Technology Reflecting Real-World Experience
Early in 1987, EG was actively engaged in a review of specifications for the new, high-efficiency coating-line system planned for introduction on Suzuka Factory's third line. The system was to be a high-density, integrated body-painting system incorporating all processes up to overcoat application. The concept was to transfer bodies at high speed and use proportionately fast-coating robots to complete the process, resulting in a shorter cycle time.
However, to reduce the cycle time by increasing the target body's feed speed to twice that of a conventional system, EG had to develop new mechanisms by creating original yet fundamental technologies. The development team was thus divided into several small groups in order to work on the core technologies required for the coating process.
In the sealing process, the team began by listing the various pieces of know-how accumulated at Suzuka Factory and Sayama Plant for distribution among the members. Then, based on the technical resources they had identified, the team continued to work on target technologies. These included a high-speed sealant application robot with greater operating range and higher body-positioning accuracy; a spraygun capable of controlling application conditions for the sealant; and a robot for the attachment of grommets after the sealant was applied.
Process integration was further enhanced in the undercoating process with the development of various orthogonal robots having built-in power servomotors. Some of these were designed for floor installation and others were used in hanging positions, in an arrangement that positioned these robots three-dimensionally around the line. In addition, the team developed a new, dual-head spraygun that could memorize the spray pattern for each target model and apply the undercoating only in specified areas by automatically avoiding holes. This led to the development of a coating technology that required no masking. Capable of memorizing spray patterns for multiple models, the new masking-free spraygun produced significant results, one of which was the elimination of steps needed to attach and remove masking tape before and after undercoating. As a result, the application could be done in one step.
The overcoat application process, in which the body's outer panels are painted, requires a high degree of coating technology. At Suzuka, the application of overcoat had been done using a simple, gate-shape automatic coating machine that had been known as a "reciprocator" since the production launch of the H1300 in 1969. The sections handled by the reciprocator covered nearly 80 percent of the overall body. However, coating the front and rear sections of automobiles, as well as the so-called inner-panel coating process - including the inside surfaces of the hood, trunk, and doors - required the skills of experienced operators. Because of this, the process of overcoat application was constantly reliant upon both machines and operators.
The development of a multiple-axis robot was therefore rapidly progressing in order to provide an alternative to the reciprocator. One key element was the action of the sprayguns used to paint various body sections. Normally, the operation of such sprayguns required the deft handwork of skilled operators. However, the reciprocator employed a hydraulic drive system to control the movement of sprayguns, and the bulky wiring cables and hydraulic pipes were limiting the movement of the gun.
The newly developed outer panel's top multirobot was designed to address this problem. That robot, which employed a five-axis configuration using a flameproof power servomotor, could not only move the gun head up and down, as well as in the body's direction of movement, but could also rotate the gun arm. This enabled the robot to perform accurate spray actions along the contours of the body while it was moving on the conveyor.
The team also focused on a part called the bell cup. This component, which was used to spray the coating material, was installed in a bell spraygun attached to the robot. Rotating at a speed of over 30,000 rpm, the bell cup was also subject to current input exceeding 60,000 volts, which was required in the electrostatic coating process. The coating material sprayed from the bell cup along radial lines was charged with electricity and thus attracted by the body surface to form a film coating.
Honda used to purchase its bell sprayguns from an overseas manufacturer. However, seizing upon the opportunity for another joint-development project it had started with a foreign manufacturer, EG began developing its own bell spraygun. With the expertise acquired through that research, EG was able to develop an original bell spraygun without using any of the existing patented technologies. EG's new bell sprayguns were introduced to the third line at the Honda of America Manufacturing (HAM) Plant in December 1989.