AUTOMATION AND ROBOTICS:SCOPE FOR RATIONALIZATION

ASSEMBLY: SCOPE FOR RATIONALIZATION

The early history of assembly process development is closely related to the history of the development of mass production methods. Thus, the pioneers of mass production are also considered the pioneers of modern assembly. Their ideas and concepts significantly improved the manual and automated assembly methods employed in large-volume production. In the past decade, efforts have been di- rected at reducing assembly costs by the application of flexible automation and modern techniques.

In the course of the development of production engineering, mechanization and automation have reached a high level in the fields of parts production, which permits the efficient production of individual parts with a relatively low proportion of labor costs. In the field of assembly, by contrast, automation remains limited to large-volume production. In medium and short-run production, ration- alization measures have been taken mainly in the area of work structuring and workstation design. For the following reasons, automation measures have scarely begun in assembly:

1. Assembly is identified by product-specific, and thus quite variable, work content (handling, joining, adjusting, testing activities). Once solutions have been found, however, they can be applied to other products or companies only with great difficulty, in contrast to parts manu- facturing.

2. Assembly, as the final production stage, must cope extensively with continuously shifting market requirements in regard to timing, batch sizes, derivatives, and product structure.

Although the automation trend in the assembly field has been growing remarkably over the past years, many industrial sectors still have relatively unexploited potential for rationalization. Compared to other manufacturing branches, such as parts manufacturing, assembly is characterized by a rela- tively low degree of automation. It accounts for only 60–90% of the manufacturing sequences of parts manufacturing, spot welding, and press shop in the automotive industry, for example. Specifi- cally in assembly, however, this percentage decreases dramatically to less than 15% because of the complexity of the assembly tasks. The vehicle assembly as a whole (inclusive of final assembly) is quite cost-intensive in terms of employed labor force, representing 30% portion of the whole vehicle cost of production. Because of the high assembly costs, the automation of further subassembly tasks is therefore considered a major objective towards which the most effort is being directed.

Over the past years, automation technologies have been evolving dramatically in terms of flexi- bility and user-friendly operation as for their use in assembly systems. Automated devices, especially industrial robots, have also become less and less cost-intensive. Prices have been reduced up to 50% in some cases. For this reason, the scope for rationalization and application in assembly is as prom- ising as ever.

An automation study was conducted by the Fraunhofer IPA in order to ascertain which industrial branches are characterized by exceptional scope for rationalization in the assembly. The results of this investigation are shown in Figure 9.

The objectives achieved by the industrial application of automated solutions are shown in Figure 10. The investigation gave evidence that the cost-reduction objective, followed by quality improve- ment, was considered the first priority.

The most important preconditions to the realization of the still unexploited potential for ration- alization in assembly are illustrated in Figure 11.

Despite the fact that assembly-oriented product design is perhaps the most important prerequisite for simple and automatic assembly, as has been well known for years, the enormous scope for rationalization of this field is very far from exhausted. Yet even though it is undeniable that the high manufacturing cost of a product becomes evident in assembly, the largest portion of it is due to construction. Investigations into different manufacturing areas have produced evidence that approx- imately 75% of the whole assembly costs originate in the early stages of product design and construction. The most important rules and methods of assembly-oriented product design are described in the following chapter.

The precondition to assembly systems covered next in the study is hardware and software modularization. The interconnecting implementation of standardized components, allowing assembly systems for the most varied assembly tasks to be designed simply and quickly, makes it possible to

strive for the required flexibility. The investment risk decreases in proportion to the high recoverability of most components because the volume of investment would be well paid off in the case of product change if a large portion of the assembly components could be reused.

New requirements for the control technique are imposed by modularization, such as modular configuration and standardized interfaces. Conventional SPS control systems are largely being su- perseded by industrial PC. The result is decentralization of intelligence achieved by integration, for example, its transfer to the single components of the assembly systems. Assembly systems can thus be realized more quickly and cost-effectively. Further possibilities for rationalization could be ex- ploited by simplification of the operation as well as programming of assembly systems, still char- acterized by a lack of user-friendliness. The service quality and operation of assembly systems could be greatly improved by the use of graphically assisted control panels allowing for better progress monitoring.

Industrial robots are being used more and more in flexible automation for carrying out assembly sequences. Flexibility is guaranteed by free programmability of the device as well as by the ever- increasing integration of intelligent sensory mechanisms into the systems. The application of image- processing systems directly coupled with robot control is expected to grow faster and faster in the next years. The increasing implementation of sensor technologies is due to the rapid development of computer hardware, allowing for better performance at lower prices.

Further on, the degree of automation in the assembly can be enhanced by improving the logistics and material flow around the workplaces as well as by reducing secondary assembly times. Logistical aspects can be improved by optimizing the layout of workplaces, paying special regard to the arm sweep spaces. Specific devices for local parts supply can help to reduce secondary assembly times consistently. They should be specially designed for feeding marshalled components correctly oriented as close as possible to the pick-up station to enable workers to grasp them ‘‘blindly’’ and quickly. Rigid workplace limitations can be relaxed by introducing the compact layout (see Figure 12), al- lowing workers to walk from one workstation to the next and carry out different assembling tasks corresponding to overlapping sequences. This allows the number of workers along the same assembly line to be varied flexibly (according to the task to perform) even though the whole assembly sequence is still divided proportionately among the workers employed.

As for the organizational and structural aspects in the assembly, recent research approaches and developments have revealed new prospects of better ‘‘hand-in-hand’’ cooperation between workers and robots along assembly lines or at workstations. Industrial robots, being intended to help workers interactively in carrying out assembly tasks, need not be isolated or locked any longer. For this purpose, man–machine interfaces should be improved and safety devices redeveloped. Further on, robots should learn to cope with partially undefined external conditions. This is still a vision at present, but it shows future opportunities for realizing the unexploited potential for rationalization in the assembly field.