SHADOW - a new welding technique

The new welding technique, "SHADOW - stepless high speed accurate and discrete one pulse welding", is introduced. SHADOW means the use of a single pulse to generate a quasi continuous weld of several millimeters in length. The processing time is defined by the pulse duration of the pulsed laser. At present, a state-of-the-art laser is capable of a maximum pulse duration of 20 ms. The variation of the laser power depending on time is a vital capability of the pulsed laser to adapt the energy deposition into the workpiece (pulse shaping). Laser beam welds of several watch components were successfully performed. Similar metals like crowns and axes made out of stainless steel have been welded using pulsed laser radiation. Applying a series of about 130 single pulses for the crown-axis combination, the total energy accumulates to 19.5 J. The use of the SHADOW welding technique reduces the energy to 2.5 J. While welding dissimilar metals like stainless steel and brass, the SHADOW technique has even more advantages. Gearwheels made out of brass have been joined to axes made out of stainless steel. Common pulse mode welding generates a considerable amount of contamination but SHADOW welding drastically reduces the contamination and the distortion. Laser beam welding of copper has a low process reliability due to the high reflection and high thermal conductivity. SHADOW welds of 3.6 mm length were performed on 250 mu m thick copper plates with very high reproducibility. As a result, a pilot plant for laser beam welding of copper plates has been set up.