2018209739A1 PCT/CN2017/087535 CN2017087535W WO2018209739A1 WO 2018209739 A1 WO2018209739 A1 WO 2018209739A1 CN 2017087535 W CN2017087535 W CN 2017087535W WO 2018209739 A1 WO2018209739 A1 WO 2018209739A1
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laser
impact
small hole
small
thickness
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French (fr)
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姜银方
李旭
赵勇
姜文帆
华程
季彬
朱恒
孟李林
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Jiangsu University
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Jiangsu University
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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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/352—Working by laser beam, e.g. welding, cutting or boring for surface treatment
    • B23K26/356—Working by laser beam, e.g. welding, cutting or boring for surface treatment by shock processing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K2103/00—Materials to be soldered, welded or cut
    • B23K2103/08—Non-ferrous metals or alloys
    • B23K2103/10—Aluminium or alloys thereof
    • 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

Definitions

  • the invention relates to the field of laser processing, in particular to a different thickness small hole member which adopts different laser parameters for laser impact strengthening of different thickness small hole members, so that the reinforcing effects of small hole holes of different plate thicknesses are in a good state.
  • Laser shock enhancement method is a method for laser shock enhancement.
  • the small hole member is a typical stress concentration detail, which is easy to generate fatigue crack under fatigue load, affecting the performance and service life of key structures.
  • Many mechanical parts need to be opened, especially for the parts on the plane. It is necessary to open thousands of holes, which become the weak parts of the parts, and these parts are different in thickness.
  • Conventional mechanical strengthening methods such as mechanical shot peening, extrusion strengthening, etc. are limited by the aperture, and it is not easy to strengthen small holes of 3 mm or less in diameter.
  • Laser shock peening is an advanced material strengthening method, which has the advantages of non-contact, no deformation, no heat-affected zone and significant strengthening effect, but how to control the laser parameters to ensure the small-hole components of different thicknesses of different materials after impact strengthening Achieving good reinforcement is a major difficulty in this field.
  • Patent CN102517413 describes a small hole strengthening method, which is carried out by first using a large spot and high energy laser to impact-enhance the surface of the small hole member to be opened, so that the small hole member generates residual compressive stress deeper in the thickness direction. Then, using a small spot light and small energy laser to perform secondary impact strengthening on the surface around the hole-opening member to be opened, so that the surface of the small-hole member has a good residual compressive stress, and finally punching, this method avoids the first The problem that the end face quality of the hole is not high after the laser impact strengthening is performed after the opening, but this method does not achieve the optimal strengthening state for the small holes of various thicknesses, and requires high power for the equipment and requires high power. Laser equipment.
  • Patent CN103014276 describes a small hole strengthening method using a combination of a cone pressure and a laser. One side is laser-impacted, and the corresponding side of the laser impact is pressed with a special cone indenter, and finally a hole is opened at the pressed position.
  • the method makes the hole wall of 4mm-6mm plate thickness be compressive stress, the cone pressing process easily deforms the plate, and the surface quality of the cone pressing surface cannot be guaranteed.
  • the residual compressive stress of the hole wall with different plate thickness is unstable, especially The quality of thick plate processing is difficult to guarantee.
  • Patent application No. 200610096476.5 the invention name is a method and device for strengthening the hole wall based on the laser shock wave technology, and it is proposed to insert a reflection cone into the aperture of the apertured hole member and apply it on the cone surface of the reflection cone.
  • the upper energy absorbing layer and the constraining layer are subjected to laser shock strengthening of the hole wall.
  • the method is not limited by the pore size, and the strengthening layer can be made uniform.
  • the laser will cause certain damage to the small hole, thereby affecting the precision of the hole and the wall of the hole. Surface Quality.
  • the invention aims at the above deficiencies, and provides a laser impact strengthening method for different thickness small hole members, which considers the strengthening effect of different thickness materials and the deformation of the small hole member and the surface quality requirement of the impact member, and the small hole member with different thickness for different materials.
  • Laser shock enhancement process parameter selection problem after a large number of experiments and statistical analysis, an empirical formula and process parameter determination method were proposed to ensure satisfactory fatigue gain at 95% confidence.
  • the technical solution of the present invention is that the specific steps of the parameter selection of the present invention are firstly determined according to the properties of the material, the thickness, the properties of the constraining layer and the absorbing layer used, and the requirements for the amount of deformation and surface quality of the material after impact, combined with empirical formulas.
  • the laser power density used is secondly determined according to the selected power density and the laser device, and the pulse width, laser energy, and spot size are determined in turn. Finally, the lap ratio and the number of impact layers are determined according to the selection principle of the impact region and the coverage ratio. Specific steps are as follows:
  • a laser impact strengthening method for different thickness small hole members comprising the steps of: pretreating the surface of the small hole member, then providing an energy absorbing layer on the surface of the small hole member to be opened, and providing a constraining layer on the surface of the absorbing layer,
  • the pre-treated small hole member is fixed on the numerical control workbench, and the laser is used to impact-enhance the area to be opened of the small-pore member, and different laser impact-enhancement process parameters are adopted for different thickness small-hole members, and the process parameters are selected and
  • the method of determination is as follows:
  • P is the peak pressure of the laser shock load acting on the material of the small hole member, the yield strength of the ⁇ s material, and k is a constant associated with the constraining layer and the absorbing layer;
  • t p is the laser pulse width, which is related to the laser.
  • the thicker material component uses a larger laser pulse width t p , which is 10 ns to 30 ns.
  • the laser laser energy E is related to the power of the laser. Energy E is 2J ⁇ 35J, using a small laser, using a small spot diameter D, the spot diameter D ranges from 2mm to 6mm; high power laser, large spot diameter D, improve production efficiency; ensure laser power density At I 0 , the spot diameter D and the pulsed laser energy E are appropriately adjusted; for example, a square spot, Where D is the side length of the spot;
  • Empirical formula The value of the middle A is related to the process parameters such as the component material, the constraining layer and the absorption layer.
  • the main relevant factors are the component material and the constraining layer.
  • the value of the thickness influence coefficient B in the empirical formula is related to the material.
  • the value of A ranges from 2 to 5.
  • the rigidity of the small hole member is large, and the surface hardness of the material is large.
  • A can take the upper limit value. Considering the requirements of the user on the deformation amount and surface roughness of the laser shock reinforced, A can be considered to float up and down.
  • the impact range of the laser is in the range of 2.8d to 3.8d, d is the aperture size, and the thickness of the small hole member is taken as the lower limit; the distance between the laser impact region and the boundary between the laser impact region and the other laser impact region should not be Less than 3 mm, reducing the edge effect, and the effect between the impact area and the impact area.
  • the opening is better than the impact after the first opening, the impact mode is double-sided impact, so that the hole wall has a better stress distribution; when the lap ratio is greater than 63%, the jump-shooting method is adopted to prevent absorption. Damage to the layer.
  • the method can strengthen the surface and the hole wall of various plate thickness small hole members, and can well control the deformation of the sheet material.
  • the method can meet the strengthening needs of different pore sizes and ensure the quality of the pore walls.
  • This method reduces the requirements for lasers and other equipment, and can use a small energy laser to reduce the cost of small hole reinforcement.
  • the method can meet the customer's fatigue gain effect requirements and surface quality requirements within a certain range, especially to ensure stable processing quality of thicker plates.
  • This method breaks through the limitation that the small holes with a diameter of 3mm or less can not be strengthened, and it is a difficult point in the field to ensure that the small-hole members with different thicknesses of different materials can achieve good strengthening effect after impact strengthening.
  • FIG. 1 is a schematic view of laser shock enhancement according to an embodiment of the present invention.
  • FIG. 2 is a road diagram of a laser shock process according to an embodiment of the present invention.
  • Table 1 Laser shock parameters and fatigue gain of each plate thickness of 7050-T7451 aluminum alloy in the conditions of the method
  • Table 3 The laser shock parameters and fatigue gain of each plate thickness of the 2024-T62 aluminum alloy in the conditions of the method.
  • Embodiment 1 is a diagrammatic representation of Embodiment 1:
  • the material used is 7050-T7451 aluminum alloy sheet, the thickness is 3mm, 4mm, 5mm, 6mm, and the aperture size required for opening is 2.6mm.
  • the surface of the orifice member 4 is pretreated first, and then an aluminum foil is attached as an energy absorbing layer 3 on the surface of the member to be opened, and water is used as the constraining layer 2 to allow water to flow uniformly over the surface of the aluminum foil.
  • the small hole member 4 is fixed on the numerical control worktable with a clamp, and the running path of the numerical control worktable is programmed so that the laser can just strengthen the part to be opened of the component.
  • the laser device determines energy, pulse width, spot and other parameters, wherein the spot diameter D ranges from 2 mm to 6 mm, the laser energy E is selected from 2 J to 35 J, and the laser pulse width t p is selected from 10 ns to 30 ns.
  • the impact area of the laser ranges from 2.8d to 3.8d, and d is the aperture size.
  • the final power density is close to the power density obtained by taking A 2.6.
  • the impact mode is double-sided impact, the number of layers is 2 layers, double-sided impact is the front side and the reverse side.
  • the double-sided impact once indicates that the number of impact layers is 1 layer. When the overlap ratio is 63%, the jump is used and the jump is used.
  • the spot size can be changed to control the power density of the laser; the power density, the selected parameters and the gain at 95% confidence interval used in this example are shown in Table 1. It can be seen from the table that the average coverage ⁇ is between 400% and 700%, and the fatigue gain effect is better.
  • the fatigue gain of the four plate thickness small hole members is relatively stable, mostly concentrated between 150% and 230%.
  • the stiffness and hardness of the material are not high, the selected power density is small, so the surface quality is good, and the sheet material is basically not deformed.
  • the material used in the embodiment is a TC4-DT titanium alloy sheet having a thickness of 3 mm, 4 mm, and 6 mm, and the aperture size required for the opening is 2.6 mm.
  • the surface of the orifice member 4 is pretreated first, and then the aluminum foil 3 is applied as an energy absorbing layer on the surface of the member with the opening portion, and water 2 is used as a constraining layer to allow water to flow uniformly through the surface of the aluminum foil.
  • the fixture is used to fix the component on the numerical control workbench, and the running path of the numerical control workbench is programmed so that the laser can just strengthen the part to be opened of the component.
  • the small hole member 4 with a thickness of 3 mm in this example has a laser power density of about 4.9 GW/cm 2 and a small hole member 4 with a thickness of 4 mm.
  • the power density is about 7.27 GW/cm 2
  • the laser power density of the small hole member 4 having a thickness of 6 mm is about 15.69 GW/cm 2 ;
  • the lap ratio used in this example is 50%
  • the impact mode is double-sided impact.
  • the power density, the selected parameters and their gains at 95% confidence interval are shown in Table 2.
  • the fatigue gain of the three kinds of small hole members is mostly between 200% and 270%, the fatigue gain is obvious, and the surface quality is good after impact, and the sheet material is basically free from deformation due to the material hardness and rigidity.
  • the material used in the present example is a 2024-T62 aluminum alloy sheet having a thickness of 2.5 mm and 5 mm, and the aperture size required for the opening is 2 mm.
  • the surface of the orifice member 4 was pretreated first, and then an aluminum foil was attached as an energy absorbing layer 3 on the surface of the member with the opening portion, and a 4.5 mm thick K9 glass was used as the constraining layer 2.
  • the fixture 4 is fixed on the numerical control workbench with a clamp, and the running path of the numerical control worktable is programmed so that the laser can just strengthen the portion of the material to be opened.
  • A is about 4.8
  • the laser power density of the small hole member 4 having a thickness of 2.5 mm is about 1.57 GW/cm 2
  • the laser power density of the small hole member 4 having a thickness of 5 mm is about 2.36 GW/cm 2 .
  • the laser device determines parameters such as energy, pulse width, and spot, and the resulting power density is close to the power density obtained by taking A 4.8.
  • the power density used, the selected parameters and their gains at 95% confidence intervals are shown in Table 3.
  • the fatigue gain of the sample is obvious, but due to the low hardness of the material, the value of A is large, the surface of the material is deep, and the surface quality is relatively poor.
  • the strengthening effect that can be achieved by the method is described in conjunction with Tables 1, 2 and 3.
  • the fatigue power gain obtained by using the laser power density selected by the method and the selected laser parameters is obvious and stable, the material deformation amount is close to zero, and the surface does not appear ablated.

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Abstract

一种不同厚度小孔构件（4）激光冲击强化方法，该方法中不同厚度小孔构件（4）激光冲击强化采用不同的工艺参数，并通过大量试验后进行统计分析得到了经验公式，其经验公式为功率密度与小孔构件（4）厚度的关系式AA。根据此关系式确定不同厚度小孔构件（4）激光冲击强化的功率密度，并提出了与此相关的工艺参数的选择与确定方法。根据此方法，不种厚度的小孔构件（4）采用适当的工艺进行激光冲击强化后，可以获得合理的残余压应力分布，达到良好强化效果，并对构件进行有效的冲击质量的控制，在保证小孔构件（4）的疲劳寿命的前提下，控制工件的变形。

Description

一种不同厚度小孔构件激光冲击强化方法 技术领域
本发明涉及激光加工领域，特指对于不同厚度的小孔构件激光冲击强化时采用不同的激光参数，使不同板厚的小孔孔的强化效果均达到良好的状态的一种不同厚度小孔构件激光冲击强化方法。
背景技术
小孔构件是典型的应力集中细节，易在疲劳载荷下产生疲劳裂纹，影响关键结构的使用性能和服役寿命。而很多机械零件都需要进行开孔处理，特别是飞机上的零件更是要开上千个孔，这些孔就成了零件的薄弱环节，而这些零件又厚度不一。传统的机械强化方法如机械喷丸、挤压强化等受到孔径的限制，对于直径3mm以下的小孔不容易强化。激光冲击强化是一种先进的材料强化方法，具有非接触、无形变、不存在热影响区及强化效果显著等优点，但如何控制激光参数以保证不同材料不同厚度的小孔构件在冲击强化后均能达到良好的强化效果是该领域的一大难点。
专利CN102517413中叙述了一种小孔强化方法，其实施方法是先用大光斑大能量的激光对小孔构件待开孔表面进行冲击强化，使小孔构件沿厚度方向较深处产生残余压应力，再用小光斑小能量的激光对小孔构件待开孔位置四周的表面进行二次冲击强化，使小孔构件表面产生较好的残余压应力，最后进行打孔，这种方法避免了先开孔后进行激光冲击强化而产生的孔端面质量不高的问题，但是该种方法并不能使各种板厚的小孔都达到最佳的强化状态，且对于设备要求较高，需要大功率的激光器设备。
专利CN103014276中叙述了一种用锥压与激光相结合的小孔强化方法，一面用激光冲击，激光冲击对应的背面用特质的锥压头压入，最后在压入的地方开孔。该方法虽然使得4mm-6mm板厚的孔壁为压应力，但锥压过程容易使板材变形，锥压面的表面质量也不能保证，不同板厚的孔壁残余压应力不稳定，特别是较厚板处理质量较难保证。
专利申请号为200610096476.5的发明专利，发明名称为一种基于激光冲击波技术孔壁的强化方法和装置，提出了在已开孔的小孔构件孔径内插入反射锥，在反射锥的锥面上涂上能量吸收层和约束层，再对孔壁进行激光冲击强化。该方法与机械喷丸相比不受孔径大小的限制，且可使得强化层均匀，但由于是先开孔再强化，激光会对小孔造成一定的损伤，从而影响孔的精度与孔壁的表面质量。
发明内容
本发明针对以上不足，提供一种不同厚度小孔构件激光冲击强化方法，该方法考虑不同厚度材料的强化效果以及小孔构件的变形和冲击构件的表面质量要求，针对不同材料不同厚度小孔构件激光冲击强化工艺参数选择问题，经过大量的试验和统计分析，提出一个经验公式和工艺参数确定方法，以保证在95％的置信度下获得满意的疲劳增益。
本发明的技术方案是：本发明的参数选择具体步骤是首先根据材料的性能、厚度、所用的约束层与吸收层性能以及冲击后对材料变形量和表面质量的要求，结合经验公式确定该材料所用的激光功率密度，其次根据选用的功率密度与所拥有的激光器设备，依次确定脉宽，激光能量，光斑大小，最后根据冲击区域与覆盖率的选用原则确定搭接率与冲击层数。具体步骤如下：
一种不同厚度小孔构件激光冲击强化方法，包括以下步骤：将小孔构件的表面进行预处理，然后在小孔构件待开孔部位的表面设能量吸收层，在吸收层表面设约束层，将预处理后的小孔构件固定在数控工作台上,使用激光器对小孔构件的待开孔区域进行冲击强化，对不同厚度小孔构件采用不同的激光冲击强化工艺参数，其工艺参数选择与确定方法如下：
1)依据小孔构件材料强度和材料厚度来选择功率密度，其功率密度与小孔构件厚度的关系由公式
Figure PCTCN2017087535-appb-000001
确定，此公式为通过大量试验后进行统计分析得到的经验公式，式中I0为激光功率密度，σs为材料的屈服强度，t为板厚，2/Z＝1/Z1+1/Z2，Z1是小孔构件材料的声阻抗，Z2是约束层的声阻抗，A为综合作用系数，且与小孔构件的材料、约束层和吸收层相关，B为厚度影响系数、且与小孔构件的材料和厚度相关；
2)其下限值应该满足
Figure PCTCN2017087535-appb-000002
和
Figure PCTCN2017087535-appb-000003
P为作用在小孔构件材料上的激光冲击载荷的峰值压力，σs材料的屈服强度，k为常数与约束层和吸收层相关；
3)结合公式
Figure PCTCN2017087535-appb-000004
确定光斑直径D和脉冲激光能量E；tp为激光脉宽，与激光器有关，较厚材料构件采用较大激光脉宽tp，选用10ns～30ns；激光器激光能量E与激光器的功率相关，激光能量E为2J～35J，使用小型化激光器，采用较小光斑直径D，光斑直径D的取值范围在2mm～6mm；高功率激光器，较大光斑直径D，提高生产效率；在保证激光功率密度I0下，光斑直径D和脉冲激光能量E进行适当配合调整；如方形光 斑，
Figure PCTCN2017087535-appb-000005
这里D为光斑的边长；
4)确定激光能量，激光脉宽tp，光斑直径D后，选择搭接率ψ和冲击层数n；圆形光斑搭接率ψ为50％左右，方形光斑搭接率ψ为10％左右；冲击层数n为1层～6层，n的确定与材料的屈服强度σs、激光功率密度I0、光斑搭接率ψ相关，σs小、I0大、ψ大，取下限；搭接率ψ＝相邻光斑重复距离l/光斑直径D(或光斑边长)。
光斑搭接率ψ和冲击层数n还受平均覆盖率η的限定，平均覆盖率η＝N*s1/S，N为冲击1面冲击总的光斑数，s1为一个光斑的面积，S为孔位置冲击区域的面积；平均覆盖率η取200％～800％，如果平均覆盖率η不在200％～800％范围内，需要重新选择所述搭接率ψ和冲击层数n。
经验公式
Figure PCTCN2017087535-appb-000006
中A的取值与构件材料、约束层、吸收层等工艺参数相关，主要相关因素是构件材料与约束层，当材料为铝合金，经验公式中的厚度影响系数B的取值与材料有关，当材料为铝合金时B＝6，约束层为水、K9光学玻璃、有机玻璃、硅胶或合成树脂中任意一种时，A的取值范围在2～5。
经验公式
Figure PCTCN2017087535-appb-000007
中，当材料为钛合金时，B＝2.6；当材料为钛合金时，约束层为水、K9光学玻璃、有机玻璃、硅胶或合成树脂中任意一种时，A的取值范围在0.5～1.25左右。
小孔构件的刚度大、材料的表面硬度大，A可考虑取偏上限值；考虑用户对激光冲击强化后构件对变形量和表面粗糙度的要求，A可考虑上下浮动。
激光的冲击区域的取值范围在2.8d～3.8d，d为孔径大小，小孔构件厚度大取下限；激光冲击区域距材料边界，或激光冲击区域与另激光冲击区域之间的距离应不小于3mm，减小边缘效应，以及冲击区域与冲击区域之间的影响。
先冲击处理后开孔，其效果优于先开孔后冲击，冲击方式为双面冲击，使得孔壁出现较好的应力分布；当搭接率大于63％时，采用跳冲方式，防止吸收层的损坏。
与现有技术相比，本发明的有益效果是：
1.针对不同材料不同厚度的小孔构件激光冲击强化的功率密度选择提出了经验公式
Figure PCTCN2017087535-appb-000008
明确了各激光参数的选用原则与方法，提高了激光冲击强化的科学性。
2.该方法使各种板厚小孔构件的表面与孔壁得到强化，且能很好的控制板料的变形。
3.该方法可以满足不同孔径的强化需要，且保证孔壁质量。
4.该方法降低了对激光器等设备的要求，可采用小能量激光，降低了小孔强化的成本。
5.该方法可以在一定范围内满足客户的疲劳增益效果要求与表面质量要求，特别是保证较厚板处理质量稳定。
6.该方法突破了直径3mm以下的小孔不易强化的限制，保证不同材料不同厚度的小孔构件在冲击强化后均能达到良好的强化效果是该领域的一大难点。
附图说明
图1是本发明一实施方式的激光冲击强化示意图；
图2是本发明一实施方式的激光冲击工艺路线图；
表1 7050-T7451铝合金在本方法条件中的各板厚激光冲击参数及疲劳增益；
表2TC4-DT钛合金在本方法条件中的各板厚激光冲击参数及疲劳增益；
表3 2024-T62铝合金在本方法条件中的各板厚激光冲击参数及疲劳增益。
图中，1、激光束，2、约束层，3、吸收层，4、小孔构件，5、光斑，6、激光冲击路线，7、板料边界。
具体实施方式
下面结合附图和具体实施方式对本发明作进一步详细说明，但本发明的保护范围并不限于此。
实施例一：
本实例中采用材料为7050-T7451铝合金板料，厚度为3mm、4mm、5mm、6mm，需要开孔的孔径大小为2.6mm。如图1所示，将小孔构件4的表面先进行预处理，然后在构件待开孔部位的表面贴上铝箔作为能量吸收层3，使用水作为约束层2，使水匀速流过铝箔表面。用夹具将小孔构件4固定在数控工作台上，对数控工作台的运行路径进行编程，以使激光器刚好可以对构件的待开孔部位进行强化。根据选用的约束层2为水，吸收层3为铝箔，根据P>2σs、
Figure PCTCN2017087535-appb-000009
可知，k＝1，σs＝441Mpa，I0应大于下限值0.78GW/cm2。
根据经验公式
Figure PCTCN2017087535-appb-000010
B＝6，于是A取2.6左右，可得厚度为3mm的小孔构件4激光功率密度在2.85GW/cm2左右，厚度为4mm的小孔构件4激光功率密度在3.37GW/cm2左右，厚度为5mm的小孔构件4激光功率密度在3.98GW/cm2左右，厚度为 6mm的小孔构件4激光功率密度在4.71GW/cm2左右。
根据
Figure PCTCN2017087535-appb-000011
及激光器设备确定能量、脉宽、光斑等参数，其中，光斑直径D的取值范围在2mm～6mm，激光能量E的选择为2J～35J，激光脉宽tp的选择为10ns～30ns，激光器激光的冲击区域的取值范围在2.8d～3.8d，d为孔径大小，最终得出的功率密度接近A取2.6所得出的功率密度即可。冲击方式为双面冲击，层数为2层，双面冲击即正面反面依次冲击，双面冲击一次表明冲击层数为1层，当采用的搭接率为63％，采用跳冲，跳冲即打完第一个光斑后打第三个光斑，跳开第二个，依次类推，在打完第一行后打第三行，跳过第二行，依次类推，打完后回到第一行第二个，第四个依次类推，再打第三行第二个，第四个，依次类推，这样打完后打第二行，第四行，方法同上。当激光器设备能量较小或较大时，可改变光斑大小来控制激光的功率密度；本实例所采用的功率密度、选用参数及其在95％的置信区间下的增益见表1。从表中看出平均覆盖率η在400％-700％之间，疲劳增益效果较好，本实例中4种板厚的小孔构件疲劳增益相对稳定，大多集中在150％-230％之间，虽然材料的刚度与硬度不高，但选取功率密度较小，所以表面质量较好，板料基本不发生变形。
表1
Figure PCTCN2017087535-appb-000012
实例二：
本实例与实施例一的不用之处在于，本实施例中采用材料为TC4-DT钛合金板料，厚度为3mm、4mm、6mm，需要开孔的孔径大小为2.6mm。将小孔构件4的表面先进行预处理，然后在构件带开孔部位的表面贴上铝箔3作为能量吸收层，使用水2作为约束层，使水匀速流过铝箔表面。用夹具将构件固定在数控工作台上，对数控工作台的运行路径进行编程，以使激光器刚好可以对构件的待开孔部位进行强化。根据选用的约束层 与吸收层，根据P>2σs、
Figure PCTCN2017087535-appb-000013
可知，k＝1，σs＝811Mpa，I0应大于下限值2.63GW/cm2。
根据经验公式
Figure PCTCN2017087535-appb-000014
B＝2.6，综合考虑钛合金的刚度与表面硬度，A取0.7左右，所以本实例厚度为3mm的小孔构件4激光功率密度在4.9GW/cm2左右，厚度为4mm的小孔构件4激光功率密度在7.27GW/cm2左右，厚度为6mm的小孔构件4激光功率密度在15.69GW/cm2左右；本实例所采用的搭接率为50％，冲击方式为双面冲击，所采用的功率密度、选用参数及其在95％的置信区间下的增益见表2。本实例中3种厚度的小孔构件疲劳增益大多在200％-270％之间，疲劳增益明显，且由于材料硬度与刚度较大，冲击后表面质量较好，板料基本无变形。
表2
Figure PCTCN2017087535-appb-000015
实例三：
本实例与实施例一的不用之处在于，本实例中采用材料为2024-T62铝合金板料，厚度为2.5mm和5mm，需要开孔的孔径大小为2mm。如图1所示，将小孔构件4的表面先进行预处理，然后在构件带开孔部位的表面贴上铝箔作为能量吸收层3，使用4.5mm厚K9玻璃作为约束层2，。用夹具将构件4固定在数控工作台上，对数控工作台的运行路径进行编程，以使激光器刚好可以对材料的待开孔部位进行强化。根据选用的约束层与吸收层，根据P>2σs、
Figure PCTCN2017087535-appb-000016
可知，k＝1.62，σs＝340Mpa，I0应大于0.18GW/cm2。
根据经验公式
Figure PCTCN2017087535-appb-000017
B＝6，A取4.8左右，可得厚度为2.5mm的小孔构件4激光功率密度在1.57GW/cm2左右，厚度为5mm的小孔构件4激光功率密度在2.36GW/cm2左右，根据
Figure PCTCN2017087535-appb-000018
及激光器设备确定能量、脉宽、光斑等参数，最终得出的功率密 度接近A取4.8所得出的功率密度即可。所采用的功率密度、选用参数及其在95％的置信区间下的增益见表3。该组实样疲劳增益明显，但由于材料硬度低，A取值较大，材料表面凹坑较深，表面质量相对较差。
表3
Figure PCTCN2017087535-appb-000019
结合表1、2、3说明本方法可以实现的强化效果。运用本方法所选用的激光功率密度及所选用的激光参数所得的疲劳寿命增益明显且稳定，材料变形量接近于零，表面并未出现烧蚀等现象。
所述实施例描述本发明的基本特征和优点。相关行业的人员应该明白，上述实施列不能限制本发明，说明书和实施例只是说明了本发明的核心原理，在此基础上，本发明还可以继续优化和改进，这些优化和改进都在本发明的保护范围内。

Claims (7)

  1. 一种不同厚度小孔构件激光冲击强化方法，其特征在于，包括以下步骤：将小孔构件(4)的表面进行预处理，然后在小孔构件(4)待开孔部位的表面设能量吸收层(3)，在吸收层(3)表面设约束层(2)，将预处理后的小孔构件(4)固定在数控工作台上,使用激光器对小孔构件(4)的待开孔区域进行冲击强化，对不同厚度小孔构件(4)采用不同的激光冲击强化工艺参数，其工艺参数选择与确定方法如下：
    1)依据小孔构件(4)屈服强度和材料厚度来选择功率密度，功率密度与小孔构件(4)厚度的关系由公式
    Figure PCTCN2017087535-appb-100001
    确定，式中I0为激光功率密度，σs为材料的屈服强度，t为板厚，2/Z＝1/Z1+1/Z2，Z1是小孔构件(4)材料的声阻抗，Z2是约束层(2)的声阻抗，A为综合作用系数，且与小孔构件(4)的材料、约束层(2)和吸收层(3)相关，B为厚度影响系数，且与小孔构件(4)的材料和厚度相关；
    2)以上确定的I0值，其下限值应该满足
    Figure PCTCN2017087535-appb-100002
    P为作用在小孔构件(4)材料上的激光冲击载荷的峰值压力，σs材料的屈服强度，k为常数、与约束层(2)和吸收层(3)相关；
    3)依据公式
    Figure PCTCN2017087535-appb-100003
    确定光斑直径D和脉冲激光能量E，tp为激光脉宽；光斑直径D的取值范围在2mm～6mm，激光能量E为2J～35J，激光脉宽tp为10ns～30ns；
    4)确定激光能量E、激光脉宽tp、光斑直径D后，选择搭接率ψ和冲击层数n；冲击层数n为1层～6层；搭接率ψ＝相邻光斑重复距离l/光斑直径D。
  2. 根据权利要求1所述的不同厚度小孔构件激光冲击强化方法，其特征在于，所述搭接率ψ和冲击层数n与平均覆盖率η相关；
    所述平均覆盖率η＝N*s1/S，N为一面冲击总光斑数，s1为一个光斑的面积，S为孔位置冲击区域的面积；平均覆盖率η取200％～800％，如果平均覆盖率η不在200％～800％范围内，需要重新选择所述搭接率ψ和冲击层数n。
  3. 根据权利要求1所述的不同厚度小孔构件激光冲击强化方法，其特征在于，所述公式
    Figure PCTCN2017087535-appb-100004
    中当小孔构件(4)为铝合金，厚度影响系数B＝6；
    当约束层(2)为水、K9光学玻璃、有机玻璃、硅胶或合成树脂中的任意一种，吸收层(3)为铝箔时，综合作用系数A的取值范围在2～5。
  4. 根据权利要求1所述的不同厚度小孔构件激光冲击强化方法，其特征在于，所述公式
    Figure PCTCN2017087535-appb-100005
    中，当小孔构件(4)为钛合金时，厚度影响系数B＝2.6；
    当约束层(2)为水、K9光学玻璃、有机玻璃、硅胶或合成树脂中的任意一种，吸收层(3)为铝箔时，综合作用系数A的取值范围在0.5～1.25。
  5. 根据权利要求1所述的不同厚度小孔构件激光冲击强化方法，其特征在于，所述激光器激光的冲击区域的取值范围在2.8d～3.8d，d为孔径大小；
  6. 根据权利要求5所述的不同厚度小孔构件激光冲击强化方法，其特征在于，所述激光器激光冲击区域距材料边界，或激光冲击区域与另激光冲击区域之间的距离应不小于3mm。
  7. 根据权利要求1所述的不同厚度小孔构件激光冲击强化方法，其特征在于，所述激光器冲击方式为双面冲击。
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