MIGUEL BOYAYANWelding by laser: light passes through the lens and hits the connector held to the screenMIGUEL BOYAYAN
In October of last year, the company from the state of Santa Catarina, Tupy Fundições, one of the largest in this industrial segment in Brazil, was facing a huge challenge. In order to accomplish a millionaire contract for the supply of car parts to General Motors, in the United States, the Brazilian company needed to prove that it was capable of carrying out induced fractures by laser in the car motor structures such as bearing caps. In the interior of these structures are mounted the crankshafts, axles that receive the thermal force of the explosion sent by the pistons and which transmit this energy in the form of mechanical force to the other parts of the motor.
Since they did not master the laser process, the company, located in the city of Joinville, got in touch with out engineers from the Advanced Studies Institute (IEAv in the Portuguese acronym) of the General Command of Aerospace Technology (CTA in the Portuguese acronym), situated in the town of São José dos Campos, in the interior of the state of São Paulo. A little over a month later, the specialists demonstrated the viability of carrying out micro scratches via optical fiber guided laser in an iron block that could be fractured, with safety and precision, by way of the strong pressure of a hydraulic wedge in the mounting of motors.
“The laser process separated, in a test piece, the bearing cap of the motor block in a single operation, reducing the number of tooling operations and the manufacturing cost”, says José Cláudio Macedo, the tooling director at Tupy. With this, the company proved the viability of the contract and will go on to supply, starting in 2009, some 60,000 blocks per year to the American car manufacturer. The operation’s success was possible because, as well as the IEAv researchers high level of knowledge about lasers and their industrial applications, during 2006 the institute acquired a new materials processing station with a high power optical fiber laser. “One is dealing with equipment with properties superior to the traditional lasers employed in industrial processes, such as those of carbon dioxide (CO2) and neodymium-YAG (Nd:YAG) (see box). It was very useful in this project and has wide application in cutting operations, welding and the thermal treatment of materials”, says the physicist Rudimar Riva, the IEAv’s head of the Multi-User Laboratory of the Development of Laser and Optics Applications (Dedalo). “The installation of the equipment, unique in South America, has contributed to the development of new manufacturing processes, increasing the added value of national products and allowing for the qualification of human resources in the area of laser processing”, explains Riva.
For Tupy, the equipment arrived at the right moment. “If we hadn’t managed to develop this process, we would’ve had to acquire it from German companies, the only ones who master this technology. We decided to develop it in Brazil, in partnership with the IEAv, and now we’re going to carry out an economic viability study for implanting it within our factory”, stated director Macedo. All of the mounted equipment for the lasers produced and guided by optical fiber cost around US$ 500,000.
The first difference with the equipment is the quality of the emitted beam, which makes a smaller focal diameter possible (the area illuminated by the beam), increasing the light’s intensity. “The increase in intensity allows for welding and cutting materials thinner and quicker and with greater quality. As the focal diameter is smaller, there is less loss of material during the cut”, explains Riva. Another important characteristic of these lasers is the greater conversion rate of electrical energy into light energy. For each kilowatt of electrical power consumed by the station, it’s possible to extract 250 watts of light power, whilst the Nd:YAG lasers convert only 50 watts and those of CO2, 200 watts at the very maximum. The better energy efficiency has positive reflections upon operational cost reduction.
MIGUEL BOYAYANLaser power: motor structure fractured and micro-holes on a car partMIGUEL BOYAYAN
“These three properties together – superior beam quality, better energy efficiency and maintenance cost reduction – make the high powered optical fiber lasers extremely attractive for applications in factories”, says the physicist Milton Sérgio Fernandes de Lima, a researcher at Dedalo, and responsible for various projects involving the equipment. “Companies have noticed these advantages and the optical fiber lasers are substituting the traditional equipment, mainly those using the Nd:YAG.”
Welding at Embraer
The installation of the treatment station at Dedalo cost around US$ 500,000, and the major part of these resources (US$ 400,000) came from the Financier of Studies and Projects (Finep), the Ministry of Science and Technology (MCT) and the Aeronautic Sectorial Fund. The remainder came out of the coffers of IEAv and the Millennium Factory Institute (IFM), a virtual research network focused upon the manufacturing industry of which the institute is part (read about the IFM in issue No. 133 of Pesquisa FAPESP). The financing was used for purchasing the optical fiber laser apparatus and other components of the system, as well as the implantation of a leak proof metal cabin some 4 meters in length, by 4 meters in breadth and 3 meters in height, which permits the entrance of parts of up to 2 meters in breadth. The national manufacturer of aircraft, Embraer, also collaborated in the project, in the provision of material and human resources, and is being one of the major beneficiaries of the research done using the equipment.
Embraer’s interest in the laboratory is easy to explain. “Today the technology of welding by laser is more and more used in the construction of aircraft, mainly in their structural part, substituting the process of riveting”, advised physicist Lima. This process uses rivets, which are small cylindrical and metallic parts similar to screws, in order to join two pieces of metal sheeting. A large size commercial jetliner, such as a Boeing 777, with a capacity for more than 300 passengers, has around 1.5 million rivets that increase the weight of its structure by 15% and as well, the riveting process consumes 15% of the aircraft’s manufacturing time. Also, in order to carry out the riveting it is necessary to hole the fuselage, generating a type of vulnerability in the jet. “As the airplane operates at extreme temperatures, from -50°C to +50°C, the fuselage could suffer corrosion as a function of the accumulation of ice and water in these cavities”, explains Lima. “Boeing, Airbus and Bombardier have cooperation agreements with centers researching into lasers and the first two mentioned companies are already using this technology in the manufacture of their jets.”
The IEAv has two projects under development with Embraer. The main one is the welding of high resistance aluminum alloys, which are used in the structure of aircraft. “We’ve tested a hundred test pieces of aluminum welded using the optical fiber laser, which are now being tested by Embraer. The preliminary results demonstrate that the equipment produces weld with excellent metallurgical quality and very few defects”, says Riva. The other project makes use of an Nd:YAG laser and has as its objective soldering the electrical wiring contacts used in aircraft without the use of lead. This project is vital for Embraer because various countries prohibited, in June of last year, the entrance of electrical and electronic components that contain lead and other toxic substances or are difficult to recycle. “In order to provide a solution to the impasse, we’re developing a technology that uses the Nd:YAG laser as a heat source for soldering without lead”, explains the researcher. “The results up until now show that the contacts soldered in only a few seconds present extremely high resistance to fracture, not comparable to the crimped contacts, tightened by a special pair of pliers.”
MIGUEL BOYAYANState-of- the- art Center
Installed alongside the Tamoios highway, which links the Paraíba River Valley to the São Paulo northern coast, the IEAv laboratory, established only three years ago, is also equipped with apparatus that makes use of two other types of laser, both projected and built at the institute: a high power pulsating CO2 laser and one of copper vapor, as well as a further five lasers of more common use, three Nd:YAG lasers and two continuous CO2 lasers. The equipment serves various projects in the manufacturing area. This is the case of a new treatment by laser of a tooling tool, which was born as a prospected industrial necessity within the IFM network and has a patent registered to the IEAv. “This is an innovative process of texturization by laser that increases the lifespan of drills, millers and other tooling equipment”, underlined the engineer João Fernando Gomes de Oliveira, the IFM’s general coordinator.
In the process, a laser beam with short pulses and of high energy promotes the formation of nanocraters on the tool’s surface. As these are normally covered using a coating based on nitrides and carbides, the process permits greater adherence of the coatings that remain anchored in the wrinkles. A layer of greater adherence imparts more time to the tool’s life – in some cases, the longevity was increased ten times. The project makes use of a copper vapor laser and was developed by Dedalo in partnership with the Federal University of Uberlândia and the Campinas State University of Campinas ( Unicamp). It also involves a pool of companies interested in the technology, formed by Tupy Fundições, Sandvik (specializing in tool manufacture), Brasimet and Balzers (focusing on coatings and surface treatments).
Another relevant project in the metallurgy area involves the company Thyssen Krupp Metalúrgica Campo Limpo, the São Paulo branch of a multinational that holds the world leadership in the manufacture of crankshafts, metallic axles of car motors. The project’s objective is to carry out micro-texturization via laser on these components in order to reduce friction between parts and consequent wear. “Various methods could be used in order to realize micro-texturization, such as controlled abrasion, electron cannon or chemical attack. The texturization by laser is a recent technique and one that has presented good results”, advised physicist Lima.
Fibers and crystals
In order to understand how a laser works, and the differences between them, one needs to know that the generation of a light beam is normally produced by the exciting of atoms or molecules of a determined active medium, composed of one or various substances responsible for the emission of laser radiation, through the luminous source or electrical discharge (tube). Carbon dioxide (CO2) lasers, for example, are excited by electrical discharge (tube) and have as their active medium a mixture of gases: nitrogen, helium and carbon dioxide (CO2), responsible for the laser emission. In the Nd:YAG lasers the active medium is a crystal bar of YAG, a synthetic crystal, composed of neodymium-doped (the insertion of small quantities of chemical elements in a substance) with yttrium aluminum garnet and excited by a luminous lamp source or emission diodes, devices similar to and more powerful than those used in CDs and DVDs players.
The optical fiber laser has as its active medium a silica fiber doped with ytterbium, an element belonging to the Rare Earth Metal group. More than one hundred laser emission diodes are used as the source to excite the fiber.
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