激光焊接原理及实践应用

1、激光焊接Lasers Welding,Girish P. Kelkar, Ph.D.,激光 LASER,受激辐射式光频放大器的英文第一个字母的缩写 Light Amplification by Stimulation of Emitted Radiation,参考资料 References,激光的工业应用-J.F.Ready Industrial Applications of Lasers, J. F. Ready 激光焊接，W.W.Duley Laser Welding, W.W. Duley 激光加工，W.M.Steen Laser Materials Processing, W. M.

2、 Steen AWS 焊接手册，1-4 AWS Welding Handbooks, 1-4 激光加工手册-美国激光协会出版 Handbook of Laser Materials Processing Published by the Laser Institute of America 公开的相关文献 Published literature,请记住. Remember.,学习需要积极的参与 Learning requires active participation 不耻下问 Feel free to ask questions 无所顾及地提出个人不同见解 Do not hesitate

3、 to present different viewpoints,光 Light,光是一种电磁辐射 Light is electro-magnetic radiation 我们听不到.Waves that you cannot hear 可见光的波长在0.4-0.7微米之间。Visible from 0.4-0.7 micron wavelength 波长小于0.4微米是紫外线和X光Below 0.4 ultraviolet to x-rays 波长大于700nm的光为红外线和微波。 Above 0.7 infra-red to microwaves,1 m,光的吸收和颜色Absorption

4、 and Color,物体的颜色来源于它反射的光的波长 Color of an object (wavelength that it reflects),颜色和光的波长是相关联的。 Color is associated with particular wavelength 黑色和白色代表着什么？ What is the meaning of black or white color? 黑色表面吸收了YAG光，而白色在反射了大部分光。 Black surface will absorb YAG light while white will reflect most of it,我们为什么需要激

5、光？Why do we need Lasers?,材料加工需要吸收很强的光。 Absorption for materials processing requires very intense light 高强度的光可以通过激光聚焦成光束获得。 Intensity can be generated by focusing a beam of laser light 普通光不能聚焦成很高的能量密度（或足够小的点） Ordinary light does not focus down to a high enough power density (or small enough spot size

6、) 手持放大镜可以把太阳光聚焦让纸燃烧但是不能把金属融化 Hand-held lens can focus sunlight to set fire to paper but not enough to melt metal,Light and Lasers,单频的（单波长）Monochromatic (single wavelength) 校准的（平行光）Collimated (parallel),激光Laser Light 普通光Ordinary Light,很多波长 Many wavelengths 不平行 Not parallel,Light and Lasers,激光 Laser L

7、ight 普通光Ordinary Light,激光的聚焦Focusing of Lasers,激光Laser Light 普通光 Ordinary Light,单频（单波长）和校准（平行）的光可以聚焦成很小的焦点 Monochromatic (single wavelength) and Collimated (parallel) light can be focused to a very small spot,激光的种类Types of Lasers,激光能量传输 Laser Power Delivery 连续波 Continuous Wave (CW) 脉冲 Pulsed Q-开关 Q-

8、switched 激光频率 Laser Frequencies 基频和倍频 Fundamental and multiples,连续光纤激光Continuous Wave Fiber Lasers,激光在光纤中产生Laser light is created in the fiber 可在连续波和脉冲波中使用Can be used in pulsed mode as well as CW 可以被用于焊接和切割Can be used for welding and cutting,激光二极管光Laser Diode Light,激光二极管光 Laser Diode Light,光纤Fiber,脉

9、冲YAG激光（焊接）Pulsed YAG Lasers (Welding),闪光灯开关产生脉冲Flash lamp turns on and off to create pulses 光纤用于传送激光Fiber is used to transmit laser light,闪光灯（光泵）Flash Lamp (Optical Pump),全反镜100% mirror,90%反镜 90% mirror,光纤Fiber,激光棒Laser Rod,脉冲打标激光Pulsed Marking Lasers,Q-switching produces very short pulses, 10-100 n

10、ano-sec Cannot be used for welding Laser light delivered directly; no fiber Frequency can be doubled or tripled to get green or UV light,Rod,Mirrors,Q-switch,Galvo Mirrors,Focus Lens,Frequency Multiplier (not present in all markers),Galvo-光学器件Galvo-Optics,经常用于打标。Often used for marking applications 逐

11、渐受到焊接应用的青睐。Is gaining popularity for welding applications,Nutfield, Inc.,激光频率Laser Frequencies,上表只包括了大部分常用的和商业化的激光器。 Table includes only the most common and commercialized lasers。,脉冲YAG激光焊接典型示意图Typical Layout for Pulsed YAG Welding Lasers,镀膜反光镜Coated Mirrors,激光Laser,光纤Optical Fiber,聚光头 Focus Head,工件

12、Work piece,透镜Lens,注：某些激光不通过光纤直接传输。 Note: Some lasers are delivered direct without fiber,聚焦高度和焦点尺寸Focus height and spot size,短焦距透镜将光束聚焦成更小的点。Short focal length lens (of given diameter) will focus the beam to a smaller spot 高的能量密度。Higher energy density Focus height is critical due to shallow depth of

13、focus Lens protection from work piece spatter is important,短焦距Short Focal Length 长焦距Long Focal Length,Time Share,A single laser can be used for multiple applications on a time shared basis基于同一个理论,单雷射可以一次性用于多种应用. Most convenient with transmission through optical fiber 通过可见纤维的转换是最方便的. Processing stati

14、ons can be in different rooms 工作台可以放在不同的房间.,Mirrors (100% Reflective)全反镜,Energy Share,Laser energy split into multiple fragments 雷射能量分成多个部分 Typically three outputs for circumferential spot welding 典型的是圆周点焊接的3份输出量,Mirrors (Partially Reflective)反光镜(部分反光),33% 50% 100%,30 W,10 W 10 W 10 W,Total Internal

15、 Reflection完全内反射,Light propagation through fibers depends on total internal reflection通过光纤的光线传播完全取决于完全内反射,Air空气,Glass玻璃,Core核,Cladding覆层,Protective Sheath接地屏蔽,Optical Fibers光学纤维,Single mode has very small core diameter, 10 microns单模式只有很小的直径10微米 Used for telecommunications and now for fiber lasers 用于

16、电讯,现用于光纤激光 SI and GI have cores from 0.1 mm to 1 mm单模式和分级模式的核从0.1mm到1mm Higher diameter for higher power level 能量级别越高直径越大,Stepped Index (SI)步长指数,Single Mode单模式,Graded Index (GI)分级模式,Index Profiles剖面指数,SI vs. GI单模式 vs分级模式,SI and GI most frequently used in materials processing单模式和分级模式多用于材料加工过程. SI out

17、put is “top-hat” independent of input 单模式的输出独立于输入呈大礼帽状 more robust更有活力 GI output more faithful representation of input 分级模式的输出与输入呈保持靠近, Can create problems if input beam quality changes 如果输入光束的质量改变可能会产生问题. Can make deeper welds/cuts 可能焊接/切的更深. Weld profiles could change based on focus height 焦点高度可能产

18、生焊接侧面的 变化,SI GI,0.6 Aspect Ratio纵横比 1.5,“Top Hat大礼帽状”,Weld Profiles焊接剖面,Fiber Input Alignment光纤输入排列,Good Alignment 好的排列,Could burn fiber input end 可能烧焦光线输入莫端,Could create plasma at focus 在焦点产生等离子体,Could burn cladding 可能烧伤覆层,Spot Size with Fiber光点直径带光纤,Spot size is an image of the output core diamete

19、r of the fiber 从光点的大小可以反应出光纤核直径的大小 Size depends on magnification of the two lenses in the focus head 其大小是由镜头前的两个透镜来决定的.,Optical Fiber光纤,Core Diameter核直径,Spot Size光点直径,Laser Safety,Common Sense常识 Do you not put your hand in direct path of a laser beam不要把手的头放在雷射光束的路径中. Do not look directly at a laser

20、beam不要直视雷射光束 even at those laser pointers beams!不要看雷射点. Do not look at any laser process with a naked eye不要用不防护的肉眼看任何的激光过程. use plastic safety glasses for CO2 lasers 用塑料防护眼镜来防护CO2雷射. use YAG safe glasses for YAG operations 在钇铝石榴石操作中用钇铝石榴石安全眼镜,Eye Damage,Near UV from welding plasma and UV lasers If y

21、ou see bluish white during material processing, you need UV protection; ordinary plastic safety glasses are not sufficient!如果你在材料加工的过程中看见蓝白的光,你需要UV 保护,一般的塑料防护眼镜是不起作用的 . Visible and Near IR from YAG and frequency doubled lasers,Cornea角膜,Lens透镜子,Retina视网膜,Far UV and Far IR Near UV 接近UV Visible and Nea

22、r IR,Collateral Damage,Fumes烟 Solvents, grease, etc. from the work piece 溶剂,油脂等, Metal dust could be toxic 金属颗粒可能有毒. Decomposition products of plastics processing (marking, welding, or drilling) could also be toxic 在朔料加工的规程中的分解产品,(打表,焊接,或者钻孔)也是有毒的. Install vacuum pumps and appropriate filters 安装真空泵和

23、合适的过滤器. Need special Ti dust collectors when welding Ti in a glove box for medical device applications 当在用于医疗器械的手套盒子中焊接钛的时候,需要特殊的吸钛器.,Fire Hazard火灾,Laser Beams can have been known to cause fires镭射激光能够引起火灾. Breaks in optical fiber光纤削弱 Make sure optical fiber is not wound too tightly确保光学纤维不会太击伤. Leaka

24、ge in CO2 direct optics Laser beam walking off work table onto plastic covers Laser beam interaction with gloves in a glove box,Laser-Material Interaction,For lens and windows, A and R have to be small对于透镜和窗户,A和R 应该是小的. For mirrors, R has to high对于镜子,R 应该高一些 For Laser-based materials processing, A h

25、as to be high and R should be low对于以 雷射原理为基础的材料加工,A 要高一些,R 应该要低一些.,Incident Energy入射能,Reflection反射,Absorption吸收,Transmission转播,I = A + R + T,Initial Reflectivity of Metals金属的初始反射率,Grey metals (Ag and Al) are reflective to all colors in visible spectrum 灰色金属(Ag and Al) 对所有的有色光谱中的颜色都有反射作用. Copper refl

26、ects near red wavelengths and absorbs others铜在红色波长附近反射,在其他中吸收.,0.0,0.2,0.4,0.6,0.8,1.0,0.2,0.4,0.7,1.0,10,Wavelength (mm),Reflectivity,Ag,Carbon Steel碳钢,Ni,Cu,Al,Nd:YAG,CO2,Source: Industrial Laser Applications - John Ready,Laser Angle雷射角落,For all welding applications, the laser should be angled off

27、 vertical to prevent laser energy from going back into the laser cavity and causing damage 对于所有的焊接应用,雷射应该与角落垂直以防雷射能量回到激光腔,引起损失.,5 degrees,Absorptivity of Materials材料的吸收率,Reflectivity is also affected by surface roughness, surface oxides, part geometry, and weld pool shape反射率也是由表面光滑度,表面氧化度,;零件几何,以及焊接

28、池的形状.,Laser Welding镭射焊接,Configurations结构,Gap dimensions become more critical as parts get smaller由于零件尺寸变小,缝隙的尺寸变得更重要,Butt Weld对接焊接 Gap 0.1 t,t,Cap盖子,Can罐子,t,Configurations,Gap dimensions become more critical as parts get smaller由于零件尺寸变小,缝隙的尺寸变得更重要 Can weld multiple layers罐子多层焊接,Lap Weld Gap 0.15 t,C

29、onfigurations,Prefer configurations where the molten material flows into the weld instead of pulling away from it 最好的形状是融化的物质是流入到焊接而不是脱离焊接.,Lap Weld,Lap Fillet,Lap Edge,Annular Welds,Fitup is important移动的台 面很重要 . If gap is present, stresses will develop towards the end of the weld 如果有缝隙,应力会随着焊接而增大 P

30、ress-fit preferred最好有压配合.,Small Volume Welds,Air/gas in the enclosed volume during final weld heats up and tries to escape 空气在有限的空间里会随着焊接的热量膨胀,并试图逸出. Can cause porosity towards the end of the weld可能会在焊接的最后引起多孔.,Air Pressure Increases During Welding在焊接饿过程中空气的压力增加,Pressure Relief卸压,Allow pressure reli

31、ef on enclosed volumes 如下情况需要泄压 Reduce crack-like features which may be caused by high pressure trapped inside 泄压可以减少像这种由于内部压力过大而引起的类似裂纹的缺陷.,Shield Gas,Main function of shielding gas is to protect the molten metal from reacting with oxygen 保护气体的保护作用主要是保护融化的金属不与氧气反应. Shielding gas also helps to:保护气体也

32、有助于 Protect lens/lens cover from weld splatter 保护透镜,透镜盖不受焊接泼溅 Control plasma cloud formation 控制等离子雾形成. Wash away metal vapors in the plume 吹散等离子体中的金属蒸汽.,Shield Gas,What is plasma?什么是等离子体 Plasma is ionized gas等离子是离子化气体 Electrons are separated from atoms (metal as well as shielding gas)电子与原子分离(金属和屏蔽气体

33、 ) Plasma is the fourth state of matter; other three are solid, liquid, and gas(等离子体是事物的第四种状态,其他的三种是固体,液体和气体) What is plume?什么是等离子体? Plume is a mixture of plasma and metal vapors等离子体是等离子以及金属气体的混合体.,Plume,Shield Gases for YAG Lasers,Helium is ideal but very expensive氦很理想,但是很昂贵 Argon gas is most commo

34、nly used氩气是最常用的 Nitrogen can be used for some alloys氮可以用于一些合金. Some welds are made in air (no shielding gas) but the weld surface is not very smooth有些焊接在空气中做(没有保护气体)但是焊接表面不是太顺滑 May still produce acceptable weld quality可能仍旧能够产生有效的焊接质量.,Soot,Soot is black colored dust, typically referred to as “soot”

35、though it is not composed of carbon烟是黑色的灰尘,虽然叫煤烟但它不是由碳组成的 . “Soot” is a fine dust of metal powder that is deposited from the plume煤烟是一种从等离子中沉淀下来的金属粉末.,Chemical analysis of “soot” from Inconel 600,Shield Gas Configuration,Coaxial共轴 Too high destabilizes the weld pool, increased porosity太高-动摇焊接溶池,引起多孔

36、. Too low can cause negative pressure and pull up the weld metal太低-会引起负压力,使融化的金属突起. Better for shielding最好屏蔽 Side Flow侧流 Useful for sweeping away the ionization products用于清理等离子体.,Pulsed YAG 脉冲钇铝石榴石,Important Parameters 重要的参数 Pulse 脉冲 Width宽度 Energy能量 Power能量 Shape形状 Pulse Overlap脉冲交迭 Spot Size and F

37、ocus光点和焦点,Pulsed YAG脉冲钇铝石榴石,Energy (J) 能量= Power (kW) 力x Width 宽度(msec) Initial energy peak helps the laser energy to couple with the material 初始的高能量可以使激光能量与金属耦合.,Programmed Pulse程序 脉冲,Peak Power,Pulse Energy脉冲能量,Pulse Width脉冲宽度,Actual Output实际输出,Pulsed YAG脉冲钇铝石榴石,Short pulse of high peak power can

38、cause expulsion高的峰值能量的短脉冲能引起坑. Long pulse of low peak power will produce a wider and shallower weld bead 低顶点能量的长脉冲会产生更宽和更浅的焊缝.,Power,Pulse Width,Deeper Penetration更深穿透 Greater Porosity更多多孔 More Expulsion/Spatter更多飞溅,Shallower Penetration更浅穿透 Less Porosity更少多孔 Cleaner welds with no porosity 更干净焊接没有飞溅

39、,Effect of pulse time on weld size脉冲时间对焊接尺寸的影响,Weld spot diameter increases rapidly in the first few milli-seconds; rate of growth reduces with time焊斑直径在最初的千分之一秒期间迅速变大,增长的速度随着时间的增长而降低.,Time,Weld Size,Effect of pulse time on penetration脉冲时间对焊接尺寸的影响,For a given peak power, weld penetration stabilizes

40、after a certain threshold weld time对于指定的能量高峰,焊接深度在一定的焊接时间后变得稳定 . Maximum penetration is directly proportional to peak power 最大的深度是与能量高峰成直接正比的关系. Above a certain threshold of power, the laser will end up drilling/cutting/gouging instead of welding 在一定能量的之上,雷射将钻孔,切断,咆削而不是焊接.,Time,Penetration,Peak Powe

41、r 1,Peak Power 2,Pulse Shaping脉冲形状,Single pulse or three sector pulse offered by capacitor based power supplies由电源电容器产生的单脉冲和三个脉冲 Newer machines offer inverter technology with continuous pulse shaping更新的提出的能够提供 无间断的脉冲形状.,Time (msec),Peak Power,Energy (J) 能量= Power (kW) 力x Time时间 (msec),Single 单个 Thre

42、e-sector三部分 Multi-sector多部分,Weld Cracking焊接破裂,Can is anchored in the cap while can surface has leverage 罐子被锚在夹具中,而罐子的表面有杠杆作用. Weld cooling always introduces residual stresses 焊接冷却往往引起残余压力. Combination of large weld volume and rapid cooling can introduce excessive residual stresses that cause crackin

43、g 大量焊接加之迅速冷却能产生过量的残余压力从而引起破裂.,Laser Features: Pulse Shape雷射特征:脉冲形状,Melting and Penetration Pulse溶解渗透脉冲 (Coupling Pulse偶合脉冲),Stabilization Pulse稳定脉冲 (controlled cooling to reduce expulsion and residual stresses控制冷却减少残余应力.),6.0 kW,0.5 0.5 1.0 2.0 m-sec,50%,30%,0.2,Pulse Shaping脉冲形状,Modified pulse gave

44、 time for the weld to cool slowly and allow the pore to rise above the weld interface改良脉冲使焊接冷却的时间变慢,而且使得气孔有时间从熔融的金属中上升到表面,Focus Height 焦点高度,At focus, spot size not sensitive to focus height在焦点,点大小与焦点高度不相互影响. At focus, plume is tallest and sound is highest pitch在焦点,等离子体是最高的,而且声音也是最高调的. used to find f

45、ocus height用于找出焦点高度. Focus usually set at the surface for pulsed welding焦点通常设在表面为脉冲焊接. Focus set below surface for deeper penetration and keyhole mode welding焦点射在表面以下为更深的穿透和缩定焊接,Pulse Overlap脉冲交叠,Depends on thickness of component on top and shape of weld bead取决于零件上端的厚度和焊缝的形状. Overlap should be great

46、er by a safe margin在一定安全范围之内,交叠会大一些. Note: Excessive overlap is excess unwanted heat into the weld注意:过量的交叠是过度的热量在焊接中出现 .,Non-hermetic Overlap 不密封交叠,Hermetic Overlap 密封交叠,Pulse Overlap脉冲重叠,Lap welds require higher overlap重叠焊接要求更高的重叠 Butt welds can be hermetic even at 50% overlap对接焊接可以被密封,即便是50%的重叠,Bu

47、tt Weld 对接焊接,Lap Weld 重叠焊接,Butt Weld 对接焊接,Laser Weld Quality雷射焊接 质量,Weld Surface Inspection焊接表面检测 Weld surface should be clean and free of spatter焊接表面需干净,没有滴溅 No visible cracks or holes没有可见的裂缝和孔.,Good,Not Good,Laser Weld Quality雷射焊接质量,Mechanical Testing机械测试 Burst Strength爆发力量 Pull test or Shear Test

48、拉力测试和剪切测试 Leak Test测漏测试 Strength Analysis;力量分析 It is very important to keep track of where and when the failures occurred during testing在测试中,记录在那里和什么时候失败是十分重要的 Mark locations of failure for further analysis在失败的地方做标识是以便将来进一步分析,Weld Section Analysis焊接部分分析,Cracked Weld 焊接破裂,Small Pressure Bubble ? 小压力泡

49、沫,Good Weld 好焊接,X-ray AnalysisX-RAY 分析,Cracks grow at an angle and appear as straight lines in the x-ray (shallow weld on right)破裂在一个角中扩大,在X-RAY 中显示为一条直线 Small porosities may be difficult to see in such images在这样的图片中很难看到小孔. Check for alignment查看齐边.,Weld Crack 焊接破裂,Shallow Weld 焊接阴影,Alignment,X-ray i

50、mages of good weldsX-RAY 中好的焊接,Laser Maintenance雷射维护,Feedback monitor only checks laser cavity performance does not check power at weld反馈器只查看激光腔的性能-不会查看焊接时候的能量,Laser Cavity激光腔,Focus Head焦点头,Energy Meter, Burn Marks, Plexiglas, etc.能量剂,火刺,树脂玻璃,Lens透镜,Feedback Monitor监视器反馈,Energy Meters能量计,Joule Meter

51、s焦耳 Set for single pulse or average over multiple pulses 定为单 脉冲或者平均大于多脉冲 Should be used periodically to confirm energy at the weld在焊接的时候周期性的确认能量 Automation system can be set for measurement at warm up and after set number of pulse welds 在启动的时候或者确定脉冲焊接的时候用自动化系统.来确定量度.,Spot size and shape黑点的大小和形状,Burn paper and burn plate