A laser beam machining method and a laser beam machining device capable of cutting a work without producing a fusing and a cracking out of a predetermined cutting line on the surface of the work, wherein a pulse laser beam is radiated on the predetermined cut line on the surface of the work under the conditions causing a multiple photon absorption and with a condensed point aligned to the inside of the work, and a modified area is formed inside the work along the predetermined determined cut line by moving the condensed point along the predetermined cut line, whereby the work can be cut with a rather small force by cracking the work along the predetermined cut line starting from the modified area and, because the pulse laser beam radiated is not almost absorbed onto the surface of the work, the surface is not fused even if the modified area is formed.

Laser processing method and laser processing apparatus

In this article, an overview of the hybrid welding process is given. After a short historic overview, a review of the fundamental phenomenon taking place when a laser (CO2 or Nd:YAG) interacts in the same molten pool as a more conventional source of energy, e.g. tungsten in-active gas, plasma, or metal inactive gas/metal active gas. This is followed by reports of how the many process parameters governing the hybrid welding process can be set and how the choice of secondary energy source, shielding gas, etc. can affect the overall welding process. An overview of the benefits and drawbacks of hybrid welding is presented, including reports on gap bridging ability, changes in welding speed and weld penetration, overall weld quality, and changes in heat input to the material being welded. This overview is followed by a few examples of industrial applications of hybrid welding. Finally, a section is devoted to explain about further work required in order to understand and tackle the hybrid welding process more efficiently in the future.In this article, an overview of the hybrid welding process is given. After a short historic overview, a review of the fundamental phenomenon taking place when a laser (CO2 or Nd:YAG) interacts in the same molten pool as a more conventional source of energy, e.g. tungsten in-active gas, plasma, or metal inactive gas/metal active gas. This is followed by reports of how the many process parameters governing the hybrid welding process can be set and how the choice of secondary energy source, shielding gas, etc. can affect the overall welding process. An overview of the benefits and drawbacks of hybrid welding is presented, including reports on gap bridging ability, changes in welding speed and weld penetration, overall weld quality, and changes in heat input to the material being welded. This overview is followed by a few examples of industrial applications of hybrid welding. Finally, a section is devoted to explain about further work required in order to understand and tackle the hybrid welding process more ...

Review of laser hybrid welding

Devices and methods for delivering conduits into the wall of a patient's heart to communicate a coronary vessel with a heart chamber. The devices are passed through the coronary vessel and the heart wall to place the conduit and establish a blood flow path between the vessel and the heart chamber. Additional devices and methods are provided for removing tissue from a coronary vessel or the heart wall to establish a flow path between the coronary vessel in communication with the heart chamber.

Delivering a conduit into a heart wall to place a coronary vessel in communication with a heart chamber and removing tissue from the vessel or heart wall to facilitate such communication

In-situ characterization of laser-powder interaction and cooling rates through high-speed imaging of powder bed fusion additive manufacturing

Parameters that control the solidification of castings also control the solidification and microstructure of welds. However, various physical processes that occur due to the interaction of the heat source with the metal during welding add a new dimension to the understanding of the weld pool solidification. Conventional theories of solidification over a broad range of conditions can be extended to understand weld pool solidification. In certain cases, because of rapid cooling rate effects, it is not unusual to observe nonequilibrium microstructures. Recent developments in the application of computational thermodynamics and kinetic models, studies on single-crystal welds, and advanced in-situ characterization techniques have led to a better understanding of weld solidification and microstructures.

Welding: Solidification and microstructure

The solidification microstructures of pulsed Nd:YAG laser or CW CO2 laser welds were studied in commercial SUS 310S and 304 (corresponding to AISI Types 310S and 304) austenitic stainless steels and in other several austenitic and duplex stainless steels. In the pulsed laser welding of Type 310S, neither grain growth nor recrystallization grain-refining was observed in the heat-affected zones (HAZ), and planar and cellular growth occurred epitaxially in weld metals from adjacent, incompletely-melted grains in the HAZ. According to the data relating a primary dendrite arm spacing to the cooling rate in Type 310S weld metals, the average local cooling rates within the single laser shot welds were extrapolated to be so rapid as to range from 5×104 to 5×106°C/s depending mainly on the pulse energy. In the case of Type 304, the pulsed laser weld metals were almost fully austenitic in contrast to GTA or CO2 laser weld metals containing about 5% residual delta(δ)-ferrite. It was significantly confirmed that almost fully austenitic structure of Type 304 could be produced with extremely high cooling rates obtained by CW CO2 laser welding process with low heat inputs at high traverse speeds. From the microstructural observation of several materials, it was further revealed that the solidification microstructures of pulsed laser welds were not consistent with the prediction from the Schaeffler diagram. In other words, the steels containing the calculated contents of less than 8% δ-ferrite or more than 30% δ-ferrite exhibited fully austenitic or fully ferritic microstructure, so that the compositional region indicating a duplex microstructure was very narrow in the case of pulsed laser weld metals. The disappearance of ferrite in the laser-welded microstructure was interpreted in terms of the change in the solidification process due to extremely high cooling rates accompanied with large undercooling. In addition, the change from duplex to fully ferritic structure was attributed to the suppression of the solid-state, ferrite-to-austenite transformation.The solidification microstructures of pulsed Nd:YAG laser or CW CO2 laser welds were studied in commercial SUS 310S and 304 (corresponding to AISI Types 310S and 304) austenitic stainless steels and in other several austenitic and duplex stainless steels. In the pulsed laser welding of Type 310S, neither grain growth nor recrystallization grain-refining was observed in the heat-affected zones (HAZ), and planar and cellular growth occurred epitaxially in weld metals from adjacent, incompletely-melted grains in the HAZ. According to the data relating a primary dendrite arm spacing to the cooling rate in Type 310S weld metals, the average local cooling rates within the single laser shot welds were extrapolated to be so rapid as to range from 5×104 to 5×106°C/s depending mainly on the pulse energy. In the case of Type 304, the pulsed laser weld metals were almost fully austenitic in contrast to GTA or CO2 laser weld metals containing about 5% residual delta(δ)-ferrite. It was significantly confirmed that almo...

Solidification microstructure of laser welded stainless steels

Nitriding and related hardening of titanium(Ti) and its alloys were investigated as anew method of laser surface treatment by using a pulsed Nd:YAG laser of 1.06 μm wavelength with 3.6 ms pulse width. When a laser beam was irradiated on Ti plate in nitrogen(N) atmosphere, it was found that a flat and smooth surface covered with TiN nitride layer could be produced by selecting a good combination of laser irradiation conditions such as beam energy, power density and the distance from the lens focal point to the material surface. Compared with Ti base metal having a Vickers hardness(Hv) of about 200, the hardness of the laser-nitriding surface could exceed about 700 Hv at a single pulse shot and increase up to 1700 Hv at overlap of twenty shots, and besides the fusion zone could be hardened up to about 400 to 700 Hv. These hardening mechanisms were interpreted in terms of the formation of TiN nitride layer on the surface and the enrichment of nitrogen in the fusion zone. Nitriding and hardening phenomena were observed as well in the case of titanium alloys such as Ti-6Al-4V and Ti-6Al-6V-2Sn. Moreover, it was confirmed that nitriding and hardening of Ti and its alloys were feasible by the use of a CW CO2 laser.

Surface hardening of titanium by laser nitriding

A variety of stainless steels were exposed to pulsed Nd:YAG laser with the rectangular shape power to first investigate practical problems related to pulsed laser welding. Porosities, cracks and undercuts were found as weld defects. A large porosity was formed in a key-hole mode of deep penetration weld metal of any stainless steel. Solidification cracks were present in Type 310S with above 0.017%P and undercuts were formed in Type 303 with about 0.3%S. The conditions for the formation of porosity were determined in further detail in Type 316. With the objectives of obtaining a fundamental knowledge of formation and prevention of weld defects, the fusion and solidification behavior of a molten puddle was observed during laser spot welding of Type 310S through high speed video photographing technique and the behavior was estimated by using a heat-conduction and solidification theory model. It was deduced that cellular dendrite tips grew rapidly from the bottom to the surface, and consequently residual liquid remained at the grain boundaries in wide regions and enhanced the solidification cracking susceptibility. Several laser pulse shapes were investigated and optimum pulse shapes were proposed for the reduction and prevention of porosity and solidification cracking.A variety of stainless steels were exposed to pulsed Nd:YAG laser with the rectangular shape power to first investigate practical problems related to pulsed laser welding. Porosities, cracks and undercuts were found as weld defects. A large porosity was formed in a key-hole mode of deep penetration weld metal of any stainless steel. Solidification cracks were present in Type 310S with above 0.017%P and undercuts were formed in Type 303 with about 0.3%S. The conditions for the formation of porosity were determined in further detail in Type 316. With the objectives of obtaining a fundamental knowledge of formation and prevention of weld defects, the fusion and solidification behavior of a molten puddle was observed during laser spot welding of Type 310S through high speed video photographing technique and the behavior was estimated by using a heat-conduction and solidification theory model. It was deduced that cellular dendrite tips grew rapidly from the bottom to the surface, and consequently residual liqu...

Pulse shape optimization for defect prevention in pulsed laser welding of stainless steels

The paper describes the direct observation of laser induced plume and keyhole dynamics by various optical and X-ray methods with high temporal resolution, and different types of porosity formation mechanisms and their suppression methods have been revealed in the pulsed spot laser and continuous laser welding of various materials such as Al-alloys, stainless steels, and so on.Hydrogen induced porosity is featured by small blow holes and is a serious problem in laser welding of Al-alloys. As the average temperature of molten pool is much higher than that of arc welding, soluble Hydrogen is increased and leads to the formation of large numbers of porosity. Only possible measure to reduce porosity is to cut off the Hydrogen sources during welding.Another characteristic porosity formation in laser welding is caused by the intense evaporation of metal in the keyhole which enhances the instability of keyhole as well as weld pool. This type of porosity is featured by a large size and can be reduced by proper pulse shaping in spot welding and adoption of optimum pulse modulation. Also, a proper angle of beam incidence is effective to reduce porosity formation.The paper describes the direct observation of laser induced plume and keyhole dynamics by various optical and X-ray methods with high temporal resolution, and different types of porosity formation mechanisms and their suppression methods have been revealed in the pulsed spot laser and continuous laser welding of various materials such as Al-alloys, stainless steels, and so on.Hydrogen induced porosity is featured by small blow holes and is a serious problem in laser welding of Al-alloys. As the average temperature of molten pool is much higher than that of arc welding, soluble Hydrogen is increased and leads to the formation of large numbers of porosity. Only possible measure to reduce porosity is to cut off the Hydrogen sources during welding.Another characteristic porosity formation in laser welding is caused by the intense evaporation of metal in the keyhole which enhances the instability of keyhole as well as weld pool. This type of porosity is featured by a large size and can be reduced by proper pul...

Porosity formation in laser welding - Mechanisms and suppression methods

PROBLEM TO BE SOLVED: To provide an excellent welded joining by realizing a sufficient penetration cross section and a sufficient penetration depth even in a metallic member which has a high reflectivity and a high thermal diffusion rate. SOLUTION: A first YAG laser 10 generates a YAG laser beam LBCW (wave length is 1,064 nm) having continuous fundamental waves and a second YAG laser 12 generates a second higher harmonic Q-switched YAG laser beam LBSHG (wave length is 532 nm) of a high speed repetitive pulse oscillation. The fundamental wave YAG laser beam emitted from the first YAG laser and the second higher harmonic Q-switched YAG laser beam emitted from the second YAG laser are transferred to an existing unit 16 via respective laser beam transfer path. Further, both laser beams are superimposed on a same axis by a dichroic mirror 66 after each of the beams is adjusted to a predetermined beam diameter with a collimator lens 64 and a beam expander 70 in the existing unit, and condensed at a point in the vicinity of the weld zone WP of a work W with a condenser lens 68.

Akira Matsunawa

Papers

Solidification microstructure of laser welded stainless steels

Surface hardening of titanium by laser nitriding

Pulse shape optimization for defect prevention in pulsed laser welding of stainless steels

Porosity formation in laser welding - Mechanisms and suppression methods

Method and equipment for laser beam welding