Nissan Passionate Challengers
EPISODE 03
Even 0.01 mm strain is not allowable
LASER BRAZING
Seamlessness is one of the design concepts of the Nissan Ariya. From the low, smooth roofline to the waistline that connects the front and rear in a straight line, there are no joins and they are seamlessly connected. This novel design was made possible by the newly-adopted process of laser brazing, in which panels are seamlessly joined together using laser beam.
Hiroshi Shirakawa, project leader of production technology body process (Environment and Facility Engineering Department, Vehicle Production Engineering and Development Division)
Nobuyuki Ishii, general foreman of coordination of body process at the Tochigi Plant (Body Section, Manufacturing Department No.1)
No more overlapping of sheets in the welding process
Hiroshi Shirakawa: The Nissan Ariya uses a new technology called laser brazing for welding the roof and body panels, and as the project leader of the vehicle body project, I have been playing a part in deploying this technology.
Nobuyuki Ishii: I oversee the process of stamping and assembling car bodies in the production division. When I entered Nissan, joining of the roof and rear fender was done by workers who joined steel sheets together by blazing and welding. Later, spot welding, in which an electric current is applied in the welding process, was adopted, and now welding using lasers is the mainstream.
Shirakawa： Looking at the roof of a car, you may have seen a band-like part (roof molding) made from resin attached to the car’s roof. To connect the roof and body panels so that they look like a single panel, laser brazing was adopted for this project. The roof panel, whose edge is rounded to an R shape, and body panel are perfectly aligned, and then copper wire is melted into the gap at the top of the panels with a laser to weld the two panels together. With a laser, heat is concentrated on a single point, making it possible to melt only the wire with pinpoint accuracy. With laser brazing, the join between the roof and body is no longer visible, making it possible to create a seamless design. Roof molding is no longer needed, resulting in weight reduction as well as cost reduction.
Eliminating strain associated with welding
Shirakawa: When the laser melts the metallic wire, the temperature around the area being welded is about 300 degrees Celsius. We had a hard time reducing that strain to zero as much as possible.
Ishii: I myself have over 30 years of experience in welding. Once again, I thought, there is much more to welding than one realizes.
Shirakawa: We decided to list and analyze all possible sources of strain. We had to repeat the trial-and-error process diligently, changing each condition one by one.
Ishii: The challenge was the precision with which the two panels are aligned. In laser brazing there is no overlapping, so the two panels must be perfectly aligned.
Shirakawa: To achieve this level of accuracy, a high-speed vision system is used to place the roof panel on the body panel. We also worked with the stamping shop to improve the accuracy of each panel.
Ishii: Laser brazing also requires high precision in the body press, which is the previous process. Correcting process was repeated many times.
Reducing strain to as close to zero as possible
Ishii: It was also a process of trial and error regarding the speed and angle at which the laser was moved. Those who have been welding for a long time realize that it is natural for strain to occur in the area around where heat is applied. We faced an unprecedented challenge to reduce it to as close to zero as possible. We consulted with the development division and asked them to change the design to reduce strain as close to zero.
To reduce the unevenness of the surface even after paint coating, notice and correct strains of about 0.01 mm is required. Strain of about 0.01 mm is not noticeable unless the operator is a skilled worker. Strain is checked by subtly changing the way the light shines on it and by touching the surface to pick up on the unevenness. All the staff involved felt a sense of accomplishment that the strain was finally gone.
Car body process workers take pride in their welding
Shirakawa: This is the first time Nissan has introduced this system, so we asked experts in laser welding and quality assurance in the production division.
Ishii: They set up various requirements and taught to the operators, from troubleshooting to determine what problems can be expected with laser brazing, to the mandatory equipment inspection items.
Previously, it was people, not robots, who handled the welding torch. There was a lot of know-how that had to be acquired, such as how fast to move the torch and how far to keep the torch away from the material, and these were techniques that only skilled people could perform.
Even if we use robots for welding, we have to teach the robots how to do it. Teaching accurately requires suitable knowledge and skills, and I believe that the high level of cooperation with Production Engineering Department has produced this excellent outcome.
I often tell everyone that the car body process is really the forte of the welders. Welding is an indispensable technology for car manufacturing, and the key to increasing car body rigidity. Experience and knowledge are needed to become skilled in welding, and one must also be familiar with the characteristics of steel sheets. We take pride in doing a good job of welding as we constantly seek to hone our skills. In the case of laser brazing, I was reminded that it is a new technology built on a foundation of skills that have been honed by people and brought to use in the equipment.
Shirakawa： The car body is the first process in car manufacturing to take shape, followed by the painting process, and then the assembly of the powertrain and other components. It is the very base of the car and must be built to a high level of quality. Nissan has already accumulated a great deal of know-how in the car body process, and now that we have accumulated considerable know-how in new engineering methods as well, I believe it is important to properly standardize these.
It is people who support the automated gemba
Shirakawa： When we introduce new technologies and engineering methods, communication with various divisions was necessary, including not only the production division but also the development design division and the body test division. This has increased my knowledge, as well as broadened my network of human relationships.
If the know-how accumulated at the Tochigi Plant can be horizontally deployed in Japan and overseas, and then expanded while incorporating the opinions of each region, I believe Nissan can expect great results.
Ishii： The most important part of the gemba is people. If people do not stick with you, the work will not proceed smoothly. My basic principle is to listen to what people are saying. I believe this is the first step.
Shirakawa： The design of the Nissan Ariya is really good. It is important that we get the production of this car up and running and get it out into the world. This will lead to the next new vehicle. We will continue to evolve our facilities and do our best so that many people will say, “Well done Nissan!”.
Ishii: Laser brazing is a difficult technique, but the design of the Nissan Ariya is amazing and I feel that all our hard work was worth it. I would like to continue to take on various challenges to deliver Nissan Ariya in better quality in the future, making full use of the know-how I have.