Coastings selection methodology: a strategy over the optimum surface treatment selection for maximizing design efficiency of mechanical parts

Wear and corrosion are the most important factors that the surface of the engineering parts must confront. The need for protection and improvement of the mechanical characteristics of the surface of engineering parts can be to some extent satisfied by coatings. A coating is considered to be a thin layer of a material which is deposited over the surface of another material in order to prevent or decrease the rhythm of the chemical and physical interaction between the substrate and the environment. There are various types of coatings, like deposition, conversion or diffusion coatings etc, and each type has different characteristics. However, not every coating can provide protection against everything. Combining the available deposition techniques with different materials, one can get finally the desired coating properties. The selection of the appropriate coating is a complicated process. Service conditions, compatibility of the materials, object's shape and deposition parameters are some of the variables that need to be considered. The final problem results to be multi dimensional and classic material selection theories can not cover it in full length. Yet, the benefits that can be gained by the use of coatings compensate the dedicated time to the selection process. Nevertheless, the complexity and the difficulty of selecting the suitable coating, call for the creation of a customized selection strategy. The large number of criteria that should be considered simultaneously to select the suitable coating for a given component and the different importance of each criterion, natural bring to mind the Multi Criteria Decision Making theories. MCDM, are theories invented to deal with problems where the solution is reached after considering simultaneously various criteria of different importance. During the first stages of product development the conditions are by definition unclear and material selection is made under a fuzzy environment. In addition to that, the criteria that influence the selection of the suitable coating include an extensive number of qualitative properties. Material properties that have a qualitative nature can not be expressed as crisp numbers and they are mostly described through linguistic terms. However, multi-criteria decision making theories adhere to uncertain and imprecise data. In order to deal with this, the fuzzy set theory can be used to clear up the situation. In the current thesis, an attempt is made to combine the multi criteria decision making theories with the theory of fuzzy sets. The data from the qualitative properties are treated with the fuzzy logic theory and introduced into a TOPSIS like algorithm, where they are combined with the data from the quantitative properties and the final ranking is made. The proposed method for coating selection includes the following stages: ? Specification of the design requirements ? Processing Qualitative Variables ? Processing Quantitative variables ? Combining the two matrixes ? Application of the TOPSIS like algorithm ? Final ranking Moreover, further design issues, like the differentiation of designing a new product or re-designing a product, are discussed and solutions are proposed The main advantages of the proposed method are: 1. Simultaneous consideration of various design requirements. 2. Use of a sophisticated method to handle both the qualitative and the quantitative material properties. 3. Flexibility of the method. The designer can easily redefine every time the shape of the fuzzy membership functions, matching the specific application. 4. Permits the consideration of numerous alternatives through the definition of the term ideal performance as the desired performance and not as the maximum one. 5. The described process can be easily computerized and collaborates well with databases. Coatings are not just a material; they are a combination of materials and processes. They can provide a function to the design and not only contribute by their properties. Through the proposed method the engineer is facilitated to select the adequate coating. The computerized form assists in avoiding mistakes during the selection process, while on the other hand the various selection criteria presented can even point out to the engineer requirements that he/she hadn't considered. Finally, the possibility of immersing new and innovative solutions is increased through an efficient matching of the MCDM techniques with the fuzzy logic theories. Through these, we anticipate to introduce a new parameter into the thought of the young design engineers, clear up their view on coatings technology field and finally bring them a step closer to the use of coatings.