Read and translate the text. Text b Ultrasonic Welding

When bonding material through ultrasonic welding, the energy required comes in the form of mechanical vibrations. The welding tool (sonotrode) couples to the part to be welded and moves it in longitudinal direction. The part to be welded on remains static. Now the parts to be bonded are simultaneously pressed together. The simultaneous action of static and dynamic forces causes a fusion of the parts without having to use additional material. This procedure is used on an industrial scale for linking both plastics and metals.

Ultrasonic welding of plastics is a state-of-the-art technology that has been in use for many years. When welding thermoplastics, the thermal rise in the bonding area is produced by the absorption of mechanical vibrations, the reflection of the vibrations in the connecting area, and the friction of the surfaces of the parts. The vibrations are introduced vertically. In the contraction area, frictional heat is produced so that material plasticizes locally, forging an insoluble connection between both parts within a very short period of time.

The prerequisite is that both working pieces have a near equivalent melting point. The joint quality is very uniform because the energy transfer and the released internal heat remains constant and is limited to the joining area. In order to obtain an optimum result, the joining areas are prepared to make them suitable for ultrasonic bonding. Besides plastics welding, ultrasonics can also be used to rivet working parts or embed metal parts into plastic.

Whereas in plastic welding, high-frequency vertical vibrations (20 to 70kHz) are used to increase the temperature and plastify the material, the joining of metals is an entirely different process. Unlike in other processes, the parts to be welded are not heated to melting point, but are connected by applying pressure and high-frequency mechanical vibrations.

In contrast to plastics welding, the mechanical vibrations used during ultrasonic metal welding are introduced horizontally.

UNIT 5

Read and translate the text.

Text A

Laser Beam Welding

Laser beam welding (LBW) is a welding process which produces coalescence of materials with the heat obtained from the application of a concentrated coherent light beam impinging upon the surfaces to be joined.

The focused laser beam has the highest energy concentration of any known source of energy. The laser beam is a source of electromagnetic energy or light that can be projected without diverging and can be concentrated to a precise spot. The beam is coherent and of a single frequency.

Producing a laser beam is extremely complex. The early laser utilized a solid-state transparent single crystal of ruby made into a rod approximately an inch in diameter and several inches long. The end surfaces of the ruby rod were ground flat and parallel and were polished to extreme smoothness.

The laser can be compared to solar light beam for welding. The laser can be used in air. The laser beam can be focused and directed by special optical lenses and mirrors. The laser can operate at considerable distance from the work piece.

When using the laser beam for welding the electromagnetic radiation impinges on the surface of the base metal with such a concentration of energy that the temperature of the surface is melted and volatilized. The beam penetrates through the metal vapor and melts the metal below. One of the original questions concerning the use of the laser was the possibility of reflectivity of the metal so that the beam would be reflected rather than heat the base metal. It was found, however, that once the metal is raised to its melting temperature the surface conditions have little or no effect.

The welding characteristics of the laser and of the electron beam are similar. The concentration of energy by both beams is similar, with the laser having a power density in the order of 106 watts per square centimeter. The power density of the electron beam is only slightly greater. This is compared to a current density of only 104 watts per square centimeter for arc welding.

Laser beam welding has a tremendous temperature differential between the molten metal and the base metal immediately adjacent to the weld. Heating and cooling rates are much higher in laser beam welding than in arc welding, and the heat-affected zones are much smaller. Rapid cooling rates can create problems such as cracking in high carbon steels.

The laser beam has been used to weld carbon steels, high strength low alloy steels, aluminum, stainless steel and titanium. Laser welds made in these materials are similar in quality to welds made in the same materials by electron beam process.