[Editor's note: The information on NEC and Seiko Epson that follows is based on research by David Kahaner of the Office of Naval Research, Tokyo - see reference section at the end of this chapter.]
NEC: Personal Computer Assembly
NEC's personal computer development and production center in Gunma Prefecture has had an automated assembly and inspection line for desktop computers since 1991. It produced over a million units in 1991. In 1988, the company automated packaging, and in 1989 it automated the printboard and inspection operations. In 1992, a robot line for final assembly and product inspection stages was completed that has reduced by two-thirds the skill requirements of the old manual line that required 15 skilled workers per shift. NEC's personal computer assembly factory, which produces 20% of Japan's personal computers, employs only forty people per shift to operate the factory.
NEC's aim has been to achieve production consistent with the market fluctuations of PCs. This required shorter "production lead time," the time required to double the number of PCs that the company plans to produce.
NEC has installed a new robot line that uses nine assembly operations covering a length of 50 meters and 12 inspection operations that cover 30 meters, excluding the running test room. Four of the robots employed are 6-axis vertical articulated models, 8 are 3-axis transverse models, 1 is a 2-axis transverse type, and 2 are horizontal articulated types, for a total of 15 robots. The total investment was approximately 500 million yen. Only two assembly operations and three inspection operations are done manually; the two manual assembly operations involve hooking up and stringing cables, operations still difficult for robots. Investigations are being made to eliminate cables for easier automation of this task. The line reduced the number of skilled workers from 15 to 5 and reduced waiting time from 77 seconds to 57 seconds. The line can assemble 450 PCs per eight-hour shift.
Precision assembly requires both placement accuracy and warping adjustments. Increased precision leads to more expensive equipment and component costs. The most difficult problem has been motherboard assembly. Hole position had been marked sequentially from one edge of the board, thereby decreasing accuracy as the hole distance increased from the edge of the board. One of the most important improvements in the new line was to change the printboard design to indicate the positions of holes in terms of one standard hole located near the centerline. This eliminated the need to measure hole positions. Mounting and soldering of electronic components to the printboards have now been automated. The soldering is accomplished by wetting the printboards with molten solder. The heat from this process warps the board. The printboard warp is measured with optical sensors using triangulations at three points simultaneously.
Robots have a limited adaptability to model changes unless control programs can be changed and robot hands adjusted for different components. As the number of components is increased, a robot line loses its adaptability. To keep waiting time short, it is necessary to install more robots. This is an expensive approach for equipment costs and takes a lot of time. NEC has addressed this problem by giving robots a wider range of movement. For horizontal and vertical articulated robots, the movement range is 320 degrees, leaving a 40 degree arc through which the robot cannot move. When this unreachable arc is placed behind the robot, it is difficult to supply more than two components per robot; therefore NEC placed this unreachable arc on the side, which allowed for an increase in the number of components supplied, thus increasing efficiency. This has allowed a waiting time loss of only one second but has provided increased flexibility.
A new handling problem is how to reduce component pallet sizes in order to place three pallets next to the robot. With only ten components per pallet, the carrier vehicle has trouble feeding parts fast enough from the warehouse. NEC's monorail transporters have a maximum speed of 200 m/min but operate at 180 m/min.
Inspection operations are still done manually but require devices to tell the difference between models. While external differences are easy to tell, many internal differences create difficulties. Bar codes and ID cards are used for each model. Four reflector plates on the jigs are used for identification; the robots, using sensors, tell which plates are open, and human inspectors visually view the display.
Seiko Epson: Printer Assembly
Seiko Epson redesigned its printer in order to automate its assembly using a single-direction assembly process. The company uses ten design criteria for assembly automation; unidirectional assembly is one of the criteria used consistently since Seiko Epson's first robot assembly line in 1984. The fifth-generation robot assembly line was built in April 1992. Simultaneous design of both assembly and product has preceded factory construction. According to Sachiharu Suda of the equipment rationalization center, "We have not merely tried to make printers easier to assemble, but have sought to lower mold and die costs and component costs to reduce overall production costs." In the past, easy assembly was the number-one criterion that led to complex-shaped components, more difficult design, and higher costs of molds, dies, and components.
The assembly line for the export model LQ100 printer had 53 steps using 38 assembly stages, 7 inspection stages, and 8 packaging stages, of which 5 assembly operations were manual. The automated assembly operations used Seiko transverse robots that had been used on the fourth-generation line. The tact time was reduced 10%, to 27.2 seconds, over the fourth-generation line. Vibrating parts feeders were used to supply small components to the robots, while pallets were used for large components. Three kinds of jigs were used to assemble the chassis, print head, and printboards. With the reduction in tact time, however, the most significant problem became the supply of parts to the line. Since multiple stages order parts simultaneously, the warehouse was unable to get the parts to the line fast enough. Parts locations in the automated warehouse were reevaluated to reduce the problem.
To further reduce costs, components that had been subcontracted out of the factory were reevaluated. The cost of palletizing and transporting parts to the factory could be eliminated if these parts were produced in-house. New jigs were developed to allow for the robots to assemble complex components on the line, and the assembly process was changed to accommodate this process. While cables are still installed manually, the power cable installation was robotized after developing new robot hand shapes and jigs that positioned the cables for correct cable positioning and robot grasping.
Nippondenso: Electronic Control Assembly (Kota Plant)
Engine control units are produced at Nippondenso's Kota facility. Five different engine controller product families, including over 120 different engine controllers, are made on a single assembly line. The line begins with traditional surface mount assembly, including solder paste application, component pick and place, solder reflow, and test. After test, a conformal coating is applied to the boards. The boards are then assembled into metal enclosures that are sealed and marked. The completed modules go through burn-in and temperature cycling before final test. After testing, the modules go into a stocker on the factory floor to await daily shipment to a nearby Toyota automobile assembly plant.
The entire 100-meter manufacturing line has only one direct labor worker, who folds multiple rigid boards connected by flex cables into a metal enclosure. (Automating that task has not been cost-justified.) Nippondenso claims that there is zero changeover time between products on the line. Each product is identified by a bar code reader and driven by factory-level data from the CIM system. Automated guided vehicles are used to transport production materials to and from the assembly line. Simple and complex engine controllers are intentionally mixed on the line to balance the flow. The highly automated production line at Kota provides an exceptional degree of flexibility and a maximum- quality product using minimum direct labor. Nippondenso's five-year plans are to add a second automated assembly line and to reduce the total work force from 3700 to 2000.
The production equipment at Nippondenso's Kota plant is mostly produced internally. The company employs over 200 people at the Kota site for production equipment and process development. Factory equipment and production processes are designed by teams that include both hardware and software engineers. The Kota plant is responsible for all equipment customization, fixture development, and programming requirements for the site. Because of the unique production requirements, the company finds it cheaper to develop its own equipment than to purchase general-purpose tools. (One tool for inspecting solder joints took over two years to develop.) The average piece of equipment on the manufacturing line is replaced or upgraded every two to three years. Nippondenso has begun to market some production equipment, such as robots, to external customers.