Laser Spike Welding Enables New Materials and Designs
Researchers from Philips Electronics Neder-land BV in Eindhoven and the University of Groningen, both in the Netherlands, have developed a laser welding technique that promises lightweight components for aircraft manufacturers and a host of other novel applications.
Figure 1. In laser penetration spike welding, the initial part of the laser pulse creates a "quiet" melt in the top piece of sheet metal, and the spike blasts the molten metal out the back side, bonding the top piece to one below it.
In the process, called laser penetration spike welding, an Nd:YAG laser emits 15- or 20-ms-long pulses, with an intense spike several hundred microseconds in duration near the end of the pulse (Figure 1). These pulses can join thin pieces of sheet metal separated by up to 100 percent of the thickness of the top piece: The initial part of the pulse melts a spot in the top piece of sheet metal, and the spike at the end blasts the molten material out the back side, forming a physical "spike" that bonds the top piece to the bottom one.
An advantage of this type of welding is that it allows for larger dimensional tolerances in manufacturing. Although the weld is strongest when the pieces are in contact, "good" welds can be obtained when the gap between them is hundreds of microns. This relaxed tolerance could cut the cost of manufacturing everything from alarm clocks to automobiles.
Figure 2. Welding several pieces of sheet metal with numerous penetration spike welds and with gaps equal to the thickness of the sheets yields a material with half the density of the metal. Filling the gaps with epoxy increases stiffness while adding little weight. Such materials may be suitable for applications that require lightweight components.
Figure 2 shows several pieces of sheet metal joined by penetration spike welds. Because the gaps are equal to the thickness of the sheets, the density of the welded material is half that of the metal. Materials fabricated this way could find important uses in aircraft manufacturing and in other applications that require lightweight components. The stiffness of the material could be increased, with minimal weight penalty, by filling the gaps between the sheets with epoxy.
Penetration spike welding offers other potential advantages to mechanical engineers. For example, low-cost hinges could be fabricated in three pieces of sheet metal. First, a hole is drilled through the middle piece. A penetration spike weld is then made through the hole between the top and bottom pieces, and the middle piece can pivot around the weld (Figure 3).
Figure 3. Low-cost hinges could be fabricated by laser penetration spike welding in three pieces of sheet metal. A penetration spike weld between the top and bottom pieces through a hole in the one between them serves as an axis around which the middle piece pivots.
The technique also eases the welding of dissimilar materials. With conventional laser welding, the metal on the bottom must have lower heat conductivity. If it does not, it tends to act as a heat sink and conducts heat away before the metal on top can melt. In contrast, the large gap between the two sheets in penetration spike welding minimizes such preweld heat transfer.
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