ORIGINAL ARTICLE A digraph-based expert system for non-traditional machining processes selection Nilanjan Das Chakladar & Ranatosh Das & Shankar Chakraborty Received: 15 February 2008 / Accepted: 14 August 2008 / Published online: 30 August 2008 # Springer-Verlag London Limited 2008 Abstract The presence of a number of available non- traditional machining (NTM) processes has brought out the idea of selecting the most suitable NTM process for generating a desired shape feature on a given work material. This paper presents a digraph-based approach to ease out the appropriate NTM process selection problem. It includes the design and development of an expert system that can automate this decision-making process with the help of graphical user interface and visual aids. The proposed approach employs the use of pair-wise comparison matrices to calculate the relative importance of different attributes affecting the NTM process selection decision. Based on the characteristics and capabilities of the available NTM processes to machine the required shape feature on a given work material, the permanent values of the matrices related to those processes are computed. Finally, if some of the NTM processes satisfy a certain threshold value, those are short- listed as the acceptable processes for the given shape feature and work material combination. The digraph-based expert system not only segregates the accepted NTM processes from the list of the available processes but also ranks them in decreasing order of preference. It also helps the user as a responsible guide to select the most suitable NTM process by incorporating all the possible error trapping mechanisms. This paper takes into account some new work materials, shape features and NTM processes that have not been considered by the earlier researchers. It is further observed that the developed expert system is quite flexible and versatile as the results of the cited examples totally corroborate with those obtained by the past researchers. Keywords Non-traditional machining process . Digraph . Expert system . Graphical user interface . Permanent of matrix 1 Introduction With the continuous use and development of materials like titanium, stainless steel, high-strength temperature-resistant alloys, fibre-reinforced composites, ceramics, refractories and other difficult to machine alloys having higher strength, hardness, toughness and other diverse properties, there is a need for machine tools and processes which can accurately and easily machine those materials to intricate and accurate shapes. Traditional edged cutting tool machining process- es are uneconomical for such materials as the attainable degree of accuracy and surface finish are quite poor. Machining of complex shapes in such materials by traditional processes is still more difficult. Other higher level requirements like low tolerance, higher production rate, automated data transmission, miniaturisation, etc., cannot be achieved by the traditional metal machining processes. To meet these demands, a different class of newer material removal processes has now emerged. These newer processes are called non-traditional in the sense that, instead of conventional cutting tools, energy in its direct form is used to remove materials from the workpiece [ 1, 2]. Some of these newly developed processes can also machine workpieces in areas which are inaccessible for traditional machining processes. These machining processes become still more important in the area of micro- and nano-machining. It has been observed that, in conventional machining processes where material is removed in the form of chips, attainment of the desired accuracy is a difficult task. However, such accuracy can be achieved by these non-traditional machining (NTM) Int J Adv Manuf Technol (2009) 43:226–237 DOI 10.1007/s00170-008-1713-0 N. D. Chakladar : R. Das : S. Chakraborty (*) Department of Production Engineering, Jadavpur University, Kolkata 700032 West Bengal, India e-mail: s_chakraborty00@yahoo.co.in