Research On The Machinability Evaluation Method For Difficult-to-Cut Materials

Difficult-to-cut materials such as stainless steels, titanium alloys and super alloys, have been widely used in many industrial areas as aeronautics and astronautics, nuclear energy, chemical industry, weaponry, electronic industry and modern mechanical manufacturing. These materials always satisfy the actual application requirements due to their excellent properties like super strength at high temperatures, hardness, high contents of hard-inclusions and inhomogeneity. However, the high temperature and high stress occur in the cut machining processes, which could induce worse machining conditions and thus the short life of cutting tools, bad surface quality of products and low machining efficiency. Therefore, it is of great importance to investigate the machinability of difficult-to-cut materials, address the cutting performance and explore the related technical solutions. How to machine these super materials effectively is quite crucial to those key industries like automobile, energy, aeronautics and astronautics and also known as a challenge work in cutting fields.Machinability is the property of a material which can be machined easily or difficultly by a cutting tool. The machinability of materials is always influenced by many factors like the physical properties, chemical contents and microstructures. Due to the diversity and the complex interactions among these factors and even the uncertain evaluation stands for the machinability under various cutting conditions, scientific description and evaluation of machinability is a challengeable work in the mechanical manufacture areas in recent years.The present work aims to develop a novel method to evaluate and describe the machinability of difficult-to-cut materials using polar diagrams. Based on the analyzing of the chemical contents, the mechanical and physical properties and the machining characteristics of these materials, five key parameters, i.e., hardness, ductility, strain hardening, thermal conductivity and abrasiveness, have been employed to describe the machinability. The relationships between these properties and the cutting parameters, the cutting tools or cutting results, were investigated and the related formulas were obtained. The polar diagram method for the describing the machinability of difficult-to-cut materials has been developed and the models for the evaluation of the influence of those key proper parameters on the machinability have been proposed. By using this method, the polar diagrams of several typical stainless steels and titanium alloys, as examples, were obtained and the corresponding theoretical discussion and analysis were given. Furthermore, a nickel-based alloy, Inconel 718, was used as an example and industry experiments were conducted to demonstrate the relationships between the polar diagrams and the cutting parameters as well as the cutting results like the tool wear. By combining these related models and the case-based reasoning methodology, a novel intelligent expert system for the selection of proper cutting parameters according to machinability has been developed. By calculating the similarity degree between the machinability of a given material and those known materials, the expert system can help the engineers to determine the suitable cutting parameters for a given material by considering the machining experience of those known materials in the database.The present polar diagram method can give a direct and integrated description of the relationship between the material properties and the machinability and therefore, can be applied to guide the selection of cutting conditions for new materials or unknown difficult-to-cut materials, which certainly could decrease the trial-machining time and process cost in machining these materials.