Laser-hybrid welding

Laser Hybrid welding is a type of welding process that combines the principles of laser beam welding and arc welding.

Introduction

The combination of laser light and an electrical arc into an amalgamated welding process has beenknown since the 1970's, but has only recently been used in industrial applications. There are three main types of hybrid welding process, depending on the arc used; TIG, Plasma arc or MIG augmented laser welding. While TIG augmented laser welding was the first to be researched, MIG is the first to go into industry and is commonly known as hybrid laser welding.

Whereas in the early days laser sources still had toprove their suitability for industrial use, today they are standard equipment in many manufacturing enterprises.The combination of laser welding with another weld process is called a "hybrid weldingprocess". This means that a laser beam and an electrical arc act simultaneously in one weldingzone, influencing and supporting each other.

Laser

Laser welding not only requires high laser power but also a high quality beam toobtain the desired "deep-weld effect". The resulting higher quality of beam can beexploited either to obtain a smaller focus diameter or a larger focal distance.A variety of laser types are used for this process, in particular wherethe laser light can be transmitted via a water cooled glass fiber. The beam is projected onto the workpiece by collimating and focusing optics. Carbon dioxide laser can also be used where the beam is transmitted via lens or mirrors.

Laser Hybrid process

For welding metallic objects, the laser beam is focused to obtainintensities of more than 1 MW/cm². When the laser beam hits the surface of thematerial, this spot is heated up to vaporization temperature, and a vapor cavity isformed in the weld metal due to the escaping metal vapor. This is known as a keyhole. The extraordinary featureof the weld seam is its high depth-to-width ratio. The energy-flow density of the freelyburning arc is slightly more than 100 kW/cm². Unlike a dual process where two separate weld processes act in succession, hybrid welding may be viewed as a combination of both weld processes acting simultaneously in one and the same process zone. Depending on the kind of arc or laser process used, and depending on the process parameters, the two systems will influence each other in different ways.

The combination of the laser process and the arc process results in anincrease in both weld penetration depth and welding speed (as compared to eachprocess alone). The metal vapor escaping from the vapor cavity acts upon the arcplasma. Absorption of the laser radiation in the processing plasma remainsnegligible. Depending on the ratio of the two power inputs, the character of theoverall process may be mainly determined either by the laser or by the arc.

Absorption of the laser radiation is substantially influenced by the temperature of theworkpiece surface. Before the laser welding process can start, the initial reflectancemust be overcome, especially on aluminum surfaces. This can be achieved bypreheating the material. In the hybrid process, the arc heats the metal, helping the laser beam to couple in. After the vaporisation temperature hasbeen reached, the vapor cavity is formed, and nearly all radiation energy can be putinto the workpiece. The energy required for this is thus determined by thetemperature dependent absorption and by the amount of energy lost by conductioninto the rest of the workpiece. In Laser Hybrid welding, using MIG, vaporisation takes place notonly from the surface of the workpiece but also from the filler wire, so that more metalvapor is available to facilitate the absorption of the laser radiation.

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