AD and Concurrent Engineering

Designers cannot make all the decisions about products characteristics, such as geometry, product components, and performance specification, without taking into consideration of factors and concerns about manufacturing/construction, assembly, testing, distribution, maintenance, repair, disassembly, recycling, and disposal. Certain functions or features may require specific materials, manufacturing and assembly processes, or they may limit the options for recycle and disposal of the product. Concurrent engineering (or design) can be defined as simultaneous design of all aspects of a product – from concept generation to manufacture, assembly, test, maintenance, and disposal [Voland, 2004].

Prior to 1980s, over-the-wall approach was in use in the industry, there was minimal feedback from later phases of product development lifecycle to the earlier phases. The role of the manufacturing was to build what the designers generated and presented on drawings and other design documentation whereas the role of the assembly was to put together what manufacturing produced [Ullman, 1992]. This over-the-wall approach was causing a lot of problems in production and assembly phases as well as during the use of the product. A General Electric survey indicated that 60% of all manufactured parts were not made exactly as represented in the drawings due to varied reasons, such as, (i) the drawings were incomplete, (ii) the parts could not be made as designed, (iii) the drawings were ambiguous, and (iv) the parts could not be assembled if manufactured as designed [Ullman, 1992].

The concurrent design approach has overcome most of the problems of the over- the-wall approach. In concurrent engineering, design teams are composed of members representing one or more areas of the product development lifecycle (such as design, marketing, finance, manufacturing, assembly, test, packaging, and recycling). The design teams work together throughout the design phase (preliminary and detail design, if

applicable) to ensure that all concerns and factors from different aspects of the product are taken into consideration and needs are satisfied by the final product.

Concurrent engineering establishes more effective communication links among the product’s stakeholders and allows critical issues to be resolved much earlier in the product development lifecycle, thereby reducing the need for corrective actions to be taken after substantial amounts of time, effort, and money have been invested. These characteristics of concurrent engineering have reduced the time required for producing a new product [Voland, 2004]. It was estimated that concurrent engineering has resulted in 30 to 40 percent decrease in manufacturing costs, and 75 percent decrease in scrap/rework efforts [Walker and Boothroyd, 1996].

The ability to communicate design decisions and to coordinate the creative process among diverse disciplines determines the effectiveness of concurrent engineering as a strategy for achieving shorter time to market, reduced development costs, and higher-quality products [Albano and Suh, 1994]. Albano and Suh claims that the potential benefits of concurrent engineering have not been fully realized since there is a lack of a systematic framework for conducting group design activities, and basic principles for decision-making. According to Albano and Suh (1994):

Effective communication involves much more than the traditional exchange of drawings and design specifications. The participants must be able to communicate design intent (i.e. what are the governing requirements and constraints? and how does the design satisfy these criteria?) and design rationale (i.e. why was a particular solution alternative selected for implementation?). In the absence of good communication, it is difficult to integrate the contributions of diverse disciplines into a coherent product and to identify solution concepts that may ultimately fail to satisfy, some or all of the needs of the customer. In addition to interdisciplinary communication, the flow of information between designers must also be coordinated and managed with regard to any dependencies that may arise or shared information that may be required. Proper sequencing of

interdependent design activities minimizes expensive and time-consuming design iterations as more information becomes available. pp. 500.

Axiomatic design approach was introduced as a framework of enhanced concurrent engineering by Jung (1993) and by Albano and Suh (1994). AD provides a systematic approach for product design and production planning in order to foster communication and coordination among design disciplines and help in the decision- making process [Albano and Suh, 1994].

In AD, process domain includes the process variables (PVs) that are the processes to manufacture the DPs. During product development based on the AD method, the developer has to consider the PVs in the product design (developing DPs) and make sure that the proposed design solutions can be manufactured. The process matrix [B] that relates the DPs to the PVs, like the product design matrix [A], is also supposed to satisfy the Independence Axiom to make sure that the manufacturing processes are robust enough to manufacture the proposed design.

Suh (2001) states that in terms of AD terminology, both the product design matrix [A] and the process design matrix [B] must satisfy the Independence Axiom by being a diagonal or triangular matrix so that the product of these matrices [CE]=[A][B] must

be diagonal or triangular and concurrent engineering can be possible. The elements of

the [CE] matrix are:

CEik = ΣjAij Bjk

This concept is stated as Theorem 9 (Design for Manufacturability) in AD [Suh, 2001, pg. 61].

It is not efficient and may not be practical to share the whole detail design with other design teams. The hierarchical design decomposition and the system architecture plays the role of filtering the design knowledge so that only the pertinent information is communicated [Lee, 1999]. The multi-layer or the master design matrix makes sure that the top-level design intent is still maintained and the FRs are still satisfied.