LaserHybrid Welding Drives VW Improvements — Volkswagen Phaeton

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Volkswagen Phaeton

Laser-Hybrid Welding Drives VW

Laser-Hybrid Welding Drives VW

A hybrid process that a laser beam with gas arc welding produces benefits could not achieve with process alone

Laser welding and arc welding both long been used in production and permit a wide of applications. Both processes their specific areas of as described by the physical processes of transport and by the obtained energy Energy is transmitted from the to the arc by means of high-energy infrared radiation using a fiber-optic The arc transmits the heat needed for by a high electric current to the workpiece via an arc column. Laser leads to a very narrow zone with a large of welding depth to joint (deep-weld effect). The ability of the welding process to bridge openings is low due to its small focus but, on the other hand, welding speeds can be obtained. The arc process has a much lower density, but causes a bigger spot on the surface and is characterized by a processing speed. By merging processes, useful synergies can be and, ultimately, it is possible to both quality advantages and engineering benefits, as well as cost efficiency. This process offers interesting and attractive applications in the automobile due to higher permitted tolerances on the because of higher joining and good mechanical/technological parameters. — A schematic representation of welding. This article an application at Volkswagen AG, Wolfsburg, where the doors of the Phaeton are welded with a laser-hybrid

Development of Laser-Hybrid Welding

The for combining laser light and a arc into an amalgamated welding has been known since the but for a long time thereafter, no research and development was undertaken. however, researchers have turned their attention to topic and attempted to unite the of the arc with those of the laser in a welding process. In the early the suitability of lasers for industrial use had to be nowadays lasers are standard in many manufacturing enterprises.

The of laser beam welding another welding process is a welding process, meaning a beam and an arc act simultaneously in one welding and influence and support each Fig.2 — Volkswagen’s model. The Laser

Laser not only requires high power but also a high-quality to obtain the desired deep-weld The resulting high beam can be exploited either to obtain a focus diameter or a larger distance.

For the projects currently underway at a lamp-pumped solid-state laser a laser beam power of 4 kW is The laser light is transmitted via a 600-mm glass fiber. The beam is projected onto the by a focusing module with a distance of 200/220 mm. Fig.3 Comparison of the joining techniques on the Volkswagen Phaeton’s front GMAW process: 7 joints, mm welded length; laser welding: 11 joints, 1030-mm length; laser-hybrid process: 48 3570-mm welded length. weld length equals mm. The Laser-Hybrid Process

For welding workpieces, the Nd:YAG laser is focused to obtain intensities of than 106 W/cm2. When the beam hits the surface of the the spot is heated up to vaporization and a vapor cavity is formed in the metal due to the escaping metal The extraordinary feature of the weld is its high depth-to-width ratio. The flow density of the freely arc is slightly more than 104 Figure 1 illustrates the basic of hybrid welding. The laser depicted here transmits to the weld metal in the top part of the in addition to the heat from the Unlike a sequential configuration two separate weld processes act in hybrid welding may be viewed as a of both weld processes simultaneously in the same process Depending on the kind of arc or laser used, and depending on the process the processes will influence other to a different extent and in ways (Refs. 1, 2). Fig. 4 Laser-hybrid … joint for the Concept D1 (currently called the Optimized welding parameters for cast materials: welding 4.2 m/min; wire feed 6.5 m/min; and laser power, 2.9 kW. to the combination of the laser and the arc, is also an increase in both penetration depth and welding (as compared to each single The metal vapor escaping the vapor cavity acts the arc plasma. Absorption of the Nd:YAG radiation in the processing plasma negligible. Depending on the ratio of the two inputs, the character of the overall may be mainly determined either by the or the arc (Ref. 3).

The temperature of the workpiece substantially influences absorption of the radiation. Before the laser process can start, the initial must be overcome, especially on surfaces. This can be achieved by welding with a special program. After vaporization has been reached, the vapor is formed and nearly all radiation can be put into the workpiece. The energy for this is determined by the temperature-dependent and the amount of energy lost by into the rest of the workpiece. In welding, vaporization takes not only from the surface of the but also from the welding so more metal vapor is which in turn facilitates the of laser radiation and prevents dropout (Refs. 4-9).

Using the Process at Volkswagen

strategy is to have the highest of laser weldments in the automotive Figure 2 shows the Phaeton, called the Concept D1. In this car all doors are laser-hybrid welded. The requirements included a high of stiffness in the door structure. the laser-hybrid process, big, aluminum cast materials have been necessary. The tolerances had to be very small to a perfect fit to the car body, resulting in low levels from the wind driving. To achieve a door that degree of stiffness, a combination of sheet, cast, and materials was necessary. In order to a low weight, aluminum was the preferred and material because of its low density.

The door shown in Fig. 3 of 7 gas metal arc, 11 laser, and 48 weldments. The total length of on these doors is 4980 mm.

4 shows a laser-hybrid welded of a two aluminum cast material. The wire was AlSi12 with a of 1.6 mm. The shielding gas was argon. With laser power, higher speed is possible. Combining the beam with the arc results in a weld pool compared to the beam weld process and welding of components with root openings becomes The range of the welding speed is 1.2 to 4.8 but the process is optimized at 4.2 m/min.

In the industry, there are many of overlap welding without preparation. At the moment, the state-of-the-art for this welding job is laser welding with a cold wire, due to hot cracking of the AA 6xxx When the joint is welded a welding wire, much of the energy will be lost in that welding wire.

Comparing Laser-Hybrid with Processes

Figure 5 represents the between laser-hybrid and laser on an overlap joint with a speed of 2.4 m/min. In the case of welding, there is no possibility of up the weld and undercut is produced. is also only a little into the base material. The bead width is very and, therefore, a low tensile is expected. In the case of laser-hybrid additional material is transported the weld pool. The undercut is with wire from the gas arc welding (GMAW) process and a of laser energy is now saved. saved laser energy can be to increase the penetration into the material and the weld bead is larger than the material which is required for optimum properties. Fig. 5 — between laser hybrid and beam welding without metal. In the case of laser with welding wire 6), it is necessary to use a pressure wheel to get the tolerances. But there are limits accessibility because of the higher of the welding head. Typical of this process are a welding of 2.8 m/min, laser power of W, and wire feed rate of 6.6 With the laser-hybrid process, it is possible to weld other geometries, especially fillet on lap and … joints. Fig. 6 Laser cold wire at Volkswagen. Figure 7 shows the head, which has small dimensions to ensure good to the components to be welded, a requirement needed for the automotive industry. It is to permit both a suitable connection to the robot head and of process variables such as distance and torch standoff in all Cartesian coordinates. The accuracy of is 0.1 mm in all directions. The spattering that during the welding process to increased soiling of the protective The quartz glass is coated on sides with an antireflective and is intended to protect the laser system from damage. on the degree of soiling, the spatter on the glass can cause the laser actually impacting the workpiece to by as much as 90%. Heavier generally leads to the destruction of the glass, as such a large of the radiant energy is then by the glass itself, causing stresses in the glass. To avoid a glass or a reduction of laser on the workpiece, it is possible to integrate glass monitoring equipment. The head has a changeable water-cooled gas and torch and a current load of up to 250 A at a cycle of 100%.

The welding head can be applied for welding with and without wire, laser-hybrid welding, gas arc welding, and laser hot-wire (especially for zinc-coated materials). In the of laser hot-wire brazing, the is preheated with the same source that can be used for welding. There is only a in the software, not in the hardware configuration.

of Laser- Hybrid Welding

The of the arc and laser beam results in the advantages of laser-hybrid welding laser welding:

Higher stability

Higher bridgeability

penetration

Lower capital costs because of savings in energy

Greater ductility.

The of laser-hybrid welding over are the following:

Higher welding

Deeper penetration at higher speeds

Lower thermal

Higher tensile strength

weld joints.

The arc welding is characterized by a low-cost energy good root opening and the facility for influencing the structure by filler metals. The laser process, on the other hand, large welding depth, welding speed, low thermal and narrow weld joints. The beam produces a deep-weld in metallic materials over a beam density, which components with greater thickness to be welded- providing the power is sufficiently high. welding thus allows welding speeds, process due to the interaction between the arc and the laser increased thermal efficiency, and workpiece tolerances. As the weld is smaller than in the GMAW there is less thermal and a smaller heat-affected zone. results in lesser weldment which reduces the amount of postweld straightening work. there are two separate weld the subsequent thermal input the arc means the laser beam area, especially in the case of is given a postweld tempering spreading the hardness values evenly across the joint. 8 sums up the synergies of the combined hybrid) process. Fig.7 The laser-hybrid welding head. now to the economic advantages of hybrid over laser welding, the statements can be made: The weld consists partly of a laser and partly of a GMA weld. The hybrid makes it possible to reduce the of the laser beam, thereby reducing energy consumption of the source as the laser beam has an efficiency of only 3%. In other a reduction of 1 kW in the laser beam impacting upon the workpiece to a reduction of approximately 35 kVA in the power from the electricity mains.

A laser beam apparatus approximately $120,000 per kilowatt of beam power. When of the hybrid process makes it to use a 3-kW laser instead of one 4 kW of beam power, investments of are saved. However, costs of $65,000 will be needed for the MSG equipment and welding head. Due to the welding speed, both time and welding costs can be Fig.8 — The synergies by combining laser beam and arc With the laser-hybrid welding it is possible to weld materials of steel, and stainless steel 1 to 4 mm thick. If the thickness is higher, penetration is only possible in the of steel or stainless steel up to 5 mm. For zinc-coated materials, it is preferable to use the hot-wire brazing process.

applications where the laser- welding process is suitable are trains, vessels, axles, and car

Summary

Laser-hybrid welding is a new that offers synergies for fields of application in the automotive especially where it is not possible or viable to achieve the component required for laser beam The wider range of applications and the capability of the combined process to enhanced competitiveness in terms of investments, shorter fabrication lower manufacturing costs, and productivity.

The laser-hybrid process offers a new approach to the welding of However, a stable process has possible relatively recently of the higher available output of solid-state lasers. Many have examined the fundamentals of and arc hybrid welding processes. By welding process, the combination of beam welding and the arc welding is understood, with only one process zone (plasma and Research has shown by combining the two synergies can be achieved and the drawbacks of separate process can be compensated resulting in enhanced welding weldability, and reliability for many materials and constructions. In particular, has been demonstrated for aluminum at Volkswagen on the Phaeton model. By the current process parameters, it is to selectively influence weld such as geometry and structural The arc welding process increases the by adding filler metal; it determines weld joint and reduces the amount of workpiece needed. Moreover, the interactions the processes lead to a substantial in efficiency. This combination also requires considerably investment costs compared to beam welding. New joint are possible, especially fillet or joints, and it is not necessary to use a pressure on the welding head, resulting in accessibility.

References

1. Dausinger, F. 1995. process safety at aluminum with Nd:YAG lasers. Metals and Profiles 42(9):

2. Cui, H. 1991. Study of between arc and focused laser and applicability of combined laser-arc Thesis. Technical University

3. Maier, C. Beersiek, J. and Neuenhahn, K. Combined arc-laser beam process — on-line control. DVS 170, pp. 45-51.

4. et al. 1978. Arc-augmented laser Paper No. 17 4th Int. Conf. on in Welding Processes, pp. 257-265.

5. 1996. Laser Material Springer Verlag.


6. Welding Solid Lasers, Laser in Treatment. Vol. 2. 1995.

7. Beyer, E. 1997. Welding Lasers: Basis. Springer.

8. F. Weick, J. M. Fitz, R. and Kern, M. Applications of twin focus Laser Days in Stuttgart, pp.

9. Helten, S. 1999. Qualification and of arc suported laser beam process in the production process of body lightweight construction. Germany: Diplomarbeit Audi, (ISF). T. GRAF is with Wolfsburg, Germany. H. STAUFER is Fronius International GmbH, Austria. Fronius USA can be reached at 220-4414 or sales.usa@fronius.com.

Based on a presented at the Annual Assembly of the Institute of Welding on June 27, in Copenhagen, Denmark.

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