Laser Weld Creation is established with the purpose of assisting enterprises to improve their manufacturing process by introducing new and existing laser equipment.
This site is dedicated to industrial laser technologies, namely laser welding. Today, all manufacturers are familiar with laser cutting. Many companies use various types of laser cutters in their production process, and laser marking is gaining popularity. Laser welding, however, is mainly used for welding subminiature components in instrument making industries. For this reason, it is important to emphasize that a lot of development of technologies and equipment for industrial laser welding has been carried out worldwide. This research progressed to the point of designing real technologies applicable in production, as well as performing many trial weld joints with certification purposes. In some cases these technologies went through industrial implementation. Today, when manufacturing enterprises are faced with the necessity of using laser welding technologies, they should know that they do not have to bootstrap this technology or look for suppliers across the border. There are highly skilled technologists and scientists in Canada who specialize in various aspects of laser welding technology.
In this article, we will not touch upon the subject of spot impulse laser welding, which has been widely used in the Canadian instrument-making industry for a long time. We will focus on butt-seam laser welding of thick metals – from 1 mm to 10 mm.
Physics of the process and types of laser welding
The process of laser welding consists of the dissolution (melting) of metal induced by highly concentrated light energy. Laser emission is focused upon the surface of metal in the junction area of two work-pieces. The emission is partially absorbed by the metal, heating it to the temperature of dissolution and boiling. Although the initial absorption capacity of metals and alloys is low, it increases as the temperature grows. As boiling temperature is reached, a layer of molten metal is ejected by the back pressure of the metal vapor stream, resulting in the formation of a cavity and further development of the gas-vapor duct. In such circumstances, the laser emission is almost fully absorbed. In terms of thermal physics, the heat source has the pattern of a line heat source. If the focused beam of emission moves along the junction, a melting zone forms and the surfaces are welded. Unfortunately, there is a physical phenomenon that considerably complicates the process, the plasma cloud that forms upon the surface of metal. The more easily ionized metal vapor starts absorbing the laser emission which results in the formation of a plasma flame jet.
This jet may exert negative or positive impacts on the welding process. It may hinder the process by partially block transmission of the energy beam from the metal surface and the melting canal or it may scatter the beam through the formation of a negative optical lens Or it may help the process due to the indirect heating of the metal surface during the early stages when direct emission absorption is low.
In order to eliminate the unfavorable effects of the plasma flame jet, plasma-suppressing gas mixtures are used. In laser welding argon is favored since it can simultaneously protect the melted metal from oxidation. Since the speed of laser welding is quite high, it may be necessary to use gas protection in the tail piece as well as on the other side of the weld. Pure argon can be used here too. When performed classically, laser welding needs neither adding materials nor fluxing agents. The welding process is easily controlled and is contact-free In contrast to arc welding, there is no need to use specialized energy sources with drooping characteristic.
Classification of some processes of laser welding
The spectrum of applied modifications of the laser welding process is classified by laser source type. The following types of laser are developed for industrial use:
YAG: lasers are yttrium-aluminum garnet based solid-state lasers. They differ in pumping source (tube or diode). Lasers with a tube pumping sources are successfully used in production, while lasers with a diode pumping source are expensive and are not often used for welding purposes. The emission wavelength of these lasers is 1.06 micron – close to the infrared range of the electromagnetic spectrum. The emission power is up to 5-6 kilowatt. Optical fibre lasers: These are currently the newest types of laser and have a unique structure. The actuating medium in these lasers is quartz optical fiber alloyed with rear-earth metals and pumping is carried out with laser diodes. The same fiber is used to transfer the emission to the welding head which makes it extremely convenient. The emission power is up to 5 kilowatt.
The main modes of laser welding:
а) Continuous emission welding – the laser emission power is either time-constant or impulse-type with impulse frequency approximately equal to tens of kHz
b) Impulse welding or pulse-periodic welding – in this case the laser impulse frequency is low (10-300 Hz) and energy of each pulse is high.
Laser welding can be employed to perform butt welding, lap welding, fillet welding, and other welding patterns differing in the reciprocal position of the work-pieces and the laser beam.
Quality and features of laser welding.
In terms of thermo physical and metallurgical processes, the main features of laser welding are significantly shortened melting and crystallization times as well as a highly localized heat-affected zone. This creates a special pattern of metallurgical metal transformation, namely the formation of various non-equilibrium structures in the weld metal. At the same time, numerous tests and certifications have demonstrated that laser welding is distinguished by its very high technological flexibility and the high quality of the weld joints. The properties of the weld joints are no worse than those of the parent metal in the majority of constructional materials. Conducted trials show that destruction always occurs in the parent metal, not the weld.
The technological flexibility of laser welding allows the performance of butt welding even with such metals and alloys as stainless steel, copper, titanium and titanium-based alloys.
The crucial step towards the utilization of laser welding was made in 1996 when the united European project dedicated to the possibilities of using laser welding in the shipbuilding industry was successfully completed. The engineering materials of the project were conveyed to the classification institutions of the member states which developed guidelines for employment of laser welding in shipbuilding. Today laser technology is broadly used for welding several conventional structural fragments, such as bulky honeycombs, at a number of shipyards of the United Kingdom, Germany and Japan.
The introduction of laser welding for aluminum alloys in automobile and aircraft building can be considered the second major technological application. The leading auto builders use laser to weld about 20 meters of weld seam in the body of their vehicles. Aircraft companies began employing laser welding for connecting the stringers (longitudinal load-bearing elements) with encasing during the construction of the lower part of the fuselage. The latter is especially remarkable, as aluminum welding was rarely used in aviation due to poor statistics on its behavior and the long-term damage in weld seams created with conventional methods. Laser welding reduces weight gain of joints and considerably accelerates the process of construction as compared with clinching. Laser welding makes it possible to connect up to eight meters of stringer with encasing per minute.
Main features and advantages of laser welding:
- High processing performance, with typical speeds of welding up to 200-400 m/hour.
- Capability of welding a broad range of steels, alloys and materials – from high-alloy, high-carbon steels through copper and titanium alloys as well as various high-melting alloys.
- Capability of welding dissimilar metals.
- Possibility of butt welding of thick sheets of metal in a single run.
- Ideal properties of the weld joint metal and heat-affected zone. In most cases, the mechanical properties of the weld joint metal are no worse, and often better, than those of the parent metal. Small heat-affected zone and lower grade of deformities, approximately 3-5 times lower than with arc welding.
- Possibility of welding in nooks and in diverse spatial positions
- Control and flexibility of the process, possibility of full automation
- Ability of the laser emission to travel to considerably long distances.
- Environmental purity of the process defined by the absence of fluxing agents and other welding consumables.
- High quality of weld joints: impact tests have demonstrated that tears (destructions) occur in the parent metal, not the weld. Tests have also demonstrated high bend ductility of the welds.