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A combined DFMA and TRIZ approach to the simplification of product structure

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A combined DFMA and TRIZ approach to the simplification of product structure
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  A Combined DFMA and TRIZ Approach to the Simplification of Product Structure Paolo F. Bariani Guido A. Berti Giovanni Lucchetta DIMEG - University of Padova Via Venezia 1 35131 Padova, Italy Abstract In order to more effectively tackle the problem of part count reduction, an approach that combines the Design for Manufacture and Assembly (DFMA) method with the Theory of Inventive Problem Solving (TRIZ) is presented in this paper. This new approach was developed by merging the common characteristics and connecting the complementary aspects of the two methods, and then applied to the redesign of a satellite antenna. 1 Introduction Part count reduction yields the largest contribution to the decrease in manufacture and assembly costs. In order to simplify a product’s structure, the Design for Manufacture and Assembly (DFMA) method recommends examining each component in the assembly order and then candidating it for elimination if it does not satisfy at least one of the following minimum part criteria [1]: •  the part moves with respect to all the parts already assembled; •  the part is made of a different material with respect to all the other parts already assembled; •  the part is separate from all the other parts already assembled because necessary assembly or disassembly would otherwise be impossible. When examining the components, technical or economic limitations should be ignored in order to encourage breakthrough thinking by removing the mental constraints of existing solutions. NOTICE: this is the author’s version of a work that was accepted for publication in Proceedings of the Institution of Mechanical Engineers Part B Journal of Engineering Manufacture. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Proceedings of the Institution of Mechanical Engineers Part B Journal of Engineering Manufacture 08/2005; 218(8):1023-1027. DOI:10.1243/0954405041486091  DFMA also gives specific advice on how to redesign the product by pointing out what can be done to improve an existing design and providing the designer with design rules that are extracted from good design practice. However, the DFMA guidelines for decreasing the part count concern the elimination/integration of only two kinds of components: fasteners and connectors. DFMA does not give any advice on how to eliminate all the other parts that do not satisfy the minimum part criteria. Since no design rule for the elimination of such parts has been developed up to date, the designer has to resort to the trial-and-error method. The number of trials varies depending on the complexity of the elimination/integration problem and the designer’s creativity, but it may increase significantly if the solution to the problem does not lie within the designer’s experience and knowledge field. There is, therefore, a need for a method able to manage the design synthesis process in a more effective way. This paper presents an approach that combines the Theory of Inventive Problem Solving (TRIZ) in combination with DFMA in order to tackle the part count reduction problem more effectively. 2 TRIZ According to TRIZ, problems are solved by analogy, following the general approach shown in Figure 1 [2]. Figure 1. The TRIZ general model for product structure simplification. A specific technical problem, which in part count reduction consists in reducing the number of the separate components of a complex product, is first translated into an abstract model. This is usually carried out in three stages. Abstract level Problem domain TRIZ problem solving tools Function Analysis, Ideal Final Result and Trimming Design team Trial and error Specific problem: complex product (several components) Specific solution: simple product (few components) TRIZ generic problem TRIZ generic solution  1. A function model of the product is built by defining the components in and around the system, including the interactions between all the components, considered in pairs. All the interactions are classified as either useful, harmful, insufficient or excessive. A hierarchical model of the system is defined by arranging the components and relevant functions according to the distance of each of them from the Main Useful Function (MUF) of the whole system. 2. Beginning from the lower levels of the hierarchical model (i.e. far from the MUF), each component is analysed in order to state its Ideal Final Result (IFR). According to TRIZ, all technical systems evolve in the direction of increasing their degree of ideality, which is defined as the ratio between the valuable results of the system's functioning and the expenses needed to perform this function, such as costs, time, energy and resources. The IFR of any technical system will eventually be the state in which the system itself disappears while its functionality is still performed. The underlying concept of increasing ideality implies achieving functionality with fewer and fewer components and the maximum exploitation of the remaining ones. 3. The function model may eventually be simplified by means of the trimming technique and according to the IFRs stated in the previous step. A component may be eliminated only after both the functions it performs and the ones directed towards it have been trimmed (because they are not needed) or reassigned to other existing or new components or to external resources. As a result of the trimming process, a simplified function model, which should be closer to the IFR, and a list of new problems, which have developed during simplification, are obtained. Basically, these new problems, which must be solved in order for the new simplified model to work properly, deal with how the remaining components can perform or be the object of those functions that were respectively executed or directed towards the trimmed parts. In order to solve these problems, TRIZ provides the design team with several problem-solving tools, which have been developed through the analysis of patents and inventive solutions from different fields of engineering. These tools link the generic problem model to the solution principles extracted from previously well-solved analogous problems. As a result, an abstract model of the solution is constructed. Finally, the design team adapts the model of the generic solution to the specific problem domain.  3 DFMA and TRIZ 3.1 Comparison between DFMA and TRIZ A comparison of the DFMA and TRIZ approaches reveals that they share two common characteristics [3]: •  the use of a psychological tool that encourages breakthrough thinking by removing the mental constraints of existing solutions – respectively the Minimum Part Criteria and the Ideal Final Result, and •  the use of product simplification techniques based on the reduction of part count. A more accurate analysis indicates that the two methods are more complementary than similar. •  From the point of view of the design approach, DFMA is mostly focused on the analysis phase of the design work rather than on the synthesis activities [4]. On the other hand, although TRIZ does not support any evaluation process aimed at comparing the alternative product concepts, it has proved to be a very powerful method for creating new design solutions. •  As far as focusing on the design phase is concerned, since DFMA is based on the analysis of geometrical part features, it is typically used as a post-analysis design tool in the detailed design phase, i.e. when the design details are known and the product is more or less well defined [5]. Conversely, TRIZ analysis does not consider design details such as part geometry, but it does take into account component functionalities and interactions. TRIZ may thus be regarded as a conceptual design tool. •  DFMA makes reliable estimations of the assembly and manufacturing costs available during the design phase in order to compare alternative product concepts. On the contrary, TRIZ function analysis lets the designer redefine the design problem in a new and more problem-solving-oriented way for the creation of innovative conceptual design solutions; however, it does not provide any relationship between cost information and design decisions. 3.2 Combining DFMA with TRIZ The combination of DFMA and TRIZ was carried out by merging the common characteristics and connecting the complementary aspects highlighted above. This combination made it possible to develop a framework for enhancing the application of the  two methods in both the analysis and synthesis activities of conceptual and detailed design. This framework is based on a structured sequence of the six design process steps reported in table 1. To clarify how the tasks involved in the proposed six design-process steps may be performed, the redesign of a satellite antenna is illustrated as a case study. Table 1. Combined application of DFMA and TRIZ DESIGN PHASE DESIGN APPROACH PROCESS STEP Functional Analysis 1. Perform a hierarchical function analysis of the system. 2. Identify the components that cannot be eliminated according to the Minimum Part Criteria and the functional hierarchy. 3. Simplify the function model by means of the trimming technique. Conceptual Design Synthesis 4. Apply TRIZ problem-solving tools to the problems that have arisen during the simplification. Economical Analysis 5. Perform a DFMA analysis to estimate assembly and manufacturing costs and compare alternative design solutions. Detailed Design Synthesis 6. Optimize the geometrical features of the parts for assembly and manufacture according to the DFMA guidelines. 4 Design of a new satellite antenna: a case study The srcinal satellite antenna, which is shown in figure 2, consisted of 29 components including the Low Noise Block (LNB), which is not illustrated in the figure. Figure 2. Original design of the satellite antenna. A hierarchical function analysis of the system was carried out and is reported in figure 3. Fasteners and connectors were excluded since the DFMA already provides designers with guidelines for their elimination or integration. A full pair-wise comparison of all the Reflector LNB Arm Azimuthal Elevation Bracket LNB Clamp LNB Support Pole Holder Back Structure

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Jan 13, 2019

BAB 1

Jan 13, 2019
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