Product design as an integral step in assembly system development

Citation

Onori, M. (2002), "Product design as an integral step in assembly system development", Assembly Automation, Vol. 22 No. 3. https://doi.org/10.1108/aa.2002.03322caa.001

Product design as an integral step in assembly system development

Product design as an integral step in assembly system development

Mauro Onori

Design for assembly (DFA) techniques and methodologies have been in use since the early 1980s, and the term itself no longer arouses particular ambiguities. Not only has it become a known methodology, it has led to the uncontrolled spawning of myriad other approaches, including design for variance, design for automatic assembly, design for reliability and so forth. The development of such a wide variety of design support tools is, in itself, a proof of the validity and value of such tools but, nonetheless, their use has not truly been as widespread as intially expected. Major companies have, to varying degrees, applied the technology and obtained quantifiable results. Other corporations have even gone as far as to develop their own forms of DFA, and academia has expanded the realm to encompass the modularisation of products as well. In view of such a positive evolution of events, it becomes legitimate to wonder why there still exists a rather widespread difficulty, for most companies, to adapt their production range and rates to new market needs. The answer may lie in two separate domains. The applicability of these methods has often encountered resistance by the designers or design team, primarily because further learning is required and, secondarily, because the methods are sometimes viewed as a limiting factor for creativity. The other answer is less obvious and may lie in the fact that the coupling between product design and production system has not yet been fully exploited.

The applicability factor of DFA methods has received considerable attention. Flowchart methods which avoid extensive mathematical analyses have been presented, such as the design for automatic assembly (DFA2), and concurrent engineering methodologies have proposed supportive measures. By and large, one may say that greater efforts may not result in major changes since the main hurdle still remains the distinct separation which exists, in most companies, between the design departments and production system developers. In essence, this is a management issue. The cultural, organisational, and information flow barriers must be brought down as a well-established strategic measure. All methods include consequences and implications for the production, both upstream and downstream. These implications may imply that the use of any DFA method may not give the expected results if the entire chain of events is not considered. At the end of the day, concurrent engineering is more than a methodology or philosophy, it should actually be regarded as an organisational working strategy. This lack of simultaneous development work is probably one of the main causes of the drawbacks denoted by modern assembly system solutions.

The major problems encountered by companies dealing with assembly mainly relate to uncertainty. First, it is very difficult for companies to predict the type and range of products that will have to be developed. The second uncertainty regards the production volumes and lifespans reached by these future products. The overwhelming reaction to these problems has been partially strategic, by employing DFA and similar methods, but primarily technical: that is, to attempt to develop extremely flexible assembly machines that attempt to adapt themselves to different product families and production scenarios. This has led to a series of multi-purpose machines, often classed as flexible automatic assembly (FAA) systems. Another approach has been to focus on the standardisation and modularisation of high-volume manual assembly lines, requiring advanced control solutions and special robotic cells for the automatic tasks. The common denominator to these approaches has been the dream of flexibility, a focus which has inadvertently avoided the actual assembly process and product design considerations. This fact has been further aggravated by the fact that a firm grasp of which type of flexibility is being targeted has, until recently, been neglected in favour of a general, yet vague, description of this term. Unfortunately, this existing paradigm of highly flexible assembly systems still prevails and results in expensive, highly technological solutions which cannot easily fit into existing production facilities, rarely accomodate an analysis of the product design implications, require technological competence, and are seldom able to assemble more than one product generation. Although fairly adequate to many different product types, they fail to be very performative in any domain.

The somewhat hidden problem, however, is that the major part of producing companies have to deal with planned products and existing production facilities. Ideally, they would like to fit any new product, or product variant, into an existing assembly system with as low costs as possible. To date, this has only been a dream. The common scenario is that the existing production system principles still dictate, to a varying degree, the basic design requirements for future products, and vice versa. Basically, there is a strong dependence between product development and selected system principle (parallel flow, serial line, etc.). This entails that any new FAA, or other assembly system solution, has to fit into an existing facility. The same applies for a new product design. For example, as soon as a new product design is assumed to require a new assembly system solution, a serious analysis of the components is required to ensure that the targeted volumes, costs, etc. are attained. This often leads to a change in some system component, or product part, to enable the achievement of the goals. This is exactly where the problems arise: the maximum attainable capacity and flexibility of an assembly system are ultimately dictated by the product design and assembly equipment. Therefore, if the equipment cannot easily adapt to changing market requirements and/or new products, the overall flexibility is greatly reduced. Furthermore, if the envisaged assembly system solution cannot easily fit into the existing production system scenario, it will not be deemed as fully flexible by the user. A focus on assembly system solutions as a separate entity to the actual product designs will therefore not succeed.

This vital link between product design and production system is on the verge of becoming even more crucial since new trends and developments are emerging. Although digital plant technology, or virtual factory solutions, are aware of this link and are struggling to achieve an information flow between the two domains, the products and technology around them are drastically changing. Eco-reliability, or sustainability, has become even more important and must be embedded in both product and system design. The products themselves are becoming ever smaller, inducing the development of mini and micro factory solutions, miniature systems which demand a re-consideration of known methodologies and approaches. Furthermore, since miniaturisation will, in most cases, only affect part of an entire product range, these solutions will have to be embedded within an existing production system. Other trends, such as the growing push for design for reliability, further underline the need to assess both product design and production system aspects concurrently. In terms of assembly systems, what is required is not a solution which tries to accomplish all of the envisaged assembly needs but, rather, a solution which, being based on several reconfigurable, task-specific elements (system modules), allows for a continuous evolution of the assembly system. In order for this to succeed, however, a dynamic link to the product design processes and methods must be created. In short, the challenge for design engineers and production system developers is to create a common working platform.

Basically, the most innovative product design can only be achieved if no assembly process constraints are posed. The ensuing, fully independent, product design and process selection procedure may then result in an optimal assembly system principle. The optimal layout is then linked, via a methodology, to a broad range of small, process-oriented system components. All dependency on existing assembly system principles is broken. Consequently, one has an evolvable assembly system principle (EAS) (Onori, 2002) in which the existing assembly system may dynamically adapt to the new products, technologies, and production scenarios. Consequently, the designers know, a priori, if there are technical solutions available to their designs and which particular constraints they pose on these designs. The ensuing assembly factory is, due to the small-scale modularity and standardisation, dynamically reconfigurable. This represents a shift in thinking since it implies that theoretically very flexible, multi-purpose cells will be replaced by a highly flexible concept consisting of several well-targeted but not, in themselves, highly flexible components. Hence the new paradigm.

The industrial and academic community in Europe is already at work with such issues, and networks such as the assembly net (http://www.assembly-net.org/) and CE-NET(http://www.ce-net.org/) are clear examples. The challenge is not only to bring the assembly system engineers to truly collaborate with the product design experts, but also to adapt DFA, DFR and all other methodologies to encompass new engineering domains and social trends, such as eco-sustainability, microtechnologies and the rapid decline in manual workforces. It is therefore no longer an equivocable forecast to say that automatic assembly, and the product design methods it will require, will represent a key factor for survival in future markets.

Reference

Onori, M. (2002), "Evolvable assembly systems – a new paradigm?", Proceedings of the ISR2002, Stockholm, October.