Main Tile/Definition Description Characteristic Pros: Cons:
主要平铺/定义 描述 特征 优点： 缺点： 

Q1(a) Basic principle of laser – LT1
Q1（a） 激光器 LT1 的基本原理

Q1(b) General knowledge on laser assisted manufacturing – LT1
Q1（b） 激光辅助制造常识 LT1

Q1(c) Laser hazards and safety – LT10
Q1（c） 激光危害和安全 LT10

Q2(a) Classification and applications of lasers
Q2（a） 激光器的分类和应用

Q2(b) Laser additive manufacturing – LT6
Q2（b） 激光增材制造 LT6

Q2(c/d)Q3(c)Q4(d) Laser-material interaction – LT2/3
Q2（c/dQ3（c）Q4（d）激光-材料相互作用 LT2/3

Q3(a/b/c) Laser welding – LT4
Q3（a/b/c） 激光焊接 LT4

Eg: What are the TWO modes of laser welding? process mechanisms.
例如：激光焊接的两种模式是什么？过程机制。

A: Conduction limited welding occurs when the power density at a given welding speed is insufficient to cause boiling, so generated a keyhole.
A： 当给定焊接速度下的功率密度不足以引起沸腾时，就会发生导通受限焊接，因此会产生锁孔。

Keyhole welding there is sufficient energy to cause evaporation and hence a hole in the melt pool. This hole is stabilized by the pressure from the vapor being generated.
锁孔焊接有足够的能量导致蒸发，因此在熔池中形成一个孔。这个孔通过产生的蒸汽的压力来稳定。

Eg: What is laser-arc hybrid welding? What are the major advantages of the hybrid welding over the conventional laser welding?
例如：什么是激光电弧混合焊接？与传统激光焊接相比，混合焊接的主要优势是什么？

A: Laser-arc hybrid welding is a type of welding process that uses the laser beam and arc simultaneously as heat sources. 3 main types of hybrid welding process, depending on the arc used: TIG, plasma arc or MIG augmented laser welding. ADVANTAGES: requires very close fit-up, can help to overcome problems associated with reflective surfaces such as Al surfaces, combination of the laser process and the arc process results in an increase in both weld penetration depth and welding speed
答：激光电弧混合焊接是一种同时使用激光束和电弧作为热源的焊接工艺。混合焊接工艺的 3 种主要类型，具体取决于所使用的电弧：TIG、等离子弧或 MIG 增强激光焊接。优点：需要非常紧密的配合有助于克服与反射表面（如 Al 表面）相关的问题激光工艺和电弧工艺的结合导致焊透深度和焊接速度的增加.

Q3(d) Laser drilling – LT9
Q3（d） 激光钻孔 LT9

Q4(a) Application of laser to manufacturing processes
Q4（a） 激光在制造过程中的应用

Q4(b) Laser surface treatment – LT7
Q4（b） 激光表面处理 LT7

Q4(c) Laser cutting – LT9
Q4（c） 激光切割 LT9

Eg: Briefly describe the following two laser cutting processes: laser fusion cutting and laser scribing
例如：简要描述以下两种激光切割工艺：激光熔合切割和激光划线.

A: Laser fusion cutting is a “melt and blow” process. First, laser is directed toward the surface to melt the material and then high-pressure gas is used to blow the molten material away from the cutting area.
A：激光熔融切割是一种“熔化和吹塑”工艺。首先，将激光对准表面以熔化材料，然后使用高压气体将熔融材料吹离切割区域。

Since the gas jet blows the molten material out of the kerf, the need is avoided to raise the temperature of the material any further.
由于气体射流将熔融材料从割缝中吹出，因此无需进一步提高材料的温度。

Laser scribing has two steps: • Using laser to make a groove or line of holes either fully penetrating or not, but sufficient to weaken the structure. • Breaking the scribed structure mechanically. It is usually applicable to brittle materials such as silicon chips and alumina substrates. To avoid debris and minimize HAZ (heat-affected zone), low-energy, high-power-density pulses are usually used to remove the material principally as vapor
激光划线有两个步骤：使用激光制作一个凹槽或孔线，要么完全穿透，要么不完全穿透，但足以削弱结构。机械地打破划线结构。通常适用于硅片、氧化铝衬底等脆性材料。为避免碎屑并最大限度地减少 HAZ（热影响区），通常使用低能量、高功率密度脉冲来去除主要以蒸汽形式存在的材料.

Eg: what are the major advantages of laser cutting in terms of cut quality and process characteristics?
例如：激光切割在切割质量和工艺特性方面的主要优势是什么？

A: Cut: narrow kerf width, square edge, smooth and clean, no edge burr Process: fastest, workpiece doesn’t need clamping, no tool wear, low noise, can be made in any direction, easily automated, nearly all materials can be cut
A：切割：切口宽度窄，边缘方正，光滑干净，无边缘毛刺工艺：最快，工件不需要夹紧，无工具磨损，噪音低，可以任意方向制作，容易自动化，几乎所有材料都可以切割

Q4(d) Laser cleaning, polishing, texturing – LT8
Q4（d） 激光清洗、抛光、纹理化 LT8

Lect01 Introduction to laser assisted manufacturing
Lect01 激光辅助制造简介

All Categories of manufacturing processes assisted laser: Additive (烧结selective laser sintering, SLS), Subtractive (cutting), Formative (surface treatment, improve strength, corrosion and oxidation resistance
所有类别的制造工艺辅助激光 增材制造 烧结选择性激光烧结， SLS， 减材（切割）， 成型表面处理 提高强度、耐腐蚀性和抗氧化性)

Light - electromagnetic wave, vibrates at a certain angle, so-called polarization. Thermal emission; Broad spectrum; Random radiation.
光电磁波以一定角度振动，即所谓的极化。 热发射;广泛;随机辐射。

Laser beam - transverse wave, very parallel, vibrate at almost same direction, diverge very little over long distance and be focused to very small diameter. Laser can be monochromic单色的 with just one light wavelength. One wavelength; Directional radiation; Highly focused
激光束横波，非常平行，以几乎相同的方向振动，在长距离上发散非常小，并聚焦到非常小的直径。激光可以是单色单色的，只有一个光波长One 波长;定向辐射;高度专注

 普朗克常数 h = 6.626^10-34 Js = 4.136*10^-15 eVs
普朗克常数 h = 6.626^10-34 Js = 4.136*10^-15 eVs

Frequency  光速 2.99*108 ms-1  wavelength in meter
频率光速 2.99*108 ms-1 波长 单位 米

LASER – Light Amplification by Stimulated Emission of Radiation, a coherent beam generated by a process called stimulated emission.
LASERLight Amplification by Stimulated Emission of Radiation 受激发射 由称为受激发射的过程产生的相干光束。

N1 = Population of ground state E1
N1 = 基态种群 E1

N2 = population of excited state E2
N2 = 激发态 E2 的种群

 

K = 138*10^-23 J/K (Boltzmann Const)
K = 138*10^-23 J/K（玻尔兹曼常数）

★Stimulated Emission (basis of laser action)
★受激发射（激光作用的基础）

2 photons that have been produced can then generate 4 photons, then 16, result in a cascade of intense monochromatic radiation.
产生的 2 个光子可以产生 4 个光子，然后是 16 个，导致一连串的强烈单色辐射。

Population Inversion must have a mechanism where N2>N1, can be created by introducing a metastable亚稳态的 center where electrons can piled up to achieve a situation where more N2 than N1. Generated by an external excitation process, called the pump mechanism
种群反转必须具有一种机制，其中 N2>N1 可以通过引入亚稳态的中心来产生，其中电子可以堆积以实现 N 大于 N1 的情况。由称为泵机构的外部激励过程产生.

Laser Medium: When excited by an external energy source, it emits photons, contributing to the generation of a coherent and intense laser beam. Name of laser (CO2, YAG, … contributes difference of wavelength
激光介质当被外部能源激发时，它会发射光子，有助于产生相干且强烈的激光束。激光器名称 （CO2， YAG， ...贡献波长的差异)

Substance: used for the optical amplification, all the aggregate states can be used: solid bodies, liquids, gases, plasma
用于光放大的物质 可以使用所有聚集体状态：固体、液体、气体、等离子体.

Decisive criterion 决定性标准规范: a maximum amount of population inversion is attained in a simple manner. Prerequisites先决条件: energy level appropriate as the upper laser level, with a long lifetime; appropriated and sufficiently efficient pumping mechanism.
决定性标准 决定性标准规范以简单的方式获得最大数量的种群倒置。先决条件能量水平适合于上部激光水平，使用寿命长;适当且足够高效的泵送机构。

Laser Pump: Create a population inversion in the laser medium. Pumping Mechanism: Gas discharges for gaseous laser media; Optical excitation through flash lamps or a pump laser for solid-state lasers; Pumping by electrical current for semiconductor lasers.
激光泵浦： 在激光介质中创建种群反转泵浦M参数：气体激光介质的气体排放;通过闪光灯或固体激光器的泵浦激光器进行光学激发;用于半导体激光器的电流泵浦。

Pumping process worked effectively since the ground level is quickly refilled while the upper pump level E3 remains almost empty.
泵送过程有效，因为地面水平被迅速重新填充，而上部泵位 E3 几乎保持为空。

Three-level system: the higher pump power needed to reach inversion
Three 级系统：达到逆置所需的更高泵功率.

Laser Advantages: Able to focus to a small spot size, resulting in high intensity and localized heating; Small heat-affected zone and distortion; Non-contact procedure with minimum contamination; Easy to control beam power by regulating current; Able to direct beam to normally inaccessible areas using fiber optics and mirrors. Disadvantages: Relatively higher equipment cost; High reflectivity on metals; Low efficiency; Energy wastage via beam dumping when laser is not in use
激光优点： 能够聚焦到小光斑尺寸，从而产生高强度和局部加热 热影响区小和变形 非接触式程序，污染最小 通过调节电流易于控制光束功率 能够使用光纤和镜子将光束引导到通常无法进入的区域。缺点： 设备成本相对较高 金属反射率高 效率低 不使用激光时，光束倾倒会造成能量浪费.

316L: Major challenges in manufacturing to achieve good mechanical properties include controlling material properties (like grain size and phase composition), managing thermal stresses to prevent warping and cracking, ensuring precise dimensional tolerances, and achieving consistent material deposition in additive processes. Overcoming these challenges requires advanced process control, precise equipment calibration, and thorough quality assurance practices.
316L：在制造过程中实现良好的机械性能的主要挑战包括控制材料性能（如晶粒尺寸和相组成）、管理热应力以防止翘曲和开裂、确保精确的尺寸公差以及在增材制造工艺中实现一致的材料沉积。克服这些挑战需要先进的过程控制、精确的设备校准和全面的质量保证实践。

Lect02 Laser-material interaction (Continuous & Long Pulse
Lect02 激光-材料相互作用（连续和长脉冲）)

Continuous/Long Pulse (co2, ND:YAG, excimer): pulse>10ps(10^-12s), single-photon (linear) absorption. Collateral thermal & mechanical damages.
连续/长脉冲 （co2， ND：YAG， 准分子）脉冲>10ps10^-12，单光子（线性）吸收。附带的热和机械损伤。

Absorptivity (A) = Fraction of incident absorbed at normal incidence
吸收率 （A） = 正常入射时吸收的入射分数.

A=1-R, where R=material reflectivity at normal incidence. R = function of refractive index (n) and extinction coefficient (k), i.e. From optical measurements. k is a measure of the rate of diminution of transmitted light. How to measure absorptivity/reflectivity? When laser is incident on substrate, energy absorbed is transferred as heat to water flow
A=1-R，其中 R=材料在正常入射时的反射率 R = 折射率 （n） 和消光系数 （k） 的函数，即从光学测量中，k 是透射光衰减率的量度如何测量吸收率/反射率？当激光入射到基板上时，吸收的能量以热量的形式传递到水流中.

$$ water mass flow rate (kg/s)  specific head capacity (J/kg*K)
$$ 水质量流量 （kg/s） 比水头容量 （J/kg*K）

inlet temperature (K)   outlet temperature (K)
入口温度 （K） 出口温度 （K）

Absorption coefficient
吸收系数

incident intensity  intensity at depth z
入射强度 Z 深度的强度

extinction coefficient  Absorption depth
消光系数 吸收深度

Industrial applications: Laser cutting and drilling; Laser welding; Laser surface heat treatment; Laser cladding. Heating is dominant
工业应用激光切割和钻孔 激光焊接 激光表面热处理 激光熔覆 加热占主导地位.

Lect03 Laser-material interaction (Ultrashort Pulse)(fs-ps-ns-ms-continue
Lect03 激光-材料相互作用（超短脉冲）（fs-ps-ns-ms-continue）)

Ultrashort Pulse (Ti:sapphire蓝宝石femtosecond 10^-15s): pulse<10ps, multi-photon (nonlinear) absorption. Heat conduction is negligible; No hydrodynamic motion & fluid dynamics; Direct solid-vapor transition.
超短脉冲 （Ti：sapphire蓝宝石玻璃飞秒10^-15s）：脉冲<10ps，多光子（非线性）吸收。 热传导可以忽略不计;没有流体动力学和流体动力学;直接固气转变。

For long pulse widths, avalanche ionization (free electrons absorb photon energy via inverse bremsstrahlung absorption process) is more dominant in dielectric materials.
对于长脉冲宽度，雪崩电离（自由电子通过逆轫致辐射吸收过程吸收光子能量）在介电材料中更为主导。

Industrial applications (all heat involved): Cutting transparent materials; Precise ablation with lower HAZ (heat-affected zone); Surface modification; Invisible laser markings
工业应用（涉及所有热量）切割透明材料;具有较低 HAZ（热影响区）的精确烧蚀;表面改性;隐形激光打标

Thermal effect: >60% of incident energy is retained as thermal energy.
热效应：>60% 的入射能量作为热能保留。

Damage threshold fluence decreases with decreasing pulse width.
损伤阈值通量随着 脉冲的减小而降低。

Low fluence = Multiphoton ionization dominant
低通量 = 多光子电离占主导地位

Incubation繁殖 effect: Reduction in surface modification threshold (single pulse) when irradiated with multiple pulses; Phenomenon not clearly understood, suggested to be due to long-lived excitations; Can last as long as 3 seconds after first pulse.
孵育繁殖效应：用多个脉冲照射时表面改性阈值（单脉冲）降低 现象尚不清楚，提示是由于长寿命激发在第一次脉冲后可持续长达 3 秒。

Threshold intensity decreases exponentially指数地with pulse number.
阈值强度以指数方式随脉冲数呈指数地减小。

Femtosecond Glass Machining(case) – use high intensity of fs pulse → Electrons to conductive band → Above threshold intensity → solid to plasma transition → Athermal phase transformation, direct bond breaking, explosive disintegration of lattice by electronic repulsion.
飞秒玻璃加工（外壳）使用高强度飞秒脉冲→电子到导电带→ 高于阈值强度→固体到等离子体的转变→无热相变、直接键断裂、电子排斥爆炸性晶格解体。

The integrated microchip Fabrication and integration is in one single procedure of micro-hollow structure formation, without assembly and packaging of individual micro-component. Electrodes are easily integrated into microfluidic structures using electroless plating.
集成的微芯片制造和集成是在微空心结构形成的单一程序中，无需组装和包装单个微元件。电极使用化学镀很容易集成到微流体结构中。

Lect02/3 Laser-material interaction (Basic)
Lect02/3 激光-材料相互作用（基础）

Lattice vibration is collective and propagate through material because they are bonded. Vibration is a superposition of many fundamental modes (also known as a phonon), oscillates at a single frequency
晶格振动是集体的，因为它们是粘合的，所以会通过材料传播。振动是许多基本模式（也称为声子）的叠加，以单一频率振荡.

Energy absorption mechanism:
能量吸收机制：

Insulator绝缘体: Photon→Bound electrons→Phonons -Most energy flux is carried by phonons. (doesn’t possess many free electrons
绝缘体 光子→束缚电子→声子 大多数能量通量由声子携带。（不具备很多自由电子)

Metal/Semiconductor半导体: Photon→Free electrons→Phonons. Free electrons transport most energy flux. Phonon contribution is present but less significant. In both materials, heat is also conducted by classical conduction, i.e. Molecular vibration.
金属/半导体半导体 无光子→电子→ 无声子电子传输大多数能量通量。声子贡献存在但不太重要。在这两种材料中，热量也是通过经典传导（即分子振动）传导的。

Depth of Ablation烧蚀   ablation threshold
Depth of Ablation烧蚀 ablation threshold

absorptivity coefficient  incident laser energy 临界值
Absorborptivity Coefficient Incident Laser Energy 临界值

↑fluence, ↑pulse number, ↑pulse repetition rate= ↑ablation rate
↑注量、↑脉搏数、↑脉搏重复率 = ↑消融率

Lect04 Laser welding
Lect04 激光焊接

Laser beam welding (LBM) - uses a concentrated laser beam to melt materials at a joint, creating a strong, precise bond. Categories: Fusion welding, Solid state welding. Can penetrate any material up to 3/4 inch; material don’t have to be electrically conductive; filler metal isn’t required for the excellent quality of the weld; low heat input produces low distortion; don’t requires a vacuum. High initial start-up costs; part fit-up and joint tracking are critical; Not portable; Metals such as copper and aluminum have high reflectivity and are difficult to laser weld (not impossible, using lasers with shorter wavelengths or higher power); High cooling rates may lead to materials problems (increased hardness and brittleness; Residual stresses; Porosity; Cracking). Welding – atomic bonding. Laser welding belongs to fusion welding, can use for solid state welding, Laser beam as heat source produce very high energy density. Own high joining efficiency (Lower than electron beam, better than others) Characteristics: High energy density, keyhole type weld, less distortion; high processing speed; No x-rays generated unlike electron beam; Narrow weld; Relatively little HAZ (heat-affected zone) can weld near heat-sensitive materials.
激光束焊接（LBM） - 使用集中的激光束在接头处熔化材料，形成强大、精确的粘合分类：熔焊， 固态焊接可以穿透任何材料，最大可达3/4英寸; 材料不必导电; 填充金属不需要焊接的优秀质量;低热输入产生低失真;不需要真空初始启动成本高;零件装配和接头跟踪至关重要; Not 便携式; 铜和铝等金属反射率高，使用波长较短或功率较高的激光器进行激光焊接并非不可能; 高冷却速率可能会导致材料问题（硬度和脆性增加;残余应力; 孔隙 度;Cracking焊接 原子键合。激光焊接属于熔焊，可用于固态焊接，激光束作为热源产生非常高的能量密度。 具有较高的连接效率（低于电子束，优于其他特点：高能量密度锁孔式焊缝，变形小;加工速度快; 与电子束不同，不会产生 X 射线;窄焊缝;相对较小的 HAZ（热影响区）可以在热敏材料附近焊接。

Solid state welding (SSW): Joining processes in which coalescence results from application of pressure alone or a combination of heat and pressure. If heat is used, temperature is below melting point of metals being welded; No filler metal is added in solid state welding. Sample Processes: Forge锻造; Friction (FRW) - coalescence by heat of friction between two surfaces; Ultrasonic (USW) - coalescence by ultrasonic oscillating motion in a direction parallel to contacting surfaces of two parts held together under pressure.
固态焊接 （SSW）：通过单独施加压力或加热和压力的组合导致聚结的连接过程如果使用热量，则温度低于被焊接金属的熔点固态焊接中不添加填充金属。样品工艺锻造摩擦 （FRW） - 通过两个表面之间的摩擦热聚结超声波 （USW） - 通过超声波振荡运动在平行于在压力下保持在一起的两个零件的接触表面的方向进行聚结。

Fusion welding: Joining processes that melt the base metals In many fusion welding operations, a filler metal is added to molten pool to facilitate process and provide bulk and added strength to welded joint; A fusion welding operation in which no filler metal is added is called an autogenous weld. Sample Processes: 1. Arc (AW) - Melting of metals accomplished by an electric arc; 2. Oxyfuel gas (OFW) - Melting is accomplished by an oxyfuel gas such as acetylene.
熔焊：熔化贱金属的连接工艺 在许多熔焊作中，将填充金属添加到熔池中以促进加工并为焊接接头提供体积和增加强度不添加填充金属的熔焊作称为自焊样品工艺：1。电弧 （AW） - 通过电弧 2 实现的金属熔化。纯氧燃烧气体 （OFW） - 熔化是通过纯氧燃烧气体（如乙炔）完成的。

Power densities (W/mm2): Oxyfuel 10; Arc 50; Resistance 1000; Laser beam 9000; Electron beam 10000
功率密度 （W/mm2）Oxyfuel 10;弧 50;阻力位 1000;激光束 9000;电子束 10000.

Dealing with laser reflection (tilt the workpiece by 5 degree): To avoid back reflections from entering the optics train and damaging O-rings or from being reflected right back into the laser cavity and thus affecting the beam the instant it is to be used.
处理激光反射（将工件倾斜 5 度）：避免背向反射进入光学系统并损坏 O 形圈，或直接反射回激光腔，从而在使用光束时影响光束。

2 Modes of Laser Welding:
2 激光焊接模式：

Conduction Limited: occurs when the power density at a given welding speed is insufficient to cause boiling and therefore to generate a keyhole.
当给定焊接速度下的功率密度不足以引起沸腾并因此产生锁孔时，就会发生导通受限。

Keyhole: occurs when there is sufficient energy density to cause evaporation and hence a hole in the melt pool. This hole is stabilized by the pressure from the vapor being generated, behaves like an optical black body. Narrow and deep penetration and small heat-affected zone
当有足够的能量密度引起蒸发时，就会发生锁孔，从而在熔池中形成一个孔。这个空穴由产生的蒸汽产生的压力稳定下来，表现得像一个光学黑体。窄而深的穿透和较小的热影响区.

Lasers suitable for welding:
适合焊接的激光器：

CO2: high power; cannot be delivered by optical fiber.
CO2： 高功率;无法通过光纤传输。

Nd:YAG: can be delivered by optical fiber; low power – limiting thickness of plate welded; Expensive
Nd：YAG：可通过光纤提供 - 限制焊接板的厚度;贵.

Fiber/Disk: can be delivered by optical fiber; very high power achievable; better beam quality, much higher power density; new, capital cost is high, but price is dropping.
光纤/磁盘：可以通过光纤提供非常高功率的光束质量更好，功率密度新高很多，资金成本高，但价格正在下降。

Laser-arc hybrid welding is a type of welding process that uses the laser beam and arc simultaneously as heat sources. hybrid welding can help to overcome problems associated with reflective surfaces such as Al surfaces. Combination results in an increase in both penetration depth and welding speed.
激光电弧混合焊接是一种同时使用激光束和电弧作为热源的焊接工艺。混合焊接可以帮助克服与反射表面（如 Al 表面）相关的问题。 组合导致熔深和焊接速度的增加。

The higher welding speed, the lower penetration depth
焊接速度越高，熔深越低

Lect05 Laser welding applications
Lect0激光焊接应用

Why copper (applications)? Necessary for electric drives used in automotive industry; modern battery technology uses copper for interconnection and current transport. Doctor Copper as having a strong ability to assess overall economic well-being through the price of copper because of the metal's wide-ranging applications in industrial production and electrical equipment.
为什么选择铜缆（应用）？汽车行业 中使用的电驱动所必需的 modern 电池技术使用铜进行互连和电流传输。Doctor Copper具有很强的能力，可以通过铜的价格来评估整体经济状况，因为这种金属在工业生产和电气设备中有着广泛的应用。

Why laser welding (advantages)? Non-contact, highly flexible; High precision; Easy to automate; Fast, high efficiency; can weld several seams in different orientations and of different geometries in a few seconds; laser beam can be moved dynamically in three dimensions with variable speed and laser power. Laser absorption required at interface.
为什么选择激光焊接（优点）？非接触式、高度灵活高精度易于自动化快速、高效;可在几秒钟内焊接不同方向和不同几何形状的多个接缝; 激光束可以在三个维度上以可变的速度和激光功率动态移动。界面处需要激光吸收。

Challenges? High reflectivity, low absorptivity of common lasers at room temperature; High thermal conductivity; Very low viscosity of Cu melt
挑战？高反射率，常温下普通激光器的低吸收率 高导热性 铜熔体的粘度非常低.

Solution? Use Nd:YAG laser 503nm or combine it with 1060nm Nd:YAG. Why not CO2? CO2 wavelength at 10.6 um, many metals have low absorption efficiency at this wavelength, meaning much of the laser energy can be reflected away rather than being used to heat and melt the material, makes it less effective for welding. CO2 lasers have a relatively lower electrical-to-optical efficiency and slower response times compared to solid-state lasers. This can make it more difficult to control the heat input precisely, increasing the risk of thermal damage, distortion, or inconsistencies in the weld.
溶液？使用 Nd：YAG 激光器 503nm 或将其与 1060nm Nd：YAG 结合使用 为什么不使用 CO2？CO2 波长为 10.6 um， m任何金属在此波长下的吸收效率都较低，这意味着大部分激光能量可以被反射掉，而不是用于加热和熔化材料，因此对焊接不太有效。与固态激光器相比，CO2 激光器的电光效率相对较低，响应时间较慢。这会使精确控制热输入变得更加困难，从而增加焊缝中热损伤、变形或不一致的风险。

Laser welding of plastics Basic process: 1. Transmissive upper layer 2. Absorbing lower layer 3. Contact and pressure 4. Material compatibility.
塑料激光焊接基本工艺： 1. TRansmissive 上层 2.吸收下层 3.接触和压力 4.材料兼容性。

Key issues: 1. Temperature field and welding parameters 2. Absorbent material development 3. Defect analysis and stress study 4. Surface treatment/modification. Application: Fluid tanks, number plate, implant
关键问题： 1. 温度场和焊接参数 2.吸收材料开发 3.缺陷分析和应力研究 4.表面处理/改性 应用：储液罐、车牌植入物.

Lect06 Laser addictive manufacturing
Lect06 激光令人上瘾的制造

3D printing & AM are a welding & joining process. 3D printing is a type of additive manufacturing, which uses printing head technology.
3D打印和增材制造是一种焊接和连接过程。 3D 打印是一种增材制造，它使用打印头技术。

3D printing & Welding are additive manufacturing. 3D printing is a welding & joining process.
3D打印和焊接是增材制造uring. 3D打印是一种焊接和连接过程。

What are Ultrahigh Strength Steels? Steels with minimum yield strength above 690 MPa may be regarded as Ultrahigh Strength Steels Benefits? Weight reduction; Better ballistic protection (armour steel); Energy efficiency; Economic saving. How to Achieve Ultrahigh Strength? By adding hard Ceramic Particles for dispersion strengthening (case: 316L+TiC). Major challenge? Increase in strength leads to drastic decrease in ductility. Solutions/Success factors? 1. avoid defects through process optimization 2. ensure homogeneous distribution of particles 3. use small particles, preferably nanoparticles(more difficult to process) 4. ensure bonding of particles to the matrix 5. To refine grain sizes (important for ductility).
什么是超高强度钢？最小屈服强度高于 690 MPa 的钢可以被视为超高强度钢的好处？减轻重量更好的防弹保护（装甲钢） 能源效率经济节约如何实现超高强度？通过添加硬质陶瓷颗粒来增强色散（案例：316L+TiC）。 主要挑战？强度的增加会导致延展性急剧下降。解决方案/成功因素 1.通过工艺优化N 2 避免缺陷。确保颗粒分布均匀 3. 使用小颗粒，最好是纳米颗粒（更难加工） 4.确保颗粒与基质的结合 5. 细化晶粒尺寸（对延展性很重要）。

Selective laser melting (SLM) uses a high-power laser to fully melt and fuse metallic powders layer by layer. Complex geometries; Material Efficiency; Rapid prototyping; Customization; Strong & lightweight; tool-less production. Poor surface finishing; Partially melted powders; Waviness of tracks. Solution: laser polishing
选择性激光熔化 （SLM） 使用高功率激光逐层完全熔化和熔合金属粉末。复杂的几何形状; 材料效率;快速原型制作;定制;坚固且轻便; 免工具生产。表面光洁度差;部分熔化的粉末;轨道的摆动。解决方案：激光抛光

Lect07 Laser surface treatment
Lect07 激光表面处理

Laser surface treatment - uses a laser beam to modify the surface properties of materials. precise control; localized treatment; minimal distortion; ability to enhance hardness, wear resistance, and corrosion resistance.
激光表面处理 - 使用激光束改变材料的表面特性。 精确控制 局部处理 最小变形能力 提高硬度、耐磨性和耐腐蚀性。

Why surface treatment? Surface treatment is a subject of considerable interest because it offers the chance to save strategic materials or to improve components with idealized surfaces and bulk properties.
为什么选择表面处理表面处理是一个相当有趣的主题，因为它提供了节省战略材料或改进具有理想化表面和整体特性的组件的机会。

Why using laser? The applied energy can be placed precisely on the surface only where it is needed. Advantages: Clean, less distortion, easy to automate.
为什么使用激光？施加的能量可以精确地放置在表面上需要的地方。优点：干净，失真少，易于自动化。

Laser Surface Heat treatment to induce phase transformation for surface hardening (e.g. martensite in steel). Characteristics: Defocused beam; Power density = 10³–10⁵W/cm²; no melting; cooling rates up to 10⁷ ℃/s; Co2, Nd:YAG, Diode lasers; Laser wavelength↓ absorptivity↑ By: surface roughness↑, Preheating the substrate, applying an absorptive surface coating
激光表面热处理以诱导相变以进行表面硬化（例如钢中的马氏体）特性：散焦光束;功率密度 = 10–10W/cm;无熔化;冷却速率高达 10°C/s;CO2、Nd：YAG、二极管激光器;激光波长↓吸收率↑By：表面粗糙度预热基板，应用吸收表面涂层

Hardening through austenization奥氏体化 and subsequent self-quenching to produce as-quenched martensite. leads to: higher hardness and strength; improved wear resistance; longer fatigue life
通过奥氏体化奥氏体化和随后的自淬火进行 H硬化以生产淬火马氏体。导致更高的硬度和强度;i提高了耐磨性，延长了疲劳寿命

Softening based on the tempering or partial austenitization with subsequent ferrite-perlite transformation. The softening can be used to improve the forming properties of steels.
基于回火或部分奥氏体化的软化，随后进行铁素体-珍珠岩转变。软化可用于改善钢的成型性能。

Laser surface melting similar to heat treatment, except that a focused or near-focused beam is used. Reason: High energy density; Precision and control; Efficiency; Depth of melting; Reduced HAZ. The surface to be melted is shrouded in inert gas. Reason: Prevent oxidation; improve surface quality; reduce spatter; enhance cooling rates; protect equipment. Characteristics: moderate to rapid solidification rates producing fine near-homogeneous structures; little thermal penetration, nor surface hot gases, resulting in little distortion and the possibility of operating near thermally sensitive materials; surface finishes of around 25 μm are fairly easily obtained, signifying reduced work after processing; process flexibility, due to software control and possibilities in automation.
激光表面熔化类似于 热处理，不同之处在于使用的是聚焦或近聚焦光束。原因：能量密度高;精度和控制;效率;熔化深度;减少热影响区待熔化的表面被惰性气体覆盖原因：防止氧化; 提高表面质量; 减少飞溅; 提高冷却速度; 保护设备。 特性：中等至快速的凝固速率产生精细的近乎均匀的结构;热渗透小，表面热气体也很少，因此变形小，有可能在热敏材料附近工作;大约 25 μm 的表面光洁度相当容易获得，这意味着加工后减少了工作量;由于软件控制和自动化的可能性，过程灵活。

Laser surface alloying similar to laser surface melting but with addition of alloying elements into the surface layer; Similar to cladding but the purpose is not to add a new layer of material. Application: Titanium be alloyed by carbon or nitrogen to display different colors.
激光表面合金化 类似于激光表面熔化，但在表面层中添加了合金元素类似于熔覆，但目的不是添加新的材料层应用：钛 be 由碳或氮合金化以显示不同的颜色。

Laser cladding overlay one metal with another to form a sound interfacial bond or weld without diluting the cladding metal with substrate material. Processes: Coating technique to enhance corrosion, oxidation or wear resistance; Refurbish worn or damaged surfaces of high-value components e.g. Aircraft blades; Thin layer of substrate surface is melted and mixed with clad alloy (powder, wire, foil); Alloy compatibility for strong metallurgical bonding. Process Characteristics: controlled in a wide range from cladding to dispersing & alloying. Delicate structures can be built as well as high deposition rates accomplished. Short interaction times and very low overall heat input; Limited heat affected zone, and less distortion; Low dilution, good homogeneous clad; High localized hearting and cooling rates; result formation of fine structures and retention of non-equilibrium states.
激光熔覆将一种金属与另一种金属叠加在一起，以形成良好的界面粘合或焊接，而不会用基材稀释熔覆金属。加工过程：增强耐腐蚀性、抗氧化性或耐磨性的涂层技术 翻新高价值部件（如飞机叶片）的磨损或损坏表面 基材表面的薄层熔化并与复合合金（粉末、金属丝、箔）混合 合金相容性，实现牢固的冶金结合工艺特点： 控制范围广泛，从包覆到分散和合金化。可以构建精细的结构，并实现高沉积速率相互作用时间短，总热输入非常低;有限的热影响区，并且变形较小;低稀释度，良好的均匀包层;高局部心脏和冷却速率;结果形成精细结构并保留非平衡状态。

Remanufacturing ≠ recycling. involve both subtractive and additive manufacturing, but the additive process has greater impact on quality.
再制造 ≠ 回收。涉及减材制造和增材制造，但增材制造过程对质量的影响更大。

Process: 1. Capture the core 2. Test, clean, disassemble 3. Restore to like new 4. Match supply & demand
工艺： 1. Capture 核心 2.测试、清洁、拆卸 3.Restore 到像新的一样 4. Match 供需

Pulsed Laser Deposition (PLD) a technique used to create thin films. A high-power pulsed laser beam vaporizes a solid target material in a vacuum, which then deposits as a thin layer on a substrate. PLD is noted for its ability to produce high-quality films with precise control over composition and thickness, is useful for complex materials like superconductors and ferroelectrics.
脉冲激光沉积 （PLD） 一种用于创建薄膜的技术。高功率脉冲激光束在真空中蒸发固体靶材，然后将其作为薄层沉积在基板上。PLD 以其能够生产高质量薄膜的能力而著称，并且能够精确控制成分和厚度，可用于超导体和铁电体等复杂材料。

Physical Vapor Deposition (PVD) a thin film deposition technique that involves vaporizing material from a target source in short pulses under vacuum conditions. Process: Source (solid/liquid) →(evaporation)→ Gas phase →(transport and deposition)→ solid phase
物理气相沉积 （PVD）一种薄膜沉积技术，涉及在真空条件下以短脉冲从目标源蒸发材料。工艺：源（固/液）→（蒸发）→气相 →（传输和沉积）→固相

How to generate vapor physically? Heating; Ion sputtering离子溅射; Laser ablation (using pulsed laser); in vacuum.
如何物理产生蒸汽？ 加热;Ion sputtering离子溅射;激光消融（使用脉冲激光）;在真空中。

Chemical Vapor Deposition (CVD) Chemical reaction of different gases, single gas decomposition. for W can be achieved from decomposition of tungsten hexafluride WF₆ → W+ 3F
化学气相沉积 （CVD）不同气体的化学反应，单一气体分解。 因为 W 可以由六氟化钨分解获得 WF→ W+ 3F₂.

Laser-assisted Vapor Deposition (LAVD) Reactions occur within a gas/liquid phase, or at gas/solid or liquid/solid interfaces; High vacuum environment. Nanoparticle Application: To grow single wall nanotubes (SWNTs), by laser ablation of graphite. (photothermal); Carbon atoms sintered and recombine to form nanotubes. Metal catalyst can be used to increase yield.
激光辅助气相沉积 （LAVD）反应发生在气/液相内，或在气/固或液/固界面处高真空环境纳米颗粒应用：通过石墨的激光烧蚀来生长单壁纳米管 （SWNT）。（光热）碳原子烧结并重新组合形成纳米管。金属催化剂可用于提高收率。

Laser Chemical Vapour Deposition (LCVD) a focused laser beam is used to locally heat a substrate, promoting the decomposition or reaction of gas-phase precursors to form a solid deposit only where the laser is directed. This method offers precise control over the deposition location and pattern, making it suitable for creating complex microstructures and adding material in a highly targeted manner.
激光化学气相沉积 （LCVD）一种聚焦激光束用于局部加热衬底，促进气相前驱体的分解或反应，仅在激光指向的地方形成固体沉积物。这种方法提供了对沉积位置和图案的精确控制，使其适用于创建复杂的微观结构和以高度针对性的方式添加材料。

Choice of Laser
激光器的选择

Lect08 Laser Cleaning, polishing and texturing
LectLaser 清洗、抛光和纹理加工

Why laser polishing? Environmental friendly in contrast to Abrasives研磨剂 and chemicals; Laser beams can be controlled for high-precision polishing of complex freeform surfaces
为什么要进行激光抛光？与研磨剂和化学品相比，环保;可以控制激光束对复杂的自由曲面进行高精度抛光.

Challenges & Opportunities: polishing large areas; interior surfaces; Use of AI; integration with other manufacturing processes.
挑战和机遇：抛光大面积;内表面;人工智能的使用;与其他制造流程集成。

Polishing for welding of special alloys: Better welding quality through removal of tenacious oxides on surface; Much improved efficiency–laser surface polishing makes it possible to change the manufacturing process from TIG welding to much more efficient MIG welding.
特殊合金焊接抛光：通过去除表面的顽固氧化物来提高焊接质量大大提高效率——激光表面抛光可以将制造工艺从 TIG 焊接转变为更高效的 MIG 焊接。

Lect09 Laser Cutting and drilling
LectLaser 切割和钻孔

Laser cutting - directs a high-power laser beam to cut materials, offering precise, clean cuts. Advantages: Quality characteristics: narrow kerf width; square cut edge; smooth and clean cut edge; very narrow HAZ; Blind cuts can be made; Processes Characteristics: faster cutting process; workpiece doesn’t need clamping; no tool wear; can easily automated; nearly all materials can cut.
激光切割 - 将高功率激光束引导到切割材料，提供精确、干净的切割优点：质量特性：窄切口宽度; 方形切割边缘; 光滑干净的切割边缘;非常狭窄的 HAZ;盲切可以使工艺特点 更快的切割过程; 工件不需要夹紧;不会太磨损;可以很容易地实现自动化; 几乎所有的材料都可以切割。

Methods: Vaporization cutting: The focused laser beam heats the surface of the material to boiling point and generates a keyhole. The keyhole leads to a sudden increase in absorptivity quickly deepening the hole. As the hole deepens and the material boils, vapor generated erodes the molten walls blowing ejecta out and further enlarging the hole. Moving laser beam produces moving keyhole to separate the material.
方法：汽化切割聚焦的激光束将材料表面加热到沸点并产生锁孔。锁孔导致吸收率突然增加，迅速加深孔。随着孔的加深和材料的沸腾，产生的蒸汽会侵蚀熔融壁，将喷射物吹出并进一步扩大孔。移动的激光束产生移动的锁孔以分离材料。

Fusion Cutting – melt and blow: uses high-pressure gas to blow molten material from the cutting area, greatly decreasing the power requirement. Material is heated to melting point, a gas jet blows the molten material out of the kerf avoiding the need to raise the temperature of the material any further.
熔融切割 熔化和吹塑：使用高压气体将熔融材料从切割区域吹出，大大降低了功率要求。 M材料被加热到熔点，气体射流将熔融材料从切口中吹出，无需进一步提高材料的温度。

Reactive Laser Cutting (Flame cutting/burning stabilized laser gas cutting): like oxygen torch cutting but with a laser beam as the ignition source. Mostly used for cutting carbon steel in thicknesses over 1mm, can be used to cut very thick steel plates with relatively little laser power.
反应激光切割（火焰切割/燃烧稳定激光气体切割）：类似于氧气火炬切割，但以激光束作为点火源。主要用于切割厚度超过 1mm 的碳钢，可用于切割激光功率相对较小的非常厚的钢板。

Laser Induced Thermal Stress Cracking (Controlled Fracture): A beam is focused on the surface causing localized heating and thermal expansion (but no melting). This results in a crack that can then be guided by moving the beam. The crack can be moved in order of m/s. It is usually used in cutting of brittle materials such as glass. Difficulty lies in controlling the fracture process.
激光诱导热应力开裂（受控断裂）光束聚焦在表面上，导致局部加热和热膨胀（但没有熔化）这会产生裂纹，然后可以通过移动光束来引导。裂纹可以按 m/s 的顺序移动。通常用于切割玻璃等脆性材料。难点在于控制骨折过程。

Cold Cutting: a technique with the high-powered lasers (excimer laser, ultrafast laser). Direct breaking of atomic bond.
Cold Cutting 冷切割一种使用高功率激光器（准分子激光器、超快激光器）的技术。直接破坏原子键。

Laser Drilling a process that uses a focused laser beam to create holes of various sizes and depths in materials. This technique is valued for its precision and ability to drill very small, high-quality holes quickly and efficiently.
激光钻孔 （Laser Drilling） 一种使用聚焦激光束在材料上打出各种大小和深度的孔的工艺。这项技术因其精度和快速有效地钻出非常小的高质量孔的能力而受到重视。

Trepanning: In this process, a pilot hole is first created in the center using percussion drilling, it then moves in a spiral configuration using a motion system to make a bigger hole, Most of the molten material is expelled downward through the hole, can be used to create non-circular holes.
套料在这个过程中，首先使用冲击钻孔在中心创建一个导向孔，然后使用运动系统以螺旋结构移动，以制作更大的孔大部分熔融材料通过孔向下排出，可用于创建非圆形孔。

Helical Laser Drilling: does not involve the creation of an initial pilot hole, with helical drilling the removed material shoots upwards rather than downwards. During the process, laser is always focused at the base of the hole, often to create very deep holes.
螺旋激光钻孔不涉及创建初始导向孔，螺旋钻孔去除的材料向上喷射而不是向下喷射。 在此过程中，激光始终聚焦在孔的底部，通常用于产生非常深的孔。

Applications: Cooling holes in areo engines and gas turbines.
应用：areo 发动机和燃气轮机中的冷却孔。

Lect10 Laser Hazards危害 and safety
Lect10 Laser Hazards危害与安全

Hazards: Eye injury; skin burns; fume inhalation烟雾吸入; electrical hazards.
危害： 眼睛受伤;皮肤灼伤;烟雾吸入烟雾吸入电气危害。

Safety measures include using protective eyewear, installing laser barriers, ensuring proper ventilation, and adhering to strict operational protocols to mitigate these risks.
安全措施包括使用防护眼镜、安装激光屏障、确保适当通风以及遵守严格的作规程以减轻这些风险。

Nature of a laser beam: Photon energy is proportional to the frequency of the radiation, or inversely proportional to the wavelength.光子能量与辐射频率成正比，与波长成反比
激光束的性质：光子能量与辐射频率成正比，或与波长成正比，与波长成正比，与波长成正比

Maximum Permissible Exposure(MPE): Level of laser radiation to which a person may be exposed without hazardous effect or adverse biological changes in the eye or skin. Expressed in J/cm2 or W/cm2, Depending on laser parameters: Wavelength; Exposure duration; Pulse Repetition Frequency(PRF); Nature of the exposure (specular, diffuse reflection).
最大允许暴露 （MPE） 一个人可能暴露于的激光辐射水平，而不会对眼睛或皮肤产生有害影响或不利的生物变化。以 J/cm2 或 W/cm2 表示，取决于激光参数：波长;曝光持续时间;脉冲重复频率 （PRF）;曝光的性质（镜面反射、漫反射）。

Class1 0.39mW considered intrinsically safe under normal operating conditions. Emissions from the enclosure are below MPE for the eye, no harmful radiation can escape the enclosure. Eg: Laser printers
1 类0.39mW在正常作条件下被认为是本质安全的外壳的发射低于眼睛的 MPE没有有害辐射可以逃脱 外壳 例如：激光打印机

Class2 1mW emits visible laser beams (400-700nm), invokes the “aversion response” normally within 0.25 seconds if viewed by eyes. Forced or intentional extended viewing is considered hazardous. Eg: market scanners
2 类 1mW 发射可见激光束（400-700nm通常在 0.25 秒内触发“厌恶反应”，如果被观看 强行或故意延长观看被认为是危险的。 例如：市场扫描仪

Class3a 5mW emitting visible and/or invisible laser radiation. Intentional staring should be always avoided. Eg: many construction alignment.
Class3a 5mW 发射可见和/或不可见激光辐射。应始终避免故意凝视。例如：许多结构对齐。

Class3b 5-500mW emission duration of longer than 0.25s, are medium-power and moderate-risk. Causing temporary and permanent eye injury by exposure from the direct beam or specularly reflected beam, skin injury from direct exposure to the laser may also possible. Eg: Therapeutic, acupuncture lasers.
3b 类 5-500mW 发射持续时间超过0.25是中等功率和中等风险因直接光束或镜面反射光束照射造成暂时和永久性眼损伤，直接暴露于皮肤损伤激光也可能是可能的。 例如：治疗性针灸激光。

Class4 over 500mV may be either a fire or skin hazard or a diffuse reflection hazard, very stringent control measures required, must wear goggles in area. Eg: Most industrial material processing laser power supplies.
超过 500mV 的 Class4 可能是火灾或皮肤危险或漫反射危险，需要非常严格的控制措施，在该区域必须佩戴护目镜 例如：大多数工业材料加工激光电源。

Regulations in Singapore: >=18 years old, been adequately trained, has special knowledge in safe use of laser, hold N3 (allow to use 3b &4 medical and industrial lasers and all classes of entertainment lasers) license
新加坡法规 >=18 岁，受过充分培训，具有安全使用激光的专业知识，持有 N3（允许使用 3b &4 医疗和工业激光以及所有类别的娱乐激光许可证

Biological Damage Caused by Laser Beams: Thermal effect is caused by a rise in temperature following absorption of laser energy. Parameters: Expose duration, wavelength; energy; area and type of tissue. Acoustical effect results from mechanical shockwave, propagated through tissue组织, ultimately damaging the tissue. happens when the laser beam causes localized vaporization of tissue, causing the shockwave analogous to ripples in water from throwing a rock into a pond. Photochemical effect occurs when photons interact with tissue cells. A change in cell chemistry may result in damage or change to tissue. Depend greatly on wavelength.
激光束造成的生物损伤热效应是由吸收激光能量后温度升高引起的。参数：曝光持续时间、波长、能量、组织面积和类型。声学效应是由机械冲击波引起的，通过组织组织传播，最终破坏组织。当激光束导致组织局部汽化时，就会发生，从而产生类似于将石头扔入池塘的水中的涟漪的冲击波。 当光子与组织细胞相互作用时，就会发生光化学效应。细胞化学的变化可能导致组织损伤或变化。D在波长上显著增加。

Protection:
保护：

Safety Goggles护目镜 selection based on: wavelength, radiant exposure; MPE; optical density of eyewear; visible light transmission requirements; adequate peripheral vison; prescription lens; comfort
Safety Goggles护目镜的选择基于：波长、辐射曝光;欧洲议会;眼镜的光密度;可见光透过要求;足够的周边视野;PrescrIption 镜片;舒适度

Non-beam Hazards those that do not result from direct laser beam exposure.
非光束危害那些不是由直接激光束暴露引起的。

May be grouped as:
可分为：

Process radiation: after exposure of a material to a laser beam (beam induced UV, plasma etc.).
工艺辐射：材料暴露于激光束（光束诱导紫外线、等离子体等）后。

Electrical hazard: (electrical system , capacitors). Lethal electrical hazards may be present in all lasers, particularly in high-power laser systems.
电气危险（电气系统电容器）。所有激光器都可能存在致命的电气危险，尤其是在高功率激光系统中。

Mechanical hazard: Collision, Physical injury to head, body, and limbs. Chemical hazard (gases, dyes, solvents). Some materials used in lasers (i.e., excimer, dye and chemical lasers) may be hazardous and/or contain toxic substances. In addition, laser induced reactions can release hazardous particulate and gaseous products (Fluorine gas tanks).
机械危害碰撞、头部、身体和四肢的物理伤害 化学危害（气体、染料、溶剂激光器中使用的某些材料（即准分子、染料和化学激光器）可能有害和/或含有有毒物质。此外，激光诱导反应会释放出有害的颗粒和气体产品（氟气罐）。

Secondary Hazards: Cryogenic coolant hazards; Smoke, fume, particles, toxic vapor , etc.; Explosions from faulty optical pumps and lamps; Fire hazards
次生危害低温冷却剂危害; 烟雾、烟雾、颗粒、有毒蒸气等光泵和灯故障引起的爆炸火灾隐患

Hazards rarely mentioned:
很少提及的危险：

Ultrafast laser induced X-ray, may cause cellular damage, cancer risk, radiation sickness, harmful to fetal development, skin and tissue damage.
超快激光诱导 X 射线可能导致细胞损伤、癌症风险、放射病、对胎儿发育有害、皮肤和组织损伤。

Powerful industrial lasers cutting through human body
强大的工业激光器切割人体

Paper04 Laser Net shape welding
Paper04 激光净成形焊接

What is laser net shape welding? Laser welding may produce weld beads
什么是激光净形焊接？激光焊接可能会产生焊道

with characteristics such as undercut, root cavity and root snagging. Researches have been conducted to understand effect of laser welding parameters on the geometry formation and it is now possible to produce flat weld bead (i.e.,no protrusion, no undercut, no convex surface, and no concave surface), and the welding technique is termed “laser net shape welding”.
具有咬边、根腔和根钩等特征。已经进行了研究以了解激光焊接参数对几何形状形成的影响，现在可以产生平焊道（即无突起、无底切、无凸面和无凹面），焊接技术被称为“激光净形焊接”。

Advantages of laser net shape welding? produces a flat surface and thus gets rid of stress concentration due to the geometric change.
激光净形焊接的优势？产生平坦的表面，从而摆脱由于几何变化引起的应力集中。

How did Prof Li et al attempt to solve the problem? Experimental Design: used a fiber laser to perform square butt welding on mild steel sheets, examining different combinations of laser power, welding speed, and focal plane position to influence the bead geometry. Computational Analysis: Computational fluid dynamics (CFD) and finite element models (FEM) were employed to simulate the welding process and understand the formation of the weld geometry.
李教授等人是如何尝试解决这个问题的？实验设计：使用光纤激光器对低碳钢板进行方形对接焊接，检查激光功率、焊接速度和焦平面位置的不同组合以影响焊道几何形状。计算分析：采用计算流体动力学 （CFD） 和有限元模型 （FEM） 来模拟焊接过程并了解焊缝几何形状的形成。

What is the final solution? Parameter Optimization: identified optimal settings of laser power, welding speed, and focal plane position that reliably produce net shape welds. Mechanical Validation: Tensile testing confirmed that net shape welds not only align perfectly with the parent material but also exhibit superior mechanical properties. The stress distribution in net shape welds is more favorable, reducing potential points of failure.
最终的解决方案是什么？参数优化：确定激光功率、焊接速度和焦平面位置的最佳设置，以可靠地产生净形状焊缝。机械验证：拉伸测试证实，净形状焊缝不仅与母材完美对齐，而且还表现出卓越的机械性能。净形焊缝中的应力分布更有利，从而减少了潜在的失效点。

Which welding parameters should you adjust in order to achieve laser net shape welding? by adjusting two parameters: the laser power, welding velocity.
为了实现激光净形状焊接，您应该调整哪些焊接参数？通过调整激光功率焊接速度两个参数。

Paper02 Laser Micromachining
Paper0激光微加工

Can fs laser be used for welding?
fs 激光器可以用于焊接吗？

Yes, Laser micromachining - utilizes focused femtosecond (ultrafast) laser beams for precise material removal at microscale. Pulse duration shorter than heat diffusion; peak power in Gigawatt; good for micro or nanoscale fabrication.
是的，激光微加工 - 利用聚焦飞秒（超快）激光束在微尺度上精确去除材料脉冲持续时间短于热扩散;峰值功率（千兆瓦）;适用于微或纳米级制造。

Paper06 W316L
论文0W316L

Advantage: excellent corrosion and oxidation resistance, good ductility.
优点：优良的耐腐蚀性和抗氧化性，延展性好。

Drawback: low yield strength (170- 300 MPa).
缺点：屈服强度低 （170-300 MPa）。

Paper06 Laser Additive Brazing钎焊 (LAB)
Paper06 Laser additive Brazing钎焊 （LAB）

Inert gas for shielding. removes the need for the long cycle time to get vacuum and also makes it possible to automate the process using a robot.
用于屏蔽的惰性气体。无需长时间的循环时间来获得真空，并且还可以使用机器人实现流程自动化。

Inert gas shielding would not work unless the heating and melting process is very rapid. Therefore, a powder feeder is used to feed micron-sized filler powders for rapid heating by laser
除非加热和熔化过程非常迅速，否则惰性气体保护装置将无法工作。因此，使用粉末进料器给料微米级填料粉末，以便通过激光快速加热.

Intelligent LAB with addition of closed loop temperature control
智能实验室，增加闭环温度控制

remanufacturing of a damaged turbine blade
损坏的涡轮叶片的再制造

Paper07 Laser Induced decarburization激光诱导脱碳

Paper09 Striation-free无条纹的 Laser Cutting of Mild Steel Sheets
Paper09 无条纹无条纹的低碳钢板激光切割

Is Stration-free Laser Cutting possible? why? Yes 1. Specific operating conditions such as cutting speed, laser power, and gas pressure were identified that allowed for high-speed, striation-free cutting. Notably, cutting speeds above a critical threshold were required to avoid the formation of striations. 2. oxidation reactions, gas dynamics, and hydrodynamic instabilities typically cause periodic variations in the cut surface quality, influencing roughness and geometrical precision. 3. at low cutting speeds (<40 mm/s), striation occurred in all samples. However, as the cutting speed increased, the cut surface became smoother and striation-free around cutting speeds of 60 - 75 mm/s at 1-2 bar gas pressures. Striation reappeared with further increases in cutting speed, which also led to increased surface roughness. 4. A theoretical model was proposed to predict the critical cutting speed at which striation-free cutting occurs. This model considers factors like vaporization front speed, beam power density, and material properties.
无磨损激光切割是可能的吗？为什么？是 1. 确定了特定的作条件，例如切割速度、激光功率和气体压力，以实现高速、无条纹的切割。值得注意的是，需要超过临界阈值的切割速度以避免形成条纹。 2. 氧化反应、气体动力学和流体动力学的不稳定性通常会导致切割表面质量的周期性变化，从而影响粗糙度和几何精度。3. 在低切割速度 （<40 mm/s） 下，所有样品都出现条纹。然而，随着切割速度的提高，在 1-2 bar 气压下，切割速度为 60 - 75 mm/s 时，切割表面变得更加光滑且无条纹。随着切割速度的进一步增加，条纹再次出现，这也导致表面粗糙度增加。 4. 提出了一个理论模型来预测发生无条纹切割的临界切割速度。此模型考虑了汽化前沿速度、光束功率密度和材料属性等因素。

Paper?? Microcavities in sub-surface of stainless steel
纸？？不锈钢次表面的微空腔

Explain the possible mechanism of the microcavity formation and describe a possible application of the phenomenon. Nd:YAG laser irradiation heats the stainless steel surface and generates a melt pool and metal vapour. The vapour drives the molten metal upwards. At a certain laser power density (neither too high nor too low), the molten metal ejection is stopped at the half way of the volume expulsion when the laser pulse ends. The remaining melt material rapidly solidifies and creates a microcavity in the sub-surface of stainless steel.
解释微腔形成的可能机制并描述该现象的可能应用。Nd：YAG 激光照射加热不锈钢表面并产生熔池和金属蒸气。蒸汽将熔融金属向上驱动。在一定的激光功率密度（既不太高也不太低）下，当激光脉冲结束时，熔融金属喷射在体积喷射的一半处停止。剩余的熔体材料迅速凝固并在不锈钢的子表面形成微空腔。

A possible application of the phenomenon is security marking. This can be achieved by “writing” patterned microcavities below the surface.
这种现象的一个可能应用是安全标记。这可以通过在表面下 “写入 ”图案的微腔来实现。

What is the major type of defect in the microstructures obtained? Suggest an effective method to avoid such defect. major type of defect is lack of fusion， The effective way to get rid of the defect is to increase power to 225 W and above. evolution of number and size of TiC particles As power increases, the
获得的微观结构中的主要缺陷类型是什么？建议一种有效的方法来避免这种缺陷主要类型的缺陷是缺乏熔合，消除缺陷的有效方法是将功率增加到 225 W 及以上。TiC 粒子数量和大小的演变随着功率的增加，

particles reduce in number and the particle sizes also reduce
颗粒数量减少，颗粒尺寸也减小.